Takao Nagasaki

Suggestion of Intercooled and Recuperated Jet Engine Using Already Equipped Components as Heat Exchangers

Aviation engines are strongly desired to reduce CO2, carbon dioxide, emission in the worldwide trend of CO2 reduction. Gas turbine engines are bound to remain as aviation jet engines in the next 20 years at least because of its high power density. So, the jet engines definitely have to enhance their efficiency and to reduce fuel consumption because the reduction in CO2 emission corresponds to the reduction in fuel consumption for a gas turbine engine. One of the likely solutions is an intercooled and recuperated jet engine. Some researchers have confirmed that the overall efficiency certainly increases by employing an intercooler and a recuperator, however, the increase of weight is not acceptable as aviation engine. Therefore, this paper proposes a new concept of an intercooled and recuperated jet engine using already equipped components as heat exchanger to save its weight. In this concept, the intercooler and recuperator require no additional space except a heat transfer system between each heat exchanger. Super-critical carbon dioxide (which is pure substance, not exhaust gas) is qualified as a heat transfer medium for this system. It is larger density and larger specific heat than air, it is smaller viscosity and more flexibility than liquid, it has no surface tension, and phase change never occurs against large heat input. It is circulated inside a heat transfer system by pumps. Hereby, the new intercooler and recuperater including a heat transfer system can be much smaller and lighter than the conventional ones. Therefore, they might be directly applied to the current jet engine without configuration change. This paper roughly designs the new intercooled and recuperated jet engine, and theoretically evaluates its performance, weight, and feasibility.

Effect of Airflow on Heat Transfer of Air-to-Refrigerant Airfoil Heat Exchanger

The effect of airflow on the heat transfer of the air-to-refrigerant airfoil heat exchanger was experimentally investigated. The average Nusselt number for air was estimated using wind tunnel experiments and an inverse heat transfer method. The correlations of the Nusselt number for air by use of the Reynolds or Mach number for air were estimated for an airfoil with a chord length of 44 mm at a refrigerant mass flow rate of 7.2 g/s. Furthermore, the correlation of the ratio of the average temperature difference to the logarithmic mean temperature difference was also obtained.

Estimation of Heat Transfer Performance for Compressor Stators Heat Exchangers in a New Intercooled and Recuperated Aviation Gas-Turbine Engine

In order to reduce carbon dioxide emission from aviation, the authors proposed a new intercooled and recuperated aviation gas-turbine engine, or a new IR engine, that utilizes compressor stators as heat exchanger. For more accurate cycle calculation of a new IR engine, experiments are conducted to estimate heat transfer performance. For simulating a compressor in a practical jet engine, 1: a hot air flow at Mach number of 0.75 are prepared by an open return wind tunnel, 2: a cascade of three NACA65-(12A2I8b)10 airfoils are prepared by compressor stators, 3: carbon dioxide or water as a cold refrigerant at high pressure of 6MPa are prepared in a closed loop with a recirculation pump and with a cooling section. Using this facility at angle-of-attack of 12o, proportionality factors are obtained different from conventional empirical one. For heat transfer between hot air and airfoil, proportionality factor of 0.033 is obtained in water refrigerant case and 0.057 is obtained in carbon dioxide refrigerant case instead of 0.023 in Dittus-Boelter correlation. For heat transfer between airfoil and cold refrigerant, proportionality factor of 0.034 is obtained in water refrigerant case and 0.024 is obtained in carbon dioxide refrigerant case instead of 0.037 in the Colburn analogy.

WATER VAPOR ABSORPTION ENHANCEMENT IN LiBr/H2O FILMS FALLING ON HORIZONTAL TUBES

An experimental investigation was conducted into the enhancement of water vapor absorption in aqueous lithium bromide solution films falling on horizontal tubes. The variable parameters included the solution flow rate, the inlet temperature of the cooling media, the solution inlet temperature, and the effective extended surface. The experimental results, which were correlated with the film Reynolds number, showed that the cooling effect of the tube wall was the governing factor in the absorption process for small solution flow rates, but the inlet solution subcooling dominated the absorption performance for large flow rates. Also, the R tube, which has a unique ridged fin shape, exhibited the best absorption performance among the tested tubes.

