00:00:00.060 so this time we're gonna be talking 00:00:01.55000:00:01.560 about heat exchangers now heat changes 00:00:05.42000:00:05.430 are actually very similar to evaporators 00:00:08.21000:00:08.220 and condensers in that all we have to 00:00:13.22000:00:13.230 worry about is heat transfer so what 00:00:16.55000:00:16.560 heat sugar does is literally move heat 00:00:19.07000:00:19.080 from one substance to another so we're 00:00:22.25000:00:22.260 gonna have a hot something substance 00:00:23.84000:00:23.850 losing heat to a cooler substance which 00:00:26.33000:00:26.340 gains it so let's say we have a pipe of 00:00:32.84000:00:32.850 steam and then we it comes in contact 00:00:38.66000:00:38.670 with another pipe of liquid nitrogen 00:00:44.17000:00:44.180 now obviously steam is very very hot 00:00:46.88000:00:46.890 whereas nut'n liquid nitrogen is very 00:00:49.19000:00:49.200 very cold so he's going to want to go 00:00:51.59000:00:51.600 from the water to the nitrogen it's 00:00:54.88900:00:54.899 going to be a heat transfer here so it's 00:00:56.95900:00:56.969 going to be a heat loss of the water is 00:00:59.77900:00:59.789 going to be heat gain of nitrogen now 00:01:05.09000:01:05.100 these losses are going to be equal the 00:01:07.10000:01:07.110 opposite we're going to assume that 00:01:08.89900:01:08.909 there's going to be no other ways for a 00:01:12.05000:01:12.060 key to be exchanged like there's no vent 00:01:14.17900:01:14.189 this these are well insulated they're 00:01:15.92000:01:15.930 not going to leak go out or be absorbed 00:01:17.99000:01:18.000 by the pipes so this heat transfer from 00:01:21.20000:01:21.210 here to here is going to be equal the 00:01:23.81000:01:23.820 opposite so positive here negative here 00:01:27.95000:01:27.960 but they're still going to be have the 00:01:29.66000:01:29.670 same absolute value so what we could say 00:01:32.03000:01:32.040 is key n + e l0 conservation of energy 00:01:42.13000:01:42.140 so Q in which in this case is nitrogen 00:01:50.24000:01:50.250 because it's getting a Q it is going to 00:01:52.28000:01:52.290 equal the mass flow rate of nitrogen 00:01:55.63000:01:55.640 times h2 minus h1 oh these are of 00:02:02.33000:02:02.340 mention then Q out what if I get these 00:02:08.60000:02:08.610 little dots 00:02:12.80000:02:12.810 h2o in this case not always this Q s 00:02:17.64000:02:17.650 maybe h2o + 12 X 2 minus H 1 H 2 O now 00:02:29.03000:02:29.040 notice we have six different numbers 00:02:31.64900:02:31.659 here we have mass flow rate of nitrogen 00:02:34.74000:02:34.750 mass flow rate of h2o these are two 00:02:37.38000:02:37.390 different flow rates they are not 00:02:38.52000:02:38.530 flowing in the same pipe so they can go 00:02:40.19900:02:40.209 at different rates and then we have the 00:02:42.33000:02:42.340 state one to state two both these 00:02:45.59900:02:45.609 substances so we have six things to 00:02:48.50900:02:48.519 worry about here so how would this look 00:02:51.80900:02:51.819 in practice well let's say we have a big 00:02:58.92000:02:58.930 ol heat exchangers this is a pipe cross 00:03:03.39000:03:03.400 section of a pipe where this refrigerant 00:03:07.30900:03:07.319 r134a going in and out but as it's going 00:03:11.91000:03:11.920 through this part of the pipe it's 00:03:13.50000:03:13.510 running over other pipes that are 00:03:17.06900:03:17.079 running perpendicular so it's going into 00:03:19.11000:03:19.120 the tape piece of paper of more pipes 00:03:22.50000:03:22.510 and in this is cooling water 00:03:31.83000:03:31.840 so we have gashes r134a running through 00:03:36.96000:03:36.970 these pipes and it's going to be flowing 00:03:39.69000:03:39.700 over cool what cool pipes that is water 00:03:42.93000:03:42.940 flowing through it and on the other side 00:03:46.71000:03:46.720 is going to come out as a liquid so uh 00:03:54.77000:03:54.780 