00:00:23.650 hello I welcome you all in the course on 00:00:26.38000:00:26.390 refrigeration and air conditioning today 00:00:29.20000:00:29.210 we will cover multi evaporator and 00:00:30.99900:00:31.009 cascading system in vapour compression 00:00:33.10000:00:33.110 system in a multi pressure system for 00:00:38.05000:00:38.060 last two lectures we are dealing with 00:00:39.52000:00:39.530 multi pressure system multi pressure 00:00:45.79000:00:45.800 system 00:00:54.74000:00:54.750 and multiplier systems we have already 00:00:58.61000:00:58.620 covered in the last two lectures multi 00:01:00.95000:01:00.960 compression system 00:01:11.17900:01:11.189 now in multi compression system the 00:01:14.06900:01:14.079 compression has taken place in more than 00:01:16.16900:01:16.179 one stages right and instead of having 00:01:20.24900:01:20.259 to pressure system because to pressure 00:01:21.80900:01:21.819 means to pressure system is simple 00:01:23.88000:01:23.890 vapour compression system this is a two 00:01:27.41900:01:27.429 pressure system 00:01:35.67900:01:35.689 so on a pH diagram so this is a two 00:01:40.84000:01:40.850 pressure system and we have already done 00:01:45.21900:01:45.229 this multi compression system where 00:01:46.89900:01:46.909 compression takes place in more than one 00:01:49.05900:01:49.069 stages maybe two stages or three stages 00:01:52.83000:01:52.840 another multi pressure system is multi 00:01:56.26000:01:56.270 evaporator system system in multi 00:02:05.52900:02:05.539 evaporator system there may be one 00:02:08.16900:02:08.179 compressor right compressor compression 00:02:11.44000:02:11.450 for compression there may be one 00:02:13.44900:02:13.459 compressor but there are number of you 00:02:15.72900:02:15.739 operators instead of having one 00:02:17.41000:02:17.420 evaporator they are number of 00:02:19.03000:02:19.040 evaporators evaporating at different 00:02:21.03900:02:21.049 temperatures now the benefit of this 00:02:22.99000:02:23.000 system is suppose I want to have a deep 00:02:25.24000:02:25.250 freezer to for the preservation let us 00:02:29.19900:02:29.209 say is minus 40 degree centigrade I want 00:02:34.86900:02:34.879 to have a I mean freezer also at let us 00:02:40.59900:02:40.609 say 5 degree centigrade to keep the 00:02:44.74000:02:44.750 things so at these two temperatures if I 00:02:48.94000:02:48.950 have a simple system it is difficult to 00:02:51.09900:02:51.109 operate I mean I will have to make 00:02:52.27000:02:52.280 arrangements but here if I have a multi 00:02:55.72000:02:55.730 evaporator system we can expand the 00:02:59.72900:02:59.739 compressed liquid sorry not compress 00:03:03.12900:03:03.139 liquid this condensed refrigerant at 00:03:05.55900:03:05.569 high pressure at state 3 in 2 different 00:03:08.31900:03:08.329 evaporators and these way operators are 00:03:10.90000:03:10.910 operating at different temperatures or 00:03:13.59900:03:13.609 different pressures this type of system 00:03:17.58900:03:17.599 is known as multi evaporator system the 00:03:20.05000:03:20.060 multi evaporator system is further 00:03:22.33000:03:22.340 classified as individual expansion of 00:03:26.40900:03:26.419 all system 00:03:32.69900:03:32.709 and multiple expansion wall 00:03:37.99000:03:38.000 multiple expansion wall system 00:03:40.28900:03:40.299 individual expansion wall means every 00:03:44.02000:03:44.030 evaporator has its own expansion wall so 00:03:48.25000:03:48.260 the refrigerant at state 3 is expanding 00:03:50.97900:03:50.989 in your printer 1 and evaporator 2 and 00:03:54.30900:03:54.319 both the evaporators are having their 00:03:56.74000:03:56.750 own expansion mode in multi expansion 00:04:00.09900:04:00.109 wall is the refrigerant which is 00:04:02.50000:04:02.510 entering the anyway operator is let us 00:04:04.50900:04:04.519 say we have little 1 or evaporator 2 it 00:04:07.18000:04:07.190 is expected in two stages that is why it 00:04:10.78000:04:10.790 is known as multi expansion arrangement 00:04:13.75000:04:13.760 and there is third type of system which 00:04:17.56000:04:17.570 has number of I mean two compressors or 