Thermocline Thermal Energy Storage Research Articles

Multi-objective optimisation of a thermocline thermal energy storage integrated in a concentrated solar power plant

Most of CSP plants built today are all equipped with storage devices. Most are sensitive heat storages, in particular 2-tank systems. The aim of this study is to optimise a thermocline storage, designed for the Andasol CSP plant in Spain, on the basis of exergy, environmental and economic criteria. The optimum tank geometry, particle size and heat transfer fluid/filler material pair must be determined. To achieve this, six different fillers operating with Dowtherm A synthetic oil are being investigated: machined ceramics, ceramics obtained from waste materials and natural rock. The NSGA-II multi-objective genetic algorithm is used to solve the problem. This optimisation selects recycled ceramics as best filler materials. The exergy efficiency is not affected by the filler, with more than 99.8%. The application of TOPSIS method combined with weighting derived from Shannon entropy, selects recycled ceramic obtained from electric furnaces as the best filler. This tank has a tapered shape (diameter of 27.4 m, height of 22.2 m) and a very small particle diameter (6 mm). Compared with an earlier design available in literature, the environmental impact is reduced by 19%. The LCOE reaches 10.8 c€/kWhe, a 48% reduction compared with the selling price of heat in Spain (in 2021).

Characterization of the Ratcheting Effect on the Filler Material of a Steel Slag-Based Thermal Energy Storage

Thermocline thermal energy storage systems play a crucial role in enhancing energy efficiency in energy-intensive industries. Among available technologies, air-based packed bed systems are promising due to their ability to utilize cost-effective materials. Recently, one of the most intriguing filler materials under study is steel slag, a byproduct of the steel industry. Steel slag offers affordability, ample availability without conflicting usage, stability at temperatures up to 1000 °C, compatibility with heat transfer fluids, and non-toxicity. Previous research demonstrated favorable thermophysical and mechanical properties. Nonetheless, a frequently overlooked aspect is the endurance of the slag particles, when exposed to both mechanical and thermal stresses across numerous charging and discharging cycles. Throughout the thermal cyclic process, the slag within the tank experiences substantial loads at elevated temperatures, undergoing thermal expansion and contraction. This phenomenon can result in the deterioration of individual particles and potential damage to the tank structure. However, assessing the extended performance of these systems is challenging due to the considerable time required for thermal cycles at a relevant scale. To address this issue, this paper introduces a specially designed fast testing apparatus, providing the corresponding testing results of a real-scale system over 15 years of operation.

Experimental Evaluation of a Pilot-Scale Thermocline Thermal Energy Storage Combining Latent and Sensible Materials

This work presents the experimental evaluation of pilot-scale thermocline that integrates a layer of phase change material (PCM) at the top of a sensible heat storage material in a thermocline thermal energy storage (TES) tank. The TES is integrated to the MicroSol-R parabolic trough pilot plant at the PROMES research facility in Odeillo, France. The tank is filled with alumina spheres as sensible heat storage. The PCM is NaNO3 encapsulated in stainless steel horizontal tubes that fill about 5.5% of the tank volume. The charge is evaluated at three mass flow rates 2600, 3000, and 3900 kg/h at two different operating temperature ranges 285-315 ºC and 295-330 ºC. The discharge is studied at three mass flow rates 1600, 2000, and 3000 kg/h from 315 to 220 ºC and 330 to 225 ºC. The performance of the TES is analyzed with two main indicators: the thermocline thickness and the efficiency during the charge and discharge. The results indicate that lower mass flow rates during the charging process result in smaller thermocline thickness. Similarly, during discharge, the thermocline thickness reduces with lower discharge rates. Efficiency evaluation during discharge suggests that an optimal flow rate could be achieved.

