Lecture 32 (2013). 11. Heat exchangers. 11.1 Types of heat exchangers

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Language: en

00:00:00.030
ok ladies and gentlemen let's start with
00:00:02.240 00:00:02.250 chapter 11 chapter 11 I think is
00:00:05.530 00:00:05.540 actually a very practical and the most
00:00:09.560 00:00:09.570 enjoyable of all the chapters that is
00:00:11.990 00:00:12.000 where everything comes together and that
00:00:13.999 00:00:14.009 is the chapter on heat exchangers okay
00:00:17.300 00:00:17.310 so let's start with the top of a
00:00:19.250 00:00:19.260 definition for heat exchangers
00:00:22.599 00:00:22.609 okay heat exchangers in literature in
00:00:26.779 00:00:26.789 many cases we would refer to an H X heat
00:00:31.009 00:00:31.019 exchangers and what is a neat exchanger
00:00:34.220 00:00:34.230 sort of by definition the definition of
00:00:38.299 00:00:38.309 a heat exchanger is firstly it
00:00:41.049 00:00:41.059 facilitates the exchange of heat
00:00:43.369 00:00:43.379 transfer it facilitates the chain of the
00:00:47.900 00:00:47.910 change of heat transfer that's the first
00:00:50.150 00:00:50.160 requirement then secondly there will be
00:00:52.459 00:00:52.469 two streams a string one and a stream
00:00:56.990 00:00:57.000 two and these two streams would be at
00:01:00.860 00:01:00.870 temperatures t1 and t2 where these two
00:01:04.759 00:01:04.769 temperatures are not equal to each other
00:01:07.100 00:01:07.110 of course otherwise it wouldn't make
00:01:09.230 00:01:09.240 sense otherwise it wouldn't be possible
00:01:11.450 00:01:11.460 that there can be a heat transfer and
00:01:14.050 00:01:14.060 then the third requirement of a heat
00:01:18.410 00:01:18.420 exchanger is that there is no mixing no
00:01:23.080 00:01:23.090 mixing between the two streams we keep
00:01:25.999 00:01:26.009 them separate let's start by looking at
00:01:31.130 00:01:31.140 the types of heat exchangers the
00:01:36.710 00:01:36.720 different types of heat exchangers
00:01:43.959 00:01:43.969 lots of heat exchangers and let's start
00:01:46.149 00:01:46.159 with the simplest type simplest types of
00:01:55.630 00:01:55.640 heat exchanges okay now the simplest
00:01:58.510 00:01:58.520 type it I would recommend that you
00:02:01.330 00:02:01.340 divide your page into two columns left
00:02:04.630 00:02:04.640 column and a right column and then we're
00:02:07.660 00:02:07.670 going to look at the two different types
00:02:09.130 00:02:09.140 next to each other the simplest type is
00:02:13.420 00:02:13.430 two concentric tubes the one inside the
00:02:16.690 00:02:16.700 other an inner tube and an outer tube
00:02:24.690 00:02:24.700 and in the inner tube
00:02:27.990 00:02:28.000 let's choose there the hot stream and
00:02:34.900 00:02:34.910 the cold stream dot stream in the inner
00:02:40.720 00:02:40.730 tube and the cold stream in the annulus
00:02:42.789 00:02:42.799 can be other way it can be the other way
00:02:45.160 00:02:45.170 around also doesn't have to be like that
00:02:47.680 00:02:47.690 okay so there's the hot fluid and
00:02:50.309 00:02:50.319 there's the cold fluid for if that is
00:02:57.400 00:02:57.410 the hot fluid we can put in the cold
00:03:00.400 00:03:00.410 fluid in the opposite direction so that
00:03:03.759 00:03:03.769 direction would be that way and in the
00:03:06.580 00:03:06.590 annulus the opposite direction if we
00:03:11.979 00:03:11.989 look at the temperature as a function of
00:03:15.159 00:03:15.169 H the temperature as a function of X
00:03:21.119 00:03:21.129 like that temperature as a function of X
00:03:32.199 00:03:32.209 what would the difference be the
00:03:34.780 00:03:34.790 difference typically would be that for
00:03:37.089 00:03:37.099 the hot fluid for this type of heat
00:03:40.360 00:03:40.370 exchanger the characteristics would look
00:03:44.110 00:03:44.120 something like that while the cold fluid
00:03:47.050 00:03:47.060 would do something like that so in the
00:03:51.250 00:03:51.260 beginning
00:03:59.589 00:03:59.599 so in the beginning we will have a very
00:04:02.089 00:04:02.099 high temperature difference and the
00:04:03.800 00:04:03.810 temperature difference would decrease
00:04:06.190 00:04:06.200 downstream of the heat exchanger okay
00:04:09.080 00:04:09.090 I think Richard difference at the
00:04:10.640 00:04:10.650 beginning and they need to decrease to
00:04:13.489 00:04:13.499 the end with this type of heat exchanger
00:04:16.779 00:04:16.789 the hot fluid temperature distribution
00:04:19.279 00:04:19.289 would look something like that and the
00:04:23.600 00:04:23.610 cold fluid one something like that
00:04:28.450 00:04:28.460 okay so that is hot that was cold hot
00:04:34.070 00:04:34.080 and cold this type of heat exchanger is
00:04:38.600 00:04:38.610 called a lateral heat exchanger and this
00:04:43.249 00:04:43.259 type of heat exchanger is called a
00:04:45.200 00:04:45.210 counter flow heat exchanger they are
