Thermal Storage Unit Research Articles

Numerical Investigation of Heat Transfer Characteristics of Trapezoidal Fin Phase Change Thermal Energy Storage Unit

Abstract: In order to enhance the heat transfer performance of a phase change thermal energy storage unit, the effects of trapezoidal fins of different sizes and arrangement modes were studied by numerical simulation in the heat storage and release processes. The optimal enhancement solution was obtained by comparing the temperature distribution, instantaneous liquid-phase ratio, solid–liquid phase diagram and comprehensive heat storage and release performance of the thermal energy storage unit under different fin sizes. During the heat storage process, the results show that when the ratio of the length of the upper and lower base of the trapezoid h1/h2 is 1:9, the heat storage time is shortened by 9.03% and 18.21% compared with h1/h2 = 3:7 and 5:5, respectively. During the heat release process, the optimal heat transfer effect is achieved when h1/h2 = 5:5. To further improve the heat transfer effects, the energy storage unit is placed upside down; then, the least time is achieved when h1/h2 = 2:8. When heat storage and release are considered together, the energy storage unit with h1/h2 = 2:8 takes the shortest time to melt in upright placement and then to solidify in upside-down placement.

A comparative analysis on charging performance of triplex-tube heat exchanger under various configurations of composite phase change material

In present work, the melting performance of triplex-tube latent heat thermal energy storage (LHTES) unit was numerically studied using equal volumes of PCM and metal foam composite PCM (CPCM) in various arrangements. For the n-eicosane (as PCM), the study was conducted at the fixed Rayleigh number (Ra) = 4.08x107, Prandtl number (Pr) = 62.9, and Stefan number (Ste) = 0.14. The results showed that positioning the metal foam on the bottom side and distributing segmented CPCM with alternating PCM zones effectively improved the system performance. Moreover, this also prevents the overheating of thermal layers in the LHTES unit. While the model labelled M2 exhibited the highest economic efficiency among all isotropic models, its low dimensionless thermal energy storage (TES) density (i.e., q’ ∼ 0.6) led this study to focus on models falling under the category having a TES density of ∼ 0.8. Compared to a pure PCM model, the configurations under equal volume ratio category demonstrated up to ∼ four times higher TES rate (p’) and the significant reduction of ∼ 75 % in melting time. The optimized isotropic model achieved the highest TES rate per unit cost with peak value of ∼ 3 at a price ratio (N) of 1. Lastly, the testing of metal foam anisotropy on the chosen design showed a substantial increase in melting/heat storage rates. The largest drop of ∼ 33 % in the total melting time was noticed for model M2 as compared to isotropic case.

Performance study of low temperature air heated rock bed thermal energy storage system

AbstractOne of the primary types of sensible heat storage systems in drying applications is the packed rock bed. However, to create large‐scale heat storage systems for industrial use, one must comprehend the hydrodynamic and effectiveness of the heat transport mechanism inside the bed. In this study, the thermal storage unit uses river rock as heat storage materials with equivalent particle diameters of 36 mm in bed 1 and 56 mm in bed 2. The rocks were stacked in a truncated cone‐shaped concrete wall section with an average diameter and depth of 1.1 m and 1.3 m, respectively and a volume of 2.32 m3. During the charging phase, two airflow configurations were used, one from the top with an air mass flow rate of 0.753 and 0.332 kg/m2‐s and the other from the bottom with an air mass flow rate of 0.955 kg/m2‐s. During the discharging phase, the entire flow configuration is from the bottom section. It was observed that the mass flow rate and particle equivalent diameter had an important effect on the thermal performance and behaviour of the rock bed during charging and discharging operations. Maximum efficiency was achieved with an airflow configuration provided from the bottom when charging at 0.955 kg/m2.s. Consequently, a sizable quantity of heat or energy (60 MJ) was retained. It was also observed that the relationship between air mass flow rate and particle size was significant, with smaller particles retaining more energy. When comparing bed 1 with bed 2 at this air mass flow rate, bed 1 stored 2.1 times more energy than bed 2. A wind tunnel experiment was used to measure the pressure drop in the packed rock bed. The pressure drop in the bed increases with an increase in particle Reynolds number and decreases with an increase in particle size. Rock bed heat transfer coefficient and Nusselt number were calculated using the correlation that has already been established in the literature smaller particles showed higher heat transfer coefficients and lower Nusselt numbers. This is due to the increase in particle‐to‐particle interaction and larger particle surface areas. For a given Reynolds number, the Nusselt number increases with the size of the rock particle.

