Melting Rate Research Articles

Numerical study of the melting rate enhancement of nano phase change material in a modified shell and tube heat exchanger

The current investigation employs numerical analysis using ANSYS Fluent software to explore the melting behaviour of phase change material (PCM) and nano-PCM in a semi-circular shell and tube heat exchanger, utilizing dual side heating for enhanced conduction and convection rates of heat transfer. The study incorporates aluminium oxide nanoparticles at volume concentrations of 2 %, 4 % and 6 % within paraffin wax and assessing their impact on melting and thermal energy storage rates. Notably, the 2 % nanoparticle volume concentration exhibits an enhanced storage rate as compared to higher concentrations. The increase in nanoparticle concentration from 0 % to 2 %, 2 % to 4 % and 4 % to 6 % results in percentage reduction in melting time of 21 %, 3.51 % and 2.8 % respectively. Semi-circular configuration shows significant improvement in the energy storage rate as compared to the circular triplex tube configuration. The maximum energy storage rate of PCM for the semi-circular and circular configurations is 1.15 kW and 1.04 kW respectively, marking a 9.56 % increase over the circular configuration. Moreover, the semi-circular and circular configurations using nano-PCM achieve a maximum energy storage rate of 1.19 kW and 1.14 kW, representing a 4.20 % increase over the circular configuration.

Energy and exergy investigation of a eutectic phase change material for a triplex tube thermal energy storage with various configurations

This study investigates the energy and exergy analysis of eutectic PCM melting (80% melting) within a numerically simulated triplex tube latent heat storage unit. The unit features inner pipes arranged in triangle, pentagon, square, and circular configurations. The parameters examined include mean melting temperature, melting fraction, exergetic efficiency, exergy destruction, heat transfer rate, entropy generation number, and system efficiency, all of which influence melting time. Previous research predominantly focused on cylindrical forms for all three tubes in triple-tube heat exchangers, neglecting diverse inner tube configurations. The study innovates by exploring various innermost tube shapes (triangular, square, pentagonal, circular) in a triple tube heat exchanger. The practical benefits include superior thermal performance for industries like oil and gas, chemical, food and beverage, and power generation. The pentagonal inner triplex tube thermal energy storage (TTTES) system outperforms triangular topologies with higher Stefan and Rayleigh numbers by 11.54% and 11.53%, respectively, at Fo=0.000254. In the pentagonal configuration, the eutectic phase change material (EPCM) experiences a melting rate of 75%, 200%, and 225% faster than triangular, square, and circular configurations within the TTTES. Additionally, the pentagonal inner tube stores 2.28%, 6.90%, and 5.60% more energy than its triangular, square, and circular counterparts after 200 seconds of melting. Thus, TES systems based on pentagonal configurations are more efficient in melting, surpassing triangular, square, and circular counterparts with eutectic PCM.

A low-cost and open-source approach for supraglacial debris thickness mapping using UAV-based infrared thermography

Abstract. Debris-covered glaciers exist in many mountain ranges and play an important role in the regional water cycle. However, modelling the surface mass balance, runoff contribution and future evolution of debris-covered glaciers is fraught with uncertainty as accurate observations on small-scale variations in debris thickness and sub-debris ice melt rates are only available for a few locations worldwide. Here we describe a customised low-cost unoccupied aerial vehicle (UAV) for high-resolution thermal imaging of mountain glaciers and present a complete open-source pipeline that facilitates the generation of accurate surface temperature and debris thickness maps from radiometric images. First, a radiometric orthophoto is computed from individual radiometric UAV images using structure-from-motion and multi-view-stereo techniques. User-specific calibration and correction procedures can then be applied to the radiometric orthophoto to account for atmospheric and environmental influences that affect the radiometric measurement. The thermal orthophoto reveals distinct spatial variations in surface temperature across the surveyed debris-covered area. Finally, a high-resolution debris thickness map is derived from the corrected thermal orthophoto using an empirical or inverse surface energy balance model that relates surface temperature to debris thickness and is calibrated against in situ measurements. Our results from a small-scale experiment on the Kanderfirn (also known as Kander Neve) in the Swiss Alps show that the surface temperature and thickness of a relatively thin debris layer (ca. 0–15 cm) can be mapped with high accuracy using an empirical or physical model. On snow and ice surfaces, the mean deviation of the mapped surface temperature from the melting point (∼ 0 ∘C) was 0.6 ± 2.0 ∘C. The root-mean-square error of the modelled debris thickness was 1.3 cm. Through the detailed mapping, typical small-scale debris features and debris thickness patterns become visible, which are not spatially resolved by the thermal infrared sensors of current-generation satellites. The presented approach paves the way for comprehensive high-resolution supraglacial debris thickness mapping and opens up new opportunities for more accurate monitoring and modelling of debris-covered glaciers.

