Twisted Tape가 설치된 사각 덕트에서 스월유동 및 코너효과가 미치는 열전달 성능

Heat Transfer Performance of Swirl Flow and Corner Effect Generated by Twisted Tape in a Square Duct

This paper presents numerical and experimental predictions of characteristics of turbulent flow, heat transfer and friction factors in a square sectioned duct (30 × 30mm) with twisted tape inserts and with twisted tape inserts plus rib tubulators. Turbulent swirl flows having Reynolds numbers ranging from 8,900 to 29,000, a rib height-to-channel hydraulic diameter (e/D_h) of 0.067, and a length-to hydraulic diameter (L/D_h) of 30, are considered. The rib tubulators are arranged to follow the trace of the twisted tape and along the flow direction. The twisted tape is 0.1mm thick carbon steel sheet with diameter of 28mm, length of 900mm, and 2.5 turns. Each wall is composed of isolated aluminum sections. Two heating conditions are applied for four side walls and two opposite walls. The correlation for friction factor and Nusselt number are derived from the predicted data. The results show that uneven surface heating enhances the heat transfer coefficient over uniform heating condition, and significant improvements can be achieved with twisted tape inserts plus interrupted ribs.