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최훈기(Hoon-Ki Choi),임윤승(Yun-Seung Lim) 한국기계가공학회 2021 한국기계가공학회지 Vol.20 No.6
We compared the heat transfer characteristics of the parallel and the counterflow flow in the concentric double tube of the Al₂O₃/water nanofluids using numerical methods. The high- and low-temperature fluids flow through the inner circular tube and the annular tube, respectively. The heat transfer characteristics according to the flow direction were compared by changing the volume flow rate and the volume concentration of the nanoparticles. The results showed that the heat transfer rate and overall heat transfer coefficient improved compared to those of basic fluid with increasing the volume and flow rate of nanoparticles. When the inflow rate was small, the heat transfer performance of the counterflow was about 22% better than the parallel flow. As the inflow rate was increased, the parallel flow and the counterflow had similar heat transfer rates. In addition, the effectiveness of the counterflow increased from 10% to 22% rather than the parallel flow. However, we verified that the increment in the friction factor of the counterflow is not large compared to the increment in the heat transfer rate.
보텍스튜브 유동의 에너지분리 및 열역학특성에 관한 수치적 연구
최훈기(H.K. Choi),유근종(G.J. Yoo),임윤승(Y.S. Lim) 한국전산유체공학회 2018 한국전산유체공학회지 Vol.23 No.2
A vortex tube is a simple energy separating device which splits a compressed air stream into a cold and hot stream without any external energy supply or chemical reactions. In this article computational fluid dynamics analysis of a 3-D steady state and turbulent flow has been carried out through a vortex tube. The present research has focused on the energy separation and thermodynamic behavior of a vortex tube have been investigated. The temperature separation occurs because of the heat transfer from the central flow to the peripheral flow. Through the interpretation of the second law of thermodynamics, the generation of entropy shows that irreversible processes occur in the vortex tube.