Liquid Temperature Distribution Research Articles

Structure effect of wall cooling channel on liquid metal heat transfer in aero-engines

In this study, a model of the cooling channel and an experimental system for heat transfer involving liquid metal are studied, to investigate the influence of the wall cooling channel structure of combustor on the heat transfer process. The error between the experimental and simulated outcomes fall is within 3 %, suggesting that the accuracy of the simulation is satisfactory. The simulation results found that the temperature non-uniformity coefficient can be reduced by 13 % and 7 % through adjusting the aspect ratio under the heat flux of 3 MW/m2 and 1.5 MW/m2 respectively, and the wall temperature of gas side can be reduced by 89 K and 47 K respectively. A smaller aspect ratio is favorable for homogenizing the liquid metal temperature distribution. Longer widths, however, can lead to horizontal thermal stratification, which can be unfavorable for heat transfer. With an aspect ratio and rib thickness of about 0.5 and 0.4 mm, respectively, the cooling channel outlet has the lowest non-uniformity coefficient of temperature and enthalpy, which is conducive to the improvement of the wall energy recovery rate. The optimal cooling channel effectively improves the thermal stratification in channel, and provides theoretical guidance for the suitable application of liquid metal to the combustor wall cooling channel.

Lattice Boltzmann study of liquid water flow and freezing in the gas diffusion layer

The flow and freezing process of liquid water in the gas diffusion layer (GDL) is studied using a proposed lattice Boltzmann method that integrates the multi-component pseudo-potential model and the enthalpy-based method. The evolution of liquid water, ice, and temperature distributions inside the GDL during this process is specifically analyzed, and the effect of GDL porous structure, such as porosity and carbon fiber diameter, is discussed. Results indicate that liquid water exhibits a propensity to break through the GDL through the regions characterized by larger pores, subsequently forming a liquid droplet on the GDL surface and beginning to freeze. The freezing process extends from the droplets to the CL side through the liquid pathways within the GDL. In addition, liquid water is more prone to freezing around carbon fibers. Due to the released latent heat during freezing, the temperature at the liquid water/ice interface stabilizes at 273 K. Moreover, it is also demonstrated that a large porosity and coarse carbon fibers both facilitate the flow of liquid water into the GDL where it then freezes, leading to more serious blockage of pores by ice and liquid water.

Dual-tracer laser-induced fluorescence thermometry for understanding bubble growth during nucleate boiling on oriented surfaces

Nucleate boiling is perhaps one of the most efficient cooling methodologies due to its large heat flux with a relatively low superheat. Nucleate boiling often occurs on surfaces oriented at different angles; therefore, understanding the behavior of bubble growth on various surface orientations is of importance. Despite significant advancement, numerous questions remain regarding the fundamentals of bubble growth mechanisms on oriented surfaces, a major source of enhanced heat dissipation. This work aims to accurately measure three-dimensional (3D), space- and time-resolved, local liquid temperature distributions surrounding a growing bubble on oriented surfaces that quantify the heat transfer from the superheated liquid layer during bubble growth. The dual tracer laser-induced fluorescence thermometry technique combined with high-speed imaging captures transient 2D temperature distributions within a 0.3 ºC accuracy at a 30 μm resolution. The results show that the temperature close to the heated surface and bubble interface exhibits an acute transient behavior at the time of bubble departure, and the growing bubble works as a pump to remove heat from the surface with a temperature difference of up to 10 °C during its growth and departure. The experimental results are compared with data available in the literature to validate the accuracy of the technique. It was found that the heat transfer coefficient close to the bubble interface and heater is approximately 1.3 times higher than the heat transfer coefficient in the bulk liquid.

