Variable Temperature Gradient Research Articles

Adhesion performance tests and analysis of interface damage for CRTS III prefabricated slab tracks

Debonding between the track slab and self-compacting concrete (SCC) is a common form of damage in China railway track system (CRTS) III prefabricated slab tracks. To investigate the influence of interlayer cohesive parameters on the interface connection, composite specimens of track slabs and SCC were made to be used for splitting tensile and shear tests. The variation characteristics between the interface’s tension and displacement were obtained using digital image correlation (DIC) techniques, and the key parameters of a cohesive zone model (CZM) were determined and used to simulate the cracking behavior. Also analyzed was the interlayer damage behavior of the composite specimen using ABAQUS, the results of which were compared with those of the tests. Furthermore, a finite element simulation model of the CRTS III prefabricated slab track with CZM was used to analyze the impact of different cohesive parameters on interlayer damage under train loads and varying temperature gradient loads. The results show that: I). The DIC technique accurately describes the entire process from the damage initiation and propagation, to complete failure of the interface-bonded components; II). The finite element simulation results of the concrete composite specimens agree with the experimental results, indicating the CZM accurately reflects the interlayer cracking behaviors; III). Reducing the interface stiffness and increasing the critical fracture energy can slightly delay the onset of interface damage and debonding, respectively; IV). An increase in the cohesive strength can effectively inhibit the development of interface damage, for example, increasing the normal and tangential cohesive strength can improve the starting temperature gradient for interlayer damage initiation by 150 % and 45 %, respectively; and V). Under large positive temperature gradients (>70 °C/m), the interlayer debonding rate corresponding to most cohesive parameters reaches 100 % (complete failure of adhesion), making extreme temperature areas a necessary focus on the interlayer debonding of slab tracks. The research results of this paper can be used to analyze the damage behavior between the track slab and SCC layer, and provide a theoretical basis for the design and maintenance of CRTS III prefabricated slab track.

Research on cutting temperature distribution of carbide cutter rake face considering sticking-welding layer

In the process of cutting 2.25Cr1Mo0.25V material with carbide cutter, the cutter-chip element diffusion occurs, which will cause sticking-welding layer easily produced on rake surface. In order to study the influence of the sticking-welding layer on the temperature distribution and gradient of rake face, the thermal conductivity of sticking-welding layer on rake face was calculated by using the Maxwell-Eucken diffusion phase continuum principle. According to the heat conduction theory, the theoretical model of heat transfer with or without the sticking-welding layer on rake face was established, and combined with the finite element simulation model, the temperature distribution of rake face is studied by combining model calculation and numerical simulation. The results show that: when there is sticking-welding layer on rake face of cutter, this specified layer will play the role of heat insulation, leading to relatively low temperature of rake face. The presence of sticking-welding layer will cause the temperature fluctuation of cutter rake face, and the temperature also increases with the increase of the thickness. At the same time, the variation trend of temperature gradient in sticking-welding layer is similar with different layer thickness, whereas the larger the thickness, the greater the variation of temperature gradient due to the thermal resistance. By comparing and analyzing the average cutting temperature of rake face of the actual cutting and simulation, it is concluded that the temperature simulated by the finite element model will be closer to the actual measured temperature, and the measurement error is less than 10%, which provides a theoretical basis for delaying the tool life.

Physics-informed graph convolutional neural network for modeling geometry-adaptive steady-state natural convection

