An overview is made on time-dependent buoyant convection in an enclosure with time-periodic thermal or mechanical boundary conditions. The classical models for resonant convection are reviewed. Recent numerical efforts to determine the resonance frequency and the physical rationalizations are described. Extensions and practical utilizations of resonant convection are discussed. Resonant enhancements of transport phenomena in mixed convection are illustrated, and explanations are given for physical mechanisms.

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Container refrigeration is an important technology in the modern world, where many perishable products are transported in containers which are estimated to be in excess of a quarter million units in current use world-wide. This paper reports on a multi-prong research program, which was initiated to improve the thermal performance of a container refrigeration ststem. The areas examined include studies on system modeling on both full-load control, evaporator studies to enhance its effectiveness, and incorporation of fuzzy logic control to bring about better temperature control.

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A new technique of estimating the unknown inner wall shape of eroded furnaces handling molten materials from the measured temperatures at the outside surface is developed. The inverse heat conduction problem using the conjugate gradient algorithm is extended to the case of nonlinear heat conduction, and is formulated in the general coordinate system. Instead of treating the unknown boundary directly, the heat flux distribution on a virtual boundary is estimated, and the real eroded surface is sought by a proper thermal condition for the surface. Smooth erosion with shallow depths can be estimated well by a single analysis with a flat virtual surface, but deep erosions or sharp changes as in triangular erosions cannot be well predicted by the single analysis with the flat virtual surface. When the virtual surface is modified iteratively, arbitrary shape wiht sharp changes and deep erosions could be predicted excellently even with temperature-dependent thermal conductivity.

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Soot temperatures were measured using a two-color pyrometry and an Abel inversion technique in co-flow diffusion flames at pressures up to 0.4 MPa. The measured soot temperatures are analyzed along with the soot volume fractions. The oxidation of soot particles ceased at the temperature close to 1400 K. The addition of small amount of air into ethylene does not change the temperature in sootformation regions. The added propane (up to χ_C3H8=0.27) increases the soot volume fraction without changing soot temperatures in ethylene-propane mixture flames. These results support that the enhanced C₃H₃ recombination reaction for incipient ring formation is the major contribution for the increase of soot volume fraction and the synergistic effect. The radial profiles of soot temperature are calculated from the line-of-sight soot emission data through an Abel inversion procedure. The effective soot particle brightness temperature is not simply weighted toward the regions of highest soot loading.

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The flame spread rates over PMMA sheets are measured throughout the thin and the thick regimes with varying oxygen level and pressure in normal-gravity. The prediction by Extended Simplified Theory (EST) shows good agreement with the experimental results in the thermal regime where relatively high opposed-flow exists. In micro-gravity, the spread rate over thin PMMA sheets is measured with varying opposed-flow velocity and oxygen level. When the opposed-flow velocity is very low, the thermal regime assumption breaks down so that the radiative effect becomes significant. As the radiative effect appears, the mass diffusion layer grows faster tham the thermal layer, and the flame spread is suppressed due to the shortage of oxygen. On the other hand, if the oxygen level is high and / or thickness of the fuel is sufficiently thin, the radiative effect is negligible and the steady spread is established even in a quiescent environment.

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Structure and behavior of spark-ignited propane-air premixed flames established in the quasi-turbulent and quiescent wake, which is generated by quickly moving a fine rod-array vertically downward in the quiescents stoichiometric propane-air mixtue, are observed and analyzed using tomography and PTV. It is found that the quasi-turbulent and quiescent wake proposed here is composed of Karman vortex streets with the characteristic length scale ranging 0.2∼0.5 mm and the tangential velocity of 4.0 m/s, and therefore that it satisfies rather small and intense turbulence conditions of l_d/δ_L〓1 and v_θ/S_L〓10. Since the interface between the unburnt and burnt gases exhibits complicated and rugged appearances and consists of a continuous series of wrinkled flame elements of the length scale ranging 0.2∼2 mm, the turbulent flame established in the quasi-turbulent and quiescent wake with the moderately intense turbulence conditions of l_d/δ_L〓1 and v_θ/S_L〓10 is classified into the finely wrinkled laminar flame.

