1 3 Heat Mass Transfer DOI 10.1007/s00231-015-1652-x ORIGINAL Study on heat transfer coefficients during cooling of PET bottles for food beverages Antonio Liga 1 · Salvatore Montesanto 1 · Gianluca A. Mannella 1 · Vincenzo La Carrubba 1 · Valerio Brucato 1 · Marco Cammalleri 2 Received: 23 February 2015 / Accepted: 27 July 2015 © Springer-Verlag Berlin Heidelberg 2015 k w Water thermal conductivity L Characteristic length, volume/surface m Mass Nu Nusselt number Pr Prandtl number r 1 Bottle internal radius r 2 Bottle external radius Q tot Global heat flux Q rad Radiant heat flux Q conv Convective heat flux h rad Radiant heat transfer coefficient U conv.+cond. Convective heat transfer coefficient Ra Rayleigh number Re Reynolds number T Temperature T 1 Inside temperature of water T 2 Outside temperature of cooling fluid T 0 Initial inside temperature of water T g Glass transition temperature T wall Bottle surface temperature T ∞ Bulk temperature of cooling fluid θ Dimensionless temperature t Time U g Global heat transfer coefficient Greek symbols α Thermal diffusivity α w Water thermal diffusivity α PET PET thermal diffusivity β Volumetric thermal expansion coefficient δ PET layer thickness μ Viscosity ν Kinematic viscosity (μ/ρ) ρ Density τ Characteristic time Abstract The heat transfer properties of different cool- ing systems dealing with Poly-Ethylene-Terephthalate (PET) bottles were investigated. The heat transfer coef- ficient (U g ) was measured in various fluid dynamic con- ditions. Cooling media were either air or water. It was shown that heat transfer coefficients are strongly affected by fluid dynamics conditions, and range from 10 W/m 2 K to nearly 400 W/m 2 K. PET bottle thickness effect on U g was shown to become relevant under faster fluid dynam- ics regimes. List of symbols A Sample A A S Bottle external area B Sample B C Constant c p Specific heat D Bottle external diameter g Gravitational acceleration Gr Grashof Number H Bottle height h 1 Heat transfer coefficient inside the bottle h 2 Heat transfer coefficient outside the bottle k PET thermal conductivity * Gianluca A. Mannella gianluca.mannella@unipa.it 1 Department of Civil, Environmental, Aerospace and Materials Engineering (DICAM), University of Palermo, Viale delle Scienze, Ed. 8, 90128 Palermo, Italy 2 Department of Chemical, Management, Computer and Mechanical Engineering (DICGIM), University of Palermo, Viale delle Scienze, Ed. 8, 90128 Palermo, Italy