00:04:49.760 00:04:49.770 very easy to build very very simple and
00:04:52.450 00:04:52.460 I've built or built many of them
00:04:55.129 00:04:55.139 typically up to about 100 kilowatts but
00:04:59.120 00:04:59.130 you can also do is you put the one tube
00:05:01.189 00:05:01.199 inside the other and you use soft drawn
00:05:04.339 00:05:04.349 tubing and then you can call away
00:05:06.499 00:05:06.509 otherwise the links are just too long
00:05:08.649 00:05:08.659 and you can make them typically very
00:05:12.140 00:05:12.150 compact 80 or 100 kilowatt heat
00:05:15.950 00:05:15.960 exchanger typically the size of I can
00:05:20.480 00:05:20.490 put it in here not much larger than an
00:05:23.029 00:05:23.039 overhead projector in size okay but up
00:05:26.600 00:05:26.610 to about 80 200 kilowatts
00:05:29.950 00:05:29.960 okay the next type of heat exchanger is
00:05:32.629 00:05:32.639 a compact eat exchanger
00:05:37.460 00:05:37.470 compact exchanger now the compact heat
00:05:40.830 00:05:40.840 exchanger has a definition that you can
00:05:44.190 00:05:44.200 take a melt off but you're not going to
00:05:46.710 00:05:46.720 really use it the contact heat exchanger
00:05:50.220 00:05:50.230 is described by a bita which is called
00:05:53.730 00:05:53.740 the area density the area density and it
00:06:02.760 00:06:02.770 is defined as the surface area of the
00:06:10.260 00:06:10.270 heat exchanger to which the heat
00:06:15.090 00:06:15.100 transfer occurs divided by the volume of
00:06:18.800 00:06:18.810 the heat exchanger detalls the surface
00:06:23.430 00:06:23.440 divided by the volume and typically this
00:06:27.420 00:06:27.430 beta is larger than 700 then it would be
00:06:34.100 00:06:34.110 considered as a compact heat exchanger
00:06:36.900 00:06:36.910 very compact okay a car radiator it's
00:06:44.430 00:06:44.440 approximately a thousand
00:06:50.310 00:06:50.320 correlator
00:06:56.629 00:06:56.639 okay no move you can think of a very
00:07:00.750 00:07:00.760 compact heat exchanger a fridge there
00:07:06.420 00:07:06.430 what else there's some fins and I'm
00:07:11.100 00:07:11.110 going to say something about that just
00:07:12.659 00:07:12.669 now
00:07:23.340 00:07:23.350 ladies and gentlemen any any
00:07:28.200 00:07:28.210 contributions nothing a condition is
00:07:33.150 00:07:33.160 sure okay there are a few values of beta
00:07:37.800 00:07:37.810 a gloss comic type of heat exchanges
00:07:41.880 00:07:41.890 which are found in gas turbines
00:07:46.610 00:07:46.620 typically for the Stirling engine the
00:07:49.260 00:07:49.270 regenerator about 15,000 that the most
00:07:52.440 00:07:52.450 effective and the most compact heat
00:07:54.450 00:07:54.460 exchanger is the human lung the human
00:07:57.510 00:07:57.520 lung the lungs there's a value of about
00:08:00.320 00:08:00.330 20,000 square meters per cubic meter
00:08:03.600 00:08:03.610 that is the most effective and most
00:08:06.600 00:08:06.610 compact heat exchanger the human lung
00:08:09.590 00:08:09.600 okay
00:08:11.469 00:08:11.479 right now as a rule of thumb take note
00:08:21.719 00:08:21.729 as a rule of thumb okay we in the moment
00:08:26.619 00:08:26.629 we have a gas site and with gas we
00:08:30.549 00:08:30.559 obviously include air the moment we've
00:08:33.040 00:08:33.050 got a gas site we normally have funds
00:08:35.819 00:08:35.829 how does things work obviously we will
00:08:39.909 00:08:39.919 have some tubes and the spicing of those
00:08:46.120 00:08:46.130 tubes is already an important thing let
00:08:52.329 00:08:52.339 me just draw three of these tubes and
00:08:56.069 00:08:56.079 then on the inside we will typically
00:09:00.790 00:09:00.800 have a liquid flowing through the inside
00:09:06.400 00:09:06.410 and the liquid can be a single phase
00:09:09.100 00:09:09.110 fluid or it might be a fluid which is
00:09:12.579 00:09:12.589 being condensed or evaporated or which
00:09:16.210 00:09:16.220 is being boiled so it is B it is it
00:09:19.059 00:09:19.069 might be changing its face if we've got
00:09:23.680 00:09:23.690 heat transferred to a gas or from a gas
00:09:26.050 00:09:26.060 to this liquid then normally as a rule
00:09:29.230 00:09:29.240 of thumb we will have some funds
00:09:34.490 00:09:34.500 00:09:41.490 00:09:41.500 and the fun's the function of the funds
00:09:45.490 00:09:45.500 is to increase the surface area isn't
00:09:47.980 00:09:47.990 that the funds increases the surface
00:09:50.710 00:09:50.720 area and you've done the funds in
00:09:55.720 00:09:55.730 Chapter three of the textbook of single
00:09:58.060 00:09:58.070 and you might remember that you've
00:10:02.080 00:10:02.090 worked with funds which were called and
00:10:05.560 00:10:05.570 one of the boundary conditions was an
00:10:08.020 00:10:08.030 adiabatic depth what does an adiabatic
00:10:10.690 00:10:10.700 tap means it means that there's no heat
00:10:13.870 00:10:13.880 transfer there okay so if this
00:10:16.750 00:10:16.760 temperature and that temperature is the
