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Research Papers

Exergy Performance Analysis and Optimization of a Desiccant Wheel System

[+] Author and Article Information
Mohsen Ali Mandegari

Department of Process Engineering,
University of Stellenbosch,
Banghoek Road,
Stellenbosch 7600, South Africa
e-mail: Mandegari@Sun.ac.za

Somayeh Farzad

Department of Process Engineering,
University of Stellenbosch,
Banghoek Road,
Stellenbosch 7600, South Africa

Hassan Pahlavanzadeh

Chemical Engineering Faculty,
Tarbiat Modares University,
Tehran 1415543Iran

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received January 7, 2015; final manuscript received March 30, 2015; published online May 12, 2015. Assoc. Editor: Samuel Sami.

J. Thermal Sci. Eng. Appl 7(3), 031013 (Sep 01, 2015) (10 pages) Paper No: TSEA-15-1003; doi: 10.1115/1.4030415 History: Received January 07, 2015; Revised March 30, 2015; Online May 12, 2015

This paper focused on the exergy analysis and optimization of a dehumidification desiccant wheel (DW) system. A two-dimensional unsteady state numerical model was developed for simulation of the heat and mass transfer phenomena in a representative channel of a DW matrix. The DW mathematical model was validated using a series of experimental data and parametric studies were conducted to investigate the effects of operating parameters on the DW system performance. Exergy parameters were also studied and adopted to predict the total inlet–outlet exergy and exergy destruction, as well as exergy effectivenesses. Furthermore, a new exergy effectiveness parameter was introduced based on the concept of dehumidification. Parametric studies were carried out to characterize the optimal performance of the overall system regarding exergy destruction and exergy dehumidification effectivenesses. The results demonstrate that electrical power consumption, regeneration heat, and heat and mass transfer between air and desiccant are the main sources of exergy destruction. The optimization calculation shows that at the lowest process air velocity (up = 0.2 m/s), lowest DW rotational speed (NDW = 4 Rph), highest regeneration air temperature (Ta,r,in = 140 °C), and moderate regeneration air velocity (ur = 1.7 m/s), minimum exergy destruction occurs. The optimal value of the parameters proves that, when exergy destruction effectiveness is selected as the objective function, the only regeneration air velocity is decision variable of optimization and operational limits impose on the other parameters.

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Figures

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Fig. 1

Schematic view: (a) DW and (b) air channels

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Fig. 2

Experimental DW system. (a) Simplified schematic view and (b) real experimental setup.

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Fig. 3

The side view of control volume for the two-dimensional GSSR model

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Fig. 4

Comparison between transient experimental data and simulation results at the exit of one air channel. (a) Temperature and (b) humidity ratio. (Tar,in = 120.4 °C, Yar,in = 0.0067 kg/kg, Tap,in = 35.9 °C, Yap,in = 0.0067 kg/kg, and NDW = 20 Rph).

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Fig. 5

Variation of total inlet exergy and exergy destruction rates versus process air velocity

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Fig. 6

Variation of exergy effectivenesses versus process air velocity

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Fig. 7

Variation of outlet process air temperature and humidity ratio versus process air velocity

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Fig. 8

Variation of total inlet exergy and exergy destruction rates versus regeneration air velocity

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Fig. 9

Variation of exergy effectivenesses versus regeneration air velocity

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Fig. 10

Variation of total inlet exergy and exergy destruction versus regeneration air

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Fig. 11

Variation of exergy effectivenesses versus regeneration air temperature

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Fig. 12

Variation of total inlet exergy and exergy destruction rates versus DW rotational speed

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Fig. 13

Variation of exergy effectivenesses versus DW rotational speed

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Fig. 14

Flowchart of exergy optimization problem

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