A low-cost, flexible pulsating heat pipe (PHP) was built in a composite polypropylene sheet consisting of three layers joint together by selective laser welding, to address the demand of heat transfer devices characterized by low weight, small unit thickness, low cost, and high mechanical flexibility. A thin, flexible, and lightweight heat pipe is advantageous for various aerospace, aircraft, and portable electronic applications where the device weight, and its mechanical flexibility are essential. The concept is to sandwich a serpentine channel, cut out in a polypropylene sheet and containing a self-propelled mixture of a working fluid with its vapor, between two transparent sheets of the same material; this results into a thin, flat enclosure with parallel channels hence the name “pulsating heat stripes” (PHS). The transient and steady-state thermal response of the device was characterized for different heat input levels and different configurations, either straight or bent at different angles. The equivalent thermal resistance was estimated by measuring the wall temperatures at both the evaporator and the condenser, showing a multifold increase of the equivalent thermal conductance with respect to solid polypropylene.
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.
The right choice of polymeric materials plays a vital role in the successful design and manufacture of flexible fluidic systems, as well as heat transfer devices such as pulsating heat pipes. The decision to choose an acceptable polymeric material entails a variety of evaluation criteria because there are numerous competing materials available today, each with its own properties, applications, benefits, and drawbacks. In this study, a comparative hybrid multi-criteria decision-making (MCDM) model is proposed for evaluating suitable polymeric materials for the fabrication of flexible pulsating heat pipes. The decision model consists of fourteen evaluation criteria and twelve alternative materials. For this purpose, three different hybrid MCDM methods were applied to solve the material selection problems (i.e., AHP-GRA, AHP-CoCoSo, and AHP-VIKOR). According to the results obtained, PTFE, PE, and PP showed promising properties. In addition, Spearman’s rank correlation analysis was performed, and the hybrid methods used produced consistent rankings with each other. By applying MCDM methods, it was concluded that PTFE is the most suitable material to be preferred for manufacturing flexible pulsating heat pipes. In addition to this result, PE and PP are among the best alternatives that can be recommended after PTFE. The study supports the use of MCDM techniques to rank material choices and enhance the selection procedure. The research will greatly assist industrial managers and academics involved in the selection process of polymeric materials.
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