Heat Transfer Fluid Flow Rate Research Articles

Integrated substrate and adsorbent layer additive manufacturing for asymmetrically operating minichannel adsorbent bed

Adsorption heat pumps (AHP) have conventionally used packed bed design, making their operation sluggish leading to difficulty in using heat for the adsorbent regeneration. While thin adsorbent coatings improve the performance of AHPs when implemented in microscale geometries like minichannels, integrating the adsorbent coating procedure into the scaled-up adsorbent bed manufacturing has been impractical because of the finite time required for the coating process. Meanwhile, separately coated plates manifest sealing issues. This research details an innovative avenue to fabricate a unified adsorbent bed integrated with thin adsorbent coatings. Here, a compact adsorbent bed was fabricated through the integration of additive manufacturing using a fused deposition modeling (FDM) 3D printer for the substrate and resin curing for the MIL-101 (Cr) adsorbent layer. The multi-layered bed was designed to exchange heat between heat transfer fluid (HTF) and the passages through which the refrigerant vapor flows. The vapor channels were coated with a MIL-101 (Cr) adsorbent. The research incorporated both experiments and computational models to evaluate the operation of this adsorbent bed through the measurement of pressure during the adsorption and desorption stages for this component. Various HTF temperatures (80 °C − 90 °C) and flow rates (0.125 kg min−1 – 0.25 kg min -1) were tested. The findings revealed the much-desired asymmetrical operation with long adsorption (75–80 % of the cycle time) and short desorption stages (20 %-25 % of the cycle time), opening the possibility of employing a single bed in adsorption cooling systems to produce a near continuous cooling effect leading to more compact AHPs. The computational model developed for this test setup using MATLAB strongly aligned with experimental findings, with an error margin of 4–12 %.

Benefits of zeotropic mixture for heat pump water heater with phase change material thermal energy storage

Integrating heat pump water heater (HPWH) into latent heat thermal energy storage (LHTES) with phase change material (PCM) has been recognized as a promising way to mitigate the energy use for heating water in the building sector. This paper uses zeotropic mixture R1234yf/R1234ze(Z) in HPWH and spherical PCM encapsulations in LHTES. The mathematical model is established and validated. Effects of zeotropic mixture composition, working fluid flow rate and heat transfer fluid (HTF) flow rate are discussed to reveal the instantaneous behaviors and overall performance of the integrated system. The results indicate that as the charging process progresses, the condensing pressure of the system steadily increases, leading to a decline in COP. By employing zeotropic mixtures, the system performance can be effectively improved, with the highest COP of 2.68 when the mass fraction of R1234ze(Z) is 70 %, which represents an 18.1 % and 6.8 % improved COP compared to R1234yf and R1234ze(Z), respectively. A smaller refrigerant flow rate or a larger HTF flow rate contributes to a higher COP. For heat storage capacity in LHTES, a higher mass fraction of R1234ze(Z) and a larger refrigerant flow rate are preferable, while a smaller HTF flow rate is beneficial. Finally, a multi-objective optimization is carried out. Results suggest that the best overall performance is achieved with a COP of 2.70 and a heat storage capacity of 629.24MJ, under conditions of the mass fraction of R1234ze(Z) at 70 %, a refrigerant flow rate of 0.28 kg/s, and an HTF flow rate of 0.46 kg/s.

Solar thermal cooking device for domestic cooking applications: Bridging sustainable development goals and innovation

Fossil fuels are vital in the cooking field rather than the automotive sector. Hence, solar cooking has been popularized in recent years due to the rising cost of cooking gas. However, implementing successful renewable energy for cooking in urban area is still challenging for industries. Hence, a solar thermic cooking device with a compact size suited for domestic cooking in urban area is proposed. Thus, the solar cooking device will be developed as a fully functional prototype with necessary supporting modules, depending on the heat transfer fluid (HTF) flow and heat transfer rate between fluids. The main objective is to represent various computational fluid dynamics (CFD) and thermal analysis results on different optimistic designs for a solar thermoelectric cooking device's heat exchanger and storage unit. The 3D part model of the modules has been developed using SOLIDWORKS 2019 software. CFD has also been carried out using the same workspace with an additional package called flow simulation to analyze the flow properties of heat transfer fluid at different rates when circulated in other modules.Moreover, the thermal behavior of the HTF concerning the heat transition between module surfaces is simulated using SOLIDWORKS flow simulation to evaluate the heat storage capacity and rate of heat transfer. The theoretical formulations for the modules are derived through thermodynamic equations concerning the materials and fluid involved in the unit. The thermal and CFD analysis is carried out for different optimistic 3D models based on thermal sustainability, and the results are compared with theoretical analysis, which is discussed in this paper.

