Success Story – High Heat Flux Direct Expansion Subsystem

Aspen was approached by a new customer with a unique cooling requirement. This customer required a cooling subsystem which would provide a high heat flux (150 W) to a cold plate mounted on a small chip (approximately 2 x 2 in.). The application also required a solution which would cool the cold plate to very low temperatures (-30°C) in order to respond quickly when the heat load was applied. The heat source was to be located remotely from the core of the cooling solution and the connecting lines needed to allow movement of the cold plate. In addition to performance, size, weight, and reliability were all critical for the end application.

Breadboard Proof of Concept
During the first step of this program the customer and Aspen resolved that the best path forward would be to assemble a breadboard test system to demonstrate technical feasibility of the miniature vapor compression approach to solving this problem. Aspen worked with our customer to define the system requirements. Aspen designed the system to operate using Aspen’s miniature compressor with R-404a as the working refrigerant. Flexible refrigerant hoses were selected to allow the coldplate to be located at the heat source, remote from the remainder of the refrigeration system. Aspen conducted thermal analysis on the heat exchangers (condenser and evaporator/coldplate) to ensure (a) proper heat transfer, (b) acceptable pressure drop and (c) proper flow distribution. Upon completion of the design, Aspen assembled, tested, and delivered the breadboard system to the customer. The customer did their own tests to verify system functionality and interface with their system. The customer was impressed with the performance and opted to move forward with design of a prototype subsystem.

Prototype Subsystem
Aspen and our customer established a clear technical specification for the prototype subsystem. This specification included details on the subsystem integration with the customer’s end product. The customer did not want a fully packaged system, but rather a solution which would integrate into their system, allowing them full control over the external look and feel of the system. Aspen designed a more detailed solution based on the performance of the breadboard system. The thermal analysis was refined and components were chosen to fit within the specific subsystem size constraints. Aspen conducted design reviews, both internal and with the customer, to ensure the system met the customer’s requirements as well as our own internal design standards.

Concentrated DX

Aspen built two prototype subsystems and conducted a complete design verification on the prototype units. Following the testing, the units were delivered to the customer for design validation and rigorous testing. The customer was once again pleased with the system performance and asked Aspen to quickly shift into a production mode at a rate of approximately 50 subsystems per quarter.

To meet the customer’s demand in short time, Aspen setup a production build process and established a production test plan. A production line was established within our Marlborough, Massachusetts facility to assemble, braze, inspect, and test the designed subsystem. Assembly and test fixtures were designed and built in-house to ensure repeatable, reliable product quality. Internal work instructions were established to define the build and test process and technicians were trained on these processes. Each subsystem shipped tested to verify cooling capacity, pull-down time, and temperature stability.

As of late 2014, Aspen has shipped over 200 subsystems to our customer and continues to produce these products at a moderate production rates. Based on the success of this endeavor, Aspen has continued to work with this customer on other similar programs which are intended to reach production in 2015.