Keith Hollingsworth

Verified

Keith verified their affiliation via an institutional email.

Learn more

Verified

Keith verified their affiliation via an institutional email.

Learn more

• Ph.D.
• Professor (Full) at University of Alabama in Huntsville

The Centrifugal Nuclear Thermal Rocket (CNTR) is a Nuclear Thermal Propulsion (NTP) concept designed to heat propellant directly by the reactor fuel. The primary difference between the CNTR concept and traditional NTP systems is that rather than using traditional solid fuel elements, the CNTR uses liquid fuel with the liquid contained in rotating c...

The Centrifugal Nuclear Thermal Rocket (CNTR) is a Nuclear Thermal Propulsion (NTP) concept designed to heat propellant directly by the reactor fuel. The primary difference between the CNTR concept and traditional NTP systems is that rather than using traditional solid fuel elements, the CNTR uses liquid fuel with the liquid contained in rotating c...

View Video Presentation: https://doi.org/10.2514/6.2022-0936.vid A liquid-fueled nuclear thermal rocket offers significant advantages over traditional solid-fueled nuclear thermal propulsion designs. The liquid-fueled design allows for much greater operating temperatures, which in turn means more heat can be imparted to the propellant resulting in...

View Video Presentation: https://doi.org/10.2514/6.2021-3604.vid The Centrifugal Nuclear Thermal Rocket (CNTR) is a Nuclear Thermal Propulsion (NTP) concept designed to heat propellant directly by the reactor fuel. The primary difference between the CNTR concept and traditional NTP systems is that rather than using traditional solid fuel elements,...

Improved methods for storing liquid hydrogen in larger quantities and over longer periods of time in space are becoming progressively more critical as sights are once again set on Mars. Current storage methods involve the venting of vaporized hydrogen to space, with the consequence that significant amounts of hydrogen are wasted. Extra hydrogen mus...

Confined bubbly flows in millimeter-scale channels produce significant heat transfer enhancement when compared to single-phase flows. Experimental studies support the hypothesis that the enhancement is driven by a convective phenomenon in the liquid phase as opposed to sourcing from microlayer evaporation or active nucleation. A numerical investiga...

The present study provides new heat transfer data for both the surfaces of the full coverage effusion cooling plate within a double wall cooling test facility. To produce the cooling stream, a cold-side cross-flow supply for the effusion hole array is employed. Also utilized is a unique mainstream mesh heater, which provides transient thermal bound...

A numerical investigation of a single highly confined bubble moving through a millimeter-scale channel in the absence of phase change is presented. The simulation includes thermal boundary conditions designed to match those of completed experiments involving bubbly flows with large numbers of bubbles. The channel is horizontal with a uniform-heat-g...

A numerical investigation of a single highly confined bubble moving through a millimeter-scale channel in the absence of phase change is presented. The simulation includes thermal boundary conditions designed to match those of completed experiments. The channel is horizontal with a uniform-heat-generation upper wall and an adiabatic lower boundary...

The present study provides new heat transfer data for both the surfaces of the full coverage effusion cooling plate within a double wall cooling test facility. To produce the cooling stream, a cold-side cross-flow supply for the effusion hole array is employed. Also utilized is a unique mainstream mesh heater, which provides transient thermal bound...

Experimental results are presented for a double wall cooling arrangement which simulates a portion of a combustor liner of a gas turbine engine. The results are collected using a new experimental facility designed to test full-coverage film cooling and impingement cooling effectiveness using either cross flow, impingement, or a combination of both...

Confined bubbly flows in millimeter-scale channels produce significant heat transfer enhancement when compared to single-phase flows. This enhancement has been demonstrated in experimental studies, and some of these studies conclude that the enhancement persists even in the absence of active nucleation sites and bubble growth. This observation lead...

Experimental results are presented for a double wall cooling arrangement which simulates a portion of a combustor liner of a gas turbine engine. The results are collected using a new experimental facility designed to test full coverage film cooling and impingement cooling effectiveness using either cross flow, impingement, or a combination of both...

