MECHANICAL & ELECTRICAL ENGINEERING
Jet fans and their applications by Er. Leong Cheng Wee, MASHRAE, MIES, P Eng Enhancing the design of ventilation systems. HISTORY OF JET FANS Not much information is available on jet fans, as we know of them in today’s context. Perhaps the initial concept of using jet fans for general ventilation originated from the applications of fans, without ducts, in tunnels, deep mines and underground shafts.
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Jet fan technology was developed and commercialised in the US in the early 1960s. From the US, jet fan technology was later adopted and further developed by the Japanese fan manufacturers in the 1970s. From Japan, jet fan technology spread to South Korea in 1986. Mr Lim Yun Cheol was the first Korean to refine and re-engineer Japanese and American jet fans. When Mr Lim first introduced his range and models of jet fans into the Korean market in 1987, the jet fans were very well accepted. The explosive popularity of jets fans led to many other different brands springing up overnight. Some definitions of ‘jet’ are: • An airplane that can rapidly travel long distances. • A rapid stream of liquid or gas forced out of a small opening. • A long, narrow current of high-speed winds (such as a jet stream).
WHAT IS A JET FAN? A jet fan is essentially a long cylindrical fan that generates a high-velocity jet of compressed air ejecting from the trailing edge of the blade, resulting in the forward movement of air, just like a jet plane being pushed forward by the high-velocity jet ejected from the rear of the jet engine. A synonymous term that is commonly used for jet fans is ‘duct24
THE SINGAPORE ENGINEER June 2022
External view of a jet fan. Image: MJ AirTech Co Ltd.
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High performance aero-foil impeller blades Guide vanes
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Cut-out section view of a jet fan. Image: MJ AirTech Co Ltd.
less fans’. Generally, jet fans do not need conventional ductwork from the louvres to the fans and to the diffusers/grilles for supply air, and ductwork in the reverse direction for ejecting exhaust air. The word ‘ductless’ does not always mean that no ducts are required. There may still be a requirement for a minimum amount of ductwork serving as the air plenum, where mechani-
cal fans (supply and exhaust fans) are located, usually at basement levels or where the openings provided are not large enough for efficient flows. Generally, jet fans are divided into two categories: • Impulse jet fans • Induction jet fans Impulse jet fans are axial fans, usu-
