Heat transfer | 6 | CIBSE Guide C: Reference Data | Cibse

ABSTRACT

Replace g with g cos h in the formula for (Gr), see page 3-3, for (Ra) 109

Horizontal plate A/P (surface area A and perimeter P) (a) Upper surface of

a hot plate or 104 107 (Nu) 0.54 (Ra)1/4 (3.4) lower surface of a 107 1011 (Nu) 0.15 (Ra)1/3 (3.5) cold plate

(b) Lower surface of a hot plate or 105 1011 (Nu) 0.27 (Ra)1/4 (3.6) upper surface of a cold plate

Vertical cylinder D A vertical cylinder can be treated as a vertical plate when:

Horizontal cylinder d 105 1012

Sphere d/2 (Ra) 1011 (Pr) 0.7

(3.3)(Nu) { 0.825 }[1 (0.492/(Pr))9/16]8/27 tsD

Hot surface ts

Hot surfacets

35D d (3.7)

(Gr)1/4

(3.8)(Nu) { 0.6 }[1 (0.559/(Pr))9/16]8/27

0.589(Ra)1/4 (Nu) 2 (3.9)

respective diagram) (reproduced from Introduction to Thermodynamics and Heat Transfer by YA Cengel (1997) by permission of The McGraw-Hill Companies)

Geometry Fluid H/D Range Range of Nusselt number (Nu) of (Pr) (Ra)

Vertical Gas or — — 2000 (Nu) 1 (3.10) rectangular or liquid cylindrical enclosure Gas 11 42 0.5 2 2 103 2 105

11 42 0.5 2 2 105 107

Liquid 10 40 1 20 000 104 107

1 40 1 20 106 109

Inclined Use the correlations for vertical rectangular enclosures as a ﬁrst degree enclosure approximation for h 20º by replacing

g with g cos h in the formula for (Ra), see page 3-3

Horizontal Gas or — — — (Nu) 1 (3.15) rectangular liquid enclosure (hot surface at the top)

Horizontal Gas or — — 1700 (Nu) 1 (3.16) rectangular liquid enclosure (hot surface at the bottom) Gas — 0.5 2 1.7 103 7 103 (Nu) 0.059 (Ra)0.4 (3.17)

— 0.5 2 7 103 3.2 105 (Nu) 0.212 (Ra)1/4 (3.18)

— 0.5 2 3.2 105 (Nu) 0.061 (Ra)1/3 (3.19)

Liquid — 1 5000 1.7 103 6 103 (Nu) 0.012 (Ra)0.6 (3.20)

— 1 5000 6 103 3.7 104 (Nu) 0.375 (Ra)0.2 (3.21)

— 1 20 3.7 104 108 (Nu) 0.13 (Ra)0.3 (3.22)

— 1 20 108 (Nu) 0.057 (Ra)1/3 (3.23)

Concentric Gas or — 1 5000 6.3 103 106 (Nu) 0.11 (Ra)0.29 (3.24) horizontal liquid — 1 5000 106 108 (Nu) 0.40 (Ra)0.20 (3.25)

cylinders

Concentric Gas or — 0.7 4000 102 109 (Nu) 0.228 (Ra)0.226 (3.26) spheres liquid

Cold

Hot

H 1/9 (Nu) 0.197(Ra)1/4 ( ) (3.11)D

H 1/9 (Nu) 0.073(Ra)1/3 ( ) (3.12)D

H 0.3 (Nu) 0.42(Pr)0.012 (Ra)1/4 ( ) (3.13)D (Nu) 0.046(Ra)1/3 (3.14)

Cold

Hot

from Introduction to Thermodynamics and Heat Transfer by YA Cengel (1997) by permission of The McGraw-Hill Companies)

Cross section Fluid Range of (Re) Nusselt number (Nu)

Circle Gas or liquid 0.4 4 (Nu) 0.989 (Re)0.33 (Pr)1/3 (3.29) 4 40 (Nu) 0.911 (Re)0.385 (Pr)1/3 (3.30) 40 4000 (Nu) 0.683 (Re)0.466 (Pr)1/3 (3.31) 4000 40 000 (Nu) 0.193 (Re)0.618 (Pr)1/3 (3.32) 40 000 400 000 (Nu) 0.027 (Re)0.805 (Pr)1/3 (3.33)

Square Gas 5000 100 000 (Nu) 0.102 (Re)0.675 (Pr)1/3 (3.34)

Square (tilted 45) Gas 5000 100 000 (Nu) 0.246 (Re)0.588 (Pr)1/3 (3.35)

Hexagon Gas 5000 100 000 (Nu) 0.153 (Re)0.638 (Pr)1/3 (3.36)

Hexagon (tilted 45) Gas 5000 19 500 (Nu) 0.160 (Re)0.638 (Pr)1/3 (3.37) 19 500 100 000 (Nu) 0.0385 (Re)0.782 (Pr)1/3 (3.38)

Vertical plate Gas 4000 15 000 (Nu) 0.228 (Re)0.731 (Pr)1/3 (3.39)

Ellipse Gas 2500 15 000 (Nu) 0.248 (Re)0.612 (Pr)1/3 (3.40)

Table 3.5 Nusselt numbers for fully developed laminar ﬂow in tubes of various cross sections (hydraulic diameter dh = 4Ac/P) (reproduced from Introduction to Thermodynamics and Heat Transfer by YA Cengel (1997) by permission of The McGraw-Hill Companies)

Cross section of tube a/b or h Nusselt number (Nu)

ts = const. qt = const.