High-power-density miniaturized packed-bed thermal energy storage unit via phase change material capsules

Miniaturized thermal energy storage (TES) units with phase change materials (PCMs) are promising for the production of portable thermal management devices. In this work, a 100 mm-scale miniaturized packed-bed thermal energy storage (PBTES) unit based on homemade PCM capsules fabricated via the microfluidic method is established. The thermohydrodynamic characteristics of this unit are experimentally studied and analyzed based on a comparison with a traditional shell-and-tube thermal energy storage (STTES) unit. A modified Ergun equation is obtained for predicting the pressure drop of the PBTES unit with good accuracy. The results indicate that with increasing heat transfer fluid (HTF) flow rate, the charging and discharging processes are shorter, and the charging and discharging rates are much higher. The increasing inlet temperature of the HTF produces a large temperature gradient along the axial direction of the PBTES unit and enhances the performance of the PBTES unit. Generally, the average charging rate and overall efficiency of the PBTES unit with an HTF flow rate of 0.5 L/min can reach 30.09 W and 76.99%, respectively. The average charging and discharging power densities of the PBTES unit at a flow rate of 0.5 L/min are 81.94 kW/m3 and 47.79 kW/m3, respectively, which are 39.8% and 242.8% higher than those of the STTES unit. This work demonstrates high-power-density PBTES technology for normal-temperature applications.

Characterizations and Energy Analysis of Hydroxyl Group Functionalized Graphene (Nanomaterial) Mixed with Paraffin Wax (Polymer Pcm) as Thermal Energy Storage Materials And Applications

This work comprised of Paraffin wax as phase change material mixed/doped with functionalized graphene (hydroxyl group) for countering the poor thermal conductivity of the pristine phase change material. Firstly, Experiments were conducted on Thermal energy storage system during charging (melting) of the doped PCM. The main outcomes of these experiments were that as the volume concentrations of doped PCM and flow rate of the heat transfer fluid (HTF) were increased the charging time decreases along with increments in PCM temperature and accumulated energies. In case of OH functionalized graphene mixed with paraffin wax the charging time decreases by 38.4% to 84.61% for the HTF flow rate 25 ml/s over pure paraffin wax. Secondly, the advanced functional materials i.e., Paraffin wax mixed with functionalized hydroxyl group graphene was characterized by FTIR, XRD, TGA, DSC and FESEM, . The latent heat of melting obtained was 179.36 J/g for 1% graphene doping by DSC.

Development and Investigation of Nitrate Phase Change Filler Material for Solar Process Heating Applications

Thermocline thermal energy storage system is an imperial system for solar process heating applications. The thermal energy storage system comprises filler material and heat transfer fluid. In the present study, the commercial phase change material (PCM) (filler material) solar salt (60%NaNO3+40%KNO3) is synthesized, and it is encapsulated with a 1mm thickness of stainless steel 316L encapsulation with the macro-size of 60mm; the encapsulated PCMs is considered as a single particle in the thermocline thermal energy storage system. The performance of the single encapsulated PCM is studied with a constant heat transfer fluid (Therminol-VP1) flow rate of 0.00015 kg/s during the charging process. The specific heat of the solar salt is measured in Differential Scanning Calorimeter (DSC) in the solid phase is found as 1.381 J/gK, and liquid phase is identified as 1.551 J/g-K, the enthalpy during the phase change process is found as 116.72 J/g. As well, the thermal conductivity of the solar salt is measured in Transient Heat Conduction method, and the thermal conductivity follows the linear relationship of -0.0025(T)+0.4023 (45ºC<T<100ºC) in the sensible region. The temperature variations and the phase change phenomena for the solar salt is identified and the contours are provided. The charging time for the encapsulated solar salt is identified as ~138 minutes. The energy storage cost for the single filler material (Solar Salt + SS316L encapsulation) is identified as Rs.5.93/- (USD 0.071) for the period of charging duration.

