Investigation of Heat Transfer by Natural Convection in an Open Channel

Experimental study of natural convection heat transfer
inside smooth and rough surfaces of vertical and inclined equilateral
triangular channels of different inclination angles with a uniformly
heated surface are performed. The inclination angle is changed from
15º to 90º. Smooth and rough surface of average roughness (0.02mm)
are used and their effect on the heat transfer characteristics are
studied. The local and average heat transfer coefficients and Nusselt
number are obtained for smooth and rough channels at different heat
flux values, different inclination angles and different Rayleigh
numbers (Ra) 6.48 × 105 ≤ Ra ≤ 4.78 × 106. The results show that
the local Nusselt number decreases with increase of axial distance
from the lower end of the triangular channel to a point near the upper
end of channel, and then, it slightly increases. Higher values of local
Nusselt number for rough channel along the axial distance compared
with the smooth channel. The average Nusselt number of rough
channel is higher than that of smooth channel by about 8.1% for
inclined case at θ = 45o and 10% for vertical case. The results
obtained are correlated using dimensionless groups for both rough
and smooth surfaces of the inclined and vertical triangular channels.

• Mahmoud S. Ahmed
• Hany A. Mohamed
• Mohamed A. Omara
• Mohamed F. Abdeen

• Natural heat transfer convection
• constant heat flux
• open channels
• heat transfer.

[1] Abdul-Aziz M., "Heat transfer by natural convection from the inside
surface of a uniformly heated tube at different angles of inclination,"
M.S. Thesis, Mech. Eng. Dept., Al-Azhar University, Cairo, Egypt,
1991.
[2] Hussein A. and Yasin K., "Heat transfer by natural convection from a
uniformly heated vertical circular pipe with different entry restriction
configurations," Energy Conversion & Management, vol.48, 2007,
pp.2244-2253.
[3] Sarhan A., Kamis M. and Moawed M.," Heat transfer by natural
convection in vertical and horizontal annuli," Al-Azhar Univ Eng. J. 4, ,
Cairo, Egypt, 2001.
[4] Hosseini R., Heyrani-Nobari M.,and Hatam M.,"An experimental study
of heat transfer in an open-ended vertical eccentric annulus with
insulated and constant heat flux boundaries," Applied Thermal
Engineering, vol. 25, 2005, pp.1247-1257.
[5] Omara M., Elshazly K., Moawed M. and Ibrahim E. ,"Heat transfer by
free convection from the inside surface of the vertical and inclined
elliptic tube," Energy Conversion & Management, vol.46, 2005, pp.
1443-1463.
[6] Moawed M. and Ibrahim E. ,"Free convection heat transfer inside
vertical and inclined elliptic tubes with different axis ratio and different
inclination and orientation angles," Energy Conversion & Management,
vol.49, 2005, pp. 587–595.
[7] Amr O., Emad Z. and Sayed A. "Free convection from a constant heat
flux elliptic tube," Energy Conversion and Management, vol.44, 2003,
pp. 2445–2453.
[8] Nada S.A. ,"Natural convection heat transfer in horizontal and vertical
closed narrow enclosures with heated rectangular finned base plate," Int.
J. of Heat and Mass Transfer,vol. 50 ,2007, pp. 667-679.
[9] Varol Y., Koca A. and Hakan F.," Natural convection in a triangle
enclosure with flush mounted heater on the wall," Int. Commun. In Heat
and Mass Transfer, vol.33 , 2006, pp. 951-958.
[10] Seleem K. and Kamel A. ,"Experimental study of inclination angle and
surface area effects for longitudinally finned cylinder on free convection
heat transfer in an open enclosure," Journal of Engineering and
Technology, Baghdad, Iraq ,vol.27, 2009, pp. 171-179.
[11] Abdlmonem B. and Michel A., "The effect of surface roughness on the
average heat transfer of an impinging air jet," Int Commun in Heat and
Mass Transfer, vol.27, 2000, pp. 1-12.
[12] Majid B., Michael M. and Richard J. "Role of random roughness on
thermal performance of microfins", Journal of Thermophysics and Heat
Transfer, vol.21, 2007, pp. 153-157.
[13] Hany A., Omara M., Mahmoud S. and Mohamed F. Experimental study
of natural convection heat transfer through horizontal open ended
equilateral triangular channels, Journal of Engineering Sciences,
University of Assiut, Egypt. , vol.40, 2012, pp. 1091-1103.