HW # 5 /Tutorial # 5 WRF Chapter 19; WWWR Chapter 20 ID Chapters 7-9 Tutorial # 5 WRF#19.3; WRF#19.8; WWWR #20.13,; WRF#19.23, WWWR# To be discussed on Feb. 16, By either volunteer or class list. Correction: #20.42: Table: Unit for C p 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 H C

Horizontal Cylinders g

In each of the correlations to follow the temperature of the hotter of the two large surfaces is designed in T 1, and the cooler surface is at temperature T 2. Fluid properties are evaluated at the film temperature, T f = (T 1 + T 2 ) / 2. Convective heat flux is expressed as qAqA = h(T 1 - T 2 )

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 W/m 2 -K. Find the rate of heat transfer to the oil. Ro Ri Rc Rc << Ro, Ri 295K

Example 2 Ro Ri =( )/2 Rc Rc << Ro, Ri 295K 305K?

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

Example 3

Forced Convection For External Flow Flow Parallel To Plane Surface

Cylinders In Crossflow

Tube Banks In Crossflow S L : Center-to-center distance between tubes along the direction of flow S T : Center-to-center distance between tubes normal to the direction of flow

Adapted from ID Page 437