In order to keep the environment in an air-conditioned room comfortable, it is important to anticipate the air velocity and temperature fields precisely. The numerical code, solving simultaneously the Navier-Stokes equations governing flow field inside and outside the room and the heat conduction equation applying to walls, are developed. The assumption that the heat transfer coefficient between the fluid and the surface of solids is not used. This code is applied to investigate the cooling process of a cubic shell. The computational results agree with the experimental results. We also investigated the same process of the cubic shells whose walls are internally or externally insulated. The difference of the amount of heat transfer will be discussed.

This study numerically investigated the one-dimensional freeze drying of a solution product assisted with infrared radiation heating. In order to accurately consider the spectral radiative transfer inside the moisture-rich product, the two-flux radiation model was incorporated with our previous freeze drying analysis model based on the fixed grid method. Thus, this model fully takes into account the spectral absorption characteristics of ice and the spectral composition of light emitting from an infrared heater. The infrared-assisted freeze drying characteristics were investigated in detail, along with the spatial variation of radiation intensity inside the product. Then, the effects of infrared heater temperature on freeze drying behaviors were parametrically studied, and the results were discussed in relation with the spectral effects in the radiative transfer in the moisture-rich product.

Three-dimensional direct numerical simulation (DNS) with a detailed kinetic mechanism has been conducted for statistically-planar turbulent flame and turbulent V-flame of hydrogen–air mixture to clarify the effects of mean flow velocity on principal strain rates at flame front and on flame geometry. Reynolds numbers based on Taylor micro scale and turbulent intensity are selected to 60.8 and 97.1, and mean flow velocities for V-flame are 10 and 20 times laminar burning velocity. From results of DNS, eigenvalues and eigenvectors of strain tensor are evaluated to investigate characteristics of strain field near flame and flame normal alignments with the principal axes of strain in detail. It has been revealed that Reynolds number affects both magnitude of strain rates and alignment between flame normal and principal axis of strain, and that the magnitude of mean flow velocity affects flame normal alignments in turbulent V-flame.

Three-dimensional direct numerical simulation (DNS) of turbulent hydrogen-air premixed flames in a constant volume vessel at relatively high Reynolds numbers have been conducted considering detailed kinetic mechanism and temperature dependence of the transport and thermal properties. The flame behavior and heat transfer characteristics are investigated in the vessel. The flame is strongly affected by the growth of the internal pressure which is caused by the temperature rise in the vessel. Since the pressure increase makes the flame thickness thin, the heat release rate of each flame element is augmented. The local pressure rise due to the dilatation also enhances turbulence and finer scale vortices appear, which make the flame surface more complicated and result in an increase of the flame surface area. Due to the increase of the mean pressure in the vessel, the maximum wall heat flux induced by the flame front is enhanced during the combustion.

During atmospheric (re-)entries, planetary probes encounter huge heat fluxes due to their significant speed (up to 13 km/s for an Earth re-entry). The total heat flux received by the probe can be divided into two main components: a convective one (coming from the conduction and diffusion phenomena occuring in the shock layer) and a radiative one (due to the radiation of certain species). Numerical simulations have been performed for both Titan (Huygens mission) and Earth (Fire II mission) entries. The main parameters influencing the results are the atmosphere composition, the chemical reaction scheme, the transport model and the radiative model. The results obtained gave us information on the flowfield (temperature, pressure, species densities...) and values for the heat fluxes on the wall that are useful for experimental or flight data comparison.

Direct numerical simulations (DNSs) on autoignition and flame propagation of inhomogeneous methane–air mixtures in a closed vessel are conducted with considering detailed kinetic mechanism and temperature dependence of transport and thermal properties. The mixtures with spatial inhomogeneity of temperature or equivalence ratio are investigated. Periodic condition for non-heatloss cases or isothermal wall condition for heatloss cases is imposed on the boundaries. From the DNS results without heatloss, effects of spatial inhomogeneity of temperature and equivalence ratio on mean heat release rate are clarified. Increase of spatial variations of temperature or equivalence ratio suppresses drastic rise of mean heat release rate and reduces its maximum value. Autoignition process is affected by temperature more strongly than equivalence ratio. In the cases with heatloss, ignition delay increases and the maximum mean heat release rate decreases. After autoignition process, propagating flame is formed along walls. Heat transfer characteristics in a closed vessel are also discussed with combustion mechanisms.

