TED-AJ03-130 ENHANCED HEAT TRANSFER IN AN OSCILLATING PIPE FLOW

概要

論文の詳細を見る
The objective is to study the heat transfer of an oscillating flow in a rectilinear circular pipe from first principles by simply solving the governing equations analytically. The motive and background for focusing on this problem is the reported observation, made for pulse combustors of Helmholtz type, of a heat transfer of the order two to five times higher than expected. It was for instance observed that the temperature drop along the tail pipe was found to be up to 3-400K/m. That means that the temperature of the flue gases at the end of the tail pipe and after the decoupling chamber was at room temperature, though the length of the tail pipe could be about 1,5m. The radial heat conduction transfer observed seemed to be very high, while the convection of heat seems to be for a pulse combustor rather minor. Experiments where the velocity and temperature profiles in the tail pipe of a pulse combustor have been measured give no direct indication why the heat transfer should be enhanced. The enhanced heat transfer in an oscillating flow has been examined by e.g. Kurzweg [1] and others, the very special case with a pulse combustors will be our main focus here. The interaction between the oscillating velocity field and the oscillating temperature field might be the explanation of the observed enhanced heat conduction. Another possible explanation could be that the set of constitutive relations is incomplete or insufficient to describe the phenomenon. A detailed examination of the consequences of introducing a set of general constitutive relations for a simple fluid flow would be of prime interest. Here, we will consider the case when the classical constitutive relations are used, that means having a Navier-Stokes fluid and Fourier's law for heat conduction. From the analytically obtained velocity and temperature fields we may examine the consequences of introducing a more general set of constitutive relations. From the balance equations of momentum and energy for the fluid a set of coupled non-linear differential equations are given and from which unique analytical solutions for the velocity and temperature fields can be obtained. The heat transfer over the pipe boundary can then be determined from the constitutive relation. The mean heat transfer is found to be dependent of the frequency f of the oscillations as well as the phase difference φ between the pressure and temperature gradients in the pipe direction. In the analysis here we will not assume that the phase difference is dependent of the frequency of the oscillation. In the pulsating combustion case the phase difference from experiments was found to be "out of phase", but for the cases here we will assume that the phase difference can be chosen freely. From the analysis it is found that for certain intervals of the phase difference and the frequency of the oscillating flow an enhanced heat transfer can be found. This means that maybe both enhanced heating and cooling processes can be arranged by superimposing an oscillating flow. [figure]

TED-AJ03-130 ENHANCED HEAT TRANSFER IN AN OSCILLATING PIPE FLOW

スポンサーリンク

概要

著者

関連論文

スポンサーリンク