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Heat Exchangers - Science topic

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Consider a heat exchanger with two streams A & B. Going by Fuel-Product definition for exergy analysis, suppose stream A is the fuel stream and stream B is the product stream. My question is whether the following can be possible.
Exergy @ A_in > Exergy @ A_out &
Exergy @ B_in > Exergy @ B_out.
If this will be true then Exergy destruction = Exergy of Fuel - Exergy of Product will become more than exergy of fuel and thus make the exergetic efficiency of that heat exchanger to be negative.
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Not possible if you critically rethink about what exergy is.
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Hello everybody,
i hope you're doing well,
please could you help me the question above using numerical calculations
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N = L1.L2/P1.P2, N(number of tubes), L1 (total length of flow normal to tube back), L2 (length of the no-flow side), P1 (distance between the center of one tube to the next in each column of tubes i.e., vertical separation distances), P2 (horizontal separation distance between two adjacent tubes)
see text: Heat Exchanger Design Handbook by T. Kuppan Chapter 4 section 3.2, pp 178-179
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We are currently looking for gas-to-liquid heat exchanger for the reduction of high temperature gas to low temperature gas. Which type of Heat Exchanger would you suggest to reduce temp of 200 degree C to 30-40 degree C.
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Prof. Udit Singh
It will depend on the physics that the exchanger has, and it comes from a difficult subject, physical kinetics.
Best Regards.
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I would like to model a heat exchanger by two heaters on aspen.
But the problem is that by transferring the flow from the hot side to the cold side, I end up with a final temperature of the cold fluid higher than that of the hot fluid of departure
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Maybe this video can be helpful for you since your info is somewhat limited :)
I hope you manage the modelling!
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If given inlet gas temperature is 25 degree celcius and outlet gas temperature 220 degree celcius
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With the given shell and tube type heat exchanger, determine the maximum pressure tube can sustain with the hoop stress criteria. Then corresponding to that temperature, choose any fluid whose saturation pressure is above maximum pressure, so that no phase change cannot occur. Regarding shell side, generally ambient pressure fluid is supplied.
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Hi, I need to calculate the insulation system of a plant of rice bran oil extraction that is consist of pipes, heat exchanger, flash, valve, and pump. Is there any formula to suggest? I read some handbooks, but I could not calculate them for the whole system.
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What are the temperatures and shapes of the surfaces to be insulated?
I think the temperature is not greater than 250 degree Celcius. You can use glass wool for high temperatures. For temperature up to 60 degree Celcius, you may use Thermocole but Thermocole can be put easily only on flat surface or outside the pipes or cylindrical surface if pipe section of Thermcole is available.
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I want to write my thesis for master course and i need some suggestions to increase the efficiency of plate heat exchanger.
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Plate heat exchangers are often used when the cooling fluid isn't clean because a plate heat exchanger can be dismantled and cleaned fairly easily, much more so than one that requires cutting and welding. Several things have been tried, including: rinsing, periodically reversing the flow, pulsing the flow, and introducing abrasive particles. What about acoustic stimulation to discourage accumulation of stuff on the surface; that is, keep the crud suspended and perhaps filter it out. You could also consider rather than a filter, running part of the stream through a centrifugal device to remove sludge without interrupting service. Go out and see some of these in action. One place you will find plate heat exchangers is a stationary combustion gas turbine. I've seen a variety of these at power plants. Get someone to take you on a *real* tour of a plant--not the "visitors" tour but the "maintenance" tour.
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Doing exergy analysis of steam turbine. However, the exergy balance on boiler (heat exchanger) includes exergy of fuel which is to be determined. The measured data contained the mass flow rate of fuel.
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Chemical exergy fraction = 1.0401 + 0.1728 H/C + 0.0432 O/C + 0.2169 (S/C) (1 − 2.0628 H/C )
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I am creating a heat exchanger for the lattice structure core on ntopology to be transferred to Ansys for simulation afterwards. But the meshing is faulty and Ansys cannot process it correctly. Is there any way to fix the intersecting and other types of meshing errors on ntopology? Is there any way to save the ntop filesbefore meshing?
Thanks
Hossein
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Thanks Simon. I have tried the solution in the link but didn't work in my case. WIll try to ave it as 3mf and see if it works on Ansys.
Thanks anyway.
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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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There are multiple methods to calculate cold and hot outlet temperatures, e.g. LMTD and P-NTU.
  1. P-NTU directly calculates both the hot and cold outlet temperatures using two linear equations based on (a) exchangers geometry (b) flow and (c) heat-capacity of the fluids.
  2. LMTD based method requires (a) exchangers geometry (b) flow (c) heat-capacity of the fluids and (d) one of the outlet temperatures to calculate the remaining outlet temperature.
(Note : LMTD method can find both the outlet temperatures, if heat exchanger is single-pass)
Both the methods give same answers (while designing and rating heat exchangers) !
My question is as follows:
Is recursive type calculations in LMTD can be considered as a drawback of LMTD method? , Particularly in heat exchanger networks?
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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
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can we design heat exchanger network HEN with only 1 stream on above pinch? Is it possible?
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Are you talking about pinch points and heat release diagrams? You want to avoid pinch points. Here's a typical HRSG heat release diagram.
