Solar Thermal Storage Tank Research Articles

Achieving net zero energy penalty in post-combustion carbon capture through solar Energy: Parabolic trough and photovoltaic technologies

The adoption of carbon capture systems presents a pivotal strategy for mitigating greenhouse gas emissions, notably carbon dioxide. Nevertheless, the substantial surge in energy consumption associated with such systems remains a significant challenge. Addressing this challenge necessitates the integration of renewable energy sources. This study is dedicated to optimizing the conventional post-combustion carbon capture configuration, focusing on energy, exergy, and exergoeconomic considerations. The optimized configuration showcases a noteworthy 10 % reduction in overall energy penalties compared to its conventional counterpart, primarily attributed to diminished energy utilization in the reboiler. To achieve absolute sustainability and eliminate energy penalties in the optimized configuration, integration of a parabolic trough collector for steam provision to the reboiler and photovoltaic solar collectors for powering the plant’s equipment was undertaken. Furthermore, the incorporation of solar thermal storage tanks and batteries enables the storage of excess heat and electricity, ensuring operational continuity for up to 13 h in the absence of sunlight, such as during nighttime. The final optimized configuration manifests a commendable 14 % enhancement in exergoeconomic performance relative to the conventional configuration, thereby realizing zero energy penalties. This achievement renders the optimized configuration a compelling and viable choice for carbon capture units.

Experimental study of storage system of a solar water heater equipped with an innovative absorber spherical double-walled tank immersed in a phase change material

In commercial active solar water heaters, during the thermal charge process, water is continuously circulated between the collector and the tank. The water is heated in the collector and then stored in a tank whose surface is insulated. The shape of the collector and tank is an important factor in the development of solar thermal storage systems. In this study, the collector and tank are made spherical, fixed, symmetrical and capable of tracking the sun regardless of the placement angle. Also, in an innovative idea, the solar thermal storage tank is designed as a double-walled spherical tank. The water heated by the collector is stored in the inner chamber of the double-walled tank, and this chamber is surrounded by a Phase Change Material (PCM) by embedding the PCM in the outer chamber of the tank. Therefore, the PCM has the two roles of thermal insulation and thermal storage. As well as removing the thermal insulation, it is also possible to absorb solar energy on the external surface of the tank. To reduce heat losses, the tank is surrounded by a transparent glass cover in a greenhouse space. The maximum storage temperature and the maximum thermal efficiency in the thermal charge process are 80.3 °C and 74 %, respectively, which occur at a flow rate of 1.75 l/min. In this situation, the warm water needed by 8.43 people is produced. The greatest thermal stratification occurs at a flow rate of 1.25 l/min, and it weakens by raising the flow rate.

The Effect of Pitch on Heat Transfer to an Immersed Heat Exchanger in a Solar Thermal Storage Tank With and Without a Baffle

Abstract The effect of the pitch of a copper coil heat exchanger immersed in a hot water storage tank on heat transfer from the storage tank to the heat exchanger working fluid is investigated. The storage tank is initially quiescent and full of hot water. The heat exchanger located at the top of the tank has a coil diameter just under the tank diameter and has a pitch of 2, 3, 4, 6, or 12 times the heat exchanger diameter, D. The effect of the pitch is explored both with and without a cylindrical baffle, which creates an annular region with the tank wall that has a width of 1.5D and within which the heat exchanger is located. In experiments without the baffle, increasing the heat exchanger pitch improves the rate of heat transfer to the working fluid. The improved heat transfer is attributed to the increased thermal stratification generated by the larger pitches. In experiments with the baffle, the results for experiments with pitches of 2D, 3D, 4D, and 6D are all very similar, with 3D slightly outperforming the others. Heat transfer to the heat exchanger with a 12D pitch was significantly lower than the others. In experiments both with and without the baffle, the larger pitches resulted in more variation in experimental results, despite strict standards for initial and operating conditions. As in the prior work, the presence of the baffle resulted in significantly higher heat transfer rates compared to respective experiments without the baffle.

A study on the structure of Solar/Photovoltaic Hybrid system for the purpose of preventing overheat and improving the system performance

In countries, such as Korea, where climate change is clear due to the four seasons, some of the collected energy must be released in the summer season, and these measures for heat dissipation fail to be very effective, thus causing system overload and defects frequently. In this study, we devised an overheating prevention system for the solar hot water and heating system using the variation of the shadow caused by the solar altitude angle that changes every hour, and for this purpose, a solar power generation module was placed over the solar collector. By using simulations, the system was designed in such a way that direct sunlight would be naturally blocked from reaching the solar collector due to the high solar altitude in the summer and that 100% of direct sunlight could reach the collector due to the low solar altitude in the winter. It was confirmed that the designed conditions were also satisfied in the actual test bed. In order to predict the performance of the system through simulations, the temperature of the solar thermal storage tank was calculated every hour after modifying the energy equation used in a previous study, and as a result of determining whether the system is overheated afterwards, it is expected that the degree of system overheating can be reduced. The shading did not affect the system efficiency in the season in which an actual heating and hot water load was needed.

