Abstract: A heat pump includes a compressor 1, a condenser 2, an expansion valve 3, an evaporator 4 and a heat exchanger 6a. The heat exchanger 6a is located immediately downstream of the expansion valve 3 and upstream of the evaporator 4. A controller 8 monitors one or more variables which predict may be about to occur by means of a sensor 11. When this is predicted the heat exchanger 6a will receive hot refrigerant through line 17 from the high pressure side of the compressor 1 so as to heat the refrigerant entering the evaporator 4 until ice formation is no longer likely. In an alternative embodiment, the heat exchanger may utilise an electric element to heat the refrigerant before it enters the evaporator. The heat exchanger 6a can preferably utilise a helically corrugated tube in order to enhance its heat exchange characteristics.

Abstract: A heat exchanger includes a body 4 on the surface of which are provided helical or spiral paths 5 which will provide multiple and turbulent flow paths A for a first fluid such as water which is caused to flow through chamber 3 relative to a spirally wound heat exchange tube 6 and in a heat transfer relationship with a second fluid flowing through the tube 6. The tube 6 has one or more further helical or spiral flow paths 9 on its external surface. The multiple flow paths A will extend the residence time for the first fluid within the heat exchanger 1 and this together with the turbulence will maximise heat transfer. Preferably a portion of the first fluid flow will be through a central aperture in body 4 where turbulence is also created by the helical or spiral paths of the tube 6 as it extends through the aperture.