Abstract

The most reliable and economic way to control fluid leakage from industrial equipment such as centrifugal pumps and mixers is to isolate the rotating shaft and its housing with a mechanical seal. These devices, though simple in concept, present a variety of engineering challenges to the designer.

Of particular concern is the thermofluid environment in which key components of the seal must operate. In order to protect critical parts and ensure functionality, heat caused by sliding friction is commonly removed by forced convection cooling. Experience shows that cooler operating temperatures correlate with improved, more stable performance, reduced wear, and extended life of the seal.

Visualizing Fluid Flow and Heat Transfer

in

Rotating Shaft Seals

Ray Clark and Henri Azibert

A. W. Chesterton Company

Stoneham, Massachusetts 02180

อีเมลนี้จะถูกป้องกันจากสแปมบอท แต่คุณต้องเปิดการใช้งานจาวาสคริปเพื่ออ่านมันได้

อีเมลนี้จะถูกป้องกันจากสแปมบอท แต่คุณต้องเปิดการใช้งานจาวาสคริปเพื่ออ่านมันได้

Design concepts for improved fluid sealing were studied using advanced engineering analysis and state-of-the-art data visualization. Computational Fluid Dynamics (CFD) provided the principal means for evaluating the circulation and effectiveness of coolants used in dual mechanical seal. Virtual prototype tests were carried out using FLUENT, a general-purpose fluid flow solver. Laboratory measurements were also made to confirm the CFD results.

The simulations of flow behavior in seals were examined using IBM Visualization Data Explorer. Visual programs developed within the DX environment were used to display and extract important design information from large sets of three-dimensional multivariate data.

A particularly interesting and revealing aspect of the analysis involved flythrough animation sequences created from images depicting fluid particle trajectories. From an immersed, moving frame of reference the observer travels through the flow alongside data-mapped streamribbons. This technique has proven useful for identifying causal relationships between fluid motion and local flow variables such as temperature, static pressure, turbulent kinetic energy, and vorticity.

Conclusions drawn from the project suggest simple and cost-effective ways to enhance removal of heat, while improving the thermal environment, operation, and life expectancy of seals.

Introduction

The design of fluid sealing devices involves a wide range of engineering considerations. Seals mounted to rotating shafts of pumps and mixers, for example, must often operate under severe and sometimes dangerous conditions such as those involving hazardous or toxic fluids. Concerns related to the design and operation of these seals include the thermoelastic behavior of seal faces, the tribological nature of lubricating interfacial fluid films, as well as the mechanics and thermodynamics of fluids within which seals must immersively function. It is the latter of these concerns which forms the basis for the work reported here.

For difficult sealing applications which require zero (or near-zero) emission of hazardous fluids, double (or dual) mechanical seals are often used in conjunction with some type of benign barrier fluid to form a safer, more reliable containment system. These systems typically rely on forced convection cooling by the barrier fluid to help dissipate frictional heat generated at sliding interfaces between rotating and non-rotating components. In fact, removal of heat from these components is often vital to the sustained functionality and life of the seals.

Figure 1 shows a typical configuration in which a mechanical seal is used to prevent leakage of process fluid from a centrifugal pump. Various parts of the seal are illustrated

Figure 1. Cutaway view of centrifugal pump/mechanical seal configuration.

in this cutaway cross-sectional view. Figure 2 provides a closer, more detailed picture of the seal rings or faces for this particular example. Here, the blue carbon-graphite faces rotate with the purple shaft sleeve. The silicon-carbide faces (red) are held stationary by the seal gland (green) which bolts directly to the gray mounting flange of the seal chamber (Figure 1). Also shown in Figure 2 is the translucent blue barrier fluid domain of interest. For this type of seal, the barrier fluid enters and leaves the domain via a flow distribution channel (yellow) situated between the two silicon-carbide faces.