Numerical study of phase change heat accumulator with distribution of Hanoi tower-shaped fin

Hanoi tower-shaped fin distribution was proposed to improve the shell-and-tube phase change accumulator's ability for heat storage. Unlike the common annular fin group, the fin spacing of the Hanoi tower-shaped fin distribution is distributed in an arithmetic sequence, the fin length increases in a fixed proportion, and the fin group's overall position changes with the bottommost spacing. In this paper, the effects of no fin, uniform fin distribution, and Hanoi tower-shaped fin distribution on the melting process were compared and analyzed. The single-factor effects of bottommost spacing, spacing tolerance, and length ratio were analyzed for the Hanoi tower-shaped fin distribution. The solid–liquid phase change frontier, melting time, temperature distribution, and streamline distribution were simulated and studied for different fin structures. Fins' combined effects on heat conduction and natural convection were examined. The Hanoi tower-shaped fins' structural parameters were optimized by applying response surface methodology (RSM). The results indicated that the Hanoi tower-shaped fin distribution considerably enhanced the phase change material's (PCM) melting rate and uniformity in the vertical circular tube heat accumulator. The significance levels of factors affecting the whole melting time were spacing tolerance (d) < length ratio (k) < bottommost spacing (P1). Within a certain range, the larger the bottommost spacing was, the synergistic heat transfer effect of natural convection and heat conduction was better. According to the RSM optimization results, when the length ratio was 1.2, the fin's bottommost spacing was 17.82 mm, and the spacing tolerance was 3.38 mm, the model had the shortest melting time. Compared with the uniform fin distribution, the total heat storage time was reduced by 18.04 %.

Thermal performance enhancement of multiple tubes latent heat thermal energy storage system using sinusoidal wavy fins and tubes geometry modification

In this paper, performance enhancement of a shell and multiple tube latent heat thermal energy storage system (LHTESS) is numerically investigated by implementing sinusoidal wavy fins and different geometrical designs of heat transfer tubes. The annular space of the shell is filled with the paraffin wax RT35 as phase change material (PCM) and absorbs heat from hot water through the multiple tubes. With the constant total cross-section area of all tubes and fins as the constraint condition, the effect of tube number and tube shape incorporated with the proposed fins on the heat transfer properties of PCM during the melting process is evaluated. The computational results demonstrate that the sinusoidal wavy fins can improve the phase change efficiency compared to the conventional straight fins. The double-pitch sinusoidal wavy fins decrease the total melting time by 9.5% compared to the straight fins for the single-tube case. As the number of HTF tubes increased from one to four, the complete PCM melting time decreased by 38.3%. Geometrical design alterations of heat transfer tubes from circular to petal-shaped are proposed to further improve the thermal performance of multiple tubes LHTESS. The melting rate of PCM is accelerated with an increase in the number of petals. The petal tubes with nine petals can save the charging time up to 24 % in comparison with the circular tubes in a four-tube case with double-pitch sinusoidal wavy fins, and up to 57% compared to the base case with a single circular HTF tube and straight fins.

Enhancing ice cream qualities with novel rice husk cellulose nanocrystal applications

SummaryCellulose nanocrystals derived from rice husk (CNC) using a chemical method combined with high‐pressure homogenisation, were investigated for their application in ice cream formulations. The physicochemical and sensory properties of ice cream with CNC at three different concentrations (0%, 0.15%, and 0.30% wt.) and two levels of whipping cream as fat content (5% and 10% wt.) were studied. The results indicate that increased CNC concentration enhanced the overrun and viscosity of the ice cream samples. Furthermore, 10% fat ice cream with 0.30% CNC exhibited higher total phenolic content and antioxidant activity compared to the others. The hardness and melting rate of the ice cream samples tended to decrease with higher fat levels and CNC concentrations. Moreover, CNC helped to improve the quality of low‐fat ice cream while still maintaining satisfactory sensory properties. Therefore, CNC has the potential as a stabiliser for ice cream to improve its overall properties.

