Research Papers

Heat Transfer Enhancement in a Flat-Plate Solar Water Heater Through Longitudinal Vortex Generator

[+] Author and Article Information
F. A. S. Silva

Energy Engineering,
Sao Paulo State University (UNESP)
Rosana 19274-000, SP, Brazil
e-mail: felipe.santos@unesp.br

L. O. Salviano

Department of Mechanical Engineering,
Sao Paulo State University (UNESP),
Ilha Solteira 15385-000, SP, Brazil
e-mail: leandro.salviano@unesp.br

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 July 18, 2018; final manuscript received November 30, 2018; published online January 8, 2019. Assoc. Editor: Gerardo Diaz.

J. Sol. Energy Eng 141(4), 041003 (Jan 08, 2019) (6 pages) Paper No: SOL-18-1326; doi: 10.1115/1.4042245 History: Received July 18, 2018; Revised November 30, 2018

The solar energy is a renewable source that has a great potential for conversion into thermal energy or for generation of electric power through photovoltaic panels in Brazil. Concerns about environmental impacts and the fossil resources scarcity have motivated the technological development of renewable alternatives to fill out the energy matrix. The flat-plate solar water heater is an equipment used for domestic or commercial applications to heat fluids, which can minimize the demand for electric energy and, consequently, decrease the electrical bill. However, the development of technologies to increase the conversion of solar energy into thermal energy remains a challenge in order to increase the efficiency of these devices. Thus, passive techniques to enhance heat transfer have been applied and those results seem to be promissory. Among them, delta-winglet longitudinal vortex generator (VG) is a consolidated passive technique currently applied on compact heat exchangers, although few works have been applied this technique on the solar water heater. By a computational fluid dynamics approach, in this work, we analyze the augmentation of heat transfer through delta-winglet longitudinal vortex generator inside a tube of a flat-plate solar water heater. For the Reynolds numbers 300, 600, and 900, the better ratio between the heat transfer and the pressure drop penalty is found for the attack angle of the delta-winglet of 30 deg, while the highest heat transfer was to the attack angle of 45 deg. Moreover, the first vortex generators showed significant impact only on the friction factor and could be eliminated of the solar water heater with no penalty to the heat transfer.

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Fig. 1

Transversal computational domain

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Fig. 2

Computational domain and boundary conditions

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Fig. 3

Computational domain discretization with elements of type tetrahedron

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Fig. 4

Comparison between simulation and theoretical results

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Fig. 5

The ratio of the enhancement heat transfer

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Fig. 6

The ratio of the pressure drop

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Fig. 7

The ratio between the heat transfer and pressure drop associated

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Fig. 8

Impacts of the vortex generator along the tube for Reynolds number 300

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Fig. 9

Impacts of the vortex generator along the tube for Reynolds number 600

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Fig. 10

Impacts of the vortex generator along the tube for Reynolds number 900



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