Thesis (M.S.)--University of Wisconsin--Madison, 1968. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis ( Ph.D.) -- McMaster University, 2000. / Includes bibliographical references. Also available via World Wide Web.

Heat Transfer Lab report ; no. 80047-99 / Sponsored by Empire State Electric Energy Research Corporation, New York.

M.Ing. / There are two advantages of enhanced heat transfer. Firstly a decrease in the heat exchanger size and secondly an increase in the heat transfer coefficient. A method of increasing the heat transfer coefficient is to insert spiralled wires in the annulus of a tube-in-tube heat exchanger. It was decided to investigate this method further and therefore the objectives of the investigation are twofold. First to determine what the optimum spiral angle of the wires is, and secondly what mechanism causes the enhanced heat transfer. Specifically to determine if it is an increase in the turbulence or an increase in the flow rotation. A numerical model that was experimentally verified was used to do the investigation. It was concluded from the numerical results that for optimum heat transfer, the spiral angle of the wires should be 30°. It was also found that the mechanism for enhanced heat transfer is an increase in the rotation of the flow in the annulus.

M.Ing. / There are different types of heat transfer enhancement techniques that can be used, but some of these techniques are expensive and cannot be afforded by small manufacturing firms. An easy and affordable technique considered in this paper has an angled spiralling tape inserted into the annulus of a tube-in-tube heat exchanger. The purpose of this paper was to determine the single phase heat transfer and pressure drop characteristics in the annulus. Experimental measurements were taken on four set-ups; a normal tube-in-tube heat exchanger used as a reference and three heat exchangers with different angled spiralling tape inserts. From the results correlations were developed that can be used to predict the heat transfer and pressure drop characteristics. It was concluded that the angled spiralling tape inserts resulted in an increase in the heat transfer and pressure drop characteristics as can be expected.

No description available.

The object of this investigation was to examine the transient heat flow through a composite wall. This wall was chosen to represent the type used in house construction. It consisted of a fir frame, covered on one side with hardboard and on the other with cedar, and the space between the hardboard and cedar was filled with fibreglass insulation. A vapour barrier was not included as it would offer little resistance to heat flow. This structure, therefore, offered resistances to heat flow in series and parallel. The theoretical analysis was numerical owing to the anisotropic properties of the materials and to the composite structure of the wall. Two analyses were made of the transient heat flow, an exact analysis and an approximate analysis which neglected the effect of the frame. The heat flow was three dimensional in the first analysis owing to the difference in the magnitude of the parallel resistances and was one dimensional in the approximate analysis. The two theoretical solutions both showed exponential cooling rates and agreed within five percent of each other, which shows that the effect of the frame is negligible when its surface area is small as compared to the total surface area of the wall. The ratio of total wall surface area to frame area for the wall studied was 9.6 to 1.0. The wall was mounted in a guarded hot-box apparatus and experiments were performed in order to verify the results of the theoretical analysis. The experiments consisted of establishing a steady state temperature gradient across the wall and then eliminating the heat source. The ensuing transient temperatures were measured by thermocouples and were compared with those predicted by theory. The experimental results varied from the exact solution by 14 percent and from the approximate solution by 18 percent. The experimental results indicated that the tests were consistent. The difference between the theoretical and experimental results was attributed to: (1) contact resistances, (2) nonhomogeneous wall materials, (3) nonuniform surface coefficients of heat transfer, and (k) the effect of neglecting certain heat capacities which actually were not negligible. The results indicated that the transient temperatures varied according to the equation T = Ti e [formula omitted] where T represents temperature, t represents time, and [formula omitted] is the time constant. The results also showed that the method of analysis was acceptable and that the approximate analysis is suitable for walls with small frame areas. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Fouling by a petroleum gas oil and a dilute suspension of sand in water was studied as a function of mass flow rate and wall temperature. The experiments were carried out by circulating the liquid through a single tube maintained at constant heat flux by electrical heating. The change in fouling resistance and pressure drop with time was measured. The fouling resistance of the water and of the oil at low heat fluxes grows to an asymptotic value. At higher heat fluxes the oil fouling resistance increased almost linearly with time after an induction period. The asymptotic fouling resistance of both the oil and the water decreased with increasing mass flow rate. At constant clean tube wall temperature the initial fouling rate of the oil decreased with increasing mass flow rate. The initial fouling rate of the water increased with increasing mass flow rate up to a critical mass flow rate, and then decreased with further increases in mass flow rate. At constant mass flow rate, the initial fouling rate of the oil depended exponentially on the clean tube wall temperature. An activation energy of 29 Kcal/mole was calculated for the oil fouling process by fitting the initial fouling rate data to an Arrhenius type of equation. The pressure drop increase showed the same general trends with mass flow rate and tube wall temperature as did the fouling resistance. Fouling resistances for heated Kraft cooking liquor, calculated from pulp mill operating data and from a single fouling experiment, appeared to follow similar trends to those, followed in common by the gas oil and the water. The experimental results of this study were compared to the mathematical model of Kern and Seaton. While the shape of most fouling curves was in agreement with that predicted generally by this model, dependence of the initial fouling rate and of the asymptotic fouling resistance of the gas oil on the mass flow rate were both in disagreement with the detailed predictions of the model. For low mass flow rates of the water, however, even the detailed predictions were borne out. It was, moreover, possible to remove part of the sand deposit by increasing the velocity of the water, in accord with the postulated removal mechanism of Kern and Seaton, but the coke-like deposit from the gas oil could not be similarly removed by increasing the oil velocity. Mathematical models are developed in which the deposition term is written as the product of a material flux to the wall region and a sticking probability, after Parkins, and the removal term depends on the shear stress, after Kern and Seaton. Specific cases are considered where deposition is controlled by transfer to the surface, adhesion at the surface, and a combination of both steps.. Where deposition is controlled partly by transfer and partly by adhesion, the model predicts mass flow rate and temperature dependence of the initial fouling rate in agreement with the experimental results found for the oil. The observed asymptotic fouling resistance of the oil, however, depended less strongly on the reciprocal of the mass flow rate than is predicted by the model. Where transfer alone controls the deposition process, the extended model reduces to a form similar to that of Kern and Seaton. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

