Fluid Inlet Temperature Research Articles

Comparative study on cooling method for concentrating photovoltaic system

Concentrating photovoltaic technology has been one of the important technologies among renewable energy technologies. Researchers have used one or more cooling methods to increase the output power by cooling the CPV cells. In this work, CPV systems with three typical cooling methods of air cooling, water cooling and heat pipe cooling have been comparatively studied. An Outdoor experiment was conducted under the same environmental conditions. The pump power loss factor was considered to evaluate the thermal and electrical performance of the three systems. The experimental results indicate that the average temperatures of the finned heatsink, water cooling module, and heat pipe during the test are 41 °C, 25.9 °C and 22.2 °C, respectively. The CPV cell with heat pipe cooling method exhibits the highest output power of 8.27 W. When the pump consumption is considered, the water-cooled CPV cell can provide the highest net electrical efficiency of 28.3% and electrical exergy efficiency of 30.4%. In addition, a thermal-electrical coupling model was established to investigate the effects of different parameters, such as inlet fluid temperature, mass flow rate and concentration ratio on CPV system. The results can provide some practical guidelines for the design and application of practical CPV cooling systems.

Investigation of thermohydraulic characteristics of a novel triple concentric pipe minichannel heat exchanger

In this paper, a novel triple concentric pipe minichannel heat exchanger (TCPMHE) is presented and built, which is a combination of concentric pipe heat exchanger and minichannel heat transfer technology. A range of experimental investigations are further systematically performed by varying the volume flow rate of hot water (Vh), inner annulus size (Si) and hot fluid inlet temperature (th, i) to evaluate the heat transfer and flow characteristics of TCPMHE. And the results are comprehensively compared with the double concentric pipe minichannel heat exchanger (DCPMHE), aiming to offer some references for the concentric pipe heat exchanger and minichannel heat transfer technology in further industry application. Results indicate that the friction factor (f) values for both DCPMHE and TCPMHE are almost equal under the same operating conditions. Although the Nusselt number (Nu) values of DCPMHE are 21.8%-50.7% higher than those of TCPMHE, the effectiveness (ε) values of TCPMHE are all much higher than those of DCPMHE under the same conditions, and the enhancing factor (η) ranges from 1.45 to 1.65. Compared with the DCPMHE, the volumetric heat transfer capacity of the TCPMHE is improved by up to 65.4% at Si = 0.5 mm, th,i = 60 ℃ and Vh = 209 L·h−1. In addition, the dimensionless correlations for inner annulus hot fluid Nu, ε, and f of TCPMHE were established, and the maximum deviations are ± 8%, ± 5% and ± 11% for Nu, f, and ε, respectively, which indicates that the predicted values from the correlations agree well with the measured results.

EXERGY ANALYSIS OF GRAPHENE-BASED NANOFLUIDS IN A COMPACT HEAT EXCHANGER

In this study, the exergy analysis of graphene-based nanofluids in a compact heat exchanger is examined. In experiments using distilled water as the base fluid, graphene nano-ribbon and graphene oxide nanofluids were used at 0.01% and 0.02% of the volume concentrations. The experiments were carried out at 36, 40, and 44 oC fluid inlet temperatures and 0.6, 0.7, 0.8, and 0.9 m3/h mass flow rates. As a result of the calculations made for all temperature and flow rates, it was found that the exergy efficiency values of 0.01% by volume GO nanofluid were higher than the exergy efficiency of the other nanofluids used. Also, the exergy destruction values calculated for %0.01 GO were lower than the value of exergy destruction calculated for other nanofluids. It was concluded that the exergy efficiencies of nanofluids increased with the increase of the fluid flow rates and the inlet temperature of the heat exchanger. When the exergy efficiencies were compared according to the nanofluid concentrations, it was found that the exergy efficiencies decreased with the increase of the fluid concentration. It was examined that the exergy destruction values also increases with the increase of nanofluid flow rates, as well as exergy efficiency. When the exergy destructions were compared to the nanofluid concentrations, it was concluded that the exergy destructions increased with the increase of the nanofluid concentration. It was determined that the amount of increase in exergy destruction of GO nanofluid was higher than that of GNR.

Exergetic optimization of simple and finned solar air collectors for humid subtropical regions.

