Single-Bar Coolers (SBC)

The SBC coolers are the leading seller among the products offered by MC². These coolers are mounted with single diode bars, and then are stacked with other cooler/diode to create a modular high power light source.

As shown in the photo at the right, the cooler has inlet and outlet holes on the side face (the larger holes visible in the photo). Two alignment alignment pin holes are located on the side near the bottom of the cooler (the left-most holes in the photo), and a third hole is located between the two fluid ports. The diode bar is mounted on the side, flush with the right edge of the cooler in the photo.

Description.

Internal Design. The SBC microchannel coolers use larger passages than the SA-X line of coolers, with passage widths typically ranging from 0.008" to 0.012". These larger passages call for operation of the coolers in the transitional flow regime. Internal features may be added as needed to enhance the heat transfer at lower Reynolds numbers.

External Design. The external configuration of the cooler is shown in MC2 Drawing XXXX-XX-XX. Nominal values for the tolerances, surface finish, and plating are provided in the drawing, although these specifications may be tailored as required in most cases.

Construction and Chemical Compatability. The coolers are fabricated from a dispersion-strengthened copper alloy with about 90% of the thermal conductivity of pure copper, and much higher strength at elevated temperatures. Compared to the copper microchannel coolers manufactured by other vendors, MC2's coolers are stiff and durable. The chemical resistance is the same as that of copper, so the material compatibility and corrosion resistance tables for copper may be used.

Performance. The graphs below show the thermal and flow performance of the nominal 0.008"-wide SBC microchannel design. The data was taken from evaluation units with a 1 cm x 2 cm cooled area. The thermal resistance in the left-hand graph is defined as: (T_s - T_in)/q, where T_s is the average surface temperature under a 0.04" wide diode, T_in is the inlet water temperature, and q is the average heat flux.

Usage.

Component Mounting. Typical installations involve soldering or brazing a component or component carrier to the surface of the cooler. The coolers can be processed at temperatures up to 1500 °F, and thus are compatible with conventional soldering and brazing processes. Due to the grain structure of the copper alloy, it is advisable to plate the interface with copper or nickel prior to brazing with silver-based brazes to prevent migration of the silver into the cooler (depleting the silver at the braze joint). If excessive mechanical loads are applied to the cooled surface, it is possible to deform the surface, crushing the internal channels. This may be avoided by either: 1) limiting loading on the surface to less than 1000 psi, and/or 2) requesting a custom design with a more robust surface.

Installation in Flow Systems. MC2's micro-impingement cooler packages require special mating manifolds. These manifolds are designed to allow coolers to be closely arrayed without interference from the manifolds or the coolant lines. The coolers are bolted to the manifolds, with o-rings sealing the inlet and outlet ports. Manifolds and manifold arrays can be custom-designed for the users' applications, or may be fabricated by the users themselves.

A common question during installation is: Does it matter which way the coolant flows through the cooler? The answer is yes, it definitely does matter - flowing the wrong way will yield higher pressure drops and higher thermal resistance values. Even with the flow reversed, however, the coolers are still likely to outperform any competing products.

Filtering and Cleaning. Upstream filtering should be provided for the coolers, with a filter mesh size 20 - 30% the size of the minimum microchannel dimension. Flow lines between the filter and the cooler should be cleaned prior to use of the cooler. Sealing aids such as teflon tape should be avoided as much as possible between the filter and the cooler. Standard coolers can survive pressurization to 250 psi with no ill effect. This may be compared to standard operating pressures, which are expected to be less than 50 psi.

Long Term Performance. To date only limited long-term performance data is available on MC²'s coolers. Continuous testing for 3000 hours has resulted in only a modest increase in the flow rate of the coolers. The coolers should be resistant to clogging, given proper filtering and periodic backflushing. Unlike competing coolers, MC2's coolers experience very minor internal erosion. Copper and its alloys are inherently resistant to biofouling, although for long-term usage we recommend a UV filter somewhere in the system. If in an application corrosion is determined to be a problem, a commercial additive such as OptiShield (Opti Temp, Inc., Traverse City, MI) may be introduced into the cooling water.