Multiple Evaporator and Cascade System

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Language: en

00:00:23.650
hello I welcome you all in the course on
00:00:26.380 00:00:26.390 refrigeration and air conditioning today
00:00:29.200 00:00:29.210 we will cover multi evaporator and
00:00:30.999 00:00:31.009 cascading system in vapour compression
00:00:33.100 00:00:33.110 system in a multi pressure system for
00:00:38.050 00:00:38.060 last two lectures we are dealing with
00:00:39.520 00:00:39.530 multi pressure system multi pressure
00:00:45.790 00:00:45.800 system
00:00:54.740 00:00:54.750 and multiplier systems we have already
00:00:58.610 00:00:58.620 covered in the last two lectures multi
00:01:00.950 00:01:00.960 compression system
00:01:11.179 00:01:11.189 now in multi compression system the
00:01:14.069 00:01:14.079 compression has taken place in more than
00:01:16.169 00:01:16.179 one stages right and instead of having
00:01:20.249 00:01:20.259 to pressure system because to pressure
00:01:21.809 00:01:21.819 means to pressure system is simple
00:01:23.880 00:01:23.890 vapour compression system this is a two
00:01:27.419 00:01:27.429 pressure system
00:01:35.679 00:01:35.689 so on a pH diagram so this is a two
00:01:40.840 00:01:40.850 pressure system and we have already done
00:01:45.219 00:01:45.229 this multi compression system where
00:01:46.899 00:01:46.909 compression takes place in more than one
00:01:49.059 00:01:49.069 stages maybe two stages or three stages
00:01:52.830 00:01:52.840 another multi pressure system is multi
00:01:56.260 00:01:56.270 evaporator system system in multi
00:02:05.529 00:02:05.539 evaporator system there may be one
00:02:08.169 00:02:08.179 compressor right compressor compression
00:02:11.440 00:02:11.450 for compression there may be one
00:02:13.449 00:02:13.459 compressor but there are number of you
00:02:15.729 00:02:15.739 operators instead of having one
00:02:17.410 00:02:17.420 evaporator they are number of
00:02:19.030 00:02:19.040 evaporators evaporating at different
00:02:21.039 00:02:21.049 temperatures now the benefit of this
00:02:22.990 00:02:23.000 system is suppose I want to have a deep
00:02:25.240 00:02:25.250 freezer to for the preservation let us
00:02:29.199 00:02:29.209 say is minus 40 degree centigrade I want
00:02:34.869 00:02:34.879 to have a I mean freezer also at let us
00:02:40.599 00:02:40.609 say 5 degree centigrade to keep the
00:02:44.740 00:02:44.750 things so at these two temperatures if I
00:02:48.940 00:02:48.950 have a simple system it is difficult to
00:02:51.099 00:02:51.109 operate I mean I will have to make
00:02:52.270 00:02:52.280 arrangements but here if I have a multi
00:02:55.720 00:02:55.730 evaporator system we can expand the
00:02:59.729 00:02:59.739 compressed liquid sorry not compress
00:03:03.129 00:03:03.139 liquid this condensed refrigerant at
00:03:05.559 00:03:05.569 high pressure at state 3 in 2 different
00:03:08.319 00:03:08.329 evaporators and these way operators are
00:03:10.900 00:03:10.910 operating at different temperatures or
00:03:13.599 00:03:13.609 different pressures this type of system
00:03:17.589 00:03:17.599 is known as multi evaporator system the
00:03:20.050 00:03:20.060 multi evaporator system is further
00:03:22.330 00:03:22.340 classified as individual expansion of
00:03:26.409 00:03:26.419 all system
00:03:32.699 00:03:32.709 and multiple expansion wall
00:03:37.990 00:03:38.000 multiple expansion wall system
00:03:40.289 00:03:40.299 individual expansion wall means every
00:03:44.020 00:03:44.030 evaporator has its own expansion wall so
00:03:48.250 00:03:48.260 the refrigerant at state 3 is expanding
00:03:50.979 00:03:50.989 in your printer 1 and evaporator 2 and
00:03:54.309 00:03:54.319 both the evaporators are having their
00:03:56.740 00:03:56.750 own expansion mode in multi expansion
00:04:00.099 00:04:00.109 wall is the refrigerant which is
00:04:02.500 00:04:02.510 entering the anyway operator is let us
00:04:04.509 00:04:04.519 say we have little 1 or evaporator 2 it
00:04:07.180 00:04:07.190 is expected in two stages that is why it
00:04:10.780 00:04:10.790 is known as multi expansion arrangement
00:04:13.750 00:04:13.760 and there is third type of system which