Numerical verification for different types of curved baffles as stratifiers in solar thermal storage tank

This paper aims to assist the thermal stratification in hot water storage during the partial discharge water. Three different types of curved baffle have been studied each one placed in the bottom of a rectangular standard conventional tank in order to reduce the turbulence mixing of inlet jet. The purpose of this investigation is to numerically study the impact of the curved baffle within a vertical hot storage tank and compare three different baffle designs to select the best one. A three-dimensional computational fluid dynamic (CFD) model was performed using the commercial software package CFX 18. The numerically simulated tank result was validated against the experiment data. The numerical transient temperature distribution and the flow characteristics were analyzed, and then a comparison was made between the three baffle designs and the calculated performance parameter. The results manifested that the curved baffle has a significant effect for enhancing the thermal stratification at high flow rates. Design C showed the best thermal stratification due to the downward curvature shapes.

Numerical simulations of storage-side natural convection to an immersed coiled heat exchanger with baffle-shrouds

Heat exchangers immersed in solar thermal storage tanks to charge and/or discharge energy from the tank provide several benefits over conventional systems that rely on pressurized tanks or pumps. The present study builds on a recent experimental study of heat transfer to an immersed heat exchanger with different baffle and shroud geometries (Nicodemus et al., Solar Energy, 157:911–919, 2017). A simple straight geometry was found to provide more benefit than a more complex geometry, in which the baffle underneath the heat exchanger narrows relative to the shroud around the heat exchanger. In this study, we propose an axi-symmetric model of a two-loop heat exchanger in order to investigate the mechanisms by which the straight baffle-shroud improves the heat transfer relative to the complex baffle-shroud. Further, we compare results of the two-loop model to a one-loop representation of the heat exchanger in order to determine whether or not a model with more fidelity to realistic storage systems better predicts experimental performance. Both the two-loop and one-loop models yield higher heat transfer with the straight baffle-shroud and confirm that the improved heat transfer in the straight baffle-shroud geometries is due to higher velocities around the heat exchanger relative to those in the complex baffle-shroud geometries, consistent with the experiments. However, the one-loop model significantly under-estimates the differences between the baffle-shrouds relative to the experimental results. Since the two-loop model more accurately captures the fluid dynamics in the tank and better predicts the heat transfer and rate of energy discharge, it is an appropriate tool for future studies of immersed heat exchanger performance.

New Type of Valve for Solar Thermal Storage Tank Stratification

This paper describes the working principle and characteristics of a new type of valve with a unique self-actuating principle that actuates based on observed temperature difference, which is intended for use on solar thermal storage tank inlets, where it compares the temperature of the flow coming into the valve with the temperature inside the storage tank, and switches the flow based on the observed temperature difference, in order to achieve maximum thermal stratification inside the storage tank. The novel working principle, based on mass-transfer inside the actuator driven by vapour pressure differences, is explained in detail, and results of tests with the valve are presented, which show that the valve switches very effectively, and is a very useful tool for storage tank stratification.

태양열과 재열기를 사용한 VI heat pump의 성능 특성에 관한 연구

In this study, heating performance of the air-cooled heat pump with vapor-injection (VI) cycles, re-heater and solar heat storage tank was investigated experimentally. Devices used in the experiment were comprised of a VI compressor, re-heater, economizer, variable evaporator, flat-plate solar collector for hot water, thermal storage tank, etc. As working fluid, refrigerant R410A for heat pump and propylene glycol (PG) for solar collector were used. In this experiment, heating performance was compared by three cycles, A, B and C. In case of Cycle B, heat exchange was conducted between VI suction refrigerant and inlet refrigerant of condenser by re-heater (Re-heater in Fig. 3, No. 3) (Cycle B), and Cycle A was not use re-heater on the same operating conditions. In case of Cycle C, outlet refrigerant from evaporator go to thermal storage tank for getting a thermal energy from solar thermal storage tank while re-heater also used. As a result, Cycle C reached the target temperature of water in a shorter time than Cycle B and Cycle A. In addition, it was founded that, as for the coefficient of heating performance(), the performance in Cycle C was improved by 13.6% higher than the performance of Cycle B shown the average of 3.0 and by 18.9% higher than the performance of Cycle A shown the average of 2.86. From this results, It was confirmed that the performance of heat pump system with refrigerant re-heater and VI cycle can be improved by applying solar thermal energy as an auxiliary heat source.