Thermal energy storage with flexible discharge performance based on molten-salt thermocline and thermochemical energy storage

Thermocline sensible thermal energy storage has prospects in cost-effective thermal energy storage. In this study, we combined a molten-salt thermocline with thermochemical energy storage to improve the flexibility of thermal discharge performance. For the thermochemical energy storage material, a composite was synthesized using calcium hydroxide and silicon-impregnated silicon carbide foams with an energy capacity of 1.8 MJ (0.50 kWh) and volumetric energy density of 0.79 MJ L-material−1. The composite was loaded onto an indirect fixed-bed reactor that used molten salt as the heat transfer fluid. The temperature of the composite reached 637 °C at a hydration pressure of 812 kPa. The thermochemical energy storage reactor exhibited a variable maximum outlet temperature of the heat transfer fluid in the range 524–583 °C and maximum discharge power of up to 0.6 kW (discharge power density up to 0.25 kW L-material−1) on changing the hydration pressure and flow rate of the heat transfer fluid. The results confirm the significance of thermochemical energy storage to the system in boosting the temperature of the thermocline and variable discharge performance. The novel hybrid system has a superior discharge performance compared with that of the conventional thermocline thermal energy storage, and it is a promising option for flexible large-scale energy storage and power generation driven by renewable energy.

Numerical Research on Thermodynamic Properties of a Thermocline in Thermal Energy Storage Tank Based on Modified One-Dimensional Dimensionless Model

The application of thermal energy storage (TES) has been proved effective to improve the energy utilization efficiency of renewable energy and industrial waste heat energy. In this paper, a modified one-dimensional dimensionless model for the thermocline thermal energy storage tank is derived to simulate the system more accurately. An adaptive strategy for solving region compartmentalization is proposed for reducing computing time. Based on the proposed model, the effects of three different parameters on the performance of the thermocline tank are studied. The results show that increasing the inlet velocity can reduce the thickness of the thermocline and improve the system efficiency. Increasing the temperature difference between hot and cold water leads to a thicker thermocline, but the thermal energy stored in the tank increases. Increasing the tank height has no effect on the motion characteristic of thermocline, but the system efficiency can be increased.

Compatibility Study between Ceramic Balls and Jatropha Curcas Oil Properties under Long Time Heat Treatment: Potentiality for Thermal Energy Storage

Valorisation of local and low-cost eco-materials have become an imperative for the sustainable development of Concentrating Solar Power (CSP) in West Africa. In this study, the compatibility tests were carried out. These involve the application of jatropha curcas oil (JCCO) and ceramic balls, which were developed from clay coal bottom ash and sands with a focus on Burkina dune sand ceramic. The aim was to assess the applicability of using JCCO as heat transfer fluid in CSPs with direct thermocline thermal energy storage. The tests involve the use of a small container to put in contact with Jatropha oil with ceramic balls for 2160 hours and at 210 °C. From the chemical properties’ analysis, the peroxide value in the oil decreases with aging time while the acidity increase. However, the acidity remains below the limited value that is 25 mg KOH.g-1. Therefore, thermal properties that drive heat transfer and rheological properties (density, thermal conductivity, kinematic viscosity and so on) were not adjusted significantly at the storage temperature (of about 210°C). Thermal stability temperature decreased to 261.93°C for the oil aged alone as against 263.41 °C for the one that was put in contact with filler material. In the nutshell, there is no incompatibility between JCCO, and the new thermal energy storage material (TESM) developed. These couple of materials could be suitable for thermocline energy storage in CSP plant and for other applications like there use in solar cooker box.

