The purpose of this study is to develop a new control method of vapor injection cycle with a flash tank in order to achieve optimal COP. In this cycle, temperature of vapor injection doesn’t change due to the saturation in a flash tank. Therefore, there is no simple method to detect how much vapor in a flash tank has been injected into the compressor. Hence, it has been an issue to develop a simple injection flow control method. This study proposed a new control method using a superheat index generated by active heating using discharge refrigerant from the first compression chamber. The experiment was conducted to verify the effectiveness of this index. The experimental results show that this new superheat index varies with the injection flow rate and is useful for controlling the injection flow rate properly to achieve the optimal COP.
An experimental study was conducted on gas-liquid distributions of the refrigerant flow in a multi-pass channel with vertical headers and horizontal multiport flat tubes that simulated the parallel-flow type evaporator. In particular, the influence of protrusion of branch tubes into the dividing header on gas-liquid distributions and pressure loss of the channel was examined. The refrigerant (R410A) was supplied from the bottom of the header, and experiments were conducted under an adiabatic condition. It was found that the maximum height of the liquid distribution was increased by protruding branch tubes into the header at high mass flow rates. The pressure loss of the channel increased as the mass flow rate and/or quality of the refrigerant were increased, and the pressure loss in branch tubes occupied 60-70% of the pressure loss of the channel. The pressure in the dividing header decreased gradually in the upward direction, while that in the combining header was almost constant. Based on experimental data, we made clear pressure distributions in channels. The pressure in the channel showed quite a uniform distribution in the vertical direction under a high quality condition, while the uniformity of the liquid distribution was deteriorated as the quality was increased.
To reduce the energy consumption of household refrigerators, we focused on leakage loss, one of the main losses, with the aim of improving the efficiency of reciprocating compressors. Since there are few reports on the measurement of leakage from the compression chamber during operation, the method of measuring leakage during operation was first examined, and the relationship between the piston diametral gap and leakage, and relation between the oil viscosity and leakage were investigated. After that, the relationship between groove specifications and leakage was experimentally investigated for oil grooves provided on the piston surface. As a result, the oil groove on the piston surface was effective in reducing leakage, and the oil groove specification to reduce leakage was clarified.
For conventional air conditioning systems, the efficiency degradation caused by sub cooling dehumidification in summer and air drying due to no humidification function in winter are two important issues in terms of energy efficiency and thermal comfort. Desiccant is considered to be one of options to humidity control with high efficiency instead of sub cooling dehumidification method adopted in conventional air conditioning systems. In this study, experiments were conducted to measure the dehumidification and humidification performance of a desiccant module consisting of a desiccant-coated heat exchanger and a novel slide type air flow switching device. Experimental results show that the desiccant module under the size of 500 (Height) x 700 (Width) x 1100 (Length) mm can satisfy 90% of the dehumidification and humidification demand (1050 g·hour-1 for summer and 750 g·hour-1 for winter) of a detached house at the floor space of 90m2, ceiling height of 2.4m, ventilation frequency of 0.7 times per hour.
The surface tension was measured for several low GWP refrigerants, which are grouped in HCFO and HFO, by a differential capillary rise method. The comparison between measured data and calculated value by REFPROP 10.0 were reviewed. The review results suggest that the uncertainty in surface tension calculated by REFROP 10.0 are not negligibly small for R1224yd(Z) and R1336mzz(Z). Based on the measured data and calculated orthobaric densities, “Parachor” was identified for each refrigerant. Among the measured refrigerants, the parachor of only R1336mzz(E) showed obvious temperature dependence, which means there could be an inconsistency between orthobaric densities and surface tension.
When moisture in food freezes, the growth of ice crystals caused damage to food structure. It was reported that the fine and homogeneous ice crystals could be formed when accidental supercooling during freezing. In this study, a sample of mung bean sprout was intentionally supercooled and frozen by slow freezing after blanching. The effects of the freezing conditions on mung bean sprout after thawing and the size of ice crystals were investigated. As a result, the freezing in still air at －10 ℃after blanching was easy to occur supercooling of mung bean sprout, and the textural property of thawed mung bean sprout was similar to unfrozen sample.