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A modeling for absorption / desorption of the fuel in the oil film has been developed. The effect of oil film on fuel absorption / desorption was investigated according to engine speed, load, and mean oil film temperature. Multi-component fuel was employed to quantify the oil film effect. The results showed that Henry's constant, which is related to solubility, is the most dominant parameter in absorption / desorption mechanism of the fuel into oil film. The oil segments close to the top of the cylinder liner have significant contribution to the fuel absorption and desorption process than other oil segments. At warm-up conditon, engine speed has a little influencse on the amount of fuel absorbed / desorbed. However, when the oil film temperature is low, the quantity of fuel absorbed / desorbed decreases with the increasing engine speed. The amount of fuel trapped in piston crevice is 2 to 2.3 times as large as that of fuel in the oil film. However, the fuel trapped in the oil film desorbs slower into the combustion chamber than that escaped from the piston crevices at the cold engine conditon.

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The direct infection into the cylinders has been regarded as a way of the reduction in fuel consumption and pollutant emissions. The spray produced from the direct injector is of paramount importance in GDI (Gasoline Direct Injection) engines in that the primary atomization process must meet the requirement of quick and complete evaporation and combustion especially to prohibit the excessive HC emissions. The interaction between air flow and fuel spray was investigated in a steady flow system embodied in a wind tunnel to simulate the variety of flow inside the cylinder of the GDI engine. The direct Mie scattered and Shadowgraph images presented the macroscopic view of the liquid sprays and vapor fields. The velocity and particle size of fuel droplets were investigated by Phase Doppler Anemometer (PDA) system. The processes of atomization and evaporation with a GDI injector were observed and consequently utilized to construct the data-base for the spray and fuel-air mixing mechanism as a function of the flow characteristics.

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This paper reports an experimental study of hith-pressue diesel fuel sprays in their initial stage of development. Diesel fuel is injected from a single-hole nozzle at an injection pressure of 50 MPa into a high-pressure vessel. The internal structure of the spray is visualized with a laser-induce fluorescence (LIF) method. A direct cross-correlation PIV technique is applied to the spray images acquired with a double-pulsed illumination system in order to measure the droplet velocity distributions in the intial stage of spray development. It is found that some droplets located slightly upstream of the spray tip can have substantially higher axial velocities than the droplets located on the spray tip. It is also found that some droplets near the spray tip have large radial velocities as if they are injected out of the spray core. These findings ae discussed in detail in conjunction with possible mechanisms for the generation of large-structures of diesel fuel sprays.

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This work presents the results of one-and two-dimensional numerical analysis of a choked capillary flow and the analysis of particle formation and growth in a capillary. The object of this study was to determine conditions of seed particle growth and homogeneous nucleation. The Lagrangian approach was used for the calculation of droplet grwoth, and vapor depletion and latent heat release were considered in the calculation of the two-dimensional flow field. Several parameters were derived from the analysis of the flow field and the growth rate of the droplet, and their effects are discussed. It was found that the viscous pressure loss during the expansion has a significant effect on both heterogeneous and homogeneous condensation. The difference in the results between one- and two-dimensional calculations is also discussed and conclusions are presented.

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In-tube condensation heat transfer has been investigated experimentally and theoretically. To study the condensation heat transfer characteristics of R22 and its alternative refrigerant R410A, a series of experiments were performed, and the experimental results are presented and compared with previous works. Also, a condensation heat transfer modeling is presented for two-phase turbulent annular flow inside smooth tubes. This model can account for the effects of interfacial shear stress and liquid entraimment as well as the turbulent eddy viscosity on the condensation heat transfer. Using this calculation model, local condensation heat transfer coefficients for annular flow inside horizontal smooth tubes were obtained, and the calculated values were compared with present experimental results of condensation heat transfer for R410A together with the existing correlations.

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Among the various types of diesel after-treatment device, the corona discharge reactor may be considered as a powerful tool for trapping submicron particles. But after precipitation on the electrodes occurs, the re-entrainment of particles is severe and often causes low or negative precipitation efficiency. Experiments were performed to investigate the effect of an applied voltage on the re-entrainment of soot particles from the electrodes. A co-annular laminar diffusion flame burner was used as the soot generator. When a highly negateve voltage was applied, exfoliation of the deposited soot particles and an increase in concentration of particles smaller than approximately 150 nm were observed. Turbulence induced from the negative tuft corona and sputtering caused particle re-entrainmnet from the corona wire and from plates as well. Under soot laden combustion gas, a streamer corona often occurred in the wire-cylinder reactor. Because of its transient mature, streamer corona violently increased the concentaration of reentrained particles and CO gas.