00:04:21.64000:04:21.650 more than two compressors and more than 00:04:23.17000:04:23.180 two operators also and this type of 00:04:25.65000:04:25.660 system is known as cascade system or the 00:04:31.30000:04:31.310 arrangement is known as cascading now in 00:04:35.98000:04:35.990 the cascading there are two simple vapor 00:04:40.42000:04:40.430 refrigeration or more than two simple 00:04:42.33900:04:42.349 vapour compression cycles and different 00:04:45.49000:04:45.500 refrigerants are used in different 00:04:46.81000:04:46.820 cycles we will discuss this cascading in 00:04:48.76000:04:48.770 details first of all will assume you 00:04:50.98000:04:50.990 have already covered this and now we'll 00:04:53.37900:04:53.389 start with multi evaporator system with 00:04:57.33000:04:57.340 individual expansion wall 00:05:05.90000:05:05.910 now in this type of arrangement there is 00:05:09.87000:05:09.880 one compressor or we are there used to 00:05:12.87000:05:12.880 be one evaporator 00:05:13.95000:05:13.960 now there is one compressor and one 00:05:16.40900:05:16.419 condenser the vapor going from the 00:05:23.27900:05:23.289 compressor is getting condensed in the 00:05:25.77000:05:25.780 condenser now let us come to the 00:05:28.32000:05:28.330 evaporation side the wave part is 00:05:30.96000:05:30.970 available here let us start from here 00:05:32.76000:05:32.770 one it goes to the evaporator one if n 00:05:42.21000:05:42.220 before that it gets expanded then again 00:05:48.30000:05:48.310 vapor goes to evaporator two and then 00:05:54.87000:05:54.880 again it gets expanded in expansion 00:05:59.37000:05:59.380 valve one and expansion wall two 00:06:02.77900:06:02.789 respectively and this is e 2 now vapour 00:06:10.32000:06:10.330 is emerging from e 1 and E 2 as well so 00:06:12.39000:06:12.400 this is state 1 this is state 2 this is 00:06:15.71900:06:15.729 state 3 and this is straight for let us 00:06:20.21900:06:20.229 say state 5 now pressure at state 5 4 & 00:06:24.71900:06:24.729 5 are not same pressure are different 00:06:27.87000:06:27.880 because here expansion is taking place 00:06:30.33000:06:30.340 earlier at higher pressure so pressure 00:06:32.31000:06:32.320 at state 5 is not same as the pressure 00:06:35.43000:06:35.440 in this state for state 5 is not as the 00:06:37.77000:06:37.780 pressure in state 4 and we have only one 00:06:39.87000:06:39.880 compressor and then it's only one 00:06:41.52000:06:41.530 compressor is available for this purpose 00:06:42.93000:06:42.940 in this case we have no other choice but 00:06:46.98000:06:46.990 to expand this the vapor available at 4 00:06:52.40900:06:52.419 to the pressure of 5 and here at 00:06:56.67000:06:56.680 pressure 5 it is sent to the compressor 00:06:59.37000:06:59.380 now if you I want to depict this process 00:07:02.33900:07:02.349 on pressure enthalpy diagram on a 00:07:07.35000:07:07.360 pressure enthalpy diagram 00:07:16.57000:07:16.580 there is a saturation line X is equal to 00:07:25.91000:07:25.920 zero X is equal to 1 this is condenser 00:07:32.09000:07:32.100 and at the exit of the condenser this 00:07:35.36000:07:35.370 state is 1 expansion is taking place in 00:07:39.32000:07:39.330 1 first expansion device and we are 00:07:42.53000:07:42.540 getting state 2 and state to the vapor 00:07:45.80000:07:45.810 is entering the evaporator and coming 00:07:48.77000:07:48.780 out of at state 4 00:07:57.11000:07:57.120 now further in this down the line this 00:08:00.65000:08:00.660 vapor continue to expand up to state 3 3 00:08:08.87000:08:08.880 so 2 2 it is expanded up to state 3 and 00:08:13.24000:08:13.250 after a timing state 3 it goes to the 00:08:16.79000:08:16.800 European Tour's - this is e 2 this is e 00:08:20.15000:08:20.160 1 this is condenser and after heat 00:08:24.68000:08:24.690 exchange in the second evaporator it 00:08:26.62900:08:26.639 emerges as the state v and here we have 00:08:29.87000:08:29.880 state for what we should do we should 00:08:33.82900:08:33.839 here reduce the pressure at the exit of 00:08:37.70000:08:37.710 the evaporator one through throttling so 00:08:40.04000:08:40.050 in a throttling