Energy efficient FRP axial flow fans

THE AXIAL flow fans are widely used for providing the required airflow for heat & mass transfer operations in various industrial equipment and processes. These include cooling towers for air- conditioning & ventilation, humidifiers in textile mills, air heat exchangers for various chemical processes, ventilation & exhaust as in mining industry etc. All the major industries of the national economy such as power generation, petroleum refining & petrochemicals, cement, chemicals & pharmaceuticals, fertilizer production, mining activities, textile mills, hotels etc. use large number of axial flow fans for the aforesaid operations.

The axial flow fans are conventionally designed with impellers made of aluminium or mild steel. The grey area today is the inconsistency in proper aerofoil selection & dimensional stability of the metallic impellers. This leads to high power consumption & high noise levels with lesser efficiency. The leading fan manufacturers in the world have been looking at FRP axial flow fans for higher energy efficiency. The improved design of FRP fan is aimed at higher lift to drag ratio and thereby increasing the overall efficiency. The new & improved aerodynamic fan designing, composite expected to result in consistent quality and higher productivity.

Keeping in view the international trends and energy savings potential, the project on `Development of Energy Efficient FRP Axial-flow Fans' was launched by the Advanced Composites Mission of TIFAC, Department of Science & Technology in partnership with M/s. Parag Fans & Cooling Systems Ltd., Dewas (MP).The project involved improvisation of fan design by selecting the most appropriate aerodynamic blade shape to suite specific airflow applications, development of suitable composite materials and structural design to replace the use of metals such as aluminium & mild steel in the impellers. The fibre reinforced plastics (FRP) fans have the following advantages.

- Provides higher efficiency suitable for any specific application.

- Reduced overall weight of the fan, thereby extending the life of mechanical drive systems such as motors, gearboxes and bearings.

- Low power consumption resulting in appreciable energy savings as compared to existing metallic fans.

- Lower flow noise and mechanical noise levels compared to the conventional metallic fans.

- Longer life of fans due to improved mechanical strength.

- Excellent corrosion and erosion resistance and fire retardance.

As the fan efficiency is defined as (Q x DPt)/ (Shaft horsepower), thus with reduced shaft power requirement, there is a commensurate reduction in energy consumption.

Under the project, the following five types of fans were identified for development for their bulk requirement in the country: textile mill humidifers, mine ventilation, air heat exchangers, radiator cooling for diesel locomotives and cooling towers.

The project on the development of `Energy Efficient Axial Flow FRP Fans' was launched under the Advanced Composite Mission of TIFAC/DST in partnership with M/s Parag Fans & Cooling Systems Ltd., Dewas (MP) & IIT-Mumbai in September 1998. All the developmental activities encompassing designing the fans, selection of raw materials, stabilising fabrication procedure and finally performance testing of four fans were completed by December 1999. The fifth fan for radiator cooling applications for diesel locomotives for Indian Railways was successfully performance tested in January 2000.

Higher energy savings by using FRP axial flow fans would offer a pay-back period of 6-8 months on replacement costs at current energy rates. This would substantially contribute towards industrial energy savings for the nation.

Five fans as mentioned above have been developed successfully under the project. The performance evaluation of all the five types of fans established an efficiency differential of around 25 per cent over conventional fans with aluminium impellers. The air heat exchanger fan, fabricated by Resin Transfer Moulding (RTM) technique, tested at the refinery of Indian Oil Corporation (IOC) Ltd., Panipat with over 30 per cent energy saving as compared to existing fans imported from overseas suppliers.

Air-heat exchanger (forced convection) fan is a critical application with low pressure rise but high discharge volume with low noise levels operating at high temperature.

Another critical requirement of the fan is that no electrostatic charges should generate on the impeller of the fans. Parag Fans developed the fan incorporating surface resistivity characteristics by overlapping a copper wire mesh on the woven glass fabric. In addition, necessary safeguards for preventing erosion of FRP fans could be achieved by covering the leading edge of the impeller with stainless steel foil. Radiator cooling fan for diesel locomotive was also fabricated by RTM technique and tested as per international standards with improved performance.

G. Srikanth, Sangeeta Nangia

& Atul Mittal

Technology Information, Forecasting & Assessment Council (TIFAC), New Delhi

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