Vertical Cylindrical Enclosure Research Articles

Experimental and numerical evaluation of phase-change material performance in a vertical cylindrical capsule for thermal energy storage

• Laboratory study of melting in a vertical cylinder heated from the bottom/side. • Directly visualized experimental results of convective and close-contact melting. • Original in-house numerical model encompassing all basic physical phenomena. • Melting patterns in a vertical cylindrical enclosure under realistic conditions. • Conclusions relevant for latent heat thermal energy storage units design. Thermal energy storage (TES) is considered vital for the advancement of renewable energy solutions. Latent heat thermal energy storage (LHTES) captures the thermal energy via a solid-liquid phase transition that occurs in phase-change materials (PCM). The PCM is usually encapsulated in some way. In this study, we consider PCM melting in a vertical cylindrical enclosure, that is a prototype of a capsule used in a future storage system. Moreover, we achieve the highly desirable close-contact melting (CCM), which speeds up the charging process significantly. First, different types of experiments are conducted to elucidate the melting behavior in an original experimental device that allows different types of melting in such configuration, demonstrating the prominent role of close-contact melting. The device main features are transparency of the melting chamber, separate heating methods for the periphery and the bottom of the chamber, and axisymmetric melting. To further investigate the heat transfer modes in the system, an in-house numerical model for combined convective and close-contact melting in an axisymmetric cylindrical geometry is validated with the experimental results. Then, this original model is used to simulate a vertical cylindrical shell in a practical configuration, namely, when an enclosure is exposed to fluid flow normal to its bottom. The results clearly illustrate the importance of close-contact melting for the overall melting process under practical conditions. The conclusions from this work would aid the design of LHTES installations which involve macro-encapsulated PCM.

Combined close-contact and convective melting in a vertical cylindrical enclosure

The use of phase change materials (PCM) for latent heat thermal energy storage (LHTES) is receiving considerable amount of attention in recent years. Experimental findings have demonstrated that the so-called ‘close contact melting’ (CCM) enhances heat transfer during the melting process remarkably. Yet, the commercially-available numerical schemes are not suitable for the modeling of CCM. Therefore, in this study a new numerical model for combined convective and close-contact melting in an axisymmetric cylindrical geometry is devised. A full set of the governing conservation equations is solved using finite differencing framework, integrated with an advanced immersed boundary method for the fluid-solid interaction and enthalpy formulation for the phase change process into an original in-house code. First, the model is validated carefully for each physical phenomenon with known benchmarks. Then, a numerical study is conducted to elucidate the melting process in a vertical cylindrical enclosure heated isothermally from the bottom and side wall. Twelve study cases are considered in order to reveal the transient phase-change sequence dependence on the aspect ratio and the excess temperature. Detailed data on the flow and temperature fields are obtained. The overall results are generalized using a dimensional analysis, which includes the Fourier, Stefan and Archimedes numbers and the enclosure aspect ratio. A correlation for the melt fraction, suitable for all cases studied, is suggested.

Performance Assessment of Nano-enhanced Phase Change Material for Thermal Storage

The use of nano phase change material in thermal energy storage applications appears promising, but the often-poor performance and the lack of understanding of the heat transfer mechanisms interconnectedness remains a challenge and hinders their widespread integration. The existing numerical work has unveiled numerous impediments in predicting the actual melting behaviour. They rarely combine the effects of conduction enhancement, convection degradation, and latent heat reduction, due to inaccurate characterization of the thermophysical properties and the limitations of their model assumptions. In the present study, an enhanced numerical approach was developed to investigate the melting performance of xGnP-octadecane filled in a vertical cylindrical enclosure at different weight concentrations. The model results for the pure phase change material were compared and validated against the experimental data. The progression of the melting front, temperature probes, energy storage capacity and heat transfer rate of the nano phase change material were thoroughly evaluated. The current numerical observations demonstrate that the addition of nanoparticles improves, up to a critical concentration of 0.5wt%, the melting rate. The results showed that by adding 0.5wt% of xGnP in the base phase change material (octadecane), the melting rate decreases by 9.7% and the heat storage rate increases by 12.6%. However, at higher loadings, the heat transfer rate is deteriorated due to worsening of other thermophysical properties provoking the prevalence of viscous forces over natural convection and latent capacity. The system overall efficacy was found to be dependent on the net effects of relative changes of all thermophysical properties with nanoparticle concentration and temperature in the solid, so called mushy, and liquid zones. Finally, when characterizing nano phase change material, the thermal conductivity cannot be considered alone as a criterion for nano phase change material selection. A high thermal conductivity is needed for maximum heat absorption in thermal transport applications. Nevertheless, low viscosity, high latent heat and specific heat capacities are also essential to ensure a better thermal energy storage efficiency in terms of capacity and heat extraction/release rate.

