A heat exchanger is being designed as a component of a geothermal power system in which heat is transferred from the geothermal brine to a “clean” fluid in a closed-loop power cycle. The heat exchanger, a shell-and-tube type, consists of 100 galvanized iron tubes 2 cm in diameter and 5 m long, as shown. The temperature of the fluid is 200°C, the density is 860 kg/m³, and the viscosity is 1.35 × l0^–4 N^∙s/m². The total mass flow rate through the exchanger is 40 kg/s.

a. Calculate the power required to operate the heat exchanger, neglecting entrance and outlet losses.

b. After continued use, 2 mm of scale develops on the inside surfaces of the tubes. This scale has an equivalent roughness of 0.5 mm. Calculate the power required under these conditions.

Transcribed Image Text:

5 m 2 cm Side view