The cold box is used for a delivery of perishable foods from a food center to a food store. This box has no ability to cool the food. Therefore, the large size refrigerator is used in the food center and food stores for the quality control of perishable foods. If the cold roll-box has the performance of the refrigerator with simple structure, the cold storage system of the food center and of food store become more simple. In this study, the cold roll-box with resin tube-mat as a heat transfer unit which has a role as ice energy storage vessel is manufactured and its thermal performance are verified experimentally and by employing a numerical calculation. As a result, it was found that this type cold roll-box has good performance as a cold box by employing the ice storage pack or the storage cell even small size.

View full abstract

It is known that the charged water drop in oil with electric field reciprocates between electrode plates. The drop collides repeatedly with each electrode plate. If the drop is in the supercooled state, it initiates to freeze by the collision. In this paper, the effect of the polarity of electrode and its grounding to the initiation are studied experimentally. As a result, it was clarified that neither the polarity nor the grounding influenced the initiation, and the initiation of the drop freezing by colliding with an electrode plate cannot explain according to collision velocity alone.

View full abstract

In order to form the ozone ice, we used micro-bubbles of containing ozone gas. In this method, not only ozone dissolving in water but also that in micro-bubbles trapped in ice are available when the ice is melting. Therefore, in this paper, O_2 micro-bubbles were used as a preliminary experiment. The cooling plate inclined downward was set in the micro-bubbles water, and then ice including a lot of O_2 bubbles was generated on the cooling plate surface. The trapping phenomenon of the bubbles was clarified by observing the distribution of O_2 bubbles in ice.

View full abstract

Frost formation is a transient phenomenon in which both heat transfer and mass transfer take place simultaneously. In this study, heat transfer characteristics, the amount of frost deposited, and the surface temperature of the frost layer under natural convection were investigated. The procedures of the calculation of the overall heat flux and the amount of frost deposited in the frosting process were proposed. Experimental results were compared with present calculated results, the homogeneous frost growth model, and the unhomogeneous frost growth model respectively.

View full abstract

Ice slurry has been widely utilized as thermal storage medium because of its high storage density of thermal energy. In the direct contact heat exchange process between ice slurry and a heated surface, its high storage density would not be fully used because the ice particles may not contact to the heated surface so well. In the present study, impinging flow of ice slurry into the main flow has been adopted as the method to enhance the melting of ice particles in the ice slurry. A Moving Particle Semi-implicit method has been employed to predict the movement and melting characteristics of ice particles. The effectiveness of the impinging flow for the enhancement of melting of ice particles in an ice-slurry was investigated in detail.

View full abstract

In this study, heat transfer characteristics of Tetra-n-butyl ammonium bromide (TBAB) hydrate slurry in horizontal tube were investigated experimentally. The coefficient of heat transfer was measured. The initial concentrations, solid fraction, inner diameter of pipe and Reynolds number were varied as the parameters. In the laminar flow condition, the coefficient of heat transfer increased with an increase in the solid fraction. However, in the turbulent flow condition, the coefficient of heat transfer was similar to the values without solid phase in low solid fraction. In addition, the results of measurement were arranged using the non-dimensional number such as the Nusselt number.

View full abstract

This paper is dealing with the heat transfer characteristics around horizontal cylinders immersed in ice slurry flow. A mixture of ice particles and a trehalose aqueous solution is produced and utilized as a testing ice slurry. The experimental investigation is carried out under some parameters such as a velocity of ice slurry flow, the heat flux of heated surface and a formation of cylinder array. As a result of the evaluation of the local heat transfer coefficient and the observation of the flow behavior, it is found that the distribution of the local heat transfer coefficient is strongly affected by both of the flowing behavior which depends on the formation of cylinders and the melting of ice particles.

View full abstract

When cooling a multi-component mixture, if cooling takes place past the solid-liquid co-existent region and below the solidus line temperature, the whole phase is transformed into a solid phase. This solid-liquid phase can be used as a fluid high-performance secondary refrigerant if it is possible to form a two-phase flow involving the two phases. A fluid regenerative material consisting of solid-liquid phases has a larger heat capacity than a secondary refrigerant of fluid alone. To evaluate the performance as the latent heat storage material of the mixtures, we measured the apparent density and the apparent specific heat.

