Design and performance of a new type of boiler using concentrated solar flux

Abstract

In order to reduce the amount of CO2 emissions associated with industrial boiling, the design of a new solar boiler operating with concentrated solar energy has been proposed and studied in the present work. A lab-scale solar boiler was built to show the feasibility of the concept through experiments, and a thermal model was then developed to study the efficiency of the solar boiler under different boiling conditions. Several peculiarities distinguish this new design from conventional boilers: (i) the use of vertical heating downwards from a receiver placed on top of the boiler, (ii) the conical shape of the receiver oriented upside down and submerged in the liquid, (iii) the solar receiver has a conical cavity on top where vertical solar flux is received, and its lower surface is submerged in boiling fluid, (iv) the direct use of solar energy with optical concentrating facilities for boiling without intermediate heat transfer fluids, and (v) the study of the unconventional film-boiling regime at elevated receiver temperatures which spaces the boiling fluid from the surface of the receiver. The model was validated by the data collected and showed good consistency between predictions and experimental results, with an average error of 3.79% for temperatures and 2.08% for vapor mass flow rate. For the chosen operating conditions studied, the thermal efficiency of the solar boiler varied from 80% to 90%. Such a thermal model can play an important role for the study and design of new thermal processes involving concentrated solar heating for boiling such as desalination.