This paper presents a numerical simulation of laminar heat transfer in circular tube flows with internal longitudinal fins using finite difference numerical code. Three types of fin models with three different half-included angles have been considered. Two types of fluids (coolants), namely, water and engine oil have been considered. Aluminium is considered the tube/fin material. The variation of thermal conductivity of the tube materials, fluids and viscosity of the fluids with temperature is taken into account in the solution procedure. The outer surface of the tube is exposed to constant heat flux. Steady, laminar flow and heat transfer are assumed. It is ensured that fluids used in this study have a Reynolds number equal to 1500. It is assumed that the flow of the fluid is completely developed locally, but undeveloped while considering the thermal conditions. For the purpose of discretization of the governing equations, the finite difference scheme is adopted. Each fluid has its own momentum equation and energy equation. Both these equations of the fluid as well as the energy equation of the tube wall are solved repeatedly and simultaneously.

In many engineering sectors, circular tubes are commonly used for heat transfer. Maximum heat transfer-minimum weight thermal dissipator systems are imperative in new applications such as electronic systems, compact heat exchangers and also in the well-known automotive and aerospace industries. The main aim of this paper is to present a numerical simulation of laminar heat transfer. It is carried out on circular tubes, which are all identical with a tapered lateral profile and have four internal longitudinal fins.

Schmidt (1926) suggested the adoption of a parabolic shape as an optimal profile for longitudinal fins. Such a profile was supported by Duffin (1959), on the basis of a rigorous variational model. Bejan and Morega (1993) reported an optimal geometry of an array of fins that minimizes the thermal resistance. The finite difference results of Yuwan and Faghri (1996) show that adding an internal fin is an effective way of enhancing heat transfer in the thermal energy storage system when a fluid with low thermal conductivity is used. Olson (1992) has measured heat transfer and pressure drop of three thin, compact heat exchangers in helium gas at 3.5 MPa with Reynolds number ranging from 450 to 36,000. Each of the three heat exchangers has a different flow geometry. One is of the circular type, the second is of rectangular channel type and the third is of the staggered pin fin type with tapered fins. Once the measurements are made in them, it is clear that the heat exchanger that had the pin fin internal geometry possessed a significantly better rate of heat transfer while compared to that of the others. But at the same time, it should be noted that it has a higher pressure drop too.

Fiebig et al. (1995) studied the influence of Reynolds number, ratio of fin to fluid conductivity and ratio of fin thickness to pitch on the heat transfer behavior. Jiin and Li (1997) have presented a numerical analysis of heat transfer and fluid flow in a three dimensional wavy fin and tube heat exchanger. Moa and Shou (1995) have reported results of saturated flow boiling of R-114, R-12 and R-134a in water-heated horizontal heat exchangers with integral finned tube. The heat transfer enhancement for R-22 is higher than those of R-114 and R-1343a.

Mechanical Engineering Journal, Fin Geometry, Numerical Methods, Engineering Sectors, Electronic Systems, Genetic Algorithms, Algebraic Equations, Thermal Resistance, Longitudinal Fins, Nusselt Number, Reynolds Number.