Heat Transfer and Simulated Sterilization of Particulate Solids in a Continuously Flowing System

Abstract

The heat transfer coefficients (h) between a cube and water were 239 and 303 W/m2K at 0 and 0.86 cm/s relative velocity. In 35% sucrose and 0 cm/set, h was 146 W/m*K. A model for heat lethality in cubes during continuous sterilization which used finite difference equations for heat conduction and above values of h, revealed that hold times for 6D inactivation of PA 3679 (F,=7.2 min) in an isothermal fluid at 132.2"C were 1.78 and 5.2 min for 1 and 2 cm cubes when h was 303 W/m2K and 1.23 and 4.13 min when h was 2500 or higher. When h was 239 W/mZK, hold times were 2.36 and 6.02 min for 1 and 2 cm cubes. When fluid entered the hold tube at 132.2"C and particle to fluid ratio was 0.56, fluid-particle heat exchange increased hold time to 12.2 and 119 min for 1 and 2 cm cubes.

Numerical simulation of heat transfer in aseptic processing operations involving non-Newtonian fluids

“…Most of the existing research particularly that reported in process engineering literature has been conducted at much higher Reynolds numbers. Chang and Toledo (1989) observed that when the relative velocity between particle and fluid is the same as the velocity of the fluid past a stationary particle, the heat transfer coefficients should be similar in both the cases. The fluid to particle heat transfer coefficient was found to increase with increasing slip velocity (Balasubramaniam and Sastry 1994).…”

Simultaneous Determination of Thermal Diffusivity and Heat Transfer Coefficient during Sterilization of Carrot Dices in a Packed Bed

“…In continuous aseptic processing of particulates, Chang and Toledo (1989) demonstrated that non-isothermal conditions exist and h and k may not be combined to accurately simulate the lethal effects of heat during the process. h is dependent on geometry and relative fluid velocity while k is temperature dependent.…”

“…In traditional thermal process calculations, the heating medium is at a constant temperature, therefore, the effects of h and k may be combined as an apparent (Y or in the expression for fh. In continuous aseptic processing of particulates, Chang and Toledo (1989) demonstrated that non-isothermal conditions exist and h and k may not be combined to accurately simulate the lethal effects of heat during the process. h is dependent on geometry and relative fluid velocity while k is temperature dependent.…”

A next generation, pilot-scale continuous sterilization system for fermentation media

“…Thermal properties of the surrounding fluid are less critical for heat transfer to particles since the heat transfer coefficient, h (cal/s-cm 2 −°C), between the fluid and particle is limiting [59]. Its effectiveness is shown by the Nusselt number (ratio of total heat transfer to conductive heat transfer), N Nu , given by hD p / K , where D p (cm) is the particle diameter, and K (cal-cm/s-cm 2 −°C) is the thermal conductivity of fluid at the processing temperature [22, 49]. If the predicted particle temperature profile is hotter than the actual one, it is possible to obtain incomplete inactivation [20].…”