They have also reported pool boiling heat transfer coefficients for different heat inputs, while the milk was manually stirred and boiled. ( 2011, 2013) have reported natural convection heat transfer between hot milk and air. Hence heat transfer studies in milk are significant from the point of view of optimum energy utilization and to prevent secondary reactions while heating. This is a two-stage process namely, (1) Preheating the milk to boiling condition and (2) Boiling the milk to concentrated forms for example in khoa making (Choudary et al. In many processing operations, milk is boiled by using direct flame or by steam. An empirical correlation in milk processing to make khoa has been reported by Kumar ( 1985). Out of the entire milk produced, 47% is utilised for milk based sweets (Sharma 2006). Milk production in India according to 2015–16 statistics is 155.5 million tonnes (National Dairy Development Board 2016).
Milk is a nutritive drink containing fat, protein, sugars, minerals and water. 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. Pr 0.33 have been developed for each case.In addition, empirical correlations for the forced convection heat transfer using Nu = a The Two Bladed Paddle was found to as yield the highest heat transfer coefficient h ¯ for all three types of milk. Heat transfer coefficients were determined for h ¯ for cow milk (3.5% fat), standardised milk (4.5% fat) and full cream milk (6.0% fat). 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. In the present investigation, forced convection heat transfer coefficients for milk, using mechanical agitators in vessels have been determined. Data for forced convection heat transfer coefficients for milk in agitated vessel have not been documented. Use of mechanical agitator with suitable impeller would result in uniform agitation of the liquid. This process is done either in heat exchangers or in agitated vessels, where the mode and type of heat transfer plays a significant role. Heating of milk is an important unit operation to produce many milk based products.
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