Solar Convection Research Articles

Origin of the Near-Surface Rotational Shear Layer of the Sun

Helioseismology has revealed an increase in the rotation rate with depth in a thin (∼30 Mm)near-surface layer. The normalized rotational shear in this layer does not depend on latitude. This rotationalstate is shown to be a consequence of the short characteristic time of near-surface convection comparedto the rotation period and radial anisotropy of convective turbulence. Analytical calculations within meanfieldhydrodynamics reproduce the observed normalized rotational shear and are consistent with numericalexperiments on radiative hydrodynamics of solar convection. The near-surface shear layer is the source ofglobal meridional flow important for the solar dynamo.

Solar photospheric spectrum microvariability

Context. Extreme precision radial-velocity spectrometers enable extreme precision in stellar spectroscopy. Searches for low-mass exoplanets around solar-type stars are limited by various types of physical variability in stellar spectra, such as the short-term jittering of apparent radial velocities on levels of ∼2 m s−1. Aims. To understand the physical origins of radial-velocity jittering, the solar spectrum is assembled, as far as possible, from basic principles. Solar surface convection is modeled with time-dependent 3D hydrodynamics, followed by the computation of high-resolution spectra during numerous instances of the simulation sequence. The behavior of different classes of photospheric spectral lines is monitored throughout the simulations to identify commonalities or differences between different classes of lines: weak or strong, neutral or ionized, high or low excitation, atomic or molecular. Methods. Synthetic spectra were examined. With a wavelength sampling λ/Δλ ∼ 1 000 000, the changing shapes and wavelength shifts of unblended and representative Fe I and Fe II lines were followed during the simulation sequences. The radial-velocity jittering over the small simulation area typically amounts to ±150 m s−1, scaling to ∼2 m s−1 for the full solar disk. Flickering within the G-band region and in photometric indices of the Strömgren uvby system were also measured, and synthetic G-band spectra from magnetic regions are discussed. Results. Most photospheric lines vary in phase, but with different amplitudes among different classes of lines. Amplitudes of radial-velocity excursions are greater for stronger and for ionized lines, decreasing at longer wavelengths. Matching precisely measured radial velocities to such characteristic patterns should enable us to remove a significant component of the stellar noise originating in granulation. Conclusions. The granulation-induced amplitudes in full-disk sunlight amount to ∼2 m s−1; the differences between various line groups are an order of magnitude less. To mitigate this jittering, a matched filter must recognize dissimilar lineshifts among classes of diverse spectral lines with a precision of ∼10 cm s−1 for each line group. To verify the modeling toward the filter, predictions of center-to-limb dependences of jittering amplitudes for different classes of lines are presented, testable with spatially resolving solar telescopes connected to existing radial-velocity instruments.

Differential Rotation in Convecting Spherical Shells with Non-Uniform Viscosity and Entropy Diffusivity

Contemporary three-dimensional physics-based simulations of the solar convection zone disagree with observations. They feature differential rotation substantially different from the true rotation inferred by solar helioseismology and exhibit a conveyor belt of convective “Busse” columns not found in observations. To help unravel this so-called “convection conundrum”, we use a three-dimensional pseudospectral simulation code to investigate how radially non-uniform viscosity and entropy diffusivity affect differential rotation and convective flow patterns in density-stratified rotating spherical fluid shells. We find that radial non-uniformity in fluid properties enhances polar convection, which, in turn, induces non-negligible lateral entropy gradients that lead to large deviations from differential rotation geostrophy due to thermal wind balance. We report simulations wherein this mechanism maintains differential rotation patterns very similar to the true solar profile outside the tangent cylinder, although discrepancies remain at high latitudes. This is significant because differential rotation plays a key role in sustaining solar-like cyclic dipolar dynamos.

The energy, emissions, and drying kinetics of three-stage solar, microwave and desiccant absorption drying of potato slices

In this study, a three-stage solar dryer using solar convection, convection-microwave, and solar desiccant absorption-assisted convection drying was developed and evaluated. This process was designed to reduce energy consumption and Carbon emissions while retaining the color properties of the dried food product. Potato slices were dried in the first stage using solar convection and the process was assisted by Microwave radiation in the second stage to increase the drying rate. The final stage combined solar desiccant absorption with solar convection to maintain the drying rate at a lower temperature, thereby reducing energy use and minimizing thermal damage to the biomass. Compared to Microwave-Convection drying, the three-stage drying process was found to consume 46 % lower specific energy and reduced Carbon emissions by 53 %. The Vitamin – C retention and color retention were found to improve by 27 % and 8.55 % respectively. The proposed design is promising and can be used to improve the overall performance of solar thermal drying methods in terms of temperature control, energy efficiency, sustainability, and product quality. It also has the potential to be deployed in rural areas with minimal dependence on grid energy.

