Phase Change Material Slurry Research Articles

Experimental assessment of heat storage properties and heat transfer characteristics of a phase change material slurry for air conditioning applications

A new microencapsulated phase change material slurry based on microencapsulated Rubitherm RT6 at high concentration (45% w/w) was tested. Some heat storage properties and heat transfer characteristics have been experimentally investigated in order to assess its suitability for the integration into a low temperature heat storage system for solar air conditioning applications. DSC tests were conducted to evaluate the cold storage capacity and phase change temperature range. A phase change interval of approximately 3 °C and a hysteresis behaviour of the enthalpy were identified. An experimental set-up was built in order to quantify the natural convection heat transfer occurring from a vertical helically coiled tube immersed in the phase change material slurry. First, tests were carried out using water in order to obtain natural convection heat transfer correlations. Then a comparison was conducted with the results obtained for the phase change material slurry. It was found that the values of the heat transfer coefficient for the phase change material slurry were higher than for water, under identical temperature conditions inside the phase change interval.

Heat transfer characteristics of microencapsulated phase change material slurry in laminar flow under constant heat flux

Due to its large apparent specific heat during the phase change period, microencapsulated phase change material slurry (MPCMS) has been suggested as a medium for heat transfer. In this paper, the convective heat transfer characteristics of MPCMS flowing in a circular tube were experimentally and numerically investigated. The enhanced convective heat transfer mechanism of MPCMS, especially in the thermal fully developed range, was analyzed by using the enthalpy model. Three kinds of fluid–pure water, micro-particle slurry and MPCMS were numerically investigated. The results show that in the phase change heat transfer region the Ste number and the Mr number are the most important parameters influencing the Nusselt number fluctuation profile and the dimensionless wall temperature. Re b , d p and c also influence the Nusselt number profile and the dimensionless wall temperature, but they are independent of phase change process.

Numerical Investigation of Flow and Heat Transfer Performance of Nano-Encapsulated Phase Change Material Slurry in Microchannels

Microchannels are used in applications where large amount of heat is produced. Phase change material (PCM) slurries can be used as a heat transfer fluid in microchannels as they provide increased heat capacity during the melting of phase change material. For the present numerical investigation, performance of a nano-encapsulated phase change material slurry in a manifold microchannel heat sink was analyzed. The slurry was modeled as a bulk fluid with varying specific heat. The temperature field inside the channel wall is solved three dimensionally and is coupled with the three dimensional velocity and temperature fields of the fluid. The model includes the microchannel fin or wall effect, axial conduction along the length of the channel, developing flow of the fluid and not all these features were included in previous numerical investigations. Influence of parameters such as particle concentration, inlet temperature, melting range of the PCM, and heat flux is investigated, and the results are compared with the pure single phase fluid.

Investigation of energy transportation capability of a phase change slurry through a cold storage-cooling coil system

Microencapsulated phase change materials slurries (MEPCM slurries) have the advantage that they can be used as heat transport and storage medium, and therefore provide improved continuity of energy transport. Energy transportation capability of a MEPCM slurry based on Rubitherm RT6 through a cold storage-air handling system was investigated for various concentrations and pump powers. The transport properties of the MEPCM have been identified. The optimum concentration for maximum energy transportation capability and energy transportation effectiveness of the system has been found. This investigation is intended for determination of the optimum concentration of MEPCM slurry for an air conditioning system that uses MEPCM slurry as a secondary cooling medium directly into air handling units and stored for load shifting. Copyright © 2009 John Wiley & Sons, Ltd.