Numerical simulation and experimental verification of constrained melting of phase change material in cylindrical enclosure subjected to a constant heat flux

The transient melting process of the phase change material (PCM) is controlled by heat conduction and natural convection. Several experimental investigations are essential to understand the heat transfer mechanisms and performance for different designs of PCM thermal storage systems. Therefore, the present study experimentally investigated paraffin wax's melting process in a vertical cylindrical enclosure. The PCM, initially at 30 °C, was heated using an electric heater located at the center of the enclosure. The heat flux density varied to 1300, 1000, and 700 W/m2. Local temperatures of the PCM were measured, and the solid-liquid interface was tracked. A CFD (computational fluid dynamic) model was developed to numerically investigate the melting process with and without considering the convection effect. The CFD model was validated with the current experiments and with data from the literature. A very good agreement was obtained. The results showed that; the melting was initially dominated by conduction at an early stage, and this period increased with a decrease in heat flux. Natural convection was promoted, at a later time, leading to a curved shape of the solid-liquid interface. Numerical results indicated a robust thermal stratification of the molten liquid in the upper half of the storage unit. It was observed that increasing the input power from 700 W/m2 to 1000 W/m2 and 1300 W/m2 decreased the total melting time by 24.82% and 43.58%, respectively. It is recommended for the future modeling of the PCM melting process to consider the convection effect.

Natural convective heat transfer characteristics of Al<sub>2</sub>O<sub>3</sub>-water nanofluids in a vertical cylindrical enclosure

Natural convective heat transfer characteristics of Al<sub>2</sub>O<sub>3</sub>-water nanofluids in a vertical cylindrical enclosure

Natural Convection Heat and Mass Transfer in the Vertical Cylindrical Porous Channel Under the Effects of Time-Periodic Boundary Condition

Abstract Heat and mass transfer are investigated numerically with steady-state laminar natural convection through a vertical cylindrical enclosure filled with a liquid-saturated porous medium. The vertical wall is under a constant magnetic field and various durations of periodic heating boundary condition; the top and bottom surfaces are kept at a constant cold temperature. Continuity, momentum, and energy equations are transformed to dimensionless equations. The finite difference approach with the line successive over-relaxation (LSOR) method is used to obtain the computational results. This study covers the heat transfer, the temperature distribution, and the velocity field in the domain under the variation of different parameters. The code used is validated by modifying it to analyze the Nusselt number in the existing experimental literature of Izadpanah et al. (1998, “Experimental and Theoretical Studies of Convective Heat Transfer in a Cylindrical Porous Medium,” Int. J. Heat Fluid Flow, 19(6), pp. 629–635). This work shows that Nusselt number decreases (with varying gradient) as the aspect ratio increases, and that it increases as the Rayleigh number increases. The centerline temperature has a proportional relationship with the heating amplitude and the heating period (as the system receives more heat) and is inversely proportional with Rayleigh number. Increasing the Rayleigh number causes increased convective velocity, which affects the position of the hot region, and causes a decrease in the temperature field. Increasing the aspect ratio results in a warm stream at the center of the cylinder, and when the time period of the heating increases, the circulation becomes faster and the intensity of the temperature contour layers decreases. In this work, a correlation for Nu as a function of the mentioned parameters is developed.

Conjugate unsteady natural heat convection of air and non-Newtonian fluid in thick walled cylindrical enclosure partially filled with a porous media

