This section discusses a vertical tubular ohmic heater: a collinear heater.
Figure 22.2(c) shows a typical apparatus consisting of two basic parts: an electrode housing with an electrode and a spacing tube placed between the electrode housings. Usually, several housings and tubes are placed in series. The electrode is a ring in the wall or a cantilever tube. The spacing tube is usually made from plastic-lined steel to ensure that the electric current flows only through the liquid product. Most of the heating takes place in this tube. Here, the tube is assumed to be a perfect electrical insulator, and a single spacing tube is modeled (
Figure 22.3). The electric field near the electrode is ...