Corrugated Tube Heat Exchangers (corrugated tubes instead of smooth tubes creates turbulence in the medium flow and ensure high Reynolds number even at low velocity. Corrugated tube is produced by indenting a plain tube with a spiral pattern, as example the helical flow contributes to the situation that the fluid particles are alternatively in the near of the tube wall and then in the main flow and the helical effect secondary flow (eddies) around the circumference of the tube will occur. 📷 The flow regime ensures that the rate of decrease in boundary layer resistance exceeds the rate of increase in pressure loss and so high heat transfer coefficients with minimum increase in pressure drop can obtained. The increase in heat transfer coefficient lets the temperature of the tube wall nearest to the bulk fluid temperature on the tube. Corrugated tube shell and tube HE have many advantages over smooth tube as: compactness of HE, long time of running because of turbulent flow, low maintenance cost, high transfer coefficient (2 to 3) times, low HE area, minimum fouling, uniform thermal operation, more annular space size and wide range of diameters.

Corrugated Tube Heat Exchangers (corrugated tubes instead of smooth tubes creates turbulence in the medium flow and ensure high Reynolds number even at low velocity. Corrugated tube is produced by indenting a plain tube with a spiral pattern, as example the helical flow contributes to the situation that the fluid particles are alternatively in the near of the tube wall and then in the main flow and the helical effect secondary flow (eddies) around the circumference of the tube will occur. 📷 The flow regime ensures that the rate of decrease in boundary layer resistance exceeds the rate of increase in pressure loss and so high heat transfer coefficients with minimum increase in pressure drop can obtained. The increase in heat transfer coefficient lets the temperature of the tube wall nearest to the bulk fluid temperature on the tube. Corrugated tube shell and tube HE have many advantages over smooth tube as: compactness of HE, long time of running because of turbulent flow, low maintenance cost, high transfer coefficient (2 to 3) times, low HE area, minimum fouling, uniform thermal operation, more annular space size and wide range of diameters.

I am one hundred percent agree with the answer of Saad. That is the reason and there is not a better way to explain it.

helps to reduce the resistance of the boundary layer of the tube side. As long as the fluid on the side of the tube has the highest resistance to heat flow, the overall rate at which heat is transferred will increase. Look https://www.hrs-heatexchangers.com/es/heat-exs-videos/flujo-de-particulas-dentro-de-un-intercambiador-de-calor-de-tubo-corrugado/

The pipe having corrugated surface has more heat transfer rather than plain tube. Corrugation increases heat transfer because of roughness that increases turbulence. Turbulence in addition has eddies formation which increases heat transfer rate. Strictly, plain tube is treated to be ideal and every tube more or less has corrugation. The more corrugation, the more turbulence but other effects also increase for example friction.

A pipe with corrugations act like a finned heat exchanger of sorts providing more area for heat transfer. Additionally these corrugations create more turbulence resulting in an increased heat transfer coefficient compared to a smooth pipe.