Study on solid particles as a thermal medium

This experimental study is conducted as a part of a Department of Energy funded SunShot project titled High Temperature Falling Particle Receiver. In this concept, solid particles are heated by concentrated sunlight to very high temperatures to the point that they can become a suitable heat source for various thermal power and thermochemical cycles. Furthermore, one of the great advantages of this concept is the ability to store thermal energy in the solid particles at relatively low cost. However, an important feature of any Particle Heat Receiver (PHR) system is the particle to fluid heat exchanger (PFHXer), which is the interface between the solar energy system and the thermal power or chemical system. In order to create this system material data is needed for the design and optimization of this PFHXer. This study focuses on the heat transfer properties of particulates to solid surfaces. The particulates will be evaluated for three grain sizes of sand and two grain sizes of proppants. These two materials will be tested at one, five and ten millimetres per second in order to see how the various flow rates, which will be required for different loads, will affect the heat transfer coefficient. Finally the heat transfer coefficient will also be evaluated for both finned and non-finned heat exchangers to see the effect that changes in the surface geometry and surface area have on the heat transfer coefficient. The heat transfer coefficient will help determine the appropriate material that will be used in the PHR system. An experimental procedure is under development by Georgia Institute of Technology to examine the heat transfer coefficient. To accurately characterize the size distribution of the materials, the material will be placed through a sifting unit. Afterwards the material will be placed into the testing apparatus. The main components of the testing apparatus consist of the Old's Elevator which is used to move the sand and the PFHXer. The PFHXer is made up of the constant head plenum and the heating box. The constant head plenum allows for a constant particulate head and uniform flow. The heating unit is made up of eight electric cartridge heaters. These heaters act as the non-finned tubed heaters and through the use of a metal casing can also be changed into finned tubed heaters. By running the system to steady and state and measuring the surface, inlet and outlet temperatures the heat transfer coefficient can be calculated. (C) 2013 C. Nguyen. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).