Convective Characteristics Research Articles

Effect of pump light repetition rate on thermal convection characteristics in liquid SBS-PCM (invited)

Effect of pump light repetition rate on thermal convection characteristics in liquid SBS-PCM (invited)

Assessing the impact of a NWP warm‐start system on model spin‐up over tropical Africa

AbstractConvection‐permitting (CP) models have provided a step change in the ability to forecast impactful convective storms, which pose risks such as flash flooding and lightning. Despite CP models being routinely run over tropical Africa, they typically lack data assimilation and are initialised directly from a global analysis. The CP model therefore takes time to generate convective structures and consequently precipitation, rendering the early part of the forecast unusable. A ‘warm‐starting’ method developed within the Met Office Unified Model is tested over a large tropical Africa domain, leading to substantial improvements in rainfall predictions during both the spin‐up period but also later in the forecast. The spin‐up period is found to vary considerably, both geographically and with model initialisation time, due to the differing states of the atmosphere through the day. We quantify this impact through a spin‐up diagnostic, which shows that over central Africa the spin‐up period can be as large as 24 hr. In these regions, the warm starting substantially reduces spin‐up time. Additionally, the large tropical Africa domain allows us to examine the impact of the prevailing meteorology on both the spin‐up period and the warm‐start method. We find large‐scale positive vorticity filaments over West Africa, likely tied to African Easterly Waves, increase rainfall rates across all models. The substantial reduction in the spin‐up of rainfall and increased skill at longer lead times in the warm‐start demonstrate the importance of representing convective features in the analysis for a CP model. This is especially important in large tropical domains where the initial conditions are likely to have a lasting impact on the forecast. Improvements in model performance across the forecast will enhance the ability of forecasters to provide advice on high‐impact weather events, supporting increased resilience against weather extremes in Africa.

Accelerating Flow of Carbon Nanotubes with Carboxymethyl Cellulose and Blood Base Materials with Comparative Thermal Features: Prabhakar Fractional Model

A fractional model is developed to investigate the thermal onset of carbon nanotubes containing single‐wall carbon nanotubes (SWCNTs) and multiwall carbon nanotubes (MWCNTs). The blood and carboxymethyl cellulose (CMC) are utilized to report the characteristics of the base material. The thermal phenomenon is further supported with inclined magnetic force and mixed convection features. The vertical plate with an oscillatory nature induced the flow. After formulating the problem in view of flow assumptions, the fractional framework is carried out via the Prabhakar technique. The validation of the fractional model is ensured in view of previous studies. The comparative thermal aspect of carbon nanotubes and base materials by varying flow parameters is tested.

Study on Intermittent Microwave Convective Drying Characteristics and Flow Field of Porous Media Food

Numerical simulations were carried out for moist, porous media, intermittent microwave convective drying (IMCD) using a multiphase flow model in porous media subdomains coupled with a forced-convection heat-transfer model in an external hot air subdomain. The models were solved by using COMSOL Multiphysics was applied at the pulse ratio (PR) of 3. Based on drying characteristics of porous media and the distribution of the evaporation interface, IMCD was compared with convection drying (CD). Drying uniformity K, velocity difference, temperature difference, and humidity difference were introduced to evaluate the performance of three models with different inlets and outlet wall curvature. The numerical results show that as the moisture content of slices was reduced to 3 kg/kg, the drying rate in IMCD was 0.0166–0.02 m/s higher than that in CD, and the total drying time of the former was 81.35% shorter than that of the latter. In the late drying stage of IMCD, the core of the sample still had a high vapor concentration and temperature, which led to the evaporation interface remaining on the surface. The vapor evaporated from the slices can diffuse rapidly to the outside, which is why IMCD is superior to traditional convection drying. Through the comprehensive analysis of the models with different inlet and outlet wall curvatures, the drying uniformity K of the type III was the highest, reaching 89.28%. Optimizing flow-field distribution can improve uniform of airflow distribution.

