Development of flow model for weir type orifice

Abstract

The weir type orifice is widely used as an interstage sealing device of an MSF evaporator and as a flow regulating device of brine and distillate flows. The existing flow model for a weir type orifice is described simply as an orifice without any consideration to weir hydraulic characteristics. The inaccurate level estimation requires repetitive trial orifice adjustments. A new flow model has been developed in a combination of a submerged sluice gate and a weir. This model allows us to estimate the effect of various parameters such as flow rate, gate edge shape, weir height, liquid level, flow load, gate opening, etc. The calculated level pattern shows a good consistence not only with experimental data acquired by a prototype evaporator but with operation data of large scale plants. With an application of the new model, the orifice flow characteristics are described as follows: 1. A wide range of operation can be performed by changing weir height instead of changing gate opening. 2. The round edge gate is useful for a small interstage pressure difference such as in a heat rejection section. The developed flow models are applied for the development of an automatic control system.