Experimental study of the thermal characteristics of phase change slurries for active cooling (original) (raw)
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Phase Change Slurries for Cooling and Storage: An Overview of Research Trends and Gaps
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Phase change slurries (PCSs) have great potential as both a heat transfer fluid and an energy storage medium for cooling processes, cold energy storage, and cold energy transportation due to desirable thermophysical properties. One of the major benefits of PCSs compared to pure phase change materials is their fluidity, thus making them cooled or heated by a heat exchanger, pumped through pipes, discharged, and stored directly in a thermal energy storage tank. The use of encapsulated phase change slurries and gas hydrate slurry has thus attracted considerable interest as reflected in the literature with a rising number of publications and institutions involved in the area. The use of bibliometric techniques has found a recent interest in the literature to define the progress of different scientific topics and inspire researchers to identify novelties. In this paper, bibliometric analysis and a detailed systematic review are carried out to show the state-of-the-art development of PCSs...
Thermophysical Properties Characterization of Microencapsulated Phase Change Material Slurry
Current chilled water systems require vast amount of water and pumping power to meet increasing cooling demands. Existing cooling and heating distribution systems have an inherent thermal capacity limitation (e.g., specific heat, mass flow rate, delta T), which is often neglected when adding new buildings to military, industrial or commercial facilities, resulting in higher equipment and infrastructure costs. Through the use of an advanced material concept, namely Microencapsulated Phase Change Materials (MPCM), performance enhancement of an improved heat transfer fluid is now being pursued. This paper discusses the status of experimental efforts using a linear alkane phase change material intended for a secondary coolant for space cooling applications. Initial quantitative characterization of MPCM material properties including latent heat of fusion, melting and freezing points, and temperature-and concentration-dependent viscosity data are presented. State-of-the-art equipment was used to characterize the MPCM slurry including the use of a differential scanning calorimeter and a temperature-controlled concentric viscometer. Results indicate that the freezing and melting points of microencapsulated n-Tetradecane differed by 5° C or more when no effective nucleating agent was used. Current efforts have yielded the identification of a very effective nucleating agent, which can suppress supercooling almost entirely. Other experimental results indicate that MPCM slurry viscosity significantly depends not only on volume fraction but also on temperature, which can have an impact on the heat transfer process. MPCM slurry has the potential to become a successful heat transfer fluid, which may result in significant energy and cost savings.
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A great deal of attention has been paid to energy saving devices in place of conventional air-cooled and water-cooled devices. The thermal energy storage system that uses the latent heat of a PCM (phase change material) for airconditioning or heating has recently become popular because it does not require high electric power and it saves energy. An emulsion dispersed nano-size particles of phase change material is produced. We discuss with the thermophysical properties, the stability of emulsion, and the heat transport characteristics as a thermal functional fluid. The testing emulsion, which has nano-size particles as the discrete phase, is produced with a D-phase emulsification method. The diameter of discrete phase in the emulsion is measured for evaluation of the long-term stability of emulsion. In addition, the DSC (differential scanning calorimetry) curve of emulsion is determined. Thermophysical properties such as viscosity and thermal conductivity of emulsions were studied in this work, and was compared with that of the base fluid. The results reveal that the emulsion with the D-phase emulsification method has the superior stability. From the differential thermal analysis, the DSC curve of present emulsion indicates a discontinuous change at the phase change temperature of phase change material due to its latent heat.
Journal of Thermal Analysis and Calorimetry, 2020
In modern heat transfer systems, thermal storage not only causes the balance between demand and supply, but also improves the heat transfer efficiency in these systems. In the present study, a comprehensive review of the applications of micro-or nano-encapsulated phase change slurries (MPCMs/NPCMs), as well as their effects on thermal storage and heat transfer enhancement, has been conducted. MPCMs/NPCMs have a myriad of applications and various usages such as pipe and channel flows, photovoltaic/thermal, solar heaters, air conditioning systems, storage tanks and heat pipes that have been categorized and studied. It was found that there are many advantageous adding MPCM/NPCM to the base fluid. The most important effect is that the addition of PCMs to the base fluid can intensify the capacity of energy absorption in the base fluid. These materials can absorb a high proportion of received energy by changing their phase and prevent temperature increment of the base fluid. Thereupon, the specific heat of the fluid in the presence of the micro-/nano-capsules increases. Moreover, in most studies reviewed, heat transfer coefficient and Nusselt number increase by the addition of micro-/nano-capsules to the base fluid. Also, the addition of MPCM/NPCM to the base fluid could make this material pumpable, although increment in the concentration of micro-/nano-capsules raises the viscosity of the working fluid and thereupon the pumping power. On the other hand, for a same heat load, the pumping power decreases due to the lower required flow rate in comparison with pure working fluid. The most important factor that must be considered in the application of MPCMs/NPCMs is the complete phase change of the material. Given the favorable thermal and fluid characteristics of MPCMs/NPCMs, the utilization of these materials could be a promising method to transfer heat and store it with high efficiency and low pumping power.
Micro-encapsulated paraffin in phase-change slurries
Solar Energy Materials and Solar Cells, 2005
The amount of heat that can be stored by common heat transfer fluids, e.g. water or oils, depends on the useable temperature range which can be exploited. The efficiency of such heat transfer fluids is poor if an application allows only a small temperature difference. One solution to increase the efficiency of such applications is to use phase-change materials, the so-called PCMs. The energy that can be stored at the phase transition of some materials, e.g. from solid to liquid, is very high. Paraffin is a PCM that can be pumped through pipes when it is micro-encapsulated and dispersed in a carrier fluid, e.g. water. These mixtures of PCMs and carrier fluids are called phase-change slurries (PCSs). We are working on PCSs within a project which is supported by the European Commission. One of the aims of the project is to develop micro-encapsuled PCSs that are stable enough to withstand the harsh conditions in piping system including various commonly used components. To do the necessary experiments, a test rig was built to perform thermal cycling of different PCSs. The stability of the micro-capsules was also tested by exposing them to high shear stresses, that normally occur mainly in pumps. The compatibility of different components when used together with these PCSs was also examined. After several weeks of pumping, scanning electron microscopy (SEM) was used to control the state of the capsules visually. The thermal behaviour of the PCS was measured while it was pumped through heat exchangers. Also, a simulation tool was
Mechanical Properties and Melting Heat Transfer Characteristics of Shape- Stabilized Paraffin Slurry
This article is presented in the framework of the increasing interest for the use of latent heat transfer slurries for cooling processes. Paraffin serves as a latent heat storage material, and a polymer network acts as the supporting material. The phase change material melts around 7◦C with a latent heat of fusion of 115 kJ/kg. Differential scanning calorimetry and indentation analysis were employed to investigate the thermal properties and mechanical stability of the material under freezing–thawing cycles. Results indicated that the form-stable phase change material with the advantages of no liquid leakage constitutes a potential material in the field of low-temperature thermal energy storage. Experimental investigation is made to study the melting process of a single slurry in an agitated bath. Analysis of data permits the development of a phenomenological correlation adapted to the millimetric dimension of the particle, leading to an estimation of the melting phase change time duration as a function of the main parameters of the problem.