Chilling of the agitated milk using nano-enhanced phase change materials

Maintaining cold-chain in the rural and distant locations, particularly in small to marginal dairying in the developing nations, is still challenging. Milk chilling with agitation by phase change materials bridges the breach in the cooling due to power outage as well as augments the cooling rate and ceases the phase-separation of milk constituents. In the present study, an attempt was made to numerically simulate and validate the chilling of the agitated milk using nano-enhanced phase change materials (NePCM). The test rig for the investigation comprised an insulated jacketed cylindrical module, confining NePCMs in the jackets and the milk inside the innermost cylinder, coupled with a slow speed (<= 100 rpm) agitator immersed into the milk. The computational fluid dynamics (CFD) tools of ANSYS-Fluent viz., enthalpy-porosity and volume of fluid models were employed for simulating the energy discharge from the NePCMs during milk chilling. The impeller motion during milk agitation was simulated by the multiple reference frame and Transition Shear-Stress-Transport models. The experimental results validating the CFD models showed the enhancements in energy discharging rates and milk chilling performance up to 54.23 and 30.67%, respectively. The rate of energy discharge and milk chilling were influenced by concentration of nanoparticles, speed of agitation, location of the NePCMs, local convections (at a rpm <= 30) and overall thermal distance between the heat source (milk) to the heat sink (NePCM). Such effects were clearly visualized and discussed in the numerical flow visualization of the computational domain. The investigation showcased an energy efficient milk chilling module which could be decoded into a chiller cum storage dairy vessel to be used by small to commercial scale enterprises.