Studies on Three-Dimensional Mixed Convection with Surface Radiation in a Rectangular Channel with Discrete Heat Sources

The flow behavior and heat transfer characteristics of conjugate heat transfer under mixed convection for a three-dimensional laminar flow in a rectangular channel with six protruding heat sources, mounted on the lower wall of the channel, have been studied numerically and experimentally. At higher temperatures, radiation plays an important role. This work reports the effect of radiation on conjugate mixed convection heat transfer. Air is taken as a cooling medium and is considered to be radiatively non-participating medium. The parameters considered for the study are positions (streamwise and spansise) of the heat sources, Reynolds number, emissivity of the heat sources, and the thermal conductivity of a printed circuit board (PCB) having constant fluid properties with the Prandtl number being 0.707. The Boussinesq approximation has been used. Commercial software ANSYS Fluent has been used for numerical analysis, and experiments have been carried out in a small-sized wind tunnel. The ranges of Reynolds number, emissivity, and thermal conductivity of PCB are 115–690 (corresponding inlet velocity of 0.25–1.5), 0–0.9, and 0.038–1.4 W/mK, respectively. Results indicate that the radiative heat transfer is significant at lower Reynolds number and lower thermal conductivity of PCB. The streamwise spacing of heat sources has larger influence compared to the spanwise spacing.     

Mechanical and thermal properties,morphology and relaxation characteristics of poly(lactic acid) and soy flour/wood flour blends

Poly(lactic acid) (PLA) is a biodegradable polymer derived from sugar‐based materials, and its applications are varied. PLA blends are commonly employed to overcome certain disadvantages such as poor impact strength, low heat distortion temperature, poor processability and relatively high cost. In this study, blending PLA with soy flour (SF), wood flour (WF) and sodium bisulfite‐modified SF was used to improve the adhesion to PLA. In all cases, 0.5 wt% methylenediphenyl diisocyanate (MDI) was used as a coupling agent. Mechanical and thermal properties, morphology and relaxation characteristics of the blends were investigated. The results showed that MDI was an effective coupling agent for the WF/PLA system in improving tensile strength and elongation. Differential scanning calorimetry results indicated that SF and modified SF act as nucleation agents and facilitate the crystallization behavior of PLA by increasing the percentage crystallinity. From mechanical relaxation of the temperature‐variant system, we determined how the mechanical relaxation time evolves during the course of heating and obtained the Kohlrausch–Williams–Watts parameter and activation energy (ΔE). PLA and its blends exhibited highly homogeneous relaxational dynamics in their transition from glass to liquid, and ΔE of PLA and its blends is mainly affected by their densities and compositions. Copyright © 2010 Society of Chemical Industry     

Heat transfer from a totally blocked fuel subassembly of a liquid metal fast breeder reactor: Part I. Experimental investigation

The safety issues of liquid metal fast breeder reactors (LMFBR) are crucial due to the fact that a highly reactive and hazardous fluid like liquid sodium is used as coolant. One of the extreme cases, which can occur in a fuel subassembly of an LMFBR, is a total blockage of liquid inside the subassembly, which may lead to boiling of sodium. The present study addresses this problem by conducting experiments on a 19-rod bundle assembly enclosed inside a tall hexagonal enclosure. Liquid sodium is used as the heat transfer fluid. The natural convection mode of heat transfer is the main focus of investigation with a co-flowing air through an annular packed bed to simulate the neighbouring subassemblies. The maximum temperature achieved under different rates of power generations and air flow conditions are observed. Also the radial temperature distributions at different planes under different operating conditions of power and air flow rates have been observed. The results are of significant importance for validating analysis for the purpose of prediction of boiling incipience in an LMFBR subassembly under totally blocked condition.     

Inverse radiation problem to retrieve hydrometeors from satellite microwave radiances

This study presents a new hybrid method that combines regression analysis with genetic algorithms for the retrieval of hydrometeors (cloud liquid water, ice and rain) in the atmosphere, from satellite microwave radiances. A three layered atmosphere model (divided into 30 sub-layers) is used to generate simulated profiles of hydrometeors. The equation governing the transfer of radiation is solved using the finite volume method to obtain radiances (brightness temperatures) in the microwave region. This is known as the forward problem and is solved repeatedly to create a database with which regression equations are developed for the monochromatic microwave radiances, for six typical frequencies ranging from 6.6 to 85 GHz. The regression is done using nonlinear parameter estimation techniques. The inverse problem of retrieving the hydrometeors characteristics from microwave radiances is accomplished by posing the parameter estimation problem as an optimization problem, wherein, minimization of the sum of squares of residuals between the estimated and known radiances, for the above mentioned six typical frequencies, is done. In this study, genetic algorithms have been used for solving the minimization problem.     

