Static Mixing Spacers for Heat Transfer Improvement Application in Air Cooled Steam Condensers.

摘要

A new planar static mixing spacer design has been proposed and studied in membrane operations. This spacer has shown improvements to mass transfer operations in spiral wound membranes [5]. The previous work proposed that the spacer improved mass transfer operations by disrupting the boundary layer growth. It does this by moving fluid within the boundary layer adjacent to the wall surface and brings it to the center of the channel. Fluid from the bulk flow in the center of the channel is then brought to the wall surface.;The purpose of this study is to examine this planar static mixing spacer in heat transfer operations. Specifically with regards to the air side heat transfer coefficient of air cooled steam condensers. To study this behavior an experimental apparatus and computational fluid dynamics model were constructed that mimic the air flow channel between the fins of an air cooled steam condenser. Air flow rates were used between Reynolds numbers of 3600 to 5600. Spacer material of construction varied from low thermal conductivity materials to high thermal conductivity materials.;Simulation showed an increase in the heat transfer coefficient of 38% for one nylon spacer up to 129% for five nylon spacers. It showed an increase in the heat transfer coefficient of 53% for one aluminum spacer and 207% for five aluminum spacers. Experiment showed the nylon spacers to be consistently 10%-20% lower than simulation heat transfer coefficient values. However the steel spacers used in the experiment showed consistently 20-50% higher heat transfer coefficients than the simulation values. Variances are believed to be caused by poor spacer-to-fin contact, turbulence and compressibility effects.;Power input used to drive a fluid was not examined in the experimental portion of the study. Therefore only simulation results were used. To obtain an approximation of the power input required to move air through a spacer filled fin channel the volumetric flow rate was multiplied by the pressure drop measured across the channel. This was then plotted for the two spacer designs as heat transfer coefficient versus power. Although this study only used a limited number of spacer configurations a difference in power input necessary was seen. In one case examined in the study the aluminum spacer would need half as much power to obtain the same heat transfer coefficient as the nylon spacer. This is due to the decrease in the number of spacers needed and therefore decreasing the pressure drop.