Analogous to electrical resistance; R=L/kA for a wall.
Thermal resistances combine like electrical resistances: R_cond=L/kA, R_conv=1/hA, R_rad=1/h_rA. Series walls add; parallel paths combine reciprocally. The overall heat transfer coefficient U=1/(ΣR·A). Used for building walls, pipes and heat exchangers.
A wall with R-value 3 m²K/W has U≈0.33 W/m²K.
Thermal resistance lets you treat heat flow like electrical current, which makes it easy to combine walls, layers and contact resistances.
Analogous to electrical resistance; R=L/kA for a wall.
Thermal resistance lets you treat heat flow like electrical current, which makes it easy to combine walls, layers and contact resistances.
The wall thickness divided by the thermal conductivity and the area, which gives the resistance to heat flow through the wall.
Resistances in series add, and parallel heat paths combine like parallel electrical resistors.
Typical applications include adding the resistances of a multi-layer wall to find the total heat loss, estimating the temperature of a chip from its thermal resistance to ambient and finding how much a thermal pad helps to cool a power device.
Study "Conduction" first (topic 84 of 105 in Thermodynamics & Fluids). It covers the groundwork this topic builds on.
Contact resistance. Insulation critical radius. Temperature drops proportional to R.
A wall with R-value 3 m²K/W has U≈0.33 W/m²K.
The next topic is "Convection", which builds directly on this one.
It is classed as Advanced in Thermodynamics & Fluids (topic 85 of 105). It is an advanced topic. It assumes you are comfortable with the intermediate topics in Thermodynamics & Fluids.
Want to practise? Open the interactive course for quick checks, quizzes, simulations and progress tracking.