Understanding the mechanisms that serve to increase heat transfer provides valuable knowledge to minimize the size and maximize the performance of compact heat exchangers. This document presents a detailed experimental heat transfer study of six scaled up louvered fin geometries that are typical of those found in modern louvered fin compact heat exchangers. Heat transfer measurements were performed over a range of Reynolds numbers and with two different boundary conditions. A fully heated boundary condition allowed the effects of the thermal field to be observed while an adiabatic boundary condition allowed the effects of the flow field to be observed. The results indicated that the complex thermal and flow field patterns that developed within the louvered fin geometries strongly affected the heat transfer of individual louvers. In the entrance region of the louvered array, the effects of the flow field were dominant while in the fully developed region of the louvered arrays, the effects of the thermal field were dominant. A companion two-dimensional CFD study indicated that the heat transfer trends of the louvers resulting from both the thermal and flow fields were well predicted. Based on heat transfer performance, it was determined that the theta = 27°, Fp/Lp = 1.52 geometry performed the best at Re = 230 and Re = 370, while the theta = 39°, Fp/Lp = 0.91 geometry performed best at Re = 1016. / Master of Science

A compact heat exchanger is a device used to transfer thermal energy between two or more fluids. The most extensive use of compact heat exchangers occurs in the commercial trucking industry. Most compact heat exchanger designs contain tubes carrying one fluid and external fins through which passes another fluid. To enhance the fin-side heat transfer in a compact heat exchanger, which is typically the air side of the heat exchanger, louvers are manufactured into the fins. Louvered fins initiate the growth of new boundary layers such that the average convective heat transfer coefficient is higher than that which would occur for a continuous fin. Approximately 85% of the total thermal resistance occurs on the air side of the heat exchanger. To design more space and weight efficient heat exchangers, it is imperative to gain a fundamental understanding of the mechanisms that serve to increase the heat transfer on the air side. This thesis presents the heat transfer results of three scaled-up louvered fin geometries and compares these results to six additional models in which the louver angle, fin pitch and Reynolds number were varied. Two experiments were performed to determine the reference temperature used for the calculation of the heat transfer coefficients. The use of two reference temperatures allowed the effects of the flow field and thermal field to be separated. This thesis also presents details of an optimization study performed for a louvered fin array. The results of the experimental study showed that the hot thermal wakes formed at the entrance louver have an adverse effect on the heat transfer of downstream louvers. Measuring the adiabatic wall temperature of the louvers in the array showed the effect of these thermal wakes. The experimental study showed that the optimal louver geometry was Reynolds number dependent. For the lower two Reynolds numbers of ReLp = 230 and 370, the Fp/Lp = 1.52, q = 27° model was found to be the best performer, which does not agree with previous studies. For ReLp = 1016, the Fp/Lp = 0.91, q = 39° model was shown to have optimal heat transfer performance, which is in agreement with a previous study performed by Chang and Wang (1996). / Master of Science

