N2 - Experimental investigation of natural convection heat transfer in heated vertical tubes dissipating heat from the internal surface is presented. The test section is electrically heated and constant wall heat flux is maintained both circumferentially and axially. Four different test sections are taken having 45 mm internal diameter and 3.8 mm thickness. The length of the test sections are 450 mm, 550 mm, 700 mm and 850 mm. Ratios of length to diameter of the test sections are taken as 10, 12.22, 15.56, and 18.89. Wall heat fluxes are maintained at 250–3341 W/m2. Experiments are also conducted on channels with internal rings of rectangular section placed at various distances. Thickness of the rings are taken as 4 mm, 6 mm, and 8 mm. The step size of the rings varies from 75 mm to 283.3 mm. The nondimensional ring spacing, expressed as the ratios of step size to diameter, are taken from 1.67 to 6.29 and the non-dimensional ring thickness, expressed as the ratios of ring thickness to diameter are taken from 0.089 to 0.178. The ratios of ring spacing to its thickness are taken as 9.375 to 70.82. The effects of various parameters such as length to diameter ratio, wall heat flux, ring thickness and ring spacing on local steady-state heat transfer behavior are observed. From the experimental data a correlation is developed for average Nusselt number and modified Rayleigh number. Another correlation is also developed for modified Rayleigh number and modified Reynolds number. These correlations can predict the data accurately within ±10% error.
L1 - http://sd.czasopisma.pan.pl/Content/109647/PDF/05_paper.pdf
L2 - http://sd.czasopisma.pan.pl/Content/109647
PY - 2018
IS - No 4
EP - 111
KW - heat transfer
KW - Heat flux
KW - Natural convection
KW - Ring spacing
KW - Ring thickness
A1 - Nayak, Ramesh Chandra
A1 - Roul, Manmatha Kumar
A1 - Sarangi, Saroj Kumar
PB - The Committee of Thermodynamics and Combustion of the Polish Academy of Sciences and The Institute of Fluid-Flow Machinery Polish Academy of Sciences
VL - vol. 39
T1 - Natural convection heat transfer in heated verticaltubes with internal rings
DA - 2018.11.26
SP - 85
UR - http://sd.czasopisma.pan.pl/dlibra/publication/edition/109647
T2 - Archives of Thermodynamics