الفهرس 
Computational fluid dynamics
Description of the EngineOnly 14 pages are availabe for public view
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Abstract
Stirling engines attracted the researchers to study their performance as they have many advantages as quiet operation, the capability to work with renewable resources or waste heat, and the high efficiency which is equivalent to Carnot. The regenerator, a vital part of Stirling engines absorbs heat during one half of the cycle and supplies the heat stored in the second half of the cycle. In this work, a 2D model of the Stirling engine was developed in which the oscillating flow in the engine was modeled using Comsol Multiphysics [1], continuity, conservation of momentum, and energy conservation equations were solved, free and porous media flow module and heat transfer in fluid and porous media were used to model fluid flow and transfer of heat respectively, boundary and initial conditions were defined, moving mesh module was defined to model the piston displacement and velocity. A Mesh independence test was performed to investigate the dependence of the solution on the number of elements of the mesh.
The 2D model results were validated against the work of Almajri et al. [2] where the volume variations of the hot expansion space and cold compression space at different crank angles were made the same in the current work. The resultant indicated power for different RPMs was used for validation at two charging pressures, the cycle P-V diagram was presented. Investigations for the effects of changing charging pressure and heater wall temperature on the resultant indicated power were carried out and it was concluded that the indicated power increases as the engine charging pressure increases, the resultant indicated power also increases when the temperature of the heater walls increases.
Plots for effectiveness, Nusselt number, and pressure DROP against Reynolds number as the RPM increases were presented and compared with results from the literature. Plots for temperature, velocity, and pressure fields at different crank angles were presented, this gives better visualization of the flow and transfer of heat in the engine.
Novel geometry was presented where the V-shape corrugated porous media introduced by W.Aboelsoud [3] was used as the engine regenerator, the novel geometry was placed in the same casing of the original geometry without changing any dimension of the casing to avoid adding any dead volume to the engine, as a result, the total area of the novel geometry in the 2D model was less than that of the original geometry, the 2D validated model was used to study the transport phenomena in the novel geometry. As in the case of the original geometry, the P-V diagrams for both the compression and expansion spaces were presented, plots for temperature, velocity, and pressure at different crank angles were presented as in the case of the original geometry.
Plots for effectiveness, Nusselt number, and pressure DROP versus Reynolds number at different RPMs were presented, Nusselt number increases as Reynolds increases, the Nusselt number values are more in the novel geometry than the original geometry which suggests that the convection heat transfer is more dominant than the conduction heat transfer, the pressure DROP increases with Reynolds number increase as the turbulence increases with increasing Reynolds. The resultant indicated power was plotted for different RPMs where the resultant indicated power increases as RPM increases.
Different values of V-shape angles and vertical wall thickness were presented to investigate the thermal and hydraulic performance of the V-shape regenerator and determine the best configuration. The product of the ratio of the total area of the novel geometry to the total area of the original geometry and the number of voids resulting from the V-shape i.e.: ((area of the novel geometry*number of voids)/(area of the original geometry) ) was used as the denominator in the ratios of the regenerator effectiveness, Nusselt number, pressure drop, and Reynolds number to compare the different configurations at the same area, the same number of voids, and the same piston speed.
The angles of the V-shape used in the investigation were (1, 3.76, 5, 15, and 20) degrees, the effectiveness ratio increases as the angle increases, a similar pattern was observed for Nusselt number and pressure drop, it must be noted that the pressure DROP in the novel geometry is less than that of the original geometry.
The vertical wall thickness values tested were (2.5, 7, 12, 20, and 22) millimeters, the effectiveness ratio decreases after a value of wall thickness equals 7mm, Nusselt number decreases as the thickness increases, a similar result was obtained by W.Aboelsoud et al. [4] where it was stated that 99% of the heat transfer is achieved after a short distance from the inlet, this distance was determined to be 3 times the pore size if the porous media is treated as a mini channel. The pressure DROP ratio decreases with increasing thickness.
from the above results, it was concluded that the pressure DROP in the original geometry is more than that in the novel geometry, and Nusselt number increases in the novel geometry. The best configuration to be used in the novel geometry based on the ratios of the effectiveness, Nusselt number and pressure DROP to the product of the ratio of the regenerator total area to the total area of the original geometry and the number of voids was found to be the V-shape with the largest angle and minimum thickness in the ranges of tested values of angles (1, 3.76, 5, 15 and 20 degrees) and thicknesses (2.5, 7, 12, 20 and 22 mm).