Phase Latent Heat Research Articles

The Simulation of Temperature Field in Induction Welding of Composite Aluminum Alloy Thin-Walled Tube

Welding temperature is the main factor that influences the welding quality in the high frequency induction welding of composite aluminum alloy thin-walled tubes. The finite element analysis software ANSYS was used to simulate the temperature field. One complete penetration of thin-walled tube and boundary conditions of convection and radiation as well as latent heat phase change were taken into account. Then a linear heat source is used to load and calculate the temperature distribution and to draw thermal cycle curves of welding process. Research results of the temperature filed also provided the corresponding basis for further analysis of welding stress and strain.

Experimental investigation of n-eicosane based circular pin-fin heat sinks for passive cooling of electronic devices

Efficient thermal management (TM) based on phase change material (PCM) is adopted for the cooling of portable electronic devices. PCM namely n-eicosane is employed to absorb thermal energy released by such electronics. Four different configurations of circular pin-fin heat sinks with fin thickness of 2mm, 3mm and 4mm including a no fin heat sink (used as a reference heat sink) were adopted. Pin-fins were made of aluminum due to light weight and good thermal conductivity to act as a thermal conductivity enhancers (TCEs). Pin-fin heat sinks of constant (9%) volume fraction of TCE are filled with four volumetric fractions of PCM to explore the best amount of PCM volume. A wide range of heat flux is provided at the heat sink base and the effect of fin configuration, PCM volume, latent heat phase, power densities, thermal capacity and thermal conductance are reported in this study. Three different critical set point temperatures (SPTs) are selected for this investigation. Enhancement ratios are reported against various PCM fractions to illustrate the thermal performance for passive cooling. The results show that 3mm fin thickness heat sink has best enhancement in operation for TM module controlling temperature of electronic devices.

Thermal performance of phase change material (PCM) based pin-finned heat sinks for electronics devices: Effect of pin thickness and PCM volume fraction

The present experimental investigation focuses on the passive cooling of electronic devices by using phase change material (PCM) based pin-fin heat sinks to increase reliability, to ensure sufficiently lower temperature, to stretch the operating duration and to improve the functionality of installed features. Paraffin wax is used as a PCM and filled in heat sinks made of aluminum. As the thermal conductivity of PCM is very low, aluminum square fins are used as thermal conductivity enhancer (TCE). A volume fraction of TCE is kept constant at 9% and the uniform heat flux is applied to finned and un-finned heat sinks. An un-finned heat sink is used for base line comparison. Fin thicknesses of TCE of 1mm,2mm, and 3mm with square cross sectional area are investigated with a constant height of 20mm. Volume fractions of PCM are varied as 0.00, 0.33, 0.66 and 1.00 for each heat sink to determine the thermal performance. The present study reports thermal performance at various heat fluxes to enhance the operating time for different set point temperatures (SPTs) and to compare the latent heat phase duration for various heat sinks tested. The results reveal that maximum thermal performance in operating time is achieved for 2mm thick pin-fin heat sink filled with PCM volumetric fraction of 1.00.

Solid-state thermal diode with shape memory alloys

Analogous to the electronic diode, a thermal diode transports heat mainly in one preferential direction rather than in the opposite direction. Phase change thermal diodes usually rectify heat transport much more effectively than solid state thermal diodes due to the latent heat phase change effect. However, they are limited by either the gravitational orientation or one dimensional configuration. On the other hand, solid state thermal diodes come in many shapes and sizes, durable, relatively easy to construct, and are simple to operate, but their diodicity (rectification coefficient) is always in the order of η∼1 or lower. Thus, it is difficult to find any potential applications. In order to be practically useful for most engineering systems, a thermal diode should exhibit a diodicity in the order of η∼10 or greater. In this study, a passive solid state thermal diode with shape memory alloy is built and investigated experimentally. The diodicity is recorded at about 90. This promising result could have important applications in the development of future thermal circuits or for thermal management.

Performance of the solar hybrid STIG cycle with latent heat storage

Abstract The solar hybrid Steam Injection Gas turbine (STIG) cycle uses both recuperated heat and solar heat in order to generate steam at a low temperature and pressure, and inject it into the cycle in order to augment the power output. This work addresses the addition of thermal energy storage to allow operation from solar energy beyond the daylight hours. An annual performance analysis of the Solar STIG cycle with latent heat phase change material (PCM) storage is presented for the climatic conditions of Sede Boqer, Israel. We show that the heat transfer limitation present in a real PCM storage leads to a slight performance penalty only compared to an ideal storage. We also analyze the impact of shifting electricity generation from daytime to evening, which can lead to a surprisingly high contribution of the thermal storage. Results show annual solar fraction of up to 35.2%. The annual solar to electricity efficiency was 20.1% when using the recuperated Brayton cycle as reference, and 13.9% for an optimal conventional STIG cycle as reference. These values are similar to or higher than the annual efficiency of current solar thermal power technologies, even though the hybrid STIG cycle uses low-grade solar heat at 200–280 °C.

