Phase Change - Science topic

Hi Ravi Varma ,

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

I have the same issue, what i have noticed is the free volume of reactor that should be considered for supplying the initial pressure.

Dear Ali Fakhreddine

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.

Best Regards.

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

2. Fins are never used on the surface in contact with a fluid undergoing phase change.

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.

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.

Welcome!

Dear Mohamed sayed Ahmed Mostafa ,

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.

Dear Elaine M Cardoso , this scientific contribution presents very interesting criteria that will surely be of use to you.

you can read the following articles

1. https://www.physicsforums.com/threads/negative-pressure.428998/

2.

3.

4. https://www.discovermagazine.com/the-sciences/the-physics-of-negative-pressure

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.

Please send me the case file

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.........

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.

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.

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.

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.

Hello,

hope this paper help you:

Silicon photonic waveguides & nonlinear optical effects

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.

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.

Hello

You can select the process for each domain separately.

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.

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.

You can follow this paper for multiphase flow:

I think your optimization model may be ill-posed. Following link can be useful in this regard

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.

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 ??

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.

Thanks Muhammad Waqas Qureshi

I found the provided papers very useful!

Have a look at my paper:

It will be like an heat exchanger i guess. Try heat exchanger equation.

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).

possible only if the boundary condition temperature of the low temperature(200K) side should be increased just above the dew point temperature.

Hi @Tejendra Bhanabhai Patel ;

Did you get udf. Actually, I also want to implemet VOF with thermal phase change model. Kindly provide me.

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.

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.

Kaleem Ullah

See information useful to you

https://www.researchgate.net/post/How_can_we_know_the_possible_reason_for_the_photo-induced_with_light_eg_ultra-fast_lasers_phase_change_in_monolayer_TMD_materials

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.

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.

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

Dear Muhammad-Sultan Saidvalixanovich Paizullakhanov ,

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

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.

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.

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?

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.

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

I am interested in mentoring

Please send information

Dear Shah Rukh Jamil

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.

One, can check the probability plot first and that will affect the event in the same manner.

Thanks

Dear Zhang Chunhua

I think you are using the Shan Chen model, whereas the Free Energy and Phase Field models can eliminate spurious velocity.

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.

@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.

Dear Atika,

The following article may give you some useful hints about Intercalation pseudocapacitance behavior.

Regards

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.

Excellent and Impressive article best wishes

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

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.

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.

The thermodynamically stable form will crystallise out last, sorry for the mix up, you might one to use DSC first.

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.

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.

Mennatalla Elmanzalawy , Thank you so much for your kind suggestions. I will look into it.

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.

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.

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

Of course

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.

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

Dear Xianwen Jing

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”

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...

There is direct relationship between the presser and refractive index .