In the spring, concrete surfaces such as sidewalks
Chapter 6, Problem 6.72(choose chapter or problem)
In the spring, concrete surfaces such as sidewalks anddriveways are sometimes very wet in the morning, evenwhen it has not rained during the night. Typical night-time conditions are shown in the sketch.BreezeT= 290 K,?= 0.7h_= 53 W/m2KTsky = 240 KConcreteTs = 275 K, = ?= 0.96Thin layer of liquid water (a) Determine the heat fluxes associated with convec-tion, , evaporation, , and radiation exchangewith the sky, .(b) Do your calculations suggest why the concrete iswet instead of dry? Explain briefly.(c) Is heat flowing from the liquid layer to the con-crete? Or from the concrete to the liquid layer?Determine the heat flux by conduction into or outof the concrete.
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