Richard L. Hummel

Pulsatile flow through constricted tubes: an experimental investigation using photochromic tracer methods

A photochromic tracer method has been used to record pulsatile flow velocity profiles simultaneously at three axial locations along a flow channel. Two major advantages of this multiple-trace method are that it enables velocity data to be acquired in an efficient non-invasive manner and that it provides a detailed description of the spatial relationship of the flow field. The latter is found to be particularly useful in the investigation of transitional type flows; for example, in describing coherent flow structures. Studies of the flow patterns in tubes with mild to moderate degrees of vessel constriction were performed using a 2.9 Hz sinusoidal flow superimposed on a steady flow (frequency parameter of 7.5; mean and modulation Reynolds numbers of 575 and 360, respectively). With mild constrictions (

A new method for non-disturbing turbulent flow measurements very close to a wall

Abstract A general flash photolysis method suitable for various non-disturbing turbulent flow measurements very close to a wall of any shape has been developed. A very dilute solution of 2-(2, 4-dinitro-benzyl)-pyridine in 95 per cent ethyl alcohol is employed. A tracer, in the form of a blue line, is introduced upon the exposure of the solution to the high intensity light beam formed by a parabolic mirror. The colour is due to a tautomeric shift in the structure of the dissolved substance. The tracer is recorded photographically after an increment of time has elapsed since its formation.

Average velocity distributions within falling liquid films

A photochromic dye-tracer technique was developed and used to measure the velocity distributions within falling liquid films inside a vertical pyrex tube. Three liquids with similar densities and surface tensions but different kinematic viscosities were used and the Reynolds numbers (4Q/v) investigated ranged from 124 to 2800. The fully-developed average velocity distributions were found to be a function of the Reynolds number alone and independent of the distance from the liquid inlet. In dimesionless parameters, the average velocity distributions can be represented by the equation The average film thicknesses calculated from the wall shear stresses agreed well with values obtained with other direct measurement methods.

Experimental velocity profiles in laminar flow around spheres at intermediate Reynolds numbers

Seeley, Hummel & Smith (1975) reported the results of experiments to study the dynamics of flow around spheres at intermediate Reynolds numbers using a nondisturbing flow-visualization technique. The flow patterns were recorded on cine photographs and the information stored was processed in order to obtain the velocity field. The position of fluid elements shown by the photochromic indicator traces were estimated by eye on a projection screen. In this paper, a new set of results based on the same films has been reduced and computed using the ‘POLLY’ film-reading system described by Esmail, Smith & Hummel (1976). Some numerical boundary-layer solutions are included to show the reliability of the data, and comparisons with the results previously reported by Seeley et al. (1975) are presented. J. W. Smith will be pleased to send a complete set of experimental data on request.

Detailed visualization of pulsatile flow fields produced by modelled arterial stenoses

A multiple trace photochromic method was used to visualize the pulsatile flow field created by modelled arterial stenoses of 38% and 65% area reductions. Using flow parameters similar to those of a medium sized artery in man, the flow patterns at seven axial locations in relation to the stenosis were simultaneously photographed at various times throughout the flow cycle. With the 65% stenosis, the wall shear stress in the vicinity of the reattachment point was found to fluctuate quite strongly during the turbulent phase of the flow cycle, giving rise to instantaneous shear stresses that were at least eight times larger than those measured upstream. For the 38% stenosis, much smaller shear stresses were observed. These and other results are described in detail.

Potential limitations of center-line pulsed Doppler recordings: An in vitro flow visualization study

In this study an in vitro model that permits visualization of the flow velocity profile has been used to determine if duplex pulsed Doppler recordings made with a small sample volume in the center line of the vessel can determine the severity of a stenosis in the 38% to 75% range of cross-sectional area reduction. Because most Doppler instruments measure the maximum peak frequency and the extent of spectral broadening, observations in the flow model included changes in the center-line maximum velocity and the location and intensity of flow disturbances. The results showed that center-line measurements of maximum velocity (equivalent to peak Doppler frequency) were directly related to the severity of the stenosis as long as the recordings were made from within the throat to about 1.5 to 3 tube diameters downstream, depending on the shape of the stenosis. However, flow disturbances (equivalent to spectral broadening) did not always occur in the center line of the vessel. Stenoses greater than 50% area reduction produced turbulence across the entire vessel in the region 4.5 to 7.5 diameters downstream. The turbulent period started just before peak systole and extended to just less than half the pulse cycle. In the more proximal zone a forward flow jet was present in the central part of the vessel, and reverse flow was present in the outer region. The interfacial layer between these two regions is subjected to high shear rates that resulted in the formation of waves and vortices.(ABSTRACT TRUNCATED AT 250 WORDS)

Solar distillation with economies of scale, innovation and optimization

Solar distillation of seawater can be economical on a large scale, combining the advantages of free solar energy with cost effective design. To do this, we have designed a large scale, solar unit topped by covers at two levels, the top resists the wind, creating a quiet space for more traditional covers which trap the solar energy and condense water vapor. These lower covers would arch over a large pool of brine built in a shallow sandy bay. The solar energy would be converted to heat beneath the brine to distill water vapor condensed on the cover. Air would flow over a brine pool, collecting vapor. In some pools, the air would then be blown through inflated plastic under the brine where the heat released by condensation of vapor would be passed back into the brine pool to create more vaporization. This system, Distributed Multieffect Distillation (DMD), offers improvements over the traditional solar energy system because it reuses the heat of condensation and over the usual MSF, MED, and LTV systems, which also reuse the heat, because it has much lower construction costs. To update these early assumptions, using todays powerful low-cost computers, we can determine the economics and maximize the ability to compete against todays best systems by modeling and optimizing, design and operation. Small-scale experiments, for data such as heat transfer coefficients, are essential for valid modeling.

Instability of two‐phase flow in vertical cylinders

The stability of two‐phase flow in a vertical cylinder is considered. The liquid phase is assumed to flow past the cylinder surface in a thin layer, assuming no mixing with the core gas flow. The complete system of Navier–Stokes and continuity equations for both phases is treated analytically, using a perturbation procedure based on expansion in powers of small wavenumbers. The results of the first approximation determine the phase velocity of waves developed on the liquid‐gas interface. The second approximation reveals the complete pattern of hydrodynamical stability of two‐phase flow over the entire range of gas‐flow velocities. The topological features of stability curves are depicted. The effects of surface tension, cylinder radius, and interface curvature on the two‐phase flow stability are revealed.

Flow visualization using photochromic grids

In order to generate well defined photochromic grids needed in complex flow analysis, we are developing a multi-stage nitrogen laser to produce UV beams with high intensity and low divergence. The objective of this paper is to present our preliminary results that include the generation of a 6 X 6 photochromic grid together with a description of the analysis scheme used to determine the velocity and vorticity fields.