Master's Thesis Florian Schulte

 

Application of Kármán Vortex Streets in Convector Channels for Heat Transfer Enhancement

Thismaster thesis consists of a simulative and experimental study proving the enhancement of heating
power for flat radiators via the application of Kármán Vortex Streets in Convector Channels. The
applied methodology includes the definition of a reference state and a modified state, for which a
cylinder is placed in the convector channel. In a first step, the simulative examination of a range of
different values for the parameter „channel width“ is done for the reference state. In this case the air
near the walls of the channel is heated up more than the air in the middle of the channel and there
is little mixture between the two areas. Both, simulation and experiments show the rising enhancement
of the heat transfer between steel and air, when the diameter of the cylinder placed in the
channel is decreased. This effect is analyzed for a channel width of 28 mm. The reason for the increasing
heating power is the mixing effect of the vorteces of the Kármán Vortex Street, which increases
the local temperature difference between the steel walls and the air, which is the driving force of
the heat transfer. This influence on the heating power is higher for smaller cylinder diameters. This
tendency is based on the velocity field and the mass flow within the convector channel. For smaller
cylinders the blockage ratio for the channel is smaller and the velocities are higher than in the case
of bigger cylinder,which leads to a higher influence of the Kármán Vortex Street.On the contrary, the
average output temperature of the air decreases with smaller diameters of the cylinders due to the
shorter time period the air needs to transit the channel. The maximum heat transfer enlargement
in this thesis is found for a cylinder diameter of 8 mm and amounts to 5,52 %. An economic view
on the subject shows that the enhancement of heating power for flat radiators via the application of
Kármán Vortex Streets in Convector Channels offers an interesting investment potential.