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Phase Change - Science topic

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Dear members,
I am trying to predict temperature distribution in laser melting process using FEM. It is a 3D transient heat conduction problem.
I have modelled it without considering phase change at the melting temperature of metal, but I am not able to understand how to incorporate the phase change, particularly how to handle the nonlinearities associated with the phase change (the latent heat, enthalpy as well as heat conductivity might not be continuous at the point of phase transition)?
Please provide some resources or any kind of help will be helpful.
Sincerely,
Ravi Varma
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I assume that you are only modelling heat transfer in the material by conduction. There will be convective currents inside the melt pool, so a model based upon conduction alone will not correctly predict this behaviour. Some publications have described the use of an increased thermal conductivity in material that has melted to attempt to model the increased heat transfer. However, the latent heat could be incorporated via an increase of the specific heat capacity in a temperature range based around the melting point. Some FE codes provide a latent heat option with a temperature range for the release.
Regards,
Simon
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I have a 750 ml reactor and working volume is 300 ml. my working temperature is 350 C. By using ideal gas law i found at the pressure to be around 2 bar. But  I need final pressure build up @ 350 C to be around 25Mpa in order to keep my solvent in liquid phase. So, how should i calculate the initial  head space pressure required. I'm planing to use Ngas for pressure build up
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I have the same issue, what i have noticed is the free volume of reactor that should be considered for supplying the initial pressure.
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The dirac delta function delta(n) is often approximated as the magnitude of the gradient of the color function "c" since it has the property of being non-zero only at a phase boundary. However, unless this magnitude is normalized, its value will always change based on grid resolution in discrete form.
Source terms used in phase change in the context of VOF are by definition only active at the interface and therefore are multiplied by the magnitude of the gradient of the color function, however in all the literature I've read so far that magnitude is never normalized which motivates my question.
How is it that one can using the dirac delta based on the VOF definition without taking into account the fact that on a discrete level the magnitude changes with grid resolution?
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You can check the following research paper to start with and see who has cited it, it is very instructive and it has 50 citations, which undoubtedly can lead to a discussion of the issue you have raised in your thread.
Lee, H.G. and Kim, J. (2012), Regularized Dirac delta functions for phase-field models. Int. J. Numer. Meth. Engng, 91: 269-288. https://doi.org/10.1002/nme.4262
Best Regards.
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In Ansys Fluent, there is an option to solve your multiphase flow problem using either Eulerian, Mixture or VOF models. Can we analyze phase change of water to steam using VOF?
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VOF is used where surface tracking among the phases is desired. In rest of the cases scholar mostly used Eulerian Model for steam water direct interaction problems.
VOF:DOI:
Eulerian Model : Numerical study of flow and direct contact condensation of entrained vapor in water jet eductor
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Any recommendations on books would be really helpful.
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2. Fins are never used on the surface in contact with a fluid undergoing phase change.
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I am trying to model the OCV of an electrochemical reaction where: ACT(g) + 2H+ + 2e- --> IPA(l), at T = 25 Celcius (Standard Temperature) and P = 19.6 KPa (P < Standard Pressure). The phase change occurs due to the low pressure and the differences in saturation properties between these substances. Any help is appreciated.
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I suggest you create functions for a complete set of thermodynamic properties for the reactants and products and subtract (after minus before). This is not as intimidating as it might seem. I do this sort of thing all the time. Without getting too fancy you can accomplish this with an Excel spreadsheet. To calculate g=h-Ts anywhere all you need is a curve for the ideal gas specific heat (probably in the NASA Glenn report) plus the residual enthalpy (you could use RKS or BWR or Nelson-Obert see attached spreadsheets) plus the residual entropy (same approach as residual enthalpy). Residual h or s is the difference between real and ideal gas so just put them together. You can read most of this book by just clicking on "look inside" https://www.amazon.com/dp/B07Q5L1CHT All the software is free on the web at the link listed below the Foreward. I will be out of town for a week but after that if you still haven't got it, collect all the data you can get (molecular weights, critical properties, etc.) and I'll put it together for you.
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During latent heat storage, the temperature of the material remains the same. So the question is what parameter changes during latent heat so that the energy stored inside the PCM material can be directly calculated as a function of X (just like we can calculate the energy in material as a function of temperature for sensible heat storage). I believe one of the parameters that changes are density. But what is the relation between the density of PCM material and energy content in it?? I am just stuck here.
Is there a way to determine the amount of heat sored in PCM material as a function of X (some simple equations) at any given time?
Also is the rate of energy stored constant during the phase changing process??
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The dependency of heat stored with an X-value you asked depends on the step you are :
- If the step is below melting temperature, this is the quantity of sensible heat stored in the material; X is the temperature. Similarly, if you are above the melting point, the material is fully liquid and X is also temperature (with the addition of solid sensible heat and latent heat).
- If you are looking for an X-value during the melting process (at melting temperature), you can use the liquid fraction. The easiest way to have a good approximation could be visual observation with a camera. If it is not possible, you can try to measure the duration of melting (where the temperature is constant at the melting point). You would know the time needed for total melting and the quantity stored at any time.
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If we remove heat by cooling the condenser with water in air conditioner then it facilitates the phase changing(from vapor state to liquid state) by enhancing the development of London dispersion forces among the molecules of refrigerant
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Welcome!
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Can i find any DSC For binary salt LiNO3,KNO3 to see the phase change on it
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I found the following two papers that might be of interest to you:
Coscia, K., Neti, S., Oztekin, A., Nelle, S., Mohapatra, S., & Elliott, T. (2011, January). The thermophysical properties of the NaNO3-KNO3, LiNO3-NaNO3, and LiNO3-KNO3 systems. In ASME International Mechanical Engineering Congress and Exposition (Vol. 54907, pp. 889-894). (see enclosed file).
Zhang, X., Xu, K., & Gao, Y. (2002). The phase diagram of LiNO3–KNO3. Thermochimica acta, 385(1-2), 81-84. (see enclosed file).
Best regards.
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From your point of view, how engineering surfaces can be used for enhancing phase-change heat transfer and providing new generation of compact heat exchangers?
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Dear Elaine M Cardoso , this scientific contribution presents very interesting criteria that will surely be of use to you.
