HW # 5 /Tutorial # 5WRF Chapter 19; WWWR Chapter 20

ID Chapters 7-9

• Tutorial # 5• WRF#19.3;

WRF#19.8; WWWR #20.13,; WRF#19.23, WWWR#20.42.

• To be discussed on Feb. 16, 2016.

• By either volunteer or class list.

• Correction: #20.42: Table: Unit for Cp should be corrected from J/kg-K to kJ/kg-K.

Convective Heat Transfer Correlations

Natural Convection

Horizontal Plates

McAdam’s Correlations: Hot surface facing up or cold surface surfacing down

H

C

HC

Horizontal Cylinders

g

In each of the correlations to follow the temperature of the hotter of the two large surfaces is designed in T1, and the cooler surface is at temperature T2.

Fluid properties are evaluated at the film temperature, Tf = (T1 + T2) / 2.

Convective heat flux is expressed as

qA

= h(T1 - T2)

Example 1

H

H

Initial Guess T = 385K, Resulting T=381.1K Second Iteration

Forced Convection For Internal Flow

Turbulent Flow

Example 2

Hydraulic fluid (MIL-M-5606), in fully developed flow, flows through a 2.5 cm diameter copper tube, with a mean velocity of 0.05 m/s. The oil enters at 295K. Steam condenses on the outside tube surface with an effective heat transfer coefficient of 11400 W/m2-K. Find the rate of heat transfer to the oil.

Ro

RiRc

Rc << Ro, Ri295K

Example 2Ro

Ri

=(295+305)/2

Rc

Rc << Ro, Ri295K

305K?

=373-(373-300)*[98.1/(98.1+11400)]=372.3K

Example 3

Forced Convection For External Flow

Flow Parallel To Plane Surface

Cylinders In Crossflow

Tube Banks In Crossflow

SL : Center-to-center distance between tubes along the direction of flowST: Center-to-center distance between tubes normal to the direction of flow

Adapted from ID Page 437