• Energy Research

Abstract The low thermal conductivity of Phase Change Materials (PCMs), such as paraffin waxes, hinders efficient latent heat storage, especially for rapid charging and discharging cycles. To address this issue, this study explores experimentally and numerically the use of metal additive manufacturing to create a latent heat storage system operating at medium temperatures (around 90°C). A 3D Cartesian metal lattice is manufactured through laser powder bed fusion to optimize heat conduction within the PCM. Experimental tests show impressive specific power densities (approximately 714 ± 17 W kg−1 during charging and 1310 ± 48 W kg−1 during discharging). Moreover, the device exhibits stability over multiple cycles. Finally, the validated finite-element model has the potential to provides a basis for general design guidelines to boost the system’s performance further. Potential applications of this technology are highlighted in the automotive industry, where such systems could efficiently manage thermal energy, for instance, by capturing excess heat from an engine’s cooling radiator to expedite the warm-up process during a cold start, which is a critical phase for reducing pollutant emissions.

Abstract The low thermal conductivity of Phase Change Materials (PCMs), such as paraffin waxes, hinders efficient latent heat storage, especially for rapid charging and discharging cycles. To address this issue, this study explores experimentally and numerically the use of metal additive manufacturing to create a latent heat storage system operating at medium temperatures (around 90°C). A 3D Cartesian metal lattice is manufactured through laser powder bed fusion to optimize heat conduction within the PCM. Experimental tests show impressive specific power densities (approximately 714 ± 17 W kg−1 during charging and 1310 ± 48 W kg−1 during discharging). Moreover, the device exhibits stability over multiple cycles. Finally, the validated finite-element model has the potential to provides a basis for general design guidelines to boost the system’s performance further. Potential applications of this technology are highlighted in the automotive industry, where such systems could efficiently manage thermal energy, for instance, by capturing excess heat from an engine’s cooling radiator to expedite the warm-up process during a cold start, which is a critical phase for reducing pollutant emissions.

Abstract More than two billion people live in areas affected by water stress. In some coastal regions, freshwater supply has been progressively improved by large-scale desalination systems, which are nowadays mostly driven by non-renewable energy sources. Here we discuss, and experimentally investigate, the use of small-scale desalination devices for freshwater production powered by waste heat from electric power generators. The water purification technology relies on a passive, multi-stage and thermally-driven membrane distillation device, recently proposed by some of the authors of this work. The distiller is powered by low-grade (temperature lower than 80 °C) waste heat, recovered from the coolant circuit of small diesel engines for electricity production. Field experiments show that, for the tested engine, up to 1.12 kW m - 2 can be recovered in standard operating conditions, which yield a nearly 2.61 L m - 2 h - 1 freshwater production from seawater. A lumped parameter model, validated by experiments, shows that this productivity could be eventually enhanced by tuning the number of distillation stages. Utilization with exhaust gases, and thus higher feeding working temperatures, is also discussed. The proposed solution may provide a sustainable, simple, inexpensive and efficient means for freshwater production from recovered waste heat, which would otherwise be wasted to the ambient. Therefore it could be particularly effective, for instance, for field hospitals in remote or impoverished areas, especially in emergency situations.

Abstract More than two billion people live in areas affected by water stress. In some coastal regions, freshwater supply has been progressively improved by large-scale desalination systems, which are nowadays mostly driven by non-renewable energy sources. Here we discuss, and experimentally investigate, the use of small-scale desalination devices for freshwater production powered by waste heat from electric power generators. The water purification technology relies on a passive, multi-stage and thermally-driven membrane distillation device, recently proposed by some of the authors of this work. The distiller is powered by low-grade (temperature lower than 80 °C) waste heat, recovered from the coolant circuit of small diesel engines for electricity production. Field experiments show that, for the tested engine, up to 1.12 kW m - 2 can be recovered in standard operating conditions, which yield a nearly 2.61 L m - 2 h - 1 freshwater production from seawater. A lumped parameter model, validated by experiments, shows that this productivity could be eventually enhanced by tuning the number of distillation stages. Utilization with exhaust gases, and thus higher feeding working temperatures, is also discussed. The proposed solution may provide a sustainable, simple, inexpensive and efficient means for freshwater production from recovered waste heat, which would otherwise be wasted to the ambient. Therefore it could be particularly effective, for instance, for field hospitals in remote or impoverished areas, especially in emergency situations.

