New Design Boosts Air Conditioning Performance

Denso Corporation has developed a unique double-pipe internal heat exchanger for a car air conditioning system, increasing cooling performance by up to 12 percent.
Denso is the first to develop the double-pipe internal heat exchanger for a front air conditioning system that needs to be installed in a limited space. The air conditioning system was introduced this year in the Middle and Near East on the Toyota Prado and in North America on the Lexus GX470.
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.
In Denso’s double-pipe internal heat exchanger, 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. Specifically, with this unique structure, Denso’s double-pipe internal heat exchanger can increase cooling performance by 5 percent to 12 percent at the same power level, with a length of only 40 centimeters (approximately 16 inches).
Further, Denso’s double-pipe internal heat exchanger can easily be manufactured by inserting the inner tube into the outer tube and by fixing the tubes at both ends.
When the air conditioning system is installed in the engine compartment, pipes need to be flexible so they can be bent to fit with the other systems and 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. Denso solved this problem by creating the spiral grooves on the inner tube wall.
As a result, the tubes are not crushed when bent, and air conditioning systems using Denso’s double-pipe internal heat exchanger can be installed in the same space as a conventional front air conditioning system.
“Denso has been dedicated to mono-zukuri or the art of making things since we opened our doors more than 50 years ago,” said Hikaru Sugi, Denso Corporation managing officer in charge of the Thermal Systems Business Group. “That focus helped us develop the spiral grooves on the inner tube wall of the double-pipe internal heat exchanger.”