Effect Of Heat Storage Research Articles

Study the influence of the environment on heat transfer processes in sewing sheaths with heat-accumulating properties

In the article research results are presented, which aim to modeling of heat transfer processes in a system for evaluating the heat storage effect of combined cooling shells. Clothing and equipment corresponding to the type and activity of movements and work performed by a person are considered as a shell. To a certain extent, the task of compensating for excessive heat load is solved by special materials that are used in the manufacture of such shells. Such shells are multicomponent structures of materials from various fiber systems with the inclusion of ice modules. The main means of processes for evaluating and improving such technologies are mathematical modeling tools, in particular, heat transfer modeling in multilayer shells. The structure of a heat transfer model with the inclusion of a heat storage module in a fibrous sheath. To describe the heat transfer the mean radii of curvature of the geometric system “manheat-shielding shell” were calculated. The problem is considered when layers of various materials separate the external environment from ice. For the “man-clothing” section, the temperature field is calculated. The data obtained make it possible to evaluate the heat storage effect in combined cooling shells.

Application of solar energy storage system in building structure design and its thermal process analysis

In order to understand the application and thermal process of solar energy storage system in building structure design, a research on the application and thermal process analysis of solar energy storage system in building structure design is put forward. This paper will take the outdoor climate conditions of residential buildings in a province as an example to conduct thermal analysis on the heat collection components and heat storage components of urban residential buildings. The building under test is a university teacher?s residence located in the university campus of Chengguan District of the city. It is a multi-storey building with a total of five floors, and the building is on the top floor. The experimental results show that the heat storage effect of the thick exterior wall can effectively reduce the temperature fluctuation of the exterior wall. The difference between the maximum and minimum values of the exterior wall surface temperature is 19?C, and the difference between the maximum and minimum values of the interior surface temperature is 5.4?C. The difference between the maximum and minimum temperature of the north exterior wall is 4.9?C, and the difference between the maximum and minimum temperature of the inner surface is 1.6?C. The work of this paper lays a foundation for the quantitative research on the temperature control of building heat collection and storage components, and provides a theoretical basis for solar heat storage.

Experimental study on the flexible peak shaving with pulverized coal self-preheating technology under load variability

The integration of renewable energy sources into power grids has led to power fluctuations, necessitating coal-fired power units to provide flexible peak shaving. The pulverized coal self-preheating technology can potentially provide broad-load regulation and rapidly respond to load changes. In this study, the impact of the self-preheating technology on fuel preheating modification, combustion characteristics, and NOx emissions are investigated. Load-stabilization bases are proposed based on preheating temperature, preheated coal gas composition, combustion temperature, and flue gas emissions. Load change rates are calculated using these bases to character the load response. The results demonstrate that the preheated fuel has similar properties as the highly reactive gaseous fuel and exhibits excellent ignition and combustion performances at 25 % load. Preheating treatment improves combustion efficiency, and burnout ratio and reduces NOx emissions. The NOx concentration approaches the ultra-low emission standard at 50 % load. Four load-stabilization bases, covering the preheating and combustion sides, comprehensively characterize the load response performance. The rates based on preheating indicators and combustion indicators maximize to 3.30 %/minute and 2.71 %/minute, respectively. The load change rate in the ramp-up phase is higher than that in the ramp-down phase, which is related to the effective internal heat storage carrier and external thermal insulation conditions. The driving force formed by high load step ranges and the deviation from the full load capacity are conducive to increasing the load change rates.

Improving the Heat Transfer Performance of the Tower Molten Salt Solar Receiver With the Novel Folded Flow Tubes

Abstract The molten salt has been widely used in concentrated solar power generation as an effective high-temperature heat transfer and heat storage working fluid. However, due to the concentrating characteristic of the tower receiver, the solar flux distribution of the molten salt receiver is extremely non-uniform, and thus the circumferential non-uniform heat flux has a prominent effect on the heat transfer performance and reliability of the traditional solar molten salt receiver tube (TRT). In this contribution, in order to solve above problems, we propose some novel folded flow tubes (NFTs), which add a partition in the tube and seal the top with end cap so that the inflow and outflow of the fluid can only proceed from the same cross section. Then, we apply the binary nitrate (solar salt) as a heat transfer fluid, which is a mixture of 60% sodium nitrate and 40% potassium nitrate. First, we analyze some effects such as flow parameters, structure, and heat flux loading direction on the convective heat transfer performance of the NFTs. The results show that the circumferential temperature difference of NFTs is about 17–92 K lower than that of TRT, and the molten salt temperature distribution is more uniform accordingly. Moreover, the heat transfer coefficient is increased about 88.37–122.85%, which can provide a guidance for the structural optimization of practical solar molten salt receivers to improve the heat transfer performance and reliability.

