Final report: numerical and physical models of urban heat islands

CER74-75RNM26.Prepared by Robert N. Meroney, Principal Investigator.NSF Grant, ENG-72-03938 (GK33800).Includes bibliographical references (pages 17-20).December 1974.The response in the atmosphere of stratified shear layers to nonhomogeneous surface features is the subject of this report. Many interesting atmospheric circulations such as the sea breeze, the urban heat island, and flow over a heated island in the ocean (heat mountain) are induced by unbalanced bouyancy forces as a result of differential surface temperature. Such phenomena are very complex since the motion is coupled with several dominant features such as thermal stratification, high roughness elements, nonuniformity of surface roughness and/or surface temperature, nonplanar boundaries, and unsteadiness of boundary conditions. These problems may be successfully examined, however, by a coordinated laboratory-analytical research effort. This report summarizes a numerical and experimental research program which examined such a complicated airflow over nonhomogeneous surface complexities in two- and three-dimensional space

Charged particle concepts for fog dispersion

Charged particle techniques hold promise for dispersing warm fog in the terminal area of commercial airports. This report focuses on features of the charged particle technique which require further study. The basic physical principles of the technique and the major verification experiments carried out in the past are described. The fundamentals of the nozzle operation are given. The nozzle characteristics and the theory of particle charging in the nozzle are discussed, including information from extensive literature on electrostatic precipitation relative to environmental pollution control and a description of some preliminary reported analyses on the jet characteristics and interaction with neighboring jets. The equation governing the transfer of water substances and of electrical charge is given together with a brief description of several semi-empirical, mathematical expressions necessary for the governing equations. The necessary ingredients of a field experiment to verify the system once a prototype is built are described

Limitations and opportunities for wire length prediction in gigascale integration

Wires have become a major source of bottleneck in current VLSI designs, and wire length prediction is therefore essential to overcome these bottlenecks. Wire length prediction is broadly classified into two types: macroscopic prediction, which is the prediction of wire length distribution, and microscopic prediction, which is the prediction of individual wire lengths. The objective of this thesis is to develop a clear understanding of limitations to both macroscopic and microscopic a priori, post-placement, pre-routing wire length predictions, and thereby develop better wire length prediction models. Investigations carried out to understand the limitations to macroscopic prediction reveal that, in a given design (i) the variability of the wire length distribution increases with length and (ii) the use of Rent s rule with a constant Rent s exponent p, to calculate the terminal count of a given block size, limits the accuracy of the results from a macroscopic model. Therefore, a new model for the parameter p is developed to more accurately reflect the terminal count of a given block size in placement, and using this, a new more accurate macroscopic model is developed. In addition, a model to predict the variability is also incorporated into the macroscopic model. Studies to understand limitations to microscopic prediction reveal that (i) only a fraction of the wires in a given design are predictable, and these are mostly from shorter nets with smaller degrees and (ii) the current microscopic prediction models are built based on the assumption that a single metric could be used to accurately predict the individual length of all the wires in a design. In this thesis, an alternative microscopic model is developed for the predicting the shorter wires based on a hypothesis that there are multiple metrics that influence the length of the wires. Three different metrics are developed and fitted into a heuristic classification tree framework to provide a unified and more accurate microscopic model.Ph.D.Committee Chair: Dr. Jeff Davis; Committee Member: Dr. James D. Meindl; Committee Member: Dr. Paul Kohl; Committee Member: Dr. Scott Wills; Committee Member: Dr. Sung Kyu Li

Experimental Investigation on the Impact of Wall Heating on Mixed Convection Turbulent Boundary Layer Flow Structure

