Microencapsulated Phase Change Material Particles Research Articles

Experimental study on cooling performance of minichannel heat sink using water-based MEPCM particles

Experimental study was performed to investigate the cooling performance of a minichannel heat sink (Mini-CHS) with microencapsulated phase change material (MEPCM) particles/water as the coolants. Emphasis was focused on the evaluations of the hydraulic and thermal performance of water-based MEPCM particles in a Mini-CHS from the results of friction factor, average Nusselt number, heat transfer efficacy, temperature control effectiveness, and figure of merit with the Reynolds number ranging from 133 to 1515. The measured results reveal that the thermal performance can be enhanced by addition of MEPCM particles in water with low values of latent-sensible heat ratio (ωpcm/Stebf⁎) and using a low flow rate of coolant as compared to those of the pure water. For instance, an increment of 52% heat transfer effectiveness can be achieved for Rebf=133 and ωpcm/Stebf⁎=0.0472. It is also found that the case with lower flow rate and latent-sensible heat ratio has a better improvement of thermal resistance compared with that for the pure water. However, results also indicate that the enhancement effect may be reduced by increasing the values of latent-sensible heat ratio and the thermal performance of the MEPCM particles with higher latent-sensible heat ratio is not necessarily better than that of pure water.

Thermal conductivity enhancement of form-stable phase-change composites by milling of expanded graphite, micro-capsules and polyethylene

Structured form-stable phase change composites were prepared by wet milling and hot-compaction of microencapsulated phase change material (MPCM), expanded graphite (EG) and high density polyethylene (HDPE). In the composites, MPCM serves as a latent heat storage material, EG as a heat transfer promoting agent and HDPE as a matrix. Scanning electron microscope (SEM) characterization reveals that MPCM particles kept undamaged with a uniform dispersion in the composites. Thermal conductivity of the composites with 20 wt% EG loaded could be enhanced by 22 times compared to HDPE/MPCM composites without EG. And thermal conductivity of the composite could be increased by 10 times at a loading of 10 wt% EG.

An experimental study on heat transfer and pressure loss of microencapsulated phase change material suspension flowing in rectangular minichannels

Comparative experiments were conducted in order to investigate the heat transfer and pressure loss characteristics of water-based suspensions of microencapsulated phase change material (MEPCM) flowing through rectangular minichannels. MEPCM particles with an average size of 4.97 μm were used to form suspensions with mass concentrations ranging from 0% to 20%. The heat transfer experiments were performed for varying mass flow fluxes (mass flow rate per unit area) in the laminar region and varying thermal conditions. It was found out that the mass flow flux, wall heating flux and MEPCM mass concentration play significant and combinational roles in the heat transfer performance of the MEPCM suspensions. It is believed that the decreased thermal conductivity of MEPCM suspensions with the concentration and the different thermally developing flow patterns are mainly responsible for the heat transfer characteristics of MEPCM suspensions with various concentrations. The flow friction experiments showed that the friction factors of the MEPCM suspensions agreed reasonably well with those of continuous Newtonian fluid in the laminar flow region. The measured pressure drops of the MEPCM suspensions flowing in the minichannels increase over the entire range of the velocity as the concentration increases.

Thermal simulation of composite high conductivity laminated microencapsulated phase change material (MEPCM) board

In this paper, 3-dimensional geometric models have been developed to evaluate the particle distribution effect on the thermal performance of a composite high conductivity laminated MEPCM board. For the purpose of comparison three geometric configurations (rectangular, triangular and pyramidal) were considered for the distribution network. Copper foam was used as the base material for fixing the positions of the MEPCM particles and to enhance the thermal conductivity of the composite laminated board. The simulation results show that the thermal response times for the rectangular and triangular geometries were about half that of the pyramidal geometry during cooling and heating processes of the board. Even though there were no significant differences in their effective thermal conductivities, the values were more than ten (10) times that of pure MEPCM but suffered from a reduction in energy storage capacities by about 48%. Other methods of enhancing both thermal conductivity and energy storage are therefore encouraged.

Heat Transfer to Suspensions of Microencapsulated Phase Change Material Flowing Through Minichannels

The heat transfer to water-based suspensions of microencapsulated phase change material (MEPCM) flowing laminarly through rectangular copper minichannels was investigated both experimentally and numerically. The MEPCM-particles had an average size of 5 μm and contained as phase change material n-eicosane, which has a theoretical melting temperature of 36.4 °C. Water and suspensions with particle mass fractions of 10% and 20% were considered. While the experiments result in rather global values such as wall temperatures at certain points, suspension in- and outlet temperatures, and the pressure drop, the numerical simulations allow additionally a more detailed insight, for example, into the temperature distribution in the flowing suspension. The results show that MEPCM suspensions are only advantageous in comparison to water in a certain range of parameter combinations, where the latent heat is exploited to a high degree. The available latent heat storage potential, which depends on the particle fraction in the suspension and on the mass flow rate, has to be in the same order of magnitude as the supplied heat. Moreover, the mean residence time of the particles in the cooling channels must not be considerably shorter than the characteristic time for heat conduction perpendicular to the flow direction. Otherwise, the particles in the center region of the flow leave the cooling channels with still solid cores, and their latent heat is not exploited. Furthermore, the benefit of the added MEPCM particles depends on the inlet temperature, which has to be slightly below the theoretical melting temperature, and on the subcooling temperature after the heat supply, which has to be sufficiently low to guarantee that the entire phase change material solidifies again before it re-enters the cooling channels. The suspensions showed Newtonian behavior in the viscosity measurement. The actual pressure drop determined in the experiments is smaller than the pressure drop estimation based on the measured viscosities. The difference between the two values increases with increasing particle mass fraction. This shows that the particles are not evenly distributed in the flowing suspension, but that there is a particle-depleted layer close to the channel walls. This reduces the required pumping power, but makes it even more important to provide conditions, in which a sufficiently large amount of the supplied heat is conducted to the center region of the channels.