Impact of buoyant jet entrainment on the thermocline behavior in a single-medium thermal energy storage tank

This paper presents the characterization and management of dynamic thermocline behaviors in a single-medium thermocline (SMT) thermal energy storage tank with the aim of its performance improvement. In particular, the flow mixing induced by the entering thermal jet, its impact on the temperature stratification and its mitigation measure are systematically explored by both numerical and experimental methods. Results of CFD simulation and Particle Image Velocimetry (PIV) visualization clearly demonstrate the jet entrainment phenomenon and the typical flow patterns featured by the rising buoyant plumes. For the storage tank with simple inlet port, this thermal jet would cause the thermal overturning, the strong fluid mixing and convection heat transfer, resulting in the degradation of temperature stratification and the thermocline decay (Rigradient<0.25 at certain positions of the tank). It has also been shown by PIV measurement that the impact of thermal jet, characterized by the jet penetration length, becomes stronger with the increasing injecting flow rate and with the decreasing temperature difference between the injecting and existing fluids.Orifice baffle-type distributor has then been proposed and optimized, showing clearly its effectiveness for mitigating the impact of thermal jet on the temperature stratification. Both the initial uniform orifice baffle and the optimized orifice baffle distributors are then fabricated and installed into a lab-scale cuboid SMT storage tank. Charging operations are performed under different inlet flow rates (Qin: 0.3 to 1.5 L·min−1) and temperature differences between hot and cold fluids (∆T: 30 to 50 K). Experimental results obtained show that the optimized distributor could always lead to the better thermal performance (capacity ratio up to 0.94 and charging efficiency up to 0.8) than the initial uniform baffle distributor, providing more flexible operating conditions of the SMT storage systems in different industrial sectors.

Combining entropy weight and TOPSIS method for selection of tank geometry and filler material of a packed-bed thermal energy storage system

Thermocline thermal energy storage systems are promising alternatives for recovering waste heat lost by industry around the world. The aim of this work is to extend the methodology presented in previous work, by optimising an existing industrial packed-bed storage system on two geometric optimisation variables, considering exergy, environmental and economic aspects. Seven filler materials are compared for the same heat transfer fluid, to include discrete variables in the model. The multi-objective optimisation problem is solved using the NSGA-II multi-objective genetic algorithm. For each filler material, a Pareto set is obtained. The non-dominated solutions within the union of the different Pareto sets are then selected, which give a new single set of optimised solutions. A multi-criteria decision-making method (TOPSIS) is then applied to obtain the optimal solution. To avoid any subjective choice from the decision-maker by determining the objective weights of each of the optimisation criteria, the Shannon entropy is used. The combination of TOPSIS and Shannon entropy led to the selection of a recycled ceramic obtained from hard coal ashes as the best filler. This solution has a stocky tank shape (2.4 m diameter, 2.1 m height) and a small particle diameter (7 mm). The exergy and environmental performance is improved compared to the reference storage. They reach 98.0% (vs 95.6%) and 58 hab.year (vs 67 hab.year) respectively. The levelised cost of energy is close to that of the reference tank (3.35 vs 3.31 c€/kWhth).

CFD modelling of an indirect thermocline energy storage prototype for CSP applications

Thermocline thermal energy storage is a (potentially) cost-effective alternative to the more widespread two-tank solution, as both the hot and the cold medium are stored in a single tank.An innovative single-medium indirect thermocline technology was recently developed by ENEA and a prototype was experimentally tested at the Casaccia laboratories. The storage tank is equipped with two flat-coil heat exchangers (HXs) located at the bottom and at the top of the tank, for the charge and discharge phases, respectively. The storage medium is a mixture of molten salt (Hitec XL) and the heat transfer fluid is a mineral oil (Delcoterm Solar E15). An internal vertical channel, which assists the motion of the storage medium during the charge and discharge transients, connects the two HXs.In this paper, a detailed, transient 2D axisymmetric Computational Fluid Dynamics (CFD) model of the prototype has been developed. The model simulates the charge and discharge transients, determining the heat losses and the temperature distribution of the molten salt in the tank. The computational domain includes the storage medium, the tank insulated walls and the main components immersed in the molten salt, i.e., the heat exchangers and the vertical channel.The model has been first calibrated by best-fitting the data measured during a test conducted without any thermal load, then validated against another independent set of experimental data.A first comparison against a charge transient showed some discrepancies between the computed and the measured temperatures of the salt, which could be explained by assuming the presence of a bypass at the location of the HXs. This assumption is discussed and justified in the paper. The CFD domain has then been modified to include the bypass, and this allowed to successfully validate the model against experimental data in both charge and discharge phases.The validated model is finally exploited to assess how a variation in the diameter of the internal vertical channel could affect the thermal performance of the storage system in a charge transient. The results indicate that decreasing the channel diameter leads to an increase of the salt temperature at the very top of the tank at the cost of a longer time to fully charge the storage.

