The composite wall experiment determines how heat conducts through several material layers in series and finds the overall thermal resistance and conductivity of the assembly. It applies Fourier’s law to layered walls, exactly how heat loss is calculated for furnace linings, building walls, and insulated equipment.
Aim of the experiment
To determine the total thermal resistance and overall thermal conductivity of a composite wall made of different materials in series.
Theory and formulas
For steady one-dimensional conduction through layers in series, the same heat flows through each layer and the thermal resistances add, just like resistors in series:
- Fourier’s law: Q = −kA (dT/dx)
- Thermal resistance of a layer: R = L / (kA)
- Total: Q = ΔToverall / ΣR = A · ΔToverall / Σ(Li/ki)
where L is layer thickness, k its thermal conductivity, and A the area. Measuring the heat input and the temperature drop across each layer gives each material’s conductivity and the overall U-value.
Apparatus required
- Composite wall apparatus, slabs of different materials (e.g. mild steel, brass, wood or asbestos, aluminium) clamped together
- Central electric heater between the slab stacks and a cooling plate
- Thermocouples at each interface and a wattmeter/heater control
Procedure
- Clamp the slabs firmly together and switch on the central heater.
- Allow the assembly to reach steady state, then record the heater input (Q) and the temperature at every interface.
- Compute the temperature drop across each layer.
- Calculate the thermal resistance of each layer and the total, then the overall conductivity.
Result
The total resistance equals the sum of the layer resistances, and the layer with the lowest conductivity (the insulator) shows the largest temperature drop, proving why insulation works.
Applications
Composite-wall heat flow governs furnace and boiler wall design, building insulation, cold-storage panels, and lagged equipment. It builds directly on the heat conduction experiment (linear & radial) and underpins exchanger design such as the double-pipe heat exchanger. Thermal conductivity is defined in the engineering lab glossary.
Frequently asked questions
Why do thermal resistances add in series for a composite wall?
Because the same heat flows through each layer in turn, the temperature drops add up, exactly like voltage drops across series resistors.
Which layer has the largest temperature drop?
The layer with the lowest thermal conductivity (the best insulator) has the highest resistance and therefore the largest temperature drop.
What is the U-value of a wall?
The U-value is the overall heat-transfer coefficient (the reciprocal of the total resistance per unit area); a lower U-value means better insulation.
Need a composite wall apparatus for your heat-transfer lab? Request a quote from Scientico India, ISO 9001:2015 certified, CE marked, exporting to 60+ countries, reply within 24 hours.
Turn a composite-wall demonstration into a measurable experiment
A composite-wall rig should let students relate heat flow to the temperature drop across known layers. The specification must distinguish the heater, specimen stack, insulation and temperature locations. If layer materials or thicknesses can change, the quotation should identify which specimens and clamping parts are supplied.
What to confirm before requesting a quotation
- List the layer materials, thicknesses and usable specimen area.
- Confirm heater control, input measurement and temperature-sensor positions.
- State insulation, guarding and safe surface-temperature provisions.
- Request the steady-state procedure and calculation method used in the manual.
For an international order, also state the quantity, destination, electrical supply, documentation, installation or training needs and requested delivery basis. Treat catalogue information as a starting point; the current model page, datasheet and written quotation must confirm the exact configuration.
Composite-wall apparatus: specimens, sensors and calculation method
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