Bubble images were acquired from within the channel for a bubbly gas/liquid flow in large-aspect-ratio minichannel with heat transfer. The purpose of these images is to document measurands that address bubble shape and confinement and to relate these measurands to the heat transfer enhancement. Data were collected under different operation conditio...

A three-dimensional numerical study is conducted of a single FC-87 vapor bubble rising in non-uniformly heated FC-87 liquid and interacting with an inclined superheated wall. A complete phase-change model that takes into account the effect of interface heat flux on the local interface temperature is used to capture, in particular, the phase change...

Studies published over the past decade have established the importance of sliding bubbles in enhancing the heat transfer in subcooled two-phase flow in channels small enough to confine the bubbles. Recent work in this laboratory (Ozer et al., 2011, 2012) proposed that the primary enhancement mechanism is a single-phase convective mechanism: the tra...

A quenching/diffusion analytical model has been developed for predicting the wall temperature and wall heat flux behind bubbles sliding in a confined narrow channel. The model is based on the concept of a well-mixed liquid region that enhances the heat transfer near the heated wall behind the bubble. Heat transfer in the liquid is treated as a one-...

A method is developed to capture the distribution of surface temperature while simultaneously imaging the bubble motions in diabatic flow boiling in a horizontal minichannel. Liquid crystal thermography is used to obtain highly resolved surface temperature measurements on the uniformly heated upper surface of the channel. High-speed images of the f...

An apparatus that produces flow and heat transfer in horizontal narrow channels was used to explore the physics of the onset of subcooled nucleate boiling for R-11 and Novec 649. The apparatus uses a downward-facing electrically-heated thin foil as a heater, with the outside of the heater coated with a liquid crystal to display full-field temperatu...

Surface-tension forces can drive fluid motion within thin liquid layers with a free surface. Spatial variations in the temperature of the free surface create surface tractions that drive cellular motions. The cells are most commonly hexagonal in shape and they scale on the thickness of the fluid layer. This investigation documents the formation of...

The time-dependent temperature distribution on an inclined, thin-foil uniform-heat-generation heater was used to infer the surface heat transfer enhancement caused by the passage of an FC-87 bubble sliding beneath the lower surface of the heater. A two-camera system was used: one camera recorded color images of a liquid crystal layer applied to the...

Sliding vapor bubbles are known to create high heat transfer coefficients along the surfaces against which they slide. The details of this process remain unclear and depend, in part, on the evolution of the liquid microlayer that forms between the bubble and the surface. A mechanistic model of the micro-layer thickness verified by direct observatio...

Data resulting from photographic studies of FC-87 vapor bubbles rising under a constant temperature plate are used to describe the growth and motion of the bubbles. Such bubbles are known to cause significant enhancement of heat transfer during their passage along the surface because of conduction through a thin liquid microlayer on which they slid...

The transition from the onset of nucleate boiling up to fully developed nucleate boiling in a rectangular minichannel was investigated. This transition has been called the “turning angle” phenomenon in the past because it involves a set of heat flux–wall superheat points with negative slope between the onset of nucleate boiling and the fully develo...

Flow regimes and bubble growth are observed in a pin-fin micro-scale heat exchanger with R-11 as the working fluid. The heat exchanger is machined in silicon and derived from a DNA micro-array consisting of 150 m-square fins separated by 50 m-square passages. The fins are staggered and oriented 45 degrees to the flow direction such that approxima...

Measurements were made of the effective emittance of three types of radiator coatings as a Martian dust simulant was added to the radiator surfaces. The apparatus consisted of multiple radiator coupons on which Carbondale Red Clay dust was deposited. The coupon design employed guard heating to achieve the accuracy required for acceptable emittance...

A laser-based method has been developed to measure the thickness of the liquid microlayer between a cap-shaped sliding bubble and an inclined heated wall. Sliding vapor bubbles are known to create high heat transfer coefficients along the surfaces against which they slide. The details of this process remain unclear and depend on the evolution of th...