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I've been working on the heat exchanger design for fermentation systems, and found an explanation in the literature on how to calculate the cooling-coil length. However, I haven't found information on the volume or area that a cooling coil should occupy in a fermenter yet.
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The formulas for the shell and tube heat exchanger can't exactly be used for this since the coolers/heaters only have 1 inlet and 1 outlet, unlike heat exchangers that have tube inlet & outlet, as well as shell inlet and outlet. Also, there is no heat transfer coefficient for coolers/heaters unlike heat exchangers.
What other parameters can I compute? Can I ask for formulas that I can use for the specification sheet I'm making for coolers and heaters?
Thank you so much!
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Hi Hannah
The heater and cooler block are meant as shortcuts when we know what a heat exchanger must do but we don't want to model in detail. If you want to size the exchanger you will have to convert it into a shell and tube or air called etc, and then use either the Hysys calculations or EDR to calculate the size.
Regards
Kevin
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I am using k-epsilon turbulent model for heat exchanger design and i am facing this error consistently.
what i have done so far to try to solve this error is:
a) run the stationary model that converged and is in agreement with our experimental data
b) Then i used the solution of stationary model to run the transient model but finding this error every time.
If any one of you knows how to resolve this error kindly give your suggestions.
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thank you all for your suggestions.
Luigi Candido yes the model is in 3D and converges in steady state..
I will try to do what you have suggested and see the result.
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Hello,
I am trying to simulate a simple heat exchanger which has a laminar flow of water inside the single slab channel and a phase change material stored underneath. The heat exchanger has one row of fins on the slab with air between the fins. The photo of the heat exchanger is attached.
While I run the transient simulation, the time steps of the transient solver are extremely low resulting in a very long runtime. As seen in the convergence graph, the Reciprocal of Time Step Sizes are extremely high and after 175 time steps, the simulation has reached only 0.0711 seconds. The simulation was running for over a day. This is while a simple heat transfer simulation without adopting the phase change material is not so time-consuming.
Is there any way to improve the timing or is COMSOl generally so slow on phase change material modeling?
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Try to solve using different solver and you can also change meshing type
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Greetings !
respected dear i am working to a novel design of wet cooling tower for my final year project as B.E requirement.
I am confused about that if i use cars radiator instate of air to Air tube heat exchanger at the top of the tower ?
kindly help me and guide me , what will be results if i use car's radiator instate of air to air tube heat exchanger ? it would increase the efficiency of wet cooling tower or may decrease ?
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Dear Khalid! yes you may able to use such radiators, however, consider thermal efficiency (as it might ought to loss). Perhaps, Varying the parameters to optimal state could help!
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I am now modelling shell and tube heat exchanger using COMSOL Multiphysics 5.3a.
I have several questions:
1. What is the benefit of modelling these equipments in finite element software, in terms of safety?
2. Does this FEM software really helpful on consultant engineer in designing the equipment. If yes, in what way? If not, why?
3. Do FEM software really credible and powerful? Many of the journal state that the error obtained ~15%, but ain't this software too good to be true?
4. One with skills using FEM software, is it in demand?
Thank you for answering!
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Simulation software is very helpful in a lot of ways. Firstly, it allows you to develop a better idea about the big picture of your project without having to run too many tests. Sometimes the simulation results can be more accurate compared to the experimental results, since there are more factors that can affect the uncertainty of the trials, operating errors, systematic errors and random errors, etc. I believe a lot of consulting engineers use the simulation software, such as fluent, starccm+, comsol in their research. The simulation result can serve as a strong indicator for the researchers when they scale up their reactors. In terms of the demanding situation for this type of skills, yes, as far as I know, people who are skillful in this area is highly competitive.
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Hello everyone,
I am working on a heat transfer and pressure drop study on a heat exchanger.I need to measure the inlet and exit temperatures as well as the wall temperatures at different locations along the exchanger length.For wall temperature,I am attaching thermocouples on the wall .However ,I am facing a problem how to accurately measure the Inlet and Exit temperatures of Fluid streams.Anyone working on the same area can  help me .Thanks in advance
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Hi Dr Tarikayehu Amanuel . I agree with Dr Paul Gateau .
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As a part of my thesis I am designing Finned pack heat exchangers for cooling/condensing warm air with water. I am not getting the exact procedure for it. I am reffering multiple research papers but all seem to have different information. Does anyone know of a relevant literature where I can find the process.
The exact type of heat exchanger I want to design : http://www.deltacoils.it/?locale=it_IT
Actually my part is to check the efficiency of the preinstalled heat exchanger I thought by designing the heat exchanger I would get a better under the efficiency is this approach correct also please suggest as per your experience.
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I presume you are cooling moist air using a coolant (water) having a lower temperature than the moist air dew point temperature. Depending on the level of detail required, you may either
a) assume thorough mixing of the condensate formed and the air flow, i.e. assuming equilibrium condition, or
b) take into account the fact that moisture might be condensed 'independently' from the air cooling, i.e having non-equilibrium flow.
Case a) is the simplest, and the gas side heat transfer coefficient might be established using the method of Silver or Bell/Ghaly. Of course you will need to integrate along the heat exchanger, as the gas side heat transfer coefficient will tend to vary in the flow direction.
