Far-field Temperature Research Articles

Optical super-resolution nanothermometry via stimulated emission depletion imaging of upconverting nanoparticles.

From engineering improved device performance to unraveling the breakdown of classical heat transfer laws, far-field optical temperature mapping with nanoscale spatial resolution would benefit diverse areas. However, these attributes are traditionally in opposition because conventional far-field optical temperature mapping techniques are inherently diffraction limited. Optical super-resolution imaging techniques revolutionized biological imaging, but such approaches have yet to be applied to thermometry. Here, we demonstrate a super-resolution nanothermometry technique based on highly doped upconverting nanoparticles (UCNPs) that enable stimulated emission depletion (STED) super-resolution imaging. We identify a ratiometric thermometry signal and maintain imaging resolution better than ~120 nm for the relevant spectral bands. We also form self-assembled UCNP monolayers and multilayers and implement a detection scheme with scan times >0.25 μm2/min. We further show that STED nanothermometry reveals a temperature gradient across a joule-heated microstructure that is undetectable with diffraction limited thermometry, indicating the potential of this technique to uncover local temperature variation in wide-ranging practical applications.

Enhanced imaging of electronic hot spots using quantum squeezed light

Detecting electronic hot spots is important for understanding the heat dissipation and thermal management of electronic and semiconductor devices. Optical thermoreflective imaging is being used to perform precise temporal and spatial imaging of heat on wires and semiconductor materials. We apply quantum squeezed light to perform thermoreflective imaging on micro-wires, surpassing the shot-noise limit of classical approaches. We obtain a far-field temperature sensing accuracy of 42 mK after 50 ms of averaging and show that a 256×256 pixel image can be constructed with such sensitivity in 10 min. We can further obtain single-shot temperature sensing of 1.6 K after only 10 μs of averaging, enabling a dynamical study of heat dissipation. Not only do the quantum images provide accurate spatiotemporal information about heat distribution but also the measure of quantum correlation provides additional information, inaccessible by classical techniques, which can lead to a better understanding of the dynamics. We apply the technique to both aluminum and niobium microwires and discuss the applications of the technique in studying electron dynamics at low temperatures.

Uncertainty assessment of thermal recovery and subsurface temperature changes induced by high-temperature aquifer thermal energy storage (HT-ATES): A case study

High-temperature aquifer thermal energy storage (HT-ATES) systems can store renewable-based or waste heat in the subsurface on a seasonal scale and may thus reduce the carbon footprint of future heat supply systems. Thermal recovery, i.e. the ratio of extracted to injected heat over one cycle, is required in a pre-application assessment because it determines the operational and economic viability of a HT-ATES system. The induced temperature changes in the subsurface are required to obtain the legal permits and are of interest for the design of a monitoring network. However, uncertainty in our knowledge on subsurface hydraulic and thermal parameters translates into uncertainties of the expected thermal recovery and the temperature changes induced during HT-ATES operation. In order to address these uncertainties for a case study in Hamburg, Germany, we use numerical modeling of the coupled thermo-hydraulic processes during the design stage of a HT-ATES system, based on a realistic load curve and the local geological setting of the storage aquifer. An ensemble of 50 scenarios was parameterized based on site-specific parameter uncertainties using Latin hypercube sampling to reflect the global parameter distributions, and the HT-ATES operation was simulated over a period of 26 years in each case. Most of the scenarios show high thermal recoveries with a median of 89 % in the 26th year, with thermal recovery most sensitive to the vertical hydraulic conductivity. The expected temperature distribution is well defined by the ensemble of model simulations, with far-field temperature changes reaching for hundreds of meters and showing greater variability between scenarios than those in the near-field region of the warm HT-ATES well on the tens of meters scale. Locations with large temperature differences between scenarios are identified as suitable for the placement of temperature monitoring wells. The presented work thus contributes directly to the design and permitting of HT-ATES systems and can also be used for uncertainty assessment of future HT-ATES plants and the identification of suitable monitoring setups.