00:10:18.490 00:10:18.500 same then there if you would measure the
00:10:21.940 00:10:21.950 temperature gradient the temperature
00:10:25.630 00:10:25.640 gradient like that DT DX would be equal
00:10:29.050 00:10:29.060 to zero okay and that would then there
00:10:31.930 00:10:31.940 will be an adiabatic fun so those
00:10:35.350 00:10:35.360 conditions for those funds in Chapter
00:10:37.360 00:10:37.370 three can then be applied to these
00:10:40.660 00:10:40.670 conditions and usually if you've got
00:10:43.630 00:10:43.640 funds like this you'll have the gas side
00:10:46.620 00:10:46.630 moving over the funds in the same
00:10:49.690 00:10:49.700 direction as the funds so that you can
00:10:53.110 00:10:53.120 have a very good heat transfer so the
00:10:58.540 00:10:58.550 funds so the rule of thumb is to use
00:11:04.450 00:11:04.460 funds on the gas side
00:11:10.809 00:11:10.819 since on the gas side increases the
00:11:15.739 00:11:15.749 surface area that would be the function
00:11:19.249 00:11:19.259 of the funds now terms of nomenclature
00:11:24.679 00:11:24.689 and definitions we are also going to
00:11:28.489 00:11:28.499 refer to a cross flow heat exchanger
00:11:34.780 00:11:34.790 cross flow
00:11:37.160 00:11:37.170 and cross-flow by definition means that
00:11:41.090 00:11:41.100 if that is the fluid stream direction of
00:11:44.990 00:11:45.000 fluid 1 and that is the direction of
00:11:51.620 00:11:51.630 fluid 3 - and that angle is 90 degrees
00:11:56.120 00:11:56.130 then it is called a cross flow heat
00:11:58.670 00:11:58.680 exchanger so this heat exchanger would
00:12:01.250 00:12:01.260 also be a cross flow heat exchanger the
00:12:04.639 00:12:04.649 two flow directions is perpendicular to
00:12:06.860 00:12:06.870 each other okay now there are two
00:12:11.720 00:12:11.730 different types of cross flow heat
00:12:13.880 00:12:13.890 exchangers two different types the first
00:12:17.750 00:12:17.760 type is called unmixed and the second
00:12:23.000 00:12:23.010 type is called a mixed one an unmixed
00:12:27.319 00:12:27.329 cross flow heat exchanger and a mixed
00:12:29.960 00:12:29.970 cross flow heat exchanger the unmixed
00:12:34.100 00:12:34.110 one looks like this
00:12:41.480 00:12:41.490 and show it schematically this would be
00:12:47.560 00:12:47.570 the one stream moving through these
00:12:50.840 00:12:50.850 tubes typically like that and year we
00:12:57.829 00:12:57.839 will have the plates which are the fins
00:13:05.000 00:13:05.010 and because it's a cross flow heat
00:13:09.060 00:13:09.070 exchanger the to flow directions must be
00:13:12.900 00:13:12.910 perpendicular to each other and this
00:13:21.270 00:13:21.280 flow stream cannot move in the
00:13:23.880 00:13:23.890 transverse direction okay
00:13:31.230 00:13:31.240 Conte moving the transverse direction
00:13:41.370 00:13:41.380 now this is specifically very important
00:13:44.470 00:13:44.480 if on the tube side they are not in
00:13:46.870 00:13:46.880 picture differences these plates are
00:13:49.510 00:13:49.520 actually forcing the flow that it can't
00:13:54.190 00:13:54.200 go into the transverse direction the
00:13:57.370 00:13:57.380 mixed one on the other side would be
00:13:59.350 00:13:59.360 these tubes I can show all five of them
00:14:08.530 00:14:08.540 like that
00:14:14.760 00:14:14.770 and again there is our fruit stream won
00:14:17.370 00:14:17.380 and now our fruit stream to causes the
00:14:21.720 00:14:21.730 flow to be a cross flow heat exchanger
00:14:23.570 00:14:23.580 but now they might be movement in the
00:14:27.540 00:14:27.550 diet in the transverse direction in
00:14:30.750 00:14:30.760 terms of the temperature gradient okay
00:14:36.300 00:14:36.310 if you don't like my sketches there's
00:14:38.519 00:14:38.529 two better sketches in the textbook to
00:14:41.850 00:14:41.860 make it more clear okay the unmixed and
00:14:45.150 00:14:45.160 the mixed type of cross flow heat
00:14:47.610 00:14:47.620 exchanger any questions situation I beg
00:14:56.460 00:14:56.470 your pardon indeed a situation that
00:14:58.170 00:14:58.180 flows actually mixing with each other in
00:15:01.380 00:15:01.390 either one now it love we all know let's
00:15:06.269 00:15:06.279 let's look at this one
00:15:10.950 00:15:10.960 and let's look at it from above okay in
00:15:13.980 00:15:13.990 both cases so what you're going to have
00:15:19.710 00:15:19.720 here is that this temperature gradient
00:15:26.360 00:15:26.370 of of that fluid is going to do
00:15:30.480 00:15:30.490 something like that maybe
00:15:33.790 00:15:33.800 and with that one it might be something
00:15:36.249 00:15:36.259 like that in this case if you look at
00:15:41.379 00:15:41.389 the fluid particle there then because of
00:15:45.249 00:15:45.259 the temperature difference that this
00:15:47.499 00:15:47.509 particle might have some convection
00:15:50.189 00:15:50.199 characteristics and you might get that
00:15:52.210 00:15:52.220 the two particles does that in terms of
