[en] A subgrid-scale model is discussed for the scalar dissipation rate in nonpremixed turbulent reacting flows. The model contains a coefficient which is determined by assuming a form for the scalar energy spectrum. The model is tested a priori using Direct Numerical Simulation (DNS) results for a temporal reacting mixing layer. The estimated dissipation rates are in good agreement with dissipation rates computed directly from the DNS data. Furthermore, the assumed spectrum methodology is found to accurately predict the model coefficient, including its spatial and temporal variations. copyright 1999 American Institute of Physics

[en] Rigorous upper bounds are derived for large-scale turbulent flame speeds in a prototypical model problem. This model problem consists of a reaction-diffusion equation with KPP chemistry with random advection consisting of a turbulent unidirectional shear flow. When this velocity field is fractal with a Hurst exponent H with 0< H<1, the almost sure upper bounds suggest that there is an accelerating large-scale turbulent flame front with the enhanced anomalous propagation law y = C_Ht^1+H for large renormalized times. In contrast, a similar rigorous almost sure upper bound for velocity fields with finite energy yields the turbulent flame propagation law y = C_Ht within logarithmic corrections. Furthermore, rigorous theorems are developed here which show that upper bounds for turbulent flame speeds with fractal velocity fields are not self-averaging, i.e., bounds for the ensemble-averaged turbulent flame speed can be extremely pessimistic and misleading when compared with the bounds for every realization

[en] The objective of this report is to have a comprehensive overview of heat exchanger fouling problems as they occur in the industrial manufacturing sector. Specifically the types of fouling, conditions that influence fouling, the mitigation and accommodation techniques currently being used and mitigation technology trends are discussed. Finally a table top apparatus is designed and fabricated to develop an on line mechanical technique of rubber ball system for the removal of dirt and scales of that exchangers. Experimental results of this apparatus show that the cleaning efficiency can be raised if this mechanical technique is used together with current chemical fouling removal methods. (author)

[en] Published in summary form only

[en] A brief historical survey is given of the development of radiation processing, with special emphasis on the field of organic polymers. Sterilisation and other applications are discussed. Reasons for delay or difficulty in getting processes accepted commercially are examined. (U.K.)

[en] The potential theory centres on the standard decomposition and representation theorems for subharmonic functions. In addition, the first and second fundamental theorems of Nevanlinna's theory of meromorphic functions are derived and, after two applications to differential equations, some open problems are discussed. Systematic use is made of L. Schwartz's theory of distributions. (author)

[en] This conference contains 11 papers, all of which are abstracted separately. The subject matter is primarily concerned with common flow-induced vibration problems in the power generation industry as related to tube banks and bundles. Field problems occurring in nuclear power plants are studied, involving high flow rates and fragile structures

[en] Poster presentation. 3 refs, 2 tabs

[en] It is found that a large deviation function for the frequency of events of a size not equal to the system size in the one-dimensional forest-fire model with a single ignition site at an edge is independent of the system size, by using an exact decomposition of the modified transition matrix of a master equation. An exchange in the largest eigenvalue of the modified transition matrix may not occur in the model. (paper)

[en] A new approach for fabricating open and closed porous structures based on laser processing is presented. Liquid polyimide (PI) was mixed with azodicarbonamide which is a chemical blowing agent (CBA), and the mixture was spin-coated and pre-cured in order to fabricate solid PI films. Porous PI was prepared by irradiating PI films mixed with azodicarbonamide. The PI film with azodicarbonamide was etched by using laser ablation, and the azodicarbonamide was decomposed due to the heat induced by the absorbed laser energy. At higher laser beam irradiation, more pores were fabricated due to the resulting increase in the CBA decomposition from 27 mJ/cm2 to 40 mJ/cm2 per single pulse. A fluence of about 50 mJ/cm2 resulted in fewer and larger open pores, which were formed by the coalescence of small pores. In contrast, a closed porous structure was fabricated at a fluence of less than 1 mJ/cm2 because PI was barely etched. The proposed method can be used to create open and closed porous structures selectively and is not limited to thermosetting polymers, but is also effective with thermoplastic polymers.