Modelling of a low temperature differential Stirling Engine.

Abstract: A full theoretical model of a low temperature difference Stirling engine is developed in this paper.The model, which starts from the first principles, gives a full differential description of the major componentsof the engine: the behaviour of the gas in the expansion and the compression spaces; the behaviour of thegas in the regenerator; the dynamic behaviour of the displacer and the power piston/flywheel assembly. Asmall fully instrumented the engine is used to validate the model. The theoretical model is in goodagreement with the experimental data and describes well all features exhibited by the engine

Solar application for Drying Woodchip in Scotland.

A novel solar dryer for drying woodchip has been developed in Scotland. In this paper, designs and performance of both solar collector and dryer have been presented separately. Woodchip drying performance has been analysed for a range of temperatures (10ºC to 51ºC) and flow rates (70m³/h to 280m³/h). Page model has been used for modelling the drying curves as a function of temperatures and drying velocities.The thermal solar system considered consisted of a solar collector based on the transpired plate type and a small 10We PV panel unit employed to run a 5We fan. The performance of the system is presented in terms of air flow rate and temperature increments as a function of irradiance levels.Keywords: Solar air heating, solar dryer, woodchi

Solar application for Drying Woodchip in Scotland.

A novel solar dryer for drying woodchip has been developed in Scotland. In this paper, designs and performance of both solar collector and dryer have been presented separately. Woodchip drying performance has been analysed for a range of temperatures (10ºC to 51ºC) and flow rates (70m³/h to 280m³/h). Page model has been used for modelling the drying curves as a function of temperatures and drying velocities.The thermal solar system considered consisted of a solar collector based on the transpired plate type and a small 10We PV panel unit employed to run a 5We fan. The performance of the system is presented in terms of air flow rate and temperature increments as a function of irradiance levels.Keywords: Solar air heating, solar dryer, woodchi

Limits on the penetration of coiled tubing in horizontal oil wells: effect of the pipe geometry.

To carry out remedial work in oil wells through the production tubing string, a method using a continuous length of steel coiled tubing is used. In horizontal wells substantial friction forces are generated which resist the motion of the tubing as it is pushed into the well. As the penetration increases, the friction forces arising from the contact of the tubing with the inner casing wall increase too, and the tubing buckles. The buckling is initially sinusoidal but eventually transforms into helical. At this point the force required to push the tubing rises dramatically, and the maximum penetration is then rapidly reached. Considerable economic benefits could be gained if the limits on the maximum penetration of coiled tubing in horizontal oil wells could be increased. This article discusses ways of increasing the penetration of coiled tubing in horizontal oil wells by managing the geometry of the coiled tubing. It is shown that the best strategy is to keep the external diameter of the coiled tubing constant, and to make up the coiled tubing from several sections, each with uniform, but increased wall thickness. It is shown that with two sections the maximum penetration can be increased by about half, and that with three sections the maximum penetration can be increased by about two-thirds

Evaluation of a new photodiode sensor for measuring global and diffuse irradiance, and sunshine duration.

A new integrated device (called the BF3) has been developed, which enables the simultaneous measurement of horizontal global and diffuse irradiance as well as sunshine presence at any time. The sensor needs no specific polar alignment or routine adjustment, and works at any latitude. To evaluate the performance of this new device, a BF3 sensor was installed on the roof of a six-story building in the Merchiston Campus of Napier University, Edinburgh from February 22–July 3, 2001. Horizontal global and diffuse irradiance data were collected from the BF3. To enable a cross check, two Kipp and Zonen CM11 sensors, one with a shade ring, have also been installed beside the BF3 sensor on the same roof. These were used to give a reference measure of the horizontal global and diffuse irradiance. To evaluate the BF3 sunshine duration performance, the direct beam normal irradiance was calculated from the CM11 global and diffuse readings, and compared with a threshold of 120 W.m–2 to give sunshine presence according to the WMO definition. This was compared against the BF3 output, and also with data from two Campbell-Stokes sunshine recorders on the same site. The results show a stable performance on the part of the BF3 sensor for the measurement of horizontal global and diffuse irradiance. The global irradiance measured by the BF3 showed values 4.7% high, with a standard error of 16.5 W.m–2 compared to the Kipp and Zonen sensors. Diffuse values were 1.4% high with a standard error of 13.4 W.m–2. The BF3 sunshine duration was within 2% of that calculated from the WMO definition over the study period, with a typical daily error of less than 20 min. This is well within the WMO requirements for a sunshine recorder. In comparison, the Campbell-Stokes recorders gave readings up to 7% different from the WMO values, with a typical daily error of almost an hour

Heat transfer: a problem solving approach.

A core task of engineers is to analyse energy related problems. The analytical treatment is usually based on principles of thermodynamics, fluid mechanics and heat transfer, but is increasingly being handled computationally.The book emphasizes how complex problems can be deconstructed into a series of simple steps. All thermophysical property computations are illustrated using diagrams within text and on the companion CD

A design tool for predicting the performances of light pipes

Light pipes are simple means of directing daylight (diffuse and direct light) into interior spaces. Previous work by the authors described the initial work on a luminous flux and illuminance predictive model for straight light pipes, using a basic equation for illuminance distribution as a function of horizontal distance. Further work has now produced a model that uses the cosine law of illuminance to describe the distribution of light from the light pipe diffuser as well as takes into account pipe elbow pieces or bends. The resulting illuminance model can be described as a quartic cosine model. By producing a “luxplot” prediction for any given light pipe application, it is possible to maximise the potential of these daylight providers and design their configuration to suit any given need. As part of this study, wide-ranging illuminance and luminous flux data were collected both for the formulation of this model (as the formula is semi-empirical) and its validation

Heat transfer: a problem solving approach.

A core task of engineers is to analyse energy related problems. The analytical treatment is usually based on principles of thermodynamics, fluid mechanics and heat transfer, but is increasingly being handled computationally.The book emphasizes how complex problems can be deconstructed into a series of simple steps. All thermophysical property computations are illustrated using diagrams within text and on the companion CD

A numerical study of the behaviour of a gas-liquid interface subjected to periodic vertical motion.

A numerical study has been undertaken to examine the behaviour of a gas liquid interface in a vertical cylindrical vessel subjected to a sinusoidal vertical motion. The computational method used is based on the simplified marker-and-cell method and includes a continuum surface model for the incorporation of surface tension. The numerical results indicate that the surface tension has very little effect on the period and amplitude of oscillations of the interfacial waves. The stability of the interfacial waves has been found to depend on the initial pressure pulse disturbance, and exponential growth of the interfacial wave has been observed in some cases. The influence of the amplitude and frequency of the forcing oscillations has also been investigated. The results are in good agreement with available experimental and analytical solutions