ACTS- P00510 NUMERICAL STUDY ON HEAT TRANSFER CHARACTERISTICS OF SLUSH NITROGEN IN A HORIZONTAL PIPE Y. J. Li , S. Q. Wu, T. Jin* Institute of Refrigeration and Cryogenics / Key Laboratory of Refrigeration and Cryogenic Technology of Zhejiang Province, Zhejiang University, Hangzhou 310027, China Presenting Author: [email protected]* Corresponding author: [email protected]ABSTRACT Slush nitrogen is considered as a potential coolant for high-temperature superconductors with decreased nitrogen consumption and storage cost, thanks to its lower temperature, higher density and higher heat capacity than those of liquid nitrogen. The heat transfer characteristics are key factors for application of slush nitrogen as cooling fluid. In the present study, a three-dimensional Euler-Euler two-fluid numerical model based on the PBM (population balance model) has been built to predict the heat transfer characteristics of slush nitrogen in a horizontal pipe. The PBM was ever used to predict the evolution of the particle size distribution for breakage due to the particle-particle interactions and effects between particles and wall in the pipe. Meanwhile, an effective viscosity of mixture which takes the particle shape and size into consideration is introduced into the model and adopted for the drag law and the mass and heat transfer, since the slush nitrogen usually has non-spherical and coarse particles with an average size of 0.5 mm - 2 mm. The improved model is then used to predict the particle size distribution and to analyze the effects of inlet velocity, solid concentration and heat flux on the heat transfer characteristics to discuss the heat transfer deterioration. KEYWORDS: slush nitrogen, multiphase flow, heat transfer, population balance model 1. INTRODUCTION Slush nitrogen is the cryogenic suspension of solid nitrogen particles and subcooled liquid nitrogen and has been considered as a potential coolant for high-temperature superconductors with decreased nitrogen consumption and storage cost, thanks to its lower temperature, higher density and higher heat capacity than those of liquid nitrogen[1]. The flow and heat transfer characteristics are key factors for application of slush nitrogen as cooling fluid. Earlier studies on slush nitrogen focus on the production, measurement and transfer characteristics[2-4]. Pressure drop reduction and heat transfer deterioration phenomena (i.e. pressure drop for subcooled liquid nitrogen is greater than that of slush nitrogen and heat transfer coefficient for slush nitrogen is smaller than that of liquid nitrogen) has been found in the experimental study on slush nitrogen flow in a horizontal pipe[3]. Previous CFD (Computational Fluid Dynamics) models are mainly applicable to the ambient slurry flow like sand-water suspension and oil slurry and the solid phase is usually treated as even particles with constant size[5-10]. However, the model for cryogenic slurries should also consider the interphase mass and heat transfer. Also, the effects of particle size distribution should be concerned. QMOM (the quadrature method of moments), one of the solution 1 Proceedings of the Asian Conference on Thermal Sciences 2017, 1st ACTS March 26-30, 2017, Jeju Island, Korea
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ACTS- P00510
NUMERICAL STUDY ON HEAT TRANSFER CHARACTERISTICS OF
SLUSH NITROGEN IN A HORIZONTAL PIPE
Y. J. Li, S. Q. Wu, T. Jin*
Institute of Refrigeration and Cryogenics / Key Laboratory of Refrigeration and Cryogenic
Technology of Zhejiang Province, Zhejiang University, Hangzhou 310027, China