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Abstract
A newly developed empirical model based on the effectiveness–NTU approach was developed for a dry-cooling simulation to evaluate the thermal performance of air-cooled heat exchangers. The value of this model is that air-cooled heat exchanger performance can be studied in a variety of working conditions. This information is useful in dry-cooling system evaluation. The purpose of this study was to present a calculation that would be accurate and simple to implement, and could be applied to evaluate and optimize the thermal performance for hybrid (wet/dry) cooling towers, in which dry- and wet-cooling towers are designed to work in combination. This study was only limited to a dry-cooling section. The tests showed that the predictions of the model were accurate and efficient.
NOMENCLATURE
| A | = | air range (°C) |
| Ap | = | approach (°C) |
| C | = | a constant |
| cp | = | specific heat (kJ/kg-K) |
| G | = | air flow rate (kg/s) |
| H | = | height of automotive-radiator (m) |
| ITD | = | initial temperature difference (°C) |
| L | = | water flow rate (kg/s) |
| = | mass flow ratio of water to air | |
| Ka | = | volumetric mass transfer coefficient (kg/m3-s) |
| = | wet-cooling tower characteristic | |
| NTU | = | number of transfer units |
| n | = | a constant |
| Q | = | heat load (kW) |
| R | = | range (°C) |
| T | = | temperature (°C) |
| v | = | velocity (m/s) |
| V | = | volume of fill (m3) |
| W | = | width of automotive-radiator (m) |
Greek Symbols
| ϵ | = | effectiveness |
| ϵ* | = | estimated effectiveness |
| ρ | = | density |
Subscripts
| a | = | air |
| db | = | dry bulb |
| in | = | inlet |
| max | = | maximum |
| out | = | outlet |
| w | = | water |
| wb | = | wet bulb |
| 1 | = | inlet dry section |
| 2 | = | outlet dry section |
Additional information
Notes on contributors
Wanchai Asvapoositkul
Wanchai Asvapoositkul graduated from King Mongkut's University of Technology Thonburi (KMUTT) in 1985. He obtained his Ph.D. in 1995 from University College London (UCL). He is an associate professor at King Mongkut's University of Technology Thonburi, Department of Mechanical Engineering. His research interests lie in the fields of thermal fluids and computational fluid dynamics.
Mantheerapol Kuansathan
Mantheerapol Kuansathan is a postgraduate student at King Mongkut's University of Technology Thonburi (KMUTT), Department of Mechanical Engineering. He received his B.Eng. degree in 2009 from KMUTT, Thailand. His main research interests are thermal and fluid dynamics.