Natural convection of liquid metal in a vertical annulus with lateral and volumetric heating in the presence of a horizontal magnetic field

MHD free convection of a liquid metal is studied in a closed vertical annulus in which the upper and bottom walls are adiabatic while the cylindrical walls are kept at different temperatures. The flow is driven by two mechanisms; the temperature difference between the two cylindrical walls and the volumetric heating. A constant horizontal magnetic field is also imposed resisting the fluid motion. The laminar and turbulent regimes of the flow are assessed by performing three-dimensional direct numerical simulations. The results show that in the absence of the magnetic field, turbulent flow is developed in most of the cases, while as the magnetic field increases the flow becomes laminar. The highest temperature is found in the upper-central part of the annular cavity when the fluid is heated volumetrically, resulting in the creation of two convection currents as the hot fluid ascends in the central part and descends close to both colder walls. The Hartmann and Roberts layers developing near the walls normal and parallel to the magnetic field, respectively, are found to be responsible for the loss of axisymmetry of the present flow.     

Laminar Heat Transfer in a Rotating Disk under Conditions of Forced Air Impingement Cooling: Approximate Analytical Solution

The laminar heat transfer of a rotating disk under conditions of forced impingement cooling with a uniform velocity profile at infinity is investigated. The integral method is used to obtain an approximate analytical solution whose constants are found by adjustment to the exact numerical solution of the problem for different values of the Prandtl number Pr = 0.1–1 and the exponent in the power radial distribution of the disk temperature n* = –2–4. Boundaries of different modes of heat transfer are determined. The results of simulation are in good agreement with experiments in the stagnation region for impinging jets flowing coaxially against the disk.     

On the heat transfer characteristics of heat sinks: Influence of fin spacing at low Reynolds number region

This study examines the thermal–hydraulic performance of heat sinks having plate, slit, and louver fin patterns. Comparison of the associated heat transfer performance and the effect of fin spacing are made. The results indicate that the enhanced fin patterns like louver or slit fin operated at a higher frontal velocity and at a larger fin spacing is more beneficial than that of plain fin geometry. The heat transfer performance of louver fin is usually better than that of slit fin but accompanies with higher pressure drops. However, it is found that the pressure drops for slit fin is comparable to the louver fin geometry when the fin spacing is reduced to 0.8 mm. This is associated with the appreciable rise of entrance/exit loss (form drag) caused by the slit fin geometry. The test results also reveal a significant drop of heat transfer performance at a low Reynolds number and at a small fin spacing, or the so-called “maximum” phenomenon of Colburn j factor. This is applicable to all the tested geometries. By a careful examination of the test results, it is concluded that this phenomenon is related to the developing/fully developed flow characteristics. In fact, the maximum point occurred roughly at x⁺ = 0.1 where fully developed and developing flow is separated.     

Experimental Study of Melting Heat Transfer in an Enclosure with Three Discrete Protruding Heat Sources

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Harvest of electrical energy from fermented microalgal residue using a microbial fuel cell

The application of microalgal biomass for fermentation has been highlighted as a means of producing a range of value-added biofuels and chemicals. On the other hand, the microalgal residue from the fermentation process still contains as much as 50% organic contaminants, which can be a valuable substrate for further bioenergy recovery. In this study, a microbial fuel cell and automatic external load control by maximum power point tracking (MPPT) were implemented to harvest the electrical energy from waste fermented microalgal residue (FMR). The MFC with MPPT produced the highest amount of energy (1.82 kJ/L) compared to the other MFCs with fixed resistances: 0.98 (1000 Ω), 1.16 (500 Ω), and 1.17 kJ/L (300 Ω). The MFC with MPPT also showed the highest maximum power density (88.6 mW/m²) and COD removal efficiency (620.0 mg COD/L removal with 85% removal efficiency). The implementation of MPPT gained an approximate 12.9% energy yield compared to the previous fermentation stage. These results suggest that FMR can be an appropriate feedstock for electrical energy recovery using MFCs, and the combined fermentation and MFC system improves significantly the energy recovery and treatment efficiency from FMR.     

Unsteadiness of Shock Wave／Boundary Layer Interaction in Supersonic Cascade

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Numerical analysis of 3-D unsteady flow in a vaneless counter-rotating turbine

To reveal the unsteady flow characteristics of a vaneless counter-rotating turbine (VCRT), a three-dimensional, viscous, unsteady computational fluid dynamics (CFD) analysis was performed. The results show that unsteady simulation is superior to steady simulation because more flow characteristics can be obtained. The unsteady effects in upstream airfoil rows are weaker than those in downstream airfoil rows in the VCRT. The static pressure distribution along the span in the pressure surface of a high pressure turbine stator is more uniform than that in the suction surface. The static pressure distributions along the span in the pressure surfaces and the suction surfaces of a high pressure turbine rotor and a low pressure turbine rotor are all uneven. The numerical results also indicate that the load of a high pressure turbine rotor will increase with the increase of the span. The deviation is very big between the direction of air flow at the outlet of a high pressure turbine rotor and the axial direction. A similar result can also be obtained in the outlet of a low pressure turbine rotor. This means that the specific work of a high pressure turbine rotor and a low pressure turbine rotor is big enough to reach the design objectives. Translated from Journal of Engineering Thermophysics, 2006, 27(1): 35–38 [译自: 工程热物理学报]     

Experimental Studies on Combustion Characteristics of Mixed Municipal Solid Waste

In our country, municipal solid wastes (MSW) are always burnt in their original forms and only a few pretreatments are taken. Therefore it is vital to study the combustion characteristics of mixed waste. In this paper, thermogravimetric analysis and a lab scale fluidized bed facility were used as experimental means. The data in two different experimental systems were introduced and compared. It took MSW 3-3.5 min to burn out in FB, but in thermogravimetric analyzer, the time is 20-25 min. It can be concluded that, in general, the behavior of a mixture of waste in TGA can be expressed by simple combination of individual components of the waste mixtures. Only minor deviations from the rule were observed. Yet, in Fluidized Bed, it was found that, for some mixtures, there was interference among the components during fluidized bed combustion.     

An Improvement on the Method for Calculating the Capillary Limit of Axial—Grooved Heat Piper

A new model has been developed to predict the capillary limit of axial-grooved heat pipe.In the model the concepts of liquid saturation or liquid fraction of the cross-sectional area of groove,the modified relative permeability,absolute permeability of groove and Leverrt‘s function are used.The Leverrt‘s function is well represented by the functionf(s)=1(1/√5)(1/2-)^0.175.In the model the effects of gravitational force,capillary force and viscous force are considered.The calcuated results are in good agreement with existing experimental data reported in the literature.     

循环流化床锅炉耐火耐磨材料的设计与施工

耐火耐磨材料的质量和施工是保证循环流化床(CFB)锅炉可靠运行的关键技术之一.文章介绍了内蒙古华电乌达热电有限公司的480t/h CFB锅炉燃烧系统中各部位的耐火耐磨材料的结构设计、施工与烘炉经验.