1 00:00:00,012 --> 00:00:04,067 Hello, Energy 101. We're talking about laws of nature 2 00:00:04,067 --> 00:00:09,516 controlling the energy conversion. And we're deep into the second law of 3 00:00:09,516 --> 00:00:13,798 thermodynamics, or the second law of energy conversion. 4 00:00:13,798 --> 00:00:19,672 We've talked about energy quality, which is really a result of the second law. 5 00:00:19,672 --> 00:00:26,328 But this is probably the most difficult aspect of this whole course energy 101 6 00:00:26,328 --> 00:00:32,967 but it is one that I feel feel strongly about that we have to talk about because 7 00:00:32,967 --> 00:00:38,745 it's it's the one people don't understand when they come to me about new 8 00:00:38,745 --> 00:00:44,822 technologies the processes they feel they have come up with That will solve our 9 00:00:44,822 --> 00:00:49,462 energy crisis because they don't understand it violates the second law of 10 00:00:49,462 --> 00:00:54,062 thermal dynamics most frequently. The first law a lot of time, most of us 11 00:00:54,062 --> 00:00:57,722 have some concept of that and that's fairly easy to grasp. 12 00:00:57,722 --> 00:01:02,857 The second law being a negative statement we have talked about is more difficult. 13 00:01:02,857 --> 00:01:07,527 Stay with me here and we will this is the last one on the laws of energy 14 00:01:07,527 --> 00:01:12,294 conservation, first and second law. [COUGH] But I want to give you a little 15 00:01:12,294 --> 00:01:17,305 bit of feel for those [COUGH] excuse me. I want to give you a little bit of feel 16 00:01:17,305 --> 00:01:22,776 for those, so that you'll know when I say What you can and can't do from the laws 17 00:01:22,776 --> 00:01:26,581 of nature you will understand where it's coming from. 18 00:01:26,581 --> 00:01:32,037 and of course this is the law of controlling the conversion of energy from 19 00:01:32,037 --> 00:01:36,599 input when we convert it to a different form on the at the output. 20 00:01:36,599 --> 00:01:41,771 And you've seen this before. we went through this example about energy 21 00:01:41,771 --> 00:01:46,795 quality, which is inherent in the second law that I'll, we would need to talk 22 00:01:46,795 --> 00:01:50,647 about again today. But just showing that example quickly, 23 00:01:50,647 --> 00:01:54,428 reviewing it. if we have waste heat or any heat that's 24 00:01:54,428 --> 00:01:57,772 available at 240 degrees Fahrenheit. Then 25 00:01:57,772 --> 00:02:03,632 the quality we can calculate of that thermal energy comes out to be between 26 00:02:03,632 --> 00:02:06,679 .29. That means it has a value per unit of 27 00:02:06,679 --> 00:02:13,445 energy of approximately less than 30% less than what work at that unit of work 28 00:02:13,445 --> 00:02:19,078 would have, or unit of electricity, or unit of potential energy, or unit of 29 00:02:19,078 --> 00:02:22,377 kinetic energy. All of what had a quality 1. 30 00:02:22,377 --> 00:02:28,176 So we're not going to pay as much for it. Because it's not only as lower value from 31 00:02:28,176 --> 00:02:32,491 the thermodynamic sense. That means it has lower economic value. 32 00:02:32,491 --> 00:02:37,052 It, it filters through the system. So that's the example that we had. 33 00:02:37,052 --> 00:02:41,722 And the second law, as I briefly put it up last time, tells us that the. 34 00:02:41,722 --> 00:02:48,285 Fraction of the thermal energy Q that can be converted to work has to be less than 35 00:02:48,285 --> 00:02:53,167 the quality of that work. So since the quality of 240 degree 36 00:02:53,167 --> 00:02:59,351 fahrenheit thermal energy is 29 percent that means that the fraction of the 37 00:02:59,351 --> 00:03:05,682 thermal energy produced by whatever is producing the 240 degree fahrenheit 38 00:03:05,682 --> 00:03:10,319 Thermal temperature that can be converted to work is less than 30%. 