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{
"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')"
]
}
],
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