Electric water heating device with decreased mineral scale deposition

Abstract

An electric water heater includes an outer cylindrical structure having first and second openings defining a water inlet and outlet, respectively, and an inner cylindrical structure having an inner passage therethrough and coaxially disposed in the outer cylindrical structure to define an outer passage therebetween. The inner and outer passage are interconnected at one end of the structures and communicate respectively with the first and second openings. The inner cylindrical structure includes a cylindrical ceramic support secured at one end to the other end of the outer cylindrical structure, an electric resistance heating element on the outer surface of the ceramic support and a ceramic sheet having a thickness smaller than the ceramic support wound on the heating element so that it is embedded in the sheet. A helical structure is provided in the outer passage for generating turbulence therein so that thermal energy is transferred from the heating element to the outer surface of the inner cylindrical structure at a rate greater than the rate at which energy is transferred from the heating element to the inner surface of the inner cylindrical structure whereby the temperature at the inner and outer surfaces of the inner cylindrical structure are equalized when water is supplied at a predetermined flow rate and kept at a level lower than that at which mineral scale is likely to be deposited in the passages.