Thermal performance of cascaded and combined sensible-latent heat storage tank under fluctuations in sunlight and electric demand

Based on its composite construction and usage of low-cost filler materials, thermocline thermal energy storage technology, which uses the molten as a heat transfer fluid, is more expensive than a conventional two-tank storage system. However, when integrated with concentrated solar power plants, the thermocline tank type experiences a significant disadvantage of low capacity and utilization ratio due to fluctuations in solar energy availability or an alteration in the electrical demand. The major concern of this subject is to look into, determine, and assess the charge and release cycle systems using various storage designs and under fluctuations in solar energy availability or a change in electricity demand. To examine the tank's cyclical thermal properties, a two-phase mathematical approach is developed. The current numerical formulas have been solved using the MATLAB program, and the findings of this analysis have been verified. The findings show that the combined sensible-latent heat storage scenario has the highest capacity ratio of 52.4%, the utilization ratio of 45.5%, retrieved energy of 181.06 MWh, and comprehensive efficiency of 67.3% than the cascaded layers heat storage scenario at a charging time of 11 h.

Geometry optimisation of an industrial thermocline Thermal Energy Storage combining exergy, Life Cycle Assessment and Life Cycle Cost Analysis

Recently, packed-bed storage has been considered as a promising alternative solution for thermal energy storage especially for waste heat recovery in industrial plants. This work aims to optimise environmental footprint, costs and exergy efficiency of a thermocline thermal energy storage through two optimisation variables. These variables describe the tank shape and the particle grain size. Two solid filler materials are compared: machined ceramic and ceramic from fly ashes. The reference storage is an existing industrial high-temperature air/bauxite packed-bed storage called Eco-Stock®. A one-dimensional two-phase (fluid and solid) model is used to determine the energy and exergy performance of the thermocline tank. For the life cycle assessment, four indicators are selected: cumulative energy demand, global warming potential, abiotic depletion potential and particulate matter. Finally, a life cycle cost analysis is performed to determine levelised cost of energy used as economic criterion. This multi-objective problem is solved by the multi-criteria genetic algorithm available on the Matlab® platform. A Pareto set is obtained, bounded by the single exergy and environmental optimisation solutions. The economic optimisation is found on the Pareto set, close to the environmental optimal solution. Favouring economic performance reduces the environmental footprint of the storage. Despite better exergy performance and smaller tank volume, the exergy-optimised tank increases environmental impacts and costs due to higher pumping work. The environmental and economic optimisations lead to stocky tank shapes while a tapered tank is obtained for the exergy optimisation. According to the TOPSIS method, the economic optimal solution appears to be the best trade-off for both fillers tested. Despite poorer thermophysical properties, the solution with ceramic from fly ashes shows similar exergy and economic performance as the machined ceramic solution (more than 96 % of exergy efficiency for 3.1 c€/kWhth), while the environmental footprint is greatly reduced (61 vs 87 ca.year). This tank has a diameter of 2.6 m and a height of 1.7 m. The particle diameter is 11 mm.

