Heat & Mass Transfer - Science topic

Dear Albert Samai your contribution would be highly welcomed to CESBP 2025 conference.

I not engineering department and my department agriculture economics

You may want to check my post elsewhere at this forum ― as a case study related to transient mass balance analysis:

I've looked at the polynomials that you have noted: none of them make sense, whether using actual temperatures or reduced temperatures.

I suggest going back to the original data and making your own, (lower order) curve fit using Excel.

One further comment, you would be mis-calculating enthalpy if you used your last equation as it assumes a constant specific heat over the temperature range: the correct form is to integrate Cp.dT over the range, I would integrate the secific heat equation (if it was correct).

Hi

I tried to run an ANSYS FLUENT simulation with SST Model and it was hard to converge. The laminar model should converge, I'd suggest using a better quality mesh.

In some cases the SST will resolve to low/zero turbulence, but that is not always the case. The SST model will have turbulent fluid coming in the inlet, as set by your boundary condition. This would take time/distance to convert to laminar using the SST model. Check your Viscosity ratio in your results, see how turbulent the SST model is showing your flow to be. Laminar flows can have problems converging where they are actually turbulent flows, or where transient laminar flow structures exist. (This is assuming you have a good quality mesh and the simulation is correctly set up.) If you say the flow should be laminar then it is still quite possible that a laminar steady state simulation will not converge because of transient flow structures. This is very common in heat transfer simulations with natural convection - the natural convection tends to have transient laminar structures. If this is the case the only way to proceed is to do a transient laminar simulation. If you solve a laminar simulation with a turbulence model you are adding extra dissipation to the model. This dissipation is not real, it is a product of the turbulence model you are using, but it can have the effect of damping out these transient flow structures and apparently converging. The SST turbulence model is better than most turbulence models as when the turbulent kinetic energy goes to zero (it is exactly zero in a laminar flow, by definition) the turbulent viscosity also goes to zero, so SST does not add much dissipation to the model and you might get away with it. But k-epsilon based models are well known to have far too much dissipation in the low Reynolds number regimes because as k goes to zero the turbulent viscosity goes to a finite value, and this is false additional dissipation. This is why the k-e model is a bad choice for low Reynolds number flows, and you either need to modify it or use a k-omega based model like SST which does give zero turbulent viscosity at zero turbulent kinetic energy. However, if your flow is steady state laminar and you use the SST turbulence model the turbulence model is likely to give effectively zero turbulent viscosity, meaning that your answer probably will be reasonably accurate (only with a small amount of extra dissipation). If your flow is transient laminar and you use the SST turbulence model there is a good chance the turbulence model will generate too much dissipation and damp out the transient flow, which is wrong. You are likely to get a big error in this case. In this case using the SST turbulence model is wrong. A transient laminar model is correct. Note you will need to do time step, mesh and convergence criteria sensitivity studies to work out what you need for time step and mesh size, and convergence criteria.

Hopefully that explains things a bit.

Carry out the tensile test and record percentage elongation (after the yielding up to the fracture)..

Recursive vs. one-step calculations are of little concern with current computer resources and readily available software. The bigger issue arises from the fact that these two methods solve the same separable differential equation, but using different assumptions when separating the variables before integrating. This means that the two different methods handle some things differently, like implicitly/explicitly averaging properties, heat transfer coefficients, etc. You should consider EPRI TR-107397 (Service Water Heat Exchanger Testing Guidelines). The principal author of 1997 version is Jeffrey Rabensteine of Power Generation Technologies, here in Knoxville. The 2015 version was updated by Lindon C. Thomas, who is a friend and also lives in Knoxville. Dr. Thomas is a renown authority on the P-NTU method and wrote a textbook covering the subject https://www.amazon.com/Lindon-C-Thomas/e/B001HOVPI4

Please refer to this reference.

Zhang, Y., Li, Q. and Zhou, H., 2016. Theory and calculation of heat transfer in furnaces. Elsevier.

Surely by adding Ti alloys

Dear Afroza Begum, but the end groups of a peptide are also carboxylic acid and an amine, not a radical 'R'. My Regards

Thank you for the writer of the first answer.

