Our Car is First Year EV and I need to cool Motor&Motor Controller through Radiator, For designing Radiator First I need to calculate Heat Transfer Coefficient For Radiator, so how do i calculate? I read many research papers but didn't understand anything. Any help will be much appreciated.
We are working on calculating the Overall Heat Transfer Coefficient of the packed bed
The following reference talks about the Overall Heat Transfer but calculates it from the wall Heat Transfer Coefficient.
A. G. Dixon, An improved equation for the overall heat transfer coefficient in packed beds, Chemical Engineering and Processing, 35 (1996) 323-331
But we are unsure about the "wall heat transfer coefficient"
Would love to have some input from you.
Not: we are not interested in using the Software as our specialized case does not fit with the software.
Hello there! I am working on my thesis on Students version ANSYS Fluid. I am facing a situation that i have to set U [W/m^2*K] as Boundary Condition for an experiment. The experiment is about heat loss from walls if i am heating the inside of the building with A/C with and without thermal insulation. I cant find a formula to get the U as Boundary Condition except this youtube video: https://www.youtube.com/watch?v=ygR31_vhvJI
I run on some ideas of Nusselt Number but cant figure it out for walls at the moment.
So, anyone else tried something close to what i am trying and have a clue of how to calculate the U Convection Heat Transfer as Boundary Condition?
I'm sincerely grateful in advance.
Hello.
I am modelling non-isothermal flow in a channel with boundary heat sources at the gas-solid interface. I am using the "heat transfer in solid and fluids" module, but I am not sure how it calculates the convective heat transfer coefficient.
I wanted a way to extract it from the solution, but I couldn't find methods that do not eventually use some Nusselt number correlation. Also, I am new to FEM and am not sure what way (other than Nusselt number correlations) could be used to implement a convection boundary condition.
Any advice or resource recommendations would be much appreciated.
Hello there!
I have been tasked to introduce Ansys within the company. No one had any experience with Ansys including myself, so I was chosen to do this since I'm rather fresh (1,5 years) out of my bachelor's degree and ''I still have that studying mindset''.
Long story short: I'm struggling to understand how to use the Nusselts number to calculate my heat transfer coefficient.
I'm working with a Reynolds number that is practically always between 8000 < Re < 45000. This link: Slide 1 (usp.br) shows I can use 2 formulas for that, but as an example let's only look at:
https://preview.redd.it/z953s2e0xfy61.png?width=416&format=png&auto=webp&s=f79571433028721d4f046295b5269e0e1e6f6442
Now the Nusselts number is also defined as:
https://preview.redd.it/gb9n8l9hxfy61.png?width=71&format=png&auto=webp&s=1a7e4df3f112c0e2d17403d8ef03ea84c2d498ee
Where Ξ΄ is the characteristic length, i.e. D for my tubes, h is the heat transfer coefficient that I need to calculate and k is the thermal conductivity.
Now for my actual question. Am I allowed to combine and rewrite the 2 formulas as:
https://preview.redd.it/2pqgo84tyfy61.png?width=251&format=png&auto=webp&s=258d412da41b84fd635face35cd7b9720c85eed4
The reason I'm asking this is that Re and Pr are dimensionless approaches, that I am using in another dimensionless approach to conclude a number that has dimensions. It is confusing me a lot and it feels like I'm not allowed to use these formulas like this at all.
Any help would be greatly appreciated.
Kind regards,
I am currently looking into the Heat transfer coefficient and mass flow and how the two are related, and have found that they are. However, one part that remains unclear to me is how this will affect the temperature.
An example, if a we have a flowing pipe, with a variety of options for the flow rate, would a faster flow rate result in it losing heat quicker or slower than a slower flow rate.
Maybe I'm missing something from what I've looked into, but in essence the question is, how is the temperature affected by the flow rate?
Hello all,
I'm taking thermal engineering course and while studying and conducting labs, I have this one question comes up to my mind: How are the overall heat transfer coefficient and the temperature change (or log mean temperature) related to each other?
And since I'm only an undergraduate student, I found it would be better to ask the actual engineers. I appreciate all the responses in advance!
Thank you,
Edit: Would there be any way to relate the LMTD to thermal stress?
Hi, I'm a bit of a beginner at CFD and need some help. I'm trying to calculate the heat transfer coefficient and the total convective heat transfer from a cylinder at 600K with an air inlet velocity of 2m/s.
I have a feeling that I'm making some mistake with either defining boundaries/interfaces or the boundary conditions.
I'd set the wall of the cylinder (both trg and src) to 600K for the first attempt and later tried setting the inner wall of the cylinder to 600K with a heat transfer coefficient of 20 W/m^2K for the cylinder wall, but both attempts gave me a total heat transfer rate from the interface between the cylinder and the flow domain as 0 W when I tried using the report definitions feature.
