(90f) CONDUCTION CONTROLLED FREEZING of PCMs IN CYLINDERS

Freezing and melting of materials in cylinders have several applications including solar energy and processing industry.A knowledge of partial and total freezing rates is vital for design of such systems.In renewable energy literature the material undergoing phase change is often referred as PCM. It is known that freezing rate depends on geometry of PCM holder,any initial superheat of PCM,temperature difference between PCM and cooling surface and thermophysical properties of solid and liquid.In addition,the nature of solid/liquid interface during freezing complicates the process.From literature and our preliminary experiments ,significant differences between predictions and data were noted for PCMs n ?eicosane and n-octadecane.The practical frozen mass is above theoretical value at any instant for isothermal cooling surface condition. In the present work,we intend to make a detailed study using three PCMs.In addition the process of freezing is carried out in cylinders of different diameters.The general details are given below. PCM: n-octadecane(Melting point 28C) Lauric acid (MP 42C) Wax(MP 58-60C) Volume:30 to 500cc Cylinder(L/d);1 to 5 Temperature drop across PCM:3 to 50C Isothermal water baths are used for freezing of PCM. The experiments are being coducted with negligible superheat.The freezing process is therefore predominantly conduction controlled.The partial frozen mass and time data obtained would cover a broad range of mentioned variables as well as a range of thermophysical properties of PCM.This would enable a critical evaluation of literature models and also the limitations of theoretical models would be discussed.