Chemical reaction fouling is one of several categories of fouling of heat exchangers. It is encountered mostly in petroleum, petrochemical, and food processing industries, where it results in severe economic penalties. Olefins have been associated with fouling during heating of organic mixtures, and gum formation during storage and use of hydrocarbon fuels. In this work, thermal fouling studies are reported for a number of olefins, present at 10 % wt. in kerosene, undergoing sensible heating in the liquid phase at relatively high heat fluxes. Experimental work was done on an available fouling rig consisting of an annular probe and a coiled wire probe mounted in parallel. The annular probe with its heated central core operated in turbulent flow whilst the coiled wire, with flow normal to it, was in the laminar flow regime. Runs were conducted both under oxygenated (air-saturated) and deoxygenated conditions. The range of bulk temperatures was from 70 - 85 ℃, the initial wall temperatures were 180 - 205 °C, with a system pressure of 410 kPa (abs.). The range of heat fluxes was 150 - 350 kW/m². Only minor differences were noted between the extent or rate of fouling on the two different probes. Runs at heat fluxes below 180 kW/m² and bulk temperatures below 80 °C generally showed no measurable fouling with any of the olefins tested. Linear and falling rate fouling curves were observed at more severe conditions over 45 hours of typical runs. Under air saturated conditions, straight chain terminal olefins of C₈ - C₉ showed little or no measurable fouling. The longer chain length hexadecane-1, showed a significant increase in fouling. Moderate fouling was observed for 4-vinylcyclohexene. The cyclic olefins, dicyclopentadiene and indene, yielded the greatest R[formula omitted] values, being about 30 - 50 times those of the straight chain terminal olefins. Under deoxygenated conditions, typical R[formula omitted] values were a factor of about 30 below the corresponding values for air saturated conditions. R[formula omitted] generally increased with increasing heat flux. Where the antioxidant initially present in the olefin was not removed before use, very little fouling occurred. The effects of deoxygenation, heat flux and species effects are discussed and a probable fouling mechanism involving formation of polymeric peroxides by autoxidation of the olefins suggested. The fouling rates over the linear portions of the fouling curves have been calculated and the deposit thermal conductivity based on the maximum fouling resistance and deposit thickness have been estimated. Analyses of selected deposits have been presented and compared with both theoretical calculations for the expected polymeric peroxides and values in the literature. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

A study of heat exchanger tube wear has been completed. A simple theoretical model of elastic/plastic deformation has been developed and used in a new model of wear. Experimental results were used to corroborate the theoretical developments. A literature survey of wear mechanisms and wear models was conducted to provide the author with an opportunity to familiarize himself with current knowledge of the field of tribology. Experiments were conducted to simulate a heat exchanger tube/support wear system. For the first series of experiments, a simple impacting rig was used, while a second set was conducted using a much more accurate rig and facilities of the National Research Council of Canada's Tribology Laboratory. Modifications to the NRC rig were designed by the author to incorporate the specific specimen geometries. The main operating parameters of the test apparatus were varied in an effort to determine their effect on wear rates. Force and displacement data were collected and the normal and shear forces calculated, as was the work input. Comparison between the frictional work input and the measured wear showed that there was an approximately linear correlation between work and wear rates. Inspection of the surfaces of the worn specimens showed that a number of wear mechanisms operate in this wear system but that wear is primarily due to delamination and shear fracture. Also, it was noticed that the micro-surface geometry of the worn specimens has a consistent texture, regardless of magnitude and angle of impact between the tube and ring. A model of plastic contact deformation was developed to allow calculation of the contact parameters between two surfaces, given that the softer surface is repeatedly plastically deformed. This model says that repeated stress cycles lead to the introduction of residual stresses, which combined with work hardening of the material, lead the softer material to an elastic shakedown state. Once the typical asperity contact state is known, the typical stress distribution is calculated using Hertzian line contact stress formulae. A series of computer programs were developed to calculate the stress distribution beneath a sliding contact. The depth of maximum shear stress can then be found. This depth corresponds to the expected wear particle thickness. A wear sheet was assumed to form when the frictional work input is equal to the energy required to cause failure in ductile shear. A wear equation was then developed to predict the wear rate between a heat exchanger tube and its support. The final wear model has seen limited comparison with experimental results. The theoretical work input was found to be about 25% of the correlated bulk work. This indicates that the geometry assumptions of the model are quite reasonable. Unfortunately, the predicted wear rate was found to exceed the measured values by a factor of about 5000. If this empirical value is factored into the the wear model, then the predicted results are found to correspond well with the experimental values. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate