This study focused on chilled storage before freezing fish muscle in order to explore the relation between postmortem physiological changes and ice crystal morphology in frozen muscle tissue. Specimens of horse mackerel (Trachrus japonicus) were killed by decapitating, pan-dressed and stored at 4 °C. Subsequently, a portion of dorsal muscle tissue was dissected. The dissected tissue was used for ATP-related compounds analysis, measurements of water holding capacity (WHC), scanning electron microscopic observation of endomysial connective tissue and freezing experiment for fluorescent microscopic observation of ice crystal morphology and endomysium in the frozen tissue. Changes in the ratio of ATP-related compounds and decrease of the WHC were observed during chilled storage. The connective tissue became looser during storage. On the other hand, size or number of ice crystal in frozen tissue seems to depend on chilled storage period before freezing. There were large ice crystals enough to disrupt cells, especially in the tissue of fish frozen after chilled storage. These results suggest that postmortem physiological changes in muscle tissue should have a large effect on the ice crystal morphology in freezing process.
In this study, the flow boiling heat transfer and pressure drop characteristics of R1234ze(E) and R32 in a horizontal multi-port tube with rectangular mini-channels of 1.13 mm in mean hydraulic diameter are investigated experimentally. The heat transfer and pressure drop characteristics are measured for the boiling flow in the mass velocity range of 100 to 400 kg/(m2 s) and heat flux range of 5 to 20 kW/m2. The pressure drop characteristics are also measured for adiabatic two-phase flow. The effects of mass velocity, vapor quality and heat flux on the boiling heat transfer characteristics are clarified. The measured frictional pressure drop and boiling heat transfer characteristics of R1234ze(E) and R32 are compared with previous correlations.
A desiccant air conditioning system processes sensible and latent heats separately, which improves the ystem efficiency and indoor air quality. A desiccant heat pump system consists of a heat pump and a desiccant otor. To design such a system, the adsorption and desorption characteristics of the desiccant rotors should be nown. In this study, we experimentally investigated the adsorption and desorption characteristics of actual rotors made from mesoporous silica and a polymeric sorption material. The average pore sizes of the esoporous silica were 4 and 2 nm. The materials do not require a high-temperature heat source for regeneration. effects of the air velocity and air temperature on the adsorption and desorption speeds were determined. It as found that the equivalent diffusion coefficients of the sorbent materials were not affected by the air velocity, they decreased with decreasing temperature. The resistance of the mass diffusion in the desiccant rotor as evaluated.
This paper proposes a desiccant hybrid heat pump for enabling frost-free operation of heat pumps in humid regions in winter.Experimental measurements using mesoporous silica, which can operate at low temperatures, validated that removal of water vapor from the incoming air of the evaporator was effective in preventing the formation of frost. The results also confirmed that this system provides higher efficiency if the absorbed water can be used for humidification. Based on the experimental results, a theoretical model was constructed and results of a simulation using this model showed that the proposed system could meet the humidity requirement in a relatively wide range (0.5-1) of the sensible heat factor.
In the motor vehicle industry, the familiarization of electric vehicle (EV) is accelerating. High efficiency and securement of the heating are requested for the air conditioning equipment for vehicles. The most effective way to heating is using heat pump, but the decreasing of heat transfer coefficient and the pressure drop caused by the frost of evaporator could be a big problem. Therefore the inhibition of frost in evaporator is especially required. The performance increase of the finless heat exchanger is expected, because it can flush the dew condensation water. In this study, we aimed to establish the evaluation technique of the defrosting characteristic. About frost growth the weight of frost was measured and frost growth was observed by micro CCD camera. The fundamental characteristic of the heat transfer coefficient, the pressure drop, and the frost growth was grasped. From the experiment, the block of flow channel by frost was seen in the angle part of upper position of concavity and convexity plate (test section).
Absorption heat pump water heaters are expected to be more efficient than conventional gas-fueled water heaters. However, such absorption systems are large and not widely accepted in the market. In this paper, we propose the use of adiabatic absorbers as smaller alternatives to conventional shell-and-tube or plate-fin-type absorbers to downsize absorption heat pump water heaters using H2O/NH3. The adiabatic absorption system consists of two components: a subcooler and an adiabatic absorber. The absorption performance and size of the adiabatic absorber are important for achieving higher efficiency. In this study, three types of adiabatic absorbers are proposed: atomizing-spray, spreading-tray, and packed-column absorbers. They are modeled and their absorption performances are analyzed.
