Akihiko Horibe

Melting Heat Transfer Characteristics of Microencapsulated Phase Change Material Slurries With Plural Microcapsules Having Different Diameters

The present study has been performed for obtaining the heat transfer enhancement characteristics of the plural microencapsulated solid-liquid phase change materials (PCM) slurry having different sizes, which flows in a straight tube heated under a constant wall heal flux condition. In the turbulent flow region, the friction factor of the plural PCM slurry was found to be lower than that of pure water flow due to the drag reducing effect of the ACM slurry. The heat transfer coefficient of the plural PCMs slurry flow in the tube was increased by both effects of latent heat evolved in phase change process and microconvection around plural microcapsules with different diameters

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

Abstract 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 (

Numerical simulation of Rayleigh–Bénard convection in non-Newtonian phase-change-material slurries

A two-dimensional numerical study has been conducted to obtain fluid flow and heat transfer characteristics for Rayleigh–Benard natural convection of non-Newtonian phase-change-material (PCM) slurries in a rectangular enclosure with isothermal horizontal plates and adiabatic lateral walls. Generally, with the melting of PCM, the slurrys density draws down sharply but continuously and the slurrys specific heat capacity shows a peak value. Some PCM slurries such as microemulsions can exhibit pseudoplastic non-Newtonian fluid behavior. This paper deals with the differences in natural convection and flow patterns between Newtonian and non-Newtonian fluids with or without PCM theoretically. Due to the participation of PCM in natural convection, the dependency of Rayleigh number Ra alone cannot reflect its intensity that a modified Stefan number has to be taken into account. A correlation is generalized in the form of Nu=C·Ral·Ste−m which has a mean deviation of 10.4% in agreement with the calculated data. The numerical simulation has been performed with the following parameters: a shear thinning pseudoplastic fluid for pseudoplastic index 0.8⩽n⩽1.0, 6×103⩽Ra⩽2×106, Prandtl number Pr=70–288, and the aspect ratio of the rectangular enclosure from 10:1 to 20:1.

Drag and Heat Transfer Reduction Phenomena of Drag-Reducing Surfactant Solutions in Straight and Helical Pipes

Flow drag and heat transfer reduction phenomena of non-ionic aqueous surfactant solutions flowing in helical and straight pipes have been experimentally investigated at surfactant solution concentration range of 250-5000 ppm and temperature range of 5-20°C. The helically coiled pipes have curvature ratios range of 0.018-0.045. Experimental findings indicate that the friction factors and the heat transfer coefficients of the surfactant solution in helical pipes are significantly higher than in a straight pipe and lower than Newtonian fluid flow like water through the same coils in the turbulent drag reduction region. Drag reduction and heat transfer reduction increase with an increase in surfactant solution concentration and temperature in the measured concentration and temperature ranges. On the other hand, they decrease with increasing of the curvature ratio. A set of empirical expressions for predicting the friction factor and the average Nusselt number for the surfactant solutions flow through helical and straight pipes have been regressed based on the obtained data in the present experiments.

Fin Efficiency of an Annular Fin Composed of a Substrate Metallic Fin and a Coating Layer

An analytical solution to a composite annular fin made of a substrate metallic fin and a coating layer has been carried out. Useful expressions for calculating temperature distribution and fin efficiency have been derived. Comparing the analytical results to those of numerical calculation, the premise for the expressions is also explored. Theoretical analyzing results show that fin efficiency of a coated fin decreases with an increase of the coating layer thickness if the thermal conductivity of coating layer is much less than that of the substrate metallic fin. Whereas, the reverse influence of the coating layer thickness on the fin efficiency appears if the thermal conductivity of the coating layer is beyond the above range.

Heat, mass and momentum transfer of a water film flowing down a tilted plate exposed to solar irradiation

Abstract This paper has investigated the heat, mass and momentum transfer of a water film falling over a tilted plate with solar radiant heating and water evaporation. A cluster of physical models which include conduction, convection with flow turbulence, diffusion, radiation and phase change was developed for predicting the characteristics of heat, mass and momentum transfer. A fully implicit control-volume finite-difference procedure was used to solve the coupling equations. The effects of various parameters on heat, mass and momentum transport were investigated. The results revealed that the gradients of temperature and the mass fraction of water vapor in the gas layer, and the wind velocity played a key role in the heat and mass transfer along the gas-water interface. The water film Reynolds number related to the film thickness and the plate tilt angle markedly exerted an influence on the eddy viscosity and the turbulent Prandtl number of the water film. The ambient atmospheric temperature only dramatically affected the interfacial sensible heat transfer. The magnitude of solar incident flux had intense influence on the water film temperature but not on the interfacial heat and mass transfers.

Study on the critical conditions of ice formation for a continuous ice making system in a cooling pipe

This paper deals with a continuous ice making method which could be used to provide an ice storage system using off-peak electricity during nighttime. The critical condition for an ice blockage to occur in the cooling tube has been examined in terms of the concentration of water-propylene glycol solution and thermo-hydraulic operating parameters. The results obtained show that nondimensional correlation equations for the critical condition have been derived as a function of thermo-hydraulic parameters in the laminar and the turbulent flow regions. The equations can be used to predict whether an ice making system is operating in a continuous ice making condition or is in the ice blocking phase.

Surface tension of aqueous binary solutions

Measurements of surface tension have been performed to determine the effects of both temperature and concentration on the surface tension of aqueous solutions of D-Sorbitol, potassium chloride, and ammonium chloride. A differential capillary-rise method was employed for the measurements. The results showed that the surface tension of test solutions increased as the temperature decreased and that the surface tension of chloride solutions increased with an increase in its concentration, while for D-Sorbitol solution the surface tension decreased with increasing concentration. Correlation equations for the surface tension of three aqueous binary solutions as a function of temperature and concentration were determined.

An experimental investigation of sorption process in fluidized bed with cooling pipe

An experimental investigation of a fluidized bed with multiple cooling pipes was conducted to study adsorption characteristics of a new organic sorbent desiccant material (HU300P) for a new air conditioning system. The mass ratio of the present sorbent desiccant powder type is from 1.3 to 2.3 times greater than that of silica gel. The sorption rate of the water vapor in the sorbent bed was measured under various conditions. It was found that the sorption rate is highly dependent on the effect of cooling pipes. The sorption ratio increases and the completion time for the sorption process decreases by using multiple cooling pipes.

Microalgal Culture for Chlorella sp. using a Hollow Fiber MembraneModule

A hollow fiber culture system has been proposed for supplying the carbon dioxide to the microalgae, to replace the conventional air bubbling system which has been adopted to supply carbon dioxide in most conventional microalgal culture. In order to examine the usefulness of hollow fiber membranes for the microalgal culture, the microalgal growth rate for Chlorella sp. and the effective mass transfer coefficient of carbon dioxide through the hollow fiber membranes have been measured using the proposed photobioreactor filled with hollow fibers. The microalgal growth rate using hollow fiber membranes was found to be three times greater than that observed in the conventional non-membrane photobioreactor. An experimental investigation has been conducted so as to evaluate the effect of the volume flow rate of the carbon dioxide and its concentration of the feed air through the hollow fibers on the microalgal growth rate. The present study clearly indicates that the hollow fiber membrane is quite useful for the microalgae culture in terms of enhancing both microalgal growth rate and dissolution rate of the carbon dioxide.