process and third P 00:08:42.32000:08:42.330 remains constraints so through a 00:08:44.32900:08:44.339 throttling process the pressure is 00:08:49.76000:08:49.770 reduced and mixing takes place here 00:08:54.05000:08:54.060 mixing takes place and after mixing the 00:08:58.70000:08:58.710 mixture it goes to the compressor and 00:09:01.54000:09:01.550 compression takes place and we attain 00:09:05.53000:09:05.540 state 6 so this is a this is an 00:09:11.96000:09:11.970 arrangement of multi evaporator system 00:09:15.23000:09:15.240 it is very useful especially in the 00:09:16.97000:09:16.980 shopping area it is very useful we are 00:09:19.34000:09:19.350 some of the items in for some of the 00:09:22.85000:09:22.860 food products we can preserve at a very 00:09:26.15000:09:26.160 low temperature let us say minus 40 00:09:27.89000:09:27.900 degree centigrade or minus 30 degree 00:09:29.75000:09:29.760 centigrade and some of the items which 00:09:32.84000:09:32.850 are to be preserved on high temperature 00:09:34.49000:09:34.500 may be minus 10 or 0 degree centigrade 00:09:36.32000:09:36.330 so we can have this type of arrangement 00:09:38.63000:09:38.640 where we have two operators and both the 00:09:41.54000:09:41.550 evaporators are operating at different 00:09:44.50000:09:44.510 temperatures so this is the arrangement 00:09:47.48000:09:47.490 for multi evaporator system with 00:09:50.81000:09:50.820 individual expansion one we can have 00:09:53.81000:09:53.820 another arrangement also where there are 00:09:57.86000:09:57.870 multiple expansion valves in this type 00:10:01.07000:10:01.080 of arrangement we'll start with the 00:10:02.66000:10:02.670 compressor because then we have only one 00:10:04.34000:10:04.350 compressor so we will start with the 00:10:06.98000:10:06.990 compressor so there is a compressor 00:10:09.81000:10:09.820 and there are two operators again this 00:10:13.35000:10:13.360 is a e 2 and this is e 1 and there is a 00:10:22.11000:10:22.120 condenser and vapor is of a condensation 00:10:27.39000:10:27.400 again the vapor is emerging from 00:10:29.64000:10:29.650 condenser vapor is emerging from sorry 00:10:38.55000:10:38.560 the liquid refrigerant is emerging from 00:10:40.50000:10:40.510 the condenser state 1 and the entire 00:10:46.17000:10:46.180 liquid is expanded in one expansion wall 00:10:48.78000:10:48.790 and that we get the state 2 so state 1 00:10:55.62000:10:55.630 to state 2 we get this expansion we get 00:10:59.97000:10:59.980 in one expansion wall this is state 2 00:11:02.90000:11:02.910 and after the attaining state to the 00:11:06.90000:11:06.910 vapour enters the evaporator one part of 00:11:09.99000:11:10.000 the vapor and the process then it picks 00:11:13.62000:11:13.630 up heat in the evaporator and we get 00:11:16.35000:11:16.360 state 3 here now remaining part of the 00:11:23.34000:11:23.350 expanded vapor 00:11:24.95000:11:24.960 remaining part of expanded paper which 00:11:28.41000:11:28.420 is available at this pressure is again 00:11:31.47000:11:31.480 expanded and a flash gas type of removal 00:11:36.72000:11:36.730 arrangement is also provided here so 00:11:38.88000:11:38.890 that only liquid enters here only liquid 00:11:43.83000:11:43.840 enters here and we get these processes 00:11:47.22000:11:47.230 so liquid enters here means that is 00:11:51.45000:11:51.460 state 4 that is state 4 after expansion 00:11:56.82000:11:56.830 is state 5 and then we get state 6 00:12:04.59000:12:04.600 now after restraining attaining state 00:12:07.63000:12:07.640 six again these two have to be mixed and 00:12:11.91000:12:11.920 for mixing again there is same issue 00:12:14.38000:12:14.390 that this pressure has to be reduced to 00:12:17.11000:12:17.120 this one okay so again third link takes 00:12:20.92000:12:20.930 place here and mixing of both the 00:12:24.13000:12:24.140 refrigerants and then compression in a 00:12:27.16000:12:27.170 compressor compressor so this is how the 00:12:31.90000:12:31.910 multi expansion system multi expansion 00:12:35.71000:12:35.720 multi evaporator system works it is 00:12:38.17000:12:38.180 called multi expansion because 