Joseph A. C. Humphrey

A consistently formulated QUICK scheme for fast and stable convergence using finite-volume iterative calculation procedures

Abstract Previous applications of QUICK for the discretization of convective transport terms in finite-volume calculation procedures have failed to employ a rigorous and systematic approach for consistently deriving this finite difference scheme. Instead, earlier formulations have been established numerically, by trial and error. The new formulation for QUICK presented here is obtained by requiring that it satisfy four rules that guarantee physically realistic numerical solutions having overall balance. Careful testing performed for the wall-driven square enclosure flow configuration shows that the consistently derived version of QUICK is more stable and converges faster than any of the formulations previously employed. This testing includes the relative evaluation of boundary conditions approximated by second- and third-order finite-difference schemes as well as calculations performed at higher Reynolds numbers than previously reported.

Fundamentals of fluid motion in erosion by solid particle impact

Abstract Judging from the extensive literature on the subject, the phenomenon of material erosion by solid-particle impact continues to challenge both practitioners and theoreticians with very complex problems. Although the importance of fluid motion to this form of wear was recognized in early works, many researchers continue to interpret and attempt to understand particle impact erosion almost exclusively in terms of the material properties involved. Little attention has been given to clarifying the influence of fluid motion, especially in the turbulent flow regime. A review of some relevant issues is presented here. It starts with an exposition of the general problem and the need for better understanding. The discussion of experimental techniques is followed by various fundamental considerations relating to the motion of solid particles conditioned by the presence of a carrier fluid, neighboring particles, and a constraining solid surface. Of the experimental techniques used in erosion studies, nonintrusive optical methodologies are the most promising for measuring particle and fluid-phase velocities simultaneously near a surface. Numerical models for calculating particle-laden flows and their application to predict erosion in practical engineering flow configurations are briefly discussed. Emphasis is placed on uncovering areas of inadequate fundamental understanding of fluid mechanics phenomena that significantly affect erosion by solid particle impact.

Sensors and sensing in biology and engineering

INTRODUCTORY REMARKS Sensors and sensing: a biologists view (F. G. Barth), Sensors and sensing: an engineers view (H. Meixner) MECHANICAL SENSORS Waves, Sound and Vibrations How nature designs ears (A. Michelsen), How to build a microphone (P. Rasmussen), The middle and external ears of terrestrial vertebrates as mechanical and acoustic transducers (J. J Rosowski), The outer hair cell: a mechanoelectrical and electromechanical sensor/actuator (K.V. Snyder, F. Sachs, W. E. Brownell), The silicon cochlea (R. Sarpeshkar), Biologically-inspired microfabricated force and position mechano-sensors (P. Dario et al.) Force and Motion The physics of arthropod medium-flow sensitive hairs: biological models for artificial sensors (J. A. C. Humphrey, F. G. Barth, M. Reed, A. Spak), Cricket wind receptors: thermal noise for the highest sensitivity known (T. Shimozawa, J. Murakami, T. Kumagai), Arthropod cuticular hairs: tactile sensors and the refinement of stimulus transformation (F. G. Barth, H.-E. Dechant), The fish lateral line: how to detect hydrodynamic stimuli (J. Mogdans, J. Engelmann, W. Hanke, S. Krother), The blood vasculature as an adaptive system: role of mechanical sensing (T. W. Secomb, A. R. Pries), Mechanism of shear stress-induced coronary microvascular dilation (L. Kuo, T. W. Hein), A possible mechanism for sensing crop canopy ventilation (T. Farquhar, J. Zhou, H. W. Haslach Jr.) VISUAL SENSORS AND VISION From fly vision to robot vision: re-construction as a mode of discovery (N. Franceschini), Locusts looming detectors for robot sensors (F. C. Rind, R. D. Santer, J. M. Blanchard, P. F. M. J. Verschure), Retina-like sensors: motivations, technology and applications (G. Sandini, G. Metta), Computing in cortical columns: information processing in visual cortex (S. W. Zucker), Vision by graph pyramids (W.G. Kropatsch) CHEMOSENSORS AND CHEMOSENSING Mechanisms for gradient following (D.B. Dusenbery), Representation of odor information in theolfactory system: from biology to an artificial nose (J. S. Kauer, J. White), The external aerodynamics of canine olfaction (G. S. Settles, D.A. Kester, L.J. Dodson-Dreibelbis), Microcantilevers for physical, chemical, and biological sensing (T. Thundat, A. Majumdar) THE EMBEDDING OF SENSORS Embedded mechanical sensors in artificial and biological systems (P. Calvert), Active dressware: wearable kinesthetic systems (D. de Rossi, F. Lorussi, A. Mazzoldi, P. Orsini, E. P. Scilingo)