Y.E

Dear Manoj Kumar Sharma

Have a look:

Kind Regards

Thank you all for your help.

I already found my solution through this book:

G.G.F. Froment, K.B.K. Bischoff, J. De Wilde, J. De Wilde, Chemical reactor analysis and design, third, John Wiley & Sons, Inc., New York, 2011.

I think the most simple 1D model for such problem can be:

1. Mass + species balance

2. Energy balance + effective Radial and near wall HTCs. Dixon model for those HTCs are correct for wide range of Re.

The fluid properties such as viscosity, heat capacity, thermal conductivity can be calculated via polynomial fitted equations.

I solved the above 1D model correctly using only few lines of code. The difference between rigorous 1D model ant this one is less than 10%.

About the stiffness matrix size: you can do it, but it is just a purely numerical solution (no science behind) if you make your steps independent (I mean if you move from step n to step n+1 and between those 2 steps there is a dimension change, export results from step n and make a transfer to a new model corresponding to your step n+1 putting zeros wherever there is no data from the previous step results and add whatever you want to add in the formulation of the initial state of your new calculation, ie the n+1) however, about adding mass, yes you would be infringing the fundamental law of mass conservation if you consider your system at step n and step n+1 the same, this is why I propose to numerically separate the model into one corresponding to step n and one other to step n+1. I hope I explained well my point

Dear Professor Brian G Higgins,

Thank you so much for sharing information

Grashof’s Number.

Hello.

You can find the equations here:

They used the equations indicated in EnergyPlus Manual. For this, you need to select your desiccant wheel based on the inlet airflow and use the performance data given by the manufacturer.

You must solve continuity equation, Darcy or modified Darcy equation and Energy Equation

Many Thanks

This is a theoretical work where the chemical compound A and which B are not specified clearly. It is only known that A is a substrate and B acts as an autocatalyst. Moreover, both reactions take place in two different phases. We may deal with such situations in bioogical systems.

Thanks, everyone for the feedback.

Hi, I am facing the same problem. Can you explain the solution?

Dear Dawid,

I would advise use MATLAB instead of Fortran code for steam cycle performance.

Power plant can use couple of process simulators such as e.g. Aspen Plus, Unisim, and Pro II. . To evaluate the model’s performance, its predictions may be compared with those of an equivalent model from Gate Cycle or other cycle. Use the Steam table for steam, count enthalpy values of cycle performance, and predict the inlet temperature, mark steam deviations and efficiency range. Just assume, the relative deviations in the plant power output and efficiency must be less than 0.65% for 100% loads. Use MTALAB, it can solve your issue(Reference: Aklilu and Gilani adopted the normalized parameters from to describe the characteristics of compressor and turbine and developed a simulation model in MATLAB to identify the plant operation mode from field data. Zhang et al).

The simulation can follow the recycle modules.

The following assumptions perhaps you have made for simulating the pressure in power plant using Aspen.

1. Plant at Steady state (2) Fuel combustion (3) Cooling water flow (4) No water leak.

Refer the site:

file:///C:/Users/3020/Cookies/Desktop/Downloads/SimulatingcombinedcyclegasturbinepowerplantsinAspenHYSYS.pdf

Ashish

I am following the discussion...

In the the Stefan-Boltzmann law , only one variable parameter is epsilon. This will come under heat exchange between surface. You need to feed the both the emissivity of surfaces which are considered.

Dear Franklin Uriel Parás Hernández

Useful information can be found in the attached files.

Regards,

Dear hakeem,

Phase change materials (PCMs) are classified according to their phase change process, temperature, and composition. Temperature-based models are divided into three categories: apparent heat capacity (AHC), effective heat capacity (EHC), and heat integration (HI) etc. The main issue existing in the apparent heat capacity method emerges when significant temperature changes occur (in a time step) in a control volume that is close to the phase change temperature.

The apparent heat capacity method, often referred to as the effective heat capacity method, takes into account the latent heat of the phase change by means of an artificial increase of the physical heat capacity in the temperature range of the phase change.

