{ "cells": [ { "cell_type": "markdown", "metadata": {}, "source": [ "# Chapter 12: Convection Heat Transfer1" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## Exa 12.1" ] }, { "cell_type": "code", "execution_count": 1, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Heat transfer rate from both sides of the plate (Btu/hr) = 40.50\n", "press enter key to exit\n" ] }, { "data": { "text/plain": [ "''" ] }, "execution_count": 1, "metadata": {}, "output_type": "execute_result" } ], "source": [ "#An electrically heated vertical plate, 5 in square has a temperature of \n", "#150 F and is being cooled by natural convection in 50 F air. What is the \n", "#heat transfer rate from both sides of the plate?\n", "import math\n", "#initialisation of variables\n", "d= 5. \t\t\t\t\t\t\t\t#ft\n", "Tw= 150. \t\t\t\t\t\t\t#F\n", "T= 50 \t\t\t\t\t\t\t\t#F\n", "Pr= 0.72\n", "k= 0.015 \t\t\t\t\t\t\t#Btu/hr ft F\n", "r= 1.76*1000000. \t\t\t\t\t#(F ft^3)^-1\n", "#CALCULATIONS\n", "D= d*(0.42/5.) \t\t\t\t\t\t#Diameter\n", "dt= Tw-T \t\t\t\t\t\t\t#change in temp\n", "Gr= r*D*D*D*dt \t\t\t\t\t\t#Grashof number\n", "z= Gr*Pr \t\t\t\t\n", "h= 0.59*(math.pow(z,(0.25))) *(k/D) #Heat transfer coefficient\n", "q= (2*h*dt*d*d)/144. \t\t\t\t#Heat transfer rate\n", "#RESULTS\n", "print '%s %.2f' % ('Heat transfer rate from both sides of the plate (Btu/hr) = ',q)\n", "raw_input('press enter key to exit')" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## Exa 12.2" ] }, { "cell_type": "code", "execution_count": 2, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Heat transfer coefficient when the flow is fully devoloped (Btu/hr ft^2 F) = 1311.13\n", "press enter key to exit\n" ] }, { "data": { "text/plain": [ "''" ] }, "execution_count": 2, "metadata": {}, "output_type": "execute_result" } ], "source": [ "#Cooling water at an average temperature of 70 F flows through a tube of \n", "#0.9 in ID, with an average velocity of 7 ft/s. What is the heat transfer\n", "#coefficient when the flow is fully developed?\n", "#initialisation of variables\n", "import math\n", "T= 70. \t\t\t\t\t\t\t\t\t\t#F\n", "l= 0.9 \t\t\t\t\t\t\t\t\t\t#in\n", "v= 7. \t\t\t\t\t\t\t\t\t\t#ft/s\n", "d= 62.3 \t\t\t\t\t\t\t\t\t#lbm/ft^3\n", "m= 6.58*math.pow(10,-4) \t\t\t\t\t#lbm/ft s\n", "Pr= 6.82 \n", "k= 0.347 \t\t\t\t\t\t\t\t\t#Bt/hr ft F\n", "#CALCULATIONS\n", "l1= l*0.075/l\n", "Re= (d*v*l1)/m \t\t\t\t\t\t\t\t#Reynold's number\n", "Nu= 0.023*math.pow(Re,0.8)*math.pow(Pr,0.4) #Nusselt number\n", "h= Nu*k/l1 \t\t\t\t\t\t\t\t\t#Transfer coefficient\n", "#RESULTS\n", "print '%s %.2f' % ('Heat transfer coefficient when the flow is fully devoloped (Btu/hr ft^2 F) = ',h)\n", "raw_input('press enter key to exit')" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## Exa 12.3" ] }, { "cell_type": "code", "execution_count": 3, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Heat transfer rate per unit lenght (W/m) = 23.21\n", "press enter key to exit\n" ] }, { "data": { "text/plain": [ "''" ] }, "execution_count": 3, "metadata": {}, "output_type": "execute_result" } ], "source": [ "#Air at 1 atm pressure and a mixing cup temperature of 450k flows through \n", "#a 3 cm diameter tube with a velocity of 6 m/s. determine the heat transfer\n", "#rate per unit length if tube if a constant heat flux condition is maintained\n", "#at the tube wall and the wall temperature is 10 C above the air temperature\n", "import math\n", "#initialisation of variables\n", "P= 1 \t\t\t\t\t\t\t\t\t\t#atm\n", "d= 0.783 \t\t\t\t\t\t\t\t\t#Kg/m^3\n", "K= 0.0371 \t\t\t\t\t\t\t\t\t#W/m C\n", "m= 2.48*math.pow(10,-5) \t\t\t\t\t#Ns/m^2\n", "Pr= 0.683\n", "D= 0.03 \t\t\t\t\t\t\t\t\t#m\n", "v= 6 \t\t\t\t\t\t\t\t\t\t#m/s\n", "T= 10 \t\t\t\t\t\t\t\t\t\t#C\n", "#CALCULATIONS\n", "Re= d*v*D/m \t\t\t\t\t\t\t\t#Reynolds number\n", "Nu= 0.023*math.pow(Re,0.8)*math.pow(Pr,0.4) #Nusselt number\n", "h= Nu*K/D \t\t\t\t\t\t\t\t\t#Heat transfer coefficient\n", "ql= h*math.pi*D*T \t\t\t\t\t\t\t#Heat transfer rate\n", "#RESULTS\n", "print '%s %.2f' % ('Heat transfer rate per unit lenght (W/m) = ',ql)\n", "raw_input('press enter key to exit')" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## Exa 12.4" ] }, { "cell_type": "code", "execution_count": 4, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Heat transfer rate per unit lenght of cylinder (W/m) = 3023.70\n", "press enter key to exit\n" ] }, { "data": { "text/plain": [ "''" ] }, "execution_count": 4, "metadata": {}, "output_type": "execute_result" } ], "source": [ "#Air at 1 atm pressure and 25 C flows past a horizontal 5 cm diameter with\n", "#a velocity of 46 m/s. If the surface of the cylinder is kept at 135 C, determine\n", "#the rate of heat flow from the cylinder\n", "import math\n", "#initialisation of variables\n", "T= 25 \t\t\t\t\t\t#C\n", "P= 1 \t\t\t\t\t\t#atm\n", "v= 46 \t\t\t\t\t\t#m/s\n", "d= 5 \t\t\t\t\t\t#cm\n", "T1= 135 \t\t\t\t\t#C\n", "d1= 0.998 \t\t\t\t\t#kg/m^3\n", "k= 0.03 \t\t\t\t\t#W/m C\n", "m= 2.08*math.pow(10,-5) \t#Kg/s m\n", "c= 0.024\n", "n= 0.81\n", "#CALCULATIONS\n", "Tf= (T+T1)/2. \t\t\t\t#Final temp.\n", "D= d/100.\n", "Re= d1*v*D/m \t\t\t\t#Reynolds number\n", "h= c*math.pow(Re,0.81)*k/D \t#Heat transfer coefficient\n", "dt= T1-T \t\t\t\t\t#temp diff.\n", "ql= h*math.pi*D*dt \t\t\t#Heat transfer rate\n", "#RESULTS\n", "print '%s %.2f' % ('Heat transfer rate per unit lenght of cylinder (W/m) = ',ql)\n", "raw_input('press enter key to exit')" ] } ], "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": "2.7.6" } }, "nbformat": 4, "nbformat_minor": 0 }