COHEX: a computer model for solving the thermal energy exchange in an ultra high temperature heat exchanger. Part B: validation and results

Abstract

The paper reports the development of a computer program that solves the thermal energy exchange and pressure drop characteristics for bayonet-element heat exchangers. The prime motivation for the study was to aid the design of a heat exchanger for the externally-fired combined cycle (EFCC) energy generation process. The essential feature of this high-efficiency process is the CMC (ceramic matrix composite) bayonet-tube gas–gas heat exchanger for use with shell-side temperatures up to 1600°C. It is envisaged that similar heat exchangers can be designed for applications in the metallic extraction and production industries. The program, named COHEX (composite heat exchanger), solves the basic governing equations of the exchanger. It makes use of a numerical iterative approach from an initial tube-side outlet temperature estimate to converge to a solution. For given inlet conditions, the program evaluates the heat transfer between the shell-side and tube-side streams and arrives at the outlet conditions. This two-part paper presents a computational solution method using accepted techniques for conduction, convection and radiation in the high temperature heat exchanger. Part A addresses the technological background of the EFCC application and the theoretical content of COHEX in terms of accuracy and sophistication of the code. The second part of this paper reported here, part B, describes the experimental facilities used to gather data in order to validate the program output. A comparison of computed and experimental data is presented. The paper progresses to illustrate the effects of parameter variation on heat exchanger output.