Turbulent Heat Transfer Enhancement by a Row of Twisted Plates

Abstract

A new heat transfer promoter is devised. It is composed of a row of thin plates twisted by 90° alternately in different directions. The heat transfer coefficient and pressure loss are measured in an air flow through a circular tube around which the promoter is set. Six types of promoters are examined. The heat transfer coefficients are found to increase. This result is explained by two enhancement mechanisms, namely some swirl motions and raised turbulence intensity. As the flow proceeds along the twisted plates, many axial vortices are produced and a flow-separation occurs at the lateral edge of the plates. The heat transfer performance is evaluated in terms of the area goodness factor and increase of the Nusselt number under the same pumping power.