绝热毛细管长度的设计计算

分析了毛细管内制冷剂的流动过程,运用两相流动的均相流模型建立了绝热毛细管的数学模型,开发了毛细管长度的计算程序,该程序对新工质制冷系统毛细管的设计具有一定的参考价值。     

Simulation on refrigerant flow in adiabatic capillary tube

This paper proposes a new mathematical model to calculate flow characteristics of the adiabatic capillary tube, which is aimed at solving problems existing in some earlier models. The Stocker’s model was modified with consideration of various effects due to sub-cooling, area concentration, and rolling diameter. The new model can be used not only for R22, but also for its substitutes such as R410A and R407C. A comparison of simulation results of the modified model with those in literature showed that the errors are within 10%. The flow characteristics are finally analyzed.     

绝热毛细管长度数值计算

根据均相流假设,运用两相流动基本方程建立了绝热毛细管分布参数的稳态数学模型,结合制冷工质HFC-134a基于MH状态方程的热力学性质计算模型,采用新的基团贡献法计算粘度,用熵增判据考虑壅塞流动的影响,进行数值模拟计算确定毛细管长度。对理论计算结果与相关文献的实验数据进行比较,结果吻合得很好,计算精度有所提高。     

Quality measurement of refrigerant two-phase flow in refrigeration cycles

In refrigeration cycles, quality measurement of two-phase refrigerant flow is required to monitor the cycle operation. Although sectional void fraction of the two-phase flow can be detected in several ways, the quality of the two-phase flow is hardly obtained from the sectional void fraction since velocities of liquid- and gas-phase in the pipe are different from each other. In this study, a new quality measuring method was developed by installing multiple narrow tubes in a test section. By installing a gas bypass tube with the multiple narrow tubes, the quality measurement having an accuracy within 0.03 was achieved in the quality range from 0.05 to 0.8. In addition, the influence of oil contamination in the refrigerant flow on the flow pattern in the narrow tube was examined. It was found that the flow pattern in the narrow tube became bubble flow by the mixing of oil.     

Performance investigation of capillary tubes for machine tool coolers retrofitted with HFC-407C refrigerant

The machine tool coolers are the best managers of coolant temperature in avoiding the deviation of spindle centerline for machine tools. However, the machine coolers are facing the compressed schedule to phase out the HCFC (hydro-chloro-floro-carbon) refrigerant and little attention has been paid to comparative study on sizing capillary tube for retrofitted HFC (hydro-floro-carbon) refrigerant. In this paper, the adiabatic flow in capillary tube is analyzed and modeled for retrofitting of HFC-407C refrigerant in a machine tool cooler system. A computer code including determining the length of sub-cooled flow region and the two phase region of capillary tube is developed. Comparative study of HCFC-22 and HFC-407C in a capillary tube is derived and conducted to simplify the traditional trial-and-error method of predicting the length of capillary tubes. Besides, experimental investigation is carried out by field tests to verify the simulation model and cooling performance of the machine tool cooler system. The results from the experiments reveal that the numerical model provides an effective approach to determine the performance data of capillary tube specific for retrofitting a HFC-407C machine tool cooler. The developed machine tool cooler system is not only directly compatible with new HFC-407C refrigerant, but can also perform a cost-effective temperature control specific for industrial machines.     

Air velocity and flow measurement using a Pitot tube

The accurate measurement of both air velocity and volumetric airflow can be accomplished using a Pitot tube, a differential pressure transducer, and a computer system which includes the necessary hardware and software to convert the raw transducer signals into the proper engineering units. The incorporation of sensors to measure the air temperature, barometric pressure, and relative humidity can further increase the accuracy of the velocity and flow measurements. The Pitot tube measures air velocity directly by means of a pressure transducer which generates an electrical signal which is proportional to the difference between the pressure generated by the total pressure and the still air (static pressure). The volumetric flow is then calculated by measuring the average velocity of an air stream passing through a passage of a known diameter. When measuring volumetric flow, the ‘passage of a known diameter’ must be designed to reduce air turbulence as the air mass flows over the Pitot tube. Also, the placement of the pitot tube in the passage will influence how accurately the measured flow tracks the actual flow through the passage. Calibrating the measurement system in a wind tunnel can further increase the accuracy of the velocity and the flow measurements. This objective of this paper is to provide the field engineer with single, concise source of information on flow measurement using a Pitot tube.     