This paper presents a novel deep learning-based surrogate model for steady-state natural convection problem with variable geometry. Traditional deep learning based surrogate models are more or less limited by the requirement for large amounts of training data, loss of accuracy due to pixelization of the original data, the low accurate prediction near the boundaries and low geometry adaptive capability. To overcome the above challenges, the proposed natural convection prediction framework is mainly composed of a physics-informed neural network (PINN) and a graph convolutional neural network (GCN), called natural convection prediction model based on physics-informed graph convolutional network (NCV-PIGN). The GCN serves as the prediction module, inferring and predicting natural convection phenomena by considering the interactions between unstructured nodes and their neighbor; the PINN incorporates the governing equations of natural convection into the loss function of the neural network, allowing the predictions from GCN to satisfy the constraints imposed by the physical laws. The advantages of this framework are twofold: the operation principles of the GCN better align with the development of the temperature field in real situations, and the embedding of physical information strengthens the model's understanding of the flow field, accurately describing the variations of temperature gradients at the boundary positions while reducing the model's reliance on training data. Finally, to validate the superiority of the NCV-PIGN, we analyze its geometric adaptability and accuracy of prediction using single and dual heat source cases. We compare the model's prediction results at different sampling point quantities and contrast them with those of purely data-driven models. The results demonstrate that the excellent geometric adaptability and prediction capability of the proposed model can be achieved with only 20 training data and once the fully trained the model can solve natural convection problems within 3 ms. The max and mean relative errors in predicting the temperature field are less than 2% and 0.4% for both single and dual heat source cases. Compared to the pure data-driven model, the proposed model has reduced the maximum error by 65.5% and the mean error by 72%. These results validate the effectiveness of the developed NCV-PIGN model, enabling better performance of the deep learning-based surrogate models for natural convection problems.

Dynamic Stability Study on an Exponentially Tapered Rotating Asymmetric Sandwich Beam Under the Action of a Pulsating Axial Load with Variable Temperature Gradient

In this research article stability study of an exponentially tapered rotating sandwich beam having different elastic parameters in temperature environment has been done. The sequential steps followed up to reach the goal are extended Hamilton’s principle, non-dimensionlization of equations, selection of shape functions for the mathematical modeling of the system from the past research work depending upon the boundary conditions, use of general Galerkins method, help of modal matrix and finally the use of Saito-Otomi conditions. Here the effects of variable thermal gradient, on the Young’s modulus of the elastic layers have been considered in place of constant thermal gradient as earlier. Consideration of effect of variable thermal gradient, while analyzing the stability of the system is the most significant contribution of this research article to the society as non-uniform elastic layers are considered here. The influence of different parameters on the regions of instability are studied and presented graphically. Comparison of the results with uniform and variable thermal gradient is carried out.

Temperature variation and distribution in underground sidewall: On-site monitoring and finite simulation

Sidewall is the main structure with the highest crack risk in underground engineering, and temperature deformation is an essential factor leading to cracking. Quantitative study on temperature variation and temperature gradient is the basis of temperature deformation research. However, there are few related research reports. This paper aims to quantitatively study the effect of thickness, demolding time, and construction season on the sidewall's temperature variation and temperature gradient. Sensors were installed on-site to collect temperature data, and a finite element model of the sidewall was established to analyze the temperature change process. The temperature variation and distribution under different conditions were analyzed by changing the simulation parameters. Results show that heat is mainly lost in the thickness direction and temperature gradient variations from outside to inside. After demolding, sidewall's surface temperature gradient will suddenly increase, and the cracking risk will be the highest. Sidewall's surface temperature gradient is the largest during construction in winter. Simultaneously, mitigation measures were put forward to reduce the risk of temperature deformation and cracking. The research results can provide a reference value for engineering practice.

A thermal load identification method based on physics-guided neural network for honeycomb sandwich structures

The identification of thermal load/thermal shock of aircraft during service is beneficial for collecting information of the service environment and avoiding risks. In the paper, a method based on multivariate information fusion and physics-guided neural network is developed for the inverse problem of thermal load identification of honeycomb sandwich structures. Two thermal feature parameters: temperature gradient and temperature variation rate are used to build the dataset. A 16-layers physics-guided neural network is presented to achieve the predicted results consistent with physical knowledge. In the work, laser irradiation is used as the thermal load, and two laser parameters are to be identified, i.e. spot diameter, power. Simulations and experiments are conducted to verify the effectiveness of the proposed method. The effects of physics-guided loss function and multivariate information fusion are discussed, and it is found that the results based on the proposed method are much better than the results based on the method without physical model. Besides, results based on multivariate information fusion are better than results based on single temperature response. Then, the effects of network models and hyper parameters on the proposed method are also discussed.