00:04:17.560 00:04:17.570 has number of I mean two compressors or
00:04:21.640 00:04:21.650 more than two compressors and more than
00:04:23.170 00:04:23.180 two operators also and this type of
00:04:25.650 00:04:25.660 system is known as cascade system or the
00:04:31.300 00:04:31.310 arrangement is known as cascading now in
00:04:35.980 00:04:35.990 the cascading there are two simple vapor
00:04:40.420 00:04:40.430 refrigeration or more than two simple
00:04:42.339 00:04:42.349 vapour compression cycles and different
00:04:45.490 00:04:45.500 refrigerants are used in different
00:04:46.810 00:04:46.820 cycles we will discuss this cascading in
00:04:48.760 00:04:48.770 details first of all will assume you
00:04:50.980 00:04:50.990 have already covered this and now we'll
00:04:53.379 00:04:53.389 start with multi evaporator system with
00:04:57.330 00:04:57.340 individual expansion wall
00:05:05.900 00:05:05.910 now in this type of arrangement there is
00:05:09.870 00:05:09.880 one compressor or we are there used to
00:05:12.870 00:05:12.880 be one evaporator
00:05:13.950 00:05:13.960 now there is one compressor and one
00:05:16.409 00:05:16.419 condenser the vapor going from the
00:05:23.279 00:05:23.289 compressor is getting condensed in the
00:05:25.770 00:05:25.780 condenser now let us come to the
00:05:28.320 00:05:28.330 evaporation side the wave part is
00:05:30.960 00:05:30.970 available here let us start from here
00:05:32.760 00:05:32.770 one it goes to the evaporator one if n
00:05:42.210 00:05:42.220 before that it gets expanded then again
00:05:48.300 00:05:48.310 vapor goes to evaporator two and then
00:05:54.870 00:05:54.880 again it gets expanded in expansion
00:05:59.370 00:05:59.380 valve one and expansion wall two
00:06:02.779 00:06:02.789 respectively and this is e 2 now vapour
00:06:10.320 00:06:10.330 is emerging from e 1 and E 2 as well so
00:06:12.390 00:06:12.400 this is state 1 this is state 2 this is
00:06:15.719 00:06:15.729 state 3 and this is straight for let us
00:06:20.219 00:06:20.229 say state 5 now pressure at state 5 4 &
00:06:24.719 00:06:24.729 5 are not same pressure are different
00:06:27.870 00:06:27.880 because here expansion is taking place
00:06:30.330 00:06:30.340 earlier at higher pressure so pressure
00:06:32.310 00:06:32.320 at state 5 is not same as the pressure
00:06:35.430 00:06:35.440 in this state for state 5 is not as the
00:06:37.770 00:06:37.780 pressure in state 4 and we have only one
00:06:39.870 00:06:39.880 compressor and then it's only one
00:06:41.520 00:06:41.530 compressor is available for this purpose
00:06:42.930 00:06:42.940 in this case we have no other choice but
00:06:46.980 00:06:46.990 to expand this the vapor available at 4
00:06:52.409 00:06:52.419 to the pressure of 5 and here at
00:06:56.670 00:06:56.680 pressure 5 it is sent to the compressor
00:06:59.370 00:06:59.380 now if you I want to depict this process
00:07:02.339 00:07:02.349 on pressure enthalpy diagram on a
00:07:07.350 00:07:07.360 pressure enthalpy diagram
00:07:16.570 00:07:16.580 there is a saturation line X is equal to
00:07:25.910 00:07:25.920 zero X is equal to 1 this is condenser
00:07:32.090 00:07:32.100 and at the exit of the condenser this
00:07:35.360 00:07:35.370 state is 1 expansion is taking place in
00:07:39.320 00:07:39.330 1 first expansion device and we are
00:07:42.530 00:07:42.540 getting state 2 and state to the vapor
00:07:45.800 00:07:45.810 is entering the evaporator and coming
00:07:48.770 00:07:48.780 out of at state 4
00:07:57.110 00:07:57.120 now further in this down the line this
00:08:00.650 00:08:00.660 vapor continue to expand up to state 3 3
00:08:08.870 00:08:08.880 so 2 2 it is expanded up to state 3 and
00:08:13.240 00:08:13.250 after a timing state 3 it goes to the
00:08:16.790 00:08:16.800 European Tour's - this is e 2 this is e
00:08:20.150 00:08:20.160 1 this is condenser and after heat
00:08:24.680 00:08:24.690 exchange in the second evaporator it
00:08:26.629 00:08:26.639 emerges as the state v and here we have
00:08:29.870 00:08:29.880 state for what we should do we should
00:08:33.829 00:08:33.839 here reduce the pressure at the exit of
00:08:37.700 00:08:37.710 the evaporator one through throttling so
00:08:40.040 00:08:40.050 in a throttling process and third P
00:08:42.320 00:08:42.330 remains constraints so through a
00:08:44.329 00:08:44.339 throttling process the pressure is
00:08:49.760 00:08:49.770 reduced and mixing takes place here
00:08:54.050 00:08:54.060 mixing takes place and after mixing the
00:08:58.700 00:08:58.710 mixture it goes to the compressor and
00:09:01.540 00:09:01.550 compression takes place and we attain
00:09:05.530 00:09:05.540 state 6 so this is a this is an
00:09:11.960 00:09:11.970 arrangement of multi evaporator system
00:09:15.230 00:09:15.240 it is very useful especially in the
00:09:16.970 00:09:16.980 shopping area it is very useful we are
00:09:19.340 00:09:19.350 some of the items in for some of the
00:09:22.850 00:09:22.860 food products we can preserve at a very
00:09:26.150 00:09:26.160 low temperature let us say minus 40
00:09:27.890 00:09:27.900 degree centigrade or minus 30 degree
00:09:29.750 00:09:29.760 centigrade and some of the items which
00:09:32.840 00:09:32.850 are to be preserved on high temperature
00:09:34.490 00:09:34.500 may be minus 10 or 0 degree centigrade
00:09:36.320 00:09:36.330 so we can have this type of arrangement
00:09:38.630 00:09:38.640 where we have two operators and both the
00:09:41.540 00:09:41.550 evaporators are operating at different
00:09:44.500 00:09:44.510 temperatures so this is the arrangement
00:09:47.480 00:09:47.490 for multi evaporator system with
00:09:50.810 00:09:50.820 individual expansion one we can have
00:09:53.810 00:09:53.820 another arrangement also where there are
00:09:57.860 00:09:57.870 multiple expansion valves in this type
00:10:01.070 00:10:01.080 of arrangement we'll start with the
00:10:02.660 00:10:02.670 compressor because then we have only one
00:10:04.340 00:10:04.350 compressor so we will start with the
00:10:06.980 00:10:06.990 compressor so there is a compressor
00:10:09.810 00:10:09.820 and there are two operators again this
00:10:13.350 00:10:13.360 is a e 2 and this is e 1 and there is a
00:10:22.110 00:10:22.120 condenser and vapor is of a condensation
00:10:27.390 00:10:27.400 again the vapor is emerging from
00:10:29.640 00:10:29.650 condenser vapor is emerging from sorry
00:10:38.550 00:10:38.560 the liquid refrigerant is emerging from
00:10:40.500 00:10:40.510 the condenser state 1 and the entire
00:10:46.170 00:10:46.180 liquid is expanded in one expansion wall
00:10:48.780 00:10:48.790 and that we get the state 2 so state 1
00:10:55.620 00:10:55.630 to state 2 we get this expansion we get
00:10:59.970 00:10:59.980 in one expansion wall this is state 2
00:11:02.900 00:11:02.910 and after the attaining state to the
00:11:06.900 00:11:06.910 vapour enters the evaporator one part of
00:11:09.990 00:11:10.000 the vapor and the process then it picks
00:11:13.620 00:11:13.630 up heat in the evaporator and we get
00:11:16.350 00:11:16.360 state 3 here now remaining part of the
00:11:23.340 00:11:23.350 expanded vapor
00:11:24.950 00:11:24.960 remaining part of expanded paper which
00:11:28.410 00:11:28.420 is available at this pressure is again
00:11:31.470 00:11:31.480 expanded and a flash gas type of removal
00:11:36.720 00:11:36.730 arrangement is also provided here so
00:11:38.880 00:11:38.890 that only liquid enters here only liquid
00:11:43.830 00:11:43.840 enters here and we get these processes
00:11:47.220 00:11:47.230 so liquid enters here means that is
00:11:51.450 00:11:51.460 state 4 that is state 4 after expansion
00:11:56.820 00:11:56.830 is state 5 and then we get state 6
00:12:04.590 00:12:04.600 now after restraining attaining state
00:12:07.630 00:12:07.640 six again these two have to be mixed and
00:12:11.910 00:12:11.920 for mixing again there is same issue
00:12:14.380 00:12:14.390 that this pressure has to be reduced to
00:12:17.110 00:12:17.120 this one okay so again third link takes
00:12:20.920 00:12:20.930 place here and mixing of both the
00:12:24.130 00:12:24.140 refrigerants and then compression in a
00:12:27.160 00:12:27.170 compressor compressor so this is how the
00:12:31.900 00:12:31.910 multi expansion system multi expansion
00:12:35.710 00:12:35.720 multi evaporator system works it is
