Summary

Due to the shortage of the electric energy sources and also to the strict environmental controls regarding the use of the actual refrigerants, alternative cooling technologies are now being introduced into the market, all of them with innovative features related to the energetic efficiency and also to the use of environmental friendly substances. However, all those technologies are based on a warm and a cold surface, both generated by and located at the refrigeration machine. That requires the utilization of secondary heat transfer loops to connect the cold surface to the refrigerated compartment and the warm surface to the external air. Such secondary circuits must be compact, in addition of having low energy consumption, high cooling capacity and producing a small temperature drop between the heat transfer source and sink. One of the alternatives for the warm side of alternative refrigeration systems is a Capillary Pumped Loop#CPL, considered in this work. A CPL is a two-phase flow system that uses heat and the capillary forces generated in a porous media to pump fluid in a closed loop, comprised by an evaporator, a condenser and a liquid reservoir. The required pressure difference to pump the fluid is generated in the meniscus that separates the liquid and vapor phases, located in the evaporator. Since its introduction, the CPL concept has been used mainly by the aerospace industry. In order to explore its use in refrigeration equipments some specific operational characteristics must be addressed: i) high heat transfer fluxes, ii) high condensation temperatures and iii) low temperature drops between the heat transfer source and sink. In addition to that the gravity is another factor that differentiates the aerospace and earth applications. The main objective of this work is therefore to explore the operational characteristics of a CPL working as a secondary heat transfer circuit in alternative refrigeration systems. For doing so a CPL prototype was designed and manufactured, having a flat geometry and using a heating block to simulate the warm surface of the refrigeration machine. The prototypes were tested in specific operational conditions required by the refrigeration sector, using ethyl alcohol and water as working fluids, and varying the thickness and the porous size of the porous wick, the height difference bet.

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