Case b) is more complex, however, any 'film model' (e.g. the model of Colburn/Hougen) can be applied. Note also that the heat transfer coefficient along the height of the fin might vary significantly (due to the vapor condensation rate), i.e. the traditional calculation of fin efficiency becomes void.
Case a) will most likely provide erratic air exit temperature and condensation rates, but for some mysterious reason the heat duty might not be that far off. Case b) will be more correct, and will most likely result in more condensate formed but less air cooling than case a). Which method ends up being correct will depend on the degree of mixing between the condensate and air.
As far as design methodology is concerned, it will be a trial-and error procedure, as all heat exchanger designs are.
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This is my industry production problem. In the air conditioner heat exchanger coil bending process, There must be a polyester film between the 2 layers of heat exchanger coil for preventing deformation of aluminum fin plate. It's inserted by a man and be removed by a man.
I'm thinking to make a foolproof system for a forgetting remove this film but can't figure out what kind of sensor would suitable for this situation. Could anyone here suggest any product or method for this situation ?
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perhaps it would be possible to make a resistance measurement with a simple digital tester, keeping one tip on a conductive part and moving the other by placing it on the parts to be investigated ....
Simple but it could work.
My best regards, Pierluigi Traverso.
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In your opinion, which cooling technology is the best option to support the increasing demand for heat removal in modern engineering designs used in aircraft systems?
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It would really depend on the cooling targets but heat pipe based thermal management provide an answer to the reliability requirements needed for aircraft.
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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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As a part of my system, there is a heat exchanger.
Hot stream - water vapour - comes in at 17.12degC, 0,00714648 bar, completely in the vapour phase
Cold stream - refrigerant R1234ze in a saturated liquid state. The properties of HEATX is given below in the image. I get this error - ** ERROR T-LOOP NOT CONVERGED IN 37 ITERATIONS. FLASH FAILED FOR HOT STREAM DURING ENERGY BALANCE CALCULATION
I would be grateful if someone could clarify what this error could be due to. Thank you.
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Hi,
It can be a numerical problem. You can try to increase the number of cycles for the convergence from the different setups for the convergence; after you have to reinitialize your simulation and so you have to run.
bye
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What is the best and easy to realize method to heat hydrogen / carbon dioxide mixture at10 bar to 320degC? My first idea is to use a thermostat with circulating thermal fluid at 350degC and a plate heat exchanger. But I can not find a heat exchanger with hydrogen resistance and such temperature / pressure spec. The mass flow is about 20 kg/h.
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Looks like a simple electric resistance heater in a tube would do this low duty. An 8kW element looks about right but needs to be suitable for high temperature and the gases used, so probably stainless steel casing and tube needed.
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Hello, I am tasked with designing a heat exchanger for pasteurizing beer. I am currently using the Log Mean Temperature Difference LMTD method to do the thermal analysis. I am struggling to find the temperature that beer would often be at before entering a shell and tube heat exchanger for pasteurization and the temperature that the heating water would be at when entering the heat exchanger. The heat exchanger is meant to handle a maximum mass flow rate of 14kg/s if that information is of any help.
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I recommend that you get this excellent book. It will be very helpful. Well, this book develops several exercises similar to the work that you have to do. This book was very useful to me.
Bergman, T. L., Incropera, F. P., DeWitt, D. P., & Lavine, A. S. (2011). Fundamentals of heat and mass transfer. John Wiley & Sons.
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Dear all,
Would you please help me to find out the best approach to calculate the potential heat recovery from exothermic reactions? Are there any good references to introduce me in order to enhance my knowledge over recovering heat from exothermic reactions. I will be very thankful for your helpful advice and recommendations.
Thanks in Advance for your kind considerations.
Yours faithfully,
Nashmin
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There are a number of methods for measuring the heat of an exothermic reaction. But in any case, not so simple equipment is needed. One option is to use a bomb calorimeter (see https://en.wikipedia.org/wiki/Calorimeter). An example can be found here https://arc.aiaa.org/doi/abs/10.2514/3.25795?journalCode=jsr.
Another option is to find a laboratory that performs thermogravimetric analysis (TGA, see, for example, https://link.springer.com/chapter/10.1007/978-3-030-11599-9_7) or differential scanning calorimetry (DSC). From the processing of these data, one can obtain the heat of reaction. An example can be found here Kong Y., Hay J. N. The measurement of the crystallinity of polymers by DSC //Polymer. 2002. V. 43. Iss. 14. Pp. 3873-3878 or here Faleeva J. M. et al. Exothermic effect during torrefaction //Journal of Physics: Conference Series. IOP Publishing, 2018. V. 946. Iss. 1. Art. # 012033; Zaichenko V. M. et al. Thermal effects during biomass torrefaction //Solid Fuel Chemistry. 2020. V. 54. Iss. 4. pp. 228-231.
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I want to determine the Nusselt number (Nu=hDh/k) in the heat exchanger. In calculate of heat transfer coefficient (h=q''/(Tw-Tb)), for the q'' parameter, I use the total heat flux of the channel walls that is the contact with the fluid and use the average temperature of these walls for the Tw parameter. In this equation, I need the bulk temperature (Tb). How can I calculate it in Comsol multiphysics?