In modeling the atomizing-spray absorber, we discuss the breakup position of the liquid film and the diameter of the generated droplets on the basis of the instability theory of liquid films. In analytically modeling the spreading-tray absorber, we discuss the breakup length of the liquid column and the diameter of the generated droplet. In the case of the packed-column absorber, we discuss the effective interfacial area of the dumped packings. Based on the simulation results, we develop design guidelines and compare the expected sizes of the absorbers.
The objective of this study is to develop a desiccant system using Wakkanai Siliceous Shale (WSS). This article is the 7th report of the series. In the previously articles, we reported a developed desiccant unit to achieve the target amount of dehumidification. This unit consists of two desiccant rotors and two heat exchangers for precooling and two heat exchangers for regeneration. In this paper, the authors have made a mathematical simulator of this desiccant unit to estimate the supply air conditions. The input conditions for regeneration and precooling have been evaluated by using this program. Firstly, the calculation precision of the program is confirmed by comparison with experimental results. Secondly, to minimize the input energy for the desiccant unit, input temperature for precooling and regeneration are evaluated. The conditions are obtained by controlling of precooling temperature depression without occurrence of dew condensing on the heat exchangers. Finally, performance prediction was carried out to obtain the energy saving efficiency in various areas in Japan. As a result, the unit reduced the energy for dehumidification by 30 % to 18 % in comparison to dew condensing process.
A hybrid system with a vapor compression heat pump and a desiccant rotor was developed to enable the frost-free and drain-free operation of air-cooled air conditioners. If the occurrence of frost on the heat exchanger of the outdoor unit can be avoided, the heat transfer performance can be improved by narrowing the fin pitch of the heat exchanger, thereby improving the coefficient of performance, COP, of the system. To achieve drain-free operation in summer, three types of hybrid systems were constructed and their performance was tested: a standard desiccant hybrid air conditioner, one with a high-performance heat exchanger, and one with a pre-cooler. The experimental results showed that the system with a high-performance heat exchanger improved the COP, and the system with a pre-cooler achieved drain-free operation at the rated cooling condition. Thus, it can be concluded that a desiccant hybrid air conditioner equipped with both a high-performance heat exchanger and a pre-cooler can achieve drain-free operation with a high COP.
To reduce energy consumption utilizing heat recovery systems is increasingly important in industrial applications. The screening of refrigerants is discussed with a case study for high temperature heat pump cycles in this study. The overall coefficients of performance of four different cycle configurations to increase water temperature up to 160 °C using waste heat of 80 °C are thermodynamically compared for several selected refrigerants. This case study suggests that a multiple stage cycle drastically reduces throttling loss in expansion valve and exergy loss in condensers, and consequently achieves the highest overall coefficient of performance (COP) among the cases with a refrigerant having the critical temperature about the target outlet water temperature. Considering many practical benefits, also a cascade cycle that performs relatively high COP can become an expedient solution.
Scroll compressor has two main leakage paths, i.e. an axial gap and a radial gap. Tangential leakage which flows through the radial gap is prevented by pressing an orbiting scroll wrap against a fixed scroll wrap. The pressing force is called as a contact force. When the contact force is not enough, the tangential leakage increases. In contrast, frictional loss increases when the contact force is excess. In this study, the characteristic of the contact force is examined with taking account of an oil film pressure generated in bearings by which a rotational shaft is supported. The influence of the oil film formed between the wraps on the contact force is also discussed. Generation mechanism of the contact force is clarified by the analytical result. It is also found that the contact force increases due to the oil film thickness formed between the wraps. The analytical model developed in this study allows us to examine the influence of operating condition and design parameters on the contact force.
In the data center, air conditioning has been carried out throughout the year to remove waste heat of servers. In order to realize efficient cooling, it is important to use cold outdoor air in winter. Therefore we study the performance of the air conditioning system that uses outside air in winter. In the proposed system, it is possible to switch compression cycle and free cooling cycle. In this report, we construct the static mathematical models of this system and verify the validity of this mathematical model by experiment. Validity of the mathematical model has been confirmed as a result. And we elucidated the static characteristics of this system in regard to outdoor temperatures and Indoor temperatures.
A new method to suppress frost formation on a cylinder with a cryogenically cooled surface using a v-shaped obstacle was proposed and verified in this study. The v-shaped obstacle protects the cylinder from the main flow and reduces frost formation. We conducted experiments under refrigerant temperature conditions of -20 °C and -196 °C. When the refrigerant temperature was -20 °C, the effect of the obstacle was insufficient to eliminate frost formation. Although we succeeded in reducing the frost thickness in front of the cylinder, the pressure drop and heat transfer rate were not sufficiently improved. On the other hand, when the refrigerant temperature was -196 °C, the frost formation in front of the cylinder was completely suppressed. Further, the pressure drop and heat transfer rate were obviously improved. We concluded that this frost suppression method is effective when the surface temperature is low.