In this paper, an exergetic optimization of simple and finned flat plate solar air collectors is established to determine the optimal design and operational parameters for humid subtropical climatic conditions. Solar air collectors are commonly used for space heating, irrigation, greenhouses, grain drying, hot air generation, etc. A detailed solar energy radiation model is developed for solar energy conversion. A comprehensive optical, energy, and exergy analysis is carried out for evaluating the performance, energy and exergetic efficiency for simple and finned flat plate solar air collectors under humid subtropical climatic conditions. A simulation program is developed for solar energy model, energy and exergetic calculations. The following geometric and operating parameters are considered as decision variables: absorber plate area, dimensions of simple and finned solar collectors, fluid inlet and outlet temperatures, average velocity, overall loss coefficient, glass cover temperatures, plate temperature, and useful heat gain. The proposed model is optimized using computational intelligence technique (single phase multi-group teaching learning optimization) for maximum mean exergy efficiency in simple and finned solar air collectors for humid subtropical regions. The maximum exergy efficiency is achieved in the case of finned solar air collectors with a yearly optimal average exergy efficiency of 6.10% for a collector area of 5 m2 and a yearly average heat flux of 601W/m2. Thus, beneficial applications of exergetic optimization in design and operation of solar collectors for humid subtropical climatic conditions based on maximum exergy efficiency according to the optimized parameters and benefits of this approach for such systems have been highlighted.

Improving the accuracy of predicting the performance of solar collectors through clustering analysis with artificial neural network models

Accurate prediction of collector performance is important for optimal planning of solar thermal systems. Here, a novel prediction method combining clustering of data with artificial neural network (ANN) model is presented. A novel all-glass straight-through tube solar collector is employed as reference solar technology. In the present approach, experimental collector performance data was first collected during different weather conditions (sunny, cloudy, rainy days) subject to a clustering analysis to screen out outlier samples. The data was then used to train and verify the neural network models. For the ANN, the Back Propagation (BP) and Convolutional Neural Network (CNN) models were used. For predicting the performance (thermal efficiency) of the solar collector, solar radiation intensity, ambient temperature, wind speed, fluid flow rate, and fluid inlet temperature were used as the input parameters in the model. The prediction accuracy of the neural network models after full-data-screening were superior to that of the pre-screening and partial-screening models. The CNN model provided somewhat better efficiency predictions than the BP model. The R2, RMSE and MAE of the CNN model prediction in sunny conditions with full-screening was 0.9693, 0.0039 and 0.0030, respectively. The average MAPE of the BP and CNN models for all three weather types dropped by 30.7% and 13.8%, respectively, when applying data pre-screening and partial-screening only. The accuracy of the ANN collector prediction model can thus be improved through data clustering, which provides an effective method for performance prediction of solar collectors.

Performance Comparison and Analysis of the Curtain-Wall-Type Liquid-Type Photovoltaic Thermal Unit According to the Pipe Connection Method

Recently, there has been increasing attention on the use of renewable energy in buildings, particularly, the photovoltaic thermal (PVT) system that uses both solar power and thermal energy. However, there is a limit to adopting the PVT system in real buildings because many architects value the aesthetics of buildings or spaces. This study developed a curtain-wall-type liquid-type PVT (CW-PVT) that can be installed on a wall as it integrates with the building. To analyze the system performance, a real-scale experimental plant was established in an outdoor environment. The performance of the CW-PVT unit was verified for two different module pipe connection types: parallel and serial. Meteorological variable data, the inlet and outlet fluid temperatures, surface temperature, and electrical energy generation of the modules were measured and collected using the measurement equipment according to the module pipe connection type. Consequently, the parallel-type method was approximately 10% more efficient than the serial type in energy production, whereas the serial-type method produced water with a temperature approximately 47% higher than that of the parallel type. Notably, it was advantageous to apply the parallel-type connection to maximize the energy generation efficiency in buildings where the system efficiency is vital and the serial-type connection in buildings where the high temperature of hot water is required.

Experimental Analysis of Flow Boiling in Horizontal Annulus—The Effect of Heat Flux on Bubble Size Distributions

Subcooled flow boiling was experimentally investigated in a horizontal annulus with a temperature-controlled boiling surface and transparent outer pipe facilitating visualization. Boiling occurs on a copper tube with a diameter of 12 mm in an annulus with a 2 mm gap. Refrigerant R245fa is used as a working fluid. The focus of this study is to explore the effect of heat flux variation on the boiling flow patterns at approximately constant inlet flow conditions of the working fluid (fixed mass flux and inlet fluid temperature). Subcooled flow boiling is recorded by a high-speed camera, images are analyzed by a neural network to determine the bubble size distributions and their variation with the heat flux. The experimental setup being a part of the laboratory THELMA (Thermal Hydraulics experimental Laboratory for Multiphase Applications) at the Reactor Engineering Division of Jožef Stefan Institute, analysis methods and measurement results are presented and discussed.

