Chapter 0101 PDF

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CHAPTER 1 1. A reversed Carnot cycle is used for refrigeration and rejects 1,000 kW of heat at 340 K while receiving heat at 250 K. Determine (a) the COP, (b) the power required, and (c) the refrigerating effect. Solution: Th = 340 K , Tc = 250 K QR = 1000 kW Tc 250 (a) COP = = = 2.778 Th − Tc 340 −...

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CHAPTER 1

1. A reversed Carnot cycle is used for refrigeration and rejects 1,000 kW of heat at 340 K while receiving heat at 250 K. Determine (a) the COP, (b) the power required, and (c) the refrigerating effect. Solution:

Th = 340 K , Tc = 250 K Q& R = 1000 kW Tc 250 = = 2.778 Th − Tc 340 − 250 Q& T  250  (b) W& = Q& R − Q& A = Q& R − R c = (1,000)1 −  = 264.7 kW Th  340  (c) Q& A = Q& R − W& = 1000 − 264.7 = 735.3 kW

(a) COP =

2. A reversed Carnot cycle has a refrigerating COP of 4. (a) What is the ratio Tmax Tmin ? (b) If the work input is 6 kW, what will be the maximum refrigerating effect, kJ/min and tons. Solution:

(a) COP =

Tmin Tmax − Tmin

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CHAPTER 1 T −T T 1 = max min = max − 1 COP Tmin Tmin Tmax 1 1 = + 1 = + 1 = 1.25 Tmin COP 4 (b) QA = W (COP ) = (6 )(4) = 24 kW in kJ/min, QA = (24)(60) = 1440 kJ min in Tons 24 QA = = 6.826 TR 3.516

3. A reversed Carnot engine removes 40,000 kW from a heat sink. The temperature of the heat sink is 260 K and the temperature of the heat reservoir is 320 K. Determine the power required of the engine. Solution:

QA = 40,000 kW Tmin = 260 K Tmax = 320 K (T − T )Q (320 − 260)(40,000) Q W = A = max min A = = 9230.8 kW COP Tmin 260

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