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# Heat Exchangers - Science topic

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I am student and I want to know about the best heat exchanger
Several types of heat exchangers are commonly used in industrial settings, each with its own advantages and best use cases. Here are some of the most common types:
1. Shell and Tube Heat Exchangers: These are aptly named – the primary components are a tube pack and a shell to contain them. One fluid goes through the tubes, and the second goes through the larger shell surrounding the tubes. They can support higher operating temperatures and pressures than your typical plate heat exchanger. However, if the fluid in your application is very viscous or has particulates, it can foul up the tube and undermine the heat transfer process.
Plate Heat Exchangers: These are becoming preferred due to better heat transfer, easier maintenance and cleaning, modularity, and compactness. They are more efficient than shell and tube heat exchangers in many industrial and most HVAC applications.
1. Dimple Plate/Plate Coil Heat Exchangers: These offer the best of the above kinds of heat exchangers – they’re cheap, customizable, and compact but can withstand incredibly high pressures and temperatures due to design and materials.
The best type of heat exchanger for industrial use depends heavily on the particular process in which the heat exchanger is installed. Factors such as the type of fluids being used, the desired temperature change, the pressure, and the flow rate will all impact which type of heat exchanger is most suitable.
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It's a tube & shell exchanger
.
Here's a general approach to estimating the fluid velocity without knowing the surface area:
1. Determine the flow rate: If you know the volumetric flow rate (Q) or mass flow rate (m) of the fluid passing through the exchanger, you can use this information in the calculation.
2. Estimate the cross-sectional area: If you can approximate the shape of the flow channel in the exchanger, you can estimate the cross-sectional area (A) based on that assumption. For example, if the flow channel is rectangular, you can estimate the area using the width and height of the channel. If the channel is circular, you can estimate the area using the radius or diameter of the channel.
3. Calculate the fluid velocity: Once you have an estimated cross-sectional area, you can calculate the fluid velocity (V) using the equation V = Q / A, where Q is the flow rate and A is the cross-sectional area.
It's important to note that this method provides an estimation and may not be as accurate as directly measuring the surface area of the exchanger. Additionally, the actual flow path and configuration of the exchanger may impact the fluid velocity distribution, so it's recommended to consult specific design guidelines or seek expert advice if possible.
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the magnetic field
1. Enhanced Heat Transfer: Magnetic waves can significantly enhance the heat transfer rate, especially for nanofluids, when an external magnetic field is imposed. This can lead to improved efficiency in heat exchange systems.
2. Direct Conversion: Using magnetic waves eliminates the need for an intermediate conversion process, directly converting solar energy into electric energy in solar energy-driven power-generating systems.
1. Increased Flow Resistance: The magnetoviscous effects induced by magnetic fields can increase flow resistance and offset the possible convective heat transfer enhancement in ferrofluids. This makes their use as potential heat transfer mediums challenging, especially in strong magnetic fields1.
2. Economic Evaluation: The economic potential and cost of magnetic refrigerators and heat pumps need to be evaluated.
It’s important to note that these are general points, and the specific advantages and disadvantages can vary depending on the application and system design.
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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.
I think this definition has some problem! the onlt parameter which can be considerd is entropy generation which should be positive, other things are only a difinition! not law!
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The difference air heat exchanger and water heat exchangers
The terms of type of used pipe
air operated heat exchangers have air as the heat transfer fluid. For high performance of the hex material of high or reasonable thermal conductivity is preferred, e.g copper, aluminum, steel, stainless steel. An example is the domestic filament heater.
for water operated hex, water is the htf and the material similarly should be ideal for maximum heat transfer i.e., high thermal conductivity. In addition should be reasonably corrosion resistant. materials can be copper, steel, stainless steel. an example can be an economizer.
a steam boiler is a good example of a combination of both. The boiler tubes have hot gases as the htf and the shell side has water as the htf. here relatively affordable material with reasonable thermal conductivity and with an ability to withstand high pressure is required so schedule 40 steel can be used.
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For a regular Low Temperature Striling Engine, how much mechanical energy can I produce by using hot water at around 350K?
The mechanical energy produced by a Stirling engine using hot water at around 350K depends on factors like engine efficiency, temperature difference, and design. Generally, small engines might produce a few watts, while larger ones can generate several kilowatts or more. Specific values vary based on these factors.
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I want to calculate Rayleigh number and Nusselt number of a PCM-heatsink to analyze the intensity of the natural convection of PCM. There are some fins inside my heatsink to enhance the heat transfer. Now I am having trouble calculating the characteristic length to use in Rayleigh and Nusselt dimensionless numbers.
I would be grateful if you could help me.
