How Does a Pipe Diffuser Work?

A pipe diffuser is a specialized radial vane diffuser that is widely utilized in the centrifugal compressors of gas turbine engines. In fact, the incorporation of pipe diffusers can improve the overall efficiency of centrifugal compressors by an average of 2-4% compared to other vane diffusers. More specifically, the efficiency gains are very obvious at high-pressure ratios over 5.0.

What Does a Pipe Diffuser Consist of?

In terms of composition, pipe diffusers are made up of a main cylindrical section called the throat and a conical diffuser. The axis of the pipe diffuser must be tangent to the circle created by the tip of the centrifugal compressor. In other words, the circle that is defined by the impeller tip radius.

Meanwhile, the leading edge of the pipe diffuser channel is elliptical due to the sloping intersection of the cylindrical throat and the cylindrical surface of the diffuser radius. The configuration of this intersection allows the unit to gradually adapt the effluent flow from the impeller and enable it to flow through the cylindrical and conical sections of the diffuser. Keep in mind that the downstream duct of a compressor with a pipe diffuser is called a diffusing trumpet or “fishtail” diffuser.

Why You Should Add a Pipe Diffuser

There are numerous reasons why you should adopt pipe diffusers over alternatives in many applications. To begin, they provide a better flow-area-to-wetted-area relationship that results in reduced frictional losses when compared to wedge diffusers. Additionally, you can achieve an improved diffusion area with a pipe diffuser than a wedge diffuser given that they have the same geometrical constraints. Moreover, the elliptical leading-edge geometry has the capacity to handle highly-distorted flows; thus, pipe diffusers can yield lower losses at the impeller outlet.

It is worth noting that pipe diffusers perform well at high inlet Mach numbers, which is important in higher-pressure-ratio stages. More than that, they are especially ideal for supersonic inlet conditions and do not suffer from performance deterioration at low Mach numbers when compared to other diffuser types. To use them at their full potential, the Mach number must be greater than one at the diffuser inlet which corresponds to pressure ratios of 4.0 and higher.

Due to their wide-ranging benefits, pipe diffusers are used in many sectors, from industrial production to aviation. Despite the advantages they offer, there is no standard approach to the design of pipe diffusers, which presents both a challenge and an opportunity for turbomachinery designers. As such, pipe diffusers are continuously being changed and adjusted as per operational requirements.

Conclusion

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