Developing mixed convection in a coiled heat exchanger

Abstract In this paper the development of mixed convection in a helically coiled heat exchanger for Re = 500, Pr = 5 and δ = 1 14 is studied. The influence of buoyancy forces (Gr = ¢O (10 5 )) on heat transfer and secondary flow is analyzed. In the method used the parabolized equations are solved using a finite difference discretization. The code is tested on mixed convection flow in a 90° curved tube of which the results are compared to the results obtained with an elliptical code. For the helically coiled tube a constant wall temperature is considered. It appeared that heat transfer is highly influenced by secondary flow induced by centrifugal and buoyancy forces. For low Grashof numbers a splitting phenomenon of the temperature field is observed due to large secondary velocities, resulting in two separated areas of fluid. For high Grashof numbers the fluid in the coiled pipe becomes almost linearly startified which results in small secondary velocities. A wavy behaviour in the Nusselt number is observed for medium Grashof numbers.

[1]  D. B. Spalding,et al.  Prediction of laminar flow and heat transfer in helically coiled pipes , 1974, Journal of Fluid Mechanics.

[2]  Edward W. Merrill,et al.  Effect of secondary fluid motion on laminar flow heat transfer in helically coiled tubes , 1971 .

[3]  J. Farey,et al.  XXXVI. On blasting with gunpowder , 1804 .

[4]  N. Padmanabhan.  Entry flow in heated curved pipes , 1987 .

[5]  K. C. Cheng,et al.  Laminar forced convection in the thermal entrance region of curved pipes with uniform wall temperature , 1974 .

[6]  J. D. Seader,et al.  Fully developed viscous—flow heat transfer in curved circular tubes with uniform wall temperature , 1974 .

[7]  B. Morton.  LAMINAR CONVECTION IN UNIFORMLY HEATED HORIZONTAL PIPES AT LOW RAYLEIGH NUMBERS , 1959 .

[8]  W. H. Chen,et al.  Finite element analysis of incompressible viscous flow in a helical pipe , 1986 .

[9]  J. Humphrey,et al.  On the spatial stability of tube flows subject to body forces , 1993 .

[10]  J. Prusa,et al.  Numerical solution for fully developed flow in heated curved tubes , 1982, Journal of Fluid Mechanics.

[11]  R. Shah.  Laminar Flow Forced convection in ducts , 1978 .

[12]  C. Fletcher.  Computational techniques for fluid dynamics , 1992 .

[13]  C. Hirsch,et al.  Numerical Computation of Internal and External Flows. By C. HIRSCH. Wiley. Vol. 1, Fundamentals of Numerical Discretization. 1988. 515 pp. £60. Vol. 2, Computational Methods for Inviscid and Viscous Flows. 1990, 691 pp. £65. , 1991, Journal of Fluid Mechanics.

[14]  K. C. Cheng,et al.  Flow Visualization Experiments on Secondary Flow Patterns in an Isothermally Heated Curved Pipe , 1987 .

[15]  Jy-Ber Lee,et al.  Buoyancy in developed laminar curved tube flows , 1985 .

[16]  K.G.T. Hollands,et al.  A review of low-flow, stratified-tank solar water heating systems , 1989 .

[17]  W. R. Dean,et al.  Note on the motion of fluid in a curved pipe , 1959 .

[18]  C. Y. Wang,et al.  On the low-Reynolds-number flow in a helical pipe , 1981, Journal of Fluid Mechanics.

[19]  W. R. Dean.  XVI. Note on the motion of fluid in a curved pipe , 1927 .

[20]  Stanley A. Berger,et al.  Flow in heated curved pipes , 1978, Journal of Fluid Mechanics.

[21]  W. Roger Briley,et al.  Numerical method for predicting three-dimensional steady viscous flow in ducts , 1974 .

[22]  C. J. Hoogendoorn,et al.  Laminar convective heat transfer in helical coiled tubes , 1978 .

[23]  J. Turner,et al.  Buoyancy Effects in Fluids , 1973 .