John R. Stark

Estimating the time and temperature relationship for causation of deep-partial thickness skin burns

The objective of this study is to develop and present a simple procedure for evaluating the temperature and exposure-time conditions that lead to causation of a deep-partial thickness burn and the effect that the immediate post-burn thermal environment can have on the process. A computational model has been designed and applied to predict the time required for skin burns to reach a deep-partial thickness level of injury. The model includes multiple tissue layers including the epidermis, dermis, hypodermis, and subcutaneous tissue. Simulated exposure temperatures ranged from 62.8 to 87.8°C (145-190°F). Two scenarios were investigated. The first and worst case scenario was a direct exposure to water (characterized by a large convection coefficient) with the clothing left on the skin following the exposure. A second case consisted of a scald insult followed immediately by the skin being washed with cool water (20°C). For both cases, an Arrhenius injury model was applied whereby the extent and depth of injury were calculated and compared for the different post-burn treatments. In addition, injury values were compared with experiment data from the literature to assess verification of the numerical methodology. It was found that the clinical observations of injury extent agreed with the calculated values. Furthermore, inundation with cool water decreased skin temperatures more quickly than the clothing insulating case and led to a modest decrease in the burn extent.

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.

Prediction of convection from a finned cylinder in cross flow using direct simulation, turbulence modeling, and correlation-based methods

ABSTRACT Direct numerical simulation (DNS), two shear-stress transport (SST) turbulence models, and three k-ε models are used to predict mixed convection associated with air in cross flow over an isothermal, finned cylinder. The DNS predictions reveal complex time-variation in the flow field. Convection heat transfer coefficients predicted by the SST models are in good agreement with those generated by DNS, whereas the k-ε models do not accurately predict heat fluxes. Correlation-based predictions of heat transfer coefficients are, in general, in poor agreement with the DNS and SST predictions. The impact of various geometrical modifications on convection coefficients is also presented.

Tissue burns due to contact between a skin surface and highly conducting metallic media in the presence of inter-tissue boiling

A numerical-based model was developed and implemented to determine the spatial and temporal temperature distributions within skin tissue resulting from thermal contact with a heated and high thermal conductivity metallic medium. In the presence of wet tissue, boiling is likely to occur, thereby affecting the probability of inducing burns. This investigation deals with how contact between a hot, highly conductive metallic material and skin gives rise to burns. In particular, the study focuses on the likelihood that metals typically used in cooking or industrial applications may cause burns. Insofar as the surfaces under consideration are above the boiling temperature of water, a mathematical model including phase change was developed. That model allowed different thermophysical properties to be respectively employed for dry and wet tissues. Multiple processes and their governing parameters were investigated to assess their impact on burn severity, including the temperature of the metal, the duration of contact, the contact resistance between the surface and the skin, the temperature range over which phase change occurred, and the cooling environment after the exposure. It was discovered that the most important parameters are the surface temperature and exposure duration. The other conditions/parameters had lesser impacts on the results.