**Thesis Type:** Doctorate

**Institution Of The Thesis:** Gazi Üniversitesi, Fen Bilimleri Enstitüsü, Turkey

**Approval Date:** 2018

**Student:** DUYGU İPCİ

**Supervisor: **HALİT KARABULUT

In this study, the flow and heat transfer characteristics of the radiator air ducts with isosceles triangular, sinusoidal and parabolic cross sections are investigated by using a new numerical solution method for temperature and flow field equations. The flow and heat transfer in air ducts are modeled for both the fully developed and developing flows. For both situations, the flow was assumed to be incompressible and laminar. In the entrance region, the velocity and temperature boundary layers are assumed to be simultaneously developing. The flow field in the entrance regions of the ducts are modeled with three dimensional momentum equations and a Poisson type pressure field equation obtained from the combination of the continuity and momentum equations. Due to that the sinusoidal, parabolic and isosceles triangles are non-regular solution domains of the governing equations of the flow and heat transfer fields, some difficulties are confronted. To eliminate these difficulties, the cross-sectional areas of ducts were transformed into square-shaped solution domains by using appropriate transformations. Velocity components and fluid temperature involved by governing equations are converted to dimensionless quantities by means of using appropriate transformations as well. Governing equations are solved numerically via Newton-Raphson method after being converted to the finite difference form. The heat transfer in the fully developed flow zone are investigated for two different thermal wall conditions as constant heat flux (H1) and constant wall temperature (T). Nusselt and Poiseuille numbers are calculated for various height /width ratios of the ducts. The results are compared with the literature data and found to be consistent. The maximum deviation is determined to be less than 3 %. In the analysis of entrance flow heat transfer, the condition of constant wall temperature is implemented. Axial distributions of Nusselt numbers are determined corresponding to 250, 500, 750, 1000 and 1200 values of Reynolds numbers. The axial distribution of the Nusselt number of a triangular duct with constant wall temperature is calculated for 1,0 of height/width ratio via ANSYS Fluent software and compared with the results of the developed method in the thesis. Result were found to be very compatible with each other.