Experimental investigation of heat pipe thermal performance with microgrooves fabricated by wire electrical discharge machining

Abstract

Original scientific paper https://doi.org/10.2298/TSCI180227206BThis work presents the use of electrical discharge machining (EDM) technology for manufacturing of three different types of axial microgrooves in heat pipes. This specific process, called wire electrical discharge machining (wire-EDM), allows the fabrication of microgrooves on the inner wall of a heat pipe with accuracy. Different from other capillary structures, such as composite wick and screen mesh, the material is removed from the pipe's container in order to conceive the capillary structure, which contributes with the mass reduction of the passive two-phase heat transfer device. The heat pipes were manufactured from a straight copper pipe with the external diameter of 9.45 mm, the inner diameter of 6.20 mm, and a total length of 200 mm. Three types of axial microgrooves were manufactured for constant width (35 μm) and varying the depth (from 30-48 μm), and thickness (from 35-70 μm). The number of microgrooves was also varied from 21-32 microgrooves. Water was used as the working fluid and the loading filling ratio was 60% of the evaporator volume. The condenser was cooled by air forced convection, the adiabatic section was insulated and the evaporator was heated by an electrical resistor and it was insulated from the environment with aeronautic thermal insulation. The thermal performance of the heat pipes are analyzed based on experimental results, so the heat pipes were tested at the horizontal and different inclinations under different low heat loads (from 5-50 W or a heat flux from 0.21-2.10 W/cm 2 ). The experimental results showed that the axial microgrooves manufactured by the wire-EDM process worked satisfactorily in all analyzed cases and microgrooves of Type 1 showed a better thermal performance when compared with the others.

Experimental research of capillary structure technologies for heat pipes

“…Figure 2 presents the axial microgroove details with an average diameter of 220 µm through a micro-scale image obtained by a Backscattered Electron Detector (BSD) on a Scanning Electron Microscope (SEM). Additional characteristics of grooved heat pipes are reported by Nishida et al (2020).…”

“…The most common capillary structures are screens, sintered metals, and axial grooves (Krambeck, Nishida, Aguiar, Santos, & Alves, 2019). There are several types of groove crosssections inside copper heat pipes, such as triangular, rectangular, trapezoidal, and inverse trapezoidal cross-sections, resulting in different heat transfer performances (Nishida, Krambeck, Santos, & Alves, 2020). How to produce ideal inner grooves is the primary problem with heat pipes (Wang, Tang, & Chen, 2009).…”

Thickness Influence of the Copper Powder Sintered Capillary Structure in the Thermal Performance of Heat Pipes

“…The heat pipe consists of an evacuated metal tube, an internal capillary structure, and a working fluid (Krambeck, Nishida, Aguiar, Santos, & Alves, 2019). This device is applied to improve the transfer of heat in many industrial areas, such as electronics, aerospace, telecommunications, food, among others (Faghri, 2014;Nishida, Krambeck, Santos, & Alves, 2020).…”