Heat transfer limitation in a vertical annular closed two-phase thermosyphon with small fill rates

A thermosyphon with R113 as the working fluid employing fill ratios between 0.02 and 0.4, i.e. 2 and 40% of the evaporator volume, was experimentally and theoretically investigated. A critical heat flux (for which dry-out occurs) was measured which increases from about 10⁴W m⁻² at 5% fill ratio to about 5 × 10⁴W m⁻² at 40% fill ratio. The theoretical predictions are in close agreement with the experimental results.     

Heat transfer performance of a toluene loaded two-phase thermosyphon

Large dimension thermosyphons are efficient heat transfer components in heat recovery systems. Their performance limits depend on the following parameters: geometrical (length, diameter, inclination angle), physical (fluid, fill charge), thermal (temperature, heat flux).An experimental investigation was carried out with a large dimension, closed, two-phase thermosyphon which correspond to a device used in industrial recuperators. A vertical or inclinded steel thermosyphon, 3 m long and 27 mm inner diameter, was tested at temperatures varying from 100°C to 300°C with toluene as the working fluid. The lower part of the pipe was electrically heated along a variable length and the upper zone was cooled with an air stream whose flow rate and temperature were controlled. The maximum heat flux was measured as a function of temperature for different liquid fill charges and inclination angles. From these experimental data, boiling and condensation heat transfer coefficients were deduced. It was observed that the critical heat flux depends little on the fill ratio unless the charge is less than 20% for which a local dry-out occurs. The optimal fill charge was found to be between 20% and 50%. Experimental data have been compared with existing theories. The inclination effects have been taken into account with an empirical formula.     

A method to simultaneously and continuously measure the 222Rn and 220Rn exhalation rates of soil in an open loop

This paper presents a process in which a radon monitor based on the electrostatic collection method is used to measure the ²²²Rn and ²²⁰Rn exhalation rates simultaneously and continuously employing a ventilation-type accumulation chamber. Generally, the radon exhalation rate can be measured by accumulation technique, but cannot be measured continuously. The advantage of this method using a ventilation-type accumulation chamber is that the radon exhalation rates can be measured continuously. Even though the environmental air is drawn into the chamber, the low atmospheric values of radon and thoron do not influence the measurement accuracy. The ²²²Rn and ²²⁰Rn exhalation rates error from the environmental air is less than 5% in this experiment.     

A ring of instantons inducing a monopole loop

We consider the superposition of infinitely many instantons on a circle in . The construction yields a self-dual solution of the Yang-Mills equations with action density concentrated on the ring. We show that this configuration is reducible in which case magnetic charge can be defined in a gauge invariant way. Indeed, we find a unit charge monopole (worldline) on the ring. This is an analytic example of the correlation between monopoles and action/topological density, however with infinite action. We show that both the Maximal Abelian Gauge and the Laplacian Abelian Gauge detect the monopole, while the Polyakov gauge does not. We discuss the implications of this configuration.     

一种超小型专用黑体的温度控制

介绍了一种野外用超小型高稳定度的热象基准源。通过控制该信号源可以消除环境温度的影响,可用于调校仪器的光轴、线性热敏电阻组件的稳压源及蓄电池故障报警器。     

Numerical analysis of convective heat transfer in a closed two-phase thermosyphon

Mathematical modeling of the processes of heat transfer and hydrodynamics in a closed two-phase thermosyphon is carried out in a wide range of key parameters. The mathematical model is based on the laws of conservation of mass, momentum, and energy in dimensionless variables of stream function-vorticity vector-temperature. The influence of the Rayleigh number and the dimensionless time on the local and integral thermal hydrodynamic characteristics is estimated.     

A miniature prototype of a resonance photoacoustic cell for gas sensing

We present a miniature prototype of a resonance photoacoustic cell with a banana-shaped internal cavity with a volume of less than ～5 mm³. The cell design and the experimental setup used for testing operational characteristics of the prototype are described. The results of testing the prototype in the experiments on photoacoustic detection of radiation absorption by ammonia in a nitrogen flow by using a single-mode diode laser generating radiation near ～1.53 μm are presented. The amplitude-frequency characteristic of the photoacoustic response induced by absorption of radiation in the presence and absence of ammonia is analyzed. The experiment revealed that sensitivity of gas sensing is limited only by the microphone noise. The measured noise-limited minimal detectable absorption was found to be about 8.48 × 10^?8 cm^?1 W Hz^?1/2.     

旋转工况下小型液冷源设计

设计了一种适用于旋转工况的小型液冷源,该液冷源采用强迫风冷换热器的原理。液冷源液路循环采用闭式系统设计以适应旋转工况的要求,液位检测采用光电式液位传感器,通过单向阀和电磁阀的组合使用可有效防止水锤效应。该系统具有体积小、重量轻、环境适应性强等优点。     

A miniature ultransonic pump using a bending disk transducer and a gap

It is known that if a pipe end is faced at a vibrating surface in liquid with a small gap, liquid is suctioned into the pipe. As a miniature configuration, we introduce a bending disk transducer 30 mm in diameter using a ring-shaped PZT element. The disk vibrator is worked at the fundamental resonance frequency of 19 kHz of the bending mode. To optimize the pipe geometry, we experimentally investigated the effect of the outer diameter on the pump performance. As a result, the outer/inner diameter ratio of 3:2 is optimum for the gap smaller than 20 microm. We achieved the maximum pump pressure of 14.8 kPa and the maximum flow rate of 10 ml/min. using the prototype pump.     