铜管行星轧制过程金属流动规律的研究

采用有限元软件MSC.MARC的三维网格重划分功能对铜管行星轧制从咬入到稳定轧制的全过程进行了有限元仿真分析,对轧制过程中金属的流动规律进行了研究。结果表明:管坯在轧制过程中发生了两次扭转;运用目前的设备,无法实现轧件在轧制过程中完全不转动,只能调试电机转速使轧件出口不转动。     

Application of averaging bidirectional flow tube for measurement of single-phase flow rate in a piping system

A new instrument, an averaging bidirectional flow tube (BDFT), is proposed to measure single-phase flow rates. This averaging BDFT has unique measuring characteristics foremost among which is the capability to measure bidirectional flow and insensitivity of the fluid attack angle. Single phase calibration tests were conducted to demonstrate the performance of the averaging BDFT. Likewise, to enhance the applicability of the averaging BDFT on various flow conditions, flow analyses using CFD code were performed focusing on design optimization of the BDFT. The calibration test results indicated that this averaging BDFT has a linearity within 0.5 % in the Reynolds (Re) number range of above 10,000 where it is meaningful in terms of application. The flow analyses results demonstrate a good linearity of the averaging BDFT with various design features. Therefore, averaging BDFT can be applied for measurement of flow rates within a wide range of flow conditions. This paper was recommended for publication in revised form by Associate Editor Won-Gu Joo Kyoung-Ho Kang received his B.S. and M. S. degrees in Nuclear Engineering from SNU (Seoul National University), KOREA in 1993 and 1995, respectively. He then received his Ph.D. degree in Nuclear and Quantum Engineering from KAIST (Korea Advanced Institute of Science and Technology) in 2009. Dr. Kang is currently a senior researcher at the Korea Atomic Energy Research Institute in Daejeon, Korea. Dr. Kang’s research interests include analysis and experiments for the nuclear safety, thermal hydraulics, and experiments and modeling for the severe accidents. Byong-Jo Yun received his B.S. degree in Nuclear Engineering from SNU (Seoul National University), KOREA in 1989. He then received his M.S. and Ph.D. degrees from SNU in 1991 and 1996, respectively. Dr. Yun is currently a principal researcher at the Korea Atomic Energy Research Institute in Daejeon, Korea. Dr. Yun’s research interests include analysis and experiments for the nuclear safety, thermal hydraulics, two-phase flow, scaling analysis, and development of instrumentation for two-phase flow. Dong-Jin Euh received his B.S. degree in Nuclear Engineering from Seoul University, Korea, in 1993. He then received his M.S. and Ph.D. degrees from same university in 1995 and 2002, respectively. Dr. Euh is currently a researcher at thermal hydraulic safety research department of Korea Atomic Energy Research Institute in Daejeon, Korea. Dr. Euh’s research interests include two-phase thermal hydraulics in the Nuclear Systems and Fundamental Phenomena. Won-Pil Baek has been working at KAERI as the general project manager (director) for development of nuclear thermalhydraulic experiment and analysis technology since 2001. He received his B.S. degree in nuclear engineering from Seoul National University and his M.S. and Ph.D. degrees from KAIST. In 1991–2000, he worked for KAIST as a researcher and research professor. Currently he also serves as an executive editor of the Nuclear Engineering and Technology, an international journal of the Korean Nuclear Society. His research interests include critical heat flux, integral effect tests, modeling, nuclear safety, and advanced reactor development.     

CO_2跨临界循环中非绝热毛细管传热性能的试验研究

为了测试在相同工况下,CO2跨临界循环非绝热毛细管各区段的换热能力;并测试毛细管进口压力10MPa,进口温度39℃,蒸发温度7℃,制冷量1k W时,5种内径毛细管所需的长度,以及毛细管换热量随毛细管管径的变化情况,搭建了CO2跨临界循环试验台,进行了相关试验,试验结果表明:非绝热毛细管在超临界区域换热能力最强,亚临界两相区换热能力最弱,毛细管换热量随毛细管内径增大而增加。     

管壳式换热器壳程流动和传热的数值模拟研究进展

介绍了管壳式换热器壳程流体流动和传热的数值模拟的国内、外研究状况及其发展方向。     

基于阵列探头的 PFA 管超声导波流量测量

PFA管材耐腐蚀性好、性能稳定,被广泛应用在半导体等行业的药液运输中,为精确控制药液的用时和用量,需要研究小管径PFA管的非接触式流量测量方法。本文使用超声阵列外卡探头在PFA细管上激励超声导波,并利用导波测量流量。首先比较超声斜探头模态选择和阵列探头模态选择原理的不同,说明阵列探头的频率选择特性,进而设计阵列探头阵元宽度、厚度并制作了三种间距的阵列探头,通过频率扫描得到阵列探头的激励接收特性,比较分析了阵列探头的模态选择效果,并进行了流量测量实验。结果表明阵列探头可增强接收信号强度,提高测量灵敏度,改变阵列间距可以选择不同导波模态,在3 mm PFA管上选择L(0,5)导波模态时流速范围0～6.70 m/s内的测量结果误差限为±0.22 m/s。     

制冷与空调系统中毛细管流量的测试方法研究

分析了目前制冷工业生产中对毛细管进行检测的现状,指出了现有检测方法存在的缺陷,提出了一种新的方法——等效对比代换法。根据此新方法,设计了一种新的毛细管流量检测装置。同时,在研究分析的基础上,对毛细管实验方法的国家标准GB/T23683—2009提出了新的建议和补充。     