In 21 century finned surfaces are used in almost all condensers to enhance their heat transfer capabilities. A lot of different models are presented in the literature: on horizontal and vertical finned tubes, inside finned tubes. The validation method of the theoretical models is based on comparison between measurement of average heat transfer coefficient and one calculated by the model. But in this case it is impossible to validate all approaches made in the theory. The presented work aims to understand the real relation between assumptions made in the theory and flow of the condensate film along a fin. Therefore a comprehensive investigation of the film condensation phenomena on curvilinear surfaces has been done. This investigation has been done in the framework of the preparation of “SAFIR” and “EMERALD” space experiments aboard International Space Station. A special attention has been given to clarify some technical and technological problems that could eventually have a positive feedback for industrial applications. The model of the fin shape optimization has been developed. It takes into account surface tension forces and finite heat conductivity of the fin material. Developed model allows to significantly increase the condensate outflow as compared with the case of the optimal isothermal fin shape at the finite heat transfer conductivity. Enhancement coefficient increases with fin heat conductivity decreasing. The experimental and theoretical investigation of film condensation on a disk-shaped fin has been done under groun condition. 3D condensation model at different gravity levels has been developed. This model allows to reveal the area of dominant influence of surface tension forces. First prototype of experimental cell for the space experiments has been developed and tested. The temperature distribution along the curvilinear fin surface has been measured. The measurements of the film thickness at the fin top shows that the film thickness does not equal to zero as was assumed in some previous theoretical models. Developed model is in a good agreement with experimental results. In the ground set-up the measurement techniques as in future space experiments were realized: local temperature measurement of the fin surface, measurement of non-condensable gas mole fraction, optical system for local film thickness measurement and system of average heat transfer coefficient measurement. Experimental results approve the usefulness of these systems. Optical system based on schlieren technique for film surface deformation has been investigated and developed. This system was used for the investigation of shear driven liquid film on the mirror like substrate under microgravity condition. The microgravity condition was simulated during ESA Parabolic Flight Campaign of October-November 2009. The experimental results show the high capabilities of this system. In the framework of the space experiments preparation the analysis of appropriate liquid has been done. Three candidates have been compared: Water, Ethyl alcohol and FC-72. Third liquid has been chosen as applicable liquid for the “SAFIR” and “EMERALD” experiments. The optimal fin shapes and film thickness distribution have been calculated for the working liquid. Using obtained results requirements for space experiments have been prepared.

No description available.

Jawed vertebrates (gnathostomes) consist of two clades with living representatives, the chondricthyans (cartilaginous fish including sharks, rays, and chimaeras) and the osteichthyans (bony fish and tetrapods), and two fossil groups, the "placoderms" and "acanthodians". These extinct forms were thought to be monophyletic, but are now considered to be paraphyletic partly due to the discovery of early chondrichthyans and osteichthyans with characters that had been previously used to define them. Among these are fin spines, large dermal structures that, when present, sit anterior to both median and/or paired fins in many extant and fossil jawed vertebrates. Making comparisons among early gnathostomes is difficult since the early chondrichthyans and "acanthodians", which have less mineralized skeleton, do not have large dermal bones on their skulls. As a result, fossil fin spines are potential sources for phylogenetic characters that could help in the study of the gnathostome evolutionary history. This thesis examines the development and internal structure of fin spines in jawed vertebrates using two-dimensional (2D) thin sections and three-dimensional (3D) synchrotron datasets. The development of the dorsal fin spine of the holocephalan, Callorhinchus milii, was described from embryos and compared to that of the neoselachian, Squalus acanthias, whose spine has been the model for studying fossil shark spines. It was found that the development of the C. milii fin presents differences from S. acanthias that suggest it might be a better candidate for studying "acanthodian" fin spines. The 3D histology of fossil fin spines was studied in Romundina stellina, a "placoderm"; Lophosteus superbus, a probable stem-osteichthyan; and sever­­al "acanthodians". The 3D vascularization reconstructed from synchrotron radiation microtomographic data reveal that "acanthodian" and Lophosteus spines grew similarly to what is observed in chondrichthyans, which differs slightly from the growth of the Romundina spine. Chondrichthyans and "acanthodians" also share similarities in their internal organization. Overall, Lophosteus and Romundina spines are more similar in terms of morphology and histology compared to chondrichthyans and "acanthodians". These results support the current hypothesis of gnathostome phylogeny, which places "acanthodians" on the chondrichthyan stem. They also emphasize the need for further study of vertebrate fin spines using 3D approaches.

No description available.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Diss.--Münster--Univ., 1992. / Bibliogr. p. 327-355.

Texte remanié de: Dissertation--Halle an der Saale, 2004. / Bibliogr. p. 326-340.

Texte remanié de: Thèse de doctorat--Littérature québécoise--Bordeaux 3, 2004. Titre de soutenance : Figures d'apocalypses dans l'oeuvre de Michel Tremblay. / Bibliogr. p. 349-360.