The effective heat capacity method is an improvement on the apparent heat capacity method. The value of the effective heat capacity (Ceff) is obtained through the integration in the control volume,

Ce f f = Integration Cap dV / V

where V is the control volume. It is worth mentioning that the adoption of the effective heat capacity method allows the use of higher time steps and smaller phase change intervals when compared with the apparent heat capacity method. However, the integration necessary for the calculation of effective heat capacity represents an increase in computational cost.

The solidification of a semi-transparent material by a front tracking method, computational demands of front tracking method can be reduced via the acceleration by means of graphics processing units and NVIDIA CUDA. Heat capacity methods with enthalpy and heat capacity both for solidification in various grain zones studies reveals that only very limited information is available about the computational demands and efficiency of front tracking methods. Browne et al. (2004) carried out simulations of the grain growth during the solidification of an alloy(look at the reference: {https://www.aidic.it/cet/17/61/171.pdf, Klimeš L., Štětina J., 2013, Parallel Dynamic Solidification Model of Continuous Steel Casting on GPU, 22th International Conference on Metallurgy and Material (METAL 2013), Brno, Czech Republic, 74-79- Results show that the front tracking method, which is accelerated by means of the GPU computing approach, can provide results having higher order accuracy than the other two interface capturing methods].

Hope this is helpful for you.

Ashish

Dear Amir Reza Ansari Dezfoli :

Thank you very much for your help, I already adjusted the "Pressure Point Constraint" and the reference value for the Pressure, and nothing.

I'll send you my model on Inbox, I'm using the Comsol's 5.1. ver

Thank you again , hopefully I was close to the answer, with the model, I'm sure you will be able to tell me what my problem was.

Regards !

The interface between two phases is very important (regarding to Subhasis's answer)

DOI: 10.1016/j.diamond.2019.107561

I do like both good answers related to Dears; Matija Perne and Kaveh Zamani . I don't have to think about the available dimensionless numbers, instead, I should understand my problem and determine precisely the numbers that are associated with it. Good luck,,,

You could use a pure copper pipe and spot weld to it small constantan (0.1mm diameter) single wires so making a series of T thermocouples. Be sure they are not electrically shorted on the cold side.

The copper tube will also ensure a temperature very close to the pipe internal one.

These effects are generallly negligible. Counter-examples are:

- for Soret effet the chemical composition of detached flows,

- for Dufour effect expansion of mixtures containing species of very different molecular masses.

Dear Isuru Sajith Rathnayaka :

I have some questions :

1. The "primary air" stream you drew entering to the reactor from the bottom.

How is it produced ? I mean, what is the mechanism which puts this aire in motion ? And, What is the Temperature of this air stream ?

2. What is the average temperature of the Albizia Lebbeck Sawdust ? Are you consider a uniform temperature in the z-direction ?

3. Does your reactor have some kind of insulating materials (since your drawing does n't show the reactor wall as layers of different materials) ?

4. Can you give a little more detail on how the combustion flame is in contact with the sawdust in the upper part?

I mean, is the flame, or combustion gases, in direct contact with the sawdust ? or you have any kind of contact interfase/heat transfer interfase ? a Heat exchanger ? to avoid having the sawdust mass in direct contact with the combustion gases ...

Best Regards !

The heat transfer coefficient depends directly on the thermal conductivity of the fluid. Most dispersion are solids which have many order of magnitude higher thermal conductivity. Therefore, the mixture has higher thermal conductivity and then higher heat transfer coefficient. The solutal dispersion can be understood by analogy to heat transfer.

Thank you very much Sir. I would like to use Silicon wafer for cost reduction.

Could you please share any reference on spectroscopy of carbon dioxide other than CDSD-1000?

Thank you so much for your help.

How can you be so sure about Rayleigh number?

You should be able to measure temperature difference inside air bulk and wall of the cylinder for it.

There is concept called 'conduction shape factor' for such problems, you can find it in Cengel's Heat transfer book, McGraw Hill, also you can refer some Heat transfer data books for correlations of natural convection.

