Negative Temperature Gradient Research Articles

Linear dynamics of a thick liquid layer subjected to an oblique temperature gradient

The present study aims to demonstrate the application of the oblique temperature gradient (OTG) to manipulate the buoyancy instabilities and resulting mixing. To accomplish this, we consider a model consisting of a liquid layer supported by a perfectly conducting bottom wall from below and the upper surface is exposed to ambient inert gas in a shallow container. The stability analysis employs the pseudospectral method and perturbation energy budget approach. The imposed OTG consists of a negative vertical temperature gradient (VTG), which leads to unstable density stratification, and a negative horizontal temperature gradient (HTG) component responsible for the Hadley circulation, which can be utilised to control instabilities. Without the HTG, a Rayleigh–Bénard mode of instability exists due to the imposed VTG termed as a VTG mode. The imposed HTG induces a linear VTG term and a quintic polynomial VTG term in the bottom wall-normal coordinate $y$ . The induced linear VTG term reinforces the imposed VTG, while the induced quintic polynomial VTG term opposes the imposed VTG. For the vanishing Biot number ( $Bi$ ), the induced quintic VTG term stabilises the VTG mode for the Prandtl number, $Pr=7$ . However, for $Pr=0.01$ , the Reynolds stresses associated with the Hadley circulation destabilise the VTG mode. For non-zero $Bi$ , new streamwise and spanwise instability modes arise for $Pr=7$ due to the induced linear VTG term. Physical arguments show that the unstable density stratification near the gas–liquid interface caused by the synergistic effect of the imposed VTG and the induced linear VTG term lead to the existence of the predicted new modes. The present study thus shows that the strength of the HTG can be utilised to control the instability modes and critical parameters, thereby demonstrating the utility of the OTG in manipulating the buoyancy instabilities.

Theoretical and finite element analysis of engineered cementitious composite (ECC) link slab in hollow slab beam bridge base on different load conditions

In order to reveal the feasibility of engineering cementitious composite (ECC) link slab applied to hollow slab beam bridge, the construction process of ECC link slab was simulated based on the birth-death element method and tracking element. Nonlinear analyses of ECC link slab under six load conditions were carried out based on Chinese bridge code. The theoretical formulas are derived and calculated for three of the unfavourable conditions. Finally, the effects of five support conditions on ECC link slab were analysed. The results show that the maximum tensile stresses of the ECC link slab under the overall cooling and negative temperature gradient are 3.569 MPa and 3.440 MPa, and the ECC material has entered plasticity. Theoretical calculations and finite element (linear) results are similar and conclude that temperature-induced axial deformation is the main cause of ECC link slab damage, especially the overall cooling and negative temperature gradient. At the same time different support conditions do not change this result, but rubber bearings can well improve the force behaviour of ECC link slab due to its good deformation coordination ability.

Temperature Distribution Characteristics and Action Pattern of Concrete Box Girder under Low-Temperature and Cold Wave Conditions

In regions with severe cold and high latitudes, concrete structures are susceptible to cracking and displacement due to uneven temperature stress, which directly impacts their normal utilization. Therefore, to investigate the temperature distribution characteristics of concrete box girders under the combined influence of low temperatures and cold waves, a temperature test was conducted on a model of concrete box girders in Xinjiang Province, China. Based on the measured data, the distribution pattern of the most unfavorable negative temperature differential observed in high-latitude regions was determined. Long-term numerical simulation and extreme value analysis were performed using historical meteorological data, revealing that the vertical negative temperature gradient in the concrete box girder structures follows a composite exponential distribution. The temperature differential at the top complies with Chinese code requirements, while at the bottom, it aligns more closely with British standard BS5400. Statistical analysis of historical meteorological data predicts that the 50-year temperature differential will result in a drop amplitude of 26.42 °C, which is 1.44 times higher than measured values obtained from experiments. The proposed negative temperature gradient pattern for concrete box girders presented in this study can encompass general design codes and provide guidance for designing concrete bridges in severe cold areas.