Influence of the Main Working Parameters and Geometrical Parameters on the Supercritical CO2 Flow Instability in a Heated Tube

Supercritical CO2 (sCO2) flow instability is an issue that must be considered in the reasonable design of sCO2 boiler. Because it can cause equipment vibration and heat transfer deterioration. In this article, a numerical model for the sCO2 flow instability in the single tube was developed. Different from the traditional model, the effects of metal heat storage and axial heat conduction in the tube wall were considered. The influence of main parameters on trans-pseudo-critical number (N TPC) and oscillation period (t 0) was studied, with the tube length (L) from 3 to 11 m and the inner diameter (D in) from 10 to 22 mm. N TPC increases with increasing the inlet pressure (P in), mass flux (G), inclination angle (α), and the inlet local resistance coefficient (K in). N TPC decreases with D in and outlet local resistance coefficient (K out). The effects of the sub-pseudo-critical number (N SUBPC), wall thickness (WT) and L on N TPC are nonlinear. With increasing N SUBPC, WT, L, D in, and K out, t 0 increase. As G, α, and K in increase, t 0 becomes smaller. When N SUBPC is lower than 0.9146, t 0 rises with P in increasing. It is opposite with N SUBPC higher than 0.9146.

Fluid and Thermal Analysis of Pre-Columbian Tiwanaku (500–1100 CE) Raised-Field Agricultural Systems of Bolivia

Raised-field agricultural systems have received attention from scholars involved in the analysis of prehistoric agricultural intensification in the New World. This paper discusses the function of raised fields associated with the Tiwanaku society (500–1100 CE) located on the southern rim of Lake Titicaca in Bolivia. The overnight internal heat storage capacity of Tiwanaku raised-field berms located at the high-altitude (~3810 masl) Bolivian altiplano is analyzed through ANSYS (version 4.2B) finite difference methods to provide an understanding of ancient agricultural engineers’ knowledge regarding how to protect crops from nightly subzero freezing temperatures and water saturation. The present analysis concludes that enhanced berm heat storage capacity derived from solar radiation into multi-layered moist berm agricultural soils, together with radiative heating of berm-surrounding swale water (swale water depth determined from excavation into the groundwater aquifer), was an essential Tiwanaku design element of raised-field agriculture to protect crops from freezing damage during both wet and dry seasons. This paper reports the ANSYS temperature distribution results derived from a raised-field berm swale computer model of ancient excavated raised fields in the form of a 24 h heat input and cooling cycle, which indicates the presence of an internal berm heat storage effect designed to protect crops from freezing damage. The calculations performed use specific hydrological and climatological conditions characteristic of the littoral and near-shore environment of Lake Titicaca. The use of the ANSYS finite element code to investigate the source of internal berm heat storage protecting crops from freezing temperatures, compared to the field test results from experimental use of reconstructed ancient, raised fields, provides an understanding of the technologies developed by Tiwanaku agricultural engineers to increase raised-field agricultural production.

Expanded Vermiculite/D-Mannitol as Shape-Stable Phase Change Material for Medium Temperature Heat Storage.

Aiming to promote the application of D-mannitol in the field of phase change thermal storage, obstacles, including low thermal storage efficiency and high supercooling, should be properly disposed of. The adoption of adaptable and low-cost supporting materials to make shape-stable phase change materials (ss-PCMs) affordable is a primary solution to solve the above shortcomings. In this study, high-performance ss-PCM for effective medium-temperature heat storage was prepared using expanded vermiculite as the support for D-mannitol preservation. Among the three candidates that treated the raw vermiculite by dilute acid, calcination, and microwave heating, the calcinated expanded vermiculite (CV) was characterized as the most suitable one. After impregnating D-mannitol into the CV carrier by vacuum, a melting enthalpy of 205.1 J/g and a crystallization enthalpy of 174.1 J/g were achieved by the as-received CV/D-mannitol ss-PCM. Additionally, the supercooling of the ss-PCM was reduced to 45.6 °C. The novel CV/D-mannitol ss-PCM also exhibited excellent reusability and stability. All the findings indicate that the abundant and inexpensive CV exhibited great potential as the supporting material for D-mannitol-based ss-PCMs, which allow effective waste heat recovery and temperature regulation.