Using field-based, photogrammetric point cloud, orthophoto and LiDAR-derived metrics to assess forest structure–snowpack relationships in the Great Lakes–St. Lawrence Forest region

The efficacy of field-based, photogrammetric point cloud, orthophoto and light detection and ranging datasets to describe forest structure and resolve forest–snowpack relationships in a mixed forest region was evaluated over two years at the point and transect scales. Hemispheric photo-derived canopy metrics correlated well with remotely sensed metrics, but tree bole metrics were not effectively derived from remotely sensed data. Significant differences in melt rate and snow-free date were found across forest type at the transect scale. Field and remotely sensed estimates of canopy cover were highly correlated with melt rate and snow-free date at the point scale, which aligns with previous literature and understanding of snowmelt processes. However, significant correlations were only present during the 2016 study year, which was attributed to canopy-controlled solar radiation-driven melt in 2016 versus more spatially uniform turbulent flux-driven melt in 2017. Peak snow water equivalent metrics were not correlated well with canopy or tree height metrics, contrary to previous research. This was likely due to mid-winter melt events throughout both study years, where a mix of accumulation and melt processes confounded forest–snowpack relationships. This study demonstrates that widely available remotely sensed data with a broad coverage can be used to: (i) describe forest–snowpack relationships in mixed hardwood, coniferous forests and (ii) elucidate the variability of forest–snowpack relationships under different climate conditions in this environment.

Coupling MAR (Modèle Atmosphérique Régional) with PISM (Parallel Ice Sheet Model) mitigates the positive melt–elevation feedback

Abstract. The Greenland Ice Sheet is a key contributor to sea level rise. By melting, the ice sheet thins, inducing higher surface melt due to lower surface elevations, accelerating the melt coming from global warming. This process is called the melt–elevation feedback and can be considered by using two types of models: either (1) atmospheric models, which can represent the surface mass balance (SMB), or SMB estimates resulting from simpler models such as positive degree day models or (2) ice sheet models representing the surface elevation evolution. The latter ones do not represent the surface mass balance explicitly as well as polar-oriented climate models. A new coupling between the MAR (Modèle Atmosphérique Régional) regional climate model and the PISM (Parallel Ice Sheet Model) ice sheet model is presented here following the CESM2 (Community Earth System Model; SSP5-8.5, Shared Socioeconomic Pathway) scenario until 2100 at the MAR lateral boundaries. The coupling is extended to 2200 with a stabilised climate (+7 ∘C compared to 1961–1990) by randomly sampling the last 10 years of CESM2 to force MAR and reaches a sea level rise contribution of 64 cm. The fully coupled simulation is compared to a one-way experiment where surface topography remains fixed in MAR. However, the surface mass balance is corrected for the melt–elevation feedback when interpolated on the PISM grid by using surface mass balance vertical gradients as a function of local elevation variations (offline correction). This method is often used to represent the melt–elevation feedback and prevents a coupling which is too expensive in computation time. In the fully coupled MAR simulation, the ice sheet morphology evolution (changing slope and reducing the orographic barrier) induces changes in local atmospheric patterns. More specifically, wind regimes are modified, as well as temperature lapse rates, influencing the melt rate through modification of sensible heat fluxes at the ice sheet margins. We highlight mitigation of the melt lapse rate on the margins by modifying the surface morphology. The lapse rates considered by the offline correction are no longer valid at the ice sheet margins. If used (one-way simulation), this correction implies an overestimation of the sea level rise contribution of 2.5 %. The mitigation of the melt lapse rate on the margins can only be corrected by using a full coupling between an ice sheet model and an atmospheric model.