Thermal rectification in novel two-dimensional hybrid graphene/BCN sheets: A molecular dynamics simulation

The graphene-like monolayer of carbon, boron and nitrogen that maintains the native hexagonal atomic lattice (BCN), is a novel semiconductor with special thermal properties. Herein, with the aid of a non-equilibrium molecular dynamics approach (NEMD), we study phonon thermal rectification in a hybrid system of pure graphene and BCN (G-BCN) in various configurations under a series of positive and negative temperature gradients. We begin by investigating the relation of thermal rectification to sample’s mean temperature, T, and the imposed temperature difference, ΔT, between the two heat baths at its ends. We then move to explore the effect of varying strain levels of our sample on thermal rectification, followed by Kapitza resistance calculations at the G-BCN interface, which shed light on the interface effects on thermal rectification. Our simulation results reveal a BCN-configuration-dependent behavior of thermal rectification. Finally, the underlying mechanism leading to a preferred direction for phonons is studied using phonon density of states (DOS) on both sides of the G-BCN interface.

Research on the heat–humidity coupling transfer model of the CRTS Ⅱ type track slab and its characteristics

After operation for more than 10 years, CRTSⅡtype track slab structures have developed interlayer diseases in continuous extreme high-temperature environments, which are dominated by track slab-CA mortar layer cracking. To reveal the formation mechanism of track slab-CA mortar layer cracking under complicated operation conditions, a heat–humidity coupling transfer model, which is utilized to analyze track slab deformation, was developed. Furthermore, to enhance the precision of the model, we investigated the variation law that regulates relevant parameters of concrete materials with respect to temperature and humidity. Moreover, a testing apparatus was established to validate the accuracy of the transfer model under natural conditions. The analysis revealed that the maximum temperature error in the track slab was 3.33 K, and that the maximum error of relative humidity (RH) was 6.04 %. The distribution characteristics of temperature and humidity fields in the track slab during 10 consecutive rainless days under different seasonal climates in a hot-summer and cold-winter zone (Hangzhou) in China were calculated and analyzed using COMSOL Multiphysics® software. The results indicated that in the distribution of the summer temperature field, the maximum negative temperature gradient could attain -48.67 K/m, and that the maximum positive temperature gradient could attain 76.37 K/m. Moreover, RH values at 10 mm, 20 mm, 30 mm, and 40 mm decreased by 30.85 %, 15.51 %, 9.17 %, and 5.9 %, respectively. In a year, a higher track slab temperature, a greater temperature fluctuation range, and more apparent positive and negative temperature gradients were observed during summer, and the influencing depth of water also attained the maximum value during summer.

Numerical simulation of temperature gradient effects on gallium nitride crystal growth by sodium-flux method

During the growth of gallium nitride single crystals by sodium-flux method, temperature significantly impacts crystal quality. In this study, the mechanism of the effect of different temperature gradients on crystal growth is analyzed in depth using a combination of numerical simulation and experiment. The experimental results show that epitaxial growth of crystals occurs under positive temperature gradient conditions, while there is dissolution of seed crystals under negative temperature gradient conditions. The temperature, flow, and concentration data of the melted material during crystal growth were calculated using numerical simulation. The simulation findings reveal that the distribution of solution supersaturation varies according to temperature. High supersaturation at the bottom of the melt is favorable for crystal epitaxial growth on the surface of seed crystals under a positive temperature gradient. Meanwhile, low supersaturation at the top of the melt suppresses the hard polycrystalline layer here. Under negative temperature gradient conditions, low supersaturation at the bottom of the melt may lead to remelting of seed crystals, which is consistent with the experimental phenomenon. Furthermore, we propose an optimized heat source profile. This profile manages high supersaturation near seed crystals, aiding continuous growth. Finally, we have applied the curve in an applied way by proposing a multi-stage heating device, based on which the desired arbitrary temperature profile can be modulated. This research has broad applications in a variety of crystal growth experiments using fluid as the mother phase.

Ab-initio General-relativistic Neutrino-radiation Hydrodynamics Simulations of Long-lived Neutron Star Merger Remnants to Neutrino Cooling Timescales

We perform the first 3D ab-initio general-relativistic neutrino-radiation hydrodynamics of a long-lived neutron star merger remnant spanning a fraction of its cooling timescale. We find that neutrino cooling becomes the dominant energy loss mechanism after the gravitational-wave dominated phase (∼20 ms postmerger). Electron flavor antineutrino luminosity dominates over electron flavor neutrino luminosity at early times, resulting in a secular increase of the electron fraction in the outer layers of the remnant. However, the two luminosities become comparable ∼20–40 ms postmerger. A dense gas of electron antineutrinos is formed in the outer core of the remnant at densities ∼1014.5 g cm−3, corresponding to temperature hot spots. The neutrinos account for ∼10% of the lepton number in this region. Despite the negative radial temperature gradient, the radial entropy gradient remains positive, and the remnant is stably stratified according to the Ledoux criterion for convection. A massive accretion disk is formed from the material squeezed out of the collisional interface between the stars. The disk carries a large fraction of the angular momentum of the system, allowing the remnant massive neutron star to settle to a quasi-steady equilibrium within the region of possible, stable, rigidly rotating configurations. The remnant is differentially rotating, but it is stable against the magnetorotational instability. Other MHD mechanisms operating on longer timescales are likely responsible for the removal of the differential rotation. Our results indicate the remnant massive neutron star is thus qualitatively different from a protoneutron stars formed in core-collapse supernovae.