Integration of a conical frustum PCM system for enhanced thermal energy storage in a diesel engine cogeneration system

An effective heat storage system was achieved by fabricating a 400-L cylindrical thermal energy storage (TES) tank equipped with 9 conical frustum containers. These conical frustum containers with PCM (CFC-PCM) contain paraffin wax in the upper third of the tank and water as the heat transfer fluid (HTF) in the circulation process. The TES tank was integrated with a 40 kW diesel generator, and experiments were conducted by operating the engine at six different loads. During the charging process, heat was recovered from the engine exhaust gases and jacket cooling water. The performance parameters were evaluated and reported based on the transient behavior of a hybrid sensible/latent TES tank under the charging process. The results showed that at 72.55% of the engine peak load, the energy utilization factor (EUF) and the exergy efficiency of the system were 91.17% and 81.22%, respectively. Although adding PCM to water only resulted in a 3% enhancement in heat storage capacity, it improved the durability of heat charging by providing thermal stratification and increasing charging efficiency compared to the reference state in some of the studied cases.

Energy conversion through deep borehole heat exchanger systems: Heat storage analysis and assessment of threshold inlet temperature

The heating capacity of deep borehole heat exchanger (DBHE) systems gradually attenuates due to the cold accumulation of rock and soil during long-term operation. Therefore, heat storage in rock and soil is crucial to alleviate thermal attenuation and ensure stable operation. However, the mechanism and design methods for heat storage are unclear. In this paper, heat extraction and storage models for DBHE systems are established, the effects of heat storage on system operation are revealed, and a design method for the threshold inlet water temperature of heat storage is proposed. The results show that the fluid in the DBHE should inflow from the inner pipe to release more heat into the rock and soil when adopting heat storage. The heat storage power under fluid inflow from the inner pipe is 10.81 kW higher than that from the annular space under the same operating conditions. Increasing the inlet water temperature is more beneficial than increasing the flow rate to enhance the heat storage power. After 2880 h of operation, the heating power of the DBHE is increased by 3.44% for the next heating season when the storage flow rate is increased from 8 m3/h to 38 m3/h. Thus, a high heat storage inlet temperature with a low flow rate should be adopted during the heat storage period. Furthermore, the threshold inlet water temperature of heat storage is highly dependent on the depth of the DBHE and the geothermal gradient, with percentage contributions of 57.14% and 39.26%, respectively. The multiple linear regression model (R2 = 0.972) has shown high predictive accuracy in the assessment of threshold inlet water temperatures, with a maximum relative error of −5.60%. The findings of this paper provide technical support for designing heat storage using DBHE systems.

Experimental Investigation on a Novel Temperature-Controlled Phase Change Aggregate Concrete: Thermo-Mechanical Properties and Hydration Heat Control.

