00:00:01.960 --> 00:00:03.000 - [Instructor] Welcome to the lesson 00:00:03.000 --> 00:00:06.000 on plate heat exchanger plates. 00:00:06.000 --> 00:00:07.350 I'm quite excited to do this lesson 00:00:07.350 --> 00:00:08.560 because I find the plate 00:00:08.560 --> 00:00:12.030 of a plate heat exchanger very interesting. 00:00:12.030 --> 00:00:13.430 And hopefully by the end of lesson 00:00:13.430 --> 00:00:15.483 you will also feel the same. 00:00:16.407 --> 00:00:17.820 You can see we've got three plates. 00:00:17.820 --> 00:00:19.500 We've got an A plate on the left, 00:00:19.500 --> 00:00:20.910 a B plate in the middle, 00:00:20.910 --> 00:00:22.870 and an End plate on the right. 00:00:22.870 --> 00:00:25.070 This could also be a our start plate 00:00:25.070 --> 00:00:27.800 because the design is the same. 00:00:27.800 --> 00:00:29.000 So let's imagine for a moment 00:00:29.000 --> 00:00:31.410 the A plate is a Hot plate, 00:00:31.410 --> 00:00:33.380 or is for our hot fluid. 00:00:33.380 --> 00:00:35.380 The B plate is for our cold fluid, 00:00:35.380 --> 00:00:36.310 and this one on the end, 00:00:36.310 --> 00:00:39.830 would be both our start and end plates. 00:00:39.830 --> 00:00:42.830 The end plate usually has a gasket 00:00:42.830 --> 00:00:46.070 on the front side and the back, 00:00:46.070 --> 00:00:47.340 on this one it doesn't but it 00:00:47.340 --> 00:00:49.510 should also have one here. 00:00:49.510 --> 00:00:53.480 Where as the other two plates, the A plate and B plate, 00:00:53.480 --> 00:00:55.920 these hot and cold fluid plates, 00:00:55.920 --> 00:00:59.030 they will have a gasket only on one side. 00:00:59.030 --> 00:01:02.580 That's because the gasket on the back of each plate, 00:01:02.580 --> 00:01:05.383 is gonna press up into this area, 00:01:06.920 --> 00:01:09.540 and into these channels around here. 00:01:09.540 --> 00:01:11.040 So there's always one plate, 00:01:11.040 --> 00:01:12.640 that presses onto the back of another, 00:01:12.640 --> 00:01:14.672 that does the ceiling. 00:01:14.672 --> 00:01:17.240 If we spin around here, we can see we got 00:01:17.240 --> 00:01:20.690 our alternating gasket pattern again, 00:01:20.690 --> 00:01:22.950 and this allows us to control the direction 00:01:22.950 --> 00:01:26.150 of the fluid through the heat exchanger. 00:01:26.150 --> 00:01:29.860 So why are the plates so interesting? 00:01:29.860 --> 00:01:33.900 We'll let's analyze them first visually. 00:01:33.900 --> 00:01:36.550 All heat exchangers have a large 00:01:36.550 --> 00:01:39.060 cross-sectional area, 00:01:39.060 --> 00:01:41.780 in order that the two fluids can have 00:01:41.780 --> 00:01:45.750 a large thermal contact area. 00:01:45.750 --> 00:01:48.000 So you're never gonna get a heat exchanger 00:01:48.000 --> 00:01:50.540 that has a small thermal contact area, 00:01:50.540 --> 00:01:52.140 because that doesn't make sense. 00:01:52.140 --> 00:01:55.410 We wanna maximize the thermal contact area 00:01:55.410 --> 00:01:58.800 between whatever is flowing through the heat exchanger. 00:01:58.800 --> 00:02:01.540 This ensures we get good heat transfer 00:02:01.540 --> 00:02:02.933 between the fluids. 00:02:04.200 --> 00:02:07.870 So each of our plates has a large cross-sectional area, 00:02:07.870 --> 00:02:10.230 and because of this large 00:02:10.230 --> 00:02:12.940 and because we have a hot fluid on one side, 00:02:12.940 --> 00:02:14.470 for example here, 00:02:14.470 --> 00:02:17.660 and a cold fluid on the backside, 00:02:17.660 --> 00:02:22.660 for example here, we're gonna get very good heat transfer. 00:02:23.510 --> 00:02:25.180 In addition to that you'll notice that 00:02:25.180 --> 00:02:29.160 each of the plates is very thin, 00:02:29.160 --> 00:02:33.840 and this also ensures that we keep the fluids separated, 00:02:33.840 --> 00:02:36.670 but only by as much as needed, 00:02:36.670 --> 00:02:40.840 because the plate itself forms a barrier 00:02:40.840 --> 00:02:42.510 between the two fluids, 00:02:42.510 --> 00:02:45.350 and hinders heat transfer between them. 00:02:45.350 --> 00:02:49.270 So we wanna make the plate as thin as possible, 00:02:49.270 --> 00:02:53.230 so that we can get as much heat transfer as possible. 