Volume 5 Issue 3
Authors: K. A. R. Ismail; L. M. Sousa; F. A. M. Lino
Abstract: This paper presents the results of a numerical study on the solidification of PCM around a bent tube with a cooling fluid flow inside it. The proposed model is based on the two-dimensional energy and momentum equations. The Landau interface immobilization technique is used to immobilize the solid-liquid interface, while the finite volume method is used to numerically treat the equations, boundary, and initial conditions. The numerical predictions were validated against available experimental results, showing good agreement. Because of the circulatory flow in the bend region, the heat transfer coefficient on the external side is higher than that on the internal side of the bent tube. It was found that an increase of the wall temperature, an increase of the initial liquid PCM temperature, or an increase of the curvature radius would reduce the interface position and consequently reduce the solidified mass and decrease the interface velocity. This increases the time for complete solidification. These results can be useful in predicting ice formation over helical coils and curved tubes used in latent heat storage systems.
Keywords: PCM; Solidification; Curved Tubes; Interface Immobilization; Latent Heat Storage; Coiled Tubes
Authors: Omar Mohamed Alhosani; Abdulla Ali Alhosani; Zin Eddine Dadach
Abstract: The first objective of this research was to conduct an exergy analysis for a power-generation plant in Abu Dhabi (UAE) in order to determine the main source of its irreversibilities. Our results indicated that the combustion chamber was the main contributor (70.2%) to the total exergy destruction of the plant. The compressor had the lowest contribution towards exergy destruction (12.4%). In the second part of this investigation, Aspen Hysys with the Soave-Redlich-Kwong (SRK) equation of state was utilized in order to simulate the effects of high temperatures and absolute humidity of ambient air on the exergy efficiency of different equipment in the power plant. Our data showed that the temperature of ambient air had more negative effects on the performance of the plant than the absolute humidity. The exergy efficiency of the combustor and compressor decreased with temperature while the exergy efficiency of the turbine increased with temperature. Finally, a comparative study on the performance of the power plant between design conditions (T=288K, RH=60%) and summer conditions (T=316K, RH=50%) in Abu Dhabi indicated that the power plant lost 4.66 % of its net power output and 4.61 % of its exergy efficiency.
Keywords: Power Plant; Exergy Analysis; Exergy Destruction; Process Irreversibilities
Authors: Guoqi He; Hongzhi Yan; Ming Liu; Ying He
Abstract: According to the processing principles of gear cutting, tool structure, and the relevant position and movement between the machine and the work piece, this study established the optimal meshing coordinate for gear cutting by using the gear cutting meshing principle. Nonlinear equations were established by data discrimination of theoretical tooth surfaces; they were solved by MATLAB software, and three-dimensional coordinates of disperse points on the tooth surface are obtained. Three-dimensional coordinates were introduced into Pro/E software, and a three-dimensional geometry model of cycloid hypoid gear was built. Finally, dynamic simulation of the cycloid hypoid gear was performed, verifying the accuracy of the 3D model.
Keywords: Cycloid Tooth; Hypoid Gear; Tooth Surface Equation; Geometric Modelling