View full abstract

Numerical simulation of ice crystal growth in supercooled aqueous solution was carried out using 2 dimensional phase field model. An ice nucleus was placed in supercooled aqueous solution and the time evolution of the ice crystal was calculated. As a result, dendritic crystal with hexagonal symmetry could be reproduced. Growth rate of the dendritic crystal in the aqueous solution was compared with that in pure water, and it was found that the growth rate in aqueous solution became slower. In addition, it was found that the growth rate depends on the degree of supercooling.

View full abstract

We have carried out an experiment on the freezing aqueous solution flow of winter flounder antifreeze protein in a micro-channel of 0.15mm in height, 1.2mm in width and 21mm in length. An electro-osmotic pump was used to create the flow of the solution in the channel. The flow was cooled from the side wall. An ice/solution interface is observed at low magnification in a high-resolution biological microscope. It is found from our experiment that, as the flow rate increases, the growing rate of the ice/solution interface decreases and the interface becomes more serrated. This is because the interaction between the interface and the protein, continuously approaching the interface due to the flow, occurs more frequently with an increase in the flow rate.

View full abstract

Formation process of hydrate was studied experimentally. Propane hydrate was formed in a pressure vessel, where ice plate was set and propane gas filled. In order to investigate growth shape of hydrate on the ice surface, formation process was observed especially under isobaric and isothermal conditions. In addition to these experiments, formation rate of hydrate was measured from the variation of shape of growing hydrate. As a result, it was found growth shape of hydrate on the ice surface became circle, and is hardly affected by the side wall of test section. Then, average formation rate depends primarily on pressure and temperature though local formation rate of hydrate may be affected by roughness of ice surface and crystal direction of ice.

View full abstract

Experimental study has been conducted to examine the CO_2 absorption into the water/oil emulsion. Test emulsion was prepared of silicone oil, distilled water and a small amount of surfactant. CO_2 and its N_2 mixture was fed at constant pressure condition of 3.0 MPa and 4.3 MPa into container filled stirred test emulsion. The result shows the silicone oil tested absorbs only carbon dioxide from carbon dioxide and nitrogen mixed gas. It is also obvious that the sufficient partial pressure needs to make carbon dioxide hydrate in emulsion. Effects of N2 component and time histories of its absorption was also discussed.

View full abstract

Experimental study has been conducted to produce the carbon dioxide hydrate in emulsions for improving a fluidity of the hydrate slurry. Water in oil emulsions composed of hydrocarbon saturation and purified water doped with a small amount of surfactant were prepared by briskly mixing of homogenizer. Carbon dioxide absorption and hydrate production experiment was carried out for various water content and hydrocarbon saturation at 275K under 3.0MPa. The results show that the carbon dioxide hydrate in fine water droplet dispersed in hydrocarbon saturation was successfully produced. Effect of carbon number of alkanes was also revealed.

View full abstract

Experimental study has been conducted to examine the heat transfer characteristics of water in oil emulsion with THF hydrate. Test emulsion as a base medium was prepared of silicon oil, distilled water and small amount of surfactant. Tetrahydrofuran hydrate was produced in the test emulsion. Heat transfer experiments has been carried out in the temperature controlled vessel on electrical heated Pt wire. It is obvious that the higher heat transfer coefficient indicates than the silicone oil. Effect of water contents and transient of heat transfer was also discussed.

View full abstract

An experimental study was performed for freeze-concentration of 1% or 10% water-solution of sodium chloride in a cylindrical container, where a heat transfer pipe was set vertically. Experimental results denoted that concentration in case of non-insulation is better than the case of insulation for outside of a container. In case of keeping the temperature at inner wall constant, distribution factor shown better results as preset temperature is raised. In terms of a relation of freezing speed and coefficient of distribution, high temperature at inner wall prevent ice surface from figuration of mushy region. Though measurement of density distribution, it was suggested that natural convection enhances the concentration.

