G3 Heat Transfer in Helically Coiled Tubes

1 Introduction

Centrifugal forces in a fluid flowing through a curved pipe cause secondary flows circulating outward into the core region of the pipe to form a pair of symmetric vortices. The combination of both the main and the secondary flows creates a flow pattern in which the maximum velocity is shifted outward from the center of the tube. The secondary flow produces a transverse transport of the fluid over the cross section of the pipe. This additional convective transport improves heat transfer between the fluid and the wall of the pipe but increases the pressure drop when compared to that in a straight tube. The differences are particularly apparent in laminar flows.

2 Determination of the Average Diameter of Curvature

The intensity of the secondary flow depends on the relative curvature (d/D) of the coil, where d is the inner diameter of the tube and D the diameter of the curvature. The average diameter of a spiral with n turns and a pitch h formed from a tube of the length l...