Experimental and numerical investigation of the temperature and flow rate variation on an industrial high-temperature thermocline storage for recovering waste heat

For the valorization of industrial waste heat, the implementation of a thermal heat storage becomes essential. Since the waste heat fields show fluctuations in operating conditions, such as temperature and flow rate, a thermal energy storage must be able to accommodate these variations, by storing and then releasing this heat at constant temperature and flow rate. The aim of such a storage is to make the best use of the waste heat from industry. An industrial-scale high-temperature air/ceramic horizontal thermocline thermal energy storage (Eco-Stock®) has been tested through different operating parameters. The objective is to measure the influence of temperature and flow rate variations on the storage performance, in order to simulate a real heat ceramic process. The results revealed that the Eco-Stock® is able to store degraded heat fields and to restore heat at the average temperature of the heat field. As long as the characteristic time is an order of magnitude less than the charging time, the thermocline storage has a good energy performance. Despite gradual variations in temperature and flow rate during the charging process, the storage yield remains high and close to the reference storage (charging temperature of 525 °C). Indeed, it reaches 66% for an outlet temperature of 350 °C for all the temperature tests. For scenarios where the flow rate varies, the yield reaches up to 73.5% at 420 °C. When heat is supplied from a ceramic manufacturing process, the Eco-Stock® can achieve a yield of 68%, which is 5.5% less than the reference case. In addition, the numerical model predicts the storage performance very accurately, proving its ability to absorb high temperature and flow rate constraints.

Quasi-analytical study of dynamic performance of the thermocline heat storage system under time-varying inlet flow and temperature environment

The dynamic thermal performance of single-tank thermocline (STTC) thermal energy storage (TES) system under oscillating boundary conditions (BCs) during cloud cover or start-up period is critical to the safety and efficiency of the whole concentrating solar power (CSP) plant. In this study, the approximate analytical solution of the STTC TES system under oscillating velocity and temperature BCs are derived from the one dimensional-two phase (1D-2P) models, which can be applied in arbitrary realistic BCs with Fourier decomposition method. After model validation with dynamic experimental data, the effects of typical sinusoidal oscillating parameters on packed bed transport phenomena and TES efficiency were investigated. It is found both of the oscillating inlet velocity and temperature lead to degradation of thermal stratification, such as outlet temperature fluctuation, while it also causes enhanced heat transfer effect and increased charging/discharging cut-off efficiency. Cut-off efficiency increases with amplitude of oscillating inlet velocity or oscillating inlet temperature, while for oscillating frequency there is optimum value. On that basis, the general optimum equation of cut-off efficiency and oscillating frequency is proposed, and the relative error is smaller than 1.0% when outlet temperature is larger than 0.011 for the discharging process with oscillating inlet velocity BC and smaller than 3.2% for oscillating inlet temperature BC. Moreover, the thermocline region movement velocity increases with inlet velocity for oscillating inlet velocity BC and decreases with oscillating frequency for oscillating inlet temperature BC.

Development of an effective algorithm for selection of PCM based filler material for thermocline thermal energy storage system

Thermocline Thermal energy storage is an imperial technology to improve the reliability of solar thermal energy systems. Inorganic Phase Change Materials (PCM) are more promised filler materials to increase the energetic and exergetic efficiency of the thermocline tank. Due to technological advancement, new materials are developed every year that support thermal energy storage. This article proposes the ITARA-TOPSIS-MODM methodology for the PCM selection process effectively. The final obtained results are experimentally validated, and the performance has been evaluated in the computation domain - Ansys, Fluent-21. The 62-commercially available inorganic salt and its mixture of PCM are collected and solved in the ITARA-TOPSIS method. The weightage of the attributes is found from the proposed ITARA method, and results are compared with conventional methods. In the pre-screened process, the attribute weights are obtained and substituted in the TOPSIS algorithm and sorted into ten materials in each category (i.e., L, M, and H). The properties of the sorted material are formed by two vital variables such as energy storage per unit volume and equivalent thermal diffusivity. The collected results are solved by the MODM tool. Finally, found L7, M7, and H17 (i.e. LiOH (6)-NaNO3(67)-NaOH (27), NaOH, Li2CO3(44)-Na2CO3(56), and NaF) to be more promised materials for the thermocline tank in solar thermal concentrating applications.

