Comparing single-phase thermal hydraulic performance of a right and left turn twisted tape insert in a tube

Single-phase heat transfer and pressure drop tests were conducted in a tube with two types of twisted tapes. Each tape had exactly similar physical parameters and were made of the same material except that each had an opposite twist that resulted in a clockwise and anticlockwise flow swirl, i.e., left turn and right turn, respectively. Each type had twist ratio of 4 and 5.5 on a 180° twist. The tapes were tested in a tube-in-tube heat exchanger having 2 m length. The internal tube of the heat exchanger had 19.05 mm outer diameter and 1.65 mm wall thickness. Fresh water and 30% water/glycol solution were used as cold and hot fluids. Experiments were performed with Reynolds number varying between 2500 and 11,500 at Prandtl numbers of 9 and 14. Heat transfer and pressure drop enhancement was observed compared to plain tube at all operating conditions with 6–7% higher thermal performance with tighter twist tape. The Left Turn tape with a twist ratio of 5.5 showed slightly better thermal performance beyond Re > 8000 and with a twist ratio of 4 beyond Re > 4000. Similar trends were observed for the pressure drop. This is the first time a study on the subject was initiated assuming that the earth’s rotational effect “could” play a role in the flow swirl pattern inside a conduit. It is recommended to carry out intensive work on the subject with different tape twist ratios, fluids and more importantly larger conduits. The information generated could be of interest to the Concentrated Solar Power industry that uses high-temperature thermal oils. Any improvement in performance could result in lowering the operational cost, and therefore suitable type of twisted tapes could be used for upper and lower hemispheres.