A robust real-time energy scheduling strategy of integrated energy system based on multi-step interval prediction of uncertainties

The uncertainties of renewable energies and loads in integrated energy system (IES) result in unstable operation and performance degradation. To consider the impact of the uncertainties, the scheduling strategies of IES with the prediction of uncertainties are required. This paper designs a hybrid solar and gas turbine IES, in which the thermal and electrical storage units are integrated to address the uncertainties. A robust real-time energy scheduling strategy is proposed according to the real-time load and the predicted loads in the future time, in which the errors of multi-step interval prediction of renewable sources and loads are combined. The multi-step prediction method based on gated recurrent unit and time classification is constructed for the interval prediction of uncertain sources and loads by analyzing the probability statistics of prediction errors. In the robust optimization, the penalty factors of time sequences are proposed and considered to decrease the influences of future predicted information on current real-time scheduling, in which the future uncertainties in larger interval with current time has less influence. The optimal results in the hybrid IES demonstrate that the daily operation cost is 13.67 % lower than the method that does not consider the prediction parameters. Compared to the traditional scheduling strategies, the proposed strategy declines the operation cost by 2.93 %. The analysis of the confidence level of predictions ranging from 60 % to 98 % illustrates that the operation cost under the penalty factor of 0.94 is the lowest when the confidence level is from 94 % to 96 %.

Techno-economic analysis of a novel concept for the combination of methane pyrolysis in molten salt with heliostat solar field

Methane pyrolysis has emerged as a promising low-carbon hydrogen production method, serving as a bridge from conventional fossil fuels to renewable energies (REs). A recent technique for sustainable hydrogen production involves the process of methane pyrolysis in molten salt. To better understand the potential of sustainable turquoise hydrogen production, this paper presents a techno-economic assessment of methane pyrolysis in molten salt combined with a high-temperature heliostat solar field. In addition, a high-temperature thermal energy storage (HTES) unit is utilized to ensure uninterrupted hydrogen production during periods of solar unavailability, thereby contributing to the economic viability of the overall system. The proposed system can produce about 9 tons of H2/day and 27 tons of solid carbon/day with a round-trip efficiency of 49.8 % and a levelized cost of hydrogen (LCOH) of 1.93 $/kg. To further decarbonize the process, the feasibility of utilizing REs as the source of electricity for the HTES was analyzed, yielding a synergistic achievement of clean and economic hydrogen production. This configuration resulted in a LCOH of 1.25 $/kg, after including the United States (US) clean hydrogen production tax incentives. The proposed system shows the potential to achieve the US Department of Energy target of 1 $/kg of hydrogen with a 20 % reduction in the cost of RE infrastructure.

Response to the design conditions of a tube-bundle thermal energy storage unit with paraffin-copper foam composite as a storage medium

Owing to its potential to limit the issues of intermittency and instability in solar energy by means of phase-change materials (PCMs), latent heat thermal energy storage (LHS) has met increasing attention and been widely employed in thermal-based systems. Most PCMs, however, inherently exhibit poor heat conductance leading to modest rate of charging. To master this drawback, highly conductive metal foams are utilized to upgrade the bulk heat conductance of a PCM resulting in an enhanced rate of heat transport; hence, accelerating the melting process. This enhancement way is employed to promote the response of a tube-bundle thermal energy storage unit configured of staggered tubes filled with high-porosity copper foam embedded in paraffin wax as a storage medium. To charge the thermal energy storage (TES) unit proposed, a relatively hot stream of water is allowed to flow across the bundled tubes through the voids in-between. To check how feasible the proposed design is, the tubes enclosing the TES medium and the water flow in the shell surrounding have been simulated by ANSYS Fluent CFD code. A variety of design factors has been examined to explore their influence on the charging performance attained including structural properties of the metal foam employed along with the configuration of the tube-bundle considered. The foam structural characteristics inspected are the porosity ∅∈(0.89∼0.97) and pore density ω∈(5∼80)PPI, while various tube-bundle configurations have been tested in terms of the packing density N∈(15∼65)TubesLines/meterwidth as well as the shape of PCM tubes used b/a∈(0.25∼1). Results indicate that for a certain tube-bundle configuration, the best response is acquired when denser foam with lower porosity is used, while the best performance can only be achieved with higher porosity due to the better TES capacity offered. For certain foam structural properties of (∅=0.93&ω=80PPI), it has been observed that increasing the packing density can save up to 56 % of the time taken for charging completion with up to 200 % increase in storage capacity leading to up to 48 % improvement in the system overall performance. It has also been found that using paraffin embedded with copper foam as a TES medium accelerates the melting process considerably and saves more than half the time taken to charge the corresponding TES unit based on pure paraffin. It is also worth mentioning that the currently suggested LHS unit is not only of simple configuration, but practically efficient as well, with outstanding gross performance OP∈(104∼105). Through a proper manipulation of design conditions, it has been found that the charging response can be notably improved leading to substantial promotion in the overall performance realized.

