Convection Regime Research Articles

Integrating LEO and GEO Observations: Toward Optimal Summertime Satellite Precipitation Retrieval

Abstract Reliable quantitative precipitation estimation with a rich spatiotemporal resolution is vital for understanding the Earth’s hydrological cycle. Precipitation estimation over land and coastal regions is necessary for addressing the high degree of spatial heterogeneity of water availability and demand, and for resolving the extremes that modulate and amplify hazards such as flooding and landslides. Advancements in computation power along with unique high spatiotemporal and spectral resolution data streams from passive meteorological sensors aboard geosynchronous Earth-orbiting (GEO) and low Earth-orbiting (LEO) satellites offer exciting opportunities to retrieve information about surface precipitation phenomena using data-driven machine learning techniques. In this study, the capabilities of U-Net–like architecture are investigated to map instantaneous, summertime surface precipitation intensity at the spatial resolution of 2 km. The calibrated brightness temperature products from the Global Precipitation Measurement (GPM) Microwave Imager (GMI) radiometer are combined with multispectral images (visible, near-infrared, and infrared bands) from the Advanced Baseline Imager (ABI) aboard the GOES-R satellites as main inputs to the U-Net–like precipitation algorithm. Total precipitable water and 2-m temperature from the Global Forecast System (GFS) model are also used as auxiliary inputs to the model. The results show that the U-Net–like algorithm can capture fine-scale patterns and intensity of surface precipitation at high spatial resolution over stratiform and convective precipitation regimes. The evaluations reveal the potential of extracting relevant, high spatial features over complex surface types such as mountainous regions and coastlines. The algorithm allows users to interpret the inputs’ importance and can serve as a starting point for further exploration of precipitation systems within the field of hydrometeorology.

Scaling Laws for Mixed Heated Convection With Pseudoplastic Rheology: Implications for the Bistability of Tectonic Mode

AbstractPlate tectonics is a tectonic style thought to be the hallmark of habitable planets, and yet the inherent complexities of plate tectonic convection have clouded the establishment of simple scaling laws with which to model convective behavior and thermal evolution. We have recently developed a scaling approach for mixed heated convection, based upon several simple physical principles. Here, we generalize our scaling approach to mixed heated convection with pseudoplastic rheology, which gives rise to the plate tectonic mode of convection. We then apply our scaling results to the so‐called bistability of tectonic mode. By illustrating common pitfalls regarding heating mode and nondimensionalization, we demonstrate that tectonic mode is unique with respect to key planetary properties, and that a convective regime diagram for terrestrial planets is within reach.

Impacts of Permeability Heterogeneity and Background Flow on Supercritical CO2 Dissolution in the Deep Subsurface

AbstractMotivated by CO2 capture and sequestration (CCS) design considerations, we consider the coupled effects of permeability heterogeneity and background flow on the dissolution of a supercritical CO2 lens into an underlying deep, confined aquifer. We present the results of a large‐scale Monte Carlo simulation study examining the interaction of background flow rate and three parameters describing multi‐Gaussian log‐permeability fields: mean, variance, and correlation length. Hundreds of high‐resolution simulations were performed using the PFLOTRAN finite volume software to model CO2 dissolution in a kilometer‐scale aquifer over 1,000 years. Predictive dimensionless scaling relationships relating CO2 dissolution rate to heterogeneity statistics, Rayleigh (Ra) and Péclet (Pe) numbers were developed for both gravitationally dominated free convection to background flow‐dominated forced convection regimes. An empirical criterion, Pe = Ra3/4, was discovered for regime transition. All simulations converged quickly to a quasi‐steady, approximately linear dissolution rate. However, this rate displayed profound variability between permeability field realizations sharing the same heterogeneity statistics, even under mild permeability heterogeneity. In general, increased heterogeneity was associated with a lower mean and higher variance of dissolution rate, undesirable from a CCS design perspective. The relationship between dissolution rate and background flow was found to be complex and nonlinear. Dimensionless scaling relationships were uncovered for a number of special cases. Results call into question the validity of the Boussinesq approximation in the context of modest‐to‐high background flow rates and the general applicability of numerical simulations without background flow.

