I have a process tank that boils water to approximately 250 degrees F. It is horizontal and has dimensions of 36 inches in diameter and 5 ft. sidewall. There is a mixer .75 HP in the center of the tank operating at 1750 RPM. The mixer has a shaft that is 5\8 inches in diameter and uses a marine style propeller at 8 inches from the bottom (length to bearing approximately 28 inches). What would my critical speed be? What speed should I target for maximum agitation? I don't think full agitation is possible, due to prop size vs. amount of water. However, I would like to move as much water as possible. Should I consider a steady bearing at the bottom of the vessel? What would the critical speed be for a 5\8 inch shaft 28 inches in length with a marine prop in water be?
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Dave Dickey Forum Moderator 279 Posts
Re: What speed should I target for maximum agitation?29 July 2010 at 1:29pmWith some practical assumptions, the critical one of which is a propeller weight of 2.2 lbs for an 8.0-inch diameter marine propeller, the critical speed for a 5/8-inch diameter shaft, 28 inches long is about 580 rpm. With that critical speed, the mixer should not be operated over 490 rpm. It the prop is heavier than 2.2 lbs, the critical speed will be reduced, along with the maximum operating speed. With considerable care, operating the mixer in air (no liquid in the vessel) and gradually increasing the operating speed should identify a speed at which vibrations begin to occur. Operating at or above that speed should be avoided.