Experimental investigations on the effect of geometrical properties of helical wire turbulators on thermal performance of a helically coiled tube

Abstract

As like to straight tubes, experts try to use heat transfer enhancement techniques to improve the thermal performance of helical tubes. Present study provides an experimental investigation on the effect of geometrical properties of spiral wire turbulator on thermal performance of helical tube. Spiral wire is the only kind of turbulator which can be easily inserted into helical tubes. The quality and quantity of helical wire turbulator inside helical tubes are different with strait tubes, due to the presence of centrifugal forces. Besides variation of geometrical properties of spiral wires (including spring pitch, wire diameter and spring diameter) can significantly influence on thermal behavior of helical tubes. In this study spiral wire with different geometrical properties (four different spring pitch and four different wire diameter) is employed and the thermal behavior of helical heat exchanger is experimentally investigated. The helical tube containing spiral wire was put under constant heat flux supplied by means of an electrical heater. In order to calculate the convective heat transfer coefficient, the inlet, outlet and wall temperature of helical tube was measured. The results revealed that variation of the pitch and wire diameter have significant effect on thermal performance of helical heat exchanger. Increment in spring pitch and wire diameter of spiral tube caused increment in Nu (Nusselt) number up to 73% and 70% respectively. Also it was revealed that increment in wire diameter increases the heat transfer coefficient whereas the effect of increment of spring pitch on heat transfer coefficient is vice versa and the increment of spring pitch decrease the heat transfer coefficient.