Evaluation of Convective Heat Transfer and Natural Circulation in an Evacuated Tube Solar Collector
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Abstract
The evacuated tube solar collector ETC is studied intensively and extensively by experimental and
theoretical works, in order to investigate its performance and enhancement of heat transfer, for Baghdad climate
from April 2011 till the end of March 2012. Experimental work is carried out on a well instrumented collector
consists of 16 evacuated tubes of aspect ratio 38.6 and thermally insulated tank of volume 112L. The relation
between convective heat transfer and natural circulation inside the tube is estimated, collector efficiency, effect of
tube tilt angles, incidence angle modifier, The solar heating system is investigated under different loads pattern (i.e
closed and open flow) to evaluate the heat loss coefficient from tank and tubes, test the collector with various
aspect ratios (32.9 and 27.2). The enhancement in collector performance is studied by using two reflectors (Flat
Plate and Curved Plate) and nanofluid (Water-AL2O3).Theoretical work is run by software (Fluent 6.3), to compute
the velocity and temperature profiles within the tube, for different tube diameters, effect of tube junction angle and
stagnant region in the bottom of the evacuated tube. The experimental results shows that the heat loss coefficient
for tube is W/m2.K and for tank is W/m2.K, the maximum collector temperature is 79°C in winter and
99°C in summer, while that belong to nanofluid collector is 99°C in winter. The best tilted angle (optimum) of
evacuated tube is 41° annually. The collector efficiency increased when using nanofluid of (1, 0.6, 0.3)% volume
fraction as(28.4, 6.8, 0.6)% respectively. The efficiency decreases as (33, 62)% when decreasing tube aspect ratio
from 38.6% to 32.9% and 27.2% respectively. An increase of (16.9 and 7.08)% in collector efficiency is obtained
when using curved and flat plate reflectors respectively. From simulation the best junction angle of the tank is
22.5°. The stagnant region is influenced with changing heat flux, tilted angle and aspect ratio.
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References
Evacuated Tube Heat Pipe Solar Water Heating System, Ph.d. Thesis, University of Baghdad, Mechanical Engineering Department2009.
Al-asadi Q. M., Heat Transfer Numerical Analysis Of a Thermosyphon Solar Heating System, M.Sc. thesis, University of Basra, Chemical Department,1993.
Budihardjo I., Morrison G.L., Performance of Water-in- Glass Evacuated Tube Solar Water Heaters,Solar Energy, Vol. 83, Issue 1, pp. 49-56, 2009.
Duffi J. A., Beckman W., Solar Engineering of Thermal Processes, University Of Wisconsin-Madison, Solar Energy Laboratory.
Eiyad A.N.,Ziyad M., Hakan F. O., Antonio C.,Effect of Nanofluid Properties on Natural Convection enclosure,International Journal of Heat and Mass Transfer, Vol 49, pp. 479-491, 2009.
Eiyad A.N., Hakan F. O., Effect of Inclination Angle on Natural Convection in Enclosure Filled with Cu-water Nanofluid, International Journal of Heat and Fluid Flow, International Journal of Heat and Fluid Flow, Vol. 30, Issue 4, pp. 669-678, 2009.
G.L. Morrison, I.Budihardjo, M.Behnia, WATER-INGLASS EVACUATED TUBE SOLAR WATER HEATERS, Solar Energy, Vol. 76, No. 1, pp. 135-140, 2004.
Hamza J. H.,Thermal Performance of Evacuated Tube Solar Heating System, University of Baghdad, Mechanical Engineering Department, 2009.
I. Budihardjo, G.L. Morrison, M. Behnia, Development of TRNSYS Models for Predictingthe Performance of Water-in-Glass Evacuated Tube Solar Water Heaters, University of New South Wales in Australia, School of Mechanical and Manufacturing Engineering, available at www.academicsearch.com , 2003.
I. Budihardjo, G. L. Morrison, M. Behnia, Performance of a Water-in-Glass Evacuated Tube Solar Water Heater,Solar Energy, Vol. 83, pp. 49- 56, 2009.
I.Budihardjo, G. L. Morrison, M.Behnia Measurement and Simulation of Flowrate in a Water -In-Glass Evacuated Tube Solar Water Heater, Mina S., Amir H. M., Farhad T., Numerical Simulation of Steady Natural Convection Heat Transfer in a 3-Dimensional Single-EndedTube Subjected to a Nanofluid, Int. Comm.in Heat and Mass Transfer, Vol. 37,pp. 1535–1545,2010.
John H. L.IV, John H. L. V.,A Heat Transfer Text Book, Third edition. University Of Houston, Department of Mechanical Engineer, Department of Mechanical Engineer Massachusetts Institute of Technology, 2008.
Michel H., Investigation of Evacuated-Tube Solar CollectorsPerformanceUsing Computational Fluid Dynamics, IEEE Xplore, pp. 240-244, 2009. Solar Energy , vol. 78, no. 2, pp. 257-267, 2005.
S. Yan, W. Yu, R. Tian, S. LI “Flow Structure in a Water-in-Glass Evacuated Tube Solar Water Heater, National Natural Science Foundation, pp. 4018-4021,IEEE, 2010.