Turbulent Processes and Mean-Field Dynamo

Mean-field dynamo theory has important applications in solar physics and galactic magnetism. We discuss some of the many turbulence effects relevant to the generation of large-scale magnetic fields in the solar convection zone. The mean-field description is then used to illustrate the physics of the alpha effect, turbulent pumping, turbulent magnetic diffusivity, and other effects on a modern solar dynamo model. We also discuss how turbulence transport coefficients are derived from local simulations of convection and then used in mean-field models.

Refined Analysis of the Transient Temperature Effect during the Closing Process of a Cross-Sea Bridge

In order to study the transient temperature effect during the construction of a cross-sea bridge off the coast, based on the Hong Kong-Zhuhai-Macao Bridge-Pipe Bridge Crossing Cliff 13-1 Gas Field, a refined analysis was conducted and the prediction of transient temperature gradient and structural response was carried out under the conditions of strong solar radiation and atmospheric convection using the method of combining theoretical research and numerical simulation. Firstly, the partial differential equation of uniform heat flux density on the outer surface of the main girder under the action of solar radiation and atmospheric convection was established. The equation was realized by calculating the solar radiation intensity and the comprehensive heat transfer coefficient, as well as fitting the atmospheric temperature on the outer surface of the main girder, and the equivalent comprehensive temperature at any time on the main girder was obtained. Secondly, a numerical analysis model of the heat conduction of the main girder section was established, and the equivalent comprehensive temperature was input into the numerical model as the temperature field boundary to solve the transient temperature gradient of the section, and the result was verified in comparison with the measured data. Finally, the transient temperature gradient was applied to the girder, and the temperature effect of the main girder during the closing process was also calculated. Construction control measures were also discussed. The research results show that the predicted value of the transient temperature gradient is consistent with the measured value (the maximum deviation is less than 2 °C), and the predicted value is slightly larger than the measured value, which makes the structure safer. During the closing process, the temperature gradient of the main girder has obvious non-linear characteristics: the temperature gradient is relatively high within 0.4 m of the top surface of the roof while tending to zero outside 0.4 m. The best closing time for the main girder is from 21:00 in the evening of the closing day to 6:00 a.m. the next day. For the small angles at both ends of the closure segment during the best closing time, temporary adjustment jacks and temporary counterweights can be adopted to eliminate the small angles at both ends of the closure segment in order to facilitate the welding construction and meet the smoothness requirements of bridge alignment.

Arbitrarily high-order accurate simulations of compressible rotationally constrained convection using a transfinite mapping on cubed-sphere grids

We present two major improvements over the Compressible High-ORder Unstructured Spectral difference (CHORUS) code published in Wang et al., “A compressible high-order unstructured spectral difference code for stratified convection in rotating spherical shells,” J. Comput. Phys. 290, 90–111 (2015). The new code is named CHORUS++ in this paper. Subsequently, we perform a series of efficient simulations for rotationally constrained convection (RCC) in spherical shells. The first improvement lies in the integration of the high-order spectral difference method with a boundary-conforming transfinite mapping on cubed-sphere grids, thus ensuring exact geometric representations of spherical surfaces on arbitrary sparse grids. The second improvement is on the adoption of higher-order elements (sixth-order) in CHORUS++ vs third-order elements for the original CHORUS code. CHORUS++ enables high-fidelity RCC simulations using sixth-order elements on very coarse grids. To test the accuracy and efficiency of using elements of different orders, CHORUS++ is applied to a laminar solar benchmark, which is characterized by columnar banana-shaped convective cells. By fixing the total number of solution degrees of freedom, the computational cost per time step remains unchanged. Nevertheless, using higher-order elements in CHORUS++ resolves components of the radial energy flux much better than using third-order elements. To obtain converged predictions, using sixth-order elements is 8.7 times faster than using third-order elements. This significant speedup allows global-scale fully compressible RCC simulations to reach equilibration of the energy fluxes on a small cluster of just 40 cores. In contrast, CHORUS simulations were performed by Wang et al. on supercomputers using approximately 10 000 cores. Using sixth-order elements in CHORUS++, we further carry out global-scale solar convection simulations with decreased rotational velocities. Interconnected networks of downflow lanes emerge and surround broader and weaker regions of upflow fields. A strong inward kinetic energy flux compensated by an enhanced outward enthalpy flux appears. These observations are all consistent with those published in the literature. Furthermore, CHORUS++ can be extended to magnetohydrodynamic simulations with potential applications to the hydromagnetic dynamo processes in the interiors of stars and planets.

