Write down the chemical formula of R -134a. What does ‘a’ signify in the nomenclature? Explain the effect of critical temperature and critical pressure of refrigerant on the COP of the cycle. A straight-charged Thermostatic Expansion Valve (TEV) is designed to operate at an evaporator temperature of 70C with a degree of superheat of 50C. R – 134a is the refrigerant used in the refrigeration system as well as the bulb. Find:
i. The required spring pressure at the design condition,
ii. Assuming the spring pressure to remain constant, find the degree of superheat, if the same TEV operates at an evaporator temperature of – 230C.
The saturation temperature and corresponding pressure of R-134a are given in the Table below:
|
Tsat, 0C
|
–23
|
–13
|
–12
|
–11
|
|
Psat (kPa)
|
116.39
|
177.92
|
185.24
|
192.8
|
|
Tsat, 0C
|
2
|
7
|
12
|
13
|
|
Psat (kPa)
|
314.62
|
374.63
|
443.01
|
457.76
|