Investigation of Shroud Geometry to Passively Improve Heat Transfer in a Solar Thermal Storage Tank

A shroud and baffle configuration is used to passively increase heat transfer in a thermal store. The shroud and baffle are used to create a vena contracta near the surface of the heat exchanger, which will speed up the flow locally and thereby increasing heat transfer. The goal of this study is to investigate the geometry of the shroud in optimizing heat transfer by locally increasing the velocity near the surface of the heat exchanger. Two-dimensional transient simulations are conducted. The immersed heat exchanger is modeled as an isothermal cylinder, which is situated at the top of a solar thermal storage tank containing water (Pr = 3) with adiabatic walls. The shroud and baffle are modeled as adiabatic, and the geometry of the shroud and baffle are parametrically varied. Nusselt numbers and fractional energy discharge rates are obtained for a range of Rayleigh numbers, 105 ≤ RaD ≤ 107 in order to determine optimal shroud and baffle configurations. It was found that a baffle width of 75% of the width of the heat exchanger provided the best heat transfer performance.

Transient calculation of charge and discharge cycles in thermally stratified energy storages

A stable thermal stratification in solarthermal storage tanks increases the energy efficiency of these systems. Especially in charging and discharging cycles, mixing occurs due to jet flows. The reliable prediction of the influence of the storage and of the charging device geometry on the loading behaviour is essential for the layout and improvement of stratified storage systems. A model approach for the computational calculation of the time-dependent temperature distribution in stratified storage tanks based on the one-dimensional heat transport equation is described in the present study. The numerical solution was obtained by application of the first order Upwind-discretization scheme. This basic approach was further refined by the consideration of charging jet flows and local turbulences in the area of stratification according to the strategies of Jirka (2004) and Mott and Woods (2009) and implemented in MATLAB. Two simulation examples of different complexity have shown that the enhanced model could increase the calculation accuracy in comparison to similar CFD and experimental studies. The results of the MATLAB program were reached with much less calculation effort than the results of the CFD simulation.

A passive house with seasonal solar energy store: in situ data and numerical modelling

This paper presents parametric analysis of solar collector area and solar energy storage volume for a passive house in Galway, Ireland. Using the simulation tool Transient System Simulation Tool (TRNSYS), a model was developed to represent a 215 m2 home built to Passivhaus standards and incorporating a 10.6 m2 solar thermal collector and a 23 m3 solar thermal storage tank. This model was validated through comparison with data collected in situ from the operation of the home over the period of 1 year. Once validated, the model was used to investigate the effect of varying solar collector area and solar energy storage volume on the fraction of heat demand met by solar energy. Results indicate that increasing collector area from 10.6 to 20 m2 could increase total solar fraction from 0.47 to 0.63, decreasing fossil-fuel-derived energy demand at the home under study by a further 30%.

Generalized charts of energy storage effectiveness for thermocline heat storage tank design and calibration

Abstract Solar thermal energy storage is important to the daily extended operation and cost reduction of a concentrated solar thermal power plant. To provide industrial engineers with an effective tool for sizing a thermocline heat storage tank, this paper used dimensionless heat transfer governing equations for fluid and solid filler material and studied all scenarios of energy charge and discharge processes. It has been found that what can be provided through the analysis is a series of well-configured general charts bearing curves of energy storage effectiveness against four dimensionless parameters grouped up from the storage tank dimensions, properties of the fluid and filler material, and operational conditions (such as mass flow rate of fluid and energy charge and discharge periods). As the curves in the charts are generalized, they are applicable to general thermocline heat storage systems. Engineers can conveniently look up the charts to design and calibrate the dimensions of thermocline solar thermal storage tanks and operational conditions, without doing complicated modeling and computations. It is of great significance that the generalized charts will serve as tools for thermal energy storage system design and calibration in energy industry.

Heat flow in a horizontal solar thermal storage tank with an auxiliary heater

An experimental and numerical study is conducted to verify the applicability of a one dimensional heat flow model in a horizontal storage tank of a thermosyphon solar system equipped with an auxiliary heater. Measurements of temperature are conducted in the vertical, axial and radial directions to examine the temperature stratification in the tank. A maximum average temperature deviation of 3.6% is found throughout the tank.

