This thesis is devoted to heat transfer and fire dynamics in enclosures. It consists of a main part which summarizes and discusses the theory of heat transfer, conservation of energy, fire dynamics and specific fire scenarios that have been studied. In the second part of this thesis, the reader will find an Appendix containing seven scientific publications in this field. In particular, one- and two-zone compartment fire models have been studied. A new way of calculating fire temperatures of pre- and post-flashover compartment fires is presented. Three levels of solution techniques are presented including closed form analytical expressions, spread-sheet calculations and solutions involving general finite element temperature calculations. Validations with experiments have shown good accuracy of the calculation models and that the thermal properties of the surrounding structures have a great impact on the fire temperature development. In addition, the importance of the choice of measurement techniques in fire engineering has been studied. Based on the conclusions from these studies, the best techniques have been used in further experimental studies of different fire scenarios. / Denna avhandling behandlar problem kopplade till värmeöverföring och branddynamik i slutna utrymmen med tonvikt på värmeöverföring mellan gaser och utsatta konstruktioner. Avhandlingen består av en huvuddel och ett appendix innehållande sju vetenskapliga artiklar. I huvuddelen sammanfattas och diskuteras grundläggande teorier och principer inom värmeöverföring och branddynamik samt studier av ett antal specialfall av brandscenarion som baseras på dessa teorier. I de avslutande bilagorna (Artiklar A1-A3 och Artiklar B1-B2) finns sju vetenskapliga artiklar som grundligare beskriver de ovan nämnda specialfallen. Huvudfokus i avhandlingen ligger på temperaturutveckling vid brand i slutna utrymmen. I avhandlingen studeras i synnerhet en- och två-zonsmodeller för brand i slutna utrymmen, och en ny metod för att beräkna brandgastemperaturer före och efter övertändning i rumsbränder är framtagen. Validering av dessa modeller med experiment visar att deras noggrannhet är bra. Modellerna visar också att de termiska egenskaperna hos de omgivande ytorna har stor inverkan på brandtemperatursutvecklingen. I tillägg studeras i denna avhandling betydelsen av val av mätmetoder i brandtekniska tillämpningar. På grundval av slutsatserna från dessa studier har de främsta mätteknikerna använts i ytterligare experimentella studier av olika brandscenarier.

Polymer matrix composites (PMC's) are now being used more and more extensively and over wider ranges of service conditions. Large changes in pressure, chemical environment or temperature influence the mechanical response of such composites. In the present effort, we focus on temperature, a parameter of primary interest in almost all engineering applications. In order to design composite structures without having to perform extensive experiments (virtual design), the necessity of establishing theoretical models that relate the macroscopic response of the structure to the microscopic properties of the constituents arises. In the first part of the present work, a new stiffness versus temperature model is established. The model is validated using data from the literature. The influence of the different polymer's properties (Molecular weight, crystallinity, and filler content) on the model are studied by performing experiments on different grades of four polymers PMMA, PEEK, PPS, and PB. This statistical model is proven to be applicable to very different polymers (elastomers, thermoplastics, crystalline, amorphous, cross-linked, linear, filled, unfilledâ ¦) over wide temperature ranges (from the glassy state to the flow region). The most attractive feature of the proposed model is the capability to enable a description of the polymer's mechanical behavior within and across the property transition regions. In order to validate the feasibility of using the model to predict the mechanical response of polymer matrix composites, the stiffness-temperature model is used in various micromechanical models (rule of mixtures, compression models for the life prediction of unidirectional PMC's in end-loaded bendingâ ¦). The model is also inserted in the MRLife prediction code to predict the remaining strength and life of unidirectional PMC's in fatigue bending. End-loaded fatigue experiments were performed. A good correlation between theoretical and experimental results is observed. Finally, the model is used in the Classical Lamination Theory; some laminates were found to exhibit stress reversals with temperature and behaved like thermally activated mechanical switches. / Ph. D.

This study focused on the development and evaluation of die-attach material and substrate technology for high-temperature applications. For the die-attach material, a low-temperature sintering technique enabled by a nanoscale silver paste was developed for attaching large-area (>100 mm2) semiconductor chips. The nanoscale silver paste can be sintered at a much lower temperature (<300 oC) than in the conventional sintering process (>800 oC), and at the same time reached about 80 vol% bulk density. Analyses of the sintered joints by scanning acoustic imaging and electron microscopy showed that the attachment layer had a uniform microstructure with micron-sized porosity with the potential for high reliability under high temperature applications. We also investigated the effects of a large temperature cycling range on the reliability of direct bonded aluminum (DBA) substrate. DBA substrates with different metallization were thermally cycled between -55 oC and 250 oC. Unlike with the DBC substrate, no delamination of aluminum from the aluminum nitride ceramic base-plate was observed for the DBA substrates. However, aluminum surface became roughened during the thermal cycling test. It was believed that in the high-temperature regime, the significant amount of thermomechanical stress and grain-scale deformation would cause recrystallization and grain-boundary sliding in the aluminum layer, which would further lead to the observed increase in surface roughness. The influence of metallization over the aluminum surface on the extent of surface roughness was also characterized. In addition to evaluating the reliability of nanoscale silver paste and DBA substrate individually, this work also conducted experiments that characterize the compatibility of nanoscale silver paste on DBA substrate in terms of reliability in a high-temperature environment. In the large-area attachment, the sintered silver was found to be very compliant with the deformed aluminum. The device-to-silver and silver-to-substrate interfaces remain intact after up to 800 cycles. No large scale delamination and horizontal cracks were observed. However, some vertical crack lines began to show after certain number of cycles. It was believed that these vertical cracks were caused by the thermomechanical stresses in the sintered silver layer. In addition, with regard to the thermal performance, since most of the heat was generated from the semiconductor devices and were transferred vertically through the die-attach material to substrate, these vertical cracks were also considered more advantageous than horizontal cracks. / Ph. D.

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Call number: LD2668 .T4 1961 S42

Call number: LD2668 .T4 1963 T65 / Master of Science

Call number: LD2668 .T4 1979 C52 / Master of Science

Call number: LD2668 .T4 1979 B76 / Master of Science