A Low Cost, Flexible Pulsating Heat Pipe Technology

Abstract

A novel flexible pulsating heat pipe technology (FPHP) is presented, which enables fabrication of flexible, lightweight and low cost heat transfer devices using thermoplastic materials (polypropylene). A flexible and lightweight PHP is advantageous for space, aircraft and portable electronic applications where the device weight is crucial. Although the thermal performance of thermoplastics is usually poor, this technology enables the creation of composite thermoplastic materials having a significantly enhanced thermal conductivity. The basic concept is to sandwich a serpentine channel, which is cut out in a polypropylene sheet and contains a self-propelled gas-vapour mixture, between two transparent polypropylene sheets, bonded together by selective laser welding. This results into a heat transfer device with a large surface and very small thickness (approximately 1.5 mm), which makes it suitable for many existing and future applications where thermal management is not possible using existing technologies. The thermal performance of FPHPs was characterised for different heat input levels; local heat transfer coefficients were estimated by measurement of the heat fluxes and the wall temperatures at different positions in the FPHP. Results showed that the effective thermal conductance of the FPHP was nearly three times higher than that of the material constituting its envelope.

Thermal Performance of Pulsating Heat Stripes Built With Plastic Materials

“…Tests were interrupted earlier in case any point of the PHS reached a temperature of 110°C. Preliminary experiments [16] showed the start-up of two-phase circulation in the PHS occurs with a heat input of about 2.5 W at the evaporator.…”

“…The present work investigates the thermal performance of a flexible, lightweight, low-cost heat pipe technology, which has the potential to overcome the above issues. The basic concept is to sandwich a serpentine channel, which is cut out in a polypropylene sheet and contains a self-propelled gas-vapour mixture, between two transparent polypropylene sheets bonded together by selective laser welding [16]. The resulting channel has a rectangular cross-section characterized by a large aspect ratio, hence the denomination "Pulsating Heat Stripes" (PHS).…”

Characterization of polypropylene pulsating heat stripes: Effects of orientation, heat transfer fluid, and loop geometry

“…Experiments were conducted by applying to the evaporator section an ascending/descending stepped power ramp ranging approximately between 4 W and 30 W, and measuring the temperatures on the PHS surface at a sampling rate of 1 Hz. The magnitude of the first step was approximately 6 W to ensure start-up, based on preliminary tests [7], while the magnitude of subsequent steps was approximately 9 W. For each power step, the heat supply was kept constant until a pseudo steady-state regime was attained, which typically required about 30 minutes. Tests were interrupted earlier in case any point of the PHS reached a temperature of 120 • C, to avoid polypropylene softening and/or melting.…”

“…First, the serpentine channel was cut-out in a black sheet (0.7 mm thickness) using a commercial laser cutter (HPC Laser LS1290 Pro). Then, the channel was sandwiched between two transparent sheets (0.4 mm thickness each), which were tightly bonded to the black sheet by selective transmission laser welding using a nanosecond pulsed fibre laser (SPI Lasers G4 HS-L 20W) [7,8,11,12]. The resulting composite polypropylene sheet had an overall thickness of 1.5 mm.…”

“…To address the demand of heat transfer devices characterized by low weight, small unit thickness, low cost, and high mechanical flexibility, it was recently proposed to embed the PHP serpentine channel into a composite polypropylene sheet [7,8]. The concept is to cut out the serpentine channel in a black polypropylene sheet, sandwiched between two transparent sheets of the same material and bonded together by selective transmission laser welding [9,10].…”