Experimental and numerical investigations with multifunctional heat transfer fluid to evaluate the performance of a thermal energy storage system

In the upcoming decades, concentrated solar power (CSP) technology is expected to be one of the most promising methods of producing electricity.Along with the reduction in energy waste coupled with an increase in efficiency, the thermal energy storage (TES) systems are vital in refining the dependability and efficacy of the energy infrastructure and in reducing gap between supply and demand. This study aims to evaluate a parabolic trough collector by means of experimental investigation and mathematical modelling. Nanofluid is employed as an energy absorption material and transport medium from concentrating tube to storage tank. At consistent flow rate of 3.0 L per minute, a comparative evaluation is conducted between water and ZnS/ water-quantum dots at different volume concentrations (0.1, 0.2, 0.3, and 0.4 %). Heat exchanger-delivered sensible heat, thermal efficiency, heat removal factor, and energetic efficiency are used to examine the qualitative and quantitative performance of the system. The ZnS/ water-quantum dots ratio of 0.3 % (wt%) has been found to yield the maximum thermal and energetic efficiencies. At a solar intensity of 1210 W/m2, the highest thermal efficiency of 57.81 % is reflected by the experimental observations. At the same intensity, there is a 20.63 % increase in the energy efficiency. The charge and discharge of phase-changing material (PCM) are highly influenced by the flow rate of heat transfer fluid (HTF). By increasing the HTF flow rate from 1 to 3 L per minute, the solidification and melting times are shortened by 30 % and 10 %, respectively. This study emphatically reflects a high potential of employing nanofluid in TES to enhance the performance of energy infrastructure coupled with energy waste reduction.

Kinetic investigation and numerical simulation of reactor with prepared diatomite/CaCO3 for high-temperature thermal energy storage application

Calcium looping (CaL) thermochemical energy storage (TCES) gradually appears in high temperature concentrating solar power (CSP) plants. However, the CSP-Cal integrated system has encountered challenges related to the high temperature stability of calcium-based materials and reactor design. Firstly, the wet ball milling-impregnation method was used to experimentally prepare the diatomite calcium-based thermal storage materials, and a natural diatomite skeleton matrix was obtained. A modified diatomite/CaCO3 composite thermochemical energy storage material was synthesized. The material can keep maintaining an effective conversion rate of up to 85 % by repeating charging and discharging heat storage processes for 20 times. At the same time, the 3-dimensional diffusion model was applied to investigate the reaction kinetics during the heat storage process. Secondly, numerical studies were carried out to simulate the decarbonization process of the packed bed reactor used in CSP, illustrating the complex coupling mechanism of the multiple physical processes. The results reveal that increasing the temperature and velocity of heat transfer fluid (HTF) can accelerate the heat storage process and changing porosity can modify the reaction pattern. Finally, in order to enhance the heat transfer and flow rate of HTF inside the reactor, spiral metal porous channels of large permeability with high thermal conductivity are embedded in the reactor, which promotes CO2 emission and reduces the completion time during a decarbonization reaction. This study not only proposes a novel approach to prepare the calcium-based heat storage materials but optimizes the energy storage performance of packed bed reactors.

On the effect of nanoparticles in different PCM configurations in the thermal performance of a packed bed energy storage system

When it comes to storing energy and releasing it when needed, packed bed storage systems are considered to be one of the most efficient systems available. This paper studies the thermal performance of the melting process in a packed bed system using spherical capsules through CFD modeling. The effective packed bed model was used to simulate the fluid flow in the packed bed and enthalpy porosity method was used to solve the phase change material (PCM) domain. The capsules were filled with three various types of phase change materials, while water was utilized as the heat transfer fluid (HTF). Due to the importance of configurations of materials in the packed beds, the effects of various layouts of them on the performance of the system were investigated. Moreover, Al2O3 nanoparticles as a cheap and easily available nanoparticles were added to the materials. Also, the change in inlet flow rate of the HTF was examined. According to the results, positioning the materials in decreasing order of melting temperature in the flow direction is able to decline the charging time of the system by about 1600 s and increase the charging efficiency by 6.8 %. The addition of Al2O3 nanoparticles was able to decrease the charging time by about 1900 s in the best case and increase the system's efficiency by about 7.5 %. Increasing the inlet flow rate of HTF from 2.5 × 10−5 to 5 × 10−5 (1.5–3 Lit/min) reduced the charging time about 1800 s.

