In regard to a pre-heating operation for an air-conditioned location (which has a storage heat load), the possibility of energy-saving pre-heating operation was studied in consideration of energy consumed during the pre-heating. The results of the study are summarized as follows. (i) When the storage heat load decreases with time after the air-conditioner is turned on, by using finite-time optimal control instead of the PID control method, it is possible to decrease power consumption and required heating capacity for the pre-heating operation. (ii)According to an example calculation based on a 5-HP packaged air-conditioner used in Shizuoka, Japan, compared to PID control, the finite-time optimal control can decrease pre-heating power consumption and required heating capacity for the pre-heating operation during the heating season by 42%.

This study deals with water single-phase flow and air-water two-phase flow characteristics in plate fin heat exchangers with offset fin. Single channel test sections simulating plate-fin heat exchanger were made by transparent acrylic resin. The length and width of the channel were 435 mm and 90 mm, respectively. Two kinds of offset fins with the fin pitch of 3.2 mm and 2.0 mm were used. Pressure loss characteristics and flow behaviors in the vertical channel test sections were experimentally examined. It was confirmed from the experimental results that the friction factor of water single-phase flows could be correlated by a modified Hagen-Poiseuill equation. In the air-water two-phase flow experiment, two-phase multipliers were larger than the calculation results by a conventional equation in the area of χ > 1 due to flow pulsation and maldistribution. The tendency was larger for the channel with larger fin pitch. Two-phase multipliers for each flow direction in each test section could be correlated by a modified Tribbe-Müller-Steinhagen equation.

Supercooling phenomenon is focused as one of methods to suppress expansion of ice crystal size by freezing. So, the purpose of this research is to investigate the relation between cooling condition and ice crystal size experimentally, and find a cooling condition to suppress the expansion of ice crystal size. Tuna was selected as a specimen. As a result, temperature distribution at the instance of freezing was obtained by simulation, and the relationship between ice crystal size and the temperature distribution was clarified by comparing with an image of X ray CT scan. It was found that expansion of ice crystal size exists at the region having the temperature above -4℃ which is the degree of supercooling of 2.3K for tuna. Temperature of around -5℃ was found to be the limited boundary to sustain a supercooling and freezing may occur at region where the temperature is below this point. Furthermore, by introducing the model in the previous report to find the probability of freezing, the possibility to obtain a suitable cooling condition for various sizes and aspect ratios of food to suppress the expansion of ice crystal size by food freezing was presented.

This paper proposes a frost-free air source heat pump water heater (ASHPWH) system with integrated solid desiccant, in which frosting can be retarded by dehumidifying air before it enters the ASHPWH evaporator. A numerical simulation is carried out at a dry-bulb temperature of -7-5.5 °C and a relative humidity of 60-80 % depending on the frosting conditions. The results show that the coefficient of performance (COP) is within the range 3.3-3.8, which is 5-30 % higher than that of the ASHPWH system using the hot-gas defrosting method. Experiments have been carried out to measure the adsorption and desorption characteristics of the desiccant-coated heat exchanger (DCHE), the key component of the frost-free system, and confirm whether frost-free can be realized and how long to keep it, whether the DCHE can be effectively regenerated under the condensation temperature of the heat pump. Experimental results show that frost-free operation can be realized and the frost-free operation times are 17, 20 and 42 minutes at air temperatures of 5, 2 and -7 °C. And the DCHE can be regenerated at a relatively low temperature (around 50 °C), so the condensation heat of the heat pump can be used to regenerate the DCHE. Furthermore, design calculation based on those experimental results was conducted to determine the physical characteristics of the DCHE and evaporator, the layout and dimensions of the heat pump unit. Results show that the heat pump unit at the dimensions of 700 (height) x 1000 (width) x 300 (depth) mm, has a water heating capacity of 4.5 kW under ambient air conditions of 2 °C and 80%.

To meet the growing demands for energy saving, ejectors are increasingly being considered in refrigeration cycles. The two-phase internal flow of these ejectors, which has slower sound velocity than the single gas phase, easily becomes supersonic and generates a shock wave. As this shock wave greatly contributes to the pressure increase in the ejector, elucidating its characteristics is essential for increasing the efficiency of the ejector. In this study, we experimentally visualized the internal flow in a two-dimensional ejector using hot-water as coolant and observed the form changes in the two-dimensional shock wave occurring in the nozzle. We also measured the speed changes in the two-phase flow induced by the shock wave. The experimental results showed that, within the area of its formation, the shock wave altered from oblique to near-normal. Furthermore, the temporal changes in luminance distribution were captured in a video and those in the droplet velocity were measured using a luminance cross-correlation method. The droplet velocity behind the shock waves of two-phase flow found to decease gently. And this phenomenon is characteristic for the shock wave of two-phase flow.

Numerical simulations and magnetic resonance imaging (MRI) measurements have been carried out for a better understanding of the behavior in ice crystal growing after breaking of super cooling condition in aqueous solutions. The numerical simulations showed that a fast cooling from outside caused ice nucleation from the outer edge and the expansion of bulky ice crystal, on the other hand, a slow cooling showed ice nucleation from inside and expansion of fibrous ice crystal. Temperature measurements and MRI measurements for a phantom test sample with cylindrical double layer structure showed that frisky ice crystals were outbreak throughout the outer layer inducing the temperature increase up to 0 degree after the breaking of super cooling condition and the inner layer stayed as a liquid at the lower temperature, and after that, bulk ice crystals were expanded from the surface of the inner part in outer layer causing the increase of temperature of inner part.