Mechanics:- Way to calculate the thrust

Replies

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  skstheking

  what is mean about thrust????
• 

  harsh15

  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?
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  g_rakesh2

  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.
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  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;-)
• 

  g_rakesh2

  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...