What is Direct Impingement Heat Transfer?
Direct impingement heat transfer uses air as an energy transferring agent to heat a product to change the product's properties to a more desirable product. In the converting industry this is often to dry a coating or print ink but is also used to change the properties of the product by heat treating. Direct impingement is usually done from one side of the product (web) but in some cases dryers utilize heat from both above and below the web.
There are two primary types of convection dryers used in the converting industry, direct impingement and flotation, each with their own benefits for particular converting industry products. Drying is a process made up of two basic actions; application of heat energy to provide the heat of vaporization to the liquid you are drying, which turns it into vapor and is called heat transfer; and mass transfer, which is the means to which the vapor is removed from the product surface. This series will specifically address the heat transfer aspect of drying and touch more briefly on the practical matters of mass transfer.
In the next weeks look here for a series of papers that discuss the various uses of, and design principles behind good direct impingement dryer design for the converting industry, in particular the web converting industry.
