Page 111 - Modelling in Transport Phenomena A Conceptual Approach

4.4. FLOW NORMAL TO A SINGLE CYLINDER 91

Analysis

The rate oaf heat loss from the body can be calculated from Eq. (4.4-9):

Determination of (h) an Eq. (1) requires the Reynolds number to be known. The
Reynolds numbers at T, and Tf are

Whitaker correlation

The use of Eq. (4.4-6) gives the Nusselt number as

Nu = (0.4ReT +0.06Red3) (p,/p,)1/4

= b.4 (9.65 x lO4)li2 + 0.06 (9.65 x 104)2/3] (0.72)0.4 ( ;;;;xy;6)1/4
= 214

Hence, the average heat transfer weficient is
(h) = Nu (a)

-
- (214) (23.28 x low3) = 16.6 W/ m2. K
0.3
Substitution of this result into Eq. (1) gives the rate of heat loss as

Q = (Z x 0.3 x 1.8) (16.6) [30 - (- lo)] = 1126W

Zhukauskas correlation

Since ReD = 9.65 x lo4 and Pr < 10, from Table 4.3 the constants are: c = 0.26,
m = 0.6 and n = 0.37. Hence, the use of Eq. (4.4-7) gives

Nu = 0.26R,eg6 Pr0.37(Pr, / Pr,)1/4
0.72 'I4
= 0.26 (9.65 x 104)0.6(0.72)0.37 = 226