CrazyEngineers
CrazyEngineers
  • A three blade fan is being fixed to a electric motor held in the horizontal plane.The motor is being rotated with some angular velocity.The fan is being fixed in such a way that it throws the air downwards.Suggest me the way to calculate the thrust experienced by the system.assume the parameters required.
    Replies
Howdy guest!
Dear guest, you must be logged-in to participate on CrazyEngineers. We would love to have you as a member of our community. Consider creating an account or login.
Replies

  • skstheking

    Member • Apr 23, 2009

    what is mean about thrust????
    Are you sure? This action cannot be undone.
    Cancel

  • harsh15

    Member • Apr 23, 2009

    See a the air is pushed downwards ,according to Newton's third law the fan will be experiencing a reaction force in the upward direction.This is reaction force i m referring as a thrust.
    And as the action and reaction forces are equal and opposite calculate the force with which the air is pushed downward?
    Are you sure? This action cannot be undone.
    Cancel

  • g_rakesh2

    Member • Apr 23, 2009

    Thrust is a reaction force described quantitatively by Newton's Second and Third Laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a proportional but opposite force on that system.

    T=(dm/dt).V

    where:
    T is the thrust generated (force)
    (dm/dt) is the rate of change of mass with respect to time i.e (mass flow rate of exhaust)
    v is the exhaust velocity.

    This thrust formula used to calculate the motorboat/rocket thrust. And same you can use for a fan also as a motorboat generates thrust (or reverse thrust) when the propellers are turned to accelerate water backwards (or forwards). The resulting thrust pushes the boat in the opposite direction to the sum of the momentum change in the water flowing through the propeller, and in a rocket mass is propelled forward by thrust force only, which is equal and opposite to the exaust mass from combustion chamber.
    Are you sure? This action cannot be undone.
    Cancel

  • Rohan_sK

    Member • Apr 25, 2009

    The explaination about Thrust is very well given Rakesh, well explained buddy.
    The design of the fan actually needs the relation between the angular velocity or rpm of the fan and the air it can push or draw along with the blades. This includes the size, width, thickness and profile of the blades essentially. What Harsh requires is the formula for calculating the relation betwen fan rpm and thrust produced. This can be easily obtained from any basic book of fan design where everything will be explained in detail.
    So best of luck Harsh!! Happy designing;-)
    Are you sure? This action cannot be undone.
    Cancel

  • g_rakesh2

    Member • Apr 27, 2009

    Rohan_sK
    The explaination about Thrust is very well given Rakesh, well explained buddy.
    The design of the fan actually needs the relation between the angular velocity or rpm of the fan and the air it can push or draw along with the blades. This includes the size, width, thickness and profile of the blades essentially. What Harsh requires is the formula for calculating the relation betwen fan rpm and thrust produced. This can be easily obtained from any basic book of fan design where everything will be explained in detail.
    So best of luck Harsh!! Happy designing;-)
    Yes Rohan_sK you are right, but air and water both are fluids.
    and if you know mass flow rate and velocity as per your requirement you will get to know thrust. why to design whole fan or blade, if you know your requirements that's it...
    Are you sure? This action cannot be undone.
    Cancel
Home Channels Search Login Register