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Research Papers

Numerical Study on Heat Transfer Enhancement and Friction Factor of LS-2 Parabolic Solar Collector

[+] Author and Article Information
Omid Karimi Sadaghiyani

Department of Mechanical Engineering,
Khoy Branch, Islamic Azad University,
5881666763 Khoy, Iran
e-mail: st_O.sadaghiyani@urmia.ac.ir

Seyed Mehdi Pesteei

e-mail: sm.pesteei@urmia.ac.ir

Iraj Mirzaee

e-mail: i.mirzaee@urmia.ac.ir
Department of Mechanical Engineering,
Urmia University,
7947664857 Urmia, Iran

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING DIVISION. Manuscript received November 19, 2011; final manuscript received May 7, 2012; published online October 21, 2013. Assoc. Editor: Zahid Ayub.

J. Thermal Sci. Eng. Appl 6(1), 012001 (Oct 21, 2013) (10 pages) Paper No: TSEA-11-1157; doi: 10.1115/1.4024699 History: Received November 19, 2011; Revised May 07, 2012

In this work, the distribution of solar heat flux around receiver was calculated by Mont-Carlo statistical technique that has been written using matlab. The numerical investigations of convective heat transfer process, friction factor, and efficiency of LS-2 parabolic collector have been performed. Based on finite volume methods, the influence of Rayleigh number (Ra), diameter of plugs, and thermal conductivity of the tube were studied on Nusselt number, outlet temperature, and the efficiency of collector. Because of using several central plugs with different diameters, the amounts of flow velocity have been changed, as the mass flow rate of each case study was considered constant. The diameters of plug were as: 10, 15, and 25 mm, respectively. The diameter of LS-2 collector plug was 50.8 mm (r* = 0.765). So, in order to validate the numerical simulation method, the outlet temperature of LS-2 collector (Dp = 50.8 mm) was compared with Dudley et al. (Dudley, V., Kolb, G., Sloan, M., and Kearney, D., 1994, “SEGS LS2 Solar Collector—Test Results,” Report of Sandia National Laboratories, Report No. SANDIA94-1884) experimental results. Finally, the results show that, for r*<0.6 m, the natural convection conquers to forced convection and for r*>0.6 m the mixed convection is the dominant mechanism of heat transfer. Also, with the increase of plug diameter, friction factor decreases and the minimum amount of Nusselt number is occurred at r*=0.6 m.

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References

Figures

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Fig. 1

Parabolic trough collector and the cross section of LS-2 absorber tube

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Fig. 2

The specification of a sun ray in the cone via two guide angles

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Fig. 7

The variation diagram of Nu versus the ratio of diameters

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Fig. 8

The distribution of temperature in outlet cross section of absorber tube

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Fig. 3

The algorithm of MCRT in matlab software

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Fig. 4

The solar heat flux distribution around absorber tube in LS-2 PTC

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Fig. 6

The variation diagram of Nu and fRe versus Ra

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Fig. 5

The diagram of outlet temperature and collector efficiency versus nondimensional plug diameter

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Fig. 9

The fRe rising under different r*

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Fig. 10

The value comparison of case studies

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Fig. 11

The diagram of nondimensional outlet temperature versus the substances of tube and working fluid

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Fig. 12

The view of outlet cross section (dp =  50.8 or r* = 0.77)

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Fig. 13

The distribution of temperature in outlet cross section of tube (dp = 50.8 or r*=0.77)

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Fig. 14

The view of inner wall of absorber tube, plug surface, and specified paths

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Fig. 15

The amounts of local Nu on plug and inner wall of tube at three different positions

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Fig. 16

The view of linear paths on the inner wall of absorber tube

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Fig. 17

The Nu diagram versus z/L nondimensional parameter on the inner wall of tube

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Fig. 18

The view of linear paths on the plug

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Fig. 19

The Nu diagram versus z/L nondimensional parameter on plug surface

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