ENHANCEMENT OF HEAT TRANSFERRED RATE THROUGH HEAT EXCHANGERS DURING CONCENTRATION PROCESS OF MILK

Fouling problems of heat exchangers affect severely the performance of heat transfer process during the concentration of milk. In this investigation the strategy of anti-fouling is focused on investigate the optimal hydrodynamic flow. Two combined techniques, for resulting oscillating high values of shear stress on heat transfer surfaces, were applied in the current investigation. The two techniques are dissolved air flotation for microbubbles generation in the milk stream with pulsed flow for hydrodynamics conditions modifications. Four different applied air pressures of 0.1, 0.2, 0.3, and 0.6MPa for controlling the microbubbles discharge and three modes of pulsation were nominated as uniform pulsation, gradient pulsation and without pulsation. Plate heat exchanger used commonly in milk industry for thermal treatments. Commercial pilot scale of plate heat exchanger was operated at milk flow rate of 0.078 m^3h^-1 and heating level from 42 to 61°C. The results show that the application of air pressure for microbubbles generation and pulsation type have a significant effect on fouling layer prevention for more while 105 minutes (the experimented time). For these reasons, the use of the two integrated techniques can progress thermal process of the plate heat exchanger. The optimum treatment for fouling deterrence is at applied air pressure of 0.6MPa and gradient pulsation, frequency with 0.16Hz and two states of steadily, unsteady of 20 seconds and steady of 10 seconds, the fouling layer decreases by 76.5%, and the maximum value of the overall heat transfer coefficient obtained is 9688.4Wm^-2K^-1.