00:00:00.030 okay let's look at some different 00:00:02.24000:00:02.250 overall designs plate heat exchanger 00:00:05.15000:00:05.160 turban shell spiral plate fin heat 00:00:08.45000:00:08.460 exchanger and a regenerative heat 00:00:10.87900:00:10.889 exchanger so the plate heat exchanger I 00:00:13.12900:00:13.139 have a small model here you have 00:00:15.47000:00:15.480 different plates and the hot medium 00:00:19.64000:00:19.650 flows on every second and the cold 00:00:21.74000:00:21.750 medium on every second so the hot medium 00:00:24.32000:00:24.330 goes in and distributes and goes in the 00:00:27.29000:00:27.300 same direction on all plates and the 00:00:29.77900:00:29.789 core medium goes in if you want to 00:00:31.51900:00:31.529 counter current setup in the other way 00:00:33.28000:00:33.290 and then goes on every second and these 00:00:38.72000:00:38.730 plates are rather thin they can look 00:00:42.44000:00:42.450 like this if it's mono model so this is 00:00:47.33000:00:47.340 slightly bigger but again these can be 00:00:49.01000:00:49.020 like 6 meters high or they can be really 00:00:51.04900:00:51.059 really tiny so that many different sizes 00:00:54.47000:00:54.480 and there are number of pros and cons 00:00:57.02000:00:57.030 with this one it's it's very flexible if 00:00:59.45000:00:59.460 you want to increase the area you can 00:01:01.16000:01:01.170 just put in more plates you get high K 00:01:05.53900:01:05.549 values because this material is rather 00:01:09.20000:01:09.210 thin so if you look from that side that 00:01:13.19000:01:13.200 it's it's really thin so the overall 00:01:15.74000:01:15.750 heat transfer coefficient that's high 00:01:17.99000:01:18.000 you can have something like three point 00:01:20.42000:01:20.430 five to five point five kilowatts per 00:01:22.13000:01:22.140 square meter and Kelvin and this is one 00:01:23.60000:01:23.610 of these it's easy to disassemble your 00:01:26.30000:01:26.310 stack report and then you can clean it 00:01:28.39900:01:28.409 easily it's easier to inspect and see if 00:01:31.19000:01:31.200 everything seems to be working fine and 00:01:33.05000:01:33.060 it's a rather compact thing and due to 00:01:36.31900:01:36.329 the the thin walls you can also work 00:01:38.60000:01:38.610 with small temperature differences but 00:01:42.31900:01:42.329 not everything is good one problem is 00:01:45.85900:01:45.869 that these gaskets are typically 00:01:49.92900:01:49.939 sensitive to high temperature and high 00:01:51.92000:01:51.930 pressure so that's the downside but 00:01:54.88900:01:54.899 there is a workaround for that and 00:01:56.20900:01:56.219 that's to weld or braise these together 00:02:00.91000:02:00.920 this different place now you lose some 00:02:04.55000:02:04.560 of the pros with this thing because if 00:02:06.80000:02:06.810 you weld the bracelet together then you 00:02:09.16900:02:09.179 can't take it apart it's more difficult 00:02:10.66900:02:10.679 to clean so things 00:02:13.02000:02:13.030 tend to get stuck in here and should you 00:02:18.36000:02:18.370 weld it or should you brace it your 00:02:20.64000:02:20.650 welding is a bit more difficult and 00:02:22.19900:02:22.209 bracing when you weld you the material 00:02:24.84000:02:24.850 you melt is very similar to the material 00:02:28.62000:02:28.630 you want to put together so the plates 00:02:30.66000:02:30.670 are made of essentially the same 00:02:32.16000:02:32.170 material as esta material you melt while 00:02:35.67000:02:35.680 you if you brace you use a different 00:02:38.19000:02:38.200 metal typically a metal that melts at 00:02:42.03000:02:42.040 the lower temperature making it much 00:02:44.28000:02:44.290 easier to put together but if you have 00:02:46.29000:02:46.300 different metals well then you get 00:02:49.44000:02:49.450 corrosion because of the difference 00:02:51.57000:02:51.580 between the two metals the next one is a 00:02:54.15000:02:54.160 tubular shallot exchanger you will see 00:02:57.03000:02:57.040 one at the lab I don't have a model of 00:02:59.82000:02:59.830 the table shell but I have a model of 00:03:02.55000:03:02.560 the or something very similar the 00:03:06.12000:03:06.130 lamellar heat exchanger so the only 00:03:12.50900:03:12.519 difference here is that instead of these 00:03:15.57000:03:15.580 things here being pipes surroundings 