The effects of pH on the protein solubility, film-forming ability of lizardfish viscera (stomach and intestines) and physico-chemical properties of the biodegradable films were investigated. The new approach could successfully yield protein-based films from lizardfish viscera at a narrow pH range (2 - 4, and 13) without the need for a protein extraction process. All films were observed to completely block UV light transmission. Films at pH 13 were hydrophilic, exhibited the lowest mechanical strength, highest deformability, and greatest yellowish color, while films at pH 4 were mechanically stronger, slightly deformable and showed superior light transmission barrier properties compared to other film samples. The substantial contribution of disulfide bonds to the formation of the three-dimensional network of films at pH 4 was confirmed by SDS-PAGE. Thus, films from lizardfish viscera can be utilized as a renewable packaging material in food systems.
In this study, we investigated the influence of thermal conductance of a boiling surface on the pool boiling heat transfer to saturated liquid nitrogen at atmospheric pressure. A cooled sample was a copper sphere, 25 mm in diameter. The thermal conductance of the copper surface was changed by the ice layer and the frost layer coated on it. The experimental results show that the effects of ice layers on the copper surfaces on cooling curves and boiling heat transfer characteristics are remarkable. When a frost layer is used as a thermal insulation layer on the cooling surface, the heat flux in the transition boiling region increased markedly and both the critical heat flux and heat flux in the nucleate boiling region increased.
In this study, to clarify the fundamental characteristics of condensation heat transfer of refrigerant in a horizontal rectangular mini-channel at low mass fluxes down to 40 kg/(m2ꞏs), experiments were performed using a single rectangular small tube with a hydraulic diameter of 1.02 mm. HFC134a, HFC32 and HFO1234ze(E) are used as test refrigerants. The range of refrigerant mass flux condition was 40-400 kg/(m2ꞏs), and that of heat flux was 2-8 kW/m2. From the present data, it was clarified that the condensation heat transfer coefficient at a low mass flux 100 kg/(m2ꞏs) or less was noticeably high value compared with that at relatively high mass flux conditions. Besides, this tendency was different from that was seen in experimental studies using multiport tubes and tendency predicted by existing correlations applied by extension to the low mass flux condition.
Dehydrated ice slurry produced from sea water is effective in maintaining freshness of marine products, and are therefore expected to be utilized as cooling media during long-distance transport of marine products. Because the temperature history of dehydrated ice slurry during melting strongly depends on the initial water content, detailed knowledge of the water content of dehydrated ice slurry is required. In this study, ice slurry produced from NaCl aqueous solution was dehydrated by gravity, and the water content in the dehydrated ice slurry was measured. The results showed that the water content decreases with increasing the diameter of ice particles and has a unique distribution in the vertical direction. We compared the present results with existing data of water permeation in snow, and then found that dehydration of ice slurry can be elucidated based on the physical model of water permeation in snow, despite the difference in the diameter of ice particles and type of liquid phase between ice slurry and snow.
The objective of this study is to investigate the effect of frequency of acoustic wave on the adsorption enhancement. Experimental measurements were conducted, which results were analyzed to derive the condition of acoustic wave in which the adsorption rate is increased. 3 cases with different frequency which corresponding to the resonance mode indicated that the enhancement rate would depend on the frequency. It was also found that the critical velocity amplitude of the acoustic wave above which the enhancement effect was observed would increase as the frequency is higher. The authors proposed a model that the enhancement effect occurs when the effective displacement amplitude of the oscillation flow is larger than the certain value. Mathematical analysis of the model suggested the critical velocity amplitude would be expressed in a linear function with the frequency, which was verified based on the observation of the experimental results. It revealed that the mechanism of the enhancement effect would be explained by the model.