Link for your reference. Case 6 is helpful for you.

After finding inside wall temperature of the cylinder wall find natural convection coefficient for channel flow based on characteristic length along vertical direction (H).

You can also neglect convection and straight away consider conduction for the cylinder, it will be valid only after your Insulation condition holds.

There are some papers for cpt critical pitting temperature for NiMo alloys, that could help.

You are in the realms of measuring very small temperature differences. Do you have access to any micro-scale welding apparatus and know someone who can use it! I would suggest that you make your own thermocouples using very fine wire, adding radiation shielding if necessary. For industrial applications the standard bead is several mm in diameter and enclosed in a sheath (for robustness). You need something much, much finer than that.

I don't know where you are located, but if stuck, talk to thermocouple suppliers in Europe or North America (USA or Canada). Many will give free knowledge/advice if you are doing fundamental research.

You will need a measuring device - it will need high input impedance. In addition, if your thermocouple output is in tiny fractions of a milli-volt, then I would suggest that you use a true second thermocouple in an ice bath rather than an automatic (assume internally generated) second junction.

Trust that the above helps.

Regards Stephen.

If nanoparticles are uniformly suspended in base fluid and there are no signs of sedimentation and agglomeration then you can say that the use of nanofluid in thermal system is useful. On other hand if particles are agglomerated or settled in bottom of storage tank or the system through which they are flowing then thermal performance may be poor than simple base fluid.

@Prem_Baboo

I truly appreciate you.

Particles made of high thermal conductivity and low density such as Carbon nano spheres can be an ideal material for maximum heat transfer enhancement. However, stability can be an important aspect in the preparation of the nanofluid.

Ahmed Abdelhameed Is it possible that such conditions might happen in low mach number flows.

Hi,

if you have a purchased ANSYS license, than your software vendor should provide you with a legal opportunity for the download of the ANSYS Software. Generally it is available through the ANSYS Customer Portal for registered ANSYS customers.

https://support.ansys.com/portal/site/AnsysCustomerPortal

Answer from Dr. Silas E. Gustafsson - Pioneers of Thermal Conductivity Measurement( silas.gustafsson@thermetrol.se): Silas E. Gustafsson

When comparisons are made between data obtained with the Hot Disc (HD) method and those of most other methods, it should be remembered that the transport properties measured with this method are the properties of the substrate beyond the surface, where the structure starts to repeat itself and assumes stable or bulk properties. The reason why it is possible to avoid the influence from the thermal contact resistance between the sensing spiral of the probe and the first surface representing the “bulk” properties of the substrate stems from the fact that the transient recording of the thermal transport properties of the substrate is normally much longer than the time it takes to establish a constant temperature difference across the thin layer comprising the probe insulation and the surface roughness of the substrate (cf Gustavsson, J. S., M. Gustavsson, and S. E. Gustafsson. (1998). On the Use of the Hot Disk Thermal Constants Analyser for Measuring the Thermal Conductivity of Thin Samples of Electrically Insulating Materials. Thermal Conductivity 24, Technomic Publ. Co. Inc., pp 116 -122.). In this paper we discussed how to separate the thermal contact resistance between the probe and the substrate from the transiently recorded data in this ITCC communication some 20 years ago. After this conference professor Cahill applied the suggested procedure for all the measurements he has made on very thin insulating layers with his 3-omega method. The reason why it is possible to separate the thermal contact resistance between the probe and the substrate surface from the measurements of the bulk of the substrate is the different time scales we are dealing with.

