CFD Investigation Of Cross Flow Over Tube Banks

Teh, Wei Yuan (2019) CFD Investigation Of Cross Flow Over Tube Banks. Project Report. Universiti Teknikal Malaysia Melaka, Melaka, Malaysia. (Submitted)

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Abstract

Heat exchangers are devices that facilitate the exchange of heat between two fluids that are at different temperatures while keeping them from mixing. Heat transfer in a conventional heat exchanger usually involves convection in each fluid and conduction through the wall separating the two fluids. Tube banks are usually found within a heat exchanger and circular tube bundle is one of the simplest geometries that is widely used. However, in the recent years, thermoacoustic heat engine has been receiving increased attention. Thermoacoustic engines are devices which use high-amplitude sound wave to pump heat from one place to another. The main difference between conventional heat exchanger and thermoacoustic heat engine is that one uses one-directional steady flow and the other one uses unsteady oscillatory flow. The main purpose of this project is to gain insight into the characteristics of heat transfer and fluid flow of cross flows over tube banks for both steady and oscillatory flows. All flows are investigated under similar operating condition. Two-dimensional numerical CFD model is conducted using finite volume discretization to evaluate the performance of these systems. The effect of cross flows on temperature, velocity, enthalpy (heat flux), and pressure drop are all investigated. Effect of cross flows over tube banks on fluid flow characteristic and heat transfer performance has been investigated. Numerical simulation has been conducted on a design model of circular tube banks with staggered arrangement using commercial CFD package, Ansys Fluent 16.0. Constant variable is the material, in which air will be flowing over tube banks while the tube is made of aluminium. The flow velocity of air is standardized which implies that Reynold number is constant. The manipulating variables are steady flow and transient oscillatory flow. Mesh independence study has been conducted by increasing the number of element. Best grid is the one with 19170 elements. Oscillatory flow model is a wave function and is ran for 7 cycles for stabilization of variables. The results are validated with theoretical results and consistency is achieved. It is found that steady flow with higher Re has better heat transfer performance compared to those with low Re. Oscillatory flow with higher drive ratio has better heat transfer performance. Steady flow has better heat transfer performance compared to oscillatory flow at identical Re. However this statement is inconclusive and more works are required to substantiate it. Recommendation for future work is to develop appropriate correlation or equation to compute heat transfer coefficient for oscillatory cross flow over tube banks

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