A desiccant rotor divided into four sectors realizes a double-stage dehumidification or regeneration in one adsorbent rotor. In this study, the amount of dehumidification and efficiency of two typical configurations of the four-divided silica gel rotor, one is called “adjacent type” whose adsorption or regeneration zones are adjacent to each other and the other is called “diagonal type” in which adsorption or regeneration zones located diagonally opposite to each other, were experimentally investigated and compared with a conventional configuration. It was found that the dehumidifying performance of the “adjacent type” was the highest among these three configurations and the inlet air temperature of 2nd regeneration zone significantly influenced on the amount of dehumidification. Also, measurement of air temperature profiles along with the rotating and axial directions of the rotor hel transfer occurred in the four-divided silica gel rotor.
Electric vehicle doesn’t generate much amount of waste heat. Therefore, electric vehicles consume a relatively larger amount of electricity for heating. Normally, dry and low-temperature winter air is heated and supplied to the vehicle cabin to avoid water condensation on the windows. This results in further reduction of the vehicle cruising range. This paper discusses the applicability of a thermally regenerative desiccant block for dehumidification and heating of electric vehicles. Regenerated desiccant block adsorbs the water vapor generated by the passengers, therefore fogging of the windows can be avoided without air ventilation. Also, simultaneously generated heat due to heat of adsorption can support the heating. Experimental results employing a commercialized silica gel honeycomb block indicated that the regeneration time of the block was much shorter than dehumidification duration. This must be a suitable feature for the actual use. A field-test using a silica gel honeycomb block of four-liters set in a real vehicle cabin with two passengers showed anti-fogging effect during 30 min or more. This desiccant dehumidification and heating could reduce the heating load by 40 percent or more comparing to the conventional heating and ventilation.
In this study, a two-vessel circulating-fluidized-bed in which particulate sorbents are circulated by air was created to confirm that moisture could be transferred between two air flows continuously, and to investigate its basic behavior. The amount of humidification and dehumidification, which means the amount of moisture transferred between two air flows, was evaluated when changing the air flow velocity and humidity conditions of the air flow. As a result of the experiments, it was found that the amount of humidification and dehumidification influences by the circulating amount of particulate sorbents, and there is an optimum condition for the circulating amount. As the air flow velocity increases, the moisture transfer amount increases because the amount of circulating sorbents also increases. On the other hand, if the amount of circulation sorbents is too large, the moisture transfer amount decreases. Moreover, even if the air flow humidity is changed, no significant difference is found in the circulation amount, but it was found the amount of humidification and dehumidification increases as the relative humidity difference between the two air flows increases.
This paper provides an analysis of the adsorption kinetics by using image processing algorithm. Rapid adsorption kinetics is increasingly important because it offers a good mass transfer hence improves the efficiency of the sorption system. For adsorption kinetics, it is required to determine the first stage of the measurement precisely. Therefore, selecting the proper method becomes essential. Simple experimental setup was developed for evaluating adsorption equilibrium and adsorption kinetics of Silica gel/water pair. The test apparatus comprises of adsorption cell, evaporator/condenser, piping line, and measurement devices for temperature and pressure. Silica gel types A was employed in the present study as the adsorbent material. A new method is proposed to calculate the adsorption kinetics by using the digital image analyzing. Algorithm for image analysis could semantically segment the adsorption process by creating images which represented the dataset for water level changes inside the evaporator.
Adsorption/desorption rate of vapor to adsorbent on an adsorption heat exchanger is one of the important characteristics in order to design and improve the performance of adsorption chillers and dehumidifying/humidifying desiccant systems effectively. In the present study, for a silica gel thin film adsorbent coated on an aluminum plate in a cross-fin tube heat exchanger, measurement of equilibrium adsorption of water vapor by TGA and measurement of adsorption/desorption rate by gravimetric method under different flow velocities of moist air were performed. The equilibrium adsorption was formulated with function of relative humidity. In addition, the overall mass transfer resistance related to both the mass diffusion in the film and the mass transfer in the boundary layer on the film was investigated. It was clarified that the influence of the resistance on the reaction rate appeared only at the beginning of reaction, and the resistance decreased with the increase of the velocity, especially in adsorption. Furthermore, the resistance in desorption was less than half in adsorption. Consequently, the resistance in the boundary layer was a negligible quantity for desorption when the flow rate was above 0.1 m ･s-1. Finally, correlations were proposed to predict these resistances.