2.69  The steady-state temperature distribution in a   compos-

 

.            .                                        ite plane wall of three different materials, each of   con-

 

volumetric generation rate of qB  = -qA. The surfaces

at   x = ±L   are   insulated.   Sketch   the   steady-state temperature   and   heat   flux   distributions   T(x)   and qx"(x),  respectively,  over  the  domain -L x L  for kA  = kB,   kA  = 0.5kB,   and   kA  = 2kB.   Point   out   the important features of the distributions you have drawn. If qB = -2qA, can you sketch the steady-state tempera- ture distribution?

2.68 Typically, air is heated in a hair dryer by blowing it across a coiled wire through which an electric current is passed. Thermal energy is generated by electric resis- tance heating within the wire and is transferred by  con-

stant thermal conductivity, is shown.

 

1              2              3              4

T

 

 

 

 

 

 

x

 

(a)    Comment on the relative magnitudes of q2" and q3", and of q" and q".

 

vection from the surface of the wire to the air. Consider                                    3               4

 

conditions for which the wire is initially at room temperature, Ti, and resistance heating is concurrently initiated with airflow at t = 0.

 

(b)   Comment on the relative magnitudes of kA and kB,

and of kB  and kC.

(c)    Sketch the heat flux as a function of x.