Turbulent heat and mass lines in finite difference regime

AbstractFinite difference modelling of turbulent heat and mass flow visualization finds numerous applications in atmospheric flows/oceanic currents, wind turbines, thermal transfer in nuclear reactors, drag in oil pipelines, cooling of industrial machineries, and to investigate the complexity, dynamic and chaotic nature of the physical system. A turbulent phenomenon is effectively implemented in engineering, physics, earth sciences, bio‐engineering and medicine. Hence, motivated by the advantages of turbulence in various engineering fields, in the current article, a finite difference analysis is performed to demonstrate the k‐ε turbulence model‐based heat and mass lines visualization in boundary layer regime under turbulent buoyancy‐driven convective conditions along a cylinder. Turbulent flow characteristics are accurately explored by deploying the classical Newtonian flow model. Further, to accomplish a more sophisticated finite difference simulation, the effects of extra kinetic energy and its dissipation rate equations are considered. The produced Navier‐Stokes equations for time‐dependent turbulent heat and mass transmission are rendered to non‐dimensional by deploying suitable dimensionless numbers. The advanced coupled nonlinear turbulent unsteady buoyancy‐motivated vertical convection problem is then solved with a well‐sophisticated finite difference scheme such as Crank‐Nicolson technique using computational software. Authentication of current results with former solutions over a range of buoyancy number, Schmidt, and Prandtl parameters are presented. An extensive tabular and graphical discussion along with contours, heat and masslines visualization is included to enumerate the hydro‐dynamic, thermal and mass diffusion behaviour for the impact of emerged regulating numbers in the Prandtl regime. It is confirmed that, the accelerating turbulent buoyancy‐ratio number, maximizes the velocity, kinetic energy and dissipation rate at . Further, the numerical values of laminar thermal and mass diffusion rates are monotonically enhanced when compared to the turbulent values. Also, to verify the current findings, the authors compared the LRN k‐ε model turbulent results with the existing solutions and found good agreement. Further, the uniqueness and novelty of the current investigation is the exploration of heat and masslines in unsteady buoyancy‐driven convection regime under the influence of k‐ε turbulence model which extends the former studies and offers a more precise appraisal of the thermal and mass diffusion lines via the Crank‐Nicolson analysis.

Stress regime analysis for the transition to a stagnant-lid convection regime in the terrestrial mantle

A series of numerical simulations of terrestrial mantle convection with temperature-dependent viscosity in a three-dimensional spherical geometry was performed to investigate the thermal structure of the mantle interior and the mechanical condition of the lithosphere. The common “sluggish-lid” convection regime has the thermal structure of the mantle interior with a slowly mobile lid under a moderately temperature-dependent viscosity of mantle rocks, whereas the “stagnant-lid” convection regime has a convection pattern in which the entire surface is covered by a highly viscous lid due to the strongly temperature-dependent viscosity. This study focused not only on the thermal structure of the mantle but also on the mechanical conditions in the lithosphere on an intermediate, transitional convection regime between these end-member convections both under the standard- and the extended-Boussinesq approximations. In this “quasi-stagnant-lid” convection regime, the entire surface of the planet is covered by a highly viscous stagnant-lid that moves slowly, whereas the mantle interior is dominated by a long-wavelength (i.e., degree-one) thermal structure. The stress regime analyses revealed that the strike-slip regime is highly restricted spatially in the lid. If the constitutive laws allow the formation of faults in the future numerical model, the time-dependent formation of weak faults that can initiate plate tectonics may differ among the three convection regimes (i.e., degree-one, quasi-stagnant-lid, and stagnant-lid convection regimes). The range of viscosity contrast of the lid required to realize the “quasi-stagnant-lid” convection regime in the model under the extended-Boussinesq approximation was wider than under the standard Boussinesq approximation, because the adiabatic heating of the mantle increased the mantle temperature with the depth and enhanced the formation of stagnant-lid owing to the strong mechanical decoupling between the cold lid and the underlying hot mantle.

