Design methods for thermal systems with predominant radiation are given, followed by applications of these methods to idealized but practical engineering systems. It is argued that such designs in general present inverse mathematical problems, in that an outcome (the desired output of the systems) is prescribed, and the necessary inputs (geometry, heater placement, heater power distribution) are to be found that will achieve the desired output. Such inverse problems require some methods for handling their ill-conditioned nature. Two general techniques are discussed: Regularization methods, which remove or ameliorate the ill-conditioned portion of the problem at the expense of some degree of accuracy; and optimization methods, which replace the ill-conditioned problem with a well-posed problem that must be solved repetitively through a systematic approach to a useful solution. Applications of both methods to a variety of radiative transfer problems are discussed and demonstrated, including problems in which heater power is determined, problems in which the geometry of the enclosure must be determined, and problems with a prescribed transient power distribution on the processed material that must be provided by the heaters. Problems with conduction and/or convection in addition to radiation are also discussed, as are problems with specularly reflecting surfaces, participating media between the heaters and the processed materials, and enclosures with complex geometries.
This paper reviews recent advances in enhancing boiling heat transfer from electronic components immersed in dielectric liquids by use of surface microstructures. The microstructures developed include rough surfaces produced by sanding, vapor blasting hard particles, sputtering of SiO2 followed by wet etching of the surface, chemical vapor deposition of SiO2 film etc., laser-drilled cavities, a brush-like structure (dendritic structure), reentrant and micro-reentrant cavities, microfins, and porous structures fabricated by alumina particle spraying and painting of silver flakes, diamond particles, aluminum particles and copper particles. Heat sink studs with drilled holes, microfins, multi-layered micro-channels and pores, and pin fins with and without microporous coating have also been developed. The height of microstructure ranges from 0 to 12mm. The primary issues discussed are the mitigation of temperature overshoot at boiling incipience, enhancement of nucleate boiling heat transfer and increasing the critical heat flux.
Recent advancement in industrial furnaces brought by highly preheated air combustion is reviewed. Highly Preheated Air Combustion in regenerative furnaces has been paid much attention for its accomplishment in not only energy saving but also low nitric oxides emission. Characteristics of combustion with highly preheated air were studied to understand the change of combustion regime and the reason for the compatibility between high performance and low nitric oxides emission. It was found that combustion was sustained even in an extremely low concentration of oxygen if the temperature of oxidizer was higher than the auto-ignition temperature of the fuel. As an application of the principle, we can reduce nitric oxides emission by dilution of combustion air with plenty of recirculated burned gas in the furnace. Dilution makes the oxygen content of the oxidizer low, which decreases temperature fluctuations in flames as well as the mean temperature, hence low nitric oxides emission. Finally, the applicability of highly preheated air combustion to other fields than industrial furnaces has been discussed.
Surface microstates of real surfaces of solid materials change in industrial environments, or they are changed in industrial surface processes positively. A real time diagnosis technique for the surface microstates should be developed for the process control. We propose a diagnosis technique for temperature and microstructure of real surfaces on a basis of the hardware performance of our wide-spectral-range high-speed spectrophotometer system. With respect to the temperature, an active spectral pyrometer technique is adopted, in which the reflection of the surface is measured as well as the self-emission. With respect to the microstructure, an attention is paid to the interference and diffraction of radiation in a new real surface model. An experiment is made on a metal surface in a high-temperature oxidation process to verify the performance of this technique. Spectra of emission and reflection energy of radiation in a near-infrared through infrared region are measured at every 2s, and analyzed. Time transition of the surface temperature of an order of 1100K is estimated within an inaccuracy of 10K. The average thickness d and rms roughness σI of the surface film are estimated to be in regions of d=0.08∼3.8µm and σI=0.01∼0.71µm, respectively.
A prototype version of a knowledge database on thermal control in manufacturing processes, specifically, molding, semiconductor manufacturing, and micro-scale manufacturing has been developed. The knowledge database has search functions for technical data, evaluated benchmark data, academic papers, and patents. The database also displays trends and future roadmaps for research topics. It has quick-calculation functions for basic design. This paper summarizes present research topics and future research on thermal control in manufacturing engineering to collate the information to the knowledge database. In the molding process, the initial mold and melt temperatures are very important parameters. In addition, thermal control is related to many semiconductor processes, and the main parameter is temperature variation in wafers. Accurate in-situ temperature measurment of wafers is important. And many technologies are being developed to manufacture micro-structures. Accordingly, the knowledge database will help further advance these technologies.
