The Influence of Loop Heat Pipe Evaporator Porous Structure Parameters and Charge on Its Effectiveness for Ethanol and Water as Working Fluids

Abstract

This paper presents the results of experiments carried out on a specially designed experimental rig designed for the study of capillary pressure generated in the Loop Heat Pipe (LHP) evaporator. The commercially available porous structure made of sintered stainless steel constitutes the wick. Three different geometries of the porous wicks were tested, featuring the pore radius of 1, 3 and 7 µm. Ethanol and water as two different working fluids were tested at three different evaporator temperatures and three different installation charges. The paper firstly presents distributions of generated pressure in the LHP, indicating that the capillary pressure difference is generated in the porous structure. When installing with a wick that has a pore size of 1 μm and water as a working fluid, the pressure difference can reach up to 2.5 kPa at the installation charge of 65 mL. When installing with a wick that has a pore size of 1 μm and ethanol as a working fluid, the pressure difference can reach up to 2.1 kPa at the installation charge of 65 mL. The integral characteristics of the LHP were developed, namely, the mass flow rate vs. applied heat flux for both fluids. The results show that water offers larger pressure differences for developing the capillary pressure effect in the installation in comparison to ethanol. Additionally, this research presents the feasibility of manufacturing inexpensive LHPs with filter medium as a wick material and its influence on the LHP’s thermal performance.

Heat and Mass Transfer in Porous Materials

“…In [ 22 ], the results of studies of the capillary effect in porous structures with different pore sizes are presented in order to develop passive cooling systems based on the mechanisms of the liquid-vapor phase transition to remove large heat fluxes. The high intensity and density of energy flow in some industries require efficient and reliable heat transfer.…”

“…Although significant attention has been paid to these issues, there remains a constant demand for innovative solutions to address a wide range of problems in this area. Therefore, this special issue attempts to highlight and propose new solutions to these problems [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 ]. These works develop a basic understanding of the scientific problems of heat and mass transfer in porous materials.…”

Archives of Thermodynamics

“…An extensive need exists to perform a full thermodynamic analysis of the behaviour of this capillary two-phase sys-tem to understand its thermal and hydraulic processes occurring in the LHPs operating at elevated temperature ranges. NGCs have been reported as one of the most common causes of the failure of two-phase heat transport devices [3][4][5][6]11]. One of the main consequences of incompatibility among the materials and working fluid of a heat transport device is the generation of NCG, which is linked to the fact that elevated temperatures accelerate the NCG generation process, making it essential to dedicate special attention to the NCG impact in the LHP for elevated temperature, which would potentially include novel combinations of fluids and materials.…”

Additive Manufacturing as a Solution to Challenges Associated with Heat Pipe Production

“…HPs are commonly used as heat sinks and heat spreaders in multiple challenging fields such as security, communications, medical, test and power systems, military, consumer electronics cooling systems, aircraft and spacecraft applications, amongst others [3][4][5][6]. All aforementioned target application benefits from all the advantages of HPs (e.g., noise and vibration-free operation, passive, long-distance heat transfer, flexibility in design and assembly, compactivity, robustness, anti-gravity capability) [1,9]. (2) saturated vapour travels to the colder condenser section driven by the vapour pressure difference; (3) in the condenser, vapour releases the heat to a heat sink where it condenses back to a liquid state and is absorbed by the wick; (4) condensed liquid returns to the evaporator section through the wick structure by capillary forces [2].…”

“…HPs are commonly used as heat sinks and heat spreaders in multiple challenging fields such as security, communications, medical, test and power systems, military, consumer electronics cooling systems, aircraft and spacecraft applications, amongst others [3][4][5][6]. All aforementioned target application benefits from all the advantages of HPs (e.g., noise and vibration-free operation, passive, longdistance heat transfer, flexibility in design and assembly, compactivity, robustness, antigravity capability) [1,9].…”