Pengujian Karakteristik Aliran Fasa Tunggal Aliran Air Vertikal Ke Atas Pada Penukar Kalor Saluran Rectangular Bercelah Sempit

Abstract

Abstract : This research was conducted to investigate the flow characteristics of single phase vertical upward water flow with/without heat exchange in narrow gap rectangular channel heat exchanger. Test section was a concentric tube heat exchanger. The inner tube was made of aluminium with inner side and outer side lengths of 17. 4 mm and 18.4 mm. The outer tube was made of aluminium with inner side and outer side lengths of 23.68 mm and 24.68 mm. The pressure measuring length was 1,200 mm. Hydraulic diameter of the narrow rectangular channel was 5.28 mm. Flows in the inner tube and in annulus were in opposite directions. Working fluid used in this research was water. For the flow with heat exchange, the water temperature at the inlet of inner tube was maintained at 60 oC. In the research, the mass flow rate and pressure drop across narrow annulus were measured at steady states. Results of the research were compared with predictions from conventional flow theory. Results of the research shown that the flow characteristics of water through the narrow annulus were different from those in conventional pipes. For the flow without heat exchange in narrow annulus, the flow transition from laminar to turbulent flow was initiated earlier than that in normal pipes at a Reynolds number range from 1,850 to 2,333. The flow transition with heat exchange occurred for a Reynolds number in the range of 1,657 to 2,245. Flow friction factor of the downward flow with heat exchange was larger than that without heat exchange at the Reynolds number was lower than 734. The flow friction characteristics in narrow annulus had relations to the liquid temperature difference at the inlet and outlet of the annulus. Their influences on the flow friction were concentrated in the laminar flow area.

Keywords : Narrow rectangular channel, Reynolds number, Friction factor