Design of Cooling Towers by the Effectiveness-NTU Method

1989 ◽  
Vol 111 (4) ◽  
pp. 837-843 ◽  
Author(s):  
H. Jaber ◽  
R. L. Webb
Keyword(s):  
Heat Exchanger ◽  
Cooling Tower ◽  
Design Method ◽  
Design Methods ◽  
Parallel Flow ◽  
Basic Method ◽  
Cooling Towers ◽  
Flow Configuration ◽  
Heat Exchanger Design

This paper develops the effectiveness-NTU design method for cooling towers. The definitions for effectiveness and NTU are totally consistent with the fundamental definitions used in heat exchanger design. Sample calculations are presented for counter and crossflow cooling towers. Using the proper definitions, a person competent in heat exchanger design can easily use the same basic method to design a cooling tower of counter, cross, or parallel flow configuration. The problems associated with the curvature of the saturated air enthalpy line are also treated. A “one-increment” design ignores the effect of this curvature. Increased precision can be obtained by dividing the cooling range into two or more increments. The standard effectiveness-NTU method is then used for each of the increments. Calculations are presented to define the error associated with different numbers of increments. This defines the number of increments required to attain a desired degree of precision. The authors also summarize the LMED method introduced by Berman, and show that this is totally consistent with the effectiveness-NTU method. Hence, using proper and consistent terms, heat exchanger designers are shown how to use either the standard LMED or effectiveness-NTU design methods to design cooling towers.

EFFECT OF INLET CONFIGURATION ON DISTRIBUTION OF AIR–WATER UPWARD FLOW IN A HEADER OF A PARALLEL FLOW HEAT EXCHANGER

2010 ◽  
Vol 18 (04) ◽  
pp. 265-277 ◽  
Author(s):  
NAE-HYUN KIM ◽  
SOO-HWAN KIM ◽  
JI-HOON PARK
Keyword(s):  
Heat Exchanger ◽  
Mass Flux ◽  
Flow Distribution ◽  
Parallel Flow ◽  
Upward Flow ◽  
Flow Configuration ◽  
Water Flows ◽  
Rear Part ◽  
Flat Tubes ◽  
Flow Heat

The effect of inlet configuration (parallel, normal, vertical) on flow distribution in a parallel flow heat exchanger consisting of round headers and ten flat tubes is experimentally studied using air and water. The effects of tube protrusion depth as well as header mass flux, and quality are investigated for upward flow configuration. It is shown that best flow distribution is obtained for vertical inlet configuration, followed by normal inlet and parallel inlet configuration. For upward flow, significant portion of the water flows through the rear part of the header. As protrusion depth increases, more water is forced to the rear part of the header. The effect is most significant for parallel inlet, followed by normal and vertical inlet. The effect of mass flux or quality is opposite to that of the protrusion depth. Possible explanation is provided from flow visualization results.

Heat Exchanger Design Methodology for Electronic Heat Sinks

2006 ◽  
Vol 129 (7) ◽  
pp. 899-901 ◽  
Author(s):  
Ralph L. Webb
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Temperature Difference ◽  
Transfer Rate ◽  
Design Methodology ◽  
Design Method ◽  
Heat Sinks ◽  
Inlet Temperature ◽  
Heat Exchanger Design ◽  
Electronic Heat

This paper discusses the “inlet temperature difference” (ITD) based heat-exchanger (and its variants) design methodology frequently used by designers of electronic heat sinks. This is at variance with the accepted methodology recommended in standard heat-exchanger textbooks—the “log-mean temperature difference,” or the equivalent ε-NTU design method. The purpose of this paper is to evaluate and discuss the ITD based design methodology. The paper shows that the ITD based method is an approximation at best. Variants of the method can lead to either under- or overprediction of the heat transfer rate. Its shortcomings are evaluated and designers are directed to the well established and accepted design methodology.

A Constant-Wall-Temperature Model for Prediction of Thermal Performance of Gas-to-Gas Counter-Flow and Parallel-Flow Microchannel Heat Exchangers

2011 ◽  
Author(s):  
Kohei Koyama
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Difference Method ◽  
Heat Exchangers ◽  
Parallel Flow ◽  
Counter Flow ◽  
Partition Wall ◽  
Transfer Rates ◽  
Flow Configuration ◽  
Microchannel Heat Exchanger

Thermal performances of gas-to-gas counter-flow and parallel-flow microchannel heat exchanger have been investigated. Working fluid used is air. Heat transfer rates of both heat exchangers are compared with those calculated by a conventional log-mean temperature difference method. The results show that the log-mean temperature difference method can be employed to a parallel-flow configuration whereas that cannot be employed to a counter-flow configuration. This study focuses on the partition wall which separates hot and cold passages of the microchannel heat exchanger. The partition wall is negligibly thin for a conventional-sized heat exchanger. In contrast, the partition wall is thick compared with channel dimensions for a microchannel heat exchanger. A model which includes the effect of the thick partition wall is proposed to predict thermal performances of the microchannel heat exchangers. The heat transfer rates obtained by the model agree well with those obtained by the experiments. Thermal performances of the counter-flow and parallel-flow microchannel heat exchangers are compared with respect to one another based on temperature of the partition wall. The comparison results show that thermal performances of the counter-flow and parallel-flow microchannel heat exchangers are identical. This is due to performance degradation induced by the thick partition wall of the counter-flow microchannel heat exchanger. This study reveals that the thick partition wall dominates thermal performance of a gas-to-gas microchannel heat exchanger.

The Concept of Irreversibility in Heat Exchanger Design: Counterflow Heat Exchangers for Gas-to-Gas Applications

1977 ◽  
Vol 99 (3) ◽  
pp. 374-380 ◽  
Author(s):  
A. Bejan
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Design Method ◽  
Thermal Design ◽  
Design Parameters ◽  
Regenerative Heat ◽  
Pressure Drops ◽  
Heat Exchanger Design ◽  
Thermodynamic Irreversibility ◽  
Useful Power

The thermal design of counterflow heat exchangers for gas-to-gas applications is based on the thermodynamic irreversibility rate or useful power no longer available as a result of heat exchanger frictional pressure drops and stream-to-stream temperature differences. The irreversibility (entropy production) concept establishes a direct relationship between the heat exchanger design parameters and the useful power wasted due to heat exchanger nonideality. The paper presents a heat exchanger design method for fixed or for minimum irreversibility (number of entropy generation units NS). In contrast with traditional design procedures, the amount of heat transferred between streams and the pumping power for each side become outputs of the NS design approach. To illustrate the use of this method, the paper develops the design of regenerative heat exchangers with minimum heat transfer surface and with fixed irreversibility NS.

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