No description available.

An apparatus and technique based on Angstrom's method is developed for measuring the thermal diffusivity of fruits and vegetables. The reproducibility of the results is found to be satisfactory with typical standard deviations of less than 6&'37. A detailed error analysis reveals that the accuracy of the technique is 7.1&'37. However, on checking the system with materials of known thermal diffusivities there was found to be a systematic error of the order of a factor of 2. A number of possible reasons for this are discussed. A method is outlined for predicting the optimum heat treatment parameters for the control of the potato disease blackleg. Some field trials were conducted which allowed the theory to be tested. During the field trials a varietal susceptibility to heat treatment was detected. The last part of the thesis concentrates on developing a means of quantifying this. Two methods were developed, the first based on the principle of increased cellular membrane permeability of damaged tissue and the second on a change in the speed of sound in damaged tissue.

No description available.

No description available.

A programme of work was instigated to investigate and improve the efficiency, and stability of intra-cavity étalons for the Argon ion laser, especially in the far blue to near ultra-violet wavelength region, by using sol-gel prepared silica. The original program has been modified by experiences outlined below. We have attempted to differentiate between the sol-gel derived and the high temperature prepared silica. We confirm that relatively small changes in thickness of silica monoliths can give rise to proportionally much larger changes of refractive index. Our main target has been to assess whether it is possible to make a new optical material that shows insignificant changes in optical path length or refractive index with temperature.

The work described in this dissertation is concerned with some aspects of heat transfer in shallow gas fluidised beds. Results from the experimental investigations with the single heater indicated that fluidising velocity, particle size, bed height, heater diameter and heater position influence heat transfer. As expected, heater material has no influence. Unlike previous work, this work has concentrated upon the range of dependency of heat transfer on each of the tested parameters (e.g., heater diameter has no influence on heat transfer with heater diameter greater than 25.3 mm and bed depth has no influence on heat transfer for depths greater than 150 mm). The variation of this dependency with respect to the other parameters (e.g., influence of fluidising velocity on heat transfer coefficient increased with an increase in bed depth. The influence of heater location decreased with an increase in particle size, fluidising velocity and heater diameter), The effect of horizontal rod spacing on heat transfer was also examined, when unheated rods were used to complete the rod bundle. The effect of rod spacing was dependent on the other parameters (e.g., fluidising velocity, bed depth and heater diameter). Since the heat transfer depends primarily on frequent renewal of the particles at the heat transfer surface and particle mixing, these were improved by the use of gas jets. Heat transfer was found to increase by up to 50%. The following parameters were investigated: volumetric flow rate, particle size, heater size, bed height, jets position and direction and jets velocity to find their effect on the influence of gas jets on heat transfer. The data were compared with some earlier correlations and two dimensionless correlations developed. One was for a single heater and the other was for one row of horizontal rods. Unlike previous correlations, these correlations took account of both the effect of heater size and bed depth. The data for the single heater were compared with some earlier models and the fit with one of these models is good.

I report the results of numerical studies of 2-dimensional fully compressible convection of a fluid in which the dependence of the radiative conductivity on temperature T is taken as K, (V + aT -5)1 so that central regions of the layer are unstable to convection whereas the surrounding layers are stable. Calculations have been undertaken for Rayleigh numbers at the centre of the unstable layer Rc,, = 4.78 106 -9-56 107 and Prandtl numbers a=0.05 - 1. The main result found is that in a (statistically) stationary state the viscous dissipation decreases with decreasing Prandtl number, and that the equilibrium of the whole layer is governed by a substantial penetrative region in which the convective flux is negative. The results found here suggest that the so called "Roxburgh criterion" can be used to give a good estimate of convective penetration at small Prandtl numbers. I also report the results of three sets of numerical experiments involving the interaction of magnetic fields with 2-dimensional fully compressible convection, were the fluid has the same conductivity. For these experiments R9subscript cen)= 4.78 106 and [sigma]=1.0, typically. For one set of experiments a simple model of the evolution of a toroidal flux tube is considered. The purpose of these numerical experiments was to test the role played by magnetic buoyancy in the rise of the magnetic flux tube. It was found that magnetic buoyancy was not important, except possibly when the initial field strength was large (Chandrasekhar number Q= 10'). In another set of numerical experiments the initial magnetic field was an uniform horizontal field. One of the results found was that the magnetic field did not significantly reduce convective penetration, even when the total (integrated) magnetic energy was of the same order as the total kinetic energy. The general behaviour found was that magnetic field was expelled from the convective region, until Q- 10'. Then the initial field strength was strong enough to suppress convection completely. No oscillatory solutions were found. Finally experiments were made for initially vertical magnetic fields. An oscillatory solution is presented. Also reported are preliminary calculations of 2-dimensional penetrative convection, for a model were the effects of energy generation and self gravity are included.

