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Subject: Biotransport

1. Sterilization of a bacterial Clump To properly sterilize, all bacteria must be heated for the required duration and time. Although individual bacterial size is small. when present in large clumps, some bacteria located deep mside the clump may take sigmificant time to reach the medum (air or water) temperature. Thus, they cannot be assumed to be at the medium temperature all the time. Consider bacterial clumps of different sizes heated m air. The shape of the clump can be assumed spherical with a radms R which is related to , the number of bacteria in a clump, and 7, the radius of individual bacteria by the equation R = r [n / (1 E)]' where E = 0.40 is porosity. The surface heat transfer coefficient for the air flow over the clump is given by 7 = 4 x 10* &/ R where kr is the air thermal conductivity and 1s equal to 0.0317 W/m -K. Consider an individual bacterial radius of 1 um and the specific heat, density, and thermal conductivity of the bacterial clump of 3.6 kI'kg 'K, 1080 kg / m', and 0.49 W /m -K respectively. For three bacterial clumps given by n = 102, 10 and 10%, (1) Determine the clump radius and the heat transfer coefficient. i1 2) Show that the lumped parameter approach is valid. 3) Calculate the time required for the bacterial temperature to mncrease by 99% of the total possible change in temperature