Exhaust Gas Re-circulation Heat Exchanger (mixed/unmixed): Heat Transfer Examples for Mechanical Eng

[@ghaliabintouq429]

Your videos are so clear and easy to comprehend,thank you so much for this!

[@eng.hawraz7100]

thanks for your video, please do you have any video about two-pass cross-flow.

[@mikeschertzer941]

I think this is the only other video I have with cross flow: kzbin.info/www/bejne/jJK5fIx_nMeBi7c There is also this one with multiple passes in a shell and tube heat exchanger: kzbin.info/www/bejne/bp_Eq4aihJKYb9E

[@diyaazaghloul756]

Amazing video thank you

[@alish5598]

Sir if there is phase changement in flue gas side (hot) what will change in calculation . Thanks

[@mikeschertzer941]

Having a two phase fluid in the system will change the heat transfer coefficient (h). So you'd likely need a chance different correlation.

[@alish5598]

@@mikeschertzer941 thanks sir if you have any refrence for that situation plz?

[@mikeschertzer941]

@@alish5598 Sally I don't. It will be specific to your situation. Try a heat textbook (maybe an advanced one). Or you can hunt around in the literature. Google scholar maybe. I'm not sure how common this situation is. Perhaps you could try to discuss with someone that works with a device similar to what you are thinking of.

[@paulmayorga7611]

Hello sir, one question, in the case of cooler grate cross flow heat exchange. What will be the case for NTU calculation ?

[@mikeschertzer941]

I think you want to follow the same 2x2 matrix as in this video. You will use effectiveness NTU. Then figure out if you are solving for heat transfer (known size) or size (known heat transfer). Go through the checklists on the 2x2 for these cases. You might benefit from watching a couple of my heat exchanger videos to see examples solving for heat and solving for size. Good luck!

[@yukselkarabulut1203]

Hello, My pipe diameters are Ri = 0.045 m and Ro = 0.05 m. The pipe metal I use is aluminum. How do I calculate the total heat transfer coefficient if we calculate it similarly to your question? Thank you.

[@yukselkarabulut1203]

Actually, here's my problem. I want to design a simple recuperator. Exhaust gas temperature 610 degrees and room temperature 20 degrees. I'd like to increase the room temperature to 250 degrees using the exhaust gas. I wonder how long I should use pipes. And what should be the surface area of these pipes ? Actually, the problem you solved was very helpful, but I couldn't calculate the total heat transfer coefficient. I'd be very happy if you could help me. Thanks.

[@mikeschertzer941]

You don't calculate the total HTC directly. You'll need h on both sides of the heat exchanger. If your heat exchanger looks like the one in this problem, one side is internal convection in a pipe, and the other is external convection over a cylinder (at least as a first approximation). I have videos for both of these cases in the same Playlist as this one. The resistance of the wall may or may not be important depending on its relative resistance.

[@udaymahajani1990]

In all the examples, UA is given. But if you do not know U. ? Can we hv one example of such situation?

[@mikeschertzer941]

I'm not making these anymore. But the process is essentially the same. You'd have to have the rest of the information (i.e. a known heat transfer and size). Then you just solve for U instead of A. I think design wise, this wouldn't be a common occurrence, but you can certainly construct a problem where U is unknown. I believe that in real-world situations, it would be more likely that you find U using internal or external flow calculations. Then use that U to determine your area or heat transfer. There are several examples here on how to find "h" for internal and external flow. In this case, the U would be constructed by finding the h value inside the tubes (internal) and around the tubes (external). Then if you didn't think it was negligible, you'd include the conduction resistance to find U.

[@udaymahajani1990]

@mikeschertzer941 Thanks for reply. In order to know U, we calculate film HT coefficient on both sides based on appropriate co relation of Nu-Re-Pr and friction factor -Re. But to evaluate these we need physical properties at say average temp. Then the problem is we do not know outlet temp.

[@mikeschertzer941]

@@udaymahajani1990 Might require building a model in that case and iterating to find a suitable design.

[@udaymahajani1990]

@@mikeschertzer941 thanks for reply. Do you hv info on LMTD correction factors for cross flow mixed flow in multi pass arrangement?

[@mikeschertzer941]

@@udaymahajani1990 No. You'll need a text book. Or try to find them online.

[@thedecisions8681]

That was amazing sir, I have problem to solve a calculating of heat exchanger cross flow. This heat exchanger is used for heating the brine before entering the desalination flash evaporator Chamber. We are usually called this heat exchanger as a brine heater. The tube side is containing by a brine and the Shell side is containing by a steam. I'm so confused to solve this problem because i don't know how much is outlet steam temperature, and my lecture ask me to find LMTD and the efficient of this heat exchanger. Perhaps if u want help me, I'm so grateful for it. But, i have one wishes. Could you send the LMTD and NTU matrix to US? I think that matrix can help me Thanks for your education in this video

[@mikeschertzer941]

Sounds like there is one side of the Heat Exchanger where the change in temperature is unknown and another side where it's known? If you know how much heat is added / removed from one side, you can assume no losses and find how much heat is removed / added from the other side. Sounds like you have phase change, so you have to remember that once you hit the saturation temperature for a given pressure (i.e. phase boiling starts), you account for the extra energy by increasing the quality (i.e. more vapor formation). While you are "under the vapor dome" you can use latent heat.

[@thedecisions8681]

@@mikeschertzer941 thank you very much sir, let my try your advice 🙏🏼 and maybe I'll be back again to asking if Im still confuse with this problem