00:15:54.309 00:15:54.319 the temperature distribution that is
00:15:56.679 00:15:56.689 what we mean with mixed these two plates
00:16:03.280 00:16:03.290 who will sure that I can't mix well in
00:16:07.629 00:16:07.639 this case the temperature gradients in
00:16:10.359 00:16:10.369 this direction remember the temperature
00:16:12.789 00:16:12.799 there there and there or not the same
00:16:16.509 00:16:16.519 might decreases and that might cause the
00:16:19.689 00:16:19.699 same picture streams on the outside to
00:16:22.629 00:16:22.639 be mixed okay I haven't seen many
00:16:28.329 00:16:28.339 applications in industry of this many
00:16:30.910 00:16:30.920 thanks
00:16:33.260 00:16:33.270 okay now the most important type of heat
00:16:36.980 00:16:36.990 exchanger is the shoaling shoot the
00:16:50.480 00:16:50.490 shouted tube heat exchanger that is the
00:16:54.230 00:16:54.240 one you're going to find most in
00:16:55.940 00:16:55.950 industry for heat transfer applications
00:17:04.040 00:17:04.050 of a few hundred and megawatts so the
00:17:07.010 00:17:07.020 moment you talking of hundreds of
00:17:08.600 00:17:08.610 kilowatts or megawatts then you're going
00:17:12.770 00:17:12.780 to go into the shell and tube
00:17:14.090 00:17:14.100 application usually there are too needy
00:17:17.689 00:17:17.699 to be used in in transport in course and
00:17:22.809 00:17:22.819 or aerospace too heavy but in terms of
00:17:30.040 00:17:30.050 workhorses and good value for money
00:17:34.100 00:17:34.110 that is really the base type of heat
00:17:36.020 00:17:36.030 exchanger and the most common type of
00:17:38.270 00:17:38.280 heat exchanger you're going to find an
00:17:40.370 00:17:40.380 industry now let's start with it very
00:17:42.650 00:17:42.660 simple and then we're going to make it
00:17:44.840 00:17:44.850 more complicated okay make it start
00:17:49.100 00:17:49.110 simple by starting with a shell
00:17:55.870 00:17:55.880 okay there is the show and the show we
00:18:01.820 00:18:01.830 must have an inlet and an outlet right
00:18:11.530 00:18:11.540 in the bay and the outlet there okay and
00:18:18.200 00:18:18.210 you can see that if a flow stream is
00:18:21.770 00:18:21.780 coming in there then obviously it is
00:18:24.170 00:18:24.180 going to go out there okay that is the
00:18:26.450 00:18:26.460 shell side now what we do is we put in
00:18:34.460 00:18:34.470 the header header like that and we put
00:18:42.890 00:18:42.900 in tubes through them
00:18:50.080 00:18:50.090 that is the first tube just to keep
00:18:53.419 00:18:53.429 things simple I'm going to put in three
00:18:55.220 00:18:55.230 tubes here's the city tube like that and
00:19:01.640 00:19:01.650 yes the third tube
00:19:11.390 00:19:11.400 typically like that
00:19:24.820 00:19:24.830 and now I can put the fluid through the
00:19:29.420 00:19:29.430 inner tubes through the three inner
00:19:31.130 00:19:31.140 tubes and for reasons that's but going
00:19:35.930 00:19:35.940 to become clearer to you later let's put
00:19:39.050 00:19:39.060 it in a counter flow type of direction
00:19:41.300 00:19:41.310 which means that we put the fluid
00:19:44.240 00:19:44.250 through in there coming out there and
00:19:47.540 00:19:47.550 let me just use another color to make it
00:19:50.600 00:19:50.610 clearer so the tube side go in there it
00:19:56.150 00:19:56.160 would go out there and through the tube
00:19:59.000 00:19:59.010 side the flow would be then going
00:20:01.700 00:20:01.710 through Vale like that okay and you can
00:20:06.980 00:20:06.990 see now that in the shell side the flow
00:20:09.950 00:20:09.960 is going to do primarily that degree
00:20:17.650 00:20:17.660 now this is called the front in tether
00:20:26.280 00:20:26.290 the front in headed
00:20:28.740 00:20:28.750 why is this the front because it's the
00:20:31.660 00:20:31.670 site with the flow comes into the tubes
00:20:34.350 00:20:34.360 okay that is why we call that the front
00:20:36.670 00:20:36.680 side the side through which the flow
00:20:40.450 00:20:40.460 comes into the tubes and that would now
00:20:42.970 00:20:42.980 be the inside the rear inside now this
00:20:55.120 00:20:55.130 type of heat exchanger is called the one
00:21:00.130 00:21:00.140 shell pause and a one to pause a one
00:21:10.600 00:21:10.610 shell side and a one to force
00:21:42.440 00:21:42.450 okay now it wasn't long after people
00:21:46.710 00:21:46.720 started building these one shelters and
00:21:49.200 00:21:49.210 one to pause it exchanges when people
00:21:53.040 00:21:53.050 start looking at it and and think well
00:21:55.140 00:21:55.150 maybe I should modify it a little bit
00:21:57.290 00:21:57.300 okay and what type of modifications can
00:22:00.750 00:22:00.760 we make well the one type of
00:22:03.270 00:22:03.280 modification that we can make is we can
00:22:05.370 00:22:05.380 say well let's change things a little
00:22:09.390 00:22:09.400 bit in the shell what we do is we put in
00:22:15.660 00:22:15.670 a baffle like that so what is going to
