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RESEARCH PAPERS

Flow Control and Unsteady-State Analysis on Thermal Performance of Solar Air Collectors

[+] Author and Article Information
Sadasuke Ito

Department of Vehicle System Engineering,  Kanagawa Institute of Technology, Atsugi, 243-0292, Japanito@sd.kanagawa-it.ac.jp

Minoru Kashima, Naokatsu Miura

Department of Vehicle System Engineering,  Kanagawa Institute of Technology, Atsugi, 243-0292, Japan

J. Sol. Energy Eng 128(3), 354-359 (Mar 31, 2006) (6 pages) doi:10.1115/1.2210493 History: Received October 21, 2003; Revised March 31, 2006

Promotion of the use of renewable energy, such as solar heat, for space heating and drying crops and wood is desired to prevent global warming. High-temperature collection of heat by air collectors producing as much as 50°C in winter for space heating and about 80°C in summer for exchanging heat to circulating water for hot water supply would be appropriate applications. In this study, first, a flow control system for constant outlet temperature was installed in a hot air supply system to examine the feasibility of the control system. After experiments, it was found that the control system could function satisfactory. Second, an unsteady-state analysis was made to predict the thermal performance of a flat-plate collector under a given condition of variable flow rate. The analytical model became simple by the assumptions that the heat capacity of the air in the collector and heat conduction in the flow direction through the air and the materials of the collector could be neglected. The maximum differences in outlet temperature and collector efficiency for constant flow rate between the analysis and the experiment were 1.8°C and 6% of the collector efficiency, respectively, except in the beginning of experiments. The biggest difference in the collector efficiency was 30% at 3:00 P.M. , which occurred at the end of one of the experiments. The analytical results generally agreed well with the experimental results even when the flow rate and solar radiation changed greatly as time went on. Transient effects are important to predict outlet temperature for variable solar radiation intensity, wind speed, and flow rate.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic diagram of experimental apparatus

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Figure 2

Cross section of collector

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Figure 3

Model of heat transfer in collector

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Figure 4

Experimental results at Re=1400

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Figure 5

Experimental results and results of steady-state analysis at Re=1400

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Figure 6

Experimental results and results of unsteady-state analysis at Re=1400

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Figure 7

Experimental results at Re=2800

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Figure 8

Experimental results and results of steady-state analysis at Re=2800

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Figure 9

Experimental results and results of unsteady-state analysis at Re=2800

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Figure 10

Experimental results when the exit temperature of the air was set at 55°C

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Figure 11

Experimental results and results of unsteady-state analysis for operation at constant outlet temperature

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