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Q. I am a recently-retired rocket-propellant scientist. A friend of mine believes he has found a way of adding heat back to a Carnot Cycle heat engine so as to increase its efficiency above that predicted by the Second Law of Thermodynamics. Could you please give me some pointers so that I will be able to either prove him right or prove him wrong.
Q. I have a heat transfer problem, which was raised by a group of students. The problem is concerned with the design of a cooling reservoir that is part of their final year project. Basically, they asked me how to calculate the temperature at time, t, of the water in a reservoir. The reservoir receives a constant water supply, say, 100 m^3/hour at a temperature of, say, 45 C. The reservoir has an initial volume of water, for example, 100 m^3 at a temperature, say 10 C. If we assume that the reservoir has a size of 1m x 30m x 30m (water exposed area is 900 m^2), about 8 hours are required to fill the reservoir and then the excess of water will be over flown. The problem is how to estimate the water temperature, Tt, at a time, t. In other words, to check the time required for the water in the reservoir, to cool down to the ambient temperature (8 C). I would be very grateful if you can help me with this problem. Kind regards.
Q. My classmates and I have heard that you have a special interest in the concept of exergy in thermodynamics. As it is we find the sign convention for heat and work quite confusing, but the situation gets even more complicated in exergy analysis. Can you please let us have your views on this matter.
Q. An acquaintance of mine is fascinated by a company that has made an astonishing discovery: a technology that can provide a free and continuous supply of energy from nothing. However, my acquaintance has been disappointed at the slow progress of the company, so far, in validating the principle of the technology. My acquaintance accepts that validation is a time-consuming process, but they are anxious that the benefits of the technology should be realised as quickly as possible. This technology will eliminate the need for batteries in mobile devices and for fuel in vehicles, aircraft and spacecraft. It will also replace traditional power plants, eliminate pollution from burning fossil fuels and solve the problem of global warming. There will be no further need to mine coal or extract oil or natural gas. There will be no further need to exploit nuclear power or renewable energy sources. My acquaintance is not perturbed by the fact that this technology is highly controvesial and appears to violate the principle of conservation of energy: they are aware that many previous discoveries that have upturned contemporary scientific understanding were vehemently rejected by the establishment at the time. Neither is my acquaintance unduly perturbed that the company seems to have incurred increasing losses over a number of years as it has sought to validate the technology.
I know that you are a distinguished scientist and engineer and I realise that you may have doubts about the validity of the technology that has fascinated my acquaintance. I too have such doubts, although I am not an expert. However, I would ask you to please consider giving a hypothetical respose to my question on the premise that free-constant-energy technology is valid and implementable. My acquaintance has considerable means and, I suspect or fear, would perhaps like to use their influence or even, conceivably, provide further investment, in order to speed up the process of validating the technology so that the benefits can be realised as quickly as possible. My acquaintance has a philanthropic disposition and is not in need of increasing their personal wealth. However, they are anxious that mankind should benefit from free-constant-energy technology as soon as possible. How would you advise my acquaintance to proceed?
Q. I need your help with a question as follows:
Two reversible heat engines operate in series between a source at 527°C and sink at 17°C. Assuming that each engine operates on the Carnot cycle, if the engines have equal efficiencies and the first rejects 400 kJ to the second what is:
1. the temperature at which the heat is supplied to the second engine?
2. the heat taken from the source?
3. the work done by each engine?
I would welcome any pointers you can offer.
© Jim McGovern, 2001 – 2009
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