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V. The recursive least squares algorithm (RLS) allows for (real-time) dynamical application of least squares (LS) regression to a time series of time-stamped continuously acquired data points. As with LS, there may be several correlation equations with the corresponding set of dependent (observed) variables. RLS is the recursive application of the well-known LS regression algorithm, so that each new data point is taken in account to modify (correct) a previous estimate of the parameters from some linear (or linearized) correlation thought to model the observed system. For RLS with forgetting factor (RLS-FF), acquired data is weighted according to its age, with increased weight given to the most recent data. No prior 'learning phase' is required.
VI. Application example ― While investigating adaptive control and energetic optimization of aerobic fermenters, I have applied the RLS-FF algorithm to estimate the parameters from the KLa correlation, used to predict the O2 gas-liquid mass-transfer, while giving increased weight to most recent data. Estimates were improved by imposing sinusoidal disturbance to air flow and agitation speed (manipulated variables). The proposed (adaptive) control algorithm compared favourably with PID. The power dissipated by agitation was accessed by a torque meter (pilot plant). Simulations assessed the effect of numerically generated white Gaussian noise (2-sigma truncated) and of first order delay. This investigation was reported at (MSc Thesis):
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I am analyzing two adjacent interconnected rectangular channel flow patterns. The image of my numerical model is attached below.
The fluent solver was pressure based, and velocity formation was absolute. The SIMPLE algorithm was used. Laminar regime was selected and energy equation was kept on. Boundary conditions were checked carefully. Inlet velocity and pressure outlet conditions were applied. Uniform Heat flux was applied at the bottom face. Solid fluid interfaces are thermally coupled. Second order upwind equations were used for energy and momentum equations. The residuals were kept 10^−5 range, and the solution was fully converged.
I have drawn a centerline inside a mini-channel for observing velocity distribution. Is my solution right? and velocity profile having zigzag is okay? if not, pls explain.
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I think this article might helpful for your research:
Wish you all the best luck!
KHOA
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I have double pipe heat exchanger and I want to calculate numerically the local temperature reference that used for calculation heat transfer coefficient locally .If the heat flux is constant are known and all properties is known too.I want to compare with experimental work .The temperature will change as mesh change and cannot be used for comparison with experimental work . This mean can not be calculated where Tref=f(y).
you know h=q/(Tw-Tref) where q heat flux.
must I calculate h or Tref manually with another assumptions?
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In compact heat exchanger, when the heat transfer coefficient is needed locally, and we have numerical results we can determine the temperature difference between the wall, and the bulk temperature above it. The bulk temperature is obtained considering the mixing cup of fluid in each section. The bulk temperature could be obtained as a function of length and a polinomial curve can be fitted for the heat exchanger. It's a additional work but the results are goods at least in my case.
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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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Stoitchkov and Dimitrov produced a short-cut method for the measurement of heat exchangers for wet surface crossflow plate quality. This involves a correction to the effectiveness determined in compliance with the Maclaine-cross and Banks procedure. For this reason, a new model has been developed with a moving water film, referring to the real conditions in these heat exchangers.
Reference.
N. Stoitchkov and G. J. I. j. o. r. Dimitrov, "Effectiveness of crossflow plate heat exchanger for indirect evaporative cooling: Efficacité des échangeurs thermiques à plaques, à courants croises pour refroidissement indirect évaporatif," vol. 21, pp. 463-471, 1998.
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Intrested
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Solution to dissolve phosphogysum in heat exchanger of SS-316 moc.
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Hi everyone
I am working on a shell and helically coiled tube heat exchanger with laminar flow through the shell and turbulent flow through the coil tube. I have performed iterations for coil by selecting different types of turbulence models but in each case, energy starts to diverge after some iterations (images attached).
What is the possible reason for this?
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I think it may be due to BCs. Can you please your problem in detail, so that I may help you in diverg. Issue
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Dear all,
e-NTU equation can be written as follows:
e = {1-exp[-NTU(1-CR)]} / {1-CR*exp[-NTU(1-CR)]};
To simplify above, we can write it as follows:
e = 1-exp[C*(1-X)] / 1-X*exp[C*(1-X)]
Can we linearize e , given that X is a variable in both the numerator and denominator?
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Have you noticed that my linearization is incorrect, because I took your C = 1, when C = –NTU (Number of Transfer Units) and NTU > 0? I'm not a Chemical Engineer, but I rechecked the info on MathWorks and Wiki; the effectiveness (ε) of a heat exchanger is bounded: 0 < ε < 1. The X, or the heat capacity ratio, Cr = Cmin/Cmax. Since both Cmin > 0 and Cmax > 0, then Cr is also bounded 0 < Cr < 1. Can you verify if the above figure is the surface plot of the E-NTU function? I tend to agree with Prof. José Arzola-Ruiz that linearization is not necessary.
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I want to analyse the impact of heat exchange mechanisms in a fluid contained in a box under different pressure levels using Star-CCM+. 
The Navier-Stokes solver fails when the pressure is low enough to produce KN>>1, under free molecular flow regime. I think this can be achieved by defining the physics continuum by selecting a User Defined EOS. 
I just wanted to know if this has been attempted or maybe a different method is better.
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Mauricio Aguilar Cardenas Were you finally able to model rarefied flow in Star-CCM+?
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Please see attached formed plate to be used as base of heat transfer area in a heat exchanger?