Experimental investigation of the flow distribution of high-pressure CO2 flowing in heated parallel channels

This study experimentally investigated the flow distribution characteristics of high-pressure CO2 flowing in parallel heated pipes with an inner diameter of 2 mm. The test conditions were as follows: a system pressure of 7.5–9.5 MPa, an inlet mass flow of 200 g/min to 400 g/min, a heat flux of 55 kW/m2 to 400 kW/m2, and an inlet fluid temperature of 20–35 °C. The influences of working parameters on flow distribution were analyzed. The results showed that heat flux deviation between the parallel channels was the primary cause of the nonuniform flow distribution, and the flow deviation intensified with increasing heat flux deviation. Furthermore, a flow distribution model for high-pressure CO2 was established, which could effectively predict flow distribution in parallel channels, with an error of ± 1.5%. Thus, the results provide a theoretical foundation and technical support for the design and optimization of heat exchange systems in supercritical CO2 Rankine cycles.

Numerical analysis of the flow parameters on the heat transfer performance of a two-stage spiral casing heat exchanger

The study of the performance of high-efficiency heat pump systems has been a hot issue of general interest in the field of heat pump air conditioning. For the designed and developed two-stage casing tandem heat exchanger of heat pump system, the 3D finite volume method and the realizable k-ε model are used to numerically analyze the influence law of inlet fluid temperature and flow velocity on the overall heat transfer coefficient as well as the Nussle number of inner and outer tubes. The results show that decreasing the inlet water temperature or increasing the inlet refrigerant temperature can improve the overall heat transfer performance; Nuin increases with the increase of water and refrigerant flow rates, while Nuout increases with the increase of water flow rate but decreases with the increase of refrigerant flow rate; Nuin and Nuout both increase with the decrease of water temperature or refrigerant temperature increases.

Experimental investigation on thermo-hydraulic performance of a helical plate heat exchanger

ABSTRACT The current research presents an experimental study on heat transfer and fluid flow characteristics of a helical plate heat exchanger (HP-HEx). Helical plate with different pitches and cross sectional area of the flow channel was investigated for various fluid mass flow rates and inlet temperatures. The results show that the proposed heat exchanger performed an overall heat transfer coefficient (U) and exergy efficiency (ηex ) about 279.77 W/m2.K and 60.87% respectively. Also, the HP-HEx showed effectiveness (ε) and number of transfer unit (NTU) reach about 0.694 and 1.79 respectively with pressure loss reached 202 kPa, for hot and cold fluids flow rate 0.083 kg/s and 0.07 kg/s at inlet hot and cold fluid temperature 45°C and 28°C respectively, and pitch = 56 mm. The pitch and cross sectional area of the flow channel variation can augment heat transfer rate and decrease the pressure loss. For pitch decreasing from 76 mm to 46 mm, the U, ε, NTU, ηex , and pressure loss increase by 50.60%, 22.39%, 50.60%, 10.35%, and 20.87% respectively. Empirical general correlations were obtained from the experimental data of the present study with maximum deviations about ±16.81%, ±13.33%, ±17.73%, ±16.60% and ±15.60% for U, ε, NTU, ηex , and pressure loss, respectively.

Heating properties of bridge decks using hydronic heating systems with internal or external circulation tubes

A comparison analysis of the heating properties of the hydronic heating system of bridge decks with external (exchange tubes installed at the bottom of the existing bridge deck with voids inside) or internal (exchange tubes embedded in pavement of the newly built bridge deck) tubes was carried out through field tests. Two heating methods (constant heating power and constant inlet fluid temperature) were used to analyze the heat exchange flux and the temperature increments as well as thermally induced stress of the slab. Numerical simulation was conducted to model the bridge deck heating process to analyze the temperature distribution of the bridge surface. The results shows that the heat exchange flux are the same under the same constant heating powers for the two embedded tube position heating systems; the maximum temperature increment of the bridge deck surface obtained by the external heating system is 0.46 times that obtained by the internal heating system; the maximum thermally induced stress caused by the external heating is 20.4% of the concrete strength (19.1 MPa), which is much higher than that caused by the internal heating under the same heating powers. The thermal efficiencies of the external and internal heating systems are approximately 24.4% and 47.9%, respectively. Under the same constant inlet temperatures, the temperature increment of the bridge deck caused by the external heating is 20.4% of that of the internal heating.

Transient Charging Characteristics of Shell and Tube Latent Heat Storage System—A Novel Two-Dimensional Analytical Approach

Abstract Energy storage using latent heat of solid–liquid phase change material (PCM) is an efficient option due to high energy density and low volume variation during phase change. Such type of storage is suitable to exploit untapped solar energy and waste heat energy. The present work explores the analytical approach to study the unsteady charging behavior of PCM inside latent heat thermal energy storage (LHTES) system. The radial, axial as well as temporal effects on the melting of PCM are investigated analytically. Relation between time, temperature, radius, and axial distance of storage system is developed using energy equation in cylindrical coordinates. The 49% reduction in melting time of PCM was noted with an increase in heat transfer fluid inlet temperature from 185 °C to 200 °C. It was also observed that melt front moves 1.28 times faster when axial position changes from 100 mm to 200 mm. Convection heat transfer plays a vital role during the charging process, and it is found that the melt front moves radially outward and axially upward during the melting of PCM. It can also be concluded that analytical tools like the one presented in this study can be instrumental in analyzing the thermal performance of storage units.

Benchmark assessment of performance indices of a selection of hybrid nanofluids in a hybrid photovoltaic/thermal system

Abstract This research is a study assessing the performance of hybrid nanofluids in hybrid photovoltaic (PV)–thermal systems. This study addresses 10 hybrid nanofluids applied to hybrid PV–thermal systems. The transition to carbon-free energy can mitigate the worst effects of climate change, ensuring that global sustainability is addressed. Clean energy is now responsible for one-third of the global capacity, of which 20% is attributed to solar energy. Renewables continue to be economically viable, with declining costs driving growth. This study aims to compare the yearly performances of a model hybrid PV–thermal system using 10 different hybrid nanofluids. Hybrid nanofluids constitute two or more dissimilar materials stably suspended in a base fluid (e.g. water). MATLAB and COMSOL Multiphysics® computational fluid dynamics software are employed together for the benchmarking assessment with good agreement observed. Various fluid inlet temperatures (Tin ∈ [300, 360] K), nanofluid volume concentrations (φ ∈ [0, 4]%) and storage-tank volumes (V ∈ [50, 300] L) were simulated. The meteorological data applied were those for Lagos, Nigeria (6° 27’ 55.5192” N, 3° 24’ 23.2128” E). The assessment based on analytical-numerical solutions reveals that the thermal enhancement by hybrid nanofluids ranges from 6.7% (graphene oxide [GO]—multiwalled carbon nanotube [MWCNT]/water) to 7% (ZnO—Mn–ZnFe2O4/water) for φ = 2% and V = 300 L. The yearly exergy efficiency ranges from 2.8% (ZnO—Mn–ZnFe2O4/water) to 2.9% (GO—MWCNT/water), also for φ = 2% and V = 300 L. These findings have implications for a vast range of industrial processes, expanding the knowledge that is critical to a sustainable future. A combined solar PV-thermal system that stores thermal energy using nanofluids is modelled. Hybrid nanofluids (two or more dissimilar materials stably suspended in a base fluid) are shown to enhance the annual electrical, thermal and exergetic outputs of the system.

Numerical study on heat transfer performance of geothermal piles in a Brazilian sandy soil

The worldwide consumption of electric energy destined for air conditioners, expected to triple by 2050, can be lessened by geothermal piles, which transfer heat from the internal environment of buildings to the subsoil. This paper shows the influence of pile geometry and properties of soil, pile, and pipe materials on the heat transfer of a geothermal pile to the surrounding soil, to support design from the viewpoint of thermal performance optimization. A numerical model was developed with ANSYS CFX 19.2, a high-performance Computational Fluid Dynamics tool, and calibrated using data from a thermal response test performed in a saturated sandy soil in São Paulo, Brazil. A parametric analysis was carried out varying pile length, diameter, and slenderness; soil and pile material conductivities; degree of saturation; fluid inlet temperature; fluid flow rate; and pipe thermal resistance. Results show that the fluid inlet temperature is the most influential parameter on the thermal performance of the pile. Heat transfer grows when geometrical parameters (diameter and length) are increased mainly due to an increase in heat exchange surface area, whereas the normalized heat transfer rate per unit of surface area of the pile is practically unaltered. Higher soil, pipe and pile thermal conductivities improve thermal performance. The degree of saturation increases the thermal conductivity of the soil; however, the effect is not remarkable on the system’s thermal performance for saturation degrees higher than 20%. The fluid flow must be turbulent but increases above a certain flow rate do not improve the thermal performance.

