This current motor uses a water-driven propeller in a casing, with a chain drive carrying rotation to an upper support frame. The calculator compares the incoming kinetic power per unit area at two stream speeds. It does not predict the power delivered by this historical device.
Current Motor Interactive Calculator
Compare incoming kinetic power flux at two stream speeds. See the submerged propeller, cutaway casing and chain transmission of the historical current-motor arrangement.
Equation Used
- Same entered density in both cases.
- Uniform incoming velocity normal to the comparison area.
- No capture-area, efficiency or shaft-power model.
- Equal chain wheels and prescribed motion used only for illustration.
Animation speed and construction proportions are illustrative. Duct amplification, rotor rpm, torque and delivered output are not calculated.
A submerged propeller and an above-water drive
Hiscox figures 473–474 show a flared casing around an axial propeller, a shaft leaving its rear, and a chain connection to the suspension frame. The animation reconstructs that arrangement with the upper part of the casing removed so the rotor can be seen.
The rotor shaft, lower chain wheel and upper chain wheel turn together in the illustrative equal-wheel layout. The chain follows a closed path between them. Blade dimensions, sprocket proportions and speed are drawing choices; the three calculator inputs cannot establish them.
Compare the stream resource
Use the two velocity entries to compare the same water density at different current speeds. Both entries can be higher or lower than the other. The bars share a scale based on the larger result, so a faster second case is displayed as an increase rather than clipped to 100 percent.
These values describe the incoming kinetic-energy transport through a unit area normal to the current. A real installation also needs its capture area, device behavior and losses to estimate delivered output.
Why velocity is cubed
Mass passing through area A each second is ρ A v. Multiplying that mass flow by kinetic energy per unit mass, v²/2, gives P=ρ A v³/2. Dividing by A gives flux p=ρ v³/2 in W/m². The calculator divides by 1000 to display kW/m².
For a common density, p₂/p₁=(v₂/v₁)³. The percentage ratio is 100 p₂/p₁. Signed decrease is 100−100 p₂/p₁; a negative value means the second case has more incoming flux.
Worked speed comparison
At ρ=1000 kg/m³ and v₁=2 m/s, the incoming flux is 4 kW/m². At v₂=1.5 m/s it is 1.6875 kW/m². The second case retains 42.1875 percent of the first, a decrease of 57.8125 percent.
If the velocities are exchanged, the second case becomes 237.04 percent of the first. The signed decrease becomes −137.04 percent. Doubling density doubles both absolute fluxes and leaves their ratio unchanged.
What the animation does not calculate
The rotating propeller explains the construction. Its animation rate is prescribed and does not claim to be the rotor speed at either entered stream velocity. No blade pitch, rotor diameter, load torque or performance map is supplied.
The flared inlet is shown because it belongs to the historical arrangement. The illustration does not establish a velocity increase through that casing or extra energy capture. Actual shaft output must be distinguished from undisturbed incoming kinetic power.
Current-motor questions
Why is this no longer a paddle wheel?
The referenced current motor is an axial propeller in a casing with a chain drive. A paddle wheel is a different construction.
Does the calculator return generator power?
No. It returns incoming kinetic power per square metre.
Why does the rotor not speed up with the velocity slider?
Velocity alone cannot establish its loaded rpm. The animation demonstrates motion at a stated illustrative speed.
Why can the decrease be negative?
The second input is allowed to exceed the first, which increases the calculated flux.
References
Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances, printed page 133, figures 473–474, for the motor and casing construction. Oak Ridge National Laboratory, Hydrokinetic Principals, section 3.1.5, for stream power density and the distinction between resource and technology-specific capture.
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