John P. Abraham

Handbook of numerical heat transfer

A comprehensive presentation is given of virtually all numerical methods that are suitable for the analysis of the various heat transverse and fluid flow problems that occur in research, practice, and university instruction. After reviewing basic methodologies, the following topics are covered: finite difference and finite element methods for parabolic, elliptic, and hyperbolic systems; a comparative appraisal of finite difference versus finite element methods; integral and integrodifferential systems; perturbation methods; Monte Carlo methods; finite analytic methods; moving boundary problems; inverse problems; graphical display methods; grid generation methods; and programing methods for supercomputers.

Supercritical droplet vaporization and combustion studies

Abstract Droplet vaporization and combustion studies in environments where the ambient pressure and temperature are supercritical relative to the droplet are reviewed. The conditions under which the droplet vaporization and combustion may be approximated as quasi-steady are discussed. It is shown that this approximation is not valid for paraffin fuels in conditions where the reduced temperature and pressure exceed approximately twice the fuels critical values. Conditions in which the pseudo wet-bulb and critical mixing states are obtained are also discussed. Results indicate that for the paraffin fuels n-pentane through n-dodecane, a vaporizing droplet can reach the critical state for ambient pressures greater than approximately twice the fuels critical pressure and for ambient temperatures approximately twice the fuels critical temperature while combusting droplets can reach this state when ambient pressure is approximately 2.5 times that of the fuels critical pressure. Droplet vaporization and combustion lifetimes are shown to be significantly influenced by the ambient temperature and pressure conditions, with a minimum in the latter occurring near the fuels critical pressure. Key modeling assumptions and their relative importance in supercritical droplet vaporization and combustion are also reviewed. These include real gas effects, effects of liquid-phase gas solubility, and anomalies in thermophysical properties near the critical region. We outline areas of research in need of further study and the challenges in the field.

Entrainment characteristics of transient gas jets

Results are presented of theoretical analysis and computations of transient gas jets in a quiescent ambient environment, with injected to ambient density ratios of 2, 1, and 0.5. Comparisons of these results with those from previous work in gas jets art also presented. Turbulence is represented using a k-∊ model. Entrainment rate is found to scale linearly with axial penetration, and the total mass entrained is shown to have a cubic dependence on axial penetration of the gas jet. The actual values of these quantities depend on a constant whose value obtained from measurements and quoted in the literature varies by as much as a factor of 2.

Improved estimates of ocean heat content from 1960 to 2015

A new assessment of how much heat Earth has accumulated since 1960 is made by examining ocean heat content changes. Earth’s energy imbalance (EEI) drives the ongoing global warming and can best be assessed across the historical record (that is, since 1960) from ocean heat content (OHC) changes. An accurate assessment of OHC is a challenge, mainly because of insufficient and irregular data coverage. We provide updated OHC estimates with the goal of minimizing associated sampling error. We performed a subsample test, in which subsets of data during the data-rich Argo era are colocated with locations of earlier ocean observations, to quantify this error. Our results provide a new OHC estimate with an unbiased mean sampling error and with variability on decadal and multidecadal time scales (signal) that can be reliably distinguished from sampling error (noise) with signal-to-noise ratios higher than 3. The inferred integrated EEI is greater than that reported in previous assessments and is consistent with a reconstruction of the radiative imbalance at the top of atmosphere starting in 1985. We found that changes in OHC are relatively small before about 1980; since then, OHC has increased fairly steadily and, since 1990, has increasingly involved deeper layers of the ocean. In addition, OHC changes in six major oceans are reliable on decadal time scales. All ocean basins examined have experienced significant warming since 1998, with the greatest warming in the southern oceans, the tropical/subtropical Pacific Ocean, and the tropical/subtropical Atlantic Ocean. This new look at OHC and EEI changes over time provides greater confidence than previously possible, and the data sets produced are a valuable resource for further study.

Breakdown of Laminar Pipe Flow into Transitional Intermittency and Subsequent Attainment of Fully Developed Intermittent or Turbulent Flow

The breakdown of laminar pipe flow into transitional intermittency is predicted numerically here for the first time. Subsequent to transitional intermittency, a fully developed regime is achieved wherein the flow may be either intermittent or fully turbulent. Fully developed friction factors are predicted as a function of the Reynolds number throughout the intermittent regime. These predictions successfully bridge the gap between well-established laminar friction factors and turbulent friction factors. Definitive numerical information is provided about the locations in the pipe at which both laminar breakdown and fully developed attainment occur. These locations are a function of the Reynolds number. The streamwise changes in the velocity profiles reflect the complex evolution of the flow as it passes through the successive regimes. For design purposes, information is provided for the pressure drop that characterizes the evolving flow. The numerical results correspond to an inlet turbulence intensity level of 5%.

A Study of Near-Field Entrainment in Gas Jets and Sprays Under Diesel Conditions

This paper presents a computational study of entrainment characteristics in the near-field of gas jets under atmospheric and Diesel conditions and sprays under Diesel conditions. Computed flowfield information is used to estimate the rate of mass entrainment in the jet and derive the entrainment rate constant, The value of the entrainment rate constant is compared to experimental results in the literature. It is found that the computed values of the constant in the near-field are less than the values in the self-similar region of the jet with the values increasing monotonically from the orifice to the self-similar region. These results are consistent with experimental results. In the case of sprays, it is found that it is difficult to arrive at firm conclusions because the results are sensitive to several parameters that are not well known and to the numerics. The computed results for sprays are also discussed relative to measurements in sprays quoted in the literature.

