ENHANCEMENT OF HEAT TRANSFER DURING FILM CONDENSATION OF R32 VAPOUR OVER SINGLE HORIZONTAL INTEGRAL-FIN TUBES

Abstract

The demand for energy conservation and environmental issues have become a critical global concern, which mandates deep investigation and improvement in engineering and technology appliances. Global energy consumption has grown in a century from the 1900s with only 1 TWh to an energy consumption of 17 TWh in 2011. As the world population grows faster, energy consumption has climbed by approximately 4-6 TWh. It is also expected to rise in the same trend in the upcoming years. Various researchers have tried to bring about new technologies that comply with energy conservation and environmentally friendly technologies to combat these issues. The improvement of heat transfer devices, such as shell and tube condensers, makes a substantial contribution to energy conservation, system performance efficiencies, and device compactness. A chiller unit is one of the devices found as a central component in air-conditioning systems, marine propulsion, process industries, and oil refineries. A shell-and-tube heat exchanger is a chiller unit employed for extracting heat energy from the vapor form of fluid, through which the vapor changes its phase into liquid form. Researchers have been developing different external surface structures to achieve augmented values of the coefficient of condensation heat transfer, such as two-dimensional and three-dimensional integral finned tubes, dimpled surfaces, petal-shaped fins, and serrated surfaces. In fact, unless optimal retrofit design considerations are taken on the augmented surface, structured tubes increase the pressure drop, which would cost extra pumping power and reduce the overall performance of the chiller unit. The advancements in manufacturing technology can help with the flexible development of three-dimensional fin profiles from the optimum two-dimensional finned tubes. However, condenser tubes with various three-dimensional surfaces, which exhibit superior enhancement factors in single condenser tests, have a stronger bundle effect in the full set condenser than the common two-dimensional integrally finned tubes. The continuous fins of integral fin tubes may operate as dams to avoid the axial diffusion of film condensate, which would explain the favorable row effect. Although increasing the active surface area for condensation heat transfer is the primary goal of low-finned integrated fin tubes, determining the ideal fin spacing for a particular refrigerant becomes crucial. Since the surface tension effect increases, the condensation heat transfer coefficient decreases as the fin spacing decreases. During film condensation over the outer surface,