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To my understanding, liquid pressure/stress can not drop below absolute zero as it would reach vapor pressure first and undergo a phase change. However, would it be possible that the liquid pressure go below zero under transient conditions where the pressure gradient undergo a rapid change in direction and magnitude?
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I am going to simulate condensation of moist air using ANSYS-Fluent (only 20% water vapor and the rest is non-condensable gas). How should I set this up?
We believe we need to write UDFs for the phase change process. But what is the best multiphase approach?
(In VOF, there are different mass transfer mechanisms. In an "evaporation-condensation" model, only Lee model is available; we don't use it in this simulation.)
Please share with me your ideas and also any relevant theses or papers.
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Dear
In my opinion the best approach for to predict the condensation phenomenon is wet-steam model. This model contains all of equations related to condensation and droplet generation process. However, it assumes all of the species is water-vapor, and cannot add any other non-condensate gas. Thus, UDF will be your best option.
I hope this helps.
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Hello everyone,
I am trying to understand the phase change boundary layer formation for flow between two parallel plates. Both plates are at -20 degrees and the water inlet temperature is 10 degrees. I am initially trying to visualize the phase change boundary layer (i.e., ice layer) on both plates. Trying to understand the steady-state case.
However, velocity & thermal boundary layer formation is perfect. Once I switch on the solidification/melting model in FLUENT, the solution becomes wrong. Velocity and thermal boundary layer becomes wrong and no phase change happens.
Any help/insight is greatly appreciated.
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Please send me the case file
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Can we see a phase change in the cyclic voltammetry plot of a faradaic reaction for Supercapacitor, If yes please tell me how?
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Actually in battery and capacitors normally, redox (Ox/Red) reaction occur without change of its crystal structure. Therefore, i suggest you to look change of oxidation state rather phase change through CV analysis. The phase change could be checked via different numerous characterization tools.........
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Using metal wire as the spraying material, through the high-energy density and large current to generate ohmic heating, the metal wire rapidly undergoes solid→liquid→vapor→plasma phase change, resulting in an electric explosion. The explosion shock wave is used to partially melt but not vaporize The metal droplets are sprayed on the surface of the workpiece at a high speed to form a high temperature and ablation resistant coating.
Is that possible for inner coating for oil and gas pipeline if outer diameter 139.7 (5-1/2) and inner diameter 127.3 (5.012)?
Kindly, I hope if I see you answers. I appreciate your advices and guidance for me.
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Hi Mohamed,
wire spraying techniques (flame spraying and electric arc metallization) are the oldest thermal spraying technologies invented by Max Ulrich Schoop about 100 years ago. At that time, these were advanced methods of coating, but over 100 years the technique has gone ahead and now there are better technologies. The problem with wire spraying methods is that the coatings are porous, permeable to gases and liquids, and in your case this is completely unacceptable.
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I am trying to realize the method in the literature:
A New Efficient and Stable 3D Conformal FDTD
and got the simulation result in the attached picture. The phase of S11 changed 180 degrees suddenly, what's the possible explanation for this? A bow tie antenna is simulated. In traditional FDTD, the phase changes gradually.
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The phase of the reflection coefficient does not change 180 degrees suddenly in the plot you have shown, it changes 360 degrees. This is because your maths and plotting only gives results between -180 and 180, when actually the phase decreased smoothly from about -20 to -320. It has gone nearly once round the Smith chart. Your maths can't tell the difference between -181 degrees and +179 degrees, so it jumps to the top of the page.
Some codes have functions like "unwrap" which can stop this happening, or recover if it has happened.
Phase can jump 180 degrees when the return loss is very large. In this case the complex return loss crosses the centre of the Smith chart (0,j0) and appears at the opposite angle on the other side of the centre, so a change of 180 deg. This only happens when the return loss is so big that the locus actually seems to pass through the centre. This depends on the return loss, and the spacing between your frequency points, and their exact value, and the accuracy of your maths.
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I want to simulate the phase change through out the heat exchanger that may be used in refinery by fluent. The point where the phase of oil will change is very important in this type of stations ,how I can find it or indicated using fluent.
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Hi, usually the point of the phase change has be introduced by yourself as an input parameter. You can't estimate it through the simulation.
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We have synthesized certain electrode material for DSSC application and coated electrodes material on FTO. We have connected one electrode with counter and reference electrode assembly and the other one with working and sensing electrode assembly. The electrolyte has been immersed between both electrodes. However, we are not getting proper Nyquist plot as well as bode plots, as you can see there is no phase change with varying frequency.
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Dear Dr. Ioannis Samara,
Thank you so much for your valuable comment. We have sort out the issue, it was arising due to evaporation and early consumption of electrolytes. We immersed the electrodes inside the beaker filled with electrolyte, instead of immersing the electrolyte inside the electrodes.
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Hi Everyone,
I want to know is there any way to do nonlinear simulation in lumerical interconnect except using the thermal nonlinear waveguide? I designed a waveguide and import the properties from FDE to interconnect. Now I want to see some nonlinear aspect of it by setting up a high power loopback system. Will it be possible to see any phase changes in the loopback in Lumerical interconnect?
Thanks.
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Hello,
hope this paper help you:
Silicon photonic waveguides & nonlinear optical effects
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Can I connect 2 capacitors in series/parallel to get 180 deg phase shift,? only 2 capacitors?
I need to have total impedance of 200 ohms at 2.4 GHz.
please advise
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Both are different things :
1.phase shift between input and output across a device
2. phase shift between current and voltage across a device
Two capacitors in series can not provide phase shift of 180 between input and output. So, it depends upon the quantities in which you need phase shift. No, nowadays amplifiers are available in miniature form or IC form (maybe you can use that, comparable or even smaller than the size of conventional capacitors).
That's how I can help, may be some faculty or researcher from the concerned domain may provide a useful answer and suggestion to your query.
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Hi. I am simulating a rotating heat pipe with phase change. It is divided into three sections, evaporator, adiabatic part and condenser. I have an initial fill ratio of 8% liquid. I have big problems for phase change. Using Lee's model either via UDF or as a standard fluent model I cannot observe the phase change. I also have problems with turbulent viscosity instability which leads me after a short while to Courant Number over 250 and diverging solution. Do you have any suggestions? My idea is to implement a new multiphase model, Sun's model via UDF, as mentioned in the paper I am referring to. Big problem is the inability to write the udf of this model, do you have any suggestion or help to give me please? I will leave the model below.
