LAUSR

It is worth noting that hot fluid foods can cause even severer thermal injury, due to their high viscosities. The apparent viscosities of typical fluid foods are from 0.1 to 100 PaS at shear rate 10–50 S, compared with the viscosity of water, 0.001 PaS at 20°C (Tabilo-Munizaga and Barbosa-Cánovas, 2005). Figure 1a illustrates the apparent viscosity of tomato puree as a function of the solids concentration. The flow of fluids in circular tubes has been solved in classical fluid mechanics. We consider a laminar flow with viscosity μ in a vertical tube of length L, radius R, and pressure difference ΔP. The velocity distribution for the downward flow is parabolic, as shown in Fig. 1b. The average velocity vz can be obtained by the Hagen–Poiseuille equation.