Heat exchanger barrier ribbon with polymeric tubes

#The invention relates to plastic tube fluid handling means for use in heat exchangers and more particularly to such means with a metal barrier layer in the form of heat transfer ribbon.

#Among the challenges in making plastic heat exchangers is the need for improved barrier properties. In some applications, such as air-air heat exchange, such as in a charge air cooler, permeability of the plastic tubes is not a problem. In other applications, permeability must be well managed. Among the highest demands for low permeability are refrigeration applications. There is a need to keep the refrigerant in and both water vapor or moisture and air out. Refrigerants are also under pressure, higher in condensers and lower in evaporators, adding to the need for good permeation control.

#It has been recognized that metal layers will provide impermeability to polyamide tubes for use in heat exchangers. However, structures and procedures for obtaining good impermeability for practical use in refrigeration systems from the combination of metal and plastic or polyamide and aluminum are not available. Some have suggested applying metal after assembling a structure, such as by sputtering. However, sputtering, while it may give a complete coating, does not provide the impermeability needed. Also, thicker metal layers would be needed to permit improved heat transfer from a web to the tubes. Much of the art uses fins of aluminum brazed onto aluminum tubes perpendicular to the tubes to improve heat exchange, which is not readily done with plastic tubes.

#FIG. 1 is an illustration of the structure of the invention in perspective.

#FIG. 2 is a more detailed end view of a cross section of a typical structure of the invention.

#FIG. 3 is a plan view of a structure of the invention.

#Typically an evaporator in a refrigeration or air conditioning system consists of a number of finned metal tubes, the tubes having a greater internal diameter than the liquid refrigerant inlet tubes, to allow for expansion and cooling, and having a specified length to allow for complete evaporation to the gaseous phase. Condensers are configured in an analogous manner, but usually must operate at higher pressures to effect conversion of the gaseous refrigerant to a liquid phase. When attempting to design a refrigerant-capable exchanger from polymeric tubing, a number of factors must be considered:

#i) The refrigerant must be retained inside the tubing structure for a long time such as for many years, with minimal losses.

#ii) Moisture and air must be prevented from permeating into the tubing. Air is non-condensable and would diminish the performance of the heat exchanger. Moisture reacts with refrigerants such as hydrofluorocarbons (HFC's) and hydrochlorofluorocarbons (HCFC's) and the products of this reaction can lead to failure of the system due to corrosion and sludge.