Experimental, computational, and analytical investigation of cooktop thermosyphon heat transport device for its feasibility in indoor solar cooking system

Cooking is a key contributor to worldwide energy usage and subsequent greenhouse gas emissions. Given this, clean and green energy-based cooking technologies are being explored globally. Though many solar cooker designs are being researched, the social acceptance rate is low due to operational, financial, and accessibility aspects. Hence in the present study, an indoor solar cooking system has been proposed, which has a cooktop Thermosyphon heat transport device (THTD) as an integral part. It transports heat from the outdoor receiver to the indoor kitchen through natural circulation (buoyancy-driven flow) of a heat transfer fluid (HTF). For the first time, different aspects of cooktop THTD are explored through experimental, analytical, and computational approaches. Based on the recommendations from a previous study, the flat design of cooktop THTD was constructed and tested with Therminol-VP1 as the HTF for both steady-state and transient performance. The steady-state results predicted by analytical and computational models were in good agreement with the experimental outcome. The HTF flow in the system is unidirectional, except in the cooktop region, where a combination of radial flow maldistribution and localized recirculation loops are seen (from velcoty contours and vectors) due to a larger flow passage. However, such flow anomalies vanish once the flow gap is reduced. Further, the transient tests witnessed a longer time for boiling (41–68 min) one litre of water in the first trial, which was reduced to 18–27 min with subsequent refills. An important observation is the increment in boiling time with increase in hot leg length. The rise in HTF flow rate (due to increased center-line elevation) and subsequent reduction in the bulk average temperature of HTF in the THTD was the reason for it. Further, the cooktop THTD could cook 315 g of rice in 40–45 min against 35–40 min using an electric induction stove, which justifies the proposed system’s efficacy. The study also demonstrated the criticality of thermal contact resistance between the cooktop surface and the surface of the cooking vessel. Hence devising an efficient and practically viable method (other than thermal paste) is essential. Also, due diligence is required while selecting the HTF as viscous fluid leads to a poor transient performance due to reduced flow rate. Hence, the transient behavior (practically the boiling time) of cooktop THTD is a trade-off between the bulk average temperature of the HTF and its flow rate.

Experimental investigation on thermodynamic performance of a copper foam-based cascaded latent heat storage tubes

Cascaded latent heat storage (CLHS) systems offer an effective means for energy storage from moderate to medium and low temperature heat sources (100-200℃). In this study, a three-stage shell-and-tube cascaded latent heat storage system was designed and fabricated. Three types of paraffin wax with distinct melting points were employed as phase change materials (PCMs), and foam copper was utilized to enhance heat transfer. By adjusting the inlet temperature and flow rate of heat transfer fluid (HTF), the thermodynamic performance of each LHS stage and the entire system under different operating conditions were investigated. Exergy analysis, entransy analysis, and sensitivity analysis were employed to study the primary influential factors on system performance and the impact weights of diverse operating conditions. Experimental results highlighted the crucial significance of maintaining consistency in the physical parameters of PCMs across different stages in the CLHS system for its thermodynamic performance. The high thermal conductivity and low latent heat of PCM#2 in the second stage result in substantial energy losses during the heat storage process, reducing the efficiency of energy cascaded utilization within the system. With an increase in the HTF inlet temperature and flow rate, the energy storage capacity and rate increase, while the energy storage efficiency exhibits a decreasing trend. Moreover, the effect of varying inlet temperature on the energy storage efficiency is much smaller compared to that of inlet flow rate. This study emphasizes that heat dissipation is a critical factor affecting the thermodynamic performance of the cascaded latent heat storage system. For CLHS systems targeting high-temperature and high-flow rate heat sources, enhancing insulation is crucial for ensuring the sustained high-efficiency operation.

