The heat transfer and pressure drop characteristics of tubes containing either Pall rings, or helical (180°) strips of metal, were studied experimentally. Tests were performed with water in the Reynolds number range of 11000 to 104000, approximately. Rotameters were used to measure the volumetric flowrate of the water. The effect of fluid temperature on this measurement was determined. The insertion of a continuous length of Pall rings into a tube increases the Nusselt number and pressure drop by factors of 1.5 and 15. (These factors are relative to the empty tube over the same flow range). Smaller increases were obtained while using rings that were equidistantly spaced along the tube.

The main purpose of this investigation was to study the mechanisms of mixed salt crystallisation fouling on heat transfer surfaces during convective heat transfer and sub-cooled flow boiling conditions. To-date no investigations on the effects of operating parameters on the deposition of mixtures of calcium sulphate and calcium carbonate, which are the most common constituents of scales formed on heat transfer surfaces, have been reported. As part of this research project, a substantial number of experiments were performed to determine the mechanisms controlling deposition. Fluid velocity, heat flux, surface and bulk temperatures, concentration of the solution, ionic strength, pressure and heat transfer surface material were varied systematically. After clarification of the effect of these parameters on the deposition process, the results of these experiments were used to develop a mechanistic model for prediction of fouling resistances, caused by crystallisation of mixed salts, under convective heat transfer and subcooled flow boiling conditions. It was assumed that the deposition process of calcium sulphate and calcium carbonate takes place in two successive events. These events are the combined effects related to transport phenomena and chemical kinetics. The effect of the extra deposition created on the heat transfer surface due to sub-cooled flow boiling was considered by inclusion of an enhancement factor. The newly developed model takes into account the effects of all important parameters on scaling phenomena and also considers the simultaneous precipitation and competition of various minerals in the scale formation process. Model predictions were compared with the measured experimental data when calcium sulphate and calcium carbonate form and deposit on the heat transfer surface simultaneously. While deviations ranging from 6% to 25% between model predictions and measured experimental data can be considered good in the context of such a complex process, fouling morphology is clearly a factor to be considered in more detail. This is particularly problematic in the context of more complex fouling solutions encountered in industry. Furthermore, the crystalline samples were analysed using Scanning Electron Microscopy, X- Ray Diffraction and Ion Chromatography techniques. Fractal analysis performed on Scanning Electron Microscopy photographs of the deposits was used to quantify deposit characteristics by introducing a new quantity called the fractal dimension.

No description available.

No description available.

The application of room radiators for the purposes of cooling and dehumidification in buildings for hot and humid climates is investigated. The radiator is purposely brought below the dew point temperature of the room air thereby creating condensation on the radiator surface. The condensate is then collected at the base of the radiator and removed. Mathematical models describing the heat transfer regime within a room when this system is used have been verified using climate chamber tests. The models show good agreement with the experimental results for radiator (a) with a height of 1 m, but not as accurate for radiator (b) with a height of 2 m. The underestimation of the real values by the convective heat transfer model used for the geometric construction of the radiator tested is attributed to the effect of air entrainment along the height of the radiator. Results indicate the importance of the radiant transfer component of the radiator, as well as its effectiveness to remove latent heat. In view of improving thermal comfort and energy efficiency, the implication of the results from this investigation of the heat transfer characteristics of the radiator used for cooling and dehumidification is such that the chilled radiator may offer a definite alternative to conventional air conditioning systems. Partial or full matching of the sensible and latent component of the radiator output to the load requirements of a building should prove particularly effective in hot and humid regions where the latent heat factor of the total cooling load is high.

The development of multi-kilowatt space-based systems requires the transport of waste heat loads over long distances in micro-gravity conditions. In this context two-phase heat transport systems are attractive enabling a high rate of heat transport with low pump powers compared to single phase systems. In this context the design of a two-phase heat exchanger to transfer heat from a single-phase fluid (water) to a two-phase fluid (Freon 114) is discussed. Until reliable micro-gravity (< 10-3g) test data on the heat transfer and pressure drop in a two-phase flows are available, it is deemed necessary that the design of heat exchangers' passages should promote gravity-independent flow regimes. This would make the design and test data, obtained at ground conditions, applicable in micro-gravity environments. The design concept investigated hinges on utilising a set of helical flow passages (with small cross sectional area) to ensure a predictable flow regime, annular flow, up to high vapour qualities (>0.8), in both micro-gravity and one Ig' environments. The concept was applied to the design of a 5kW helically coiled evaporative heat exchanger for space-based systems, which was subsequently manufactured and tested. Ground tests gave results close to analytical predictions based on computer simulations of the heat transfer and pressure drops in helical flow passages. Finally design guideline for a two-phase evaporative heat exchanger for space-based systems is provided, along with . conclusions and areas to be further researched.