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The results of an insitu investigation into the thermal performance of a range of wall constructions are presented. The investigations were mainly undertaken to establish the uncertainty introduced by the measurement, the variability in the performance of the wall due to factors such as workmanship and the relevance of design values in practice. This study provides a useful addition to the otherwise sparse literature of actual measured heat flow and temperature data available from large scale field surveys in UK. A review of methods and equipment used to recover the thermal transmittance value of wall constructions is presented. The Heat Flow Sensor measurement method was found to be most suitable for the needs of the study and was evaluated both theoretically and experimentally. An experimental design approach was devised which enabled the separation of the variability involved in the measurement process and the variability involved in the performance of the wall to be obtained. The four generic wall types sampled included a representative range of existing and new build constructions. The indications are that the wall constructions investigated broadly perform as expected. However, for certain wall types there were significant differences between measured and standard design calculation values. This was because the appropriate theoretical model was not applied in order to establish the transmittance of the wall construction at the design stage. It would appear that the overall error in the measurement process, which is a combination of both the systematic and the random error, was typically of the order of +/-11%, whereas the variability in the wall performance was seen to vary as a function of the wall type with the resulting values ranging between 4% and 39.5%. The differences in the observed performance of the wall may be potentially attributed to 4 major causes, namely: (a) dimensional tolerances and material properties, (b) changes in material properties, (c) the wall as part of the construction and (d) workmanship. The average wall performance in some circumstances can be estimated satisfactorily by using a one dimensional model where a relatively homogeneous wall construction is assumed. While the area weighted one dimensional model gives a reasonable estimate of the average wall performance by taking into account the cold bridging of the mortar joints, a more complete understanding of the wall performance can only be achieved by the use of a three dimensional model.

This thesis provides a commentary on the author's publications submitted herewith for the PhD degree. These publications present twelve general. predictive techniques for two-phase heat transfer developed by the author. These include those for: (a) Heat transfer during film condensation in tubes and annuli, boiling of saturated and subcooled fluids in tubes and annuli, film boiling in tubes, flow of twocomponent gas-liquid mixtures in tubes, and pool boiling of liquid metals. (b) Critical heat flux during boiling in tubes and annuli, and pool boiling of liquid metals. (c) Heat transfer to surfaces in fluidized beds. (d) Rate of evaporation from water pools The thesis consists of fourteen chapters. The first is the "Introduction. " Each of the following chapters (except the last) presents one predictive technique and has the following arrangement. The practical significance of the work is first pointed out. The predictive technique is then briefly presented. It is followed by the "Discussion" section in which the topics discussed include verification by others, recommendations in reference books, other correlations and how they compare in merit with the author's predictive technique. The chapter ends with the "Conclusion" section in which conclusion is drawn from the evidence presented in the rest of the chapter regarding the contribution of the author's work. In the final chapter, the conclusions made in the earlier chapters regarding the contributions of the author's publications are summarized. It is shown in this thesis that each of these predictive techniques is either the best or among the best available as shown by the author's own as well as other researchers' data analyses, that most of these are recommended in design reference books and are in use in practical designs and analyses as well as in research. The publications submitted for PhD which presented these predictive techniques are therefore significant, coherent, and original contributions to knowledge