Wall impact on efficiency of packed-bed thermocline thermal energy storage system

Packed-bed single-tank thermocline system with reduced cost is an alternative to the conventional two-tank system for thermal energy storage. This work systematically explores the wall impact on thermocline behavior of packed-bed tanks. For this purpose, adapted transient models were developed and fully exploited for the first time. Two tank configurations were investigated and compared: a high-temperature pilot-scale tank with a steel wall and a low-temperature lab-scale tank with a polycarbonate wall, both tanks being insulated by mineral wool. Results showed that the maximum energy stored in the wall at fully charged state can be up to 10% of the total stored energy. This part of stored energy has a negative impact on the discharging, causing up to 15% increase of the thermocline thickness. The energy stored in the insulation is very small so that this phase can be simplified as a thermal resistance in the modeling. The optimal wall parameters for packed-bed TES tanks were obtained that a thinner wall has a smaller impact on the energy and exergy efficiencies at the discharging cutoff time. The findings of study could provide useful design guideline for pack-bed thermocline TES tanks for different industrial applications.

Development of Sensible Heat Storage Materials Using Sand, Clay and Coal Bottom Ash

In this paper, the mechanical and thermal properties of a sand-clay ceramic with additives coal bottom ash (CBA) waste from incinerator coal power plant are investigated to develop an alternative material for thermal energy storage (TES). Ceramic balls are developed at 1000°C and 1060°C using sintering or firing method. The obtained ceramics were compressed with a compression machine and thermally analyse using Decagon devise KD2 Pro thermal analyser. A muffle furnace was also used for thermal cycling at 610°C. It was found that the CBA increased the porosity, which resulted in the increase of the axial tensile strength reaching 3.5 MPa for sand-clay and ash ceramic. The ceramic balls with the required tensile strength for TES were selected. Their volumetric heat capacity, and thermal conductivity range respectively from 2.4075 MJ·m-3·°C-1 to 3.426 MJ·m-3·°C-1 and their thermal conductivity from 0.331 Wm-1·K-1, to 1.014 Wm-1·K-1 depending on sand origin, size and firing temperature. The selected formulas have good thermal stability because the most fragile specimens after 60 thermal cycles did not present any cracks. These properties allow envisioning the use of the ceramic balls developed as filler material for thermocline thermal energy storage (structured beds) in Concentrating Solar Power plants. And for other applications like solar cooker and solar dryer.

A Review on the Performance Indicators and Influencing Factors for the Thermocline Thermal Energy Storage Systems

Thermal energy storage (TES) system plays an essential role in the utilization and exploitation of renewable energy sources. Over the last two decades, single-tank thermocline technology has received much attention due to its high cost-effectiveness compared to the conventional two-tank storage systems. The present paper focuses on clarifying the performance indicators and the effects of different influencing factors for the thermocline TES systems. We collect the various performance indicators used in the existing literature, and classify them into three categories: (1) ones directly reflecting the quantity or quality of the stored thermal energy; (2) ones describing the thermal stratification level of the hot and cold regions; (3) ones characterizing the thermo-hydrodynamic features within the thermocline tanks. The detailed analyses on these three categories of indicators are conducted. Moreover, the relevant influencing factors, including injecting flow rate of heat transfer fluid, working temperature, flow distributor, and inlet/outlet location, are discussed systematically. The comprehensive summary, detailed analyses and comparison provided by this work will be an important reference for the future study of thermocline TES systems.