基于 C 4 D 技术的非满管液体流速测量方法研究

为满足目前小型化设备中液体流速测量的需求,通过将空间滤波测速与电容耦合非接触电导测量(C~4D)技术相结合,提出了一种适用于非满管液体流速测量的新方法。设计了一种轴向两电极结构的C~4D传感器,采用COMSOL仿真软件建立了传感器的三维仿真模型,并对其空间灵敏度分布特性进行了分析,然后基于该传感器的空间滤波效应对液体流速测量原理进行了理论推导,并采用等效峰值频率的方法得到了速度测量的数学表达式;在此基础上,设计了一套可适用于空间滤波的C~4D液体流速测量系统,并通过该测量系统验证了C~4D传感器具有良好的空间滤波效应,且实验结果表明,该测量方法具有良好的可行性,在1.39～2.35 m/s的速度范围内,测量速度的绝对误差均在5%以内。     

微管中界面滑移的流体运动

在微流尺度下液体的流动研究表明:流体在固液边界处存在滑移现象,由此引起液体的流动阻力减小.许多试验证明,水在疏水表面流动时,具有流动边界速度滑移现象.该文通过推导得到了层流条件下,滑移速度和滑移长度的线性关系;然后通过计算得到滑移长度随着块相粘度和边界层粘度比值的变化关系;最后通过图形方法,分析了滑移长度对流速剖面和流...     

钢管冷斜轧成型研究

提出了采用冷斜轧方法生产冷轧钢管的新工艺 ,对其理论成型的特点进行了研究 ,对实践该新工艺进行了探讨。冷斜轧技术的应用将会给企业带来好的经济效益     

变径毛细管代替毛细管组件在冷暖空调器上的应用研究

变径毛细管在正向流动和反向流动时其制冷剂流量特性不同,因而可以作为节流元件代替现有冷暖空调器中使用的毛细管组件。为实现这一目的,利用制冷剂流量试验台,先测定原毛细管组件制冷、制热时的制冷剂流量特性,然后通过调整变径毛细管规格尺寸,使变径毛细管制冷、制热时的流量特性与原毛细管组件基本一致,再安装在空调器整机上进行整机性能对比试验。试验表明,在标准工况下,新空调器与原空调器相比,其制冷量减少0.5%,制冷能效比增加0.3%,制热量减少1.1%,制热性能系数增加1.4%。因此可以得出,变径毛细管经过精确匹配,完全可以作为节流元件代替现有冷暖空调器中使用的毛细管组件。     

制冷空调系统毛细管和压缩机流量匹配研究

对小型制冷系统毛细管和压缩机的匹配进行理论实验研究,分别建立毛细管和压缩机的流量模型,然后用实验值对压缩机模型进行修正,对Ｒ１２,Ｒ１３４ａ,Ｒ１５２ａ分别进行了计算和实验。     

基于MPI技术的注射成型流动数值模拟研究

以塑料注射成型流动分析软件MPI为工具,对注塑过程中流动数值模拟技术进行了深入研究,建立了塑料熔体流动过程的数学模型。对注射成型模型进行了简化数值计算,以更清楚的认识各物理变量对成型过程的影响,并通过实例说明MPI技术在注射成型流动数值模拟技术的合理应用,用软件预测了温度、压力分布,注射充填型腔计算机模拟,以指导模具设计工作。     

Analysis of flow and stresses in a tube stretch-reducing hot rolling schedule

Analytical expressions for the roll-pass geometry, velocity, strain, strain rate and stress components are obtained for steady-state tube stretch-reducing hot rolling. From these expressions the reduction in tube diameter and wall thickness, inter-stand tensions, roll load and rolling torque have been determined in relation to the roll gap opening and the inter-stand velocity increase ratio. The results have shown that increasing the interstand velocity increase ratio will increase the inter-stand tension while the roll load remains almost unchanged. The rolling torque increases with the increase of the back inter-stand velocity increase ratio and decreases with the increase of the ratio at the front. There is a limiting value for the inter-stand velocity increase ratio at which the rolling process will tend to become unstable. The analysis has been validated by comparing the theoretical results with on-line power measurements on an industrial tube stretch-reducing hot rolling mill.     

热连轧机垂直振动的建模与仿真

针对某钢厂热连轧机在轧制过程中出现的异常振动现象，采用理论分析和试验模态分析，建立了一种较全面的分析热连轧机垂直振动的动态仿真模型。通过计算机仿真并与实际结合，得出轧机异常振动是由于传感器连接杆和传感器壳体的不合理相对运动耦合的结论。最后对传感器壳体进行结构动力学修改，修改后，消除了异常振动，解决了该热连轧机的自激振动。