Heat Transfer Characteristics of Liquid Flow With Micro-Encapsulated Phase Change Material: Numerical Study

This numerical investigation fundamentally explores the thermal boundary layers’ characteristics of liquid flow with micro-encapsulated phase change material (MEPCM). Unlike pure liquids, the heat transfer characteristics of MEPCM slurry cannot be simply presented in terms of corresponding dimensionless controlling parameters, such as Peclet number. In the presence of phase change particles, the controlling parameters’ values change significantly along the tube length due to the phase change. The MEPCM slurry flow does not reach a fully developed condition as long as the MEPCM particles experience phase change. The presence of MEPCM in the working fluid slows the growth of the thermal boundary layer and extends the thermal entry length. The local heat transfer coefficient strongly depends on the corresponding location of the melting zone interface. The heat transfer characteristics of liquid flow with MEPCM are presented as well.

Characterization and Thermal Properties of the Microencapsulated PCM Slurry

The microencapsulated phase change material (PCM) slurry is a kind of mixture with the PCM microcapsule particles and water. The actual PCM in the microcapsule is composed of several kinds of paraffin waxes (mainly nonadecane), and the membrane is a type of melamine resin. This study is focused on preparation, characterization, and thermal properties of the microencapsulated (PCM) slurry. The microencapsulated PCM particles are prepared by in-situ polymerization method. Four different levels of mass concentration Cm of the PCM will be used such as Cm=10%, 20%, 30% and 40%, respectively. The diameter of the particles is distributed in the range of 0µm~4.5µm, and most (61%) of them occur in the range of 0.5µm~1.5µm. The average volumetric diameter of the PCM microcapsule particle is about 0.78µm. And the average membrane thickness is about 11nm.Thermal properties of the microencapsulated PCM slurry are determined using differential scanning calorimeter (DSC). From DSC analysis, the melting and freezing temperatures and the latent heats of Cm=30% are measured as 38°C and 25°C, and 37.9 kJ/kg, respectively. The rheological properties are measured by a rotating cylinder type of rheometer, which the slurry shows the pseudo plastic non-Newtonian fluid behavior with the power-law fluid index n.

On laminar convective cooling performance of hybrid water-based suspensions of Al 2O 3 nanoparticles and MEPCM particles in a circular tube

Laminar forced convection of a hybrid water-based suspension of Al 2O 3 nanoparticles and microencapsulated phase change material (MEPCM) particles through a circular tube was investigated experimentally. In addition, an integral energy balance with scaling estimation is presented to elucidate influences of thermal properties of the hybrid suspension on its internal convection effectiveness. Experimental results show considerable enhancement in cooling effectiveness of the hybrid suspension over the pure PCM suspension, nanofluid, or water. However, the convection efficacy of utilizing the hybrid suspension appears severely outweighed by pressure drop penalty from its drastically increased viscosity with respect to the pure PCM suspension or the pure nanofluid.

Water-based suspensions of Al 2O 3 nanoparticles and MEPCM particles on convection effectiveness in a circular tube

This work compares experimentally the effectiveness of substituting the water-based suspensions of Al 2O 3 nanoparticles (nanofluid) and of micro-encapsulated phase change material particles (PCM suspension) for the pure water for laminar forced convective cooling through an iso-flux heated circular horizontal tube. Convection heat transfer experiments have been undertaken for the tube using the pure water, the PCM suspensions ( ω PCM = 2, 5, and 10 wt.%) and the nanofluids ( ω np = 2, 6, and 10 wt.%) as the working fluids under the following operating conditions: the volume flow rate Q = 25–240 cm 3/min (the Reynolds number Re f = 195–1801), the heating power applied at the outer wall of the tube q o = 20, 30, 40 W, and the inlet fluid temperature T in = 32.8–33.2 °C. In addition, a scale analysis together with integral energy balance is presented concerning thermally developing heat transfer characteristics of the water-based suspension flow in the tube. The convective cooling performance of the water-based suspensions was gauged in terms of local and surface-averaged temperature control effectiveness along the tube wall compared with that obtained for the pure water. Furthermore, the water-based suspensions were compared based on the figures of merit for their heat transfer performances against the corresponding pressure drop penalty.

Convective heat transfer characteristics of microencapsulated phase change material suspensions in minichannels

A comparative experimental study was conducted in order to investigate the convective heat transfer characteristics of water-based suspensions of microencapsulated phase change material (MEPCM) flowing through rectangular copper minichannels. The hydraulic diameter of the channels was 2.71 mm. MEPCM particles with an average size of 4.97 μm were used to form suspensions with mass concentrations ranging from 0 to 20%. The comparative experiments were performed for varying mass flow rates in the laminar region and varying thermal conditions. The cooling performance of the MEPCM suspensions strongly depended on the mass flow rate and the MEPCM mass concentration. The 5% suspension always showed a better cooling performance than water resulting in lower wall temperatures and enhanced heat transfer coefficients within the whole range of mass flow rates. The suspensions with higher mass concentrations, however, were more effective only at low mass flow rates. At higher mass flow rates they showed a less effective cooling performance than water.