Natural convection from vertical helical coiled tubes in air

Conference · Thu Jul 01 04:00:00 EDT 1999

OSTI ID:20002477

Ali, M E

Helically coiled tubes are used in many engineering applications, such as heating, refrigerating and HVAC systems. They are used also in steam generator and condenser design in power plants because of their large surface area per unit volume. In spite of their widespread use, there is very little information available in the literature on natural convection from such coils. Two experimental investigation have been reported on steady state laminar and transition natural convection from the outer surface of vertically oriented helical coiled tubes in air. Four coils at constant heat flux boundary condition have been used with coil diameter to tube diameter ratio of 16.45 and 23.94. Six more coils have been used at variable surface temperature boundary condition with coil diameter to tube diameter ratio 19.923, 15.904, and 12.798. Local average heat transfer coefficients are obtained for laminar and transition natural convection. The data are correlated with Rayleigh number using the tube diameter as a characteristic length. It has been found that the Nusselt number decreases as Rayleigh number increases for constant heat flux. Transition to turbulent natural convection regime has obtained at a critical Rayleigh number of about 5,000 and it characterizes by a waveform like relation between Nusselt number and Rayleigh number.

• Research Organization: King Saud Univ., Riyadh (SA)
• OSTI ID: 20002477
• Report Number(s): CONF-990805--
• Country of Publication: United States
• Language: English

Related Subjects

20 FOSSIL-FUELED POWER PLANTS
32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION
CORRELATIONS
LAMINAR FLOW
NATURAL CONVECTION
REFRIGERATING MACHINERY
SPACE HVAC SYSTEMS
STEAM GENERATORS
THERMAL POWER PLANTS
TRANSITION FLOW
TUBES
VAPOR CONDENSERS