00:12:39.40000:12:39.410 refrigerant is expanded in to stage four 00:12:41.98000:12:41.990 evaporator two and now these are 00:12:44.11000:12:44.120 connected yes these are connected and it 00:12:48.25000:12:48.260 goes to seven state seven and then it is 00:12:52.18000:12:52.190 compressed and get state eight now one 00:13:01.09000:13:01.100 arrangement we can make here in this 00:13:03.91000:13:03.920 type of system instead of having one 00:13:07.93000:13:07.940 compressor if we provide two compressors 00:13:09.64000:13:09.650 now we have variety of components with 00:13:12.76000:13:12.770 us we have flash gas removal system we 00:13:15.22000:13:15.230 have multi compression system we are 00:13:16.72000:13:16.730 reverse with multi evaporation system 00:13:20.08000:13:20.090 evaporator system evaporator system with 00:13:22.87000:13:22.880 individual expansion valve a power 00:13:24.46000:13:24.470 system with multiple expansion wall so 00:13:26.83000:13:26.840 we can have combination of all these 00:13:29.02000:13:29.030 arrangements to find to to develop a 00:13:32.41000:13:32.420 system which can give the best 00:13:34.72000:13:34.730 performance so instead of it is also 00:13:36.46000:13:36.470 recommended that instead of expanding 00:13:39.21000:13:39.220 vapor from state 3 to state this state 00:13:42.61000:13:42.620 and then again compressing it instead of 00:13:45.22000:13:45.230 that if we are able to make use of two 00:13:49.36000:13:49.370 compressors instead of using one 00:13:51.58000:13:51.590 compressor there are two compressors and 00:13:57.31000:13:57.320 one compressor for this and both the 00:14:02.38000:14:02.390 compressors are compressing gas up to 00:14:04.54000:14:04.550 state eight so this type of a rich beta 00:14:07.60000:14:07.610 if I want to make here then definitely 00:14:12.51000:14:12.520 the 00:14:16.08000:14:16.090 the in fact they are not paralyzed 00:14:19.24000:14:19.250 they're diverging line so instead of 00:14:21.12000:14:21.130 writing them like this I would like to 00:14:23.86000:14:23.870 draw them like this so we will get this 00:14:26.47000:14:26.480 type of pH diagram for multi expansion 00:14:31.54000:14:31.550 original now the problem with these type 00:14:35.50000:14:35.510 of multi compression systems the 00:14:37.18000:14:37.190 pressure ratio is high these systems are 00:14:38.95000:14:38.960 used where the pressure ratio is high 00:14:40.74000:14:40.750 but the problem with the multi expansion 00:14:43.48000:14:43.490 system says that a refrigerant suppose I 00:14:47.56000:14:47.570 will give you some numerical values then 00:14:50.17000:14:50.180 things will become clear to you because 00:14:52.30000:14:52.310 sometimes it is not possible to see you 00:14:55.42000:14:55.430 same refrigerant at a wide range for 00:14:57.97000:14:57.980 example in chemical applications the 00:15:02.59000:15:02.600 temp we required temperature of the 00:15:03.94000:15:03.950 order of let us say 100 degree 00:15:05.76900:15:05.779 centigrade or in some of the 00:15:09.28000:15:09.290 applications we require temperature as 00:15:11.32000:15:11.330 minus 80 degree centigrade or minus 60 00:15:13.42000:15:13.430 degree centigrade condenser temperature 00:15:16.18000:15:16.190 is 50 degree centigrade or 40 degree 00:15:18.70000:15:18.710 centigrade so this temperature 00:15:21.16000:15:21.170 difference temperature variations is 00:15:22.78000:15:22.790 very high this temperature variation is 00:15:25.66000:15:25.670 very high similarly corresponding 00:15:26.86000:15:26.870 pressure ratio PK by PU or p2 by p1 or 00:15:32.97000:15:32.980 pH by PL pressure and condenser and 00:15:38.07900:15:38.089 pressure in evaporator this ratio 00:15:39.61000:15:39.620 becomes very very high for certain range 00:15:43.09000:15:43.100 we can go for this multi compression 00:15:45.79000:15:45.800 system but for pressure ratio it is okay 00:15:49.66000:15:49.670 multi compression system can be accepted 00:15:52.00000:15:52.010 but for this wide variation in 00:15:54.07000:15:54.080 temperature same refrigerant may not be 00:15:57.73000:15:57.740 recommended for the use let us