Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/ijhydene Nozzle injection displacement mixing in a zero boil-off hydrogen storage tank Son H. Ho, Muhammad M. Rahman à Department of Mechanical Engineering, University of South Florida, 4202 E. Fowler Avenue, Tampa FL 33620, USA article info Article history: Received 10 May 2007 Received in revised form 17 October 2007 Accepted 18 October 2007 Available online 11 December 2007 Keywords: Liquid hydrogen Cryogenic storage Forced convection Heat transfer abstract This paper presents a steady-state analysis of fluid flow and heat transfer in a zero boil-off cryogenic liquid hydrogen storage tank in microgravity environment. The storage tank is equipped with an assembly of an inlet tube and a nozzle head that contains many nozzles on its front face. Liquid hydrogen is cooled by an external cryocooler, flows along the nozzle head assembly, penetrates into the bulk liquid through the nozzles in order to prevent the boiling off due to heat leak from the surroundings through the tank wall insulation, exits the tank through an annular outlet opening coaxial with the inlet, and then goes back to the external cooling system. Eleven cases for different geometry settings were analyzed. Typical distributions of velocity and temperature are presented. The results show that thermal performance of the system can be improved by increasing the inlet diameter and properly selecting the depth and the span of the nozzle head. & 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. 1. Introduction Hydrogen has been recognized as a powerful and clean fuel for a few decades for space applications [1], and recently for general transportation such as automotives [2]. Hydrogen has been identified to play an important role as an energy source in the future. It has the highest energy content per unit mass of any known fuel. When burned in an engine, hydrogen produces effectively zero emission. When powering a fuel cell, its only waste is water. Hydrogen can be produced from abundant domestic resources including natural gas, coal, biomass, and even water. However, significant technological challenges exist towards reducing its cost and storage volume and assuring its safety. Although hydrogen has many advantages over most conventional fuels, efficient storage of hydrogen is difficult because of its very low density [3]. Cryogenic storage techniques for liquid hydrogen as well as other liquefied gases are of widely increasing interest. Liquid storage of hydrogen has significant advantage over gaseous or chemical storage because of much lower storage volume and ease of regeneration of the fuel with its demand. Since hydrogen has a very low boiling point (20 K at atmospheric pressure, about 1 bar or 0.1MPa), liquid hydrogen’s most challenging aspect in conventional cryogenic storage is the losses due to boil-off under the effect of the heat leakage through the insulation layers of the tank from the surround- ing environment. Due to evaporation during boiling-off, vapor pressure increases significantly. In order to control the internal pressure within structural limits of the storage tank, the stored fluid needs to be bled off periodically. The zero boil- off (ZBO) concept has evolved as an innovative means of storage tank pressure control by a synergistic application of passive insulation, active heat removal, and forced mixing within the tank. A cryocooler (with power supply, radiator, and controls) is integrated into a traditional cryogenic storage subsystem to reject the storage system heat leak. Therefore, the hydrogen fuel can be stored for a very long time without any loss. ARTICLE IN PRESS 0360-3199/$ - see front matter & 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2007.10.042 à Corresponding author. Tel.: +1 813 974 5625; fax: +1 813 974 3539. E-mail address: rahman@eng.usf.edu (M.M. Rahman). INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 33 (2008) 878– 888