Question

A natural draft-cooling tower is to remove 50 MW of waste heat from cooling water, which enters the tower at 42 °C and leaves at 27 °C. Atmospheric air enters the tower at standard atmospheric pressure with dry and wet bulb temperatures of 23 °C and 18 °C respectively (approximately 62% relative humidity), and leaves saturated at 37 °C.

a) Sketch a fully labelled schematic diagram of the system identifying all the state points. Illustrate the process on a psychrometric chart.

b) Construct a property table giving the dry-bulb temperature, relative humidity, partial pressure of dry air, specific volume of dry air, enthalpy of dry air, and specific humidity for the air at both the inlet and the exit of the tower. Construct a separate property table giving the temperature, enthalpy, and phase for both the warm water and the cool water.

c) Using the first law of thermodynamics, calculate the mass flow-rate of cooling water, and the

volume flow-rate of air into the cooling tower.

d) Calculate the mass flow rate of the required makeup water.

Answer 1

using mass and energy balance and data from phychrometric chart we can find the required variables

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