Assessment of flow and heat transfer characteristics for proposed solid density distributions in dilute laminar slurry upflows through a concentric annulus

A computational model is developed to predict the hydrodynamic and heat transfer characteristics of dilute liquid-solid laminar upflows through a concentric annulus. The dilute slurry is treated as a single phase Newtonian fluid of locally variable physical and thermal properties. Available experimental data of radial solid density distributions in dilute water-feldspar annular upflows is used in the model. Various important characteristics of laminar slurry flows were successfully predicted. It was also shown mathematically that in the limiting case of zero average solid loading, the solution reduces to that of the single phase. The radial location of maximum slurry density in the annular gap was found to be an important factor in determining both the flow and heat transfer behavior of the present system; also, the higher heat transfer enhancement ratios were predicted at the lower slurry Reynolds numbers.     

Unsteady flow and heat transfer on an accelerating surface with blowing or suction in the absence and presence of a heat source or sink

The problem of unsteady flow and heat transfer in the laminar boundary layer on a linearly accelerating surface with suction or blowing in the absence and presence of a heat source or sink is considered. The governing partial differential equations for this investigation are transformed into the non-dimensional equations by using pseudo-similarity time and pseudo-similarity coordinate. The resulting two points boundary-value problem is solved numerically by the central finite difference method associated with Newton's iteration from the initial stage (ξ=0) to a steady state (ξ=1) completely. A parametric study is performed to illustrate the effects of Prandtl number, power-law surface temperature (PLST) or power-law heat flux (PLHF), heat sink or heat source, and suction or blowing parameter on the dynamic velocity and temperature fields as well as the transient development of the skin-friction coefficients and the Nusselt number. These results are depicted graphically to display special aspects of unsteady flow and heat transfer characteristics in all time.     

Studies on the hydrodynamic and heat transfer in a vapor-liquid-solid flow boiling system with a CCD measuring technique

The vapor-liquid-solid (V-L-S) flow boiling evaporator has the features of fouling preventing and heat-transfer enhancing. However, the mechanisms of flow and heat-transfer are still not well understood due to the system complex and the limitation of the measuring methods due to the characteristic of opaque of the system in practice. In this paper, a charge coupled device (CCD) measuring system is developed to investigate the hydrodynamic characteristics including the axial profiles of solid holdup and of solid velocity in a V-L-S three-phase natural circulating flow boiling system. The CCD measuring technique makes the three-phase qualitative observation and quantitative research possible. The heat-transfer characteristic of this system is also studied. The main results are as follows. The distributions of solid holdup and velocity are not uniform along the axial direction of the heating tube and both in liquid-solid two-phase region and in V-L-S three-phase region; however, the particle velocity in V-L-S three-phase region is much higher than that in liquid-solid two-phase region in heating tube. When increasing the heat flux, the solid holdup first increases and then decreases and the solid velocity gradually increases in heating tube. But in circulating tube, both the solid holdup and the solid velocity gradually increase. With the increase of the volume of added solid particles, the measured local solid holdup increases in both tubes; however, the variation of the solid velocity with the increase of the solid particles shows a characteristic of the wave and the general tendency is climbing for both tubes. The solid particles holdup in heating tube is always larger than that in circulating tube and the solid velocity in heating tube is lower than that in circulating tube. The presence of solid particles enhances the boiling evaporation process. The heat-transfer coefficient of the system increases with the increase of the heat flux and the volume of added solid particles. These research results provide some valuable references for the academic interest and for the industry application of this fouling preventing and heat-transfer enhancing installation.     

Four stages of the simultaneous mass and heat transfer during bubble formation and rise in a bubbly absorber

We studied nonisothermal absorption of a solvable gas from growing at an orifice and rising bubble when the concentration level of the absorbate in the absorbent is finite (finite dilution of absorbate approximation). It is shown that simultaneous heat and mass transfer at all stages of bubble growth and rise in a bubbly absorber can be described by a system of generalized equations of nonstationary convective diffusion and energy balance. Solutions of diffusion and energy balance equations are obtained in the exact analytical form. Coupled thermal effects during absorption and absorbate concentration level effect on the rate of mass transfer are investigated. It is found that the rate of mass transfer between a bubble and a fluid increases with the increase of the absorbate concentration level. The suggested approach is valid for high Peclet, Prandtl and Schmidt numbers. It is shown that for the positive dimensionless heat of absorption K thermal effects cause the increase of the mass transfer rate in comparison with the isothermal case. On the contrary, for negative K thermal effects cause the decrease of the mass transfer rate in comparison with the isothermal case. The latter effect becomes more pronounced with the increase of the concentration level of the absorbate in the absorbent. Theoretical results are consistent with the experiments of Kang et al. (Int. J. Refrigeration 25 (2002) 127) for absorption from ammonia gas bubbles rising in water and aqueous ammonia solutions.     

Investigation of the combustion of neat cottonseed oil or its neat bio-diesel in a HSDI diesel engine by experimental heat release and statistical analyses

An experimental study is conducted to evaluate the effects of using neat cottonseed oil or its neat ME (methyl ester) bio-diesel, on the combustion behavior of a standard, high speed, direct injection (HSDI), ‘Hydra’ diesel engine located at the authors’ laboratory. Combustion chamber and fuel injection pressure diagrams are obtained at medium and high load using a developed, high-speed, data acquisition and processing system. A heat release analysis of the experimentally obtained cylinder pressure diagrams is developed and used. Plots of histories in the combustion chamber of the heat release rate and other related parameters reveal some interesting features, which shed light into the combustion mechanism when using these bio-fuels. These results, combined with the differing physical and chemical properties of the bio-fuels between themselves and against those for the diesel fuel, which constitutes the baseline fuel, aid the correct interpretation of the observed engine behavior performance- and emissions-wise. Moreover, the possible existence of cyclic (combustion) variability is examined as reflected in the pressure indicator diagrams, by analyzing for the maximum pressure and its rate, and the dynamic injection timing and ignition delay, by using statistical analysis for averages, standard deviations and probability density functions. The key results are that with the use of these bio-fuels against the neat diesel fuel case, the ignition delay is hardly affected, the fuel injection pressure diagrams are very slightly advanced accompanied with higher injection pressures, maximum cylinder pressures remain the same with the vegetable oil and slightly increased with the bio-diesel, maximum cylinder pressure rates are increased with the bio-diesel and decreased with the vegetable oil, while the cyclic irregularity is not affected with these bio-fuels remaining at the acceptable neat diesel fuel case levels.     

Adjustable amine–epoxy composition in a stratified thin film with a spin‐coating process: A useful tool for establishing relationships between the local glass‐transition temperature at the interface and the network structure

An easy method for preparing supported homogeneous epoxy–amine thin films on a silica surface consisting of two distinct layers was developed via spin coating from epoxy–amine solutions. Because of these two layers had the controlled properties of the upper layer, we showed that it was possible to precisely control the epoxy–amine stoichiometry in the sublayer through the initial epoxy–amine ratio, the spin‐cast process, and the overall film thickness. First, in the thin films, the primary amine–epoxy conversion was constant, whatever the thickness and initial epoxy–amine stoichiometry for a given curing schedule. As the primary amine conversion can be independently tuned in thin films, it thus provided a rather unique and easy method for better understanding the relationship between the network structure curing at the interface and the resulting properties, such as the glass‐transition temperature (T_g) and elastic modulus. Here, we also showed that we could access the local T_g; this implied a potential application of these experimental data in predictive composite material properties. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42078.