Integrated Thermal Architecture based on Advanced Control Loop (ACL) with multiple evaporators and condensers

A highly-integrated thermal architecture based on Advanced Control Loops (ACLs) has been developed and tested. This architecture consists of a Constant Conductance Heat Pipe (CCHP) network thermally connected to two ACLs. Heat-dissipating units are mounted on the CCHP network. Each ACL has 4 independent evaporators and 4 independent condensers, in the sense that they can be coupled to independent power dissipation sources or sink conditions respectively. The CCHP network has 4 primary CCHPs and 4 spreader CCHPs which serve to equalize the heat load between the primary CCHPs. The CCHP network can be embedded in a honeycomb panel to act as an equipment panel or deck. The ACL cylindrical evaporators, without the thermal interface flanges (saddles), are embedded in dedicated bores as part of the primary CCHP extruded profiles. In this way, the overall thermal gradient between the dissipating units and the condensers is minimized by eliminating the standard bolted interface between evaporator and CCHP flanges. An extensive thermal test campaign was performed on the ACL to validate the novel thermal architecture concept, to characterize the system performance under worst-case operational conditions, and to determine the system performance envelope. The campaign included a number of tests: thermal performance (conductance and heat transfer capability) under various power conditions and with a �split� (ACLs share the thermal sink) and �nonsplit� (each ACL has a dedicated thermal sink) condenser design, minimum and maximum power, start-up, transient input power and heat sink temperature variations, and NCG influence. To cope with transients in the power and thermal boundary conditions, an innovative method of control is also presented. Ammonia is selected as the working fluid for both CCHPs and ACLs taking into account the standard operating and non-operating temperature ranges of most heat-dissipating electronics.