Masafumi Katsuta

RESEARCH OF HEAT TRANSFER AND PRESSURE DROP CHARACTERISTIC OF CONCAVO-CONVEX PLATE

For an automobile air-conditioning system, performance improvement of the heat exchanger is needed to fit in the change of refrigerant and heat pump system. In this study, the heat transfer and pressure drop characteristic of air flow between parallel plates with concavity and convexity is grasped, and the possibility of using a fin-less heat exchanger is considered analytically. And it has been shown that a fin-less heat exchanger has the possibility of increasing performance compared to a conventional heat exchanger, which uses a corrugated louver fin.

EXPERIMENTAL STUDY OF MERCURY HEAT PIPE

Abstract The purpose of this study is to collect basic data required for the development of mercury heat pipes operating in the temperature range of 623 to 873 K, which will be used in the industrial field. For this purpose, three kinds of mercury heat pipes were made of stainless tubing (SUS316L) 25 mm in diameter and 1000 mm in length. As a result of these tests, it is concluded that the mercury heat pipe exhibits good performance except during startup, but the material compatibility between the stainless steel tubing and mercury is not very good.

Numerical analysis of a metal hydride reactor with embedded heat pipes to enhance heat transfer characteristics

Numerical analysis was conducted for a heat pipe application in a metal hydride (MH) reactor for hydrogen gas storage. The hydriding and dehydriding characteristics of MH strongly depend on temperature and pressure. Due to its extremely low thermal conductivity however, it is very difficult to control the temperature of MH, especially when it is of vast bulk as in an MH reactor. This study deals with heat pipes embedded into the MH to increase the effective thermal conductivity of the system and thus to enhance the thermal control characteristics. The existing model was a brine-tube type MH reactor having cylindrical container with outer diameter of 76 mm and length of 1 m, which was partially filled with 8 to 10 kg of MH material. The hydriding and dehydriding processes occur at 10°C and 80°C, respectively. The heat-pipe type reactor model replaced the brine tubes and channels with copper-water heat pipes of the same dimensions. Three-dimensional numerical analysis predicted that the heat-pipe type MH reactor model enhanced thermal performance with faster response to the change of boundary conditions and higher degree of isothermal characteristics. Discussion is presented based on the numerical results of the two models compared with experimental results.Copyright

Critical temperature differences of a standing wave thermoacoustic prime mover with various helium-based binary mixture working gases

Thermoacoustic prime movers are energy conversion devices which convert thermal energy into acoustic work. The devices are environmentally friendly because they do not produce any exhaust gases. In addition, they can utilize clean energy such as solar-thermal energy or waste heat from internal combustion engines as the heat sources. The output mechanical work of thermoacoustic prime movers are usually used to drive a thermoacoustic refrigerator or to generate electricity.A thermoacoustic prime mover with low critical temperature difference is desired when we intend to utilize low quality of heat sources such as waste heat and sun light. The critical temperature difference can be significantly influenced by the kinds of working gases inside the resonator and stacks channels of the device. Generally, helium gas is preferred as the working gas due to its high sound speed which together with high mean pressure will yield high acoustic power per unit volume of the device. Moreover, adding a small amount of a heavy gas to helium gas may improve the efficiency of thermoacoustic devices.This paper presents numerical study and estimation of the critical temperature differences of a standing wave thermoacoustic prime mover with various helium-based binary-mixture working gases. It is found that mixing helium (He) gas with other common gases, namely argon (Ar), nitrogen (N2), oxygen (O2), and carbon dioxide (CO2), at appropriate pressures and molar compositions, reduce the critical temperature differences to lower than those of the individual components of the gas mixtures. In addition, the optimum mole fractions of Hegas which give the minimum critical temperature differences are shifted to larger values as the pressure increases, and tends to be constant at around 0.7 when the pressure increases more than 2 MPa. However, the minimum critical temperature differences slightly increase as the pressure increases to higher than 1.5 MPa. Furthermore, we found that the lowest critical temperature difference for He-Armixture gas is around 66 °C which is achieved in pressure range of 1.5 MPa - 2.0 MPa and mole fractions of helium of 0.55 - 0.65. The He-N2 and He-O2 mixture gases demonstrate almost the same performances, both have the lowest critical temperature difference around 59 °C atpressures of 1.0 MPa - 1.5 MPa and heliums mole fractions of 0.35 - 0.55. For all tested gases, the lowest critical temperature difference of around 51 °C is provided by He-CO2 mixture gas at pressures of 0.5 MPa - 1.0 MPa with heliums mole fractions of 0.15 - 0.40.

The Study and Development of Roll Heat Pipe Performance

A new type of heat pipe called roll heat pipe (RHP) is considered in this study. In RHP, the evaporator and the condenser are separated in the radial direction, and the energy is moved in radial direction. RHP is composed of two concentric annular pipes of unequal diameter, wick structure, and bridge wicks, which provide the return path of the working fluid to evaporator. A heat source is inserted in the inner pipe, which works as the evaporator region. RHP can be applied as heat roll in the laser printers or copy machines where isothermal heating as well as rapid response is desired. Three RHP samples are fabricated and tested in this work. They differ in the number of bridge wicks and inner tube diameter. The length of all samples is 300 mm. In this paper, the transient thermal characteristics of RHP samples are investigated experimentally and compared with numerical analysis results. Also, the effects of fill charge on the performance of RHP samples are studied. By using infrared thermography camera, we observed that the level of temperature uniformity on the outer surface of heat roll is very good in comparison with real heat roll.

