This study experimentally investigated the effects of lubricant oil on flow boiling heat transfer and pressure drop characteristics of R32 in a horizontal multiport tube with circular mini-channels (Dh = 0.81 mm). The heat transfer coefficients and pressure drops of R32 pure refrigerant and R32+oil mixture with oil concentration of 3.7 wt% were measured for the boiling flow with the mass velocities of 50–400 kgm^-2s^-1, heat fluxes of 5–40 kWm^-2, and at a saturation temperature of 15 °C. The boiling heat transfer coefficient of R32+oil mixture increased at higher heat flux and lower quality regions compared with that of R32. Further, the heat transfer coefficient of the mixture decreased in the higher quality region, and it also decreased in the lower vapor velocity and lower heat flux conditions where thin liquid film evaporation was dominant. The frictional pressure drops of R32+oil mixture were 30–80% higher compared with that of R32 and increased with increasing heat flux in the lower quality and higher mass velocity condition.

The foaming of lubricating oil in a compressor induces oil to flow out from the compressor when starting. This study investigated the dynamic characteristics of the flowing oil in a horizontal compressor when starting, in a refrigerant-oil experiment. We used the oil separation system to measure the dynamic oil flow rate and visualized the liquid level in the horizontal compressor to measure the liquid volume. The experimental result showed that the rotating of the rotor and refrigerant gas flowing to suction port generates oil droplets and induces the oil to flow out from the horizontal compressor when starting. And the experimental result showed the effect of the inlet pressure of the compressor on the dynamic oil flow rate when starting.

One of the main concerns regarding in-vessel retention (IVR) during a severe accident is guaranteeing sufficient cooling performance to avoid the melt-through of the pressure vessel. In such an event, the vessel is submerged in water, and boiling is occurred to remove the heat. However, the main problem is that there is a limit to the pool boiling heat transfer at the outer surface of the reactor vessel due to occurrence of critical heat flux (CHF) conditions. Therefore, CHF enhancement is important to increase safety margin of IVR. In previous studies, CHF was enhanced approximately twice compared to bare surface by attaching honeycomb porous plate (HPP) to the heated surface. In order to establish the IVR, the cooling technology should be considered in forced flow boiling with the downward heat transfer surface. Moreover, we proposed a two-layer structured HPP for further CHF enhancement. Therefore, in the present paper the effect of the single and two layers HPPs on the critical heat flux under flow boiling with the downward heat transfer surface was investigated experimentally. As a result, the coalescent vapor bubbles cover the heated surface for a long period depending on the flow pattern under the flow boiling condition, resulting in liquid drying inside a HPP and reduction of CHF. Even in this situation, a two-layer structured HPP can be applied to CHF enhancement in flow boiling with the downward heat transfer surface.

A novel heat exchanger using parallel small refrigerant channels has recently been developed for high performance air conditioning systems. However, due to non-uniformly heat load among channels, boiling flow tends to be unevenly distributed in parallel channels. This phenomena makes accurate prediction of heat transfer capacity difficult. In this study, experiments on flow boiling in non-uniformly heated two parallel mini-channels were carried out, and averaged heat transfer coefficients in two channels were investigated. When non-uniformly heat load was applied, dryout occurred in relatively wide range in a higher heated channel. As a result, the averaged heat transfer coefficients in non-uniformly heated channels tended to reduce compared with those under the uniform heat flux conditions of the same averaged heat fluxes.

It is very important to improve a compressor efficiency in low capacity region for refrigerators and develop a compressor with wide range operation. In low speed operation, a compressor efficiency is influenced by characteristics of an oil pump which supplies the lubricant oil to frictional faces. Many oil pumps in compressors utilize a rotational motion of a shaft. In this study, we develop the viscous oil pump for reciprocating compressor using a robust parameter design method. The result showed that shallow spiral groove, small pitch and small clearance of stationary piece and moving piece make a high signal to noise ratio in terms of the oil viscosity error factor. The optimized viscous oil pump showed good oil flow characteristics and enable a compressor to operate lower speed than conventional centrifugal oil pumps.

Transient two-dimensional numerical computations are carried out to clarify the laminar flow forced convective heat transfer characteristics of Al₂O₃-water nanofluids in a horizontal tube. A tube with the length of 50 times of a diameter is insulated from the inlet to the central part and is cooled isothermally from the central part to the outlet. The high-temperature Al₂O₃-water nanofluids flowing into a tube is assumed to be Hagen-Poiseuille flow. The thermophysical properties of Al2O3-water nanofluids, such as the effective density, the effective specific heat capacity, the effective viscosity, and the effective thermal conductivity, are estimated by the experimental correlation equations reported by Khanafer and Vafai. The present numerical computations are implemented under different particle diameters (dp = 25, 50, 100 nm), different volume fractions of nanoparticles (φp = 0.01 - 0.04), and different reference temperatures (θ´= 20, 30, 40 ℃). When the numerical conditions were dp = 25 nm,φp = 0.04, and θ´= 40 ℃, the ratio of the average Nusselt number of Al₂O₃-water nanofluids to that of water took a minimum value (= 0.929), the ratio of the average heat transfer coefficient of Al₂O₃-water nanofluids to that of water took a maximum value (= 1.136), and furthermore, the ratio of the pressure loss of Al₂O₃-water nanofluids to that of water took a maximum value (= 1.802). In addition, when the computed local Nusselt numbers of Al₂O₃-water nanofluids were estimated with the Pe number defined by the thermophysical properties of water, they were distributed below the Graetz solutions. On the other hand, when the computed local Nusselt numbers of Al₂O₃-water nanofluids were estimated with the Pe number defined by the thermophysical properties of Al₂O₃-water nanofluids, they almost agreed with the Graetz solutions.

In many cases, frozen whale meat in the Japanese market is prepared before rigor mortis (pre-rigor). A serious problem for frozen whale meat is the occurrence of thaw rigor, which is the strong development of rigor mortis during thawing. To prepare frozen whale meat without thaw rigor and maintain a high meat pH, the temporal changes in adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide (NAD) contents of frozen meat stored at -2.5, -5.0, -7.5, and -10°C were investigated. The rate of decrease of ATP was higher than that of NAD at all storage temperatures. ATP nearly disappeared after holding the meat at -2.5°C for a few days; however, NAD existed yet, so pH decreased thereafter. ATP levels were maintained for a long period at a temperature of -5.0 to -10°C, resulting in the occurrence of thaw rigor. Compared to the muscles of fish such as tuna, the rates of decrease of ATP and NAD were extremely slow in whale meat.