NUMERICAL CALCULATION OF THERMALLY DRIVEN TWO-DIMENSIONAL UNSTEADY LAMINAR FLOW IN CAVITIES OF RECTANGULAR CROSS SECTION

Numerical results are reported for thermally driven laminar flow in two-dimensional rectangular geometries with one plane, the aperture plane, removed. Finite-difference expressions are derived from a set of approximated transport equations in which large temperature and density variations are allowed but high-frequency pressure oscillations are not. The approach allows small time step limitations to be removed from the calculation procedure. A second-order accurate quadratic upstream interpolation technique is used for the finite differencing of convection terms in the transport equations, thus reducing numerical diffusion error. Parameters varied in the calculations were cavity aspect ratio and inclination angle with respect to gravity, inside wall temperature, and Grashof number. A value of Prandtl number corresponding to air was fixed (Pr = 0.73). For the conditions studied, flow and temperature fields within the cavity are determined mainly by local heat transfer events.

Genetic algorithms for thermosciences research: application to the optimized cooling of electronic components

Abstract Genetic algorithms are adaptive search procedures loosely based on the Darwinian notion of evolution. They use rules of natural selection to investigate highly complex, multidimensional problems and have been employed successfully in a variety of search, optimization and machine learning applications in science and engineering where other more traditional methods fail. In this study genetic algorithms are presented and discussed within the framework of an adaptive solution methodology for investigating otherwise intractable optimization problems in the thermosciences. The exposition focuses on their application to an electronics cooling problem where it is required to find optimal or nearly optimal arrangements of convectively cooled components placed in-line on the bottom wall of a ventilated two-dimensional channel. The present application is specific only for purposes of illustration. The power of the methodology rests on its generality of application and an indifference to the source of data (experimental, analytical or numerical) used in the optimization process. The study shows that genetic algorithms allow a cost-effective approach for investigating highly complex numerical and/or experimental thermosciences problems where it is desirable to obtain a family of acceptable problem solutions, as opposed to a single optimum solution.

Numerical simulation of buoyant, turbulent flow. I: Free convection along a heated, vertical, flat plate

Abstract Two models have been developed for predicting free convection low Reynolds number turbulent flows. The models also apply to mixed convection flows. The first, a k-e model, is based on the notion of eddy diffusivities for momentum and heat. The second, an algebraic stress model, is based on approximations derived for the anisotropic turbulent fluxes by a suitable truncation of their conservation equations. Both formulations apply to variable property flows with high overheat ratios, ΔT T ∞ , and have not required the definition of new model constants. No attempt has been made to modify previously established values of the constants in order to improve agreement between measurements and predictions of the flow investigated. Such an optimization must await the availability of more detailed and reliable experimental measurements of turbulence-related quantities. Fully elliptic forms of the differential transport equations, subject to appropriately specified boundary conditions, have been solved numerically for two flow configurations. Both are two-dimensional. The first corresponds to free convection along a heated vertical flat plate and is the subject of Part I of this study. The second corresponds to free and mixed convection from a heated cavity of arbitrary rectangular cross-section and variable orientation, and is the subject of Part II. For the case of the vertical plate, a comparison between measurements and predictions shows that both models yield fairly accurate results for the mean flow and heat transfer. Near-wall velocity and temperature distributions predicted by both models reveal the 1 3 power-law dependence derived by George and Capp [Int. J. Heat Mass Transfer22, 813–826 (1979)] and confirmed for temperature by Siebers et al [J. Heat Transfer107, 124–132 (1985)]. Values of the constants in the power-law relations for velocity and temperature have been obtained here numerically for high and low ΔT T ∞ . Predictions of the anisotropic Reynolds stress and turbulent heat flux distributions are in good qualitative agreement with the measurements of Miyamoto et al. [Proc. 7th Int. Heat Transfer Conference, Vol. 2, pp. 323–328 (1982)]. In particular, regions of negative buoyant and shear production of turbulent kinetic energy observed experimentally are clearly revealed by the calculations.

Enhanced heat conduction in phase-change thermal energy storage devices

Abstract Phase-change energy storage devices have an inherent disadvantage due to the insulating properties of the phase-change materials (PCMs) used. Such systems are difficult to analyze theoretically due to the nonlinearities of the moving liquid-solid interface and the presence of natural convection as shown by several recent numerical and experimental investigations. Previous work has been unsuccessful in predicting the performance of phase-change devices in the presence of fins and natural convection. This study presents a simplified numerical model based on a quasi-linear, transient, thin fin equation, which predicts the fraction of melted PCM, and the shape of the liquid-solid interface as a function of time with sufficient accuracy for engineering purposes. Experimental results are compared in dimensionless form with model predictions, and show fairly good agreement. To achieve high heat-transfer rates with a fixed amount of PCM and metal fin material, the model indicates that melting the PCM in a pure conduction mode with closely spaced thin fins is preferable to melting PCM with thicker fins spread further apart, even in the presence of natural convection.

