Film flow is defined as a thin layer of liquid flowing over a surface under the action of external force such as gravity, shear stress etc. and having at least one free boundary. In general, thin liquid film flow occurs widely in nature and also in various industrial processes viz. thin liquid films are encountered in any lubrication problem (e.g. lubricating gears, bearings, metered coating, cold rolling of steel); in microelectronics industry (e.g. manufacture of CDs, DVDs and computer disks ); in printing technology (drop spreading process); in heat and mass transfer devices (e.g. spinning disk reactors and distillation columns) to limit fluxes and to protect surfaces etc. Thin film is widely used in the coating industry. In manufacturing of micro-electronics gadgets like the hard disk, screen, electronic circuit, micro-electronics chips, the coating is required in many processing steps. Apart from this, coating of any surface or equipments is necessary to enhance its efficiency of work, durability, heat transfer performance/cooling performance, etc. All coating process demands a smooth glossy finish to meet the requirements for best appearance and optimum performance such as low friction, transparency and strength. The rate of heat and mass transfer within the thin liquid film has a direct bearing on the success of the coating process and chemical characteristics of the product. In the coating process, we are covering any surface or substrate by a thin uniform layer of liquid. The thin layer of liquid can be developed over a surface by many ways e.g., liquid flow over a stretching surface, spin coating (liquid flow over a rotating disk), spreading of a liquid, spray coating, blade coating, thin film flow over a incline plane etc.
In the recent past, nanoliquids have attracted the researchers because of their possible applications in industries. The nanoliquids are of colloidal suspensions having typically metals, oxides, carbides or carbon nanotubes in a base fluid, etc. Common base fluids include water, ethylene glycol etc. The nanoliquids exhibit enhancement of thermal conductivities and heat transfer coefficients compared to the base liquid. For this reason nanoliquids are often preferred over conventional coolants like oil, water, ethylene glycol mixtures. The main application of nanoliquids is in the coating process such as in microelectronic chips coating, wire and fiber coatings etc.
Due to the advancement of the technology there are retaining a trend towards smaller microelectronic devices that produce increasing thermal load to the devices. Therefore, there is an urgent need to improve the cooling performance of the smaller microelectronic devices. The cooling performance of such microelectronic devices may be increased by using nanoliquid in the coating process. But little is known about the mathematical modeling of then nanoliquid film development over the surface of the stretching sheet or the surface of a horizontal rotating disk. So, it is needed to investigate the development of thin nanoliquid film under the action of different physical circumstances (i.e., effects of non-Newtonian fluids, gravity, porosity, surface tension, slip