Enhancement of an air conditioning system performance utilizing a PCM-based heat exchanger: Impact of aspect ratio

This research emphasizes enhancing air conditioning (AC) system performance through the integration of a phase change material (PCM)-based annulus heat exchanger (HEX) within the condenser unit. The present study delves into how aspect ratio (AR), inlet velocities, and inlet air temperature impact the coefficient of performance (COP) and melting rate. Moreover, it considers the variable specific heat of the PCM, a less-explored aspect in AC-integrated PCM systems. Results have revealed that the AR notably affects the complete melting time. Specifically, an increase in the AR from 15 to 21 has led to a noteworthy reduction of 30.07% in the total melting time under fixed velocity conditions at 2.55 m/sec and θ = 0.429. The present study has also established a correlation to demonstrate how total melting time is influenced by AR, inlet air temperature, and inlet velocity. Also, modifying AR and inlet velocity to the HEX could lead to lower outlet temperatures from the HEX. Initially, at a given velocity of 2.55 m/sec and θ of 0.429, increasing the AR from 15 to 18 leads to a 1.61% decrease in the outlet air temperature from the HEX, while increasing AR from 15 to 21 results in a 3.12% decrement. PCM-enhanced AC systems consistently exhibit improved COP values, especially in low-velocity scenarios, outperforming systems without PCM. At the onset of melting, for a given velocity of 2.55 m/sec and θ of 0.429, the percentage increase in the COP for the altered system compared to a system without the PCM is found to be 11.28%, 12.84%, and 14.01% for ARs of 15, 18, and 21, respectively. Configurations with higher ARs are found to be more suitable for higher cooling loads with shorter working periods.

Improved Parameterizations of Vertical Ice‐Ocean Boundary Layers and Melt Rates

AbstractBuoyancy fluxes and submarine melt rates at vertical ice‐ocean interfaces are commonly parameterized using theories derived for unbounded free plumes. A Large Eddy Simulation is used to analyze the disparate dynamics of free plumes and wall‐bounded plumes; the distinctions between the two are supported by recent theoretical and experimental results. Modifications to parameterizations consistent with these simulations are tested and compared to results from numerical and laboratory experiments of meltwater plumes. These modifications include 50% weaker entrainment and a distinct plume‐driven friction velocity in the shear boundary layer up to 8 times greater than the externally‐driven friction velocity. Using these updated plume parameter modifications leads to 40 times the ambient melt rate predicted by commonly used parameterizations at vertical glacier faces, which is consistent with observed melt rates at LeConte Glacier, Alaska.

Climatic Drivers of Ice Slabs and Firn Aquifers in Greenland

AbstractRecent observations revealed the existence of ice slabs and aquifers on the Greenland ice sheet (GrIS). Both affect the ice sheet's hydrology: ice slabs facilitate runoff and aquifers modulate drainage to the bed. However, their climatic drivers and history remain unclear, as most observations cover only two decades. Here, we present a model simulation of the evolution of GrIS ice slabs and aquifers (1980–2020), evaluated using radar measurements. The results show that accumulation, melt and rain rates are good predictors for the spatial distribution of ice slabs and aquifers. Both features were already present in the late 1980s, and their extent remained relatively constant until the beginning of this century, after which increased melt led to their expansion. We show that almost any transect from the coast to the ice‐sheet interior will cross either an ice slab region, or an aquifer, or both.

Shape effect on solid melting in flowing liquid

Iceberg melting is a critical factor for climate change. However, the shape of an iceberg is an often neglected aspect of its melting process. Our study investigates the influence of different ice shapes and ambient flow velocities on melt rates by conducting direct numerical simulations of a simplified system of bluff body flow. Our study focuses on the ellipsoidal shape, with the aspect ratio as the control parameter. We found the shape plays a crucial role in the melting process, resulting in significant variations in the melt rate between different shapes. Without flow, the optimal shape for a minimal melt rate is the disk (two-dimensional) or sphere (three-dimensional), due to the minimal surface area. However, as the ambient flow velocity increases, the optimal shape changes with the aspect ratio. We find that ice with an elliptical shape (when the long axis is aligned with the flow direction) can melt up to 10 % slower than a circular shape when exposed to flowing water. Following the approach considered by Huang et al. (J. Fluid Mech., vol. 765, 2015, R3) for dissolving bodies, we provide a quantitative theoretical explanation for this optimal shape, based on the combined contributions from both surface-area effects and convective-heat-transfer effects. Our findings provide insight into the interplay between phase transitions and ambient flows, contributing to our understanding of the iceberg melting process and highlighting the need to consider the aspect-ratio effect in estimates of iceberg melt rates.

