Book Description

With the increased world population, fossil fuel consumption and Co2 emissions, solutions are being sought to provide for the increase in energy demands and to reduce emission levels. One promising approach is the use of renewable energy and waste heat sources to drive thermo-mechanical conversion systems, such as Stirling engines. Recently, interest in developing efficient and cost effective Stirling engine technology has increased, particularly in many academic and industrial organizations. In this context, this thesis has first focused on the development of thermodynamic and numerical simulations for the V-type alpha Stirling engine. Secondly, the development of efficient regenerator that can improve the engine performance, it is a new non-annulus segmented micro-channels regenerator of parallel geometry. Using non-ideal adiabatic analysis approach, a successful thermodynamic model was developed for a V-type alpha Stirling engine, and it was validated using published experimental data available for the engine prototype. Also, the development of a detailed 3D CFD model for V-type alpha Stirling engine was carried out and its results were validated using the developed thermodynamic model. The results have shown good agreement in the estimation of the engine indicated power. The combination of the thermodynamic analysis with the 3D CFD modelling to predict the engine performance was an advantage of this work. The effects of different design parameters and operating conditions have been investigated on the performance of a V-alpha type Stirling engine by using the developed CFD model. Those parameters including the dead volume, cold/hot ends temperatures, charge pressure, porosity and matrix wire diameter of regenerator. The PV diagram for the engine was used to predict the power output contributed by each parameter. The maximum power output in this parametric study was achieved 162 W by using a wire matrix diameter of 0.02 mm, porosity of 80%, cold side temperature of 20 0C, and hot side temperature of 600 0C. Also, results predicted that, further increase of the heater and the cooler heights (up to 140 mm) pushed the power output to reach 170 W. A detailed 3D CFD model for segmented micro-channel regenerator was developed and its results were validated against experimental measurements showing maximum deviation of 10.6% and 6.03% for both unidirectional and oscillatory flows respectively in terms of measuring the outlet temperature. The validated CFD model was used to carry out an investigation on the effect of increasing the number of segmentations on the regenerator effectiveness and engine performance. The effects of changing the micro-channel diameter on the regenerator performance in terms of heat transfer and pressure loss was also investigated. The micro- channels regenerator with diameter of 0.5 mm and 32 segments performed better than all other configurations investigated in this study including the Random Fibre matrix. In order to reduce the time and cost for Stirling engine development, this work investigated the route to upgrade commercially available V-type compressor to develop V-type alpha Stirling engine through detailed 3D CFD modelling. The correlations of Nusselt number and friction factor for the developed segmented regenerator were used as porous media parameters in the CFD model for the developed Stirling engine. Also, a new concept for the engine cooler design was modelled and integrated in the overall engine model, showing improved performance for the engine due to lowering of the coolant temperature. The maximum indicated power observed from the developed engine using the 32-segmented regenerator with 0.5 mm micro-channel diameter was 132.89 W. This is higher by 18.33% and 44.4% than those of the two commercial matrix regenerators, namely the Random fibre and the Screen woven respectively.