Heating of milk is an important unit operation to produce many milk based products. This process is done either in heat exchangers or in agitated vessels, where the mode and type of heat transfer plays a significant role. Use of mechanical agitator with suitable impeller would result in uniform agitation of the liquid. Data for forced convection heat transfer coefficients for milk in agitated vessel have not been documented. In the present investigation, forced convection heat transfer coefficients for milk, using mechanical agitators in vessels have been determined. Experiments have been conducted in vessels (Baffled as well as Unbaffled vessel) that were designed and fabricated under standard procedure employing: (1) Flat Six Blade Turbine impeller, (2) Inclined Six Blade Turbine impeller, (3) Three Blade Propeller impeller and (4) Two Bladed Paddle. Heat transfer coefficients were determined for for cow milk (3.5% fat), standardised milk (4.5% fat) and full cream milk (6.0% fat). The Two Bladed Paddle was found to as yield the highest heat transfer coefficient for all three types of milk. In addition, empirical correlations for the forced convection heat transfer using have been developed for each case. These heat transfer correlations derived will find application in large scale design and the experimental setup would be useful for future investigation with different liquids and impellers.
Keywords: Agitator; Empirical correlations; Forced convection heat transfer coefficient; Impellers; Milk.