Compound Heat Transfer Enhancement of a Converging-Diverging Tube with Evenly Spaced Twisted-tapes

Pressure drop and compound heat transfer characteristics of a converging-diverging tube with evenly spaced twisted-tapes （CD-T tube） have been investigated experimentally. Swirl was generated by evenly spaced twisted-tape elements which vary in twist ratio and rotation angle. Space ratio also has an important effect on the characteristics. For comparison, experiments in a smooth circular tube and a converging-diverging （CD） tube with-out twisted-tapes were carried out. The results show that the twisted-tape with twist ratio y=4.72 and rotation angle θ=180° has the best performance among the four types of twisted-tapes presented in this paper. At Reynolds number ranging from 3400 to 20000, when space ratio s=48.6, the heat transfer efficiency index, which increases as the Reynolds number increases, is 0.85-1.21 and 1.07-1.15 compared to that of a smooth circular tube and a CD tube without twisted-tape inserts, respectively.

Simulation of Greenhouse Heating System Using Fuzzy Smith Cascade Compound Control

Aiming at characteristic of time delay, time-varying parameters and much disturb in glass greenhouse heating system, fuzzy smith cascade compound control policy based on typical PID cascade compound control policy is proposed. Simulation results show that it is effective to overcome the influence of time delay on stability of control system and the system possesses strong robust and good dynamic performance..

Heat balance of solar-soil source heat pump compound system

Based on the state-of-the-art studies of solar-soil source heat pump compound system, operation patterns of solar-soil compound system were analyzed, particularly the advantages of parallel operation pattern. It is found that parallel operation pattern is better for solar-soil compound system. Furthermore, the heat balance issue of solar-soil compound system was emphatically analyzed from four aspects, which were annual analysis of heating and cooling load, the heat exchange of ground heat exchanger, capacity determination of solar-assisted heat sottrce and heat balance calculation of solar-soil compound system. Moreover, annual rate of heat balance in a solar-soil source heat pump compound system was calculated with a case study. It is shown that the annual heat unbalance ratio is 19%, which is less than 20%. As a result, the practical solar-soil compound system can basically maintain the heat balance of soil.

Effects of heat treatment on the intermetallic compounds and mechanical properties of the stainless steel 321–aluminum 1230 explosive-welding interface

The effects of heat treatment on the microstructure and mechanical properties of intermetallic compounds in the interface of stainless steel 321 explosively bonded to aluminum 1230 were investigated in this study. Experimental investigations were performed by optical microscopy, scanning electron microscopy, and microhardness and shear tensile strength testing. Prior to heat treatment, increasing the stand-off distance between samples from 1 to 2.5 mm caused their interface to become wavy and the thickness of intermetallic layers to increase from 3.5 to 102.3 μm. The microhardness increased from HV 766 in the sample prepared at a stand-off distance of 1 mm to HV 927 in the sample prepared at a stand-off distance of 2.5 mm; in addition, the sample strength increased from 103.2 to 214.5 MPa. Heat treatment at 450°C for 6 h increased the thickness of intermetallic compound layers to 4.4 and 118.5 μm in the samples prepared at stand-off distances of 1 and 2.5 mm, respectively. These results indicated that increasing the duration and temperature of heat treatment decreased the microhardness and strength of the interface of explosively welded stainless steel 321-Al 1230 and increased the thickness of the intermetallic region.

A Compound Cycle for Power Generation by Utilizing Residual Heat of Flue Gas in Electric Steelmaking Process

Electric furnace short process steelmaking is one of the most important steelmaking methods in the world today, and the waste heat recovery potential of electric furnace flue gas is huge.?The research on the recovery of electric furnace flue gas waste heat is of great significance. In order to make better use of this part of the heat,?in this paper, a compound cycle of nitrogen Brayton cycle as a first-order cycle and toluene transcritical Rankine cycle as a second-order cycle is proposed to recover waste heat from furnace flue gas in steelmaking process for power generation. A mathematical model was established with the net output power as the objective function and the initial expansion pressure, the final expansion pressure, the initial expansion temperature and the initial pressure of the second cycle as the independent variables. The effect of multivariate on the net output power of the waste heat power generation cycle is studied, and then, the optimal parameters of the compound cycle are determined. The results show that under the general electric furnace steelmaking process, the power generation efficiency of this new cycle can be increased by 21.02% compared with the conventional cycle.