00:03:18.66000:03:18.670 these are flat but the basic principle 00:03:23.46000:03:23.470 is the same you have one media that goes 00:03:25.56000:03:25.570 inside these channels so tubes in inner 00:03:30.87000:03:30.880 tube I shall heat exchanger and you have 00:03:33.00000:03:33.010 one media that goes on the outside it's 00:03:36.12000:03:36.130 usually difficult to understand drawings 00:03:38.22000:03:38.230 of the bandshell heat exchanger if you 00:03:39.93000:03:39.940 haven't seen one before and that's why 00:03:42.39000:03:42.400 we took the lab where you you you look 00:03:46.25900:03:46.269 at one in real life and see what is a 00:03:49.31900:03:49.329 baffle for example how does that work a 00:03:53.52000:03:53.530 nice thing with the two beshallach 00:03:55.74000:03:55.750 exchanger is that you it's really 00:03:58.25900:03:58.269 flexible at the design stage you can for 00:04:02.43000:04:02.440 example decide if you want these tubes 00:04:04.71000:04:04.720 to be just long or if you want to bend 00:04:08.58000:04:08.590 them so that the flow goes several times 00:04:12.18000:04:12.190 through the equipment you can have 00:04:16.13000:04:16.140 another approach that you can have 00:04:19.56000:04:19.570 really large differences in flow rates 00:04:21.83900:04:21.849 on the hot and cold side if you want to 00:04:23.96900:04:23.979 you can build it so that it would stand 00:04:26.67000:04:26.680 really high pressures or temperatures 00:04:29.33000:04:29.340 but there are also problems one problem 00:04:33.09000:04:33.100 is that you don't get as high k values 00:04:36.87000:04:36.880 over all the transfer coefficients as 00:04:38.64000:04:38.650 you do for plate heat exchanger and it's 00:04:41.52000:04:41.530 rather difficult to clean the shell side 00:04:45.74000:04:45.750 so I mean if you want to clean the 00:04:48.18000:04:48.190 inside of of these channels yeah what 00:04:52.71000:04:52.720 you can do is see use high pressure 00:04:54.83000:04:54.840 water for example and flush through or 00:04:58.08000:04:58.090 take something to scrub but in between 00:05:04.90900:05:04.919 becomes difficult 00:05:06.90000:05:06.910 I mean imagine you have let's say you 00:05:10.02000:05:10.030 have 100 tubes in a large package to get 00:05:14.61000:05:14.620 in in the center between those that's 00:05:17.64000:05:17.650 really difficult the next one is the 00:05:22.05000:05:22.060 spiral heat exchanger it looks like this 00:05:27.14000:05:27.150 there is a hot side and the cold side so 00:05:33.02000:05:33.030 and there is a lid here so we can put it 00:05:37.29000:05:37.300 here and then for example have the hot 00:05:40.23000:05:40.240 medium going in in the center and then 00:05:43.23000:05:43.240 spiraling out and if you want that to be 00:05:46.50000:05:46.510 a counter current than we want then you 00:05:53.70000:05:53.710 want the core meaning to go the other 00:05:56.70000:05:56.710 direction right and then we have a lid 00:05:58.77000:05:58.780 there as well 00:05:59.76000:05:59.770 if that's difficult to understand 00:06:02.58000:06:02.590 perhaps it's easier to if I show you 00:06:04.64900:06:04.659 like this 00:06:10.82000:06:10.830 though of course pros and cons with this 00:06:13.23000:06:13.240 one as well it's suitable for different 00:06:15.96000:06:15.970 combinations of liquid steam gas so you 00:06:18.36000:06:18.370 can liquid on one side and gas on the 00:06:20.34000:06:20.350 other side for example it's rather 00:06:23.82000:06:23.830 limited in the temperature and pressure 00:06:29.06000:06:29.070 because of these zones here 00:06:32.51000:06:32.520 better than the plate heat exchanger but 00:06:35.13000:06:35.140 still rather limited in temperature and 00:06:37.47000:06:37.480 pressure and you get medium K values as 00:06:39.87000:06:39.880 perhaps 1.5 to 2 kilowatts per square 00:06:42.57000:06:42.580 meter in Calvin you can't equip a heat 00:06:49.17000:06:49.180 exchanger with surface enlargement and 00:06:51.48000:06:51.490 that you can do in different ways 00:06:53.01000:06:53.020 sometimes you see that those on 00:06:54.63000:06:54.640 radiators and why do I say that the 00:06:59.34000:06:59.350 radiator is a heat exchanger it's only 00:07:01.77000:07:01.780 one medium isn't it 00:07:03.21000:07:03.220 well no it's two you have the radiator 00:07:07.47000:07:07.480 and on the inside you have