Melting and solidification characteristics of a double-pipe latent heat storage system with sinusoidal wavy channels embedded in a porous medium

The aim of this investigation is to explore the combined effects of porous medium and surface waviness on the melting and solidification of PCM inside a vertical double-pipe latent heat storage (LHTES) system. The results are compared with the cases of smooth channels and pure PCM. In the system, water is passed through the inner tube while composite PCM is placed in the annulus side. Different effective parameters including wavelength and wave amplitude of the sinusoidal wavy channels, porosity and pore size of the porous structure, Reynolds number and inlet temperature of water are examined to find the optimum geometric as well as operating conditions in both melting/solidification processes. The results show that utilizing both the high conductive porous structure and wavy channel reduces the melting/solidification times significantly. For the best case, the melting and solidification times of PCM reduce by 91.4% and 96.7%, respectively, compared with the smooth channels pure PCM system. The average rate of transferred heat for the wavy channel composite PCM are 10.4 and 18.9 times that for the smooth channel pure PCM case. Comparing with the pure PCM system, the presence of copper foam reduces the effect of channel waviness significantly for both melting/solidification processes

Conjugate heat transfer in porous annulus

Link to publisher's homepage at http://www.begellhouse.com/The effect of conductivity ratio on temperature at a solid-porous interface is one of the most important aspects in conjugate heat transfer. The present work is undertaken to investigate heat transfer behavior in a porous annular vertical cylinder having a solid wall at the inner surface. The main objective of the present study is to evaluate the effect of solid wall thickness and conductivity ratio on heat transfer characteristics of the porous medium. The inner and outer surfaces of the annulus are maintained isothermally at Th and T∞, respectively, such that Th > T∞. The increase in conductivity ratio leads to an increase in temperature at the solid-porous interface. It is noticed that the temperature variation along the porous region is almost linear for higher values of conductivity ratio and wall thickness ratio. It is found that the fluid velocity decreases with increase in wall thickness. It is observed that the Nusselt number decreases with increase in solid wall thickness. The effect of the aspect ratio is found to be negligible when porous conductivity is much higher than that of the solid wall conductivity. The attainment of the maximum Nusselt number at Ar ≈ 1 in a porous annulus does not hold good for the conjugate heat transfer problem. The variation in Nusselt number is sensitive for higher wall thickness ratio and lower conductivity ratio

Investigation the effect of pulsed laser parameters on the temperature distribution and joint interface properties in dissimilar laser joining of austenitic stainless steel 304 and Acrylonitrile Butadiene Styrene

Direct laser joining of metal to plastic materials is one of the cost effective methods of joining. The demand for laser welding of stainless steels and thermoplastics is going on increase because of having many applications such as automotive, aerospace and aviation industries. This paper presents the experimental investigation of direct laser joining of stainless steel 304 and Acrylonitrile Butadiene Styrene (ABS). The effects of pulsed laser parameters including laser welding speed, focal length, frequency and power on the themperature field and tensile shear load was investigated. The results showed that excessive increase of the joint interface temperature mainly induced by high laser power density results in exiting of the more volume of the molten ABS from the stainless steel melt pool. Also, increasing the laser power density through decreasing the focal length or increasing the laser power led to an increase in the surface temperature, higher beam penetration and high volume of molten ABS. Decreasing the focal length from 5 to 2 mm significantly rose the temperature from 150 to 300 °C. By increasing the laser pulse frequency, the number of bobbles at the ABS interface surface remarkably increased where the temperature increased from 120 to 180 °C. The X-ray spectroscopy results showed the existence of the polymer elements on the metal surface at the joint interface zone. The tensile shear load clearly increased from 280 to 460 N with augmentation of laser average power from 180 W to 215 W. Applying higher levels of laser power has clearly decreased the tensile shear load due to creating bigger bobbles and more cavities at the adhesive zone

Effect of evaporator temperature on vapor compression refrigeration system

AbstractThis paper presents a comparable evaluation of R600a (isobutane), R290 (propane), R134a, R22, for R410A, and R32 an optimized finned-tube evaporator, and analyzes the evaporator effect on the system coefficient of performance (COP). Results concerning the response of a refrigeration system simulation software to an increase in the amount of oil flowing with the refrigerant are presented. It is shown that there is optima of the apparent overheat value, for which either the exchanged heat or the refrigeration coefficient of performance (COP) is maximized: consequently, it is not possible to optimize both the refrigeration COP and the evaporator effect. The obtained evaporator optimization results were incorporated in a conventional analysis of the vapor compression system. For a theoretical cycle analysis without accounting for evaporator effects, the COP spread for the studied refrigerants was as high as 11.7%. For cycle simulations including evaporator effects, the COP of R290 was better than that of R22 by up to 3.5%, while the remaining refrigerants performed approximately within a 2% COP band of the R22 baseline for the two condensing temperatures considered