00:02:53.230 --> 00:02:57.090 In order to build a very thin plate, 00:02:57.090 --> 00:03:00.260 we're gonna have to use corrugations. 00:03:00.260 --> 00:03:04.070 Now corrugations are these weird squiggly lines 00:03:04.070 --> 00:03:05.962 that are on each other plates. 00:03:05.962 --> 00:03:08.590 You can see them in this section here. 00:03:08.590 --> 00:03:11.620 This is what we referred to as a herringbone pattern. 00:03:11.620 --> 00:03:15.650 You'll often see herringbone patterns on gears. 00:03:15.650 --> 00:03:18.350 Now this herringbone pattern that forms a corrugation, 00:03:19.400 --> 00:03:23.310 is used to stiffen the thin plates. 00:03:23.310 --> 00:03:25.430 It allows us to produce a thinner plate, 00:03:25.430 --> 00:03:29.113 then if we were using simply a flat-rolled plate. 00:03:29.970 --> 00:03:31.670 The stiffness is needed to give 00:03:31.670 --> 00:03:34.318 mechanical strength to the plate, 00:03:34.318 --> 00:03:38.674 but the corrugations also serve other purposes. 00:03:38.674 --> 00:03:39.860 If you have a look you can see 00:03:39.860 --> 00:03:42.600 that we have this weird squiggly pattern, 00:03:42.600 --> 00:03:46.230 and that's going to interrupt the flow of the fluid 00:03:46.230 --> 00:03:49.110 as it passes over each other plates, 00:03:49.110 --> 00:03:52.470 this creates a very turbulent flow. 00:03:52.470 --> 00:03:55.953 The turbulent flow increases the heat transfer rate. 00:03:56.870 --> 00:03:59.010 Not only that but the turbulent flow 00:03:59.010 --> 00:04:01.200 prevents depositS building up on 00:04:01.200 --> 00:04:02.560 the plate's surfaces. 00:04:02.560 --> 00:04:05.140 So the turbulent flow helps to keep 00:04:05.140 --> 00:04:06.753 the plates clean. 00:04:07.650 --> 00:04:10.490 If the plates get dirty, then we're actually going to 00:04:10.490 --> 00:04:15.490 form a barrier between the plates and the fluids. 00:04:15.830 --> 00:04:18.770 Let's imagine for a moment that we have some deposits 00:04:18.770 --> 00:04:21.173 in our hot water circuit. 00:04:21.173 --> 00:04:23.610 And let's imagine that these deposits build up 00:04:23.610 --> 00:04:26.420 as a thin layer spread all across 00:04:26.420 --> 00:04:30.130 these herringbone pattern, so all across the corrugations, 00:04:30.130 --> 00:04:33.720 and they're gonna form a insulator. 00:04:33.720 --> 00:04:36.570 Now the insulator is not gonna allow heat 00:04:36.570 --> 00:04:39.130 to transfer through it very well, 00:04:39.130 --> 00:04:42.030 and this means we're gonna get a corresponding drop 00:04:42.030 --> 00:04:43.670 in the heat transfer rate, 00:04:43.670 --> 00:04:46.100 of our plate heat exchanger. 00:04:46.100 --> 00:04:48.400 If we get a drop in the heat transfer rate, 00:04:48.400 --> 00:04:50.840 this is gonna express itself when we look 00:04:50.840 --> 00:04:54.460 at the temperature in and out of the heat exchanger. 00:04:54.460 --> 00:04:56.823 We call this sometimes the Delta T. 00:04:58.000 --> 00:05:00.900 So normally perhaps we get a temperature difference, 00:05:00.900 --> 00:05:02.650 between the inlet and the outlet 00:05:02.650 --> 00:05:06.190 of say 10 degrees, but once we have 00:05:06.190 --> 00:05:08.750 these deposits forming on the plates 00:05:08.750 --> 00:05:11.560 maybe we only get a drop in temperature, 00:05:11.560 --> 00:05:15.010 or a Delta T of about eight degrees, 00:05:15.010 --> 00:05:16.530 and as this problem gets worse 00:05:16.530 --> 00:05:19.810 the Delta T is gonna reduce, and reduce, and reduce 00:05:19.810 --> 00:05:22.400 until we get an almost no heat exchange 00:05:22.400 --> 00:05:24.130 between the fluids at all. 00:05:24.130 --> 00:05:27.373 So the corrugations help to prevent this occurring. 