Laboratory experiments of melting ice in warm salt-stratified environments

Melting icebergs provide nearly half of the total freshwater flux from ice shelves to the ocean, but the availability of accurate, data-constrained melting rate parametrisations limits the correct representation of this process in ocean models. Here, we investigate the melting of a vertical ice face in a warm, salt-stratified environment in a laboratory setting. Observations of the depth-dependent melting rates ${m}$ and boundary layer flow speed $U$ are reported for a range of initially uniform far-field ambient temperatures $T_a$ above ${10}\,^{\circ }{\rm C}$ . Ice scallops are characteristic features observed in all experiments, with the width of the scallops consistent with the theory of double-diffusive layers. The morphology of the scallops changes from symmetric about the scallop centre in the colder experiments to asymmetric in the warmer experiments. Observed melting rates are consistent with a melting rate scaling of the form ${m}\propto U\,\Delta T_a$ proposed by previous work in less extreme parameter regimes, where $\Delta T_a$ is the magnitude of thermal driving between the ambient and ice–fluid interface. Our results indicate that ice scalloping is closely linked to the naturally convecting flow of the ambient fluid. Depth-averaged melting rates depend on the buoyancy frequency in the ambient fluid, and double-diffusive convection promotes a turbulent-flux regime distinct from that explained previously in an unstratified regime. These findings have implications for parametrising melting rates of icebergs and glaciers in numerical models or potential freshwater harvesting operations, and provide insights into the interplay between stratification and ice melting.

Wireless Passive Ceramic Sensor for Far-Field Temperature Measurement at High Temperatures.

A passive wireless high-temperature sensor for far-field applications was developed for stable temperature sensing up to 1000 °C. The goal is to leverage the properties of electroceramic materials, including adequate electrical conductivity, high-temperature resilience, and chemical stability in harsh environments. Initial sensors were fabricated using Ag for operation to 600 °C to achieve a baseline understanding of temperature sensing principles using patch antenna designs. Fabrication then followed with higher temperature sensors made from (In, Sn) O2 (ITO) for evaluation up to 1000 °C. A patch antenna was modeled in ANSYS HFSS to operate in a high-frequency region (2.5-3.5 GHz) within a 50 × 50 mm2 confined geometric area using characteristic material properties. The sensor was fabricated on Al2O3 using screen printing methods and then sintered at 700 °C for Ag and 1200 °C for ITO in an ambient atmosphere. Sensors were evaluated at 600 °C for Ag and 1000 °C for ITO and analyzed at set interrogating distances up to 0.75 m using ultra-wideband slot antennas to collect scattering parameters. The sensitivity (average change in resonant frequency with respect to temperature) from 50 to 1000 °C was between 22 and 62 kHz/°C which decreased as interrogating distances reached 0.75 m.

A sustainable approach towards printed graphene ink for wireless RFID sensing applications

Graphene-based printable inks are advanced and promising candidates for flexible printed electronic devices. To develop large-scale graphene-based highly conductive electronics based on existing printing approaches of the material, it is imperative to scale up its ink production methods and optimize the electrical properties of the printed films. Here, a sustainable approach is reported for preparing high-conductive screen-printing graphene ink by recycling cellulose solvents. The ink uses Cyrene solvent in circulation and produces highly concentrated and conductive graphene ink to conquer the limitation of graphene inks in massive industrial production brought by the high cost of the cellulose solvents. A systematic study of the sheet resistance variation with the number of cycles has been carried out. The average conductivity of the ink can exceed 3 × 104 S m−1, with only a 2-h shear exfoliation process, which exhibits about the same conductivity of recent works (using toxic NMP solvent, complex centrifugation, ultrasonication, etc.) but with much more straightforward and cost-effective fabrication process. The formulation of graphene inks allows flexible metal-free far-field tag antenna to be screen-printed and integrated with an off-the-shelf sensory chip to achieve battery-free wireless UHF RFID far-field temperature sensing. The high responsiveness, accuracy, and sensitivity of the RFID sensing tag were observed with instantaneous detection of accurate and reliable wireless data transmission.