Influence of ultrasound and ethanol as a pretreatment on papaya infrared and convective drying characteristics and quality parameters

AbstractThis study aimed to evaluate the effectiveness of pretreatments on papaya drying behavior and quality parameters. The pretreatment consisted of submerging the samples in ethanol or distilled water for 20 min. The ultrasonic step was conducted in an ultrasonic bath (25 kHz). Samples were dried in an infrared dryer and a convective oven at 60°C. The material pretreated with ultrasound and ethanol and submitted to infrared drying presented the shortest drying time (84 min). The two‐term exponential model was the most predictive for the drying data fitting. All dried samples showed water activity values below 0.60. Among the pretreatments performed, the use of ultrasound associated with ethanol was more effective in reducing losses of total phenolics, ascorbic acid, and antioxidant activity of dried papaya when compared to the use of water. Infrared drying of the fruit pretreated with the combination of ultrasound and ethanol resulted in no significant difference from the untreated papaya concerning the evaluated quality parameters.Practical applicationsThe consumption of tropical fruits and their derived products has increased in national and international markets, due to the growing recognition of their nutritional properties and subsequent use in the food industry. The presence of nutrients such as bioactive compounds, demonstrates their potential for use in different sectors, increasing the added value of the cultivar. Thus, this study represents a contribution to society, recognizing and valuing the consumption of fruit, contributing to the nutritional conditions of the population, favoring food and nutritional security, and conservation of the species. It also allows, with the use of pretreatments and different types of drying, advances, and information about food preservation methods that have a low environmental impact and the exploration of new forms of fruit consumption, increasing its shelf life and facilitating their transport and marketing.

Numerical simulation for two‐phase dusty thermally developed Marangoni forced convective flow of Williamson material: A finite difference scheme

AbstractPresent research work reports some novel investigation regarding thermal Marangoni convection features for Williamson fluid flow along with utilization of dust particles. In order to improve the transportation process, the thermal radiation and mixed convection aspects are also taken into account. The surface tension has been considered a linearly fluctuating with the surface temperature. The temperature of interface dust particles and fluid attained quadratic relation with interface arc length. The flow problem is based on dust particle phase and associated fundamental laws of heat/mass phenomenon. The valuable transformations acquired the flow problem in non‐dimensional form which are further proceeded numerically via novel finite difference procedure. The outcomes from simulated theoretical analysis are graphically underlined in view of novel physical relevance. The fluid velocity increasing versus Grashof number. Also, fluid velocity declines for dust particle mass concentration, suction/injection and momentum dust parameter. The temperature of working fluid boosts against larger radiation parameter.

Natural convection characteristics of nano-encapsulated phase change materials in a rectangular wavy enclosure with heating element and under an external magnetic field

Recently, nano-encapsulated phase change material (NEPCM) has received great attention due to its ability to absorb and release heat, making it a perfect choice for many engineering and industrial applications. The current work examines the natural convection of NEPCM confined in a cubic enclosure having two wavy sidewalls and under the effect of an external magnetic field. The enclosure is heated from below via a duct or cavity having a U shape; both wavy sidewalls experience cold temperatures, and the other walls are thermally insulated. The impacts of different operational and geometrical parameters on heat transfer inside the enclosure were numerically investigated. These parameters include the external magnetic field applied, Rayleigh number (Ra), sidewall wavenumber (N), Hartmann number (Ha), nanoparticle volume fraction (φ), and heat source position. Heat transfer within the enclosure was found to be most affected by the Ra and Ha numbers, while the other factors studied had little to no effect. The maximum local Nusslet number at Ra = 106 was four times greater than that at Ra = 103. As for the effect of the Ha number, increasing Ha from 0 to 100 decreased the average Nusselt number by 38 %.

Entropy generation and characteristics of mixed convection in lid-driven trapezoidal tilted enclosure filled with nanofluid

The investigation of steady, incompressible, laminar mixed convective fluid flow within two different types of tilted lid-driven trapezoidal enclosures filled with nanofluid composed of water and Al2O3 nanoparticles has been carried out in this paper. The upper wall of the enclosure is an isothermal cold surface that travels at a constant speed, while the bottom surface of the cavity maintains a constant high temperature. Non-dimensional governing equations along with the appropriate boundary conditions are solved using Galerkin finite element technique. Parametric simulation has been conducted by varying tilt angle of the base wall from 0° to 45°, Reynolds number from 0.1 to 103, Grashof number from 10−2 to 106, and Richardson number between 0.1 and 10 for three different cases. The streamlines and the isotherms are used to describe the fluid flow and heat transfer characteristics within the enclosure. Besides, the quantitative evaluations of thermal enhancement in terms of the average Nusselt number, average fluid temperature, and Bejan number of the enclosure are presented. Effects of base wall tilt angle and the presence of nanofluid on convection heat transmission characteristics as well as Bejan number are also explored.