View full abstract

The Solar energy is available at extremely high-energy, transportation, and storage is difficult. In contrast, a chemical reaction by applying a field of solar energy, converting chemical energy, attempts have been made be provided transportation and storage. In this trial, has pointed out the problem of high-temperature resistant nano-particulate heterogeneous catalyst has been used to take advantage of the atmosphere much more efficiently obtained by solar ℃ 1000. In this study, without compromising the catalytic activity, ie, remains in nano form, we propose a new structure with improved heat resistance of the catalyst has been designed to perform the demonstration.

View full abstract

The solar chimney is a passive cooling technique to enhance the natural ventilation of buildings. The effect is, however, limited under hot and humid climatic conditions. In the study, the solar chimney was accompanied by a dew-point evaporative cooler. The dew-point evaporative cooler was integrated with the ceiling of the building. The air flow induced by the solar chimney was predicted by the thermal network model, and the cooling effect of the dew-point evaporative cooler was analyzed by heat and mass transfer simulation. The results showed that the system was capable of coping with approximately 10% of the perimeter cooling load of an office building.

View full abstract

The thermosyphon can operate without an external power supply, and have simple structures. Therefore, thermosyphon can be expected to reduce energy consumption and consequently reduce CO_2 emissions. Recently, Ippohshi et al. developed a thermosyphon in which heat is transferred from an evaporator near its top to a cooler at its base by exploiting the density difference of two-phase flow. However, this device has a large heat capacity due to the reservoir and condenser being housed within a single case and it also takes a considerable amount of time before the water in the pipe starts to circulate. Ito et al. developed a device that the reservoir and the condenser are separate. Using this device, it was possible to drastically reduce the time before circulation commences. In this study, we examined performance of Ito's thermosyphon system. Experimental results show that operation statuses are affected by the reservoir structure and the angle of condenser.

View full abstract

Solar CO_2 Rankine System (SCRS) has been proposed, which can generate electrical and thermal energy by using solar thermal energy as an energy source and carbon dioxide as a working fluid. Now, this system is needed to be optimize. For the optimization of driving, a thermal pump is installed in parallel with a feed pump. Driving source of thermal pump is only the solar energy. The thermal pump is composed of two heat exchangers and has low power consumption. As a result, we can see rankine cycle including supercritical region by using thermal pump. In addition, to investigate superiority of the thermal pump over the feed pump, thermal efficiency of this system was simulated. We can see thermal efficiency of the thermal pump is higher than that of the feed pump.

View full abstract

This paper describes the result of photonic structure design to control solar/thermal radiation by using evolutionally algorithm (EA) which is powerful method to find optimal solution for complex systems. We used EA-FDTD method to design photonic structure which can concentrate solar/thermal radiation according to photosensitivity of PV/TPV cells. In the EA-FDTD, a combination of genetic algorithm and immunity algorithm was incorporated with FDTD method. The results show that the EA-FDTD method can automatically generate possible optimal geometry of the photonic structure which can work as a wavelength selective concentrator.

View full abstract

Temperature measurement of aqueous solution in a micro-fluidic chip by using near-infrared spectroscopy is presented. The principle is based on the temperature dependence of the v_2 + v_3 absorption band of water. Absorbance spectra for two areas in 50-μm thick water in a temperature controlled Y-channel were measured simultaneously by two photospectrometers. The spectra indicated the temperature difference between the two areas. The images of absorbance at 1905 nm corresponding to temperature images were obtained by using a near-infrared camera and narrow bandpass filter. Calibration measurements on water in the Y-channel from 24.0℃ to 46.0℃ demonstrated a temperature coefficient of 4.5 x 10^<-4>℃^<-1>. Finally, temperature distributions caused by a heating wire were visualized.

View full abstract

In microwave heating, interference of transmission wave and reflection wave in a sample has an important meaning. We focus on the high performance of the heating efficiency due to changing the surface structure of the sample. Using the microwave of TE_<10> mode and frequency of 2.45GHz in rectangular waveguide, we have investigated the effect of the only one rectangular concavity surface structure of the material on the characteristics of microwave heating, and have indicated the guideline for the optimization of microwave heating by controlling reflected and transmitted waves. It was found that the only one rectangular concavity surface structure was effective for the high performance of the heating efficiency, by considering the relationship between the mode and the surface structure.

