Temperature moderation in a structure by solidification of a phase-change material

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.The current numerical study focuses on the feasibility of temperature moderation in a structure located at mid-storey in a multi-storey building, by using a phase-changing paraffin wax stored on an aluminum tray under the floor tile. Inside the building, at each level, walls are exposed to the ambient. In winter the walls are cooled, and the paraffin wax serves as the heat source, by solidifying in day-time, and melting at night. The numerical model relates to day-time temperature variations, outside and inside the structure. The heat conduction from the paraffin wax is coupled with the free convection of air in the space, radiation between the inside surfaces, heat conduction across the walls and accumulation in the walls. The dimensions of the analyzed structure are: 8m long, 8m wide and 2.5m high. Effects of wax layer thickness and of fins along the tray, on the rate of solidification are parametrically investigated. The simulations are performed for the structure using Fluent 6.3 software.dc201

Effect of Xenon gas and foils on a multi-foil insulation

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.The miniaturization of thermal installations has been also extended to compact insulations in processes maintained at low or high temperatures, and restricted to minimal heat losses or gains. The current investigation has been conducted experimentally and numerically, aiming to predict the performance of a multi-foil array, in which xenon gas is entrapped between steel foils, separated and supported by widely spaced ceramic particles. A parametric study of the effect of an increased number of foils, as compared to the experimental array, shows the preferred directions to design of such arrays. The performance of an array operated with xenon gas near-atmospheric pressure is compared to the performance of arrays filled with other gases. The low thermal conductivity of xenon gas leads to a lower effective conductivity of the array, as compared to arrays operated with other gases. The equations of conduction and radiation are solved numerically for a wide range of pressures and temperatures. Good agreement with experimental results is achieved.dc201

Temperature moderation in a multistorey building by melting of a phase-change material

The current numerical study focuses on the feasibility of furnishing thermal comfort in a structure, by using paraffin wax stored on a plate below the ceiling in a multi-storey building. The method is aimed to reduce energy demands at the increasing thermal loads. In summer, in daytime, walls of the building are exposed to the ambient thermal load, and heat transferred inside is absorbed by the melting wax. The study is numerical. It relates to temperature variations outside and inside, coupled with heat conduction and accumulation in walls, with radiation between the surfaces, with natural convection of air inside and melting of the wax at the ceiling. Fins spacing on the storage plate, visualization of the melting process, and its parametric investigation provide an insight into the physical phenomena. Temperature and flow fields were investigated for 3 mm and 12 mm thick layers of wax. At the specified conditions of the present study a 3 mm layer provides thermal comfort for most of the day, while a 6 mm layer may suffice for the entire day. Fluent 6.3 software was used in the computations

IPACK2005-73113 TRANSIENT PERFORMANCE OF A FINNED PCM HEAT SINK

ABSTRACT The present study explores numerically the transient performance of a heat sink based on a phase change material (PCM), during the process of melting. Heat is transferred to the sink through its horizontal base, to which vertical fins made of aluminum are attached. The phase change material is stored between the fins. Its properties, including the melting temperature, latent and sensible specific heat, thermal conductivity and density in solid and liquid states, are based on a commercially available paraffin wax. A parametric investigation is performed for melting in a relatively small system, 10mm high, where the fin thickness is 1.2mm, and the distance between the fins varies from 2mm to 8mm. The temperature of the base varies from 12°C to 24°C above the mean melting temperature of the PCM. Transient numerical simulations are performed, yielding temperature evolution in the fins and the PCM. The computational results show how the transient phase-change process, expressed in terms of the volume melt fraction of the PCM, depends on the thermal and geometrical parameters of the system, which relate to the temperature difference between the base and the mean melting temperature, and to the thickness of the PCM laye

An analytical technique of transient phase-change material melting calculation for different phase-change material containers cases

An analytical model earlier developed for calculation of transient phase-change material (PCM) melting (Dubovsky et al. [1]) proved to be a useful tool for use in the analysis of various structures. As shown in our subsequent studies, despite the serious assumptions in its development, the model is effective in optimization of the design and parameters of systems, including the case of transition from analytical methods to numerical calculations. The present work shows that the use of the analytical technique and its modifications for the analyzed PCM arrangements is beneficial. Proper application of the technique makes it possible to obtain the parameters of the real PCM melting process in the form of algebraic formulas, both for the transient values of variables over time, and for the overall process characteristics. Our analysis is performed for the commonly used PCM containers where we use classifications in terms of the geometry and configuration as defined in the literature. A comparison with the results of numerical calculations of transient melting by CFD FLUENT, confirms the validity of algebraic formulas and allows to assess the nature and value of the introduced error in the results of our analytical method, for each analyzed case.Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016