The purpose of this study is to point out the dominant factor of heat and mass distribution in single cell of polymer electrolyte fuel cell (PEFC). The numerical simulation by simple 3D model of PEFC has been investigated to clarify the influence of cell components structure on heat and mass transfer phenomena in PEFC. In addition, the power generation experiment and the measurement of in-plane temperature distribution by thermograph were carried out. From the simulation results, the gas channel pitch of separator was the key factor to unify in-plane distribution of temperature and gas concentration on the reaction surface. The compression of gas diffusion layer (GDL) by cell binding caused wider distribution of mass concentration in GDL. According to the experimental results, the power generation performance was promoted with the decrease in gas channel pitch irrespective of relative humidity of supply gas. In addition, the temperature range in observation area was lower with the decrease in gas channel pitch.

In the present study, an immersed-boundary method is adopted to simulate natural and forced convection within a domain with complex geometry. The method is based on the direct momentum and energy forcing on a Cartesian grid and issues involving implementation of both the thermal (Dirichlet and Neumann) and dynamic (stationary and nonstationary) boundary conditions are addressed. The second order accuracy of the present method was validated based on natural convection in an annulus between horizontal concentric cylinders. Simulations of flow over a stationary cylinder with heat convection were further conducted to validate the capability of present technique for both temperature boundary conditions. Finally, the influence of the lock-on phenomenon in heat transfer is investigated for flow over a transversely oscillating cylinder. All computed results are in generally good agreement with previous experimental measurements and numerical simulations.

To investigate the thermal behavior during fast hydrogen filling process, the simple one-dimensional analysis considering the heat conduction in tank wall and the three-dimensional numerical simulation dealing with inner gas region were carried out. The numerical analyses were subject to the fast filling test of 35 MPa hydrogen gas into 34 litter tank for 80 seconds. The one-dimensional analysis predicted the temperature rise and the heat loss into surrounding air qualitatively and the averaged temperature of tank wall was underestimated. On the other hand, the three-dimensional simulation overestimated the temperature distribution because of using adiabatic wall condition. However, the effects of buoyant force and convective flow on local thermal profile were fully explained from our numerical results.

The plate-pin fin heat sink (PPFHS) is composed of a plate fin heat sink (PFHS) and some pin fins planted between the flow channels. In this paper, a numerical investigation was performed to compare the thermal and hydraulic performances of the PPFHSs and PFHS. PPFHSs with five forms of pin cross-section profiles (square, circular, elliptic, NACA 0050, and dropform) were numerically simulated. The influence of pin fin cross-section profile on the flow and heat transfer characteristics was presented by means of Nusselt number and pressure drop. It is found that the Nu number of a PPFHS is at least 35% higher than that of a PFHS used to construct the PPFHS at the same Reynolds number. Planting circular and square pins into the flow channel of heat sinks enhances the heat transfer at the expense of high pressure loss. Using the streamline shaped pins, not only the pressure drop of the compound heat sinks could be decreased considerably, the heat transfer enhancement also makes a step forward. The present numerical simulation provides original information of the influence of different pin-fin cross-section profiles on the thermal and hydraulic performance of the new type compound heat sink, which is helpful in the design of heat sinks.