00:22:21.930 00:22:21.940 happen now with a flow coming in through
00:22:24.030 00:22:24.040 the shell side it's going to do that
00:22:26.550 00:22:26.560 but at the in it it is being forced to
00:22:30.320 00:22:30.330 actually flow like that so it means we
00:22:33.570 00:22:33.580 have to put the outlet there now okay
00:22:37.020 00:22:37.030 the baffle in
00:22:39.430 00:22:39.440 the other function of the baffle is that
00:22:41.950 00:22:41.960 these tubes are very long they start
00:22:43.840 00:22:43.850 sagging so if we put the baffle in we
00:22:46.900 00:22:46.910 actually support the tubes better but at
00:22:51.040 00:22:51.050 the same time we are actually changing
00:22:52.750 00:22:52.760 the heat exchanger from a counterflow
00:22:55.870 00:22:55.880 type of heat exchanger to a cross-flow
00:22:58.750 00:22:58.760 type of heat exchanger and in the graphs
00:23:01.480 00:23:01.490 that we are going to do later on you're
00:23:02.980 00:23:02.990 going to see that the effectiveness of
00:23:04.630 00:23:04.640 these types of heat exchanges or better
00:23:07.560 00:23:07.570 okay so that is the first type of
00:23:10.180 00:23:10.190 modification that can be made the second
00:23:13.330 00:23:13.340 type is to say well these tubes
00:23:20.100 00:23:20.110 why don't we modify things a little bit
00:23:25.230 00:23:25.240 so that we do the following the tube the
00:23:31.150 00:23:31.160 flow through there let's not let it go
00:23:34.840 00:23:34.850 out there
00:23:35.380 00:23:35.390 what we do is we actually connect the
00:23:39.310 00:23:39.320 tube like that okay so that the flow
00:23:42.340 00:23:42.350 through this tube would go in this
00:23:43.750 00:23:43.760 direction and then it would go back in
00:23:46.000 00:23:46.010 that erection okay and then here again
00:23:49.090 00:23:49.100 we can connect it like that so that this
00:23:53.230 00:23:53.240 flow direction is now in that direction
00:23:55.110 00:23:55.120 and then it goes out like that that is
00:23:59.320 00:23:59.330 called a three to pause it exchange are
00:24:03.010 00:24:03.020 now three tube pause because the tube is
00:24:07.300 00:24:07.310 through three times so let's make things
00:24:11.230 00:24:11.240 a little bit more simple and schematic
00:24:14.710 00:24:14.720 so without blowing all the detail
00:24:17.880 00:24:17.890 without looking at all the detail if
00:24:21.280 00:24:21.290 that is the shell okay that is the shell
00:24:25.000 00:24:25.010 and the tube goes in and out like that
00:24:30.150 00:24:30.160 if we look at the shell
00:24:32.260 00:24:32.270 how many flows are they through the
00:24:34.510 00:24:34.520 shallow one so it is a one shell pass
00:24:40.600 00:24:40.610 and the to to boss heat exchanger one
00:24:50.210 00:24:50.220 shell pause and the two coupe pours it
00:24:53.420 00:24:53.430 exchanger okay the next one would be
00:24:57.460 00:24:57.470 again
00:24:58.730 00:24:58.740 let's get that let's suppose that is the
00:25:01.760 00:25:01.770 shell and now we say one two three four
00:25:08.650 00:25:08.660 okay so immediately it's a full force
00:25:16.750 00:25:16.760 for to pause heat exchanger and let's
00:25:21.850 00:25:21.860 make the shell like that
00:25:29.720 00:25:29.730 and the shell flow through the show let
00:25:34.580 00:25:34.590 me just use another color does this
00:25:40.270 00:25:40.280 because of that battle there the flow is
00:25:42.760 00:25:42.770 being forced to flow like that and out
00:25:46.299 00:25:46.309 there so this is the in course call a to
00:25:50.560 00:25:50.570 shell us to shell us and a four to
00:25:58.840 00:25:58.850 fourth heat exchanger later on you're
00:26:04.240 00:26:04.250 going to see some sketches like that in
00:26:05.950 00:26:05.960 your text look so you don't have to
00:26:07.240 00:26:07.250 remember it just look at the schematics
00:26:09.010 00:26:09.020 to lead you in terms of the nomenclature
00:26:11.380 00:26:11.390 it is obviously important because in the
00:26:13.990 00:26:14.000 taste going in exam I might say the heat
00:26:17.020 00:26:17.030 exchanger is a a four shell pause and a
00:26:21.130 00:26:21.140 twelve tube or heat exchanger and then
00:26:24.279 00:26:24.289 you need to understand what the flow
00:26:26.440 00:26:26.450 configuration is on the inside okay any
00:26:30.610 00:26:30.620 questions on the shell and tube heat
00:26:31.899 00:26:31.909 exchanger okay this a little bit of a
00:26:36.789 00:26:36.799 better sketch if you don't like mine
00:26:39.180 00:26:39.190 terms of there you can see the function
00:26:42.940 00:26:42.950 of all the battles on the inside I'm
00:26:45.909 00:26:45.919 going to come back to that heat exchange
00:26:47.409 00:26:47.419 changes just now but that is typically
00:26:50.950 00:26:50.960 how it is how it looks during
00:26:52.930 00:26:52.940 construction okay
00:26:55.090 00:26:55.100 it is huge okay few hundred tubes going
00:26:58.510 00:26:58.520 through it you can see the battles on