CFD Analysis of a Latent Thermal Storage System (PCM) for Integration with an Air-Water Heat Pump

Heat pumps driven by sustainable electricity sources have been identified as a technology that can contribute to reduce carbon dioxide emissions. Furthermore, a heat pump can also provide energy savings when combined with a thermal energy storage system. Heat pumps can optimize their efficiency by accumulating thermal energy during periods of lower electricity demand, resulting in shorter operational durations and decreased overall energy consumption. In this work, the combination of a latent heat storage system with an air-water heat pump has been numerically analysed and experimentally tested. A phase change material (PCM) heat exchanger with an immersed plate was designed using a 3D CFD model (COMSOL Multiphysics®). The heat exchanger configuration with six steel plates immersed in the phase change material tank was proposed to enhance heat transfer in the storage system. The developed model is validated against experimental data from a real case study, demonstrating a maximum error of approximately 3% during the discharging phase. Additionally, the study explores the effects of different inlet heat transfer fluid temperatures and flow rates on the PCM solidification time.

Numerical analysis of demolition waste‐based thermal energy storage system for concentrated solar power plants

AbstractThermal energy storage (TES) is an enabling system that provides uninterrupted energy from concentrated solar power (CSP) plants. Packed‐bed TES systems have great opportunity to significantly enhance the cost‐effectiveness, efficiency, and sustainability of CSP plants by employing an affordable and sustainable packing material. The objective of this study is to design a demolition waste‐based packed bed TES system with a maximum storage capacity of 40 kWh, specifically tailored to store heat within the temperature range of 290°C to 565°C using solar salt as heat transfer fluid (HTF), thereby making it suitable for integration into CSP plants. Performance and thermal behavior of demolition waste‐based packed‐bed TES system was assessed through numerical analysis. The results demonstrate that a high discharging efficiency of 76.0% was achieved when the HTF flow rate was set at 100 kgh−1. However, it is important to note that at lower HTF flow rate, heat loss increases, leading to a decrease in discharging efficiency to 70%. The experiment also revealed a uniform thermal gradient within the packed‐bed TES system, up to a fluid flow rate of 300 kgh−1. It is worth mentioning that lower flow rates can further improve the stratification effect; however, they may also result in increased heat loss and reduced storage capacity. Based on these findings, an optimal flow rate range of 100 to 200 kgh−1 is recommended to achieve the best performance for the packed‐bed TES system.

Experimental investigation of thermal performance of vertical multitube cylindrical latent heat thermal energy storage systems

The multitube design in the shell-and-tube type latent heat thermal energy storage (LHTES) system has received intensive attention due to its promising benefits in enhancing heat storage efficiency. In this paper, single and multi-tube shell LHTES systems were experimentally investigated. First, this study experimentally compared the thermal characteristics between a multiple-tube heat exchanger (MTHX) and a single-tube heat exchanger (STHX). The STHX’s geometrical parameters coincided with a virtual cylindrical domain in the MTHX, being similar to the single-tube model formulated by simplifying the numerical solution to investigate the MTHX. The experimental data was then used to validate the simplified numerical model commonly used in the literature that converted the multi-tube problem to a single-tube model by formulating a virtual cylindrical domain for each tube in the MTHX system. The results showed that there was a noticeable difference in the thermal characteristics between the actual STHX and the virtual cylindrical STHX domain in the MTHX system. The comparison indicated that the simplified numerical model could not accurately reflect the thermal performance of the MTHX system. An experimental study or three-dimensional numerical modelling was required for the thermal analysis of the multi-tube problems. Second, the effect of tube number in the MTHX was experimentally investigated. It was found that an increase in tube number boosted both charging and discharging rates without inhibiting the natural convection. The five-tube configuration decreased the total charging and discharging duration by 50% compared to the two-tube one. Finally, the effect of heat transfer fluid (HTF) operating parameters on the system performance was evaluated on the five-tube MTHX system. The results revealed that the adoption of higher HTF temperature considerably improved the charging performance. The charging time decreased by up to 41% with the HTF temperature increasing from 70 to 80 °C. Meanwhile, a variation in the HTF flow rate from 5 to 20 L/min showed a more pronounced influence on charging than on discharging due to the different dominant heat transfer mechanisms.