Microstructure characteristics under varying solidification parameters in different zones during CMT arc additive manufacturing process of 2319 aluminum alloy

The microstructure affects the performance of the formed component during the wire arc additive manufacturing (WAAM) process of aluminum alloy. The present research utilized a finite element model to investigate the temperature field, thermal cycle curve, temperature gradient and cooling rate curve of the deposition layer at different positions in the WAAM process. The microstructure distribution and grain size variation of the deposition layer at different positions were examined according to the experimental results. The microstructure evolution of the deposition layer in the WAAM was simulated using a macro-micro coupled grain growth model. The variation law of solid phase and liquid phase distribution with solidification time steps of molten pool under varying temperature gradients is analyzed. The results indicated that the average length and width of the grains continuously decrease from right to left in the top zone of the deposition layer. When the temperature gradient increases to a certain extent, both the liquid phase area difference and the solid phase area ratio difference within the same time step gradually decrease with the development of the temperature gradient. This research supplies a reference for optimizing the microstructure of WAAM aluminum alloy by adjusting the heat input and solidification parameters.

Predicting Maximum Effective Temperatures and Thermal Gradients for Steel I-Girder in Canadian Climate Regions

The constant fluctuation of thermal loads on steel members, especially during construction, causes non-uniform distributions of temperatures, resulting in possible constructional and structural defects leading to unfavorable thermally induced responses and potential safety risks. The Canadian Highway Bridge Design Code (CHBDC) provides one thermal gradient variation profile without accounting for the differences in the geometrical parameters of the steel members and the variations in the climate regions of Canada. Therefore, in this study, three-dimensional finite element (FE) thermal simulations were conducted to investigate the maximum effective temperatures and positive vertical thermal gradients for different Canadian climate regions. Parametric studies were performed to conduct the FE thermal analysis using the thermal model validated in ANSYS. The comprehensive study results showed that Canada could be divided into two main zones for vertical thermal gradient calculations, meaning that one stationary thermal gradient profile cannot be applicable to all climate regions of Canada, as recommended by the CHBDC. Based on the FE thermal analysis results, empirical formulas as a function of the significant parameters were proposed to predict the maximum effective temperature and thermal gradient variations of the steel I-girder. The predicted maximum effective temperature and thermal gradient variation values were found to be highly correlated with the FE values with coefficients of determination R2 of approximately 0.97 and 0.98, respectively.

Impact of installation error and tracking error on the thermal-mechanical properties of parabolic trough receivers

As the solar energy utilization technology for renewable clean energy, actual parabolic trough receivers are subject to tracking errors and absorber tube installation errors, and the bellows and Kovar ring under these errors have a significant impact on the receiver's safety. Based on the MCRT-FVM-FEM principles in this paper, a receiver's optical-thermal-stress mathematical model is modeled and the thermal-stress performance and safety of the receiver's key components under two errors are evaluated. The correlation between the bellows and Kovar ring's performance and the two errors is analyzed. The results demonstrate that the lower tracking errors and larger installation errors markedly increment the absorber's deformation and have a negative impact on the receiver safety. Bellows and Kovar ring's asymmetrical temperature distribution causes variable swell and uneven stress under tracking and installation errors. Temperature gradient variation of bellows is more sensitive under errors than Kovar rings. Kovar ring's compressive stress rises substantially as the Y-directional installation error varied from −15 mm to 15 mm compared to other errors. With tracking errors exceeding 8 mrad, bellows' tensile stress and Kovar ring's compressive stress diminish under installation error. Thus, larger tracking errors significantly reduce the threat to the receiver when installation errors exist.

