The object of this paper is to investigate thermoacoustic refrigerator driven by noise energy and waste heat generated from engine plants. The noise has complicated frequency characteristics and low energy density. Therefore, the selective amplification of acoustic wave by using thermoacoustic energy conversion has been studied. The stacked wire-mesh screen with steep temperature gradient was installed in the one-third length of pipe with one closed end. In experiments, the pressure, particle velocity, and phase difference were measured by varying the frequency of acoustic wave and the channel size of the stack. The acoustic wave at third harmonic-frequency was amplified by thermoacoustic effect. On the other hand, the acoustic waves at other frequency were damping by viscosity dissipation in the stack. The optimum size of aperture in the stack for thermoacoustic amplification was also depicted. Summarizing these results, the proposed selective amplification was tested for noise energy generated in marine ship.

Ammonia falling film and pool boiling evaporation experiments were conducted on three horizontally placed types of stainless tubes, namely smooth, low fin and 3D fin and enhancement of heat transfer was examined. For the falling film tests, heat transfer coefficients of the smooth tube decreased with increasing circumferential angle starting from the top of the tube. For finned tubes, however, liquid film was held between the fins, thus causing decrease in heat transfer coefficients. A comparison of average heat transfer coefficients in the low Reynolds number range shows that the smooth tube had the highest heat transfer coefficients followed by 3D and low finned tubes respectively. Heat transfer enhancement by the fins was not observed. In the high Reynolds number range, convection occurred in the liquid film between the fins of the 3D tube but it was not very significant and the heat transfer coefficients are similar to those of the smooth tube. Pool boiling heat transfer coefficients of the smooth tube agree well with Jung et al. correlation while those of the low fin and 3-D fin are 20-30% lower. A comparison of falling film and pool boiling heat transfer coefficients of the three types of test tubes shows that falling film heat transfer is higher than pool boiling.

This study reported computational fluid dynamics analysis on the behavior of R290 when it leaked into the room from a split household air conditioner. A leak experiment from a wall-mounted indoor unit was conducted to verify the validity of the analytical model and calculation method. The research aims to evaluate the necessity of operating the indoor unit fan when the refrigerant leaks to ensure safety when the refrigerant leaks from the air conditioner indoor unit. Blowing air diagonally downward from a wall-mounted indoor unit effectively facilitated refrigerant diffusion. Blowing air upward at 45 degrees from a floor-standing indoor unit was effective. Regarding the effect of the room area on the fan wind speed, it was essential to blow out the fan airflow in a direction that facilitates the formation of indoor circulating flow.

For low-temperature refrigeration applications down to -70 ◦C such as frozen tuna storage, freeze-dry foods,and semiconductor production processes, HFC refrigerant R23 is widely used. It is also used for testing equipment for the evaluation of electronics and automobiles. Some COVID-19 vaccines require such low-temperature storage. R23, however, has an extremely large global warming potential (GWP100=12,690). To comply with the Kigali Amendment, it will be very important to develop a low GWP alternative in that technical field. This work presents intensive evaluation results of screening refrigerant candidates to substitute R23. More than 20 refrigerant candidates were filtered by comparing their theoretical cycle COP and volu[1]metric capacity with a ”Pareto front” of the performance. R23, CO2 and thus filtered substances, R1132a,R41, and N2O, have some drawbacks such as high GWP, flammability, toxicity, or freezing issues. In thiswork, therefore, possible binary pairs including these 5 substances were investigated.

The research of alternative refrigerants to R23 for ultra-low temperature applications has not progressed actively due to the difficulty of measurement. A theoretical prediction using a molecular simulation for the thermophysical properties of R1132a down to the triple point can stimulate the research. The intramolecular potentials and atomic charges were determined from quantum chemical simulations. The intermolecular potentials were adjusted by referring to the measured saturated liquid density near the critical point. The saturation density and pressure predicted by the simulation agreed well with the measured data and were extrapolated to lower temperatures, where no measurement data were available. The vapor state pressures were precisely reproduced over a wide temperature and density ranges, and the second and third virial coefficients were obtained. A comparison with R1123, which has a similar molecular structure, was made to examine the effect of the potential on the physical properties.

R 473A is an emerging four-component refrigerant blend for replacing high GWP and flammable refrigerants currently used for low temperature applications. Since limited prior publications on the thermodynamic properties of R 473A are available, the initial investigation of its vapor phase pvT properties were carried out and are presented here. The pvT properties were measured using two separate isochoric apparatus for the temperature range of 270 K to 400 K, density range of 43 kg·m^-3 to 210 kg·m^-3 and at pressures below 7 MPa. The virial equation of state was used to verify the measured properties. The linearized virial equation was used to determine the second and third virial coefficients. This method provided an absolute average deviation in pressure and density of 0.29% and 0.38%, respectively. The measured properties were all within 1% deviations which signify the accuracy of the results and the potential for them to be used as preliminary data for developing a more accurate representation of R 473A properties through equations of state.

In order to explore alternatives to R23 refrigerant for ultra-low temperature applications, information on the liquidus point temperature, which serves as a guideline for the lowest operating temperature limit, is required. Accordingly, the liquidus point temperature of R469A (R744/R125/R32:35.0/32.5/32.5 mass%), which is recently being considered for commercial use, was experimentally determined to be 184.3 K ± 0.7 K. In comparison with the prediction equation, the activity coefficient representing the deviation from the ideal mixing was adjusted to be 0.887 for R744 for better agreement between prediction and measurement. The composition dependence of the liquidus point temperature was predicted by using the activity coefficient of 0.887 for R744/R125/R32 ternary system. It was confirmed that the liquidus point temperature depends dominantly on the mass composition of R744 and that the R744 mass composition must be less than 15 mass% to keep the liquidus pointe temperature below -100 °C. On the other hand, a volumetric capacity is maintained as that of R23 at R744 mass compositions more than approximately 81 mass%, which is a trade-off with the liquidus point temperature.