A steady-state two dimensional numerical simulation was carried out to optimize the heat transfer rate density from cylinders under different conditions. The geometric design of the cylinders was varied in two ways. In the first case the cylinders are located on a plane where their leading edges are aligned, and in the second case the cylinders are aligned on a plane which passes through their respective centre-lines. The rotation of the cylinders is within the range of 0 ≤ ω˜ ≤ 1, and the dimensionless pressure drop number, Be, which drives the flow is in the range of 10 ≤ Be ≤ 10 4 . The continuity, momentum and energy equations describing the flow of the coolant, across the cylinders in the computational domain are performed using a computational fluid dynamics code, the results obtained were validated by comparing it with past results in the open literature for stationary cylinders. The effects of the various parameters (dimensionless pressure drop number, rotation) on the maximum heat transfer rate density from the cylinders in terms of augmentation and the suppression were analysed and reported.

This paper is concerned with the direct energy conversion of waste heat into electricity using pyroelectric materials. It reports detailed numerical simulations of a prototypical pyroelectric energy converter assembled experimentally and previously reported. The device consisted of a hot and cold source separated by a series of microchannels supporting pyroelectric thin films. A piston was used to vertically oscillate a working fluid back and forth between the thermal sources. The experimental device was fully instrumented with thermocouples and pressure sensor. The transient two-dimensional mass, momentum, and energy equations were solved numerically to determine the local and time-dependent temperature at various locations inside the device for operating frequency varying from 0.025 to 0.061 Hz. Excellent agreement was found between the simulated and experimentally measured local temperatures at all operating frequencies considered. These results confirm our previous numerical results and the simulation tool can now be used to design the next generation of pyroelectric energy converters.

The instability of cylindrically expanding premixed flames with radiative heat loss was studied by two-dimensional unsteady calculations of reactive gases, based on the diffusive-thermal model equation. When the Lewis number was unity, instability phenomena were not observed. When the Lewis number was sufficiently low, on the other hand, cellular-shaped fronts on adiabatic and non-adiabatic cylindrical flames were observed, which was due to diffusive-thermal instability. As radiative heat loss increased, the behavior of cellular fronts became more unstable. This indicated that the radiation promoted the unstable behavior of flame fronts at low Lewis numbers. When radiative heat loss was much large compared with the quenching condition of a planar flame, cylindrical flames were broken up and several small flames appeared. This was in qualitative agreement with the experimental results on the dynamic behavior of lean hydrogen-air premixed flames with radiative heat loss under the low gravity condition. Several small flames appeared on the grounds that large curvature of flame fronts was necessary to keep high temperature against radiative heat loss.

Key challenges to the acceptance of Polymer Electrolyte Membrane Fuel Cells (PEMFCs) for automobiles are the cost reduction and its improvement in power density for compactness. In order to get the solutions for these issues, further improvement in the cell performance is required with high current density operation. In this study, the impacts of heat and water transport on the cell performance under high current density were investigated by experimental evaluation of liquid water distribution and numerical validation. Liquid water distribution in-plane direction was evaluated by neutron radiography. Furthermore, electrochemical reaction distribution was also evaluated by using inserted metal wires at anode, and then the experimental results were qualitatively validated by the numerical model. The experimental and numerical validation results revealed that significant increase in mass and ohmic loss was induced by temperature, liquid water, and electrochemical reaction distribution in-plane direction.

Heat and Fluid flow through infinite porous media is numerically studied. The pore structure considered is body-centered cubic (BCC) and face-centered cubic (FCC) whose porosity is ranged 0.93–0.98 by changing the pore diameter. For the thermal condition, a constant heat flux from the porous wall is considered. The heat and fluid flow simulations are carried out separately by the lattice Boltzmann method (LBM). It is confirmed that the LBM can simulate them properly and the permeability depends on the pore structure compared at the same porosity. The heat transfer coefficient is found to be affected not only by the permeability but also the pore structure. That is, even at the same permeability, the Nusselt number depends on the structure.

