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In this work, detailed investigations of convection heat loss from conical cavity receiver of solar parabolic dish collector using a numerical method and artificial neural network have been performed. The convective heat loss from the cavity receiver is primarily influenced by geometrical parameters, receiver orientation, and wind characteristics. The heat loss estimation is carried out by considering wind speed (V = 0–10 m/s), wind direction ( ψ = 90 ° and −90 °), receiver tilt ( γ = 0–90 °), diameter to height ratio (d/h = 0.5–1.5), and surface temperature (Ts = 500–800 K). The utmost heat loss occurs at a tilt of 60 ° for d/h < 1 and 75 ° for d/h ≥ 1 in head-on high wind speed, while in back-on high wind speed, it occurs at a tilt of 30 ° for all d/h values. The heat loss is lowest at 90° for V > 4 m/s. The d/h value of 0.5 performs well compared to other values. Further, the correlation for the Nusselt number has been proposed for the conical cavity receiver. [ABSTRACT FROM AUTHOR]

A quantitative analysis of total radiation heat loss from a cavity receiver is numerically studied. Gaussian eliminations method is used to solve the set of radiosity equations to estimate total radiation heat losses from entire cavity surface. The radiation heat loss increases with increase in cavity wall temperature, aspect ratio, and emissivity. For the aspect ratios (L/d) in the range of 2–3, the view factor of all cavity surfaces is lower and most suitable for design. The mean radiation heat loss model always overestimates the radiation heat loss and the overall effect of temperature, aspect ratio, and emissivity may estimate mean radiation heat loss even 14% higher as compared to total loss from entire cavity. The mean radiation model is not appropriate to design a large size, high temperature cavity with low emissivity cavity material. [ABSTRACT FROM AUTHOR]

Performance characteristics of a concentrated solar volumetric absorber are examined numerically. The thermal system considered consists of parabolic trough, glass tube, absorbing plate, and slurry containing 7% lauric acid as a phase change material and water as a carrier fluid. To assess the effect of the absorbing plate on performance characteristics, two locations of the absorbing plate on the glass tube surface are incorporated in the analysis. A selective surface is considered at the absorber plate surface for improved absorption of solar radiation and reduced thermal emission due to temperature increase at the surface. Temperature ratio, gain parameter, and pump power loss parameters are introduced to quantify the performance characteristics of the volumetric receiver. The study is extended to include the effect of Reynolds number on the receiver performance characteristics. A heating model incorporating radiation, convection, and conduction is adopted to simulate the thermal process. It is found that the gain parameter of the concentrated solar volumetric receiver improves by 15% when the absorber plate is located at the left face of the glass tube opposing the trough surface. The effect of Reynolds number on gain parameter is found to be inconsiderable. [ABSTRACT FROM AUTHOR]

The thermal performance of a cylindrical solar cavity with a convective boundary is modeled using Monte Carlo ray tracing to evaluate the impact of the geometry and the spectral characteristics of the surface on the absorption efficiency and the spatial distribution of temperature. Increasing cavity size for a fixed aperture size increases absorption efficiency and reduces wall temperature. Inconel, which serves effectively as a selective surface, provides the highest absorption efficiencies at over 90%. A surface coating of aluminum oxide produces a more uniform and lower average temperature distribution. [ABSTRACT FROM AUTHOR]

Results are reported of a numerical analysis of conduction heat loss from a parabolic trough solar receiver with controlled pressure within the annular gap between the tubular absorber and the glass vacuum jacket. A direct simulation Monte Carlo (DSMC)model of rarefied gas within the annular gap is coupled to radiation heat transfer for directional- and spectral-dependent concentrated incident solar radiation. This modeling approach is valid for high Knudsen numbers, and consistently predicts slightly higher heat loss than a continuum model using slip boundary conditions in the range of pressures of interest around 1 Pa. 3-D simulations of axial flow through the annular gap predict higher gas conductance by the DSMC method than by slip flow models, with values converging as pressure increases. [ABSTRACT FROM AUTHOR]