The Development of Performance Prediction Methods for an Automotive CO2 A/C Cycle

In previous research, we have been focusing on the performance of the each element heat transfer and hydraulic performance of refrigeration cycle. Experimental investigations have been repeated several times, and finally, we have substantial database including the effect of lubricant oil. Moreover, the maldistribution of two-phase in an evaporator can be also predicted from the experimental database. Under these circumstances, this study is intended to effectively put the construction of an automotive CO 2 air conditioning system into practical design use through the simulation using the above-mentioned database. This paper describes the refrigeration cycle performance prediction of each element (e.g., an evaporator, a gas-cooler, and so on) by a simulation using substantial database and various available correlations proposed by us and several other researchers. In the performance prediction model of heat exchangers, local heat transfer and flow characteristics are considered and, in addition, the effects of lubricant oil on heat transfer and pressure drop are duly considered. The comparison is also made between simulation results and bench test results using a real automotive air conditioning system. Finally, the developed simulation method can predict the cooling capacity successfully within ±10% for A/C system simulation. By incorporating the lubricant oil effect, the simulation results are improved to ±5% and ±15% for the cooling capacity and pressure drop for evaporator simulation, respectively.

Simulation on Solar Energy Collection to Power a Thermoacoustic Prime Mover Using Pressurized Hot Steam

It has been performed a simple simulation and calculation on solar energy collection which is used indirectly to power a thermoacoustic prime mover by producing pressurized hot steam which would supply thermal energy to the prime mover via sealed-off hot heat exchangers. The solar energy collection took place in Yogyakarta City - Indonesia where the average energy of solar global radiation of 4.8 kWh/m2 /day (17.3MJ/m2 /day) is available around the year. The calculation including the amount of the remaining heat stored, steam pressure, and steam temperature for various areas of the collector unit (Fresnel lens) and volume of water, were done as a function of time for several days. We found that appropriate combinations of lens area and water volume would enable us to operate the thermoacoustic prime mover continuously all day and night.Copyright

Influence of Inserting the Heat Pipe Into the MH Particle Bed on Refrigeration Performance

In the refrigeration and air conditioning fields, the needs of energy conservation and renewable energy spread have become stronger recently. In this study, we aim at the development of the heat driven type metal hydride (abbr, MH) that can be driven by the low temperature exhausted heat or solar heat under 100°C. In order to commercialize this system, the heat transfer characteristics and the activation characteristics of MH particle bed must be more improved, and production cost must be more reduced. In this study, we use the two heat transfer enhancement methods for improving the low effective thermal conductivity of MH particle bed. One is by heat pipe (abbr., HP) and another is by brush type carbon fiber. HP is inserted into heat source part MH (abbr., MH1). By this method, we aim not only to enhance the heat transfer of MH1 particle bed but also to achieve the temperature uniformity of MH1 particle one. The effective thermal conductivity of cooling part MH (abbr., MH2) particle bed is enhanced by inserting the brush type carbon fiber. The influence of these heat transfer methods on our MH refrigeration system is estimated by measurement and calculation.Copyright

Study on the Looped-Type Thermoacoustic Prime Mover for the High Efficient and Practical System( The 14th National Symposium on Power and Energy System)

A thermoacoustic prime mover, due to its simple structure, would serve as very desirable systems because it can be driven with the waste heat such as an exhaust gas from engines, and with heat from the nature such as sunlight and a geothermal heat. The advantages of this prime mover are the flexibility for various heat sources as an external engine and a possibility as the cost effective system due to simple structure. On the other hand, the energy conversion from waste heats to more effective energy such as motion energy or electric energy is desired in the automotive area because of demands of improvement of fuel efficiency. In this research, our interests focused on the performance improvement of looped-type thermoacoustic prime mover by varying stack configuration, inserting membrane to cut off the DC flow and adopting equipment of phase adjustment between pressure and velocity of gas oscillation. The experimental setup we use here is operated under the condition of a 4.2m loop length, the working fluid is argon, the 75Hz operating frequency and stacked screen mesh as a stack configuration. To improve the total thermal efficiency, various efforts have been made experimentally to grasp the optimization of stack structure which plays an important role to energy conversion. Finally, discussions on the future application of prime mover aiming to utilize the waste energy of exhaust gas are made and, by installing a membrane of natural rubber inside the tube, the acoustic intensity has increased by 20%.

Performance of Heat Driven Type Water Cooler Using Metal Hydride

In this study, we aim at developing the heat driven type water cooler using metal hydride (abbr., MH) alloy. Heat driven type MH water cooler is one of the chemical heat pumps, and the endothermic reaction on the cooling part MH (to put it simply, MH2) is used for the cooling. Because MH is too expensive (200∼300