Numerical simulations of bubbly turbulent convection in cubical geometriesMarichal, J; Ruyer, P; Bartosiewicz, Y
doi: 10.1088/1742-6596/2766/1/012030pmid: N/A
In this work we present numerical results of pool boiling flow in a turbulent Rayleigh-Bénard convection configuration, using our in-house code in a cubical geometry. The problem in hand is encountered in various natural phenomena as well as in industrial applications. An Eulerian-Lagrangian approach is developed for the mixture of liquid water and vapor bubbles. The liquid mean temperature is close to the saturation temperature and is governed by the quasi-incompressible Navier-Stokes equations that are solved using DNS standards. The motion and growth/shrinkage of each individual vapor bubble is modeled and the backward effect of the bubbles on the fluid is accounted via momentum and energy exchanges between the two phases (two-way coupling), as well as variations in fluid phases volumetric fractions (volumetric coupling). In such pool configuration the non-dimensional parameters governing the flow are both those relative to Rayleigh-Bénard convection, namely Rayleigh number, Prandtl number and aspect ratio, and those to boiling, namely the overall vapor volumetric fraction, the bubble size based Reynolds number, the degree of superheat of the liquid scaled by the overall temperature difference, and the Jakob number (sensible heat to latent heat ratio).At first, we describe the model used and its corresponding validation, involving natural convection, isolated bubble dynamics and coupling between bubbly and bulk flows. In the second part, we consider the study of the relationship between heat transfer through the pool (Nusselt number) and the flow topology for different settings of the bubbly configurations.
Ventilation system with heat recovery and PCM thermal energy storage for “free” cooling in buildingsJocić, A; Lenassi, P; Osterman, E; Stritih, U
doi: 10.1088/1742-6596/2766/1/012232pmid: N/A
For the conventional cooling of buildings, we are using electrical energy from the network, which increases annually due to the increase in comfort. Alternatives are being sought to reduce electricity consumption. Phase change materials (PCMs) in ventilation systems can provide us with the accumulation of night-time coolness in the summer months, resulting in a reduction in the consumption of electricity for cooling. Heat storages that take advantage of the phase change are used for short-term storage of thermal energy, as in this case, they have the greatest potential. In the introduction to the paper, a review of heat storage devices and their use is made which shows their connection with the Energy Performance Building Directive (EPBD) and the Energy Efficiency Directive (EED). Based on the measured results of the measurements in the Laboratory for Heating, Sanitary and Solar Technology and Air-conditioning (LHSA), a comparison with the model that calculates the storage of heat and cold in a phase change material (PCM - Phase Change Material) developed by a group of researchers from BUT Brno was made. With the TRNYSY software tool and the model simulations of the ventilation gains in the summer season were made and compared with the gains when using the heat exchanger (recuperator) and the PCM heat accumulator for the selected room.
Effect of hydrophobic coating on optimization of dropwise condensation of steam on hybrid surfacesSuzzi, Nicola; Croce, Giulio
doi: 10.1088/1742-6596/2766/1/012143pmid: N/A
Dropwise condensation of pure vapor on hybrid surfaces, characterized by alternate hydrophobic-hydrophilic regions, is numerically investigated via phenomenological, Lagrangian modelization of dropwise condensation on hydrophobic regions. The drop size distribution over the hydrophobic domain, which knowledge is crucial for development of accurate simplified, statistically based models, is computed. Comparison with literature correlations shows that the theoretical correlation for size distribution of small droplets gives an inaccurate estimate, while the improved correlation, derived from the droplet population balance, better describes the numerical size distribution and, if incorporated in the statistically based model, allows to accurately predict the condensing flux.
Thermal performance against gravity of an AlSi10 AM heat pipe with a diamond lattice structureVitali, L; Menini, S; Guilizzoni, M; Niro, A
doi: 10.1088/1742-6596/2766/1/012020pmid: N/A
Metal Additive Manufacturing has gained momentum as a viable production technique for specialized heat transfer devices, in particular for industrial sectors characterized by small production numbers associated with high-performance requirements. Within the space industry, ESA is leading and funding several applied research programs to explore the possibility to employ AM for building electronic boxes with embedded heat pipes, in order to reduce manufacturing post-processing steps and contact thermal resistances. In the context of tender 1-10238, the project “Heat Pipe Solutions for High Power Systems” (HPS2) has developed and tested lattice-based heat pipes, that are intended to be integrated in electronic modules. In this paper, the heat transfer performances as function of input power and tilt angle against gravity of a 150 mm long heat pipe with a 20 mm evaporator section and a 40 mm condenser section are presented and compared with the results of the models of performance limits, based on the measured properties of the lattice.
Direct air capture with renewable heating based on the technical lime cycleKlockow, E; Linder, M
doi: 10.1088/1742-6596/2766/1/012098pmid: N/A
The industry and space heating demand contributes significantly to the CO2 emissions in Germany, as it is mainly supplied by the combustion of fossil fuels. In this contribution a concept is presented that not only provides heat based on renewable sources, but is also able to actively capture CO2 from the atmosphere. Thereby, the reversible reaction of lime with water is utilised to store and provide heat on demand – all based on abundantly available resources. By closing the technical lime cycle this long-term energy storage could additionally be combined with a Direct Air Capture technology.
