在有机合成实验中使用液体速热器

易燃、易爆、易气化是有机化合物的特性,但在制备有机化合物的过程中,又常要把物料加热到反应所需的温度,而实验室常用的热源是酒精灯、煤气灯和电热丝裸露的电炉,因此在有机化学实验中,由于反应物不慎溢出器皿外与明火接触而发生火灾和爆炸的事故时有发生。 为此我们从1984年开始在有机化学实验课中使用液体速热器,经过二年多来的实践证明,由于它直接插入需要加温的液体,没有明火与物料的接触,具有安全可靠,使用方便,快速高效的优点,值得推广应用。

自来水速热器工作原理剖析

自来水速热器具有体积小、发热快、安装方便等优点。该速热器电路原理简单,元件少,加热部分使用 PTC 元件,漏电保护电路是利用互感电压使可控硅导通,通过电磁铁切断电源,电路原理如附图所不。正常情况下,按下电源开关 K 后,220V 市电通过 K、L1、PTC 发热元件、L2形成回路,PTC元件开始加热自来水。绕组 L1、L2与 L3以及D5、C1、C2等组成漏电检测保护电路。正常工作时,流过 L1和 L2的电流相等,其相位相反,

自动断电式速热器

通常,插入热水瓶内加热的速热器在水沸腾后,如使用者忘记断电,会多耗电,而且可能由于少水而烧坏速热器。天翔牌自动安全节能速热器是一种新型自动断电式速热器。它的外形如图1。

用音乐片制作的两用报警器

本文介绍的报警器可在厨房烧开水时用,由于市售的速热器是由水开后产生的水蒸气推动发音器的膜片振动发声的,极易损坏。 若将本文中的报警器探头装在发音器上使用,一旦水开后,产生的水蒸气在探头上遇冷凝成水后即可产生报警信号。同时,只要拨动开关S还可作水满报警用。这是由于通常冷水和热水的导电能力是不同的,冷水导电能力比热水差,故用作水满报警器时要增加探头金属片的面积,这样当水满时两金属片遇水导通发出报警声。

Simulation study on combustion system of tankless gas water heater

This paper simulates the combustion system of a regular tankless gas water heater under different static pressure conditions.The simulation results are in accordance with the test results.It proves that the used physical and mathematical models are reasonable.The results show that the flame height and the excess air ratios depend on the system pressure drop but not on the absolute pressure at the combustion chamber.The pressure drop and the amount of combustion air have an inverse relationship with CO generation,and they also impact on the temperature and velocity fields.To reduce CO emission,a stronger fan is needed to provide extra pressure head to ensure that enough combustion air is introduced into the system.This study provides a useful research tool to develop products through computational fluid dynamic analysis and laboratory testing.

Application of high temperature heat pipe in hypersonic vehicles thermal protection

In order to develop further the application of high temperature heat pipe in hypersonic vehicles thermal protection, the principles and characteristics of high temperature heat pipe used in hypersonic vehicles thermal protection were introduced. The methods of numerical simulation, theory analysis and experiment research were utilized to analyze the frozen start-up and steady state characteristic of the heat pipe as well as the machining improvement for fabricating irregularly shaped heat pipe which is suitable for leading edge of hypersonic vehicles. The results indicate that the frozen start-up time of heat pipe is long （10 min） and there exists large temperature difference along the heat pipe （47 ℃/cm）, but the heat pipe can reduce the temperature in stagnation area of hypersonic vehicles from 1 926 to 982 ℃ and work normally during 1 000-1 200℃. How to improve the maximum heat transfer capability and reduce the time needed for start-up from frozen state of the heat pipe by optimizing thermostructure such as designing of a novel wick with high performance is the key point in hypersonic vehicles thermal protection of heat pipe.

Numerical investigation of optimal geometry parameters for ejectors of premixed burner

An ejector of low NO~ burner was designed for a gas instantaneous water heater in this work. The flowing and mixing process of the ejector was investigated by computational fluid dynamics （CFD） approach. A comprehensive study was conducted to understand the effects of the geometrical parameters on the static pressure of air and methane, and mole fraction uniformity of methane at the outlet of ejector. The distribution chamber was applied to balance the pressure and improve the mixing process of methane and air in front of the fire hole. A distribution orifice plate with seven distribution orifices was introduced at the outlet of the ejector to improve the flow organization. It is found that the nozzle exit position of 5 mm and nozzle diameter d 〉1.3 mm should be used to improve the flow organization and realize the well premixed combustion for this designed ejector.

