Heat Transfer Technologies is a participant sub-contractor
OBJECTIVE: Develop compact heat transfer technologies to improve the performance of two-phase heat exchangers.
DESCRIPTION: Tube-fin heat exchangers are used to acquire or reject heat in a wide range of military and commercial thermal control systems, including ground and sea-based environmental control units, refrigeration systems, and waste heat regeneration systems. As power-density of tactical systems continue to increase, the use of two-phase thermal control systems is becoming more widespread due to improved thermal capacity when cooling or heating through the latent heat of a working fluid. Improving the effectiveness of two-phase heat exchangers used to transfer heat between the working fluids and air streams will lead to reductions in size, weight, and power consumption of military environmental control systems.
Improved heat exchanger designs utilizing microchannels, plate-fin configurations, and surface enhancements offer performance advantages over traditional tube-fin heat exchangers, but have not yet been fully utilized in many military and commercial systems. While developers have incorporated these improvements in single-phase systems, they have yet to be utilized reliably with two-phase systems. This is largely due to two-phase flow maldistribution and condensation build-up in the heat exchanger, which results in poor heat transfer performance, as well as high manufacturing costs.
Technologies are sought to improve the volumetric heat transfer performance over tube-fin heat exchangers while maintaining flow rates, temperatures, and differential pressures characteristic of heat exchangers used for environmental control. Methods to ensure proper distribution of a two-phase mixture at the entrance to multiple fluid passages and through the device must be proven.
PHASE I: Develop concepts to provide improved heat transfer performance over conventional heat exchangers and provide a uniform distribution of a two-phase working fluid at the inlets to multiple fluid passages. Validate design performance through analytical modeling or subscale demonstration of components as appropriate.