Numerical Study to Investigate the Thickness of the PCM Layer for the Three Layers Tank for the CSP Plants

In the present study, the phase change material (PCM) layer thickness of the top and bottom PCMs change gradually with constant the middle PCM layer thickness for the three-layers thermocline thermal energy storage (TES) tank. It has been studied using spherical capsules packed with three types of PCMs with different thermophysical properties. A transient two-phase dispersion-concentric (D-C) model is used to calculate the process of phase change inside pellets to identify the temperature allocation. The method of heat transfer among molten salt and PCMs capsules is extensively discussed, with multiple numerical results shown. The results show that the thickness of the PCM layer has a high impact on the thermal performance of the TES tank. As the layer thickness of the top PCM increases, the time required to discharge the thermocline TES tank increases. The (80 % high phase change material (HPCM) -10 % intermediate phase change material (IPCM) - 10 % low phase change material (LPCM)) configuration has 14.6 %, 27.2 %, and 46.8 % higher overall efficiency than (33.3 % HPCM - 33.3 % IPCM -33.3 % LPCM) configuration, (70 % HPCM - 10 % IPCM - 20 % LPCM) configuration, and (10 % HPCM -10 % IPCM - 80 % LPCM) configuration. In contrast, the (80 % HPCM - 10 % IPCM - 10 % LPCM) configuration shows the highest capacity and utilization ratio.

Thermocline thermal energy storage optimisation combining exergy and life cycle assessment

Thermocline thermal energy storage is one of the most promising solutions for recovering waste heat in industrial plants. This paper aims to optimise the shape of a thermal energy storage to minimise its environmental impacts and maximise its exergy efficiency. The reference storage is an existing industrial high-temperature air/ceramic packed-bed heat storage called EcoStock®. The physical model used to determine the performances of the tank is a one dimensional model with two equations: one for the heat transfer fluid and one for the filler material. The environmental impacts are analysed using a life cycle assessment through four selected indicators: cumulative energy demand, global warming potential, abiotic depletion potential and particulate matter. To solve this multi-criteria problem, a particle swarm optimisation algorithm was applied with several exergy and environmental weighting factors. A Pareto set is obtained, bounded by the single exergy or environmental optimisations. Favouring exergy efficiency reduces the volume of the tank. However, environmental footprint of the tank is increased: the indicators of cumulative energy demand and abiotic depletion potential are considerably higher. The shape of the tank evolves with the exergy weight, from a square shape (environmental optimisation) to a tapered shape (exergy optimisation).

Stability analysis of the thermocline thermal energy storage system during high flow rates for solar process heating applications

The thermal energy storage system is a pivotal system for solar thermal plants for improving reliability. The stability in the thermocline is more significant to clarify and improve the performance of thermal energy storage tank which legitimately shows the quality of the thermocline. In this stability analysis investigation, the modern engineering energy storage material concrete was used as a filler material for high-temperature thermal energy storage applications as a result of the intrinsic properties. A comprehensive laminar and k-ε turbulent flow energy transport model accounts for the heat transfer fluid and filler material with adiabatic and non-adiabatic conditions using LTNE (Local Thermal Non-Equilibrium model). The axial, radial, and diagonal temperature differences were identified which was used to calculate the stability of the thermocline. A thermal energy storage tank size of 1 m height and 0.250 m diameter with a 0.030 m size of filler material packed with an average porosity of 0.3 for the storage capacity of 150 kWh/m3 is used for solar process heating applications considered for the present study. The thermocline stabilities are performed with Reynolds numbers, Re varied from 1 to 3000. It is found that the Re = 1 provides better stability in the axial and radial direction as well as diagonal than other Reynolds number. It is observed that Re = 1 provides superior discharging efficiency for nearly 5.84 hrs which is highly suitable for solar process heating applications and the discharging efficiency consistently drops, when Re increases from 1 to 3000. The wall condition of the tank and velocity of the heat transfer fluid is highly disturbing the thermocline in the radial direction and it creates a ‘spike’ profile in the axial direction. Based on the newly introduced stability scale, the effective length of packing and timing to achieve stability is identified for H/D = 4. From that result, the top and bottom layer of the thermocline tank porosity is also found which is used to decide the porosity of the packed bed distributors. The identified porosity for the top and bottom distributors in the ɛ = 0.3 thermal energy storage tank is less than 0.3 is more suitable for provide the uniform flow in the tank.