ABSTRACT
The surface heat transfer coefficient is used to quantify the rate of convective heat transfer to or from the surface of an object. Convective heat transfer is the mode of energy transfer between a solid surface and the adjacent fluid that is in motion, and it involves the combined effects of conduction and fluid motion. The faster the fluid motion, the greater the convection heat transfer. In the absence of any bulk fluid motion, heat transfer between a solid surface and the adjacent fluid is by pure conduction. The rate of convection heat transfer is observed to be proportional to the temperature difference and is conveniently expressed by Newton’s law of cooling as
Q ¼ hAs(Ts T1) (21:1)
where Q is the net energy added to the system (w) h is the surface or convective heat transfer coefficient (W=m2 K) As is the surface area (m
2) through which convection heat transfer takes place Ts is the surface temperature (K) T1 is the temperature of the fluid (K) sufficiently far from the surface
The surface heat transfer coefficient is not a property of a fluid or thematerial. It is an experimentally determined parameter whose value depends on all the variables influencing convection such as the surface geometry, the nature of fluid motion, the properties of the fluid, and the bulk fluid velocity (Cengel, 2003). In food applications, it is needed to quantify heat transfer during heating or cooling of food materials in fluids. The surface heat transfer coefficient is an important parameter needed in the design and control of food processing equipment where fluids, such as air, nitrogen, steam, water, oil, etc., are used as heating, cooling, frying, freezing, or cooking media (Rahman, 1995).
