COHEX - A COMPUTER-MODEL FOR SOLVING THE THERMAL-ENERGY EXCHANGE IN AN ULTRA-HIGH TEMPERATURE HEAT-EXCHANGER - PART A - COMPUTATIONAL THEORY

The paper reports the development of a computer program that solves th e thermal energy exchange and pressure drop characteristics for bayone t-element heat exchangers. The prime motivation for the study was to a id the design of a heat exchanger for the externally-fired combined cy cle (EFCC) energy generation process. The essential feature of this hi gh-efficiency process is the ceramic bayonet-tube gas-gas heat exchang er for use with shell-side temperatures up to 1600 degrees C. It is en visaged that similar heat exchangers can be designed for applications in the metallic extraction and production industries. The program, nam ed COHEX (Composite Heat Exchanger), solves the basic governing equati ons of the exchanger. It makes use of a numerical iterative approach f rom an initial tube-side outlet temperature estimate to converge to a solution. For given inlet conditions, the program evaluates the heat t ransfer between the shell-side and tube-side streams and arrives at th e outlet conditions. This two-part paper presents a computational solu tion method using accepted techniques for conduction, convection and r adiation in the ceramic heat exchanger. Part A addresses the technolog ical 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, part B, describes the experimental facilities use d 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 out put. (C) 1998 Elsevier Science Ltd. All rights reserved.