a liquid like 00:07:10.83000:07:10.840 hot water for example and on the outside 00:07:13.35000:07:13.360 you have air so air is one medium and 00:07:16.41000:07:16.420 the liquid inside the radiator is 00:07:18.48000:07:18.490 another now this is an example with 00:07:24.44000:07:24.450 surface enlargement so why would you 00:07:28.56000:07:28.570 need this well if you have a gas gases 00:07:32.19000:07:32.200 have very low heat transfer coefficients 00:07:37.05000:07:37.060 and by increasing the air you can can't 00:07:41.28000:07:41.290 counteract that so this one is made for 00:07:44.01000:07:44.020 liquid on the inside and then a gas on 00:07:46.80000:07:46.810 the outside and there are different kind 00:07:49.23000:07:49.240 so this one I would call a plate and fin 00:07:53.61000:07:53.620 heat exchanger so plates here and fin 00:07:57.57000:07:57.580 like things there and there are many 00:08:00.24000:08:00.250 different variants of that you can have 00:08:03.03000:08:03.040 for example a yes the type and then you 00:08:05.79000:08:05.800 have circular things all the sometimes 00:08:11.90900:08:11.919 in old houses the radiators that are 00:08:14.88000:08:14.890 made like this large pipe and then those 00:08:17.64000:08:17.650 metal things metal plates that enlarged 00:08:20.73000:08:20.740 area 00:08:24.63900:08:24.649 regenerative heat exchangers here is one 00:08:28.87900:08:28.889 example the idea with a regenerative 00:08:37.27900:08:37.289 heat exchanger is that when I breathe 00:08:40.33900:08:40.349 out my hot air hits these metal things 00:08:46.55000:08:46.560 here so there's some metal channels 00:08:49.43000:08:49.440 there and when then when I inhale the 00:08:54.94900:08:54.959 cold air is being heated up by these 00:08:57.05000:08:57.060 metal things so this particular thing 00:09:02.12000:09:02.130 that's made for running skiing similar 00:09:06.05000:09:06.060 things when it's really cold outside and 00:09:08.09000:09:08.100 actually helps a lot 00:09:10.73000:09:10.740 the only problem of course is that a 00:09:13.56900:09:13.579 your breath contains a lot of water 00:09:16.93900:09:16.949 water vapor and if you exercise heavily 00:09:21.05000:09:21.060 then also some spit and other things get 00:09:24.59000:09:24.600 tend to get stuck in this and it freezes 00:09:27.88900:09:27.899 and it becomes rather yucky but still 00:09:31.38900:09:31.399 this actually works really good there is 00:09:37.49000:09:37.500 an efficiency issue with this one and 00:09:40.40000:09:40.410 that's if you breathe out the these 00:09:45.88900:09:45.899 channels are filled with used air and 00:09:49.10000:09:49.110 then you breathe in and then you take 00:09:51.35000:09:51.360 some of that air back in again you can 00:09:54.05000:09:54.060 compare that with the snorkel 00:09:55.63900:09:55.649 you shouldn't have very long snow 00:09:58.12900:09:58.139 clothes because when you breathe in and 00:10:00.35000:10:00.360 you breathe out if you have a very long 00:10:01.91000:10:01.920 snorkel the only thing that happens is 00:10:03.92000:10:03.930 that you take the same air in and out 00:10:06.11000:10:06.120 and in and out and in and out and then 00:10:08.36000:10:08.370 you die from asphyxiation so that's not 00:10:11.12000:10:11.130 good a more common regenerative heat 00:10:16.49000:10:16.500 exchanger than this one is what you can 00:10:20.36000:10:20.370 see on houses so then you have a big 00:10:23.38900:10:23.399 circular thing and then channels like 00:10:26.72000:10:26.730 this that goes round round round so and 00:10:30.41000:10:30.420 then on one side you have on the top 00:10:33.01900:10:33.029 side for example you can have indoor air 00:10:34.61000:10:34.620 going out and the 00:10:36.07900:10:36.089 bottom half you can have outer air going 00:10:38.44900:10:38.459 in and as these channels go around they 00:10:44.76900:10:44.779 get indoor air and unless heated up and 00:10:49.04000:10:49.050 then they come to the other side and 00:10:52.00900:10:52.019 then the outer air is heated up by these 00:10:56.84000:10:56.850 channels and if you look really 00:10:59.98900:10:59.999 carefully they have made attempts there 00:11:02.54000:11:02.550 to to solve the this inefficiency issue 00:11:04.96000:11:04.970 so they typically have a small small 00:11:08.03000:11:08.040 section where they try to purge the used 