Effect of surface roughness on heat transfer in heat exchangers

FOR THESIS University of Oulu Faculty of Technology Degree Programme (Bachelor's Thesis, Master’s Thesis) Major Subject (Licentiate Thesis) Bachelor's Thesis Process Engineering Author Thesis Supervisor Geethanchali Sivanantharaja Tiina M. Pääkkönen Title of Thesis Effect of surface roughness on heat transfer in heat exchangers Major Subject Type of Thesis Submission Date Number of Pages Environmental and Chemical Engineering Bachelor’s thesis November 2017 39 Abstract The heat exchanger is a device that transfers heat from one fluid to another or between fluid and the environment. Over the last few decades, the role of heat exchangers has increased in the process of heat recovery and introduction of new energy sources. Surface roughness of heat exchanger wall plays a vital role in the efficiency of heat transfer. Therefore, significance of surface roughness is examined by many researchers applying different shapes of roughness. Roughness is the variation in the height of a surface. It could be either a part of the geometry or due to deposition of undesired materials (which decreases the thermal function of the heat exchanger, increases the pressure drop and could cause corrosion). Dimensionless heat transfer correlations such as Nusselt number provides a clear view about the effect of heat transfer by surface roughness. This thesis combines different Nusselt correlations for distinct shapes of surface roughness and investigates the suitability of them on a test experiment by comparing the values gotten. From this investigation it was clear that the value of Nunner correlation delivers the most reasonable results for a fouled layer formed by means of crystallization. Also the Nusselt correlation by Saini et al. could be more suitable for artificial surface roughness than for a fouled surface. Additional Information