The Puzzling Structure of Solar Convection: Window into the Dynamo

The Puzzling Structure of Solar Convection: Window into the Dynamo

Rotational radial shear in the low solar photosphere

Context. Radial differential rotation is an important physical ingredient in stellar dynamo theory. In the case of the Sun, heliosismology techniques have revealed the existence of a near-surface shear layer covering 15–20% of the upper convection zone. It was recently shown that the rotation velocity gradient is not uniform in this layer and that it displays a steep increase in a shallow layer near the surface. Aims. We report the detection of a rotation velocity depth-gradient in the low photosphere that is not accessible to heliosismology techniques. Methods. We applied differential interferometric methods to spectroscopic data obtained with the solar telescope THEMIS, which is equipped with an efficient adaptative optics system. The detection was based on the measurement of a systematic east-west shift between images of the solar granulation at different depths in the FeI 630.15 nm at the center of the solar disk. The same technique was applied to obtain the depth-difference between the images from their perspective shift when they are observed away from the disk center. Both THEMIS and HINODE/SOT data were used for the height-difference measurement, giving similar results. Results. At the center of the solar disk, we measured a systematic retrograde shift of the photospheric granular structures on the east-west axis and with no shift in the north-south direction. The retrograde shift increases linearly with height. We interpret these findings as a signature of a steep decrease in the angular velocity in the low photosphere. Conclusions. The rotational radial shear in the low solar photosphere is likely related to the dynamics of the subsurface shear layer. Its measurement yields a valuable constraint on the numerical simulations of the solar upper convection zone.

Radiation burnthrough measurements to infer opacity at conditions close to the solar radiative zone–convective zone boundary

Recent measurements at the Sandia National Laboratory of the x-ray transmission of iron plasma have inferred opacities much higher than predicted by theory, which casts doubt on modeling of iron x-ray radiative opacity at conditions close to the solar convective zone-radiative zone boundary. An increased radiative opacity of the solar mixture, in particular iron, is a possible explanation for the disagreement in the position of the solar convection zone-radiative zone boundary as measured by helioseismology and predicted by modeling using the most recent photosphere analysis of the elemental composition. Here, we present data from radiation burnthrough experiments, which do not support a large increase in the opacity of iron at conditions close to the base of the solar convection zone and provide a constraint on the possible values of both the mean opacity and the opacity in the x-ray range of the Sandia experiments. The data agree with opacity values from current state-of-the-art opacity modeling using the CASSANDRA opacity code.

Rainy downdrafts in abyssal atmospheres

Context.Results from Juno’s Microwave Radiometer (MWR) indicate nonuniform mixing of ammonia vapor in Jupiter’s atmosphere down to tens of bars, far beneath the cloud level. Helioseismic observations suggest solar convection may require narrow, concentrated downdrafts called entropy rain to accommodate the Sun’s luminosity. Both observations suggest some mechanism of nonlocal convec-tive transport.Aims.We seek to predict the depth that a concentrated density anomaly can reach before efficiently mixing with its environment in bottomless atmospheres.Methods.We modified classic self-similar analytical models of entraining thermals to account for the compressibility of an abyssal atmosphere. We compared these models to the output of high-resolution three-dimensional fluid dynamical simulations to more accurately model the chaotic influence of turbulence.Results.We find that localized density anomalies propagate down to ~3−8 times their initial size without substantially mixing with their environment. Our analytic model accurately predicts the initial flow, but the self-similarity assumption breaks down after the flow becomes unstable at a characteristic penetration depth.Conclusions.In the context of Jupiter, our findings suggest that precipitation concentrated into localized downdrafts of size ~20 km can coherently penetrate to on the order of a hundred kilometers (tens of bars) beneath its initial vaporization level without mixing with its environment. This finding is consistent with expected convective storm length scales and Juno MWR measurements of ammonia depletion. In the context of the Sun, we find that turbulent downdrafts in abyssal atmospheres cannot maintain their coherence through the Sun’s convective layer, a potential challenge for the entropy rain hypothesis.

