User Manual

17
Thermal Solutions Design Guide | Specifications subject to change
Estimating power requirements
The total amount of power required for an application is the larger
of two values:
1. Warm-up power + Heat lost during warm-up
2. Process heat + Heat lost in steady state
Warm-up power: Watts required to bring an object to
temperature in a given time. The basic formula is:
()
()
t
TTmC
wattsP
ifp
−
=
where:
m = Mass of object (g)
C
p
= Specific heat of material (J/g/°C)
T
f
= Final temperature of object (°C)
T
i
= Initial temperature of object (°C)
t = Warm-up time (seconds)
For other materials see Minco white paper “Prototyping Techniques for
Etched-Foil Heaters” at www.minco.com.
To get: Multiply:
J/g/°C BTU/lb/°F × 4.19
g/cm³ lbs/ft³ × 0.016
Process heat: Heat required to process a material when the heater
is performing useful work. The formula above also applies here,
but must also include latent heat if material changes state (melts
or evaporates).
Heat loss: All systems lose heat through convection (air or
liquid movement), conduction through support structures,
and thermal radiation.
For more tips on designing and testing with Thermofoil heaters,
visit the Heaters page on Minco.com.
Material Specific heat (J/g/°C) Density (g/cm³)
Air 1.00 0.0012
Aluminum 0.88 2.71
Copper 0.38 8.97
Glass 0.75 2.64
Oil (typical) 1.90 0.90
Plastic (typical) 1.25 Varies
Silicon 0.71 2.32
Solder 0.19 8.65
Steel 0.50 7.85
Water 4.19 1.00
INNER ELEMENT
POWER SUPPLY
OUTER ELEMENT
POWER SUPPLY
Estimating power distribution
A mosaic of standard heaters, with dual power supplies,
helps to determine edge profiling for uniform temperature.
The resulting custom heater looks like this.
Prototyping with Thermofoil Heaters
Use multiple standard heaters to prototype a proled heating solution
Create a Mosaic of Heaters
Etched-foil heaters provide excellent temperature control and
uniformity in a broad range of applications. Their thin profile
and foil elements contribute to fast warm-up, consistent
heat distribution, and extended heater life. To achieve
ideal performance, however, the heater must be properly
configured to the thermal demands of the application.
The complex physics of heat transfer makes it difficult to
predict all aspects of system performance in the early design
stages. Therefore, applications requiring tightly regulated
temperature may require extensive prototype work.
Minco offers off-the-shelf stock heaters in a variety of sizes
and insulation packages, including polyimide, silicone rubber,
mica, optically-clear polyester, or PTFE.
If the size or shape of your heat sink precludes using a single
standard heater, you can often construct a mosaic to cover the
surface. Grouped etched-foil heaters mimic profiled designs.
Simply increase power to certain heaters until temperature
stabilizes in the desired pattern. The resulting power settings
tell you how to profile the watt density zones in a custom
design.