View full abstract

The present study proposes a high-performance thermal insulator using a functional fibrous material of high reflectivity for thermal radiation, and the performance of thermal insulation was experimentally investigated for the glass fiber having aluminum powder on its surface as one of such functional fibrous materials. The heat transfer coefficient was measured in a rectangular cavity for vacancy, glass wool, glass wool with aluminum powder and glass wool with multilayer of aluminum foil. The experimental results showed that radiation heat transfer has serious effects on the performance of thermal insulator and that glass wool with aluminum powder is effective in thermal insulation.

View full abstract

CNTs (Carbon nanotubes) are synthesized from catalyst metal nano-particles that were generated by laser vaporization in LCCVD (laser vaporized catalytic chemical vapor deposition) technique. DMA (Differential Mobility Analyzer) classify metal nano-particles diameter according to the difference of electrical mobility. We expected to be able to observe effect of the catalyst metal nano-particles diameter on CNTs diameter by CNTs synthesis from size classified catalyst metal nano-particles. CNTs and The particle diameter distributions of the metal nano-particles were observed by TEM.

View full abstract

An experimentally simple method utilizing the excitation laser of the Raman system to heat the VA-SWNT film and measure temperature simultaneously for measuring the thermal conductivity and the film-substrate thermal contact resistance of the vertically-aligned single-walled carbon nanotubes (VA-SWNTs) is applied to measure the thermal contact resistance of the transferred film. The method finds the thermal contact resistance at the film-substrate interface of the transferred film to be around four times larger than the original VA-SWNT film grown on Si substrate.

View full abstract

Ion transport in mesoporous silica SB A-16 films was investigated. Thin films of SB A-16 were synthesized on Si substrates via dip-coating method. SEM analysis revealed that SBA-16 films with highly ordered 3D-cubic pore structure were uniformly coated on Si substrates. After the mesopores of a SBA-16 film were filled with pure water, the ionic current passing through the pores was measured by applying electric field. The measured current-voltage (I-V) curve was non-liner and the measured current was larger than the theoretical prediction. This study discusses the relationship between the non-liner I-V curve and the ionic flow inside ink-bottle shaped pores.

View full abstract

Self-assembled honeycomb-patterned porous polymer films are fabricated by breath figure method. The The porous film of polystyrene, polyimide and polysulfone are made. Pores with a few hundred nanometers to several micrometers have been generated by controlling various process parameters, such as solution concentration, substrate temperature and humidity. The numerical calculations of water cluster growth on the polymer surface are carried out. The relationship between pore size and time, and the method of getting smaller pore size is suggested.

View full abstract

In this article, we discuss microscopic behavior of the particle in micro porous media such as Diesel Particulate Filter (DPF). We developed a numerical simulation technique on particle transport and deposition using a Lattice Boltzmann Method, that was applied to the DPF structures obtained by micro-focus X-ray Computed Tomography. The LBM simulation on a small DPF domain showed a pressure drop curve related to the transition of filtration phenomena. We also conducted the LBM simulation on a large DPF domain. Particle deposition was identified in the middle of porous domain, resulting in variation of stream line due to particle loading.

View full abstract

The objective of this study is the development of a meniscus tip for micro-manipulation. The meniscus tip thermally controls the meniscus force between the tip and an objective through varying wet state of the tip by supplying or drying water. To evaluate the adhesion characteristics between the tip surface and small glass sphere was evaluated and the reduction of the adhesion force of 12μN was indicated for temperature variation of 100℃ with the heating rate of 0.69W. It can be thought that the reduction of the adhesion force is due to the evaporation of the liquid film on the tip rather than a decrease in surface tension of the water film, can be thought to be generated by decrease in surface tension of the water but decrease in liquid film. Additionally, a micromanipulation of the glass beads of 100μm diameter was demonstrated.

