Thermo-hydraulic Design of Solar Collector Networks for Industrial Applications

The design and selection of banks of solar energy collectors for thermal applications requires that two simultaneous design objectives be met: the working fluid must provide the heat load to the process and this must be supplied within the specifications of pressure drop. In this work, a solar collector will be termed heat exchanger and the total collector surface area is referred to as the network of solar collectors (NSC). A NSC is used in large scale applications and they can exhibit arrangements in series, parallel or any combination of these. Contrary to domestic applications where water flow through the exchanger on natural convection, in the case of large scale applications the flow of water is forced through the use of a pumping system. This paper looks at the selection of the most appropriate arrangement for a given application. The approach presented in this paper is based on the assumption of constant wall temperature; however, it can easily be extended to account for the case of variable wall temperature. The approach is graphically displayed with the length of the exchanger plotted against the number of arrays in parallel. Two curves are produced: the curve that shows the thermal length (constant heat load) and the hydraulic length (constant pressure drop). The thermal length is the dimension for which the exchanger meets the required heat duty and the hydraulic length is the dimension for which the exchanger absorbs the specified pressure drop. The point where the two curves meet determines the network structure that fulfils the required heat duty at the specified pressure drop. A systematic approach to solve this design problem is looked at in this work.