Cooling underground substations worldwide using heat pumps

The use of underground space in urban environments has increased at an accelerated rate over the past few years, particularly to satisfy transport infrastructure needs. Transport tunnels are being constructed at increasingly greater depths in the already congested subsurface. While transport tunnels have demonstrated significant potential as sustainable heat sources for heating under - and above-ground spaces, due to the large area in contact with the ground [4,5], cooling the substations that serve the tunnels, containing plants and machinery, is a task that poses a significant economic and environmental challenge. To tackle this, a new method that takes advantage of airflow in the tunnels and the thermal mass of the ground surrounding the tunnels has been recently introduced [2]. Similar to energy tunnels [1], these systems use water-filled high-density polyethylene (HDPE) pipes integrated into the tunnel space to exchange heat, however using the pipes to reject heat from the substations to the tunnels. This work adopts four cities, namely Sydney in Australia, Guangzhou in China, London in the UK, and Stuttgart in Germany, and investigates the suitability of this approach to cool substations for different meteorological and geological conditions around the world. Moreover, varying heat exchanger lengths and tunnel air temperatures are incorporated in the analysis, to assess the impact of these key parameters on system efficiency and performance.
 A detailed 3D finite element heat and mass transport model is utilised in this work, simulating the tunnel lining, surrounding soil, the airflow within the tunnel, the pipes attached to the tunnel linings (tunnel air side), and the circulating fluid within the pipes [2]. The location farfield temperature and material properties are shown in Table 1, for the soil conditions in the four locations and for the common materials (shaded in grey). A parametric analysis is undertaken to investigate the performance of these systems under varying conditions. For each of the locations, five different pipe leg length values are used: 50 m, 100 m, 150 m, 200 m, and 300 m and the air velocity is assumed as 0.5 m/s, typical of these tunnels. In addition, two different distributions for the temperature of the air entering the tunnel are used: the estimated tunnel air temperature () distributions based on available literature and measurements [3, 6, 7], as well as the surface air temperatures (), both shown in Figure 1-left. The latter is used to understand the impact of natural ventilation of tunnels on the system, which could inform the placement of the pipes with respect to the positions of ventilating shafts along the tunnel length.
 The results are shown in Figure 1-right, in terms of the cooling thermal power that a single pipe loop can provide (total pipe loop length being ), when operating constantly over 20 years – to replicate the real conditions in cooling substations. These values are obtained such that the temperature of the fluid does not reduce below 5 °C, such that the heat pump efficiencies remain high. The locations are shown based on the line colour and the air temperature distribution used for each location is represented by the line type (solid:, dashed:). The results show that the cooling provided can vary significantly based on the investigated parameters and suggest that the temperature of the air flowing in the tunnel is very influential to the system performance. The most favourable outcome is achieved for Stuttgart (green), which has the lowest tunnel air and farfield temperature, and the least favourable for Guangzhou (red), which has the higher air and farfield temperature. Comparing the two air temperature distributions used (solid vs dashed), using instead of , which is lower in all cases, increases the performance of the system. This is most obvious for the case of London, with an increase between 2.5 kW and 5 kW, likely due to the low value of the farfield temperature as opposed to the significantly high tunnel air temperatures (). The length of the pipes used in all cases increases the amount of energy, however that increase is logarithmic in nature and therefore after about 150 m to 200 m the investment might not be justified. Overall, this work shows that there is significant potential to utilise heat pump technologies to cool tunnel substations, especially in cooler climates such as central-northern Europe.

