Doctoral Degrees (Mechanical Engineering)

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The development of instrumentation for the direct measurement of heat loss from man in a normal working mode.
(1974) Hodgson, T.; Bindon, Jeffrey Peter.; Reed, M.
Based on a theoretical analysis of the heat transfer process between the human body and its environment, graphs are presented for determining the theoretical skin surface temperatures and sweat rates as a function of the physiological conductance, under certain assumed environmental conditions with regard to air temperature, relative humidity and wind speed. In addition, the development of unique measuring techniques for the direct measurement of the evaporative and radiative heat transfer rates between a human body in a natural working position and its environment as well as the development of a low-cos~ radiometer for the measurement of the emissivity and temperature of human skin are described. The heat loss measuring equipment was installed in the horizontal test section of the climatic chamber of the Human Sciences Laboratory of the Chamber of Mines. Basically the evaporative heat loss measuring system consists of two air-sampling probes, for sampling the air on the upstream and downstream sides of the body , a double circuit heat exchanger, for equalising the dry- bulb temperatures of the two air samples and a differential humidity- measuring system incorporating electrical resistance hygrometero, for measuring the difference in specific humidity between the two air samples. In addition, a steam generator is provided for introducing a known amount of steam at a predetermined rate into the wake of the body. Since the output of the humidity-measuring system is linearly related to the evaporative heat loss rate, the unknown rate of evaporation of moisture from the human body can be determined relatively easily from a knowledge of the respective outputs of the humidity-measuring system due to the moisture evaporation rate of the human body and the known vapour production rate by the steam generator. The direct- measuring instrument for determining the radiation energy exchange rate of a working subject is in the form of a rotating hoop. The inside and outside surfaces of the hoop are lined with thermal radiation-sensing elements, so connected as to measure the net radiation energy exchange between the subject and the surroundings. The hoop integrates over the circular strip formed by the elements and upon rotation, integrates the radiation over the total 4n surface enveloping the subject . While the interposition of a surface between the body and its surroundings must of necessity influence the radiation exchange, the method introduces a small surface only . The significance of the evaporative and radiative heat loss measuring techniques which were successfully used in animate studies, is reflected in the, hitherto unknown, accuracy regarding partial calorimetric studies . The low- cost radiometer for measuring the skin temperature and emissivity is equipped with two non-selective thermal radiation detectors in the form of semi-conductor thermocouples. The one radiation-sensing element faces a built-in reference black body. The other detector, which can be temperature controlled, is used to detect the incoming radiation from the target. The output of the radiation-sensing elements which is sufficiently high to be measured on a recorder without the use of a chopper-amplifier system, can either be measured differentially or the output of the radiation-sensing element facing the target can be measured separately; for the purpose of temperature and emissivity measurements, respectively. The unique facility of being able to vary the temperature of the radiation detector enabled a new method of determining the emissivity of a surface to be developed. As a result, accurate measurements of the emissivities of samples of excised skin could be carried out. An improvement in the response of the radiometer would, however, be necessary for the rapid determination of the emissivity of . living skin by this means. The accuracy with which surface temperatures could be determined by means of the radiometer compared favourably with more sophisticated radiometers.
The effect of tip clearance and tip gap geometry on the performance of a one and a half stage axial gas turbine.
(1996) Kaiser, Ivan.; Bindon, Jeffrey Peter.