look at 00:16:00.40000:16:00.410 the properties of some of the 00:16:02.05000:16:02.060 refrigerants 00:16:02.74000:16:02.750 for example r22 so r22 has normal 00:16:06.31000:16:06.320 boiling point minus 40 point 8 1 degree 00:16:08.38000:16:08.390 centigrade right so if I am using this 00:16:12.73000:16:12.740 r22 8 minus 20 the pressure is 2 point 4 00:16:16.06000:16:16.070 5 bar and if I were using our 20 t at 00:16:19.94900:16:19.959 minus 80 it is point one zero three 00:16:22.66000:16:22.670 seven bar remember the moment we 00:16:26.88900:16:26.899 reduce the pressure specific volume 00:16:30.18900:16:30.199 increases 00:16:48.28000:16:48.290 so the moment we reduce the pressure the 00:16:51.50000:16:51.510 specific volume increases the specific 00:16:54.59000:16:54.600 volume increases here also you can see 00:16:56.48000:16:56.490 for this r22 if the evaporator 00:17:00.74000:17:00.750 temperature is 80 degree by necessity 00:17:02.42000:17:02.430 the pressure is only 0.1 bar and 00:17:05.23000:17:05.240 specific volume is also very high it is 00:17:08.63000:17:08.640 one point seven seven eight two meter 00:17:10.04000:17:10.050 cube per kg and if you look at the 00:17:12.62000:17:12.630 refrigerant r23 00:17:13.94000:17:13.950 it is normal boiling point is minus 82 00:17:16.61000:17:16.620 degree centigrade so at at one 00:17:18.74000:17:18.750 atmospheric pressure it will boil at 00:17:20.39000:17:20.400 minus eighty to two point two degree 00:17:22.13000:17:22.140 centigrade and specific volume is our 00:17:24.53000:17:24.540 only 0.192 three specific volume is 00:17:27.38000:17:27.390 important because a specific volume at 00:17:29.54000:17:29.550 the exit of the evaporator decides the 00:17:33.02000:17:33.030 size of the compressor so specific 00:17:35.66000:17:35.670 volume of the vapor at the exit of the 00:17:37.64000:17:37.650 evaporator should be as low as possible 00:17:39.37000:17:39.380 that is one thing second thing is if you 00:17:42.68000:17:42.690 look at pressure at 40 suppose I choose 00:17:47.18000:17:47.190 23 okay 4 minus 80 it is okay it is 00:17:50.09000:17:50.100 giving minus 82 degree centigrade at 00:17:54.68000:17:54.690 normal boiling point is normal 8 minus 00:17:56.60000:17:56.610 82 degree centigrade so it will boil 00:17:58.67000:17:58.680 suppose I want temperature minus 80 00:18:00.50000:18:00.510 degree centigrade our 23 will boil below 00:18:03.83000:18:03.840 the atmospheric pressure it is okay I 00:18:05.30000:18:05.310 can use it for minus hundred also but 00:18:07.61000:18:07.620 the problem is when it is taken at 40 00:18:11.87000:18:11.880 degree centigrade it is critical 00:18:13.79000:18:13.800 temperature is twenty six point four 00:18:15.02000:18:15.030 seven so I will be operating the system 00:18:17.75000:18:17.760 above the critical temperature and the 00:18:20.18000:18:20.190 COP of the system will reduce so I 00:18:22.19000:18:22.200 cannot use this refrigerant for this 00:18:23.51000:18:23.520 purpose and similarly if I use low 00:18:28.70000:18:28.710 pressure refrigerant that is our 123 our 00:18:32.36000:18:32.370 123 is okay when the pressure is 40 00:18:34.94000:18:34.950 degree centigrade pressure is one point 00:18:36.86000:18:36.870 five bar one point five times 00:18:38.30000:18:38.310 approximately atmospheric pressure it is 00:18:40.28000:18:40.290 okay but when I use our 123 at minus 00:18:45.23000:18:45.240 eighty the pressure is zero point zero 00:18:47.63000:18:47.640 zero one three bar so very very low 00:18:50.21000:18:50.220 right and in that case the specific 00:18:53.12000:18:53.130 volume is also very high minus eighty 00:18:54.77000:18:54.780 the specific volume is eighty three 00:18:56.00000:18:56.010 point six six seven huge amount of vapor 00:18:58.91000:18:58.920 has to be handled by the 00:19:00.08000:19:00.090 compressor so now we have two option we 00:19:03.14000:19:03.150 have to trade off we have low pressure 00:19:05.60000:19:05.610 refrigerant low pressure refrigerant is 00:19:07.58000:19:07.590 like our 123 which are at high 00:19:11.24000:19:11.250 temperature at condenser temperature the 