The influence of oil viscosity and refrigerant quality on evaporator performance

The presence of oil in an evaporator degrades performance by reducing evaporator heat pick-up and by increasing the evaporator pressure drops. It can be demonstrated that there is an optimum refrigerant mass flow rate for a given refrigerant-oil combination and oil concentration. Also, oil viscosity has an effect on the evaporator performance at low oil concentrations. Finally, it is suggested that low viscosity oil be used at low oil concentrations and high viscosity oil at high oil concentrations.     

SEM—past,present and future

The development of the technology of the scanning electron microscope (SEM) is traced from the early pioneering work in the 1930s to the present day. Recent trends are described and, based on these, some speculative forecasts are made of possible future developments. It is suggested that these will include better vacuum conditions in conventional SEM to permit more accurate surface characterization, and improved electron optics for higher resolution, particularly with low-voltage operation.     

Images of paraffin monolayer crystals with perfect contrast: minimization of beam-induced specimen motion

Quantitative analysis of electron microscope images of organic and biological two-dimensional crystals has previously shown that the absolute contrast reached only a fraction of that expected theoretically from the electron diffraction amplitudes. The accepted explanation for this is that irradiation of the specimen causes beam-induced charging or movement, which in turn causes blurring of the image due to image or specimen movement. In this paper, we used three different approaches to try to overcome this image-blurring problem in monolayer crystals of paraffin. Our first approach was to use an extreme form of spotscan imaging, in which a single image was assembled on film by the successive illumination of up to 50,000 spots, each of a diameter of around 7 nm. The second approach was to use the Medipix II detector with its zero-noise readout to assemble a time-sliced series of images of the same area in which each frame from a movie with up to 400 frames had an exposure of only 500 electrons. In the third approach, we simply used a much thicker carbon support film to increase the physical strength and conductivity of the support. Surprisingly, the first two methods involving dose fractionation in space or time produced only partial improvements in contrast whereas the third approach produced many virtually perfect images, where the absolute contrast predicted from the electron diffraction amplitudes was observed in the images. We conclude that it is possible to obtain consistently almost perfect images of beam-sensitive specimens if they are attached to an appropriately strong and conductive support; however great care is needed in practice and the problem remains of how to best image ice-embedded biological structures in the absence of a strong, conductive support film.     

Digitisation of electron microscope films: six useful tests applied to three film scanners

A series of simple tests have been used to measure the performance of flat-bed film scanners suitable for digitisation of electron micrographs. Two of the film scanners evaluated are commercially available and one has been constructed in the laboratory paying special attention to the needs of the electron microscopist. The tests may be useful for others.     

Development of engineering design data for new refrigerants I: Pure fluids and azeotropic mixtures

It is important to correlate thermodynamic data for replacements for CFCs and HCFCs and present it in a form that will allow industry to design equipment from charts rather than complicated thermodynamic equations. This paper outlines the development of such equations for the more popular of these fluids. Sample pressure-enthalpy diagrams are then given for the pure fluids. In addition, since replacements for CFCs and HCFCs can be formed from both zeotropic and azeotropic mixtures of these fluids, the use of a typical mixing rule is discussed and initial results presented.     

From pure fluids to zeotropic and azeotropic mixtures: The effects of refrigerant-oil solubility on system performance

This paper highlights the effects of circulating compressor lubricants on the performance of vapour compression refrigeration systems. It will give a baseline case of R12 and a mineral oil and show to what degree the alternative refrigerants and their mixtures conform to this.     

Solid-based processes for the direct reduction of iron

Solid-based processes for the direct reduction of iron are discussed and compared in terms of their costs and energy effectiveness. Possible future lines of development are presented.     

Improvements in controlled-environment facilities for testing domestic air-to-water heat pumps

A control system is described, based on a microcomputer, which maintains constant temperature and relative humidity in a controlled-environment laboratory used for research on air-to-water heat pumps. The performance of the control system is measured under both steady-state and changing conditions, and optimum values of the control constants are deduced. The temperature can be maintained at the set value to within 0–1°C, and the relative humidity to within 1 per cent, under steady-state conditions. The effects of transients, such as the starting or stopping of the heat pump under test, or the deliberate changing of the controlled conditions, are studied in detail. In addition, a system is described for controlling the temperature of the condenser cooling water, which can be held to within 0–1°C of the set value.     

A device for recording electrical load information

An electronic circuit is described which enables a standard multi-point chart recorder to measure voltage, current, power, reactive power, kilo-volt-amps and power factor in AC electrical loads.