Heat Transport Characteristics of a Pulsating Heat Pipe

Heat transport characteristics of a closed loop pulsating heat pipe (PHP) have been investigated experimentally. The heat pipe consists of 12 turn copper pipes with 2mm inner diameter. The lengths of heating, adiabatic and cooling sections are 53mm, 100mm and 51mm, respectively. The heat load was varied up to nearly 1000W for water and R141b as the working fluid. Three kinds of orientation, bottom heat vertical, horizontal, and top heat vertical, were tested. Detailed measurements of wall temperature fluctuations for water revealed several characteristic operating behaviors, such as intermittent oscillation and thermosyphon-like behavior. The performance of PHP with R141b is better than that with water in small heat load range due to its independence of orientation, conversely, PHP with water was more efficient than R141b in large heat load range. In order to improve the performance of PHP with R141b, diamond particles were added, resulting in better performance than water in the whole range of heat load.Copyright

STUDY OF HEAT TRANSFER AUGMENTATION IN A HIGH-TEMPERATURE FIELD BY A RADIATION PROMOTER GENERATING A SECONDARY FLOW

Characteristics of flow and heat transfer have been investigated for a circular pipe in which a pair of twisted tapes were inserted to enhance the convective and radiative heat transfer. From the measurement of the three-dimensional velocity field, it was clarified that a secondary flow was induced by the present promoter, heat transfer performance was enhanced about three times compared with that of a smooth pipe, and a remarkable increase of the local heat transfer rate was observed near the impinging region of the secondary flow. The performance of the present promoter was evaluated based on the total surface area for heat transfer under the same conditions of flow rate, pressure loss, and heat load. It was found that, at room temperature, the total heat transfer area could be reduced to about 30% less than for a smooth pipe. In the case of high temperature, above 450°C, the heat transfer rate was further increased 50% due to the effect of radiation between the pipe watt and the promoter. By using a ve...

Thermodynamic Effect on Backflow Vortex Cavitation

An experimental apparatus was developed to visualize a rotating inducer with speeds of 0 to 8000 rpm. The transparent casing outside the inducer was made of quartz glass, so that tip clearance remained almost constant. All other key parts were chosen based on their suitability for both cryogen and water. Backflow vortex cavitation on a rotating inducer was observed in either liquid nitrogen or water. Consequently, the orbital rotational rate, the orbital rotational diameter, and the diameter of each backflow vortex cavitation should be sorted by head coefficient. Further, thermodynamic effects were observed for the diameter of each backflow vortex cavitation.

Characteristics of Flow and Heat-and-Mass Transfer in a Falling Liquid Film With Three-Dimensional Interfacial Waves

Numerical simulations have been made on the flow and heat-and-mass transfer in a laminar liquid film falling down along a vertical wall by using a boundary-fitted coordinate system. The development of a two-dimensional wave was successfully predicted, which consists of a large solitary wave and ripple waves in front of it. In the large wave a circulating flow exists, and the heat and mass transfer is enhanced by the wave. Further, it was shown by a three-dimensional calculation that a two-dimensional wave becomes unstable with the increase of Re number, resulting in U-shaped three-dimensional wave. The mass transfer rate increases with the transition from two-dimensional to three-dimensional waves. The calculated mass transfer coefficient roughly agrees with empirical correlations.Copyright

Numerical and Experimental Studies for the Conjugate Direct Cooling of a Micro Heat Generating Element

This paper deals with the heat transfer characteristics of a micro heat generating element on a substrate. Both steady-state and periodic steadystate heat transfer characteristics of a small heating element on a substrate are investigated numerically and experimentally.

Heat Transfer Enhancement by Bubble Formation near the Heating Surface.

Convective boiling heat transfer of an immiscible binary liquid mixture has been investigated by using water as the main fluid. R113 and R11 were atomized into the water as volatile materials. When boiling of the volatile material occurs, the heat transfer is enhanced by bubble formation near the heating surface. The heat-transfer enhancement occurs by the addition of a small amount of volatile material, and is insensitive to further increases in its concentration. The enhancement is remarkable in the case of low Reynolds numbers. The heat-transfer enhancement was also observed under the condition that gas bubbles were generated on the heating surface by electrolysis, and it was clarified that the enhancement is caused by the agitation effect of bubbles near the wall