let's see we have to give you a few a 00:03:58.35000:03:58.360 few notes we have for the refrigerant we 00:04:01.97900:04:01.989 know that it has a mass flow rate of one 00:04:05.13000:04:05.140 kilogram per second 00:04:07.69900:04:07.709 we know that at state one as it comes in 00:04:15.08000:04:15.090 has a pressure of one mega Pascal we 00:04:23.28000:04:23.290 know that has a temperature of 60 00:04:25.20000:04:25.210 degrees Celsius 00:04:27.44000:04:27.450 no one stake to it has a pressure of 880 00:04:37.88000:04:37.890 7.6 kPa we know has a temperature of 35 00:04:45.69000:04:45.700 degrees Celsius and we also know that it 00:04:48.90000:04:48.910 is a liquid and for water 00:05:02.87900:05:02.889 so you know he won it's been equal e to 00:05:09.03900:05:09.049 which equals to mega pascals 00:05:12.21900:05:12.229 that's something I gave you pressure 00:05:13.74900:05:13.759 doesn't have to stay the same but since 00:05:17.70900:05:17.719 it's got to stay water throughout it's a 00:05:19.71900:05:19.729 good assumption let me know it goes from 00:05:22.26900:05:22.279 20 degrees Celsius to 40 degrees Celsius 00:05:31.40900:05:31.419 and what this problem is asking is I'm a 00:05:34.20900:05:34.219 mass flow rate of water right so we're 00:05:40.80900:05:40.819 going to use this equation here in plus 00:05:43.29900:05:43.309 Q out equals 0 conservation of energy so 00:05:47.16900:05:47.179 Q in that's going to be water so he wins 00:05:51.21900:05:51.229 is going to equal mass flow rate of 00:05:52.98900:05:52.999 water times h2 water minus h1 of water 00:06:02.27900:06:02.289 plus mass flow rate of the refrigerant 00:06:08.75900:06:08.769 times h2 minus h1 so we need no no all 00:06:19.23900:06:19.249 these enthalpies fairly straightforward 00:06:22.74900:06:22.759 looking the trap in the tables we know 00:06:26.63900:06:26.649 each one of the refrigerant at 1 00:06:30.06900:06:30.079 megapascal and 60 degrees Celsius is 400 00:06:37.05900:06:37.069 for 440 1.89 kilojoules per kilogram and 00:06:45.48900:06:45.499 we know that h2 is a liquid at least at 00:06:50.40900:06:50.419 this state of pressure and temperature 00:06:52.56900:06:52.579 it's a it's somewhere along saturation 00:06:56.94900:06:56.959 line so we have we know that it says 00:07:00.60900:07:00.619 when it's liquid we just take the liquid 00:07:02.88900:07:02.899 value from the table which is 249 point 00:07:06.81900:07:06.829 10 kilojoules per kilogram 00:07:12.17000:07:12.180 ah for water and to megapascals 20 00:07:15.92000:07:15.930 Celsius that's super cool you go through 00:07:18.05000:07:18.060 the table and we know that it's enthalpy 00:07:24.61000:07:24.620 is a three point eight - coming in at 00:07:30.77000:07:30.780 four degrees it's one sixty seven point 00:07:34.88000:07:34.890 two nine so like like for the last video 00:07:38.54000:07:38.550 we know we noticed a gain in the water 00:07:41.66000:07:41.670 these heats coming into the water we 00:07:43.67000:07:43.680 notice a loss in the refrigerant B's is 00:07:46.91000:07:46.920 cooling down so mass flow rate of water 00:07:56.86000:07:56.870 is going to equal ms flow rate the 00:08:01.94000:08:01.950 refrigerant times h2 minus h1 or h2 00:08:12.40000:08:12.410 minus h1 refrigerant water plug and chug 00:08:20.03000:08:20.040 two equals one program plus second times 00:08:36.24000:08:36.250 right equals zero so there's actually 00:08:39.56900:08:39.579 going to be a negative side of it 00:08:40.94900:08:40.959 because we're going to have to subtract 00:08:42.64900:08:42.659 over this over so we can divide void 00:08:49.61900:08:49.629 equal to 4 9.1 - 4 4 1.9 all over one 00:09:02.12900:09:02.139 six seven point two nine - a three point 00:09:07.05000:09:07.060 eight two negative sign which equals two 00:09:14.91000:09:14.920 point three one kilograms assign
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