A state-of-the-art review of enhanced evaporation and condensation in horizontal microfin tubes and micro-channels that are used for air-conditioning and refrigeration applications is presented. The review covers the effects of flow pattern and geometrical parameters of the tubes on the heat transfer performance. Attention is paid to the effect of surface tension which leads to enhanced evaporation and condensation in the microfin tubes and micro-channels. A review of prior efforts to develop empirical correlations of the heat transfer coefficient and theoretical models for evaporation and condensation in the horizontal microfin tubes and micro-channels is also presented.

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Performance enhancement of adsorption cooling system has been required for commercial use. Therefore, revealing details of adsorption phenomena are important for optimizing adsorber/desorber heat exchanger which is the bottle-neck of the system. This study deals with the experimental investigation of ethanol vapor adsorption on activated carbon fiber (ACF) under equilibrium condition along with one-dimensional transient numerical simulation of heat and mass transfer in the adsorbent bed is also performed. In order to suggest optimizing method for performance improvement, the present study considered the relationships between cooling capacity and system performance inducing parameters, such as cooling water temperature, ACF height and apparent density in the simulation model. Simulation results agreed well with the experimental data and it is found that the cooling capacity can be enhanced by optimizing ACF bed thickness. Simulation results also shows that the temperatures of adsorber and evaporator do not have significant effects on the optimum adsorption cycle time.

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An unitized reversible cell stack (URC) which can work as both water electrolyzer and fuel cell is an interesting device in the wide use of hydrogen energy in the near future. We have manufactured a single cell, as practical electrode size, with electrode area of 250cm². From the results of a cell performance evaluation, suitable conditions for high performance operation of the URC and the switching criteria of both modes were identified. Moreover, based on the results of single cells, we manufactured the 1kW-class URC stack. The round-trip efficiencies of both water electrolyzer and fuel cell modes of the URC stack were examined. From the obtained results, it was confirmed that the energy conversion efficiency of the URC developed here were comparable with that of the dedicated systems. In addition, it was demonstrated that the switching operation mode of the URC between water electrolyzer and fuel cell was performed successfully.

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A transfer function approach is found to be a practical method for ensuring stable operation of absorption chiller-heaters. The transfer function model is based on a solution-circuit of the machine, which dominates the stability of the operation. This model includes a solution pump, a generator with an overflow weir, and a float valve. We found that the solution-circuit system is designed with the cascade control, which makes the system stable. In this construction, the float valve actuates a primary control loop, and the overflow weir actuates a secondary loop. The effects of the characteristic of the solution pump and the overflow weir are estimated by the degree of the stabilities, which are the gain margin and the phase margin. We found that the characteristic of the solution pump strongly effects the stability by enhancing the effect of the cascade control and improving the stability. So it is essential for a better stability analysis model. According to these results, the established model is useful for quantitatively predicting the stabilities of a chiller-heater in operation, and simultaneously reducing its size and improving the stability of operation. We conclude that the methodology based on transfer function can provide compact and reliable absorption chiller-heaters.

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The performance test of plate type evaporators was carried out. Ammonia/Water mixtures were utilized as working fluid and warm water was utilized as heat source. Five kinds of ammonia mass fraction are tested. The overall heat transfer coefficient of ammonia/water mixtures was lower than the pure ammonia in the same experimental condition. In the convection dominant region, the mean evaporation heat transfer of ammonia/water mixtures was almost the same as ammonia by considering thermophysical properties. In the region where nucleate boiling contributes to the heat transfer, the mean evaporation heat transfer coefficient was influenced of mass fraction. An empirical correlation was proposed in order to predict the mean evaporation heat transfer coefficient of ammonia/water mixtures for plate type evaporators.

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The study aims at clarifying the performance of a 3-bed, mass recovery silica gel-water adsorption refrigeration cycle. The cycle with mass recovery can be driven by waste heat at near ambient temperatures (between 50 and 90°C). All components of adsorption cycle are operated in different pressure levels. The 3-bed chiller with mass recovery process utilizes those pressure levels to enhance the refrigerant mass circulation. The innovative adsorption chiller comprises with three sorption elements (SEs), one evaporator and one condenser. The configuration of SE1 and SE2 are uniform but the configuration of SE3 is taken as half of SE1 or SE2. Two cycles (cycle-1, cycle-2) with mass recovery process are used and compare the performance with each other. In cycle-1, mass recovery process occurs between SE3 with either SE1 or SE2 and no mass recovery between SE1 and SE2 occurs. In cycle-2, mass recovery process occurs between SE1 and SE2, and no mass recovery process occurs between SE3 with either SE1 or SE2. The mathematical model shown herein is solved numerically. Simulated results are obtained from transient to cyclic steady state. Simulated results show that the COP and SCP of cycle-1 are better than those of cycle-2.