Modeling of stratified two‐phase flows with non‐uniform evaporation based on the exact solution of convection equations

Within the framework of the Oberbeck–Boussinesq approximation, the exact solution of equations of thermoconcentration convection is studied, which has the group origin. The issue of applicability of the exact solution for describing steady‐state convective flows of a liquid and a co‐current gas flux under the conditions of inhomogeneous evaporation of the diffusive type in a flat horizontal channel is discussed. Algorithms for obtaining analytical representations of the required functions for various types of the boundary conditions for the temperature function on the outer channel wall are proposed. The influence of the external thermal load and boundary thermal conditions on the structure of the velocity and temperature fields, evaporation mass flow rate, and vapor content in the gas layer is investigated at an example of the HFE‐7100–nitrogen system. The solution correctly predicts hydrodynamical, temperature, and concentration parameters of convective regimes appearing in the two‐phase system. The main characteristics are compared with the characteristics of the system in the case of uniform evaporation with a constant intensity.

Influence of smooth heater size on critical heat flux and heat transfer coefficient of saturated pool boiling heat transfer

In order to study the influence of smooth heater size on the performance of pool boiling heat transfer, saturated boiling experiments of FC-72 were conducted on eight sized smooth silicon chips (the test surfaces are denoted as S5 ∼ S30, and their dimensionless dimensions are in the range of Lh/Lc = 7 ∼ 42). The bubble dynamics during boiling were observed with a high-speed camera. The results indicated that in natural convection regime, the heat transfer coefficient decreases with increasing heater size at a given heat flux. Besides, the larger surfaces enter into the nucleate boiling regime earlier. In a fully developed nucleate boiling regime, S5 surface displays the optimal heat transfer performance. The reality is that no vapor columns are produced even in the high heat flux range due to its small bubble departure diameter and high bubble departure frequency. For S8 ∼ S15 surfaces, the wall temperatures increase continuously with the increase of heat flux, while S20 ∼ S30 surfaces present a trend of first keeping constant and then increasing. The active nucleation site densities on S15 ∼ S30 surfaces follow the law of Na = 0.45q2 in the whole nucleate boiling regime. By contrast, for S5 ∼ S12 surfaces, the nucleation site densities abide by this law only in a fully developed nucleate boiling regime. In addition, the departure diameter and departure frequency of bubbles increase with the increase of heat flux for all surfaces. It is observed that with the increase of smooth heater size, CHF presents a changing trend of first increasing (in range of Lh ≤ λD, λD is the most dangerous Taylor wavelength), then decreasing (in range of λD < Lh ≤ 3λD) and finally leveling off (in range of Lh > 3λD). Accordingly, the CHF value maximizes at the heater size Lh = λD. In the segment of decreased CHF, the decline rate of CHF in range of λD < Lh ≤ 2λD is larger than that in range of 2λD < Lh ≤ 3λD. Meanwhile, the influencing mechanisms of heater size on CHF were explained by consideration into bubble patterns and behavior.

Rayleigh–Bénard type PCM melting and solid drops

In this paper we document both theoretically and numerically the melting of PCM in an enclosure heated from the bottom, in the presence of vertical metallic fins. We start with the analysis of the PCM melting in the absence of fins to discover the main scales of the problem, stressing the occurrence of Rayleigh-Bénard cells generated during the convection regime of melting. We continue with predicting the impact of fins on the development of the melting interface. The numerical experiments allow to understand the impact of the aspect ratio between the height of the enclosure and the distance between fins on the melting dynamics. They highlight the existence of solid drops for a certain range of aspect ratios when the horizontal flow channels in the convective loops along the fins become in contact, and they show how the solid drop is dragged downward to finish melting on the heated bottom of the enclosure.

