KEK Annual Report 2010
For highly integrated modern detector systems, a very efficient and reliable cooling system is one of the most critical components. In this project, we develop a two-phase cooling technology that adopts the concept of cooling with fluids in mixed states and makes use of the large latent heat for liquids vaporizing into gases, thereby achieving highly efficient extraction of heat with a low flow rate of the coolant fluids. It should be emphasized that the temperature of the coolant is determined solely by the pressure and hence is nearly constant along the entire cooling circuit. This is because the absorbed heat is used only for phase transition. As a coolant, CO2 is considered ideal because of its large latent heat and an operating pressure that can be set very high to minimize the vapor volume, ensuring high cooling power even with thin cooling pipes, while keeping the pressure drop negligible to realize nearly uniform temperature along the cooling line. In order to develop a two-phase CO2 cooling system for a large-scale experiment in the next generation, we formed an R&D team in FY2010. As our first milestone, we started developing an open two-phase CO2 cooling system, as shown in Fig. 4-6-3-2. The system consists of a CO2 bottle, a heat exchanger that precools the input liquid with the return two-phase mixture, a needle valve to turn the liquid into the two-phase (liquid/vapor) mixture, a dummy heat load, a pressure valve, and a heat bath to fully vaporize the CO2 for venting it to the atmosphere. In FY2011, the system will be tested and used to accumulate data as a basis for developing a closed system.
|Fig. 1 Open two-phase CO2 cooling system|