00:27:03.340 00:27:03.350 the inside which are also being used to
00:27:06.520 00:27:06.530 support all the tubes with typically a
00:27:09.580 00:27:09.590 header there you can see some of the
00:27:12.190 00:27:12.200 tubes on the inside and you can start
00:27:14.980 00:27:14.990 making things more interesting these
00:27:17.289 00:27:17.299 baffles do not have to do not have to be
00:27:20.740 00:27:20.750 like that you can go and put in inert
00:27:22.720 00:27:22.730 angles okay
00:27:24.220 00:27:24.230 which means that the flow is being
00:27:26.080 00:27:26.090 forced to do that a longer pause or flow
00:27:29.890 00:27:29.900 through the heat exchanger okay
00:27:35.360 00:27:35.370 okay before we go on to the next type of
00:27:37.670 00:27:37.680 heat exchanger any questions on the
00:27:39.500 00:27:39.510 shelling tube heat exchanger nothing
00:27:42.290 00:27:42.300 okay let's look at the plate and flame
00:27:45.950 00:27:45.960 heat exchanger that is what they call it
00:27:48.770 00:27:48.780 in the textbook we normally call it call
00:27:50.840 00:27:50.850 it a plate heat exchanger might eat
00:27:57.080 00:27:57.090 exchanger okay a plate heat exchanger is
00:28:01.130 00:28:01.140 very very simple
00:28:12.450 00:28:12.460 this is just schematically let's suppose
00:28:16.810 00:28:16.820 this your first plate and then and plate
00:28:24.490 00:28:24.500 next to it
00:28:27.510 00:28:27.520 third one and a fourth one and there
00:28:36.610 00:28:36.620 will be many more I'm just not going to
00:28:39.160 00:28:39.170 draw all of them in
00:28:50.130 00:28:50.140 so what you can imagine now is that
00:28:52.810 00:28:52.820 between these two plates I can let my
00:28:58.240 00:28:58.250 fluid 1 flow through it
00:29:00.779 00:29:00.789 and then here on this side I will have
00:29:06.310 00:29:06.320 my second fluid between these two plates
00:29:12.270 00:29:12.280 through two two and then here I can have
00:29:17.799 00:29:17.809 something that redirects the flow in
00:29:20.890 00:29:20.900 between those two plates again the
00:29:25.690 00:29:25.700 result would be
00:29:35.330 00:29:35.340 something like that okay so between
00:29:39.540 00:29:39.550 every plate we will be hot side and a
00:29:42.240 00:29:42.250 cold side okay as you can imagine these
00:29:48.900 00:29:48.910 types of heat exchanges can be quite
00:29:50.760 00:29:50.770 compact very compact type of heat
00:29:53.700 00:29:53.710 exchanges they are very flexible in the
00:29:56.430 00:29:56.440 sense that many of them you can actually
00:29:58.170 00:29:58.180 buy for a certain number of kilowatts
00:30:01.260 00:30:01.270 and maybe things changes in your
00:30:03.960 00:30:03.970 production and you need to increase the
00:30:06.690 00:30:06.700 heat transfer right and then you can do
00:30:08.790 00:30:08.800 it by just adding on a few more plates
00:30:11.300 00:30:11.310 so which is very nice however they
00:30:15.390 00:30:15.400 cannot take large pressure differences
00:30:17.930 00:30:17.940 so is the pressures or about the same
00:30:20.820 00:30:20.830 order of magnitude typically liquids
00:30:24.260 00:30:24.270 liquids works very well in the milk
00:30:28.500 00:30:28.510 industry we want to eat a cool milk for
00:30:33.060 00:30:33.070 example process in the street is being
00:30:35.550 00:30:35.560 used a lot but it is not being used a
00:30:38.970 00:30:38.980 lot as condensers or evaporators in
00:30:42.330 00:30:42.340 heating and ventilation industry the
00:30:44.760 00:30:44.770 reason why because then the refrigerant
00:30:48.600 00:30:48.610 side the pressures on the orders of mega
00:30:51.660 00:30:51.670 Pascal's and the liquids are in the
00:30:55.620 00:30:55.630 orders of kilo Pascal's okay and the
00:30:59.220 00:30:59.230 result is that the pressure difference
00:31:00.960 00:31:00.970 over the plates are so large that the
00:31:03.450 00:31:03.460 plates would Bend and you will have
00:31:06.030 00:31:06.040 problems with the seals so that is
00:31:08.430 00:31:08.440 normally the problems that we have with
00:31:10.800 00:31:10.810 plate heat exchangers that are very well
00:31:13.770 00:31:13.780 suited for liquid to liquid type of
00:31:16.950 00:31:16.960 applications
00:31:22.040 00:31:22.050 the good to liquid type of heat
00:31:25.080 00:31:25.090 exchanges
00:31:30.500 00:31:30.510 here's some examples of these type of
00:31:35.419 00:31:35.429 heat exchanges and yet what you will see
00:31:37.460 00:31:37.470 is that people originally started with
00:31:41.030 00:31:41.040 flat plates and then they decided now
00:31:43.549 00:31:43.559 wait a minute we can make it much more
00:31:45.110 00:31:45.120 interesting if this is the flat plate we
00:31:48.020 00:31:48.030 can actually change the geometry like
00:31:50.510 00:31:50.520 that to purposes it makes it
00:31:54.039 00:31:54.049 structurally stronger so that it doesn't
00:31:56.690 00:31:56.700 bend that easily but at the same time it
00:31:59.930 00:31:59.940 increases the turbulence and if I look
