Herein, we proposed a cascade refrigerant system with R1270 and carbon dioxide refrigerants. The natural refrigerant R1270 was adopted in the high-temperature circuit to replace NH3 and R290. A prototype cascade refrigerant system with two semi-hermetic piston compressors was manufactured, and its performance was investigated experimentally. The results establish R1270 as a good alternative in the high-temperature circuit of the cascade refrigerant system. Moreover, with a constant condensation and evaporation temperature of cascade system, as the R1270 evaporation temperature was decreased (from -7 degrees C to -19 degrees C), the coefficient of performance (COP) of the cascade system increased. The isentropic efficiency of R1270 compressor decreased from 78.5% to 74.7% when the R1270 evaporation temperature increased from -19 degrees C to -7 degrees C. (C) 2020 Elsevier Ltd and IIR. All rights reserved.

A theoretical calculation of the R1270/CO2 cascade refrigeration system has been carried out to get a comprehensive understanding of the performance.The paper analysis the evaporating temperature,the condensing temperature,the condensing temperature of CO2 and the heat transfer temperature difference of condenser evaporator on the COP and exergy destruction with the thermodynamics and exergy analysis method.In the condition of other variables there was a maximum COP and minimum exergy destruction with a optimal condensing temperature of CO2.In order to increase the COP and decrease the loss of exergy,it is necessary to increas the evaporating temperature,reduce the ondensing temperature and heat transfer temperature difference of condenser evaporator.Therefore the main section causing the loss of exergy at high temperature part and the condenser-evaporator,need to make it optimize.Reducing the condensation temperature of CO2,the condensing temperature of the system and increasing the evaporation temperature of the system can reduce the charge of R1270 in the system.

The sloshing characteristic of LNG in the container with five identical arcuate and hole-shaped baffles was simulated under the condition of suddenly braking for some object.By comparing the impacts of changes in pressure of the container wall and baffles,the result shows that arcuate baffles can be significantly reduced against liquid sloshing,however the pressure difference between the five arcuate baffles is large,likely to cause a single baffle damaged due to excessive force.Research on the performances of three kinds of baffles for 4-hole,12-hole,36-hole shows that the number of hole-shaped on the performance of baffle is not obvious when the effective area of baffle is equal to half of container cross-sectional area.

FLUENT software was adopted to simulate the sloshing process of liquid in container under the sudden braking condition based on VOF (volume of fluid) model.The pressure variation of front and back head was compared,which showed that the sloshing liquid mainly had a greater impact on the front head.Baffles could effectively weaken the sloshing in the container,reduce the impact on the head and improve the container safety.The liquid impact on front head was studied in the condition of different filling ratio for different baffle arrangement(all down,all up,up and downinterlaced,left and right interlaced) of five same arc baffles.Results show that the arrangement style of left and fight interlaced 、all down could reduce impact load on front head for low filling ratio,however the arrangement style of up and downinterlaced all up had poor anti-wave effect.The anti-wave effect of the arrangement style of left and right interlaced became poorer and poorer with the increment of filling ratio.Compared with other arrangement style,the arrangement style of all down had better anti-wave effect.

A three-dimensional one-channel model was established,the effect of corrugated clination angle and corrugated pitch on heat transfer and pressure drop of phase change flow was simulated.The results show that the heat transfer characteristics of the flow boiling are affected by both the flow pattern and the contact point.The "helical flow" promots evaporation of liquid film,and the contact point has less effect on gas than liquid,therefore,the phenomenon of gas-liquid phase transition is not obvious at the higher gas volume fraction.The heat transfer coefficient increases with the increasing of the corrugated inclination angle,and decreases with the increasing of the corrugated pitch.The heat transfer coefficient of λ=16 mm is larger than that of λ=14 mm at same Reynolds number,because the change of the flow pattern may prevent the heat transfer caused by the reduction of the number of contacts.The heat transfer is the best at β=75° and λ=10 mm.The pressure drop of the flow boiling increases at first and then decreases with the increasing of the corrugated inclination angle,and reaches the peak at about β=65°,and decreases with the increasing of the corrugation pitch.

