Problem 5-8 (A-E) A \" runaround heat-recovery system is to be simulated As show

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Problem 5-8 (A-E)

A " runaround heat-recovery system is to be simulated As shown in Fig. P5-8. the system consists of two identical water/finned-tube, cross-flow heat exchangers connected by a piping network containing a pump. Characteristics are as follows. WATER LOOP 100 ft of nominal 2-in schedule 40 pipe 10 standard elbows 6 gate valves One l 1/2 times 3 - 7 Goulds pump with a 6-in rotor (Fig, 4-32) Pump is powered by a motor with a speed of 3.500 rpm HEAT EXCHANGERS Finned tube,cross flow Air mixed, water unmixed Head loss in each exchanger HX- 0.0049q 1.852 HX in ft-lbf/ 1bm Q in gpm Area of each exchanger 5,000 ft2 Overall heat transfer coefficient U in Btu/hr-ft2 - degree F Q in gpm For the purposes of the simulation, use the properties of water at 50degree F. The inside air is at 72 degree F. the outside air at 10degree F. The mass-flow rate of both the inside and outside (make-up) air is 41 75 1bm/sec (This corresponds to about 2 air changes per hour for the structure under consideration.) Consider the water loop. Derive and explain the equation necessary to simulate the water loop. Develop a curve fit for the pump head vs. flow rate using the manufacturer's data. Consider the heat exchangers. Derive and explain the equations necessary to simulate the heat-exchange process. Devise a computer program to solve the system of equation generated in (a) and (b). What is the steady state operating point? Water flow rate (Q). pump increase in head. heat-exchanger head loss. cold-water temperature, hot-water temperature, total heat transfer, and air exit temperatures are needed as outputs. What problems might be encountered it the outside air drops to-20 degree F? Support your answer with simulation output. Find the bypass rate for the pump system shown in Fig. P5-9. The orifice is square edged with a 3/4 -in.-diameter hole and has a "K-factor" of aproximately 660 in a 3-in. pipe. All pipe steel, and all valves are gates. The fluid is water at 80 degree F.

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