RADIATION HAZARD AND PROTECTION OF LOW ENERGY ACCELERATORS

In this paper, the origin and type of radiation hazards as well as the main aspects of radiation protection for low-energy accelerators are discussed in general, and the problems of radiation protection and the experimental results of the operational monitoring of the five accelerators in the institute of Nuclear Science and Technology,Sichuan University, namely, one 1.2 M cyclofron, two Cockroft-waltons and two Van de Graafts, as well as a powerful electron accelerator for industrial irradiation are described. The discussion and evaluation are made according to the requirments of the National standards GB 5172-85.

AIR VELOCITY SENSOR

During the last twenty years there has been rapid progress in the use of automation in a wide range of industries,as well as in military, scientific application. However, the progress in the application of automatic control is often hindered by the lack of accurate, reliable measuring apparatus. An economic thermal couple air flow sensor with better linearity (accuracy is ±5% of full scale) has been successfully made at Trolex Ltd. Many other existing sensors fail in the application of industries because of non-linearity.

Effects of thermal transport properties on temperature distribution within silicon wafer

A combined conduction and radiation heat transfer model was used to simulate the heat transfer within wafer and investigate the effect of thermal transport properties on temperature non-uniformity within wafer surface. It is found that the increased conductivities in both doped and undoped regions help reduce the temperature difference across the wafer surface. However, the doped layer conductivity has little effect on the overall temperature distribution and difference. The temperature level and difference on the top surface drop suddenly when absorption coefficient changes from 104 to 103 m-1. When the absorption coefficient is less or equal to 103 m-1, the temperature level and difference do not change much. The emissivity has the dominant effect on the top surface temperature level and difference. Higher surface emissivity can easily increase the temperature level of the wafer surface. After using the improved property data, the overall temperature level reduces by about 200 K from the basis case. The results will help improve the current understanding of the energy transport in the rapid thermal processing and the wafer temperature monitor and control level.

Heat Transfer in a Liquid-Solid Circulating Fluidized Bed Reactor with Low Surface Tension Media

Heat transfer characteristics between the immersed heater and the bed content were studied in the riser of a liquid-solid circulating fluidized bed, whose diameter and height were 0.102 m (ID) and 2.5 m, respectively. Effects of liquid velocity, particle size, surface tension of liquid phase and solid circulation rate on the overall heat transfer coefficient were examined. The heat transfer coefficient increased with increasing particle size or solid circulation rate due to the higher potential of particles to contact with the heater surface and promote turbulence near the heater surface. The value of heat transfer coefficient increased gradually with increase in the surface tension of liquid phase, due to the slight increase of solid holdup. The heat transfer coefficient increased with the liquid velocity even in the higher range, due to the solid circulation prevented the decrease in solid holdup, in contrast to that in the conventional liquid-solid fluidized beds. The values of heat transfer coefficient were well correlated in terms of dimensionless groups as well as operating variables.

FMLSMETHODOFPARAMETERESTIMATIONANDITSAPPLICATIONTOHEAT┐EXCHANGERIDENTIFICATION

Using the inversion of the auto correlation function Toeplitz matrix of pseudo random binary sequence (PRBS) derived in this paper and the theorem of partitioned matrix inversion, a fast multistage least squares (FMLS) method is developed. Its performances are theoretically analyzed and digital simulation is made to compare FMLS with multistage least squares (MSLS), correlation least squares(COR LS) and LS for their computer speed and identification accuracy. Finally, FMLS is applied to identifying the heat excharger dynamics. It is shown that FMLS is a good and effective identification technique.

Trends in Significant Wave Height and Surface Wind Speed in the China Seas Between 1988 and 2011

Wind and waves are key components of the climate system as they drive air-sea interactions and influence weather systems and atmospheric circulation. In marine environments, understanding surface wind and wave fields and their evolution over time is important for conducting safe and efficient human activities, such as navigation and engineering. This study considers long-term trends in the sea surface wind speed(WS) and significant wave height(SWH) in the China Seas over the period 1988–2011 using the Cross-Calibrated Multi-Platform(CCMP) ocean surface wind product and a 24-year hindcast wave dataset obtained from the WAVEWATCH-III(WW3) wave model forced with CCMP winds. The long-term trends in WS and SWH in the China Seas are analyzed over the past 24 years to provide a reference point from which to assess future climate change and offshore wind and wave energy resource development in the region. Results demonstrate that over the period 1988–2011 in the China Seas: 1) WS and SWH showed a significant increasing trend of 3.38 cm s^(-1)yr^(-1) and 1.52 cm yr^(-1), respectively; 2) there were notable regional differences in the long-term trends of WS and SWH; 3) areas with strong increasing trends were located mainly in the middle of the Tsushima Strait, the northern and southern areas of the Taiwan Strait, and in nearshore regions of the northern South China Sea; and 4) the long-term trend in WS was closely associated with El Ni?o and a significant increase in the occurrence of gale force winds in the region.