39 00:03:10,319 --> 00:03:14,775 Now, that's the ceiling. Notice, you can't get 29% out, because 40 00:03:14,775 --> 00:03:19,360 the real world has friction in it. We have temperature drops that, 41 00:03:19,360 --> 00:03:22,672 transferring in through heat exchangers, and. 42 00:03:22,672 --> 00:03:27,986 And and flued flow through pipe friction that we have to pump it that it's not 43 00:03:27,986 --> 00:03:31,381 reverseable. So what the second law does is put a 44 00:03:31,381 --> 00:03:36,602 ceiling on it it doesn't say that we can do that well, it says we can not do 45 00:03:36,602 --> 00:03:41,552 Better than that in the real world we actually cant do that well because in 46 00:03:41,552 --> 00:03:46,677 real world iriversablity we call it. So that's what the second law tells us, 47 00:03:46,677 --> 00:03:52,202 that with thermal energy is not of equal value to work and when will convert 48 00:03:52,202 --> 00:03:56,462 thermal energy to work, we cannot convert 100% of it. 49 00:03:56,462 --> 00:04:00,647 And that's what I'm showing graphically right here. 50 00:04:00,647 --> 00:04:07,022 So, here, we, we've got thermal energy at some temperature coming in. 51 00:04:07,022 --> 00:04:10,692 Where some quality over on the left hand side. 52 00:04:10,692 --> 00:04:15,052 And I show a theoretical process that upgrades that. 53 00:04:15,052 --> 00:04:19,173 Thermal energy, quality is...is the vertical scale here. 54 00:04:19,173 --> 00:04:22,554 The higher up we are, the higher the quality is. 55 00:04:22,554 --> 00:04:28,243 And the second law I've done an X through it, saying you cannot take that 1 unit of 56 00:04:28,243 --> 00:04:34,710 thermal energy And converted to 1 unit of energy with the quality of 1, like 57 00:04:34,710 --> 00:04:40,083 electricity or work. Now, and this is so many times I read it 58 00:04:40,083 --> 00:04:46,306 in...in the Press, or see it on the national news The fact that why are we 59 00:04:46,306 --> 00:04:49,652 wasting all of this energy at a power plant. 60 00:04:49,652 --> 00:04:55,667 Why aren't we using all of this heat, thermal energy that we're paying for, and 61 00:04:55,667 --> 00:04:59,039 coal and natural gas And nuclear thermal energy. 62 00:04:59,039 --> 00:05:03,927 Why are we taking that thermal energy, and only converting a fraction of it into 63 00:05:03,927 --> 00:05:08,772 electricity, and then throwing the west of the, of it away to the atmosphere or 64 00:05:08,772 --> 00:05:13,277 the rivers? Well, it's because the second law tells us we cannot do that. 65 00:05:13,277 --> 00:05:16,908 Why can't we do that? Why does gravity pull down? I don't know. 66 00:05:16,908 --> 00:05:19,450 But it's a hund-, we've known it for 150 years. 67 00:05:19,450 --> 00:05:23,120 When people say that. Well, they found a way around the second 68 00:05:23,120 --> 00:05:26,361 law of thermodynamics. And I tell them they got to go talk to 69 00:05:26,361 --> 00:05:29,577 somebody else. Because I firmly believe in the second 70 00:05:29,577 --> 00:05:31,952 law of thermodynamics. It served me well. 71 00:05:31,952 --> 00:05:37,276 And, and has used it to design many, many energy systems of all types, and new, new 72 00:05:37,276 --> 00:05:42,368 technologies, and it always works. It's worked for 150 years, and we don't 73 00:05:42,368 --> 00:05:47,232 expect to see that happening, like we don't expect to see the laws of gravity 74 00:05:47,232 --> 00:05:52,147 repealed. so that's a statement of the second law. 75 00:05:52,147 --> 00:05:59,379 and so but but so you say how do we get thermal energy to produce, converted to 76 00:05:59,379 --> 00:06:04,244 electricity. Well it what the second law does allow is 77 00:06:04,244 --> 00:06:09,623 upgrade Upgrading some of the thermal or heat energy while downgrading the 78 00:06:09,623 --> 00:06:13,242 remainder, which is exactly what a power plant does. 79 00:06:13,242 --> 00:06:18,512 So, here again, a similar diagram where the higher quality Is on the vertical 80 00:06:18,512 --> 00:06:22,389 scale here. And we have combustion energy or nuclear 81 00:06:22,389 --> 00:06:27,303 reaction from the uranium that produces thermal energy. 