To enhance the environmental performance of vehicles, CO₂ emission should be reduced and the fuel efficiency should be improved. The fuel efficiency can be improved by reducing the aerodynamic drag of vehicles and improving the thermal efficiency of engines. Further improvement can be achieved by currently developed systems such as the hybrid vehicle (HV), which employs the internal combustion engine and the motor, and by the fuel cell vehicle, which does not require fossil fuel. However, HV and FCHV (Fuel Cell Hybrid Vehicle) have piles of concerns to be tackled such as thermal issues of new devices including the motor, the inverter, the battery and the fuel cell. This paper reviews the thermo-fluid dynamic approaches, which are indispensable to manage these concerns.

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Impingement process of a small droplet on solid wall was investigated with molecular dynamics simulation technique. A liquid droplet consisting of about 14,000 Lennard-Jones particles was thrown with a given speed onto a smooth wall, and the change of its size and shape was analyzed. After the collision, the droplet spreads on a “hydrophilic,” or strongly interacting, wall, but bounces on a “hydrophobic” wall. The spreading behavior is suppressed by surrounding gas.

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The condensing heat transfer coefficient is one of the important factors to evaluate the pressure change under BWR (Boiling Water Reactors) abnormal transients. Condensing condition is about 7 MPa of pressure with vapor flow. Many condensing studies have been done under atmospheric conditions with stagnant vapor. However, the condensing test results under BWR conditions have not reported. Therefore, the condensing heat transfer test of the saturated vapor with vertical upward vapor flow has been done under high temperature and high pressure conditions.
The final purpose of this study is to develop the condensing correlation under BWR conditions. In this report, the data under pressures of 0.5 and 1 MPa are reported. Test section is tube. The inner diameter and condensing length is 57.6 mm and 2000 mm. Test fluid is saturated vapor. The following test results were obtained
(1) Flooding may have occurred at a higher vapor velocity. (2) Vertical vapor flow has the effect to enhance the condensing heat transfer. (3) The measured heat transfer coefficients are larger than that of Nusselt model due to the vertical vapor flow

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The effect of delta-wing-vortex generators (combination of a delta wing and a delta winglet pair) on the heat transfer performance of fin-and-tube heat exchangers for vending machines has been investegated. Flow visualizations, numerical simulations and heat transfer experiments were conducted to find an optimum geometrical shape and arrangement of the vortex generators. Maximum heat transfer enhancement was achieved by the combination of (a) the delta wing with the apex angle of 86 degrees and (b) the delta winglet pair with the inline angle of 45 degrees. In relatively low Reynolds number range, about 40 % increase in heat transfer coefficient was attained with the above mentioned combination of the vortex generators compared to the ordinary heat exchangers with plain fins. It was revealed that the heat transfer enhancement was attributed to (1) the longitudinal vortexes generated by the delta wing and (2) the reduction of wake area behind the tube. It was also found that an increase in the apex angle of the delta wing brought about heat transfer enhancement, and the scale as well as the streggth of the induced longitudinal vortices played an important role in the heat transfer performance.

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Numerical analysis has been performed for load-following capability of a 465 MWth Three-Core Molten Salt Reactor (MSR). “Reactor-slaved-to-turbine control technique” is adopted for reactor control. As for this control technique, a turbine is controlled by a speed regulator of a generator, and subsequently the reactor is controlled so as to follow the turbine output. In this study, the turbine power is rapidly changed in a range of 50-150% of the rated power. Then transient characteristics of fuel salt and graphite temperatures, neutron fluxes, delayed neutron precursors, and reactor output are calculated. The analysis result shows that the reactor output is capable of following the turbine power in the range of the turbine output of 50-150%.

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A special purpose computer is developed for two-dimensional steady heat conduction problem by FPGA (Field Programmable Gate Array) chip on a PCI (Peripheral Component Interconnect) board. The computer consists of four internal memories, a calculation circuit, two adders, and one multiplier. The computational domain is divided by 64×64 meshes. The computation is adopted 32 bit fixed-point calculation to obtain stationary solution. The same calculation is performed by a general PC with C language. FPGA results are evaluated about the performance accuracy and the calculation time compared with C language results. Although computational time of FPGA is three times larger than that of C language, more speed-up will be achieved if the program is directly installed in the LSI chip.

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