00:11:12.43900:11:12.449 air I mean if you if you work in a 00:11:14.96000:11:14.970 restaurant for example you want to get 00:11:16.81900:11:16.829 rid of all the smells from the kitchen 00:11:21.23000:11:21.240 and get in fresh air you don't want the 00:11:25.28000:11:25.290 used air to get back in and then there's 00:11:27.55900:11:27.569 a way of actually blowing the base 00:11:31.12900:11:31.139 channels one time with fresh air to 00:11:36.25900:11:36.269 empty them okay so that was a number of 00:11:40.28000:11:40.290 different designs but I said that the 00:11:42.55900:11:42.569 overall heat transfer coefficient is 00:11:44.15000:11:44.160 really important and you need to be able 00:11:46.12900:11:46.139 to estimate that somehow and when we 00:11:50.96000:11:50.970 estimate that we need a number of 00:11:52.73000:11:52.740 different dimensionless numbers nusselt 00:11:58.05900:11:58.069 pronto Raynald and Glossop's number 00:12:03.36900:12:03.379 that's so there is a definition for 00:12:06.82900:12:06.839 nusselt number from Prandtl number 00:12:08.88900:12:08.899 Reynolds number and grossers number and 00:12:13.34000:12:13.350 you can calculate those for your 00:12:16.54900:12:16.559 particular set setup so you need to 00:12:18.79900:12:18.809 decide for example how what is should it 00:12:20.96000:12:20.970 velocity be in these channels and from 00:12:24.53000:12:24.540 that you can calculate the Reynolds 00:12:25.81900:12:25.829 number 00:12:27.91000:12:27.920 what is the medium what is the viscosity 00:12:31.06900:12:31.079 of the medium what is the heat capacity 00:12:32.74900:12:32.759 was this the conductivity from that you 00:12:35.50900:12:35.519 can calculate the Prandtl number you 00:12:37.81900:12:37.829 need a characteristic distance and the 00:12:41.98900:12:41.999 overall heat sorry the heat transfer 00:12:43.93900:12:43.949 coefficient and the connectivity to 00:12:46.42900:12:46.439 calculate nozzle number but 00:12:49.17000:12:49.180 you need something else as well 00:12:50.79000:12:50.800 something that tells you about okay in 00:12:53.76000:12:53.770 this situation how can I estimate the 00:12:56.64000:12:56.650 nusselt number based on reynolds 00:12:58.95000:12:58.960 implanted or rain if it's force 00:13:01.14000:13:01.150 connection or Raynald and Glossop's 00:13:04.47000:13:04.480 number if it's natural connection like 00:13:06.21000:13:06.220 in a radiator outside of the radiator at 00:13:09.45000:13:09.460 home when you do estimations it's good 00:13:17.82000:13:17.830 if you know approximately what values 00:13:21.18000:13:21.190 you can expect of in different 00:13:23.37000:13:23.380 situations and different media but note 00:13:26.52000:13:26.530 that numbers such as these they are just 00:13:30.44000:13:30.450 suggestions that can be examples where 00:13:33.72000:13:33.730 you have deviations small or large from 00:13:36.90000:13:36.910 these values one particular difficult 00:13:42.51000:13:42.520 problem is to say what is the heat 00:13:44.94000:13:44.950 transfer coefficient when the liquid is 00:13:47.43000:13:47.440 boiling 00:13:48.89000:13:48.900 the thing with boiling is that there are 00:13:51.72000:13:51.730 different kinds of boiling natural 00:13:54.96000:13:54.970 convection boiling is just one of them 00:13:57.98000:13:57.990 so if you look carefully when you boil 00:14:01.35000:14:01.360 water if you look carefully in the pan 00:14:04.08000:14:04.090 you can see that first small bubbles are 00:14:06.81000:14:06.820 formed and then after a while and it 00:14:09.27000:14:09.280 boils really lot you essentially have a 00:14:11.10000:14:11.110 gas layer at the bottom and this these 00:14:16.89000:14:16.900 different cases will lead the totally 00:14:19.05000:14:19.060 different heat transfer coefficients so 00:14:22.32000:14:22.330 if you really want to calculate heat 00:14:24.51000:14:24.520 transfer because the overall heat 00:14:26.64000:14:26.650 transfer coefficient carefully for 00:14:28.68000:14:28.690 situation when they have a heat 00:14:29.76000:14:29.770 exchanger where you have boiling on one 00:14:32.28000:14:32.290 side or if you have condensing on one 00:14:34.02000:14:34.030 side then you actually need to divide it 00:14:36.99000:14:37.000 a change in different part and say okay 00:14:39.60000:14:39.610 on this part I have overheated steam and 