12,767 research outputs found
Assessing durability of superhydrophobic surfaces
No full textSuperhydrophobic surfaces (SHS) show remarkable water repellency properties, and their use may have a tremendous impact for a plethora of applications, where liquid water accumulation needs to be controlled or minimised. However, the durability of SHS in operational conditions is a severe issue that currently represents a bottleneck for the technology transfer from laboratory to industrial applications. In the present work, we try to fill in the gap caused by the absence of a standard for evaluation for SHS durability, by developing a protocol for testing surface durability. The proposed protocol includes nine tests as follows: water immersion, acidic environment, alkaline environment, ionic solution, mechanical erosion, ultraviolet exposure, resistance to heating, alcohol immersion and hydrocarbon immersion. The protocol can serve to give an indication of surface robustness in a variety of potentially harmful environments, by providing a global figure of merit and ranking for different SHS and thereby allowing for identifying those surfaces fulfilling requirements for a specific application. To illustrate the protocol, we tested a SHS developed in-house by grafting of lauric acid molecules on an aluminum substrate
Fabricating superhydrophobic aluminum: An optimized one-step wet synthesis using fluoroalkyl silane
No full textIn this paper we present a simple but effective procedure to impart superhydrophobicity to aluminum through a one-step wet chemistry synthesis. The synthesis is performed in one step, thanks to simultaneous etching with NaOH and grafting with fluoroalkyl silane (FAS) molecules, which allow aluminum surface functionalization. By optimizing the proper amount of reagents, controlling the reaction batch temperature and particularly by allowing pre-activation of the solution, we showed that the process can be used turn into water repellant superhydrophobic surfaces four aluminum samples in sequence, using the same reaction batch. Also, if FAS is further added to the solution the procedure can impart superhydrophobicity to further aluminum samples. The synthesis with the optimized parameters is green and cost effective, since it was developed to minimize the use of both base and fluorinated molecules. In addition, it is easy to scale up to large area treatments and to industrial application, because the procedure is one-step, is reproducible, and allows multiple use of the same reaction batch, for the treatment of multiple samples. Finally, we show that not only the surfaces show excellent non-wetting properties in quasi-static conditions, with contact angles ∼150̊ and with very low contact angle hysteresis, ∼4̊, but also in dynamic conditions, as proved by means of drop impact analysis up to Weber number of 690
A Comparative Life Cycle Analysis of an Active and a Passive Battery Thermal Management System for an Electric Vehicle:A Cold Plate and a Loop Heat Pipe
Full text linkThis study extends beyond conventional Battery Thermal Management System (BTMS) research by conducting a Life Cycle Analysis comparing the environmental impacts of two technologies: a traditional active cold plate system and an innovative passive Loop Heat Pipe (LHP) system. While active cold plate BTMS requires continuous energy input during operation and charging, leading to significant energy consumption and emissions, the passive LHP BTMS operates without external power or moving parts, substantially reducing the climate change impact. This analysis considered two materials for LHP construction: copper and stainless steel. The results demonstrated that the LHP design achieved a 9.9 kg reduction in overall BTMS mass compared to the cold plate system. The implementation of stainless steel effectively addressed the high resource consumption associated with copper while reducing environmental impact by over 50% across most impact categories, compared to the cold plate BTMS. The passive operation of the LHP system leads to substantially lower energy usage and emissions during the use phase compared to the active cold plate. These findings highlight the potential of passive LHP technology to enhance the environmental sustainability of Battery Thermal Management Systems while maintaining effective thermal performance
Water drops dancing on ice: how sublimation leads to drop rebound
No full textDrop rebound is a spectacular event that appears after impact on hydrophobic or superhydrophobic surfaces but can also be induced through the so-called Leidenfrost effect. Here we demonstrate that drop rebound can also originate from another physical phenomenon, the solid substrate sublimation. Through drop impact experiments on a superhydrophobic surfaces, a hot plate, and solid carbon dioxide (commonly known as dry ice), we compare drop rebound based on three different physical mechanisms, which apparently share nothing in common (superhydrophobicity, evaporation, and sublimation), but lead to the same rebound phenomenon in an extremely wide temperature range, from 300 C down to even below -79 C. The formation and unprecedented visualization of an air vortex ring around an impacting drop are also reported
A Novel Loop Heat Pipe Based Cooling System for Battery Packs in Electric Vehicles
Full text linkA novel cooling method for Electric Vehicles battery modules by means of Loop Heat Pipe and graphite sheets is proposed. The Loop Heat Pipe is a passive two-phase system and as such it reduces the parasitic power consumed by the EV thermal management. A validated lumped parameter mathematical model has been created describing the thermo-fluid-dynamic problem and used to simulate the performance of the cooling system during highway driving and ultra-fast charging conditions. The numerical predictions show a clear potential to contain the cells’ temperature below 40°C even during ultra-fast charging, with a 3.3K peak temperature reduction in comparison to a conventional liquid cooling method. Moreover, this system adds only 8% of the battery pack mass and it shows potential parasitic power reductions of one order of magnitude
Critical review and ranking of novel solutions for thermal management in electric vehicles
Full text linkNumerical investigation on a combined loop heat pipe and graphite sheets cooling system for automotive applications
Full text linkAn innovative Battery Thermal Management System for a 3-cell Electric Vehicle module is proposed, involving Loop Heat Pipes and graphite sheets, with the particular aim of fast charging and reacting to automotive requirements. The design feasibility is verified through a Lumped Parameter Model, which has been validated comparing the data from an experimental demonstrator which included a copper/copper flat plate Loop Heat Pipe running ethanol. Results show that this solution is able to maintain the maximum temperature below 32°C after a 10 min fast charge cycle. System performance with a standard working fluid such as ethanol are compared with the system performance using a novel fluid, Novec™ 649, which has desirable features for the automotive industry, such as non-flammability, non-toxicity, below-zero freezing point and outstanding environmental properties (GWP = 1, ODP = 0). Nevertheless, comparison between the results with the two fluids reported no significant difference in thermal performance showing no contraindication in the use of the novel working fluid. Moreover, the model was used to estimate the effect of the Loop Heat Pipe building material, resulting in no sensible difference between the utilization of copper and aluminium, de facto justifying the choice of the lighter material for future applications
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