Transactions of the Korean Society of Mechanical Engineers B (대한기계학회논문집B)

The Korean Society of Mechanical Engineers (대한기계학회)
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Numerical Investigation of Urea Freezing and Melting Characteristics Using Coolant Heater

냉각수 순환 가열 방식을 이용한 요소수의 동결 및 해동 특성에 관한 수치적 연구

  • Lee, Seung Yeop (Dept. of Aerospace Engineering, Chounbuk Nat'l Univ.) ;
  • Kim, Nam Il (Dept. of Aerospace Engineering, Chounbuk Nat'l Univ.) ;
  • Park, Yun Beom (Dept. of Automotive Engineering, Jeju College of Technology) ;
  • Kim, Man Young (Dept. of Aerospace Engineering, Chounbuk Nat'l Univ.)
  • 이승엽 (전북대학교 항공우주공학과) ;
  • 김남일 (전북대학교 항공우주공학과) ;
  • 박윤범 (제주산업정보대학 자동차과) ;
  • 김만영 (전북대학교 항공우주공학과)
  • Received : 2012.06.12
  • Accepted : 2013.07.05
  • Published : 2013.08.01
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Abstract

Urea-SCR technology is known as one of the powerful NOx reduction systems for vehicles as well as stationary applications. For its consistent and reliable operation in vehicle applications, however, the freezing and melting of the urea solution in cold environments have to be resolved. In this study, therefore, a numerical study of three-dimensional unsteady problems was analyzed to understand the urea freezing and heating phenomena and heat transfer characteristics in terms of urea liquid volume fraction, temperature profiles, and phase change behavior in urea solutions with time by using the commercial software Fluent 6.3. As a result, it was found that the freezing phenomenon proceeds with a phase change from the tank wall to the center, whereas the melting phenomenon occurs faster in the upper part of the storage tank by natural convection and in the adjacent part of the coolant pipe than in other parts. Furthermore, approximately 190 s were required to obtain 1L of urea solution using a 4-coiled coolant heater under conditions of $70^{\circ}C$ and 200 L/h.

Urea-SCR은 동절기, 북유럽과 북미지역과 같은 $-20^{\circ}C$ 이하의 환경에서 요소수가 동결되는 문제점을 해결해야 한다. 따라서 이러한 요소수 저장탱크에 해동 시스템을 적용하여 시동 초기, 요소수를 적정 시간 내 분사하기 위한 기술의 확보가 필요하다. 본 연구에서는 저장탱크 내 요소수의 동결현상과 냉각수 순환 가열방식을 적용한 해동현상에 대하여 상용 소프트웨어인 Fluent 6.3을 이용하여 3차원 비정상상태 수치해석을 수행하였다. 이를 통하여 요소수의 동결 및 해동과정 중 나타난 온도분포, 상경계면, 그리고 액상분율을 분석하여 열전달 특성을 고찰하였다. 결론적으로 요소수의 동결은 저장탱크 벽면으로부터 중심부로 이루어졌으며, 해동현상은 순환 파이프와 인접할수록 요소수의 상변화가 빠르게 진행하였다. 또한, 냉각수의 $70^{\circ}C$, $200{\ell}/h$ 조건에서 $1{\ell}$의 액상 요소수를 얻는데 약 190초의 시간이 필요하였다.

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