# Variables
tp = 200.; # Temperature of heated plate in degF
ta = 60.; # Temperature of air in degF
tf = (tp+ta)/2; # Temperature of film in degF
delt = tp-ta; # Temperature difference in degF
Z = 950000.; # As referred from the chart for corresponding temperature
L = 18/12.; # Height of vertical plate in ft
# Calculations
X = L**3*(delt)*Z;
# This value shows that it is laminar range so formula is as follows
h = 0.29*(delt/L)**.25; # Heat transfer coeeficient in Btu/hr-ft**2-degF
# Results
print "The film coefficient for free convetion for the heated plate is %.1f Btu/hr-ft**2/degF"%(h)
# Variables
tp = 300.; # Temperature of heated plate in degF
ta = 80.; # Temperature of air in degF
tf = (tp+ta)/2; # Temperature of film in degF
delt = tp-ta; # Temperature difference in degF
Z = 610000.; # As referred from the chart for corresponding temperature
L = 7./12; # Height of vertical plate in ft
# Calculations
A = L*L; # Area of square plate in ft**2
X = L**3*(delt)*Z;
# This value shows that it is turbulent range , so formula for heat transfer coefficient is as follow
h = 0.22*delt**(1./3); # Temperature coeeficient in Btu/hr-ft**2-degF
q = h*A*delt; # Heat loss in Btu/hr
# Results
print "The film coefficient for free convetion for the heated plate is %.2f Btu/hr-ft**2-degF"%(h);
print " The heat loss by natural convection from the square plate is %.2f Btu/hr"%(q);
# book answer is wrong.
import math
# Variables
D = 0.375; # Outer diameter in ft
T1 = 200.; # Pipe surface temperature in degF
T2 = 70.; # Air temperature in degF
Tf = (T1+T2)/2; # Film temperature at whih physical properties is to be measured
delT = T1-T2;
rho = 0.0667/32.2; # Density in slug/ft**3
u = 0.0482/32.2; # Vismath.cosity in slug/ft-hr
b = 1./(460+T2 );
Cp = 0.241*32.2; # Heat capacity in Btu/slug-ft
# Calculations
# The value of specific heat is related to 1 lb mass so it must be multiplied to 32.2 to convert it into slugs
k = 0.0164; # Thermal conductivity in Btu/hr-ft-degF
g = 32.2*3600;
# Unit of time used is hour so it must be converted to sec. Hence 3600 is multiplied
Ngr = D**3*rho**2*b*g*delT/(u**3); # Grasshops number
Npr = u*Cp/k; # Prandtls number
A = math.log(Ngr*Npr);
# Tha value of A is 6.866
# Now seeing the value of nusselt number from the table
Nnu = 25.2; # Nusselt number
h = Nnu*k/D; # Heat transfer coefficient
q = h*delT; # Heat loss per unit area in Btu/hr
# Results
print "Heat loss per unit square foot is %d Btu/hr-ft**2"%(q);
# Variables
tp = 200.; # Temperature of heated plate in degF
ta = 70.; # Temperature of air in degF
tf = (tp+ta)/2; # Temperature of film in degF
delt = tp-ta; # Temperature difference in degF
Z = 910000.; # As referred from the chart for corresponding temperature
D = 4.5/12; # Diameter of pipe in ft
# Calculations
X = D**3*(delt)*Z;
# This value lies between X = 1000 to X = 10**9 , so formula for heat transfer coefficient is as follow
h = 0.27*(delt/D)**(1./4); # Temperature coeeficient in Btu/hr-ft**2-degF
q = h*delt; # Heat loss in Btu/hr
# Results
print "The film coefficient for free convetion for the heated plate is %.2f Btu/hr-ft**2-degF"%(h);
print " The heat loss by natural convection from the square plateis %d Btu/hr"%(q);