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The present paper reports numerical modeling of multi-dimensional two-phase boiling flows with a multi-dimensional two-fluid model and prediction of the Departure from Nucleate Boiling (DNB) under PWR accidental conditions. The conventional two-fluid model is adopted and various constitutive equations are incorporated to develop a computer code capable of predicting multi-dimensional void fraction distribution in a flow-boiling channel. The numerical results are compared with the data in literature of the measured profile of void fraction, with the agreement being satisfactory. To predict the occurrence of DNB, the Weisman-Pei model is adopted, which predicts the occurrence of DNB when the local void fraction exceeds a predetermined value in the near-wall buble layer. The predicted DNB power is compared with the results from an experiment of DNB power in an annular channel under PWR flow and pressure conditions, and the agreement is encouraging.

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Pressue loss characteristics of flow in rotating coolant passages of gas turbine intermediate shaft were studied experimentally. The effects of rotational Reynolds number and coolant flow rate on the pressure loss characteristics of flow in the coolant passages were investigated by using a rotatinal test facility with disks having diameter of 0.5m and maximum rotational speed of 4800 rpm. A multi-points pressure measurement system with a rotary connector was employed to measure both the wall static pressure along the passages and the total pressure in the intermediate shaft. The results led to an understanding that the strength of the swirl flow controls the total pressure distribution in the central portion of the shaft. On the other hand, there occurreed a large pressure loss at both the junction and in the region of branching of coolant passages.

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The spatial variations of temperature field around the room air conditioner model were measured using the LIF(Laser Induced Fluorescence) temperature field measurement technique. The room model and air conditioner model are scaled down by 1/20. And rhodamine B was used as at temperature indicator. The intensity variations of LIF signal from Rhodamine B excited by the laser light sheet were captured with an optical filter and CCD camera. Laser light sheet of an Nd-Yag laser illuminated a two-dimensional cross section of the discharge region of air conditioner. The true temperature field data were derived from the intensity information acquired from LIF temperature calibration. The measured results for propagation of heat and flow in the room model are discussed in this paper.

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In this study, in-situ Performance test of a 20 RT (70 kW) air-to-air heat pump which has a feature of recovering ventilation energy is carried out. Since test conditions such as indoor and outdoor air conditions cannot be controlled to satisfy the standard test conditions, experiments are done with the inlet air conditions as they exist. From the experimental data obtained with the non-standard test conditions, simulation program is developed to estimate the performance of standard test conditions. The map-based compressor model, ε-NTU method with the assumption of refrigerant-side mixed and air-side unmixed and necessary parameters determined from the measurements are used. From the simulation, performance of a large capacity air source heat pump for various conditions and effects of ventilation are calculated. This study provides method of predicting the performance of air source heat pumps in which in-situ performance test is necessary.

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Microchannel is one of the essential components that construct various micro systems. However, it has been reported that the flow and heat transfer behavior in microchannel deviates from predictions based on the conventional assumptions generally accepted in macro scale. In this study, frictional characteristics of nitrogen (N₂), argon (Ar) and helium (He) flowing through microtubes whose diameter ranges from 5 to 100 μm have been investigated experimentally. Inlet / outlet pressure difference and volumetric flow rate were measured. In the range of Reynolds number (Re=0.03∼29.7) tested in this study, the measured friction constant was observed to take the values around 50, which is about 20% less than 64, the value regarded to be correct for macro scale tube predicted by the incompressible flow assumption. Transition from incompressible to compressible flow regimes was observed experimentally. The onset of compressibility effect was dependent on the inlet / outlet pressure difference (or the pressure ratio) as well as on the Mach number. The frictional resistance of nitrogen flow showed a Knudsen number dependence, which is in rough agreement with the first-order slip model.

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In the present study, the characteristics of heat transfer and flow pattern are investigated experimentally for evaporation of pure refrigerant HFC134a in capillary tubes of 2.0 and 0.84mm I. D. The test section consists of a heating stainless steel tube section and a glass-tube section, which is located at the right after the outlet of the heating section. The experiments were carried out in the ranges of mass velocity of 100∼600kg/m²s and heat flux of 1.16∼46.8kW / m² at a constant inlet pressure of about 920kPa. Experimental results of local heat transfer coefficient, pressure drop and flow pattern were compared with previous studies.

