# Fundamentals of Heat and Mass Transfer

Language: English

Pages: 0

ISBN: 1118989171

Format: PDF / Kindle (mobi) / ePub

The rate of heat loss can be found by evaluating the conduction through the skin/fat layer: T Ϫ Ts (308 Ϫ 307.2) K ϭ 146 W qs ϭ kA i ϭ 0.3 W/m ⅐ K ϫ 1.8 m2 ϫ ᭠ L 3 ϫ 10Ϫ3 m 2. Since liquid water is opaque to thermal radiation, heat loss from the skin surface is by convection only. Using the previous expression with hr ϭ 0, we find 0.3 W/m ⅐ K ϫ 308 K ϩ 200 W/m2 ⅐ K ϫ 297 K 3 ϫ 10Ϫ3 m Ts ϭ ϭ 300.7 K 0.3 W/m ⅐ K ϩ 200 W/m2 ⅐ K 3 ϫ 10Ϫ3 m ᭠ and qs ϭ kA Ti Ϫ Ts (308 Ϫ 300.7) K ϭ 1320 W ϭ 0.3 W/m ⅐

analysis techniques included in Chapter 13. Chapter 14 Diffusion Mass Transfer was revised extensively for the previous edition, and only modest changes have been made in this edition. Problem Sets Approximately 250 new end-of-chapter problems have been developed for this edition. An effort has been made to include new problems that (a) are amenable to short solutions or (b) involve finite-difference solutions. A significant number of solutions to existing end-of-chapter problems have been

illustrated has negligible variation of temperature in the r- and z-directions. Assume CH002.qxd 2/24/11 12:22 PM Page 103 103 Problems that ⌬r ϭ ro Ϫ ri is small compared to ri, and denote the length in the z-direction, normal to the page, as L. Insulation φ ri r o T2 T1 (a) Beginning with a properly defined control volume and considering energy generation and storage effects, derive the differential equation that prescribes the variation in temperature with the angular coordinate

parallel to the x-direction are adiabatic. Different results are obtained for Rtot, and the corresponding values of q bracket the actual heat transfer rate. These differences increase with increasing ΈkF Ϫ kGΈ, as multidimensional effects become more significant. 3.1.4 Contact Resistance Although neglected until now, it is important to recognize that, in composite systems, the temperature drop across the interface between materials may be appreciable. This temperature change is attributed to

N ϭ H/S ϭ 0.15 m/(0.004 ϩ 0.006) m ϭ 15. The parametric calculations yield the following variation of qt with N: 1600 1400 t = 6 mm 1200 qt (W) CH003.qxd 1000 800 600 5 7 11 9 Number of fins, N 13 15 The number of fins could also be increased by reducing the fin thickness. If the fin gap is fixed at (S Ϫ t) ϭ 4 mm and manufacturing constraints dictate a minimum allowable fin thickness of 2 mm, up to N ϭ 25 fins may be accommodated. In this case the parametric calculations yield