This preview shows page 1. Sign up to view the full content.
Unformatted text preview: Chapter 9 Natural Convection 941 It is proposed that the side surfaces of a cubic industrial furnace be insulated for $550 in order to reduce the heat loss by 90 percent. The thickness of the insulation and the payback period of the insulation to pay for itself from the energy it saves are to be determined. Assumptions 1 Steady operating conditions exist. 2 Air is an ideal gas with constant properties. 3 The local atmospheric pressure is 1 atm. Properties The properties of air at 1 atm and the film temperature of ( T s + T )/2 = (110+30)/2 = 70 C are (Table A15) Hot gases T = 30 C Furnace T s = 110 C = 0.7 2 m 2 m 1 2 5 K 002915 . K ) 273 70 ( 1 1 7177 . Pr /s m 10 995 . 1 C W/m. 02881 . = + = = = = = f T k Analysis The characteristic length in this case is the height of the furnace, m. 2 = = L L c Then, 10 2 2 5 31 2 2 3 10 301 . 3 ) 7177 . ( ) /s m 10 995 . 1 ( ) m 2 )( K 30 110 )( K 002915 . )( m/s 81 . 9 ( Pr ) ( = = =...
View Full
Document
 Fall '10
 Dr.DanielArenas
 Thermodynamics, Convection, Mass, Heat

Click to edit the document details