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The objective of the present study was to investigate the effect of a chip spacing in a multichip module on the cooling characteristics of phase change material slurry. The experimental parameters were chip spacing in a multichip module, heat flux of simulated VLSI chip, mass fraction of paraffin slurry, and channel Reynold number. The removable that flux at the same chip surface temperature decreased as the chip spacing decreased. The local heat transfer coefficients for the parafin slurry were larger than those for water, and the chip spacing on the local heat transfer coefficient for paraffin slurry influenced less than that for water. The enhancement factor for the paraffin slurry showed the largest value at a mass fraction of 5% rregardless of the chip spacing, and the enhancement factors increased as the chip spacing decrased. This means that the paraffin slurry is more effective than water for cooling of the highly integrated multichip module.

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An experimental study has been conducted to investigate the heat / mass transfer and flow characteristics for flow over a backward-facing step and cavities with various aspect rations. A naphthalene sublimation method is employed to measure the heat / mass transfer coefficients on the bottom wall. Acoustic excitations are forced on the spearated flow using a woofer speaker placed above the step edge for Strouhal numbers between 0.2 and 0.4 In the spectra of streamwise velocity fluctuations for the flow excited at St_H=0.2, a sharp peak appears at the forcing frequency. For the backward-facing step, the reattachment length of about 6.7H is reduced by 0.7∼1.5H when the flow is forced by acoustic excitation. The peak Sh is located about 1.1H upstream from the reattachment point. For the 10H cavity, the reattachment of separated flow, which is unclear for a natural case, is produced clearly by the acoustic excitaition. For the 5H cavity, the turbulence intensity and heat / mass transfer coefficient in the recirculation region are slightly enhanced.

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The structure of counter-rotating vortex pair of round jet issuing normally into a crossflow was studied using a flow visualization technique and PIV measurements. Experiments were performed at a jet-to-crossflow velocity ratio of 3.3, and the Reynolds number of 1, 050, based on the crossflow velocity and jet diameter. Instantaneous velocity field was acquired using two frame cross correlation PIV technique. The angle of laser sheet beam was set to be perpendicular to the ensemble averaged trajectory of the crossflow jet. The mean velocity field was obtained by ensemble averaging over 300 realizations of instantaneous velocity fields for each plane. It was found that the counter-rotating vortex pair was initiated from the hanging vortices appearing at both sides of the jet colunm. The detailed characteristics of the velocity fields were discussed with the evolution of the counter-rotating vortex pair.

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In the present work, a two-dimensional surface model using random number and the Abbott's bearing area curve is proposed to investigate heat transfer between contacting rough surfaces with spheical from microscopic point of view. Numerical calculations are conducted for 20 sorts of roughness configurations under each of five representative surface conditions. From the calculations performed on a cylindrical system, the temperature fields near the contact interface are clarified microscopically, and further the mean thermal contact conductance (mean TCC) is evaluated for each surface condition. To verify the validity of the model, the mean TCCs are also measured using cylindrical brass test specimens. The calculated results are compared to the measured values, and the present model is shown to be valid for simulating heat transfer throuth contacting wavy rough surfaces.

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The noise equivalent temperature difference (NETD) and the minimum detectable size (MDS) as a spatial resolution, are most important performance indices of thermogrph. For such indices, a wide variety of standards and test / evaluation methods have been defined until now, but, it is very important to establish more objective standards for the quantificaton of thermographs. This paper presents two matters, one is a new method to obtain noise equivalent temperatue difference by standard deviation of radiance temperature at individual pixels in thermogram, and the another is the necessity to clarify the relationship between the size of an object to be measured and the temperature reading. In the former, we can treat the noise equivalent temperature difference quantitatively and objectively, as this method depends upon statistical treatment, while in the latter we can quantitatively measure the temperature of the measuring object in the detectable size.

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Three-dimensional unsteady numerical computations were carried out for buoyancy driven convection of an oxide melt (Pr=10) and radiation from the free surface of the fluid in a vertical cylinder. The fluid was assumed to be incompressible, Newtonian and Boussingesq. Three-dimensional structures of the non-axisymmetric flow were investigated in the present stuyd. Temperature distributions on the vertical wall of the cylinder and radiative heat transfer from the free surface of the melt were found to play a key role.