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Thanks for your help @ Luigi Candido
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I am designing a heat exchanger and I set the shell diameter, tube diameter, and shell length as input parameters to perform an optimisation analysis. The output parameters I set are the temperatures at the outlets and the effectiveness of the heat exchanger.
The temperature at the inlet of the shell is 85C, and at the inlet of the tube is 15C.
When update the DoE for the response surface, I am getting unreasonable results for the temperatures at the outlets (some are greater than 100C).
I want to know why this is happening and if there is a way to fix it..
If i delete the unrealistic design points, would I still be able to generate the response surface? Or should I find the source of the problem and run the DoE again?
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Ashkan Ghafari Okay makes sense..
Yea i decided to run each case separately and import the design points to the DoE, may be inconvenient but I’m running out of time to come up with a more practical approach
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Fouling or scaling is becoming a major hurdle for getting high heat transfer exchange between two fluids. Scaling is formed in tubes and the type of scale formation is difficult to assess since it has a combination of several impurities. Thermal resistance of scale formation is taken for the type of fluid flowing in a heat exchanger to estimate the practical heat transfer. In order to prevent fouling or scale formation what are the precautions and remedies to be taken?
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I am designing an isothermal multitubular reactor and have sized and completed the tubular design. the tubular volume required and the outer surface area of the tubes has been defined (9000 tubes an outer surface area of 14,000m^2). the heat needed to be removed has also been defined and is 9 MW. How would i calculate the temperature rise on the shell side of the heat exchanger. would the formula Q=UATlm still apply and if so how could I solve Tlm for the temperature rise on the shell side.
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If it is isothermal there will be no temperature change. I assume that the tubes are adding (or removing ) heat to control the shell side temperature at isothermal conditions.
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I am working on a shell and helically coil tube heat exchanger as shown. The flow through the shell is laminar and through the coil is turbulent. Which model should I select from Fluent to solve this problem. Is it possible to differentiate the laminar and turbulent regions in fluent and then applying the models?
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You can do it by
1. Split the laminar and turbulent regions manually by using the BC panel.
2. Use a transition model
for more help, you can used this link where a similar question has been asked
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I did a pretty simple simulation of an exothermic reaction using RPlug in Aspen plus. Initially the feed was heated using a heater block. Since the reaction is exothermic, I tried to use the reactor product stream to heat the reactor feed using heat exchanger block in aspen plus. After replacing the heater with heat exchanger, the simulation converged fairly easily, at first. But once I purge the simulation results, I cannot get the simulation converged again. Any idea how can I get the simulation converged after purging the results.??
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I do not think you needed to remove the heater instead you keep the two but instead of eliminating one, you can introduce a controller (using logic blocks) to either adjust the heating role played by the heater when once the product stream is ready for the heat exchanger or to completely switch off the heater. Zeeshan Uddin
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I just need a validation equation or a research with a similar heat exchanger feature such as an air-to-air Hx
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Hi Ahmed Usaama Ifthikhar,
What particular type of HX you have Designed?? There are many options for air-to-air HX with a variety of arrangements, fins, geometries, etc. You will have to specify first.
however, Compact HX (by A. Louis London, W. Kays) is a very comprehensive book for air-to-air HX.
regards,
Ahmad
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Most of the literature on shell and tube heat exchangers presenting the heat transfer coefficient correlations does not specify if there are any differences when dealing with vertical and horizontal orientations. Would the differences be only in terms of the shell-side fluid velocity ( and consequently Re) but the correlations would remain the same? How do these differences in orientation play out in the design?
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A vertical shell and tube heat exchanger in which the tubes extend through oversized holes in a liquid distribution plate. Liquid flows through the holes and down each tube exterior surface as a falling film. More details here:
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If the entrance and exit teperatures of a fluid which is flowing through a heat exchanger is known, how could i plot the cooling curve of the fluid along the tube?
The overall heat coefficient, mass flow rate and the diameter of the tube are also known.
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I was reading this research paper titled ' A Fully Wet and Fully Dry Tiny Circular Fin Method for Heat and Mass Transfer Characteristics for Plain Fin-and-Tube Heat Exchangers Under Dehumidifying Conditions ', and tried to implement the algorithm mentioned in it for wet heat exchangers. But, I could not find any data related to outlet air enthalpy and outlet water temperature to calculate the Qavg as mentioned in the first step of the algorithm. Can anyone tell me where I can find that data?
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Try contacting authors, it may resolve your issue.
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Should I mesh the solid domain ? or should I use wall thickness? or Shell conduction? for Heat Transfer between two fluids of a Heat Exchanger.
what is recommended?
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I would prefer to mesh the solid and use wall thickness and material conductivity.
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I want to cool Natural Gas from 195 Kelvin to 138 Klevin in a heat exchanger by using liquid nitrogen as the coolant medium. When entering the heat exchanger, the liquid nitrogen will have a pressure of 10 bar and temperature of 80 Kelvin. I need to find the necessary lenght of the heat exchanger. For this purpose i need to know the overall heat transfer coefficient of liquid nitrogen. I would be very glad if you could advise me where to find this value. I would also be glad if you could advise me other coolants in order to cool natural gas to 138 Kelvin.
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In a heat exchanger, considering the conduction and convective heat transfer is enough to do a good calculation.
