High-frequency self-defrosting evaporator coil

An evaporator comprising

• a refrigerant tube providing an electrical path and a heat transfer surface, the electrical path being formed of an electrically conductive material having a relative magnetic permeability higher than 40 and being in thermal communication with the heat transfer surface to transfer heat to the heat transfer surface;
• an upstream refrigerant conduit for supplying a refrigerant to the refrigerant tube;
• a downstream refrigerant conduit for receiving the refrigerant from the refrigerant tube;
• an upstream electrical isolation element for electrically isolating the refrigerant tube from the upstream refrigerant manifold;
• a downstream electrical isolation element between the refrigerant tube and the downstream refrigerant manifold;
• an electrical coupler connectable to a standard line voltage from an external power source, the standard line voltage having an externally determined voltage value and standard line frequency;
• and
• an electronic circuit electrically connectable between a standard line voltage and the refrigerant tube, in operation the electronic circuit receiving and transforming the standard line voltage to provide a high-frequency alternating current at a target frequency in the refrigerant tube, most of the high-frequency alternating current being provided in the electrical path, and the target frequency being higher than an externally determined frequency of the externally determined voltage;
• wherein
• a total resistance obtained from applying the high-frequency alternating current to the electrical path of the refrigerant tube is at least 1.5 times a notional resistance obtainable from providing a direct current to the electrical path of the refrigerant tube.