Tsuyoshi Totani

Evaluation of mass transfer coefficient and hydrogen concentration in supersonic flow by using catalytic reaction

The authors propose a new simple method to evaluate hydrogen concentrations in a hydrogen/air supersonic mixing layer without the need for costly apparatus. Catalytic reaction occurs on an electrically heated platinum wire in the supersonic flow of a hydrogen/air mixture. By adopting the technique of a constant-temperature hot-wire anemometer, the heat transfer coefficient and the catalytic heat release rate are measured. A series of experiments with different platinum wire temperatures shows that the platinum wire temperature does not affect the catalytic heat release rate, implying that the rate of mass transfer from the flow to the platinum wire surface is the controlling factor. This means that the catalytic heat release rate gives the mass transfer coefficient of the controlling species, which is hydrogen/oxygen in lean/rich mixtures. It is found that the effect of hydrogen concentration on the ratio of heat and mass transfer coefficients is very weak, suggesting that the mass transfer coefficient, is obtained with reasonable accuracy from the heat transfer coefficient by assuming the equivalent spatial distributions of heat and mass transfer. Based on this result, a method to translate the catalytic heat release rate into the hydrogen concentration of the flow is proposed. To prove the accuracy of this method, hydrogen concentrations of hydrogen/air premixed supersonic flows were measured successfully. Finally, one example applying this method to an actual supersonic mixing layer is presented.

Opposed-flow flame spread in a circular duct of a solid fuel: Influence of channel height on spread rate

The influence of channel height on flame spread in a circular duct of the solid fuel in an opposed-flow configuration was examined. Polymethylmethacrylate cylinders with a circular duct (diameter of 1, 2, or 3 mm) were used as fuel specimens, and both flame-spreading and stabilized combustion were observed. In the case of stabilized combustion, the flame cannot spread into the duct because of the high oxygen velocity. The flame-traveling velocity is the velocity at which the flame widens the duct by fuel consumption. Therefore, the flame-traveling velocity in stabilized combustion is significantly low compared with flame-spreading combustion. In the case of flame-spreading combustion, the equivalence velocity, which contains channel height information, defines whether the regime is the thermal or the chemical regime. When the equivalent velocity is higher than a certain value, the flame-spread rate is controlled by chemical effects. On the whole, the flame-spread rate decreases with the decrease of channel height in the case of flame-spreading combustion because of the curvature effect. Owing to the curvature effect, the area ratio of the flame to that of the solid surface decreases with decreasing channel height, and this is conspicuous when the channel height is low. The curvature effect is negligible when the channel height is sufficiently large compared with the flame stand-off distance.

Thermal Design of Liquid Droplet Radiator for Space Solar-Power System

The waste heat from the space solar-power system, which supplies 5 MW of electricity to a power transmission line on Earth, is estimated, and the liquid droplet radiator for handling the waste heat are examined on the basis of experimental results obtained under microgravity for droplet generation and droplet collection of the liquid droplet radiator. The following results have been obtained. First, an active heat removal system for the power generation unit in the photovoltaic power system is not necessary when the concentration ratio of solar energy is smaller than 1.34, whereas for the liquid droplet radiator, with silicon oil as working fluid, in the solar dynamic power system, the droplet sheet for radiating the waste heat must be 147 m long, 65.1 m wide, and 0.998 m thick. Second, the droplet sheet of the liquid droplet radiator, in which the working fluid is silicon oil, must be 107 m long, 43.2 m wide, and 0.998 m thick to manage the waste heat from the power distribution unit and the power transmission unit in the photovoltaic power system, whereas it must be 107 m long, 65.2 m wide, and 0.998 m thick in the solar dynamic power system. Nomenclature A = area, m 2 a = entrance length of a nozzle, = 0.065 Ca = transmittable energy per unit area perpendicular to the transmission direction, = 2.3 kW/m 2 , W/m 2

Performance of droplet generator and droplet collector in liquid droplet radiator under microgravity

The Liquid Droplet Radiator (LDR) has an advantage over comparable conventional radiators in terms of the rejected heat power-weight ratio. Therefore, the LDR has attracted attention as an advanced radiator for high-power space systems that will be prerequisite for large space structures. The performance of the LDR under microgravity condition has been studied from the viewpoint of operational space use of the LDR in the future. In this study, the performances of a droplet generator and a droplet collector in the LDR are investigated using drop shafts in Japan: MGLAB and JAMIC. As a result, it is considered that (1) the droplet generator can produce uniform droplet streams in the droplet diameter range from 200 to 280 [µm] and the spacing range from 400 to 950 [µm] under microgravity condition, (2) the droplet collector with the incidence angle of 35 degrees can prevent a uniform droplet stream, in which droplet diameter is 250 [µm] and the velocity is 16 [m/s], from splashing under microgravity condition, whereas splashes may occur at the surface of the droplet collector in the event that a nonuniform droplet stream collides against it.