00:12:38.170 00:12:38.180 called multi expansion because
00:12:39.400 00:12:39.410 refrigerant is expanded in to stage four
00:12:41.980 00:12:41.990 evaporator two and now these are
00:12:44.110 00:12:44.120 connected yes these are connected and it
00:12:48.250 00:12:48.260 goes to seven state seven and then it is
00:12:52.180 00:12:52.190 compressed and get state eight now one
00:13:01.090 00:13:01.100 arrangement we can make here in this
00:13:03.910 00:13:03.920 type of system instead of having one
00:13:07.930 00:13:07.940 compressor if we provide two compressors
00:13:09.640 00:13:09.650 now we have variety of components with
00:13:12.760 00:13:12.770 us we have flash gas removal system we
00:13:15.220 00:13:15.230 have multi compression system we are
00:13:16.720 00:13:16.730 reverse with multi evaporation system
00:13:20.080 00:13:20.090 evaporator system evaporator system with
00:13:22.870 00:13:22.880 individual expansion valve a power
00:13:24.460 00:13:24.470 system with multiple expansion wall so
00:13:26.830 00:13:26.840 we can have combination of all these
00:13:29.020 00:13:29.030 arrangements to find to to develop a
00:13:32.410 00:13:32.420 system which can give the best
00:13:34.720 00:13:34.730 performance so instead of it is also
00:13:36.460 00:13:36.470 recommended that instead of expanding
00:13:39.210 00:13:39.220 vapor from state 3 to state this state
00:13:42.610 00:13:42.620 and then again compressing it instead of
00:13:45.220 00:13:45.230 that if we are able to make use of two
00:13:49.360 00:13:49.370 compressors instead of using one
00:13:51.580 00:13:51.590 compressor there are two compressors and
00:13:57.310 00:13:57.320 one compressor for this and both the
00:14:02.380 00:14:02.390 compressors are compressing gas up to
00:14:04.540 00:14:04.550 state eight so this type of a rich beta
00:14:07.600 00:14:07.610 if I want to make here then definitely
00:14:12.510 00:14:12.520 the
00:14:16.080 00:14:16.090 the in fact they are not paralyzed
00:14:19.240 00:14:19.250 they're diverging line so instead of
00:14:21.120 00:14:21.130 writing them like this I would like to
00:14:23.860 00:14:23.870 draw them like this so we will get this
00:14:26.470 00:14:26.480 type of pH diagram for multi expansion
00:14:31.540 00:14:31.550 original now the problem with these type
00:14:35.500 00:14:35.510 of multi compression systems the
00:14:37.180 00:14:37.190 pressure ratio is high these systems are
00:14:38.950 00:14:38.960 used where the pressure ratio is high
00:14:40.740 00:14:40.750 but the problem with the multi expansion
00:14:43.480 00:14:43.490 system says that a refrigerant suppose I
00:14:47.560 00:14:47.570 will give you some numerical values then
00:14:50.170 00:14:50.180 things will become clear to you because
00:14:52.300 00:14:52.310 sometimes it is not possible to see you
00:14:55.420 00:14:55.430 same refrigerant at a wide range for
00:14:57.970 00:14:57.980 example in chemical applications the
00:15:02.590 00:15:02.600 temp we required temperature of the
00:15:03.940 00:15:03.950 order of let us say 100 degree
00:15:05.769 00:15:05.779 centigrade or in some of the
00:15:09.280 00:15:09.290 applications we require temperature as
00:15:11.320 00:15:11.330 minus 80 degree centigrade or minus 60
00:15:13.420 00:15:13.430 degree centigrade condenser temperature
00:15:16.180 00:15:16.190 is 50 degree centigrade or 40 degree
00:15:18.700 00:15:18.710 centigrade so this temperature
00:15:21.160 00:15:21.170 difference temperature variations is
00:15:22.780 00:15:22.790 very high this temperature variation is
00:15:25.660 00:15:25.670 very high similarly corresponding
00:15:26.860 00:15:26.870 pressure ratio PK by PU or p2 by p1 or
00:15:32.970 00:15:32.980 pH by PL pressure and condenser and
00:15:38.079 00:15:38.089 pressure in evaporator this ratio
00:15:39.610 00:15:39.620 becomes very very high for certain range
00:15:43.090 00:15:43.100 we can go for this multi compression
00:15:45.790 00:15:45.800 system but for pressure ratio it is okay
00:15:49.660 00:15:49.670 multi compression system can be accepted
00:15:52.000 00:15:52.010 but for this wide variation in
00:15:54.070 00:15:54.080 temperature same refrigerant may not be
00:15:57.730 00:15:57.740 recommended for the use let us look at
00:16:00.400 00:16:00.410 the properties of some of the
00:16:02.050 00:16:02.060 refrigerants
00:16:02.740 00:16:02.750 for example r22 so r22 has normal
00:16:06.310 00:16:06.320 boiling point minus 40 point 8 1 degree
00:16:08.380 00:16:08.390 centigrade right so if I am using this
00:16:12.730 00:16:12.740 r22 8 minus 20 the pressure is 2 point 4
00:16:16.060 00:16:16.070 5 bar and if I were using our 20 t at
00:16:19.949 00:16:19.959 minus 80 it is point one zero three
00:16:22.660 00:16:22.670 seven bar remember the moment we
00:16:26.889 00:16:26.899 reduce the pressure specific volume
00:16:30.189 00:16:30.199 increases
00:16:48.280 00:16:48.290 so the moment we reduce the pressure the
00:16:51.500 00:16:51.510 specific volume increases the specific
00:16:54.590 00:16:54.600 volume increases here also you can see
00:16:56.480 00:16:56.490 for this r22 if the evaporator
00:17:00.740 00:17:00.750 temperature is 80 degree by necessity
00:17:02.420 00:17:02.430 the pressure is only 0.1 bar and
00:17:05.230 00:17:05.240 specific volume is also very high it is
00:17:08.630 00:17:08.640 one point seven seven eight two meter
00:17:10.040 00:17:10.050 cube per kg and if you look at the
00:17:12.620 00:17:12.630 refrigerant r23
00:17:13.940 00:17:13.950 it is normal boiling point is minus 82
00:17:16.610 00:17:16.620 degree centigrade so at at one
00:17:18.740 00:17:18.750 atmospheric pressure it will boil at
00:17:20.390 00:17:20.400 minus eighty to two point two degree
00:17:22.130 00:17:22.140 centigrade and specific volume is our
00:17:24.530 00:17:24.540 only 0.192 three specific volume is
00:17:27.380 00:17:27.390 important because a specific volume at
00:17:29.540 00:17:29.550 the exit of the evaporator decides the
00:17:33.020 00:17:33.030 size of the compressor so specific
00:17:35.660 00:17:35.670 volume of the vapor at the exit of the
00:17:37.640 00:17:37.650 evaporator should be as low as possible
00:17:39.370 00:17:39.380 that is one thing second thing is if you
00:17:42.680 00:17:42.690 look at pressure at 40 suppose I choose
00:17:47.180 00:17:47.190 23 okay 4 minus 80 it is okay it is
00:17:50.090 00:17:50.100 giving minus 82 degree centigrade at
00:17:54.680 00:17:54.690 normal boiling point is normal 8 minus
00:17:56.600 00:17:56.610 82 degree centigrade so it will boil
00:17:58.670 00:17:58.680 suppose I want temperature minus 80
00:18:00.500 00:18:00.510 degree centigrade our 23 will boil below
00:18:03.830 00:18:03.840 the atmospheric pressure it is okay I
00:18:05.300 00:18:05.310 can use it for minus hundred also but
00:18:07.610 00:18:07.620 the problem is when it is taken at 40
00:18:11.870 00:18:11.880 degree centigrade it is critical
00:18:13.790 00:18:13.800 temperature is twenty six point four
00:18:15.020 00:18:15.030 seven so I will be operating the system
00:18:17.750 00:18:17.760 above the critical temperature and the
00:18:20.180 00:18:20.190 COP of the system will reduce so I
00:18:22.190 00:18:22.200 cannot use this refrigerant for this
00:18:23.510 00:18:23.520 purpose and similarly if I use low
00:18:28.700 00:18:28.710 pressure refrigerant that is our 123 our
00:18:32.360 00:18:32.370 123 is okay when the pressure is 40
00:18:34.940 00:18:34.950 degree centigrade pressure is one point
00:18:36.860 00:18:36.870 five bar one point five times
00:18:38.300 00:18:38.310 approximately atmospheric pressure it is
00:18:40.280 00:18:40.290 okay but when I use our 123 at minus
00:18:45.230 00:18:45.240 eighty the pressure is zero point zero
00:18:47.630 00:18:47.640 zero one three bar so very very low
00:18:50.210 00:18:50.220 right and in that case the specific
00:18:53.120 00:18:53.130 volume is also very high minus eighty
00:18:54.770 00:18:54.780 the specific volume is eighty three
00:18:56.000 00:18:56.010 point six six seven huge amount of vapor
00:18:58.910 00:18:58.920 has to be handled by the
00:19:00.080 00:19:00.090 compressor so now we have two option we
00:19:03.140 00:19:03.150 have to trade off we have low pressure
00:19:05.600 00:19:05.610 refrigerant low pressure refrigerant is
00:19:07.580 00:19:07.590 like our 123 which are at high
00:19:11.240 00:19:11.250 temperature at condenser temperature the