Thermo-hydraulic characteristics of thermal interface induced by natural convection in water tank with internal heat source

Large-scale water tank or pool with internal heat source is common structures in solar energy and nuclear power. In this paper, a visible thermal interface is captured in the experiments in a square water tank with a horizontal heating rod, which is an interesting phenomenon hardly reported before. The direct shadowgraphy method is employed to record gray graphs of the forming process and flow regimes of the thermal interface. Corresponding transient numerical simulations with the large eddy simulation (LES) method are conducted to display detailed thermo-hydraulic characteristics of the thermal interface. Based on the temperature distribution and flow field, a natural convection circulation driven by buoyancy is formed above a stagnant zone, which is regarded as a two-layer stratified shear flow. The horizontal shear flow above the stagnant zone induces the visible thermal interface. Because the heat transfer mode switches from convection to conduction when crossing the interface, the sharp temperature gradient and density variation occur at the interface. The effect of the heat flux of the heating rod is investigated, and three different flow regimes of the thermal interface are observed under different heat loads. The stability of the flow regimes is analyzed by the gradient Richardson number, which is the ratio of the buoyancy to the turbulent shear. At low heat load, the thermal interface is destabilized because the turbulent shear overcomes the density barrier. As the heat loading increases, the buoyancy increasing rate exceeds the shear increasing rate, and the stronger potential barrier dominates the flow structure, which is beneficial to the interface stability.

On the invariance of flame-motion-induced variations of the generalized disturbance energy

The response of a one-dimensional laminar premixed flame to an inlet velocity forcing is investigated within the disturbance energy budget (DEB) framework. It is evidenced that the flame behaviour can be characterized through two dimensionless numbers. The first is a Strouhal number St, which is related to the flame motion and compares the flame front flapping length scale to the laminar premixed flame thickness δL0. The second is the normalized velocity forcing level η, i.e., the ratio between the amplitude of the inlet velocity variation and the laminar flame speed. Among the various disturbance energy sources, three terms, which do involve temperature (entropy) fluctuations, have significant growth-rates. These are: (i) the thermoacoustic source, (ii) an entropic term related to the coupling between entropy and temperature gradient variations, and finally (iii) a sink term relevant to thermal diffusion effects. For moderate forcing levels, the sole knowledge of these three terms together with St are sufficient to describe the flame dynamics. However, for larger forcing levels, the aforementioned contributions are no longer predominant over the transient variations of the disturbance energy that are induced by velocity fluctuations. Indeed, although the growth-rates of the corresponding source terms remain marginal — regardless of forcing amplitude and frequency — they must be taken into account so as to predict the evolution of the system, and the second non-dimensional number η becomes necessary to proceed with its precise characterization.

Rainfall–Mixed Layer–SST Feedback Contributing to Atlantic Meridional Mode Development

Abstract A simple air–sea coupled model for wind–evaporation–sea surface temperature (SST), wind-induced turbulence–mixed layer (ML)–SST, and wind–evaporation–ML–SST feedback is extended to unitedly represent the precipitation anomaly associated with moisture convergence and the ML depth (MLD) anomaly due to freshwater-induced buoyancy flux. An eigenanalysis reveals the presence of yet another feedback accompanying a cross-equatorial SST gradient. The feedback operates as follows: A cross-equatorial SST gradient anomaly forces surface wind anomalies to blow toward the warmer hemisphere, causing low-level convergence (divergence) and hence a positive (negative) precipitation anomaly in the warmer (cooler) hemisphere. The positive (negative) precipitation anomaly stratifies (destabilizes) the near-surface ocean and results in a shallower (deeper) ML, which enhances (reduces) the warming by climatological shortwave radiation, and thus provides positive feedback to the initial SST gradient anomaly. The strength of this feedback is similar to the three known feedbacks in terms of stability. Sensitivity experiments with the coupled general circulation model MIROC6 reveal that the precipitation-induced buoyancy flux anomaly accounts for up to ∼14% of the Atlantic meridional mode (AMM) amplitude in boreal spring through affecting the MLD anomaly in the deep tropics, which is consistent with the simple model results, supporting the existence of the feedback. In contrast, the evaporation-induced buoyancy anomaly contributes only marginally to the MLD and thus the SST anomalies. The ML temperature budget from MIROC6 confirms that sensitivity changes of the ML to the warming by climatological shortwave radiation due to the MLD anomaly are important in generating the SST anomalies associated with the AMM, which is consistent with previous observational studies. Significance Statement It is known that year-to-year variations in the sea surface north–south temperature gradient in the tropical Atlantic can affect the climate in both surrounding and remote regions. In this study, we used theoretical and state-of-the-art climate models to investigate a tropical air–sea coupled process and establish its contribution to the Atlantic climate variability. As a result, we identified a previously unknown process contributing to north–south gradient variations in which the atmosphere and ocean interact to enhance the initial variation, thus forming a positive feedback loop. In particular, precipitation and near-surface ocean state changes were determined to be essential. This feedback process accounts for up to 14% of the north–south temperature gradient variations in the tropical Atlantic during the boreal spring.

