A 1/1-U counter flow plate and frame heat exchanger is being used to cool liquid ammonia using a chilled 15% magnesium chloride solution. The ammonia enters the heat exchanger at 32°C with a flow rate of 5 kg/s. The ammonia must not cooled any lower than 14°C. The calcium chloride solution enters the heat exchanger at −8°C at a flow rate of 4.2 kg/s. The plates of the heat exchanger are made from AISI 304 stainless steel. The plate thickness is 0.6 mm and the plate pitch is 3.5 mm. The vertical port distance is 0.9 m and the horizontal port distance is 0.25 m. The port diameters are 42 mm. The plate enlargement factor is 1.16. The fouling factors for ammonia and the magnesium chloride solution can be taken as 2 × 10−6 m2-K/W and 3.2 × 10−6 m2-K/W, respectively.

a. Determine the maximum number of plates that can be in this heat exchanger.

b. Determine the thermal and hydraulic performance of the heat exchanger with the specified number of plates. Summarize your results 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