IN-SITU HVEM STUDY ON PHASE TRANSITION OF YBa_2Cu_3O_(7-x) SUPERCONDUCTING COMPOUND IN PROCESS OF HEATING

In-situ HVEM observation on phase transition of the YBa_2Cu_3O_(7-x) superconducting compound in pro- cess of heating was carried out,and high temperature X-ray diffraction analysis in air and X-ray diffraction phase analysis for the sample treated in vacuum condition were made.The results showed that the temperature of phase transition is related to oxygen content in the sample and in general,is 100℃ to 120℃ lower in vacu- um condition than in air.At 320℃ to 350℃ twin bands begin to disappear,and some Cu_2O are formed on the surface of the sample and transit from orthorhombic YBa_2Cu_3O_(7-x) to arthorhombic Y_2BaCuO_5 compound. This transition was completed at about 500℃.Above 900℃,this compound consists of the Y_2BaCuO_5, BaCuO_2,Y_2O_3 and some other minor compounds.No phase transition was observed during cooling the sample.

Anomalous low-temperature heat capacity in antiperovskite compounds

The low-temperature heat capacities are studied for antiperovskite compounds AX M_3（A = Al, Ga, Cu, Ag, Sn, X = C,N, M = Mn, Fe, Co）. A large peak in（C- γ T）/T^3 versus T is observed for each of a total of 18 compounds investigated,indicating an existence of low-energy phonon mode unexpected by Debye T^3 law. Such a peak is insensitive to the external magnetic field up to 80 k Oe（1 Oe = 79.5775 A·m-1）. For compounds with smaller lattice constant, the peak shifts towards higher temperatures with a reduction of peak height. This abnormal peak in（C- γ T）/T^3 versus T of antiperovskite compound may result from the strongly dispersive acoustic branch due to the heavier A atoms and the optical-like mode from the dynamic rotation of X M_6 octahedron. Such a low-energy phonon mode may not contribute negatively to the normal thermal expansion in AX M_3 compounds, while it is usually concomitant with negative thermal expansion in open-structure material（e.g., ZrW_2O_8, Sc F_3）.

Performance analysis on solar-water compound source heat pump for radiant floor heating system

A solar-water compound source heat pump for radiant floor heating (SWHP-RFH) experimental system was introduced and analyzed. The SWHP-RFH system mainly consists of 11.44 m2 vacuum tube solar collector,1 000 L water tank assisted 3 kW electrical heater,a water source heat pump,the radiant floor heating system with cross-linked polyethylene (PE-X) of diameter 20 mm,temperature controller and solar testing system. The SWHP-RFH system was tested from December to February during the heating season in Beijing,China under different operation situations. The test parameters include the outdoor air temperature,solar radiation intensity,indoor air temperature,radiation floor average surface temperature,average surface temperature of the building envelope,the inlet and outlet temperatures of solar collector,the temperature of water tank,the heat medium temperatures of heat pump condenser side and evaporator side,and the power consumption includes the water source heat pump system,the solar source heat pump system,the auxiliary heater and the radiant floor heating systems etc. The experimental results were used to calculate the collector efficiency,heat pump dynamic coefficient of performance (COP),total energy consumption and seasonal heating performance during the heating season. The results indicate that the performance of the compound source heat pump system is better than that of the air source heat pump system. Furthermore,some methods are suggested to improve the thermal performance of each component and the whole SWHP-RFH system.

Prediction of Heat of Fusion of Rare Earth Compounds from Binary Phase Diagrams

Based on the thermodynamical principle the new formula for calculation of heat of fusion and its error have been derived from binary phase diagrams which could be classified to eutectic,solid solution,degenerate eutectic and involving a compound phase diagram and so on.Using these formulae heats of fusion of some rare earth ox- ides have been predicted.

An Overview on Exogenous Compounds That Mitigate Heat Stress in Crops

With the global warming and climate change in recent years, heat stress has become one of the major abiotic factors constraining production and productivity of crops in many regions around the world. Although the plants have developed some adaptive behaviors and avoidance mechanisms against heat stress, they will be hurt under extreme high temperature. Exogenous compounds could enhance plant growth and development, antioxidant enzymes activities, chlorophyll and nutrient contents under stress conditions. Meanwhile, application of exogenous compounds sustains physiological and biochemical process and prevents plants from physiological changes under stress conditions. In this review, effects of heat stress upon crops, and the functions of hormones in plant adaptation to heat stress are simply stated. Then, we intend to appraise how various phytohomrnones that are related to plant adaptation to heat stress. The role of abscisic acid(ABA), salicylic acid(SA) and polyamines(putrescine and spermine) under heat stress conditions are mainly discussed.