TRANSIENT NATURAL CONVECTION FROM A FINNED SURFACE FOR THERMAL STORAGE IN AN ENCLOSURE

Abstract A numerical study of transient natural convection heat transfer from a finned surface has been conducted for thermal storage in an enclosure. The motivation of this work is found in solar thermal storage tanks. The finned heat exchanging surface provides a means to charge and discharge the thermal energy in the tank. The governing time-dependent conservation equations are solved by a finite difference method. Solutions are obtained for 106 < Ra < 108, for 0-3 fins, for fins of length L/H = 0.3 and 0.75, and for fins parallel and perpendicular to the gravity vector. Results indicate that the storage process is characterized by three distinct heat transfer regimes and that most of the energy is stored during the last regime, referred to as the decay period. The time-changing Nussett number at the heat exchanging surface is strongly dependent on the Rayleigh number and the number of fins. It is, however, much less sensitive to the size of the fins and their orientation. The storage times are shorten...

Transient Natural Convection in Enclosures With Application to Solar Thermal Storage Tanks

Many previously studied natural convection enclosure problems in the literature have the bounding walls of the enclosure responsible for driving the flow. A number of relevant applications contain sources within the enclosure which drive the fluid flow and heat transfer. The motivation for this work is found in solar thermal storage tanks with immersed coil heat exchangers. The heat exchangers provide a means to charge and discharge the thermal energy in the tank. The enclosure is cylindrical and well insulated. Initially the interior fluid is isothermal and quiescent. At time zero, a step change in the source temperature begins to influence the flow. The final condition is a quiescent isothermal fluid field at the source temperature. The governing time-dependent Navier-Stokes and energy equations for this configuration are solved by a finite element method. Solutions are obtained for 103≤RaD≤106. Scale analysis is used to obtain time duration estimates of three distinct heat transfer regimes. The transient heat transfer during these regimes are compared with limiting cases. Correlations are presented for the three regimes.

Diffuser design influence on the performance of solar thermal storage tanks

The effect of the inlet and outlet diffuser design on the performance of thermal stratification in a vertical water tank is investigated experimentally. Two sets of diffusers are used in the experiments, which are conducted with a moving thermocline (both up and down) for different flow rates. The results indicate that the preservation of the initial thermocline is excellent when using a settling mesh. It is also shown that the extraction efficiency of the tank is higher at low flow rates during charging, whereas it is lower at low flow rates during discharging.

Factors Affecting Static Stratification of Thermal Water Storage

Abstract The thermal storage is a key component of any successful solar thermal system. A good thermal storage should allow minimum thermal energy losses while permitting the highest possible extraction efficiency of the stored thermal energy. Despite the many available examples of successful designs of solar thermal storage tanks, the static behavior of the solar thermal storage is not fully understood. Among the many factors influencing such behavior are heat losses, tank geometry, dead zones, and tank wall material. In this study laboratory-scale models with different geometries were built for the purpose of examining thermal behavior during the period after charging. During this period, called the thermal diffusion period, the extraction efficiency was temporarily decreased until natural stratification was achieved. After the thermal diffusion period, the extraction efficiency decreased primarily as a result of thermal losses to the environment and thermal degradation caused by the storage tank walls....

A comparative economic analysis of straight-through and recirculation solar hot water systems

A thermal and life cycle analysis was conducted to compare two types of solar service hot water systems: 1. (1) the straight-through system with the water driven by the pressure of the mains through a heat exchanger in which it is heated by the warmer water in the solar-thermal storage tank, whenever demand for service hot water is created, and 2. (2) the recirculation system in which a temperature-difference-controlled recirculation loop is used between the solar-thermal storage tank and the auxiliary (or backup) service hot water tank. The latter configuration which needs to have these additional components (controller, pump, and piping) and may thus also be less reliable, is more frequently used when the solar system is to supply both space heat and service hot water, because it is generally though to provide a larger fraction of the hot water from the solar source. A computer program, combining TRNSYS with a comprehensive present-value life-cycle model and an optimization link was prepared and run for a representative year in Philadelphia to determine the thermal storage, heat exchanger, and controller-setting combination which produces the minimal present-value life-cycle costs. To provide more generality to the results, these calculations were repeated for a wide range of temperature levels and transient patterns of the solar-collector-heated water in storage and of the service hot water demand patterns, quantities, and temperatures. Apart from some uncommon cases, it was found that the straight-through solar heating system is better than the recirculation one with respect to all comparison criteria: present-value life-cycle cost, auxiliary energy consumption, and reliability.