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Images are from Fundamentals of Engineering Thermodynamics (Moran et al). But I think this content would be in most Thermodynamics books you'd see in a Mechanical Engineering book. The difference from the text is that I don't switch the signs for power like they do. I think it's confusing when you can't get the equations we're using directly from the 1st law. That way you can use your understanding to answer every question in the same way as long as you understand the process.

And I don't think they talk about the graphical solution method in the text...I could be wrong though. You could solve this same problem using thermodynamic tables.

@@mikeschertzer941 bless your heart

Pressure stays approximately constant as you go through the combustor.

Just whatever the ambient value is. Your want to look it up on a table. Cp x delta T works for changes, but not for the single value. 1st law only needs changes anyway though.

@@mikeschertzer941 I see, I don't have the table for air in the booklet given by my professor. So I calculated each of the enthalpies with Cp*Temperature. I needed the change in enthalpies to calculate the net power output and didn't know how to calculate the enthalpy. I don't know if I've done it correctly I will have to wait to see what he says when he marks my paper.

My understanding is that these come from emperical correlations and it fits the data better in these cases

@@mikeschertzer941 but there may be some dependency of Pr no. with heating and cooling phenomena

I did not have this issue. I also would have returned in this case

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.

@@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

no

In problems like these, we need to (1) define fluid properties and (2) pick a good equation to find the Re. You can see where we get properties at around 5:00. We get properties for water at around 6:05. We put that information into the Re equation at ~ 11:55. This equation might look a bit different than you are used to, but you could also use (/rho)(U)(D)/(\mu) = (U)(D)/( u). Note that in the heat exchanger videos, I seem to have often made the mistake of taking the specific volume (v_f) instead of the kinematic viscosity (/nu). But in this problem, the equation with mass flow rate works better because (m\dot) is given in the problem, as is the tube diameter (remember to convert to m). So the only property we needed to look up for Re is the dynamic viscosity (\mu). Others have pointed out that there may be a clerical error in the math here...I didn't go back to check if they are correct. The general method is correct, but you might want to double check the algebra.

Yes. I still use this chair in my home office. Same as when I got it. I think that's the advantage of these chairs. My last Steelcase was used for ~ 15 years before it had problems.

I've seen Amias from years ago and still look brand new.

I didn't add the extra foam. I'm not sure it's necessary. My old Steelcase that's from 1998 is still comfortable from the cushion standpoint. That said, my experience with these chairs is that they last a long time. So, I doubt that it's bad to add extra padding. Just not strictly necessary IMO.

@@mikeschertzer941 I see, thanks for the quick reply. I just ordered one with the extra padding. Hopefully it turns out good!

@@CoolCraig31 Did you receive your chair with the extra padding yet? What are your thoughts?

@@phoenixbluex I like it so far. It doesn't seem to be bottoming out. Really good chair. The only thing that I wished it had was a little more lumbar support, but other than that it's really comfortable. Way better than my previous office chair.

I only briefly read the problem you posted. But it seems to me like it's not a heat exchanger design problem like what's tackled in this video. And it seems to me that you need to determine the pumping requirements from the given information. Since it's not related to the topic here, I don't think it's the right venue to discuss in detail here.

Yes it requires a great pump for this heat exchanger I was hoping you'll have an idea of how to start

Thanks Erick. I'm glad that this helped you. I'm not sure how much I'd be able to help with the design and build of a TJ engine though. My guess is that you'd get better, more valuable help from someone you could speak to IRL.

@@mikeschertzer941 maybe could you help me with a e-mail for contact you? Regards

@@ericklamilla I'd prefer not to write it in the comments here.

Good catch. Looks like I was doing these too quickly. I appreciate you pointing out these errors.

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

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

@@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.