In a previous work of a similar nature, the performance of a low speed axial turbine with a second stage nozzle was examined with respect to the effect of the variation of tip clearance for various tip shapes. Present findings suggest some interesting phenomena, including the effect of tip clearance on the flow within the rotor and show that poor resolution from a transducer and insufficient data points in the critical tip region, where a high velocity peak was found, were responsible for a number of incorrect conclusions in the original study. In terms of blade tip geometry, a standard flat tip shape was found to deliver only a marginally better performance when compared to a double squealer tip and the two streamlined shapes previously investigated. Although contemporary opinion suggests that a streamlined tip should increase the leakage flow and hence cause greater mixing losses, the machine efficiency was not significantly reduced. This is an exciting result since it suggests that a streamlined tip shape can be used to alleviate the problem of blade tip burnout without significantly reducing machine efficiency. When the single stage performance in the absence of a second nozzle was examined, slightly different trends were obtained. The low entropy tips produced slightly lower mixing loss, suggesting that the internal gap loss is an important parameter in determining the rate at which the leakage jet mixes downstream of the rotor. The flow behind the rotor (ie time averaged) was found to be in remarkable agreement with linear cascade data when time averaged even though the latter did not include any effects of relative motion. An increase in clearance was seen to reduce the Euler work and also to cause a deficit of mass flow across the remainder of the blade right down to the hub. The leakage flow was also seen to induce a flow blockage which resulted in a higher driving pressure across the rotor for the same mass flow rate. As in the previous study, the second stage nozzle efficiency was seen to be independent of tip clearance or tip shape and was moderately better than that of the first nozzle. However, the improvement was not found to be as large, due to a previously undetected very thin ring of high energy leakage fluid. When this is taken into account, the efficiency of the second stage nozzle is comparable to the first. The second nozzle was seen to have a flow straightening effect on the poorly deflected, high energy leakage flow, causing a rapid mixing process within these downstream blade passages. The growth of secondary flow was reduced at both the hub and the tip and this is believed to result in a slight decrease in loss. The outlet flow was closer to design conditions than that of the first stage nozzle.
The performance of a one and a half stage axial turbine including various tip clearance effects.
(1993) Morphis, George.; Bindon, Jeffrey Peter.
The necessary clearance at the tip of unshrouded rotors of axial turbines allows fluid to leak from the pressure to the suction side of the blade and produces an important component of loss that is ultimately responsible for approximately 25 % of the total turbine rotor losses. Leakage fluid can pass through the tip clearance gap with either high or low loss generation. It has been customary in turbine design to employ high loss designs since it is only by the creation of loss that the gap mass flow rate can be restricted. The present work, however examined the effect of streamlined tips that have low entropy generation within the tip and high leakage flows. An axial turbine followed by a second stage nozzle (ie one and a half stages) was designed, built and instrumented and used to evaluate performance with particular reference to the understanding of tip clearance effects in a real machine and possible benefits of streamlined low loss rotor tips. A radiused pressure edge was found to improve the performance of a single stage and of a one and a half stage turbine at the selected tip clearances. This was in contrast to previous cascade results where mixing losses reduced the benefits of such tips. Clearance gap flow appears to be similar to other turbine flow where the loss mechanism of separation must be avoided. Loss formation within and downstream of a rotor is more complex than previously realized and does not appear to obey the simple rules used to design for minimum tip clearance loss. For example, approximately 48 % of the tip leakage mass flow within a rotor may be a flat wall-jet rather than a vortex. Second stage nozzle efficiency was significantly higher than first stage nozzle efficiency, and even increased with tip clearance. This was a surprising result since it means that not only was there a reduction in secondary flow loss but also that rotor leakage and rotor secondary flows did not generate significant downstream mixing loss. The manner in which the second nozzle responds to the complex leakage flows presented to it and how it completes the formation of tip clearance loss for various rotor tip clearances was identified. The tangentially averaged relative rotor flow in the tip clearance region differed radically from that found in cascades which was seen to be underturned with a high axial velocity. There was evidence rather of overturning presumably caused by secondary flow. Axial velocity followed an almost normal endwall boundary layer pattern with almost no leakage jet effect. Cascade tip clearance models are therefore not accurate in predicting leakage flows of real rotors. The reduction in second stage nozzle loss was seen to occur near the hub and tip confirming a probable reduction in secondary flow loss. Nozzle exit loss contours showed that the leakage flow suppressed the formation of the classical secondary flow pattern and that a new tip clearance related loss phenomenon existed on the suction surface. The second stage nozzle reduced the hub endwall boundary layer below that of both the first nozzle and that behind the rotor. It also appeared to rectify the secondary and tip clearance flows to the extent that a second stage rotor would experience no greater flow distortion than the first stage rotor would. Radial flow angles behind the second stage nozzle were found to be much smaller than those measured in a previous study of low aspect ratio, untwisted blades.

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Browsing Doctoral Degrees (Mechanical Engineering) by Author "Bindon, Jeffrey Peter."