In this paper a new form of the pseudo-spectral method is presented. The method is theoretically simple yet robust enough to produce very accurate solutions to hyperbolic and parabolic PDE's while avoiding the effects of Gibb's phenomenon. Moreover the method uses a relatively small amount of computational memory. The method is based on the observation that an analytical function may be well represented in a set of small neighborhoods that share common boundaries, called sub-domains, by low order Chebyshev polynomials. A collocation solution scheme is used in each sub-domain to march facilitate a time. Throughout this process the Chebyshev expansion coefficients of the highest order terms are monitored. If these coefficients grow beyond a specified small size, the new sub-domains are then redefined so that the function is again well represented by Chebyshev polynomial expansions. An approach for the determination of computational sub-domains of the physical domain for the special case of a discontinuous function is discussed. The strategy for solving the PDE's is presented. The method is then applied to Fourier and non-Fourier heat conduction problems.
Flashover is a phenomenon describing a room fire changed from the growth stage to the development stage. There is a rapid increase in size and intensity. The radiant heat flux back to the fuel surface and the floor of the room is known to be one of the key parameters leading to flashover. Indeed, a heat flux (largely due to radiation) of 20kW/m2 to the room floor is often taken to be the condition of flashover. To understand the importance of radiation, a zone model is developed to simulate the transient fire growth in a compartment. Heat and mass transfer correlations available in the literature are used to simulate the non-radiative effect. A three-dimensional non-gray soot radiation model is used to simulate the radiative exchange between the fuel surface, the hot gas/particulate layer and the surrounding wall. Results show that the hot layer temperature alone may not be an effective indicator for flashover. Other parameters such as particulate volume fraction in the hot layer, venting area and heat transfer to the surrounding wall are also important in determining the occurrence of flashover.
Using the fully developed laminar velocity distributions obtained by applying the modified power-law model proposed by Irvine and Karni, the thermal-entrance-region heat transfer of non-Newtonian fluids flowing in parallel plates with one plate moving is investigated taking into account both viscous dissipation and fluid axial heat conduction for two kinds of thermal boundary conditions, namely, constant temperature and constant heat flux at the moving wall. The energy equation subject to a constant temperature at upstream infinity, fully developed temperature profile at downstream infinity and the appropriate thermal boundary conditions at the upper and lower walls is numerically solved by the finite difference method as an elliptic type problem. The effects of the moving plate velocity, rheological properties, Brinkman number and Peclet number on the temperature distribution and Nusselt numbers are discussed for both Newtonian and pseudoplastic fluids.
There is an optimum condition on water electrolysis efficiency due to the effects of generated bubbles between electrodes. In this paper, in order to explain the existence of the optimum condition, a model of alkaline water electrolysis was established. The model can express void fraction and current density profiles along electrodes, and show the existence of the optimum condition. For verification of this model, rising velocity, diameter distribution of bubbles between electrodes and current density profiles along electrodes were measured during water electrolysis of KOH solution. Two-phase flows between electrodes were observed by a still camera and a digital video camera. The results showed that bubble rising velocity ranges from 4-24cm/s and becomes larger as current density increases. Bubble diameter ranges from 0.01-0.8mm, where average diameter becomes large as current density increases. Obtained results showed the sound validity of present model.
This study is concerned with the discrepancies between the results of experimental measurements and molecular dynamics(MD) studies on the condensation coefficient of water. We consider that the presence of a noncondensing gas may increase the interface resistance and reduce the experimental condensation coefficient. One-dimensional condensing flow of water vapor has been analyzed by the direct simulation Monte Carlo(DSMC) method in the presence of a noncondensing gas. The results show that the condensing flow causes an accumulation of the noncondensing gas in the vicinity of the liquid surface that increases resistance and reduces condensation heat transfer rate. Even if the concentration of the noncondensing gas is low in the bulk phase, the noncondensing gas accumulates at high concentrations at the interface. This indicates the possibility that the low experimental condensation coefficients may be due to the existence of noncondensable gases.
The detailed knowledge of air flow structures as well as particle transport and deposition in the human lung for typical inhalation flow rates is an important precursor for dosimetry-and-health-effect studies of toxic particles as well as for targeted drug delivery of therapeutic aerosols. Focusing on highly toxic JP-8 fuel aerosols, 3-D airflow and fluid-particle thermodynamics in a human upper airway model starting from mouth to Generation G3 (G0 is the trachea) are simulated using a user-enhanced and experimentally validated finite-volume code. The temperature distributions and their effects on airflow structures, fuel vapor deposition and droplet motion/evaporation are discussed. The computational results show that the thermal effect on vapor deposition is minor, but it may greatly affect droplet deposition in human airways.
