The severity of a burn on human skin is determined by the surface temperature of the hot object contacting the skin and the time of exposure. Skin is considered to be in a damaged state if its temperature is allowed to reach 62.5°C. Consider that, for relatively short times, near the surface of the skin, the skin tissue will behave as a semi-infinite medium. Skin also has three distinct layers, as shown in the figure. For the wet sub-dermal layer of living skin, k_skin= 0.35 W/m · K, C_p,skin= 3.8 kJ/kg · K, ρ_skin= 1.05 g/cm³(Freitas, 2003). The thermal diffusivity of dry €œcadaverous€ epidermal skin is 2.8 × 10^-4cm²/sec (Werner et al., 1992). A composite thermal diffusivity of 2.5 × 10^-7m²/sec is to be assumed for the skin tissue (Datta, 2002).

a. What is the thermal diffusivity of living skin vs. dry cadaverous skin? Why is there such a big difference?

b. If a patch of skin is exposed to a hot metal surface at 250°C for 2 s, what will be the severity of the burn? Normal body temperature is 37°C.

c. At the time identified in part (b), what will the temperature at the top face of the dermal layer (thickness of approximately 0.5 mm) be?

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hair surface epidermal layer epidermal/partial thickness burn hair follicle deep dermal burn 1 mm- 2 mm full thickness burn 3 mm cross section of skin tissue