Measuring and modeling of two-phase gap flow for oil-refrigerant mixtures in rotary positive displacement machines

油喷式旋转正排量（RPDC）压缩机（如双螺杆机）广泛用于压缩HVAC（采暖、通风和空调）系统中的制冷剂。这些流体能机器的效率在很大程度上取决于转子叶前不可避免的喘振流动和随后转子和外壳之间的两相油-制冷剂间隙流动。在分项目A1内，在5595研究股的第一个供资期间正在编制两阶段间隙流动的一维计算模型。考虑到控制效应，例如由于间隙或移动间隙边界的压力梯度而导致制冷剂从油中放气。同时解决了壁面摩擦引起的局部耗散问题。气瓶中旋转轮廓的一般实验构成了该模型发展的基础。作用在流动方向上的摩擦力与惯性力的比值是系统变化的。因此，实验开始时以旋转圆柱为轮廓线（Couette-flow实验），逐渐发展为旋转转子叶形线（Couette-Poiseuille flow实验，变间隙截面）。在库埃特流实验中，驱动扭矩是作为作用壁面剪应力的度量来测量的。在Couette-Poiseuille实验中，测量了两相间隙质量流率以及间隙流动方向上的压力分布。研究的两相混合物首先是水与氮（低溶解度），然后是水与二氧化碳（中等溶解度），然后是正癸烷与二氧化碳（强溶解度）。这些日益不对称的流体混合物的复杂热物理性质将由B组子项目开发。基于高速视频，结合子项目A2 （Kriegseis）对间隙内的流态进行分析，并转换成流态图。进而建立作用于流动方向的惯性力和壁面摩擦力的计算方法。必要的模型，例如气相和液相之间的滑移，与子项目A2和子项目A3的高分辨率数值流动模拟（Schröder）一起开发。最后，利用经过验证的惯性力和摩擦力计算方法，通过对每相一维守恒方程（分离两相流模型）进行数值积分，可以计算所寻求的两相油-制冷剂间隙质量流量和间隙压降的耗散。

Oil-injected rotary positive displacement (RPDC) compressors such as twin-screw machines are widely used to compress refrigerants in HVAC (heating, ventilation, and air conditioning) systems. The efficiency of these fluid energy machines is determined to a significant extent by the unavoidable surge flows in front of a rotor lobe and the subsequent two-phase oil-refrigerant gap flow between the rotor and the housing. Within subproject A1, models for the one-dimensional calculation of the two-phase gap flows are being developed in the 1st funding period of the Research Unit FOR 5595. The governing effects, such as the outgassing of the refrigerant from the oil due to the pressure gradient in the gap or the moving gap boundary, are taken into account. At the same time, the local dissipation due to wall friction are resolved. Generic experiments of a rotating contour in a gas cylinder form the basis for this model development. The ratio of the frictional forces acting in the direction of flow to the inertial forces is systematically varied. Accordingly, the experiments are started with a rotating circular cylinder as contour (Couette-flow experiments) and varied towards a rotating rotor lobe contour (Couette-Poiseuille flow experiments with variable gap cross section). In the Couette-flow experiments, the driving torque is measured as a measure of the acting wall shear stress. In the Couette-Poiseuille experiments, the two-phase gap mass flow rate is measured together with the pressure distribution in the gap flow direction. The two-phase mixtures studied are first water with nitrogen (low solubility), then water with carbon dioxide (moderate solubility), and then n-decane with carbon dioxide (strong solubility). The complex thermophysical properties for these increasingly asymmetric fluid mixtures will be developed by the B group subprojects. Based on high-speed videos, the flow patterns in the gap are analyzed together with subproject A2 (Kriegseis) and transferred into flow pattern maps. Subsequently, approaches for the calculation of the inertial forces and wall friction forces acting in the flow direction will be established. The necessary models, e.g. for the slip between the gaseous and liquid phases, are developed together with subproject A2 and the high-resolution numerical flow simulation by subproject A3 (Schröder). Finally, with the validated approaches for the inertial and frictional forces, the sought two-phase oil-refrigerant gap mass flow rate and the gap dissipation for an imposed pressure drop across the gap can be calculated by numerically integrating the one-dimensional conservation equations per phase (separated two-phase flow model).