00:32:02.240 00:32:02.250 at the plate from this side I can
00:32:04.370 00:32:04.380 actually also start putting in very
00:32:06.760 00:32:06.770 interesting fourth ways for the liquids
00:32:09.880 00:32:09.890 which means that the flow doesn't only
00:32:12.980 00:32:12.990 go in this direction but maybe you know
00:32:16.490 00:32:16.500 something like that
00:32:17.299 00:32:17.309 much more complicated and there you can
00:32:19.789 00:32:19.799 see some of the the plates which are
00:32:23.330 00:32:23.340 being bent like that there are some
00:32:28.520 00:32:28.530 examples
00:32:34.830 00:32:34.840 okay any questions on the plate heat
00:32:37.330 00:32:37.340 exchangers okay another type of heat
00:32:40.870 00:32:40.880 exchanger is called the regenerative
00:32:44.130 00:32:44.140 heat exchanger
00:32:53.440 00:32:53.450 regenerative type and in that clause
00:32:58.280 00:32:58.290 there are two different types the first
00:33:00.650 00:33:00.660 one is the static top the static done
00:33:07.630 00:33:07.640 and usually in these types of heat
00:33:10.400 00:33:10.410 exchangers we've got a porous material
00:33:14.860 00:33:14.870 so this is the porous material it can be
00:33:21.730 00:33:21.740 steel wool for example is a very good
00:33:25.520 00:33:25.530 one we want a material that can absorb a
00:33:29.210 00:33:29.220 lot of heat and if I look at this porous
00:33:37.370 00:33:37.380 material what has then being done is
00:33:40.760 00:33:40.770 that I've got a flute one flowing
00:33:47.330 00:33:47.340 through it and increases the heat until
00:33:50.570 00:33:50.580 it is being heated where this
00:33:53.360 00:33:53.370 temperature and that temperature is
00:33:54.920 00:33:54.930 approximately the same okay and once it
00:33:58.400 00:33:58.410 has been heated and let's call that T
00:34:02.120 00:34:02.130 equal t1 to t2 we do that and then after
00:34:09.080 00:34:09.090 that you're going to use fluid two and
00:34:12.530 00:34:12.540 it's put through to through then this
00:34:16.129 00:34:16.139 will - and that would be for time equal
00:34:19.310 00:34:19.320 T 3 - 2 for T 4 so it has been heated
00:34:23.740 00:34:23.750 okay and now you use the other stream
00:34:26.680 00:34:26.690 flow to flow through it and then you
00:34:29.240 00:34:29.250 transfer the heat from the one stream to
00:34:31.369 00:34:31.379 the other stream but usually never flow
00:34:36.020 00:34:36.030 with both streams active at the same
00:34:39.169 00:34:39.179 time okay first the one and then the
00:34:42.260 00:34:42.270 other another very interesting
00:34:44.210 00:34:44.220 application of this is that we install
00:34:48.050 00:34:48.060 abortion University are being funded as
00:34:52.820 00:34:52.830 a so-called concentrated solar up and we
00:34:56.930 00:34:56.940 are looking at the problem of generating
00:34:59.990 00:35:00.000 electricity the Sun as you know during
00:35:03.230 00:35:03.240 the night time there is no Sun then you
00:35:05.600 00:35:05.610 can't generate
00:35:06.360 00:35:06.370 electricity and that is one of the big
00:35:07.890 00:35:07.900 disadvantages of concentrated solar
00:35:10.380 00:35:10.390 power but if during the day you can
00:35:13.080 00:35:13.090 store the heat then you can actually
00:35:16.710 00:35:16.720 generate electricity during the night
00:35:18.420 00:35:18.430 and one other method of using a
00:35:21.210 00:35:21.220 regenerative type of heat exchanger is
00:35:23.970 00:35:23.980 to use Rock okay if you use Rock in big
00:35:28.980 00:35:28.990 open spaces falling up with rock and
00:35:31.500 00:35:31.510 then during the day you've got the hot
00:35:33.810 00:35:33.820 stream you in increases the temperature
00:35:37.170 00:35:37.180 of the rock you store the energy there
00:35:39.180 00:35:39.190 then during night you can actually do
00:35:42.930 00:35:42.940 the heat transfer and get all the heat
00:35:44.670 00:35:44.680 back okay so that is an example of a
00:35:48.150 00:35:48.160 static type of regenerative type of heat
00:35:50.550 00:35:50.560 exchanger okay what can also be done is
00:35:54.570 00:35:54.580 it can be bought as a dynamic type and
00:35:58.880 00:35:58.890 as a dynamic type
00:36:03.120 00:36:03.130 very simple example would be a wheel
00:36:06.510 00:36:06.520 like this a porous wheel porous wheel
00:36:13.430 00:36:13.440 which rotates usually very slowly and
00:36:20.750 00:36:20.760 then on this side we will have fluid one
00:36:27.110 00:36:27.120 you will be a baffle and they will be
00:36:30.840 00:36:30.850 fluid too now let's suppose this is the
00:36:37.290 00:36:37.300 heating fluid it will increases the
00:36:39.870 00:36:39.880 temperature of the material the porous
00:36:42.540 00:36:42.550 material it would move through the
00:36:44.910 00:36:44.920 baffle and then it will be exposed to
00:36:47.070 00:36:47.080 the cold fluid and the heat transfer
00:36:48.720 00:36:48.730 will be from that fluid to the cold
