Vacuum Steam Desuperheating and Condensation: An Experimental Investigation

摘要

Steam condensation plays an essential role in supplying and removing heat in many industrial applications, including the energy sector. It therefore is a phenomena of significance that requires deep understanding. This thesis presents effective vacuum steam condensation on the shell-side of vertical shell and tube condenser (VSTC) accompanying steam desuperheating. It describes a fundamental study of heat transfer in VSTC with considerations of several factors; explicitly degree of superheat related with each vacuum steam pressure, temperature waviness in desuperheating section, and steam condensation in absence of non-condensable gas (NCG). Experiments performed on the VSTC are: Steam desuperheating and condensation in the shell-side VSTC at a variety of vacuum steam pressures and respective steam flowrates, vacuum steam desuperheating and condensation in the shell-side of VSTC at reduced steam flowrates, and vacuum steam desuperheating and condensation at tube wall temperatures up to steam saturation temperature (T₂ ≥ Tsat) to analyse dry heat transfer in the desuperheating section. To examine the stated aim, test facility was built in the laboratory of the University of Waikato.By generating desuperheating and condensation models for each test pressure, this investigation proves that vacuum steam condensation best occurs without involvement of superheat. About 60% of the VSTC occupied with desuperheating, and the heat transfer involved in desuperheating is minor approximately 1 kW, whereas, the condensation section of VSTC has heat transfer about 10 kW. By reducing the steam flowrate, 10% reduction in the desuperheating section and 20% to 50% reduction in the Reynolds number was observed. After raising the tube wall temperature up to the steam saturation temperature, a smooth temperature profile across the desuperheating the section was seen with significant sensible heat transfer. Obstruction linked with superheated steam condensation in the dairy industrial leads to poor heat transfer area utilization by the desuperheating section and therefore, reduction of the evaporator rating or oversizing of the heat exchangers to attain appropriate duty.