Improving phase change heat transfer in an enclosure partially filled by uniform and anisotropic metal foam layers

Anisotropic metal foams exhibit exceptional potential for improving the efficiency of latent heat thermal energy storage (LHTES) units by enhancing heat transfer and thermal energy storage rates. This study explores the largely uncharted area of thermal behavior of anisotropic metal foams in varied configurations and enclosure designs. The research focuses on an LHTES unit with a specific channel configuration, constructed using copper and containing three layers of copper metal foam, one of which is anisotropic and infused with paraffin wax. The finite element method was utilized to manage the complexities emerging from phase change, and the anisotropic angle varied from 0 to 90° in three different placements of the AMFL: top, middle, or bottom of the enclosure. The ideal design was achieved with an AMFL in the middle with a 0°angle, resulting in a 3.7 % reduction in melting time and approximately a 2.3 % reduction in solidification time. However, AMFL designs at the middle placement with a 75° anisotropic angle were less effective, hampering the melting and solidification processes, thus potentially extending charging and discharging times. The study concludes that the placement and angle of the AMFL layer are vital for the heat transfer capabilities of phase change materials. AMFL at the middle with a 0° angle optimally leverages temperature gradients, enhancing heat transfer compared to other investigated cases. An AMFL in the middle with a 0° angle exhibits approximately 7.1 % and 6.3 % improvements for melting fractions of 0.9 and 0.95, respectively, underscoring its potential for efficient thermal energy storage.

Experimental and numerical investigation on latent heat/cold stores for advanced pumped-thermal energy storage

Pumped-thermal energy storage plays a pivotal role in large-scale harvesting and utilization for renewable resource endowments with intrinsic properties such as intermittency and instability. Here, we conducted detailed experimental and numerical studies on latent heat/cold stores of Brayton-like pumped-thermal energy storage. A demonstration thermal energy storage system with rated power of 20 kW including phase change materials (PCMs) preparation and structural design of energy storage units is synergistically designed and built. In this paper, the operating mechanism behind the theoretical experiment and control groups that raises the intake temperature through an air heater is uncovered and compared. Moreover, an auxiliary numerical model for further energy and exergy analyses is established to perfect the system-wide assessment. In terms of the first law of thermodynamics, the speed of energy storage and efficiency increase with higher operational pressures. For instance, system properties like roundtrip efficiency can reach up to 0.37 at an operating pressure of 0.7 MPa. As for systematic exergy despite the total destruction of thermal energy storage units amounts to 12.25 kWh the maximum exergy efficiency could reach 0.61 simultaneously.

Numerical simulation of the influence of different heating directions on charging performance of the cubic combined sensible-latent heat storage structure

The sensible and latent heat storage system (CSLHS) has become a research hotspot. In this paper, we construct a thermal storage unit structure by using the method of cubic macro-encapsulation, and its charging performance is simulated by CFD. The material of sensible heat storage is magnesia brick or concrete, and the material of the latent heat storage is molten salt. First, we analyze the effects of different heat surfaces on the charging performance of the CSLHS. The charging performance is better when heating from the bottom than when heating from the top or the side. Then, the heat storage of concrete brick and CSLHS is compared, under the premise of heating from the bottom surface. When the PCM starts to melt, the heat transfer inside the hybrid configuration is 39% higher than the solid heat storage structure. When the heat storage is nearing completion, its temperature distribution is more uniform than the solid heat storage structure, and its heat transfer inside the hybrid configuration is at the same level as the concrete.