00:19:13.46000:19:13.470 pressure is 1.5 it is okay but on the 00:19:16.94000:19:16.950 evaporator side they have very high 00:19:19.46000:19:19.470 specific volume so if I use this 00:19:22.54900:19:22.559 refrigerant and the size of the 00:19:24.01900:19:24.029 compressor will be very large that is do 00:19:25.66900:19:25.679 not recommend it if I use high pressure 00:19:28.13000:19:28.140 refrigerant like our 23 in that case you 00:19:32.72000:19:32.730 have Pareto side is okay the the 00:19:34.60000:19:34.610 refrigerant will evaporate at minus 82 00:19:38.33000:19:38.340 degree centigrade it is its normal 00:19:39.71000:19:39.720 boiling point specific volume is also 00:19:42.38000:19:42.390 good 0.192 three very small specific 00:19:45.26000:19:45.270 volume but when it comes to the 00:19:47.18000:19:47.190 condenser it is become it becomes 00:19:49.90900:19:49.919 supercritical see this case with the 00:19:52.97000:19:52.980 ammonia so you take any refrigerants so 00:19:55.07000:19:55.080 we can see that any of the refrigerant 00:19:58.01000:19:58.020 which we have to deal in a very high 00:19:59.72000:19:59.730 range of your operator and condenser let 00:20:01.85000:20:01.860 us say - hundred - 50 degree centigrade 00:20:04.78900:20:04.799 the difference is approximately 150 00:20:06.91900:20:06.929 degree centigrade one refrigerant cannot 00:20:09.16900:20:09.179 work and there are many other reasons 00:20:11.77900:20:11.789 for going for cascading system I am just 00:20:15.88900:20:15.899 justifying why we should use a cascading 00:20:17.96000:20:17.970 system the single reference system is 00:20:20.06000:20:20.070 used in the system the reference should 00:20:21.38000:20:21.390 have high critical temperature and low 00:20:22.94000:20:22.950 freezing point further we operate from 00:20:26.38000:20:26.390 critical temperature more we are close 00:20:29.48000:20:29.490 to the Cu P of a Carnot cycle so Co P of 00:20:33.08000:20:33.090 the system of CO P of the cycle 00:20:35.02900:20:35.039 increases when it operates far away from 00:20:38.20000:20:38.210 critical temperature so that will not be 00:20:41.06000:20:41.070 possible when we use a single 00:20:42.64900:20:42.659 refrigerant for a such a wide range the 00:20:45.23000:20:45.240 operating pressure with the single 00:20:46.78900:20:46.799 refrigerants become - I or to low that I 00:20:49.07000:20:49.080 have just now I have explained to you 00:20:51.78900:20:51.799 likelihood of migration of lubricant oil 00:20:54.47000:20:54.480 from one compressor to another leading 00:20:56.14900:20:56.159 to a compressor program yes this happens 00:20:58.13000:20:58.140 in multi staging compressors when 00:21:00.88900:21:00.899 refrigerant from one compressor enters 00:21:02.84000:21:02.850 to the other compressor in that case the 00:21:06.95000:21:06.960 lubricating oil also shift to the 00:21:09.02000:21:09.030 another compressor and 00:21:12.11000:21:12.120 the the lower pressure compressor 00:21:14.33000:21:14.340 becomes the short of lubricating oil so 00:21:16.58000:21:16.590 that is another problem in multistage ik 00:21:19.37000:21:19.380 and very low temperature in vibrator and 00:21:22.52000:21:22.530 large suction volume for high boiling 00:21:23.99000:21:24.000 refrigerant that I have already 00:21:25.40000:21:25.410 explained you if the high boiling 00:21:26.96000:21:26.970 refrigerant means normal boiling point 00:21:28.40000:21:28.410 is high in that case if we take 00:21:31.91000:21:31.920 therefore every end for the application 00:21:33.62000:21:33.630 of very low temperature the specific 00:21:35.48000:21:35.490 volume will be high and that is also not 00:21:37.52000:21:37.530 acceptable the high pressure in 00:21:39.71000:21:39.720 condenser for low boiling refrigerant 00:21:41.45000:21:41.460 high pressure ratio low CU P so if we go 00:21:45.47000:21:45.480 for a single if we take a single stage 00:21:47.51000:21:47.520 simple cycle for vapour compression 00:21:50.30000:21:50.310 cycle so definitely the moment the 00:21:52.40000:21:52.410 pressure ratio increases the co P of the 00:21:55.25000:21:55.260 cycle goes down and