Flow regimes and bubble growth are observed in a pin-fin micro-scale heat exchanger with R-11 as the working fluid. The heat exchanger is machined in silicon and derived from a DNA micro-array consisting of 150-µm square fins separated by 50-µm square passages. The fins are staggered and oriented 45 degrees to the flow direction such that approxima...

Experiments were performed to investigate nucleate flow boiling and incipience in a vertical flow channel, 20 mm wide X 357 mm long, with one wall heated uniformly and others approximately adiabatic. Three channel spacings, 2, 1 and 0.5 mm, were investigated. Initially subcooled R- 11 flowed upward. through the channel; the mass flux varied from 60...

A laser-based method has been developed to measure the thickness of the liquid microlayer between a cap-shaped sliding bubble and an inclined heated wall. Sliding vapor bubbles are known to create high heat transfer coefficients along the surfaces against which they slide. The details of this process remain unclear and depend on the evolution of th...

Experiments were performed in which the effective emittance of three types of radiator coatings was measured as Martian dust simulant was added to the radiator surface. The apparatus consisted of multiple radiator coupons on which Carbondale Red Clay dust was deposited. The coupons were powered by electric heaters, using a guard-heating configurati...

Quantitative liquid crystal thermography was used to investigate boiling incipience and nucleate flow boiling in rectangular mini-channels with channel heights of 2 mm to 500 μm. Distributions of surface temperature along the heated surface were measured from the liquid crystal images, and streamwise profiles of heat transfer coefficient on the hea...

A turbulent boundary layer was subjected to grid-generated freestream turbulence to study the effects of turbulent length scale and intensity on skin friction. The study emphasized the importance of the turbulent-to-viscous length scale ratio and focused on correlating skin friction without the use of conventional boundary-layer Reynolds numbers. T...

Measurements that illustrate the enhancement of heat transfer caused by a bubble sliding under an inclined surface are reported. The data were obtained on all electrically heated thin-foil surface that was exposed on its lower side to FC-87 and displayed the output of a liquid crystal coating on the upper (dry) side. A sequence of digital images wa...

Turbulent boundary layers were subjected to grid-generated free-stream turbulence to study the effects of length scale and intensity on heat transfer Relative to conventional boundary layer thickness measures, test conditions included very small-scale free-stream turbulence. The boundary layers studied rangedfirom 400-2700 in momentum-thickness Rey...

A new heat transfer correlation for turbulent boundary layers subjected to free-stream turbulence was developed. The new correlation estimates dimensionless heat transfer coefficients without the use of conventional boundary-layer thickness measures and the associated Reynolds numbers. Using only free-stream parameters (mean velocity, turbulence in...

A calibrated thermochromic liquid crystal technique was used to acquire wall temperature data for laminar and turbulent forced convection in an asymmetrically heated channel. The experiments were carried out in upward flow in rectangular channels with channels spacings of 2.0, 1.0, and 0.5 mm and aspect ratios of 1:10, 1:20, and 1:40. One side was...

Turbulence length scale calculation methods were critically reviewed for their usefulness in boundary layer heat transfer correlations. Using the variance of the streamwise velocity and the dissipation spectrum, a rigorous method for calculating an energy-based integral scale was introduced. A principal advantage of the new method is the capability...

Surface tension forces can drive fluid motion within thin liquid layers with a free surface. Spatial variations in the temperature of the free surface create surface tractions that drive cellular motions. The cells are most commonly hexagonal in shape and they scale on the thickness of the fluid layer. This investigation documents the formation of...

Experiments were performed to investigate nucleate flow boiling and incipience in a flow channel, 1 mm high × 20 mm wide × 357 mm long, vertical, with one wall heated uniformly and others approximately adiabatic. Subcooled R-11 flowed upward through the channel; the mass flux varied from 60 to 4586 kg/(m2s). The inlet subcooling varied from 3.0 to...

Experiments were performed to investigate nucleate flow boiling and incipience in a flow channel, 1 mm high × 20 mm wide × 357 mm long, vertical, with one wall heated uniformly and others approximately adiabatic. Subcooled R-11 flowed upward through the channel; the mass flux varied from 60 to 4586 kg/(m2s). The inlet subcooling varied from 3.0 to...