A numerical study describes the conjugate unsteady natural heat convection of air on top of a non-Newtonian polymer-water solution characterized by a power-law model within a sealed vertical thick-walled cylindrical enclosure partially filled with a porous media in the lower section. Enzymes immobilized in an inorganic polymer, silica, used in synthesis processes constitute the porous media. Heating is by a constant high temperature at the bottom and at the vertical walls while the upper horizontal wall remains at the initial cold temperature. The Finite Volume Method allows the solution of the continuity, linear momentum and energy equations for a power law shear thinning fluid in a porous media with the Darcy-Brikman-Forchheimer model. The evolution of fluid mechanics of air and of the non-Newtonian fluid is described by the history of the streamlines. Transient heat transfer by conduction in the sealed tube walls and by natural convection of air and in the non-Newtonian fluid flow in the porous media is characterized by the evolution of isotherms. Experimental results are used to verify that the natural convective heat transfer conjugate computational model allows the prediction of temperature evolution in a thermal resistance challenge for free and immobilized enzymes. A difference of 1% is found between the experimental and the numerical results for the temperature history during the immobilized enzyme convective heating process. The applied numerical method has the capability of designing the enzyme temperature challenge test, by predicting the time needed to reach the uniform target temperature for biocatalyst processing, 500 s, in agreement with the experimental findings. The computational model contributes to the development of a technique to describe the kinetics of both immobilized and free enzyme during heating. This is a key issue for several industries, such as food modification, biofuel development, agroindustry and fishery waste valorization, that require enzymes operating at high temperature ranges in a reliable way for a long time.

Experimental investigation of natural convection flow in a laterally heated vertical cylindrical enclosure

Vertical cylindrical enclosures are used in the crystal growth industry as crystal growth reactors. Gallium nitride crystals are grown in ammonothermal growth reactors that requires temperatures in the range of 600–1000 K (620–1340 °F) and pressures in the range of 1000–6000 bar (14,504–87,022 psi). The process conditions make any experimental measurements difficult, in particular, flow pattern visualization and velocity measurements. A geometrically similar transparent reactor and similar fluid dynamic conditions for crystal growth were used in the process of experimental observation and measurement of the flow. Boundary and fluid temperatures along with velocity vectors were recorded. The flow proved to be oscillating in nature with steady and uniform time-averaged patterns. Fluid temperatures showed a higher standard deviation in the mixing region suggesting that the fluctuations are stronger at this location. Flow patterns and fluid temperatures indicated that the heat transfer between the two sections is driven by conduction and advection.

Numerical simulation of natural convection heat transfer of copper-water nanofluid in a vertical cylindrical annulus with heat sources

In this work, natural convection of Cu—water nanofluid in a vertical cylindrical annulus enclosure with two discrete heat sources of different lengths is numerically investigated using the finite volume method with SIMPLER algorithm. The adiabatic unheated portions and the discrete heat sources are mounted at the inner wall. The top and bottom walls are thermally isolated, while the outer wall is maintained at a lower temperature. The effects of nanofluid solid volume fraction on hydrodynamic and thermal characteristics such as average and local Nusselt numbers, streamlines, and isotherm patterns for the Rayleigh number ranges from 103 to 106 and solid volume fraction ranges from 0 to 0.1 are presented. The heat transfer and temperature of heaters depend on the Rayleigh number, the solid volume fraction of nanoparticles, and the length of heaters.

Numerical Study of Natural Convection in Vertical Cylindrical Annular Enclosure Filled with Cu-Water Nanofluid under Magnetic Fields

The two dimensional study of natural convection in vertical cylindrical annular enclosure filled with Cu-water nanofluid under magnetic fields is numerically analyzed. The vertical walls are maintained at different uniform hot and cold temperatures, THand TC, respectively. The top and bottom walls of the enclosure are thermally insulated. The governing equations are solved numerically by using a finite volume method. The coupling between the continuity and momentum equations is effected using the SIMPLER algorithm. Numerical analysis has been carried out for a wide range of Rayleigh number (103≤Ra≤106), Hartmann number (1 ≤Ha≤100) and nanoparticles volume fraction (0 ≤φ≤0.08). The influence of theses physical parameters on the streamlines, isotherms and average Nusselt has been numerically investigated.

Mathematical and Numerical Modeling for Energy Valorization of Sugarcane

This study concerns the numerical modeling of the pyrolysis of sugarcane waste. The potential application of pyrolysis products obtained (fuel) is in use in domestic or industrial combustion plants. To facilitate the digital modeling of the process of pyrolysis, the waste particles are assumed arranged in a vertical cylindrical enclosure (fixed bed). Their heating is provided by an ascending vertical stream of hot inert gas. Solving the equations of the balances on a two-dimensional flow and nonstationary provides the axial development of the temperature, the solid concentration of the carbonaceous residue (coke) and the pyrolysis gas. The method of finite differential was used for spatial discretization of the equation system, and method of Rang-Kutta order4. After validation, this model was applied to a configuration of a fixed bed. The results are in good agreement with the experimental results reported in the literature.