Thermal fluid–structural interaction of three cylinders undergoing flow-induced vibration with cross thermal buoyancy

The effect of cross thermal buoyancy on the characteristic of flow-induced vibration and mixed convection of three circular cylinders is numerically studied. Two-dimensional simulations were conducted for a Reynolds number (Re) of 100 and five Richardson numbers (Ri) of 0–1.00. The range of the reduced velocity is 3 ≤ U* ≤ 15. Three circular cylinders C1, C2, and C3 are arranged in an equilateral triangle with C1 in upstream. The results show that the maximum amplitude of the C1 increases by up to 21% with considering cross thermal buoyancy in comparison to the case of Ri = 0. The galloping-like response is observed on the C1 at Ri = 1.00. The lift coefficient of three circular cylinders increases with the increase in Ri at U* ≥ 6. When U* exceeds a critical value, the vibrations of the C2 and C3 are in-phase, and the “2S” pattern is observed in the near-wake of three circular cylinders. The near-wake becomes wider, and the vortex shedding frequency increases at U* = 6 and Ri = 0.25 and 0.50. The higher the reduced velocity, the more significant is the effect of cross thermal buoyancy in enhancing heat transfer. The maximum space time-averaged Nusselt number increases by 10.42% in comparison to the case of fixed cylinders.

Dynamic Downscaling the South Asian Summer Monsoon From a Global Reanalysis Using a Regional Coupled Ocean‐Atmosphere Model

AbstractIn this study, we present the results of a regional model (regional spectral model‐regional ocean model [(RSM‐ROMS]) simulation of the South Asian Summer Monsoon (SASM). The RSM‐ROMS integration is carried out at 20 km grid spacing over a period of 25 years (1986–2010). The simulation is forced by global atmospheric and oceanic reanalysis. The RSM‐ROMS simulation shows a realistic alignment of the simulated rainfall along the orographic features of the domain. Furthermore, the RSM‐ROMS simulates the observed feature of convection over continental SASM region being more vigorous with dominance of mixed warm and cold phase hydrometeors in contrast to the dominance of the warm rain process in the neighboring tropical oceans. Similarly, the upper ocean features of contrasting mixed layer and thermocline depths between the northern and equatorial Indian Ocean are also simulated in the RSM‐ROMS. Intra‐Seasonal Oscillation (ISO) of the SASM at 10–20 and 20–70 days are also simulated in the RSM‐ROMS with many of its features verifying with observations. For example, the 20–70 days ISO are of higher amplitude and its meridional propagation is slower in Bay of Bengal compared to that over Arabian Sea. Additionally, RSM‐ROMS shows 12.3 Monsoon Low Pressure Systems (LPSs) per season that is comparable to 14.6 per season from observations. Furthermore, the observed intraseasonal contrasts of LPS between the wet and dry spells of ISO is also reproduced in the RSM‐ROMS.

Convective heat transport features of Darcy Casson fluid flow in a vertical channel: a Lie group approach

This work is devoted for the flow analysis and to explore the characteristics of thermal energy transport in non-Newtonian Casson fluid flow in a channel. The flow between the two walls is controlled by constantly slipping between them (fixed on a cold plate or a suction wall). The flow of Casson fluid is explored under the effects of MHD and mixed convection. The impacts of Joule heating and viscous dissipation are incorporated to investigate the thermal transport in the flow. Beside this, the heat transport behavior is properly examined by taking heat source/sink effects into account. The partial differential equations (PDEs) scheme is resolved with the Lie group method. After applying the Lie group theory, we have a system of ordinary differential equations (ODEs) numerically processed. The effects of physical constraints are analyzed with ND-Solve technique in MATHEMATICA and illustrated graphically with reasonable physical arguments. It is detected that because of escalation in the Eckert number the thermal transport in the flow significantly raised. While the flow velocity retarded in case of higher Hartmann number.

