... type or immerging type. Various coating, such as Teflon, ceramic paint, or oxygenation on surface of ... with shell is commended firstly. Electric power of one part is between 100~1500W, and parallel several ... parts can be used for larger power. PTC as heating element, it fits for high safety, ... assembling, and using high heat-conducting materials such as copper or aluminum. The power density is about ...