Francisco J. Collado

Calculation of the annual thermal energy supplied by a defined heliostat field

This paper presents a new simplified procedure for evaluating the annual energy produced by a defined heliostate field, based on two continuous functions: annual energy per unit of mirror with its center placed at some point; and annual average density of mirror per unit area of level terrain (which defines the field) at the same point. The first function is based on an analytic model for the flux density due to a focused heliostat, and the second on some simplifying assumptions; in particular: radial staggered configuration, azimuthal spacing constant through the field, blocking only calculated with the two shoulder heliostats in the first row in front, and the exclusion of shading. This allows the density function (and thus the field) to be defined through a constant (in time) blocking factor, a constant azimuthal separation and the tower height. The annual energy will be the integral of the product of these two functions over all the domain of the field. This continuous evaluation is compared with a discrete evaluation in a real case of a solar central receiver: CESA-1 in Almeria (Spain). The thermal losses are not included.

New considerations on the mass and energy balances in one-dimensional two-phase flow at steady state

Abstract A new equation to be added to the classical mass balance expressions for two-phase flow is presented. It is based on the definition of new differential control volumes of variable length which are proportional to the gas velocity in a compressible flow. The new equation is equivalent to the gas—solids velocity ratio being constant throughout the duct, and it is used to derive a new expression of the energy balance for a twophase, non-reacting flow. Through this energy balance, new correlations for the pressure drop in pneumatic conveying lines are obtained, showing an excellent agreement with experimental data from the high-pressure research facility of the Institute of Gas Technology, Chicago, IL. Finally, a more general equation, which is also valid for the mass balance of reacting flows, is supplied.

Reynolds transport theorem for a two-phase flow

Transport equations for one-dimensional (1d), steady, two-phase flow have been proposed based on the fact that if the phases have different velocities, they cannot cover the same distance (the control volume length) in the same time. Thus, working in the same control volume for the two phases, the time scales of the phases have to be different. From this approach, transport balances for 1D, steady, two-phase flow have been already derived, supplying acceptable correlations for two-phase flow. Here, based on the strict application of the Reynolds transport theorem, general transport balances for two-phase flow are suggested.

Improved heliostat field design for solar tower plants

In solar power tower (SPT) systems, selecting the optimum location of thousands of heliostats and the most profitable tower height and receiver size remains a challenge. Campo code is prepared for the detailed design of such plants in particular, the optimum layout, provided that the plant size is known. Therefore, less exhaustive codes, as DELSOL3, are also needed to perform preliminary parametric analysis that narrows the most economic size of the plant.