Page 252 - Mechanical Engineers' Handbook (Volume 4)

8 Heat Transfer 241

Figure 22 Maximum and minimum load temperatures, and ln Y s or ln Y c as a function of heating
time with constant source temperature. 1

Table 6 Non-Steady-State Conduction Factors and Symbols
T Furnace temperature, gas or wall as defined
ƒ
T Load surface temperature
s
T Temperature at core or unheated side of load
c
T Initial load temperature with all temperatures in units of ( F 460)/100 or S
0
T T s
ƒ
Y
s
ƒ
T T 0
T T c
ƒ
Y
c
T T 0
ƒ
R External/internal thermal resistance ratio k/rH
X Time factor tD/r 2
D Diffusivity as defined in Section 45.7
r Depth of heat penetration in feet
k Thermal conductivity of load (Btu/ft hr F)
2
H External heat transfer coefficient (Btu/ft hr F)