Simulation studies on combined effect of variable geometry, rotation and temperature gradient on critical speed of gas turbine disc

PurposeThe present findings report a significant influence of disc profile and thickness on the order of excitation leading to critical speed condition. Certain transverse modes of vibration of the disc have been obtained to be more susceptible to get excited while recording the lowest critical speeds.Design/methodology/approachNumerical simulation using finite-element method has been adopted due to the complicated geometry, complex loadings and intricate analytical formulation. A comprehensive analysis of exclusive as well as combination of thermal and centrifugal loads has been taken up to determine the intensity and characteristics of the individual/combined effects.FindingsThe typical gas turbine disc profile has been analyzed to predict the critical speed under the factual working condition of an aero-engine. FEM analysis of uniform and variable thickness discs have been carried out under stationary, rotating and rotating-thermal considerations while emphasizing the effect of disc profile and thickness. Centrifugal stresses developed due to rotational effect result in unceasing stiffening of the discs with higher stiffening for a greater number of nodal diameters. On the other hand, a role reversal of thermal effect from stiffening to softening is figured out with increasing numbers of nodal diameters. However, the discs are subjected to an overall stiffening effect on account of the combined centrifugal and thermal loading, with the effect decreasing with an increase in disc thickness. Under the combined loading, the order of excitation leading to critical speed condition is dependent on disc profile and thickness. Moreover, the vibrational modes (0,1) and (0,2) are identified as more prominent adverse modes corresponding to lowest critical speeds.Practical implicationsThe present findings are expected to serve as guidelines during the design phase of gas turbine discs of aeroengine applications.Originality/valueThe present work deliberates on the simulation and analysis of gas turbine disc specific to aeroengine application. The real-life disc geometry has been analyzed with due consideration of major factual operating conditions to identify the critical speed. The identification of various critical speed using numerical analysis can help to reduce the number of experimental tests required for certification.

Thermocline variability in the subtropical northwestern Pacific since the last deglaciation

Thermocline conditions in the tropical western Pacific are closely linked to regional- and basin-scale hydrological variation and may have played a critical role in global climate evolution on various timescales. However, long-term changes in thermocline hydrology in the subtropical northwestern Pacific and their connection to the tropical Pacific remain unclear. Based on planktonic foraminiferal Mg/Ca and δ18O, we reconstructed the temperature and salinity of thermocline water since the last deglaciation, using core OKI02 from the Okinawa Trough (OKT) in the subtropical northwestern Pacific. The results indicated a discrepancy in evolution of both temperature and δ18O between the thermocline and surface water over the past 19 ka. Unlike for surface water, changes in thermocline hydrology correlated with changing conditions in the tropical western Pacific, indicating a close relationship between these regions since the last deglaciation. Thermocline temperature and salinity gradients between the OKT and the tropical western Pacific increased from ∼16.5 to 10 ka BP, reached their maximum values at approximately 10 ka BP, and then decreased from the Early Holocene to present. Variations in temperature and salinity gradients correlated with changes in the El Niño–Southern Oscillation (ENSO) over the past 19 ka, which were coupled with equatorial summer insolation variations. We suggest that the ENSO-like process, forced by equatorial summer insolation, regulated thermocline dynamics in the subtropical northwestern Pacific Ocean since the last deglaciation, by influencing the strength of the Kuroshio Current.

