影响注射成型冷却时间的因素分析

介绍了一种估算注射成型过程中冷却时间的数学公式,并用它和CAE软件一起,以一平面薄板为例,全面讨论了冷却管道和制品距离、不同塑料材料和不同制品厚度、开模温度、模具热传导率、冷却介质(水)初始温度对冷却时间的影响程度,得出最大的影响因素是制件的厚度,开模温度及冷却水温度。

Combination effect of seasonal freezing and artificial freezing on frost heave of silty clay

To investigate the frost-heave properties of silty clay under the combination action of seasonal freezing and artificial freezing, and verify the feasibility of combined freezing, eight combined freezing experiments were performed on silty clay with water content (mass fraction) of 23.5% and 28.0%, through developed frost-heave test apparatus, in closed or open system. Two sorts of freezing temperature models, namely, constant and sine models, were applied to artificial freezing. The experimental results indicate that the frost-heave degree in seasonal freezing stage accounts for over 90% of the total in open system and it is up to 95% in closed system; the change of artificial sine-freezing temperature has no influence on the frost-heave degree in closed system, however, slight influence in open system. It is found that the variation of temperature gradient of sine-freezing specimen lags behind that of sine-freezing temperature with half phase; sine-freezing temperature model can reduce frost-heave degree of soil. Brand new technology is proposed for the application of artificial ground freezing and new study field of artificial freezing is created.

Research on software development of air temperature prediction in coal face

With ever-increasing depth of coal mine and the continuous improvement of mechanization, heat damage has become one of the major disasters in coal mine exploitation. Established the temperature prediction models suitable for different kinds of tunnels through analysis of the heat of shafts, roadways and working faces. The average annual air temperature prediction equation from the inlets of shafts to the working faces was derived. The formula was deduced using combine method of iteration and direct calculation. The method can improve the precision of air temperature prediction, so we could establish the whole pathway air temperature prediction model with high precision. Emphasizing on the effects of leakage air to air temperature of working face and using the ideology of the finite difference method and considering the differential equation of inlet and outlet at different stages, this method can significantly improve the accuracy of temperature prediction. Program development uses Visual Basic 6.0 Language, and the Origin software was used to fit the relevant data. The predicted results shows that the air temperature generally tends to rapidly increase in the air inlet, then changes slowly on working face, and finally increases sharply in air outlet in the condition of goaf air leakage. The condition is in general consistent with the air temperature change tendency of working face with U-type ventilation system. The software can provide reliable scientific basis for reasonable ventilation, cooling measures and management of coal mine thermal hazards.

Development of a toy column model and its application in testing cumulus convection parameterizations

A single-column model is constructed based on parameterizations inherited from the Finite-volume/Spectral Atmospheric Model F/SAMIL and tested in simulations of tropical convective systems. Two representative convection schemes are compared in terms of their performances on precipitation types, individual physical tendencies, and temperature and moisture fields. The main difference between the two selected schemes is in their representation of entraining/detraining process. The Tiedtke scheme assumes bulk entrainment, while the Zhang–Mc Farlane scheme parameterizes entrainment/detrainment rates under the spectrum concept. Large-scale forcing and verification data are taken from the GATE phase III field campaign, during which abundant convective events were observed. Given the same triggering function and closure assumption, results show that entrainment/detrainment representation remains the dominant factor on the simulation of cumulus mass flux and of temperature and moisture fields. By analyzing sources and sinks of heat and moisture, this study reveals how parameterization components compensate for each other and make model results insensitive to parameterization changes in certain fields, thus suggesting the need to treat parameterizations as systems rather than individual components.

Evaluation of cracking potential for concrete arch dam based on simulation feedback analysis

It is still very difficult for researchers and engineers to implement the simulation analysis including a complete process and a full model with the complicated arch dam and the foundation, and to evaluate the cracking potential in the construction and service periods. To take Xiaowan project of China for an example, a practical system of simulation feedback analysis, a specific cracking criterion, and a resolution for the conflicting requirements of temperature and stress/strain simulation are presented, which are put into a successful practice. The simulation results of temperature, stress, and cracking are identical well with the monitor data. A modified temperature control measure is propounded, and the significant effect is gained by adopting the new scheme.

Popcorning-type cracking failure in thermohyperelastic packaging materials in the presence of “wet” and “dry” cavities

Thermal cracking occurs in the plastic packaging materials due to the presence of moisturized micro-cavities in the material.The moisture resident in the micro-cavities gives rise to the internal vapor pressure that drives the thermal expansion of micro-cavities as temperature rises.The plastic packaging materials are considered a class of thermo-hyperelastic materials,thus allowing the micro-cavities to thermally expand to the substantial extent before the cracking failure.The micro-cavities can be moisture-abundant(i.e.,wet) or substantially dry when cracking occurs.Cracking appears to be almost certain in the presence of wet cavities.The possibility of cracking in dry cavities turns to be two-sided:when the initial volume fraction of the micro-cavities is relatively small,cracking cannot occur in the dry cavities regardless of the phase transition temperature;when the initial cavity volume fraction is relatively large,cracking tends to occur in the dry cavities especially when the phase transition temperature is large.Because of the two-sided cracking possibility,the dry-cavity cracking mode presents a scenario that might reveal the mechanism of popcorning-type cracking failure in plastic packaging materials.

Dynamic Simulation and Performance Investigation of No-Frost Refrigerator:PartⅡSystem Simulation and Performance Analysis

The methodology for modeling no-frost refrigerator is described based on the component models developed in PartⅠ,and then,system simulation is applied to a BCD-235W refrigerator-freezer(RF).Experiments are carried out to study'pull-down'and steady-state performance of the RF,and to determine how the experiment and simulation temperature stack up against each other.Good match is found between simulated and measured results for the'pull-down'period.For the steady-state period,the simulation results are also found to agree well with experiment ones except for the temperature profiles of the refrigerator compartment(RC) and freezer compartment(FC).The average temperature and the energy consumption errors between measurement and simulation are less than 10%.Although the model can not reflect the non-uniform air temperature fields in the RC and FC,the variation range and periodicities of the temperature correlate well between the simulation and experiment.We conclude that such a model is valid for investigating the performance of no-frost refrigerator.