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hi, usually all the udf used for the evaporation and condensation use Lee formula, even there is a gap between the experimental and the numerical methods. As this formula developed several decades ago.
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I am modeling a simulation where in I have a heat source from outside which tracks the effect of PCM on heat storage and better evaporation of the other fluid.
Evaporation and Condensation model was added to one fluid whose Liquid Fraction is to be tracked. I want to add a Phase Change Material using Solidification/ Melting Modeling which will affect our dominant fluid. How do you I carry out both in ANSYS Fluent? As soon as I select the VOD modelling, and give PCM Cell Zone a fluid material input, it considers the PCM also to be part of VOF. I want it to be a separate fluid just undergoing phase change and no interaction with dominant fluid.
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Hello
You can select the process for each domain separately.
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I need two model heat exhanger between air and water. But air will be admitted in liquid state at negative temperature and on leaving the heat exchanger it should be in gaseous state.
In this problem two fluids are involved
Water
Air
Once again Air has enter in
Liquid state
On transferring heat from water it has to be converted to
Vapour.
I'm aware interphasechangefoam for phase change and CHTMultiregionfoam for two fluids. But in this case two fluids are involved. In this two fluid, one fluid has to undergo phase change.
Regards
Dr. Ijaz Fazil.
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Yes you can, if those different fluids are separated. Just add another fluid region to your case.Then you can define individual thermophysicalProperties.
Let's say you have your heat exchanger which is set as a solid region, then you can define water as one fluid region on the outside of the HX and and Air as another flui region on the inside of the HX. The two fluids will be interacting with eachother only thermally.
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Many literatures pointed out that soil sand content has a greater contribution to soil thermal conductivity. However, I couldn't find any models that can quantify soil thermal conductivity using the results of soil particle size distribution. In frozen soils, things seems more complicated considering the phase change of soil water. I want to find a model to express the soil thermal conductivity. I just want to find a soil thermal conductivity model that takes into account both the soil phase change process and the soil mechanical composition
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Acturally, I want to find the relationship or model on the effect of soil texture on thermal conductivity in frozen soil. Thank you all the same.
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I want to simulate conditions inside conditions of a "Solar Still Distillating Tank". I have a few ideas like using may using phase change module in comsol or simulating vapour pressure but I don't know how to do it. Any help is appreciated. Thank You!
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You can follow this paper for multiphase flow:
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Hello everybody
I‘m using the topology optimization module to optimize a time-dependent phase change problem.
After the first optimization step, these errors appear many times:
Warning: Forward solution failed, requesting reduced step.
Warning: Adjoint solution failed: requesting reduced step.
can anybody help me, how can I solve this problem?
thank a lot!
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I think your optimization model may be ill-posed. Following link can be useful in this regard
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In the attached paper to resolve the FP like SPP resonance, the authors calculated the reflection phase change from the full field simulation. Can anyone kindly explain how the phase change can be numerically calculated ?
Thank you.
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If FP means Fabry-Perot, there is clearly no such effect for the reflected light! This has nothing to do with multipass interference.
If you want to find out the additional phase by Wood's anomaly you can do this by applying Kramers-Kronig relations to the absorption shown in the paper.
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I am trying to simulate phase change process of paraffin wax inside a metal mesh. I am planning to use solidification/melting model in ANSYS (with energy, viscuous laminar ON). Do i need to use VOF with it as well? The metal mesh containing PCM is heated from the bottom with a constant heat flux and rest all sides are insulated except the top one which is under ambient condition (convective heat loss).
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Hi
I would like you to answer my question
I used aluminum foam with PCM
how can I explain porosity(0.92), pore density(PPI=10), permeability, and.. for metal foam in fluent in Ansys Fluent ??
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Hello,
I am running a simulation that includes water phase changes. These phase changes will take place below the boiling point of water so I need a method that can accurately model this. From my understanding and testing so far, the evaporation-condensation model in Fluent will only simulate the phase changes at the water's boiling point. Therefore, I need to code a UDF to model the phase changes more realistically. I have looked into vapourization modeling but frankly have been overwhelmed by the number of methods and I am really unsure which to pick for my scenario. Temperature, pressure, and relative humidity all need to be taken into consideration.
Does anybody know of any models that seem well suited to my needs off the top of their heads? Also, I'd appreciate any literature/tutorials that summarise different models or their application in Fluent.
Thanks.
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Hello!Regarding the model for Vaporization and condensation simulation, mainly involves the problem of vapor–liquid phase-change. For solving this problem, the feature of mass conservation is particularly important. The volume-of-fluid (VOF) method and the level set (LS) method are usually used for simulation calculation. At the same time, the VOF method has an inherent mass conservation property, more easily capturing interface with heat transfer of phase change. However, the default VOF method cannot simulate heat and mass transfer through the phase interface, so a user-defined function (UDF) was required.
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Hello RG,
Is this possible to investigate the stability of a specific intermetallic phase with DFT calculations? Technically said, can I use the DFT calculation as an alternative of thermodynamic calculation to study the stability, component solubility range and stability temperature range for a specific ternary phase?
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I found the provided papers very useful!
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My model is a rectangular multi layered structure under which refrigerant flows through cylindrical pipes. A heat flux of 600W/m2 applied on panel and internal forced convection is used for refrigerant flow. Trying the phase change option from heat transfer in solids and fluids node but I am not getting any sollution.
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I have water flowing at 4 GPM at 2.5 feet per second through 50ft of 0.375 in. outer diameter tubing with 0.014 in. wall thickness. The water flows through copper tubing into the 50ft coil section, which is submerged in an adiabatic container of 22lbs of ice, and then out again. How do I set up the heat transfer equation to find the time it will take the ice to melt, as well as the temperature of the water as it leaves the adiabatic container? Thank you.
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It will be like an heat exchanger i guess. Try heat exchanger equation.
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Hello,
I am simulating evaporation condensation model in Ansys fluent. Water heats at 250 degrees and evaporates and then reaches heat exchanger at top which cools at 70 degrees. But when vapours reaches heat exchanger it does not show any phase change from vapor to water. Kindly help me.
Thanks
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In Fluent, default values of evaporation frequency (Be), and condensation frequency (Bc) is set equal to 0.1. In order to see condensation, you can increase the condensation frequency (Bc) from values near zero to values near 1000.
you can also calculate the condensation frequency using the following eq.