Characterization of a miniature Paul-Straubel trap

Frequency standard applications and ultra-high resolution spectroscopy of a confined single ion require traps of drastically reduced dimensions (about or below 1 mm). These small dimensions increase the sensitivity of the trapping behavior to imperfections in the trap geometry and to patch potentials. For the aim of the metrological laser interrogation of a single Ca⁺ ion, a miniature cylindrical ring trap was built. In order to optimize the laser cooling process and to reach strong binding conditions, the boundaries of the stability diagram and the zones of low confinement as well as the ion motion properties were characterized. Received 14 November 2000 and Received in final form 1st February 2001     

A simple method to prepare miniature quartz fiber boats with superhydrophobicity

According to the reformed Cassie-Baxter equation, a superhydrophobic quartz fiber bundle boat was fabricated from mimicking the lotus leaf venation using chemical surface modifications and roughness introductions. Water contact angles as high as 165.8° were achieved for quartz fiber cloths. The loading capacities of the miniature boats made from the superhydrophobic quartz fiber bundles were measured. The highest loading weight, 10.19 g, was obtained by the boats with 2.0 mm spacing distance between fiber bundles. The striking loading capacities were believed to stem from the air film surrounding the superhydrophobic surfaces of the boats. The results of this study presented new applications of artificial hydrophobic surfaces in areas of aquatic devices.     

Experimental simulation of a liquid-metal heat-transfer fluid flow in a T-shaped mixer

The structure of the temperature field in a liquid-metal heat-transfer fluid flowing through a T-shaped mixer is studied experimentally. The experiments are carried out using Rose’s alloy as a working fluid. To find the temperature distribution over the wall of a working section, IR thermography is applied. It is shown that the wall temperature distribution in the zone where fluid flows with different temperatures mix is heavily nonuniform. The temperature distribution substantially depends on the ratio between the hot and cold fluid flow rates. The results can be used to verify the thermal hydraulic computational codes for fluid metal flows.     

The thermal characteristics of a closed two-phase thermosyphon at low temperature difference

The applications of closed two-phase thermosyphons are increasing in heat recovery systems because of their high effective conductivity. However, their range of application is limited by the need for some minimum temperature difference between the evaporator and condenser sections to initiate nucleate boiling. In the project described, the steady state heat transfer characteristics for vertical two-phase closed thermosyphons at low temperature differences with R11, R22, and water as working fluid were studied experimentally. From these experimental results, the minimum temperature differences required to initiate and sustain boiling in the low temperature thermosyphons have been established for the above working fluids. A method for improving the performance at low temperature difference was devised on the basis of a thermal triggering system. Triggering could also be achieved by mechanical vibration.     

小型热声制冷机的优化

简要介绍了热声制冷机的发展,特别介绍了Husam El—Gendy等人小型热声制冷机的优化的工作。结果表明:优化的高频微型热声制冷机能达到每平方厘米数百瓦的制冷功率密度,可完全用于激光制冷、电子制冷和其它需要热控制的器械。     

Design,manufacture and testing of a closed cycle thermosyphon rankine engine

The Thermosyphon Rankine Engine (TSR) is a recent concept for power generation using solar or other available low grade heat sources. The basis of the engine is the modification of a heat pipe, with its excellent heat and mass transfer characteristics, to incorporate a turbine, thereby making the system into a Rankine Cycle Engine.The TSR is directed towards power production from solar ponds, geothermal energy and heat produced by solar collectors, as well as for waste heat utilisation for electrical power generation.A theoretical formulation and results from experiments on prototype units are presented. Based on the results, it is concluded that the TSR engine may play an important role for conversion into electrical energy of thermal energy produced by conventional solar collectors, geothermal sources and waste heat.     

A theoretical model to predict the low-frequency sound absorption of a helmholtz resonator array

A theoretical method based on mutual radiation impedance is proposed to compute the sound absorption performance of a Helmholtz resonator array in the low-frequency range. Any configuration of resonator arrangement can be allowed in the method, while all the resonators may or may not be identical. Comparisons of the theoretical predictions with those done by the past studies or experiments show that the present method can accurately predict the absorption performance in more general cases.     

A phenomenological treatment of dual loop contributions to inclusive reactions

A phenomenological B₆ type amplitude is constructed which contains Regge singularities of twisted loop graphs such as ordinary trajectories, Regge cuts and Pomeron trajectories. With this amplitude possible implications of the different one and two-loop graphs for single particle distributions are derived for different kinematical regions including the fixed angle limit. The results emphasize the importance of dual loop contributions to single particle distributions.     

一种小型光谱色彩分析仪的设计

为解决目前颜色测量仪器测速慢、体积大的问题，采用先进的颜色测量方法——光电摄谱法，建立了一个测色的数学模型，设计了一种全自动测色的小型光谱色彩分析仪。仪 器由照明系统、光电摄谱仪、信号采集与处理电路、测色软件四部分组成。详细阐述了照明系统和光电摄谱仪的设计。光电摄谱仪采用平场凹面光栅分光，线阵CCD接收，缩小了仪 器体积。利用此仪器测量7块标准色板，色品坐标测量不确定度小于0.01，测试周期为1秒。结果表明，此仪器不仅精度高，还满足了工业生产中对测色的速度和准确度要求。