Spiral or helical counterflow heat exchanger

A helical counterflow heat exchanger, comprising:

• three flexible flat monolithic double-sided enameled steel bands annealed at temperatures above 500° C., that define two chambers and are wound helically around a central longitudinal axis that is parallel with and equidistant to a surface of each respective enameled steel band, the surface of each respective enameled steel band extending parallel to the longitudinal axis, the first chamber being configured to guide a first fluid therethrough, the second chamber being configured to guide a second fluid therethrough in an opposite direction with respect to a guiding direction of the first fluid;
• and
• a first corrosion-resistant helical spacer provided between windings of the heat exchanger to impose a mutual distance between the windings and a curve of the respective windings in the heat exchanger formed by the enameled steel bands, to prevent corrosion of the steel bands at edges of the steel bands and to allow successive windings of the helical heat exchanger to fit against one another in the direction of the longitudinal axis.