To reduce the structural deterioration of mass concrete structures from temperature cracks, and lower energy consumption caused by the traditional mass concrete hydration heat cooling process, this paper reports the preparation of concrete temperature-controlled phase change aggregate (PCA) by a vacuum compaction method using light and high-strength black ceramite and No. 58 fully refined paraffin wax as phase change material (PCM), and the encapsulation technology of the aggregate by using superfine cement and epoxy resin. Further, through laboratory tests, the cylinder compressive strength, thermal stability and mixing breakage rate of the encapsulated PCA were tested, and the differences in mechanical properties such as compressive strength, flexural strength and splitting tensile strength between phase change aggregate concrete (PCAC) and ordinary concrete were studied. A test method was designed to test the heat storage effect of PCA, and the temperature control effect of PCAC was analyzed based on the law of conservation of energy. The research conclusions are as follows: (1) Both superfine cement and epoxy resin shells increase the strength of the aggregate, with the epoxy resin increasing it more than the superfine cement. The thermal stabilization of the PCA is good after encapsulation of superfine cement and epoxy resin. However, PCA encapsulated in superfine cement is more easily crushed than that encapsulated in epoxy resin. (2) Under the condition of water bath heating and semi-insulation, when the water bath temperature reaches 85 °C, the temperature difference between the PCA and the common stone aggregate can be up to 6 °C. Based on the law of energy conservation, the test results will be converted to mass concrete with the same volume of aggregate mixture;, the difference of PCAC and ordinary concrete temperature can be up to 10 °C, so the temperature control effect is significant. (3) The mechanical properties of PCAC with 100% aggregate replacement rate compared to ordinary concrete are reduced to varying degrees, and the performance decline of the epoxy-encapsulated PCA is smaller than that encapsulated with superfine cement; in an actual project, it is possible to improve the concrete grade to make up for this defect.

Enhanced thermal performance of shell and tube phase change heat accumulator with novel biomimetic spider web fins

Shell and tube phase change heat accumulator (STPCA) has many advantages such as flexible arrangement, simple structure and high operation temperature and pressure. However, there are some limitations such as the low thermal conductivity of phase change material (PCM) and much un-melted PCM at the bottom of STPCA. In this contribution, in order to solve aforementioned problems of STPCA, we firstly designed novel biomimetic spider web fins and applied the enthalpy-porosity method to solve the problem of phase transition and obtain the liquid fraction and location of the solid–liquid interface at different times. Then, we compared the enhance heat storage effect of the novel fins with that of normal radial fins. In addition, we further analyze the effects of three different fin arrangements and four different fin radial angles on the thermal storage performance. The results show that the novel biomimetic spider web fins can accelerate the melting of PCM at the bottom of the accumulator, uniform the temperature distribution and greatly improve the heat storage rate of the accumulator. The complete melting time of PCM of the accumulator with the novel web fins is only 48 s, but the radial fins is 140 s, which is much longer than that of the accumulator with the novel web fins. Moreover, the radial angle mainly affects the later melting period, because the angle can affect the natural convection. In this work, the model with a radial angle of 75° shows the better thermal storage performance. This contribution can provide a guidance for STPCA design to improve the heat storage performance.

Synthesis and characterization of stearic acid/waste filler materials as composite phase change material in thermal energy storage application

This paper investigates the potential of waste materials, i.e. recycled aluminum cans and carbon biochar (carbon BC) wastes as fillers in stearic acid as PCM supporting matrix material. Using recycled aluminum powder (recycled Al powder) and carbon BC, a new invention of composites phase change material (C-PCM) was established. These C-PCM, which has been was incorporated with different waste fillers, were prepared at different waste mass loading and further characterized using scanning electron microscope (SEM), Fourier infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), pycnometer density analysis, and thermal thermogravimetric analysis (TGA). The result showed that both C-PCM were uniformly dispersed into stearic acid (SA) and portrayed a good contact surface area. The C-PCM with recycled Al powder filler results in higher melting and freezing latent heat than C-PCM with carbon BC filler. Thermal cycle test analysis of selected C-PCM exhibited good thermal stability, reliability, and effective latent heat storage. From the thermal evaluation test, the storage performance of C-PCM was found to perform better compared to lone SA as PCM (SA-PCM). Despite having low latent heat compared to lone PCM, the addition of waste materials into SA has increased C-PCM's thermal stability. Al/SA C-PCM is identified as the most effective TES medium since it gives the best thermal stability and latent heat values.

Investigation on properties of phase change foamed concrete mixed with lauric acid-hexadecanol/fumed silica shape-stabilized composite phase change material