An investigation of the melting process of RT-35 filled circular thermal energy storage system

Abstract One of the main solutions to the issue of global warming and greenhouse gas emission caused by burning fossil fuels is storing energy in an efficient way. In this work, the detailed melting process of RT-35 as a phase change material (PCM) inside a cylindrical latent heat thermal energy storage (TES) system is investigated both numerically and experimentally. To achieve this aim, an experimental setup comprising of a transparent vertical cylindrical enclosure as a latent heat TES system, a constant temperature bath, and a temperature regulator is built. Moreover, a numerical model using COMSOL multiphysics is developed to simulate the melting process and provide a more detailed information on the flow and thermal fields. The model is able to provide the temperature and velocity fields, heat transfer behaviour, melting fraction, and the trend of solid-liquid interface at different time intervals. To validate the numerical model, a comparison between melting fraction and solid-liquid interfaces of the numerical model and experimental work is conducted which shows a good agreement between experimental and numerical results.

Experimental investigations on the evolution of stratified layer of helium in the unventilated vertical cylindrical enclosure of AIHMS facility under wall temperature induced natural convection

An experimental facility called the AIHMS facility has been installed and commissioned within the IIT Madras premises, to study the phenomenology of hydrogen distribution in confined spaces and generate experimental data for validation of CFD codes before further studies on hydrogen distribution and mitigation in nuclear reactor systems can be carried out. In the present article, experimental studies have been performed on the evolution of the helium stratified layer due to wall temperature induced natural convection. The base case is an isothermal release of helium within the test chamber. Subsequently, two cases are considered in which the wall temperature is above or below the gas temperature in the enclosure. Experimental data has been obtained for gas concentration at seven locations and temperatures at twenty locations within the enclosure. The results show that recirculation regions are formed near the walls. Cooler walls lead to favourable natural convection currents and promote rapid mixing of the stratified layer with lean gas mixture below. On the other hand, warmer walls lead to unfavourable natural convection currents that initially promote stratification and later on promote mixing at a slower rate. In either situation, the rate of mixing is faster than the isothermal case. Repeatability studies have been performed.

Natural convective heat transfer characteristics of Rayleigh-Benard convection of Al<sub>2</sub>O<sub>3</sub>-water nanofluids

Transient three-dimensional numerical computations are implemented to clarify the natural convective heat transfer characteristics of the Rayleigh-Benard convection of Al2O3-water nanofluids induced in a shallow vertical cylindrical enclosure. The thermophysical properties of nanofluids, assumed to be a single-phase fluid in the numerical computations, are estimated using the experimental correlation equations reported by Khanafer and Vafai (2011). When the average Nusselt numbers of nanofluids are plotted against the Rayleigh number defined by the thermophysical properties of water, computations for four different volume fractions of nanoparticles were below the average Nusselt number curve experimentally reported by Silveston (1958). The diagram also reveals that the increase of nanoparticles in the base fluid delays the generation of Rayleigh-Benard convection. However, the average Nusselt numbers of nanofluids almost agreed with the average Nusselt numbers of Silveston without depending on the volume fraction of nanoparticles when plotted against the Rayleigh number defined by the thermophysical properties of nanofluids. Thus, the natural convection heat transfer rates of Al2O3-water nanofluids can be considered to be similar to the general fluids reported by Silveston as long as experimental thermophysical properties are employed.

Experimental investigation on helium distribution and stratification in unventilated vertical cylindrical enclosure – Effect of jet release rates and total release volume

Hydrogen leakages into enclosed spaces may occur in hydrogen storage and usage facilities and in nuclear power plants (NPP) following a severe accident. In the absence of either mitigation or combustion processes, hydrogen leaked into the enclosed space may accumulate and form large cloud of explosive mixture with air. This, when gets ignited, can lead to a strong deflagration or even detonation and cause huge threat to both life and property. In NPP, such events can cause over-pressurization of the containment, causing problems in the structural integrity of the containment and consequently result in the leakage of radioactivity into the environment. The present study reports the experimental investigation of the phenomenology of hydrogen distribution inside a cylindrical test enclosure (AIHMS). Different hydrogen leak scenarios are experimentally simulated using helium gas, which is its inert surrogate. The effect of helium release velocities on mixing and distribution of helium within the enclosure, for different quantities of helium released has been experimentally investigated. The experimental studies are conducted in a test enclosure having a volume of around 2 cubic-meters, specifically designed for the purpose and the results have been presented systematically.