Rapid optimisation of API crystallisation in a segmented flow reactor with a continuous, variable temperature gradient

A continuous flow reactor capable of a continuous, variable temperature gradient allows for the rapid optimization of reproducible crystallization conditions and control of crystal growth of small organic molecules.

Thermal monitoring of laser metal deposition strategies using infrared thermography

The thermal monitoring of additive manufacturing techniques implementing high-power energy sources is essential to ensure process quality. Although the number of research works on thermal process monitoring has grown in recent years, there are still few works that focus on using thermal camera monitoring on Laser Metal Deposition (LMD), to analyze thermal effects caused by changes in deposition strategy. This work aimed to monitor the entire thermal field produced by the LMD process during the multitrack deposition of a Nickel-based superalloy. The temperature field monitoring was carried out using an IR thermal camera capable of detecting temperatures up to 2117 °C. Experimental tests were carried out on six deposition strategies, showing that for unidirectional hatch strategies maximum temperatures of 1620 °C were reached, while contouring strategies exceeded 2100 °C. The thermographic map assessed the spatial distribution of the temperature generated by each strategy. Moreover, some key points are chosen to analyze the thermal cycles and relative cooling rates generated during the process. Additionally, an ad-hoc algorithm was elaborated to calculate the thermal gradient of every frame acquired by the thermal camera, and a routine was elaborated to create the thermal gradient map. The thermal gradient profiles were evaluated, showing mean values around 550 °C/mm and marked variations (between 200 and 700 °C/mm) only for contouring strategies. The thermal characteristics are then correlated with the metallographic and microhardness analyses. A high number of cracks was found in areas with higher temperature and thermal gradient variations. Finally, microhardness tests were carried out, and mean values and standard deviations were correlated with the thermal gradient distribution.

Experimental and Theoretical Study on Mechanical Performance of a Sustainable Method to Simultaneously Generate Power and Fresh Water

Many regions around the world have limited access to clean water and power. Low-grade thermal energy in the form of industrial waste heat or non-concentrating solar thermal energy is an underutilized resource and can be used for water desalination and power generation. This paper experimentally and theoretically examines a thermoelectric-based simultaneous power generation and desalination system that can utilize low-grade thermal energy. The paper presents concept design and the theoretical analysis of the proposed system followed by experimental analysis and comparison with the theoretical estimations. Experiments were carried out at three heat loads 50, 100 and 150 W to achieve varying temperature gradients across thermoelectric generators. During the experiments, thermoelectric generators were maintained at a hot to cold side temperature difference between 20 to 60 °C. The experiments showed that the power generation flux and freshwater mass flux increased with the increase in the thermal energy source temperature. The power flux varied between 12 to 117 W/m2 of thermoelectric generator area, while freshwater mass flux varied between 4.8 to 23.7 kg/m2⋅h. The specific thermal energy consumption varied between 3.6 to 5.7 MJ/kg of freshwater; this is comparable to the single-stage conventional distillation system.

