To examine soot and PAH formation processes for rich methane/air and acetylene/air mixtures, a micro flow reactor with a controlled temperature profile was employed. In the experiment for a methane/air mixture, four kinds of responses to the variations of flow velocity and equivalence ratio were observed as follows: soot formation without a flame; a flame with soot formation; a flame without soot formation; and neither flame nor soot formation. Soot formations were observed in low flow velocity and high equivalence ratio. Starting point of soot formation shifted to the upstream side, i.e., low-temperature side, of the micro flow reactor with the decrease of flow velocity. One-dimensional steady-state computation was conducted by a flame code. In high flow velocity, low mole fraction of C 2 H 2 and high mole fraction of OH were observed in the whole region of the micro flow reactor. Soot volume fraction did not increase in this case. On the other hand, in low flow velocity, high mole fraction of C 2 H 2 and low mole fraction of OH were observed at the downstream side of the micro flow reactor. Soot volume fraction increased in this case. Since significant soot formation was observed at the low flow velocity and the high equivalence ratio, experiments with gas sampling were conducted for acetylene/air mixture to investigate temperature and equivalence ratio dependence of soot precursor production in such condition. Volume fractions of benzene increased with an increase of temperature. They were larger at higher equivalence ratio at the same temperature. Volume fractions of styrene increased with an increase of temperature. They were larger at higher equivalence ratio when the temperature is less than 1000 K. However the tendency was changed at 1000 K, styrene volume fraction at equivalence ratio of 7.0 was larger than that at equivalence ratio of 8.0.

A numerical investigation of laminar natural convection heat transfer from small horizontal wires at near-critical pressures has been carried out with carbon dioxide as the test fluid. The parameters varied are: (i) Pressure ( P ): 7.50–9.60 MPa, (ii) Bulk fluid temperature ( T b ): 5–50°C, (iii) Wall temperature (T w ): 5.1–200°C, and (iv) Wire diameter ( D ): 25.4, 76.2 and 100 μm. The steady-state Navier-Stokes equations (low Mach number asymptotic form) are solved with variable properties. The results of the numerical simulations agree reasonably well with available experimental data. The dependence of heat transfer coefficient ( h ) on P , T b , T w and D were investigated. The results obtained are as follows: (i) For given P and D , h is strongly dependent on T b and T w . (ii) The heat transfer coefficient decreases with increasing values of P ( P/P c > 1). (i) For fixed P , T w and T b , the dependence of h on D varies from h ∝ D −0.47 to h ∝ D −0.29 as D increases. (iii) For a given P , the maximum heat transfer coefficient is obtained for conditions where T b < T pc < T w , where T pc denotes the pseudocritical temperature. Based on the analysis of the temperature and flow field once can qualitatively show that this peak in h when k , C p and Pr in the fluid peak close to the heated surface.

The lower limit for the occurrence of homogeneous nucleation boiling explosion during water heating at atmospheric pressure has been determined by applying a new theoretical model proposed by the authors. Two different cases of liquid heating have been considered for the study of homogeneous nucleation boiling explosion. In one case, the liquid on the surface is linearly heated at a rate of 10 K/s to 10 9 K/s. In another case, the liquid suddenly contacts with a high temperature surface such as in case of quenching with jet impingement or droplet. For the linear boundary heating case, the liquid temperature limit at which homogeneous boiling explosion occurs without any cavity or surface effect, essentially corresponds to a value of 302 °C even though the surface is heated very slowly. On the other hand, during water contact with hot surfaces, the occurrence of the homogeneous boiling explosion within a characteristic time period of 1 millisecond is obtained at a maximum liquid temperature of 303 °C for a limiting steady state boundary temperature of about 304 °C. From the definition of the steady-state interface boundary temperature of two 1-D semi-infinite body contact, the lower limiting surface temperatures for the occurrence of the homogeneous nucleation boiling explosion have been determined for water contact with various solid surfaces with different liquid initial temperatures ranging from 0 °C to 100 °C. The effects of the parametric variation in the boundary heating conditions on various characteristics of the homogeneous boiling explosion such as liquid temperature and time of boiling explosion, heat-flux across the liquid-vapor interface at the boiling explosion etc. are also determined and discussed in context with other results available in the literature.

Accurate CFD simulation of full vehicle enables vehicle development specialists to gain access to detailed flow and temperature field for the entire vehicle and for arbitrary driving conditions. Information of that nature is invaluable to vehicle development and design since it leads to detailed understanding of the problem areas and pointers to how the design and performance can be improved from the thermal management perspective. Presented are simulations of the vehicle Renault Scenic II cruising at 60 kilometers per hour using PowerFLOW. The simulations were performed using a coupling between the flow solver PowerFLOW and the thermal simulation package PowerTHERM that accounts for conduction and radiation effects. The simulation results were compared with the test data for steady state forced convection case. In order to gauge the accuracy of the simulations, extensive validations were made with thermocouple data and flow measurements. Good agreement was observed between the simulation results and the measurements.