Application of Superposition Principle for Solving a Nonlinear Energy Equation

Abstract A new procedure to solve a nonlinear energy equation using the superposition principle is proposed. As an example of the utilization of this procedure, forced convection in a tube with temperature-dependent fluid properties was considered. The tube wall was maintained at uniform wall heat flux axially that varies with time, and the average fluid temperature at the outlet was calculated. This problem simulates convection heat transfer inside a solar collector tube. In the proposed procedure, the average fluid temperature at the outlet for a single heat pulse was determined for fluid properties evaluated at 15 different temperatures by solving the energy equation numerically assuming constant fluid properties and subsequently applying the superposition principle. The choice of the temperature at which fluid properties were evaluated as an important parameter in the simulation. This temperature was determined by using the inlet and outlet average fluid temperatures at the previous time-step multiplied by a weighting function. The average fluid temperature at the outlet obtained by this procedure was compared with the temperature obtained by solving the nonlinear energy equation using variable properties to determine the predictive accuracy of this procedure. The results for one-day operation of a sunny day with fluid velocity of 0.6 m/s, showed the highest root-mean-square (RMS) error of 0.25 K, and the highest mean absolute deviation (MAD) error of 0.16 K which agreed well with the result obtained by the numerical simulation of the nonlinear problem using variable properties.

Experimental research and numerical simulation of the thermal performance of a tube-fin cold energy storage unit using water/modified expanded graphite as the phase change material

In this study, experimental and numerical investigations were conducted on a tube-fin heat-exchanger latent-heat cold energy storage unit. The fin side of the heat exchanger was filled with water as the energy storage medium, and modified expanded graphite (MEG) was employed to improve the thermal characteristics of water. The water contact angle of the expanded graphite decreased from 106.31° to 0°, and the hydrophilicity and the absorption rate of water significantly improved after the modification. Moreover, the experimental analyses of the charge/discharge process showed that the cooling capacity of the system filled with 90 wt.% water/MEG was 80.8% of that of pure water, whereas its cooling time was only 69.7% of that of pure water. The average power increased by 15.9% compared with that of water. The system filled with 90 wt.% water/MEG completed two energy charging and discharging cycles, whereas the system filled with water completed only 1.5 cycles within 15000 s. Furthermore, the effects of the flow rate and inlet temperature of the heat transfer fluid on the charging process were explored. Finally, a numerical model was built and validated to investigate the phase change behavior and the effect of the structure size on the performance of the system. The heat-exchanger fin spacing had no significant effect on the cold energy storage unit, whereas the vertical spacing of the tube pass had the highest effect. It can be concluded that the heat exchanger combined with high-thermal-conductivity water/MEG exhibits better energy storage capacity and working power, showing a wide application prospect in the field of cold energy storage.

Numerical simulation of the calcium hydroxide/calcium oxide system dehydration reaction in a shell-tube reactor

The Ca(OH)2/CaO system is a promising candidate for thermochemical energy storage because of its high energy density, low cost and negligible heat loss. Coupling mechanisms of multiple physiochemical processes still need further investigation and the system performance should be further improved. In this work, for the first time, a three-dimensional numerical model is developed to study the thermochemical energy storage process by Ca(OH)2 dehydration reaction in a shell-tube reactor. The turbulent heat transfer fluid flow in the shell side, and the steam flow, heat transfer and dehydration reaction in the tube side are comprehensively taken into account. Effects of operation conditions and reactor geometry parameters on the dehydration process are also investigated in detail. Five indicators are proposed to comprehensively evaluate the reactor performance, including reaction time, energy storage density, heat exchange power, heat exchange efficiency and energy storage efficiency. The results reveal that higher inlet temperature and inlet velocity of heat transfer fluid can enhance the heat transfer and accelerate the reaction. Lower porosity, although increases the energy storage density, leads to higher flow resistance and impedes the reaction. With deep understanding of the physiochemical processes, 16 more tubes are properly added in the by-pass flow region, leading to shorter reaction time and higher energy storage amount. The low values of heat exchange efficiency and energy storage efficiency reveal that the input heat cannot be efficiently transferred to the tube side. To improve the energy conversion performance of reactor, additional schemes are discussed including regenerative HTF, optimization of reactor geometry, increase of reactant thermal conductivity, reducing tube-side flow resistance and extending HTF residence time. The numerical model and simulation results in the present work could be helpful for optimizing the shell-tube Ca(OH)2/CaO reactor and improving the thermochemical energy storage performance.