Basaltic sills emplaced in organic-rich sedimentary rocks: Consequences for organic matter maturation and Cretaceous paleo-climate

Many continental large igneous provinces coincide with climate perturbations and mass extinctions. When basaltic plumbing systems traverse carbon-rich sedimentary rocks, large volumes of greenhouse gases may be generated. We document how intrusive sills of the Mesozoic High Arctic Large Igneous Province affected surrounding fine-grained, organic-rich siliciclastic rocks of the Sverdrup Basin in the Canadian Arctic Archipelago. Petrographic and X-ray diffraction data from samples located near sills show the presence of high-temperature metamorphic phases (diopside, andalusite, garnet, and cordierite). Raman thermometry on organic matter yields peak temperatures of 385−400 °C near sill contacts, tailing off to far-field temperatures of ≤230 °C. Samples located >20 m from sills show no systematic change in vitrinite reflectance and have a VRo eq% value of ∼2.5%, which indicates a temperature of ∼210 °C. The finite element thermal modeling tool SUTRAHEAT was applied to the 17-m-thick Hare Sill, emplaced at 3 km depth at 1105 °C. SUTRAHEAT results show that contact-proximal rocks attain temperatures of >700 °C for a brief period (∼1 year). By 5 years, the Hare Sill is completely solidified (<730 °C), and the temperature anomaly collapses rapidly thereafter as the thermal pulse propagates outward. By 10 years, all rocks within 10 m of the Hare Sill are between 450 °C and 400 °C, rocks at 20 m from the contact attain 200 °C, yet far-field temperatures (>50 m) have barely changed. When multiple sills are emplaced between 4 km and 6 km depth, all rocks between sills reach ∼250 °C after 100 years, showing that it is possible to raise regional-scale background temperatures by ∼150 °C for the observed High Arctic Large Igneous Province sill density. Vitrinite reflectance data and pyrolysis results, together with SILLi thermal modeling, indicate that much of the hydrocarbon-generating potential was eliminated by High Arctic Large Igneous Province intrusions. The SILLi model yields ∼20 tonnes/m2 of organic equivalent CO2 (all carbon gas is reported as CO2) from the Hare Sill alone when emplaced into Murray Harbour Formation rocks with 5.7 wt% organic carbon, and ∼226 tonnes/m2 by emplacement of multiple sills throughout the 2-km-thick Blaa Mountain Group with 3 wt% organic carbon. On a basin scale, this yields a total of ∼2550 Gt CO2 from the Hare Sill, with ∼13,000 Gt CO2 being generated by the multiple sill scenario, similar to estimates from other large igneous provinces. Much of the Blaa Mountain Group rocks now have organic carbon contents of <1 wt%, which is consistent with large volumes of carbon-species gas having been generated, likely a mixture of CO2, CH4, and other species. However, organic-rich Murray Harbour Formation rocks show no obvious reduction in organic carbon content toward the Hare Sill intrusive contacts, which suggests that not all of the carbon was lost from the sedimentary package hosting High Arctic Large Igneous Province magmas. We suggest that some of the gas generated by contact metamorphism failed to drain out for lack of high-permeability conduits, and then back-reacted to form calcite cements and pyrobitumen during cooling.

Unsteady thermal transport in an instantly heated semi-infinite free end Hooke chain

We consider unsteady ballistic heat transport in a semi-infinite Hooke chain with free end and arbitrary initial temperature profile. An analytical description of the evolution of the kinetic temperature is proposed in both discrete (exact) and continuum (approximate) formulations. By comparison of the discrete and continuum descriptions of kinetic temperature field, we reveal some restrictions to the latter. Specifically, the far-field kinetic temperature is well described by the continuum solution, which, however, deviates near and at the free end (boundary). We show analytically that, after thermal wave reflects from the boundary, the discrete solution for the kinetic temperature undergoes a jump near the free end. A comparison of the descriptions of heat propagation in the semi-infinite and infinite Hooke chains is presented. Results of the current paper are expected to provide insight into non-stationary heat transport in the semi-infinite lattices.