The Rayleigh number (Ra) is a dimensionless number used to predict the flow regime (conduction, convection, or mixed) in a fluid when it is heated from below. In the context of a phase change material (PCM)-heatsink system with fins, the characteristic length is an important parameter for calculating the Rayleigh number.
The characteristic length (L) used in the Rayleigh number calculation can vary depending on the geometry of the system. In the case of a PCM-heatsink with fins, the characteristic length can be defined based on the specific geometry you are dealing with. Here are a few possibilities:
1. Fin Height (H): If the characteristic dimension of interest is the height of the fins (assuming they are vertically oriented), you can use the height of the fin as the characteristic length. This would be suitable when the heat transfer is mainly driven by natural convection along the fins.Rayleigh Number (Ra) = (g * β * ΔT * H^3) / (ν * α)Where:g: Acceleration due to gravity β: Coefficient of volumetric expansion ΔT: Temperature difference between the heated surface and the surrounding fluid ν: Kinematic viscosity of the fluid α: Thermal diffusivity of the fluid
2. Fin Base Width (W): If the characteristic dimension is the width of the fin base, you can use this value as the characteristic length. This might be more appropriate if the heat transfer occurs primarily through the base of the fins.Rayleigh Number (Ra) = (g * β * ΔT * W^3) / (ν * α)
Remember that the choice of characteristic length depends on the dominant heat transfer mechanism in your specific setup. The key is to select a length scale that is relevant to the phenomenon you are trying to analyze.
Additionally, when dealing with PCM systems, keep in mind that the melting and solidification of the PCM can introduce additional complexity to the heat transfer process. You might need to consider the effects of latent heat and phase change in your analysis.
Before performing calculations, ensure that the physical properties of the fluid, PCM, and the geometry are accurately determined. It's recommended to consult relevant literature, research articles, or textbooks in the field of heat transfer to find appropriate values and guidance for your specific configuration.
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Hi friends, i am doing simulation on heat exchanger. when i am trying with Coupled algorithm, solution is easily converged. but when i am changing to PISO, iteration run for 24 iteratio(within 1min), after that no response. more than 30 min. no error like thing come. (simply as in attached file. why this occur? what to do?
Surendra Singh Rathore Surendra Singh Rathore sir thank you for reply, I tried with all algorithms.it is working only in coupled. In remaining all algorithms, getting the same result only difference is the number of iterations it is stuck(No response why ? ). I tried relaxation factor in all quantities as u said. Now am looking for other alternatives in coupled algorithm. because in this algorithm alteast iteration process is running.
Thanks
T.Saravanakumar
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I am working on modeling and optimization of evaporator and condenser, both are plate type heat exchanger. The primary fluid is refrigerant mixture (zeotropic) and secondary fluid is hot water. For water, the open literature has numerous heat transfer correlations but for refrigerant mixtures I could not find any flow boiling or condensation correlation in heat exchangers. Although there are few studies that provide flow boiling or condensation correlation of zeotropic fluids in tube. But since the flow pattern is different in tube and plate heat exchanger (vortex or swirl flow), is it reasonable to use flow boiling or condensation correlation of zeotropic fluids in tube instead for flow in plate heat exchanger as well?
The flow boiling and condensation heat transfer correlation for refrigerant mixtures in tube wi
Muhammad Imran , Khaled Hossin , Shazia Farman Ali , I agree with you about the existing research gap in having the correlations for Zeotropic mixtures in the case of Plate type HX. I was also facing a similar issue. In my case, the intended fluid is CO2; and I didn't find any heat transfer coefficient as well as pressure drop correlation in the case of CO2 evaporation inside a plate type HX. However, there are numerous existing correlations for the in-tube flow boiling as well as condensation. I am hereby providing one reference for a unified correlation in the case of in-tube flow boiling inside a mini/micro/conventional channel. This correlation generally accounts the "hydraulic diameter" concept in a tube flow. As there is no existing correlation for CO2 and zeotropic mixtures in the case of flow boiling inside a plate HX, could this "hydraulic diameter" concept for mini/micro/conventional channel be a starting point for estimating the HTC and PD for flow inside a plate HX?
[1] Shah, M. M. (2017). Unified correlation for heat transfer during boiling in plain mini/micro and conventional channels. international journal of refrigeration, 74, 606-626.
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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.
Hi,
I guess you could chose one of the two fluid inter solvers. They are based on Volume of Fluid and easy to apply. But you should really take care about cell resolution for good results of course. To take account for natural convection just apply boussinesq or polynomial thermophysicalProps. For polynomials you need to fit function coefficients according to your const. Pressure and temperature range. Unfortunately it can happen, that property calculation is not that precise.
On the other hand it is possible to chose euler solvers instead of inter solvers of course. But in my opinion you need really deep knowledge about all those empirical coefficients.
Hope that helps.