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Hi Guys. I'm a mechanical engineer and have a bit trouble, would be very glad if you could help me with my questions.
I have a pressurized tank which contains Natural Gas at 200 Bar and 293 Kelvin. This tank is directly connected to a heat exchanger and in that device, the gas must be cooled to 150 Kelvin and will be stored as LNG at 20 Bar. I have to determine the necessary tube dimensions of the heat exchanger (Radius and Lenght) but I'm a bit confused since I dont have any informations about the flow velocity nor the flow rate. I need an idea how I could determine the flow rate of the gas. If i select the tube diameter randomly, what would be the flow rate of the gas at the exit of the pressurized tank?
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maybe you can adapt it out of some literature research... so, you have an additional parameter for your case study.
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How to find the air side pressure drop in a spiral fin cross flow heat exchanger?
The pressure difference at the inlet and outlet is very low compared to the experimental results, which I calculated according to the average pressure.
When I take the difference of the maximum and minimum pressures, the pressure drop comes closer to the experimental results.
Does anyone have an idea for cfd analysis in Comsol program for this situation?
thanks for your help in advance
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Imagine a heat exchanger made of spiral finned tube shown in the file. It consists of 4 rows of tubes diverted parallel to the air flow. In the experiments I measured the pressure drop of the air passing through the closed rectangular channel. I modeled this in COMSOL. When I take the difference in the mean pressures at the inlet and outlet in the Comsol Model, it comes out much lower than the experimental results. But when I take the difference of the maximum and minimum pressures in the Comsol model, the results are very close to the experimental results. Is the second method acceptable for finding the pressure drop in numerical models? I wanted to ask this. The problem here is that I accepted the fins as thin wall, because my computer was insufficient. There is no problem in heat transfer, but it is very low in pressure calculation because of this acceptance.
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Basically, it's a cylindrical tube of steel with inlet temperature of milk at 4 degrees Celsius and the outlet temperature would be 72 degrees Celsius. The mass flow rate is 1 Kg/s while the length and diameter of the tube are to be chosen, and the heat energy requirement to fulfill the above conditions is to be found.
Can someone guide me how to proceed. What is the relationship to be used, which would include these parameters, length and diameter of the Tube and the uniform heat energy supplied to the tube to make the temperature reach 72 degrees at the outlet, from the 4 degrees inlet temperature?
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Q=m Cp delta T
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I need to design an spiral heat exchanger, buy I don't know what reference or bibliography (preferably a book) should I consult in order to get an updated and reliable methodology related with this topic.
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maybe you find some small aspects in: Perry's chemical engineers handbook ISBN 0-07-049841-5
more is possible in "VDI Wärmeatlas":
S 2032
S52
S862
S1415
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How to write the fuel and product exergy balances in the cascade heat exchanger in the cascade refrigeration system?
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The definition of fuel and product exergies depends on the chosen reference temperature. For a heat exchanger, possible formulations of fuel/product exergies are shown in the attached figure.
For more detailed information, you can have a look at the following publication:
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I'm currently designing a single pass shell and tube heat exchanger. In the Nusselt number equation I have chosen to use, it requires me to calculate the Prandtl number at the SURFACE of the tube, shell side. I'm trying to find what the temperature at the surface of the tube will be. I've tried calculating this using constant heat flux however I do not know what the convective heat transfer coefficient is yet so I cannot use this method. Any suggestions?
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i used for calculate the surface temperature by numerical simulation
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HI
I am using a differential controller for giving control signal to variable pump for keeping a constant difference between the temperature of the cold side of heat exchanger i.e (dT=12) can anyone tell me if I am using the equation right pictures attached.
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With little thermal mass in the system and no deadbands the operation you are seeing is to be expected. Why not use some of the built-in controller types with dead bands, there are quite a few options that could work.
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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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Hi,
I'm working on a project to extract heat energy from vehicle exhaust gasses using Solid and Gel type thermoelectric modules. For this I've designed a heat exchanger with flat surface so that we can install Thermometric Modules on it. The temperature difference will create current in the Peltier modules on the surface.
Can someone help me in getting the right boundary conditions for this simulation considering we are using exhaust of a 4 cylinder gasoline vehicle ?
Is it possible to couple Fluent with Thermo Electric System in Ansys ? (I've no idea how system coupling works)
I was thinking to use temperature results from Fluent as input in thermo electric system so we can estimate the power generation of different TECs.
Thanks
Muaaz
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Salih Kaya Yes, I've built a model using COMSOL Multiphysics after checking video tutorials on their wesbsite.
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Dear colleagues;
I modeled 3D melting and solidification of phase change material filled heat exchanger and generated a (as in the picture below). First, I enabled melting and solidification model and energy, the result after 5400 second show liquid fraction is 0.61 and it remained constant over time. Then, I used vof model but after switching on the model I cannot choose material for fluids (cell zone conditions). Can anyone explain why?
Notices:1- The hot fluid domain in the bottom pipe and the cold fluid domain in the top pipe. 2-The heat exchanger linking cold water with hot water in counter flow arrangement.
Please, suggest what i can fix to make it right?