Anisotropic effect of natural convection on the temperature field in an enclosure in the presence of stable temperature stratification

Unsteady natural convection in a vertical cylindrical enclosure is numerically modeled in the case of heat input from above and from the side. The anisotropic effect of intense convection on the temperature field is established. It is shown that in the stratified region the temperature is well described by the time-dependent one-dimensional heat conduction equation with a three-dimensional heat source.

Heat transfer rate characteristics of the magnetothermal Rayleigh–Benard convection of paramagnetic air

We carried out complete transient three-dimensional numerical computations to clarify the heat transfer rate characteristics of magnetothermal Rayleigh–Benard convection of paramagnetic air induced by both magnetic and gravitational buoyant forces. The shallow vertical cylindrical enclosure filled with air was heated from below and cooled from above. The enclosure was assumed to be located inside the bore space of a superconducting magnet. In addition, the enclosure was fixed at the location where the magnetic force in the axial direction was more uniform in the radial direction, as was the gravitational force. The average heat transfer rates were computed for various Rayleigh numbers and magnetic strengths. The results are plotted versus both the Rayleigh number and the magnetic Rayleigh number, Ram, defined by Braithwaite et al. in comparison with experiments by Silveston. For the range 2310 < Ram ≤ 10,000, the average Nusselt numbers are found to distribute around the data by Silveston. However, in the range Ram ≤ 2310, the average Nusselt numbers are overestimated compared to those by Silveston. Probably, this is because the magnetic force approximated with a one-turn coil includes radial directional acceleration force and the convection mode differs from the unidirectional gravitational one. On the other hand, in the rage, Ram > 10,000, the overestimated Nusselt numbers may be due to a linear model.

Simulation of heat pipe-assisted latent heat thermal energy storage with simultaneous charging and discharging

Abstract Melting and solidification of a phase change material (PCM) held within a vertical cylindrical enclosure that is integrated with a heat pipe (HP) is simulated as a single module. The HP is heated from the bottom to melt (charge) the PCM that is positioned in the middle of the HP length, and is cooled from the top to solidify (discharge) the PCM. Three modes of operation are considered in this study (i) charging-only, (ii) simultaneous charging and discharging, and (iii) discharging-only. All modes of operation are handled with a single HP within a PCM (single HP-PCM) of which the top and bottom sections are inactivated during charging-only and discharging-only modes, respectively. A parametric study of the influence of the PCM enclosure height and input/output heat transfer rates shows that, for the same mass of PCM, a longer enclosure exhibits a lower HP bottom average wall temperature and relatively more PCM melting during simultaneous charging and discharging. Increasing either the input, output, or both heat transfer rates has a significant effect on the temperature of the HP bottom and top sections, but only a minor impact on the temperature of the HP middle section.

Three-dimensional PCM melting in a vertical cylindrical enclosure including the effects of tilting

Experiments have been conducted in order to generate detailed data associated with the outward melting of a PCM induced by a heated rod that is placed concentrically within a cylindrical enclosure. Heat transfer and melting effects in a base-case configuration consisting of a vertically-oriented enclosure are successfully simulated with an established two-dimensional numerical model, partially validating the experimental apparatus and procedure. Experimental measurements indicate that modest tilting of the test cell significantly affects measured local temperatures within the PCM, as well as the temporal evolution of the solid morphology as it melts. The modification is attributed to the establishment of three-dimensional flow within the molten PCM. The experimental data for the tilted enclosure cases might be used to validate three-dimensional models for PCM melting in geometrical configurations relevant to, for example, latent heat thermal energy storage systems.

CFD analysis of heat transfer within a bottom heated vertical concentric cylindrical enclosure

The CFD analysis of heat transfer within a bottom heated vertical concentric cylindrical enclosure is important with respect to the process in the chemical and process industries. The research work focuses on the CFD analysis of the enclosure with respect to the machines used for the segregation of chemicals in the chemical industries. The CFD simulations are performed to study the effects of inner cylinder material and outer cylinder geometric configurations on the heat transfer mechanism in the enclosure. The CFD simulations are conducted at a bottom disc temperature of 393 K and compared with the published results at a temperature of 433 K. This research study depicts the behavior of bottom heated vertical concentric cylindrical enclosure at different bottom disc temperatures. This study also investigates the heat transfer mechanism of the enclosure using different inner cylinder materials and different configurations of the outer cylinder. In such enclosures a uniform temperature is required for the segregation of chemicals. A more uniform temperature is observed in the enclosure by using aluminum inner cylinder of the bottom disc and using two different diameter outer cylinders as compared to the mild steel and stainless steel.