Bc = Bv * (  liquid density / vapor density).
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Hi all,
I hope everyone is doing well and is in good health.
In the simulation it is needed to change the phase of water that flows through an air domain. So I used Laminar Flow and Level Set physics in order to simulate the interface between air and water. At the end of the air domain, there is a Wetted Wall and water reaches this boundary. Now, if I want to change the phase of the water, how can I use Heat Transfer in Fluids--->Fluid 1--->Phase Change Material 1 for the water that is interfaced with air in one domain? When I am using Heat Transfer I have to select a domain; So the Heat Transfer does not follow the new geometry of water. Do anyone have an idea about changing phase of water in this case?
I appreciate your time and consideration.
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possible only if the boundary condition temperature of the low temperature(200K) side should be increased just above the dew point temperature.
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Kindly suggest the solution of a above question rather i have already gone through Evaporation-condensation model available in it but did not get success.
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Hi @Tejendra Bhanabhai Patel ;
Did you get udf. Actually, I also want to implemet VOF with thermal phase change model. Kindly provide me.
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I have to analyze an existing ammonia line to estimate the pressure drop in it.
The line is designed to transport liquid ammonia. I can compute the pressure drop with standard friction factor approach. If I reach a point were the pressure is small that the corresponding vapor pressure, partial vaporization is to be expected.
What method is recommended to compute the pressure drop from that point onwards??
I have a two phase flow textbook, but guidance would be helpful as to what is the recommended procedure.
Best regards.
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Flow in a two phase state is quite complex. Basically, depending on the vapor fraction different correlation should be used . However, some correlation are more general and can be used in the whole two phase domain. These correlations are discussed in this article :
Ould Didi, M. B., Kattan, N. & Thome, J. R. Prediction of two-phase pressure gradients of refrigerants in horizontal tubes. Int. J. Refrig. 25, 935–947 (2002).
With this method you keep the traditional linear pressure drop formula, but you have a specific pressure loss coefficient.
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I want to design a shell and tube heat exchanger with kern's method.
The problem in the two phase flow. I didn't find enough information.
I know that in the two phase section the evaporator is discretized and divided into N parts.
How I assume the value of U, and how calculate the surface area.
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Phase change within a shell and tube heat exchanger occurs in a Moisture Separator Reheater (MSR), which I cover in Chapter 9 of my book, Heat Exchangers. I have attached a few figures plus there is more info and software available free at my web site.
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Hello dear researchers, I want to know the possible reasons (all possible reasons) for the phase change in single layered or thin film of 2 D materials probing under the ultra-fast laser spectroscopy?? For example if we obtained a spectrum indicated the phase change in that TMD then how can we know the underlying physics behind this change. Thanks
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I'm familiar with how concepts such as the latent heat of fusion and vaporization work for a system consisting of a single phase-changing gas. q = mH, q=mc dt, all that fun stuff. I'm not familiar with any work in how these concepts manifest when the system consists of multiple gases, or how to determine how much of the heat energy is being transferred to a given component of the gas.
If I had, for instance, a gas containing oxygen, krypton and hydrogen, and I wanted to determine how much energy I'd need to put in in order to get the krypton to devaporize into a liquid while it was mixed in with the other gases, any idea how I'd go about calculating this?
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I assume you mean "How much heat needs to be removed for the Krypton to devaporize into a liquid". You have to look at the partial pressure for each component. If you are above the boiling/condensation point for Krypton (at its partial pressure) you first need to remove heat for all gas components to reach the boiling/condensation point of Krypton. Then you need to remove heat to devaporize (heat of vaporization) the Krypton. This will give you a rough idea. I assume the gas composition is contained in some way and as the Krypton gets liquid the pressure will change which implies that you have to remove a little bit more heat. How big the differnce is depends on how much Krypton there is in the gas composition.
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Can anybody explain how to do thermal charecterization for parrafin wax.It would be of great help if any one can atleast share me journals or research papers on charecterization of parrafin wax?
Basically we are doing thermal analysis of lithium ion battery with the help of phase change materials.So we have taken parrafin wax has a phase change material.So we want to do characterization for parrafin wax.
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Dear Yella Dhawaleswar,
TGA and DSC analysis is the best analysis that can be used to measure thermal stability and properties of paraffin wax.
I have attached some articles which the mentioned analysis had been performed. I hope they would be useful.
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Our group are investigating the influence of malonic acid on CaCO3 phase changes (calcite, aragonite, vaterite). It is evident that the carboxylic acid used (up to 20.00 ppm) was able to alter both the morphology and the crystalline phase of the CaCO3 polymorph.
However, it is difficult to analyse the phase transition through TG-DTA, as shown in the files attached.
If you could help us with the DTA analysis please.
Thanks.
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Dear Stefanus Muryanto,
I think the plots you have shown are DSC thermograms and the following article may help you.
doi: 10.1023/A:1010158918395
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I would like to simulate the process of heating a material in a stream of concentrated solar radiation, taking into account the spectrum of solar radiation, flux density, absorption coefficient of the material, phase changes in the material by changing the temperature of the material. how to apply the Stefan problem?
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You have to physically describe your material by defining its:
Geometrical dimensions,
The specific heat of the material,
The density of the material,
The melting temperature,
The material of container and its shape as well as its thermal
properties as listed before.
The incident solar radiation power incident on the furnace,
The reflected part,
The absorbed part,
The re-radiated part by the black body radiation.
If there is vacuum you do not need to consider the convection.
The heat lost by conduction through the support of the container.
Then all you need is to write the heat balance equation and solve it to get the temperature as a function of T and get the steady sate temperature and whether you will reach the melting temperature or not.
Best wishes
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Pure deionized and degassed water were studied freezing kinetics. The sample size is 3 mL with the freezing rate 4-degree celcius/ min and freezing temperature -20 degree celcius. Temperature measurements were taken at the geometrical centre where the sample is kept in 1.5 cm diameter cylindrical glass holder. The freezing curve was studied with automatic data logger and the response was different each time. The Precooling time (time taken to decrease the temperature from 4 degrees to the ice-nucleating temperature), Ice nucleating temperature, phase transition duration (time taken for complete phase change of the sample from liquid to solid-state) were studied. The ice-nucleating temperature is the lowest temperature detected which is always lower than the freezing point.