A numerical study has been performed to analyze the working principle of refrigeration in basic pulse tube refrigerator. There is a mechanism called “surface heat pumping” as one of the working principles of refrigeration for basic pulse tube refrigerator of the first generation. This is the mechanism that heat is pumped from the cold end to the hot end by the successive heat exchange between the pulse tube wall and the working gas. Transient axisymmetric two-dimensional equations of continuity, momentum and energy were solved by means of TVD scheme. The transient behaviors of pressure and gas temperature, and heat transfer from the working gas to the tube wall are analyzed. Also the behavior of surface heat pumping is explained by analyzing the axial movements and temperature changes of gas particles.
Super-adiabatic combustion engine proposed here has a high thermal efficiency of 57.5% over a wide range of operation conditions. The engine consists of a displacer piston, a power piston and a porous medium in a cylinder. These create reciprocating motions with a phase relation angle. After scavenging, a mixture introduced is compressed by the displacer piston and preheated by the porous medium, and then, ignited in the vicinity of the downstream end of the porous medium. The main reaction occurs in the power piston side cylinder. By the heat recirculation from the residual combustion-gas enthalpy to the enthalpy increase in the mixture, the maximum temperature becomes higher than the theoretical (adiabatic) flame temperature. As a result, the system has such a high thermal efficiency and extends the flammability limit to a concentration of 1.58vol.% methane in air.
Novel developments in the numerical simulation of diffusion limited dendritic growth are discussed in the context of two-dimensional simulations of solidification of pure substances and of binary alloys. The three most important numerical difficulties encountered in the simulations of dendritic growth of binary alloys are discussed: 1) the need to accurately calculate the position and velocity of the interface as part of the solution; 2) the disparity of length scales between the thermal diffusion length and the solute diffusion length; and 3) the instability of the solid-liquid interface, particularly at high concentrations of solute. Dealing with the third difficulty constitutes the main objective of this paper. The stability of calculations is studied using the continuity condition on the heat flux across the interface and numerical simulations. The latter are used to assess the current modeling capabilities and the hurdles faced to produce more powerful simulators.
Ratcheting electrophoresis microchip (REM) is a novel concept of a microfluidic device proposed by the authors for the electrophoretic separation of macromolecules such as DNA and proteins in aqueous solution. In the present report, a new type of REM is proposed. The first prototype of the REM, which consists of a microchannel and an array of thousands of parallel linear microelectrodes with a width of ∼2µm and a pitch of ∼10µm embedded in the wall of the microchannel, has some problems: dispersion of analyte molecules is large when they leave the surface of the electrodes in the direction parallel to the surface, and the small width of the microelectrodes that are needed to minimize the dispersion of molecules makes the chip susceptible to the Debye screening. To solve these problems, the crosswise migration type is proposed here, where electrophoretic migration is driven as crossing the microchannel, which results in minimized dispersion of analyte molecules and effective electric field over the whole channel that is free from the Debye screening. Computational simulation has been performed and satisfactory results were obtained.
This paper describes a new numerical method for computing the motion of a toroidal bubble that is formed after a liquid microjet threads the bubble surface. We used the boundary element method combined with the finite volume method to calculate the toroidal bubble dynamics with consideration of the heat transfer inside the bubble. The unstructured triangular grids were used to analyze the internal field. We investigated the bubble collapse near a plane rigid wall. The results show that the initial bubble radius affects the motion of the toroidal bubble, the temperature fields inside the bubble and the pressure fields outside the bubble. When the initial radius is small, the internal thermal boundary layer becomes thick and the bubble collapse is accelerated. This violent collapse induces an extremely high-pressure region near the point of liquid microjet impact. The pressure at a rigid wall, therefore, becomes locally very high when the tiny bubble collapses near the wall.
