The basic requirement for testing draft fans is to find the amount of air and exhaust gases flowing out of the furnace or boiler. Draft fans may accumulate some dust particles on the blades of the fan, resulting in lower flow rates of the air and exhaust gases. Strength test is performed based on the rigidity of the system to determine the amount of stress that the system can withstand.
Measuring air and gases flow rate
- The main purpose of the draft fans is to either provide fresh air into boiler or to remove the exhaust gases from it.
- Flow rate can be measured in many ways. Simple way to measure is by knowing the pressure difference in the boiler between induced draft and forced draft.
- If the pressure head, kinetic head and potential heads are known then the mass flow rate is known by which the flow rate of the air and gases are calculated.
- In modern world there are some advanced devices which use electric energy to find out the flow rate of the gases when placed on their path of motion.
- The flow rate of the fans are tested after they are installed in the boiler. The strength test can be performed any time either before installing or after installing.
- Strength test determines the amount of stress that can be hold by the system.
A system may be subjected to either thermal stress or structural stress.
- The thermal stresses are induced as a phenomenon of the conduction due to temperature difference among the parts of the fan.
- Structural stresses are induced due to the action of various factors such as vibrations caused at the lower speed of the fans.
The thermal stresses are tested on the conditions of conduction, convection, radiation and heat flux.
- The structural stresses are tested depending on the strain energy and the Young’s modulus of the material used.
- In the convection method they are tested using a model of the system and the model is applied for real conditions such as temperature and pressures in case of thermal stresses, and ultimate stress & yield stress in case of structural stress distribution.
- The above mentioned testing may sometimes result in destruction of the system.
- Due to advancement of computer technology there are many software’s which use numeric methods such as FEA to find the thermal and structural stress of the system.
- By the aid of these numeric systems one can give the exact values of the stresses induced in the system.
In industries, testing is very important as it increases the life of the system. If the system is not tested thoroughly, there can be huge loss of money or human life in the organization.