Many of the solid surfaces for which values of thethermal

Chapter 8, Problem 8.112

(choose chapter or problem)

Many of the solid surfaces for which values of thethermal and momentum accommodation coefficientshave been measured are quite different from thoseused in micro- and nanodevices. Plot the Nusselt num-ber NuDassociated with fully developed laminar flowwith constant surface heat flux versus tube diameterfor 1?m?D?1 mm and (i) ?t?1, ?p?1, (ii)?t?0.1, ?p?0.1, (iii) ?t?1, ?p?0.1, and (iv)?t?0.1, ?p?1. For tubes of what diameter do theaccommodation coefficients begin to influence con-vection heat transfer? For which combination of ?tand?pdoes the Nusselt number exhibit the least sensitivityto changes in the diameter of the tube? Which combi-nation results in Nusselt numbers greater than the con-ventional fully developed laminar value for constantheat flux conditions, NuD?4.36? Which combinationis associated with the smallest Nusselt numbers? Whatcan you say about the ability to predict convection heattransfer coefficients in a small-scale device if the accommodation coefficients are not known for mate-rial from which the device is fabricated? Use proper-ties of air at atmospheric pressure and T?300 K.