Experimental study on frost phenomena on metal fin-shaped plate in forced convection was carried out. The humidity and temperature of supplied air flow were controlled by using the bubbling system and the constant temperature water bath, respectively. The air flow velocity and humidity were changed as the experimental condition. Direct observation using two video cameras during the frosting and defrosting was performed. The temperature measurements on fin-shaped plate by thermo couples attached by spot welding on the fin-plate were also carried out. The effects of the humidity and the flow velocity on the frosting and defrosting characteristics were discussed concerning the heat and mass transfer during the air flow and fin-shaped plate.
Frost formation on the air-side surface of the air-to-refrigerant heat exchanger reduces heat transfer performance in many refrigeration systems. Typically, the design of fin-and-tube heat exchangers having large fin pitch is used because of tolerance to frost growth. In this study, a design concept of finless tube heat exchanger, which is composed of only flat tubes, was proposed for achieving high performance instead of such design of fin-and-tube heat exchangers. Heat transfer and pressure drop performance were measured to evaluate the effectiveness of the proposed heat exchanger under frosting conditions. The effects of inlet air velocity and inlet air temperature were investigated. Furthermore, the heat transfer performance of the proposed exchanger was compared with that of the fin-and-tube heat exchanger. The results showed that the heat transfer performance became much higher for the case of proposed heat exchanger compared with that for the case of fin-and-tube heat exchanger in terms of heat transfer rate per unit temperature and pressure drop penalty under no-frost and frost conditions.
Frosting is the formation of a porous layer consisting of ice and air on a cooled surface, and it is an unsteady phenomenon involving both simultaneous heat and mass transfer. This phenomenon is complex and has not yet been systematically understood. In this work, the objective is to investigate the fundamentals of the frosting phenomenon. In order to do so, we focused on the frost layer thickness, which is one of the quantifying variables of the frosting phenomenon and investigated the effect of cooling surface’s orientation on the frost layer thickness at different wettabilities of the cooling surface, the reason being the wettability is considered as effective for frost reduction. Results show that frost layer thickness is drastically affected by the cooling surface’s orientation. Our research found that the followings are the factors that affect the frost layer thickness: effect of gravity on the rate of linear crystal growth, the mutual relationship between heat and mass transfer, and detachment of crystals.
The internal osmosis of melted water from the upper side to the lower one was visualized and observed. The thermo-physical properties of the frost layer which consist of three phases that is ice, air and water were predicted. The possibility to predict the termination of melting was evaluated, and it was calculated based on frost layer model with non-homogeneous growth. Melting began at the upper side of frost layer, and melting water moved to the adjoining lower side one by one. Simultaneously, melting water was suddenly absorbed to the lowest part due to capillary force. The thermo-physical properties to be determined by the ratio of three phases became uncertain, because it was difficult to calculate the osmosis distance and amount, and to estimate the behavior of melting water absorbed by capillary force. So, it turned out to be the great difference between prediction and experiment.
An analytical and an experimental study have been conducted on the formation of snowdrifts at solar photovoltaic panels on the flat-roofed residences that are common in the snowy regions of Japan, such as in Hokkaido. Toward this, solar photovoltaic panels were installed on the flat roof of a building in Sapporo, Hokkaido. The amount of electric power generated after the formation of the snowdrift was also determined. The Moving Particle Semi-implicit (MPS) method was applied two-dimensionally to simulate the formation of snowdrifts around the panel, and the snow particles were blown with air into the calculation area to observe snowdrifts that formed by the interaction between the snow particles and the panel. We have presented an analytical model of snowdrift formation at a photovoltaic panel, and we compare its results with those of empirical examinations. The snowdrift was found to cover part of the panel surface if the panel had a clearance of less than 200 mm.
Secondary refrigerants have been used in various indirect heat pump and refrigeration systems. The fundamental properties of potassium formate aqueous solutions are a key component of these refrigerants. We have investigated the fundamental properties of potassium formate aqueous solutions, such as refractive index, density, specific heat and viscosity. The measurements of fundamental properties were performed in the concentration range varied from 0.0 to 50.0 wt% for measurements of refractive index, density and specific heat, 10.0 to 50.0 wt% for viscosity, while the temperature range varied from 5 to 50 oC for measurements of refractive index and specific heat, 0 to 70 oC for density and 0 to 50 oC for viscosity. The results indicate that the measured properties increase with solution concentration and decrease with increasing solution temperature except for specific heat. In addition, the empirical equations of these properties are presented and are in good agreement with experimental results.