East Antarctic Ice Sheet variability during the middle Miocene Climate Transition captured in drill cores from the Friis Hills, Transantarctic Mountains

This study describes 16 well-dated, terrestrial glacial sedimentary cycles deposited during astronomically paced climate cycles from the termination of the Miocene Climatic Optimum (MCO) through the middle Miocene Climate Transition (MMCT) (15.1−13.8 Ma) in the Friis Hills, Transantarctic Mountains, Antarctica. Three locations were continuously cored (79% recovery) to a maximum depth of 50.48 m through a succession of interbedded till sheets and fossil-bearing, fluvio-lacustrine sediments. A composite chronostratigraphic framework is presented for the cores based on the previous mapping, a seismic refraction survey that defines basin geometry, and a new, integrated age model based on paleomagnetic stratigraphy that is constrained by radioisotopic 40Ar/39Ar numeric ages on two newly identified silicic tephra. The paleoecologic and sedimentologic characteristics of organic-rich lithologies are relatively consistent up-section, which implies that successively younger interglacial deposits during the MMCT represented broadly similar environmental and climatic conditions. During these interglacials, the Friis Hills hinterland was likely ice-free. Major disconformities in the section suggest a transition to colder climates, and after ca. 14.6 Ma, thicker, more extensive and erosive ice cover occurred across the Friis Hills during glacial episodes. Diamictites in the upper three cycles suggest that climate cooled and became drier after ca. 14.2 Ma. However, cyclical retreat of the ice and a return to warm climate conditions during interglacials continued through ca. 13.9 Ma. These direct records reflect a highly variable East Antarctic Ice Sheet margin but show that the ice margin became progressively more extensive during successive glacial intervals, which is consistent with a cooling trend toward more glacial values in the far-field benthic foraminifera δ18O proxy ice volume and temperature record. Age constraints show that glacial-interglacial variability at the terrestrial margin of the East Antarctic Ice Sheet was primarily paced by astronomical precession (∼23 k.y.) through the onset of the MMCT (15−14.7 Ma). Precession-driven cycles are modulated by short-period (∼100 k.y.) eccentricity cycles. Intervals of maximum eccentricity (high seasonality) coincide with sedimentary cycles comprising thin diamictites and relatively thick interglacial sandstone and mudstone units. Intervals of minimum eccentricity (low seasonality) coincide with sedimentary cycles comprising thick diamictites and relatively thin interglacial sedimentary deposits. Major disconformities in the Friis Hills succession that span more than ∼100 k.y. reflect episodes of expansion of erosive ice across, and well beyond, the Transantarctic Mountains and coincide with nodes in eccentricity (∼400 k.y.). These relationships suggest that during relatively warm intervals in the middle Miocene, the East Antarctic Ice Sheet expanded and contracted over 100 k.y. cycles, while its margins continued to fluctuate at higher (∼23 k.y.) frequency. After 14.5 Ma, obliquity is the dominant frequency in δ18O records, marking a period during which large regions of the Antarctic Ice Sheet grounded in marine environments.

Effect of Finite Element Mesh Size and Time-Increment on Predicting Part-Scale Temperature for Powder Bed Fusion Process

Simulating powder bed fusion processes (PBF) can reveal temperature evolution in transient mode. Accurate temperature prediction using finite element (FE) method demands both mesh and timeincrements to be very small; thus, requiring a high computational cost. To avoid this, in part-scale simulation, coarse meshes representing multiple powder layers added at once, are usually used which results in fast solving of FE models. Powder layers and time increments are lumped in such a configuration, which results in a deviation of the temperature history. This research proposes a methodology to predict the nodal temperature (NT) due to the combined effect of space and time lumping for part-scale FE thermal simulation for PBF processes. It shows its effects in predicting both the local temperature history and the average far-field temperature.

