Contents lists available at ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng Porous shroud tube design evaluation of a control plug in a liquid metal cooled reactor Ankit Kumar Gautam, Sunil Kumar, Pradipta Kumar Panigrahi ⁎ Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, India HIGHLIGHTS • Lower free surface turbulence at higher free surface height of shroud tube. • Amplification of hump instability due to eccentricity of control rod. • Gas entrainment initiation at low Froude number for small shroud tube pore size. • Lower radial velocity through pores for higher shroud tube thickness. ARTICLE INFO Keywords: Shroud tube Control plug Porosity Gas entrainment Shadowgraph visualization Free surface ABSTRACT Shroud tube is a porous protective covering over the Control Safety Rod Driving Mechanism assembly vertically submerged just below the free-surface of liquid sodium coolant pool of a Fast Breeder Reactor. Pore size and its arrangement over the shroud tube are important design parameters, which influence the gas entrainment and flow induced vibration inside the liquid coolant pool leading to several reactor operation related risks. The present study focuses on performance evaluation of three shroud tube designs of same porosity but with different pore diameter, thickness of shroud tube and arrangement of pores (staggered and uniform). A parametric in- vestigation with respect to parameters viz. Froude number, free-surface height, and the eccentricity of the control rod has been carried out using white light imaging and high speed laser based Shadowgraphy. The present study effectively demonstrates the complexity in design of porous shroud tube and the role played by several design parameters. The radial flow from the pores and its interaction with the downward flow due to hump motion influence the air-water interface dynamics which influences the gas entrainment process. The flow induced fluctuation of the hump increases with increase in eccentricity of the control rod. 1. Introduction Porous tubes are used to achieve required flow distribution in sev- eral engineering applications, such as distribution manifolds of heat- exchangers, ventilation ducts, micro-fluidics devices, control plug as- sembly of nuclear reactors, and catheter tubes in medical applications. For majority of applications, degree of flow distribution uniformity is the most important criteria for evaluating performance of a porous tube. The uniformity of flow effusing through the pores is affected by several geometrical parameters, such as tube geometry, pore diameter, pore geometry (rectangular, square, round, etc.), pitch between con- secutive pores, and porosity of the porous tube (which is defined as ratio of total cross-sectional area of pores to curved surface area of tube without pores). The important design consideration for high perfor- mance porous tubes is geometry of pores and their arrangement on the surface of tubes. Chen and Sparrow [1] studied the effect of pore geometry on the uniformity of mass-flow-rate discharge from the manifold for three different outlet geometry: (a) an array of discrete slots, (b) an array of discrete circular pores, and (c) a single, continuous longitudinal slot. Among three geometries, they observed near uniform outflow from the tube with continuous slot case. Subsequently, computational in- vestigation by Yang et al. [2] observed worsening of flow uniformity with the increase in aspect ratio of the rectangular exit-ports on flow distribution manifolds. Lee et al. [3] studied flow distribution in hor- izontal multi-perforated square tubes with different thickness and with a varied number of rectangular orifices of same dimension installed on both sides of square tubes. They observed more uniform flow dis- tribution with increase in the number of pores and thickness of the tube. Foust and Rockwell [4] reported flow structures of jets emanating from https://doi.org/10.1016/j.applthermaleng.2018.04.121 Received 3 February 2018; Received in revised form 25 April 2018; Accepted 26 April 2018 ⁎ Corresponding author. E-mail address: panig@iitk.ac.in (P.K. Panigrahi). Applied Thermal Engineering 139 (2018) 264–282 Available online 27 April 2018 1359-4311/ © 2018 Elsevier Ltd. All rights reserved. T