Hey Mike, your videos are amazing. Is there anyway we could print your slides, the two by two matrix would be perfect to have a hard hard copy of. All of your slides are full of detail, did you create them?
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.
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
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.
When calculating the area of the parallel or counter flow heat exchanger, I noticed that the units in the denominator do not align. You left the log-mean temperature in units of Celsius but the overall HT coefficient as W/m^2 K. In this case, wouldn't we have to convert the log-mean temperature to Kelvin in order to get the correct area for the heat exchangers?
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'm planning on ordering this chair as well, but I'm not sure if I should add the extra 1/2 inch foam seat padding option though, would you recommend it?
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.
@@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.
A Stainless-Steel Plate Heat Exchanger Requires a Pump. A performance test for water and ethylene glycol mixture fluid at 50%/50% mixing ratio is done on a stainless-steel plate heat exchanger. The 15 L mixture of Water (50%)/Ethylene Glycol (50%) is the hot side fluid and water from the tap is used as the cold side fluid. The total heat transfer area of over 600 њ2, the length of the plate is 175 mm, the width of the plate is 60 mm, the thickness of the plate is 18 mm and the gap between the parallel plates is 2.2 mm. The flow rates chosen for the performance test are 1 L/min, 2 L/min, 3 L/min, 4 L/min and 5 L/min. The plate heat exchanger requires the use of a hot fluid pump as part of its service module. The service module also consists of the following specifications: ▪ Flow meters for hot and cold fluids ▪ Heater 3000 W ▪ Hot fluid stainless steel tank (15 L) with level switch ▪ Two sets temperature indicators ▪ Temperature control Unit 1. You are required to establish the type of pump to be used and to select possible parameters for the pump, include all possible omitted specifications in your selection, such as size of pump required, the pump efficiency, and all required pump parameters. 2. As part of the maintenance team, provide maintenance procedures for the type of pump You have selected. Could coupling be required for the size of pump selected? 3. Provide calculations for pump analysis, and draw the characteristic curves associated with pumps for Your pump selection using MS Word/Excel. 4. In addition, provide calculations for the Reynolds Number for the hot fluid at T=45 °C average temperature for all the flow rates indicated. ( ђ=ѣĎ where Ď is the hydraulic diameter, dynamic viscosity). Could the flow be considered laminar or turbulent? Plot on a single graph Reynolds Number against the Flow rates. Compare and discuss these results. 5. You should be able to discuss any limitations on the project and present further recommendations for the limitations. You are not expected to do the following
Nice explanation, we are building a turbo jet engine (basic) for educational purposes... Does it exist the possibility to contact you via email or zoom? Regards
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.
05:46 At T=323K, the dynamic viscosity (mu) should be 548*10^-6 Ns/m^2 (typo with the units on the slide). The density (1/specific volume) should be 987 kg/m^3 (not 0.987 kg/^3). 12:13 With these, I computed the Reynolds Number to be 2.32*10^5. Similar to Eduardo Suarez's result in the other comment. Thanks again for putting these videos up on RU-vid.
@@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.
03:40 Looks like we picked up the specific volume value from the table and used it as the kinematic viscosity. I think we need to use mu_f from the table and assume the density of water is 1000kg/m^3 when computing the Renolds Number.
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!
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!
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.
I don't know if you still read this but I have the same question but air temperature is 30°C, diameter 0.15 mm , Q is 15W/m and the wire temperature is 80 °C. When i calculate the velocity i get 4.85 but my book says the answer is 13.12.
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.
This was insightful! Thank you sir. Do you have a favorite textbook you could recommend where I could learn more about Turbojet problems like this? Take care. Additionally, working both versions of the problem: constant Cp and temperature-dependent Cp is appreciated. Lastly, I appreciate you starting from the first principles each time and canceling out the terms. I think it is easy for a professor to assume everyone understands what cancels and why, but it's easy to forget the rationale for most of them
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. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-JLcBAWPHijw.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.
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!
I really like the lectures content, the clarity and the graphics. Thank you very much. I think you are helping a lot of aspiring professional Engineers. [Q=731,850 W, Re=232,401, NU=750, A=27sq.m, L=4.30m]
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.