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Dear colleague
i hope this Video help you
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Dear all,
I am trying to couple a simulation with two codes, say code A and code B (different discretizations). For code A we solve simply the conduction equation (solid), while in B we solve the NS + temperature convection/diffusion (fluid).
The coupling is explicit, while the time scheme for each code is implicit.
at each iteration, code A gives code B the heat flux to impose at the boundary of domain B, while code B gives code A the temperature to impose at the boundary of domain A. So in short, the coupling is done via a Neumann/Dirichlet BCs.
I am facing stability issues that don't allow me to finish correctly the transient solution.
Let us focus only on domain A (code A). When code A receives the temperature values from code B to apply a Dirichlet BC, the values are stocked in a layer of cells; so called the ghost cells. We denote these values as T_wall.
Now, we need to compute the heat flux at the boundary to give to code B. There are two possibilities to compute such a flux :
1- use T_wall and one inner temperature value
2- use 2 or 3 inner temperature values to calculate the flux, and then extrapolate it to the boundary.
I am getting serious instabilities if I calculate the flux via the first approach (T_wall and 1 inner temperature value). Otherwise, with the second approach (only inner temperature values), the simulation is stable and a steady-state is reached.
Can I have please your opinion on this subject. Have you ever faced such kind of problems ?
Is it really that computing the flux with the second approach leads to a stable solution, but to a non-consevative scheme ?
Best regards
Elie Saikali
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Thanks for the answer and for the reference.
Regards
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I want to calculate the heat removal in crystallization cooling of maltose. Maltose sugar was cooled from 57°C to 10°C. In order to identify the amount of heat to be removed, I need to ensure the value for solubility of maltose at 10°C (g/10g water), heat of solution for maltose monohydrate, and the specific heat of the maltose solution.
Thank you.
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Thank you Sir for clearification. This time we both are very close (66.8 & 63.4 g/100 mL)! @ Freze Richard.
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Hello I am simulating a Shell and tube heat exchanger. Model info is given below;
Boundary Conditions: velocity inlet and Pressure Outlet , Model: K epsilon realizable with standard wall function. , Mesh Metrics: Skewness max .84, average .23 , Mesh type hex with tetra as shown in the attachment below , All of these settings are based on previous research papers that have been identified to be satisfactory.
My Problem Case 1: I have to validate my results against a previous research(geometry same as that of paper With Baffle Cut 36 %). But my outlet temp is 336 K when it should be 330 K. My pressure results are okay in this case.
My Problem Case 2: in second case when I do simulations for the same heat exchanger but changing one parameter( baffle cut to 25% as in paper), my temp results are reasonably fine. In paper out temp is 336, mine is 338 but pressure results are almost double. Paper gives 9000 pa mine are 18000 pa.
Solutions Tried By me: 1) All tetra mesh gives same results. 2) K epsilon with RNG, Standard Same result. 3) Finer Mesh No improvement. 4) Convergence is fine.
Help would be highly appreciated. Thanks In advance
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The ratio inmesh cell count between first and finest mesh is just as small as 2.1. If we assume, that the mesh cell count increase is equally distributed in all three coordinate directions x,y,z, then the mesh cell count in a single coordinate direction is approx. increased by as little as:
dx3=dx1 / (2.1)^1/3 = dx1 / 1.687
If we assume a full second order scheme in space, than the error on the third mesh is in relation to the discretization error on the first mesh:
O (dx3^2) = O (dx1^2 / 1.687^2) = 1/2.84 * O(dx1^2) = 0.35 * O(dx1^2)
So by this kind of "mesh refinement" the discretization error on the finest mesh is a little bit more then dived by half (approx. factor 1/3). This is not very much. In order to see a substantial difference in the results at least an error reduction by an order of magnitude (1/10) would be required.
And predicting heat transfer without boundary layer resolution is not good scientific practice from my perspective. For a heat transfer case the avg y+ ~18 is still too large, which is most likely a direct consequence of missing boundary layer mesh. An avg y+ of about 1 would be required for good heat transfer predictions.
Last but not least I would encourage to use the k-omega based SST model - at least for comparison.
Regards,
Dr. Th. Frank.
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Basically I am simulating a heat exchanger in which a cold fluid is entering with the temperature of about 11degrees and hot fluid is entering with 33degrees. i have used the pressure outlet boundary condition and as you know by default backflow temperature is 300k by default. but as soon as i execute simulation i get reverse flow again and again. The reverese flow comes then dissapears again, comes and then again dissappears. it has not completely vanished after the first reverse flow. with the default settings i am more frequently getting reverse flow. mesh quality and rest of the important aspects of problem are okay i have cross checked again and again and i think the problem is due to backflow temperature. could you please give me an idea how to set backflow temperatures for both cold and hot outlets.? which typical values i should choose except 300k to avoid reverse flow.
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You can do 1-d energy calculation based on the heat exchange
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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 everyone
We are looking for thermocouples with very small size. I can call them Micro-thermocouples. We need to measure the internal walls' temperatures inside a special heat exchanger design. So, we have small channels with the area as triangular, roughly 0.5x12x12mm. We want to place the thermocouples inside the channel and on the wall.
So, has anyone idea for which type of thermocouples could be used ?and is there such a micro-thermocouple to sense the temperature between 0-250c?
best regards
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You don't have do that on the surface. I meant creation of the thermocouple bead by welding two thermocouple wires. Also, you don't have to cover the surface. Just take care of electric insulation and proper grounding to suppress possible noises. Covering the junction is not for accuracy but for reliability.
