A comprehensive review is presented for the study on the thermodynamic properties of R 1234yf (2,3,3,3- tetrafluoropropene) and R 1234ze(E) (trans-1,3,3,3-tetrafluoropropene), which are considered as a possible replacement for conventional refrigerants with far from negligible global warming potential. Available experimental data for the critical parameters, vapor pressures, liquid/vapor densities, heat capacities, and speeds of sound are compiled, and reliability of each data is evaluated. A brief summary is also given for equations of state developed for these refrigerants, including comparison of deviations from experimental values and valid ranges of each equation of state. Recommended equations are selected which can be applied to refrigeration system analysis.
Freezing phenomena of carbon-nano-fiber (CNF) mixed water are investigated experimentally. The test fluid, whose CNF concentration is varied at 0.86-2.53wt%, is filled in a vessel and is frozen until the vessel is filled with ice. It is shown that a little of CNF is swept out at ice-water interface with freezing and that the swept-out CNF is piled up at the interface. Ice growth rate accelerates due to high thermal conductivity of CNF included in the ice. However, the piled up CNF prevents water supply to the ice-water interface, which results in suppression of ice growth. Analytical results obtained under quasi-steady state assumption give more understandings for freezing characteristics of CNF mixed water.
We experimentally studied thermal storage in water around a cooling tube placed in an insulated rectangular cavity. The cavity (a thermal storage cavity) was filled with water and very thin copper foils. In order to control time variation of heat flux, the copper foils were installed in the cavity in such a way that a space is provided between them and the cooling tube. The experiments were conducted by filling the cavity with eight different volume fractions of copper foil and water at three different initial temperatures. According to the experimental results, by filling the thermal storage cavity with water and the optimal volume fraction of copper foil, time variation of heat flux can be reduced and thermal storage capacity can be increased even if the amount of water, a phase-change material, decreases. As a result, we have ascertained the effectiveness of using layered copper foils in a thermal storage device.
This paper describes an application of an electrical contact resistance method to measure contact conditions of sliding parts between a suction-side bush and a blade in a swing compressor, and examined the contact conditions under some operating conditions. In addition, solid contact ratios between the suction-side bush and the blade were calculated from the measured results of contact conditions. The solid contact ratios were compared with those of a vane tip in a rotary compressor. The results indicate that the sliding parts between the suction-side bush and the blade are in the mixed lubrication condition that the solid contact occurs in fluid lubrication. An upper edge side of the suction-side bush is noncontact even though discharge pressure or operating frequency of the compressor increases. Solid contact between a lower edge side of the suction-side bush and the blade increases with an increase of discharge pressure or a decrease of operating frequency of the compressor. The solid contact ratio between the suction side bush and the blade is less than that of the vane tip.
Measurement of the PρT property for HFO-1234yf (2,3,3,3-tetrafluoropropene) in the gaseous phase was carried out using metal-bellows volumometer. Two hundreds and three PρT properties were obtained in the range of temperatures from (310 to 360) K, of pressures from (927 to 2895) kPa and of densities from (52 to 239) kg/m3. The experimental uncertainties are estimated to be 10 mK for temperatures, 2 kPa for pressures, and (0.11 to 0.31) kg/m3 for densities. The sample purity was better than 99.85 % in mole fraction. On the basis of the present data, the virial equation of state was correlated and the virial coefficients were obtained. In addition, the saturated vapor densities were determined from present virial equation of state by substituting the available vapor pressure values. Moreover, the present data were compared with values calculated from existing equations of state.
Ice making method using evaporation of ethanol solution is useful to ice thermal storage system. In the method, ethanol solution is evaporated under low pressure condition, and ice is produced in it due to the latent heat of evaporation. From our previous experiment, it was found that ethanol concentration of vapor decreases when ice particles floats on the surface of the solution. In this study, the effect of sublimation of ice on the evaporation phenomenon of ethanol solution was investigated. In the experiment, the ethanol concentration of vapor in ice producing chamber was measured under the various conditions. As a result, it was found that the ethanol concentration of vapor significantly decreases due to formation of ice layer, which covers surface of the ethanol solution. It was also found that the amount of decrease in ethanol concentration of vapor mainly depends on thesurface area of the covering ice.
