A special model of the BEW and BEM types is the double-tube (safety) heat exchanger, which is applied when it is absolutely unacceptable that both media in the heat exchanger mix in case of leakages (for instance transformer oil and water) or when leakage to the environment should be prevented at all costs.
Depending on the application the double-tube heat exchanger can be equipped with externally finned outer tubes (to enlarge the heat exchanging area) or with plain outer tubes. Inside these tubes are normal plain tubes. Early detection of leakage in case one of the tubes becomes defective is provided by the grooves between the outer and the inner tubes. Well before any harm should occur, the leak detection has become active.