In order to improve heat transfer performance of the evaporative condenser plate and enhance the gas-liquid two-phase flow,four heat-exchange plates of internal fin-plate evaporative condenser were developed. The water film flowing form with different spray densities and the influence of spray density on heat transfer of heat-exchange plate were investigated. The results showed that the thickness of water film thinned with the decrease of the spray density. Affected by the plate type and gas fluid shear stress,water film flowing gathered toward the center area,and the splash of water film appeared in local area with larger spray density. With the decrease of spray density,the splash of water film disappear gradually. However,in the low spray density,the"dry sports"phenomenon had produced on the some internal fin-plate. When the spray density were 0.524kg/(m·s),0.738kg/(m·s),0.905kg/(m·s),the performance of heat transfer of semicircle corrugated plate was superior to the other plates. Also,heat-exchange area of plate and stable time of water film were the main factors that affected heat transfer performance under these spay densities. The experimental results provide the theoretical reference of engineering application and design of internal fin-plate evaporative condenser.

新形势下专业英语课程培养必须与时俱进,充分发挥学生的主体作用,激发学生学习的主动性和积极性,兼顾学生翻译、听、说、读、写综合能力的培养.论文针对目前理工科专业英语课程存在的教学现状,结合新时代复合型人才的培养目标以及相关教学经验,从课程设置、教学内容、教学模式、考核方式等几方面对理工科专业英语教学改革提出了几点意见.

To study the impact of natural gas with different components on the performance of LNG spiral-wounded ex changer,numerical simulation was conducted in this paper to analyze the flow and heat transfer characteristics of different components natural gas in the spiral-wounded tube.Six natural gases with different composition of methane and ethane at 6.4MPa were used as working fluids.The impact of the proportion of component ethane in the mixture,Re and Pr on the pressure drop and Nu of these 6 natural gas mixture in the spiral-wounded tube were studied carefully.The results show that with the increase of the proportion of component ethane in the mixture,the increasing amplitude of the pressure drop of the gaseous mixture with the increase of Re will become smaller,while that of the pressure drop of the liquid mixture will become larger.In the state of gas,the increase of ethane component will enhance the heat transfer in the tube,whereas in the state of liquid,the increase of ethane component will weaken the heat transfer in the tube.The Nu formulae are also fitted in terms of simulation results.

In order to improve the cooling capacity of radiant cooling plate and the performance of the plate sur-face condensation,different water temperature,tube velocity and indoor relative humidity conditions were used as experimental study variables with the method of visual research on the established radiant cooling condensa-tion system and the test platform of the change of thermal performance.The results showed that when the water flow rate increases from 40 L/h to 1 20 L/h,the cooling capacity increased nearly doubled and condensation time was reduced by 1 5 min;The indoor temperature and humidity was 26 ℃,75%,the first condensation time was 8 min;the cooling capacity of copper plate was stronger compared with PPR capillary tube radiation model;The state of dew condensation on the surface of the radiation plate was more disorganized with lower water temperature and amount of condensation.When the indoor temperature and humidity was 26 ℃,60%,the maxi-mum size of water drops the length was 9.6 mm,the width was 8.8 mm on the surface of the radiant panel.

In order to improve the heat transfer and fluid flow performance of external gas-liquid two phase flow of plate in the evaporative condenser, the new surfaces of plate are comparatively analyzed. The effect of the different kinds of surface structure，spray density of water and air inlet velocity on the characteristics of gas-liquid two-phase flow and the performance of heat transfer are investigated. The results show that: the semicircle wavy plate has longer time of water film forming and larger heat transfer area and better performance of heat transfer; different plate structures of the evaporative condenser have different optimal spray density of spray water, and the optimal spray density are from 0.48 kg/m?s to 0.93 kg/(m?s); when the air inlet velocity is constant, the wall temperature of semi-circle wavy plate is increased and the temperature of gas-liquid interface is decreased with the increasing of spray density; when the air inlet velocity is less than 2.5 m/s, the increasing air inlet velocity can effectively reduce thickness of water film of external semicircle wavy plate and enhances heat transfer.

建立冷热双流道模型,研究了不同波纹参数对其传热和压降性能的影响,分析了传热机理.结果表明,板式换热器的传热和压降性能主要受流体流动形式和触点密度的影响.波纹倾角β=70°时传热效果最好但压降较大,波纹深度对传热性能的影响效果比波纹倾角和波纹节距大8％和15％左右,波纹倾角对压降性能的影响大于波纹节距.

相变蓄冷技术在食品冷链的各个环节中都具有广泛的应用前景,对促进食品冷链的快速发展具有重要意义.本文阐述了相变蓄冷技术在冷库、冷藏车和冷藏陈列柜等冷链环节的研究现状,同时对相变蓄冷材料在食品冷链中的应用进行了论述,最后分析了我国食品冷链的发展趋势.

