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Property Charts: Thermal Conductivity I
Manufacturing advantages and improved recyclability are clearly benefits of using all-aluminium for heat exchangers, but what about material properties and the choice of alloys, and the competition with copper alloys?
Good thermal conductivity is the first consideration, so we will use charts displaying this property. Strength, density and price are all important, so we compare alloys on charts showing these properties.
Heat exchanger design must also take account of less easily quantified material characteristics - in particular the corrosion response.
Aluminium alloys vs. copper alloys
The material property chart below shows thermal conductivity vs. yield stress, with a number of common heat exchanger alloys included.
Al heat exchanger alloys
1000 series alloys (e.g. 1050 and 1197) have the highest thermal conductivity, which is not influenced by strengthening by cold working. Higher alloy content non-heat-treatable alloys (e.g. 3102, 5000 series) show lower conductivity but potentially higher strength. Heat-treatable (age hardening) alloys have the highest strengths, with a greater spread in conductivity (depending on the exact composition and heat treatment).
Al alloys vs. Cu alloys
Pure Cu offers thermal conductivity up to 1.5 times higher than aluminium, with comparable strength. On these properties, some Cu alloys overlap with the Al alloys. Standard Cu alloys (e.g. brass) have similar strengths but their thermal conductivities are typically 1.5-2 times lower than 1000 or 3000 series Al alloys (due to the high Zn content of brass). All other metals (except silver!) have much lower thermal conductivity.
The dominance of 1000 and 3000 series alloys suggests that strength is not
an over-riding concern after thermal conductivity, so what else is important?