Simulation of Freezing Cryomagma Reservoirs in Viscoelastic Ice Shells

Brine reservoirs in Europa’s icy crust, if they exist, could represent the most accessible liquid water bodies in the outer solar system. Any potential subsurface reservoirs are key for the exploration of ocean worlds and the search for habitability and life beyond Earth. Previous studies have demonstrated that freezing cryoreservoirs might trigger eruptions due to the pressurization associated with volume change as liquid water expands to become water ice, but those studies did not take into account the deformation of the reservoir wall. Viscoelastic deformation of the wall can act to accommodate the growing overpressure and prevent eruptions. Here we utilize a semianalytical numerical approach to calculate the pressure-induced deformation of a freezing cryoreservoir on Europa as a function of the far-field ice temperature. We find that shallow reservoirs located in relatively cold ice deform slightly and can be pressurized by freezing, but that deeper reservoirs located in warmer ice deform more easily and in some cases cannot reach the threshold overpressure required for spontaneous eruption. We identify a transition depth around 4–8 km depending on the reservoir radius, assuming a conductive ice shell structure consistent with current best estimates. Further, we find that shallow lens-shaped reservoirs may store a large volume of cryomagma and can be easily pressurized by freezing; they represent the best candidates for the mobilization of cryovolcanic material at Europa’s surface.

Anomalous Convective Flows Carve Pinnacles and Scallops in Melting Ice.

We report on the shape dynamics of ice suspended in cold fresh water and subject to the natural convective flows generated during melting. Experiments reveal shape motifs for increasing far-field temperature: Sharp pinnacles directed downward at low temperatures, scalloped waves for intermediate temperatures between 5 °C and 7 °C, and upward pointing pinnacles at higher temperatures. Phase-field simulations reproduce these morphologies, which are closely linked to the anomalous density-temperature profile of liquid water. Boundary layer flows yield pinnacles that sharpen with accelerating growth of tip curvature while scallops emerge from a Kelvin-Helmholtz-like instability caused by counterflowing currents that roll up to form vortex arrays. By linking the molecular-scale effects underlying water's density anomaly to the macroscale flows that imprint the surface, these results show that the morphology of melted ice is a sensitive indicator of ambient temperature.

Ice-shelf ocean boundary layer dynamics from large-eddy simulations

Abstract. Small-scale turbulent flow below ice shelves is regionally isolated and difficult to measure and simulate. Yet these small-scale processes, which regulate heat and salt transfer between the ocean and ice shelves, can affect sea-level rise by altering the ability of Antarctic ice shelves to “buttress” ice flux to the ocean. In this study, we improve our understanding of turbulence below ice shelves by means of large-eddy simulations at sub-meter resolution, capturing boundary layer mixing at scales intermediate between laboratory experiments or direct numerical simulations and regional or global ocean circulation models. Our simulations feature the development of an ice-shelf ocean boundary layer through dynamic ice melting in a regime with low thermal driving, low ice-shelf basal slope, and strong shear driven by the geostrophic flow. We present a preliminary assessment of existing ice-shelf basal melt parameterizations adopted in single component or coupled ice-sheet and ocean models on the basis of a small parameter study. While the parameterized linear relationship between ice-shelf melt rate and far-field ocean temperature appears to be robust, we point out a little-considered relationship between ice-shelf basal slope and melting worthy of further study.