Next Generation Phase Change Materials as Multifunctional Watery Suspension for Heat Transport and Heat Storage

AbstractThe phase change materials (PCM) are known since years with high thermal storage capacity but with limited applications. The modified PCM mainly paraffin watery suspensions, so called PCM slurry, improve some PCM drawbacks (thermal conductivity) and as paraffin multifunctional fluids can work in both, heat transport and heat storage for cooling technology applications. The structural and thermophysical properties of two types PCM slurry were good basis for comparison of their efficiency: paraffin microcapsule slurry (A) and paraffin emulsion slurry (B), both working in temperature range of phase transition from 2-12 degreesC. The equipments as differential scanning calorimetry (DSC), model NETZSCH DSC 200 PC; scanning electron microscopy (SEM), JOEL model JSM-5510; hot stage optical microscopy, LINKAM model TMS 94 and hand made thermal cycling system operational with Danfoss cooling machine that ensured 2 kW cooling capacity at 40oC; gave accurate results, characterizing completely, from structural and thermal point of view both types of PCM multifunctional structured fluids. Structural stability of the advanced phase change multifunctional fluids was discussed on sample imaging in variable magnifications made by method of Hot Stage microscopy and precise SEM study. Systematization of the DSC results obtained, including temperature range of phase transition and thermal storage capacity, measured before and after repeatable thermal cycling of the PCM multifunctional fluids, allowed selection of the PCM slurry working samples with relatively high thermal capacity applicable to further development in prototypes. Heat absorbed/released, calculated by NETZSCH DSC software, was for PCM slurry A in the range of 80 to 82 kJ/kg, while PCM slurry B showed thermal storage capacity from 56 to 53 kJ/kg. Correlation between the structural properties and thermal storage capacity of the phase change multifunctional fluids led to practical conclusions concerning: homogeneity; crystal growth/conditions; structural compatibility between components; prediction of the heat flow behavior of multifunctional PCM slurries in cooling technology for storage and transport of heat.

Performance of cooled-ceiling operating with MPCM slurry

Microencapsulated phase change material (MPCM) slurry is advantageous for thermal storage systems to use as a heat transfer and storage medium. In this paper, a new design of air-conditioning system is proposed, which is a combination of CC and a MPCM slurry storage tank. The mathematical model of the combined system is provided and used to predict the system performance of an office room under Hong Kong weather condition using hour-by-hour calculations. A feasibility analysis for the combined system was also made with computer calculations. The results indicate that a small MPCM slurry storage tank is able to shift the part of cooling load from the daytime to nighttime. It is also revealed that the proposed combined system is an energy saving and economy-favorable air-conditioning system.

Forced convection heat transfer with slurry of phase change material in circular ducts: A phenomenological approach

A model describing the thermal behaviour of a slurry of phase change material flow in a circular duct is presented. Reactors connected in series are considered for the representation of the circular duct with constant wall temperature. A phenomenological equation is formulated to take account of the heat generation due to phase change in the particles. Results of the simulation present a plateau of temperature along the longitudinal direction, characteristic of the phase change. The effect of different parameters such as the Reynolds number, the weight fraction and the temperature of the cold spring on the length of the plateau is analysed. A correlation resulting from numerical results is proposed for use in the determination of the characteristics of the exchanger for a phase change material slurry.

Heat transfer of microencapsulated PCM slurry flow in a circular tube

AbstractHeat transfer characteristics of microencapsulated phase change material (MPCM) slurry flow in a circular horizontal tube are presented in this paper. Phase change due to the melting is investigated for water‐based slurries using microencapsulated 1‐bromohexadecane (C16H33Br) with a mass concentrations varying from 0 to 27.6%. The local heat transfer coefficients varied significantly along the test section when PCM particles were melting. The average Nusselt numbers were calculated based on the local heat transfer data and found to be significantly higher than those for single‐phase fluid flow. Two new heat transfer correlations, one used for the slurry under laminar condition (0 < Re < 2000) and another used for the slurry under slightly turbulent condition (2200 < Re < 3500), were proposed for predicting the heat transfer behaviors of MPCM slurry in a circular tube. © 2008 American Institute of Chemical Engineers AIChE J, 2008

Heat transport in a three-stage thermal energy system using phase change material slurries

