Techniques for Reducing Thermal Conduction and Natural Convection Heat Losses in Annular Receiver Geometries

Abstract

Analytical and experimental work has been undertaken to analyze thermal conduction and natural convection heat losses in annular receiver geometries. Techniques studied for reducing conduction heat loss include evacuation of the annulus gas, oversizing of the annular space while maintaining slight vacuum levels, and use of gases other than air in the annular space. For the geometry considered, total heat loss reductions of 10 percent to 50 percent may be obtained depending on the means by which the conduction heat loss is limited. In addition, natural convection studies considering the effects of nonuniform temperature distributions and eccentric cylinders are discussed. The numerical analysis performed indicates that highly nonuniform temperature distributions are required to appreciably affect the natural convection process between concentric cylinders and that rather large eccentricities cause only a slight increase in natural convection heat transfer.

Two Dimension Numerical Modeling of Receiver Tube Performance for Concentrated Solar Power Plant

“…The convection heat transfer between the outer surface of the absorber and inner surface of the glass envelope occurs by free-molecular convection [11] when the annulus between the absorber and the glass envelop is under vacuum (pressure < 133.3 pa). gi so g s , cv so gi , so cov, T T h d Q [4] The heat transfer coefficient between the outer surface for the absorber and the inner surface of the glass envelope h cv,s-g is calculated as follow [7] When the HCE annulus loses its vacuum (pressure > 133.3 pa), the convection heat transfer mechanism between the absorber and glass envelope occurs by natural convection.…”

Comparison of different heat transfer models for parabolic trough solar collectors

“…It's one of the important influence factors for improving calculation precision and analyzed below. Q r-g:conv:i ¼ pd r-ou Dlh r-g:conv:i ðt r:i -t g:i Þ ð 15Þ (A) Vacuum in annulus When pressure in the annulus is lower than 0.013 Pa, the heat transfer coefficient h r-g.conv.i is given by [6,16,18]:…”

Transient Infrared Thermography Heat Loss Measurements on Parabolic Trough Receivers under Laboratory Conditions

“…This term is a function of the absorber thermal emittance abs [%]. The second term abs-gl,gas accounts for the receiver annulus gas thermal conduction and natural convection [1].This term is a function of the annulus heat transfer coefficient h ann [W/m 2 .K]. The last term bellows corresponds to the sum of radial thermal losses at each receiver bellow.…”