Abstract
Background Direct Contact Condensation (DCC) is extensively used in process industry due to high rate of mass and heat transfer of the process with use of lower temperature coolant. However, these heat and mass transfer rates are directly related to the rates of external and internal oscillations in the systems may become significant in situations such as earthquakes. Additionally, DCC is also influenced by laminar, transitional and turbulent nature of flow.
Purpose In current work, externally forced oscillations of the pipe containing steam and water are studied in relation to DCC. Externally induced vibrations which, in turn, affect the rate of heat and mass transfer that occurs during the interaction of steam and water resulting in condensation. These vibrations become significant if the pipes being used for condensation are part of in powerplants which require stable operation. Although, these vibrations are not a regular feature of the systems, however, they become significant if an earthquake or other natural disasters occurs.
Methods In this work, a pipe having 10 cm diameter and 3 m in length was used to study the effects of external oscillations (i.e., 15, 30, 45 and 60 rpm) on the steam-water pipe flow in horizontal and vertical orientations. Hot Film Anemometer (HFA) and K-type thermocouples were used to determine the steam's mean velocity at the pipe's exit which corresponded to the Reynolds number (Re) varying from 1998 to 4290 and the steam's inlet pressure varied from 0.5 to 2.0 gauge pressure. The corresponding Re based on water mean velocity in pipe varied between 1432 and 6448.
Results For horizontal pipe flow, with rise in the rpm of more than 15, the pressure fluctuations reduce along the plane and the rise in the frequency of oscillations at fixed steam pressure of 0.5 bars influence the flow by flattening the pressure fluctuations across the flow. Similarly, for vertical pipe flow, the pressure fluctuations were reduced along the plane due to flattening of the pressure fluctuations across the flow. The intensity of flattening was observed to be more in case of vertical flow than the horizontal orientation. For both laminar and transition regimes, the intermittency decreases with rise in external oscillations' frequency at fixed Re and the amplitude of the external oscillations. While it increases due to the rise in the amplitude of the external oscillations at fixed Re and external oscillations' frequency.
Conclusions The variations in the frequency of external oscillations and Re confirmed their dominance over the mean wall shear stress for vertical orientation and on the friction factors for horizontal orientations. In the case of the horizontal orientation, 5-9% rise in the values of the time averaged frictional factor was recorded.