Performance measures of the axicon solar fluid heater

The definition of performance indices for the axicon solar fluid heater is essential for the assessment of a particular heater's performance or the comparison of different heaters of different designs, working under different conditions and producing different outputs. Two indices, the effectiveness and the efficiency, are introduced to describe the performance from two different aspects. The first index is the achieved fluid-temperature rise across the heater, while the second is the beneficially-utilized fraction of the available energy input. The study covers the two possible arrangements of fluid flow, i.e. counter and parallel. Mathematical formulae are derived to express the two performance indices in terms of the governing lumped dimensionless groups encompassing the numerous pertinent physical variables. The understanding of the performance of this radiant heater is deepened through exposing its resemblance to an imaginarily equivalent two-stream recuperator. The effect of the various factors on the performance, as described by the two performance indices, is investigated. The effect of manipulating certain parameters is shown to have contradictory effects on the two performance indices.