A UV-Reflective Organic-Inorganic Tandem Structure for Efficient and Durable Daytime Radiative Cooling in Harsh Climates.

Radiative cooling shows great promise in eco-friendly space cooling due to its zero-energy consumption. For subambient cooling in hot humid subtropical/tropical climates, achieving ultrahigh solar reflectance (≥96%), durable ultraviolet (UV) resistance, and surface superhydrophobicity simultaneously is critical, which, however, is challenging for most state-of-the-art scalable polymer-based coolers. Here an organic-inorganic tandem structure is reported to address this challenge, which comprises a bottom high-refractive-index polyethersulfone (PES) cooling layer with bimodal honeycomb pores, an alumina (Al2 O3 ) nanoparticle UV reflecting layer with superhydrophobicity, and a middle UV absorption layer of titanium dioxide (TiO2 ) nanoparticles, thus providing thorough protection from UV and self-cleaning capability together with outstanding cooling performance. The PES-TiO2 -Al2 O3 cooler demonstrates a record-high solar reflectance of over 0.97 and high mid-infrared emissivity of 0.92, which can maintain their optical properties intact even after equivalent 280-day UV exposure despite the UV-sensitivity of PES. This cooler achieves a subambient cooling temperature up to 3 °C at summer noontime and 5 °C at autumn noontime without solar shading or convection cover in a subtropical coastal city, Hong Kong. This tandem structure can be extended to other polymer-based designs, offering a UV-resist but reliable radiative cooling solution in hot humid climates.

Convective blueshift strengths for 242 evolved stars

Context. With the advent of extreme precision radial velocity (RV) surveys, seeking to detect planets at RV semi-amplitudes of 10 cm s−1, intrinsic stellar variability is the biggest challenge to detecting small exoplanets. To overcome the challenge we must first thoroughly understand all facets of stellar variability. Among those, convective blueshift caused by stellar granulation and its suppression through magnetic activity plays a significant role in covering planetary signals in stellar jitter. Aims. Previously we found that for main sequence stars, convective blueshift as an observational proxy for the strength of convection near the stellar surface strongly depends on effective temperature. In this work we investigate 242 post main sequence stars, covering the subgiant, red giant, and asymptotic giant phases and empirically determine the changes in convective blueshift with advancing stellar evolution. Methods. We used the third signature scaling approach to fit a solar model for the convective blueshift to absorption-line shift measurements from a sample of coadded HARPS spectra, ranging in temperature from 3750 K to 6150 K. We compare the results to main sequence stars of comparable temperatures but with a higher surface gravity. Results. We show that convective blueshift becomes significantly stronger for evolved stars compared to main sequence stars of a similar temperature. The difference increases as the star becomes more evolved, reaching a 5× increase below 4300 K for the most evolved stars. The large number of stars in the sample, for the first time, allowed for us to empirically show that convective blueshift remains almost constant among the entire evolved star sample at roughly solar convection strength with a slight increase from the red giant phase onward. We discover that the convective blueshift shows a local minimum for subgiant stars, presenting a sweet spot for exoplanet searches around higher mass stars, by taking advantage of their spin-down during the subgiant transition.

Dynamic performance of CRTS III ballastless track structure under the train load and temperature

Due to the thermal deformation of the track structure under natural temperature, it inevitably changes the initial condition of the track, and causes significant influence on the dynamic performance of the track under the moving vehicle. This work aims to reveal the interfacial damage and dynamic behaviors of the track structure subjected to the temperature and a moving vehicle. For this purpose, a thermomechanical coupling analysis method of CRTS III is developed by loading the temperature and train load. Among them, a three-dimensional vehicle-track interaction model is established to obtain the rail-supporting force. Besides, a transient heat transfer model of CRTS III is developed by introducing the complex thermal boundary where the solar radiation and heat convection are taken into account, and thus the temperature field of CRTS III under the natural environment is obtained in a space–time scale. The dynamic behaviors of the track and interfacial damage under different temperatures, interface strength and speeds of vehicle are investigated by the proposed methodology. The results indicate that the temperature significantly influences the acceleration and displacement of the track slab, especially in the frequency range of 25 Hz–75 Hz and the response amplitudes also increase 2–6 times. The temperature is the main factor inducing interface damage instead of the train load, therefore, we should pay more attention to the interface debonding in summer.