AbstractPassive energy‐conversion devices based on water uptake and evaporation offer a robust and cost‐effective alternative in a wide variety of applications. This work introduces a new research avenue in the design of passive devices by replacing traditional porous materials with rigid capillary layers engraved with optimized V‐shaped grooves. The concept is tested using aluminum sheets, which are machined by femtosecond laser and covered by silica or functionalized by oxygen plasma to achieve stable long‐term capillary properties. The durability of the proposed material is experimentally evaluated when functioning with aqueous salt concentrations: both the coated and functionalized specimens exhibit stable wettability after being immersed in saltwater for all the duration of the experiments (≈250 h in this work). The proposed new class of materials is envisaged for use in passive solar or thermal energy‐conversion devices. As a case study, a time‐discretized capillary model is coupled with a validated lumped‐parameters heat and mass transfer model, aiming to estimate the maximum size and productivity of a passive solar distiller employing porous materials of known thermal and capillary properties. This study paves the way to the use of a new class of rigid, highly thermally conductive materials that can significantly improve the performance of passive devices by simplifying the assembly of multistage setups, thus helping to extend their use to real‐scale applications.

AbstractPassive energy‐conversion devices based on water uptake and evaporation offer a robust and cost‐effective alternative in a wide variety of applications. This work introduces a new research avenue in the design of passive devices by replacing traditional porous materials with rigid capillary layers engraved with optimized V‐shaped grooves. The concept is tested using aluminum sheets, which are machined by femtosecond laser and covered by silica or functionalized by oxygen plasma to achieve stable long‐term capillary properties. The durability of the proposed material is experimentally evaluated when functioning with aqueous salt concentrations: both the coated and functionalized specimens exhibit stable wettability after being immersed in saltwater for all the duration of the experiments (≈250 h in this work). The proposed new class of materials is envisaged for use in passive solar or thermal energy‐conversion devices. As a case study, a time‐discretized capillary model is coupled with a validated lumped‐parameters heat and mass transfer model, aiming to estimate the maximum size and productivity of a passive solar distiller employing porous materials of known thermal and capillary properties. This study paves the way to the use of a new class of rigid, highly thermally conductive materials that can significantly improve the performance of passive devices by simplifying the assembly of multistage setups, thus helping to extend their use to real‐scale applications.

Thermal storage devices are becoming crucial for the exploitation of solar energy. From the point of view of seasonal energy storage, the most promising technology is represented by adsorption thermal batteries, which allow storing energy without heat loss with time. The improvement of thermal batteries design is related to a better understating of transport phenomena occurring in the adsorption/desorption phases. In this work, we discuss an efficient computational protocol to characterize adsorbent materials, in terms of both heat and mass transfer proprieties. To this purpose, a hybrid Molecular Dynamics and Monte Carlo method is developed. The proposed model is then tested on two types of 13X zeolite, with 76 and 88 Na cations. The results obtained, such as adsorbate diffusivity, adsorption curves, and heat of adsorption are validated with the literature. Finally, in the view of a multiscale analysis of sorption thermal storage devices, the possible use of the simulation outputs as inputs of thermal fluid dynamics models of adsorbent beds is discussed.

Thermal storage devices are becoming crucial for the exploitation of solar energy. From the point of view of seasonal energy storage, the most promising technology is represented by adsorption thermal batteries, which allow storing energy without heat loss with time. The improvement of thermal batteries design is related to a better understating of transport phenomena occurring in the adsorption/desorption phases. In this work, we discuss an efficient computational protocol to characterize adsorbent materials, in terms of both heat and mass transfer proprieties. To this purpose, a hybrid Molecular Dynamics and Monte Carlo method is developed. The proposed model is then tested on two types of 13X zeolite, with 76 and 88 Na cations. The results obtained, such as adsorbate diffusivity, adsorption curves, and heat of adsorption are validated with the literature. Finally, in the view of a multiscale analysis of sorption thermal storage devices, the possible use of the simulation outputs as inputs of thermal fluid dynamics models of adsorbent beds is discussed.