Capacitive measuring system for two-phase flow monitoring. Part 1: Hardware design and evaluation

Two-phase flows are commonly found in many industrial applications, such as oil and gas production. The monitoring of such flows is performed either in field applications or in pilot plant studies. In both cases, simple and robust measuring techniques are required. Capacitive probes have been applied for void fraction measurement in pipes in research and industry. However, capacitive measuring systems applied so far are tailored for specific applications and may not be easily adaptable. In addition, more and more soft-computing methods are applied for advanced data processing and parameter extraction which requires more computational power of sensor systems for online data processing. We develop a capacitive system provided with a microcontroller in which necessary routines for data processing may be embedded. System design is detailed explained and system's performance is evaluated, showing appropriate accuracy and time response for the investigation of two-phase flows.     

Analysis of crude palm oil composition in a chemical process conveyor using Electrical Capacitance Tomography

In this work, we aim to analyse the capability of using a 16-segmented Electrical Capacitance Tomography (ECT) sensor system to monitor the internal composition of a chemical process conveyor that carries crude palm oil (CPO) multiphase flow. The source used to excite the electrodes is a differential potential, instead of the conventional single potential source, in order to obtain an improved sensitivity of the sensor, especially in the central area of the pipe. This system aims to recognise the phase concentration of the flow. The attained concentration profile that is received from the capacitance measurements is capable of providing an image of the liquid and liquid mixture in the pipeline, making the separation process (between oil and liquid waste) much easier and the CPO's quality can be dependably monitored. Experimental results and analysis are presented, and the new excitation technique is shown to provide better sensor sensitivity in the central pipe area. The visualisation results deliver information regarding the flow regime and concentration distribution in a two-phase flow-rate measurement system incorporating a liquid flow-measuring device. The information obtained will assist the design of process equipment, and the verification of existing computational modelling and simulation techniques.     

Study on the basic capacitance–voltage characteristics of organic molecular semiconductors

Capacitance–voltage (C–V) characteristics of organic molecular semiconductors attracted much research interest recently, but no convincing physical mechanism has been established so far. In this work, the C–V characteristics of pentacene-based devices have been systematically investigated at various frequencies. Only one peak occurs when the measuring frequency is less than 3 kHz or greater than 8 kHz. While within the frequency range between the two, two C–V peaks are observed with quite different dependence on temperature, which suggests that the origins of these two C–V peaks are respectively mobile holes and trapped carriers. This conclusion is also experimentally validated with the C–V characteristics of intentionally doped devices.     

Assessing the width of Gaussian density of states in organic semiconductors

The Density of States (DOS) is an ingredient of critical importance for the accurate physical understanding of the optoelectronic properties of organic semiconductors. The disordered nature of this class of materials, though, renders the task of determining the DOS far from trivial. Its extraction from experimental measurements is often performed by driving the semiconductor out of thermal equilibrium and therefore requires making assumptions on the charge transport properties of the material under examination. This entanglement of DOS and charge transport models is unfavorable since transport mechanisms in organic semiconductors are themselves still subject of debate. To avoid this, we propose an alternative approach which is based on populating and probing the DOS by means of capacitive coupling in Metal Insulator Semiconductors (MIS) structures while keeping the semiconductor in thermal equilibrium. Assuming a Gaussian shape, we extract the DOS width by numerical fitting of experimental Capacitance–Voltage curves, exploiting the fact that the DOS width affects the spatial distribution of accumulated charge carriers which in turn concurs to define the MIS capacitance. The proposed approach is successfully tested on two benchmark semiconducting polymers, one of n-type and one of p-type and it is validated by verifying the robustness of the extraction procedure with respect to varying the insulator electrical permittivity. Finally, as an example of the usefulness and effectiveness of our approach, we study the static characteristics of thin film transistors based on the aforementioned polymers in the framework of the Extended Gaussian Disorder transport model. Thanks to the extracted DOS widths, the functional dependence of current on the gate voltage is nicely predicted and physical insight on transistor operation is achieved.     

DYNAMIC VOIDAGE MEASUREMENTS IN A GAS SOLID FLUIDIZED BED BY ELECTRICAL CAPACITANCE TOMOGRAPHY

Based on the electrical capacitance tomography technique, a voidage measurement system that can implement a voidage distribution display and voidage measurement of a gas-solid fluidized bed simultaneously is developed. The back projection algorithm is selected as the image reconstruction algorithm to satisfy the requirement of voidage distribution display. Combining the Tikhnov regularization principle with the ART algorithm, a new quantitative hybrid image reconstruction algorithm is presented to implement the voidage measurement of a gas-solid fluidized bed. Experimental results show that the developed measurement system is successful. The speed of image reconstruction of voidage distribution is greater than 20 frames per second. The maximum error of voidage measurement can be less than 5%.     

Surface treatment of Si by annealing and effect on Mott-Schottky plots

Annealing has a healing effect on the surface of p-Si. This leads to a shift of the flatband potential of up to 2V. This effect was studied by capacitance measurements (Mott—Schottky plots) on p-Si samples in acetonitrile in a wide range of acceptor concentrations from N_A = 1 E+21 up to N_A = 1 E+25.     

Capacitive level meter for liquid rare gases

An international project to search μ→eγ decay includes the use of a liquid xenon gamma ray detector. So, a liquid level meter working at a low temperature with low outgassing is needed and the prototype is constructed. The meter shows the liquid level by measuring the capacitance between electrodes with small intervals immersed in the liquid. The operation was successful with the estimated precision of 1 mm in RMS or better.     

Effect of frequency and thermal aging on various parameters of a dielectric

This paper deals with the experimental analysis to see the effect of frequency and thermal aging on the various parameters such as capacitance and loss factor to see the behavior of a dielectric material (synthetic insulation paper) used in various electrical machines. Firstly the studies were conducted on a fresh sample and then the samples were aged at three different times and temperatures. The various parameters for the fresh as well as aged samples were determined experimentally. The studies showed that with the increase in frequency the capacitance and loss factor of the sample decreases, however with aging (increasing time and decreasing temperature) the values of capacitance and loss factor increases at a particular frequency.     

异步电动机无功功率补偿技术

异步电动机为感性负载，这行时要消耗一定的无功功率，使得电动机的功率因数不高，造成电能的大量浪费。如果给电动机补偿电容，就能减少无功功率，同时由于补偿后的总电流减小，使线路的有功损耗也有所减少，因此无功补偿技术具有很高的经济价值．本文分析了无功功率对电网的影响，并根据异步电动机的特征和对无功功率补偿的要求，给出了无功功率补偿电容的几种计算方法．     

几种超声位移检测用电容换能器的设计

介绍了3种用于检测超声波与声振动位移信号的电容换能器,可较灵敏地测试宽声带发射瞬态信号,具有简易的结构,尤其适合在实验室条件下对试样作测试。