A one-pass condenser-heat exchanger, shown in the sketch, has 64 tubes arranged in a square array with 8 tubes per line. The tubes are 1.22 m long and are made of copper with an outside diameter of 1.27 cm. They are contained in a shell at atmospheric pressure. Water flows inside the tubes whose outside wall temperature is 98°C. Calculate (a) the rate of steam condensation and (b) the temperature rise of the water if the flow rate per tube is 0.0454 kg/s.

Question

GIVEN

? One-pass condenser heat exchanger with 64 tubes in a square array

FIND

(a) Rate of steam condensation

(b) Water temperature rise

SKETCH



PROPERTIES AND CONSTANTS

From Appendix 2, Table 13, the properties of saturated water at the film temperature (100 + 98)/2 = 99°C are

Answer 1

Wall temperature= 98°C

Saturation temperature = 100°C

Tube OD= 0.0127 m

Tube length = 1.22 m

Water flow rate= 0.0454 kg/s

From Equation (9.24), we can obtain the average heat transfer coefficient



where



and



Neglecting the vapor density compared to the liquid density, the quantity in the right bracket in the equation for the heat transfer coefficient is



so



The tube surface area is



The rate of heat transfer is therefore



(a) The flow rate of condensate is then



The heat transfer per tube is 83,688/64 W = 1308 W and this must equate to the increase in sensible heat in the cooling water, giving for the water temperature rise

(b)