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"source": [
"# Chapter 18 - Refrigeration"
]
},
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"metadata": {},
"source": [
"## Example 1: pg 612"
]
},
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"text": [
"Example 18.1\n",
" (a) The coefficient of performance of the refrigerator is = 4.49\n",
" (b) The mass flow of refrigerant/h is (kg) = 166.94\n",
" (c) The mass flow of water required is (kg/h) = 579.74\n",
"The answer is a bit different due to rounding off error in textbook\n"
]
}
],
"source": [
"#pg 612\n",
"print('Example 18.1');\n",
"\n",
"# aim : To determine\n",
"# (a) the coefficient of performance\n",
"# (b) the mass flow of the refrigerant\n",
"# (c) the cooling water required by the condenser\n",
"import math\n",
"from math import log\n",
"# given values\n",
"P1 = 462.47;# pressure limit, [kN/m**2]\n",
"P3 = 1785.90;# pressure limit, [kN/m**2]\n",
"T2 = 273.+59;# entering saturation temperature, [K]\n",
"T5 = 273.+32;# exit temperature of condenser, [K]\n",
"d = 75*10**-3;# bore, [m]\n",
"L = d;# stroke, [m]\n",
"N = 8;# engine speed, [rev/s]\n",
"VE = .8;# olumetric efficiency\n",
"cpL = 1.32;# heat capacity of liquid, [kJ/kg K]\n",
"c = 4.187;# heat capacity of water, [kj/kg K]\n",
"\n",
"# solution\n",
"# from given table\n",
"# at P1\n",
"h1 = 231.4;# specific enthalpy, [kJ/kg]\n",
"s1 = .8614;# specific entropy,[ kJ/kg K\n",
"v1 = .04573;# specific volume, [m**3/kg]\n",
"\n",
"# at P3\n",
"h3 = 246.4;# specific enthalpy, [kJ/kg]\n",
"s3 = .8093;# specific entropy,[ kJ/kg K\n",
"v3 = .04573;# specific volume, [m**3/kg]\n",
"T3= 273+40;# saturation temperature, [K]\n",
"h4 = 99.27;# specific enthalpy, [kJ/kg]\n",
"# (a)\n",
"s2 = s1;# specific entropy, [kJ/kg k]\n",
"# using s2=s3+cpv*log(T2/T3)\n",
"cpv = (s2-s3)/log(T2/T3);# heat capacity, [kj/kg k]\n",
"\n",
"# from Fig.18.8\n",
"T4 = T3;\n",
"h2 = h3+cpv*(T2-T3);# specific enthalpy, [kJ/kg]\n",
"h5 = h4-cpL*(T4-T5);# specific enthalpy, [kJ/kg]\n",
"h6 = h5;\n",
"COP = (h1-h6)/(h2-h1);# coefficient of performance\n",
"print ' (a) The coefficient of performance of the refrigerator is = ',round(COP,2)\n",
"\n",
"# (b)\n",
"SV = math.pi/4*d**2*L;# swept volume of compressor/rev, [m**3]\n",
"ESV = SV*VE*N*3600;# effective swept volume/h, [m**3]\n",
"m = ESV/v1;# mass flow of refrigerant/h,[kg]\n",
"print ' (b) The mass flow of refrigerant/h is (kg) = ',round(m,2)\n",
"\n",
"# (c)\n",
"dT = 12;# temperature limit, [C]\n",
"Q = m*(h2-h5);# heat transfer in condenser/h, [kJ]\n",
"# using Q=m_dot*c*dT, so\n",
"m_dot = Q/(c*dT);# mass flow of water required, [kg/h]\n",
"print ' (c) The mass flow of water required is (kg/h) = ',round(m_dot,2)\n",
"\n",
"print 'The answer is a bit different due to rounding off error in textbook'\n",
"# End\n"
]
},
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"metadata": {},
"source": [
"## Example 2: pg 614"
]
},
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"text": [
"Example 18.2\n",
" (a) The mass flow of R401 is (kg/h) = 592.6\n",
" (b) The dryness fraction of R401 at the entry to the evaporator is = 0.244\n",
" (c) The power to driving motor is (kW) = 5.86\n",
" (d) The ratio of heat transferred from condenser to the power required to the motor is = 4.74 :1\n"
]
}
],
"source": [
"#pg 614\n",
"print('Example 18.2');\n",
"\n",
"# aim : To determine\n",
"# (a) the mass flow of R401\n",
"# (b) the dryness fraction of R401 at the entry to the evaporator\n",
"# (c) the power of driving motor\n",
"# (d) the ratio of heat transferred from condenser to the power required to the motor\n",
"from math import log\n",
"# given values\n",
"P1 = 411.2;# pressure limit, [kN/m^2]\n",
"P3 = 1118.9;# pressure limit, [kN/m^2]\n",
"Q = 100*10**3;# heat transfer from the condenser,[kJ/h]\n",
"T2 = 273+60;# entering saturation temperature, [K]\n",
"\n",
"# given\n",
"# from given table\n",
"# at P1\n",
"h1 = 409.3;# specific enthalpy, [kJ/kg]\n",
"s1 = 1.7431;# specific entropy,[ kJ/kg K\n",
"\n",
"# at P3\n",
"h3 = 426.4;# specific enthalpy, [kJ/kg]\n",
"s3 = 1.7192;# specific entropy,[ kJ/kg K\n",
"T3 = 273.+50;# saturation temperature, [K]\n",
"h4 = 265.5;# specific enthalpy, [kJ/kg]\n",
"# (a)\n",
"s2 = s1;# specific entropy, [kJ/kg k]\n",
"# using s2=s3+cpv*log(T2/T3)\n",
"cpv = (s2-s3)/log(T2/T3);# heat capacity, [kj/kg k]\n",
"\n",
"# from Fig.18.8\n",
"h2 = h3+cpv*(T2-T3);# specific enthalpy, [kJ/kg]\n",
"Qc = h2-h4;# heat transfer from condenser, [kJ/kg]\n",
"mR401 = Q/Qc;# mass flow of R401, [kg]\n",
"print ' (a) The mass flow of R401 is (kg/h) = ',round(mR401,1)\n",
"\n",
"# (b)\n",
"hf1 = 219;# specific enthalpy, [kJ/kg]\n",
"h5 = h4;\n",
"# using h5=hf1+s5*(h1-hf1),so\n",
"x5 = (h5-hf1)/(h1-hf1);# dryness fraction\n",
"print ' (b) The dryness fraction of R401 at the entry to the evaporator is = ',round(x5,3)\n",
"\n",
"# (c)\n",
"P = mR401*(h2-h1)/3600/.7;# power to driving motor, [kW]\n",
"print ' (c) The power to driving motor is (kW) = ',round(P,2)\n",
"\n",
"# (d)\n",
"r = Q/3600./P;# ratio\n",
"print ' (d) The ratio of heat transferred from condenser to the power required to the motor is = ',round(r,2),\":1\"\n",
"\n",
"# End\n"
]
}
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