00:14:42.54000:14:42.550 this part I have condensing steam and in 00:14:45.90000:14:45.910 this part I only have liquid and then 00:14:48.60000:14:48.610 you will get different heat transfer 00:14:51.12000:14:51.130 coefficients in a different part and 00:14:52.65000:14:52.660 actually all also in the part where it 00:14:56.22000:14:56.230 actually boils you will have different 00:14:58.05000:14:58.060 values in our course 00:15:02.24000:15:02.250 that's too tough so we will instead just 00:15:05.93000:15:05.940 use natural convection boiling say that 00:15:08.15000:15:08.160 okay the heat transfer coefficient if 00:15:11.80900:15:11.819 it's boiling it's somewhere close to 00:15:14.18000:15:14.190 what the natural convection boiling is 00:15:16.24900:15:16.259 in fact equations for estimating boiling 00:15:22.00900:15:22.019 the heat transfer coefficients you get 00:15:23.96000:15:23.970 for boiling if they can be rather 00:15:27.01900:15:27.029 complicated and as one of the road a 00:15:30.01900:15:30.029 couple of years back he suggested a new 00:15:35.92000:15:35.930 equation that he said was easier than 00:15:40.85000:15:40.860 most and about as accurate as any so all 00:15:46.24900:15:46.259 these different equation X that you can 00:15:48.19900:15:48.209 find Ana literature you can't trust the 00:15:51.86000:15:51.870 values that much see what you typically 00:15:54.11000:15:54.120 want to do in a real situation is that 00:15:56.36000:15:56.370 you use one of these equations and try 00:15:58.91000:15:58.920 to calculate the best you can and then 00:16:01.87900:16:01.889 you need to make an experiment so you 00:16:04.28000:16:04.290 build a small factory for example see 00:16:06.47000:16:06.480 does this work they're tested in the lab 00:16:09.05000:16:09.060 and so on the one we're going to use for 00:16:12.53000:16:12.540 natural convection boiling comes from 00:16:14.30000:16:14.310 Stephan and others alarm in their paper 00:16:16.81900:16:16.829 nineteen eighty and in the handbook I 00:16:19.68900:16:19.699 have a simplified growth so they 00:16:25.12900:16:25.139 published several different graphs I've 00:16:27.29000:16:27.300 put them together in a simplified manner 00:16:30.24900:16:30.259 and note that the power there the cue 00:16:34.61000:16:34.620 the smoker there is the watts per square 00:16:37.49000:16:37.500 meter that is being transferred and the 00:16:42.17000:16:42.180 end there is different if it's water or 00:16:44.38900:16:44.399 if it's hydrocarbons not much but a 00:16:47.15000:16:47.160 little 0.67 three compared to 0.67 when 00:16:56.15000:16:56.160 you try to estimate these values the 00:17:03.35000:17:03.360 overall heat transfer coefficients you 00:17:05.65900:17:05.669 need the characteristic dimension in the 00:17:08.68900:17:08.699 nusselt number and you need it also in 00:17:10.66900:17:10.679 the reynolds number and what is the 00:17:13.15900:17:13.169 characteristic 00:17:14.79000:17:14.800 distance well outside two bundles it's 00:17:19.44900:17:19.459 the if it's the flow is along the tubes 00:17:22.43900:17:22.449 then it's four times the area of the 00:17:25.39000:17:25.400 water-filled cross section divided by 00:17:27.49000:17:27.500 the sir confuse in contact with the 00:17:29.26000:17:29.270 liquid so that's the hydraulic diameter 00:17:31.21000:17:31.220 and for flow of long tubes that becomes 00:17:34.45000:17:34.460 this study so this first equation here 00:17:37.45000:17:37.460 that's actually valid for more cases and 00:17:39.58000:17:39.590 the second one is if it's flow along 00:17:43.09000:17:43.100 tubes and P there that's the distance 00:17:46.51000:17:46.520 between center to center of these tubes 00:17:49.72000:17:49.730 the out that's the outer diameter of of 00:17:53.56000:17:53.570 the tubes if you have natural convection 00:17:59.20000:17:59.210 you still need to have a characteristic 00:18:01.87000:18:01.880 distance and if you have a vertical 00:18:04.84000:18:04.850 surface that's simply the height the 00:18:07.84000:18:07.850 same is if you have a vertical tube it's 00:18:09.79000:18:09.800 the height of the tube but if you have a 00:18:12.58000:18:12.590 horizontal surface 00:18:13.93000:18:13.940 it's instead the width of the surface 00:18:17.94000:18:17.950 okay let's try to calculate an example
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