Spatially Resolved Temperature and Density Structures of Nearby H ii Regions

Photoionization models frequently assume constant temperature or density within H ii regions. We investigate this assumption by measuring the detailed temperature and density structures of four H ii regions in the Large Magellanic Cloud and the Small Magellanic Cloud, using integral-field spectroscopic data from the Wide-Field Spectrograph on the ANU 2.3 m telescope. We analyze the distribution of emission lines of low-ionization, intermediate-ionization, and high-ionization species. We present the complex electron temperature and density structures within H ii regions. All four nebulae present a negative gradient in the electron density profile. Both positive and negative temperature gradients are observed in the nebulae. We create a series of nebula models with constant interstellar medium (ISM) pressure and varying temperature and density distributions. A comparison of the line ratios between our H ii regions and models suggests that none of the simple nebula models can reproduce the observed temperature and density structures. Comparison between the models and the data suggests that the ISM pressure of nebulae in the LMC and SMC is between log(P/k) = 6 and 7.5. Complex internal structures of the nebulae highlight the importance of future Monte Carlo photoionization codes for accurate nebula modeling, which include a comprehensive consideration of arbitrary geometries of H ii regions.

Analysis on crack propagation of CRTS III slab ballastless track under temperature loads and freeze–thaw deterioration

In seasonal frozen region, the Chinese Rail Track System (CRTS) III slab track is subject to temperature loads and freeze–thaw deterioration, which may lead to further expansion of microcracks in track slabs. Mechanical parameters of track structure materials after freeze–thaw cycles are obtained through the experimental tests in this study. A finite element model of CRTS III slab track on subgrade section is then established by ABAQUS. Based on fracture mechanics theory, the types of cracks generated in track slabs under temperature loads and freeze–thaw deterioration, and crack expansion law are analyzed by using extended finite element method. The results show that under temperature loads, the expanded cracks in track slab are mainly Mode Ⅰ - Opening mode. There is the possibility of expansion for transverse cracks with larger size on the upper surface of track slab under negative temperature gradient load. Vertical capillary cracks at the location where track slab is bonded to self-compacting concrete are more likely to expand. Freeze-thaw deterioration will reduce the difference between the SIFs of cracks and fracture toughness of track slab material, which has a certain promotion effect on crack expansion.

Temperature gradient of ballastless track in large daily temperature difference region and its influence on dynamic responses of vehicle-track-bridge system

Due to the large daily temperature difference on the ultra-high altitude plateau of China, the actual vertical temperature gradient (TG) of ballastless track may exceed the design value in the Code. The temperature monitoring platform of the double-block ballastless track was established to obtain the temperature distribution characteristics of track. The finite element model of the temperature field of the track is developed to study the warping deformation of track, and then the influence of TG on the dynamic responses of the vehicle-track-bridge system (VTBS) are investigated. The results show that the maximum positive temperature gradient (PTG) and negative temperature gradient (NTG) of the track bed slab are 88.875 ℃/m and − 47.159 ℃/m, respectively, and the latter exceeds the design value in the Code. The dynamic responses are positively correlated with the TG, and the influence of the NTG is more significant. The dynamic response of the rail is most sensitive to the TG.

Temperature gradient effect on high-speed railway frame structure yard based on fluid-solid coupling analysis

As the frame structure can effectively save the lower space and optimize overall layout of the yard, it was first applied in the railway double-layers yard in Beijing Fengtai, including the elevated high-speed yard and the ground common-speed yard. To identify the most unfavorable temperature gradient effect on railway frame structure yard, the present study combined with CFD (Computational Fluid Dynamics) and FEM (Finite Element Method) to analyze the temperature gradient and corresponding temperature stress of the structure, and utilizes ray tracing method to analyze the shielding effect between components of structure under the sunlight. The results show that, the temperature gradients of the slab need to be focused. Both positive and negative temperature gradients are observed in the vertical direction of the slab at the end of September (autumn equinox), which are 80.95℃/m and −29.85℃/m, respectively. Under the most unfavorable temperature gradient, the maximum principal tensile stress of the structure lies at the junction of positive and negative temperature gradients of the slab, accounting for 45.6% of the concrete tensile strength, which is the controlling index of the frame structure.