CFD simulation of a solar collector integrated with PCM thermal storage

AbstractThermal energy storage is indeed a valuable solution for addressing the time lag or mismatch between energy supply and demand. The study aims to computationally model the melting and solidification processes of phase change material (PCM) using ANSYS Fluent that utilizes the finite volume technique. The simulations provide insights into the shapes of the liquid fraction, corresponding times, and temperature distribution of the PCM particles under the given conditions. The study considers factors such as solar radiation, thermal conductivity, density, latent heat, and the melting temperature of the PCM. The study finds that paraffin wax melts more quickly under a higher average maximum solar irradiance of 985 W/m2, while a lower solar radiation of 300 W/m2 has the opposite effect. Enhanced heat transfer resulting from conduction within the molten PCM, especially at a thermal conductivity of k = 0.25 W/m·K, accelerates the melting process. The thermal conductivity of the PCM affects the overall performance of the thermal energy storage system. The study highlights the potential application of thermal storage for drying purposes. Through the controlled release of stored heat energy, thermal storage enables the provision of heat in the absence of sunlight.

Revolutionizing the latent heat storage: Boosting discharge performance with innovative undulated phase change material containers in a vertical shell-and-tube system

Abstract This paper examines the impact of various parameters, including frames, zigzag number, and enclosure shape, on the solidification process and thermal energy storage rate of a vertical phase change material (PCM) container. The study also assesses the effects of the flow rate of the heat transfer fluid as well as changing the materials of the PCM between RT35 and RT35HC. In addition, the study compares the framed versus unframed systems and, subsequently, the best case was tested with various zigzag pitch numbers before changing the zigzag-shaped structure to arc and reversed-arc. The findings are examined by contrasting the different scenarios’ liquid fractions, temperature distributions, solidification rates, and heat storage rates. The results show that the framed geometry is 66% faster to reach the target temperature compared with the unframed geometry and employing a zigzag enclosure in a PCM can significantly improve the solidification time and heat recovery rate. As the number of pitches in the zigzag enclosure increases, the improvement rate decreases but still improves the solidification time and heat recovery rate. The reversed-arc-shaped structure has the best performance compared with the other undulated surfaces. For the system with RT35HC, the discharge time is 55% higher compared with that of the system with RT35, while the discharge rate is 8.2% higher for the former during the first 3000 s of the discharging process.

Numerical study on the characteristics of sodium heat pipes for space application at operation limits

Sodium heat pipes are important thermal conductive components in space nuclear power sources. They efficiently transfer heat within the range of 500–1000 °C by utilizing the latent heat of phase change. However, their maximum heat transfer capacity is limited by various factors. In this study, numerical simulations were conducted to investigate the operating conditions of sodium heat pipes when encountering different heat transfer limits, with a focus on analyzing the vapor–liquid distribution and axial temperature distribution in evaporator section. It is revealed that as reaching the heat transfer limits, sodium heat pipes exhibit wall temperature fluctuations in evaporator section. When encountering the viscous limit, liquid aggregation occurs within the wick, causing discontinuous flow. As reaching the sonic limit, a vapor blockage zone forms at the outlet of evaporator section, disrupting the flow circulation within heat pipe. For the entrainment limit, the liquid inside wick is carried away by vapor flow, reducing the amount of liquid involved in phase change cycle. As in the capillary limit, inadequate liquid reflux leads to thinner liquid layer, weakening the flow circulation. During the transition from the viscous limit to the sonic limit, no significant phenomena of phase distribution occur in the evaporator section. As the sonic limit and the entrainment limit act together, both vapor blockage and liquid entrainment occur, accompanied by liquid accumulation. The phenomena when the entrainment limit and the capillary limit act together differ from those occurring individually. The simulation results provide references for a deeper understanding of heat transfer limit mechanism and other operating characteristics.