00:36:50.790 00:36:50.800 fluid equations right other types of
00:36:59.850 00:36:59.860 heat exchanges means that sort of riff
00:37:04.520 00:37:04.530 or typically names that reflect the
00:37:07.530 00:37:07.540 application and the first type is a
00:37:10.320 00:37:10.330 condenser
00:37:15.040 00:37:15.050 condenser now a condenser is a heat
00:37:21.620 00:37:21.630 exchanger where if we look at the TS
00:37:27.470 00:37:27.480 diagram that is a constant pressure line
00:37:32.620 00:37:32.630 the fluid is being cooled from a gas to
00:37:38.630 00:37:38.640 a liquid fluid is called from the gas to
00:37:50.270 00:37:50.280 a liquid okay so it will enter as a gas
00:37:56.560 00:37:56.570 to being contains until everything as a
00:37:59.720 00:37:59.730 liquid and during that process the heat
00:38:02.750 00:38:02.760 rolls for right would be equal to the
00:38:05.690 00:38:05.700 mass flow rate multiplied by H okay
00:38:11.750 00:38:11.760 let's rather use F
00:38:16.440 00:38:16.450 if they're and if they're indicate the
00:38:20.260 00:38:20.270 fluid heat transfer rate would be equal
00:38:22.990 00:38:23.000 to the mass flow rate multiplied by the
00:38:24.790 00:38:24.800 change in enthalpy between those two
00:38:27.070 00:38:27.080 values that is a condenser a boiler is
00:38:37.090 00:38:37.100 for example where we generate power
00:38:40.020 00:38:40.030 we've got water which is being pumped to
00:38:43.420 00:38:43.430 a high pressure and here we've got the
00:38:46.750 00:38:46.760 fluid and there's the gas okay and now
00:38:50.980 00:38:50.990 the fluid is vaporized from the fluid to
00:39:02.530 00:39:02.540 the gas
00:39:08.650 00:39:08.660 the kinds of a condenser it has been
00:39:11.520 00:39:11.530 rejected with a boiler we need to put in
00:39:17.410 00:39:17.420 the heat to vaporize it and again the
00:39:22.540 00:39:22.550 heat transfer rate would be equal to the
00:39:25.870 00:39:25.880 mass flow rate multiplied by H FG
00:39:46.220 00:39:46.230 okay the third type is the evaporate
00:39:49.110 00:39:49.120 that
00:39:56.640 00:39:56.650 evaporator the evaporator métiers
00:40:01.840 00:40:01.850 diagram we typically be in a vapour
00:40:06.940 00:40:06.950 compression cycle but what is important
00:40:11.530 00:40:11.540 is is that the heat transfer right is
00:40:20.110 00:40:20.120 now from this point here okay from a
00:40:23.980 00:40:23.990 mixing point in so the process again is
00:40:31.390 00:40:31.400 the Viper is the fluid vaporize and now
00:40:37.840 00:40:37.850 it is from m2g evaporator remember
00:40:43.870 00:40:43.880 usually we do not get everything as a
00:40:46.830 00:40:46.840 saturated fluid it goes through the
00:40:52.390 00:40:52.400 expansion valve and then the heat
00:40:55.810 00:40:55.820 transfer rate is equal to the mass flow
00:40:57.940 00:40:57.950 rate multiplied by a by H it's called in
00:41:02.530 00:41:02.540 G
00:41:06.870 00:41:06.880 and to make that possible again we need
00:41:12.520 00:41:12.530 some heat some temperature at a higher
00:41:15.730 00:41:15.740 temperature
00:41:21.140 00:41:21.150 okay there are two more types of heat
00:41:23.509 00:41:23.519 exchanges okay and it's going to take me
00:41:26.870 00:41:26.880 one minute to explain them both are
00:41:29.239 00:41:29.249 called the radiators but with different
00:41:31.549 00:41:31.559 meanings radiators okay the first one is
00:41:39.319 00:41:39.329 the type that you get into your car okay
00:41:43.489 00:41:43.499 lots of tubes with fins and usually a
00:41:48.769 00:41:48.779 fan here in the back through some ear if
00:41:53.210 00:41:53.220 you drive that cools the water which is
00:41:57.739 00:41:57.749 on the inside at a high pressure and so
00:42:01.579 00:42:01.589 that is called a radiator core radiator
00:42:03.849 00:42:03.859 then the other type of radiator is also
00:42:07.880 00:42:07.890 an heat exchanger but now it transfers
00:42:14.269 00:42:14.279 heat by radiation
00:42:23.289 00:42:23.299 my radiation transfers eat by radiation
00:42:32.049 00:42:32.059 so if that is the ambient temperature
00:42:34.880 00:42:34.890 and that is the surface temperature then
00:42:38.599 00:42:38.609 they don't have a good toilet on in the
00:42:40.190 00:42:40.200 textbook but my feeling would be if that
00:42:43.370 00:42:43.380 temperature difference is in the order
00:42:47.870 00:42:47.880 of about a hundred degrees Celsius maybe
00:42:50.270 00:42:50.280 even already at 50 or 80 degree Celsius
00:42:53.529 00:42:53.539 then there would be a significant amount
00:42:55.910 00:42:55.920 of heat transfer by radiation on me okay
00:43:03.079 00:43:03.089 ladies and gentlemen that is the basic
00:43:04.730 00:43:04.740 types of heat exchanges we didn't do any
00:43:06.920 00:43:06.930 theory today we'll start doing that with
00:43:09.440 00:43:09.450 the next lecture and they will also look
00:43:11.450 00:43:11.460 at some problem solving thank you very
00:43:14.000 00:43:14.010 much
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