Analysis of mechanical properties and deformation characteristics of debonding-repaired slab track

ABSTRACT To investigate the influence of debonding-repair materials on interface damage and deformation characteristics in track structures, a finite element model was established to represent CRTS III prefabricated slab track with debonding repairment under various conditions. The mechanical properties and deformation law of the track structure under the combined loads of train and temperature gradient were analysed under intact interlayer, debonding without repairment, and debonding-repaired conditions. Results show that both the interface damage area and stress increase in line with the temperature gradient, and that positive temperature gradients have a greater effect on interface damage than negative temperature gradients. In addition, the interface damage area and stress increase can be effectively slowed down with debonding repairment materials. Specifically, under a temperature gradient of 90°C/m, the failure rate of interfacial bonds is 21.2%, 29.6%, and 2.1% for conditions of intact interlayer, debonding without repairment, and debonding with repairment, respectively. In debonding conditions, the maximum vertical displacements along the lateral and longit udinal direction increase about 1.1 times ~ 2.3 times under positive temperature gradients more than the intact interlayer condition. Further, the pattern and peak vertical deformation for track slab are basically the same between the intact interlayer and the repaired debonding conditions. The calculation results indicate that the repair measures can alleviate interfacial adhesive deterioration and reduce the deformation of the track structures.

Warping deformation of the track slab and their influence on the interlayer stiffness and vibration transmission characteristics of the unit ballastless track

The unit ballastless track partially segments the concrete track bed in the longitudinal direction, and relieves the concrete temperature stress by isolating the upper and lower layers. However, the layer isolation leads to the incompatible deformation of the upper and lower track structures under the effect of the temperature gradient. A large temperature gradient on the track slab will cause local contact between layers, the contact area between layers will then decrease, thus leading to “stiffness softening” between layers. When the vehicle passes, the contact area between layers will gradually increase, which, in turn, leads to “stiffness hardening”. The analysis results show that the greater the design stiffness between layers, the more significant the “stiffness softening” effect will be under the temperature gradient. When k0 = 400 × 106 (N·m−1)·m−2 and Tg = 90 °C·m−1, the interlayer stiffness decreases by 88%.The simulation analysis results of the wheel-drop impact test show that under a positive temperature gradient, the peak value of rail vibration acceleration increases, and the peak value of the track slab and base plate vibration acceleration decreases. The greater the stiffness designed between layers, the more obvious the influence will be. With the increase of the positive temperature gradient, the vibration acceleration of the rail and the track slab will be reduced in the 1–30 Hz and 40–100 Hz frequency domains. With the increase of the negative temperature gradient, the vibration acceleration of the rail in the 4–10 Hz, 20–50 Hz frequency domains, and the vibration acceleration of the track slab in the 70–200 Hz frequency domains will be increased. A large positive temperature gradient inhibits the transmission of high-frequency vibrations above 40 Hz to the substructure, while a negative temperature gradient inhibits the transmission of low-frequency vibrations within 30 Hz and 70–200 Hz to the substructure. A positive temperature gradient is beneficial to restrain the downward transmission of low-frequency vibration. When k0 = 200 × 106 (N·m−1)·m−2, the low-frequency vibration transmission loss of the track slab to the base plate is close to 0 dB without temperature gradient, but the positive temperature gradient increases the transmission loss by about 10 dB, the greater the temperature gradient, the higher the transmission loss of the track slab to the base plate under high stiffness.

Effect of Temperature on Moisture Migration in Earth and Fiber Mixtures for Cob Materials

This paper highlights the impact of environmental conditions on cob buildings. Different factors such as wall thickness, material permeability and interactions between moisture and heat fluxes can all have significant effects on the performance and durability of cob buildings. An experimental and modeling-based study was conducted on the hygrothermal characterization of cob building materials, which were obtained by mixing earth and fibers. Two types of cob materials that can be used as insulation and to form structural materials in buildings were tested. The effect of outside temperature on adsorption isotherms was investigated for both materials. The experimental data were fitted using the GAB model, after which a new correlation of water content correlation was proposed. Three specific configurations were investigated in which cob material was subjected to moisture transfer and a zero, positive or negative temperature gradient. Based on the resulting measurements, a high coupling effect between heat and moisture transfer inside the structural material was analyzed. A comparison of the experimental and modeling results demonstrated the satisfactory correlation and reliability of the developed model. Simulations were carried out for various wall thicknesses, in order to assess the effect of heat and moisture transfer on water content. The three scenarios were simulated and distributions of water content inside the walls were determined. The results show that the wall thickness of cob buildings and the direction of heat and moisture fluxes affect water content distribution in the structure. A greater thickness of the cob wall leads to higher water content, but this relationship reverses when the heat and moisture fluxes move in the same direction.

