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Notes from the field ·

Build a Cool Box That Beats the Heat: A Design Challenge

By Ahmed, founder

Design challenges teach engineering: build, test, find the weak spot and improve. A cool box challenge is a good one, because the result is a number (millilitres of meltwater) and the best designs are cheap.

The challenge

Design a container that keeps ice from melting for 40 minutes on a warm day. Your design is tested against a plain tub with the same amount of ice.

What you need

  • Plastic tubs or boxes
  • Recycled insulation: newspaper, bubble wrap, foam trays, cardboard, old socks
  • Aluminium foil
  • Tape and scissors
  • Ice cubes, all from the same tray
  • Measuring cup and a timer

Rules

  • Same number of ice cubes in each container.
  • A budget: each material costs points, and teams stay under the limit.
  • A size limit, so no one builds a giant box.
  • A lid is allowed, but the ice must be inside for the full 40 minutes.

Steps

  1. Plan. Sketch the design and label where heat could get in: sides, top, bottom, gaps.
  2. Build.
  3. Test. Place the ice, close it, start the timer and leave it in a warm spot.
  4. Measure. After 40 minutes, pour out and measure the meltwater. Less is better.
  5. Improve. Change one thing and test again.

What usually works

Layers that trap air do well. A tight lid matters a lot. Gaps let warm air in, so seal them with tape. Foil on the outside can reflect radiant heat, especially in sun. A box within a box with air or filler between them often beats a single thick layer. Results vary, so say what surprised you.

The science

Heat travels three ways: conduction (through materials), convection (moving air or liquid) and radiation (light and infrared). A good cool box slows all three: insulation slows conduction, tight seals and trapped air limit convection, and shiny surfaces reflect radiation.

Reflect

  • What was the weakest part of your design?
  • What would you change with double the budget?
  • How is your design like a commercial cooler?

The full lesson is Can you build a cool box that beats the heat? in Keep It Cool. For a similar challenge, see Can you keep an ice cube frozen the longest? Sign up for three lessons free.