This study investigated the feasibility of creating a phase-change slurry in which a phase-change material is microencapsulated and suspended in a carrier fluid. The heat transportation, pumping power consumption, viscosity, and pressure loss of the flowing slurries were measured in order to determine the most suitable concentration of micro encapsulated phase change material (MCPCM) used in the slurry over the range 5-40%. The effects of repeated use of liquid-solid phase-change particles upon melting and solidifying were studied using a small-scale rig of a closed loop circuit comprised of heating and cooling sections. Results indicated that the use of a MCPCM slurry can improve the performance of a working fluid by up to 52% as compared to a single-phase fluid. However, increasing the concentration of the MCPCM to 40% was found to have little effect on heat transport. MCPCM slurry containing a high concentration of MCPCM had a high apparent viscosity. Use of an ionic surfactant was found to be effective in reducing the viscosity. Results also showed that a 20-30% concentration was the most suitable concentration for the working fluid due to the associated heat capacity and reasonable pressure drop. The use of such a slurry could reduce the power consumption of the pump by 16%. Stratification between the solid particles and the carrier fluid was a major drawback and made it difficult to use a conventional open system. This problem was overcome by combining an open and a closed system into a three-stage (open-closed-open) operation.

Raising evaporative cooling potentials using combined cooled ceiling and MPCM slurry storage

Evaporative cooling is able to generate the cooling medium at a temperature approaching to the ambient wet bulb temperature. In this paper, a low-energy air-conditioning strategy is proposed, which is a combination of cooled ceiling (CC), microencapsulated phase change material (MPCM) slurry storage and evaporative cooling technologies. The assessment of evaporative cooling availability and utilization is done for five representative climatic cities, including Hong Kong, Shanghai, Beijing, Lanzhou and Urumqi in China, and the energy saving potential of the proposed air-conditioning system is analyzed by using a well validated building simulation code. The results indicate that the new system offers energy saving potential up to 80% under northwestern Chinese climate and up to 10% under southeastern Chinese climate. The optimal design method of the slurry storage tank is also proposed based on the slurry cooling storage behaviors and cooling demand variations of the ceiling panels.

Improving the heat retention of integrated collector/storage solar water heaters using Phase Change Materials Slurries

SYNOPSIS Integrated Collector/Storage Solar Water Heaters are very efficient at collecting solar radiation and transferring thermal energy to store during the day in northern latitudes. However the culture and lifestyle in these latitudes tend to require hot water at the beginning of the day and not at the end. The use of phase change materials, and specifically phase change material slurries, as a heat retention material, to hold heat overnight so that it can be used the next day has been investigated. While it was found that with the right concentration of PCM in a carrier fluid a temperature of 50°C could be maintained until 6am the following day, the nature of the slurry material over time disaggregates and quickly becomes unusable.

Flow and heat transfer behaviors of phase change material slurries in a horizontal circular tube

The flow and convective heat transfer behaviors of microencapsulated phase change material (MPCM) slurries in a horizontal circular tube have been experimentally investigated. The slurry consisted of microencapsulated 1-bromohexadecane (C 16H 33Br) and water, with the mass fractions of MPCM varying from 5% to 27.6%. The pressure drop and local heat transfer coefficients were measured, and the influences of capsule fractions, heating rates, and flow structures on heat transfer performance were also studied. Heat transfer coefficients measured for MPCM slurry are significantly higher than for those for single-phase fluid flow in laminar flow conditions, but exhibit more complicated phenomena at low turbulent conditions. Moreover, a new simple heat transfer correlation equation was proposed that accurately predicts the local heat transfer coefficients of laminar MPCM slurry flow in a horizontal circular tube.

Thermal performance of microencapsulated phase change material slurry in turbulent flow under constant heat flux

Current cooling and heating distribution systems that use water as secondary fluid exhibit limited thermal capacity which can only be overcome by high flow rates and large (volume) capacity. A successful way to enhance the thermal capacity of secondary fluid systems is by incorporating microencapsulated phase change material (MPCM) slurry. However, a full understanding of the physical properties and heat transfer characteristics of MPCM slurry in the 2–8 °C range (35.5–46.5 °F) still is lacking. In the paper, latent heat of fusion, melting and freezing points, and temperature- and concentration-dependent viscosity data, are presented. Results indicate that selection of nucleating agent type and concentration is required to prevent the supercooling phenomenon. Pressure drop and convective heat transfer data were measured using a heat transfer loop operated at different flow rates and heat flux values. Results indicate that the phase change process and slurry mass fraction affect the heat transfer process. The paper also examines the impact of using enhanced surface tubing in combination with MPCM slurry under constant heat flux and turbulent conditions.

