Turbulent bubbly mixing layer was experimentally investigated by PIV and analyzed by using the swirling strength method. The velocity ratio between high speed and low speed was 4:1 and the Reynolds number based on the...
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A one-dimensional and two-dimensional combined computational model (1-D and 2-DCC model) was set up to simulate the performances of the basic type, orifice type and double inlet type pulse tube refrigerators (PTRs). T...
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A one-dimensional and two-dimensional combined computational model (1-D and 2-DCC model) was set up to simulate the performances of the basic type, orifice type and double inlet type pulse tube refrigerators (PTRs). The Darcy-Brinkman-Forchheimer model and the thermally non-equilibrium model were adopted to depict the flow and heat transfer in the regenerator which was modeled by taking the mesh as a porous medium. Parameter communicating algorithms were defined to calculate velocity and temperature at the junctions between the 1-D and 2-D computational regions. Then the simulation codes for the whole PTRs were developed. The working process and complex flow phenomena such as velocity and temperature annular effects and DC flow in PTRs were revealed. The results show that a close loop in the PTR can be formed by using a double-inlet valve which leads to the occurrence of DC flow. For the case studied, the DC flow rate accounts for 4.66% of the total mass flow rate under the present parameters and working conditions.
The scale inhibition and removal processes by electronic water treatment were investigated in this study. The results show that the treatment of scale inhibition with 7.0V can be used first for the water with the hard...
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The scale inhibition and removal processes by electronic water treatment were investigated in this study. The results show that the treatment of scale inhibition with 7.0V can be used first for the water with the hardness over 300 mgL-1(CaCO3), and then the treatment of scale removal with 5.0V can be applied when the water hardness decreases to less than 130 mgL-1(CaCO3). With the present energy-saving approach, more than 90 percent of the scale ions can be removed after treatment and no obvious scale will decompose on the surface of the heat exchanger. The SEM figures depict that the crystal morphology of scale is affected by the electronic water treatment. The crystal morphology of scale with and without the electronic water treatment is calcite and aragonite, respectively.
In present paper a three dimensional discrete vortex filament method is proposed to simulate unsteady incompressible vortical flows, through which the interaction of two coaxial vortex rings was studied. First the pro...
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In present paper a three dimensional discrete vortex filament method is proposed to simulate unsteady incompressible vortical flows, through which the interaction of two coaxial vortex rings was studied. First the process of head-on collision of two circular rings was reproduced and compared with experimental result. The good agreement between numerical work and experiment verified our model. Then the motion of single elliptic ring was studied and a fit expression was given, through which the axis-switching period of single elliptic ring can be calculate effectively. At last the head-on collision and leapfrogging process of two coaxial elliptic rings was studied respectively. For the case of head-on collision of two elliptic rings, the shape of new generated ring was similar but larger than initial elliptic ring. While for case of two elliptic rings moving in same direction, the axis-switching process of elliptic ring is accompanied with the leapfrogging process.
For efficiently cooling electronic components, the flow boiling heat transfer performance of FC-72 on micro-pin-finned silicon chips were studied. Two kinds of micro-pin-fins were used, which have the same fin thickne...
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For efficiently cooling electronic components, the flow boiling heat transfer performance of FC-72 on micro-pin-finned silicon chips were studied. Two kinds of micro-pin-fins were used, which have the same fin thickness of 30m but different fin heights of 60 and 120m, respectively. The boiling heat transfer performance was much better for the micro-pin-fined surfaces than that for a smooth surface, and increased with increasing fin height. The critical heat flux increased with fluid velocity and subcooling, and the wall temperatures at the critical heat flux for micro-pin-finned chips were less than the upper temperature limit for the normal operation of electronic components, 85C.
A local refinement method of unstructured grid generated by bubble packing method (BPM) is proposed. In the present method, different size bubbles are added to the real and artificial vertices of the domain and bubble...
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A local refinement method of unstructured grid generated by bubble packing method (BPM) is proposed. In the present method, different size bubbles are added to the real and artificial vertices of the domain and bubble information of these vertices is transferred to the inner nodes of the domain by the Shepard interpolation method. Moreover, a method to control the population of bubbles is presented to add bubbles in large gap between bubbles and remove bubbles to eliminate overlapping so that the generation of skinny triangles is avoided and the grid quality is clearly improved. Furthermore, the improved BPM is applied to generate unstructured grid with local refinement near boundary for square domain to simulate the lid-driven flow in a square cavity with Re=1 000. The numerical result agrees well with the benchmark solution, indicating that the improved BPM is effective to the computation of fluid flow and heat transfer.
In this work, the vapor pressure equation, saturated liquid density equation, saturated vapor density equation and Helmholtz equation of state for dimethyl ether are developed by genetic optimization algorithm combine...
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In this work, the vapor pressure equation, saturated liquid density equation, saturated vapor density equation and Helmholtz equation of state for dimethyl ether are developed by genetic optimization algorithm combined with a weighted least-square fit of selected experimental data based on extensive collection of DME's experimental data. The average absolute deviation of vapor pressure equation, saturated liquid density equation and saturated vapor density equation is 0.50%, 0.38% and 0.55%, respectively. The uncertainty in density of the equation of state ranges from 0.1% in the liquid to 1% near the critical point.
An experimental study has been performed to investigate pool water instantaneous flash evaporation in a rectangle chamber. Some key parameters such as superheat, initial water temperature and water level have been stu...
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An experimental study has been performed to investigate pool water instantaneous flash evaporation in a rectangle chamber. Some key parameters such as superheat, initial water temperature and water level have been studied. The water level was at 40 mm, 60 mm, 100 mm, 150 mm. Initial conditions of the liquid varied from 36C to 88C temperature and 2.1C to 48C superheat. The experimental results showed that the initial water temperature, the superheat and the water level are the key parameters. The experimental results showed that the greater the superheat and the higher the initial water level approaches, the longer the flashing will persist. Under a constant superheat, the initial water temperature has little influence on duration of flashing. Experimental study allows us to correlate the flashing duration time with the superheat and the initial water level as well as the initial water temperature.
Based on the wavelet analysis theory of signal singularity detection, the critical heat flux (CHF) and minimum film boiling starting point (qmin) of boiling curves can be detected and analyzed by using the wavelet mul...
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Based on the wavelet analysis theory of signal singularity detection, the critical heat flux (CHF) and minimum film boiling starting point (qmin) of boiling curves can be detected and analyzed by using the wavelet multi-resolution analysis. To predict the CHF in engineering, empirical relations were obtained based on genetic algorithm. The results of wavelet detection and genetic algorithm prediction are consistent with experimental data very well.
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