The hydrodynamic and thermal boundary layers are known to be key regulators of the interfacial transport of mass, momentum and heat, which are crucial in a wide range of engineering and environmental applications. The boundary layers encountered in these applications are often turbulent in nature and characterized by the presence of three-dimensional motion and non-linear dissipative phenomena. The presence of heat transfer between the bulk fluid and the solid wall increases flow complexity due to the interaction of the buoyant force with flow inertia and non-linear coupling between thermo-fluid variables. As a key contributor to multiple engineering systems and environmental phenomena, advancement of the current knowledge on turbulent boundary layer dynamical behaviors is crucial. In the present study, turbulent boundary layer flow over a heated horizontal smooth wall was investigated utilizing an experimental approach. The current state-of-the-art techniques for 3D flow characterization are often limited in their broad applicability. The present knowledge is improved upon with the development of a novel technique based on volumetric illumination with a multi-color pattern. In the absence of heat transfer, the turbulent boundary layer is known to contain a wide range of dynamical phenomena whose behaviors still lack a comprehensive understanding. The present study investigated the unheated turbulent boundary layer utilizing a unique implementation of the Particle Image Velocimetry (PIV) technique to characterize the three-dimensional (3D) nature of the flow and reported new findings on near-wall turbulent flow behavior. In the presence of heat transfer, once the buoyant force magnitude is sufficiently large, thermals detach and rise from the heated wall. The characteristics of thermals in a heated turbulent boundary layer was investigated in 3D utilizing PIV. A novel image processing algorithm was developed to detect thermals. The modification to the turbulent boundary layer velocity field by wall heating was studied utilizing PIV data. Results indicate that boundary layer behavior is influenced by the buoyant force via modification to the turbulent velocity field and associated velocity statistics. This study provides multiple new contributions on flow characterization techniques and the behaviors of the turbulent boundary layer in the presence and absence of heat transfer

Experimental Investigation of the Wake behind the Bluff Body with Heating

Wake behind heated cylinder have been experimentally investigated at low Reynolds numbers. The electrically heated cylinder is mounted in a horizontal circulation water channel facility. The dimensionless parameter Reynolds number is varied to examine flow behavior by forced convection experimental condition. Particle Image Velocimetry (PIV) and Planar-Laser Induced Fluorescence methods (PLIF/LIF) has been used for flow visualization and analysis of the flow structures. The complete vortex-shedding sequence has been recorded using a high speed camera. The dynamical characteristics of the vertical structures - their size, shape and phase are reported. On heating, the changes in the organized structures with respect to shape, size, and their movement are readily perceived from the instantaneous camera images before they reduce to a steady plume.Wake behind heated cylinder have been experimentally investigated at low Reynolds numbers. The electrically heated cylinder is mounted in a horizontal circulation water channel facility. The dimensionless parameter Reynolds number is varied to examine flow behavior by forced convection experimental condition. Particle Image Velocimetry (PIV) and Planar-Laser Induced Fluorescence methods (PLIF/LIF) has been used for flow visualization and analysis of the flow structures. The complete vortex-shedding sequence has been recorded using a high speed camera. The dynamical characteristics of the vertical structures - their size, shape and phase are reported. On heating, the changes in the organized structures with respect to shape, size, and their movement are readily perceived from the instantaneous camera images before they reduce to a steady plume

Improved micro-contact resistance model that considers material deformation, electron transport and thin film characteristics

This paper reports on an improved analytic model forpredicting micro-contact resistance needed for designing microelectro-mechanical systems (MEMS) switches. The originalmodel had two primary considerations: 1) contact materialdeformation (i.e. elastic, plastic, or elastic-plastic) and 2) effectivecontact area radius. The model also assumed that individual aspotswere close together and that their interactions weredependent on each other which led to using the single effective aspotcontact area model. This single effective area model wasused to determine specific electron transport regions (i.e. ballistic,quasi-ballistic, or diffusive) by comparing the effective radius andthe mean free path of an electron. Using this model required thatmicro-switch contact materials be deposited, during devicefabrication, with processes ensuring low surface roughness values(i.e. sputtered films). Sputtered thin film electric contacts,however, do not behave like bulk materials and the effects of thinfilm contacts and spreading resistance must be considered. Theimproved micro-contact resistance model accounts for the twoprimary considerations above, as well as, using thin film,sputtered, electric contact

Measurement of electric fields in the ionosphere, volume 2 Final report, Aug. 1966 - Sep. 1967

Electric field meter, using electron beam deflection techniques, for ionospheric measurement