View full abstract

Near-field radiation that has a high intensity of electric field was applied to enhance conversion from thermal energy to electricity in a wavelength range less than 1.1μm or 1.8μm. A commercial Si-photovoltaic cell and a thermophotovoltaic cell made of GaSb semiconductors were used to confirm that the near-field radiation effect (the evanescent wave effect) can be applied to enhance generation of electricity. As a result, an increase in output power generation of electricity by the evanescent wave effect was detected and the short-circuit current density increased about 1.3 times for the Si-PV cell and 3.0 times for the GaSb-TPV cell as larger than those obtained by the conventional propagating-wave radiation.

View full abstract

Heat transfer enhancing method is more and more needed to decrease power consumption. This study was carried out to develop a high performance vortex generator, and find out the relationship between vortex structure and heat transfer. Double delta winglet pair was developed to reduce pressure drop with keeping up vortex strength. It was clarified that double delta winglet pair had higher performance than delta winglet pair by 10% at flow velocity of 1.4m/s by measuring average heat transfer coefficient and pressure drop. It was found out that double delta winglet pair had the position of vortex core at short distance from heat transfer surface than delta winglet pair. Therefore, the heat transfer coefficient was larger than delta winglet pair's one, even though it's vortex strength was smaller than that.

View full abstract

Two-dimensional numerical simulations have been conducted to investigate the heat transfer in a square cavity where a heat source of a constant and uniform temperature is on the middle of a vertical side wall, the other side wall is kept isothermal at a temperature lower than that of the heat source and the rest of the wall is adiabatic and an adiabatic object is located inside. It has been found that in the cases where the flow pattern between the heat source and the object resembles the one in the channel between two parallel plates, the heat transfer characteristics are well correlated by using modified Nusselt and Grashof numbers proposed in this study.

View full abstract

Fundamental thermal performance of a liquid cooling system for small electronic equipment has been studied. A liquid cooling system is attracting attention because an increase of heat generation density in electronic components requires effective cooling. The cooling system proposed in this study uses a Mini-pipe and pulsatile laminar flow with Microencapsulated Phase Change Material (MEPCM). The coolant including the MEPCM with an average diameter of 4 μm was circulated in the flow channel including the Mini-pipe having a diameter of 2 mm. The mass concentration of MEPCM was changed from 0 to 5 %. The increase of the MEPCM mass concentration enhances convective heat transfer.

View full abstract

This paper introduces power estimation equation for the multi-core microprocessor and describes transient heat conduction simulation using the equation on simplified thermal model by sub-millisecond time step. With the latest CMOS process technology, microprocessor's current is not only voltage but also temperature dependent due to leakage. Unlike steady state analysis, transient analysis requires power information for each time step to calculate temperature on each time step. Moreover, since temperature and power interact with each other through temperature dependent power estimation equation, precise power estimation is critical for microprocessor's transient thermal analysis. While, sufficient heat conduction path expression is important for transient heat conduction simulation and is investigated in this paper.

View full abstract

The present authors have been conducting experimental study of high performance flat heat pipes to apply cooling of electronic devices, especially CPU in server. By using self-rewetting fluids, which show positive surface tension dependence on temperature, as working fluids, the thermal performances of flat heat pipes were improved. In addition, nanofluids with wire-shaped nano particles that nano particles directly synthesized in base fluids by the microwave polyol method are also used for heat transfer enhancement. Demonstration experiment of cooling system with these thin flat heat pipes for CPU was also carried out in real server, and cooling effect comparable to current air cooling system by fans was shown. In the meanwhile, thin plate-type heat pipes which have several kinds of wick structures have been developed and the encouraging thermal performance was obtained.

View full abstract

Many studies on a small-sized heat sink used for cooling of small electronic parts have been reported. However, there were few studies for a large-sized heat sink used for cooling of the backlight unit of liquid crystal display device. In order to design electronic instruments, it is important that the relationship between nusselt numbers and rayleigh number is clarified. In this study, the tested heat sink was made of extruding aluminum, had fins length of 400mm, and was natural convection type heat sink. The numerical analysis on the nusselt numbers of heat sink were conducted under the various conditions, as the results, following conclusions were obtained. The equations for the natural air cooling heat sink which could predict nusselt number and the rayleigh number were proposed.

