Thermo-structural studies of spores subjected to high temperature gas environments

One of the major mechanisms of deactivating the spores is to expose them to elevated temperatures. Experimental research carried out to study the effects on spores by a high temperature gas environment provides evidence of spore destruction in such exposures. Numerical studies have been performed to complement the experimental work and to study the effects of various parameters, such as gas temperature level, exposure time and internal pressure on spore survivability. The present work involves studying the performance of a spore thermal exposure system. It is shown that, in order to have uniform distribution of spores lifetimes inside the device and to avoid the flow transition from laminar to turbulent, which involves difficult-to-model flow instabilities, the flow inside the thermal exposure system is better to be set as pure turbulent rather than pure laminar or that involving transition from laminar to turbulent. The flow field inside the thermal exposure system is simulated by CFD using turbulence models. Flow field data such as residence times of spores inside the device are then used for the computation of thermal response of spores to the high temperature gas environment under different operating conditions. Furthermore the possibility of spores conjoining to form conglomerates and the impact of such a process on survivability of spores is studied. A case study is carried out in which trace of water is assumed inside the spores. Water, if present, expands when heated and thus exerts pressure on the spore wall, and this process in turn may lead to the destruction of spores due to structural failure. A thermo-structural analysis is carried out in the present work to take into account the dynamic response of spore to the internal pressure exerted by heated fluid inside the spore. Moreover, it is shown that the incorporation of inertia effect is essential for capturing the dynamics of spores undergoing structural deformation. Finally, the survivability of spores through the thermal exposure system is discussed.