ABSTRACT
The present experimental investigation is focused on the study of heat transfer and pressure drop of heat exchanger tube fitted with dimpled ribs on the inner wall. The effect of geometrical parameters, predominantly the streamwise spacing, spanwise spacing, and dimpled depth to print diameter has been investigated. The heat exchanger tube has streamwise spacing () in range of 15–35, spanwise spacing (
) in range of 15–35, ratio of dimpled depth to print diameter (
) of 0.5–1.5, and Reynolds number (
) ranges from 5,000 to 27,000. Experimental results show that the heat transfer and thermal hydraulic performance enhances by 4.19 times and 2.53 times, respectively, for of
of 15,
of 15, and
of 1.0. The experimental data collected are utilized for the development of the statistical correlations for
and
for selected values of roughness parameters and flow Reynolds number.
Nomenclature
Area of tube
Cross-section area of the orifice
Coefficient of discharge of orifice
Specific heat of air
Hydraulic diameter of tube (m)
Print diameter of dimpled rib (m)
Height of rib
Dimpled depth to print diameter
Relative rib height
Friction factor
Friction Factor of roughened heat exchanger tube
Friction Factor of smooth surface heat exchanger tube
Convective heat-transfer coefficient
Manometric height in U-tube manometer
k Conductivity of air (W/m°C)
L Length of test section (m).
Mass flow rate of air
Nusselt Number of roughened heat exchanger tube
Nusselt Number of smooth surface heat exchanger tube
P Pitch of rib
Relative rib pitch
Prandtl number of air
Pressure drop across orifice plate
Pressure drop across test section
Heat-transfer rate to air
Reynolds number
Stanton number
Inlet air temperature
To Average outlet air temperature (°C)
Tfm Mean air temperature (°C)
Tpm Mean plate temperature (°C)
V Flow velocity in pipe (m).
Streamwise spacing
Spanwise spacing
Greek symbols
Thermal–hydraulic performance
Ratio of orifice diameter to pipe diameter
ρair Density of air