Question

PROBLEM 1: Answer/Define/Explain shortly and/or Fill in the blanks (40 P) a) What are the two types of energy transfer in Convection? b) A thermal boundary layer must develop if ....... c) Define the critical Reynolds number. d) What are the assumptions for Boundary Layer Equations for Laminar Flow? e) Define the Nusselt number. f) Define the Prandtl number. g) How the Pr influences the relative growth of the boundary layers, explain briefly ? h) Explain favorable pressure gradient. i) Explain adverse pressure gradient j) How the boundary layer transition influences the position of the separation point., explain briefly? k) Which correlations can be used for the average Nu in case of cylinder in cross flow? (just names) 1) The tube rows of a bank can be either ........ or ......... in the direction of the fluid velocity m) Which correlation was proposed for the average heat transfer coefficient for the entire tube bank? n) In case of flow in a circular tube, flow is then said to be fully developed if .......... o) Explain the radial dependence of the axial velocity in the fully developed laminar pipe flow? p) Explain the Figure 8.3 briefly. r) How is the pressure drop correlated to the friction factor? s) How is the pressure drop correlated to the fan/pump power required? t) Explain thermally fully develop condition briefly? How is it related to the thermal BC. ? u) Explain Fig 8.5 briefly.

Answer 1

SOLUTIONS(first 4 parts)

(a) Convection is combination of advection and conduction in which transfer of thermal energy takes place. It is also a major mode of mass transfer.

(b) A thermal boundary layer must develops if there is a difference in the temperature of the fluid and the surface in which it is in contact.

(c) Critical reynolds number defines where the flow changes from laminar to turbulent. At this transition point the reynold number is called critical reynolds number.

(d) Assumptions-

i. 2 D flow

ii. Steady flow

iii. In the region near to the surface of body viscous effects cannot be neglected.

iv. High velocity flow