I've attached an image of the geometry for reference. I've split the geometry about its axis of symmetry to reduce computational time.
https://preview.redd.it/ygn9yoosrx761.png?width=1074&format=png&auto=webp&s=e7c73e7fe15e448b135d37b9a674b927b2453c2f
Any help would be appreciated, thanks!
Hello All,
Iβve been going through this presentation (https://www.nrel.gov/docs/fy07osti/40848.pdf) and I have been scratching my head to understand what parameters were controlled/held constant in the calculation of the heat transfer coefficient vs hydraulic diameter plot (Slide - 10). The paper published by the same authors doesnβt offer any additional clarity.
What am I missing here?
Cheers!
So basically the title, looking to do some predictions for an experiment and I canβt get my hands on this data.
Any help would be great thanks!
Guys this question is plaguiging me for a while..
I am trying to do a 2D CFD simulation of a solar thermal collector.
I need to input the heat transfer coefficient as convective boundary condition at the inner walls of the tubes through which fluid flows. Its a 2D, so there is no actual flow, but I have to approximate that with the convective BCs.
I know, from experiments, the velocity of flow, the inner and outer diameter of the tubes, the length of the tube, the inlet and outlet temperature of the fluid, material properties (water flowing through copper pipes).
How do I calculate the heat transfer coefficient at the inner edges of the tubes?
Thank you in advance! :)
Hi all, I'm working on a SolidWorks simulation for heat treatment/quenching of steel. I'm all but ready to run my simulation, but am having trouble finding one key value. I am submerging a steel shaft previously heated to 800C into water at 20C, so to simulate this I am running a transient analysis with water as the convection medium. However, I am having trouble finding any reliable information for the convection coefficient of still water at 20C. I'd appreciate any help!
Similar substances would probably work too. I'm making a convection tabletop vape and need to know how hot the air needs to be to heat weed to 210Β°C
Hello, I'm trying to create a plot in Starccm representing heat transfer coefficient or pressure coefficient around a turbine blade. I'm trying to separate the pressure and suction side for greater visibility and comparison with other data. I'm trying to create sth like this:
https://preview.redd.it/hrb4utwtflf41.png?width=359&format=png&auto=webp&s=54a7399797aa6395523116ec075408407a684c50
This is what I have at this point:
https://preview.redd.it/mmztz2f1glf41.png?width=886&format=png&auto=webp&s=6bb0d60d2f062643fd6c92b316283df39726a6ac
Any guidance with this will be greatly appreciated
Hi r/thermodynamics,
I am working on a question involving a shell and tube heat exchanger.
An experiment was carried out, and values obtained (for temepratures in and out, for hot and cold flow).
I would like to calculate U analytically to compare with the values I got for U from the experiment. I believe I can do this from the below equations:
https://preview.redd.it/4pjorqtggu341.png?width=616&format=png&auto=webp&s=89822edb97be9caafa26d3d86ab42dfd388ad00f
https://preview.redd.it/f1zwinfjgu341.png?width=128&format=png&auto=webp&s=89152db6f62042817f96e4cf17005fc2121f71dc
This brings me back to my title question, how do I calculate ho and hi?
From the experiment, I have calculated Q values for the hot and cold fluid - I believe this does not meet the first law of thermodynamics and Q for the cold is higher - is this due to bad readings from the temperature sensors?
Please let me know if you require more detail.
Thanks in advance.
Hey Guys,
I am really struggling with this for whole day now.
I am trying to do a CFD simulation of a flat plate collector. It is 2D so I am not actually simulating the flow of water through the absorber tubes, but approximating that through imposing a convective heat transfer coefficient at the inner walls of the tubes.
The ambient temperature is the mean fluid temperature (I know the tube inlet and outlet temperatures from experiments). I also know the mass flow rate. I am simulating for 5 different mean fluid temperature cases.
So, how did I go about it?
- Calculated the flow velocity from continuity equation (m dot = density * velocity * cross section area of pipe).
- Calculated the mass flux by diving mass flow rate by area.
- Got the density, dynamic and kinematic viscosity values from Engineering toolbox.
- Calculated Reynolds Number (all turbulent)
- Got Prandtl number, thermal conductivity and isobaric specific heat capacity from another website (for the different temperatures)
- Calculated Friction Factor from Incropera (page 474, equation 8.21 in the eighth edition)
Now here comes a problem:
I am getting two different nusselts numbers when I use two different forumulas. Page 497 in Incropera there are two expressions, and one of them is supposed to be more accurate. Equations 8.60 and 8.62. But the results vary a lot. Here is the link to the excel sheet.
Big issue:
As you can see from the Excel spreadsheet, I have three very different heat transfer coefficients.
The first one, I calculated using the formula above point 3 in page 501 of Incropera.
The second, from the formula on wikipedia page for Heat transfer coefficient. The expression used is the formula under Internal flow, turbulent flow.
The third expression I used to calculate the HTC is on page 6 of this web document. The formula is immediately above Colburnβs j-factor analogy heading.
Please, please help me out here.
What am I doing wrong? Which is the right formula to take?
Thank you so fkin much if you have read thus far!
Assume 2 identical cylindrical rods (acting as fins, i.e. extended surfaces) of different materials (i.e. steel and copper) that are attached to a hot base. The rods are long enough so that the temperature at the tips is essentially the ambient temperature. Under natural convection conditions, will the two fins have the same overall heat transfer coefficient even though they have drastically different conductivity ?
I'm tempted to say YES, because for a given surface geometry, "h" is mostly dependent on the velocity and properties of the surrounding fluid (same air around both fins).
However, the properties of the fluid are dependent on its temperature...which will be impacted by the local temperature of the surface....which will depend on the conductivity of the material. Would this be overall negligible or significant ?
How would I determine this? I'm assuming it would have to be done experimentally. What should I set up? Bonus if I can set it up in my own home kitchen.
So imagine you have water at 100 Celsius flowing through a pipe. You measure the convective heat transfer coefficient of the fluid inside the pipe. What is considered high and what is low for the h value? What effect does a high h value have on the system compared to a low one? Im just curious, thanks.
My favorite book was H&M Trans for that exact resource. But of course, never lend out a book you want to keep. Specifically I'd like to make a cooking time calculator website, so my main focus is meat.
Hi,
I'm doing an internship where I'm to dimension a plate heat exchanger (water-water). For calculating the needed area I use a overall heat transfer coefficient. My question is what are typical values for a plate heat exchanger. In Perry's is found values form 5700-7400 W/(m2K). In VID Heat Atlas I found values ranging form 1000-4000 W/(m2K). I found another source stating it from 3000-6000 W/(m2*K).
In my company there already exists a plate heat exchanger (Alfa Laval). In the data sheet there is a test run specified. If I calculate the overall heat transfer coefficient from this test run I find a value of 6514 W/(m2*K).
In my calculations I chose a value of (7400-5700)/2=6650 W/(m2K). By iteration my final value of the overall heat transfer coefficient comes down to 2624 W/(m2K). This seems a bit on the low side to me. If I fool around a little bit with the initial overall heat transfer coefficient, the final answer I get after iteration remains 2624 W/(m2*K). My question is: what is an average value for a PHE?
Hi all,
I read that the convective heat transfer coefficient (h) is around 15-30 for still ambient air (25 degrees Celsius). Will this value be same for a block of carbon steel metal cooling down in open ambient conditions from about 1000 degree Celsius?
I cannot seem to find any literature anywhere giving a decent explanation as to why the heat transfer coefficient across a pipe increases with fluid velocity. Context of the rig is a pipe with air flowing through at varying velocities, a steam jacket surrounding a section of the pipe and calculating the heat transfer coefficient from the steam to the air
Hi, I am trying to design a Once-Through Steam Generator for my university design project. Canβt find values for typical flue gas/water coefficients, only flue gas/steam. Would these values be similar?
Also is there a way/need to calculate maximum water velocity in the tube bank or is this not necessary?
Thanks! (I am desperate for help)
I am wondering what the proper way to evaluate heat transfer coefficients in a total condenser/ what methods are used in industry. I am currently working on evaluating the total condenser used in the distillation column at my university for the unit operations lab. Everything I have read either goes into a detailed theoretical analysis that isn't transferable with the information that I have from lab or it splits the area of the condenser based on the degree of sub cooling. I am trying to avoid splitting the condenser into fictitious areas as it lacks concrete physical meaning. I was wondering what other methods I can look into in order to more accurately represent the heat transfer coefficient or if there is some standard method used in industry.
Hi,
So I'm looking at a heat transfer problem where there is an enclosed area with a sphere inside. This sphere is being heated by air moving over its surface, and also radiative heat transfer from the enclosure walls. I've calculated a heat transfer coefficient for both mechanisms, however I'm unsure how they should be used?
Because the wall and the air do are not at the same temperature, surely they cannot be put into the same heat transfer equation? How is it I go about this?
Cheers.
Hi all, I've got myself a little confused over a heating problem. I'm validating a model of a heating process originally done by someone else. Would appreciate any help.
If you're heating the inside surface of an empty vessel/furnace with a heat source of some description, does it make sense for there to be both a convention heat transfer coefficient as well as a heater efficiency? So in effect Q = h A(T2-T1)*e Where e is heater efficiency.
My current thinking is that since heat transfer coefficients and efficiencies are both empirical factors which account for the real conditions, then the e shouldn't be there and instead you've actually just got a different h term.
