PROBLEM 1.1 KNOWN: Heat rate, q, through one-dimensional wall of area A, thickness L, thermal
conductivity k and inner temperature, T1. FIND: The outer temperature of the wall, T2. SCHEMATIC:
ASSUMPTIONS: (1) One-dimensional conduction in the x-direction, (2) Steady-state conditions, (3) Constant properties. ANALYSIS: The rate equation for conduction through the wall is given by Fourier’s law,
q cond = q x = q ′′ ? A = -k x
Solving for T2 gives
T ?T dT ? A = kA 1 2 . dx L
T2 = T1 ?
q cond L . kA
Substituting numerical values, find
T2 = 415 C -
3000W × 0.025m 0.2W / m ? K × 10m2
T2 = 415 C - 37.5 C T2 = 378 C.
COMMENTS: Note direction of heat flow and fac…(생략)
t that T2 must be less than T1.
KNOWN: Inner surface temperature and thermal conductivity of a concrete wall. FIND: Heat loss by conduction through the wall as a function of ambient air temperatures ranging from -15 to 38°C. SCHEMATIC: