When there are large temperature differences between the
wall and the fluid, the friction factors and heat transfer
coefficients of forced laminar convection with variable fluid
properties are different from the theoretical results deduced
with constant property assumptions. However, most existing
equations for variable properties are obtained by regression
analysis of experimental data with a specific kind of fluid, and
cannot reflect the property-temperature sensitivities at different
fluid temperatures and for different kinds of liquid. In this
paper, the governing equations of forced laminar convection of
ethanol and water are numerically solved using CFD method
and the results are used to verify the deduced equations.
Compared with dynamic viscosity, the variations of density,
thermal conductivity and specific heat capacity in the cross
section can be neglected. A new explicit equation of friction
factor and a new explicit equation of heat transfer coefficient
for forced liquid laminar convection with variable properties
heated in straight tubes are obtained. The deduced equations
show good predictions of friction factors and Nusselt numbers
for different kinds of liquid. Based on the equations, a
dimensionless parameter is derived to predict the heat flux
effects and viscosity-temperature sensitivities on friction
factors and heat transfer coefficients.
Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .