Keishi Kariya

FUEL CELL WASTE HEAT POWERED ADSORPTION COOLING SYSTEMS

In the present paper, the effect of desorption temperature on the performance of adsorption cooling systems driven by waste heat from fuel cells was analyzed. The studied adsorption cooling systems employ activated carbon fiber (ACF) of type A-20–ethanol and RD type silica gel–water as adsorbent–refrigerant pairs. Two different temperature levels of waste heat from polymer electrolyte fuel cell (PEFC) and solid oxide fuel cell (SOFC) are used as the heat source of the adsorption cooling systems. The adsorption cycles consist of one pair of adsorption–desorption heat exchanger, a condenser and an evaporator. System performance in terms of specific cooling capacity (SCC) and coefficient of performance (COP) are determined and compared between the studied two systems. Results show that silica gel–water based adsorption cooling system is preferable for effective utilization of relatively lower temperature heat source. At relatively high temperature heat source, COP of ACF–ethanol based adsorption system shows better performance than that of silica gel–water based adsorption system.

Local Condensation Heat Transfer Characteristics of Refrigerant R1234ze(E) Flow Inside a Plate Heat Exchanger

In the present study, local condensation heat transfer coefficients of the R1234ze(E) inside a vertical plate heat exchanger (PHE) were investigated experimentally. In the experiment, three vertical flow channels are formed in the test section where refrigerant flows downward in the middle channel and cooling water flows upward in other two channels. The test section consists of eight plates: two of them form a channel of chevron type PHE for refrigerant flow channel, other two flat plates are set for heat transfer measurements, and another consist on cooling water flow channel. Down flow of the condensing refrigerant R1234ze(E) in the center channel releases heat to other channels of cooling water. In order to measure local heat transfer characteristics, a total of 60 thermocouples were set at middle of flow direction and also in the right and left sides of plates in test section. Experiments were conducted for mass fluxes ranging from 10kg/m2s to 50kg/m2s. The measurement results show that local heat transfer coefficients decrease with increase of wetness with different values in horizontal direction. Further, characteristics of local heat flux and wall temperature distribution as a function of distance from inlet to outlet of refrigerant channel were explored in detail.

A Study on Characteristics of Cooling Heat Transfer of Supercritical Pressure Fluids in a Plate Heat Exchanger

For the development of industrial heat pump systems supplying a high-temperature heat source over 130°C, experiments were carried out on cooling heat transfer of supercritical pressure fluids flowing in a plate heat exchanger (PHE). Using two refrigerants of HFC134a and HCFC22 as the test fluids, heat transfer coefficient data were obtained at different pressure, flow rate, and heat load conditions. The heat transfer coefficient generally had a maximum in the vicinity of the pseudocritical point and showed seven- to ninefold values compared with tube flow. Based on the measurements, characteristics of cooling heat transfer of supercritical pressure fluids in the PHE were clarified and a correlation of heat transfer coefficient was developed.

Boiling Heat Transfer and Pressure Drop of a Refrigerant R32 Flowing in a Small Horizontal Tube

In this study, experiments were performed to examine characteristics of flow boiling heat transfer and pressure drop of a low global warming potential refrigerant R32 flowing in a horizontal copper circular tube with 1.0 mm inside diameter for the development of a high-performance heat exchanger using small-diameter tubes or minichannels for air conditioning systems. Axially local heat transfer coefficients were measured in the range of mass fluxes from 30 to 400 kg/(m2·s), qualities from 0.05 to 1.0, and heat fluxes from 2 to 24 kW/m2 at the saturation temperature of 10°C. Pressure drops were also measured in the rage of mass fluxes from 30 to 400 kg/(m2·s) and qualities from 0.05 to 0.9 at the saturation temperature of 10°C under adiabatic condition. In addition, two-phase flow patterns were observed through a sight glass fixed at the tube exit with a digital camera. The characteristics of boiling heat transfer and pressure drop were clarified based on the measurements and the comparison with data of R410A obtained previously. Also, measured heat transfer coefficients were compared with two existing correlations.

Experimental Investigation of Condensation Heat Transfer and Adiabatic Pressure Drop Characteristics Inside a Microfin and Smooth Tube

Experiments on condensation heat transfer and adiabatic pressure drop characteristics of R134a were performed inside smooth and microfin horizontal tubes. The tests were conducted in the mass flux range of 50kg/m2s to 200kg/m2s, vapor quality range of 0 to 1 and saturation temperature range of 20∘C to 35∘C. The effects of mass velocity, vapor quality, saturation temperature, and microfin on the condensation heat transfer and frictional pressure drop were analyzed. It was discovered that the local heat transfer coefficients and frictional pressure drop increases with increasing mass flux and vapor quality and decreasing with increasing saturation temperature. Higher heat transfer coefficient and frictional pressure drop in microfin tube were observed. The present experimental data were compared with the existing well-known condensation heat transfer and frictional pressure drop models available in the open literature. The condensation heat transfer coefficient and frictional pressure drop of R134a in horizontal microfin tube was predicted within an acceptable range by the existing correlation.