00:19:13.460 00:19:13.470 pressure is 1.5 it is okay but on the
00:19:16.940 00:19:16.950 evaporator side they have very high
00:19:19.460 00:19:19.470 specific volume so if I use this
00:19:22.549 00:19:22.559 refrigerant and the size of the
00:19:24.019 00:19:24.029 compressor will be very large that is do
00:19:25.669 00:19:25.679 not recommend it if I use high pressure
00:19:28.130 00:19:28.140 refrigerant like our 23 in that case you
00:19:32.720 00:19:32.730 have Pareto side is okay the the
00:19:34.600 00:19:34.610 refrigerant will evaporate at minus 82
00:19:38.330 00:19:38.340 degree centigrade it is its normal
00:19:39.710 00:19:39.720 boiling point specific volume is also
00:19:42.380 00:19:42.390 good 0.192 three very small specific
00:19:45.260 00:19:45.270 volume but when it comes to the
00:19:47.180 00:19:47.190 condenser it is become it becomes
00:19:49.909 00:19:49.919 supercritical see this case with the
00:19:52.970 00:19:52.980 ammonia so you take any refrigerants so
00:19:55.070 00:19:55.080 we can see that any of the refrigerant
00:19:58.010 00:19:58.020 which we have to deal in a very high
00:19:59.720 00:19:59.730 range of your operator and condenser let
00:20:01.850 00:20:01.860 us say - hundred - 50 degree centigrade
00:20:04.789 00:20:04.799 the difference is approximately 150
00:20:06.919 00:20:06.929 degree centigrade one refrigerant cannot
00:20:09.169 00:20:09.179 work and there are many other reasons
00:20:11.779 00:20:11.789 for going for cascading system I am just
00:20:15.889 00:20:15.899 justifying why we should use a cascading
00:20:17.960 00:20:17.970 system the single reference system is
00:20:20.060 00:20:20.070 used in the system the reference should
00:20:21.380 00:20:21.390 have high critical temperature and low
00:20:22.940 00:20:22.950 freezing point further we operate from
00:20:26.380 00:20:26.390 critical temperature more we are close
00:20:29.480 00:20:29.490 to the Cu P of a Carnot cycle so Co P of
00:20:33.080 00:20:33.090 the system of CO P of the cycle
00:20:35.029 00:20:35.039 increases when it operates far away from
00:20:38.200 00:20:38.210 critical temperature so that will not be
00:20:41.060 00:20:41.070 possible when we use a single
00:20:42.649 00:20:42.659 refrigerant for a such a wide range the
00:20:45.230 00:20:45.240 operating pressure with the single
00:20:46.789 00:20:46.799 refrigerants become - I or to low that I
00:20:49.070 00:20:49.080 have just now I have explained to you
00:20:51.789 00:20:51.799 likelihood of migration of lubricant oil
00:20:54.470 00:20:54.480 from one compressor to another leading
00:20:56.149 00:20:56.159 to a compressor program yes this happens
00:20:58.130 00:20:58.140 in multi staging compressors when
00:21:00.889 00:21:00.899 refrigerant from one compressor enters
00:21:02.840 00:21:02.850 to the other compressor in that case the
00:21:06.950 00:21:06.960 lubricating oil also shift to the
00:21:09.020 00:21:09.030 another compressor and
00:21:12.110 00:21:12.120 the the lower pressure compressor
00:21:14.330 00:21:14.340 becomes the short of lubricating oil so
00:21:16.580 00:21:16.590 that is another problem in multistage ik
00:21:19.370 00:21:19.380 and very low temperature in vibrator and
00:21:22.520 00:21:22.530 large suction volume for high boiling
00:21:23.990 00:21:24.000 refrigerant that I have already
00:21:25.400 00:21:25.410 explained you if the high boiling
00:21:26.960 00:21:26.970 refrigerant means normal boiling point
00:21:28.400 00:21:28.410 is high in that case if we take
00:21:31.910 00:21:31.920 therefore every end for the application
00:21:33.620 00:21:33.630 of very low temperature the specific
00:21:35.480 00:21:35.490 volume will be high and that is also not
00:21:37.520 00:21:37.530 acceptable the high pressure in
00:21:39.710 00:21:39.720 condenser for low boiling refrigerant
00:21:41.450 00:21:41.460 high pressure ratio low CU P so if we go
00:21:45.470 00:21:45.480 for a single if we take a single stage
00:21:47.510 00:21:47.520 simple cycle for vapour compression
00:21:50.300 00:21:50.310 cycle so definitely the moment the
00:21:52.400 00:21:52.410 pressure ratio increases the co P of the