Performance of chilled ceiling panels using phase change material slurries as the heat transport medium

Phase change materials (PCM) are advantageous for the dynamic and static storage of thermal energy. By encapsulating PCM in a solid material, of small enough diameter to be suspended in a liquid, partially melting and solidifying slurries can be created with very high energy densities and heat transfer rates. Such slurries are both transport medium and energy storage medium, and can be designed for a specific set temperature. A microencapsulated PCM slurry with melting/crystallisation temperature around 18 °C has been analysed in a test chamber containing a chilled ceiling. The results from the test chamber are presented.

저 에너지형 축냉식 저온유통 시스템 개발

The purpose of this study is to find the optimal conditions of PCM slurry manufacturing equipment for saving the marketing cost and keeping the original quality of products. In addition, the characteristics of the movable container for shipping or distributing products is analysed. The major results are as follows. 1. PCM thermal storage system is designed with the conditions of temperature(), cold chain time(30 minutes), and one time usage(50 liter). This system includes tank, freezer, circulating pump, cycle type heat exchanger, swelling tank, equipment of supplying PCM supplying unit includes cold tank, cycle type heat exchanger, suction unit and control equipments, etc. 2. After ability test of PCM thermal storage system, it shows that the required freezing time of PCM thermal storage system is less than one of the previous system. The reason is that churn (top and bottom) and compulsion circulation are occurred simultaneously and unit cooler type method is better than chiller type method. 3. By the experiment of transportation latent heat container, it is decided that the best container is with latent heat temperature() and density(0.15%). However, for , it is necessary more studies on latent heat thermal conditions and conditions of making method.

Thermal behaviour of integrated solar collector/storage unit with 65°C phase change material

A transient finite volume model was used to predict collection and retention of heat for rectangular cross section solar collector/storage systems when filled with water and various concentrations of phase change material (PCM) slurries with a 65 °C phase change temperature. It was found that the PCM slurry systems collected heat marginally less effectively than water filled stores. Retention of heat at higher temperatures in the PCM slurry systems may allow higher solar savings fractions to be realised depending on heat demand patterns.

The Convective Instability in a Microemulsion Phase-Change-Material Slurry Layer

In the present experimental study, the stability of Rayleigh-Benard convection has been investigated in rectangular enclosures filled with microemulsion Phase-Change-Material (PCM) slurry. The PCM slurry exhibited a pseudoplastic non-Newtonian fluid behavior. Hysteresis in convection was clearly observed while the PCM were in a solid phase and in phase changing. The critical Rayleigh number decreases with the PCM mass concentration while the PCM is in phase changing. The fluid temperature at the center of the enclosure showed a time-dependent oscillation during the transition from a heat conduction state to a convection state. The maximum Nusselt number has been observed for all of the slurries while the heating plate was controlled at a temperature that most of PCM was in phase changing.

Theoretical analysis of convective heat transfer enhancement of microencapsulated phase change material slurries

This paper analyzes the convective heat transfer enhancement mechanism of microencapsulated phase change material slurries based on the analogy between convective heat transfer and thermal conduction with thermal sources. The influence of each factor affecting the heat transfer enhancement for laminar flow in a circular tube with constant wall temperature is analyzed using an effective specific heat capacity model. The model is validated with results available in the literature. The analysis and the results clarify the heat transfer enhancement mechanism and the main factors influencing the heat transfer. In addition, the conventional Nusselt number definition of phase change slurries for internal flow is modified to describe the degree of heat transfer enhancement of microencapsulated phase change material slurries. The modification is also consistent evaluation of the convective heat transfer of internal and external flows.