Predicting the performance of a photovoltaic unit via machine learning methods in the existence of finned thermal storage unit

The process of cooling the photovoltaic (PV) cells is essential since increasing solar cell temperatures reduces electrical effectiveness. One suggested method to reduce cell temperature is employing PCM (phase change material) mixed with nanomaterial. Thermoelectric modules between the layers are also recommended to increase electrical efficiency. By taking advantage of machine learning predictive algorithms, the objective is to forecast the effectiveness of a PV unit equipped with finned thermal storage unit in existence of nanomaterials, while maintaining an appropriate accuracy based on two evaluation metrics throughout prediction. According to the data analytics of the simulation, the selected models used to achieve this goal are linear regression, polynomial regression, lasso regression, and an Auto-Regressive Integrated Moving Average (ARIMA) model. These models were then examined employing the root mean squared error (RMSE) and mean absolute percentage error (MAPE) across three cases, namely plain mode, mode with fins, and plain mode with the effect of gravity. The test RMSE and MAPE of these models across the above-mentioned cases were then calculated for comparison purposes, where the best-performing model for predicting both PCM temperature and melting fraction (MF) was ARIMA, with an average RMSE of 0.11, and an average MAPE of 0.0003 for predicting PCM temperature and an average RMSE of 0.003, and an average MAPE of 0.0034 for predicting MF across all cases. The ARIMA model was then used to predict the MF, PCM temperature, and PV temperature of the last case, namely mode with fins and the effect of gravity. Finally, this model was also used to predict the time at which the PCMs are completely melted in all modes, as well as to predict PV temperature. The total electrical efficiency of the mode with fins and the effect of gravity were calculated using the predicted PV temperature, yielding a result of 13.993 %.

Influence of fin shape design on thermal efficiency of phase change material-based thermal energy storage unit

The present numerical study treats the impact of fin shape design on the thermal efficiency of phase change material (PCM)-based thermal energy storage (TES) unit, focusing on the same surface area occupied by fins. Comparing two different finned TES units equipped with rectangular and triangular fin shapes, respectively, showed significant enhancements in PCM melting activity. Comparative analysis demonstrated that triangular fin shape lowers PCM melting time by 12.64% for equivalent fin numbers, and by 15.38% for equal fin lengths due to the enlargement of the heat transfer area provided by the triangular shape. Further examination of fins with triangular shape in terms of spacing and length, under fixed thickness and size parameters, revealed significant reduction in melting time with increasing fins length. Notably, 50.75% decrease in melting time was achieved by decreasing the number of fins to 20 while increasing fin length to 10 mm. Moreover, maintaining a heat transfer fluid (HTF) temperature 20 K higher than the melting PCM temperature maximizes TES thermal efficiency. These outcomes emphasize the importance of optimizing fin shape design for enhancing heat transfer without affecting the energy storage capacity of TES systems, with potential applications in building thermal management.

Natural convection and field synergy principle analysis of the influence of fins redistribution on the performance of a latent heat storage unit in a successive charge and discharge

The present study focuses on analyzing the impact of enhancing the heat exchanges on the shell side by surface extension on the kinetics of melting/solidification in a latent heat thermal energy storage (LHTES) unit. Particular attention is paid to the influence of fins redistribution on the performance of the LHTES unit, natural convection, and Phase Change Material (PCM) melting/solidification kinetics. The particularity of this study lies in the improvement of the LHTES unit performances in a successive charging-discharging operation by only redistributing the fins while keeping the same total heat transfer surface, PCM volume, and compactness. The first part of the study consists of evaluating the impact of fin redistribution for the same total heat transfer surface on the LHTES unit performance. Attention was paid to the fully charging and discharging times and the heat duty absorbed or released during the melting or solidification process. For this purpose, 4 configurations of LHTES units having 4 and 8 radial fins with the same total transfer surface were analyzed, with the aim of ensuring a maximum performance on charging process. In a second part, an improved configuration was proposed in order to minimize the successive charging and discharging time for a cyclic operation of the LHTES unit. The coordination factor derived from the field synergy principle, PCM liquid fraction, the heat duty exchanged, phase change kinetics, and liquid PCM velocity were used as performance key factors. They were used to analyze and compare the different configurations in order to find the best configuration for a successive charging-discharging operation. The selected improved configuration has been found to enhance both the charging and discharging processes. It leads to the reduction of the successive charging-discharging overall duration by 10 % to 47 % compared to the other configurations investigated with the same heat transfer surface. The enhanced LHTES unit developed in the present study is intended to improve the thermal comfort of buildings by valorizing and storing renewable and waste energies.