Thermal isolation of microchip reaction chambers for rapid non-contact DNA amplification

This paper describes further optimization of a non-contact, infrared-mediated system for microchip DNA amplification via the polymerase chain reaction (PCR). The optimization is focused on heat transfer modeling and subsequent fabrication of thermally isolated reaction chambers in glass devices that are uniquely compatible with non-contact thermal control. With a thermal conductivity approximately an order of magnitude higher than many plastics, glass is not the obvious substrate of choice for rapid thermal cycling in microfluidic chambers, yet it is preferable in terms of optical clarity, solvent compatibility and chemical inertness. Based on predictions of a lumped capacity heat transfer analysis, it is shown here that post-bonding, patterned etching of surrounding glass from microfluidic reaction chambers provides enhancements as high as 3.6- and 7.5-fold in cooling and heating rates, respectively, over control devices with the same chamber designs. These devices are then proven functional for rapid DNA amplification via PCR, in which 25 thermal cycles are completed in only 5 min in thermally isolated PCR chambers of 270 nL volume, representing the fastest static PCR in glass devices reported to date. Amplification of the 500-base pair fragment of ?-DNA was confirmed by capillary gel electrophoresis. In addition to rapid temperature control, the fabrication scheme presented, which is compatible with standard photolithography and wet etching techniques, provides a simple alternative for general thermal management in glass microfluidic devices without metallization.

On the flow in the unobstructed space between shrouded corotating disks

A model of a computer hard disk drive was constructed and measurements of the air flow in the unobstructed space between a pair of disks were obtained. The disks were centrally clamped to a common hub, and rotated within an axisymmetric (cylindrical) enclosure or shroud. Measurements of the circumferential velocity component were made at five radial locations and three rotation rates (Ω=300, 1200, and 3600 rpm) using a laser‐Doppler velocimeter. The resulting mean and rms circumferential velocity profiles are presented and discussed. The data show that the circumferential velocity component profiles are fairly uniform in the axial direction in the space between the disks, except near the shroud where the flow is strongly sheared. The circumferential velocity peaks at a critical radius. Between the hub and the critical radius location the flow is in solid body rotation. Between the critical radius and the shroud the circumferential velocity decreases to zero, gradually at first and then very quickly as the...

Unsteady flow and heat transfer for cylinder pairs in a channel

Abstract The incompressible, two-dimensional, unsteady flow past a pair of cylinders of square cross-section, placed in tandem normal to the flow in a channel, has been investigated by dye visualization and direct numerical simulation. The objective has been to evaluate the effect of cylinder separation distance, λ, on the flow behavior and heat transfer, for cylinder diameter ratios, D d , of 1 and 2 over a range of Reynolds numbers 200 ⩽ Re ⩽ 1600, based on the larger (downstream) cylinder diameter. A comparison between the experimental and numerical results for cylinders of equal cross-section dimensions shows very good agreement. The results for D d = 1 reveal three distinct flow patterns as a function of λ and Re which, apparently, have not been previously reported: (1) For 0.25 ⩽ λ ⩽ 4 with Re ⩽ 200, the inter-cylinder flow consists of a pair of steady counter-rotating eddies which do not exchange fluid with the surrounding flow and eddy shedding is observed only for the downstream cylinder. (2) For 0.25 ⩽ λ ⩽ 1.0 with 400 ⩽ Re ⩽ 1600, vertical flow oscillations arise in the inter-cylinder space, and the periodic ingestion of backward-jetting fluid from the top and bottom walls of the downstream cylinder into the inter-cylinder space is observed. For fixed λ the unsteadiness increases with Re but only the downstream cylinder sheds large eddies. (3) At a critical inter-cylinder spacing related to Re according to λ c ∼ Re − 2 3 , the shedding of large eddies also occurs at the upstream cylinder and this results in a highly mixed inter-cylinder flow. For a cylinder diameter ratio of D d = 2 , with the smaller cylinder located upstream of the larger heated cylinder, it is shown that for Re fixed an optimal location exists for the upstream cylinder such that the heat transfer from the downstream cylinder is maximized. The optimal location corresponds to a spacing smaller than the critical inter-cylinder spacing.