Effect of heat loss to ambient on steady-state behaviour of a single-phase natural circulation loop

This study aims at modelling of a single-phase rectangular natural circulation loop as a conjugate problem to investigate the influence of ambient temperature on the steady-state temperature profile for the loop fluid and wall temperature. Finite volume technique has been employed for the solution of non-dimensional governing equations. Numerically predicted values have been compared with available test data from literature. Natural convection heat loss to the ambient is found to cause significant changes in the loop fluid and wall material temperature along the bare sections. Warmer ambient conditions increase the fraction of input power transferred to the cooling stream and hence cause a rise in coolant temperature across the cooler. Increase in ambient temperature results in higher coolant outlet temperature and thus higher heat exchange effectiveness for the system. The loop temperature profiles gradually approach the ideal condition of perfect insulation with increase in ambient temperature. The combined effect of change in power input and ambient temperature predicts a particular ambient condition, when the system produces a constant effectiveness regardless of the power input.

[1]  Michel Bernier,et al.  A 1-D/2-D model and experimental results for a closed-loop thermosyphon with vertical heat transfer sections , 1992 .

[2]  H. Kretzschmar,et al.  The IAPWS Industrial Formulation 1997 for the Thermodynamic Properties of Water and Steam , 2000 .

[3]  Lingen Chen,et al.  Optimal configuration of a two-heat-reservoir heat-engine with heat-leak and finite thermal-capacity , 2006 .

[4]  Y. Zvirin,et al.  Two-Dimensional Study of Heat Transfer and Fluid Flow in a Natural Convection Loop , 1982 .

[5]  H. F. Creveling,et al.  Stability characteristics of a single-phase free convection loop , 1975, Journal of Fluid Mechanics.

[6]  Francesco Saverio D'Auria,et al.  Transient and stability analysis in single-phase natural circulation , 2004 .

[7]  H. S. Isbin,et al.  Oscillatory behavior of a two‐phase natural‐circulation loop , 1956 .

[8]  V. Gnielinski,et al.  Equations for calculating heat transfer in single tube rows and banks of tubes in transverse flow , 1979 .

[9]  P. Vijayan.  Experimental observations on the general trends of the steady state and stability behaviour of single-phase natural circulation loops , 2002 .

[10]  P. Welander.  On the oscillatory instability of a differentially heated fluid loop , 1967, Journal of Fluid Mechanics.

[11]  J. Keller.  Periodic oscillations in a model of thermal convection , 1966, Journal of Fluid Mechanics.

[12]  A. Bejan.  Theory of heat transfer-irreversible power plants , 1988 .

[13]  Yuyan Jiang,et al.  Flow stability in a natural circulation loop: influences of wall thermal conductivity , 2003 .

[14]  S. Churchill,et al.  Correlating equations for laminar and turbulent free convection from a vertical plate , 1975 .

[15]  Pallippattu Krishnan Vijayan,et al.  Mathematical modelling of the stability characteristics of a natural circulation loop , 1995 .

[16]  R. Viskanta,et al.  Natural convection: Fundamentals and applications , 1985 .