Regards David
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Suppose we have a HEN with several multi-pass heat exchangers. However, due to some technical constraints all these exchangers are modelled simply using single pass equations.
What will the impact if such a simplistic model is used in optimization problems, such as network optimization for retrofitting or cleaning scheduling?
For instance, it is clear that we may not end up with global optimal solutions but still what will the qualitative impact of such approximations?
To formulate of this model you need to consider the amount of information included in it:
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The open literatures provide lots of correlation for estimating the in-tube CO2 flow boiling heat transfer coefficient. In the case of plate heat exchanger, the correlations are available for R134a, R410A, etc. I was looking for something generalized or specific correlation that accounts the phase change (boiling/evaporation) for CO2 inside a brazed plate heat exchanger (BPHX). Because, the flow inside a BPHX should be very different than the in-tube flow.
Thank you very much for your valuable feedback. I agree with you on the points stated above.
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Do obstacles in a channel change the regime from laminar to turbulent while the Reynolds number is under 2300 (approximately 1000)?
The Reynolds number UD/nu=2300 is based on a smooth circular pipe of diameter D, with STEADY mean flow velocity U and fluid of kinematic viscosity nu. Below this critical Reynolds number any perturbation due to an obstacle will not cause persistent turbulence to occur far downstream of the obstacle. Of course locally the wake of a blunt body placed in the pipe can be turbulent, but soon the flow will relaminarize if we travel further downstream. Above Re=2300 the flow does not need to be turbulent. It can be turbulent if there is a sufficiently large initial upstream perturbation. In principle the flow can remain laminar if the inlet is very smooth and care is taken to avoid vibrations. Experimentally fully developed laminar pipe flows have been achieved for Re=500. 000. It is important to realize that this critical Reynolds number does depend on the geometry of the cross-section of the channel. For a rectangular channel of height h and width w >>h, usually one considers a Reynolds number Re=Uh/nu based on the channel heigth. The critical Reynolds number for allowing turbulence is around Re=hU/nu=1100. There is however much less literature on flows through slit shaped channels than circular pipes. If you consider an open channel flow, clearly the critical Reynolds number will be quite different from Re=2300 and of course it does depend on the length scale used in the definition of this Reynolds number!
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May below article will help u,
Counter current heat exchanger
A counter current heat exchanger is a type of heat exchanger used to transfer heat between two fluids that flow in opposite directions, creating a counter current flow. The two fluids flow through separate channels separated by a thin, thermally conductive wall, which allows heat to transfer between the two fluids without mixing them. In this type of heat exchanger, the hot fluid enters at one end and flows in the opposite direction of the cooler fluid, which enters at the other end. As the fluids flow in opposite directions, heat is transferred from the hot fluid to the cooler fluid, resulting in a more efficient heat exchange process compared to other types of heat exchangers. This design ensures that the temperature difference between the two fluids remains high throughout the exchanger, allowing for maximum heat transfer. Counter current heat exchangers are commonly used in a variety of applications, including HVAC systems, chemical processing, and power generation.
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Hello everyone,
I would like to simulate a heat exchanger with tear stream in aspen plus. I got convergence in shortcut mode. But when I change it into the rigorous mode, I no longer can get the convergence. I tried the following ideas to get the convergence but no luck in getting it.
1) Changed the method
2) Relaxed tolerance
3) Initialized the stream
Any idea to solve the problem will be appreciated.
Regards,
Kamalidevi
I appreciate your enthusiasm Abdul Wahab. To converge the tear streams, we have to give correct appropriate initialization. This initialization you can find by breaking the tear open and doing trial and error analysis until the tear values are almost equal. If attaining this equality is difficult, then we can export the steady state with the tear open and run it in the dynamics by joining the tear. I hope it is understandable! For more information, you can have a look at the paper I attached.
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Scaling in heat exchanger with causes and types ?
Another reference text is the excellent
Fouling of Heat Exchangers - T.R. Bott
Web13 Apr 1995 · This unique and comprehensive text considers all aspects of heat exchanger fouling from the basic science of how surfaces become fouled to very practical ways of …
• Author: T.R. Bott
• Publisher: Elsevier, 1995
I would note that fouling is a massive cost factor in many industries.
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I am trying to size a radiator for a car. Is there is a specific software used by automobile engineers for sizing the radiator? Can I use Aspen EDR for compact heat exchangers?
yes by using ASPEN EDR
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How to measure thermal conductivity of Fins in heat sink or heat exchanger.
Thermal Conductivity: A measure of the ability of a material to transfer heat. Given two surfaces on either side of a material with a temperature difference between them, thermal conductivity is the heat energy transferred per unit of time and per unit of surface area, divided by the temperature difference (T). Thermal conductivity is a bulk property that describes the ability of a material to transfer heat.
