Double-pipe heat exchanger is made of concentric inner and outer pipe. Cold and hot liquid respectively flows in the gap of inner pipe and sleeve pipe and changes heat at the same time. lnner pipe is used U tube to connect. Sleeve pipe is used direct pipe to connect at both ends . Structure of double pipe heat exchanger is simple and heat transmission is large. It's easy to clean an convenient to disassemble and assemble. Flow rate is appropriate and it is possible to have a backwash. Flow rate of exchanging heat is high.