Radiative heat flux control over spherical surfaces

Abstract

Tremendous efforts have been and are being devoted to control the radiative heat flux over complex spherical surfaces such as solar energy collectors. Classical energy balance methods and network analysis have been used by previous investigators to evaluate the relevant exchange-factors of any spherical collector. The complex characteristics of the radiative flux in automatic control systems of such surfaces, the simplifying assumptions, and the complexity and the size of the equation matrices used, limit the application of such methods even to very simple cases, and also does not often supply the desired accuracy because of the very high temperatures at the solar collectors focal point. As a realistic engineering solution, in the current work, a fast and accurate measurement system in conjunction with the relevant online closed loop control system is suggested. In the suggested method, measurement of the radiative heat flux of the complex surfaces is conducted using the Monte-Carlo statistical technique. The technique avoids many of the difficulties inherent in the averaging processes of the usual integral equation formulations. It also does not require the simultaneous solution of the complex equation matrix for the entire energy involved. The difference between either maximum or desired heat and the measured value of the radiative heat flux of the surface is reduced to an acceptable value by the closed loop control actuating signal. The system may also be used to control other types of radiation rather than "heat fluxes", over spherical and complex surfaces.