Helical-coil is a common structure of heat exchanger unit in phase change heat accumulator and usually has the equal coil pitch between adjacent coils. Its thermal performances could be improved by improving the unifo...Helical-coil is a common structure of heat exchanger unit in phase change heat accumulator and usually has the equal coil pitch between adjacent coils. Its thermal performances could be improved by improving the uniformity of the phase change material （PCM） temperature distribution. Thus, a novel non-equidistant helical-coil structure was proposed in this study. Its coil pitch decreased along the flow direction of heat transfer fluid, which made the heat exchange area in unit volume increase to match the decreasing temperature difference between the heat transfer fluid and PCM. The structure was optimized using numerical simulation. An experimental system was developed and the experiment results indicated that the proposed non-equidistant helical-coil heat accumulator was more effective than equidistant helical-coil for latent heat storage. The uniformity of the temperaalre distribution was also confirmed by simulation results.展开更多
In this paper, the low Mach number he- lium and nitrogen flows in micro-channels are inves- tigated numerically with variations of inlet to outlet pressure ratios, aspect ratios, out pressures and fluid mediums by usi...In this paper, the low Mach number he- lium and nitrogen flows in micro-channels are inves- tigated numerically with variations of inlet to outlet pressure ratios, aspect ratios, out pressures and fluid mediums by using different continuum-based slip models. Theoretical solutions based on perturbation expansions of the Navier-Stokes equations have been developed under different order slip conditions. The validity of slip models has been examined by the corresponding experiments and the DSMC method at different Knudsen numbers. Simulations have shown good predictions of the compressibility, rarefaction and thermal creep effects on micro-channel flows with the present slip models. The higher order slip models relatively decrease the rarefaction effects comparing with a first-order slip model. Both of the Knudsen number and the Reynolds number have been identified as key parameters, which govern the rarefaction effects and thermal creep effects, respec- tively. The present slip models have been also dem- onstrated to be appropriate for micro-channel nitro- gen flows with the Knudsen number less than 0.15, and the higher order slip conditions improve the Na- vier-Stokes predictions in the slip flow regime with Kn<0.08. However, the continuum-based slip models significantly under-predict the rarefaction effects in the transitional flow regime as the Knudsen number exceeds 0.2.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.51576187)Fundamental Research Funds for the Central Universities(Grant No.WK2090130016)
文摘Helical-coil is a common structure of heat exchanger unit in phase change heat accumulator and usually has the equal coil pitch between adjacent coils. Its thermal performances could be improved by improving the uniformity of the phase change material （PCM） temperature distribution. Thus, a novel non-equidistant helical-coil structure was proposed in this study. Its coil pitch decreased along the flow direction of heat transfer fluid, which made the heat exchange area in unit volume increase to match the decreasing temperature difference between the heat transfer fluid and PCM. The structure was optimized using numerical simulation. An experimental system was developed and the experiment results indicated that the proposed non-equidistant helical-coil heat accumulator was more effective than equidistant helical-coil for latent heat storage. The uniformity of the temperaalre distribution was also confirmed by simulation results.
基金This work was supported by the National Natural Science Foundation of China （Grant Nos. 50376060 and 10372099）.
文摘In this paper, the low Mach number he- lium and nitrogen flows in micro-channels are inves- tigated numerically with variations of inlet to outlet pressure ratios, aspect ratios, out pressures and fluid mediums by using different continuum-based slip models. Theoretical solutions based on perturbation expansions of the Navier-Stokes equations have been developed under different order slip conditions. The validity of slip models has been examined by the corresponding experiments and the DSMC method at different Knudsen numbers. Simulations have shown good predictions of the compressibility, rarefaction and thermal creep effects on micro-channel flows with the present slip models. The higher order slip models relatively decrease the rarefaction effects comparing with a first-order slip model. Both of the Knudsen number and the Reynolds number have been identified as key parameters, which govern the rarefaction effects and thermal creep effects, respec- tively. The present slip models have been also dem- onstrated to be appropriate for micro-channel nitro- gen flows with the Knudsen number less than 0.15, and the higher order slip conditions improve the Na- vier-Stokes predictions in the slip flow regime with Kn<0.08. However, the continuum-based slip models significantly under-predict the rarefaction effects in the transitional flow regime as the Knudsen number exceeds 0.2.
