A computational and experimental investigation of clamshell heat exchangers in residential gas furnaces

Lei Fang, Purdue University

Abstract

The focus of the research described herein is to study the physical processes of a clamshell heat exchanger commonly used in residential gas-fired furnaces. The main objective is to develop a computational model of the furnace heat exchanger that is able to simulate furnace performance. The purpose of the model is to provide design engineers a tool that can predict performance trends for given design variations. ^ A one-dimensional steady-state analytical model of the clamshell heat exchanger was developed. The model is general and permits variation in heat exchanger geometry, materials of construction, and operating conditions. The model also takes into account the external flow pattern of the heat exchanger. The outputs of the model are total pressure drop of the flue gas, axial temperature distribution of the flue gas, and temperature distribution of the heat exchanger surface. ^ Experimental tests of a standard furnace were performed to obtain benchmark data. The computed results were compared with the experimental data and the capabilities of the model to predict performance trends was assessed. The model was also used to predict performance characteristics of a different clamshell heat exchanger of similar geometry. The predictions agreed well with the corresponding experimental data. Finally, the model was used to perform parametric studies and to analyze the magnitude of different modes of heat transfer. ^ Most of the relevant physical transport processes associated with the clamshell heat exchangers are well understood. However, the dimples found on the clamshell heat exchangers have not been described in the literature. The pressure drop associated with a dimpled channel was investigated experimentally. Numerical simulations using a CFD (Computational Fluid Mechanics) package, FLUENT, were also performed to clarify the effects of the dimples. It was found that the dimples caused large pressure drop without significantly increasing heat transfer. As a result, it is suggested that the dimples be removed from the clamshell heat exchanger. Improved designs of the clamshell heat exchanger are suggested and their performances are evaluated with model predictions. ^

Degree

Ph.D.

Advisors

Major Professors: John Abraham, Purdue University, Victor W. Goldschmidt, Purdue University.

Subject Area

Engineering, Mechanical

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