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Technical Paper

Thermal Characteristics of a Flat Evaporator Miniature Loop Heat Pipe

A miniature LHP has been designed, built and tested in order to evaluate its thermal characteristics when operating with concentrated heat loads, on an available heat dissipation area of 3 cm2, using pure water as the working fluid. Tests results show that the miniature LHP presented reliable operation for the range of designed heat loads for two different condensation temperatures used. The concentrated heat flux caused the miniature LHP to present operating temperatures around 100 ºC for the highest heat load. However, even when operating at high temperature levels, the miniature LHP always showed reliable thermal behavior without indication of evaporator depriming or failure. The results point the importance of evaluating the thermal characteristics when miniaturizing LHPs, leading to potential applications for a wide range of temperatures.
Technical Paper

Evaluating Loop Heat Pipes Performances Regarding Their Geometric Characteristics

This paper presents the performance tests of small-scale loop heat pipes (LHPs) that have being developed in order to perform the heat dissipation using acetone as working fluid. Two LHPs have being designed and built to accomplish the thermal management on power cycles of up to 80 W, where each LHP has a different set of compensation chamber/capillary evaporator, being one detached from the evaporator while the other is an integral part of it. Laboratory life tests have shown reliable operation with negligible non-condensable gas influence along time. The basic difference between tests with both LHPs is that the one with an integral compensation chamber showed higher operation temperatures due to the smaller thermal resistances between the evaporator and the compensation chamber. The life tests results show the potential in using acetone as an alternative working fluid in LHPs with reduced active lengths.
Technical Paper

Extensive Development of the Loop Heat Pipe Technology

The development of LHPs for space applications have shown the possibility of using them in several ground applications, such as water heating systems, electronics cooling, etc. Some issues related to the use of LHPs rely on their design and development depending on the required use. In this case, the most indicated configuration for their reliable operation will depend on the correct selection of working fluid, materials and configuration regarding the maximum heat management requirement. This paper presents what has been developed in this institute regarding the LHP technology, which includes devices for electronics cooling operating at its classical design (one evaporator and condenser), reversible, ramified and miniature LHPs. The results obtained have shown the great potential in using LHPs as passive thermal control devices.
Technical Paper

Comparing the Behavior of a Loop Heat Pipe With Different Elevations of the Capillary Evaporator

During the life tests required for the development of a loop heat pipe (LHP), the device must operate at different capillary evaporator elevations in order to compare its thermal behavior, specially related to the operation temperature. As an effort in developing LHPs for future space missions, a LHP was designed and tested for a system operating with acetone as the working fluid. Tests were performed for the LHP at horizontal position and with the capillary evaporator above and below the condenser. The experimental results show the operationability of the LHP tested at all situations, where the system presented reliable operation at power levels as low as 1 W. Tests with the capillary evaporator above and below the condenser also show the reliability of the LHP operation, showing higher operation temperatures with the evaporator above and lower operation temperatures with the evaporator below.
Technical Paper

Characteristics of an Open Loop Pulsating Heat Pipe

This paper presents an experimental investigation of an open loop pulsating heat pipe (OLPHP), where several issues related to its performance were evaluated. Tests were conducted with different working fluids for the OLPHP operating at both vertical and horizontal orientations. The experimental results show that the system presented better performance when operating at horizontal orientation, as lower evaporation section temperatures were achieved. Regarding the working fluids used, the system showed better performance when acetone was used on vertical orientation and methanol on horizontal orientation.