Thermal Environment Regulating Effects of Phase Change Material in Chinese Style Solar Greenhouse

Phase change material (PCM) can store and release heat within a certain temperature range during the phase transitions. Compared with sensible heat material, latent heat phase change material (PCM) is very attractive, because of its high-energy storage density and isothermal behavior during the phase change process. This paper attempts to research the application of PCM in Chinese style solar greenhouse. The PCM we used is butyl stearate with the phase change temperature about 18°C, and spinach of F1 from Italy is chosen to be the test plant. The research is a contrast test with the same two greenhouse models, one is installed with PCM and the other is not. By recording the temperature with T type thermocouples on the different set-points and observing the growth situation of the plants in two greenhouses, we can recognize the effect of the PCM on the thermal environment of greenhouse.

Thermal behavior of porous stainless-steel fiber felt saturated with phase change material

Integrating high thermal conductive porous media and high latent heat phase change materials (PCMs) is an efficient method for heat dissipation in passive cooling applications. In this study, the enhanced heat transfer performance of porous stainless-steel fiber felt saturated with paraffin as PCM was experimentally studied. The effects of the porosity and the fiber diameter on the surface temperature and the solid/liquid interface evolutions were investigated. The solid/liquid interface evolution was tracked using a digital camera. The increase in fiber felt porosity augmented the natural convection of the melted PCM and the moving rate of the solid/liquid interface, but reduced the effective thermal conductivity of the composite. The surface temperature and the moving rate of the interface increased with the fiber diameter. The measured surface temperature showed a good agreement with the interface shape and evolving rate. Two heat transfer mechanisms dominated the melting process, namely, the combined heat conduction and the natural convection of the inside fluid. The dominant heat transfer mechanism switched from combined thermal conduction to natural convection of the liquid wax as porosity increased. Furthermore, the effect of interfacial surface area exceeded that of the fiber felt permeability in the natural convection prevailed regime.

Role of polymers in developing phase change materials for energy storage

store energy over longer periods and to effectively release the energy when needed. Research on sensible heat and latent heat phase change materials (PCMs), which started about 20 years ago, still plays an important role in addressing this problem. PCMs absorb and store heat energy when undergoing a solid-solid or solid-liquid phase change. Problems associated with the use of PCMs are their lack of long-term stability, especially under conditions of thermal cycling, the stability of the PCM-container system, and effective heat transfer, because most PCMs have very low thermal conductivity. Apart from a multitude of inorganic materials investigated and commercially used as PCMs in energy storage, commercial waxes and fatty acids were found to be the most promising organic latent heat PCMs. Normally the latent heat of melting method for energy storage is used, but some research focused on the latent heat of solid-solid transitions. Commercial paraffin waxes are cheap with moderate thermal storage densities and a wide range of melting temperatures. They undergo negligible sub-cooling and they are chemically inert and stable with no phase segregation. On the downside they have low thermal conductivity, relative high liquid viscosities, and they are difficult to contain in a certain shape or size. This is where polymers come into the picture. A fair amount of research has been done on the microencapsulation of PCMs by different polymers. Work has also been done on preparing phase change materials consisting of paraffin wax dispersed in a polymer as a supporting material (shape-stabilised PCM). In this case research concentrated mostly on the use of polyolefins. The effective temperature range of such a PCM falls between the melting point of the wax and that of the polymer. It is, however, important that there must be little co-crystallization between the paraffin wax and the polymer. This system has long-term thermal stability under cycling conditions, and the PCM is well contained within the polymer matrix. There are only two persistent problems: low thermal conductivity (which may be overcome by using conductive polymers or by doping) and poor mechanical properties in the presence of high paraffin wax contents.

Mixture continuum formulation of convection-conduction energy transport in multiconstituent solid-liquid phase change systems for BEM solution techniques

This paper describes the two nonlinear boundary-domain integral equations for Fourier heat conduction and convection governed energy transport. The equations are compatible with the mixture continuum formulation of an incompressible multiconstituent solid-liquid phase change system. The equations assume the boundary conditions to be functions of thermal field, and thermal conductivity and specific heat to be functions of temperature and species concentrations. The constitutive enthalpy-temperature relation is assumed to be a function of the species concentrations. The integral equations are derived on the basis of time-domain weighting with the fundamental solutions of the Laplace and Fourier equations and are suitable for boundary element discrete approximative method solution techniques. The nonlinearity that appears in thermal conductivity is treated by the Kirchhoff transform and the nonlinearities of specific heat and specific latent heat phase change are both transformed into the nonlinearity of the source term. The presented equations, in connection with a similar integral description for mass, momentum and species conservation, will be used as a basis for the boundary element method computation of macroscopic transport phenomena characteristics for melting and solidification.

Thaw contracture and the disappearance of adenosinetriphosphate in frozen lamb

AbstractDuring the freezing of lamb adenosinetriphosphate disappearance markedly accelerates over the latent heat phase and contines virtually to completion with 20–30 days frozen storage at – 12°C. At commercial freezing rates in which carcasses are fully frozen in ∼ 6–20 h the ATP concentration falls to 0.4–1.2 μmol/g or about 5–20% of that present immediately post‐slaughter. Although small in quantity it is still capable of inducing severe thaw contracture (60–70% in boneless strips) due to active ATP turnover of ∼ 60 μmol/g linked to the glycolytic production of ∼ 30 μmol/g of lactate. Glycolysis does not occur during frozen storage whereas the ATP concentration further falls through enzymic hydrolysis to ∼0.1 μmol/g, insufficient to cause thaw contracture. Thus through the disappearance of ATP in the frozen meat, toughness development from thaw contracture is avoided.