Heat Transfer

11

The Dietus-Boelter equation for convective leat transfer`[ ( i.e.) h = 0.023 k/D (Re)^0.8 (Pr)^0.4]`

cannot be used for

A. low Reynold's number
B. very low Grashoff number
C. molten metals
D. all (a), (b) and (c)

12

What is Nusselt number ?

A. `(C_p mu)/(k)`
B. `(hD)/(k)`
C. `(h C_p)/(mu)`
D. `(C_p mu)/(h)`

13

The local surface conductance for laminar film condensation on vertical surface is (where, t = film thickness)

A. `prop `t
B. `prop `1/t
C. `prop sqrt(t)`
D. independent of 't'

14

The energy radiated from a surface Q at absolute temperature T is related as

 
A. `Q prop T^2`
B. `Q prop T^4`
C. `Q prop T^3`
D. none of these

15

The interchange factor for radiation heat transfer from surface 'x' to surface 'y' in case of an infinite parallel planes with emis-sivities `epsi_x` & `epsi_y`s given by

 
A. `epsi_x + epsi_y`
B. `epsi_x .epsi_y`
C. `1/epsi_x + 1/epsi_y`
D. `(epsi_x + epsi_y)/(epsi_x + epsi_y - epsi_x .epsi_y)`