Modeling a class of thermal ice probes for accessing the solar system’s ocean worlds

The subsurface oceans of icy moons in the outer solar system are prime candidates for harboring extra-terrestrial life. Missions to melt through the ice shells of these worlds utilizing an ice probe or “cryobot” to access the oceans have been proposed. To design such a cryobot for a successful mission, the relationship between a cryobot’s heat budget and descent speed within any given environment must be understood. Large uncertainties in the ice shell thickness and temperature profile require that the problem be treated via probabilistic techniques, such as a Monte Carlo simulation. By contrast, the speed of a cryobot descending through ice with specified far-field temperature and material properties can, in principle, be quantified with little uncertainty. A model of cryobot performance that can be computed quickly and accurately will save significant computational time for the broader simulation, and allow for the mission’s basic thermal needs to be understood. The work reported here builds upon an existing analytic thermal model of ice probes that, while suitable for terrestrial conditions, begins to incur potentially problematic errors in extraterrestrial environments. The new model provides improvement to the previous model for flight-relevant probes in extra-terrestrial ice conditions, predicting the total heat budget to within 1.2% of high-fidelity numerical simulations while requiring a small fraction of the computational time. The model can be non-dimensionalized in a compact form, making it suitable for modeling a broad class of cylindrical ice probes in a probabilistic modeling framework for determining the time required to access the sub-surface ocean. Such models can then provide the high-level requirements for cryobot system architectures that will enable successful ocean-access missions.

Numerical investigation of a high temperature heat injection test

High Temperature-Aquifer Thermal Energy Storage (HT-ATES) is a promising option to compensate for the seasonal mismatch between heating supply and demand in the heating sector based on renewable energies. To test and verify numerical and experimental methods for predicting HT-ATES thermo-hydraulic impacts, a small-scale heat injection test with injection temperatures of >70 °C was conducted in a shallow aquifer and monitored using a dense temperature sensor network. Prior to the heat injection test, the hydraulic and thermal properties of the field site were investigated and a predictive high-resolution numerical simulation model of the coupled thermo-hydraulic processes was derived based only on this a priori information. The comparison of measured and predicted temperature breakthrough curves showed a good correspondence, suggesting that the model is able to predict the overall thermal behavior. The model predictions were most accurate for long-term and far-field temperature evolution, with lower accuracy for temperature peaks closer to the injection well. Density-driven buoyancy flow was identified as an active heat transport process, due to the relatively high vertical hydraulic conductivity. The numerical model, parameterized based only on a priori site investigation data, is shown suitable for predicting heat transport processes due to a high temperature heat injection, as well as the induced thermal impacts of an HT-ATES system.

Cool Pavement Strategies for Urban Heat Island Mitigation in Suburban Phoenix, Arizona

Urban areas are characterized by a large proportion of artificial surfaces, such as concrete and asphalt, which absorb and store more heat than natural vegetation, leading to the Urban Heat Island (UHI) effect. Cool pavements, walls, and roofs have been suggested as a solution to mitigate UHI, but their effectiveness depends on local land-use patterns and surrounding urban forms. Meteorological data was collected using a mobile platform in the Power Ranch community of Gilbert, Arizona in the Phoenix Metropolitan Area, a region that experiences harsh summer temperatures. The warmest hour recorded during data collection was 13 August 2015 at 5:00 p.m., with a far-field air temperature of about 42 ∘ C and a low wind speed of 0.45 m/s from East-Southeast (ESE). An uncoupled pavement-urban canyon Computational Fluid Dynamics (CFD) model was developed and validated to study the microclimate of the area. Five scenarios were studied to investigate the effects of different pavements on UHI, replacing all pavements with surfaces of progressively higher albedo: New asphalt concrete, typical concrete, reflective concrete, making only roofs and walls reflective, and finally replacing all artificial surfaces with a reflective coating. While new asphalt surfaces increased the surrounding 2 m air temperatures by up to 0.5 ∘ C, replacing aged asphalt with typical concrete with higher albedo did not significantly decrease it. Reflective concrete pavements decreased air temperature by 0.2–0.4 ∘ C and reflective roofs and walls by 0.4–0.7 ∘ C, while replacing all roofs, walls, and pavements with a reflective coating led to a more significant decrease, of up to 0.8–1.0 ∘ C. Residences downstream of major collector roads experienced a decreased air temperature at the higher end of these ranges. However, large areas of natural surfaces for this community had a significant effect on downstream air temperatures, which limits the UHI mitigation potential of these strategies.