Transport properties measurement on low GWP alternative refrigerants

New experimental data on the thermal conductivity and the viscosity of low-GWP refrigerants such as HFOs are reported in order to contribute to the development of low-GWP refrigeration/heat pump systems. Accurate data on thermodynamic and transport properties are indispensable to design and to manufacture the systems with high efficiency. However, there are only limited data on the properties. In this study, the thermal conductivity and viscosity of low-GWP refrigerants were measured by a transient hot-wire method and tandem capillary tubes method respectively with wide temperature and pressure range covered from subcooled liquid to superheated vapor region.

Adsorption Performance of Round Fin and Tube Type Adsorber Employing Activated Carbon Fiber/Ethanol Pair

The severity of the ozone layer destruction problem has been calling for rapid developments in environment friendly adsorption cooling systems. However, the widespread dissemination of adsorption system is hindered due to its poor performance, which mainly results from the inadequate design of adsorber/desorber heat exchanger. The present paper deals with the numerical investigation on the adsorption performance of a round fin-and-tube type adsorber/desorber heat exchanger using activated carbon fiber (ACF)-ethanol as adsorbent-refrigerant pair. The effects of the local heat and mass transfer as well as the fin geometry of the adsorber/desorber are accounted in the present two-dimensional modeling. Adsorption performance have been determined varying five parameters, such as the ACF bed apparent density, fin thickness, fin pitch, fin height and tube diameter along with evaporator and cooling water inlet temperatures. The results show that the adsorption performances increase by optimizing the tube diameter, fin height and fin pitch. It is also found that all parameters have some influence on the optimum adsorption cycle time and the optimum cycle time is found to be around 150 s.Copyright

Heat transfer characteristics of various kinds of ground heat exchangers for ground source heat pump system

Three kinds of vertical-type ground heat exchangers, U-tube; double-tube; multi-tube, and two kinds of horizontal-type ground heat exchangers, standing Slinky; reclined Slinky, were experimentally and numerically investigated in order to clarify their heat transfer characteristics. Experiments and simulations were carried out under two operation conditions which are continuous operation mode and discontinuous operation mode and effects of temperature recovery and thermal storage on the heat transfer rate were shown. Differences of the heat transfer rate between standing Slinky and reclined Slinky were also indicated.Three kinds of vertical-type ground heat exchangers, U-tube; double-tube; multi-tube, and two kinds of horizontal-type ground heat exchangers, standing Slinky; reclined Slinky, were experimentally and numerically investigated in order to clarify their heat transfer characteristics. Experiments and simulations were carried out under two operation conditions which are continuous operation mode and discontinuous operation mode and effects of temperature recovery and thermal storage on the heat transfer rate were shown. Differences of the heat transfer rate between standing Slinky and reclined Slinky were also indicated.

Experimental adiabatic two-phase pressure drop of R134a flowing inside a multiport minichannel

The paper reports experimental adiabatic two-phase pressure drop of R134a in smooth and groove mnichannels having 20 channels with hydraulic diameters of 0.81 mm and 0.64 mm, respectively. The pressure drop measurements were done under mass flux range of 50-200 kg/m2s, saturation temperature range of 30-35 °C, and inlet vapor quality range of 0.1-0.9. The effects of mass flux, saturation temperature, inlet vapor quality and channel geometry on pressure drop were investigated. The results showed that the mass flux, inlet vapor quality, saturation temperature and channel size play an important role in increasing or decreasing the pressure drop. The results also showed that the total pressure drop is dominated by the frictional pressure drop. The present experimental data were compared with some existing well known pressure drop correlation available in the open literature.The paper reports experimental adiabatic two-phase pressure drop of R134a in smooth and groove mnichannels having 20 channels with hydraulic diameters of 0.81 mm and 0.64 mm, respectively. The pressure drop measurements were done under mass flux range of 50-200 kg/m2s, saturation temperature range of 30-35 °C, and inlet vapor quality range of 0.1-0.9. The effects of mass flux, saturation temperature, inlet vapor quality and channel geometry on pressure drop were investigated. The results showed that the mass flux, inlet vapor quality, saturation temperature and channel size play an important role in increasing or decreasing the pressure drop. The results also showed that the total pressure drop is dominated by the frictional pressure drop. The present experimental data were compared with some existing well known pressure drop correlation available in the open literature.

Application of the extended corresponding states model for prediction of the viscosity and thermal conductivity of cis-1,3,3,3-tetrafluoropropene (R1234ze(Z))

Prediction of the transport properties of low global warming potential refrigerants is a key issue for the refrigeration industry. In this work, the extended corresponding states models coupled with density-independent shape factors (empirical shape factors) or density-dependent shape factors (exact shape factors) are individually applied to predict the viscosity and thermal conductivity of 1,3,3,3-tetrafluoropropene (R1234ze(Z)). These models use 1,1,1,2-tetrafluoroethane (R134a) as a reference fluid. Empirical shape factors are obtained from the vapor pressures and saturated liquid densities of R1234ze(Z) and R134a. Exact shape factors are calculated from equations of state for these refrigerants. Predicted values with the extended corresponding states models are compared with experimental data, and the prediction capability of each model is discussed. In addition, viscosity and thermal conductivity shape factors are introduced to improve the prediction capability. With these additional shape factors, the extended corresponding states models represent the experimental data of the viscosity and thermal conductivity of R1234ze(Z) within ±2% and ±1%, respectively.