Numerical study of phase change heat accumulator with distribution of Hanoi tower-shaped fin

Hanoi tower-shaped fin distribution was proposed to improve the shell-and-tube phase change accumulator's ability for heat storage. Unlike the common annular fin group, the fin spacing of the Hanoi tower-shaped fin distribution is distributed in an arithmetic sequence, the fin length increases in a fixed proportion, and the fin group's overall position changes with the bottommost spacing. In this paper, the effects of no fin, uniform fin distribution, and Hanoi tower-shaped fin distribution on the melting process were compared and analyzed. The single-factor effects of bottommost spacing, spacing tolerance, and length ratio were analyzed for the Hanoi tower-shaped fin distribution. The solid–liquid phase change frontier, melting time, temperature distribution, and streamline distribution were simulated and studied for different fin structures. Fins' combined effects on heat conduction and natural convection were examined. The Hanoi tower-shaped fins' structural parameters were optimized by applying response surface methodology (RSM). The results indicated that the Hanoi tower-shaped fin distribution considerably enhanced the phase change material's (PCM) melting rate and uniformity in the vertical circular tube heat accumulator. The significance levels of factors affecting the whole melting time were spacing tolerance (d) < length ratio (k) < bottommost spacing (P1). Within a certain range, the larger the bottommost spacing was, the synergistic heat transfer effect of natural convection and heat conduction was better. According to the RSM optimization results, when the length ratio was 1.2, the fin's bottommost spacing was 17.82 mm, and the spacing tolerance was 3.38 mm, the model had the shortest melting time. Compared with the uniform fin distribution, the total heat storage time was reduced by 18.04 %.

Theoretical Study of Liquid Flow and Temperature Distribution in OF-Cooled Power Transformers

The objective of the paper is to analyse the effects of various geometrical and operating parameters on the liquid flow distribution in OF-cooled power transformers. Our investigation includes two cases: one with a simplified winding geometry and another that closely resembles the actual winding geometry. The analyses were carried out using computational fluid dynamics (CFD) and custom, internally developed thermo-hydraulic models. Our findings confirm that buoyancy forces rather than the pump drive the liquid flow within the windings of an OF-cooled power transformer. The results also show that the liquid flow distribution, which is influenced by the winding geometrical properties and liquid properties, has a significant impact on the hot-spot temperatures of the windings. The comparison between the results of the CFD simulations and the results of the simple model demonstrates a high level of agreement in calculating both the mass flow rates and temperatures.

Heat transfer near a growing bubble during nucleate boiling using dual-tracer laser-induced fluorescence thermometry

Boiling heat transfer associated with bubble growth is perhaps one of the most efficient cooling methodologies due to its large latent heat during phase change. Despite the significant advancements, numerous questions remain regarding the fundamentals of bubble growth mechanisms, which is a major source of enhanced heat dissipation. This work aims to accurately measure three-dimensional (3D), space and time-resolved, local liquid temperature distributions surrounding a growing bubble to quantify the heat transfer in the superheated liquid layer during bubble growth. The dual tracer laser-induced fluorescence thermometry technique combined with high-speed imaging captures transient 2D temperature distributions, that will render 3D temperature distributions by combining multiple 2D layers, within a 0.3 °C accuracy at a 30 μm resolution. Two fluorescent dyes, fluorescein and sulforhodamine B, were used to measure transient temperatures, by account of their temperature-sensitive emissions. The results show that the temperature close to the heated surface and bubble interface exhibits an acute transient behavior at the time of bubble departure. The growing bubble works as a pump to remove heat from the surface with a peak temperature difference of up to 10 °C during its growth and departure. The experimental results were compared with previously reported studies to validate the accuracy of the technique. It was found that the heat transfer coefficient close to the bubble interface and heater is approximately 1.3 times higher than the heat transfer coefficient in the bulk liquid.