The ice-nucleating temperature does not appear in some cases. Any possible reason? How to overcome that.
Thanks.
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Robert Tournier Thank you for your suggestion. I always heat the water up to 100 °C and then cool it before using it as a sample. Since water in normal condition contains a lot of dissolved gas. So it is very much important to remove the gas to have a standard outcome in each experiment. Yet the problem remains the same, the freezing curve does not show any depression caused by nucleation phenomena. There are no issues with the temperature measurements.
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I am trying to simulate DC Casting of Aluminum Alloys in Comsol. I found an example related to Continuous Casting that it couples fluid flow, heat transfer and phase change during solidification of the liquid alloy. Is it possible to involve solid mechanics for the solidified shell that is computed from phase change model?
If it is not possible to do a fully-coupled model: Could you please tell me how can I set the model concerning only solid mechanics and heat transfer ? Is there a way in COMSOL to add in the presence of time, new layers of material while moving the boundary conditions (mold, water colling) silmutaneously, to simulate fluid flow ?
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As Dr. Rudolf Hellmuth said, it is possible and complex.
You have to go for coupled field analysis. First you need to run the Heat transfer analysis and you can capture the fluid flow behavior too. Then the temperature gradient has to be given to Structural analysis to avail the mechanical stresses. Boundary conditions plays a major role in both the cases.
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Like if for eg. Gd2O3, its phase change by pressure and temperature from cubic to hexagonal to monoclinic then there must be changes in angles and lattice parameters but is there any change in atomic positions in unit cell as composition is not changing?
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Yaa sure sir, we may discuss on this... Actually as u stated.. Obviously there must be change in phase structure but my concern is in drawing these different phase structure.. Like their positions in corresponding unit cell. How one can get to know atomic position of atom corresponding to same composition but of diiferent phase.. Like for eg. U have taken CdS, hexagonal and cubic structure,, let us discuss on drawing these two,, firstly we must have to know their position in unit cell?
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Hi guys,
I’m recently dealing with in situ XRD heating experiment of epitaxial thin film on single crystalline STO(100) substrate.
There are two problems I ran into:
1. Multiple background peaks from the heating stage. Any suggestions of how to deal with that? Especially when there are overlap of film characteristic peaks and stage background peaks?
2. The STO(001) peak seems to experience thermal expansion upon heating (which is reversible, meaning the peak position of the heating cycle overlaps with the cooling cycle). How can I get rid of this effect since there are BOTH phase change information and thermal expansion information for the film?
Anyone has similar experience in the related field can provide some reading literatures or insight? Thanks a lot!
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Zhimin Qi, in a clarification, you say "2. Why I don't see other publications having a problem with the thermal expansion? In other words, how would you isolate the real change of lattice parameter (e.g. from phase transformation) from the thermal expansion of lattice?"
One of us is confused. You want to separate "real change of lattice parameter (from phase transformation" from "thermal expansion of lattice."
First, thermal expansion of lattice is real. It make no sense to contrast a "real" change in lattice parameter with a change due to thermal expansion.
Second, you refer to change in lattice parameter due to phase transformation, but if there are no new peaks or vanished peaks, there is no phase transformation. If there are only lattice parameter changes, there is no phase transformation. In other words, a phase change will cause at least some new peaks to appear and some old peaks to disappear. In addition, there will usually be a suddden change in lattice parameter. That is how you separate thermal expansion effects from phase change effects.
Third, thermal expansion of the overall sample+substrate will shift your peaks due to radial displacement of the sample. Is this what you are trying to separate from thermal expansion of the lattice? Contact Anton Paar to help with this. They have lots of educational literature available. One way to do this is to calibrate the radial displacement (height or z shift on a vertical motion theta-theta instrument) by adding a standard such as Si or LaB6 to the top of your sample to use as an internal standard. Then, at each temperature, fit to lattice parameter and radial displacement using a whole pattern fitting program such as GSAS. The known variation of your standard material's lattice parameter with temperature will allow you to know the true sample temperature, which will not equal the stage temperature. From that you will determine sample temperature as a function of set temperature (or equivilently, delta-T, the temperature difference between set temperature of the stage and actual sample temperature). The temperature will depend on your sample. The radial displacement as a function of temperature will allow you to fit lattice parameters of that and subsequent scans. Used a fixed radial displacement in the fitting program, then you can get the lattice parameters from the fit, even if there are too few peaks to fit both.
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I would like to simulate for the energy exchanged between hot and cold fluid.It will involve phase change of the cold fluid.it would be really helpful if the suggested software is Open-Source
Thanking oyu in advance
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Greetings
Depending on your simulation needs
as Ruben Borrajo stated Open Foam is probably the best open source CFD software
Fluent is paid however Ansys has a student version with some limitations offcourse but its free for students.
If you want to take a more mathematical approach to the simulation coding the heat exchanger model Scilab is open source and works almost like Matlab
For flow sheet steady state there is Coco and DWSim also open source
Regards
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The Eric Birse Trust was founded in 1984 by the family of Dr Eric A B Birse to commemorate his life and work. The primary intention of the Trust is to fund, via The Eric Birse Studentship, PhD research in the field of Chemical Engineering. To date the Studentship has supported eight PhD students, each of whom has progressed to have successful careers in industry and academia.
A PhD Scholarship supported by the Eric Birse Trust is available at the School of Engineering at the University of Edinburgh. The Studentship is open to all who wish to work in this discipline subject to meeting the Eligibility criteria and to complying with the Application Procedure. Student must apply with your own Research Proposal and nominate the most suitable academic within the Institute of Materials and Processes (IMP) or the Institute of Multiscale Thermofluids (IMT) to supervise this research.
More specifically at the Institute of Mutliscale Thermofluids we are carrying out research work on both experiments and computations, with an emphasis on multiscale and multiphase fluid systems interfaces and phase change from nano- to macro-scales undergoing heat transfer. Topics include phase change, wetting and associated capillary phenomena, and boiling (e.g. at microfluidic scales). IMP and IMT academics can be found using this filterable list. The closing date for applications is 31 December 2019.
This is an excellent opportunity for mentoring a young researcher in the ambit of phase-change and heat transfer. If interested and not aware of the type of project that can be carried out, feel free to contact Daniel Orejon for more information on d.orejon@ed.ac.uk and 0131 650 5735.
