An investigation of thermo-fluid dynamic performance of a Stirling engine regenerator by means of OpenFOAM

Abstract

A good design of the regenerator of a Stirling engine is required to obtain high performance and efficiency of such an engine. The regenerator is basically a heat-exchanger placed between the hot and cold working streams. It usually consists of stacked woven wires. The fluid pressure drop and heat transfer are the main parameters of the regenerator influencing the engine performance. In this work, friction coefficient, thermal efficiency and Nusselt number are numerically evaluated in order to assess the performance of the regenerator. The open-source software OpenFOAM is used to analyse the thermo-fluid dynamic behaviour of a regenerator wire netting at different Reynolds numbers. Firstly, isothermal air flows and adiabatic wire matrices are considered, by assuming the fluid flowing through the regenerator as incompressible. Then, air flows with a fluid temperature of 500 K and wires at a temperature of 300 K are analysed. The results are compared with those obtained by means of the commercial software Ansys Fluent.

A Porous Media Numerical Approach for the Simulation of Stirling Engine Regenerators

“…In Figure 4 the friction coefficient is plotted versus the Reynolds number. The results obtained by means of the porous media model are compared with those obtained in [7]. It is possible to observe a good agreement between the two curves, characterized by the same trend.…”

“…In general, two different approaches are considered: in the first approach, the flow is considered as incompressible and no thermal phenomena are involved; in the second, the flow is considered as compressible and the heat fluxes between flow and wires is taken into account. The compressibility effects result to be not negligible above ≈ 200, as shown in [7], leading to a non-monotonic behavior of the friction coefficient, , as a function of Re. Indeed, above ≈ 200 the pressure losses along the domain increase with , whereas under the incompressible assumption the pressure losses decrease by increasing .…”

“…The first consists in modelling the wires as walls and simulating one element of the matrix, by evaluating the behavior of the flow passing through the wires, as reported in the works of Costa et.al. [5,6], Faruoli et al [7] and Bello et al [8], where the fluid-dynamic and the thermal performances are computed in terms of friction coefficient, thermal efficiency and Nusselt number. The second approach defines the matrix as a porous block with a porosity that enables to simulate the flow behavior of the actual geometry.…”

Numerical Investigation of Thermofluid Performance of a Regenerator Relative to the Matrix Geometry

“…To study the performance of a regenerator, Faruoli et al, [6] simulated the thermo-fluid behavior using OpenFOAM code.…”

“…The performance of a regenerator is measured by pressure drop in the system and its ability to exchange heat with the working fluid [6,7]. This depends on the thermal properties of the regenerator matrix and flow channel architecture [4].…”