Evaluation of Convective Heat Transfer and Natural Circulation in an Evacuated Tube Solar Collector

The evacuated tube solar collector ETC is studied intensively and extensively by experimental andtheoretical works, in order to investigate its performance enhancement of heat transfer, for Baghdad climatefrom April 2011 till the end March 2012. Experimental work carried out on a well instrumented collectorconsists 16 tubes aspect ratio 38.6 thermally insulated tank volume 112L. relationbetween convective transfer natural circulation inside estimated, efficiency, effect oftube tilt angles, incidence angle modifier, heating system investigated under different loads pattern (i.eclosed open flow) evaluate loss coefficient from tubes, test with variousaspect ratios (32.9 27.2). using two reflectors (FlatPlate Curved Plate) nanofluid (Water-AL2O3).Theoretical run software (Fluent 6.3), computethe velocity temperature profiles within tube, diameters, junction andstagnant region bottom tube. results shows that coefficientfor W/m2.K W/m2.K, maximum 79°C winter and99°C summer, while belong 99°C winter. best tilted (optimum) ofevacuated 41° annually. efficiency increased when (1, 0.6, 0.3)% volumefraction as(28.4, 6.8, 0.6)% respectively. decreases as (33, 62)% decreasing ratiofrom 38.6% 32.9% 27.2% An increase (16.9 7.08)% obtainedwhen curved flat plate From simulation is22.5°. stagnant influenced changing flux, ratio.