# -*- coding: utf8 -*- from _future_ import division from math import log from sympy import symbols, integrate #Example: 8.4 ''' Consider Example 5.7, in which oxygen is heated from 300 to 1500 K. Calculate the work and heat transfer required to accom- plish this process''' #Variable Declaration: u1 = 87.94 #specific internal energy of R-12 at state 1 in kJ/kg u2 = 276.44 #specific internal energy of R-12 at state 2 in kJ/kg s1 = 0.3357 #specific entropy at state 1 in kJ/kg-K s2 = 1.2108 #specific entropy at state 2 in kJ/kg-K V = 0.001 #volume of saturated liquid in m**3 v1 = 0.000923 #specific volume in m**3/kg T = 20 #temperature of liquid in celsius #Calculations: m = V / v1 #mass of saturated liquid in kg Q12 = m * ( T + 273.15 ) * ( s2 - s1 ) #heat transfer in kJ to accomplish the process W12 = m * ( u1 - u2 ) + Q12 #work required to accomplish the process #Results print "Work required to accomplish the process: ", round ( W12, 1 ), 'KJ' print "Heat transfer: ", round ( Q12, 1 ), 'KJ' The piston now slowly expands, maintaining constant temperature to a final pressure of 400 kPa in a reversible process. # -*- coding: utf8 -*- from _future_ import division #Example: 8.2 ''' A cylinder/piston setup contains 1 L of saturated liquid refrigerant R-410a at 20◦C. Find the pressure after compression, before the heat rejection process, and determine the COP for the cycle.''' #Variable Declaration: Th = 60 #temperature at which heat is rejected from R-134a Tl = 0 #temperature at which heat is absorbed into the R-134a s1 = 1.7262 #specific entropy at 0 Celsius s3 = 1.2857 #specific entropy at 60 celsius s4 = s3 #process of state change from 3-4 is isentropic #Calculations: s2 = s1 #process of state change from 1-2 is isentropic P2 = 1400 + ( 1600 - 1400 ) * ( 1.7262 - 1.736 ) / ( 1.7135 - 1.736 ) #pressure after compression in kPa B = ( Th + 273 ) / ( Th - Tl ) #coefficient of performance of refrigerator #Results: print "Pressure after compression is P2: ", round ( P2, 1 ), 'KPa' print "Coefficient of performance of refrigerator: ", round ( B, 2 )
The heat is rejected from the R-134a at 60◦C and ends up as saturated liquid. Heat is absorbed into the R-134a at 0◦C, during which process it changes from a two-phase state to saturated vapor.
# -*- coding: utf8 -*- from _future_ import division #Example: 8.1 ''' Consider a Carnot-cycle heat pump with R-134a as the working fluid.
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