Compressible turbulent convection in highly stratified adiabatic background

Buoyancy-driven turbulent convection leads to a fully compressible flow with a prominent top-down asymmetry of first- and second-order statistics when the adiabatic equilibrium profiles of temperature, density and pressure change very strongly across the convection layer. The growth of this asymmetry and the formation of an increasingly thicker stabilized sublayer with a slightly negative mean convective heat flux$J_c(z)$at the top of the convection zone is reported here by a series of highly resolved three-dimensional direct numerical simulations beyond the Oberbeck–Boussinesq and anelastic limits for dimensionless dissipation numbers,$0.1 \le D\le 0.8$, at fixed Rayleigh number$Ra=10^6$and superadiabaticity$\epsilon =0.1$. The highly stratified compressible convection regime appears for$D &gt; D_{crit}\approx 0.65$, when density fluctuations collapse to those of pressure; it is characterized by an up to nearly 50 % reduced global turbulent heat transfer and a sparse network of focused thin and sheet-like thermal plumes falling through the top sublayer deep into the bulk.

Ice Shelf Water Structure Beneath the Larsen C Ice Shelf in Antarctica

AbstractUnderstanding ice shelf water (ISW) structure is crucial for studying the basal melting of ice shelves. In this study, we performed large‐eddy simulation experiments to assess ISW structure and basal melt patterns under different current velocity scenarios observed in the Larsen C ice shelf, Antarctica. The LES results revealed that the thickness of ISW is primarily determined by the meridional velocity (perpendicular to the grounding line), while the zonal velocity influences the potential temperature and salinity of ISW. We found that a key parameter determining the basal melt rate was northward meltwater advection which originates from variances in meltwater generation. This advection, in turn, leads to the tilted isopycnals and the potential for thermohaline interleaving in a diffusive convection regime. The different slopes of isopycnals induce distinct heat fluxes, resulting in different basal melt rates far from and near the grounding line (∼0.44 and 1.59 m yr−1, respectively).

Modes of Mantle Convection, Their Stability, and What Controls Their Existence

AbstractThe motion of Earth's tectonic plates is the surface expression of mantle convection beneath. Analytical convection models have attempted to relate observables, such as plate velocities and surface heat flow, with the thermo‐mechanical state of the mantle, and remain deeply influential in global geophysics. While such models tend to focus on describing the mantle's behavior today, there is evidence that suggests they may not be the best description for an earlier, hotter mantle. Early in Earth's history, higher temperatures may have led to different convective regimes that include active‐lid (today's form of convection), sluggish‐lid, and stagnant‐lid convection. In this study, we adopt and extend the analytical theory laid out by Crowley &amp; O'Connell (2012, https://doi.org/10.1111/j.1365-246X.2011.05254.x) that self‐consistently characterizes the first two of these convection regimes. For a given thermo‐mechanical state, the theory predicts one to multiple solutions that each represent distinct modes of mantle convection. Here, we derive new scaling laws that connect these modes to the mantle's Rayleigh number and identify a new fundamental, dimensionless number, which we term the O’Connell number (named after Richard “Rick” J. O'Connell (1941–2015)), that describes a plate's resistance in context of the overall convection of the system. In addition, we identify two key bifurcations that bracket the Rayleigh‐O'Connell number space within which multiple solutions may exist. Finally, we remove the assumption of steady‐state in their original framework in order to perform a linear stability analysis to characterize the relative stability of each convection mode.