Direct Chill (DC) casting is a semi-continuous casting technique which is used to produce aluminum rolling ingots and extrusion billets. The knowledge of temperature field is highly essential for the prediction of displacement field and hot tears. Modeling the thermal field of DC casting is a challenging task due to the liquid-solid phase transition, time-dependent domain and boundary conditions, inverse nature of secondary boundary conditions, etc. Therefore, an attempt is made to model the thermal field of DC casting using a finite element method. A temperature-based finite element model is used to capture the effect of latent heat release. A temperature-dependent heat transfer coefficient is employed to incorporate the bottom block and mold boundaries. The influence of casting speed is studied in detail. Through the proper ramping procedures, it is proved that the start-up phase sump depth and mushy length can be lowered. However, it is found that the steady-state sump parameters are independent of ramping. Further, the influences of secondary cooling profile, and melt superheat are investigated. AA1201 alloy is considered for the study.

A novel modified 3ω thermal conductivity measurement technique called metal coated 3ω is introduced for use with liquids, gases, and powders. This technique employs a micron-scale metal coated glass fiber. Metal coated 3ω exceeds alternate 3ω based fluid sensing techniques in a number of key metrics including fraction of heat generated entering fluid, signal strength per temperature oscillation intensity and thermal boundary sensitivity. The advantages of this technique to Transient Hot-Wire (THW) and steady-state techniques are also discussed. A generalized n-layer concentric cylindrical periodic heating solution that accounts for thermal boundary resistance is presented. The technique is validated through a benchmark study of gases and liquids.

Film cooling performance of two hole geometries is evaluated on a flat plate surface with steady-state IR (infrared thermography) technique. The base geometry is a simple cylindrical hole design inclined at 30° from the surface with pitch-to-diameter ratio of 3.0. The second geometry is an anti-vortex design where the two side holes, also of the same diameter, branch out from the root at 15° angle. The pitch-to-diameter ratio is 6.0 between the main holes. The mainstream Reynolds number is 3110 based on the coolant hole diameter. Two secondary fluids — air and carbon-dioxide — were used to study the effects of coolant-to-mainstream density ratio (DR = 0.95 and 1.45) on film cooling effectiveness. Several blowing ratios in the range 0.5 –4.0 were investigated independently at the two density ratios. Results indicate significant improvement in effectiveness with anti-vortex holes compared to cylindrical holes at all the blowing ratios studied. At any given blowing ratio, the anti-vortex hole design uses 50% less coolant and provides at least 30–40% higher cooling effectiveness. The use of relatively dense secondary fluid improves effectiveness immediately downstream of the anti-vortex holes but leads to poor performance downstream.

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.

Both traditional discretization-based numerical methods and alternative hybrid analytical-numerical techniques have been successfully applied for solving a considerable number of convective heat transfer problems. Despite the number of studies dedicated to separately solving a given problem by one methodology or the other, there are very few studies dedicated to comparing the computational solution performance of these approaches. In this context, this paper presents a comparison of solutions using the Finite Volumes Method (FVM) and the Generalized Integral Transform Technique (GITT) for a three dimensional steady-state convective heat transfer problem. The selected problem is that of thermally developing laminar flow within a square duct. The flow is considered kinetically developed and a constant wall temperature condition is employed. Both solutions are computationally implemented using the Mathematica system and, in order to guarantee a fair comparison, both implementations employ the same numerical ODE integrator to handle the solution in the flow direction. The comparisons are made by observing the convergence behavior of the Nusselt number for different positions along the flow direction, for both methodologies. In addition to these comparisons, combined solution strategies are analyzed, in which the velocity is obtained by one methodology and the temperature by the other.

The reduction of interfacial resistance continues to be a significant challenge in thermal management of semiconductor and other microscale devices. Current state-of-the-art thermal interface materials (TIMs) have resistances in the range of 5–10 mm 2 ·K/W. At these values, particularly for the emerging highly nonhomogeneous materials, standard measurement techniques often fail to provide accurate results. This paper describes the use of infrared microscopy for measuring the total thermal resistance across multiple interfaces. The method is capable of measuring samples of wide ranging resistances with thicknesses ranging from 50–250 μm. This steady-state technique has several advantages over other methods, including the elimination of the need for intrusive temperature monitoring devices like thermocouples at the area of interest and the need for a priori knowledge of the specific heat and density of the materials of interest, as in the transient techniques for determining thermal resistances. Results for three different commercially available TIM and uncertainty analysis are presented.

A mathematical model of lime calcination process in normal shafts kiln has been developed to determine the heat and mass transfer between the gas and the solid. The model is one-dimensional and steady state. The transport of mass and energy of the gas and the solid is modeled by a system of ordinary differential equations. A shrinking core approach is employed for the mechanics and chemical reactions of the solid material. The model can be used to predict the temperature profiles of the particle bed, the gas phase along the length of kiln axis. The calcination behavior of the particle bed can be also investigated. The influences of operational parameters such as: energy input, the origin of feed limestone and the lime throughput on the kiln performance including pressure drop are considered. Additionally, the local heat loss through the kiln wall is studied. The results of this study are direct utility for optimization and design of large-scale technical shaft kilns.

