Thermodynamic origin of nonimaging optics

Abstract

Thermodynamic origin of nonimaging optics Lun Jiang, a and Roland Winston, a* a University of California, Merced Abstract. Nonimaging Optics is the theory of thermodynamically efficient 1 optics and as such depends more on thermodynamics than on optics. Hence in this paper a condition for the best design is proposed based on purely thermodynamic arguments, which we believe has profound consequences for the designs of thermal and even photovoltaic systems. This new way of looking at the problem of efficient concentration depends on probabilities, the ingredients of entropy and information theory while “optics” in the conventional sense recedes into the background. Much of the paper is pedagogical and retrospective. Some of the new development of flowline designs will be introduced at the end and the connection between the thermodynamics and flowline design will be graphically presented. We will conclude with some speculative directions of where the new ideas might lead. Keywords : nonimaging optics, thermodynamics, geometric flowline, *Corresponding author, email to:rwinston@ucmerced.edu Introduction Nonimaging Optics is the theory of thermodynamically efficient optics and as such depends more on thermodynamics than on optics. It is by now a key feature of most solar concentrator designs. What is the best efficiency possible? When we pose this question, we are stepping outside the bounds of a particular subject. Questions of this kind are more properly in the province of thermodynamics which imposes limits on the possible (like energy conservation) and the impossible (like transferring heat from a cold body to a warm body without doing work). And that is why the fusion of the science of light (optics) with the science of heat (thermodynamics), is where much of the excitement is today. When the problem of maximal concentration from extended sources was first confronted 2 , the tools of Hamiltonian mechanics were utilized, because classical geometrical optics was concerned with “point sources” 3,4 . In this paper we first present the failure of classical point source optics. The purpose to repeat the illustration of this paradox, is to show that, the conventional point and line understanding of geometric optics cannot fully represent the nature of the physics behind modern optical designs.