Numerical verification of the continuous calculation method for tip stress during the driving process of the dynamic penetration test

This paper presents a calculation method for obtaining the continuous variation in stress between the tip and the soil during dynamic penetration tests, particularly in the case of using the Panda 3® penetration testing device. The originality of the method is that the tip stress can be computed continuously throughout the driving process. For each impact of the hammer on the penetrometer, data are recorded by sensors located at the top of the apparatus. Then, the stress at the tip and the displacement of the apparatus are calculated with a method based on the propagation of waves in the device. A three-dimensional numerical model of the penetration test, based on the Panda 3® specifications and using the discrete element method (DEM), is proposed in this paper. The purpose of the simulations is to validate the calculation method by comparing the curves of the tip stress versus the penetration distance obtained in two different ways, the first being the distance directly observed at the tip and the second being the distance calculated from the data recorded at the top of the penetrometer, as with the experimental device. The entire apparatus is represented, including the hammer, the rod, and the tip, and is driven into the model soil. The calculation method is applied, and the results are compared to the actual response of the soil to the driving of the penetrometer directly at the tip, which can be obtained with the numerical model. The responses are found to be very similar, confirming the theoretical framework and its underlying assumptions. This method is applied to dynamic penetration tests and provides the opportunity to obtain mechanical parameters other than the tip resistance from the tests.     

Reducing the power consumption of household refrigerators through the integration of latent heat storage elements in wire-and-tube condensers

This study evaluates the influence of latent heat storage elements on the condenser temperature of a commercial household refrigerator. In order to determine the power consumption and the temperature distribution, a standard wire-and-tube condenser is equipped with different heat storage elements (containing water, paraffin or copolymer compound). The results indicate that particularly the application of phase change materials (PCM) lowers the condenser temperature, which leads to a significantly reduced power consumption.     

A general model for two-stage vapor compression heat pump systems

Two-stage vapor compression technology has high potential of performance improvement for cold climate heat pumps, and there are several types of inter-stage configurations that need to be evaluated before making a choice. A general model of these configurations is first derived from a subcooler cycle and then is extended to be capable of evaluating many other inter-stage configurations by employing an “input domain”. The model is solved with a sequential algorithm and an analytical initial solution of the intermediate pressure is presented. After an experimentally validation with additional calculations of the subcooling parameter, the evaporating and condensing pressure, this general model is then used in the performance comparison and analysis of eight different inter-stage configurations. At last, case studies show that, this general model is capable of performing performance comparison among cycles with different types of inter-stage configurations, as well as refrigerant selection and operational analysis.     

Experimental study on the heat transfer and flow characteristics of nanorefrigerants inside a corrugated tube

The heat transfer and flow characteristics of MWCNT-R141b nanorefrigerant with different mass fractions have been studied through experiments. Experimental results were compared with existing correlations. A two-step method was used to prepare the nanorefrigerants. Span-80 was used as surfactant with an average particle diameter of 20 nm. Transmittance method was used to evaluate the stability of nanorefrigerants. Results showed that the stability of MWCNT-R141b nanorefrigerant, which is the added dispersant, was good during the experiments. The 0.3 wt% MWCNT-R141b nanorefrigerants had optimal heat transfer enhancement effects compared with pure refrigerants. The maximum Nusselt number increased by 40%. The specific pressure drop of nanorefrigerant increased as the Reynolds number (Re) increased, and the specific pressure drop of the pure refrigerant was minimum, which is similar to R141b.     

Maldistribution in air–water heat pump evaporators. Part 1: Effects on evaporator,heat pump and system level

This paper presents an approach to quantify the effect of evaporator maldistribution on operating costs of air–water heat pumps. In the proposed simulation model maldistribution is induced by two parameters describing refrigerant phase and air flow distribution. Annual operating costs are calculated based on heat pump performance at distinct operating conditions. Results show that percentage increase of operating costs is similar for the three considered climate zones, even though the effect of maldistribution on heat pump performance varies with operating conditions. Differences in terms of absolute cost increase for the climate zones arise mainly due to a varying number of operating hours. Absolute cost increase is considerable in the average and especially colder climate zone and can only partly be reduced by enlarging the evaporator.     

Development and validation of a micro-fin tubes evaporator model using R134a and R1234yf as working fluids

This paper presents a model of shell and tube evaporator with micro-fin tubes using R1234yf and R134a. The model developed for this evaporator uses the ε-NTU method to predict the evaporating pressure, the refrigerant outlet enthalpy and the outlet temperature of the secondary fluid. The model accuracy is evaluated using different two-phase flow boiling correlations for micro-fin tubes and comparing predicted and experimental data. The experimental tests were carried out for a wide range of operating conditions using R134a and R1234yf as working fluids. The predicted parameter with maximum deviations, between the predicted and experimental data, is the evaporating pressure. The correlation of Akhavan– Behabadi et al. was used to predict flow boiling heat transfer, with an error on cooling capacity prediction below 5%. Simulations, carried out with this validated model, show that the overall heat transfer coefficient of R1234yf has a maximum decrease of 10% compared with R134a.     

An experimental investigation of refrigerant mixture R32/R290 as drop-in replacement for HFC410A in household air conditioners

In the present paper, the refrigerant mixture R32/R290 (68%/32% by weight) is investigated as the drop-in replacement for R410A in household air conditioners. The GWP of it is only 22% of that of R410A. Theoretical and experimental investigations are conducted on the performance of the air conditioners working with both R32/R290 and R410A. Experimental results show that the refrigerant charge amount of R32/R290 is reduced by 30.0%–35.0%; the cooling and heating capacities are increased by 14.0%–23.7%. For further reducing charge amount and flammability, the micro-channel heat exchanger (condenser) is employed to replace the finned tube one. Compared with the R32/R290 system using finned tube heat exchanger, the R32/R290 charge amount and the power consumption are reduced by 34.1% and 0.4%, respectively; the cooling capacity and the COP are increased by 6.4% and 6.8%, respectively.     

单片机网络在智能化小区中的设计和应用

随着控制技术的发展，控制系统越做越复杂，由单片机构建的控制系统已经由一个单片机组成的系统发展到多个单片机组成的多机控制系统和多个单片机组成的网络系统。在工业监控和民用产品中单片机系统使用的越来越多。随着技术的发展和市场竞争的加剧，生产厂家除了考虑到产品的性能也要考虑到产品成本。Microehip公司的PIC16C57是一款性价比较高的单片机。由该单片机建立起来的系统成本大大降低。本文介绍了一种由PIC16C57单片机建立起来的分级总线型网络系统，系统可以用于工业系统监控和民用楼宇监控系统，该网络系统在硬件和软件上都采取了特别的保护措施，系统具有非常好的稳定性和可靠性。     

智能气门电镦机人机交互及串行通讯程序

介绍了智能气门电镦机的数据显示和命令输入的人机界面(HMI)和实现电镦机实时控制功能的下位计算机之间利用RS232串行接口的通讯程序的编写，以及实现硬件定时的原理和方法．实践证明，该系统人机界面美观、实时性能可得到保证，符合气门电镦的工艺要求．     

无人值班变电站监控系统三级通讯网络的设计与实现

文中主要介绍了井下采区无人值班变电站监控系统中测控单元、智能通讯接口 (工控机 )、监控主机三级网络通讯的硬件设计与软件实现。实践证明 ,该系统具有较高的可靠性 ,并在现场取得良好的效果