I would have to question the professor's motives, or at least consider what the professor has emphasized in lectures leading up to that question. I would also look at the rest of the test to see if other questions lead towards his emphasises.Tim Booth wrote:All I'm saying, if you think the engine is 5% efficiency, on an 85 watt heat source there should be about 80 watts of that arriving at the "sink" (according to the Carnot formula) If that had been a test question for a thermo exam': "If Qh is 85 Joules and Qc is 1.32 Joules what is the efficiency of the engine" what would the correct answer be?
A. 5%
B. 98.5%
Is he stressing Carnot? They all are. Is he talking Earth based normal materials and air engines? Atmospheric pressures? Or, exotic material and pressures and Pluto based engines and associated local ambient temperatures? Is he emphasizing good laboratory investigation?
As a non-multiple guess test question, I would begin by telling what I do know:
1: n=(Qh-Ql)/Qh=(85-1.32)/85•100
approximately equals 98.447%
2: Carnot Therom 0.98447 = (Th-Tl)/Th
If:
Th = 1000 K and Tc = 15 K
n = (1000-15)/1000 = about 0.985
It would be difficult to find a workable gas at that low a temperature. Helium might be an only choice. Even it might not work.
Or if 50 K for use of helium or hydrogen and 3333K:
n = (3333-50)/3333 = about .985
It might be difficult finding a material that would work at that high a temperature 3333 K and not melt. It might be too cold for even hydrogen and helium, especially if at a higher pressure. And nitrogen liquefies at 77 K and one atmosphere.
It would get progressively worse, hotter, as Tc is brought up to a workable temperature.
As a PhD level question, this would then need to go on to ponder if the the experimental results were flawed, and demand a relook with better instrumentation. It would be a question of accepting a very very extraordinary outcome with very limited single point data, or getting more data.
In other words, you have not verified that the steamer puts into your engine 85 Watts. It is only wishful thinking from the label on the bottom. A label that is required to show only absolute maximum for safety sake, and is probably conservative, or even boastful. You haven't verified that it even puts out 85 Watts of steam, let alone that all the heat from that steam enters your engine. You haven't even verified that the steamer absorbed 85 Watts from the power line. You haven't measured the temperature of the hot plate, which would potentially give some indication of how much heat maximum the amount of gas in the engine could possibly absorb per cycle assuming it gets cooled fully to ambient each cycle. A very bad set of assumptions. I don't remember if you took any Rpm readings, but that also would be needed. All those things must agree with your one claim of 85 Watts before even talking of the Qc rejected. Furthermore, the Qc rejected, as calculated, is a minimum amount, and it doesn't account for the heat lost by the cold plate being warmer than ambient. So it will definitely be a higher number. Lastly how much power output from even a simple homemade Dynamometer would be very important.
It really is very difficult to do good science because it requires a lot of cross checks, and mathematical theory. Things a good scientist is trained for in a good classroom and lab, or by good self training. Good science is not merely reading a thermometer, uncalibrated or even calibrated. It so much more. And even then can be very bad science. I'm thinking Ponds and Freshman, cold fusion.
Please be careful, but please cary on.
What I find most interesting in that experiment and data is that the cold plate warmed up, got hotter. That is interesting, not so much that it happened or how much, about par for tiny power output, but that you dismiss it from being a direct flaw in your quest to disprove 200 years of Thermodynamics, and you go on Bashing great men in many threads. Very entertaining though, thanks.
If you stuck to, why does a LTDS engine idle faster with the cold plate insulated, it would be great. You would, of course, need to fit it in with this data showing a significant increase in cold plate temperature.