Rationalization of thermal injury quantification methods: Application to skin burns

Classification of thermal injury is typically accomplished either through the use of an equivalent dosimetry method (equivalent minutes at 43 °C, CEM43 °C) or through a thermal-injury-damage metric (the Arrhenius method). For lower-temperature levels, the equivalent dosimetry approach is typically employed while higher-temperature applications are most often categorized by injury-damage calculations. The two methods derive from common thermodynamic/physical chemistry origins. To facilitate the development of the interrelationships between the two metrics, application is made to the case of skin burns. This thermal insult has been quantified by numerical simulation, and the extracted time-temperature results served for the evaluation of the respective characterizations. The simulations were performed for skin-surface exposure temperatures ranging from 60 to 90 °C, where each surface temperature was held constant for durations extending from 10 to 110 s. It was demonstrated that values of CEM43 at the basal layer of the skin were highly correlated with the depth of injury calculated from a thermal injury integral. Local values of CEM43 were connected to the local cell survival rate, and a correlating equation was developed relating CEM43 with the decrease in cell survival from 90% to 10%. Finally, it was shown that the cell survival/CEM43 relationship for the cases investigated here most closely aligns with isothermal exposure of tissue to temperatures of ~50 °C.

An Archive of Skin-Layer Thicknesses and Properties and Calculations of Scald Burns With Comparisons to Experimental Observations

A numerical model has been constructed to assess the depth of injury incurred when skin is exposed to heated water. The model includes an extended duration that occurs when clothing, saturated with hot water, is kept in contact with the skin after the direct exposure has ended. The model takes data from a broad summary of literature, which examines the ranges of reported tissue thicknesses, tissue thermophysical properties, and blood perfusion. Water temperatures ranging from 60°C to 90°C and total exposure durations up to 110 s were modeled. As expected, longer durations and elevated temperatures lead to a greater extent of tissue injury. For lower values of temperatures (60°C), burns range from mild (0.1 mm) to severe (2.2 mm) depending on the exposure duration. On the other hand, for higher exposure temperatures (90 °C), all durations led to burns that extended at least halfway through the dermal layer. As expected, burn depths with intermediate temperatures fell between these ranges. Calculated values of tissue injury were compared with prior injury reports. These reports, taken from literature, reinforce the present calculations. It is seen that numerical models can accurately predict burn injury as assessed by clinical observations; in fact, the calculations of burn injury presented here provide more information for the appropriate treatment of burn injuries compared with visual observation. Finally, literature values of a number of skin-layer thicknesses, thermophysical properties, and burn-injury parameters were collected and presented as an archival repository of information.

Optimal Techniques with the Diamondback 360° System Achieve Effective Results for the Treatment of Peripheral Arterial Disease

The Diamondback 360® Orbital PAD System (DB360) is a novel orbital atherectomy system for the treatment of calcified lower extremity lesions associated with peripheral arterial disease (PAD). This percutaneous, endovascular system incorporates the use of centrifugal force and differential sanding to modify plaque morphologies. The mechanism of differential sanding discriminates between compliant arterial tissue and diseased fibro-calcific or calcific plaque. An eccentrically mounted diamond-coated crown orbits at high speeds and removes a thin layer of calcific plaque with each pass of the crown. The crown creates a more concentric, smooth vessel lumen with increased diameter, increased lesion compliance and improved blood flow while protecting the vessel media. As a result, the risk for post-procedure thrombus formation and potential for restenosis may be reduced. The risk of intra-procedural events (slow flow, hemolysis, spasm and pain) may be reduced due to the design of this orbital sanding system along with proper technique. Extensive benchtop, in vivo, and clinical testing has confirmed these results and is presented within this paper. In addition, guidelines for selecting the most appropriate crown size and type (solid versus classic) and step-by-step procedural technique and pharmacology information are presented. The DB360 System provides a safe, efficacious, and cost-effective endovascular method for PAD treatment. Careful understanding of procedural methods, use of pharmacological drugs, and understanding of device operation contributes to improved treatment success.

Numerical simulation of fluid flow around a vertical-axis turbine

A novel, vertical-axis turbine has been designed to meet a specific power-generation need. It is intended that the turbine will provide local electricity to off-grid cellular communication towers. It is intended that the turbine will reduce or eliminate the use of diesel-power generation for these towers and result in a reduction of operating costs and greenhouse gas emissions. The design effort has had two main stages. First, a prototype turbine blade was designed and tested in a large-scale wind tunnel. The initial design was based on available literature information. Subsequently, numerical simulations of the fluid flow patterns around the turbine blade were used to create improvements to the design. These improvements include the use of venting apertures in the turbine blade to reduce negative drag and thrust loading and the use of caps to improve power-generation efficiency. Through numerical modeling, significant improvements in performance were achieved resulting in a viable turbine design.