Denso Corporation has developed a claimed unique double-pipe internal heat exchanger for car air conditioners, increasing cooling performance by up to 12%.

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The parts maker said it was first to develop the double-pipe internal heat exchanger for a front air conditioning system that needs to be installed in a limited space. It’s already in production vehicle: Middle and Near East-specification Toyota Prado and North American Lexus GX470 SUVs.


The double-pipe internal heat exchanger integrates two pipes, which are separated in a conventional refrigeration cycle, into one pipe with inner and outer tubes. In the refrigeration cycle, the low-temperature gaseous refrigerant flows in the inner tube, and exchanges heat with the high- temperature liquid refrigerant flowing in the gap between the inner and outer tubes.


The inner tube wall has spiral grooves that face the outer tube, enhancing heat exchange. This allows the internal heat exchanger to achieve a higher cooling performance within a shorter pipe length. With this unique structure, the double-pipe internal heat exchanger can increase cooling performance by 5% to 12% at the same power level, with a length of only 40 centimetres (about 16 inches).


The part can easily be made by inserting the inner tube into the outer tube and fixing both at each end.

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Where the air conditioning system is installed in the engine compartment, pipes need to be flexible so they can be bent to fit alongside other components. However, in the double-pipe internal heat exchanger, the gap between the inner and outer tubes is likely to be crushed during the bending process, making it unable to function as a refrigerant path. Engineers solved this problem by creating the spiral grooves on the inner tube wall.


As a result, the tubes are not crushed when bent, and an air conditioning system using this heat exchanger can be installed in the same space as a conventional unit.