Three classes of methods exist to measure the thermal conductivity of a sample: steady-state, time-domain, and frequency-domain methods.
In general,
Steady-state-Steady-state techniques perform a measurement when the temperature of the material measured does not change with time.
K= Q.Δx/A.ΔT
Time-domain methods
• The transient techniques perform a measurement during the process of heating up. The advantage is that measurements can be made relatively quickly. Transient methods are usually carried out by needle probes
Transient hot wire method
The transient hot wire method (THW) is a very popular, accurate, and precise technique to measure the thermal conductivity of gases, liquids, solids, nanofluids (hybrid Fluids), and refrigerants in a wide temperature and pressure range
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I have calculated the power losses of the system and the inlet and outlet temperatures for both air and waterside. Using LMTD method, the overall heat transfer coefficient of the CHE was found.
I am unable to proceed further, mainly because I could not find any reports on the heat exchanger(it is similar to a car radiator but smaller form factor) I am working with. How do I find the heat transfer coefficient for the air and water side?
I am unsure of which relations to use from Kays and London book on Compact Heat exchangers (CHE).
Any suggestion on software/books/reports on finding the heat transfer coefficient of this type of heat exchanger would be greatly helpful.
Measure the heat transfer. Vary the inputs. Switch to water on the outside and air on the inside. Use Reynolds Analogy, St=f/2. Kays & London is an excellent reference. So is TEMA and HEI and various ASME documents.
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In my car radiator, the coolant leaking due to minor crack in the plastic. The crack is in the initial stage so no problem now. But coolant leak by drop by drop.
I like to fill the crack in the plastic. What type of glue is used to fill the crack in plastic?
J-B weld original would be the best option since you're talking about the plastic part of your radiator: https://www.amazon.com/J-B-Weld-8265S-Cold-Weld-Reinforced/dp/B0006O1ICE
It can glue everything. I used it to glue acrylic to aluminium and acrylic to polyethylene to create pipe-flange leak-free joints. My acrylic-aluminium joint holds 0.35 bar gauge pressure of water and the acrylic-polyethylene holds about 0.15 bar gauge of water.
Before going with J-B weld original, I tried plastic specific J-B weld epoxies. None of the worked. Only J-B weld original saved me.
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Normal car uses Radiatior system to cool down the engine system. But in Electric vehicle that there is no nead of radiators i think.
Someboby told me electric vehicles using heatsink. Please clarify what type of heatsink is used and how heat in Electric vehicle is controlled.
Hello Nekin Joshua ,
You can find the answer to your question on the Internet by simply typing the phrase "do electric vehicles have radiators" into the Google search field. One of the most important EV components that needs to have its temperature regulated is the battery. If the battery overheats, it can catch fire or explode. Most EV batteries are liquid cooled with the heat dissipated by a radiator.
Regards,
Tom Cuff
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It must have high thermal conductivity even if it is not electrically conductive. However, it should had high stiffness value so that it will not warping
May I recommend you to use ULTEM or PEI filament (Polyetherimide); It is similar to PEEK but better in thermal resistance.
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I need a test bench of a heat exchanger to do experiments on the theme 'fouling of heat exchangers.'
Are you looking for a laboratory that would perform tests on a heat exchanger to determine fouling? That would be extremely expensive and entirely impractical unless you had some critical motivation and funding. Are you looking for experimental studies on heat exchanger fouling that have already been performed? There are many in the literature. Are you looking for codes, standards, and methods? There also many of these (see HEI, TEMA, EPRI, ASME, ASHRAE, AIChE, and many more).
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Hello everybody,
i hope you're doing well,
please could you help me the question above using numerical calculations
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.
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
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
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.
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.
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.
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
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.
2. Fins are never used on the surface in contact with a fluid undergoing phase change.
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I'm a Mechanical Engineering student fin heat exchanges. I would like to the know the best material for make fin. But because of lack of knowledge on the subject, I'm confused about where to start my design. hopefully someone who knowledgeable in heat transfer field can answer my question. thank you.
The fitting can be selected based on its conductivity
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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?
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?
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!
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.
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?
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 ?
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?
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
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.
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 ?
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?
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.
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.
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.
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.
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.
Yours faithfully,
Nashmin
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?
You can evaluate the Nu number as the integral of the local Nu numer of your pipes surfaces. The last one can be easily evaluated with COMSOL since it is proportional to dT/dn|A where n is the normal vector and A is the surface of the pipe. The local Nu number depends also on the bulk temperature which is can be evaluated by integrating u*T and dividing by the integral of u*A.
Good luck
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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.
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?
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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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.
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?
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?
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.
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?
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?
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.
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?
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.??
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
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,
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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?
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?
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?
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.
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?
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?
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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