Natural convection heat transfer of microemulsion phase-change-material slurry in rectangular cavities heated from below and cooled from above

An experimental study has been conducted in dealing with natural convection heat transfer characteristics of microemulsion slurry in rectangular enclosures. The microemulsion slurry used in the present experiment was composed of water, surfactant, and fine particles of phase-change-material (PCM). The PCM mass concentration of the microemulsion slurry was varied from a maximum 30 mass% to a diluted minimum 5 mass%, and the experiments have been done separately in three subdivided temperature ranges of the dispersed PCM particles in a solid phase, two phases (coexistence of solid and liquid) and a liquid phase. The results showed that the Nusselt number increased slightly with the PCM mass concentration for the slurry in solid phase. In the phase change temperature range, the Nusselt number increased with an increase in PCM mass concentration of the slurry at low Rayleigh numbers, while it decreased with increasing PCM mass concentration of the slurry at high Rayleigh numbers. There was not much difference in natural heat transfer characteristics of the PCM slurry with low PCM concentrations (<10 mass%), however, the difference was getting greater with increasing the PCM concentration, especially for the enclosure at a lower aspect ratio (width/height of the rectangular enclosure). The enclosure height was varied from 5.5 to 24.6 mm under a fixed width and depth of 120 mm. Hence, the experiments were performed for a wide range of modified Rayleigh number from 3 × 10 2 to 1.0 × 10 7. The correlation generalized for the PCM slurry in a single phase was derived in the form of Nu=0.22(1− C 1 C m e − C 2AR ) Ra 1/(3 n+1) , where C 1 and C 2 were the optimum fitting constants obtained by the least square method. While the PCM was in a phase changing region, the correlation could be expressed as Nu=0.22(1− C 1 C m e − C 2AR ) Ra 1/(3 n+1) Ste −0.25, where the Ste was the modified Stefan number.

Natural convection heat transfer in enclosures with microemulsion phase change material slurry

This paper has dealt with the natural convection heat transfer characteristics of microemulsion slurry composed of water, fine particles of phase change material (PCM) in rectangular enclosures. The microemulsion slurry exhibited non-Newtonian pseudoplastic fluid behavior, and the phase changing process can show dramatically variations in both thermophysical and rheological properties with temperature. The experiments have been carried out separately in three subdivided regions in which the state of PCM in microemulsion is in only solid phase, two phases (coexistence of solid and liquid phases) or only liquid phase. The complicated heat transfer characteristics of natural convection have appeared in the phase changing region. The phase change phenomenon of the PCM enhanced the heat transfer in natural convection, and the Nusselt number was generalized by introducing a modified Stefan number. However, the Nusselt number did not show a linear output with the height of the enclosure, since a top conduction lid or stagnant layer was induced over a certain height of the enclosure. The Nusselt number increased with a decrease in aspect ratio (width/height of the rectangular enclosure) even including the side-wall effect. However, the microemulsion was more viscous while the PCM was in the solid phase, the side-wall effect on heat transfer was greater for the PCM in the solid region than that for the PCM in the liquid region. The correlation generalized for the PCM in a single phase is \( Nu = 1/3(1 - C_1 )Ra^{{1 \over {3.5n + 1}}} , \) where C 1 = e –0.09AR for the PCM in solid phase and C 1 = e –0.33AR for the PCM in liquid phase. For the PCM in the phase changing region, the correlation can be expressed as \( Nu = CRa^{{1 \over {7n + 2}}} Ste^{ - (1.9 - 1.65n)} , \) where C = 1.22 – 0.035AR for AR > 10 and C = 0.55 – 16.4e –1.1AR for AR < 10. The enclosure height used in the present experiments was varied from H = 5.5 [mm] to 30.4 [mm] at the fixed width W = 120 [mm] and depth D = 120 [mm]. The experiments were done in the range of modified Rayleigh number 7.0 × 102 ≤ Ra ≤ 3.0 × 106, while the enclosure aspect ratio AR varied from 3.9 to 21.8.