Initial experimental testing of a hybrid solar-dish Brayton cycle for combined heat and power (ST-CHP)

The Solar Turbo Combined Heat and Power (ST-CHP) project developed a novel solar-gas hybrid prototype for combined heat and power generation in Pretoria, South Africa. A vacuum-membrane faceted parabolic dish with a large-pipe open-cavity receiver was coupled to a counterflow recuperator, a combustion chamber, a micro gas turbine with air bearings and a phase change thermal energy storage unit containing solar salts. This study aimed to validate the electrical output of the full-scale dish-Brayton prototype, addressing the literature gap on micro-scale dish-Brayton plants' in-field power generation. Solar hybridization of micro gas turbine technology can significantly reduce combustion fuel consumption. A performance analysis under relevant conditions revealed a late afternoon micro gas turbine output intermittently peaking at 0.4kWe and subsequently stabilizing to a steady state of 0.145kWe at 130krpm. A SimuPact numerical model and an analytical model supplemented the telemetry data to reduce interference in the experimental setup and fully characterize the ST-CHP prototype performance, estimating a steady-state turbine isentropic efficiency of 57%, a compressor efficiency of 71% and a collector efficiency of 17% due to the late afternoon steady-state point. Analytical case studies revealed that fuel savings of between 12% and 33% at the combustion chamber were achievable from the solarized preheating. A subsequent test of the micro gas turbine without solar hybridization or a recuperator resulted in 1.05kWe being generated. The study confirms the dish-Brayton prototype's viability for combined heat and power generation, producing an initial full-scale performance characterisation during in-field testing, and highlighting the impact of solar hybridization on turbine electrical output. Optical efficiency, insulation effectiveness, pressure losses, and turbine operating conditions were identified as critical areas requiring optimization to improve electrical output. The lessons learned, and the calibrated numerical model may be used to optimize the performance of the dish-Brayton plant in future work. The successful in-field full-scale power generation of the ST-CHP prototype adds to the available literature on dish-Brayton technology and brings the technology closer to a commercial product.

Numerical investigation and optimization of the melting performance of latent heat thermal energy storage unit strengthened by graded metal foam and mechanical rotation

In this paper, a combined passive graded metal foam and active mechanical rotation strategy is proposed to simultaneously solve the problem of slow melting rate and non-uniform phase change problem of the latent heat thermal energy storage (LHTES) technology. The enthalpy-porosity method and fixed grid structure are employed to numerically investigate the effects of porosity range, the number of graded layers, and the rotational angular velocity. Moreover, the response surface method (RSM) is further selected to optimize the structural parameters and obtain the function of melting performance and various factors. The result shows that there is an optimal porosity range and the total melting time decreases first and then increases with the increase of porosity range. When the porosity range is 12 % and the graded layer is three, it can shorten the melting time by 35.54 % and increase the thermal energy storage rate (TESR) by 51.57 %. In addition, the melting performance is gradually improved as the number of graded layers increases. The strengthening effect of graded metal foam with just four layers is close to that of the maximum layers considered in this paper. The trend of the influence of rotation speed on the melting performance of the LHTES unit is consistent with the porosity range, indicating the existence of the optimal rotational speed. The RSM optimization structure, with a 14.969 % porosity range, 5-layer graded number, and 2.267 rpm rotational speed, shortens the melting time by 42.42 % and increases the TESR by 62.75 % compared with the stationary case with uniform metal foam. This work verifies the effectiveness of active rotation coupling with passive graded porous structures, which could provide a new strengthening approach to enhance LHTES.

CO2 heat pump integrated thermal storage for domestic hot water in hotels

Gas/diesel-fired water heaters are widely used in Indian hotels to deliver domestic hot water at 45–50 °C. These are substantial fossil energy consumers and pollute the environment. A CO2 (natural refrigerant) heat pump integrated thermal storage unit is an energy-efficient and eco-friendly solution for meeting heating demands. In tropical ambient conditions like in India, the energy efficiency of such heat pumps can further be improved when the heat source is the chilled water used for air conditioning purposes of the same hotel, thereby reducing the load on existing chillers. However, studies on the design of the proposed system and assessment of its potential for hotel application in tropical climates are still scarce. This information assists energy engineers and hotel management in evaluating new buildings or refurbishments. This paper demonstrates a design strategy to retrofit the conventional system with the heat pump integrated thermal storage unit and assess its energy, economic, and environmental benefits for a typical Indian hotel. Four different heat pump configurations, simple and ejector-assisted transcritical CO2 systems with and without internal heat exchangers, are analyzed and compared. The ejector-assisted CO2 heat pump without IHX having the minimum heating capacity (operates all time) integrated with a thermal storage tank of maximum capacity is observed to be an economical combination. In Chennai, where the average annual water temperature is 28 °C, the operating cost of the proposed system is only 7 % of that of a diesel-fired water heater. Also, CO2 emissions are reduced by 80 %. Thus, the proposed system is seen as an efficient and clean alternative solution for providing hot water and free AC in hotels.

