最佳过冷量控制算法在深冷处理设备中的应用

提出了深冷处理过程中的"过冷量"概念,介绍了最佳过冷量的获取方法,为某型号深冷箱建立了冷量控制模型,并设计了基于最佳过冷量控制算法的深冷处理控制系统。该系统的控制输出环节更加合理且能有效提高低温氮气与被处理材料之间的换热效率,大大降低了液氮消耗量,节约了深冷处理工艺成本。

Experimental investigation of crystallization process of nanofluid by DSC

A water-TiO2nanofluid with a weight fraction of 5% and an average particle size of 75 nm is used to investigate the effect of TiO2 nanoparticles on the crystallization and melting behaviors of deionized water by using differential scanning calorimetry（DSC）at four different cooling rates,3,5,7,9 ℃/min.The DSC experimental results show that the water-TiO2 nanofluid has a lower supercooling degree and a faster crystallization rate than the deionized water.With the increase in the cooling rate,the influence of the TiO2 nanoparticles on the supercooling degree of the deionized water becomes greater,but on the crystallization rate it turns lower.During the melting process,compared with the deionized water,the water-TiO2 nanofluid has a lower melting temperature,a less latent heat and a higher melting rate.

Critical Heat Flux with Subcooled Flowing Water in Tubes for Pressures from Atmosphere to Near-Critical Point

During last 45 years, two groups of the experimental data on critical heat flux were obtained in bare tubes, covering the pressures from atmosphere to near-critical point. One group of the data were obtained in the inner diameter of 2.32, 5.16, 8.05, 10.0 and 16.0 mm, respectively, with the ranges of pressure of 0.1-1.92 MPa, velocity of 1.47-23.3 m/s, local subcooling of 3.7-108.7 ℃ and heat flux of up to 38.3 MW/m2. Another group of the data were obtained in the inner diameter of 4.62, 7.98 and 10.89 mm, respectively, with the ranges of pressure of 1.7-20.6 MPa, mass flux of 454-4,055 kg/（m2.s） and inlet subcooling of 53-361 ℃. The results showed complicated effects of the pressure, mass flux, subcooling and diameter on the critical heat flux. They were formulated by two empirical correlations. A mechanistic model on the limit of heat transfer capability from the bubbly layer to the subcooled core was also proposed for all the results.

Temperature Measurement of Supercooled Droplet in Icing Phenomenon by means of Dual-luminescent Imaging

The collision of a supercooled water droplet with a surface result an object creates ice accretion on the surface. The icing problem in any cold environments leads to severe damages on aircrafts, and a lot of studies on prevention and prediction techniques for icing have been conducted so far. Therefore, it is very important to know the detail of freezing mechanism of supercooled water droplets to improve the anti-and de-icing devices and icing simulation codes. The icing mechanism of a single supercooled water droplet impacting on an object surface would give us great insights for the purpose. In the present study, we develop a dual-luminescent imaging technique to measure the time-resolved temperature of a supercooled water droplet impacting on the surface under different temperature conditions. We apply this technique to measure the exact temperature of a water droplet, and to discuss the detail of the freezing process.

Simulation of the stratosphere-troposphere exchange process in a typical cold vortex over Northeast China

A mesoscale weather research and forecasting(WRF)model was used to simulate a cold vortex that developed over Northeast China during June 19–23,2010.The simulation used high vertical resolution to reproduce the key features of the cold vortex development.Characteristics of the associated stratosphere-troposphere exchange(STE),specifically the spatiotemporal distribution of the cross-tropopause mass flux(CTF),were investigated using the Wei formula.The simulation results showed that the net mass exchange induced by the cold vortex was controlled by stratosphere-to-troposphere transport(STT)processes.In the pre-formation stage of the cold vortex(i.e.,the development of the trough and ridge),active exchange was evident.Over the lifecycle of the cold vortex,STT processes prevailed at the rear of the trough and moving vortex,whereas troposphere-to-stratosphere transport(TST)processes prevailed at the front end.This spatial pattern was caused by temporal fluctuations of the tropopause.However,because of the cancellation of the upward flux by the downward flux,the contribution of the tropopause fluctuation term to the net mass exchange was only minor.In this case,horizontal motion dominated the net mass exchange.The time evolution of the CTF exhibited three characteristics:(1)the predominance of the STT during the pre-formation stage;(2)the formation and development of the cold vortex,in which the CTF varied in a fluctuating pattern from TST to STT to TST;and(3)the prevalence of the STT during the decay stage.

Hierarchical aging pathways and signatures of thermodynamic transition in molecular glasses

When a liquid is supercooled,its structural equilibration timeτeqincreases sharply approaching the glass transition temperature Tg,below which it is kinetically arrested in the out of equilibrium glassy state.Upon annealing below Tg,such glassy state relaxes toward the equilibrium state.There is growing evidence that such relaxation process is quite complex,influenced by the complexity of the potential energy landscape.Here we report the observation of a hierarchical aging pathway in the process of the glass-to-supercooled liquid transition in various molecular glass forming systems.Differential scanning calorimetry reveals that the glassy state upon annealing below Tgfirstly enters a transient metastable supercooled liquid state with slightly higher enthalpies than that of the equilibrium supercooled liquid state when extrapolated to below Tg.This observation is also confirmed by structural measurements via Raman scattering.The dynamics of the transient metastable-to-stable supercooled liquid transition exhibits characteristics of thermodynamic transition at spinodal temperature Tspslightly above Tg,leading to anomalous behaviors such as the appearance of a transition-like behavior in the plot of fragility measurements.These observations imply that the free energy landscape of the supercooled liquid develops complexity with qualitative changes approaching Tgand could have strong influence on the process of the glass transition.