Circular heat exchangers have been used to increase the efficiency of engines by absorbing heat from the exhaust gas and transferring a portion of the exhaust heat to the intake air. The present heat exchanger is built to be more efficient, to better resist the internal forces and pressures and to better...http://www.google.com/patents/US5081834?utm_source=gb-gplus-sharePatent US5081834 - Circular heat exchanger having uniform cross-sectional area throughout the passages therein
