THERMAL DESIGN
THERMAL MANAGEMENT OF ELECTRONICS, HEAT EXCHANGERS GUIDES, FREE SOFTWARE AND CALCULATORS
temperature
is a measure of the average molecular kinetic energy in the matter. The normal flow of kinetic energy is from a higher temperature region (or an object) toward a lower temperature region (or an object). This flow is referred to as heat transfer. In general, there are three types of heat transfer: conduction, convection, and radiation. Conduction is the collisional transfer of energy between atoms, which occurs in solids. Convection is the motion of molecules in air or fluids. Radiation is the energy flow by electromagnetic waves. In practical electronics only the first two types are noticeable.Electric currents or alternating electromagnetic fields cause power dissipation in all electronic components, which results in increase of their temperature. The reliability and life expectancy of any component is related to its operating temperature. Failure rate and its inverse, mean time between failures (MTBF), are measures of the electronic system reliability. According to Arrhenius model, each 10°C rise in temperature increases the failure rate by 50%. At certain temperature any electronic component can be irreversibly destroyed (a typical maximum operating temperatures for semiconductors is 125-175 C at the junction, capacitors 85-125 C, wire insulation- 105-200 C). The thermal management and engineering whose task is to control the operating temperature of the product, is therefore an essential part of electronics design.
Rth-hs<(Tjmax-Ta)/P-(Rthj-c+Rthc-hs) oC/W,
where Ta- ambient temperature, Rthj-c - thermal resistance between junction and the case from the datasheet (typically 0.5-2.5 oC/W for conventional power packages), Rthc-hs - thermal resistance between the device's case and the heatsink, P- power dissipated by the device in watts. Once you found required Rth-hs, you can pick a part with equal or lower value of thermal resistance. Harry Lythall found empirically a "rule of thumb" calculation formula for Rth-hs of heat sinks made of U-shape folded aluminum sheet. Based on his equation, the required surface area in sq.cm is A=(50/Rth-hs)2.
In general, the main optimization criteria are to maximize the exposed heat exchanger's surface area, and to minimize its weight and the mean distance of the exposed surface from the component to be cooled.
Below you will find free calculators and more information on the thermal design.
HEAT AND THERMODYNAMICS BASICS
THERMAL MODELING AND ANALYSIS SOFTWARE
THERMAL DESIGN GUIDES, ANALYSIS & APPLICATION NOTES
Heat conduction formulas
Heat Radiation
A detailed heat transfer textbook for engineering students (conduction, convection, radiation)
The First Law of thermodynamics
FIND HEAT MANAGEMENT PRODUCTS BY SPEC
ThermoAnalytics demo software
Thermal conductivity units
Temperature units conversion
Flow velocity calculator
Thermal resistance and fin efficiency online calculators
THERMAL DATA OF ELECTRONIC COMPONENTS
How to determine thermal resistance for a power semiconductor heat sink
Thermal conductivity of various materials
Heatsink extrusion temperature and length correction
Fan speed controllers designs
What you need to know about cooling fans
HEATSINK PROPERTIES AND DESIGN NOTES
Analytical model for simulating electronic systems' thermal behavior
Heatsink design guide
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