Interior dynamics of super-Earth 55 Cancri e

The ultra-short-period super-Earth 55 Cancri e has a measured radius of 1.88 Earth radii. Previous thermal phase curve observations suggest a strong temperature contrast between the dayside and nightside of around 1000 K; the hottest point is shifted 41 ± 12 degrees east from the substellar point, indicating some degree of heat circulation. The dayside (and potentially even the nightside) is hot enough to harbour a magma ocean. We used results from general circulation models (GCMs) of atmospheres to constrain the surface temperature contrasts. There is still a large uncertainty on the vigour and style of mantle convection in super-Earths, especially those that experience stellar irradiation high enough to harbour a magma ocean. In this work our aim is to constrain the mantle dynamics of the tidally locked lava world 55 Cancri e. Using the surface temperature contrasts as a boundary condition, we model the mantle flow of 55 Cancri e using 2D mantle convection simulations, and investigate how the convection regimes are affected by the different climate models. We find that large super-plumes form on the dayside if that hemisphere is covered by a magma ocean and the nightside remains solid or only partially molten. Cold material descends into the deep interior on the nightside, but no strong downwellings form. In some cases the super-plume also moves several tens of degrees towards the terminator. A convective regime where the upwelling is preferentially on the dayside might lead to preferential outgassing on that hemisphere which could lead to the build-up of atmospheric species that could be chemically distinct from the nightside.

Influence of time-dependent wall temperature fluctuation on conjugate mixed convection inside a chamber with an oscillating cylinder

The current work is an attempt to examine the mixed convective heat flow in a square chamber subjected to time-dependent sinusoidal wall temperature containing a heat-conducting rotationally oscillating circular cylinder at the center. The right wall is kept at a cold temperature and the left wall is subjected to time-varying wall temperature, whereas the remaining walls are thermally insulated. A sinusoidal oscillating velocity is applied on the surface of the oscillating cylinder. This problem has practical relevance for several applications, notably solar collectors, microelectronic cooling systems, chemical reactors, radiators, and heaters. The main goal of this study is to promote heat transfer by investigating optimum system characteristics. The pressure-velocity formulation of the Navier-Stokes and heat energy equations is used to model the fluid domain inside the chamber, and heat transfer inside the cylinder is modeled by the two-dimensional heat conduction equation. Those equations are discretized using the Galerkin finite element method after converting them into non-dimensional forms. The instantaneous and time-averaged Nusselt numbers of the heated wall are examined for three different frequencies of the cylinder oscillation and sinusoidal wall temperature variation. Parametric simulation is carried out for three different cases within a mixed convection regime through a combination of Reynolds (31.62–316.23), Grashof (103–105), and Richardson (0.1–10) numbers. For each different combination, the optimum values of cylinder frequency are determined. Due to the thermal boundary layer's repeated contraction and expansion, the instantaneous Nusselt number demonstrates an oscillating pattern over time. Moreover, the maximum wall temperature frequency is found to maximize the heat transfer process.

New empirical flow-regime-based model of water boiling in rectangular microchannels

A new empirical flow-regime-based model of water boiling in rectangular microchannels is proposed and programmed using MATLAB code in the present paper. The prediction model divides the flow regime map into four parts: single-phase convection regime, sub-cooled boiling regime, saturated boiling regime, and partial dry-out boiling regime. Each zone is also divided into several sub-zones according to corresponding criteria. Suitable empirical heat transfer correlations and flow transition criteria are adopted for each flow pattern to reasonably capture the boiling heat transfer mode according to the vapor quality or the efficient heat flux. The prediction results generally present a similar trend to experimental results from the literature. The new model is also compared with the existing empirical flow-regime-based models in the literature. The Lee and Mudawar model and the Ma model can only capture up to 3 and 2 different trends of HTC, respectively. However, the new model considers a complete flow regime map and can capture up to 4 different trends of HTC.