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I am interested in mentoring
Please send information
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Recently I have proposed a new model of vapor compression heat pump for boiler flue gas waste heat recovery. The heat pump is employed for domestic water heating. I have used air as a refrigerant.
Although air is not a phase change fluid just like refrigerant but the simulation results are quite satisfied.
Now, if I publish my work, then the reviewer can raise the questions about using of air as it doesn't goes under the phase change and it also have low COP but on the other hand use of air at ambient temperature in cold climates can save the refrigerant cost as well as air have zero ODP and GWP.
How should i justify the reviewer about using air as a refrigerant?
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I think you'd better give more information.
However, please take a look at the following paper in which there is no need to change the refrigerant phase.
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Will the muon disappearance and appearance event rates be affected by a change in the value of the Dirac delta CP phase?
For eg. We have muon disappearance and appearance event rates at Delta CP=0, what will be the impact on these event distributions if the value of the Dirac phase is changed to -90?
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One, can check the probability plot first and that will affect the event in the same manner.
Thanks
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I am currently doing a gas-liquid phase change simulation, but the false phase change near the gas-liquid interface occurs due to the spurious velocity. Is there any way to reduce or eliminate this non-physical phenomenon?
Thanks for your help
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I think you are using the Shan Chen model, whereas the Free Energy and Phase Field models can eliminate spurious velocity.
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I have read that to know the composition of different phases in a ternary phase diagram of metals A,B,C (at a particular temp. T), we can apply lever rule along the tie line. But, I am not sure about how to draw the tie line and how to apply lever rule along it as some procedure says to use line and few have mentioned smaller triangles to draw (tie-triangles) to know the composition of the phases. Kindly illustrate on the concept. Thanks in advance for help.
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Dear Adhidesh,
Unfortunately, you can not predict those tie lines that you see in ternary phase diagrams, they are experimentally determined by different techniques depending on what kind of sample you have (NMR spectroscopy, low-angle x-ray scattering and etc...). Usually, when the two phases region is determined, the tie lines are determined as well. I think your question was: can i draw the tie limes (by geometry or any other mathematical means) if i know the limits of the two phases region? The answer is no, those lines are experimentally determined by analyzing the composition of the two phases.
For example, if you know the limits of the two phases, what you do is take many samples inside the two phases region and determine analytically the composition of each phase: if you have one phase with 25% of A, 50% of B and 25% of C and the other phase with 60% of A, 30% of B and 10% of C, you now have two points that can be connected to form one tie line.
Once you have sufficiently tie lines inside your two phases region, other tie lines can be predicted (conjugate lines).
Best,
Thiago.
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In FLUENT, the only model available for phase change simulation is the Lee model.
Are there other models?
And there is an option to include only a single Saturation temperature. Can the entire P-T graphs be plotted into FLUENT for best results in phase change simulation?
Your help is heartily appreciated.
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@Siddharth: I have seen this video before too. Infact I have successfully simulated the same just like 4-5 months ago. It was at the time when I was working on a DST project. I can't clearly identify where your problem is with the info specified. However, I suggest the following:
1. How about mesh quality?
2. Did you patch the zones right (especially the phase fraction values during initialization)
3. Did you try reducing URF and running the simulation?
Hope it can be of assistance.
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It is often said that there is a phase change in battery type material and no phase change in the intercalation pseudocapacitance. So can I assume that if our material's crystal structure is cubic in case of battery then it will change into hexagonal or something else phase during charging or discharging process. And this doesn't happen in intercalation pseudocapacitance. If it so then why it doesnt happen in intercalation ones. I am not able to pickup this point.Please help me to figure it out.
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Dear Atika,
The following article may give you some useful hints about Intercalation pseudocapacitance behavior.
Regards
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XRD of semiconductor material show phase change from crystalline to amorphous , but the optical band gap decresses, what is the reasons behind this ?
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The amorphous phase tends to be less dense than their crystalline counterparts. Lower density means larger inter-atomic distances (on average). So, qualitatively there is less electronic correlation compared to a crystalline material which results in a lower bandgap. Of course, this is just a qualitative assessment and you would need to look into more sophisticated simulations (DFT) to verify that trend for your specific material.
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Desalination of salty groundwater and seawater could unlock the vast water resource and provide a sustainable source of water to water-stressed regions of the world. Desalination processes have been categorized into three main areas: i) thermal or phase change processes, ii) filtration-membrane processes and iii) intensified processes which involve integration of various processes (Gude et al., 2010). However, these methods are costly.
Objectives our project are as follows:
1: To introduce an economic and viable system to the desalinated ground-waters in order to support urban and agricultural prosperity and protecting the environment.
2: To set up the introduced system in the desired region.
I am so glad that anyone gives me useful advice and experience.
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Excellent and Impressive article best wishes
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Hi every one can anybody guide me which White LED ( One -chip or Multi-chip type ) is used to analyse the phase change of light signal/pulse . Thanks
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Dear Muhammad,
May i came late to this question. The phase is strictly speaking is used for sinusoidal waves rather than pulses. For pulses you can define delay time instead of the phase. If the medium is not dispersive then it will preserve the pulse shape. If it is dispersive the shape of the pulse will change.For visible light communication the dispersion will not be cause by the difference in the refractive index for the different wavelengths contained in the light but it will be caused by multi path effect.So, in principle you can use any source of white light.
You can check this theory by using both sources in your experiment.
Best wishes
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Hi, a very basic question here. hope someone can help.
I have a PCM which has a very small change in density during phase change i.e. it has a density of 0.90 kg/liter in solid phase (measure at 25 deg C) and a density of 0.89 kg/liter in liquid phase (measured at 80 deg C). The PCM has a melting range of 50-51 deg C. I want to impregnate this PCM in two different metal matrices and capture the differences in convective heat transfer indicated by buoyancy velocities.
What i fear is that this small difference in density over a huge temperature range (i.e. from 25 to 80 deg C) would not create any buoyancy (basic principle of buoyancy is differences in densities as a function of temperature). Therefore, the heat transfer in liquid phase would also be largely conduction dominated. Hence, i wont be able to capture the effect of metal matrix morphology in convective heat transfer.
Did i say it right?
Regards,
Zahid
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Actually the convection is not driven by difference between different density of solid and liquid, but by the density variation in the liquid due temperature gradients, only liquid will flow. However it is hard to evaluate the impact of metal matrix, that would depend on its porosity.