Evaluation of non-Newtonian model to accurately predict high Rayleigh number natural convection characteristics using PIV experiment and CFD simulation

Non-Newtonian fluids exhibit variable viscosity particularly at relatively high Rayleigh numbers (Ra), resulting in the occurrence of a complex natural convection phenomenon. In this study, the flow and heat-transfer performances inside a square channel filled with carboxy methyl cellulose, which exhibits the shear-thinning behavior typical of non-Newtonian fluids, were investigated. A comparative study was conducted to develop a viscosity model that can accurately describe the thermal and flow performances. To achieve this objective, three different viscosity models were considered: Power-law, Cross, and Carreau models. A time-constant dependency study was conducted to determine the optimum time step since the numerical solution was highly sensitive to the selected time constant in the Carreau and Cross models. The heat-transfer performances were evaluated by analyzing the mean Nusselt number for the hot wall, whereas the flow performances were evaluated by analyzing the flow patterns obtained by numerical and experimental analyses using the nonintrusive particle image velocimetry technique (Ra = 3.20 × 105, 3.09 × 106, and 2.21 × 107). The mean Nusselt numbers obtained by numerical analysis using the Carreau model were approximately 1.76%, 1.23%, and 0.45% higher than those obtained experimentally. Therefore, the predictions afforded by the Carreau model were in excellent agreement with those obtained experimentally. The findings of the present experimental study will provide benchmarking data for future simulations involving shear thinning or pseudoplastic non-Newtonian fluid media.

Seismic Behavior of Sloped Bottom Tank with Internal Object

The sloped bottom tank generates higher sloshing-induced base shear with less liquid mass compared to rectangular tanks. Due to the improved sloshing characteristics, sloped bottom TLD achieves better performance than its conventional flat-bottom counterpart. These improvements in sloshing characteristics are due to the modified tank configuration, which reduces the impulsive liquid mass and results in higher convective participation of liquid mass during sloshing. To further increase the convective characteristics, a sloped bottom tank with internal object is proposed. A velocity potential-oriented finite element model has been adopted for the numerical analysis where a combination of three-node triangular and four-node quadrilateral finite elements is used to discretize the liquid domain. Seismic characteristics of liquid sloshing inside a ground-supported sloped bottom tank with internal object are investigated under six different seismic motions categorized as low-, intermediate-, and high-frequency contents. Also, the influence of the internal object on slosh dynamics is investigated suitably for different heights of the object under all earthquakes considered. The dynamic impulsive and convective components of base shear force and hydrodynamic pressure are quantified successfully. The developed numerical model in this study can be utilized in tuning and designing structures coupled with sloped-bottom TLD.

Characteristics of Environmental Parameters of Compound and Single Type Severe Convection in Hunan

Based on the multi-source observation data and the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data in Hunan from 2002 to 2021, this study statistically analyzes the climatic characteristics of compound severe convection. The distribution characteristics and prediction thresholds of environmental parameters of compound severe convective weather, thermal hail, thunderstorm gale and short-term heavy precipitation events in Hunan, are compared and analyzed. The results show that: (1) The primary type of compound severe convection is a thunderstorm gale that accompanies short-term heavy precipitation. The compound severe convection mainly occurs in spring and summer, with the most common occurrence in July. There are seasonal differences in the types of compound severe convection. The primary type in spring is a thunderstorm gale with hail and hail with short-term heavy precipitation. The primary type in summer is a thunderstorm gale with short-term heavy precipitation. The probability of compound severe convection is the highest in southeastern Hunan, and the lowest in southwestern Hunan. (2) The values of the critical physical parameters required for the occurrence of thermal hail, such as the thermal instability stratification, CAPE and 0–6 km vertical wind shear, are the highest, followed by compound severe convection. Compound severe convection also requires high water vapor, which is only inferior to short-term heavy precipitation. (3) The critical physical parameters also differ in spring and summer. For the temperature difference between 850 and 500 hPa, the seasonal difference is not apparent, indicating that all types of severe convective weather need strong convective instability. CAPE is generally higher in summer than in spring, while the surface-specific humidity and 0–6 km vertical wind shear are higher in summer than in spring.

