Papers by Keyword: Latent Heat

Abstract: In Al-Si alloy roll casting, the thickness of the foil and strip decreases as Si content decreases below 2 mass%, contrary to the expectation that the latent heat decreases as Si content decreases. This phenomenon was investigated experimentally using a melt spinning single roll caster, melt drag single roll caster, and vertical type high-speed twin roll cater. The results demonstrate that the peeling of the solidification layer influences the thickness of the foil and strip. The relationship between casting conditions and adhesion of the solidification layers was also investigated.

Abstract: The effects of modification, electromagnetic stirring and compound treatment (modification and electromagnetic stirring) on the microstructure and thermal stability of Al-13% Si alloy are experimentally investigated. The results show that the three melt treatments can change the microstructure of the alloy. The modification has obvious refining effect on primary silicon and eutectic silicon grains, electromagnetic stirring has refining effect on primary silicon grains, and eutectic silicon grains appear coarsening phenomenon. The latent heat is obviously decreased by electromagnetic stirring, while the latent heat is increased by modification. Refining eutectic silicon grains will increase the latent heat of phase transformation of the alloy. When 560 °C remains unchanged, the melting temperature of the alloy generally decreases with the increase of holding time, but fluctuates, with a decrease of 7 °C. The latent heat decreases with the increase of constant temperature time, and the decrease amplitude reaches 8.4%.

Abstract: In this paper, the effects of different Co contents on the microstructure and properties of Al-30% Si alloy were studied by means of metallographic microscope, microhardness tester, XRD, conductivity tester and DSC thermal analyzer. The results show that cobalt can effectively improve the microstructure of the alloy, the long needle eutectic silicon becomes short rod, and the coarse irregular block primary silicon particles become smaller. When 0.3% cobalt is added into the alloy, the refining effect of eutectic silicon is the most obvious. When the amount of Co is 0.6%, the refinement effect of primary silicon is the best. The addition of Co can improve the hardness of the alloy. When 0.6 ~ 0.9% cobalt is added, the hardness is the highest. With the increase of Co content, the conductivity and transformation latent heat of the alloy show the same change law. When 0.6% cobalt is added, its value is the maximum. It can be seen that when the Co content is 0.6%, the microstructure and comprehensive properties of the alloy are the best.

Abstract: The current research presents an overview of four types of carbon nanoparticles that are: carbon black nano powder, multi-walled carbon nanotube, graphene, and graphite. The aim of this paper is to show the importance of carbon-based nano-enhanced phase change materials (NEPCM). The effect of using different types of nanoparticles at various loading concentrations has been examined. It was found that the effective thermal conductivity can be enhanced by increasing the nanoparticles loading concentration regardless of NEPCM type. However, this may be accompanied by a slower melting process which also depends on the nanoparticle’s density. Thus, the duration of storage is reported as a crucial factor to check the feasibility of using such nanoparticles. The highest reported thermal conductivity enhancement is ~300% considering CaCl₂.6H₂O as a phase change material with 30 wt.% multi-walled carbon nanotube.

Abstract: This paper presents a closed-form solution for the temperature prediction in selective laser melting (SLM). This solution is developed for the three-dimensional temperature prediction with consideration of heat input from a moving laser heat source, and heat loss from convection and radiation on the part top boundary. The consideration of heat transfer boundary condition and latent heat in the closed-form solution leads to an improvement on the understanding of thermal development and prediction accuracy in SLM, and thus the usefulness of the analytical model in the temperature prediction in real applications. A moving point heat source solution is used to calculate the temperature rise due to the heat input. A heat sink solution is used to calculate the temperature drop due to heat loss from convection and radiation on the part boundary. The heat sink solution is modified from a heat source solution with equivalent power due to heat loss from convection and radiation, and zero-moving velocity. The temperature solution is then constructed from the superposition of the linear heat source solution and linear heat sink solution. Latent heat is considered using a heat integration method. Ti-6Al-4V is chosen to test the presented model with the assumption of isotropic and homogeneous material. The predicted molten pool dimensions are compared to the documented values from the finite element method and experiments in the literature. The presented model has improved prediction accuracy and significantly higher computational efficiency compared to the finite element model.

