INDEK carries a complete set of components from D.C. Pator heat sinks, active coolers, Therm-A-Pipe heat pipes to customized assemblies.
Cooling Component Selection
Each heat sink has its performance specified with a curve relating the thermal resistance
to the linear airflow across the heat sink surface, e.g., for a heat sink with the performance
curve in, its thermal resistance is 1°C/W when the airflow across it is 4m/s. Knowing
the heat sink thermal resistance (Rth) and the surrounding temperature (Tbox), we find the
CPU (with Q watts heat dissipation) casing temperature (Tcpu) using the following equation:
Tcpu=Rth(°C/W) x Q(watts) + Tbox (eq 3)
As the chip performance increases, it tends to produce more heat. For high performance chips, passive heat sinks are often too small. We then have two alternatives: i) use an oversized heat sink, or ii) use an active cooler.
In the case of tight spatial requirement, we use heat pipes to bring heat from one spot to another with enough space for a large heat sink or active coolers. Heat pipes are media that rapidly transfer heat from one end to the other. They work in either direction and even with the hot spot in the middle.
INDEK's Therm-A-Pipe are hollow copper tubes with wicks composed of grooves on the inner wall and wire. Wick helps carry condensed liquid from the cold end to the hot end. The pipe's operating fluid is a small amount of pure water injected within the pipe pumped down to near vacuum.
Thermal resistance of a heat pipe depends on the pipe size, length, bends, and orientation. When used within the recommended heat capacity range, a heat pipe assures fast heat transfer with thermal resistance around 1°C/W for its entire length. In many heat pipe applications, we are often more concerned with thermal resistance of the heat sink at the cold end and that of thermal interface material.
Whether mounting a heat sink directly on a hot chip or a full blown heat
plate, heat pipe, and heat sink assembly, we need to estimate the effect of interface material
(grease, glue, or double sided tape). Although they add to the overall thermal resistance,
these interface material eliminate air holes between metal to metal contact and contribute to
better heat transfer. We find the total thermal resistance due to one layer of interface material
Rth-Rb1 + Rm + Rb2 (eq 4)
where each term means:
Rb1, 2: Thermal resistance at boundary (°C/W)
Area (m 2)
Rm: Thermal resistance of interface material
H(W/m-°C) * Area (m 2)
Constants K and H are listed in interface material catalogs. Typical values are K-3.7x10-4= (°C-m2 /W), and K=0.3(W/m-°C). But remember, analysis never defeats a good repeatable experiment.
Man made devices continue to increase entropy and we continue to lessen the imbalance. The cycle continues as chip producers make them go faster and hotter.