Mechanical Properties of Ballastless Track Considering Freeze–Thaw Deterioration Damage

In order to investigate the stress characteristics of ballastless track under high latitude, and multi-source and multi-field extreme temperature conditions. Based on the finite element theory and the elastic foundation beam–plate principle, a finite element model of the ballastless track considering the limit convex abutment, gel resin, and interlayer bonding is established. The mechanical characteristics of the ballastless track under the slab–CAM layer bonding state, mortar separation, freeze–thaw degradation and forced deformation of the foundation are studied. Considering the deterioration of materials, the bending moment and reinforcement of track structures in cold regions are checked and calculated. The studies show that under the action of negative temperature gradient load, the edge of the track slab is subjected to tension, and structural separation occurs at the edge of the slab. When the interface between the track slab–CAM layer is poorly bonded, the bearing capacity can be improved, and the amount of separation can be reduced by increasing the structural stiffness of the CAM layer. Under the action of freeze–thaw cycles, the material performance deteriorates seriously, the separation between the track structures intensifies, the baseplate is seriously powdered and cracked, and the maximum tensile stress exceeds 6 MPa. The CAM layer and the baseplate are weak structures, and the foundation frost heave occurs at the expansion joint of the baseplate, which is the frost heave condition. Under freeze–thaw deterioration, the original reinforcement design of the substructure structure does not meet the requirements of structural cracks and reinforcement yield stress. In severely cold areas, the structural reinforcement scheme should be reasonably determined.

Gas chromatographic separation of the fatty acid methyl esters prepared from dairy products, partially hydrogenated oils, and refined vegetable oils applying a negative temperature gradient

AbstractTo date no single gas chromatographic method can simultaneously measure all fatty acids (FA), including trans‐FA (TFA), that are contained in dairy products, partially hydrogenated oils (PHO), and refined vegetable oils. Using 100% poly(biscyanopropyl siloxane) capillary columns, ruminant and dairy fats are preferentially analyzed by applying temperature programs that separate short chain FA, but not trans‐18:3 from 20:1. Refined vegetable oils and PHO are preferentially analyzed by applying isothermal elutions that provide quantification of all 18 carbon TFA including trans‐18:3 FA, but not of all short chain FA. In this short communication, we propose a temperature program method capable of simultaneously measuring short chain FA and all 18 carbon TFA including trans‐18:3 by applying a negative temperature gradient after the elution of trans‐18:1. A simplified version of the method is also described for equipment not able to perform negative temperature gradients.

Tuning the heat−salt−water balance for rapid and scalable solar desalination

The mixed temperature gradient evaporator allows us to accelerate water evaporation at low solar irradiance. However, this novel device still requires a trade-off between heat transfer, water supply, and salt rejection. This paper reports an evaporator that achieves the synchronous management of heat, water, and salt by adjusting the height of the sidewall of the solar absorber. Carbon nanoparticles-coated cotton fiber rod is adopted as the multifunctional solar absorber for sustainable solar desalination. In addition, the water pumped by the solar absorber can be far greater than that required for evaporation, which is sufficient to retain the sustainability of water evaporation. Moreover, both positive and negative temperature gradients are formed between the light-receiving surface and the water-solar absorber interface, implying that the solar absorber is allowed to harvest energy from the sun, environment, and bulk water without experiencing conductive heat loss. As a result, this configuration demonstrates a rapid evaporation rate in both light and darkness (5.04 and 3.55 kg m−2 h−1, respectively) when operating in a 3.5 % (w/w) NaCl solution. More importantly, the evaporation rate remains stable during 5 h of operation in 20 % (w/w) NaCl solution. Furthermore, according to a continuous 9-hour outdoor experiment, the water collected by the evaporator per unit area can satisfy the needs of at least three people.