以玻纤增强聚丙烯(FRPP)复合管材缠绕成型性能及其关联的成型过程参数为对象,基于留一法交叉检验的手段,采用径向基神经网络(RBFNN)建模的方法研究了FRPP复合管材缠绕成型性能预测模型.结果表明,预测层间剪切强度、环向拉伸强度时,分别存在的一种RBFNN模型的检验最大相对误差≤0.001％.对学习好的RBFNN模型进行敏感度分析表明,玻纤增强聚丙烯(FRPP)复合管材缠绕成型性能及其关联的成型过程参数之间的关系为高度非线性关系.性能最好的工艺参数分析说明所建立的模型是可靠的.

为研究CO2在热泵领域的应用,本文通过搭建跨临界CO2热泵系统实验台,对其在变工况条件下的性能进行研究和分析,找出热泵系统性能系数最佳的工况条件,为跨临界CO2热泵系统推向市场化提供试验依据.试验结果表明:当出水温度tter.w超过50℃时,随着热泵系统的高压压力Pcond升高,系统的性能系数(COPH)呈现先升高后降低的特点,有一个峰值,该峰值所对应的高压压力就是最优高压压力P嘣;且蒸发温度tev越高,热泵系统的COPH也随之升高.

In order to obtain better performance of louvered fin,four different louvered fins with the successively increasing or decreasing louvered angle are proposed based on the louvered fin and the characteristic of heat transfer and fluid flow of new louvered fins are investigated.The attack angle of five different louvered fins are LF1+2°(22°,24°,26°,28°,30°,28°,26°,24°,22°),LF2+3°(18°,21°,24°,27°,30°,27°,24°,21°,18°),LF3 0° (uniform attack angle 30°),LF4-3°(30°,27°,24°,21°,18°,21°,24°,27°,30°) and LF5-2°(30°,28°,26°,24°,22°,24°,26°,28°,30°).The numerical results show that the heat transfer coefficient of louvered fins with continuous variable angle of attack are slightly lower than the uniform louvered angle fin,but the flow resistant decreases dramatically Therefore,the overall performance of louvered fins with continuous variable angle of attack is better than that of uniform louvered angle fin.This means that under the same pressure drop,the louvered fins with continuous variable angle of attack has better heat transfer performance When Re =408 ～ 1230,the overall performance of LF2 and LF4 are the best.

In order to improve the performance of refrigerated display cabinet, decrease the food temperature and restrain the temperature fluctuation during defrosting, a kind of composite shelf is proposed in the food refrigerated display cabinet (RDC) based on the high-thermal conductivity of heat pipe and cool storage of phase change materials. The influence of three phase change materials of RT3, RT4, RT5 on the temperature of food packages, the characteristic of heat transfer and cool storage of composite shelf were investigated. Compared with the ordinary shelf, the food temperature on composite shelf of RT3 reduces by 13.7%-80%, temperature fluctuation decreases 53.3%-70%; the food temperature on composite shelf of RT4 reduces by 20%-83.3%, temperature fluctuation decreases 83.3%-87.5%; the food temperature fluctuation on composite shelf of RT5 decreases 66.7%-75%. Compared with the other two composite shelves, the average food temperature of each floor and each row on composite shelf of RT4 is the lowest and within 5℃, thus the cool storage performance of phase change material of RT4 is the best.

通过实验对一种可进行热回收即热式热水供应的家用空调进行了“制冷”、“热回收”、“供暖”功能研究.研究表明:该系统方便可行、性能稳定可靠,能满足设计的要求.标准工况下,热回收时系统综合能源利用系数COP达到了5.2,相对于单制冷工况提高了约2.78;供暖时制热功率为10.72kW,能效系数为2.72.

The design of air conditioning which is an import course of energy and Power Engineering in our unversity is applied as an example. The new refrigeration technology and equipment in air conditioning system are applied as case in the teaching process, the students can understand deeply the structure characteristics of the product, the design requirements and the scope of application through this kind of teaching mode and method and which can provoke learning interest and improve the effect of teaching in the classroom.

低温贮运设备经历堆积绝热、高真空绝热、真空粉末(纤维)绝热和高真空多层绝热四个阶段,形式有低温贮罐、低温运输车、低温铁路罐车和船载低温罐等,目前高真空多层绝热凭借优异的绝热性能被广泛采用.回顾了低温贮运设备的发展历程,对低温贮运设备的抽真空工艺、支撑结构、无损贮存和制造过程质量控制等关键技术进行了阐述并提出了发展方向.对低温贮运设备未来的发展趋势进行了展望.