82 00:06:27,303 --> 00:06:32,119 And we put it into our power plant. I was taking an example here of 3 units 83 00:06:32,119 --> 00:06:36,542 of energy, or 3 BTUs, 3 kilojoules. Take whatever unit you want. 84 00:06:36,542 --> 00:06:39,730 taking BTUs here, could be a million BTUs. 85 00:06:39,730 --> 00:06:44,487 And we put it through a power system. This is a coal fired power plant. 86 00:06:44,487 --> 00:06:49,548 It's a natural gas fired power plant. It's a nuclear power plant, that, is 87 00:06:49,548 --> 00:06:53,132 taking that thermal energy. We do produce about 1. 88 00:06:53,132 --> 00:06:57,937 Unit of electricity out of three units of thermal energy to electricity what 89 00:06:57,937 --> 00:07:01,837 happens to the rest of it? The rest of it we have to downgrade. 90 00:07:01,837 --> 00:07:06,602 Now we can't get rid of the energy we can't destroy energy so we have to throw 91 00:07:06,602 --> 00:07:11,132 it away and we throw it away to the river generally or to the atmosphere. 92 00:07:11,132 --> 00:07:16,012 More and more we are throwing it away to the air than the river because beating 93 00:07:16,012 --> 00:07:22,216 the rivers up Damages the the biological growth in the river and kills fish etc. 94 00:07:22,216 --> 00:07:27,514 It has a zero quality so people say why don't we utilize this energy the same 95 00:07:27,514 --> 00:07:33,078 reason we don't utilize all the thermal energy in the atmosphere because it has 96 00:07:33,078 --> 00:07:37,586 no quality, it has no value. But this is what the second law does 97 00:07:37,586 --> 00:07:43,154 allow That's the way if we downgrade some we can upgrade others. 98 00:07:43,154 --> 00:07:49,915 And and the limit of what percent we can upgrade is the quality of this energy. 99 00:07:49,915 --> 00:07:57,147 Before if this was 240 degrees fharenheit We could upgrade theoretically as much as 100 00:07:57,147 --> 00:08:01,888 29 percent of that, and throw away the other 71 percent. 101 00:08:01,888 --> 00:08:08,179 But that's the limit that the second law places on us, and the real world Pr- 102 00:08:08,179 --> 00:08:10,171 processes. We can't do that well. 103 00:08:10,171 --> 00:08:14,269 We try to approach it, and we spend more money on, on the power plants. 104 00:08:14,269 --> 00:08:18,851 We get, we can get a little closer to it. But that's what the second law of 105 00:08:18,851 --> 00:08:22,159 thermodynamics does. And it, I, I've talked about power 106 00:08:22,159 --> 00:08:25,058 plants. But it's also true for auto engines, 'cuz 107 00:08:25,058 --> 00:08:29,792 they take in combustion heat. And produce work to drive our rear 108 00:08:29,792 --> 00:08:33,692 wheels. Diesel engines fall into this category, 109 00:08:33,692 --> 00:08:37,087 and power plants. All 3 of those kinds of energy 110 00:08:37,087 --> 00:08:42,477 conversions systems, convert thermal energy to work or electricity. 111 00:08:42,477 --> 00:08:48,052 And the second law limits what fraction of that thermal energy we can convert. 112 00:08:48,052 --> 00:08:52,507 That's just the way life is. And may not be the way we like it. 113 00:08:52,507 --> 00:08:55,771 But that's the way the natural laws have worked out. 114 00:08:55,771 --> 00:08:58,762 And that that's what's been given us. So, thank you. 115 00:08:58,762 --> 00:09:03,453 That's noticed that, talked about the second law of thermodynamics. 116 00:09:03,453 --> 00:09:06,432 And never talked about something called enthalpy. 117 00:09:06,432 --> 00:09:11,790 because enthropy is a very abstract quantity and, and property and you don't 118 00:09:11,790 --> 00:09:16,753 need to know anything about it unless you get deep into the theoretical 119 00:09:16,753 --> 00:09:22,259 calculations of thermodynamics that we don't need to deal with in this course. 120 00:09:22,259 --> 00:09:22,889 Thank you.