A$.$ Select the most appropriate answers to the two multiple choice questions below:

$1.$ Consider steady conduction heat transfer from

Thot to cold in the two situations $(1)$ and $(2).$

L

T

K$1,$ kz and k are the thermal conductivities of the

materials.

If the heat flux a$"$ in the two cases is the same, the relationship between k$1,$ kz and k can be expressed as:

$(1)$ Thot

K$1$

$(2)$

Thot

$$

$2$L

$($a$)$ K$3=$ k$1+$ kz

$($b$)$ K$3=$

k$1$ Kz

ka$+$kz

$()$ k$3=$

$2$ k$1$k$2$

ka$+$kz