An experimental study of the shape of a single bubble similar to those observed in horizontal plug/slug flow was performed by visual observation and conductance probes in this paper. The results show that the shape of...
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An experimental study of the shape of a single bubble similar to those observed in horizontal plug/slug flow was performed by visual observation and conductance probes in this paper. The results show that the shape of the nose and body of bubble depends on the Froude number defined by gas/liquid mixture velocity, whereas the shape of the back region of bubble depends on both the Froude number and bubble length. The photographic pictures show that the motion of bubble is related to the characteristics of bubble head and the transition from plug flow to slug flow occurs when the back of the bubble changes from staircase to hydraulic jump pattern with increasing the Froude number and bubble length.
The periodically fully developed laminar heat transfer and fluid flow in a two-dimensional wavy channel in a compact heat exchanger are investigated numerically. Calculations are performed at Pr = 0.7, in the range of...
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The periodically fully developed laminar heat transfer and fluid flow in a two-dimensional wavy channel in a compact heat exchanger are investigated numerically. Calculations are performed at Pr = 0.7, in the range of Re = 100-1100 with non-orthogonal non-staggered grids. The Semi-Implicit Method for Pressure Linked Equations Revised (SIMPLER) algorithm in the curvilinear body-fitted coordinates is used. The effect of the wavy height and distance on momentum and heat transfer is studied. Performance of model parameters is evaluated. It is shown that the overall Nusselt numbers and friction factors increase with the increase of Reynolds numbers. The friction factors and overall Nusselt numbers increase as increasing the wavy height or decreasing the wavy distance. The overall Nusselt numbers increase significantly with the wavy height, especially at high Reynolds numbers. The best wavy height and distance are 1.15 mm and 13 mm, respectively.
Orthogonal array tests were carried out to investigate the optimal temperature(T), hydraulic retention time (HRT), pH and C/N ratio of anaerobic fermentative hydrogen production using a 20 L continuous stirred-tank re...
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Orthogonal array tests were carried out to investigate the optimal temperature(T), hydraulic retention time (HRT), pH and C/N ratio of anaerobic fermentative hydrogen production using a 20 L continuous stirred-tank reactor (CSTR). The results showed that hydrogen production rate, hydrogen content, glucose utilization ratio and hydrogen yield reached the maximum of 6.00 L/h, 55.0%, 99.0%, 157.86 mL/g in appropriate conditions, respectively. The optimal pH, T, HRT and C/N ratio were 5.0, 33.5-36.5 °C, 8.34 h, 112/1.55, respectively. A confirmation experiment was carried out to verify the optimal parameters obtained by orthogonal array tests. Hydrogen production rate, hydrogen content, glucose utilization ratio and potential hydrogen yield reached the maximum of 5.66 L/h, 54.0%, 0.97, 191.18 mL/g, respectively. The results of the confirmation experiment showed that hydrogen production with the optimal parameters was more efficient than that in the orthogonal array tests, and that suggested the orthogonal array tests were successful.
The structural properties of CdS thin films obtained by ultrasonic spray pyrolysis at different substrate temperature were studied by X-ray diffraction (XRD), scan electron microscope (SEM), Raman spectrum and Uv-vis ...
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The structural properties of CdS thin films obtained by ultrasonic spray pyrolysis at different substrate temperature were studied by X-ray diffraction (XRD), scan electron microscope (SEM), Raman spectrum and Uv-vis absorption spectrum. The experimental results show that the crystallinity level gets higher with increasing substrate temperature while the bandgap remains constant. This deposition method should be an effective method as the deposited film looks uniform and smooth in the SEM image. Furthermore, the photoelectrochemical activities of CdS thin films used as electrode to split water to hydrogen and oxygen were investigated. The photoelectrochemical activity increases and then decreases with increasing substrate temperature which forms a peak value at 300 °C . Under a light intensity of 187 mW/cm, the electrode deposited at 300 °C gives a saturated photocurrent of 4.1 mA/cm with increasing electrode potential. The highest energy conversion efficiency was calculated as 0.68% at electrode potential of -0.13 V (vs SCE).
As an important performance diagnosis tool, in-situ measurement of current distribution in PEM fuel cells is helpful for better understanding of internal transport phenomena and optimization of fuel cell structures an...
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As an important performance diagnosis tool, in-situ measurement of current distribution in PEM fuel cells is helpful for better understanding of internal transport phenomena and optimization of fuel cell structures and operating parameters. With a specially developed current distribution measurement gasket, the effects of reactant gas flow rates on the current distribution in a PEM fuel cell with single serpentine flowfield were investigated. Experimental results show that insufficient hydrogen or air leads to decreased current density along the gas flow direction. Higher reactant gas flow rate favors not only the local performance but also the homogeneity of current distribution. But current distribution almost ceases to change with further increase of hydrogen flow rate when it reaches certain value.