This experimental study developed a phase change foamed concrete (PCFC) with suitable temperature regulation and heat storage capabilities utilizing experimental design and numerical simulation. With the porous material adsorption method, a shape-stabilized composite phase change material (PCM) was prepared using fumed silica to absorb Lauric acid-Hexadecanol (LA-HD) binary eutectic. Through the Differential Scanning Calorimetry (DSC), Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectrometer (FT-IR), Thermal Gravimetric Analyzer (TGA) and liquid leakage tests, the results indicate that the best mass ratio of LA to HD in LA-HD binary eutectic is 53:47. The maximum adsorption ratio of fumed silica for LA-HD is 60 % (wt). The adsorption process is only a physical combination without chemical reaction, and the proposed composite PCM has stable morphological structures and physical properties. The effect of composite PCM on the dry density, compressive strength and thermal properties of PCFC was explored by changing the content (5 %, 10 %, 15 %, 20 %, 25 %, 30 %) of composite PCM in PCFC. The finite element software ABAQUS was used to establish the model of the PCFC wall, and its heat storage and temperature regulating performance was studied. The experiment results show that the dry density, compressive strength and thermal conductivity of the PCFC gradually decrease with the increase of composite PCM. When the content of composite PCM is 30 %, the dry density, compressive strength and thermal conductivity reach the minimum values of 579.6 kg/m3, 1.192 MPa and 0.105 W/(m·K), respectively. With the increase of composite PCM, the phase change temperature, latent heat and specific heat capacity of foam concrete also increase. When the content of composite PCM is 30 %, the phase change temperature is 36.13 °C, the latent heat is 35.02 J/g, and the specific heat capacity is 2467 J/(kg·°C). The finite element simulation results show that when the PCFC with 30 % composite PCM is placed in the middle of the wall, the inside surface temperature fluctuation range of the PCFC-wall-2 is 27.293 °C ∼ 28.707 °C, and the temperature difference is 1.414 °C, which is 0.0738 °C and 0.047 °C lower than that of PCFC-wall-1 and PCFC-wall-3, respectively; the time for PCFC-wall-2 to reach the peak and valley temperature is delayed by 0.1667 h than the other two walls. The results indicate that using PCFC in buildings can reduce the energy required for building cooling or heating and affect energy saving and environmental protection. Moreover, PCFCs arranged in the middle of the wall has better heat storage and temperature regulation effect than those arranged on both sides.

New library of phase-change materials with their selection by the Rényi entropy method

The secret to the successful and widespread deployment of solar energy for thermal applications is effective and affordable heat storage. The ability to provide a high energy storage density and the capacity to store heat at a constant temperature corresponding to the phase transition temperature of the heat storage material (phase-change material or PCM) make latent heat storage one of the most alluring methods of heat storage. Today, it can be challenging to obtain all the published data on PCM qualities, including relevant non-thermodynamic properties in addition to thermodynamic ones. The developed new PCM library contains various types of PCMs which possess broad range of operation temperatures. This new library consists of 500 substances along with nine associated properties such as phase change temperature, solidification temperature, maximum operation temperature, density, latent heat and specific heat capacity, thermal conductivity, cycleability and ignition temperature. Furthermore, a new PCM selection method, based on calculating the Rényi entropy for a given set of selection criteria, has been proposed. The newly developed selection method requires no subjective judgements. The idea of the method is inspired by earlier applications of fractal analysis methods in many areas of research.

Oriented High Thermal Conductivity Solid-Solid Phase Change Materials for Mid-Temperature Solar-Thermal Energy Storage.

As the global energy crisis intensifies, the development of solar energy has become a vital area of focus for many nations. The utilization of phase change materials (PCMs) for photothermal energy storage in the medium temperature range holds great potential for various applications, but their conventional forms face several challenges. For instance, the longitudinal thermal conductivity of photothermal PCMs is inadequate for effective heat storage on the photothermal conversion surface, and there is a risk of leakage due to repeated solid-liquid phase transitions. Here, we report a solid-solid phase change material, tris(hydroxymethyl)aminomethane (TRIS), which has a phase change temperature of 132 °C in the medium temperature range, enabling high-grade and stable solar energy storage. To overcome the low thermal conductivity problem, we propose a large-scale production of oriented high thermal conductivity composites by compressing a mixture of TRIS and expanded graphite (EG) using the pressure induction method to create in-plane highly thermally conductive channels. Remarkably, the resulting phase change composites (PCCs) exhibit a directional thermal conductivity of 21.3 W/(m·K). Furthermore, the high phase change temperature (132 °C) and large phase change entropy (213.47 J/g) enable a large-capacity high-grade thermal energy to be used. The developed PCCs, when combined with selected photo-absorbers, exhibit efficient integration of solar-thermal conversion and storage. Additionally, we also demonstrated a solar-thermoelectric generator device with an energy output of 93.1 W/m2, which is close to the power of photovoltaic systems. Overall, this work provides a technological route to the large-scale fabrication of mid-temperature solar energy storage materials with high thermal conductivity, high phase change enthalpy, and no risk of leakage, and also offers a potential alternative to photovoltaic technology.

