A k-Distribution-Based Spectral Module for Radiation Calculations in Multi-Phase Mixtures

k-distribution-based approaches are promising models for radiation calculations in strongly nongray participating media. Advanced k-distribution methods were found to achieve close-to benchmark line-by-line (LBL) accuracy for strongly inhomogeneous multi-phase media accompanied by several orders of magnitude smaller computational cost. In this paper, a k-distribution-based portable spectral module is developed, incorporating several state-of-the-art k-distribution methods along with compact and high-accuracy databases of k-distributions. The module construction is flexible — the user can choose among various k-distribution methods with their relevant k-distribution databases, to carry out accurate radiation calculations. The spectral module is portable, such that it can be coupled to any flow solver code with its own grid structure, discretization scheme, and solver libraries. This open source code module is made available for free for all noncommercial purposes. This article outlines in detail the design and the use of the spectral module. The k-distribution methods included in the module are briefly described with a discussion of their advantages, disadvantages and their domain of applicability. Examples are provided for various sample radiation calculations in multi-phase mixtures using the new spectral module and the results are compared with LBL calculations.

An Experimental Investigation of Microchannel Size Effects on Flow Boiling With De-Ionized Water

The heat transfer characteristics during flow boiling of deionized water in parallel microchannels are investigated. The silicon heat sinks contain an array of integrated heaters and diodes for localized heat-flux control and temperature measurement. The channel widths for the three different test pieces range from 250 μm to 2200 μm, with a nominal depth for all channels of 400 μm. The present study investigates the effects of the channel width and mass flux on the boiling performance. This study follows a previous study using a wetting dielectric liquid, and aims to understand the role of wetting since water is relatively non-wetting. From the results of the present study, a weak dependence of the boiling curve and heat transfer coefficient on mass flux was observed. Varying the channel width also does not have a strong effect on either the boiling curve or the heat transfer coefficient. The experimental results are compared to those obtained previously for a dielectric liquid. They are also compared with predictions from several correlations from the literature.

An Efficient Sparse Finite Element Solver for the Radiative Transfer Equation

The stationary monochromatic radiative transfer equation (RTE) is posed in five dimensions, with the intensity depending on both a position in a three-dimensional domain as well as a direction. For non-scattering radiative transfer, sparse finite elements [1, 2] have been shown to be an efficient discretization strategy if the intensity function is sufficiently smooth. Compared to the discrete ordinates method, they make it possible to significantly reduce the number of degrees of freedom N in the discretization with almost no loss of accuracy. However, using a direct solver to solve the resulting linear system requires O(N3) operations. In this paper, an efficient solver based on the conjugate gradient method (CG) with a subspace correction preconditioner is presented. Numerical experiments show that the linear system can be solved at computational costs that are nearly proportional to the number of degrees of freedom N in the discretization.

Low-Profile Chipset Microprocessor Heatsink Optimization for Server Form Factor

We present a methodology for optimizing footprint, metal mass and thermal performance of an aluminum extruded heatsink for cooling chipset microprocessors in server form-factor. The analysis is based on predefined volume flow rate of air at a constant temperature assumed to be available upstream of the package. The front-to-back cooling assumption covers the worst case ambient conditions, typical of chipset boundary condition in servers. We present studies covering a range of heatsink footprints in order to compare and minimize the heatsink footprint, at the same time satisfying thermal specification of the chipset microprocessor. The study also focuses on the system-level assessment of the optimum 60×40 mm2 footprint and corner cases by studying the effect of motherboard thermal conductivity as well as blockages on the heatsink case-to-ambient thermal resistance.

A Numerical Study on the Slab Heating Characteristics in a Reheating Furnace With the Formation and Growth of Scale on the Slab Surface

In this work, the development of a mathematical heat transfer model for a walking-beam type reheating furnace is described and preliminary model predictions are presented. The model can predict the heat flux distribution within the furnace and the temperature distribution in the slab throughout the reheating furnace process by considering the heat exchange between the slab and its surroundings, including the radiant heat transfer among the slabs, the skids, the hot combustion gases and the furnace wall as well as the gas convection heat transfer in the furnace. In addition, present model is designed to be able to predict the formation and growth of the scale layer on the slab in order to investigate its effect on the slab heating. A comparison is made between the predictions of the present model and the data from an in situ measurement in the furnace, and a reasonable agreement is found. The results of the present simulation show that the effect of the scale layer on the slab heating is considerable.