Theoretical Study of ECRH Heating Of HL-2A Tokamak Plasma

Electron cyclotron resonance heating （ECRH） is one of the main auxiliary heating schemes for the HL-2A tokamak. Routinely, the ohmic heating can provide a heating power about 300-450 kW in this device （ estimated from that the total toroidal current is about 300 kA while the totoidal voltage is 1-1.5 V）. The total power for the ECRH now is 1 MW and in future 2 MW.

Neutron imaging at Peking University

Neutron imaging techniques were investigated at Peking University based on a 4.5 MV Van de Graaff accelerator.The thermal neutron radiography,fast neutron radiography and fast neutron resonance radiography were tested.The low neutron flux limits the image quality.A new radio frequency quadrupole (RFQ) accelerator based on neutron source with a yield of 1 012 n/s is being set up.

The Design of TZ-2 High Voltage Pulse Modulator

There are a few assistant heating objects included electron cyclotron resonate heating （ ECRH ）. Two 500 kW gyrotrons introduced from Russia were operated to launch 1 MW energy. So two set of TZ-2 high voltage pulse modulators are needed.

A Numerical Method for Calculating Interior Ballistics of Electrothermal Accelerator

Electro-thermal accelerator uses high-voltage arc energy to heat the actuating medium, it being made from low-molecular weight material. Projectile acceleration is achieved by expansion of the actuating medium. Numerical method for calculating interior ballistics uses Lagrangian coordinates there the conservation of momentum and the energy balance are solved. A statement of the energy balance reflects the second law of thermodynamics. Lagrangian different grid and scheme for numerical calculation were used. Fully explicit scheme was employed. The solving includes two stability conditions： Courant and shock （artificial viscosity）. Numerical results were compared with the experimental research for pressure in the barrel in electro-thermal accelerator.

Technical Measures and Selections for Reducing Flue Gas Heat Loss of Large Coal-Fired Boilers

The main technologies for reducing flue gas heat loss of pulverized coal-fired boilers are introduced, and the suitability of these technologies for boiler operation and the principles for selection of these technologies are explored. The main conclusions are： 1） the non-equilibrium control over flue gas flow rates at the inlet of the air heater and the reversal rotation of the air heater rotator should be popularized as regular technologies in large boilers; 2） increasing the area of the air heater to reduce the flue gas heat loss in pulverized coal-fired boilers should be the top option and increasing the area of the economizer be the next choice; 3） low- pressure economizer technology could save energy under special conditions and should be compared with the technology of increasing economizer area in terms of technical economics when the latter is feasible; 4） the hot primary air heater is only suitable to the pnlvefizing system with a large amount of cold air mixed.

Large Area Thermionic Cathode and Its Prilimiary Experimental Results

A 2MeV thermionic cathode test stand was established to meet the requirement of the large area thermionic cathode system.A 100ram in diameter type'B'thermionic dispenser cathode was developed.A 1000A emission current was produced at the voltage of the diode about 1.8MV,the pulse width about 90ns(FWHM),and the cathode temperature about 1350℃.The emission current density is 12A/cm^2.The results indicate that a large area thermionic cathode which produces high quality and high current electron beams is visible.The results also indicate that the ability of cathode emission relies on the diode-vacuum and cathode-temperature.

Velocity Profiles between Two Baffles in a Shell and Tube Heat Exchanger

Heat exchangers are extensively utilized for waste heat recovery,oil refining,chemical processing,and steam generation.In this study,velocity profiles are measured using a 3D particle image velocimetry(PIV)system between two baffles in a shell and tube heat exchanger for parallel and counter flows.The PIV and computational fluid dynamics results show the occurrence of some strong vectors near the bottom.These vectors are assumed due to the clearance between the inner tubes and the front baffle.Therefore,the major parts of the vectors are moved out through the bottom opening of the rear baffle,and other vectors produce a large circle between the two baffles.Numerical simulations are conducted to investigate the effects of the baffle on the heat exchanger using the Fluent software.The k-εturbulence model is employed to calculate the flows along the heat exchanger.