흡수식 시스템의 판형열교환기에서 나노유체를 이용한 열전달 성능에 관한 해석적 연구

Abstract

흡수식 시스템의 판형열교환기에서 나노유체를 이용한 열전달 성능에 관한 해석적 연구

진 정 지 도 교 수: 조 홍 현 조선대학교 기계공학과 대학원

본 논문에서는 판형 열교환기의 다양한 쉐브론 각도 및 질량유량과 함께 나노입자의 유무에 따른 LiBr 용액의 성능을 조사하였다. 본 연구에서는 Al2O3, Cu, 및 MWCNT를 나노입자로 사용하였으며, 나노 입자의 농도는 0.05vol.%~0.24vol.%로 변화시키며 진행하였다. 결과적으로, Al2O3 나노유체 의 경우, 60o/60o 쉐브론 각도의 열교환기의 열전달율, 총괄 열전달계수, 유용도는 30o/30o 쉐브론 각도의 열교환기보다 각각 100%, 50%, 70% 정도 높게 나타났다. 동일한 조건에서 Al2O3 나노유체의 농도 변화에서는 3vol.%의 Al2O3 나노유체가 가장 높은 열전달율과 총괄 열전달계수를 나타내었다. Cu 나노유체 의 경우, 동일한 조건에서 30o/30o 쉐브론 각도의 판형열교환기에서 나노입자의 농도를 변화시켰으며, 2vol.% 농도의 Cu 나노유체에서 가장 높은 열전달율과 유용도를 나타내었다. 또한, 30o/60o 와 60o/60o 의 쉐브론 각도의 판형열교환기에서 나노유체의 농도변화는 4vol.% 의 농도에서 가장 높은 열전달율과 유용도를 나타났다. MWCNT 나노유체 의 경우, 안정성의 요인으로 체적 분율은 0.24vol.%를 초과할 수 없다. MWCNT 나노유체의 농도변화에서는 0.24vol.% MWCNT 나노유체가 가장 높은 열전달 성능을 나타내었다.|The nanofluid is a solid-liquid mixture Nanofluid technology has been rapidly developing over the last two decades. In this paper, the performance of a lithium bromide (LiBr) solution with and without nanoparticles in plate heat exchanger (PHE) for various chevron angles and mass flow rates was investigated. Some commonly used metallic and nonmetallic materials, such as Al2O3, Cu, and MWCNT, are used as nanoparticles. 1vol.%~4vol.% Al2O3 and Cu, and 0.05vol.%~0.24vol.% MWCNT nanoparticles are added to the LiBr solution to form different nanofluids. The heat transfer rate, overall heat transfer coefficient, effectiveness and specific heat capacity of chevron plate heat exchanger (PHE) with the formed binary nanofluids are investigated. As a result, it is found that with the increase of chevron angle, the heat transfer rate, overall heat transfer coefficient and effectiveness increased at different degree for any kinds of working fluid. The heat transfer rate and overall heat transfer coefficient also increased with the increase of mass flow rate for all working fluid while the variation of effectiveness of the PHE is more complicate. When different concentrations of Al2O3 nanofluids are used as working fluid, the heat transfer rate and the heat transfer coefficient in 60o/60o PHE is over 100% higher than that of 30o/30o PHE and 50% higher than that of 30o/60o PHE, and the effectiveness of the PHE in 60o/60o PHE is about 70% higher than that of 30o/30o PHE and 40% higher than that of 30o/60o PHE. By using nanoparticle in the working fluid, the heat transfer performance can increase significantly. The heat transfer rate of 3vol.% nanofluid increased about 3%~8% compare to that of LiBr solution for all chevron PHEs. Besides, the 60o/60o PHE using 3vol.% nanofluid produced the largest heat transfer rate and heat exchange effectiveness under given operating conditions. When copper is used as nanoparticle, in 30o/30o PHE, 2vol.% Cu-nanofluid is found to have the best heat transfer performance; while in 30o/60o and 60o/60o PHE, 4vol.% Cu-nanofluid is found to have the best heat transfer performance. When multi-wall carbon nantube (MWCNT) is used as nanoparticle, due to the requirement of stability, the volume fraction cannot over 0.24%. For all three kinds of PHE, 0.24vol.% MWCNT-nanofluid is found to have the best heat transfer performance.