Elimination of Acid Cleaning of High Temperature Salt Water Heat Exchangers: Redesigned Pre-Production Full-Scale Heat Pipe Bleed Air Cooler for Shipboard Evaluation

摘要

A conventional Bleed Air Cooler (BAC) uses a shell and tube heat exchanger (HX), in which hot bleed air is fed to the shell side and seawater is fed to the tube side. The high temperature air readily heats the seawater side of much of the tube surfaces to temperatures well in excess of the 150 degrees F temperature at which fouling occurs. This fouling precipitates dissolved solids in the seawater, which forms scaling, i.e. calcareous deposits, on the tube walls. Scaling reduces heat transfer capacity which can affect air temperature and downstream applications. Scaling will result in local temperatures which approach the inlet air temperatures; elevated temperatures accelerate corrosion and wear, which then leads to leakage and catastrophic failures. The use of heat pipes eliminates the direct contact of hot air and seawater across a thin tube wall. Instead, heat is transported from the air side to the seawater side of the HX through a number of heat pipes. Heat pipes use the evaporation and condensation of a working fluid to transport heat. One feature of saturated, two phase heat transport is that the entire inside surface of the heat pipe is very nearly the same temperature. By directly manipulating the relative heat transfer surfaces (i.e. the relative number and size of the fins and the air and water sides of the heat pipe), the surface Temperature on the water side can be maintained below the critical 150 degrees F fouling temperature.