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Recently, there has been an increase in demand for low-noise air-conditioners. The reduction of noise originating from the expansion valve in an air-conditioner is particularly important, since the propagation of noise along the piping system leads to problems for overall low-noise operation. In order to design a low-noise operating valve, it is necessary to understand the flow characteristics of the refrigerant passing through the throttle of the valve. By acquiring knowledge from the visualization of two-phase flow in an old throttle design, we manufactured an expansion valve with a new throttle design that aims for a reduction in noise generation. We compared the performances of the old and new throttle designs by monitoring the refrigerant flow conditions, refrigerant pressures and temperatures, as well as the acoustic noise generation. Flow visualization of the new throttle clearly indicates liquid or bubbly flow upstream; there is no slug flow. These results show a direct contrast to those for the old throttle design, where slug flow can occur upstream under certain operating conditions. There is also a marked reduction in the noise power spectra in the high frequency domain, which is the one that poses particular problems for the human ear.

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In general, air conditioning control in a building is operated mainly by indoor air temperature control. Although the operators of the machine in the building accepted a claim for indoor air temperature presented by the building inhabitants, the indoor conditions have been often too cool or warm. Therefore, in an attempt to create better thermal environments, the author paid attention to the PMV that is a thermal comfort index. And then, the possibility of air conditioning control using the PMV directly as the set point was verified by employing actual equipment in an air conditioning testing room and an office building. Prior to the execution of this control, the operation program of the PMV was installed in a DDC controller for the air conditioning control. And information from indoor sensors and so on was inputted to the controller, and the computed PMV was used as the feedback variable.

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The aim of this study was to evaluate the refrigerating and air-conditioning technologies in cases of introducing both cogeneration system and energy network in food industrial park. The energy data of 14 factories were classified into steam, hot water, heating, cooling, refrigerating, freezing and electric power by interviews. The author developed a micro grid model based on linear programming so as to minimize the total system costs. The industrial park was divided into the 2,500 square meter mesh in order to take steam transport into consideration. Four cases were investigated. It was found that the electric power driven freezer was introduced compared with the ammonia absorption freezer. The ammonia absorption freezer was introduced in the factory that there is a little steam demand and large freezing demand at the same time.

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The plane fin of a cross-finned tube heat exchangers is the basis for all kinds of fins used in air conditioners. In this paper, an improvement the dimensionless arrangements of pressure drop for plane fins was attempted.
The detailed calculation results for all geometrical parameters, especially tube disposition, showed the reflecting to the effect of contracted flow in the existing equations of friction factor is insufficient. Therefore, an amendment for these equations was suggested. Further, the analogy between the revised friction factor and the Colburn's j factor was verified. In addition an approximate expression for the fin efficiency using wide parameters was devised.

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This paper describes the flow and heat transfer characteristics of the mixed convection in a horizontal square duct with density inverse of water by the three-dimensional numerical analysis. The SIMPLE procedure and QUICK scheme were used to solve numerically the governing equations in three-dimensional system through a control volume method. To consider the temperature dependence of fluid properties, they were approximated by the polynomial of the temperature. Numerical results were compared with heat transfer and flow without density inverse. The spiral flow was generated along the flow direction and the starting position of spiral flow moved downward with density inverse. Two recirculation flows were generated near the bottom of side-walls across the section and its size grew up along the flow direction. The maximum intensity of the secondary flow across the section became less than that without the density inverse. Local Nusselt number on the bottom wall increased. However, average Nusselt number on the whole walls decreased.

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In this study, an adhesive condition between mushy structure and a solid cold surface is observed and an adhesive shear strength is measured. It is found that the size of crystal grain near the cold surface depends on concentrations of aqueous solution as well as characteristics of cold surface such as hydrophobics, thermal conductivity, thermal diffusivity and cooling temperature. An empirical equation is obtained by using those characteristics parameters of the cold surface. It is shown that the adhesive shear strength of pure ice is 100 to 1000 times larger than that of mushy structure of 2 to 10wt% ethanol-water solutions. The adhesive shear strength becomes large for lower concentrations, lower temperatures, larger surface free energy, larger arithmetical mean height Ra and larger arithmetical mean gradient RΔa.

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To clarify the operating and design concept of desiccant rotor, which is a most important component of an adsorptive desiccant cooling process, adsorption / desorption behavior of water vapor in a desiccant rotor has been investigated by means of computer simulation. Mass transfer coefficient in the mathematical model could be related to cycle time by applying the penetration theory. Considering this relationship, influences of the rotation speed of the desiccant rotor, process / regeneration air velocity and their velocity ratio were investigated. It was found that the optimum rotation speed tended to disappear when the regeneration air temperature was low and its humidity was considerably small compared to the process inlet air, since the product air condition approached to regeneration air condition as the rotation speed increased. Decrease of the dehumidifying performance was observed at higher air velocity and the corresponding higher rotation speed since the adsorbent rotor was not fully regenerated due to shorter regeneration time and shorter residence time of process / regeneration air in the adsorbent rotor prevented the mass transfer between air and adsorbent. It was also found that the dehumidifying performance was not improved even though the adsorbent was fully regenerated by higher regeneration air velocity as the sensible heat transferred from the regeneration zone via adsorbent itself increased and disturbed adsorption.