Cryogenic quenching process enhancement through coating and microstructure optimizationGraffiedi, Marco; Dent, Francis J.; Khodaparast, Sepideh; Bucci, Matteo
doi: 10.1088/1742-6596/2766/1/012139pmid: N/A
In this work, we explore the impact of coatings and microstructures on heat transfer during a cryogenic quenching process. An easily reproducible quenching test is presented as a benchmark for testing different solutions. The study involves two different flat polymeric coatings as well as three porous microstructures. The results show that pairing a low-conductive coating with an appropriate porous surface microstructure on top of a stainless-steel plate can reduce the chill down time, accelerating the transition from room temperature to liquid nitrogen temperature, by a factor of five. High speed video recordings have been used to analyse the quenching process with different coatings and microstructures showing how the suppression of the film boiling regime is the key to enhancing the quenching process.
Enhanced Pool Boiling Heat Transfer with Porous Ti-6Al-4V-Coatings Produced by Cold Spray Metal Additive ManufacturingGarivalis, Alekos Ioannis; Chen, Yan; Shatskiy, Evgeny; Robinson, Anthony; Marco, Paolo Di; Lupoi, Rocco
doi: 10.1088/1742-6596/2766/1/012130pmid: N/A
In advancing industrial heat transfer mechanisms, surface coatings offer significant potential. This research elucidates the efficacy of the metal additive manufacturing Cold Spray deposition technique for producing enhanced boiling surfaces, specifically focusing on Ti-6Al-4V (Ti64) coatings on Aluminium substrates. This offers a rapid and low-cost fabrication method for producing lightweight enhanced boiling surfaces. The Cold Spray method is typically used to create dense metal deposits. Here, the process has been specially tuned to create highly inhomogeneous honeycomb-type porous Ti64 coatings. Critical Cold Spray deposition parameters, such as particle velocity, preheat temperature, and deposition rate have been identified to create repeatable porous coatings, with thicknesses of up to 3.0 mm achievable. Following deposition, several samples were subjected to systematic boiling heat transfer tests in a purpose-built pool boiling apparatus. Boiling curves were generated for the augmented Cold Spray surfaces as well as a bare surface, with the latter acting as a baseline to which enhancement levels were assessed. Initial data analysis shows that some of the tested surfaces exhibit a notable increase in boiling heat transfer coefficient and Critical Heat Flux (CHF). This enhancement is potentially attributed to increased surface area, increased nucleation site density, capillary wicking, and mitigation of lateral bubble coalescence, though excessive coating thickness may degrade heat transfer. In summary, the novel Ti64 surface structures developed using the Cold Spray deposition technique exhibits high potential for industries necessitating superior boiling heat transfer performance. Importantly, the manufacturing process is industrially scalable, offering the capacity to rapidly coat large areas at low cost compared with subtractive manufacturing other metal additive manufacturing methods.
Enhanced latent thermal energy battery with additive manufacturingMorciano, Matteo; Alberghini, Matteo; Fasano, Matteo; Almiento, Mariella; Calignano, Flaviana; Manfredi, Diego; Asinari, Pietro; Chiavazzo, Eliodoro
doi: 10.1088/1742-6596/2766/1/012220pmid: N/A
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.
Mixed convection by buoyancy and magnetothermal forcesKaneda, M; Yoshimura, S; Suga, K
doi: 10.1088/1742-6596/2766/1/012205pmid: N/A
The magnetic force in the paramagnetic fluid depends on the local gradient of magnetic flux density and the temperature-dependent magnetic susceptibility. In the presence of the gravity, the buoyant force due to the temperature difference additionally overlaps, and the resultant flow becomes a mixed convection. In this study, the effect of the temperature-dependent magnetic force (magnetothermal force) on the natural convection was numerically investigated. The magnetic field formed by the permanent-magnet array was employed and effective one was discussed in terms of the heat transfer. A three-dimensional Rayleigh-Benard convection simulation was conducted with the magnet array below the bottom hot wall. It was found that the magnetothermal force enhances the convection not only where the magnet locates but also away from the magnet due to the force profile.
Simple model of liquid piston compressorCerkovnik, N; Čurović, L; Prezelj, J
doi: 10.1088/1742-6596/2766/1/012052pmid: N/A
The study proposes a new 0D thermodynamic model for the fast and simple evaluation of Liquid Piston compressors whose geometry and operation are determined by large number of parameters. With the proposed model, the evaluation of the parameters becomes easier, more dependencies are found and the understanding of the influences of parameter changes is deepened. Therefore, optimal designs for the mentioned machines can be created and tested experimentally. During the study, the model was validated with experimental and CFD data, and the results showed good agreement. It was found that evaluation criteria need to be defined for each set of geometric and operational parameters in order to compare the designs.