Heat transfer coefficient,simple example Given: Air at 20C flowing over heated flat plate at 100C.Experimental measurements of temperatures at various distances from the surface are as shown Experimental measurements Experiinental measurements 2 mm 1.2 mm =66.7 mm Air now Surface of plate 20 50 100C .Find:convective heat transfer coefficient,h
Heat transfer coefficient, simple example • Given: Air at 20ºC flowing over heated flat plate at 100ºC. Experimental measurements of temperatures at various distances from the surface are as shown • Find: convective heat transfer coefficient, h Experimental measurements
Heat transfer coefficient,simple example ·Solution: OT Rccall that h is computed by Ts-To From Table A-4 in Appendix,at a mean fluid temperature 7n7。+7 2 (average of free-stream and surface temperatures) Tm=(20+100)/2=60°C the air conductivity,k is=0.028 W/m-K ● Temperature gradient at the plate surface from experimental data is-66.7 K/mm =-66,700 K/m So,convective heat transfer coefficient is: h、 -0.028×(-66700) 80 W =23.345 m2K
Heat transfer coefficient, simple example • Solution: Recall that h is computed by • From Table A-4 in Appendix, at a mean fluid temperature (average of free-stream and surface temperatures) the air conductivity, k is 0.028 W/m-K • Temperature gradient at the plate surface from experimental data is -66.7 K/mm = -66,700 K/m • So, convective heat transfer coefficient is: 0 T T y T k h s y f x m K W 23.345 80 - 0.028 ( 66700) 2 h 2 m T Ts T T C m (20 100) 2 60