Rates of heat transfer in a double-pipe heat exchanger, 

(a) Hot oil entering the heat exchanger in Example 15.4-1 at surface 2 is to be cooled by water entering at surface 1. That is, the exchanger is being operated in countercurrent flow. Compute the required exchanger area A, if the heat transfer coefficient U is 200 Btu/hr ∙ ft² ∙ F and the fluid streams have the following properties:

(b) Repeat the calculation of part (a) if U₁ = 50 and U₂ = 350 Btu/hr ∙ ft² ∙ F. Assume that U varies linearly with the water temperature, and use the results of Problem 15B.1. 

(c) What is the minimum amount of water that can be used in (a) and (b) to obtain the desired temperature change for the oil? What is the minimum amount of water that can be used in parallel flow? 

(d) Calculate the required heat exchanger area for parallel flow operation, if the mass rate of flow of water is 15,500lb_m/hr and U is constant at 200 Btu/hr ∙ ft² ∙ F. 

Transcribed Image Text:

Mass flow Heat Temperature leaving (°F) capacity entering rate (Ib/hr) (°F) (Btu/lb, · F) 100 Oil Water 10,000 5,000 200 60 0.60 1.00