Good catch. Looks like I messed up the notation here where mu on the table is specific volume (1/density). So, you are correct that we need to pick up the dynamic viscosity from the table. Normally, we'd then divide by the density, but we can also multiple by the specific volume (you are correct that density of liquid water is ~ 100 kg/m^3 in this case). So I think our kinematic viscosity should be 855 x10^(-6) [Ns/m^2] x 0.001 [m^3/kg] = 855x10^(-9)[m^2/s]. Then I get that Re~24,000. The constants in the correlation will change C = 0.193, m=0.618. Put those in for avg(Nu) to get avg(h). The process remains the same, but the correct data will change the values of the solution. Again, great catch. It's nice to know that people are paying attention to these. And I'm teaching Heat again this semester, so I'll go back into my notes and correct this. Thanks!

Looks like my final answer was 170.3 W/m (leaving the plate) with these values...assuming I didn't make a clerical mistake.

Thanks for the kind words. I hope they help you prepare. Thermo can be pretty tough. But I think it clicks for a lot of people if you follow a good process. Good luck!

@@mikeschertzer941 thank you. I’ll refer to these during hard times.

Thanks David. These were some of the first videos i made. I agree that the pop filter helps.

Still working great. Would buy it again... Or maybe upgrade to a Leap (which is what i have in my office at work). Steelcase chairs are good long term purchases IMO.

@@mikeschertzer941 Good to hear it. Am thinking of purchasing the Amia from Crandall myself. Heard the leap gives some people tailbone pain(not for me). Thank you!

@@alexjune6414 I think it's a good chair. And my old Steelcase lasted for a long time. I witch this one still too. And the remanufactured ones seemed like a good value decision to me.

@@mikeschertzer941 you can take your amia seat pan and put it on the leapv2 if your really wanted to. It's called a Lamia.

@@MakinaDeMuerte Cool. I doubt I'll try it, but good to know if one of them fails. Then I can have a Franken-chair

I think that the general process should be the same. There are a couple of things I would check (1) did you go back and see if the velocity you got give you a Re that's in the appropriate range for the values you put into the correlation? (2) Did you double check the units you used in your calculations? (3) Just small math errors? It's possible that the solution in the book is using a different correlation, but I wouldn't expect the difference in the velocity to be that big.

That's why I went with a refurbished one. My previous Steelcase was good for more than 20 years. Wanted the same quality, but didn't want the "new" price tag. The remanufactured version seemed like a good compromise. But everyone defines value differently.

Thanks for the reply. I always like to start from the 1st law in thermo. I think part of what so many students dislike is all the memorization in the class. And starting from the 1st law takes so much of that memorization away in my opinion. I think that makes the course easier to understand. We use Moran et al. I think its a good book with very well laid out example problems. We use the newest version in our class, but i learned from the 4th edition. The principles are the same. The one thing I would change about the book if I could would be to always present the equations derived from 1st law. They stop doing this when they start cycle analysis. In this video, I use the 1st law to show that the expression for power for the Turbine and Compressor is the same, but the sign is different. And that sign tells us the direction of the power (in or out). The book switches the delta(h) for the compressor to get a positive value. I think that's confusing for students because it's hard to memorize and you can't get the equation from the 1st law. I understand why they do that and i don't think its "wrong". But (1) their way requires more memorization and (2) you can't get their answer from the 1st law. I always want my students to be able to fall back on the 1st law if they get lost.

I also did a Turbojet problem in the "ask me anything" lecture below. I do these as exam prep classes where my students can bring in problems they think look tricky and see me do them in real time without having seen them beforehand. ruclips.net/video/JLcBAWPHijw/видео.html

Good catch. Looks like there is a typo in the slide here and it should be C_h. I think I say this when narrating the slide, but have it written incorrectly on the slide. Thanks for pointing this out and sorry for the confusion.

@@mikeschertzer941 Thanks for the reply and correction. However, your's video is very useful and has been well explained.

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!

That is very kind of you Eduardo. I'm glad that you find the videos useful!

At first glance this looks like it would work. But we need to remember that the Delta(T) for convection is the temperature difference between the fluid and the tube surface. And the temperature of the tube surface varies along the length of the tube.

Thanks in glad that you find it useful!