Ballistic Missile Innovative Radar and RF Products

A pumped liquid two-phase cooling system is proposed for use in active radar thermal management systems. The technology pumps liquid refrigerant (R-134a) to offset strip fin heat exchangers that are in thermal contact with the power amplifier coldplates. The refrigerant evaporates and removes heat isothermally from active components. A two-phase mixture leaves the offset strip fin heat exchanger where it is condensed and returns to the pump inlet. Significant improvements in heat transfer coefficients, reduced pumping requirements, and isothermal operation are expected when compared to existing single phase thermal management systems in active radar applications. Two of the MDA radar systems that may benefit from this type of thermal management system are Theater High Altitude Area Defense (THAAD) program and X-Band Radar (XBR) program. Due to performance and reliability requirements, channel temperatures and the amplifier-to-amplifier temperature gradients must be kept low. Modifying the THAAD and XBR cooling systems to be pumped liquid two-phase systems will: 1) Increase thermal performance 2) Maintain isothermal operation 3) Reduce each system's flow rate, which will reduce the required pumping power and allow for smaller coolant distribution systems 4) Since R-134a is a dielectric fluid, a leak will not cause an electrical short circuit. High performance cooling of digital and power electronic components is applicable to many commercial market segments. The enterprise computer and server market in particular has been seeking cooling technologies to replace air cooled heat sinks in high density applications. The proposed pumped liquid two phase cooling technology has already been demonstrated to one large computer company and more have expressed interest. Pumped liquid two phase cooling has the potential to drive greater packaging densities while at the same time improve the cooling performance of servers and enterprise computers. In the power electronic segment of the commercial market, some applications are approaching the limit of single phase liquid cooling. Particularly, high power density motor controls could benefit from the high performance low pumping power of a pumped refrigerant two phase cooling system.