Performance of a rotating latent heat thermal energy storage unit with heat transfer from different surfaces

Due to the rapid growth in the demand for fast and efficient latent heat thermal energy storage system, multiple heat transfer enhancement techniques have been proposed and widely investigated. Actively or passively, rotation of the energy storage unit affects the internal natural convection and the heat transfer performance. Hence, this study is conducted to evaluate the potential of the heat transfer enhancement by rotation. A two-dimensional model with the phase change material filled in the annular space of a double tube energy storage unit is developed. The numerical simulations for the heat transfer through the internal or external surfaces of the annular space are respectively conducted. Both solidification and melting of the phase change material are taken into account by the enthalpy-porosity method. According to different heat transfer surfaces and the occurrence of solidification or melting, four arrangements are formed. It is found that the rotation of the thermal energy storage unit can reduce the solidification time as high as 46 % compared to its still counterpart, but variation of the rotation speed only produces a minor influence. The effect of rotation on the melting depends on the heat transfer direction (or surface). When the heat is transferred into the solid phase change material through the internal wall, the melting time can be gradually reduced as the rotation speed increases with a maximum of 69 %. However, when the heat is transferred through the external wall, influence of the rotation results in adverse effect. This study can guide the design of innovative high performance latent heat thermal energy storage system containing rotation unit.

Numerical simulation of heat pipe solar system combined with finned thermal storage unit incorporating mixture of nanoparticles and paraffin

The core aim of this investigation is to simulate the melting of paraffin within a solar heat pipe unit combined with thermal storage unit, while taking into account the presence of metallic fins. To enhance system performance, Multi-Walled Carbon Nanotube (MWCNT) nanoparticles were blended into the paraffin material (RT82) using a homogeneous mixture approximation. The temperatures of the heat pipe and inner walls were derived from previous experimental research. Three distinct fin arrangements were utilized, and simulations were carried out employing numerical method. Validation procedures were undertaken to verify the accuracy of the modeling and the applied approximations, relying on both prior experimental data and numerical publications. The investigation presents data on the liquid fraction (LF), temperature (T), and stream function for diverse configurations. This holistic approach seeks to deepen comprehension of the interactions among these elements within a solar collector system, offering vital insights for performance optimization. The outcomes demonstrated a notable improvement in LF, increasing by roughly 15.15% at t = 1200s with the integration of MWCNT. Furthermore, with the passage of time from 400 s to 1200s, the incorporation of additives results in a notable rise in LF and T, demonstrating enhancements of approximately 97.74% and 130.8% correspondingly. Notably, the utilization of fins positioned at a 90o angle expedites the melting process, yielding a 38.24% LF increase compared to the base case at t = 1200s. Moreover, the impact of fins demonstrates a 3.32% increase over time. In essence, these results emphasize the effectiveness of incorporating MWCNTs and fine-tuning fin configurations to accelerate the melting process, offering valuable insights for the progress of solar thermal systems.

Effect of local mechanical oscillation on the performance of PCM thermal energy storage with various unit configurations

The low thermal conductivity of phase change materials is an essential restriction to their usage in thermal energy storage units. In this research, applying local oscillation by an oscillator on the portion of a side wall of RT35 enclosure is presented as a novel method to enhance the charging rate. The finite volume method is conducted for the numerical study on the effect of different configuration parameters including enclosure aspect ratios in the range of 1: 6, 1:2, 1:1, and 2:1, various oscillator lengths of 5, 10, 15, and 20 mm, as well as different oscillation frequencies of 10, 100 and 1000 Hz on the melting performance. Results indicate that applying local oscillation enhances the melting rate by more than 50 % as compared to without using oscillator because of enhancing convection heat transfer originating from vorticity intensification. The improvement of required time for melting the PCM is 91.55 %, 54.66 %, 67.7 % and 71.4 % for aspect ratios of 1:6, 1:2, 1:1 and 2:1, respectively.Results show that the melting performance is enhanced as the length of the oscillator increases. The required time for complete melting is obtained equal to 24, 26, 28, and 33 min at the oscillator length of 20, 15, 10, and 5 mm, respectively. The finding on the effect of oscillation frequency reveals that the liquid fraction, mean temperature, and heat flux at a specified time of melting process becomes higher as the oscillation frequency increases with significant enhancement of vorticity around the oscillator. At the frequency of 1000 Hz, the required time for melting is reduced by 9.5 % and 20.8 % as compared to frequencies of 100 Hz and 10 Hz, respectively. Other results also indicate that the higher Nusselt number is obtained for a higher enclosure aspect ratio.