Performance study and heating simulation on novel latent heat thermal energy storage device suit for air source heat pump

Latent heat thermal energy storage (LHTES) technology can solve the problem of limited performance improvement of air source heat pump (ASHP) systems due to the time mismatch between building energy demand and operational efficiency in low temperatures. Therefore, this paper proposes a LHTES device suitable for the ASHP system. Firstly, the internal structure is obtained by ANSYS numerical simulation. Furthermore, experiments are carried out to verify the heat storage and release performance of the proposed device under different inlet water temperatures and flow rates. Finally, the operational effects of the ASHP-LHTES combined heating system are analyzed by TRNSYS. The design results show that a liquid phase ratio of 97.24 % is achieved with a pipe diameter of 16 mm, tube pitch of 70 mm, and 1/2 horizontal tube fins. Experiment results exhibit that the proposed device performs excellently under optimal conditions, with 89.7 % effective heat storage efficiency and 92.5 % available heat release efficiency. TRNSYS results indicate that the annual operating cost of the combined heating system saves 32.9 % compared with the single ASHP heating system, although the power consumption increases by 24.4 %. This study can provide theoretical support for the application of low-temperature LHTES devices in the ASHP system.

Study on refined mathematical model of solar chimney power plant integrated with seawater desalination and the influence of dewing

In order to more accurately evaluate the operation and output characteristics of the solar chimney power plant integrated seawater desalination, a refined mathematical model for unsteady heat and mass transfer was built under consideration of the convection heat transfer mechanism of the collector, dewing phenomenon, and the disturbance to the hot airflow caused by the oblique-toothed flow channel boundary. The influence of nighttime dewing and humid environments on system performance was discussed. The results show that it is feasible and more appropriate to use the forced convection heat transfer coefficient of bellows to consider the influence of the oblique-toothed flow channel boundary; the refined mathematical model is also more accurate and reliable. Due to the effect of seawater heat storage, dewing has little effect on system performance, and the integrated system has a better anti-dewing negative impact characteristic. However, when the ambient humidity reached a higher level, dewing had a greater negative impact on freshwater production. The critical value of relative humidity for dewing to occur is 51 %. When the relative humidity increases from 45 % to 60 %, the daily utilization efficiency of solar energy decreases from 27.4 % to 22.5 %.

Calculation model of non-nuclear steam rush in steam turbine of nuclear power unit Construction and application

According to the technical characteristics of steam turbines and their thermodynamic systems of various types of nuclear power units, a calculation software suitable for evaluating the feasibility of nonnuclear steam rushing of steam turbines of various types of nuclear power units is developed The software can accurately evaluate and check the non-nuclear steam rushing parameters by comparing the steam intake and heat consumption required by the steam turbine with the effective steam quantity and heat storage provided by the primary loop, and solve the quantitative evaluation problem of the feasibility of non-nuclear steam rushing for steam turbines of various types of nuclear power units.

Design optimization of circular vessel using computational fluid dynamics for the effective heat storage

Design optimization of circular vessel using computational fluid dynamics for the effective heat storage

Analysis of temperature regulation and heat storage effect of the combined phase change envelope in hot summer and cold winter zone

In order to study the character of heat storage and temperature regulation, a mathematical model of the thermal performance of an ideal passive energy storage building is established. Indoor thermal environment evaluation indexes of the passive buildings such as the temperature attenuation coefficient and supercooling degree/superheating degree are proposed. The PCM (phase change materials) layer numbers, the total thickness and the thickness ratio of PCM layers of the combined PCM envelope are analyzed based on the simulation. The result shows that the combined envelope with two-layer PCM has better temperature regulation and heat storage effect. When the total thickness of the combined PCM envelope is 40 mm, and the thickness ratio of the PCM layer from the inside to the outside is13.3:26.7, the annual thermal comfort hours are the longest.