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Let's say I have a material with a stable phase A that transitions to another stable phase B at temperature T. If the material also has a metastable phase A', I know that if I cool B fast enough I would get:
B -> A'
and if I cool very slowly I'd get
B-> A.
If I were to look at the interface between B and the new phase and somehow extract all possible information (energy/mass transfer, etc), what signal would indicate to me that I would expect A' (metastable) to form over A?
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When you refer to thermal gradients you propably refer to solidification processes. For these the temperature gradients are very important as the interface velocity is usually determined crucialy by the transport of the latent heat. Here, of course, special literature exist, but beyond what is taught in general lectures I cannot help much. Your reference to "metallurgy books" seems that there you looked at the soldification sections.
If you are more interested in solid-solid transformations, usually the thermal gradient is less important, simply becausee the latent heat associated with the transformations is much lower than for solidification (the invariant parameter is actually the transformation entropy, connected with the transformation enthalpy via the equilibrium transformation temperature). In that case there is a huge amount of concepts to describe phase transformation kinetics. Porter Easterling is a good starter (having also solidification sections). Models are of course on very different levels. If you want to find much more, you may refer to Christian.
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I have a binary system of polyalcohols. When I cool the mixture down past it's solid-solid transition point, it usually forms a metastable phase. We know this because upon reheating promptly after the cooling, the transition temperature is different than if we let the sample anneal for a few days.
Is there an alternative to annealing for several days? How can we speed up the process by which it transitions to it's stable phase? Mechanical engineer here, I apologize if this is a rookie materials science question.
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The thermodynamically stable form will crystallise out last, sorry for the mix up, you might one to use DSC first.
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We are studying a heat transfer problem of maraging steel 300. There may be a phase change (from martensite to austenite, at ~600 deg C), and I wonder if the heat associated with that phase change is significant. Is there a way to look up the latent heat or standard heats of martensite and austenite? Thanks in advance.
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I am working on paraffin wax, in which there are two phase change process, initially there is a solid to solid phase transition and followed by solid to liquid transition. This is clearly observed in a DSC curve. So if there is a solid to solid phase transition at ~600 degC for your material, the DSC curve should show a endothermic peak. Measuring the area under the peak will give your latent heat value.
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How to find heat transfer coefficient within sphere containing water which is still in nature and undergoing phase change?
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In sub-critical thermal power cycle, the thermodynamic fluid absorbs certain amount of latent heat during phase change from water to steam but in a super critical unit, this absorption is zero. Now question is, how much this factor helps in improving the cycle efficiency of a super critical thermal power cycle?
Practising Efficiency engineers in large thermal power plants can answer this question.
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Dear Bo Miao, Thank you for your attempt and answer.
Your answer is theoretical and it does not reflect any efficiency and how can it be enhanced in a traditional thermal power plant using coal as principal fuel.
The increase in efficiency by and around 5% in super critical thermal power units is effected by following factors,
1. Larger unit capacity say 660 MW in normal 500 MW units
2. Higher steam parameters say pressure 260 kg/sq.cm in stead of 171 kg/sq.cm and 580 degree Centigrade in stead of 540 degree Centigrade.
3. During process of evaporation say phase change from water(liquid) to steam(vapor or gas), since system operates above critical pressure of water/steam (225 kg/sq.cm) it absorbs nil/no latent heat.
My question is how that 5% increase in efficiency can be shared or distributed in above three heads.
You can consult your professors on Thermodynamics and Heat Engines and suggest a plausible answer.
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I would like to ask that, is there any solid material which change its lattice arrangement (Solid-Solid Phase change Material) due to heat flow and all the heat is used in transformation rather than increasing its temperature just like when heat is provided to ice, the phase change process occurs at constant temperature, latent heat of melting (Solid-liquid phase change material).
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Mennatalla Elmanzalawy , Thank you so much for your kind suggestions. I will look into it.
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It is know that austenizing steel produces hard martensite after quenching, and the properties of it can be improved by tempering to create better toughness while making the metal softer and more ductile.
Yet say this method is used for a piston (which was quenched then tempered at 600 degrees C). What happens to the hardness of the low alloy steel in standard operating temperatures up to 425 degrees C?
Are there any further phase changes? Can something like precipitation hardening occur or are these temperatures too low for an already QT steel.
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If you properly quench a hardenable steel and then temper it at 600 C, you sure can use it at 420 without any damage to microstructure and properties. The only one additional question should be asked and replied: how much time your part should serve at 420 C. If the service is long-period, it may cause some undesirable microstructural change with time.
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Hi!
I am using Ansys/Fluent to model the ice melting and formation in a horizontal enclosure heated (+5degC) from both upper and lower plates (melting case) and cooled (-5degC) from both plates (freezing case).
For this purpose I am using a fixed grid method (enthalpy-porosity approach) where the mushy zone is considered as porous (applying the Darcy law).
The density was defined in the liquid fraction, meshy zone and solid fraction in order to account for the non-linear behaviour of the water density which is characterized by a maximum at 4degC:
In the liquid phase the density was defined as given by Gebhart and Mollendrof
In the meshy region I used a linear interpolation between the density of water in liq and solid phase
In the solid phase, the density was set to that corresponding to the solid fraction.
The phase change temperature range was set to ( -0.5..0.1deg C) --> Tsolidus=-0.5 and Tliquidus=0.01degC
All properties were defined using a piecewise linear functions to define properties in both phases.
Due to the relatively large density difference between the solid and liquid phases, it is supposed that the buoyancy forces will make the ice block floating upwards as it is melting. This is not a "real movement" as I am using a fixed grid (and not a moving mesh), but it is the change in the cell properties that will characterize their fractions and then "simulate a floatting"
Unfortunately this phenomena was not captured by the enthalpy-porosity method!
Someone can help?
Many thanks :)
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Hi Yosr
About simulating the melting or solidification process of ice/water, which output parameter is more important for you?
I mean that If you wants just report the Liquid Fraction or you want just follow the melting process and temperature stratification in the domain, The enthalpy-porosity method is a efficient method but you should consider the correct value of thermal properties of the ice/water.
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Hello all,
I have a very basic question regarding the presence of interface ( presence of surface tension to be precise) between liquid or gas phase with supercritical phase.
For instance, consider oxygen (Tc ~ 150 K, Pc ~ 50 bar).
