NOVEL CONCEPT AND DEVICE OF HEAT TRANSFER AUGMENTATION
The well-known concepts of passive techniques of convective heat transfer augmentation are to increase the heat transfer area or/and the convective heat transfer coefficient by using various types of extended surfaces or inserts in terms of mixing the flow in the duct, reducing the flow boundary layer thickness, creating the secondary flow or raising the turbulence intensity. According to the analog concept between convection and conduction with heat sources, heat transfer can be enhanced through increasing the included angle between the velocity and temperature gradient vectors. Based on this novel concept of heat transfer augmentation two tube inserts composed of sparse metal filaments with high heat conductivity are specially designed. Experimental investigation shows such a device can improve heat transfer remarkably with less additional pressure drop compared with conventional heat transfer enhanced devices.