John M Gorman

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.

Drag Coefficients for Rotating Expendable Bathythermographs and the Impact of Launch Parameters on Depth Predictions

Computational fluid dynamics techniques have been applied to model fluid flow in the vicinity of oceanographic temperature probes. A major goal of the modeling effort is the determination of drag coefficients for probe descent into ocean water. These drag coefficients can be used, in conjunction with a dynamic model of the probe, to predict the depth of the probe during descent. Accurate depth information is essential for the proper measurement of ocean temperatures and, consequently, ocean heating associated with climate change. Until recently, probe depths were predicted with the use of experimental calibrations which relate time-of-flight and depth. Those calibrations are limited in their accuracy, they are confined to conditions that match the experiments from which the calibrations were determined, and they are unable to account for variations in quantities such as the drop height or initial probe mass. The dynamic model and drag coefficient calculations presented here are, to the best knowledge of the authors, the first to include the impact of probe rotation. It is hoped that this new technique can be applied to the archive of oceanographic probe measurements and that improvements to ocean temperature monitoring will result.

Evaluation of the efficacy of turbulence models for swirling flows and the effect of turbulence intensity on heat transfer

ABSTRACT Turbulent fluid flows with a swirl occur in numerous engineering practice situations. Five widely recognized turbulence models were evaluated using experimental results. Among the RANS-based two-equation models, the SST κ–ω model proved to be the most effective. The predictions obtained from a LES turbulence model were slightly better, however there was an enormous difference in the CPU time. The CPU time needed for the LES solution was 155.3 days, whereas it was only 14.2 days for the SST κ–ω solution. In this light, it is believed that the SST κ–ω model is the most efficient of those investigated. An important input for the numerical simulation of turbulent flow and heat transfer is the turbulence intensity at the inlet of a solution domain. For the evaluation of turbulence models, use was made of the measured turbulence quantities from the verification experiments. More often, simulations are executed based on the uniform values of the turbulence intensity across the inlet. The errors in the heat transfer results due to this practice are evaluated and are shown to be significant.

Quantitative Assessment of the Overall Heat Transfer Coefficient U

This investigation was performed in order to quantify the validity of the assumed constancy of the overall heat transfer coefficient U in heat exchanger design. The prototypical two-fluid heat exchanger, the double-pipe configuration, was selected for study. Heat transfer rates based on the U = constant model were compared with those from highly accurate numerical simulations for 60 different operating conditions. These conditions included: (a) parallel and counter flow, (b) turbulent flow in both the pipe and the annulus, (c) turbulent flow in the pipe and laminar flow in the annulus and the vice versa situation, (d) laminar flow in both the pipe and the annulus, and (e) different heat exchanger lengths. For increased generality, these categories were further broken down into matched and unmatched Reynolds numbers in the individual flow passages. The numerical simulations eschewed the unrealistic uniform-inlet-velocity-profile model by focusing on pressure-driven flows. The largest errors attributable to the U = constant model were encountered for laminar flow in both the pipe and the annulus and for laminar flow in one of these passages and turbulent flow in the other passage. This finding is relevant to microchannel flows and other low-speed flow scenarios. Errors as large as 50% occurred. The least impacted were cases in which the flow is turbulent in both the pipe and the annulus. The general level of the errors due to the U = constant model were on the order of 10% and less for those cases. This outcome is of great practical importance because heat-exchanger flows are more commonly turbulent than laminar. Another significant outcome of this investigation is the quantification of the axial variations of the temperature and heat flux along the wall separating the pipe and annulus flows. It is noteworthy that these distributions do not fit either the uniform wall temperature or uniform heat flux models.

Comprehensive method to predict and quantify scald burns from beverage spills

Abstract A comprehensive study was performed to quantify the risk of burns from hot beverage spills. The study was comprised of three parts. First, experiments were carried out to measure the cooling rates of beverages in a room-temperature environment by natural convection and thermal radiation. The experiments accounted for different beverage volumes, initial temperatures, cooling period between the time of service and the spill, the material which comprised the cup, the presence or absence of a cap and the presence or absence of an insulating corrugated paper sleeve. Among this list, the parameters which most influenced the temperature variation was the presence or absence of a cover or cap, the volume of the beverage and the duration of the cooling period. The second step was a series of experiments that provided temperatures at the surface of skin or skin surrogate after a spill. The experiments incorporated a single layer of cotton clothing and the exposure duration was 30 s. The outcomes of the experiments were used as input to a numerical model which calculated the temperature distribution and burn depth within tissue. Last was the implementation of the numerical model and a catalogue of burn predictions for various beverage volumes, beverage service temperatures, and durations between beverage service and spill. It is hoped that this catalogue can be used by both beverage industries and consumers to reduce the threat of burn injuries. It can also be used by treating medical professionals who can quickly estimate burn depths following a spill incident.