Experimental study of condensation characteristics and operation strategies of induction radiant air-conditioning system

To study the operation and condensation characteristics of an induction radiant air-conditioning system as a novel system that combines induction ventilation and radiant air conditioning, the characteristics of convection and condensation of an indoor terminal device radiant induction unit were studied. The mass transfer coefficient, condensation temperature, and condensation rate were analyzed experimentally. The time required to achieve a steady state indoor thermal environment was collected. The results indicated that the primary airflow rate and temperature mainly affected the mass transfer coefficient, condensation temperature, and condensation rate. When the indoor thermal environment reached a steady state, the heat transfer performance of the radiant induction unit was mainly affected by the primary air temperature. When condensation occurred, the primary airflow rate had a greater influence on the condensation rate. The start-up and response performances of the system were better than those of a traditional radiant air-conditioning system. In the condensation condition, reasonable control strategies maintain the primary air temperature and adjust the primary air flow rate, which can ensure sufficient heat transfer and stabilize the indoor thermal environment faster.

Vertically Resolved Convective–Stratiform Echo-Type Identification and Convectivity Retrieval for Vertically Pointing Radars

Abstract Using data from the airborne HIAPER Cloud Radar (HCR), a partitioning algorithm (ECCO-V) that provides vertically resolved convectivity and convective versus stratiform radar-echo classification is developed for vertically pointing radars. The algorithm is based on the calculation of reflectivity and radial velocity texture fields that measure the horizontal homogeneity of cloud and precipitation features. The texture fields are translated into convectivity, a numerical measure of the convective or stratiform nature of each data point. The convective–stratiform classification is obtained by thresholding the convectivity field. Subcategories of low, mid-, and high stratiform, shallow, mid-, deep, and elevated convective, and mixed echoes are introduced, which are based on the melting-layer and divergence-level altitudes. As the algorithm provides vertically resolved classifications, it is capable of identifying different types of vertically layered echoes, and convective features that are embedded in stratiform cloud layers. Its robustness was tested on data from four HCR field campaigns that took place in different meteorological and climatological regimes. The algorithm was adapted for use in spaceborne and ground-based radars, proving its versatility, as it is adaptable not only to different radar types and wavelengths, but also different research applications.

Three-Dimensional Convective–Stratiform Echo-Type Classification and Convectivity Retrieval from Radar Reflectivity

Abstract The Echo Classification from COnvectivity (ECCO) algorithm identifies convective and stratiform types of radar echo in three dimensions. It is based on the calculation of reflectivity texture—a combination of the intensity and the heterogeneity of the radar echoes on each horizontal plane in a 3D Cartesian volume. Reflectivity texture is translated into convectivity, which is designed to be a quantitative measure of the convective nature of each 3D radar grid point. It ranges from 0 (100% stratiform) to 1 (100% convective). By thresholding convectivity, a more traditional qualitative categorization is obtained, which classifies radar echoes as convective, mixed, or stratiform. In contrast to previous algorithms, these echo-type classifications are provided on the full 3D grid of the reflectivity field. The vertically resolved classifications, in combination with temperature data, allow for subclassifications into shallow, mid-, deep, and elevated convective features, and low, mid-, and high stratiform regions—again in three dimensions. The algorithm was validated using datasets collected over the U.S. Great Plains during the PECAN field campaign. An analysis of lightning counts shows ∼90% of lightning occurring in regions classified as convective by ECCO. A statistical comparison of ECCO echo types with the well-established GPM radar precipitation-type categories show 84% (88%) of GPM stratiform (convective) echo being classified as stratiform (convective) or mixed by ECCO. ECCO was applied to radar grids for the continental United States, the United Arab Emirates, Australia, and Europe, illustrating its robustness and adaptability to different radar grid characteristics and climatic regions.