Effects of heat exchange fluid characteristics and pipe configuration on the ultimate bearing capacity of energy piles

This paper examines the ultimate bearing capacity of energy piles in sandy and clayey soils by conducting numerical modeling under different thermal loads, fluid-pipe configurations and fluid characteristics. Accordingly, U and W-shaped fluid-pipes with different diameters were simulated using ANSYS-FLUENT software, under different inlet flow rates, fluid temperatures and ground temperatures. Moreover, a semi-empirical analytical solution is proposed for predicting the outlet temperature for different pipe configurations. Then, the energy piles were modeled using ABAQUS FE-software, and the effect of temperature distribution in U, double-U and W-shaped pipes on the ultimate bearing capacity was studied, in heating/cooling conditions. Both numerical simulations and the analytical solution were validated against experimental data. Results showed that under constant flow rate, initial inlet temperature and pipe diameter, the differences between the inlet and outlet temperature of the heat exchange fluid in the U-shaped pipes was less than that obtained for the W-shaped pipes. Also, for constant inlet temperature and pipe diameter, the temperature difference decreased when the inlet flow rate increased. It was found that under constant thermal loading conditions, the changes in the ultimate bearing capacity were higher in piles with double U-shaped pipes, followed by U-shaped pipes, and lowest for W-shaped pipes.

3D Numerical Modeling to Evaluate the Thermal Performance of Single and Double U-tube Ground-coupled Heat Pump

The heat transfer rate and borehole design represent great challenges to the thermal equipment designer of the ground-coupled heat pump. The present model represents a mathematical and numerical technique implemented to tackle such a problem. A thermal assessment was established to estimate the total energy dissipated to the ground zone for a heat pump utilized for cooling purposes in the summer season. Comsol Multiphysics 5.4 software was used to build a 3-dimensional model to assess the thermal performance of single and double U-tube boreholes that circulate water as a thermal transfer medium. The (Heat Transfer) module has been implemented for this investigation under the (Stationary) study option. The model couples both heat conduction in solids, including tube metal, grout, and soil regions, and thermal medium fluid flow inside the U-tubes. The numerical solutions were compared for both heat exchangers at fixed borehole geometry, diameter, and depth and constant operating conditions in a steady-state mode. The double U-tube heat exchanger was tested in the parallel circuiting orientation of the U-tubes. The total mean resistance of the single U-tube borehole was higher than the half-loading double U-tube heat exchangers by 14.6%. The results also revealed that the heat transfer rate enhancement for the double U-tube was in the range of 10–14% when operating at the same fluid mass flow rate and inlet temperature for a given borehole design. Doi: 10.28991/HIJ-2022-03-02-01 Full Text: PDF

Experimental evaluation of an innovative radial-flow high-temperature packed bed thermal energy storage

High-temperature packed-bed thermal energy storage represents an economically viable large-scale energy storage solution for a future fossil-free energy scenario. The present work introduces first-of-a-kind experimental setup of a radial packed-bed TES, and its performance assessment based on experimental investigations. The storage performance is analyzed based on a set of dimensionless criteria and indicators. The laboratory-scale prototype has an energy capacity of 49.7 kWhth and working temperatures between 25 °C and 700 °C with a non-pressurized dry airflow. The influence of different working fluid mass flow rates and inlet temperatures during charge and discharge is assessed. The proposed storage design ensures limited pressure drop, lower than 1 mbar, and thermal losses, about 1.11 % during dwell after charging at 700 °C until a state of charge of 55.8 %. A maximum overall thermal efficiency of 71.8 % has been recorded and trade-offs between efficiency, thermal uniformity, and thermocline thickness are highlighted. This work testifies that reduced pressure drops are the key advantage of radial-flow packed-bed designs. Thermocline degradation is shown to be the main weak point of this thermal energy storage design.