There are many issues in this measurement. If the bulk thermal diffusivity of the thermocouple is close to that of the wall, the interface temperature will be accurately attained as long as thermal no slip is guaranteed there. If the wall is polymer, you will basically measure the fluid temperature on the wall.
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The question comes up with a mixture of aluminium powder and steam is to be modelled thermodynamically. So that I assume based on the thermal conduction of aluminium some of the heat is transferred to aluminium powder from steam. But to express the overall enthalpy and energy flow of the stream. How do we consider solid phases in a flow of solid-gas mixture?
My first idea was to take the specific heat of the aluminium powder at corresponding temperature to calculate the heat transferred, but I got a little bit confused since it doesn't so true to add the amount of heat carried by aluminium to the enthalpy of the steam. As follows:
Q= hsteam + mAL . cp . Delta T (or directly T ?)
as we do the energy balance of a system component, let's say a heat exchanger.
I would really appreciate your advice.
All the best
Hüseyin
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I have completed uncertainty analysis for my heat exchanger calorimetric lab.but I am not sure the calculation of enthalpy ( it is required for Q=mr*deltaH) due to ref.prop program. Normally my main equation is U=cv*dT+P*v and I have calculated  uncertainity according to temperature and pressure sensor and I admitted constant the value of specific heat and specific weight but these values have a uncertainty due to Refprop uncertanities. I am not sure whether to add this uncertainty. I would like to learn your opinions and advices.
   
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In a heat exchanger, the cold stream is a corrosive material and it flows through the tube side. The shell side fluid is at a higher pressure than the tube side_ Recently one of the tubes in the exchanger has developed a large leakage_ Would you expect the shell side mass flowrate, tube side mass flowrate, shell side outlet temperature, and tube side outlet temperature to increase, decrease, or remain unchanged? Briefly analyze each of these variables individually to justify your answer?
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quite educating. i have learnt from this thread of discussion
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Base on my study, there is about 85 kw of heat will generate from a combustion of methane gas. I want to cool down the hot air by passing it through a heat exchanger. According to my previous study result, the internal temperature of the heat exchanger is quite high (about 1000oC). I want the hot air to cool down till 60oC. If the temperature of cooling water is about 20oC. In this case, what is the volumetric flow rate of the cooling water? How to calculate it? Is the formula Q=mCT can be applied in this condition? Can I assume the heat generated (85 kw) as Q?
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To answer whether you can assume 85 KW as Q, you have to be careful that rate of generated heat depends on the rate of reacting methane. So if the volumetric flow of methane is constant throughout your studies, then 85 KW can be true (If the number 85 is derived correctly)
As a preliminary guess, thermodynamical equation Q=m*cp*deltaT may be used but it's almost useless and not recommended.
To have a correct estimation of the volumetric flow rate, of cooling water, you have to derive U and A from Q=U*A*deltaT.
Because of high temperature and reaction, no normal shell&tube is applicable. My guess for your use is a furnace.
For calculation of U, heat transfer is done via convection and radiation mechanisms and there are figures and tables in books (you may find most useful information in furnace design books) to help you in this matter.
For calculation of A, the outer area of cooling water tubes in the designed furnace must be calculated.
For calculation of deltaT, you have to be careful that the logarithmic temperature difference is used. You can search the formula on the Internet.
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Dear all,
Can you please tell me the ways to measure differential pressures across utility sides of the heat exchangers.
Unlike process side, the utility side pressure drops may not be measured. What can be done in such cases ? Are there indirect ways to measure it?
Thank you.
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There are many gages all over the place on most refinery units. Many send signals to the control room and many others must be read in the field. Each gage will have a small bias/error they are rarely identical. So if you want an accurate indication of the pressure drop from field gages you do a survey of the pressure at all points of interest with the same gage to eliminate the error between different gages
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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 everyone,
I’m an engineering student and would like some suggestions for my current project.
I would like to simulate the temperature of a liquid contained in a box over time. This fluid is heated by a constant heat source but also cooled by a heat exchanger and by an air flow which cools the outside of the box. We can also think about the radiation of the box over to its environment but I can add that later.
Can someone suggest me the best way to simply obtain the temperature as a function of time considering all these elements ? Which software should I use for that type of simulation ?
Thanks in advance.
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In curve of temperature and time of polymers. Curves of the instantaneous modulus as a function of time do not change shape as the temperature is changed but appear only to shift left or right
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Is there any DNV clause for shell side nozzles' projections of shell and tube heat exchanger.
I want to keep the outside projection of the shell side inlet and outlet nozzles to 3" with 1" bore on each nozzle and I want to make sure I am not going against DNV standards.
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Welcome dear.
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The smaller, the better? What can we benefit from using mini/micro channel heat exchangers in refrigeration and air-conditioning systems? Any thoughts shared here will be much appreciated. The following are my bits for your comments.
1. Compact from high heat transfer area-to-volume ratio (e.g., the ratio ~ 1/d for a cylindrical flow channel while d is the channel diameter)
2. Reducing refrigerant charge from small refrigerant-side volume with small OD tubes
3. Maximising capacity/C