View full abstract

This paper describes measurement method for in-plane effective thermal conductivity of printed circuit boards (PCBs). We designed two difference shapes PCBs with some kind of wiring patterns on the surface of PCS and measured its thermal resistance. We compared thermal resistances of circular PCBs with square to investigate the effect of the wiring patterns on the in-plane thermal conductivity. The experimental results showed that the thermal resistances of circular PCBs were not dependent on the wiring patterns. On the other hand, thermal resistances of square PCBs decreased with increase of the width and the number of copper wire due to the in-plane heat dissipation effect depending on copper wires. Thus, thermal resistance difference between circular and square PCBs can be observed. Consequently, the in-plane heat dissipation effect due to copper wires can be measured with our measurement method.

View full abstract

To perform a rational thermal design of a printed circuit board (PCB) with highly anisotropic heat transfer nature, effective thermal conductivities in the direction of the thickness and in the plane direction must be given depending on the electric circuit of the board. However, a simple evaluation method for the effective thermal conductivities of the anisotropic board has not been developed yet. In this study, the heat transfer coefficient by natural convection around a horizontal disk has been evaluated, which is indispensable for measuring the effective thermal conductivity.

View full abstract

A cooling jacket for electronics devices, composed of a main heated channel with grooves and auxiliary unheated channels for additional liquid supply, was developed. The structure prevents dryout phenomena, i.e. the heat transfer limitation in boiling, by the reduction of substantial heated length. The heating surface, with a length of 30mm and a width of 30mm, was installed horizontally facing upwards in the cooling jacket. Test liquid was selected as FC72 to keep electric insulation from semiconductors integrated in the server. The measured critical heat flux (CHF) was larger than 33.3×10^4W/m^2 (300W) for inlet volumetric flow rate V_<in> = 0.8l/min and 1.0l/min (mass velocity G_<in> = 372kg/m^2 and 466kg/m^2s, respectively) at inlet liquid temperature T_<in> = 35℃ and test pressure P=0.15MPa. Larger CHF values compared to those for the channel without auxiliary unheated channels were confirmed.

View full abstract

For further development of semiconductor integrated circuit, SD-integrated circuit has been proposed. To realize SD-integrated circuit, a chip reliability test without dicing 300 mm^φ wafer is required. The test technology requires following features: wafer level (without dicing 300 mm wafer), precise temperature control between 100 and 125 degree C, heat removal capability of 15 kW/300mm^φ. Therefore, in this research, we developed advanced chip reliability test technology using latent heat of water vaporization. We divided 300 mm wafer into 69 parts and water is sprayed to each part against gravity. On the wafer, temperature is not uniform because the heat generation is different among the wafer caused by yield distribution. Since the sprayed water is controlled separately, the system can maintain the uniform temperature on the wafer. As a result of evaluation of this system, we achieve precise temperature control from 70 to 150 degree C at the heat flux of 0.1 to 20 kW.

View full abstract

A vapor-pressure-driven heat pipe is devised for sideward heat transport over a long distance. The present heat pipe is composed of a heated section, a cooled section, a reservoir, valves and pipes connecting these components. Inside the heat pipe, a condensate is returned by utilizing the vapor pressure of a working fluid. By the experiment, it is confirmed that the heat pipe works periodically corresponding to the valve operation, and the heat is transported sideward continuously from the heated section to the cooled section. The present heat pipe is effective for a large-scale thermal management.

View full abstract

This paper describes the effect of design parameters on natural convection from horizontal heated plates in an enclosure. The effects of the heat generation and the enclosure height were examined experimentally. The results show that flow characteristics have two distinctive patterns. One includes vortex motion. The other is circulated along the heated surface. The increase of the heat generation develops the vortex motion and enhances the heat transfer. The heat transfer is independent of the height of adjacent air space. In all the heated surfaces, average Nusselt number is related to modified Rayleigh number.

View full abstract