1. Introduction

The Double Orifice Air Valve is a key fluid control device in pipeline systems, with core functions of exhausting air from pipelines and preventing negative pressure damage. Its working performance directly depends on the matching degree between fluid dynamic characteristics and structural design.

2. Core Fluid Dynamic Characteristics of Double Orifice Air Valve

2.1 Flow Field Distribution Characteristics

The double-orifice structure causes its flow field to exhibit the characteristic of "two-way splitting and confluence," resulting in an asymmetrical distribution of velocity fields at the air inlet and exhaust holes. During the exhaust phase, high-pressure gas in the pipeline exits through the main exhaust hole at high speed, creating a jet effect while generating a low-pressure recirculation zone around the orifice. In the air intake phase, external air enters through the auxiliary air inlet at low speed, resulting in a more stable flow field that minimizes fluid disturbances within the pipeline.

2.2 Resistance Loss Law

Valve resistance loss mainly comes from orifice throttling, flow channel turning, and fluid viscous friction. The relationship between fluid velocity and resistance loss is a quadratic function; that is, the higher the velocity, the larger the local resistance coefficient. Compared with single-orifice air valves, the double-orifice structure can reduce the peak velocity of a single orifice through the flow distribution between the air inlet and exhaust holes, reducing resistance loss by 15%-30%.

2.3 Gas-Liquid Two-Phase Flow Characteristics

Gas-liquid two-phase flow is always present in the valve during operation. The interfacial tension and the difference in density between the gas and liquid phases can affect flow stability. During exhaust, the gas phase predominates the flow, and the liquid phase tends to form a film at the orifice, obstructing exhaust. Conversely, during air intake, the backflow of the liquid phase and the inflow of the gas phase create an impact that may cause flow field oscillation, potentially compromising the sealing performance of the valve.

3. Key Factors Affecting Fluid Dynamic Characteristics

3.1 Influence of Structural Parameters

1. Double-orifice diameter ratio: The matching of the diameters of the main exhaust hole and auxiliary air inlet directly affects flow distribution, and the optimal diameter ratio needs to be dynamically adjusted according to the pipeline working pressure and medium velocity.

2. Flow channel shape: A streamlined flow channel can reduce fluid separation and eddy currents, lowering local resistance. A right-angle turning flow channel is prone to flow separation, increasing energy loss.

3. Valve core structure: The sensitivity of the valve core's opening and closing, along with the shape of the sealing surface, impacts gas-liquid separation efficiency and alters flow field stability.

3.2 Influence of Working Conditions

1. Pipeline pressure: Under high-pressure conditions, the gas jet effect is enhanced, and resistance loss increases significantly. Under low-pressure conditions, the air intake efficiency is easily affected by external atmospheric pressure.

2. Medium characteristics: The higher the medium viscosity and density, the higher the proportion of viscous friction resistance. The presence of impurities in the medium can lead to orifice blockage, which damages the symmetry of the flow field.

3. Flow change: Under conditions of instantaneous large flow, the double orifice's flow regulation capacity is inadequate, leading to issues such as "incomplete exhaust" and "air intake lag."

4. Conclusion

The core of the fluid dynamic characteristics of the Double Orifice Air Valve lies in the adaptability between the double-orifice structure and the flow field. Resistance loss, gas-liquid separation efficiency, and flow field stability are the key indicators affecting its performance. Through multi-dimensional optimization of flow channel structure, valve core design, materials, and processes, its fluid dynamic performance can be effectively improved to meet the needs of pipeline systems under complex working conditions.