operation of 00:21:58.43000:21:58.440 equipment on low temperature I am 00:22:00.56000:22:00.570 talking about - hundred - hundred twenty 00:22:02.84000:22:02.850 or - hundred fifty degree centigrade 00:22:04.10000:22:04.110 that also becomes difficult so in order 00:22:08.18000:22:08.190 to avoid this a cascading system is 00:22:10.43000:22:10.440 recommended now in cascading system is 00:22:13.40000:22:13.410 nothing but a combination of two simple 00:22:16.97000:22:16.980 vapour compression cycle or two or more 00:22:19.10000:22:19.110 vapor compression cycles it means we 00:22:21.68000:22:21.690 have one a vapour compression cycle 00:22:23.81000:22:23.820 which has a condenser a simple vapour 00:22:26.15000:22:26.160 compression cycle compressor expansion 00:22:32.99000:22:33.000 device evaporator so this is a po1 00:22:42.08000:22:42.090 and this is PK one temperature of 00:22:45.92000:22:45.930 condenser one temperature of your petrol 00:22:47.63000:22:47.640 one now this is one simple cycle a 00:22:51.47000:22:51.480 particular refrigerant for use this 00:22:52.94000:22:52.950 cycle may be here temperature - 80 00:22:54.80000:22:54.810 degree centigrade here temperature may 00:22:56.45000:22:56.460 be zero degree or - 40 degree centigrade 00:22:58.58000:22:58.590 now this condenser is used to take away 00:23:05.92000:23:05.930 now how the condensation will take place 00:23:08.21000:23:08.220 here suppose the temperature here is 00:23:10.31000:23:10.320 minus 80 degree centigrade and 00:23:12.16000:23:12.170 temperature here is minus 20 degree 00:23:15.32000:23:15.330 centigrade now how the condensation will 00:23:18.86000:23:18.870 take this here for the condensation of 00:23:20.48000:23:20.490 vapor at minus 20 degree centigrade we 00:23:23.33000:23:23.340 need to have fluid which has temperature 00:23:25.28000:23:25.290 lower than this 00:23:26.86000:23:26.870 right so we cannot use air we cannot use 00:23:30.02000:23:30.030 deaf water water cooling is avoided it 00:23:32.00000:23:32.010 is not possible air cooling is not 00:23:34.25000:23:34.260 possible 00:23:34.90900:23:34.919 the possibility is that we have another 00:23:37.10000:23:37.110 vapour compression system we have 00:23:38.78000:23:38.790 another vapour compression system which 00:23:40.82000:23:40.830 has evaporator temperature less than 00:23:43.03900:23:43.049 this one so there is another vapour 00:23:45.50000:23:45.510 compression system this is t k2 and it 00:23:49.61000:23:49.620 has also its own expansion wall and it 00:23:52.94000:23:52.950 has evaporator t o2 and then it has its 00:24:03.47000:24:03.480 own compressor both the systems are 00:24:08.15000:24:08.160 working with different working fluids 00:24:09.89000:24:09.900 now these systems are they are made as 00:24:14.06000:24:14.070 one heat exchanger or this is known as 00:24:17.29900:24:17.309 cascading so the heat of the heat of 00:24:25.19000:24:25.200 this condenser is taken by away by this 00:24:27.77000:24:27.780 give a predator so this evaporator may 00:24:30.91900:24:30.929 be at let us say minus 25 degree 00:24:34.73000:24:34.740 centigrade operating between minus 25 to 00:24:38.28900:24:38.299 35 degree centigrade I am just taking 00:24:40.88000:24:40.890 some values so that you can have clear 00:24:42.74000:24:42.750 cut inside of the phenomena so I am 00:24:45.16900:24:45.179 repeating in a cascading system we can 00:24:48.35000:24:48.360 have two or more simple vapour 00:24:51.95000:24:51.960 compression refrigeration cycles each 00:24:54.35000:24:54.360 cycle has its own compressor evaporator 00:24:56.48000:24:56.490 and condenser let us take one cycle of 00:24:59.21000:24:59.220 suppose we have to maintain minus 80 00:25:00.86000:25:00.870 degree centigrade and one cycle will 00:25:03.04900:25:03.059 operate minus 82 minus 20 degrees for 00:25:05.24000:25:05.250 example I am just giving an example and 00:25:06.98000:25:06.990 here the condensation of vapor is taking 00:25:09.47000:25:09.480 place at minus 20 degree centigrade now 00:25:11.53900:25:11.549 in order to condense this vapour we need 00:25:14.06000:25:14.070 a fluid which has temperature