Transient Powder Melting in SLM Using an Analytical Model with Phase Change and Spherical Symmetry in a Semi-Infinite Medium

In this work, we introduce an analytical expression for approximating the transient melting radius during powder melting in Selective Laser Melting (SLM) assumed with a stationary laser heat source. The purpose of this work is to evaluate the suggested analytical approach in determining the melt pool geometry during laser processing, by considering heat transfer and phase change effects. This will allow for the rendering of the first findings on the way to a quasi-real time calculation of the melt pool during laser melting, which will contribute significantly to the process design and control, especially when new powders are applied. Initially, we consider the heat transfer process associated with a point heat source, releasing a continuous and constant power (in a semi-infinite powder bed. On the point of the heat source the temperature is infinite, and the material starts to melt spherically outwards, creating an interface that separates the solid from the molten material; we assume different properties between the two phases. Unlike the cases of the cartesian and cylindrical coordinates, (in a cartesian coordinate the heat source is over a plane, i.e., W/m2, and in cylindrical along a line, i.e., W/m), where the melting process is proportional to the square root of time, in spherical coordinates the melting stops at a finite radius, i.e., a maximum radius, which depends only on the heat source, the conductivity of the solid and the difference between the far-field temperature and the melting temperature of the material. Here we should also point out that to achieve continuous melting in spherical coordinates the power of the source must increase with the square root of the time. The obtained analytical expression for the maximum melting radius and the approximate expression for its dependence on the time compare well with the numerical results obtained by a finite element analysis.

Mushy-layer growth and convection, with application to sea ice.

Sea ice is a reactive porous medium of ice crystals and liquid brine, which is an example of a mushy layer. The phase behaviour of sea ice controls the evolving material properties and fluid transport through the porous ice, with consequences for ice growth, brine drainage from the ice to provide buoyancy fluxes for the polar oceans, and sea-ice biogeochemistry. We review work on the growth of mushy layers and convective flows driven by density gradients in the interstitial fluid. After introducing the fundamentals of mushy-layer theory, we discuss the effective thermal properties, including the impact of salt transport on mushy-layer growth. We present a simplified model for diffusively controlled growth of mushy layers with modest cooling versus the solutal freezing-point depression. For growth from a cold isothermal boundary, salt diffusion modifies mushy-layer growth by around 5-20% depending on the far-field temperature and salinity. We also review work on the onset, spatial localization and nonlinear development of convective flows in mushy layers, highlighting recent work on transient solidification and models of nonlinear convection with dissolved solid-free brine channels. Finally, future research opportunities are identified, motivated by geophysical observations of ice growth. This article is part of the theme issue 'The physics and chemistry of ice: scaffolding across scales, from the viability of life to the formation of planets'.

Vapor Solidification of Saturated Air in Two-Dimensional Stagnation Flow

In the present paper, stagnation flow solidification of vapor from saturated air is investigated. Saturated air with strain rate a impinges on a flat plate and, because the plate temperature is below the freezing temperature of water, condensation occurs and an ice layer forms on the plate. The ice surface is modeled as an accelerated flat plate moving toward the impinging fluid. The unsteady Navier-Stokes equations were subjected to a similarity transformation to obtain a single ordinary differential equation for the velocity distribution. Two methods of solution were used for the energy equation: a finite-difference numerical technique and a numerical solution of a similarity equation; these two results were compared to establish accuracy. Freezing time first increases as the far-field temperature decreases from above zero degrees Celcius and then rapidly approaches zero as the far-field temperature approaches zero Celcius. Despite the physical experiment, here the size of the nearest cell to the substrate controls the time at which condensation begins. As a result, maximum time before freezing begins occurs at about 5℃ air temperature, with the cell size 0.01 or 0.02 mm. The air temperature distribution and the ultimate frozen thickness for two saturated air temperatures are also presented.