Investigation of outside flow characteristics in elliptic tube evaporators

The main purpose of the thesis is to compare circular cross section cylinder and elliptic cross section cylinder with different diameter ratios in terms of thermo-hydraulic performance. As a result of the studies carried out in this scope, it is planned to propose its use in an evaporator application by determining the elliptical diameter ratio or ratios where better results are obtained in terms of thermo-hydraulic performance compared to circular cross section cylinders. Firstly, it is numerically investigated the flow structure around a circular cross section cylinder and cylinders with different elliptical diameter ratios. As a result of analyses, the most suitable elliptical diameter ratio was determined as b/a=0.307 in terms of hydrodynamic. PIV experiments were performed for aforementioned elliptical cylinder with b/a=0.307 diameter ratio and circular cylinders having three different diameters. Then, for multiple and staggered arrangements of the circular cylinder and elliptic cylinder with a diameter ratio of b/a=0.307, the physical events occurring in the flow volume between the two fins were compared by conducting PIV and HAD studies. In the last part of this study, heat transfer analyses were performed by HAD, assuming the operating conditions in the cooling application of a heat exchanger for multiple and staggered arrays of circular cylinder and elliptical cylinders with b/a=0.666, 0.5, 0.4, 0.333, 0.307 and 0.25 diameter ratios. As a result of analyses, highest values of dimensionless Colburn factor, which is an indicator of heat transfer, were obtained for circular tube with b/a=1.0 ratio. In the elliptical tube design, it was determined that there was less pressure drop compared to the circular tube. According to j/f1/3 values which are evaluated as thermo-hydraulic performance enhancement criteria; when elliptic diameter ratio with b/a=0.307 were compared with circular cylinder results, an improvement between 40-45% was determined in the range of ReH=750-2850.