No description available.

No description available.

No description available.

No description available.

No description available.

The behaviour of natural convective buoyancy-driven flows within a hot-water store due to the forced passage of colder water through the heat-exchanger's pipe are reviewed in the light of recent advances in experimental throughout the literature. The exchanger designs, for natural unworkable for the engineer complication arises because the heat exchanger are sensitive to and numerical studies, reported empirical development of heat convection problems, are often with a specification. The heat transfer performance of the the initial boundary conditions of the problem, ranging from the initial charged temperature of the water in the insulated tank of a fixed dimensíon, to the physical properties of the heat-exchanger's pipe. It was concluded that an improvement in the heat transfer performance can be derived by determining the optium length and the orientation of the heat-exchanger's arrangement. Further benefits are derived by correlating the thermal convective behaviour, within the hot-water store, with the forced passage of colder water through the heat exchanger's pipe. A convective flow model, based upon the experimental results, is described to advance the heat exchanger design principles in the situation of transient natural convection. Assumptions employed in the experimental work confirm that realistic and reasonable results can be obtained from the thermal analysis of the vertical cylindrícal store in two-dimensions.

The thesis reports on an experimental and computational study of kinetic heating at hypersonic speeds. Of particular interest is the transition of the laminar boundary layer to a state of turbulent motion. The experiments are performed in a Mach 9 Gun tunnel with a 5° semi-angle cone geometry. Twelve hemispherically blunted nose radii are tested at three unit Reynolds numbers. Testing has indicated that as the nose is progressively blunted, the transition region moves downstream. Further amounts of bluntness enhance other instability mechanisms and transition events are witnessed in the near nose regions. There are clearly two transitional regimes, denoted the "small bluntness" and "transition reversal" regime, respectively. This study investigates the structure of the transitional boundary layer in both regimes using thin film heat transfer rate gauges and liquid crystal surface thermography. The heat transfer measurements indicate that the small bluntness transition regime is governed by the rapid formation, growth and merging of turbulent events. Transition occurs over hundreds of boundary layer lengths. The reversal regime transition process is characterised by the birth of turbulent events in the nose and near nose regions. The temporal formation rate of the events is governed by roughness. In a low roughness environment, transition occurs over many model lengths. Increasing the roughness level, increases the spot formation rate, and transition is witnessed immediately downstream of the spherical nose region. The role of roughness is further explored using boundary layer trips. The trip causes a laminar wake which rapidly undergoes transition and forms a turbulent wedge. Event circumferential spreading angles are found for a variety of trip geometries and locations. The heat transfer distribution in the wedge is mapped using the thin film gauges. Computational work is used to perform laminar flow field predictions. Of interest is the entropy layer caused by the presence of the bow shock, and its interaction with the boundary layer. Heat transfer predictions in the transitional region are also performed aided with the experimentally obtained intermittency information.

An apparatus was designed and constructed which enabled material to be melted and heated to a maximum temperature of 10000C and then flooded with a pre-heated liquid. A series of experiments to investigate the thermal interaction between molten metals (aluminium, lead and tin) and SUb-cooled water were conducted. The cooling rates of the molten materials under conditions of flooding were measured with a high speed-thermocouple and recorded with a transient recorder. A simplified model for calculating heat fluxes and metal surface temperatures was developed and used. Experimental results yielded boiling heat transfer in the transition film and stable film regions of the classic boiling curve. Maximum and minimum heat fluxes were observed at nucleate boilin~ crisis and the Leidenfrost point respectively. Results indicate that heat transfer from molten metals to sub-cooled water is a function of temperature and coolant depth and not a direct function of the physical properties of the metals. Heat transfer in the unstable transition film boiling region suggests that boiling dynamics in this region where a stationary molten metal is under pool boiling conditions at atmospheric pressure would not initiate a fuel-coolant interaction. Low heat fluxes around the Leidenfrost point would provide efficient fuel-coolant decoupling by a stable vapour blanket to enable coarse mixing of the fuel and coolant to occur without appreciable loss of thermal energy from the fuel. The research was conducted by Gareph Boxley and was submitted for the degree of PhD at the University of Aston in Birmingham in 1980.

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A study on heat pump thermodynamic characteristics has been made in the laboratory on a specially designed and instrumented air to water heat pump system. The design, using refrigerant R12, was based on the requirement to produce domestic hot water at a temperature of about 50 °C and was assembled in the laboratory. All the experimental data were fed to a microcomputer and stored on disk automatically from appropriate transducers via amplifier and 16 channel analogue to digital converters. The measurements taken were R12 pressures and temperatures, water and R12 mass flow rates, air speed, fan and compressor input powers, water and air inlet and outlet temperatures, wet and dry bulb temperatures. The time interval between the observations could be varied. The results showed, as expected, that the COP was higher at higher air inlet temperatures and at lower hot water output temperatures. The optimum air speed was found to be at a speed when the fan input power was about 4% of the condenser heat output. It was also found that the hot water can be produced at a temperature higher than the appropriate R12 condensing temperature corresponding to condensing pressure. This was achieved by condenser design to take advantage of discharge superheat and by further heating the water using heat recovery from the compressor. Of the input power to the compressor, typically about 85% was transferred to the refrigerant, 50 % by the compression work and 35% due to the heating of the refrigerant by the cylinder wall, and the remaining 15% (of the input power) was rejected to the cooling medium. The evaporator effectiveness was found to be about 75% and sensitive to the air speed. Using the data collected, a steady state computer model was developed. For given input conditions, air inlet temperature, air speed, the degree of suction superheat, water inlet and outlet temperatures; the model is capable of predicting the refrigerant cycle, compressor efficiency, evaporator effectiveness, condenser water flow rate and system Cop.