Having known, T_h1, T_c1,, T_c2, LMTD, d_i, d_o and L, Here could be the steps to determine mass flow rates of both fluids: (1). Determine T_h2 from the equation, assuming counter flow, LMTD = [(T_h1 - T_c2) - (T_h2, -T_c1)]/ log_e ((T_h1 - T_c2)/ (T_h2, -T_c1)), (2). Overall heat transfer coefficient (U) is estimated by taking two heat transfer coefficients for saline water and other fluid from tables in data book. and estimating as appropriately as 1/U = 1/h(saline water) + 1/h(another fluid). (3). Using the equations, UA/(m_cc_pc) = (T_c2- T_c1)/LMTD and UA/(m_hc_ph) = (T_h1- T_h2)/LMTD , where A is surface area, 3.1417 d_o L , m_c m_h, c_pc, c_ph are mass flow rates and specific heats of cold and hot fluids 9determined by temperatures of fluid at bulk temperatures from data book, mass flow rates can be determined. (4).Heat transfer (Q) = m_cc_pc (T_c2- T_c1) can be determined. (5). After getting, Q, number of tubes (N) is estimated by, Q = U N A LMTD, where A represents for single tube.

In general, results from both schemes may agree very well and may not. You may have unstable results with explicit way.

Dear Alaa Temimy,

you can be fairly certain, then all commercial codes available on the market are free of coding and algorithmic errors, i.e. they implement a numerical method for the solution of your problem correctly.

However, the numerical method itself, inherently, includes sources of error. These come primarily from space and time discretization (computational grid density and time step) as well as from which method has been used and terms up to which order have been neglected.

Furthermore, the mathematical-physical model, employed to describe the process you are simulating, is usually also an approximation of reality. For example, we know fluid viscosity is temperature dependent, but we choose to neglect that in our simulations, etc.

If the problem simulated is non-linear, a user-prescribed criterion is usually used to set the desired lowering of the error norms, which also contributes to the overall error.

My suggestion is to first identify all sources of error and try to keep them of the same order.

Secondly, one should always perform a nodalization analysis (and possibly a Richardson extrapolation) to examine, how the solution changes when different grids and time steps are used.

A short answer to your question, it is impossible to give a percentage to estimate the accuracy of a simulation. And beware, the accuracy does indeed depend on the expertise of the engineer doing the simulation.

Examples: Lot of research applications of Nano fluids in 1. automobile radiators, 2. heat exchangers (double pipe, plate, shell and tube etc.), 3. In I..C. engine along with bio diesel etc.

certainly.

i'm simulating heat and mass transfer inside  two phase closed thermosyphon using 2-d axysymmetric geometry.i've selected pressure based solver and transient.I am using ANSYS /FLUENT 19 student version .VOF method with Lee Model is used . Water is used as secondary phase and Vapor is used as primary phase. SIMPLE algorithm scheme for pressure velocity coupling and a first order upwind scheme for the determination of momentum and energy is included in the model. Geo –Reconstruct and PRESTO discretization for the volume fraction and pressure interpolation scheme, respectively, are also performed in these simulations. but,after running the calculation,contour is showing phase change only in the evaporator region as shown in attached figure.I've also patched the liquid water fill ratio with volume fraction=1 in the evaporator region.Can anyone help me out?

thank you Karol sir

https://www.sciencedirect.com/search?qs=boiling%20curve%20shift&show=25&sortBy=relevance

Thanks for the knowledge shared

Dear Tom,

thank you very much for all the references, comments and reflexions :)

Here I found a document that relates the cocentration gradient in the Fick law with the chemical potential gradient, but, as you said, I think it is obtained using analogy...

Regards,

Cristina

It is a common mistake to begin an analysis of a real problem from consideration of one or another mathematical formulation. Please follow the natural logical sequence in any study: (1) A complete analysis of the engineering problem including the ranges of the main parameters and physical (thermal, optical, mechanical, etc.) properties of real substances; (2) An appropriate physical model of the process under consideration with clear formulation of all the physical assumptions; (3) Complete mathematical formulation for the physical problem including coupled equations, initial and boundary conditions and the semi-empirical relations for the physical parameters that complete the problem.

If you miss the stages (1) and (2), your work will look as a useless mathematical exercise only. I am sorry, but I am regularly rejecting such manuscripts submitted to scientific journals.

Please note that two coupled energy equations are usually important to describe correctly the heat transfer in porous media.

Below link is another source for heat pipe manufacturing.