Finite-Time Thermodynamic Simulation of Circulating Direct Condensation Heat Recovery on Chillers

A time series model is used in this paper to describe the progress of circulating direct condensation heat recovery of the compound condensing process (CCP) which is made of two water cooling condensing processes in series for a centrifugal chiller in the paper. A finite-time thermodynamics method is used to set up the time series simulation model. As a result, an upper bound of recoverable condensation heat for the compound condensing process is obtained which is in good agreement with experimental result. And the result is valuable and useful to optimization design of condensing heat recovery.

Calculated Lattice Energies of Energetic Materials in a Prediction of their Heats of Fusion and Sublimation

The paper specifies an unambiguous basic relationship between the published results of ab initio calculations of lattice energies, E L,and heats of sublimation, ΔH s,of individual energetic materials. In this relationship,the ΔH s value has been replaced by heats of fusion, ΔH m,tr . Thereby its unambiguity has been lost,and the similarity of details of molecular structure begins to be of decisive importance. The resulting partial relationships,together with the basic relationship,have been used for prediction of ΔH s,and ΔH m,tr values of technically attractive polynitro compounds.

Investigation on the interface of Cu/Al couples during isothermal heating

The evolutionary process and intermetallic compounds of Cu/A1 couples during isothermal heating at a constant bonding tem- perature of 550℃ were investigated in this paper. The interracial morphologies and microstructures were examined by optical microscopy, scanning electron microscopy equipped with energy dispersive X-ray spectroscopy, and X-ray diffraction. The results suggest that bonding is not achieved between Cu and A1 at 550℃ in 10 min due to undamaged oxide films. Upon increasing the bonding time from 15 to 25 min, however, metallurgical bonding is obtained in these samples, and the thickness of the reactive zone varies with holding time. In the interfacial region, the final microstructure consists of Cu9A14, CuAl, CuA12, and ct-A1 ＋ CuAl2. Furthermore, these results provide new insights into the mechanism of the imerfacial reaction between Cu and A1. Microhardness measurements show that the chemical composition exerts a signifi- cant influence on the mechanical properties of Cu/A1 couples.

More extreme-heat occurrences related to humidity in China

极端日夜复合高温往往会造成更为严重的社会经济影响及健康风险,受到了广泛关注。本文基于ERA5逐小时资料,针对中国区域极端日夜复合湿热和高温事件的变化及其影响进行了比较分析.结果指出,中国区域夏季极端湿热和高温在空间分布上较为一致,强度高值区主要分布在南方地区,但高频中心主要出现在北方地区.两类事件发生频次在全国范围内均呈明显增加趋势,尤其在西部和北部地区.进一步研究表明,在中国大部分地区,湿度异常在极端湿热事件变化中有着十分重要的作用,部分区域甚至超过温度异常的影响。随着极端湿热事件的增加其影响也在加剧,自1961年以来中国暴露于极端湿热事件的人口数量和城市面积增速明显大于高温事件.

Condensing Heat Recovery of Centrifugal Chiller

To a kind of centrifugal water chiller with R22 and about 1 745 kW of cooling capacity,a heat exchanger was added between the outlet of compressor and original condenser to get part of or all the condensing heat.Condensing heat can be recovered by compound condensing method,which adopts air-cooling model +water-cooling model or water-cooling model +water-cooling model at the condensing side of the system.By exergy analysis and experiment research on compound condensing heat recovery of centrifugal chiller,the results are obtained that the capability of the whole system increases,the energy efficiency ratio(EER)becomes 3.2～5.0 from 2.2～3.4,which implies the EER increases about 1.0～1.5,the exergy efficiency increases about 10%,and the chiller runs more stably after reformation.

Compound buried layer SOI high voltage device with a step buried oxide

A silicon-on-insulator （SOI） high performance lateral double-diffusion metal oxide semiconductor （LDMOS） on a compound buried layer （CBL） with a step buried oxide （SBO CBL SOI） is proposed. The step buried oxide locates holes in the top interface of the upper buried oxide （UBO） layer. Furthermore, holes with high density are collected in the interface between the polysilicon layer and the lower buried oxide （LBO） layer. Consequently, the electric fields in both the thin LBO and the thick UBO are enhanced by these holes, leading to an improved breakdown voltage. The breakdown voltage of the SBO CBL SOI LDMOS increases to 847 V from the 477 V of a conventional SOI with the same thicknesses of SOI layer and the buried oxide layer. Moreover, SBO CBL SOI can also reduce the self-heating effect.