Intraseasonal and synoptic modulation of diurnal surface solar radiation over Reunion island in the South-West Indian Ocean

Understanding the space-time variability of Surface Solar Radiation (SSR) is mandatory for the prediction and, eventually, the skillful forecasting of photovoltaic energy production. This paper addresses the modulation of local-scale SSR over Reunion, a tropical island in the South-West Indian Ocean, by the leading modes of climate variability influencing both regional-scale and local-scale atmospheric convection and its associated cloud cover. Analyses focus on synoptic (tropical cyclones [TCs], synoptic convective regimes, including Tropical-Temperate Troughs [TTTs]) and intraseasonal (Madden-Julian Oscillation [MJO]) timescales. The SSR intra-daily variability is first assessed by a diurnal classification of SARAH-E satellite SSR data, and it is then related to the climate conditions mentioned above. SSR anomalies are found larger (smaller) on the windward (leeward) side of Reunion and in the summer (winter) season. The island-scale “cloudy” conditions can typically last 1 or 2 days. Nearby TCs can strongly reduce SSR by up to 50% on average, depending on their distances from Reunion, their sizes, and particularly, their longitudinal positions, which is observed for the first time. Nearby TCs are associated with significant negative SSR anomaly when located west of Reunion but with less significant or even positive anomaly when located east of the island. Synoptic convective regimes (the intraseasonal MJO) have a relatively weaker impact on SSR, with a value up to 13% (5%) of the mean value. Potential interactions between these SSR modulators are also investigated to understand better and eventually predict the mechanisms likely to modulate SSR (and thus photovoltaic electricity production) at sub-seasonal timescales.

Evaluating Shallow Convection Parameterization Assumptions With a qt–w Quadrant Analysis

AbstractUncertainties associated with the response of shallow clouds to global warming remain a great challenge for climate projection. Due to the small size of these clouds, parameterizations are required to represent them in both current‐ and next‐generation climate models. We present a quantitative evaluation of several important assumptions used in both mass‐flux and Assumed‐PDF Higher‐Order Closure parameterizations of shallow convection. We use large‐eddy simulations (LESs) of four different shallow convection regimes as benchmarks and apply a qt (total moisture)–w (vertical velocity) quadrant analysis technique to identify the “coherent structures” of moist and dry up/down‐drafts. The statistics of these coherent structures and the environment are then used to evaluate commonly used assumptions in mass‐flux parameterizations related to (a) the convective downdrafts and (b) the subplume variability of convective updrafts. For quantitative evaluation of the PDF closure used in AP‐HOCs, we perform offline calculations with the PDF closure used in the Cloud Layers Unified By Bi‐normals and the Simplified Higher‐Order Closure schemes by supplying the closure with statistical quantities directly calculated from the LESs. Then, the impact of parameterization assumptions embedded in the PDF closure in the same two categories is analyzed and understood through comparisons of the output from the closure with the statistics of the moist and dry up/down‐drafts from the LESs.

Numerical investigation of horizontal flow film boiling of saturated liquid over two inline cylinders in the mixed convection regime

Mixed convection film boiling in a system of two cylinders positioned in an in-line configuration is numerically studied. The relative importance of inertia over buoyancy is given by Froude number. The direction of the incoming saturated liquid is perpendicular to the direction of gravity. Simulations are performed for the Reynolds number values of 50, 100, and 150; non-dimensional wall superheat values of 0.3, 0.6, and 0.9; and non-dimensional spacing between cylinders values of 2.0, 4.0, and 6.0. Three modes of vortex shedding from the cylinders are identified. An increase in the Reynolds number increases the heat transfer for the upstream cylinder and decreases heat transfer for the downstream cylinder. Increasing the non-dimensional wall superheat leads to decrease in the heat transfer rate from both the cylinders. Changing the non-dimensional spacing between the cylinders does not significantly alter the heat transfer from the upstream cylinder. However, heat transfer rate from the downstream cylinder increases significantly with increase in the non-dimensional spacing between the cylinders. The dynamic interface is affected by the shear layer instability and the vortex shedding pattern, which in turn affects the vapor film thickness around the cylinders and the rates of heat transfer from the cylinders.