A special and effective aerodynamics calculation method has been applied for the flow field around a body of revolution to find the drag coefficient for a wide range of Reynolds numbers. The body profile is described by a first order continuous axial singularity distribution. The solution of the direct problem then gives the radius and inviscid velocity distribution. Viscous effects are considered by means of an integral boundary layer procedure, and for determination of the transition location the forced transition criterion is applied. By avoiding those profiles, which result in the separation of the boundary layer, the drag can be calculated at the end of the body by using Young's formula. In this study, a powerful optimization procedure known as a Genetic Algorithms (GA) is used for the first time in the shape optimization of airship hulls. GA represents a particular artificial intelligence technique for large spaces, striking a remarkable balance between exploration and exploitation of search space. This method could reach to minimum objective function through a better path, and also could minimize the drag coefficient faster for different Reynolds number regimes. It was found that GA is a powerful method for such multi-dimensional, multi-modal and nonlinear objective function.
Two-phase flow pattern data during horizontal in-tube flow boiling are presented for pure and mixed refrigerants of R134a and R123. The flow pattern is observed through tubular sight glasses located at inlet and outlet of the test section, which is made of a stainless steel tube, 2m long with 10mm I. D., 1.5mm wall thickness. The obtained results are compared to the available various correlations for flow pattern. The flow pattern map of Hashizume was very well agreement with the present data except the region of low mass velocity. Weisman flow pattern map was also known to satisfactorily predict data for refrigerants in the region of annular flow. In order to establish the transition quality to annular flow in this study, flow pattern are simply classified into two groups; stratified (including intermittent, stratified and stratified-wavy) flow and unstratified (annular) flow. The transition quality from stratified to unstratified flow was obtained by modifying the liquid Froude number.
Experiments with radiative ignition were performed in microgravity to elucidate the events arising during the ignition process in a quiescent field. Filter paper was irradiated by Diode laser light (800.1nm), which is little absorbed in the gas phase, at various oxygen concentrations (0-50%). The ignition delay was measured for various experimental conditions. The density changes of the gas phase before ignition was observed in detail by a Mach-Zehnder interferometer. The results showed that heat conduction from the sample surface induced a weak chemical reaction in the vicinity of the sample surface, and this propagated outward to achieve combustion. The ignition delay decreased with increases in O2 concentration because the mixture near the sample surface contained more oxygen causing an immediate transition from the weak chemical reactions to the strong reactions of the combustion.
The hydrogen combustion Stirling engine utilizes internal combustion of a stoichiometric H2 and O2 mixture injected into the working gas as thermal input, and the cyclic operation is completed with the removal of water from the engine after condensation at the cooler. In the prototype engine, a catalytic combustor is substituted for the conventional heater, and the H2-O2 mixture is injected at a constant flow rate from the boundary between the regenerator and the cooler. The engine internal heating characteristics were compared to those on external heating to clarify the internal heating effect on the engine performance. The internal heating performance showed almost the same characteristics as those of external heating, except for the increase of expansion work due to the direct thermal input. The increase of expansion work improved the engine performance, particularly in the region of high engine speed. Furthermore, it was found that the steady injection method was able to suppress the mixture strength to a relatively low level.
This paper covers our investigation into a decline in FC performance resulting from hydrogen fuel containing CO. Several investigations were conducted into the dependence of CO poisoning on types of catalyst using Pt and Pt-Ru alloy. The investigations are summarized as follows: 1) The poisoning prediction formulas and the poisoning estimation coefficient to predict and estimate the performance were derived theoretically. 2) The actual process of CO poisoning was scrutinized by focusing on adsorption of CO and desorption of CO2 molecules, and changes of several polarizations caused by CO poisoning were estimated. 3) Investigations into the relationship between the CO concentration, operating pressure, operating temperature and the CO poisoning were carried out. If the FC was operated at a high CO concentration, no significant improvement could be expected when using increased pressure, and further, the effects of the operating temperature is almost the same for the two types of catalyst.
The life cycle inventory (LCI) of the electric power generation plays a vital role on LCIs of the industrial products. However there are no formal life cycle assessment (LCA) studies in Indonesia so far due to limited number of LCA expertise and lack of sufficient databases relevant to domestic conditions. The objective of this study is to introduce life cycle assessment (LCA) method for Indonesian electric power generation systems and to establish LCI for electricity grid mix of Indonesia. In this paper, the emissions of CO2, SO2, NOx, CO, CH4, NMHC, N2O, Dust (SPM), Ni, As, Cd, Cr, Hg, Pb, Zn per kWh of electricity generated were estimated for the systems using a combined method of process analysis and input-output analysis. Additional analyses on the impacts of emerging and future technologies as well as the influences of changes of various assumptions are helpful for a better understanding. As the result, the LCA evaluations are discussed for further ecological improvement.