00:21:55.250 00:21:55.260 cycle goes down and operation of
00:21:58.430 00:21:58.440 equipment on low temperature I am
00:22:00.560 00:22:00.570 talking about - hundred - hundred twenty
00:22:02.840 00:22:02.850 or - hundred fifty degree centigrade
00:22:04.100 00:22:04.110 that also becomes difficult so in order
00:22:08.180 00:22:08.190 to avoid this a cascading system is
00:22:10.430 00:22:10.440 recommended now in cascading system is
00:22:13.400 00:22:13.410 nothing but a combination of two simple
00:22:16.970 00:22:16.980 vapour compression cycle or two or more
00:22:19.100 00:22:19.110 vapor compression cycles it means we
00:22:21.680 00:22:21.690 have one a vapour compression cycle
00:22:23.810 00:22:23.820 which has a condenser a simple vapour
00:22:26.150 00:22:26.160 compression cycle compressor expansion
00:22:32.990 00:22:33.000 device evaporator so this is a po1
00:22:42.080 00:22:42.090 and this is PK one temperature of
00:22:45.920 00:22:45.930 condenser one temperature of your petrol
00:22:47.630 00:22:47.640 one now this is one simple cycle a
00:22:51.470 00:22:51.480 particular refrigerant for use this
00:22:52.940 00:22:52.950 cycle may be here temperature - 80
00:22:54.800 00:22:54.810 degree centigrade here temperature may
00:22:56.450 00:22:56.460 be zero degree or - 40 degree centigrade
00:22:58.580 00:22:58.590 now this condenser is used to take away
00:23:05.920 00:23:05.930 now how the condensation will take place
00:23:08.210 00:23:08.220 here suppose the temperature here is
00:23:10.310 00:23:10.320 minus 80 degree centigrade and
00:23:12.160 00:23:12.170 temperature here is minus 20 degree
00:23:15.320 00:23:15.330 centigrade now how the condensation will
00:23:18.860 00:23:18.870 take this here for the condensation of
00:23:20.480 00:23:20.490 vapor at minus 20 degree centigrade we
00:23:23.330 00:23:23.340 need to have fluid which has temperature
00:23:25.280 00:23:25.290 lower than this
00:23:26.860 00:23:26.870 right so we cannot use air we cannot use
00:23:30.020 00:23:30.030 deaf water water cooling is avoided it
00:23:32.000 00:23:32.010 is not possible air cooling is not
00:23:34.250 00:23:34.260 possible
00:23:34.909 00:23:34.919 the possibility is that we have another
00:23:37.100 00:23:37.110 vapour compression system we have
00:23:38.780 00:23:38.790 another vapour compression system which
00:23:40.820 00:23:40.830 has evaporator temperature less than
00:23:43.039 00:23:43.049 this one so there is another vapour
00:23:45.500 00:23:45.510 compression system this is t k2 and it
00:23:49.610 00:23:49.620 has also its own expansion wall and it
00:23:52.940 00:23:52.950 has evaporator t o2 and then it has its
00:24:03.470 00:24:03.480 own compressor both the systems are
00:24:08.150 00:24:08.160 working with different working fluids
00:24:09.890 00:24:09.900 now these systems are they are made as
00:24:14.060 00:24:14.070 one heat exchanger or this is known as
00:24:17.299 00:24:17.309 cascading so the heat of the heat of
00:24:25.190 00:24:25.200 this condenser is taken by away by this
00:24:27.770 00:24:27.780 give a predator so this evaporator may
00:24:30.919 00:24:30.929 be at let us say minus 25 degree
00:24:34.730 00:24:34.740 centigrade operating between minus 25 to
00:24:38.289 00:24:38.299 35 degree centigrade I am just taking
00:24:40.880 00:24:40.890 some values so that you can have clear
00:24:42.740 00:24:42.750 cut inside of the phenomena so I am
00:24:45.169 00:24:45.179 repeating in a cascading system we can
00:24:48.350 00:24:48.360 have two or more simple vapour
00:24:51.950 00:24:51.960 compression refrigeration cycles each
00:24:54.350 00:24:54.360 cycle has its own compressor evaporator
00:24:56.480 00:24:56.490 and condenser let us take one cycle of
00:24:59.210 00:24:59.220 suppose we have to maintain minus 80
00:25:00.860 00:25:00.870 degree centigrade and one cycle will
00:25:03.049 00:25:03.059 operate minus 82 minus 20 degrees for
00:25:05.240 00:25:05.250 example I am just giving an example and
00:25:06.980 00:25:06.990 here the condensation of vapor is taking
00:25:09.470 00:25:09.480 place at minus 20 degree centigrade now
00:25:11.539 00:25:11.549 in order to condense this vapour we need
00:25:14.060 00:25:14.070 a fluid which has temperature lower than