Development of multi-module arranged in series using U-type longitudinal fin tube in thermal energy storage system

The performance of a thermal energy storage (TES) system for commercial applications can be improved using phase change materials (PCM). This study develops a vertical multi-module from a PCM for a TES system that achieves the same effect as a single-module by arranging multiple-modules in series as a U-type longitudinal fin tube to enhance the system's performance. The U-type longitudinal fin tube is designed to enhance heat transfer within the module, and a single-module is designed for multi-module applications. The TES system is analyzed to the average heat transfer rate, overall heat transfer coefficient, quantity of heat storage/release, and utilization ratio at different heat transfer fluid (HTF) flow rates, inlet and outlet temperatures and different number of modules. Consequently, the addition of several modules improves the thermal performance, and an increase in the HTF flow rate improves the average heat transfer rate. The overall heat transfer coefficient is used to analyze the thermal characteristics of the PCM. During the heat charging and discharging processes, the average heat transfer rates are 2.4 and 2.55 kW, respectively, and the quantities of heat storage and release are 5,153.59 and 4,771.79 kJ, respectively, for three modules. The overall heat transfer coefficient of the PCM exhibits similar results with an increasing HTF flow rate; it increases marginally from 42.25 to 45.8 and 9.9–10.8 W∙m−2∙K−1 as more modules are added. Further, the results of this study confirm that the relatively low HTF flow rates in the multi-module require the addition of several modules and that increasing the HTF flow rates limits the number of modules.

Performance investigation and evaluation of a low-temperature solar thermal energy storage system under dynamic weather conditions

Designed and operational parameters matter greatly in how successful an energy storage system performs. However, a current challenge in matching suitable these parameters lies in the poor understanding of such systems’ performance under dynamic weather conditions. In this paper, we investigated a phase change material (PCM) storage unit that is particularly aimed for poor-solar areas, and connected the unit to a flat plate solar collector to establish a complete solar thermal energy storage system (STESS). To optimize the system performance, different grades of solar radiation and outdoor ambient temperatures are introduced, and the effects of heat transfer fluid (HTF) flow rates and solar collecting areas are investigated numerically through multiple performance evaluation parameters. The results indicate that the solar collecting area has a significant effect on the performance of the STESS compared to that of the water flow rate. And different collecting areas of 1 m2, 1.5 m2, and 3 m2 with an optimal water flow rate of 0.06 m3/h are matched to different average daily solar radiation of 203.4 W/m2, 155.2 W/m2, 92.7 W/m2, respectively. Further for the heat release process, different heat release efficiencies from 88.32 % to 97.12 % with different energy consumption of the fan from 0.003 kWh to 0.063 kWh are obtained when the air flow rate is increased from 30 m3/h to 90 m3/h. One of the air flow rates of 60 m3/h is superior for the STESS considering higher heat release efficiency and lower energy consumption of the fan. The findings of this paper will contribute to optimizing the performance of a STESS in practical applications.

Cascading latent heat thermal energy storage in parabolic trough solar collector as a promising solution: An experimental investigation

Solar energy system can be considered as a reliable energy source if it connects to a latent heat thermal energy storage (LHTES) system using phase change materials (PCMs). To tackle the low thermal conductivity coefficient of PCMs, the cascaded latent heat storage (CLHS) configuration is a promising solution. This study aims to illustrate the improvement of CLHS setup comparing with non-cascaded arrangement, performing a whole-scale experimental investigation. A compact parabolic trough collector (PTC) unit equipped with a LHTES module is designed and constructed for a residential purpose. Experimental results reveal that the average thermal efficiency of PTC is 73.5 %. Three paraffin waxes with melting ranges of (64–68 ℃), (57–60 ℃) and (46–48 ℃) are injected in three same series of shell-tube heat exchangers. For comparing cascaded and non-cascaded PCM performance, three experimental series, namely (Exp.1, Exp.2 and Exp.3) are performed. The experimental findings show that the deployment of the CLHS configuration improves the latent heat storage of non-CLHS-Exps.1, 2, and 3 by more than 10, 47, and 5 %, respectively. In addition, CLHS system has a potential to increase the exergy storage of non-CLHS setup by up to 27.4 %. Furthermore, impact of increasing heat transfer fluid (HTF) flow rate is examined and it is observed that the melting process is shortened by almost 39 %. Accordingly, increasing flow rate improves energy stored in PCMs1, 2, and 3 by 60 %, 59.62 %, and 72.04 %, respectively. Consequently, the latent thermal exergy storage of the PCM experiences a twofold increase. Conducting an experimental evaluation of thermal performance of the storage module integrated with PTC setup can be valuable, particularly in the realm of residential applications.

