Tabletop MHD Drive Thrust and Model Scaling

ISEF Category: Physics and Astronomy

Subcategory: Other  ·  Difficulty: Advanced  ·  Setup: University Lab  ·  Time: Full Year

The Hook

A saltwater dish can act like a tiny engine. When electric current crosses a magnetic field, the water feels a sideways push. That same physics can move lab-on-a-chip pumps and swimmer-bots. You can test how much force your setup really makes, then check whether a computer model agrees.

What Is It?

Magnetohydrodynamics, or MHD, studies how electric currents and magnetic fields push on conducting fluids. In your project, saltwater acts as the conductor. The battery sends current through the water, and the magnets create the field. Their interaction creates a force on the fluid, which can produce motion or thrust.

Think of it like a sideways tug-of-war. The battery wants charges to move one way, and the magnet nudges them at right angles. That sideways nudge transfers momentum to the water. Your job is to measure how that force changes when you change current, field strength, electrode spacing, or salt concentration, then compare the pattern with a finite-element model in FEniCSx. FEniCSx is a modeling tool for solving equations on real shapes and geometries.

Why This Is a Good Topic

This makes a strong science fair topic because you can test a real physics law and compare it with a model. The project has clear variables, measurable outputs, and room for careful controls. It connects to soft robotics, micro-pumps, and underwater vehicles, so the real-world angle is easy to explain. You can also learn fluid mechanics, electromagnetism, data analysis, and simulation in one project.

Research Questions

• How does thrust change as current increases in a fixed saltwater and magnet setup?
• What is the effect of magnetic field strength on the measured thrust of the MHD drive?
• Does changing salt concentration alter the thrust produced at the same voltage?
• To what extent does electrode spacing change the efficiency of the drive?
• Which scaling law best predicts thrust from current, field strength, and fluid conductivity?
• How closely does a finite-element MHD model in FEniCSx match the measured thrust data?

Basic Materials

• Saltwater dish or shallow nonmetal tray.
• Neodymium magnets with known dimensions.
• 9 V battery or bench power supply with current limit.
• Carbon or graphite electrodes.
• Digital multimeter.
• Small force sensor, force gauge, or improvised thrust balance.
• Connecting wires with alligator clips.
• Digital kitchen scale with 0.1 g accuracy.
• Ruler or calipers.
• Table clamp or stand to hold the setup steady.

Advanced Materials

• Bench power supply with current readout and limit control.
• Gauss meter or Hall sensor for magnetic field mapping.
• Load cell with amplifier for thrust measurement.
• Conductivity meter or salinity refractometer.
• High-speed camera for flow tracking.
• Transparent test cell with repeatable electrode geometry.
• Temperature probe.
• Computer with FEniCSx installed.
• Python environment for model fitting and uncertainty analysis.
• Nonconductive fixtures and alignment hardware.

Software & Tools

• Python: Fits scaling laws, makes plots, and handles uncertainty analysis.
• Jupyter Notebook: Keeps your data cleaning, modeling, and notes in one place.
• FEniCSx: Solves the MHD equations on your chosen geometry.
• ImageJ: Tracks visible flow motion or marker movement in video frames.
• GeoGebra: Helps sketch geometry and estimate dimensions before modeling.

Experiment Steps

1. Define the exact output you will measure, such as thrust, flow speed, or both, so your data answer one clear question.
2. Choose one geometry and keep it fixed, because changing the shape and the variables at the same time will blur your results.
3. Plan a calibration method for your force sensor or balance so your force readings convert to real units.
4. Build a control set that separates magnetic effects from plain electrolysis, heating, and buoyancy changes.
5. Set up a modeling workflow in FEniCSx that matches your experimental geometry, material properties, and boundary conditions.
6. Decide in advance how you will test a scaling law, then compare model predictions and measurements with the same metric.

Common Pitfalls

• Using steel screws, trays, or clips near the magnets, which distorts the field and changes the force.
• Letting bubbles build up on the electrodes, which blocks current and makes thrust drop during a run.
• Measuring thrust on an uncalibrated balance, which turns small force changes into noisy data.
• Changing salt concentration, magnet spacing, and voltage at the same time, which makes cause and effect impossible to separate.
• Comparing the model to raw voltage instead of current and conductivity, which hides the actual physics.

What Makes This Competitive

A strong version of this project will do more than show that force exists. You need clean controls, a repeatable geometry, and a clear uncertainty analysis. The best work will test more than one scaling law, then explain why one model wins. Matching experiment to a finite-element simulation also raises the level, especially if you check where the model fails and why.

Project Variations

• Test how electrode material changes thrust by comparing graphite, copper, and stainless steel contacts in the same geometry.
• Compare different salt concentrations to see how conductivity changes both current draw and measured propulsion.
• Replace thrust with flow mapping and measure how fast dye or floating tracer particles move under the same MHD conditions.

Learn More

• NASA Glenn Research Center educational resources: Search for pages on electromagnetism, electric motors, and fluid force concepts that support MHD basics.
• NOAA National Data Buoy Center educational pages: Use simple field-and-flow ideas to connect fluid motion with environmental systems.
• PubMed: Search review articles on magnetohydrodynamics in biomedical pumps and microfluidic devices.
• Physics of Fluids: Search for articles on low-Reynolds-number flow, MHD pumping, and conductivity effects.
• MIT OpenCourseWare: Look for fluid mechanics and electromagnetism course notes that help with governing equations and scaling.