{ "cells": [ { "cell_type": "markdown", "metadata": {}, "source": [ "# Chapter 10:Component Selection and Balancing" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## Example 10.1,PAGE NUMBER:136" ] }, { "cell_type": "code", "execution_count": 1, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "\n", "LMTD=4.5 K\n" ] } ], "source": [ "import math\n", "# Variable declaration\n", "w_a=8.4;# The mass flow rate of air in kg/s\n", "R=3.8;# Rating of an air-cooling evaporator in kW/k\n", "T_a=-15;# Entering air temperature in °C\n", "T_r=-21;# Refrigerant temperature in °C\n", "\n", "# Calculation\n", "deltaT=(T_a+273)-(T_r+273);# Rating LMTD in K\n", "E=R*deltaT;# Rated duty in kW\n", "C_pair=1.006;# kJ/kg.K\n", "T_ar=E/(C_pair*w_a);# Reduction in air temperature in °C \n", "T_al=T_a-T_ar;# Air leaving temperature in °C\n", "deltaT_min=(T_al+273)-(T_r+273);# K\n", "deltaT_max=deltaT;# K\n", "LMTD=(deltaT_max-deltaT_min)/(math.log(deltaT_max/deltaT_min));\n", "print\"\\nLMTD=%1.1f K\"%LMTD" ] }, { "cell_type": "markdown", "metadata": { "collapsed": true }, "source": [ "## Example 10.2,PAGE NUMBER:136" ] }, { "cell_type": "code", "execution_count": 2, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "\n", "Design mass air flow=7.35 kg/s\n", "The cooling capacity at 100,95,90and 85 percentage mass air flow=45,42.3,39.3and 36.7 kW\n" ] } ], "source": [ "# Variable declaration\n", "Q=45;# The sensible heat extracted by an air-cooling coil in kW\n", "T_in=24;# The entering air temperature in °C\n", "T_out=18;# The leaving air temperature in °C\n", "T_e=11;# Refrigerant evaporating temperature in °C\n", "C_pa=1.02;# The specific heat capacity of air in kJ/kg.K\n", "Af=[100,95,90,85];# Air flow (%)\n", "m=[7.35,6.99,6.62,6.25];# Mass air flow (kg/s)\n", "T_a=[24,24,24,24];# Air temperature on coil (°C)\n", "deltaT=[6,6.3,6.7,7.1];# ΔT for 45 kW (K)\n", "T_aoff=[18,17.7,17.3,16.9];# Air temperature off coil (°C)\n", "LMTD=[9.7,9.5,9.2,9.0];# LMTD,refrigerant at 11°C (K)\n", "h=[1,0.96,0.92,0.88];# h, in terms of design (from V0.8) \n", "\n", "# Calculation\n", "m_af=Q/(C_pa*(T_in-T_out));\n", "Capacity=[(45*h[0]*LMTD[0])/9.7,(45*h[1]*LMTD[1])/9.7,(45*h[2]*LMTD[2])/9.7,(45*h[3]*LMTD[3])/9.7];# kW\n", "print\"\\nDesign mass air flow=%1.2f kg/s\"%m_af\n", "print\"The cooling capacity at 100,95,90and 85 percentage mass air flow=%2.0f,%2.1f,%2.1fand %2.1f kW\"%(Capacity[0],Capacity[1],Capacity[2],Capacity[3])" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## Example 10.3,PAGE NUMBER:140" ] }, { "cell_type": "code", "execution_count": 3, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "\n", "Flow rate ratio,m_2/m_1=1.083\n", "\n", "Compressor capacity corrected for suction temperature change=9.44 kW\n", "\n", "Actual compressor capacity=10.09 kW\n", "\n", "Actual evaporator capacity=8.07 kW\n" ] } ], "source": [ "# Variable declaration\n", "P_c=10;# kW\n", "T_e=-35;# Evaporating temperature in °C\n", "T_c=40;# Condensing temperature in °C\n", "T_s=5;# Subcooling temperature in K\n", "T_cin=20;# Compressor inlet temperature in °C\n", "T_cout=0;# Zero subcooling temperature in °C\n", "\n", "# Calculation\n", "#(a)\n", "v_s1=146.46;# m**3/kg\n", "v_s2=135.25;# m**3/kg\n", "v_sr=v_s1/v_s2;# The ratio of specific volume\n", "# Assuming the compressor pumps the same volume flowrate:\n", "m_1bym_2=v_sr;# Flow rate ratio\n", "print\"\\nFlow rate ratio,m_2/m_1=%1.3f\"%m_1bym_2\n", "#(b)\n", "h_1=392.51;# Suction gas enthalpy at 20°C in kJ/kg\n", "h_2=375.19;# Suction gas enthalpy at 0°C in kJ/kg\n", "h_f=257.77;# Liquid enthalpy at the expansion valve inlet at 40°C in kJ/kg\n", "dh_1=h_1-h_f;# Evaporator enthalpy difference at rating condition in kJ/kg\n", "dh_2=h_2-h_f;# Evaporator enthalpy difference with 0°C suction in kJ/kg\n", "dh_r=dh_2/dh_1;# Enthalpy difference ratio\n", "C_c=P_c*m_1bym_2*dh_r;# Compressor capacity corrected for suction temperature change in kW\n", "print\"\\nCompressor capacity corrected for suction temperature change=%1.2f kW\"%C_c\n", "#(c)\n", "h_f=249.67;# Liquid enthalpy at the expansion valve inlet at 35°C in kJ/kg\n", "dh=h_2-h_f;# Evaporator enthalpy difference at application condition in kJ/kg\n", "dh_r=dh/dh_1;# Enthalpy difference ratio\n", "C_cact=P_c*m_1bym_2*dh_r;# Actual compressor capacity in kW\n", "print\"\\nActual compressor capacity=%2.2f kW\"%C_cact\n", "#(d)\n", "h_g=350.13;# Suction gas enthalpy at evaporator outlet, -30°C (5 K superheat) in kJ/kg\n", "dh_e=h_g-h_f;# Useful evaporator enthalpy difference in kJ/kg\n", "dh_r=dh_e/dh_1;# Enthalpy difference ratio\n", "C_eact=P_c*m_1bym_2*dh_r;# Actual evaporator capacity in kW\n", "print\"\\nActual evaporator capacity=%1.2f kW\"%C_eact" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## Example 10.4,PAGE NUMBER:142" ] }, { "cell_type": "code", "execution_count": 4, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Break-even time=1.6 years\n" ] } ], "source": [ "# Variable declaration\n", "T_c1=30;# Condensing temperature for larger condenser in °C\n", "T_c2=35;# Condensing temperature for smaller condenser in °C\n", "Rc_1=242;# Rated capacity of plant for larger condenser in kW\n", "Rc_2=218;# Rated capacity of plant for smaller condenser in kW\n", "Rt_1=1802;# Running time (kW-h)\n", "Rt_2=2000;# Running time (kW-h)\n", "Ci_1=60;# Compressor electrical input power in kW\n", "Ci_2=70;# Compressor electrical input power in kW\n", "Ec_1=11533;# Electricity cost per year (£)\n", "Ec_2=14933;# Electricity cost per year (£)\n", "C_1=14000;# Cost of the larger condenser in £\n", "C_2=8500;# Cost of the smaller condenser in £\n", "\n", "# Calculation\n", "Es=Ec_2-Ec_1;# Cost of the larger condenser in £\n", "Bet=(C_1-C_2)*Es**-1;# Break-even time in years\n", "print\"Break-even time=%1.1f years\"%Bet" ] } ], "metadata": { "kernelspec": { "display_name": "Python 2", "language": "python", "name": "python2" }, "language_info": { "codemirror_mode": { "name": "ipython", "version": 2 }, "file_extension": ".py", "mimetype": "text/x-python", "name": "python", "nbconvert_exporter": "python", "pygments_lexer": "ipython2", "version": "2.7.11" } }, "nbformat": 4, "nbformat_minor": 0 }