Simulation and optimization of square fin concentric tube heat storage exchanger

The square fin was used to improve the heat transfer rate of the concentric tube phase change heat exchanger. The effects of fin spacing, fin arrangement, and fin length on the melting process of phase change material (PCM) were studied. The influence and mechanism of non-uniform fin arrangement were discussed in detail. The liquid phase distribution and temperature distribution of PCM with time were analyzed. The results indicated that the heat exchanger with square fins can significantly improve the heat storage rate and shortened the complete melting time of PCM. Compared with heat exchangers without fins, the melting time of PCM in a 40 mm equidistant fin heat exchanger was shortened by 15.85%, and that in a 70 mm, non-uniformly spaced fin heat exchanger was shortened by 36.79%. Due to the different distances between the square fins and the outer boundary of the concentric tube, the temperature distribution near the square fin showed anisotropy, which enhanced the melting rate of PCM. The sensitivity order was fin arrangement &gt; fin length &gt; fin spacing. The research results can provide a reference for the design of phase change heat exchangers.

A molecular-kinetic theory based model for alkali liquid metal boiling incipience analysis

Boiling can lead to unexpected heat transfer performance of the components using alkali liquid metal (ALM) as working fluid for high thermal conductivity. Thus study on incipient boiling superheat of ALM is important to the design and safety operation of related components. However, existing data are in large scatter and some important parameter trends are inconsistent, indicating that more research should be done to understand the basic mechanism of ALM boiling incipience. In this paper, the local heat transfer of a wall cavity was investigated and the molecule performance at the three-phase contact line (TPL) was analyzed with molecular-kinetic theory. It was found that during transient process, the liquid temperature distribution near the interface in the cavity may result in considerable unbalanced molecule displacement at TPL and change the contact angle significantly. By estimating the evaporation rate at TPL with interface deformation rate and local temperature gradient, a model which could correlate nucleation contact angle as well as nucleation superheat with heat flux, velocity and interface deformation rate was established. The model was then used to predict the nucleation superheat data involving effects of temperature ramp, heat flux and velocity, and good agreement was gained. Besides, the characteristics of nucleation superheat of different heating methods were also analyzed and the trend of velocity effect was discussed, and some phenomena observed in different experiments were explained.

Two-phase Stefan problem for generalized heat equation with nonlinear thermal coefficients

In this article we study a mathematical model of the heat transfer in semi infinite material with a variable cross section, when the radial component of the temperature gradient can be neglected in comparison with the axial component. In particular, the temperature distribution in liquid and solid phases of such kind of body can be modeled by Stefan problem for the generalized heat equation. The method of solution is based on similarity principle, which enables us to reduce generalized heat equation to nonlinear ordinary differential equation. Moreover, we determine temperature solution for two phases and free boundaries which describe the position of boiling and melting interfaces. Existence and uniqueness of the similarity type solution is provided by using the fixed point Banach theorem.

Investigation on the heat discharge performance of a bioinspired latent heat exchanger with leaf-like fins

The low energy efficiency of phase-change thermal storage technologies leads to slow progress in promoting sustainable energy. To address this, here constructs a creative leaf-like fin and designs a bioinspired latent heat exchanger (LHE) using phase change materials (PCMs). A two-dimensional model of solidification processes considering natural convection is developed and solved numerically. The phase-change behaviors and dynamic thermal characteristics of different LHEs are investigated. Moreover, material selections and operating conditions of LHEs are studied, focusing on their effects on discharge performance. The results imply that the innovative leaf-like fin strengthens discharge performance. Compared to conventional LHEs, bioinspired LHEs shorten complete solidification time by 41.6% and increase average discharge power by 69.9%. Since the solidification procedure is driven by heat-conduction, the temperature stratification is only apparent in the early stage, while the solid–liquid phase interface and temperature distribution are almost axisymmetric for most solidification processes. For material selections, aluminum is recommended based on the trade-off between cost and thermal enhancement gain, and Stearic acid has apparent advantages in achieving satisfactory heat discharge performance for PCMs selected in this paper. Moreover, the lower temperature of the heat transport fluid facilitates the discharge rate enhancement for practical engineering.

