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Chapter 4: Mass Transfer and Evaporative Cooling

By Detlev G. Kröger
From Air-Cooled Heat Exchangers and Cooling Towers: Thermal-Flow Performance Evaluation and Design, Volume 1

4.0 Introduction

Psychrometry is the study of the properties of mixtures of air and water vapor. The subject is important in cooling system practice because atmospheric air is not completely dry but is a mixture of air and water vapor. In certain cooling systems, water is added to the air-water-vapor mixture. Psychrometric principals will be applied in this and later chapters to evaluate the performance of cooling towers, evaporative coolers, and systems incorporating adiabatic precooling of the air.

Since there is usually both a heat and mass transfer process between the air and some wetted surface, information on mass transfer is presented. Because of the analogy that exists between momentum, heat, and mass transfer, there is a similarity in the equations employed.

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Products & Services
Evaporative Coolers
Evaporative coolers are cooling devices that use the evaporation of water into the air to cool the air temperature. They are sometimes called air coolers, desert coolers or swamp coolers.
Cooling Towers
Cooling towers are defined as any open water recirculation device that uses fans or natural draft to draw or force air to contact and cool water by evaporation.
Heat Transfer Fluids and Thermal Oils
Heat transfer fluids, thermal oils, circulating coolants, and heater liquids are used to carry thermal energy in process heating and machine cooling applications.
Quenching Oils and Heat Treatment Fluids
Quenching oil and heat treatment fluids are designed for rapid or controlled cooling of steel or other metal as part of a hardening, tempering or other heat-treating process.
Refrigeration Compressors and Air Conditioning Compressors
Refrigeration compressors and air conditioning compressors provide air conditioning, heat pumping, and refrigeration for large-scale facilities and equipment. Refrigeration compressors are sometimes called refrigerant compressors.
Topics of Interest

4.1 Mass Transfer When a mixture of gases or liquids is contained such that a concentration gradient of one or more of the components exists across the system, there will be mass transfer on a...

Evaporative Cooling An ideal evaporative cooling process occurs at a constant wet-bulb temperature, cooling the air to 100% relative humidity. The inlet warm air is partly in contact with the liquid...

In dealing with processes involving exchange of mass and energy between a liquid and an essentially insoluble gas, the principles of psychrometry are useful. Important operations to consider are the...

This extended chapter can be found on the website www.cambridge.org/nellisandklein. Mass transfer occurs whenever fluid flows; that is, some mass is transferred from one place to another. However, the...

2.2 Psychrometry of Inlet Air Cooling The two most prevalent types of inlet air cooling are direct contact evaporative cooling and indirect cooling using refrigerant or fluids with cooling coils.