T. Fujii

Bio: T. Fujii is an academic researcher from Kyushu University. The author has contributed to research in topics: Convective heat transfer & Heat transfer coefficient. The author has an hindex of 5, co-authored 8 publications receiving 1289 citations.

Forced convective heat transfer to supercritical water flowing in tubes

Abstract: Experimental investigations were made of heat transfer to supercritical water flowing in a horizontal tube and vertical tubes. A comprehensive set of data was obtained for pressures from 226 to 294 bar, bulk temperatures from 230 to 540°C, heat fluxes from 116 to 930 kW/m2 and mass velocities from 310 to 1830 kg/m2s. Because the physical properties of supercritical fluids change rapidly with temperature in the pseudocritical region, the heat transfer coefficients show unusual behavior depending upon the heat flux. At low or modetate heat fluxes relatively to the flow rate, a satisfactory correlation was obtained, which predicts reasonably well the enhanced heat transfer coefficients near the pseudocritical point. The several characteristics of the deterioration in heat transfer which occurs at high heat fluxes were clarified, and the limit heat flux for the occurrence of the deterioration was determined in connection with the flow rate.

Natural-convection heat transfer from a plate with arbitrary inclination

Abstract: An experimental study is described concerning natural-convection heat transfer from a plate with arbitrary inclination. The heat is transferred from one side surface of two plates of 30 cm height, 15cm width and 5 cm height, 10 cm width. The main flow in the boundary layer is restricted two-dimensionally. The results of heat-transfer coefficients are represented in the relation of average Nu number vs. Ra number. In the laminar region the expression for the vertical plate is applicable to the inclined plate if only the gravitational term in the Ra number is altered to the component parallel to the inclined surface. For the horizontal heated plate and the slightly inclined heated plate with the horizontal both facing downwards, Nu number is proportional to one-fifth power of Ra number. For the horizontal heated plate facing upwards, the flow in the boundary layer is turbulent and the Nu expression agrees with that in the turbulent region for the vertical plate, though the Nu number for the smaller plate of 5 cm height is somewhat larger than that for the larger plate of 30cm height. For the inclined heated plate facing upwards, the larger the angle of inclination becomes, the smaller the transition Ra number becomes, and the Nu number in the turbulent region agrees with that of the horizontal heated plate facing upwards. The cause of the variation of heat-transfer coefficients with the inclination is explained by the change of flow pattern in the boundary layer shown in photos.

Experiments on natural-convection heat transfer from the outer surface of a vertical cylinder to liquids

Abstract: This paper describes the results of experimental investigations on natural-convection heat transfer from the outer surface of a vertical cylinder one metre high to water, spindle oil and Mobiltherm oil. The characteristics of the experiments are as follows. The experimental apparatus is contrived to enable us to measure local heat transfer coefficients directly; sufficiently long turbulent boundary layers are made to appear under various conditions of temperature and heat flux of the heated cylinder; correspondences of local heat transfer coefficients with flow patterns are clarified from the observations of the boundary layer by means of “mirage method” or other methods, and from the measurements of temperature profiles in it; the influence of Prandtl number upon heat transfer is found in its range from 2 to 2600. The boundary layer develops through laminar, vortex-street, transition-turbulent and turbulent flow pattern, and each flow pattern has respective characteristics of heat transfer. Vortex-street flow provokes abrupt increase of heat transfer coefficients in the transitional region from laminar to transition-turbulent. Especially with respect to water, no distinction was found between transition-turbulent and turbulent flow, and its cause is explained by an indeterminate character of the flow pattern in the transitional region. Local heat transfer coefficients are correlated nondimensionally about each flow region in the cases of uniform wall temperature and uniform heat flux. In each case, two kinds of experimental equations are proposed, respectively, by using the physical properties at a reference temperature and by using the supplementary terms referred to the variation of kinematic viscosity. Non-dimensional equations of average heat transfer coefficients are also proposed for the case of uniform wall temperature. Furthermore, some remarks on the ranges applicable to each equation are presented. The shapes of vortex-pairs, laminar sub-layers and turbulent lumps in the boundary layer as well as their development, are clearly taken in “mirage” photos. The transitions of flow patterns are also concretely described. Temperature fluctuations in the boundary layer are revealed and the time-mean temperature profiles are represented by a non-dimensional parameter. “Quasi-steady state” is defined experimentally as a state equivalent to a steady state with respect to heat transfer coefficients.