Turbulent and transitional modeling of drag on oceanographic measurement devices

Computational fluid dynamic techniques have been applied to the determination of drag on oceanographic devices (expendable bathythermographs). Such devices, which are used to monitor changes in ocean heat content, provide information that is dependent on their drag coefficient. Inaccuracies in drag calculations can impact the estimation of ocean heating associated with global warming. Traditionally, ocean-heating information was based on experimental correlations which related the depth of the device to the fall time. The relation of time-depth is provided by a fall-rate equation (FRE). It is known that FRE depths are reasonably accurate for ocean environments that match the experiments from which the correlations were developed. For other situations, use of the FRE may lead to depth errors that preclude XBTs as accurate oceanographic devices. Here, a CFD approach has been taken which provides drag coefficients that are used to predict depths independent of an FRE.

Experimental Verification of Drag Forces on Spherical Objects Entering Water

Experimental Verification of Drag Forces on Spherical Objects Entering Water Objects which pass from gas regions to liquid regions experience elevated impact forces associated with the acceleration of the surrounding liquid. In order to investigate these forces, complementary experiments and simulations were performed on a sphere that traveled from air to water with an impact velocity of 2 m/s. It was found that the two methods gave results that were in very good agreement. In particular, the depth vs. time trajectory of the sphere closely matched. A fitted polynomial allowed the entry region acceleration to be extracted.

Flow Regime Determination for Finned Heat Exchanger Surfaces with Dimples/Protrusions

There are many modalities that may be used to enhance heat transfer performance. One of these modes, the embossing of channel walls with dimples and/or protrusions, is a technique which has the advantage of simplicity of fabrication. The assessment of the quality of a geometry-based heat transfer enhancement technique frequently involves the change in pressure drop that accompanies the geometric modification. This realization provides the motivation for the investigation reported here. The focus of this work is the identification of the existence of various sub-regimes within the laminar-flow regime. The investigation was implemented by numerical simulation supplemented by a three-dimensional model of periodic fully developed flow. The selected channel-height Reynolds number range extended from 200 to 800. Within this range, three sub-regime laminar flows were identified: friction-dominated flow, inertial-loss-dominated flow, and the transition between these flows. Another focus of the results was the presentation of patterns of fluid flow and their impacts on the variation of the pressure drop with Reynolds number.

Simulation of helically wrapped, compact heat exchangers

A new category of heat exchanger has been invented which fulfills the dual requirements of compactness and high thermal efficiency. The underlying principle of the exchanger is the helical intertwining of the tubes which carry the participating fluids. To ensure a thermal bridge of high conductivity between the tubes, silver braze was introduced into the interstitial space. Numerical simulation was used to characterize the performance of this category of heat exchanger. The simulation model is three-dimensional for both fluid flow and heat transfer and is also conjugate in that it encompasses two flow passages, their walls, and the interconnecting silver braze. A fabrication means was also developed. Numerical results were obtained for two general classes of heat exchange situations, one of which dealt with single-phase flows while the other related to two-phase flows. The single-phase situation investigated here is a water-water heat exchanger. The heat exchange effectivenesses evaluated from the numeric...

Investigation of coupled systems consisting of fluid movers and heat-exchange devices

ABSTRACT A heat exchanger and the fluid mover that delivers a working fluid to the exchanger inlet may experience profound interactions, which argues against treating them as separate entities. On the other hand, the design practice commonly assumes that the fluid delivered to the heat exchanger inlet is specifiable without consideration of any possible influence of the exchanger. The magnitude of the flow rate arriving at the exchanger inlet is generally based on the pressure rise—flow rate (P-Q) curve supplied by the manufacturer of the fan and coupled with the assumption that that flow is uniformly distributed across the exchanger inlet. It was found that the complexity of the fluid flow delivered by the rotating fan gives rise to a large fluid resistance within the pin-fin array, such that the delivered air flow rate was only about 37% of that for the P-Q case. On the other hand, the corresponding reduction in the rate of heat transfer was, at most, 27%.