Theoretical Studies on Property and Structure of Silacyclohexane-based Liquid Crystal Compounds

SCF-MO-AM1 calculations have been per formed on 10 silacyclohex-ane-based liquid crystal compounds by energy gradient completed optimization. The stable configurations, electronic structures, heats of formation, dipole moments and ionization potentials of titled comPounds are first reported. The calculated results are.discussed relating to the classical organic electronic theory.

麦芽酚碳酸酯的合成及其裂解行为分析

为开发适用于加热卷烟的麦芽酚潜香化合物,将不同种类的醇与麦芽酚通过缩合反应合成7种麦芽酚碳酸酯。利用核磁共振和高分辨质谱技术对产物结构进行确认,并通过热重分析和在线热裂解-气相色谱-质谱联用分析技术考查7种麦芽酚碳酸酯的裂解行为。结果表明:在优化的合成条件下,7种麦芽酚碳酸酯产率范围为83.0%~94.3%;合成的麦芽酚碳酸酯的热失重过程主要存在直接挥发和裂解两种模式;麦芽酚碳酸酯在加热时均可裂解生成麦芽酚,其裂解能力与原料醇的类型密切相关,其中麦芽酚叔丁醇碳酸酯和麦芽酚苯甲醇碳酸酯最易发生裂解,在200℃的较低温度下便可迅速裂解并释放麦芽酚,与加热卷烟烟丝受热温度相适应,相比之下,麦芽酚仲醇碳酸酯的裂解能力较弱,而麦芽酚伯醇碳酸酯则难以在低温条件下发生裂解。

复方中药对热应激条件下肉牛生理指标、生长性能及血清生化指标的影响

试验旨在探讨复方中药对热应激条件下肉牛生理指标、生长性能及血清生化指标的影响。选取体况良好、体重相近的育肥期夏南牛24头,随机分为4组,每组6个重复,每个重复1头牛。对照组饲喂基础饲粮,试验组分别在基础饲粮中添加0.5%、1.0%和1.5%的复方中药。试验期30 d。结果显示:整个试验期间牛舍内环境温湿指数(THI)大于72,牛处于热应激状态。在试验第20、30 d,1.0%组和1.5%组牛的呼吸频率显著低于对照组(P<0.05)。与对照组相比,1.0%组牛的干物质采食量和平均日增重显著升高(P<0.05),0.5%和1.0%组的料重比显著降低(P<0.05);1.0%组的总蛋白(TP)、白蛋白(ALB)、球蛋白(GLB)含量、总抗氧化能力(T-AOC)以及谷胱甘肽过氧化物酶(GSH-Px)、超氧化物歧化酶(SOD)活性显著升高(P<0.05),尿素氮(BUN)、葡萄糖(GLU)和丙二醛(MDA)的含量显著降低(P<0.05);1.0%和1.5%组的免疫球蛋白G (IgG)和白细胞介素-6 (IL-6)含量显著升高(P<0.05)。研究表明,饲粮中添加复方中药可以改善肉牛的热应激反应,添加量以1.0%效果较好。

Thermodynamic Simulation of CCP in Air-Cooled Heat Pump Unit with HFCs and CO₂Trans-Critical

The exergy analysis and finite time thermodynamic methods had been employed to analyze the compound condensation process (CCP). It was based on the air-cooling heat pump unit. The cooling capacity of the chiller unit is about 1 kW, and the work refrigerant is R22/R407C/R410A/CO2. The MATLAB/SIMULINK software was employed to build the simulation model. The thermodynamic simulation model is significant for the optimization of parameters of the unit, such as condensation and evaporation temperature and mass flow of the sanitary hot water and size of hot water storage tank. The COP of the CCP of R410A system is about 3% - 5% higher than the CCP of the R22 system, while CCP of the R407C system is a little lower than the CCP of R22 system. And the CCP of CO2 trans-critical system has advantage in the hot supply mode. The simulation method provided a theoretical reference for developing the production of CCP with substitute refrigerant R407C/R410A/CO2.