Heat transfer and thermal resistance analysis under various heat transfer fluid flow rates based on a medium-temperature pilot-scale latent heat storage system

Assessments often rely on experimentally observed factors when examining heat transfer variations due to different heat transfer fluid (HTF) flow rates. To better comprehend limiting factors and guide operational parameter design for shell-and-tube latent heat system (LHS) systems, a quantitative analysis of thermal resistance hindering heat transfer is crucial. Hence, this article conducted experimental evaluations at various flow rates to critically analyze its thermal performance based on a large-capacity (1000 MJ) medium-temperature LHS system loaded with 4130 kg commercial nitrate mixture (peak melting temperature: 219.90 °C). The heat transfer coefficient and thermal resistance during charging and discharging were quantitatively investigated to identify the main factors influencing heat transfer and dominant mechanisms. The results suggested that augmenting the charging flow rate from 5 to 15 L/min resulted in 2.65 times increase in average power (from 24.01 to 63.64 kW). Besides, during charging, the overall thermal resistance primarily came from the phase change material (PCM) side initially. As PCM melted, the thermal resistance on the PCM side became equivalent to that on the HTF side. Increasing the charging flow rate enhanced heat transfer through two mechanisms: reducing the thermal resistance on the HTF side and increasing the driving force of heat transfer by elevating the average HTF temperature. During discharging, the overall thermal resistance was predominantly derived from the PCM side after solidification. Increasing the discharging flow rate caused a limited influence on decreasing thermal resistance. Enhancing the discharging flow rate only bolstered the driving force for heat transfer by elevating the average HTF temperature. This study provides valuable insights into the factors influencing heat transfer in LHS systems and contributes to optimizing LHS technology.

Parametric analysis of a solar parabolic trough collector integrated with hybrid-nano PCM storage tank

ApplicationNewly developed fluid called phase change materials (PCM) used to accumulate solar thermal energy. This paraffin-based fluid is mixed with hybrid nanoparticles composed of titanium dioxide “TiO2″ and copper oxide “CuO”. Using this fluid, we hope to improve the efficiency of industrial solar thermal installations. Purpose and MethodologyA computational fluid dynamics (CFD) model was developed using Ansys Fluent 19, coupled with a home code implemented in the C programming language as a “user-defined function”. Initially, the model was validated against experimental data, then a parametric study was conducted to investigate the impact of pure paraffin PCM and hybrid nanoparticles-paraffin PCM, as well as the effect of varying the mass fraction of nanoparticles and the heat transfer fluid flow rate. geometric parameters such as the number of fins installed in the storage tank were also considered during the analysis. Major findingsOn the basis of the obtained results, it was found that the incorporation of paraffin phase change materials (PCMs) within a storage tank has the potential to significantly prolong the operational duration of solar systems. Additionally, hybrid nanoparticles at 1% concentration increased the average storage tank temperature by 8% and decreased the melting time by 13.29% compared to pure PCM.

Thermal energy storage based on cold phase change materials: Discharge phase assessment

In an energy scenario characterized by strong requirements in terms of flexibility and readiness, the integration of thermal energy storage in energy systems could play an important role in demand-supply management and allows novel operational schemes. Thermal Energy Storages based on latent heat are characterized by their compactness and small temperature swing. However, there is still a lack of performance analysis on large-scale setups. This work aims to fill this gap. In this paper, a shell & tube latent heat-based cold thermal energy storage was characterized in the discharge configuration, considering different temperatures and mass flow of the heat transfer fluid, representing an opportunity to understand the behavior of a full-scale system in different operative conditions. Sensitivity analyses on heat transfer fluid flow rate, flow direction, and inlet temperature were performed. The results show that peak power increases by approximately 25 % with doubled mass flow rate, and it doubles with increased inlet temperature by 6 °C. Since the impact of the buoyancy effect occurs when the liquid phase is predominant over the solid one, there is no strong impact on the direction of the Heat Transfer Fluid, from top to bottom or viceversa. Despite no metastability phase being detected, many discontinuities in the thermal power and temperature profiles were identified and analyzed, providing new insights into full scale latent heat storage. Finally, in this work, the thermal round-trip efficiency was estimated to reach above 90 %.