Abstract: This study shows that the latent heat of the aluminum alloy in an overlay strip is the key factor affecting the bonding quality of clad strips fabricated by a vertical-type tandem twin-roll caster. Three-layer clad strips, for which the base strip was 3003 aluminum alloy and the overlay strip was Al-1%Si, Al-2%Si, Al-11%Si (4045), Al-2%Mg, and Al-4.5%Mg (5182), respectively, were cast. The 4045 overlay strip bonded to the base strip. However, overlay strips made of the other alloys did not bond to the base strip. The latent heat of Si is much higher than that of Al, which in turn is higher than that of Mg. Therefore, the latent heat of the 4045 alloy was higher than that of the other alloys. The high latent heat of the 4045 alloy allowed it to heat the base strip to a temperature at which bonding was possible.

Abstract: The viability of casting heat sinks with thin fins using Al-25%Si was investigated, based on assessing cooling curves as well as fluidity tests and emissivity analyses of the resulting heat sinks. The fluidity, castability and emissivity of the semisolid die-cast Al-25%Si were excellent and superior to the results obtained using liquid die-cast A383, an aluminum alloy typically employed for casting. The cooling curves indicate that the significant latent heat of the Si in the alloy improves the fluidity and castability of the material. The addition of P did not greatly affect the refinement of primary Si in the alloy. These findings show that Al-25%Si is suitable for the die-casting of heat sinks with thin fins.

Abstract: In the context of energy economy and thermal comfort, phase change materials (PCMs) have many useful applications. In this study, type A zeolite was tested as a matrix for impregnating obtaining a PCM-impregnated zeolite. A sample of type A zeolite was analyzed by X-ray diffraction (XRD) and X-ray fluorescence (XRF). The porosity was evaluated by scanning electron microscopy. Following that, an apparatus was mounted for vacuum impregnation to incorporate calcium chloride hexahydrate (CaCl₂.6H₂O), which is a PCM, in the pores of the zeolite. The impregnation and the retention of the phase change material in zeolites were assessed using Fourier transform infrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS) on the scanning electron microscopy (SEM) and Differential Thermal Analysis (DTA) to simulate thermal cycles testing to determine the thermal behavior of the compound. The results of the XRD and FTIR analyses showed that CaCl₂.6H₂O remains in the zeolite phase after the impregnation and the thermal cycling performed on the material shows that there is a positive influence on the thermal behavior of the impregnated material. Varying the amount of the studied PCM between 0 and 30 wt%, different grout boards were constructed. The thermal behavior of the PCM-impregnated zeolite compared to the reference material (pure zeolite) showed an effective temperature difference (38.1 to 33.9 °C), which can lead to significant energy savings.

Abstract: In this research solid-solid microencapsulated phase change material (SSMePCM) with high thermal energy storage density (177.6 Jg/1) was synthesized successfully by in situ polymerization using biodegradable natural polymer chitosan as shell and polyethylene glycol (PEG-1000) as core. The morphology, chemical structure and thermal properties were characterized by optical microscopy (OM), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC). The results show that the obtained SSMePCM dispersed individually with a spherical shape. Author (s) recommends the all set thermal and chemically steady microcapsule for thermal energy storage purposes as novel synthesized SSMePCM with latent heat storage capacities.

Abstract: The development of efficient materials for heat storage has become recently a popular research topic as amount of energy gained from solar power depends significantly on day and night cycle. That's why the right choice of material for heat storage directly affects the utilization efficiency of solar thermal energy. Research on heat storage materials nowadays focuses on phase change materials (PCMs) enabling repeatedly utilize the latent heat of the phase transition between the solid and liquid phase. Most currently used PCMs have low thermal conductivity, which prevents them from overcoming problem of rapid load changes in the charging and discharging processes. To overcome this obstacle and to obtain excellent heat storage possibility, various techniques have been proposed for enhancing the thermal conductivity of PCMs, such as adding metallic or nonmetallic particles, in-corporating of porous or expanded materials, fibrous materials, macro-, micro-, or nanocapsules, etc.The authors of this study report particularly the huge potential of oxide nanoadditives, such as titania (TiO₂), alumina (Al₂O₃), silica (SiO₂) and zinc oxide (ZnO), that are even in small quantities (up to 3 wt.%) able significantly to enhance the heat storage characteristics of conventional PCMs. Moreover, the microstructure of the granules produced by recycling of aluminum scrap refers to the possibility of their utilizing for the purpose of low cost solutions enabling to increase the thermal conductivity of PCMs. The above mentioned technical solutions are therefore the important keys to successful commercialization of materials for latent heat storage in future building industry.