For further improvement of PEMFC (Proton Exchange Membrane Fuel Cell) performance, an optimal design based not only on empirical knowledge but also systematic physical laws and numerical simulation is desirable. However, even basic parameters such as mass transport and thermal characteristics through layers are not completely clear. A GDL (Gas Diffusion Layer) is one of the key components of PEMFC, and its property strongly affects the temperature distribution, diffusion limitation, and flooding. Thus, we measured the diffusivity and thermal conductivity inside a GDL and at its surface boundaries. Anisotropic diffusivity was observed inside the GDL. The measured diffusivities inside the GDL were 59% lower than the value without a GDL in the thickness direction and 25% lower in plane direction. The measured diffusive resistance at the GDL surface was not considerably different from that achieved through conventional laminar analysis, although some special effects would have been observed at the GDL surface because of its high porosity. Regarding the thermal characteristics, the contact resistance at the GDL surface was measured to be as large as the resistance inside the GDL. However, the contact resistance became extremely small when the GDL contained water.

Precise temperature control of 0.001°C under noise-temperature change of 0.1°C is required in semiconductor manufacturing process. We made an experimental apparatus of a vertical steel plate placed in an atmosphere with a varying noise-heat-generation and a control-heater. The noise-heat-generation is that the heating-OFF and ON every 300 s, and it makes temperature change of 3°C at an object position in the plate without control. The control-heater is controlled with the model predictive control method of 5 s interval with two monitoring temperatures to minimize temperature change at the object position in the plate. In this work, we study the effect of the dynamic predictive model on the temperature change at the object position and examine how to make the best dynamic predictive model. Three methods to make the dynamic predictive model are examined: (1) dynamic step responses are obtained by experiment, (2) dynamic step responses are obtained by calculation with a network model of the object, and (3) both step response patterns are combined. When the step response patterns obtained by experiment and calculation are combined to use, the minimum temperature change at the object position is 0.06°C and 1/50 times smaller than that without control. Also, the effect of artificial error in the dynamic predictive model on temperature change at the object position is examined by numerical simulation.

Numerical simulations of the flow field and heat transfer of squealer blade tip are performed in this study. The effect of Reynolds number (Re = 10000–40000), the clearance gap to width ratios (C/W = 5%–15%) and the cavity depth to width ratios (D/W = 10%, 20% and 50%) on fluid flow and heat transfer characteristics are obtained. The temperature and velocity distributions inside the cavity, the local heat transfer coefficients, and the average Nusselt numbers for the pressure and suction sides of the turbine blade tip are determined. This paper presents the results of the effects of Reynolds number, clearance gap and width ratios on the Nusslet number for the pressure and suction sides of squealer turbine blade tip. The results show a good agreement with the experimental data obtained by Metzger and Bunker. New correlations for the average Nusselt numbers for turbine blade tip pressure and suction sides are presented.

Importance of turbulence and radiation interaction (TRI) has been investigated in a turbulent channel flow by using direct numerical simulation (DNS) to clarify detailed turbulent flow structure and heat transfer mechanisms. To investigate the effect of correlation functions between gas absorption and temperature fluctuation, the two cases of correlation are tested. Consequently, the TRI effect can be clearly observed when the correlation is positive. This fact provides the evidence that radiative intensity is enhanced by the turbulent fluctuation. The DNS results suggest the significance in the fundamental aspect of TRI. Furthermore, effects of frictional Reynolds number, Re τ , are investigated. Comparing with the case of Re τ = 150, the location of the enhancement peaks of Re τ = 300 shifts toward the walls. It is found that the relative importance of the TRI correspond to the structure of temperature fluctuation intensity originated from the differences of the Re τ .

This study focuses on the clarification of the heat transfer characteristics of the subcooled pool boiling, the discussion on its mechanism, and finally the establishment of a boiling and condensation model for numerical simulation on the subcooled pool boiling phenomena. In this paper, the boiling and condensation model is improved by introducing the following models based on the quasi-thermal equilibrium hypothesis; (1) a modified phase-change model which consisted of the enthalpy method for the water-vapor system, (2) a relaxation time derived by considering unsteady heat conduction. Resulting from the numerical simulations on the subcooled pool boiling based on the MARS (Multi-interface Advection and Reconstruction Solver) with improved boiling and condensation model, the numerical results regarding the bubble growth process of the subcooled pool boiling show in good agreement with the experimental observation results and the existing analytical equations.