Experimental investigation aiming at improving the suction flow capability of a gas expeller

An expeller performance has been evaluated in terms of its capability to induce higher suction flow for application to evacuate combustible gases from a blown down natural gas pipelines. The investigation involved a test rig and testing of a typical 150 mm (nominal size) expeller. This particular expeller has 12, 2.35 mm diameter holes, equally spaced around the throat circumference of the expeller. This was referenced to as the base (or original design). The aim of the present investigation is to improve the suction flow capability of this expeller by four modifications to both the number and/or sizes of these holes. The experimental results showed that the performance of the expeller in terms of its capability of driving higher suction flows for a given flow resistance system can be improved by increasing the number and sizes of the drive air holes which in turn permit higher drive air flow. However, with increased drive air flow, the performance of the expeller in terms of the induction ratio (IR) deteriorates, but luckily not at the same rate as the suction flow increases. Hence a cost effective means to improve the suction flow capability of an expeller is to drill more and larger size holes around its throat. The loss in the IR (which is efficiency related), however, is generally not a concern in practice when the economic benefit of evacuating the pipeline section in a timely and safe manner greatly overweigh any potential loss in the expeller IR efficiency. It was also shown that expeller performance in terms of its IR improves with smaller hole size. Therefore, to improve an expeller suction flow capability, while maintaining its performance efficiency (i.e. IR), larger number of the same or smaller holes should be considered.