Application of nano-structured coatings to the heat transfer surface of heat exchangers

Traditionally, the attempts to improve the heat exchangers performances focused on the increasing of heat transfer surface according to the need to keep overall dimensions and pressure drops restrained and heat transfer efficiency high. Now that the relationship between surface width, geometrical efficiency and dimensions is reaching its maximum limits, the attention begins to move on the increase of the heat transfer coefficient. Under this condition, the proposal of the usage of nano-structured coatings is to induce the property of super-hydrophobicity to the surfaces in contact with the fluids involved in the heat transfer. This property is able to produce an increasing of the heat transfer coefficient and a decrease of power losses caused by friction. The technology developed is based on the principle which in nature is known as "Lotus effect" to obtain a super-hydrophobic surface. Moreover, modifying a phase in the production process is possible to produce a hydrophilic behavior, depending on the customer's needs. The application of this technology to real products with measurable targets will open the doors to an entire new generation of products to be applied in fluid power systems of mobile machinery where the efficiency and dimensions constraints are in many cases critical. The paper is aimed to determine the thermal and fluid-dynamic performances of heat exchangers with super-hydrophobic surfaces. A comparison between the nano-coated heat exchanger and the "traditional" one will be shown in order to evaluate the given improvement in terms of: heat transfer coefficient, pressure drop reduction, industrial feasibility. The solution proposed by the authors is patent pending. KEYWORDS: