Refrigeration Cycle Tutorial

Refrigeration Cycle Tutorial - REFRIGERATION CYCLES Carnot...

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56 REFRIGERATION CYCLES Carnot Cycle We start discussing the well-known Carnot cycle in its refrigeration mode. Figure 1: Carnot Cycle In this cycle we define the coefficient of performance as follows: LL HL qT COP wT T == (1) Which comes from the fact that wq q = (first law) and s = Δ , HH s (second law). Note that w is also given by the area of the rectangle. Temperature differences make the COP vary. For example, the next figure shows how COP varies with T L ( T H is ambient in this case) and the temperature difference in exchangers.
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57 Figure 2: COP changes with heat exchanger temperature approximation and T L (T H =ambient) We now turn our attention to a real one stage refrigeration cycle, depicted in the next figure. Figure 3: Typical one-stage dry refrigeration Cycle We notice that: - To be able to achieve the best match possible with the rectangular shape it is necessary to operate inside the two phase region. - Compression is in this example performed outside the two phase region. Creating a “horn”, which is not thermodynamically advisable, is mechanically better. For this reason, this cycle is called “dry” cycle. A “wet” cycle is shown in the next figure.
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Refrigeration Cycle Tutorial - REFRIGERATION CYCLES Carnot...

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