Let us consider:
1. Case 1 wherein liquid oxygen (T and P > Tc, Pc, say 100 K and 45 bar) is injected into a chamber filled with gaseous oxygen ( say T = 130 K, P = 45 bar). Then if I understand well, then there will be phase change and we will have surface tension present between these phases.
2. Case 2: Oxygen above the critical point (say T = 160 K, 55 bar) injected into supercritical oxygen say T = 180 K and 55 Bar), Both are in supercritical phase. In such case there will be just diffusion ( which I understand is due to difference in concentration/density and thus self diffusion). No interface or effects of surface tension will be present.
3. Now let us take a case, say liquid oxygen is injected into supercritical oxygen.
For sake of convenience, say initial T = 120 K and P = 60 bar ( i.e above Pc but below Tc), and injected into supercrtical phase of oxygen. ( T = 180 K, P = bar).
Is this case similar to case 2 or case 1 described above.
My main concern was will there be surface tension present or will there be just diffusion.
( I am assuming here that at no local point, the T and P will fall below Tc,Pc to avoid any liquid --> gas conversion)
More precisely, will it be reasonable to consider surface tension in analytical/numerical computations?
To my understanding, we incorporate surface tension to account for increase in energy due to interfacial energy/latent heat.But here we don't have anything of this sort but as we have liquid and Supercritical state, it's slightly confusing.
How will things change when instead of liquid injection, we do same case with gas state ( say T = 190 K, P = 40 bar i.e. T> Tc , P < Pc)
Thanks
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Hi Diwakar,
I think you already know the answer and just asked to confirm.
Your explanation is very clear.
Regarding third case,injectant fluid- liquid( 120 K, 60 bar) i.e, Tr=0.8 & Pr=1.2 and supercritical chamber ( T = 180 K, P = 55bar)Tr=1.2&Pc1.1,
Since both the injectant and chamber pressure are supercritical, depends on the temperature at the interface region, the surface tension come into play.
For example, if region with Tr < 1 surface tension,and Tr >1no surface tenison.
Hope works of Arnab et al (refer attachment) would be helpful
Regards,
Senthil
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I'm trying to simulate the solidification and melting process of a PCM in ANSYS Fluent, using solidification and melting module. To do so, since properties for solid and liquid phases are different, I'm trying to apply these difference for these two phases separately. I've already tried using piecewise function for tempratures over and below phase change temprature. But it causes divergence in my simulation.
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Of course
Ali Radwan
Firstly, the PCM domain is defined as a liquid, then the properties for the solid, transition and liquid phases are applied. The density variation is simulated using boussinesq approximation. Also, for the variation of the specific heat and thermal conductivity you can use a piece-wise polynomial function with three stages (3 temperature ranges for solid, transition and liquid phases) . For the divergence you need also to check the mesh quality and apply smaller time step, especially during initializing your solution.
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The thermal radiation is dependent on Temperature , and since during phase change (latent heat) the temperature stays the same, I was wondering whether the thermal radiation (intensity) would also stay the same?
Thanks
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Hi @Payam Vahdati
Yes, radiation would stay constant during melting and boiling if these occur at constant temperatures. This only considers the temperature of the substance though.
During such phase changes the surface emissivity of the material may change, which can cause either an increase or decrease of the rate of radiative heat transfer.
All the best
Johan
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Clouds are important for their hydrological, thermodynamical, and radiative effects. That is, they redistribute water all over the globe, transport energy by up-taking and releasing the latent heat, and scatter/absorb solar and terrestrial radiation fluxes.
One question lingering in my mind is: which cloud phase (i.e., ice & liquid) possesses the most cloud water? Ice or Liquid? The reason I am interested in this question is that the understanding of the facts of cloud phase and its representation in climate models are relevant to various key problems, for example cloud microphysics (aerosol-cloud-precipitation interaction) and cloud radiative feedback (how cloud phase change modulates the scattering/absorption properties of clouds in a warming climate).
I have sawn some publications (e.g. Huang et al., 2015, JGR, doi:10.1002/2014JD022779) showing that there is more ice water than liquid water, globally. But I also found the retrieval of cloud water, especially ice water, suffer from tremendous uncertainty. So, I want to hear from the many talented people here, about your knowledge and opinions on this question. Thank you very much.
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The answer depends on the temperature in the specific cloud, it is commonly accepted that:
”At temperatures between 0°C and -15°C most clouds are composed of supercooled water droplets. Between -15°C and -40°C most clouds contain a mixture of ice crystals and supercooled water droplets”
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The evaporation wave, or "free surface boiling", is a type of violent vaporization that occurs in absence of nucleation. I understand that the thermodynamic limit for the onset of evaporation wave could be the spinodal curve. However, the spinonal curve is also the limit of homogeneous nucleation. Thus, in the metastable region, what are the key factors that determine whether the system undergoes homogeneous nucleation or evaporation wave?
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I'm no much expert on that, but i'll cite some factors.
Both evaporation wave and nucleated bubbling are the same transition from thermodynamic point of view, what change is the dynamics.
1) nucleation energy: if there is high energy barrier against nucleation of bubbles, nucleation is inhibited and you get evaporation wave. Impurities and walls-> low energy barrier.
High liquid surface tension inhibits both processes, but I'll say that favour the wave (uncertain ;)
2) How much you are away from equilibrium: very far away, get nucleation. Quite near equilibrium, surface evaporation.
3) Timescale: the evaporation wave is a slow process (slower than speed of sound) while nucleation can come from a passing shock wave.
4) difference in volume between the two phases: high difference, it helps to get the evaporation wave dynamic, while works against nucleation thanks to surface tension
5) Dynamics of the discharge: the evaporation wave need a violent discharge to keep all mixing up. A slow decrease in pressure should not provoke it, the liquid will slowly evaporate (no wave) or nucleate bubbles.
6) An high viscosity of liquid or gas inhibit evaporation wave.
You can choose now...
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More recently, Manceau et al. demonstrated the THz polarization control via the accurate control of the surrounding gas pressure of two color filaments. The change of gas pressure will induce a wavelength dependent change of refractive index, resulting in the relative phase change of the two laser fields. What is the relationship between air pressure and refractive index? Who can help me to answer this question?
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There is direct relationship between the presser and refractive index .
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It is well known that phase change memory has a SET speed problems.