Detective quantum efficiency of electron area detectors in electron microscopy

Recent progress in detector design has created the need for a careful side-by-side comparison of the modulation transfer function (MTF) and resolution-dependent detective quantum efficiency (DQE) of existing electron detectors with those of detectors based on new technology. We present MTF and DQE measurements for four types of detector: Kodak SO-163 film, TVIPS 224 charge coupled device (CCD) detector, the Medipix2 hybrid pixel detector, and an experimental direct electron monolithic active pixel sensor (MAPS) detector. Film and CCD performance was measured at 120 and 300 keV, while results are presented for the Medipix2 at 120 keV and for the MAPS detector at 300 keV. In the case of film, the effects of electron backscattering from both the holder and the plastic support have been investigated. We also show that part of the response of the emulsion in film comes from light generated in the plastic support. Computer simulations of film and the MAPS detector have been carried out and show good agreement with experiment. The agreement enables us to conclude that the DQE of a backthinned direct electron MAPS detector is likely to be equal to, or better than, that of film at 300 keV.     

On the optimum orientation of solar collectors

A simple model of atmospheric absorption and scattering, incorporating only three parameters, has been used to fit meteorological data for direct and diffuse radiation and hours of sunshine at latitude 55°N, longitude 6°W. Using this fit for insolation on a horizontal plane, annual and monthly figures for insolation on an inclined plane have been computed. It is found that the annual insolation is relatively insensitive to orientation for angles of tilt between zero and 60°, but that the optimum tilt is 30.5°. When ground reflection is included, the optimum tilt angle rises steadily to 65' as the ground albedo increases from zero to unity. Optimization for summer and winter operation is also considered, as is the effect of various characteristics of practical collectors.     

Modelling of a domestic wind power system including storage

A simulation analysis is presented of domestic heating by a wind power system including storage at a location 54°39′ N, 6°13′ W (Aldergrove, Northern Ireland). A simple theoretical model is constructed comprising a house of specified dimensions and heat loss characteristics, an aerogenerator and a thermal store. the data base used is a magnetic tape of hourly wind speed and air temperature readings taken at Aldergrove meteorological station during 1949–75. the results suggest a measure of optimization between store capacity and generator rating based on technical considerations alone, and a simple economic optimization is also presented.     

Influence of oil on evaporator heat transfer (results for R 12 and Shell Clavus 68)

Experiments are described which investigated the influence of lubricating oil on the heat transfer and the refrigerant flow in refrigeration evaporators. The particular refrigerant was R 12, and the oil used was Shell Clavus 68. Efforts were made to model actual operation as closely as possible. It was found that the oil had a significant effect on the refrigerant flow and pressure drop. Measurements made on the heat transfer coefficient indicated that the oil had different effects depending on the fluid flow regime. For annular — wavy regimes, there was no apparent effect, while for annular and film flows, the presence of oil significantly reduced the heat transfer coefficient.The dependence of heat transfer coefficient on refrigerant quality was also investigated and was found to be a maximum when the quality lay between 0.6 and 0.8. This regime corresponds to fully developed annular flow.     

Techno-economic analysis of fuel conversion and power generation systems — the development of a portable chemical process simulator with capital cost and economic performance analysis capabilities

The development is described of ECLIPSE, a suite of programs written in C for IBM PC compatible computers, which permits the full technical and economic analysis of current and proposed fuel conversion and power generation systems. A large advantage is the flexibility of approach which is possible and the degree of integration of the technical and economic aspects of the problem. The package includes extensive chemical properties, utilities and capital costing databases which can be modified by the user.     

Performance trends and heat transfer considerations in an ammonia–water resorption cycle

An experimental test facility was constructed to examine the potential of ammonia–water mixtures as the working fluid in high‐temperature heat pumps. The nature of the working fluid necessitates an alternative design to the conventional vapour compression cycle. The addition of a solution circuit in parallel with the compressor leads to the resorption cycle. The composition of the working fluid can be altered by varying the flow ratio between the compression and solution pump circuits. Changes in the composition of the circulating fluid are accompanied by changes in the dryness fraction at the end of the heat transfer process in the desorber. Higher rates of heat transfer from the source to the working fluid were measured at higher concentrations of ammonia in the circulating fluid, though this was accompanied by lower overall flow rates of the circulating fluid. A 70/30 ammonia/water mass concentration is thought to be the optimum composition of the working fluid due to a combination of temperature glide and circulation ratio. Significant differences were observed in the overall heat transfer coefficient achieved in the two heat exchangers, which may restrict the range of likely applications. Copyright © 2001 John Wiley & Sons, Ltd.     

Improving coal-fired power generation by integrating PFBC and gas-fired combined cycles in a hybrid process

Two hybrid combined cycle electrical power generating schemes burning coal and natural gas were examined using the ECLIPSE chemical process simjlator. The results of these simulations are presented and analyzed. Comparison is made with conventional power generation technologies. Two additional pieces of work are included. The first examines the effect of the hot gas filtration operating conditions on the hybrid combined cycle efficiency and the second calculates the allowable increase in capital cost for a specified improvement in power plant efficiency while maintaining the same cost of electricity.     

Martin-Hou,Peng-Robinson and Redlich-Kwong-Soave equations of state for HFC 125

Coefficients for refrigerant HFC 125 for the Martin Hou, Redlich Kwong Soave and the Peng Robinson equation of state are reported.     

The control of a refrigeration system using a compact plate heat exchanger as an evaporator

This paper will show some of the problems that may be encountered when using a compact plate exchanger as an evaporator in a refrigeration system which utilizes a thermostatic expansion valve as its controlling device.