Analysis of waste heat recovery pipe configurations using computational fluid dynamics

Abstract

negative effects on the environment. This dissertation provides a deeper understanding of heat transfer and fluid flow characteristics in cross-flow heat exchangers to analyse the effectiveness of various configurations using Computational Fluid Dynamics (CFD). The main objective of this research was to investigate the application of square pipes for the enhancement of heat transfer using both 2D and 3D CFD simulations. Using 2D modelling, assessment involved testing square cross-sections with different orientations (0⁰, 25⁰, 45⁰, 65⁰) and a circular pipe. Considering a square pipe, the best orientation for heat transfer is at 45o whilst a circular pipe offered the best heat transfer overall. Using 3D modelling, generation of an optimal mesh was a complex but a fundamental task. An in-depth mesh design is presented. It was thoroughly analysed to make sure thermal and velocity boundary layers were captured by highlighting the significance of techniques such as inflation and face-sizing. Various single-pipe and multi-pipe 3D models were designed, meshed and simulated for cross-flow heat exchange analysis. The results for the single-pipe 3D simulations are comparable to the 2D ones but 3D effects, not captured by the 2D models are discussed in detail. Additionally, temperature variations were studied to show the relationship between temperature and heat transfer. The multi-pipe simulations involved a series of tandem and staggered configurations, with varying parameters such as pipe pitch. Increasing the pipe pitch in the tandem arrangement improved heat transfer, whereas in the staggered arrangement, an increase in the pipe pitch reduced heat transfer.