Design and Construction of a Rapid Milk Chiller Using Cold Energy Storage System in the Context of Bangladesh

Milk is a highly sensitive product that must be collected and cooled within a few hours to reduce losses due to chemical spoilage and to preserve quality. As milk production is often remote from markets and processing facilities, milk chillers using thermal energy storage (TES) units provide the means for preserving quality through chilling during a power cut and hygienic storage before onward transportation to processing facilities and operation of the chiller at maximum thermal efficiency. This study gives an overview of thermal energy storage (TES) base rapid milk chiller. A review of TES for cold storage applications utilizing solid-liquid phase change materials has been done. Various perspectives were focused on the different stages of the work: phase change materials (PCMs), exemplification, improvement in exchange of heat, and the impact of the whole process on the quality of the milk Materials used as potential PCMs by specialists at low temperatures (less than 4 °C) are condensed and a portion of their thermo-physical properties are accounted for. The concept of planning and measuring procedures based on the determined load profile for structure day is introduced. In this design of a milk chilling unit using thermal energy storage, two cycles have been combined to get the desired cooling temperature. One is the vapor compression cycle, which can also be called the ice storage cycle. Another one is the milk chilling cycle. The main purpose of the milk chilling cycle is to keep the milk temperature between 2°C to 4°C. The comparison of using cold water with ethylene glycol (PCM) as a storage source of refrigeration for the milk cooling process based on the compressor capacity, ice storage box volume, and power consumed at the variable of cooling load is presented. Also, the effect of using cold storage to reduce the refrigeration capacity and energy saving is presented. The time duration of the milk chiller’s capacity to keep a specific amount (20 liters) of milk cool has been calculated to determine the variance and efficiency of the system compared to other milk chilling processes. Some suggestions concerning the planning of milk chiller hardware are given. Unique consideration was paid to the examination of explicit highlights of heat transfer phenomena in ice storage boxes including the appraisal of the length and the rate of ice arrangement and dissolution. The approach of estimating parts of the ice storage capacity framework incorporated into the milk chilling framework arranged in hot, wet, and dry atmospheres is exhibited. In light of the hourly cooling burden figuring that was completed utilizing Carrier’s Hourly Analysis Program, estimating the ice thermal capacity framework for various working procedures including full, chiller priority, and ice priority storage tasks for the design are displayed. At last, an examination of some operational qualities of the framework is broken down.

Scattered Co-anchored MoS2 synergistically boosting photothermal capture and storage of phase change materials

Pristine phase change materials (PCMs) suffer from inherent deficiencies of poor solar absorption and photothermal conversion. Herein, we proposed a strategy of co-incorporation of zero-dimensional (0D) metal nanoparticles and two-dimensional (2D) photothermal materials in PCMs for efficient capture and conversion of solar energy into thermal energy. Highly scattered Co-anchored MoS2 nanoflower cluster serving as photon and phonon triggers was prepared by in-situ hydrothermal growth of ZIF67 polyhedron on 2D MoS2 and subsequent high-temperature carbonization. After encapsulating thermal storage unit (paraffin wax), the obtained composite PCMs integrated high-performance photothermal conversion and thermal energy storage capability. Benefiting from the synergistic enhancement of 0D Co nanoparticles with localized surface plasmon resonance effect, carbon layer with the conjugation effect and 2D MoS2 with strong solar absorption, composite PCMs exhibited a high photothermal conversion efficiency of 95.19%. Additionally, the resulting composite PCMs also demonstrated long-term thermal storage stability and durable structural stability after 300 thermal cycles. The proposed collaborative co-incorporation strategy provides some innovative references for developing next-generation photothermal PCMs in solar energy utilization.