00:25:15.680 00:25:15.690 the minus twenty degree centigrade right
00:25:17.840 00:25:17.850 so the air can normally the air cannot
00:25:20.180 00:25:20.190 be used water cannot be used deaf water
00:25:22.669 00:25:22.679 cannot be used so we what we have done
00:25:25.970 00:25:25.980 we have introduced another cycle which
00:25:29.090 00:25:29.100 has evaporated temperature let us say
00:25:30.590 00:25:30.600 minus 25 or minus thirty degree
00:25:33.380 00:25:33.390 centigrade and these two are clubbed or
00:25:36.169 00:25:36.179 a heat exchange is arranged between
00:25:38.690 00:25:38.700 evaporate
00:25:39.590 00:25:39.600 of higher pressure to the operator at
00:25:41.090 00:25:41.100 lower pressure or condenser at lower
00:25:42.650 00:25:42.660 pressure and in this case the
00:25:45.140 00:25:45.150 condensation of vapor will take place in
00:25:46.940 00:25:46.950 this condenser and this heat will be
00:25:48.950 00:25:48.960 taken away by this evaporator and it
00:25:51.710 00:25:51.720 will go to the cycle so and we can have
00:25:54.770 00:25:54.780 similar type of arrangement two or three
00:25:56.390 00:25:56.400 similar type of arrangement and this is
00:25:58.370 00:25:58.380 known as cascading of vapour compression
00:26:01.640 00:26:01.650 system we assume that the CU p of this
00:26:05.960 00:26:05.970 definition cycle is equal to CU p of
00:26:07.909 00:26:07.919 these definitions again so if the co
00:26:10.490 00:26:10.500 peak our load cycle so Carnot cycle
00:26:12.409 00:26:12.419 working between this temperature between
00:26:14.659 00:26:14.669 these temperature is equal to Co P of
00:26:16.549 00:26:16.559 the Carnot cycle working between this
00:26:18.860 00:26:18.870 temperature so to1 divided by T so T CST
00:26:28.850 00:26:28.860 K 1 minus T o 1 is equal to P o 2 / PK 2
00:26:39.610 00:26:39.620 minus T 2 now in idle case we assume
00:26:44.990 00:26:45.000 that T or 2 is equal to PK 1 if e su tío
00:26:54.649 00:26:54.659 2 is equal to t K 1 then P o 1 divided
00:27:01.549 00:27:01.559 by t o2 this TK 1 is replaced by T this
00:27:04.039 00:27:04.049 temperature we assume is equal to this
00:27:05.539 00:27:05.549 temperature so TK 1 is equal to t o 2
00:27:09.260 00:27:09.270 minus to1 is equal to t o 2 divided by T
00:27:14.810 00:27:14.820 K 2 minus t o2 now we cross-multiply to1
00:27:21.250 00:27:21.260 TK 2 minus t0 1 po2 is equal to t o2 to1
00:27:31.070 00:27:31.080 tio 2 square minus to1 tio 2 we have
00:27:38.120 00:27:38.130 just simply cross multiplied this and
00:27:40.039 00:27:40.049 you can see on the left hand side to1
00:27:42.230 00:27:42.240 tio 2 here this will be cancelled out
00:27:44.000 00:27:44.010 and we will be getting po2 is equal to
00:27:49.310 00:27:49.320 under root T 0 1 P k2 it means
00:27:56.299 00:27:56.309 approximately this is not exact value
00:27:59.180 00:27:59.190 but approximate value at temperature
00:28:01.760 00:28:01.770 this is a frog approximate absolute
00:28:03.740 00:28:03.750 temperature t o2 is equal to under root
00:28:07.010 00:28:07.020 of multiplication of maximum temperature
00:28:10.490 00:28:10.500 and minimum temperature so in a cycle if
00:28:14.810 00:28:14.820 I want to develop a cascading system for
00:28:17.120 00:28:17.130 a temperature range of T 1 and T 2 T Max
00:28:20.539 00:28:20.549 and minimum so teabags multiplied by T
00:28:24.710 00:28:24.720 minimum of the cycle if we take under
00:28:28.220 00:28:28.230 all of this this is going to be the
00:28:30.799 00:28:30.809 temperature of evaporator or condenser
00:28:33.560 00:28:33.570 of high pressure or low pressure cycle
00:28:35.980 00:28:35.990 for the sake of heat transfer we can
00:28:38.480 00:28:38.490 have some adjustment in the in the in
00:28:41.419 00:28:41.429 the temperature values so that we can
00:28:43.909 00:28:43.919 attain a design of a realistic system so
00:28:47.240 00:28:47.250 that is all for today's lecture
00:28:49.130 00:28:49.140 now in last lecture we will solve a
00:28:51.620 00:28:51.630 typical example on vapour compression
00:28:53.570 00:28:53.580 system thank you
00:29:29.950 00:29:29.960 you
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