Analysis of forced convection heat transfer in microencapsulated phase change material suspensions (original) (raw)
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University of Thi_Qar Journal for Engineering Sciences, 2020
This paper aims to study the flow and heat transfer of hybrid suspension in counter flow micro channel heat exchanger (CFMCHE). In order to enhance the thermal properties of micro encapsulated phase change material (MEPCM) suspension. The hybrid suspension studied in this paper consists of nanoparticles and MEPCM particles, these particles are suspended in water as abase fluid, two types of hybrid suspension are used (Cu + MEPCM suspension) and (Al2O3+ MEPCM suspension) by n-octadecane as a PCM for both of them. The hydrodynamic and thermal characteristics of thes suspensions flow in micro channels of CFMCHE is numerically investigated. From obtained results, using of hybrid suspensions as a cooling fluid lead to modify thermal performance of a CFMCHE by increase its effectiveness but it also lead to high increasing in pressure drop. The results showed considerable enhancement in cooling effectiveness of (Al2O3 + MEPCM suspension) above of the pure PCM suspension, Nanofluids, and water. While (Cu + MEPCM suspension) showed enhancement above of the pure PCM suspension and water, but was not best effectiveness than Nanofluids. Extra increase in pressure drop in both types of hybrid suspension above are leads to reduce the overall performance compared with pure PCM suspension. Therefore its use depends on the application at which this heat exchanger is employed. Key words: Microchannel heat exchanger (MCHE), Microencapsulated phase change material (MEPCM), Phase change materials (PCM), hybrid suspension , Nanofluid. NOMENCLATURE: A Cross-sectional area (m 2) C Volume fraction % Cp Specific heat capacity (J / kg K) Dh Hydraulic diameter (m) H Channel height (m) He Enthalpy of suspension (W) he Sensible heat (W) K Thermal conductivity (W/m K) L Heat exchanger length (m) M Mass flow rate (kg/s) P Total pressure (Pa) Q Heat transfer rate (W) t Separating wall thickness (m) T Temperature (K) u Fluid x-component velocity (m/s) v Fluid y-component velocity (m/s) w Fluid z-component velocity (m/s) x Axial coordinate (m) y Vertical coordinate (m) z Horizontal coordinate (m) Wch Channel width (m) ΔP Pressure drop (Pa) ΔH Latent heat (W) Greek letters ρ Density (kg/m 3) ф Mass fraction m֗ flow rate Ƞ Performance index (1/Pa) ß Melted fraction µ Dynamic Viscosity (m 2 /s) Subscripts
Rheological and thermal properties of suspensions of microcapsules containing phase change materials
Colloid and polymer science, 2018
The thermal and rheological properties of suspensions of microencapsulated phase change materials (MPCM) in glycerol were investigated. When the microcapsule concentration is raised, the heat storage capacity of the suspensions becomes higher and a slight decline in the thermal conductivity of the suspensions is observed. The temperature-dependent shear-thinning behaviour of the suspensions was found to be strongly affected by non-encapsulated phase change materials (PCM). Accordingly, the rheological properties of the MPCM suspensions could be described by the Cross model below the PCM melting point while a power law model best described the data above the PCM melting point. The MPCM suspensions are interesting for energy storage and heat transfer applications. However, the non-encapsulated PCM contributes to the agglomeration of the microcapsules, which can lead to higher pumping consumption and clogging of piping systems.
Melting of n-octadecane with CuO nanoparticle suspensions in a square enclosure is studied experimentally and numerically. The container is subjected to a constant heat flux on one side, while the other sides are thermally insulated. The experimental study entailed recording the time-dependent temperatures at different locations inside the cell. The finite element method (FEM) is used to solve the coupled continuity, momentum, and energy coupled equations numerically. The model is validated and the results exhibited a good agreement with previous related work. The agreement between the current experimental and simulated results is reasonable. The impacts of the nanoparticle loading, the Rayleigh number, and the subcooling are analyzed. The experimental and numerical results indicate that the nanoparticle loading has a positive effect on raising the thermal conductivity of the PCM/nanoparticle composite, increasing the temperature of the composite and augmenting heat transfer rate which results in decreasing the charging time. Development of the melting interface and melt fraction volume are improved with the increasing of the nanoparticle concentration. Caution should be taken for higher values of nanoparticle concentration due to effects of increasing viscosity and possibility of agglomeration and precipitation. The effect of natural convection is pronounced in the upper part of the cell, while the lower region is characterized by conduction-dominated heat transfer. This effect intensifies with the increase of the supplied heat flux (i.e. raising the value of the Rayleigh number) which causes expediting of the melting process. The shape of the melting interface is affected highly by the competing heat transfer mechanisms. Parallelto-wall flat shape interface is present in the conduction-dominant regime, while curved shape of the interface emphasizes development of natural convection. The impact of subcooling has a negative influence on the melting process in which the high value of subcooling will prolong the charging time.
Applied Thermal Engineering, 2012
This paper is to conduct experimental investigation on the convective heat transfer of magnetic phase change microcapsule (MPCMC) suspension in the presence of an external non-homogenous magnetic field. The effects of the external magnetic field intensity, the volume fraction of MPCMC particles and the mass flow rate of MPCMC suspension on the convective heat transfer of MPCMC suspension are investigated. The experimental data reveal that the convective heat transfer of MPCMC suspension is significantly enhanced by the external non-homogenous magnetic field.
University of Thi-Qar Journal for Engineering Sciences, 2020
This paper aims to study the flow and heat transfer of hybrid suspension in counter flow micro channel heat exchanger (CFMCHE). In order to enhance the thermal properties of micro encapsulated phase change material (MEPCM) suspension. The hybrid suspension studied in this paper consists of nanoparticles and MEPCM particles, these particles are suspended in water as abase fluid, two types of hybrid suspension are used (Cu + MEPCM suspension) and (Al2O3+ MEPCM suspension) by n-octadecane as a PCM for both of them. The hydrodynamic and thermal characteristics of thes suspensions flow in micro channels of CFMCHE is numerically investigated. From obtained results, using of hybrid suspensions as a cooling fluid lead to modify thermal performance of a CFMCHE by increase its effectiveness but it also lead to high increasing in pressure drop. The results showed considerable enhancement in cooling effectiveness of (Al2O3 + MEPCM suspension) above of the pure PCM suspension, Nanofluids, and water. While (Cu + MEPCM suspension) showed enhancement above of the pure PCM suspension and water, but was not best effectiveness than Nanofluids. Extra increase in pressure drop in both types of hybrid suspension above are leads to reduce the overall performance compared with pure PCM suspension. Therefore its use depends on the application at which this heat exchanger is employed.
Heat and Mass Transfer, 2006
A two-dimensional numerical simulation of natural convection in a rectangular enclosure heated from below and cooled from above has been conducted with non-Newtonian phase-change-material (PCM) microcapsulate slurry with latent heat capacities. The formulation of the mathematical model in dimensionless coordinates and discretization of the governing equations have been done using the finite volume method. Both natural convection and heat transfer characteristics are discussed about natural convection with PCM microcapsulate slurry, which exhibits the pseudoplastic non-Newtonian fluid behavior and a peak value in the specific heat capacity with latent heat. The viscosity of the present PCM microcapsulate slurry is assumed to follow the Ostwald-de Waele power law fluid model with the power-law index n and the consistency coefficient K. The effects of phasechange material, the mass concentration, and the aspect ratio Ar on the natural convection heat transfer are described, respectively. By comparing with the results of microcapsule slurry without phase change, the enhancement in heat transfer is found in microcapsule slurry with phase change during the phase change temperature range. Numerical simulations are performed in the following parametric ranges: the widthheight aspect ratio of the enclosure Ar from 2 to 20, the mass concentrations C m of the slurry from 10 to 40%, power law index n of the slurry from 0.89 to 1.0 and Rayleigh numbers Ra ranges from 10 3 to 10 7 .
Energy Conversion and Management, 2015
Heat transfer coefficients and friction factors were determined experimentally for eight helically-finned tubes and one smooth tube using liquid water at Reynolds numbers ranging from 12,000 to 60,000. The helically-finned tubes tested in this investigation have helix angles between 25°and 48°, number of fin starts between 10 and 45, and fin height-to-diameter ratios between 0.0199 and 0.0327. An uncertainty analysis was completed and plain-tube results were compared to the Blasius and Dittus-Boelter equations with satisfactory agreement. Power-law correlations for Fanning friction and Colburn j-factors were developed using a least-squares regression. The performance of the correlations was evaluated with data of other researchers with average prediction errors between 30% and 40%.
Journal of heat transfer, 2014
Microencapsulated phase change material (MPCM) slurry is consisted of a base fluid in which MPCM is dispersed. Due to apparent high heat capacity associated with phase change process, MPCM slurry can be used as a viable heat transfer fluid (HTF) for turbulent flow conditions. Heat transfer and fluid flow properties of the slurry in turbulent flow (3000 < Re < 6000) were determined experimentally. Dynamic viscosity of the MPCM slurry was measured at different temperatures close to the melting point of the material (20-30 C). Pressure drop measurements under turbulent flow conditions were recorded for 6 MPCM samples at various concentrations. The pressure drop of the MPCM slurry was comparable to that of water despite the higher viscosity of the slurry. The effect of heat flux, MPCM mass concentration, flow rate and the type of phase change material was investigated. The effective heat capacity of slurry at the location where phase change occurs was found to be considerably higher than that of water. A nondimensional Nusselt number correlation was proposed in order to facilitate design of heat transfer loops with MPCM slurries as working fluid.
A microencapsulated phase change material (MPCM) slurry has been formulated as a high heat capacity heat transfer fluid (HTF) for turbulent flow conditions. The MPCM slurry consists of du-rable 5-μm microcapsules. The phase change material inside the microcapsules consists of methyl stearate. Heat transfer and fluid flow properties of the aqueous MPCM slurry in turbulent flow (3000 < Re < 6000) were determined experimentally. Heat transfer data were obtained under con-stant heat flux conditions using a closed heat transfer loop. The experimental system was used to determine effective heat transfer coefficient and pressure drop with and without phase change oc-curring inside the microcapsules. Dynamic viscosity data suggest that at relatively low mass con-centrations the slurry behaves as a Newtonian fluid. The pressure drop data under turbulent flow conditions were also measured at MPCM concentrations of 7 and 11% by weight. It was found that whenever the MPCM experienced a ph...