The application of polymeric and composite materials in two-phase passive heat transfer devices is reviewed critically, with a focus on advantages and disadvantages of these materials in thermal management systems. Recent technology developments led to an increase of the power density in several applications including portable electronics, space and deployable systems, etc., which require high-performance and compact thermal management systems. In this context, passive two-phase systems are the most promising heat transfer devices to dissipate large heat fluxes without external power supply. Usually, heat transfer systems are built with metals due to their excellent thermal properties. However, there is an increasing interest in replacing metallic materials with polymers and composites that can offer cost-effectiveness, light weight and high mechanical flexibility. The present work reviews state-of the-art applications of polymers and composites in two-phase passive thermal management systems, with an analysis of their limitations and technical challenges.

This work aims to find the optimum value of blade height ratio (R) for improving mixing performance and energy consumption of a Triple-Blade Concentric Double-Helix Static Mixer. In this study, mixing of two fluids at different concentrations subjected to laminar flow conditions is numerically analyzed by using finite element-based Computational Fluid Dynamics simulations. Different values of the R parameter are considered in a wide range of Reynolds numbers (Re = 200–1000). This analysis then carried out an in-depth study of R's effect on mixing performance, strength segregation, mixing index, helicity, velocity profile, pressure drop, pumping power, and efficiency. The findings showed that a blade height ratio of R = 2/3 gave the highest mixing index (MI), with the maximum value of 0.99 at a Re number of 600, which showed the best mixing performance in the channel. Helicity visualization also showed complex helicity patterns with increased vortex interactions for the 2/3 configuration. This geometry gave an improvement in MI by about 17.85% over Triple-Blade Concentric Single-Helix Static Mixer (TB-CSH-SM) with R = 0 at Re = 600. It is also important to mention that increasing the R value leads to an increase in pressure drop and, consequently, an increase in pumping energy consumption. Although R = 2/3 gives the best mixing performance, the energy consumption is relatively higher than that for R = 0, which has the lowest power input but a lower MI. The investigation concludes that R = 2/3 represents a balanced solution since it realizes an optimum mixing performance with a moderate energy consumption and hence is suitable for applications requiring an efficient compromise between mixing quality and energy consumption.

A novel methodology is proposed for the development of empirical flow pattern maps for pulsating heat pipes (PHPs), which relies on the concept of virtual superficial velocity of the liquid and vapour phases. The virtual superficial velocity of each phase is defined using solely the design and operational parameters of the pulsating heat pipe, allowing the resulting flow pattern map to serve as a predictive instrument. This contrasts with existing flow pattern maps that necessitate direct measurements of temperatures and/or velocities within one or more channels of the pulsating heat pipe. Specifically, the virtual superficial velocities are derived from the relative significance of the driving forces and the resistances encountered by each phase during flow. The proposed methodology is validated using flow visualisation datasets obtained from two separate experimental campaigns conducted on flat-plate polypropylene pulsating heat pipe prototypes featuring transparent walls and meandering channels with three turns, five turns, seven turns, and eleven turns, respectively. The PHP prototypes were tested for gravity levels ranging between 0 g and 1 g and heat inputs ranging from 5 W to 35 W. The proposed approach enables the identification of empirical boundaries for flow pattern transitions as well as the establishment of an empirical criterion for start-up.