Fuel Regression Characteristics of a Novel Axial-Injection End-Burning Hybrid Rocket

The regression characteristics of axial-injection end-burning hybrid rocket were experimentally investigated using a laboratory-scale motor. The axial-injection end-burning type fuel grains were ma...

Development of Spaceborne Small Hyperspectral sensor HSC-III for Micro Satellite

The earth observation micro-satellite “TAIKI” is 50 kg satellite which has low-cost and small bus-subsystem. TAIKI is characterized by a low-cost spaceborne small hyperspectral sensor “HSC-III”. HSC-III is targeted at the performances of 30 m ground sampling distance, visible and near infrared wavelength range, 10 nm spectral resolutions, 61 spectral bands and 10 kg weight. HSC-III consists of the telescope, the imaging spectrometer, the electrical system, the on-orbital calibration equipment. The telescope has a pupil diameter of 0.2 m, and has two mirror configuration of Ritchey-Chretien type. The spectrometer has the transmitting grating with the slit and relay lens unit, and array sensor using back-illumination type CMOS image sensor. As a SNR model of HSC-III, we did some calculations and concluded that SNR is approximately 340. Last year, we succeeded to develop the breadboard model of HSC-III optics instrument, and we obtained result of more requirement specification. Also, we have developed the on-orbit spectral calibration equipment. It achieved 0.02 nm of spectral calibration accuracy.

Verification Firings of End-Burning Type Hybrid Rockets

The authors have previously proposed the concept of end-burning-type hybrid rockets, which would use cylindrical fuel grains consisting of an array of many small ports running in the axial directio...

Driver Gas Reduction Effect of Pulse-Detonation-Engine Initiator Using Reflecting Board

To reduce driver gas usage of a pulse detonation engine operating in airbreathing mode, the authors experimentally examined a combination method of a reflecting board and overfilling of the driver gas. This method has the potential to reduce the predetonator diameter by half and shorten the overfilling distance h to the reflecting board position w. Experiments with stoichiometric hydrogen–oxygen and hydrogen–air mixtures as driver and target gases, respectively, showed that the overfilling distance necessary to have a planar detonation wave propagate in a detonation chamber is reduced to 30 mm when a reflecting board is used with a reflecting board clearance of w 10 mm. With an overfilling distance of 30 mm, the transformation of the detonation wave from cylindrical to toroidal did not occur because of the mixing effect of the driver gas and the target gas around the reflecting board. A 100-mm-thick reflecting board prevents the mixing effect, and a successful transformation from cylindrical to toroidal becomes possible with an overfilling distance as small as 17.2 mm.

Optimal Fuel Grain Design Method for CAMUI Type Hybrid Rocket

The alternative fuel grain design in CAMUI type hybrid rockets consists of multiple stages of cylindrical fuel blocks with two ports. Regression formulas as functions of local O/F were developed for a 2500 N thrust class flight model motor. Static firing tests with fuel grains of different scaling showed the validity of the similarity rule, which is available for subscale firing tests, based on convective heat transfer mechanisms. Convective heat transfer rate to the downstream end face of the rearmost block is limited comparing with other burning surfaces and radiative heat transfer is not negligible. As a result, the similarity rule is not valid for this burning surface. Because the impinging jet onto the upstream end face of the uppermost block is not high temperature combustion gas but virtually pure oxygen, a similarity about chemical reaction is necessary besides those about convective heat transfer to realize a similarity condition. These results serve as foundation for the methodology to design optimal fuel grain shape for CAMUI type hybrid rockets.

Development of Regression Formulas for CAMUI Type Hybrid Rockets as Functions of Local O/F

Regression formulas for solid fuels in CAMUI type hybrid rockets were developed as functions of local O/F. The alternative fuel grain design used in this rocket consists of multiple stages of cylindrical fuel blocks with two ports. A fuel block in a CAMUI type grain has three burning surfaces, i.e., the upstream end face, port inner walls, and the downstream end face. A series of static firing tests by a laboratory model motor revealed controlling parameters to develop a regression formula for each burning surface. Some empirical constants in the regression formulas depend on local O/F. Based on these findings, regression formulas as functions of local O/F were developed for a 2500 N thrust class flight model motor. Obtained regression formulas contribute to obtain an optimal design of a grain configuration to minimize the weight of residual fuel mass and c * loss due to the O/F shift during firing.