Soret-induced convection of ternary fluid in a horizontal porous layer heated from below

The present paper deals with the investigation of the Soret-induced convection of a three-component mixture of hydrocarbons in a horizontal porous layer. This problem is important for geological applications. The first part of the paper is devoted to the linear stability of the conductive state. The longwave instability is studied analytically by the expansion into the power series with respect to the wave number. A new long-wave oscillatory instability mode existing at negative separation ratios is found out. It is shown that this mode is more dangerous than the long-wave monotonic instability mode in the entire range of its existence. The instability to the perturbations with nonzero wave numbers is studied numerically by the shooting method. Stability map is obtained. The results confirm the predictions of the longwave analysis. In the second part of the paper, the nonlinear convection regimes are studied by the finite difference method. The calculations give the results consistent with the linear stability analysis. It is found that the primary bifurcation as a result of which the conductive state losses its stability is supercritical. The transformations of the convective flow structure with the change in the Rayleigh–Darcy number are accompanied by the hysteresis phenomena.

Transport Features on Bidirectional Nanofluid Flow with Convective Heating and Variable Darcy Regime

The performance of Au and nanoparticles in Casson flow propelled by the rotational effect subject to convective heating and variable Darcy phenomenon is presented. As a means to contribute significantly to the biomedical industry for proper prediction and treatment of diseases like cancer, stenosis, et cetera, the Casson fluid model and magnetohydrodynamic effect are employed in this study to investigate the bidirectional-rotating boundary layer flow of blood since Casson rheology best describe the mammalian blood flow dynamics and that blood is electrically conducting in nature. The enormous performance of nanoparticles made them extremely useful; hence, they gained recognition over the conventional refrigerants and were widely used by scientists, modelers, and researchers for controlling and treating diseases via drug targeting (chemotherapy), etc. In the three-dimensional plane, the assumed electrically conducting fluid conveying nanoparticles is properly mixed through the Coriolis force, thus rotating with angular velocity across the variable porous medium. A numerical tool, Chebyshev Collocation Method (CCM) with pseudo-spectral approach, is deployed on the resulting transformed ODEs. Profile distributions of respective boundary layers to distinct responses of model parameters, including the Eckman, Darcy, and Biot numbers on Au and nanoparticles, are analyzed and discussed. The dominance of nanoparticles on both velocities is revealed, while Au nanoparticles demonstrated a higher thermal performance rate. A rise in the Darcy parameter has a diametrically opposed behavior on the primary and secondary velocities.

A non-invasive measurement approach of boric acid concentration for anticipating reactivity excursion in light water integrated small modular reactors

This article presents a viability study about a non-invasive and a higher accurate experimental approach to measure boric acid concentration in water under a vast combination of pressure and temperature conditions. This novel approach has been developed to be used in a test facility simulating integral Pressurized Water Reactor - Small Modular Reactors (iPWR-SMRs), that is under development and will be operated by the Brazilian Nuclear Energy National Commission. Besides, the passive acting of the main systems is one of the most important requirements that characterize Generations III + and IV nuclear reactors. The integration of such systems in a unique hermetic enclosure has brought new technological challenges to the nuclear engineering. Among such challenges is the need for adequate and efficient instrumentation for assessing operating conditions and phenomena present in iPWR-SMRs. The boric acid solution has been used in conventional PWRs as an important option to core reactivity control, demanding the need to characterize boric acid concentrations in reactor vessels any time, justifying the interest of this research. However, in an iPWR-SMR, water flow (with boron) between the pressurizer and the nuclear core occurs under passive convection regime and is invariably very slow and small. This situation may require a non-invasive measurement approach. The objective of this work is to analyze the viability of using ultrasonic technique to characterize the concentration of boric acid in a liquid medium non-invasively under experimental conditions of a specific test facility. Ultrasonic tests were performed relating different boric acid concentrations with the path time of the ultrasonic wave. Factors able to mask the characterization of these concentrations by ultrasonic technique were also evaluated. The results showed that this technique allows the characterization of boric acid concentrations in liquid medium under very simple conditions, requiring further studies for complex conditions like those found in nuclear reactors.