Surface tension forces can drive fluid motion within thin liquid layers with a free surface. Spatial variations in the temperature of the free surface create surface tractions that drive cellular motions. The cells are most commonly hexagonal in shape and they scale on the thickness of the fluid layer. This investigation documents the formation of...

Three samples of micro-encapsulated thermochromic liquid crystals with different active temperature ranges were calibrated using a hue-based color decomposition system. A dimensionless temperature was defined that collapsed data from all three samples to a single calibration curve. For one sample, this dimensionless temperature also collapsed calib...

This experimental study documented the heat transfer into a turbulent boundary layer growing beneath a high-Reynolds-number turbulent mixing layer. The boundary layer was highly three-dimensional and altered by the presence of free-stream turbulence. The mixing layer produced a streamwise turbulence intensity of up to 16%. The interaction between t...

Experiments were performed to investigate nucleate flow boiling and incipience in a flow channel, 2 mm high × 20 mm wide × 357 mm long, vertical, with one wall heated uniformly and others approximately adiabatic. Subcooled R-11 flowed upward through the channel; the mean velocity varied between 0.04 and 3.68 m/s,. The inlet subcooling varied from 4...

A calibrated thermochromic liquid crystal technique was used to acquire wall temperature data for laminar and turbulent forced convection in an asymmetrically heated channel. The experiments were carried out in upward flow in a rectangular channel with a 10:1 aspect ratio. One side was uniformly heated, and the remaining sides were approximately ad...

This paper reports the second phase of a two-part study of jet impingement boiling. Liquid crystal thermography was used to study nucleate boiling incipience on a thin uniform-heat-generation surface that was cooled by a submerged impinging jet of refrigerant R-11. Thermographic images of the temperature distribution on the test surface were acquir...

Liquid crystal thermography was used to study nucleate boiling incipience on a thin, uniform-heat-generation surface that was cooled by a submerged impinging jet. The fluid was the refrigerant R-11. Thermographic images of the temperature distribution on the test surface were acquired synchronously with single-point temperature measurements from th...

Samples of polymer-dispersed chiral nematic liquid crystal with different active temperature ranges were calibrated using four different trichromic representations of the liquid-crystal color. Three of the representations were hue-based, and the fourth was a simple linear regression. The comparison was done using commercially available imaging equi...

Experiments were conducted to document the response of a turbulent boundary layer to a free-stream flow with high and approximately streamwise-uniform levels of turbulence intensity. Measurements were made in a flat-plate turbulent boundary layer that developed beneath a free stream produced by a two-stream mixing layer. A flat test surface was pos...

Liquid crystal thermography was used to observe time-dependent temperature patterns on an electrically heated surface during the incipience of nucleate pool boiling. The images revealed spatial and temporal differences in the process by which boiling initiated and expanded over the surface in the presence of two different single-phase convection fi...

The streamwise evolution of the turbulent Prandtl number was determined from measured data for a water boundary layer subjected to moderately strong concave surface curvature. Profiles of velocity and temperature were measured with a laser-Doppler velocimeter and a fine-wire thermocouple probe, respectively. Profiles of Prt were calculated from the...

A study was made of the visual images of a very high Reynolds number (2 x 10 to the 8th), momentum-driven jet consisting of the exhaust plume of a motor. The tests provide evidence that organized structures progress up through the jet plume in a manner that is quite similar to observations in laboratory flows at Reynolds numbers of about 10,000. It...

A baseline thermal boundary layer in water is documented and compared to the experimentally determined behavior with that predicted using a computational model accepted by the heat transfer design community. The predictions of STAN6, a finite-difference code using a standard mixing length model, compare well with the measurements of both the Stanto...

A wide-band liquid crystal paint was calibrated for its temperature versus color (wavelength) relationship and then used with a true-color digital image processing technique to measure the temperature distribution on a specimen from its color video image. The specimen was a flat, electrically heated sheet with a known heat release (W/m2) so the hea...