Distilled water is being cooled by a 20% propylene glycol solution in a 1-1/U counter flow plate and frame heat exchanger. The water enters the heat exchanger at 50°F at a flow rate of 86,000 lbm/h. For safety reasons, the water outlet temperature should never be colder than 35°F. The propylene glycol solution enters the heat exchanger at 28°F with a flow rate of 73,000 lbm/h. The port distances on the heat exchanger are Lv = 35 in and Lh = 18 in. The plate width is Lw = 21.5 in. The plate thickness is 0.04 in with a plate pitch of 0.12 in. The chevron angle is 30° and the plate enlargement factor is 1.17. All ports have a 2 in diameter.
The fouling factor of the propylene glycol solution can be estimated as 2 ×
10−5 h-ft2-°F/Btu.

a. Determine the maximum number of plates the heat exchanger can have while ensuring that the water outlet temperature never drops below 35°F.

b. Determine the thermal and hydraulic performance of the heat exchanger with the specified number of plates. Summarize your findings in a table similar to Table 5.17.

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TABLE 5.17 Results of the PHFX Analysis of Section 5.10.4 Parameter Manufacturer's Specifications Plate material Chevron angle Number of passes Number of plates Plate thickness Vertical port distance Horizontal port distance Plate width Enlargement factor Compressed plate pack length Port diameters Thermal Performance Hot fluid mass flow rate Hot fluid inlet temperature Desired hot fluid outlet temperature Cold fluid mass flow rate Cold fluid inlet temperature Value AISI 304 Stainless Steel 50 1 50 0.04 in 3.8 ft 0.9 ft 16 in 1.25 8 in 3 in 120,000 lbm/h 190F 110F 100,000 lbm/h 50F