Author: J. T. O'BaraPublisher:
ISBN:
Category :
Languages : en
Pages : 27
Book Description
In the first phase of this work equivalent heat transfer coefficients at atmospheric pressure for the dropwise condensation of steam were determined experimentally. The coefficients rangef from 1,140 to 37,200 BTU/hr sq ft deg F for heat fluxes of 167,000 down to 29,900 BTU/hr sq ft deg F with surface temperature differences carying from 2 to 45F. Vapor velocities varied from 1.75 to 7.52 ft/sec. It was observed that the vapor velocity across the condensing surface has a significant effect on the equivalent transfer coefficient with the coefficient exhibiting a maximum with increasing vapor velocity. It is believed that this maximum reflects the transition between dropwise and mixed condensation resulting from the greater vapor-liquid interfacial shear stress developed at high vapor velocities. Visual observations showed that, as the pressure increases, a transition from dropwise to mixed condensation occurs between 25 and 50 psig. This transition is posited to be associated with the decreased surface tension of the condensed phase at the higher saturation temperatures. (Author).