Axial and mixed flow fans have been in high demand for a number of years. The application of these machines span many different industries including HVAC, automotive, appliance, military equipment, and much more. Like many other types of turbomachinery, changing industry standards and market trends have resulted in fierce rivalry to compete on lifespan, efficiency, environmental and user friendliness, and overall quality. With this in mind, it goes without saying that companies are looking for tools needed to develop highly efficient equipment while minimizing noise as quiet fans are typically more desirable which results in higher demand and marketability.
Turbomachinery is a core subject in many engineering curriculums. However, many graduates joining the oil and gas industry are designated as rotating equipment engineers. Though turbomachinery and rotating equipment are used synonymously, all turbomachinery are rotating equipment but not vice versa. Turbinis in Latin implies spin or whirl, and a natural question that arises is – what are the factors that differentiate turbomachinery? In a general sense the term, “rotating” covers the majority equipment used in the industry be it in the upstream, mid-stream or the downstream segment. Yet top rotating equipment specialist in the industry are seen spending their prime time or often being associated with certain unique and specific types of critical rotating machines – the turbomachines.
In a classical sense, turbomachines are devices in which energy is added into or taken out from a continuously ﬂowing ﬂuid by the dynamic action of one or more moving blade rows. By this definition propellers, wind turbines and unshrouded fans are also turbomachines but they require a separate treatment. The subject of ﬂuid mechanics, aerodynamics, thermodynamics and material mechanics of turbomachinery when limited to machines enclosed by a closely ﬁtting casing or shroud through which a measurable quantity of ﬂuid passing in unit time makes the practical linkage to rotating equipment – those which absorb power to increase the ﬂuid pressure or head (fans, compressors and pumps) and those that produce power by expanding ﬂuid to a lower pressure or head (hydraulic, steam and gas turbines). Further classification into axial, radial and mixed type (based on flow contour), and impulse & reaction (based on principle of energy transfer) is common. It is the large range of service requirement that leads to different type of pump (or compressor) and turbine in service.
Many people speculate about the confusion on what is considered a compressor, a blower, or simply a fan. In essence, each of these turbo-machines achieve a pressure rise by adding velocity to a continuous flow of fluid. The distinctions between fans, blowers, and compressors are quite simply defined by one parameter, the specific pressure ratio. Each machine type, however, utilizes a number of different design techniques specific to lower and higher-pressure applications. As per the American Society of Mechanical Engineers (ASME), the specific pressure is defined as the ratio of the discharge pressure over the suction pressure (or inlet pressure). The table shown below defines the range at which fans, blowers, and compressors are categorized.
Similarities between the design of fans and blowers occur near the lower end of a blower’s range. As well, many design parallels exist between high-pressure blowers and compressors. For the article, we will be investigating the different design characteristics of centrifugal blowers. Blower selection depends on a number of factors including operating range, efficiency, space limitations, and material handled. Figure 1 shows a number of different impeller blade designs that are available for centrifugal blowers.