| When large differences occur between the heat transfer coefficients of two different fluids in an indirect heat exchanger, fins are commonly used to increase the heat transfer area on the side with the lower heat transfer coefficient. This type of heat exchanger is commonly referred to as a finned tube exchanger with practically all of the resistance to heat transfer on the fin-side.;The efficiency of air-cooled condensers is an especially important issue in geothermal power plant applications. Due to relatively small available temperature differentials, condenser units can be very large, representing as much as 50% of the overall capital costs of these power plants. In addition, the power required to operate the fans to drive the required airflow significantly reduces the net power production of these plants. Improvements in fin-side heat transfer would have significant benefits in both reducing capital and operating costs by reducing the size of the condenser units and the fan power required.;The goal of the research undertaken in this dissertation is to develop methods to improve fin-side heat transfer with a minimal increase in pressure drop in air-cooled condensers. A numerical investigation has been undertaken, validated by experimental data, to develop methodologies to improve the efficiency of geothermal air-cooled condensers in particular, with broad applicability to finned tube heat exchangers in general. Specifically, this dissertation investigates the use of oval tubes in combination with winglet vortex generators (WVGs). The use of oval tubes and winglet generators in combination show the promise of being able to enhance heat transfer while reducing pumping power required. This dissertation performs a systematic analysis to determine the optimal configuration of vortex generators and oval tubes to maximize heat transfer at the lowest pressure drop in a fin-tube air-cooled condenser for geothermal power plant applications. Single oval tube WVG configurations were investigated to determine the most promising configurations based on heat transfer enhancement and pressure drop. Building off this work, inline and staggered oval tube bank arrangements were analyzed numerically to determine promising configurations. |
