Based on the 1-D & 2-D combined computational model, numerical optimizing analyses on the performance of the orifice type pulse tube refrigerator (OPTR) and double-inlet type pulse tube refrigerator (DPTR) were ca...
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Based on the 1-D & 2-D combined computational model, numerical optimizing analyses on the performance of the orifice type pulse tube refrigerator (OPTR) and double-inlet type pulse tube refrigerator (DPTR) were carried out. The evolvements process of the flow field in the OPTR and DPTR were examined. The results show that in the compressor expansion process the gas separation phenomenon occurs in the pulse tube, and in the compression process, there exists the gas aggregation phenomenon. The gas velocities in the separation and aggregation interfaces are zero, so the interface is called zero interface. In a period, the zero interface will move from one end of the pulse tube to the other end, which is called zero interface effect. The zero interface effect is an important factor for the performance enhancement of the PTR. The longer the time of the zero interface effect existing in a period, the better the PTR performance. Then based on the simulation results, the mechanism analysis for the existing of zero interface effect was performed. The results show that the introduction of the orifice valve leads to the formation of zero interface effect and the introduction of the double-inlet valve could augment the zero interface effect. For the OPTR, the time of the zero interface existing is about 1/6 period and for the DPTR the existing time of the zero interface is about 1/2 period.
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.
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.
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.
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.
Combustion characteristics of diluted hydrogen-air premixed combustion were studied in a constant volume bomb over wide ranges of diluent ratios and equivalence ratios using two kinds of diluent gases. A two-zone mode...
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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 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.
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.
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.
The explosion limits of dimethyl ether, methane and different mixtures of dimethyl ether and methane were measured under the temperature ranging from room temperature to 80C and the pressure ranging from 0.1 to 0.3 MP...
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The explosion limits of dimethyl ether, methane and different mixtures of dimethyl ether and methane were measured under the temperature ranging from room temperature to 80C and the pressure ranging from 0.1 to 0.3 MPa. In addition, the effects of temperature and pressure on the explosion limit were analyzed, and the accuracies of some theoretical calculation models of explosion limit were tested with the experimental results.
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