Topographic response to ocean heat flux anomaly on the icy moons of Jupiter and Saturn

Recent studies of ocean dynamics suggest that the long-wavelength topography of some icy moons may reflect the phase transitions (melting/freezing) at the interface between the ice shell and the water ocean. Despite the obvious importance of phase changes in the evolution of icy moons, very little is known about how these processes influence their shape, gravity and near-surface stress. Here we address this issue by performing a series of numerical experiments in which we explore the thermo-mechanical response of an ice layer to heat flux variations imposed at the bottom (phase) boundary. We assume that the heat flux from the ocean consists of two components: the heat flux originating in the deep ocean and associated with the global ocean circulation, and the heat flux due to the flow of water generated by variations in the melting temperature along the deformed ice–water interface. The effect of salinity on the heat flux from the ocean is neglected. We demonstrate that the mass exchange between the ocean and the ice layer is a natural consequence of the ice–water phase transition and it occurs in both convection and conduction modes, regardless of whether the system is in equilibrium or not. The magnitude of the heat-flux induced topography strongly depends on the viscosity of ice and the flow of water controlled by the melting temperature. When heat transfer in the ice shell occurs by convection, the surface topography is dominated by small-scale convective features varying in time and its large-scale component does not exceed 10 m. When the viscosity of the ice shell is high (≳1016 Pas) and the heat is transferred by conduction, the topography is negatively correlated with the heat flux from the ocean and its amplitude increases with increasing viscosity. Topographic amplitudes comparable to those observed on Titan, Enceladus and Dione are obtained only if the water flow associated with lateral variations in the melting temperature is neglected. This suggests that this flow may be too weak to reduce the variations in ice shell thickness and the motion of water along the phase boundary is more likely to be controlled by other factors, such as variations in salinity and the presence of non-ice material. In addition, we show that the standard formulation of Airy isostasy can lead to an error of 5%–15% in determining the variations in ice thickness and we propose a new formulation that takes into account the effect of thermal expansion.

Contrasting Mesoscale Convective System Features of Two Successive Warm-Sector Rainfall Episodes in Southeastern China: A Satellite Perspective

Based on Himawari-8 satellite observations, the mesoscale convective system (MCS) behaviors of two successive but distinct warm-sector rainfall episodes (EP1 and EP2) on 6–7 May 2018 over southeastern China were compared, with the latter episode being a record-breaking rainfall event. Results showed that MCSs played a dominant role in EP2, but not in EP1, by contributing over 80% of the extreme rainfall total and all the 10-min rainfalls over 20 mm. MCS occurrences were more frequent in EP2 than EP1, especially in the coastal rainfall hotspots, along with more frequent merging processes. Overall, the MCS samples in EP2 were larger in size, more intense, and moved slower and more in parallel to their orientation, which facilitated local rainfall accumulation. Two new indices are proposed—the overlap index (OLI) and merging potential index (MPI)—to evaluate two MCS processes vital for rainfall production: the repeated passage of an individual MCS over given areas and the merging between MCSs, respectively. Both OLI and MPI in EP2 were significantly larger than in EP1, which tended to produce larger maximum rainfall amount and stronger 10-min rain rates in the following hour. These results demonstrate the potential value of satellite-based MCS information for heavy rainfall nowcasting, which is particularly significant for warm-sector rainfall with its limited predictability.

Exacerbation of Indian Summer Monsoon Breaks by the Indirect Effect of Regional Dust Aerosols

AbstractEvaluation of century‐long simulations of the Community Earth System Model (CESM) reveals model fidelity in capturing characteristics of aerosols, clouds, convection, rainfall and circulation over India associated with the active/break phase with wetter/drier than average rainfall within the summer monsoon season. During the breaks, aerosols build up over central India due to desert dust transported from the west by anomalous circulation, the trapping of dust emissions from the Thar‐desert and the increased aerosol lifetime in dry conditions. Break spells exhibit reduced cloud effective radius and enhanced lower atmospheric warming over central India as potential evidence for the indirect effect induced by dust aerosols. Consistently, break spells intensify in CESM simulation with increased loading of dust aerosols. The indirect effect of dust aerosols in warming the atmosphere and exacerbating the severity of breaks is conspicuous in simulations forced with the indirect effect of aerosols alone, both for present‐day and pre‐industrial periods.