Integration of ramped temperature oxidation and combustion tube tests for kinetic modeling of heavy oil in-Situ combustion

In-situ combustion (ISC) has been applied as a follow-up process after steam injection-based technologies to improve heavy oil recovery and lower operating costs. Comprehensive understanding of the oxidation behavior and reliable prediction of the ISC performance are of great importance in the design of a ISC process. In this work, a calibration workflow was proposed to investigate the oxidation behavior and then establish a reaction kinetics model. A Ramped Temperature Oxidation (RTO) experiment was firstly conducted to capture the detailed oxidation behavior at elevated temperature conditions. Subsequently, a Combustion Tube (CT) test was performed to further evaluate the overall performance of ISC. Based on the integration of RTO and CT results, a comprehensive reaction kinetics model was developed to predict the ISC performance within a wide temperature range, including Low Temperature Oxidation (LTO), Negative Temperature Gradient Region (NTGR), and High Temperature Oxidation (HTO) reactions. It is found that the NGTR of heavy oil with high saturate and low asphaltene exhibits a narrow temperature range. The combustion front velocity in the RTO is comparable with that in the CT. In a stable HTO region, the CO2 concentrations in the RTO experiment and CT test were kept around 17% and 14%, respectively. The existence of LTO reactions in the RTO experiment caused the deviation of CO2 concentration. With the incorporation of the reaction model into simulation, a good agreement between measured and predicted results was obtained. This demonstrates that the established reaction model is capable of capturing the key oxidation mechanisms. In addition, the proposed workflow also helps upscale the oxidation behavior from a RTO experiment to a CT test and provide benchmarks for field operations.

Heat flow variations in 2 km deep borehole Litoměřice, Czechia

Temperature in 2 km deep borehole Litoměřice, drilled in 2007, was repeatedly logged down to 1700 m in the period 2007 – 2020. We were able to monitor a return of the temperature to the equilibrium temperature-depth profile undisturbed by drilling. The uppermost part of the profile contains signal of the recent warming manifested by a negative temperature gradient close to the surface and a temperature minimum at a depth of about 40 m. The minimum has been migrating downward at a rate of 1.5 – 2 m per year in the period 2015 – 2020.A detailed knowledge of temperature gradient together with thermal conductivity, diffusivity and heat production measurements on the drill-core samples of mica-schist that occurs below 900 m depth enabled us to analyze the heat flow vertical variations in the lithologically homogeneous depth section 900 – 1700 m. We came to the conclusion that temperature-depth profile in this section contains a robust climate signal of the last glacial cycle. The reconstructed ground surface temperature history indicates the magnitude of the last glacial – Holocene warming 13 -15 K and existence of a minimum 15 – 20 ka. The long-term mean ground surface temperature +1 - +2 °C suggests that the borehole site was permafrost free for most of the glacial cycle. Existence of about 100 m deep permafrost is possible in the coldest part of the last glacial.The steady-state surface heat flow has been estimated at 88 mW/m2. The reconstructed ground surface temperature history used as a surface forcing function in a numerical solution of the transient heat conduction equation provided an estimate of the present-day heat flow in the well. The estimate is practically independent from the poorly constrained conductivity of the 900 m thick sedimentary cover. According to it the present-day heat flow is lower than the steady-state one by 20 - 30 mW/m2 in the first hundreds of meters below the surface and still by about 10 mW/m2 at a depth of 1 km.

Formation, evolution, and enhancement mechanisms of mixed temperature gradient during interfacial solar vapor generation

The solar evaporator, which generates a mixed temperature gradient (MTG) in the process of solar-driven interfacial water evaporation (SIWE), has shown great application potential in clean water production. It is also expected to provide a more comprehensive understanding to shed light on the formation, evolution, and enhancement mechanisms of the MTG. Herein, the space-time evolution of the solar absorber temperature and the evaporation performance in the column solar absorber are studied through a three-dimensional and multi-physical model coupling heat transfer and water transport. The results will demonstrate not only the temperature distribution during the SIWE process but the interface between positive temperature gradient (PTG) and negative temperature gradient (NTG). Moreover, the relationship between evaporation rate and light intensity, bulk water temperature, and environment humidity will be investigated. Importantly, the contributions of solar heating, PTG, NTG, and environment heating to the total evaporation rate will be quantitatively analyzed. Finally, based on the above results, the formation conditions, evolution characteristics, and enhancement mechanisms of MTG will be revealed. This paper will provide theoretical guidance for the successful construction and operation of an MTG evaporator for SIWE acceleration.