A NOTE ON THE LAMINAR CORE-ANNULAR FLOW OF TWO IMMISCIBLE FLUIDS IN A HORIZONTAL TUBE Sayavur I. Bakhtiyarov*, Dennis A. Siginer* * *Space Power Institute, Auburn University Auburn, AL 86849-5820, USA **Department of Mechanical Engineering, Auburn University Auburn, AL 86849-5841, USA ABSTRACT. The lubrication of a non-Newtonian liquid by a Newtonian fluid in the concentrically stratified laminar flow of two immiscible fluids in a horizontal tube has been investigated experimentally by an opto- mechanical method. Data for the interfacial velocity and the total volume flow rate for two zero shear rate viscosity ratio are presented. The results of this investigation are useful in solving high wax content crude oil transportation problems and in the design of lubricated pipelines. 1. INTRODUCTION Most crude oils are high in paraffin and asphaltene content. Deposits of these constituents on equipment and downhole cause severe problems which hamper and slow down production and transportation of crude oil 1 • A simple, efficient and economically preferable method to prevent transportation problems caused by wax and asphaltene deposits on the inner surface of pipelines is to wet the inside wall with water based surfactants. The water film with surfactant additives acts as a barrier to prevent oil contact with the inner surface of the wall. If the film is replaced with a thicker layer, that is, if the water-oil ratio is increased, the use of surfactants may not be required, and the flow of oil may be lubricated by the water layer. Experiments on water-lubricated pipelining show that water in a stratified oil-water flow tends to encapsulate the oil 2 - 4 • If the effects of gravity are negligible, the high-viscosity phase is centrally located; that is, the low viscosity fluid has a strong tendency to migrate to the region of high shear 5 - 7 • This note describes an experimental set-up on an opto-mechanical principle to measure, in particular, the interfacial velocity at the boundary of the lubricating annular fluid and the lubricated core flow. Experimental data thus obtained together with the total volume flow rate can be used to validate the results of a theoretical solution to the core-annular flow problem. 2. EXPERIMENTAL RESULTS AND DISCUSSION A non-Newtonian core fluid lubricated by an immiscible Newtonian annular liquid flows in a horizontal tube of radius R. The interface between the fluids is smooth and stable and stays circular with a radius a. The region 0::::; r::::; a is occupied by a non-Newtonian liquid with zero shear viscosity J.lt. and a Newtonian liquid with dynamic viscosity coefficient J.1 2 fills the region a::::; r::::; R, Fig. I. Flow is steady and laminar for both fluids as the pressure at either end tube is kept constant, and the liquids are of the same density. The experimental set-up to study stratified bicomponent horizontal core-annular flow is sketched in Fig. 2. The core liquid is supplied by compressed air from tank I into the constant-level tank 5, from which it flows by gravity into the test tube 7. The annular liquid is forced by compressed air from tank 8 into the constant- level tank 6, from which it flows freely into the test tube through twelve nozzles around the tube. The volume flow rate is measured using the graduated cylinder 8. The use of the constant-level tanks 5 and 6 is essential in avoiding flow rate instabilities. The test tube is a 2050-mm long glass cylinder with 1 0-mm inner diameter. The velocity at the interface between the liquids is determined by an opto-mechanical instrument originally introduced by Khabakhpasheva et aJ. 8 · A transparent prism (I) located in the path of the light rays between the lens (3) and the focal plane of the eyepiece (4) is rotated by a DC motor (2), Fig. 8. Aluminum particles of diameter 0.015 - 0.025 mm have been used as markers. Light reflected by these fine aluminum particles carried by the flow falls on the