An Angular Finite Element Method for the Solution of the Even-Parity Equation

The present article introduces a new method to solve the radiative transfer equation (RTE). First, a finite element discretization of the solid angle dependence is derived, wherein the coefficients of the finite element approximation are functions of the spatial coordinates. The angular basis functions are defined according to finite element principles on subdivisions of the octahedron. In a second step, these spatially dependent coefficients are discretized by spatial finite elements. This approach is very attractive, since it provides a concise derivation for approximations of the angular dependence with an arbitrary number of angular nodes. In addition, the usage of high-order angular basis functions is straightforward. In the current paper the governing equations are first derived independently of the actual angular approximation. Then, the design principles for the angular mesh are discussed and the parameterization of the piecewise angular basis functions is derived. In the following, the method is applied to two-dimensional test cases which are commonly used for the validation of approximation methods of the RTE. The results reveal that the proposed method is a promising alternative to the well-established practices like the Discrete Ordinates Method (DOM) and provides highly accurate approximations. A test case known to exhibit the ray effect in the DOM verifies the ability of the new method to avoid ray effects.

Steam Ejector Used as a Substitute for Cooling Tower in the Ethanol Production Process

Nowadays petroleum dependency in transportation is widely discussed all over the world. Atmospheric pollution and global warming are deleterious consequences of gasoline consumption. Ethanol is a natural substitute fuel that has been increasingly used. One of the most important raw materials used for ethanol production is the sugar cane. The exothermic fermentation reaction of the sugar cane juice in the ethanol production process requires a rigorous temperature control. This control is usually made by using cooling water from cooling towers. The heat released from cooling towers not only has an economical cost as well as it contributes to the global heating. Steam ejectors can substitute cooling towers thus improving the ethanol production plant efficiency and reducing world heating. Furthermore, steam ejectors are smaller, cheaper and are very simple equipment when compared with cooling towers. Furthermore, its use provides an improved thermal efficiency of the production plant resulting in the reduction of the global warming effects. In this work the use of steam ejector is proposed for the fermentation cooling of a typical Brazilian sugar and ethanol production plant. The steam which feeds the steam ejector is obtained from the plant utilities and the low temperature obtained from steam expansion within the ejector is used for sugar cane fermentation process cooling. The steam ejector discharge heat is recovered as it is used to sugar and ethanol production process heating. The sugar and ethanol production plant overall energy fluxes either using cooling towers as well as using steam ejectors are presented and the results are compared and discussed.

Experimental Results for Light-Induced Boiling in Water-Based Graphite Nanoparticle Suspensions

One relatively simple subset of nanotechnology is nanofluids, obtained by the addition of nanoparticles to a conventional base fluid. The promise of nanofluids stems from the fact that at relatively small particle loading (typically <1% by volume) significant enhancement in thermal transport may be possible [1–3]. Since there are a wide variety of nanoparticle materials to choose from, nanofluidic systems can be tuned to fit a number of applications. This research focuses on direct thermal collection of light energy using highly absorptive nanofluids. Experimental tests are conducted using a 0.1% by volume graphite/water (30nm nominal particle diameter) nanofluid exposed to a 130 mW, 532 nm, continuous laser. A lens is placed between the laser and the fluid to achieve a high-energy flux (∼ 490 Wcm−2). Since initially over 99.9% of the light is absorbed in a path length of 0.1 mm, the irradiated portion of the base fluid collects enough energy to vaporize. Heuristic methods of analysis demonstrate this situation incorporates several interesting modes of heat transfer and fluid mechanics. These experiments also reveal the possibility for novel solar collectors in which the working fluid directly absorbs energy and undergoes phase change in a single step.

Thermal Models for Determining Thermal Conductivity and Thermal Boundary Conductance Using Pump-Probe Thermoreflectance Techniques

Pump-probe transient thermoreflectance (TTR) techniques are powerful tools for measuring thermophysical properties of thin films, such as thermal conductivity, Λ, or thermal boundary conductance, G. TTR experimental setups rely on lock-in techniques to detect the response of the probe signal relative to the pump heating event. The temporal decays of the lock-in signal are then compared to thermal models to deduce the Λ and G in and across various materials. There are currently two thermal models that are used to relate the measured signals from the lock-in to the Λ and G in the sample of interest. In this work, the thermal models, their assumptions, and their ranges of applicability are compared. The advantages and disadvantages of each technique are elucidated from the results of the thermophysical property measurements.

Experimental Investigation of Nitrogen Flow in Long Microtubes

Nitrogen flow characteristics in Polyetheretherketone microtubes with inner diameters (D) ranging from 0.255mm to 0.553mm were experimentally investigated. It is indicated that most of the experimental points in laminar region are coincided with the conventional theoretical predicted value, but several plots caused by instrumental errors are lower than predicted values at small Re. In turbulent region, the friction factors for D = 0.255mm microtubes with L = 0.800m and 1.591m are slightly lower than conventional values; the experimental data for D = 0.553mm microtube with L = 0.800m is lower than that in D = 0.255mm pipes. The entrance effect obviously influences friction factor even if the L/D of microtubes is more than 60, where it can always be neglected in macro-scale. Due to the enhancement of compressibility effect as diameter decrease (Kn increase), friction constant is larger in smaller-size microtubes. The transition Reynolds number in current experiment (except for L = 0.200mm and D = 0.553mm) ranges from1600–2000, while a little early transition phenomenon is found in L = 0.200m, D = 0.553mm tube.