Thermal elaboration of ethylene glycol-based magnetized nanostructures via a convective permeable heated vertical surface employing modified Buongiorno model

The current goal of the research is to investigate a mathematical model for chemically reacting nanofluids with Brownian movement and diffusive thermophoretic. The present flow model is articulated with the employ of novel thermophoretic diffusion, Brownian motion considering Au, Ag and Cu nanoparticles with ethylene glycol as base fluid. The basic model equations are changed to a dimensionless non-linear coupled ordinary differential equation adopting the competent similarity variables and then solved implementing Runge-Kutta Fehlberg-45 order numerical quadrature (shooting technique) is utilized. The outcomes obtained for momentum, angular flow rate, energy, and concentration on numerous motion parameters are introduced pictorially. Computed values for the device surface friction, local thermal and mass gradients are tabulated. The outcomes reveal that thermophoresis parameter is favorable to improve the liquid temperature and concentration distribution. The impact of nanoliquid reacting species reduced the nanoparticle concentration entirely in the stretching plate. Furthermore, computed outcomes are proved for restraining cases by comparison with numerous surveys and found outstanding accuracy.

Impact of Marangoni effect of oxygen on solid–liquid interface shape during Czochralski silicon growth applied with transverse magnetic field

This study investigated the impact of the Marangoni effect of oxygen on the solid–liquid interface shape in the silicon single-crystal growth process by the transverse magnetic-field-applied Czochralski (Cz) method. To this end, the results of a 3D heat and mass transfer analysis were compared with the experimental results. The findings of the study revealed that the Marangoni effect of oxygen affected the solid–liquid interface shape predicted by the simulation. Moreover, with the introduction of this effect, both the solid–liquid interface shape and temperature distribution of the melt were found to be in good agreement with the experimental values.

Performance enhancement of triplex tube latent heat storage using fins, metal foam and nanoparticles

The inherent low thermal conductivity of latent heat storage materials hinders its effective use due to quite long charging/discharging process. Heat transfer enhancement techniques are promising solutions to overcome this major drawback. In this study, the effect of combining heat transfer techniques including fins of different arrangements, fins-nanoparticles, and fins-metal foam is numerically examined and compared for latent thermal energy storage in a triplex tube. Two fin configurations are examined uniform as well as non-uniform. The predictions of the numerical model are validated by comparisons with experimental data available in the literature. The transient liquid fraction, temperature distribution, and interface position are analyzed for the considered cases. Results show that the non-uniform fin arrangement contributes to improving the thermal energy storage. The non-uniform fin distribution expedites the melting rate by 56.45%. Furthermore, it is shown that the combination of fins-metal foam outperforms the fins-nanoparticles configuration. The time needed for full charging and discharging reduces with fin-metal foam by up to 80.12% and 90.04%, respectively, depending on the fin arrangement. The proposed storage model and results are useful for designing efficient thermal energy storage units.

Study on improving the storage efficiency of ocean thermal energy storage (OTES) unit by using fins

It is a central challenge for energy self-supplied underwater vehicles converting the huge ocean thermal energy to electrical energy effectively. However, the energy storage efficiency of ocean thermal energy storage (OTES) unit limits the conversion efficiency. Fins are proposed for OTES unit to improve energy storage efficiency in this paper. Firstly, this paper develops a non-stationary model of solidification heat transfer for OTES unit and uses FLUENT to accomplish its numerical analysis. Then, the influence of radial fin and fractal fin on the solidification behavior of phase change material (PCM) are compared. Finally, several fractal fins with different fractal levels, bifurcation angles and ambient temperature are analyzed for the evolution of the liquid phase rate and temperature distribution of PCM. The results show that fractal fins can reduce the solidification time of PCM by 34.46% compared with radial fins. Furthermore, the solidification rate of PCM can be improved by increasing the number of fractal levels and choosing a proper bifurcation angle. However, the solidification behavior of PCM changes slightly when the fractal level increases to 3. The bifurcation angle of 90° is appropriate for practical applications. Furthermore, keeping the temperature difference above 10K can achieve faster solidification.