The velocities of liquid slugs in continuous slug flow were studied experimentally in a 133 m long horizontal pipeline. Measurements were performed by cross-correlating the signals of two pairs of probes installed alo...
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The velocities of liquid slugs in continuous slug flow were studied experimentally in a 133 m long horizontal pipeline. Measurements were performed by cross-correlating the signals of two pairs of probes installed along the pipeline. Correlations of liquid slug velocities with the mixed velocities are presented. It is found that the correlations depend on Froude numbers. At low Froude numbers, the correlation from the measurements of the upstream probes is consistent with that from the measurements of the downstream probes and both correlations agree well with the results of other researchers. But there is difference between the correlation of the upstream probes and that of the downstream probes at high Froude numbers. Compared with the experimental data of other researchers, it is expected that the velocities of liquid slugs are affected by the void fraction in liquid slugs and the evolution of the lengths of liquid slugs and elongated bubbles along pipeline. However, the wake effect may have no influence on the liquid slug velocities.
Cadmium sulfide photocatalyst was prepared by hydrothermal methods with one-step and two-step methods, respectively. Platinum was loaded on the surface of prepared photocatalysts and its optimal loading amount was exa...
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Cadmium sulfide photocatalyst was prepared by hydrothermal methods with one-step and two-step methods, respectively. Platinum was loaded on the surface of prepared photocatalysts and its optimal loading amount was examined. All the prepared photocatalysts were characterized by XRD, UV-Vis, XRF, SEM and TEM and their pohtocatalytic activity was evaluated by H2 evolution from water under visible light. It was found that the photocatalyst prepared by two-step showed markedly improved hydrogen production activity.
A new vibrating tube densimeter was developed with a precision of better than ±0.5 kg/m3. Using this apparatus, the saturation liquid density of dimethyl ether was measured from 233.15 K to 320.15 K, and the max ...
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A new vibrating tube densimeter was developed with a precision of better than ±0.5 kg/m3. Using this apparatus, the saturation liquid density of dimethyl ether was measured from 233.15 K to 320.15 K, and the max relative expanded uncertainty was 0.34%(coverage factor k = 2). The experimental data of this work were correlated as a polynomial function of the temperature with the published data of our previous work. The average and maximum relative deviation were 0.13% and 0.37%, respectively.
Numerical research was carried out on the convection heat transfer characteristics in bilaterally heated annular channel with narrow gap under the conditions of fully developed flow, where the inner and outer walls ar...
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Numerical research was carried out on the convection heat transfer characteristics in bilaterally heated annular channel with narrow gap under the conditions of fully developed flow, where the inner and outer walls are heated by uniform but unequal heat fluxes. Calculation results show that the ratio of the inner wall heat flux to the outer wall heat flux has great effects on the heat transfer characteristics in bilaterally heated narrow annuli. With the increase of the inner wall heated flux, the heat transfer coefficient at the outer wall of the inner tube will decrease, while the heat transfer coefficient at the inner wall of outer tube will increase. These numerical results are in good agreement with some experimental results in open literatures. Numerical results also show that the decrease of the annuli gap will yield heat transfer deterioration during flowing in narrow annular channels.
Through experiments and numerical simulation methods a study has been conducted of the characteristics of convection heat exchange of ridged internal-finned tubes and a comparison of the above characteristics with the...
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Through experiments and numerical simulation methods a study has been conducted of the characteristics of convection heat exchange of ridged internal-finned tubes and a comparison of the above characteristics with the flow and heat transfer characteristics of straight internal-finned tubes is performed. The experimental results indicate that the heat exchange characteristics of ridged internal-finned tubes are better than those of straight internal-finned tubes in terms of intensified heat transfer performance, but at the same time there is a corresponding increase in flow resistance. Through the adoption of a turbulent flow model capable of realizing k-ε equation, the flow and heat transfer process of ridged internal-finned tubes have been simulated. The calculation results are in good agreement with the experimental ones. The calculation results indicate that the periodical ridges inside the finned tubes have changed the distribution of the inner-flow fields and temperature ones. Relative to the straight internal-finned tubes, a secondary vortex flow has emerged, which is conducive to an intensified heat exchange and plays a definite destructive role to the flow boundary layer. Meanwhile, by increasing the turbulent kinetic energy of the flow field, the temperature gradient in the neighborhood of the heat exchange wall surfaces has been enhanced, contributing to an intensification of heat transfer.
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