Design and Analysis of Recirculating Air System in an Open Volumetric Air Receiver

Abstract

Use of renewable forms of energy like solar energy has been envisaged around the world to find an alternative to the depleting fossil fuels. Solar energy is to be harnessed in an efficient manner in order to utilize this abundant natural resource to cater to the growing power requirements. The current solar thermal technologies for trapping this energy can be broadly categorized into line and point focusing techniques. Heliostat based solar tower is one of the point focusing concepts. This presented thesis aims at design aspect of a component of this technology called volumetric air receiver. The recirculating air in a volumetric receiver plays an important role in its performance and this aspect is analyzed in this work. The thesis aims at design, development and evaluation of a volumetric air receiver which could have applications in metal processing. A computational fluid dynamics tool, ANSYS FLUENT is utilized in design of such a system. The design of a recirculating air injection system in three receiverconfigurations, namely circular, hexagonal and square is presented to demonstrate the obtained cooling in the system. Also, design of the footpiece of such a receiver (porous body) to enhance mixing at the outlet of the receiver is evaluated. Further, a mathematical model for the analysis of the recirculating air system in a volumetric air receiver is presented. This model can be utilized to assess the influence of air recirculation on the outlet air temperature and approximate the temperatures of the recirculating as well as the primary air. An experimental test setup was designed at IIT Jodhpur for testing of different solar sub-systems including the volumetric air receiver. Experiments were conducted for the evaluation of the designed system. Finally the presented mathematical model is validated with the experimental results.