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A new thermosyphon using a magnetic fluid as the working fluid has been proposed for heat transport in a non-gravity field, and named "magnetic thermosyphon". A magnetic body force drives a liquid phase flow, and separates vapor and liquid phases in the magnetic thermosyphon. It has been found that a liquid bypass line between a heat input section and a heat output section is required to return a highly concentrated magnetec fluid from a boiling region to a condensation region. The thermohydrodyamic feasibility of the magnetic thermosyphon has been confirmed analytically. The performance of the magnetic thermosyphon has been evaluated, and as a result, the relationship between heat transport rate and liquid mass flow rate under steady-state operating conditions and a maximum heat transport rate of 65.5 W has been obtained for the present thermosyphon model.

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A new analysis method of measuring the thermal diffusivity of a solid using photothermal displacement is proposed. To obtain an expression for the photothermal deformation, a homogeneous and isotropic infinite plate of finite thickness with stress-free boundaries is considered. Theoretical study was carried out to investigate the influence of the parameters, such as the radius and modulation frequency of the pump beam and the sample thickness. We obtained the thermal diffusivity from the phase of the signal by two methods. The first method for finding the thermal diffusivity of the theoretical result uses the bi-section method to minimize the standard deviation between experimental and theoretical phase curves. The second method uses the relation between the normalized thermal diffusion length and normalized minimum position. The experimental data obtained by applying these methods for different samples were in good agreement with the literature values.

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Numerical and experimental investigations are performed for the rarefied gas flows in pumping channels of a helical-type drag pump. Modern turbomolecular pumps include a drag stage in the discharge side, operating roughly in the pressure range of 0.01∼10 Torr. The flow occurring in the pumping channel develops from the molecular transition to slip flow traveling downstream. Two different numerical methods are used in this analysis : the first one is continuum approach using the Navier-Stokes equations with slip boundary condition, and the second one is stochatic particle approach through the use of the direct simulation Monte Carlo (DSMC) method. The main difficulty in modeling three-dimensional flows in the rotating helical channels comes from the rotating frame of reference. In the present DSMC method, trajectories of particles are calculated by integrating a system of differential equations including the Coriolis and centrifugal forces.

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Heat transfer coefficient ratio distributions are measured for film cooling from two rows of holes with opposite orientation angles. The inclination angle is fixed at 35°, and orientation angles are set to 45° for the downstream row and -45° for the upsteam row. Four film cooling hole arrangements including inline and staggered configurations are investigated. The blowing ratios considered are 0.5, 1.0 and Configuration effects on the heat transfer are not significant at the blowing ratio of 0.5. At the higher blowing ratios of 1.0 and 2.0, however, the inline configuration produces higher heat transfer coefficient distributions compared to others. In spite of the high heat transfer level, the inline configuration shows better film cooling performance, represented by the heat flux ratio, at the blowing rations of 1.0 and 2.0 due to its higher adiabatic film cooling effectiveness.

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A new concept of a thermoelectric actuator comprised of shape memory alloy and Peltier elements has been proposed. The shape memory alloy is heated or cooled simultaneously by Peltier elements and the efficient and quick movement can be achieved. The thermoelectric actuator has been applied to a medical catheter. The operating principle and mechanism of the catheter are described. The developed active catheter, which can bend and twist according to the current supplied to the Peltier elements, shows the fast response and can be operated with less power consumption.

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Numerical simulations of the nucleation process of methane hydrate have been carried out using the molecular dynamics technique. A mixture of water and methane, consisting of 46 rigid water molecules and eight spherical methane molecules, placed arbitraily in a cubic cell of length 12.0 A, has been used as a model system to simulate the nucleation process of the hydrate mainly at a temperature of 275 K. The intermolecular interactions are described by the modified MCY potential model for water-water, and the simple Lennard-Jones potential model both for guest-guest and water-guest. As a result, the nucleation process is considered to comprise of three successive stages. In the first stage, the guest molescules undergo a dispersive process. The evidence of the transition from the first stage into the second lies in the fact that the distribution of the guests reaches nearly that in the hydrate. In the second stage, water molecules form the hydrate cavities surrounding the guests. Then, in the third stage, the hydrate structure becomes steady. It is found that the key for successful formation of the hydrate structure is that the distribution of the guests approaches that in the hydrate, since the nucleation process in much easier to evolve from the second stage into the third. Moreover, the hydrate structure is one of the most stable among all the configurations of the model system as it has the lowest systematical potential.

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