00:05:28.320 --> 00:05:31.480 Notice that each of the plates is manufactured 00:05:31.480 --> 00:05:34.440 from some sort of metal or alloy. 00:05:34.440 --> 00:05:37.610 The material selected is gonna be a material chosen 00:05:37.610 --> 00:05:40.580 for its thermal conductivity, 00:05:40.580 --> 00:05:43.233 not just based upon its mechanical strength. 00:05:44.120 --> 00:05:47.490 We wanna allow heat to transfer through the plates, 00:05:47.490 --> 00:05:50.080 almost unhindered, because this will give us 00:05:50.080 --> 00:05:51.933 the maximum heat transfer rate. 00:05:52.820 --> 00:05:56.600 So material selection of the plates is very important. 00:05:56.600 --> 00:05:59.900 Another interesting design consideration though is, 00:05:59.900 --> 00:06:02.570 how we gonna use these plates? 00:06:02.570 --> 00:06:07.280 For what system do they need to be corrosive resistant? 00:06:07.280 --> 00:06:10.200 Do they need to be erosion resistant? 00:06:10.200 --> 00:06:13.030 What system are they gonna be used in? 00:06:13.030 --> 00:06:14.920 I used to work with plate heat exchangers 00:06:14.920 --> 00:06:16.970 that we used for sea water systems, 00:06:16.970 --> 00:06:20.490 and it was not unusual to have titanium plates. 00:06:20.490 --> 00:06:24.580 Because they were very, very good for sea water systems. 00:06:24.580 --> 00:06:27.230 They would resist corrosion. 00:06:27.230 --> 00:06:29.730 Anyone who's ever worked with seawater and metal, 00:06:29.730 --> 00:06:32.770 or alloys before will know that seawater 00:06:32.770 --> 00:06:35.760 eats away at metal quite readily, 00:06:35.760 --> 00:06:38.730 and you'll often choose copper-based alloys, 00:06:38.730 --> 00:06:41.480 such as brass or bronze, in order that the metal 00:06:41.480 --> 00:06:45.390 can resist the corrosive effects of the seawater. 00:06:45.390 --> 00:06:47.200 Titanium itself is an alloy, 00:06:47.200 --> 00:06:50.230 quite an expensive one, but because it naturally builds up 00:06:50.230 --> 00:06:53.750 an oxide layer on the alloy surface, 00:06:53.750 --> 00:06:57.950 it's almost impervious to corrosion from seawater. 00:06:57.950 --> 00:07:01.440 So it's an ideal material for a heat exchanger 00:07:01.440 --> 00:07:03.573 that's gonna be exposed to seawater. 00:07:04.640 --> 00:07:06.620 So although the plates look simple, 00:07:06.620 --> 00:07:09.890 they've actually got a ton of engineering design features. 00:07:09.890 --> 00:07:13.800 To recap, they've got a 00:07:13.800 --> 00:07:15.740 to promote heat transfer. 00:07:15.740 --> 00:07:18.880 They're very thin, again, this promotes the transfer. 00:07:18.880 --> 00:07:21.560 The material selected is gonna have 00:07:21.560 --> 00:07:24.660 high thermal conductivity, which further increases 00:07:24.660 --> 00:07:26.700 the heat-transfer rate. 00:07:26.700 --> 00:07:29.980 The corrugations allow us to manufacture 00:07:29.980 --> 00:07:34.660 a thinner plate, whilst also promoting turbulent flow, 00:07:34.660 --> 00:07:37.853 and preventing deposits forming on the plate surfaces. 00:07:38.690 --> 00:07:41.440 Because the plates are so thin, 00:07:41.440 --> 00:07:45.770 we can pack a lot of them together to form a plate stack, 00:07:45.770 --> 00:07:48.840 and we're gonna get a very large cooling capacity, 00:07:48.840 --> 00:07:51.440 despite the fact that the plate heat exchanger itself 00:07:51.440 --> 00:07:53.973 is gonna be very compact and small. 00:07:54.810 --> 00:07:57.160 Compared to other types of heat exchanger, 00:07:57.160 --> 00:08:00.480 the plate heat exchanger has a very high transfer rate, 00:08:00.480 --> 00:08:01.993 compared to its size. 00:08:02.870 --> 00:08:05.820 So now we've learnt a little bit about plates. 00:08:05.820 --> 00:08:07.250 Let's have a look at the gaskets 00:08:07.250 --> 00:08:10.323 which are also not quite as simple as they appear.
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