Heat Flow Intuition

Heat is invisible, but its behavior is simple: it flows from hot to cold. Here you can see how material, thickness, area, and temperature difference change the heat flow rate.

Controls

Adjust parameters and watch heat flow change instantly. This is a 1D conduction intuition tool (steady state).

Hot side temperature (T_hot) Higher hot side = stronger driving force

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Cold side temperature (T_cold) Lower cold side = stronger driving force

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Material (thermal conductivity k) High k = heat crosses easily (metals)

Thermal conductivity (k) Bigger k = more heat flow

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Wall thickness (L) Thicker wall = heat struggles more

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Cross-sectional area (A) More area = more “lanes” for heat

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Reset Back to default values

Tip: Try switching between Metal and Foam with the same thickness. You will instantly feel why insulation works.

Visualization

Arrows show heat flowing from hot → cold. Faster motion and thicker arrows mean higher heat flow.

Live heat flow

Steady-state conduction

— hot side

— cold side

Heat flow rate (Q)

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Thermal resistance (R)

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What changed the most?

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How to use

Start with the default settings and observe the arrow speed.
Increase thickness (L). You should see heat flow slow down.
Increase area (A). Heat flow should increase.
Switch material (Copper → Foam). Notice the huge difference.
Finally, change T_hot − T_cold. Bigger difference drives stronger heat flow.

Try this quick experiment: Set L = 0.02 m, A = 0.02 m², then switch Copper → Foam. That single change explains most of insulation design.

What is heat flow, and why does it matter?

Temperature is how “hot” something is. Heat flow is how fast energy moves because of a temperature difference. Engineers care because heat flow decides whether a design is safe, comfortable, efficient, or fails.

Electronics: chips must dump heat to avoid throttling or damage.
Buildings: insulation reduces heat loss and saves energy.
Manufacturing: cooling rates change material properties and warping.
Products: geometry and materials decide how “hot to touch” something feels.

Symbols (what each one means)

T_hot: temperature on the hot side (°C)
T_cold: temperature on the cold side (°C)
ΔT = T_hot − T_cold: driving force for heat flow (°C or K)
k: thermal conductivity (W/m·K). Bigger means heat passes through easier.
A: cross-sectional area (m²). More area = more heat flow.
L: thickness (m). More thickness = less heat flow.
Q: heat flow rate (Watts). How many Joules per second move through the wall.
R: thermal resistance (K/W). Bigger resistance means heat struggles more.

Math (optional, but useful)

In steady-state 1D conduction through a flat wall, the heat flow rate is:

Q = (k · A · (T_hot − T_cold)) / L R = L / (k · A) So: Q = (T_hot − T_cold) / R

Plain English: Heat flow increases if you increase k, increase A, or increase ΔT. Heat flow decreases if you increase L.