Optimum Design of Cross-Flow Shell and Tube Heat Exchangers with Low Fin Tubes

This paper presents a simple, efficient, robust, optimum design methodology for the design of a high heat transfer and low pressure drop cross-flow shell and tube heat exchanger with integral low fin tubes. This type of heat exchanger has the potential for application in the design of coolers in hypersonic wind tunnels to cool the air that emerges from the diffuser section of the wind tunnel. The methodology described here allows for the design and optimization of any type of heat exchanger that has constraints on pressure drop, as well as the design of an exchanger for very low pressure drop on the shell side fluid.     

Differential effects of kynurenine and tryptophan treatment on quinolinate immunoreactivity in rat lymphoid and non-lymphoid organs

Quinolinate is a tryptophan metabolite and an intermediary in nicotinamide adenine dinucleotide (NAD+) synthesis in hepatocytes. Kynurenine is an upstream metabolite in the same biochemical pathway. Under normal physiological conditions, kynurenine is thought to be produced primarily in the liver as an NAD+ precursor. However, during immune stimulation or inflammation, numerous extrahepatic tissues convert systemic tryptophan to kynurenine, and its concentration subsequently rises dramatically in blood. The fate and role of extrahepatic kynurenine are uncertain. In order to begin addressing this question, the present study was performed to determine which cell types can produce quinolinate from either systemic tryptophan or kynurenine. By using highly specific antibodies to protein-coupled quinolinate, we found that intraperitoneal injections of tryptophan led to increased quinolinate immunoreactivity primarily in hepatocytes, with moderate increases in tissue macrophages and splenic follicles. In contrast, intraperitoneal injections of kynurenine did not result in any significant increase in hepatocyte quinolinate immunoreactivity, but rather led to dramatic increases in immunoreactivity in tissue macrophages, splenic white pulp, and thymic medulla. These findings suggest that hepatocytes do not make significant use of extracellular kynurenine for quinolinate or NAD+ synthesis, and that, instead, extrahepatic kynurenine is preferentially metabolized by immune cells throughout the body. The possible significance of the preferential metabolism of kynurenine by immune cells during an immune response is discussed.     

Device for reusing damaged laser mirrors

A simple mirror holder which permits the use of locally damaged laser morrors by allowing the undamaged areas of the reflector to be aligned along the laser optic axis is described. The mirror holder has an eccentric step for housing the mirror and a concentric aperture through which the undamaged surface of the reflector is utilised. By varying the eccentricity and by rotating the mirror inside the step the entire surface area of the reflector can be used successively.     

Technique for measuring the beam shape of pulsed lasers

A simple technique for the measurement of the beam shape parameters of pulsed lasers, with just a single pulse of the laser is described. It involves the use of several beam dividers inclined at very small angles to the beam axis, reflecting the beam back to a screen or a phosphor placed near the exit of the laser. The reflected images are then photographed by a camera to yield the beam parameters.     

Synthesis and characterization of Fe- and Co-based ferrite nanoparticles and study of the T 1 and T 2 relaxivity of chitosan-coated particles

In pursuit of newer and more effective contrast agents for magnetic resonance imaging, we report in this article the use of biocompatible chitosan-coated ferrite nanoparticles of different kinds with a view to determine their potential applications as the contrast agents in the field of nuclear magnetic resonance. The single-phase ferrite particles were synthesized by chemical co-precipitation (CoFe₂O₄ and Fe₃O₄) and by applying ultrasonic vibration (CoFe₂O₄ and Co_0.8Zn_0.2Fe₂O₄). Although magnetic anisotropy of CoFe₂O₄ nanoparticle leads to finite coercivity even for nanoensembles, it has been reduced significantly to a minimum level by applying ultrasonic vibration. Fe₃O₄ synthesized by chemical co-precipitation yielded particles which already possess negligible coercivity and remanence. Substitution of Co by Zn in CoFe₂O₄ increases the magnetization significantly with a small increase in coercivity and remanence. Particles synthesized by the application of ultrasonic vibration leads to the higher values of T ₂ relaxivities than by chemical coprecipitation. We report that the T ₂ relaxivities of these particles are of two orders of magnitude higher than corresponding T ₁ relaxivities. Thus, these particles are evidently suitable as contrast agent for T ₂ weighted MR images.