Buildings are complex thermally-dynamic structures serving aesthetic as well as, utilitarian functions. It is essential that careful planning is undertaken if buildings are to be energy efficient and cheap to run throughout their-expected life-spans. Although regulations have recently been introduced requiring the values of thermal transmittances (i. e. U-values) for walls and roofs of industrial and domestic buildings, to be less than specified limits, there is no guarantee that improved design will result. Also condensation has increasingly become a problem, as natural ventilation has been reduced, because of the introduction of doubleglazing and draught proofing. The use of insulating materials to increase thermal efficiencies ' through the reduction of heat losses may also create problems in industrial plant and pipework. Metal structures covered with insulants are thereby hidden from view and so any ensuing corrosion, such as the general attack upon a low-alloy steel or stress-corrosion cracking of a stainless steel, may remain undetected until catastrophic failure occurs. It is, therefore, of utmost importance that the potential for and enhancement of corrosion due to the addition of insulants should be carefully considered. The ingress of water or water vapour into the insulant layer and subsequent leaching is the major cause of corrosion, and it is essential that steps are taken to prevent or reduce the likelihood of this occurring while ensuring that metal surfaces are adequately protected. There is a need to ascertain the heat and mass-transfer behaviours of building and insulating materials. Mathematical models require realistic data to simulate effectively conditions found in real structures. Too often in the past manufacturers' data for thermal properties, measured under laboratory conditions, have been used with little attempt to check on their validity or appropriateness to the conditions which are likely to be experienced. As desk-top computers become cheaper and more powerful these dangers could well increase. The too prevalent trusting attitude that computer predictions are absolutely correct together with a potential lack of understanding of the concepts of heat transfer and moisture mitigation by the users could result in poorer, rather than better, designed buildings. The thermal-probe technique for the measurement of the thermal conductivities of building structural materials has been assessed. This rapid transient and potentially cheap technique could be suited ideally to measurements in such materials. The theoretical basis for the method has been investigated and the accuracies and repeatabilities of thermal-probe instruments have been determined in measurements with paraffin wax. Determinations made with this technique, for masonry and structural components, were found to agree well with the manufacturer's thermal conductivity data. However, further developments need to be made to improve the usefulness of this technique for measuring the effective conductivities of fibrous insulants. Also the thermal-probe technique has been assessed for use in moist materials. Initial investigations with wet-day specimens showed that the probe diameter had no significant effect on the indicated values of the apparent thermal conductivity. Tests to measure the apparent thermal conductivities of aerated concrete blocks, at various moisture contents, gave results that compared well with other published data. Attempts to reduce national energy demands have led to increases in insulation thicknesses in roof spaces in Northern Europe and North America. It has generally been assumed that the apparent thermal conductivity of each material used has been a constant and equal to the value obtained in the testing laboratory. Examination of the temperature profiles through various horizontal thicknesses of loose-fill mineral wool insulants suggests that radiation effects and convection in the upper surface layers exposed to free air result in much larger apparent thermal conductivity values than those generally quoted in the literature, and the magnitudes of these effects also increase with the thickness of the insulant layer. Heat transfer mechanisms have been examined to explain these phenomena. Mathematical models of heat transfers through multi-phase materials have been examined. A model is proposed to describe the thermal conductivity of high-porosity cellular insulant which includes heat transfers by conduction through the solid and gaseous phases and by radiation. Predictions were found to agree well with experimental data for airfilled polystyrene foams and to be of the correct order of magnitude for air/fluorocarbon filled polyurethane foams.

