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Research Papers

Experimental Study of a Solar Air Heater With a New Arrangement of Transverse Longitudinal Baffles

[+] Author and Article Information
Afaq Jasim Mahmood

Machine and Equipment Department,
Baghdad Technology Institute,
Middle Technical University,
Baghdad, Iraq
e-mail: afaqjasem@yahoo.com

1Corresponding author.

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received June 25, 2016; final manuscript received January 9, 2017; published online February 8, 2017. Assoc. Editor: M. Keith Sharp.

J. Sol. Energy Eng 139(3), 031004 (Feb 08, 2017) (12 pages) Paper No: SOL-16-1297; doi: 10.1115/1.4035756 History: Received June 25, 2016; Revised January 09, 2017

This study presents a new design for improving the convection heat transfer coefficients of double-pass solar air heater. Three cases were described by using a different number of transverse baffles (three, five, and seven) in the lower channel of the collectors; steel mesh sheets were also used to enlarge the heat transfer area. All collectors have a space of 25 mm between its glass covers and a 50 mm depth of air channel. Furthermore, this work examined the effect of air flow rate and baffles number on device's thermal efficiency and outlet temperature. The experimental results indicate raises in the thermal efficiency as the air flow rate goes from 0.011 kg/s to 0.038 kg/s. A maximum efficiency of 68% was obtained from the case of seven baffles at the air flow rate of 0.038 kg/s. Moreover, the difference between collector's inlet and outlet temperatures, ΔT, indicated an inverse relationship with air flow rate. Thus, the results show ΔT increases as the air flow rate reduced. The maximum temperature difference recorded was 54 °C, which achieved using seven baffled solar air heater at 0.011 kg/s air flow rate in the middle of the day. It has also been found that thermal efficiency of double-pass solar air heater is greater than single-pass solar air heater, using same air flow rate and number of baffles. Finally, the pressure drop associated with increasing the number of baffles and air flow rate was deliberated.

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Figures

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Fig. 1

Schematic assembly of the double-pass SAH, five baffles and wire mesh layers, section A–A, side view of double-pass SAH

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Fig. 2

Solar intensity versus time of the day for double- pass SAH, during testing of the SAHs having (a) three baffles, (b) five baffles, and (c) seven baffles, with 5 cm bed height

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Fig. 3

Inlet temperature versus time of the day for: (a) three baffles, (b) five baffles, and (c) seven baffles, for double-pass SAH, with 5 cm bed height

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Fig. 4

Temperature difference versus standard local time of the day at different mass flow rates: (a) three baffles, (b) five baffles, and (c) seven baffles, for double-pass SAH, 5 cm bed height

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Fig. 5

Glass temperature difference versus standard local time of the day, for double-pass SAH: three, five, and seven baffles, 5 cm height of bed, at air flow rates 0.011 kg/s and 0.032 kg/s

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Fig. 6

Bed temperature difference versus standard local time of the day, for double-pass SAH: three, five, and seven baffles,with 5 cm height of bed, at air flow rates 0.011 kg/s and 0.032 kg/s

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Fig. 10

Efficiencies comparison between single-pass and double-pass SAHs, for seven baffles, with 5 cm height of bed, at air flow rates 0.011 kg/s and 0.032 kg/s

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Fig. 11

Thermal efficiency of the collectors versus temperature parameter (To − Ti)/I, for single- and double-pass SAHs, at different air flow rates at (13:00 p.m.) for: (a) three baffles, (b) five baffles, and (c) seven baffles

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Fig. 7

Temperature difference ΔT, bed temperature difference ΔTbed and glass temperature difference ΔTg versus air flow rates, for double-pass SAH, seven baffles, with 5 cm height of bed

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Fig. 8

Thermal efficiency versus standard local time of the day at different air flow rates: (a) three baffles, (b) five baffles, and (c) seven baffles, for double-pass SAH, with 5 cm height of bed

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Fig. 9

Average thermal efficiency across the double-pass SAHs versus air flow rates for three, five, and seven baffles, with 5 cm height of bed

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Fig. 12

Pressure drop across the bed versus mass flow rates for: (a) three baffles, (b) 5 baffles, and (c) seven baffles, and sixteen steel mesh sheets

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Fig. 13

Pressure drop across the bed, average thermal efficiency and temperature differences versus mass flow rates for seven baffles and sixteen steel mesh sheets SAH

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