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Diffstat (limited to '572/CH6/EX6.8/c6_8.sce')
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diff --git a/572/CH6/EX6.8/c6_8.sce b/572/CH6/EX6.8/c6_8.sce new file mode 100755 index 000000000..a723da75b --- /dev/null +++ b/572/CH6/EX6.8/c6_8.sce @@ -0,0 +1,84 @@ +//(6.8) Components of a heat pump for supplying heated air to a dwelling are shown in the schematic below. At steady state, Refrigerant 22 enters the compressor at -5C, 3.5 bar and is compressed adiabatically to 75C, 14 bar. From the compressor, the refrigerant passes through the condenser, where it condenses to liquid at 28C, 14 bar. The refrigerant then expands through a throttling valve to 3.5 bar. The states of the refrigerant are shown on the accompanying T–s diagram. Return air from the dwelling enters the condenser at 20C, 1 bar with a volumetric flow rate of 0.42 m3/s and exits at 50C with a negligible change in pressure. Using the ideal gas model for the air and neglecting kinetic and potential energy effects, (a) determine the rates of entropy production, in kW/K, for control volumes enclosing the condenser, compressor, and expansion valve, respectively. (b) Discuss the sources of irreversibility in the components considered in part (a).
+
+
+//solution
+
+
+//variable initialization
+P1 = 3.5 //pressure of refrigerant entering the compressor in bars
+T1 = 268 //temperature of refrigerant entering the compressor in kelvin
+P2 = 14 //pressure of refrigerant entering the condenser in bars
+T2 = 348 //temperature of refrigerant entering the condenser in kelvin
+P3 = 14 //pressure of refrigerant exiting the condenser in bars
+T3 = 301 //temperature of refrigerant exiting the condenser in kelvin
+P4 = 3.5 //pressure of refrigerant after passing through expansion valve in bars
+P5 = 1 //pressure of indoor return air entering the condenser in bars
+T5 = 293 //temperature of indoor return air entering the condenser in kelvin
+AV5 = .42 //volumetric flow rate of indoor return air entering the condenser in m^3/s
+P6 = 1 //pressure of return air exiting the condenser in bar
+T6 = 323 //temperature of return air exiting the condenser in kelvin
+
+//part(a)
+
+//from table A-9
+s1 = .9572 //in kj/kg.k
+//interpolating in table A-9
+s2 = .98225 //in kj/kg.k
+h2 = 294.17 //in kj/kg
+//from table A-7
+s3 = .2936 //in kj/kg.k
+h3 = 79.05 //in kj/kg
+
+h4 = h3 //since expansion through valve is throttling process
+
+//from table A-8
+hf4 = 33.09 //in kj/kg
+hg4 = 246 //in kj/kg
+sf4 = .1328 //in kj/kg.k
+sg4 = .9431 //in kj/kg.k
+
+x4 = (h4-hf4)/(hg4-hf4) //quality at state 4
+s4 = sf4 + x4*(sg4-sf4) //specific entropy at state 4
+
+/////condenser!!
+v5 = ((8314/28.97)*T5)/(P5*10^5) //specific volume at state 5
+mairdot = AV5/v5
+cp = 1.005 //in kj/kg.k
+h6 = cp*T6
+h5 = cp*T5
+mrefdot = mairdot*(h6-h5)/(h2-h3)
+deltaS65 = cp*log(T6/T5)-(8.314/28.97)*log(P6/P5) //change in specific entropy
+sigmacond = (mrefdot*(s3-s2)) + (mairdot*(deltaS65))
+
+/////compressor!!
+sigmacomp = mrefdot*(s2-s1)
+
+
+////valve!!
+sigmavalve = mrefdot *(s4-s3)
+
+printf('\nthe rates of entropy production, in kW/K, for control volume enclosing the condenser is \n\t R1 = %e ',sigmacond)
+printf('\nthe rates of entropy production, in kW/K, for control volume enclosing the compressor is \n\t R2 = %e ',sigmacomp)
+printf('\nthe rates of entropy production, in kW/K, for control volume enclosing the expansion valve is \n\t R3 = %e ',sigmavalve)
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