14A-41

J. F. VéLEZ-RUIZ¹, J. F. VéLEZ-RUIZ¹, R. Verduzco, and R. C. Macedo y Ramírez. (1) Chemical and Food Engineering Department, . Universidad de las Américas-Puebla, Sta. Catarina Mártir, Cholula, Puebla, PUEBLA, 72820, Mexico

Many food process operations, including cooking, heating, pasteurization and thermal sterilization, involve heat transfer between fluids and solid particles. And, although in the last decade a considerable number of papers analyzing related physical phenomena have been published, still there are very few data of heat convective coefficients. Therefore, the objective of the present research was to evaluate heat transfer convective coefficients between food particles and food fluids for two heat transfer systems. Three particles (carrot cubes, peas, and mushrooms) and four different fluids (water, sugar solution, carboxyl methyl cellulose solution, and ketchup) were utilized in two heat transfer systems (natural and forced convection); also, the effect of number of particles (1, 3 and 5) and two medium temperatures (70 and 85ªC) were studied. A copper-constantan thermocouple was placed in the geometric center of each particle, and from the monitored sample (To and Ts) and surrounding fluid (Tm) temperatures over time (t), the heat transfer coefficient (hfP) could be estimated; the lumped parameter approach (ln [Ts-Tm)/To-Tm])=- hfpAt/mCp), assuming a Biot number less than 0.1, was applied for hfp estimation. The heat transfer coefficient ranged from 280 to 555 W/m^2 K for peas in natural convection with Newtonian fluids (NF), and from 62 to 334 in non Newtonian fluids (NNF); for carrots the estimated values for hfp were 240 to 348 in NF, and 55 to 245 in NNF; whereas for mushrooms the magnitudes of hfp were 95 to 262 in NF, and 62 to 162 in carboxyl methyl cellulose solution. Forced convection increased the convective coefficients. The results indicates the presence of higher hfp values related to one particle/Newtonian fluids, higher temperature and forced mechanism, being hfp lightly higher for pea, carrot and mushroom, respectively.