Analysis of heat transfer performance for ternary nanofluid flow in radiated channel under different physical parameters using GFEM

BackgroundAdvanced nanofluids also termed as ternary nanofluids convinced the engineers and scientists due to unique molecular structure and enrich heat transfer capability. These potentially contributes in aerodynamics, biomedical engineering, aerospace sciences and electronic devices. In many industrial purposes, these can be used as coolant more specifically in electronic and chemical industries. MethodsThis study emphasized on the development of an efficient ternary nanofluid model between parallel plates channel. The model formulation is successfully completed via ternary nanofluid correlations and also exercised similarity equations for the possible domain. Moreover, model became more fascinating due to induction of thermal radiations and viscous dissipation. To investigate the heat transfer performance of ternary nanofluid the model treated via an efficient scheme based on residuals and linearly independent set of weight functions and is known as Galerkin Finite Element Method (GFEM). Significant findingsIt is examined that the ternary nanofluid [(Al2O3-CuO-Fe3O4)/EO]mbnf is a suitable heat transport fluid than common binary nanofluid [(Al2O3-CuO)/EO]bnf nanofluids. further, induction of solar thermal radiations and convection through the plate are vital sources to upshoot the internal heat transmission of the [(Al2O3-CuO-Fe3O4)/EO]mbnf and it would allow the researchers and engineers for large scale applications. The feasible parametric ranges that pride considerable heat transfer are Bi = 0.1, 0.3, 0.5, 0.7, 0.9, 1.1 and Eckert number are Ec = 0.1, 0.3, 0.5, 0.7, 0.9, 1.1 while keeping the weight concentration of nanoparticles up to 6.0%.

The IAG spectral atlas of the spatially resolved Sun: Centre-to-limb observations

Context. Solar surface magneto-convection appears as granulation pattern that impacts spectral lines in terms of both shape and wavelength. Such induced effects also tend to vary over the observed solar disc because of the changing observation angle and, thus, the changing observation height as well. Centre-to-limb observations of the resolved Sun offer an insight into the variable spectral behaviour across different heliocentric observing positions, providing crucial information about limb darkening, convective velocities, and line profile variability relevant to radial velocity (RV) calculations. Thus, RV measurements and exoplanet transit spectroscopy depend on precise reference templates. Aims. We want to provide a spectroscopic centre-to-limb solar atlas at high spectral resolution and high-frequency accuracy. The atlas shall help improve the understanding of the solar atmosphere and convection processes. Methods. We performed high-resolution observations of the resolved quiet Sun with a Fourier transform spectrograph at the Institut für Astrophysik und Geophysik in Göttingen. Our dataset contains a wavelength range from 4200 Å to 8000 Å. We obtained 165 spectra in total, with a spectral resolution of Δν = 0.024 cm−1, corresponding to a resolving power R of 700 000 at ∼6000 Å. Results. We present a centre-to-limb solar atlas containing 14 heliocentric positions. To check for consistency, we investigated the Fe I 6175 Å absorption line and compared our line profiles with previous centre-to-limb observations and also with simulations. The line profile and also the bisector profiles are generally consistent with previous observations, but we have identified differences to model line profiles, especially close to the solar limb.

Kelvin-Helmholtz instability-driven magnetopause dynamics as turbulent pathway for the solar wind-magnetosphere coupling and the flank-central plasma sheet communication

About sixty years ago it was proposed that the solar wind entry and changes in magnetospheric magnetic topology via dayside magnetic reconnection initiate the magnetospheric convection over the poles. On the other hand, the quasi-viscous interaction via Kelvin-Helmholtz waves/vortices was proposed to lead to the solar wind entry and magnetospheric convection. Since then, the two processes have been thought to regulate the solar wind and earth’s magnetosphere coupling. However, their relative efficiency and importance leave a lot of room for enhanced and quantitative understanding. Kelvin-Helmholtz instability operating on the entire surface of the magnetopause also provide a place for not only solar wind transport but also energetic particle transport or escape, thus, being an efficient channel for two-way transport. Recent observations and simulations indicate that the flanks of the earth’s magnetosphere can act as a pathway to/from the central magnetotail current sheet. Possible causality between the flank-side dynamics and magnetotail current sheet stability has never been explored. In this paper we discuss our perspective on these unsolved areas of Heliophysics research with brief suggestions of observational and numerical approaches.

