Stackable Coolers

Typical stack of laser diodes; each diode is cooled by a dedicated cooler.

Overview. Stackable cooler designs (also known as "single-bar coolers") allow the user to create one-dimensional arrays of edge-emitting laser diodes, each cooled by its own cooler. The coolant generally enters through the forward inlet port, is conveyed to the cooling passages under the diode, and then exits via the rear outlet port. A central bolt hole is also included to allow the stack to be bolted together

Single-Bar Cooler Designs of Various Sizes

Typical cooler dimensions are 1.2 - 2 cm in width, 40 - 70 cm in length, and 0.125 - 0.225 cm in thickness. Cooling can be provided for relatively arbitrary heating footprints. Typical cooling areas are 1 cm wide by 0.1 cm to 0.7 cm deep (in the cavity length direction). Longer cavity lengths may require thicker cooler designs to obtain desire flow distribution and pressure drop targets.

Cooling Design. In the past the cooling passages were based on simple U-turn designs with passage widths ~200 microns, such as those shown on the "Microchannel Coolers" page. Recently, however, MC2 has successfully incorporated the higher performance microimpingement & lateral flow cooling passages into stackable cooler packages. This provides outstanding thermal performance in flexible packages. Cooler performance values can be obained from the "Microchannel Coolers" page.

Manifold Design. As with all cooling architectures, the design of the inlet and outlet manifold networks is critical. If a change to the design of a stackable cooler is required, it is customary to re-evaluate the flow distribution using computational fluid dynamics analysis of the flowfield. In cases where the thickness of the cooler is limited, it may be necessary to design more complex manifolds to achieve the desired flow distribution. These designs usually increase the pressure drop of the cooler by up to 25%.

Thermal and Flow Performance. As mentioned above, the thermal performance is based on the internal cooling passage design, as discussed on the "Microchannel Coolers" page. The flow performance depends on the manifold layout and geometry, as well as the particular cooling design. Examples of thermal and flow performance measurements on typical stackable coolers are shown in the chart below.

A Note on Thermal Resistance. The areal thermal resistance used in our specifications is defined as the temperature difference between the average surface temperature and the coolant inlet temperature, divided by a uniform heat flux. The geometries used in performance measurements ensure that there is no thermal spreading, so the heat transfer geometry is truly 1D.
A Note on Flow Rates. MC2 uses an areal volumetric flow rate in its performance charts. This flow rate is the total flow divided by the cooled area. Using the areal definition allows you to quickly compare performances and flow rate requirements of coolers with large size differences. For example, if you desired a thermal resistance that could be achieved with an areal flow rate of 1 LPM/cm2, you can quickly determine that the total flow for a 2 cm2 cooled area would be 2 LPM, and for a 30 cm2 area would be 30 LPM.