Theory of the steady laminar natural convectiol above a horizontal line heat source and a point heat source

Abstract: Steady laminar natural convection above a horizontal line heat source and a point heat source are analysed mathematically. The solutions of elementary functions are given for Pr = 2, and also for the flow above a point source for Pr = 1. The velocity and temperature distributions for the case of Prandtl number equal to 0.01, 0.7 and 10 are computed with an electronic computer, and differences, caused by different Prandtl number, among the velocity distributions or the temperature distributions are described in detail.

A correlation for forced convective boiling heat transfer of pure refrigerants in a horizontal smooth tube

Abstract: An experimental study is reported on the boiling heat transfer of HFC134a, HCFC22, CFC114 and CFC12 flowing inside a 7.9 mm ID horizontal smooth tube. Using a water-heated, double-tube type evaporator, the local heat transfer coefficients are measured for both counter and parallel flows. Based on the supposition of Chen that the total heat flux is represented as the sum of forced convective contribution and nucleate boiling contribution, a correlation equation is proposed for the data in the annular-flow regime. The mean deviation between the calculated and measured heat transfer coefficients is 12.2% for the present experimental data and 9.5% for the data available from literature. The proposed correlation shows that the nucleate boiling is not fully suppressed even in the high-quality region in the case of counter flow, while convective evaporation is dominant in the high-quality region with uniform heat flux condition.

Biomass Gasification and Pyrolysis: Practical Design and Theory

Abstract: This book offers comprehensive coverage of the design, analysis, and operational aspects of biomass gasification, the key technology enabling the production of biofuels from all viable sources--some examples being sugar cane and switchgrass. This versatile resource not only explains the basic principles of energy conversion systems, but also provides valuable insight into the design of biomass gasifiers. The author provides many worked out design problems, step-by-step design procedures and real data on commercially operating systems. After fossil fuels, biomass is the most widely used fuel in the world. Biomass resources show a considerable potential in the long term if residues are properly handled and dedicated energy crops are grown. 5 years of the author's research in the area Biomass fuel production First book devoted to Biomass Gasification Includes step-by-design procedures, cases studies and worked out numerical examples

The Overall Convective Heat Transfer from Smooth Circular Cylinders

Abstract: Publisher Summary Accurate knowledge of the overall convective heat transfer from circular cylinders is of importance in a number of fields, such as boiler design, hotwire anemometry, and the rating of electrical conductors. The wide dispersion in the published experimental data for the heat transfer from smooth circular cylinders by natural and forced convection is attributed to various factors associated with the experiments. The error due to heat conduction to the supports is particularly important with natural convection, especially where the heat loss and the temperature rise of the cylinder are calculated from the voltage drop across it. A common cause of error is the use of too small a space ratio, so that the temperature and velocity fields are distorted. To reduce this error to less than l%, the space ratio D c /D for natural convection or D T /D for forced convection should exceed 100. The error caused by blockage with wind tunnel measurements can be calculated depending on the type of tunnel. One of the greatest sources of error with forced convection is the failure to allow for the effect of stream turbulence.

The yield of different combined PV-thermal collector designs

Abstract: Various concepts of combined PV-thermal collectors are possible. These concepts differ in their approach to obtain the maximum yield and it is not easy to say whether the yield of a complicated design will be substantially higher than the yield of a simpler one. In order to obtain a clearer view on the expected yield of the various concepts, nine different designs were evaluated. The channel-below-transparent-PV design gives the best efficiency, but since the annual efficiency of the PV-on-sheet-and-tube design in a solar heating system was only 2% worse while it is easier to manufacture, this design was considered to be a good alternative.

The thermal and electrical yield of a PV-thermal collector

Abstract: Four numerical models have been built for the simulation of the thermal yield of a combined PV-thermal collector: a 3D dynamical model and three steady state models that are 3D, 2D and 1D. The models are explained and the results are compared to experimental results. It is found that all models follow the experiments within 5% accuracy. In addition, for the calculation of the daily yield, the simple 1D steady state model performs almost as good as the much more time-consuming 3D dynamical model. On the other hand, the 2D and 3D models are more easily adapted to other configurations and provide more detailed information, as required for a further optimization of the collector. The time-dependent model is required for an accurate prediction of the collector yield if the collector temperature at the end of a measurement differs from its starting temperature.