A novel aqueous scalable eco-friendly paint for passive daytime radiative cooling in sub-tropical climates

Passive daytime radiative cooling (PDRC) is an emerging technology that dissipates heat from terrestrial objects to the cold universe directly via the atmospheric transparency window. Along with the advancement of PDRC materials, fabrication methods by precision lithography or phase change chemistry are no longer a preferred option due to the concomitant hazardous organic solvents. Instead, it is desirable to develop radiative coolers by aqueous processing-based and cost-effective methods so as to promote their mass production and applications. Herein, we report a new scalable polymer-based aqueous paint without volatile organic compounds (VOCs) emission. By using the simple mechanical agitation-based synthetic method with mixing polymer emulsion as the matrix and glass beads as the functional additive, the cooling paint exhibits an average infrared emissivity of 92% and a solar reflectivity of 94%. A detailed field experiment was conducted in sub-tropical climates to verify the practical cooling performance of the developed cooling paint, and the experimental results showed that the achievable sub-ambient cooling temperature was up to 6 °C under high humidity conditions without any solar shading or convection cover. Meanwhile, in-depth evaluation on the cooling power of the developed cooling paints in a variety of cities was conducted, which shows its wide application potential in building roof across varying climate regions.

Solar Radiation and Thermal Convection of Hybrid Nanofluids for the Optimization of Solar Collector

This study aims to show the role of the stagnation point flow in solar optimization in the presence of a Riga plate. This requirement is conceivable in the case of solar energy management with a suitable solar collector covering and visual thermal optimization. Solar energy radiation and thermal convection of glycol (C3H8O2)-based aluminum oxide (Al2O3) and copper (Cu) nanoparticles were used for a solar collector, and were studied in terms of the stagnation point flow theoretically. Stagnation refers to the state of a solar thermal system in which the flux varies in the collection loop to control the extra heating. The CVFEM code was used to analyze the flow in the case of represented stagnation using the FEA-Tools multiple physics software that manages partial derivative equations (PDEs). The streamlined patterns and energy contours for different cases were studied in detail. The transformation equations were treated with the numerical method (RK-4 technique) and showed strong agreement of the physical results corresponding to the initial conditions and boundaries. The results showed that hybrid nanofluids have the advanced capability to enhance the thermal performance of the base solvent and provide uniform distribution to the solar panel. The solar optimization and uniform thermal expansion results are displayed graphically.

Experimental investigation of mixed mode ultraviolet tent house solar dryer under natural convection regime

A mixed mode natural convection ultraviolet (UV) tent house solar dryer is designed and installed at University Teaching Department, Chhattisgarh Swami Vivekanand Technical University, Bhilai, Chhattisgarh (21°27′N, 81°43′E) India for drying potato slices. This solar dryer is equipped with a solar flat plate collector (area 1.12 m2), covered with 5.0 mm thick glass and consists of two trays of the same size (0.57 m X 1.11 m) in a drying chamber on which equal quantities of potato slices were placed. The local atmospheric conditions including relative humidity, atmospheric temperatures, solar intensity, and wind velocity have been recorded for analyzing various parameters. The solar intensity and atmospheric temperature ranges from 134 to 993 W/m2 and 36.2 °C to 44.9 °C respectively. The initial moisture content value of 85.25% reaches 14.75% for 2.5 mm thick potato slices and for 5.0 mm thickness, the initial & final moisture content values are 85.10% & 14.90% respectively. The upper and lower tray temperature varies from 34.2 °C to 59.7 °C and 33.6 °C to 57.1 °C respectively. The open sun drying took 6 h longer than the solar natural convection drying. Moisture ratio for 2.5 mm thickness and 5.0 mm thickness lies 0.475–0.001 and 0.650–0.003 respectively. The maximum dryer efficiency is 26.62% and 21.61% for 2.5 mm and 5.0 mm thick potato slices respectively. All the drying kinetics is superior in the 2.5 mm thickness of the potato in process of drying using natural convection.