Ramla Gheith

Comparison Based on Exergetic Analyses of Two Hot Air Engines: A Gamma Type Stirling Engine and an Open Joule Cycle Ericsson Engine

In this paper, a comparison of exergetic models between two hot air engines (a Gamma type Stirling prototype having a maximum output mechanical power of 500 W and an Ericsson hot air engine with a maximum power of 300 W) is made. Referring to previous energetic analyses, exergetic models are set up in order to quantify the exergy destruction and efficiencies in each type of engine. The repartition of the exergy fluxes in each part of the two engines are determined and represented in Sankey diagrams, using dimensionless exergy fluxes. The results show a similar proportion in both engines of destroyed exergy compared to the exergy flux from the hot source. The compression cylinders generate the highest exergy destruction, whereas the expansion cylinders generate the lowest one. The regenerator of the Stirling engine increases the exergy resource at the inlet of the expansion cylinder, which might be also set up in the Ericsson engine, using a preheater between the exhaust air and the compressed air transferred to the hot heat exchanger.

Evaluation of the Gamma Stirling Engine Heat Transfers in its Heat Exchangers

In this paper, a Gamma type Stirling engine is experimented. A special care was given to the heat exchangers instrumentation. Different set of experimental measurement were made on them. Their corresponding thermal energy and efficiencies are estimated. Three operation parameters are chosen: filling pressure, cooling water flow rate and heating temperature. The influence of these parameters on the performance of each heat exchanger are presented and explained. It can be concluded that all heat exchangers parameters are critical to the performance of the Stirling engine. The regenerator performances are the most significant for the engine. The heating temperature is the parameter that greatly affects performance of heat exchangers. The cooling water flow rate is quite affecting the Cooler efficiency but has a slight influence on other exchangers. The initial filling pressure is significant for the regenerator and for the heater.Copyright

Experimental and Theoretical Investigation of Flows Inside a Gamma Stirling Engine Regenerator

The first objective of this work is to study the flow evolution through a gamma-type Stirling engine by a numerical tool. The quasi-steady model formulated by Urieli and Berchowitz (Stirling cycle engine analysis. Techno House, Radcliffe Way, Bristol ISBN 0-85274-435-8 (A. Hilger, Bristol), 1984) was adopted. The thermal and the mechanical losses generated in a Stirling engine are added to the model. The pressure drop through the heat exchangers was calculated to assess the friction factor value. The parameters characterizing the flow in the engine are calculated (Nusselt, Reynolds, and Darcy friction factor) and discussed. The proposed model will be used to estimate these factors. In a second part, the correlations proposed in the literature (Tanaka 1993; Gedeon and Wood Oscillating-flow regenerator test rig: hardware and theory with derived correlations for screens and felts. NASA CR-198442, 1996) to study the turbulent flow are applied to the gamma-type Stirling engine to proceed to the best theoretical results that better describe the experimental ones.

4.6 Stirling Engines

The Stirling engine is mainly composed by five compartments: two working spaces and three heat exchangers (heater, cooler, and regenerator). The regenerator (porous medium) characteristics, especially material and porosity, are determinant for the whole engine performance. In order to choose the adequate regenerator, numerical and experimental methods can be adopted. Numerical models, i.e., isothermal, adiabatic, and quasi steady, are applied to determine the engine performances considering the regenerator parameters. The most powerful numerical tool is the computational fluid dynamics (CFD) simulation, which allows a detailed examination of flow behavior through the porous media. The one-variate experimental method is generally considered to test regenerator operation in the Stirling engine but the figure of merit (FOM) formulation and the experimental design methodology are more precise and faster to compare several regenerators performances.

Numerical and Dynamic Study of Flow Instabilities and Heat Transfer at a Backward-Facing Step Using the Lattice Boltzmann Method

In this paper, a study of laminar flows based on lattice Boltzmann method (LBM) is presented. Numerical investigations of flow dynamics and its heat transfer at a backward-facing step were performed. We have considered an imposed temperature on system walls and chosen a convective exchange mode. The lattice Boltzmann method (LBM) was used to perform the modeling. This method is based on direct simulation at the macroscopic level of the fluid particle evolution. The influence of Reynolds number on the flow and on the temperature distribution was studied. The dynamic study of the structure of the flow at a backward-facing step allowed us to clarify its main characteristics: shear layer, mixed layer, recirculation, separation-reattachment, and the interaction between the mixture layer and the flow caused by the step. The results show the temperature oscillation distribution at a backward-facing step. This study will then give an initial appraisal of the influence of the atmosphere on airplane wings and plays a very important role in the interpretation of the pollutant dispersion mechanism at the urban scale.

A CFD Analysis of the Air Flow Through the Stirling Engine’s Singularities

In this chapter, a computational fluid dynamics (CFD numerical model) of the air flow through a 300 cm3 Beta Stirling engine has been used to characterize the pressure drop and heat transfer through the regenerator. The Stirling engine had two moving parts (i.e. piston and displacer) which were at a certain phase difference but reciprocated at same frequencies. First, particular specific mesh motion strategies were developed using the software STARCCM+, to describe the motion of the power piston and the displacer. Heat-transfer models were implemented by taking into account the presence of two heat sources and the regenerator porous structure. The results are compared with experimental data. Heat transfer between the air flow and the matrix has been considered by varying the hot end temperature from 400 to 1000 K and keeping the wall temperature of the regenerator at 300 K. Regenerator properties such as matrix material and porosity are investigated.

Study of the Regenerator Porosity Influence on Gamma Type Stirling Engine Performances

In this study, a Gamma type Stirling engine with compressed air as working fluid have been experimented. This engine operates at a maximum charge pressure of 10 bars. It runs at a maximum speed of 600 rpm, and can provide 500 W of brake power on the shaft. This Stirling engine setup was equipped with thermocouples and pressure sensors in order to measure the instantaneous temperatures and pressures. The regenerator is the key element of the Stirling engine. Its geometrical and physical properties influence directly on the engine performances. Our experimental study was focused on the regenerator, and especially on its porosity and its constituting material. We have initially made our experiments for 4 different regenerators material’s constituted of: Stainless steel, Copper, Aluminum and Monel 400. Secondly, we have experimented 3 regenerators made of copper with different porosities. From the obtained results, we conclude that the regenerator have an important role to enhance heat exchanges and to improve the Stirling engine performances. Indeed, these performances are also function of the porosity of each material constituting the regenerator, which conditions the quality and the quantity of heat exchanged in the Stirling engine.Copyright