lower than 00:25:15.68000:25:15.690 the minus twenty degree centigrade right 00:25:17.84000:25:17.850 so the air can normally the air cannot 00:25:20.18000:25:20.190 be used water cannot be used deaf water 00:25:22.66900:25:22.679 cannot be used so we what we have done 00:25:25.97000:25:25.980 we have introduced another cycle which 00:25:29.09000:25:29.100 has evaporated temperature let us say 00:25:30.59000:25:30.600 minus 25 or minus thirty degree 00:25:33.38000:25:33.390 centigrade and these two are clubbed or 00:25:36.16900:25:36.179 a heat exchange is arranged between 00:25:38.69000:25:38.700 evaporate 00:25:39.59000:25:39.600 of higher pressure to the operator at 00:25:41.09000:25:41.100 lower pressure or condenser at lower 00:25:42.65000:25:42.660 pressure and in this case the 00:25:45.14000:25:45.150 condensation of vapor will take place in 00:25:46.94000:25:46.950 this condenser and this heat will be 00:25:48.95000:25:48.960 taken away by this evaporator and it 00:25:51.71000:25:51.720 will go to the cycle so and we can have 00:25:54.77000:25:54.780 similar type of arrangement two or three 00:25:56.39000:25:56.400 similar type of arrangement and this is 00:25:58.37000:25:58.380 known as cascading of vapour compression 00:26:01.64000:26:01.650 system we assume that the CU p of this 00:26:05.96000:26:05.970 definition cycle is equal to CU p of 00:26:07.90900:26:07.919 these definitions again so if the co 00:26:10.49000:26:10.500 peak our load cycle so Carnot cycle 00:26:12.40900:26:12.419 working between this temperature between 00:26:14.65900:26:14.669 these temperature is equal to Co P of 00:26:16.54900:26:16.559 the Carnot cycle working between this 00:26:18.86000:26:18.870 temperature so to1 divided by T so T CST 00:26:28.85000:26:28.860 K 1 minus T o 1 is equal to P o 2 / PK 2 00:26:39.61000:26:39.620 minus T 2 now in idle case we assume 00:26:44.99000:26:45.000 that T or 2 is equal to PK 1 if e su tío 00:26:54.64900:26:54.659 2 is equal to t K 1 then P o 1 divided 00:27:01.54900:27:01.559 by t o2 this TK 1 is replaced by T this 00:27:04.03900:27:04.049 temperature we assume is equal to this 00:27:05.53900:27:05.549 temperature so TK 1 is equal to t o 2 00:27:09.26000:27:09.270 minus to1 is equal to t o 2 divided by T 00:27:14.81000:27:14.820 K 2 minus t o2 now we cross-multiply to1 00:27:21.25000:27:21.260 TK 2 minus t0 1 po2 is equal to t o2 to1 00:27:31.07000:27:31.080 tio 2 square minus to1 tio 2 we have 00:27:38.12000:27:38.130 just simply cross multiplied this and 00:27:40.03900:27:40.049 you can see on the left hand side to1 00:27:42.23000:27:42.240 tio 2 here this will be cancelled out 00:27:44.00000:27:44.010 and we will be getting po2 is equal to 00:27:49.31000:27:49.320 under root T 0 1 P k2 it means 00:27:56.29900:27:56.309 approximately this is not exact value 00:27:59.18000:27:59.190 but approximate value at temperature 00:28:01.76000:28:01.770 this is a frog approximate absolute 00:28:03.74000:28:03.750 temperature t o2 is equal to under root 00:28:07.01000:28:07.020 of multiplication of maximum temperature 00:28:10.49000:28:10.500 and minimum temperature so in a cycle if 00:28:14.81000:28:14.820 I want to develop a cascading system for 00:28:17.12000:28:17.130 a temperature range of T 1 and T 2 T Max 00:28:20.53900:28:20.549 and minimum so teabags multiplied by T 00:28:24.71000:28:24.720 minimum of the cycle if we take under 00:28:28.22000:28:28.230 all of this this is going to be the 00:28:30.79900:28:30.809 temperature of evaporator or condenser 00:28:33.56000:28:33.570 of high pressure or low pressure cycle 00:28:35.98000:28:35.990 for the sake of heat transfer we can 00:28:38.48000:28:38.490 have some adjustment in the in the in 00:28:41.41900:28:41.429 the temperature values so that we can 00:28:43.90900:28:43.919 attain a design of a realistic system so 00:28:47.24000:28:47.250 that is all for today's lecture 00:28:49.13000:28:49.140 now in last lecture we will solve a 00:28:51.62000:28:51.630 typical example on vapour compression 00:28:53.57000:28:53.580 system thank you 00:29:29.95000:29:29.960 you
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