Surface mass balance and climate of the Last Glacial Maximum Northern Hemisphere ice sheets: simulations with CESM2.1

Abstract. The Last Glacial Maximum (LGM, from ∼26 to 20 ka BP) was the most recent period with large ice sheets in Eurasia and North America. At that time, global temperatures were 5–7 ∘C lower than today, and sea level ∼125 m lower. LGM simulations are useful to understand earth system dynamics, including climate–ice sheet interactions, and to evaluate and improve the models representing those dynamics. Here, we present two simulations of the Northern Hemisphere ice sheet climate and surface mass balance (SMB) with the Community Earth System Model v2.1 (CESM2.1) using the Community Atmosphere Model v5 (CAM5) with prescribed ice sheets for two time periods that bracket the LGM period: 26 and 21 ka BP. CESM2.1 includes an explicit simulation of snow/firn compaction, albedo, refreezing, and direct coupling of the ice sheet surface energy fluxes with the atmosphere. The simulated mean snow accumulation is lowest for the Greenland and Barents–Kara Sea ice sheets (GrIS, BKIS) and highest for British and Irish (BIIS) and Icelandic (IcIS) ice sheets. Melt rates are negligible for the dry BKIS and GrIS, and relatively large for the BIIS, North American ice sheet complex (NAISC; i.e. Laurentide, Cordilleran, and Innuitian), Scandinavian ice sheet (SIS), and IcIS, and are reduced by almost a third in the colder (lower temperature) 26 ka BP climate compared with 21 ka BP. The SMB is positive for the GrIS, BKIS, SIS, and IcIS during the LGM (26 and 21 ka BP) and negative for the NAISC and BIIS. Relatively wide ablation areas are simulated along the southern (terrestrial), Pacific and Atlantic margins of the NAISC, across the majority of the BIIS, and along the terrestrial southern margin of the SIS. The integrated SMB substantially increases for the NAISC and BIIS in the 26 ka BP climate, but it does not reverse the negative sign. Summer incoming surface solar radiation is largest over the high interior of the NAISC and GrIS, and minimum over the BIIS and southern margin of NAISC. Summer net radiation is maximum over the ablation areas and minimum where the albedo is highest, namely in the interior of the GrIS, northern NAISC, and all of the BKIS. Summer sensible and latent heat fluxes are highest over the ablation areas, positively contributing to melt energy. Refreezing is largest along the equilibrium line altitude for all ice sheets and prevents 40 %–50 % of meltwater entering the ocean. The large simulated melt for the NAISC suggests potential biases in the climate simulation, ice sheet reconstruction, and/or highly non-equilibrated climate and ice sheet at the LGM time.

Persistent warm-eddy transport to Antarctic ice shelves driven by enhanced summer westerlies

The offshore ocean heat supplied to the Antarctic continental shelves by warm eddies has the potential to greatly impact the melting rates of ice shelves and subsequent global sea level rise. While featured in modeling and some observational studies, the processes around how these warm eddies form and overcome the dynamic sub-surface barrier of the Antarctic Slope Front over the upper continental slope has not yet been clarified. Here we report on the detailed observations of persistent eddies carrying warm modified Circumpolar Deep Water (CDW) onto the continental shelf of Prydz Bay, East Antarctica, using subsurface mooring and hydrographic section data from 2013-2015. We show the warm-eddy transport is most active when the summer westerlies strengthen, which promotes the upwelling of CDW and initiates eddy formation and intrusions. Our study highlights the important role of warm eddies in the melting of Antarctica’s ice shelves, both now and into the future.

