**6. Phase change**

This part of the chapter deals with melting and freezing of materials. The section is divided into several subsections such as phase change materials (PCMs); formation of ice and its melting; melting and freezing of radial objects; melting and solidification of metals, nonmetals, and composites; crystallization; and globule, spray, and plunge cooling for better understanding.

#### **6.1 Phase change materials**

The inability to recover latent heat after super cooling of PCMs has been pointed out, and the method to recover latent heat has been discussed [71]. The melting mechanism of PCMs in magnetic field in low-gravity atmosphere has been discussed [72]. Other works include fabrication of carbon brushes which can be used to enhance the thermal conductivity in phase change materials, the role of ultrasonic vibration on melting characterization of PCMs, and detailed examination of solid liquid phase change heat flow enhancement.

#### **6.2 Formation of ice and its melting**

Researches on the formation of ice and its melting include the thermal behavior of ice under constant heat flow per unit area and melt removal, melting of ice using natural convection, ice making by cooling water-oil emulsion with stirring, and numerical simulation of melting of ice in water under the influence of natural convection and cooling effect produced by melting of ice [73–75].

#### **6.3 Melting and freezing of radial objects**

A lot of work has been presented on phase change in radial objects such as sphere, cylinders, and slabs. A mathematical model using numerical analysis has been developed to study the melting process of PCMs in sphere [76]. A novel packed bed of spheres has been developed using graphite/PCM composite for increasing the thermal conductivity which resulted in reduction in melting and freezing time significantly [77].
