Theoretical validation of test results for the pressure drop values of circular pins with maximum length to diameter ratio of 3.0 using existing equations and test data for heat exchanger application

Abstract

Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.

Pins are a very common type of extended surface used in the field of heat transfer; their main use being in the electronics field. In this report, the use of pins as an extended surface is considered for a Heat Exchanger application in the aerospace field. The Heat Exchanger uses forced convective heat transfer mechanism for the dissipation of heat and the implicated fluid is air. For this application the pin layout and design is completely unique in that the pin’s maximum length to diameter ratio is 3.0 and the layout of the pins produces an X T value of 7, which has not been explored in any previous work. The Length: Diameter ratio of these new pins is very small when compared to the Length: Diameter ratios of tubes currently used in heat exchangers to enhance heat transfer. Moreover, the distance between the pins in this arrangement is much greater than those for the tubes. Testing has been performed on this pin design and the theoretical validation of those test results is one of the main aspects discussed in this report. Due to the innovative nature of the pin designs, there is insufficient existing test data or established equations that can be used. Assumptions are made in order to be able to apply the current equations for pressure drop calculations with valid justifications. The theoretical results for the total pressure drop show an average deviation of 6% from the test results for mass flow rates between 0.14 kg/s and 0.36 kg/s. The maximum pressure drop was found to be caused by the pins and it was in the range of 89%-91%of the total. In this article, the limitations of existing equations are discussed and the gap in the theoretical knowledge regarding novel pin designs is highlighted.