Altered Weddell Sea warm- and dense-water pathways in response to 21st-century climate change

Abstract. The transport of water masses with ocean circulation is a key component of the global climate system. In this context, the Filchner Trough in the southern Weddell Sea is critical, as it is a hotspot for the cross-shelf-break exchange of Dense Shelf Water and Warm Deep Water. We present results from Lagrangian particle tracking experiments in a global-ocean–sea-ice model (FESOM-1.4) which includes ice-shelf cavities and has eddy-permitting resolution on the southern Weddell Sea continental shelf. With backward and forward experiments, we assess changes between a present-day and a future (SSP5-8.5) time slice in the origin of waters reaching the Filchner Ice Shelf front and the fate of waters leaving it. We show that particles reaching the ice-shelf front from the open ocean originate from 173 % greater depths by 2100 (median; 776 m as compared to 284 m for the present day), while waters leaving the cavity towards the open ocean end up at 35 % shallower depths (550 m as compared to 850 m for the present day). Pathways of water leaving the continental shelf increasingly occur in the upper ocean, while the on-shelf flow of waters that might reach the ice-shelf cavity, i.e., at deeper layers, becomes more important by 2100. Simultaneously, median transit times between the Filchner Ice Shelf front and the continental shelf break decrease (increase) by 6 (9.5) months in the backward (forward) experiments. In conclusion, our study demonstrates the sensitivity of regional circulation patterns in the southern Weddell Sea to ongoing climate change, with direct implications for ice-shelf basal melt rates and local ecosystems.

A Pore Scale Study on Heat Transfer Characteristics of Integrated Thermal Protection Structures with Phase Change Material

Phase change material (PCM) are characterized by their high latent heat and low density. Combining PCM with building walls, aircraft fuselages, and other structures can significantly enhance the thermal sink capability of these structures. In order to address the issue of low heat storage efficiency resulting from the low thermal conductivity of PCM, a novel integrated thermal protection structure (ITPS) architecture with a supportive structure based on a porous lattice has been designed. Experimental and numerical methods were employed to investigate the thermal response characteristics of the ITPS with and without PCM, the melting behavior of PCM within the porous lattice, and the effects of lattice configuration and pore size on the PCM melting rate. The current ITPS study includes evaluation of two types of lattice configurations and three different pore sizes. The results indicate that the inclusion of PCM reduces the internal panel temperature of the ITPS by approximately 15%. The melting of PCM occurs primarily at the central region of the porous lattice and gradually spreads towards the periphery until complete melting is achieved. Specifically, the Gibson–Ashby lattice configuration enhances the PCM melting rate by 43.5%, while the tetradecahedron lattice configuration yields a 53.1% improvement. Furthermore, for PCM with different pore sizes, smaller pores exhibit faster melting rates during the early and intermediate stages, whereas larger pores exhibit faster melting rates in the later stages as the proportion of liquid PCM increases. The conclusions of this study provide valuable insights for the application of PCM in the field of thermal management.

Simulation of integration of photovoltaic solar system with storage unit incorporating mixture of paraffin and nanoparticles

In this study, we conducted a simulation of the cooling process for a silicon layer within a Photovoltaic (PV) system, integrating a paraffin layer. To augment the cooling rate and expedite the melting process, we introduced nanoparticles into the paraffin (specifically, RT28HC). The dynamic nature of the process was accurately modeled using an implicit method. To further enhance the melting rate, the container was equipped with fins. The incorporation of a Phase Change Material (PCM) like paraffin with PV technology represents a novel approach in this research. This combination not only improves the cooling efficiency but also addresses the issue of expedited melting, offering a significant advancement in the field. By effectively utilizing the latent heat features of the paraffin, we can enhance the overall performance and reliability of PV systems, potentially leading to more efficient energy conversion and utilization. The equations were explained using FVM, accounting for the positioning of the hot wall. Gravity was omitted from the model, and a uniform approximation was applied for mixture characteristics. The introduction of fins led to a notable increase in the melting rate by approximately 42.9 %. Additionally, the incorporation of nano-powders resulted in a reduction of melting time by about 6.27 % and 4.39 % in scenarios both with and without fins, respectively. These outcomes signify that the presence of fins and the inclusion of nano-powders significantly influence the charging process. Fins enrich the rate of melting, while the adding of nano-powders accelerates the overall melting time. This research highlights the potential benefits of utilizing these enhancements in practical applications, potentially leading to more efficient and effective melting processes.