Experimental investigation of natural convection Al2O3-MWCNT/water hybrid nanofluids inside a square cavity

ABSTRACT The use of nanofluids for convectional heat transfer has become a spry area of research in recent years with the aim of improving heat transfer efficiency. Hybrid nanofluids have attracted significant attention and are advancing research and industrial applications since they involve employing more than one type of nanoparticle(s) in a base fluid. They enhance heat transfer by combining the chemical and physical properties of several nanoparticles concurrently and providing the properties in a homogeneous state. However, few experimental studies have focused on natural convective heat transfer using hybrid nanofluids. In this study, the natural convection of alumina – multiwalled carbon nanotube/water hybrid nanofluids formulated using a two-step method at a percentage weight ratio of 10:90 Al2O3: MWCNT at various nanoparticles volume concentrations of 0.00, 0.05, 0.10, 0.15, and 0.20 vol% was studied inside a square cavity (AR = 1) with two vertical walls which are isothermal, aimed at the Rayleigh number (Ra) range of 2.81 × 108 to 8.58 × 108. The average Nusselt number (Nuav), heat transfer coefficient (hav ), heat transfer (Qav ), and Rayleigh number (Ra) were considered at varying temperature gradients of 20°C – 50°C. Al2O3-MWCNT/water hybrid nanofluid with 0.10 vol% volume concentration was discovered to have the maximum value for hav,Qav , and Nu av. However, it was also observed that a further increase in the hybrid nanoparticles’ volume concentration led to their deterioration at various temperature gradients. The maximum enhancements of 44%, 49%, and 42% were noted for hav,Qav , and Nuav , respectively, at ∆T = 50 °C, in comparison with the base fluid. Al2O3-MWCNT/water hybrid nanofluids application in a square cavity demonstrated enhanced natural convection. This present study concluded that hybrid nanofluids as heat transfer fluid significantly improved heat transfer performance compared to the base fluid.

Study of anisotropy of convective optical underwater turbulence and the effect of the mean water temperature in the presence of a varying temperature gradient on it

In this paper, the anisotropy of optical convective underwater turbulence is investigated in terms of the variance of angle of arrival (AOA) fluctuations of a narrow laser beam propagating through it in different sections of the medium. The collimated laser beam with a wavelength 532 nm and a diameter 1 cm, which passes through a convective underwater turbulence. The turbulence is generated in a water tank with dimensions of 20 cm × 36 cm × 20 cm, which is installed on a flat surface electrical heater. During the experiments, the mean water temperature (MWT) can be changed from room temperature to 34 ∘C by increasing the heater temperature. The use of the heater also generates a temperature gradient in the medium. The laser beam propagates along a horizontal path with a length of 20 cm inside the tank at different altitudes from the heater source, as well as at different distances from one of the side walls of the turbulent medium. After passing the laser beam through the turbulent medium, the fluctuations of the AOA components in the vertical and horizontal directions are measured. From the time series of the measured AOA fluctuations, their variances are determined. The anisotropy of the medium is investigated by comparing the variance of AOA components measured in the vertical and horizontal directions. We show that the variances of both of vertical and horizontal components of the AOA fluctuations are increased with the MWT, and they are saturated at higher MWTs. In addition, different anisotropic behaviors are observed for the variances of the measured AOA fluctuations at the vicinity of the lateral wall and upper surface of the water. At the vicinity of the lateral wall the variances of the AOA fluctuations in the horizontal component are larger, but at the vicinity of the upper surface the variances of the AOA fluctuations in the vertical component are dominant. This behavior may be caused by the change of the convection motion direction in the turbulent fluid.

Capillary rise phenomenon in tubes subjected to temperature gradient

Capillary rise phenomenon is studied experimentally and theoretically in this work. A Mathematical model considering temperature dependent property variation is being proposed in the present work, which is supported by experimental as well as numerical results. Effect of temperature gradient and capillary diameter on interface oscillations in capillary tubes are discussed in detail. Capillary tubes of diameter 1–10 mm and length 40 mm are subjected to varying temperature gradients of 0–2 K/mm. Effect of temperature gradient and capillary diameter on meniscus rise dynamics, amplitude and frequency of oscillations are discussed in detail. It is observed that percentage amplitude of oscillations with respect to Jurin’s height is a linear function whereas frequency of oscillations is independent of temperature gradient. The analysis presented here is of significance in the design of thermocapillarity based pumping system for future microdevices.