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Abstract
Sodium-to-air heat exchangers (AHX) are used in fast breeder reactors for removal of decay heat generated in the core after a reactor shutdown. The AHX is an important component of the safety-grade decay heat removal system in a fast reactor. Decay heat removal critically depends on the performance of the AHX, which is essentially a cross-flow heat exchanger with liquid sodium flowing on the tube side and air flowing across finned tubes in the cross-flow mode. In this paper, a three-dimensional numerical study is carried out to investigate the flow and heat transfer characteristics when air flows over a representative bank of finned tubes in an AHX. The computational model has been validated against published experimental benchmarks. Based on parametric studies, appropriate correlations for the Nusselt number and fin effectiveness are derived. A computationally efficient porous body model is then developed and an integrated thermal hydraulics study of AHX is carried out using the derived heat transfer correlation. The numerical predictions of the porous body model are compared with the results of an experimental AHX tested at the Indira Gandhi Centre for Atomic Research; Kalpakkam, India. A good agreement between the results is seen.
NOMENCLATURE
| Af | = | fin surface area of fin (m2) |
| Ai | = | tube inside surface area of fin (m2) |
| A0 | = | effective area for heat transfer (m2) |
| At | = | outside surface area of tube except fin (m2) |
| C1 ∈, C2 ∈, Cμ | = | turbulence model constants |
| Cpa | = | specific heat of air (J/kg-K) |
| C2 | = | inertial resistance factor |
| d | = | tube diameter (m) |
| Df | = | fin outside diameter (m) |
| Gκ | = | turbulent energy production rate (m2 s−3) |
| G | = | volumetric flow rate (m3/s) |
| h | = | average heat transfer coefficient (W m−2 K−1) |
| hi | = | average heat transfer coefficient of sodium (W m−2 K−1) |
| hf | = | fin height (m) |
| k | = | turbulent kinetic energy (m2 s−2) |
| ma | = | mass flow rate of air (kg/s) |
| mNa | = | mass flow rate of sodium (kg/s) |
| Nu | = | Nusselt number |
| P | = | Pressure (Pa) |
| Pe | = | Peclet number |
| Q | = | net heat transfer (W) |
| = | Reynolds number based on the minimum cross-sectional area | |
| sl | = | longitudinal tube pitch (m) |
| Shf | = | fluid heat source (W/m3) |
| S | = | tube length along header (m) |
| T | = | temperature (K) |
| tf | = | fin thickness (m) |
| U | = | overall heat transfer coefficient (W m−2 K−1) |
| u, v, w | = | velocities (m s−1) in x, y, and z directions |
Greek Symbols
| αk | = | inverse effective Prandtl number for k |
| αϵ | = | inverse effective Prandtl number for ϵ |
| γ | = | porosity |
| ΔP | = | pressure drop (Pa) |
| ϵ | = | turbulent energy dissipation rate (m2 s−3) |
| ηf | = | fin efficiency |
| κb | = | thermal conductivity of base material, (W m−1 K−1) |
| κf | = | thermal conductivity of fin material (W m−1 K−1) |
| κss | = | thermal conductivity of stainless steel (W m−1 K−1) |
| κt | = | turbulent thermal conductivity of solid (W m−1 K−1) |
| κa | = | thermal conductivity of air, (W m−1 K−1) |
| = | thermal conductivity of sodium, (W m−1 K−1) | |
| = | effective thermal conductivity | |
| μ | = | viscosity (kg m−1 s−1) |
| ξ | = | fin effectiveness |
| ρ | = | density (kgm−3) |
| ω | = | permeability (m2) |
Subscripts
| a | = | air |
| b | = | base material |
| eff | = | effective |
| f | = | fin |
| in | = | inlet |
| i | = | inside |
| Na | = | sodium |
| o | = | outside |
| out | = | outlet |
| ss | = | stainless steel |
| t | = | tube |
| w | = | wall |
Superscript
| N | = | Nth grid in tube passes |
Additional information
Notes on contributors
Satya P. Pathak
Satya P. Pathak is currently working at the Fast Reactor Technology Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, India. He completed his M.S. by research in mechanical engineering from Indian Institute of Technology, Madras, in 2013. He is working in a steam generator test facility that provides various heat transfer experiments on the steam generator and sodium-to-air heat exchanger. His areas of interest are performance enhancement of heat exchangers/boilers, computational heat transfer, and two-phase flow physics. He is a member of the Indian Nuclear Society.
Karuppanna Velusamy
Karuppanna Velusamy is currently the head of the Thermal Hydraulics Section at Indira Gandhi Centre for Atomic Research. He is also a professor at Homi Bhabha National Institute–Mumbai, India. He has specialized in computational fluid dynamics (CFD) and has solved many challenging multimodal heat transfer problems. He has participated in IAEA-Coordinated Research Projects as a principle scientific investigator. He has played an important role in seeking clearance for the Prototype Fast Breeder Reactor project from various committees appointed by the Atomic Energy Regulatory Board. He has been elected a fellow of the Indian National Academy of Engineering and was awarded the Scientific and Technical Excellence Award for the year 2006. He has been a regular reviewer for heat transfer and nuclear engineering journals. Apart from his excellent contributions in the fields of basic and applied thermal hydraulics research, he has more than 150 publications including 62 in reputed journals.
Kavumchira K. Rajan
Kavumchira K. Rajan is currently director of the Fast Reactor Technology Group and Engineering Services Group at Indira Gandhi Centre for Atomic Research, Kalpakkam, India. He graduated in electrical engineering from NIT, Calicut, India. He has been steering a multidisciplinary program in the area of sodium technology. He is primarily responsible for design, construction, commissioning, safe operation, and maintenance of high-temperature experimental sodium facilities and conducting sodium experiments in support of FBR. He has made substantial contributions toward testing of the PBFR model steam generator in SGTF and PFBR fuel handling machines at reactor operating conditions in LCTR. He was also involved in the development of permanent magnet flowmeters and special type of heaters required for FBR sodium systems. He has published more than 140 papers in reputed national and international journals. He is a member of the Indian Nuclear Society, Instrument Society of India, and a fellow of Institution of Engineers (India).
C. Balaji
C. Balaji is a professor in the Department of Mechanical Engineering at the Indian Institute of Technology (IIT) Madras. He graduated in mechanical engineering from Guindy Engineering College, Chennai (1990), India, and obtained his M.Tech. (1992) and Ph.D. (1995) both from IIT Madras. His research interests include computational and experimental heat transfer, optimization in thermal sciences, inverse heat transfer, satellite meteorology, and numerical weather prediction. He has around 140 journal publications to his credit and is an elected fellow of the Indian National Academy of Engineering.