Feasibility analysis and cutting process research on laser cutting medium-thick 20CrNiMo steel plates using a high-power fiber laser without assisted blowing

Rapid cutting of oil and gas wellhead tubing is the key to handling fire emergencies in oil and gas wells. However, it is difficult to perform close-range laser cutting on oil and gas wellhead tubing due to the impact of high temperatures on equipment. Therefore, it is necessary to conduct close-range laser cutting tests under unassisted blowing conditions to confirm the feasibility of long-distance laser cutting of oil and gas wellhead tubing. In this work, laser cutting experiments are conducted to analyze the feasibility of using a 10 kW high-power laser to cut medium-thick 20CrNiMo steel plates under unassisted blowing conditions. Firstly, the optimized cutting path, kerf width, cutting movement speed, and defocus amount for the 10 kW laser are obtained by unit cutting experiments on 20 mm thick 20CrNiMo steel plates under the condition of unassisted blowing. Secondly, a 10 kW laser source with preferable process parameters is used to cut the 50 mm thick 20CrNiMo steel plate. Qualitative and quantitative comparisons of kerf morphology and dimensions are used to evaluate the cutting quality. The results indicate that a wide kerf width with a top-down cutting path benefits the discharge of slag from the kerf under unassisted blowing conditions. Under the condition of fixed laser power, the cutting movement speed and the defocus amount affect the melting rate of metal materials, which in turn affects the cutting quality. This work confirms the feasibility of using a high-power laser with preferable process parameters to cut through medium-thick steel plates under the condition of unassisted blowing, which will help promote the application of the laser cutting technology in rescue situations such as oil and gas drilling fires and provide a reference for other industrial fields that need to conduct laser cutting experiments to medium-thick steel plates under unassisted blowing conditions.

Effect of partial cooling-heating configurations on the enhanced latent thermal energy storage performance

A low rate of ice melting can be addressed by adding nanoscale particles of high thermal conductivity; however, other simple and effective techniques are also possible for further enhancement of the thermal characteristics and melting process of ice as well as other phase storage materials for thermal energy storage. In the present numerical study, two techniques combining partial heating and inversion of the active cavity walls in addition to adding hybrid nanoparticles (Cu and Al2O3) are investigated for the sake of enhancing the phase change in the cavity. Modeling is based on Lattice-Boltzmann techniques; numerical predictions are successfully compared with experimental and theoretical published data. The thermal behavior of the enhanced phase change material is analyzed for various Rayleigh and Fourier numbers and nanoparticle concentrations. The isotherms, streamlines, interface position, liquid fraction evolution, and full melting duration are analyzed. The outcomes show that for each concentration investigated, there is a different best configuration for reducing the ice melting time. 76% reduction in the melting time was achieved with a nanoparticle concentration of 6% (hybrid copper and alumina) and proper simultaneous heating and cooling configuration. These findings can guide designing efficient ice-based systems.

Experimental comparative study on thermal performance of latent heat storage tanks with pin, perforated, and rectangular fins at different orientations

The low thermal conductivity of phase change materials (PCMs) has limited their widespread use in practical applications. In the present study, different fin structures, namely, rectangular, perforated, and pin were examined to analyze the thermal performance of the melting process in rectangular latent heat storage tanks. Experiments were performed at both horizontal and vertical orientations to evaluate the effectiveness of different fin configurations. Visual observation of the phase change evolution at different time intervals was enabled through a transparent plexiglass shell. Instantaneous heat transfer rate and energy storage were measured using thermocouple readings and melting photographs. The results show that the maximum heat transfer coefficient between the heated wall and PCM is obtained by the pin-finned tank followed by perforated and rectangular-finned tanks. This thermal behavior is justified by the intensification of the upward convection flows through the voids provided by pin fins or perforated fins. Although the rectangular fin structure has the lowest convective heat transfer coefficient, its heat transfer rate is slightly higher than the other structures due to its larger heat transfer area. At a wall temperature of 70℃, the convective heat transfer coefficient and heat transfer rate obtained by the pin fin configuration are respectively 25% higher and 4% less than those of the rectangular fin. It reveals that the pin fin structure provides the most effective heat transfer area compared to its counterparts which have a significantly larger fin volume. In addition, it was found that regardless of the fin configuration, the melting rate in the horizontal tank was significantly higher than in the vertical tank due to the formation of more vortical flow structures within the molten PCM. The melting time in the unfinned horizontal tank was less than those of the vertical finned tanks implying that the tank orientation should be well-chosen to minimize the melting time along with adding fins of various configurations.