You can always vary the loading of nanoparticles to vary the thermal conductivity. Similarly, microcapsule with various nanoparticle inclusion can be utilized to vary the thermal conductivity. Remember, the increasing thermal conductivity of organic PCM is difficult and the reverse is easy. Discharge time increase will increase the response time too. Always a compromise has to be done.

Hi!

It seems that you have not included mass-transfer in the simulation. Species transport might not be suitable for your case.

You can follow the following steps:

1. Go to phase tab and click on interaction

2. Enable mass transfer mechanism and select evaporation and condensation (Refer attached figure)

Setup all the corresponding parameters according to the physics of your problem.

Yes , Dear Rick . In this project , there was a design mistake . Instead of fired heater , shell and tube heat exchanges was used . When I realize it , it was very late and I should deal with high temperature shell and tube heat chargers . This was a bachelor degree final year project and I have finished it already .

Thanks to all of reserachgate members who had made a contribution or tried to make a contribution . Thanks you all for sharing knowledge .

There is no wealth like knowledge,and no poverty like ignorance.

(Buddha )

This may help you.

Please find the attached file.

Does not matter (I am talking about good DI water system, they could be very different)

In terms of purity/resistivity the best is millipore. DI water could be both better and worse than distilled water, depending on a system; theoretically DI water should be better.

Generally for boiling distilled water is the worst one, but if DI system is a suspicious one then distilled water should be preferred.

Dear Karam Mohammed

your comment is useful, thanks.

This article may help you.

Dear Obiajulu,

This article may help you.

Dear Mohammad,

Please find the attached article. These articles may be helpful for you.

All Additives (gas into liquides; air bubles in liquids or solid suspension in liquids "nanofluids") are considered as passive techniques, cuz they don't need any external input or power contrary to active techniques.

Greetings

Dear Dr. hayder,

As we know Nanofluids shows an effective thermophysical properties as a bulk fluids compared to host fluids which led to enhance heat exchange systems, in my point of view, that is depend on the application that you want to use nanofluid in. for example; in boiling application and as Mr. Nikolai mentioned above the nanofluid play a vital role to enhance the critical heat flux and sometimes the heat transfer coefficient because of deposition of nanoarticles on heating surface which formed a porous layer lead to wettability enhancement due to decreasing contact angle of liquid droplet on heating surface. Anyway, there is no risk to use them but there are some challenges should to overcome and make them commercially applicable. I chose this example because nanoparticles in such application have to major roles

1- Bulk effect that associated with thermophysiacl properties enhancement

2- Surface modification effect associated with of wettability, contact angle, and surface roughness etc.

My regards

Dr / Hayder Jaffal

i think to study the whole performance it is recommended to investigate the performance evaluation criteria rather than the exergy. In the other hand, increasing the exergy gain it is due to the reduction in the exergy destruction that depends on the degree of motion of the particle of fluid that decreases with increasing the volume fraction.

Unfortunately, the answer is "it depends". There is no optimum number of experimental trials. In terms of random errors... the standard deviation (and subsequently confidence intervals) decreases as the number of trials increases. Thus, the standard deviation would approach zero as the number of trials approaches infinity. Generally, you should find a confidence interval (most likely based on a Student's t-distribution) that gives you an interval that you deem satisfactory. However, increasing the number of trials only impacts the precision of your results. To increase the accuracy of your results you would have to address systematic errors (due to equipment accuracy and the propagation of uncertainty). Wheeler and Ganji have a really great text that addresses your question in detail. Reference below.

Wheeler, A. J., and Ganji, A. R., 2009, Introduction to Engineering Experimentation, 3rd Edition.

ISBN-13: 978-0131742765

Nano fluids will be more viscous compared to the base fluid. You will increase the pumping loss in forced convection. But amount of fluid to be circulated can be decreased due to its better thermal conductivity.

You may please have a look at this

Dear Hayder

Many geometric parameters such as rib cross-sectional area, rib angle with the flow direction, rib height relative to the passage hydraulic diameter, rib pitch-to-height ratio, rib aspect ratio, etc…) have effects on the overall equivalent heat transfer coefficient.

Take a look at this pdf file :

Regards