Twin Screw Pump

grabcad

My entry for this challenge is the idea to use a twin screw water pump. Keep in mind I do not have the necessary software to test pump performance but merely designed something that should get close to the performance needed. One would have to refine and test the design to get the optimal performance point. However more time would be needed. Detailed design process can then change the screw parameters like screw pitch and diameter. Also what the ideal RPM is for controlling the flow at the right pressure and flow rate.These types of pumps are already in use for multiple applications in industry pumping a lot of different fluids at different flow rates and pressures depending on what the needs are. The length and diameter and pitch of these screws as well as the tolerance between the rotating screws all play a roll in the performance output and can all be varied to achieve the desired output.The motor used is a KOVPT 57mm 24 Volt DC Brushless 3000RPM low noise and high torque motor.It can be used with a brushless DC motor controller. Motor fits onto drive shaft using spline to make assembly and servicing easier to fit new motor quickly if needed.The gear assembly is very stable and rigid by using 4 bearings to support the driving shafts. And oil seals are used at all open ends of the casing to ensure no ingress into drivetrain cavity that might damage any components. All gears and the two pumps screws are secured to the shafts by tolerance fits and shaft keys. The pump body components are sealed by use of a cut gasket to fit the profile of the bodies and is compressed between the bodies when attaching them to compress and offer perfect sealing. Both inlet and outlet is ½ thread and internal diameter is 8mm.The pump can be mounted by use of four slotted mounting locations on motor body and pump body. The pump overall dimensions are approximately (LxWxH) 300mm x 90.5mm x 82.5mm. The pump is long and thin. Making it easier to be mounted and hidden away in something like and aircraft fuselage or wing. See images of size comparison. Its about as big and long as two 330mm coke cans stacked on top of each other or just smaller than 2litre plastic bottle. See images given to give idea of size.Assembly of the pump is quite easy. The motor fits onto the first pump body part and is secured with 4 cap screws. The shafts with bearing and seals and gears are pre-assembled as complete units and introduced into the first pump body part once it is attached to the motor. The drive shafts fits over the motor shaft with a spline. The second shaft body is then secured of the shafts and screwed in place as the bearings and shaft seals slot into place. The gaskets are compressed between the body faces during assembly. Lastly the pump screws go over the exposed shafts once the second pump body part is firmly attached. These attached to the shaft with shaft keys and secured to the end with screws. Then the last pump body part goes over the pump screws and is secured.Total weight of pump and motor is approximately 2100 grams (2.1kg)High grade aluminium and titanium is used for materials to gain strength and better weight values.Other cheaper materials can also be used but will make the pump slightly heavier.The reason I chose a twin screw pump is because it has the following benefits:• Can run dry and can handle entrained air.• Runs very quite• High efficiency• Can operate at very high pressures• One can easily change the flow rates and pressure by simply changing the screw pitch.In this instance the screws can be set up to deliver high pressures at lower flow rates.This however needs to be tested with CFD software to get the right setup. The pump can also easily be controlled by using a VSD and changing the input RPM the pump can give many different performance parameters for flow to be controlled very precisely.• The pump has very little maintenance needed and these types of pumps can have extremely long service life. Up to 40 years.• One can easily and quickly change from thin to thick liquids with different viscosities without any issues. This type of pump can easily handle water or glycol or iso-propanol.• The brushless motor is very reliable and can quickly speed up the pump to establish flow immediately.• The pump can operate at any temperature or altitude. Because the performance is dependent on speeds of rotation and the screw design multiple setpoints can be achieved.Drawbacks:• These pumps tend to be more expensive initially but make up for it in long service life and reliability.• Manufacturability might be slightly more difficult. But one can use additive manufacturing technology like metal 3D printing with aluminium or titanium to assist in easier manufacturing of parts.