In shell-and-tube heat exchangers there is an unavoidable clearance between the tube bundle and the shell wall. This clearance has a relatively low flow resistance and hence a relatively large proportion of the shell-side flow will pass through it, bypassing the tube bundle and thus avoiding the heat transfer surface. The clearance can be blocked by sealingstrips, which eliminate the gap and divert the bypassing flow back into the tube bundle. This thesis details an investigation of bypass lanes in shell-and-tube heat exchangers and the use of sealing-strips. A model exchanger was designed and built to represent a rectangular tube bank in which the bypass lane width could be varied, sealing-strips could be inserted at various positions along the bypass to block completely the bypass wall-to-tube bundle clearance. For four different tube arrays, the pressure drop and exit bypass mass flow fraction were found for isothermal air flow over a range of total flow rates. Three different tube bank geometries were investigated, i) with no bypass lane (ideal bundle), ii) for a range of bypass lane widths, iii) for a range of bypass lane widths blocked by various numbers of sealing-strips. For one tube array type, flow distributions upstream of the tube bank were found using a hot-wire anemometer; from these results the inlet bypass flow fractions were estimated. From these studies it was found that ESDU generally overestimates the pressure drop coefficients when bypassing is present. Bell's (1960) correction factor generally underestimates the pressure drop coefficient when bypassing is present and overestimates the effect of sealing-strips in increasing the pressure drop over the bank. The rectangular tube bank model was modified to represent a section of a cylindrical exchanger. The effect on the pressure drop over a bank with a non-uniform bypass lane width, in the flow direction, was investigated. It was found that the inverse root mean square of the bypass clearances best characterised the "effective" bypass clearance of the whole bank. Flow visualisation studies were undertaken of shell-side flow in a cylindrical exchanger made of glass in which all leakage flows, except bypassing, were eliminated. From the dye traces produced, the shell-side flow was seen to be highly complex. For the geometries examined it appeared that there was little interchange of flow between the bypass and crossflow stream over the crossflow section of the exchanger, but that the bypass stream became crossflow at each window region, with crossflow transferring into the bypass lane. Sealing-strips were seen to produce a thorough mixing of the bypass and crossflow streams

The excess enthalpies, volumes and Gibbs free energies of mixing have been measured for a series of cyclic ethers with hexafluorobenzene. These results indicate the presence of a specific interaction in these systems. Use of a stronger fluorocarbon acceptor, pentafluorobenzonitrile, was found to enhance this interaction. The freezing curve of the system tetrahydropyran + hexaflucrobenzene has been determined shewing only a simple eutectic, indicating that the complex exists only in solution. Nuclear magnetic resonance studies of some of these systems gave an insight into the possible orientation of the complex. An improved static vapour pressures apparatus is described, using a liquid burette system for mixture preparation and incorporating a pressure transducer system. The freezing curves and enthalpies of mixing of some aromatic hydrocarbon systems with pentafluorobenzonitrile have been measured. The results indicate relatively strong interactions between the components of these mixtures.

A new three constant equation of state for fluids and fluid mixtures has been proposed. The equation contains three constants and is a more general form of the Peng-Robinson equation. In addition to the critical temperature and the critical pressure, two parameters are required to characterize a particular fluid. These parameters have been evaluated by minimizing the deviation in the saturated liquid densities while simultaneously satisfying the equilibrium criteria (equality of fugacities) along the saturation curve. Thus, prediction of volumetric properties in the saturation region and other regions of the phase diagram is improved, while accuracy in the prediction of vapour-liquid equilibrium is maintained. Parameters for hydrocarbons and nonhydrocarbons of importance to the synthetic fuel industry are presented. The new equation is extended to mixtures by using mixing rules similar to those used by Peng and Robinson. Only one binary interaction coefficient is sufficient for the accurate prediction of vapour-liquid equilibria. Optimum values of the binary interaction coefficients for hydrocarbon-hydrocarbon and hydrocarbon-non-hydrocarbon systems have been obtained using the new equation, the Peng-Robinson equation and the Soave modification of the Redlich-Kwong equation. The criterion used for selecting the optimum interaction coefficient is the minimization of deviations in bubble point pressures. The new equation has been tested for the prediction of volumetric behaviour of pure fluids and the phase and volumetric behaviour of binary, ternary and multicomponent systems. Comparisons with conventional equations (P-R, S-R-K, R-K and B-W-R-S) are shown. The applicability of van-der-Waals orie fluid model to _ generalised equations of state is demonstrated. The equations of Han and Starling, Simonet and-Behar and Chaudron et al have been compared for volumetric predictions. The Han and Starling equation has also been used with two sets of mixing rules to predict vapour-liquid equilibrium. The van-der-Waals one fluid model has been shown to be a simple and effective method of applying the complicated equations of state to the prediction of thermodynamic properties of mixtures. A generalised form of the corresponding states principle using two non-spherical reference fluids is presented. This represents an alternative method of extending the equation of state approach to fluids and fluid mixtures when experimental data are not available.