Hotspots in the construction such as actuators which dissipate heat affect e.g. the dimensional stability of the construction. In special environments such as vacuum and cryo, special care for heat abduction is needed. This sheet provides some insight in relation to this subject.
Heat transfer through molecular agitation within a material and is specified with the typical thermal conduction.
Length of barrier
Heat transfer through flow of a fluid. 2 Types: Natural and forced convection. Forced convection can be described with:
Convection heat transfer coefficient
with velocity of object trough fluid
Temperature of object
Temperature of convecting fluid
Heat transfer through the emission of electromagnetic waves from the emitter to its surroundings.
Temperature of emitter
Temperature of surrounding
Critical in contact heat transfer is contact area depended on clamp force, surface roughness, environment, cleanliness, humidity, etc. In other words it cannot be calculated analytically but must be tested and results are based on statistics.
Energy necessary to change the temperature of a mass with certain material specific heat capacity:
Specific heat capacity
Power, heat flow
Analog to stiffness and electrical resistance:
Emissivity is the ability of a surface to emit energy through radiation relative to a black surface at equal temperature. Maximum emissivity is (the black surface) and no emissivity is: .
|Material||Typical ε* [-]||@ Temp [°C]|
|Platinum (polished) / Silver (polished)||0.005||25|
|Gold (highly polished)||0.015||100|
|Stainless steel (polished)||0.02||25|
|White ceramic (Al2O||0.90||93|
*Just for indication, please verify with other resources before using
Irreversible heat transfer, typical the loss of power in an electrical resistor.
Voltage drop across resistor
Current through resistor
Special case: Piezo dissipation lossfactor
lossfactor: empirical: 30 %