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There has been some interest in the flow drag and heat transfer reduction effects of brine flow with drag reduction surfactants from the viewpoint of the effective energy consumption in an industrial cooling system. Therefore, the flow friction coefficient and mean forced convection heat transfer coefficient of brine flow (Ethylene Glycol (EG) solution for organic brine) with drag reduction surfactant (Oleyldihydroxyetyl Amine Oxide (ODEAO) of non-ion surfactant) have been discussed in the previous report. And it had been shown that the flow drag and heat transfer reduction effect of EG brine with ODEAO were influenced by each parameter of concentration of EG, concentration of ODEAO and temperature of the EG brine with ODEAO. The present report shows that the range of the flow drag and heat transfer reduction effect was determined by the break up of the surfactant's rod-like micelles aggregation, which cause the flow drag reduction effect, by a high shear stress. And it was found that the surfactant's rod-like micelles aggregation was reinforced by a polar-nonpolar solubilization between the ODEAO's rod-like micelles and the EG molecules. Finally, Useful non-dimensional correlative equations for maximum flow resistance and heat transfer reduction effect are derived in terms of various non-dimensional parameters.

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A two dimentional numerical study has been performed to investigate on heat transfer characteristics of a hydrate slurry transported by a visco-elastic fluid flowing between parallel plates with a one-sided cavity. In this study, the cavity length was changed in three steps, while the rib height and rib length were kept constant. Heat flux on the solid wall was set at 20,000W•m^-2. The concentration of hydrate particles at inlet was set at 5wt%. From the results, it is found that hydrate particles dispersed with Newtonian fluid (water) flows over the cavity without penetration. On the other hand, hydrate particles dispersed with visco-elastic fluid are observed effectively to penetrate into the cavity and sweep the bottom of cavity by Barus effect. This causes effective heat transfer from the bottom wall of the cavity. Heat transfer difference was observed that the cavity length was changed. Consequently, there exists the optimum geometry for the heat transfer enhancement in a cavity by using Barus effect.

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In this study, effects of additives on the size of ice particles in ice slurries are investigated experimentally. Ethanol solution was used as aqueous solution to make ice slurries, and PVA (poly-vinyl alcohol) was examined as an additive. The aqueous solution was kept in supercooled condition, and ice slurry was subsequently made by releasing the supercooled condition. The degree of supercooling and concentrations of additives were varied as parameters. The observations of the ice particles in the ice slurry were carried out just after generation of the ice slurry and after 24 hours of storage. Differences between results with and without additive was not observed just after generation, and dendritic ice appeared in both cases. However, finer ice particles were observed after 24 hours storage in a case of the solutions with additives. Moreover, the size of ice particles was measured from photographs to confirm the effects of PVA. As the result, it is found that the average diameter is independent of the degree of polymerization in the range of this study.

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In air-conditioning systems, it is desirable that the liquid-solid phase change temperature of a cool energy storage material is approximately 10 °C from the perspective of improving coefficient of performance (COP). Moreover, a thermal storage material that forms slurry can realize large heat capacity of working fluids. Since the solid that adheres to the heat transfer surface forms a thermal resistance layer and remarkably reduces the rate of cold storage, it is important to avoid the adhesion of a thick solid layer on the surface so as to realize efficient energy storage. Considering a harvest type cooling unit, the force required for removing the solid phase from the heat transfer surface was studied. Tetra-n-butylammonium Bromide (TBAB) clathrate hydrate was used as a cold storage material. The effect of the heat transfer surface properties on the scraping force for detachment of adhered solid of TBAB hydrate to the heat transfer surface was examined experimentally.

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In this study, the process of ice formation and melting in LiBr aqueous solution were considered in the case that the ice was formed from the upside, side and downside of the aqueous solution by the numerical calculation using the finite differential method and the consideration for the temperature of heat transfer surface and of the aqueous solution is also performed. The temperature and the concentration distribution and the flow pattern are developed, and the discussion for the apparent latent heat of ice formation and of ice melting is also performed for various position of heat transfer surface and for the various temperature of the heat transfer surface and of the LiBr aqueous solution. As a result, in the case of the solidification process, the apparent latent heat was smaller than that measured by differential scanning calorimeter because the ice was formed in the solution with a higher concentration based upon the discharge of LiBr with a solidification. In the case of the melting process, the apparent latent heat was larger than that in the solidification process because the ice was melted in the solution with the lower concentration derived from ice melting.

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Ethanol water mixture has a liquidus line ( or crystallizing line) and a solidus line (or melting line) that are separated, and therefore it can have both liquid and solid phases existing together. With advances in low temperature technology in recent days, ethanol water mixture is attaching more and more attention as an environment-friendly coolant or as a thermal storage material. In the present study, we observed the crystallization process in the mixture and carried out experiments to evaluate fluidity of the mixture, with the objective of utilizing an ethanol water mixture as a coolant or a thermal energy storage material. Crystal formation and growing process within a minute droplet of a binary mixture was modeled. As a result, we found a novel method to produce a fluid latent heat storage material continuously and an apparent coefficient of viscosity show that rotational speed and solid phase fraction have a strong effect on the fluidity of the mixture.

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