The specific isobaric heat capacity (cp) was measured for HFO-1234ze(E) (trans-1,3,3,3-tetrafluoropropene) in the gas phase. HFO-1234ze(E) has a lower GWP value of 6 and is one of new environment-friendly refrigerants. Nineteen measurements for HFO-1234ze(E) were obtained at temperatures from 303 K to 363 K and at pressures from 0.35 MPa to 1.3 MPa. The expanded uncertainty (k=2) of the temperature measurements is estimated to be less 22 mK, and that of the pressure measurements is less 4.4 kPa. The expanded uncertainty for cp is estimated to range from 14 to 21 J.kg-1.K-1.
Ground water-source heat pump (GWHP) system is currently widely used in China, because of high system energy-efficiency. However, due to the lack of effectively energy-saving diagnostic system, often leads to system operating efficiency be greatly reduced. According to the existing energy efficiency standards used in China, this paper proposes energy-saving state index for GWHP unit and its distribution system, establishes the relationship database between the system monitoring characteristic parameters and the system energy efficiency state, further develops the basic model of standard input about characteristic parameters samples and standard output about system energy-saving diagnosis. Based on the features of artificial neural network's training & learning, memory & simulation, and non-linear approximation etc., the energy-saving diagnostic function of the GWHP system operation can be obtained, and the factors of system energy-efficient performance degradation can be monitored in real-time and the system energy-saving operation state can be controlled on line.
For typical residential buildings, no-large-scale and large-scale public buildings, according to China's Technical Guide for the Energy Efficiency Labeling of Civil Buildings, makes up missing data of the calculation benchmark and determines the boundary conditions for calculating the theoretical values of civil building energy efficiency. Based on equivalent full load hours method, develops a modular program and calculates building energy consumption for the demands of dynamic cooling and heating and lighting etc., finds out the corresponding relationship between star level's theoretical value of energy saving rate and specified-term limiting value in the Guide. With orthogonal experimental design and multiple linear regression, establishes the quantitative function of both the theoretical value of energy saving rate and main factors parameters, analyzes the impact of the control parameter on energy saving rate, and reveals the law of theoretical value of energy saving rate variation with the control parameter. For building energy efficiency labeling upgrade, presents technical measure need to be taken and analyses its feasibility. The results from the study can provide theoretical guidance for energy-saving design or retrofitting of civil buildings.
Further improvement of the performance is requested to air-cooled heat pump chiller from the viewpoint of the global warming prevention. Smaller unit is needed to facilitate the renewal from absorption chiller to air-cooled heat pump chiller. To meet such needs, we developed compact new air-cooled heat pump chiller with high efficiency, 'Compact cube'. The developed machine is side-flow type with U-shaped fin and tube heat exchangers. With this structure, the uniform air velocity, high packed density of the heat exchangers, and the unit miniaturization have been implemented. The refrigeration cycle with two-evaporating temperature has also been implemented. The cooling COP of this cycle is 2% higher compared with conventional one-evaporating temperature cycle because of the rise of average evaporating temperature. In a new model, a new control system, which controls both capacity of compressors and air flow rate corresponding to heat load, has been implemented. As a result, the developed machine achieved IPLV(Integrated Part load Value) to 6.2(MCHV-P1800AE) which is 29% better than the conventional unit.
In the present study, the condensation process of R 744 in a horizontal multi-port extruded tube was investigated experimentally. The test tube is made of aluminum alloy, and has 22 rectangular channels of 0.36 mm in hydraulic diameter. Experiments were carried out in the mass velocity range of 470 to 950 kg m-2 s-1 at 5, 6 and 7 MPa in pressure, respectively. The pressure drop characteristics were measured at the both ends of the test section of approximately 730 mm in length. The sectional heat transfer characteristics were also measured in eight subsections of 75 mm in effective heat transfer length using heat flux sensors. As the mass velocity increases and the refrigerant pressure level decreases, the measured pressure drop increases. These data were compared with several previous correlations. The measured heat transfer coefficient decreases as the liquid quality increases, while it increases with increase of mass velocity. These data were compared with several correlations. The high quality data agree relatively with correlations of Moser et al. and Cavallini et al., while those of low quality do not agree with any correlations well. New heat transfer correlation considering effects of vapor shear stress and surface tension is developed.