This work utilizes a novel, generic, thermal model of an electric machine in conjunction with particle swarm optimization to optimize the electric machine’s fin array considering time varying loads. The maximum power rating on radial-flux electrical machines is typically based on the steady state temperature of the windings. This leads to over designs in applications in which only short periods of high power are required. The proposed optimization technique can be used in the design process to reduce the risk of over design therefore leading to reduced material costs for finned frames and increased power density in radial flux machines. Whilst many numerical optimization techniques exist, this paper will consider the application of particle swarm optimization techniques to optimize the fin array parameters. The parameter space to be investigated will consider the fin height (h f ), fin width (w f ), and fin spacing (s f ).

Numerical modeling of methane-steam reforming is performed in a microchannel with heat input through Palladium-deposited channel walls corresponding to the experimental setup of Eilers [1]. The low-Mach number, variable density Navier-Stokes equations together with multicomponent reactions are solved using a parallel numerical framework. Methane-steam reforming is modeled by three reduced-order reactions occurring on the reactor walls. The surface reactions in the presence of Palladium catalyst are modeled as Neumann boundary conditions to the governing equations. Use of microchannels with deposited layer of Palladium catalyst gives rise to a non-uniform distribution of active reaction sites. The surface reaction rates, based on Arrhenius type model and obtained from literature on packed-bed reactors, are modified by a correction factor to account for these effects. The reaction-rate correction factor is obtained by making use of the experimental data for specific flow conditions. The modified reaction rates are then used to predict hydrogen production in a microchannel configuration at different flow rates and results are validated to show good agreement. It is found that the endothermic reactions occurring on the catalyst surface dominate the exothermic water-gas-shift reaction. It is also observed that the methane-to-steam conversion occurs rapidly in the first half of the mircochannel. A simple one-dimensional model solving steady state species mass fraction, energy, and overall conservation of mass equations is developed and verified against the full DNS study to show good agreement.

Thermal storage is advocated as a means for energy storage in some grid-scale electric powerplants, such as for concentrating solar power (CSP). The efficiency of concentrating solar thermal collectors, however, decreases with increasing output temperature, making it difficult to achieve high thermal storage temperatures. A heat pump, as is well known, can operate in either cooling mode or heating mode, and in either case, the coefficient of performance is generally greater than one, enabling a multiplier effect that can serve to either increase or decrease the temperature of thermal storage. A simple steady-state analysis of the “round-trip” system efficiency for storing energy reveals the potential benefits of utilizing a heat pump or refrigerator in such systems. Provided that an inexpensive heat input source is available, the system storage efficiency can reach or even exceed unity, assuming that the energy supplied to the system as heat is neglected. For ice storage at 0 °C, increasing thermal input temperatures above 209 °C increases the system storage efficiency above unity.

A high temperature guarded-comparative-longitudinal heat flow measurement system has been built to measure the thermal conductivity of a composite nuclear fuel compact. It is a steady-state measurement device designed to operate over a temperature range of 300 K to 1200 K. No existing apparatus is currently available for obtaining the thermal conductivity of the composite fuel in a non-destructive manner due to the compact’s unique geometry and composite nature. The current system design has been adapted from ASTM E 1225. As a way to simplify the design and operation of the system, it uses a unique radiative heat sink to conduct heat away from the sample column. A finite element analysis was performed on the measurement system to analyze the associated error for various operating conditions. Optimal operational conditions have been discovered through this analysis and results are presented. Several materials have been measured by the system and results are presented for stainless steel 304, inconel 625, and 99.95% pure iron covering a range of thermal conductivities of 10 W/m*K to 70 W/m*K. A comparison of the results has been made to data from existing literature.

This study aims to clarify the adsorption / desorption behavior of water vapor onto / from a desiccant rotor in temperature swing. A magnetic suspension balance followed time variations of the weight of a small piece of desiccant rotor at various desorption temperature, adsorption / desorption time and their duration time ratio. Adsorption-desorption swing in steady state settled down at certain amplitude of the amount adsorbed keeping the balance of the adsorption and desorption rates averaged over each period. At low regeneration temperature around 40–50°C, adsorption and desorption rates were affected considerably by the change of driving force of adsorption q*-q rather than the temperature dependence of the mass transfer coefficient. At constant adsorption and desorption air conditions, the adsorption /desorption rates could be summarized by the amount of adsorption and temperature, independently of the length of cycle time. Also, region of the amount of adsorption at which adsorption–desorption swing occurred was predicted considering the adsorption / desorption rates – amount adsorbed relationship and the adsorption / desorption duration ratio.