Characteristics of novel polymer composite heat transfer tubes

Abstract

Papers presented to the 11th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 20-23 July 2015.

Heat transfer tubes are one of the basic components in many equipment widely used in chemical, pharmaceutical, petroleum, petrochemicals, power generation and air conditioning systems. These tubes are manufactured from a wide variety of high thermally conductive metals. Examples of such materials are: nickel alloys, copper, aluminium, stainless steels like austenitic, duplex and super duplex as well as super alloys and titanium. Metallic tubes may suffer from failure due to corrosion and erosion especially in aggressive environments. In addition, metallic tubes are characterized by high density and high costs. This is the motivation for the development of non-metallic materials for heat exchanger applications. Plastics are attractive materials for the construction of heat exchangers, especially in harsh environments. However, plastics have one essential negative character; low thermal conductivity. There are two different approaches to overcome these drawbacks. On the one hand the use of small tube/channel diameter and extraordinary small wall thickness can reduce the thermal resistance. On the other hand the more promising solution is to improve the thermal conductivity by filling plastics with very high thermally conductive materials. This paper provides an overview of different plastic materials suitable for use in heat transfer applications. Also, it summarizes the properties of different possible filling materials. The thermal conductivity of these composite materials strongly depends on the size, shape, mass fraction and orientation of the particles. The possibilities to control the particle orientation of filling materials within the wall of a plastic tube will be shown. The effect of filling material orientation on thermal conductivity of tubes in axial and orthogonal direction and the influence of the wall thickness are illustrated. The paper compares the properties of developed tubes with customary used heat transfer tubes. Properties compared in this paper include fouling and corrosion resistance, thermal and mechanical properties, erosion resistance and temperature limitations. The novel polymer composite heat exchanger tubes combine a high thermal conductivity, low density, excellent resistance against ionic corrosion with an outstanding resistance against abrasion and erosion.