Visualization experiment and numerical study of latent heat storage unit using micro-heat pipe arrays: Melting process

This study conducts experimental visualization and numerical study on the melting of phase change material (PCM) in a rectangular enclosure of a latent heat storage unit based on micro-heat pipe arrays. The solid–liquid interface and temperature distribution in the melting of PCM are recorded by photographic observation and data measurement. Numerical results based on the enthalpy–porosity model are validated by using experimental results. The effects of enclosure geometry on the melting process of PCM are numerically explored. The transition point of a pure conduction mode into the natural convection mode is analyzed by comparing the results obtained in the numerical simulation with and without considering thermal convection. The correlations of the transient heat transfer and the melting rate in the pure conduction and natural convection modes are determined through the analysis of the different heat transfer characteristics in both stages. The results are expected to provide guidance for the design of latent heat storage units using micro-heat pipe arrays in engineering applications.

Imaging of liquid temperature distribution during microwave heating via thermochromic metal organic frameworks

Microwave has been widely used as an efficient and clean method for energy supply in chemical engineering, due to its unique heating characteristics. The industrialization of microwave is obstructed by the problem of uneven heating; the inhomogeneous temperature distribution results in inaccurate prediction of reaction kinetics, uncertain product yields, and unstable energy utilization efficiencies. With the aim to overcome this problem, we use a non-contact nano-thermometer to achieve in situ imaging of liquid temperature distribution during microwave heating. A zinc-based metal organic framework material (ZMOF) is employed as the temperature indicator in microwave field, due to its microwave transparency, thermal stability and good dispersibility in solvents. A case study was conducted by dispersing the ZMOF particles in a 95% ethanol solution, where the color of ZMOF changes from yellow to orange with the increase of temperature in the range of 30–120 °C with the sensitivity of 1.512%/°C. By linearly correlating the hue value of ZMOF suspension with the temperature, the color images of liquid heated in microwave cavity were transformed into temperature distribution maps. ZMOF also has shown the advantages of good dispersion, cyclic temperature measurement, continuous linear discoloration, and visible light excitation. This facile route of temperature field imaging can provide experimental validation for numerical simulation and guide the equipment optimization in microwave-assisted chemical engineering.

Experimental analysis and transient numerical simulation of a large diameter pulsating heat pipe in microgravity conditions

A multi-parametric transient numerical simulation of the start-up of a large diameter Pulsating Heat Pipe (PHP) specially designed for future experiments on the International Space Station (ISS) are compared to the results obtained during a parabolic flight campaign supported by the European Space Agency. Since the channel diameter is larger than the capillary limit in normal gravity, such a device behaves as a loop thermosyphon on ground and as a PHP in weightless conditions; therefore, the microgravity environment is mandatory for pulsating mode. Because of a short duration of microgravity during a parabolic flight, the data concerns only the transient start-up behavior of the device. One of the most comprehensive models in the literature, namely the in-house 1-D transient code CASCO (French acronym for Code Avancé de Simulation du Caloduc Oscillant: Advanced PHP Simulation Code in English), has been configured in terms of geometry, topology, material properties and thermal boundary conditions to model the experimental device. The comparison between numerical and experimental results is performed simultaneously on the temporal evolution of multiple parameters: tube wall temperature, pressure and, wherever possible, velocity of liquid plugs, their length and temperature distribution within them. The simulation results agree with the experiment for different input powers. Temperatures are predicted with a maximum deviation of 7%. Pressure variation trend is qualitatively captured as well as the liquid plug velocity, length and temperature distribution. The model also shows the ability of capturing the instant when the fluid pressure begins to oscillate after the heat load is supplied, which is a fundamental information for the correct design of the engineering model that will be tested on the ISS. We also reveal the existence of strong liquid temperature gradients near the ends of liquid plugs both experimentally and by simulation. Finally, a theoretical prediction of the stable functioning of a large diameter PHP in microgravity is given. Results show that the system provided with an input power of 185W should be able to reach the steady state after 1min and maintain a stable operation from then on.