Thermal Storage Time Research Articles

Heat Transfer Behaviors of Parallel Plate Systems in Sensible Thermal Energy Storage

In the present investigation a simplified analysis is accomplished to handle a parallel plate system with parallel channels as a porous media and to evaluate the permeability, inertia coefficient, the interfacial heat transfer coefficient between solid matrix and fluid and the specific area for the equivalent porous medium. In the local heat transfer coefficient is also considered the radiative heat transfer which will be temperature dependent. The evaluation of these two terms will be carried out numerically by the Ansys-Fluent code to compare the simplified and numerical model results. The analysis should allow the estimation of an optimized configuration, in terms of number of pore per inch (PPI) or channels per unit of length (CPL), as a balance between pressure drop and heat transfer rate inside the parallel plates configuration. Results show the effects of storage medium, different porosity values, porosity effect and mass flow rate on stored thermal energy and storage time. Results in terms of stored thermal energy as function of time are presented. Moreover, the behavior related to fluid pressure losses and internal heat transfer is analyzed.

Numerical method and model for calculating thermal storage time for an annular tube with phase change material

For calculating the thermal storage time for an annular tube with phase change material (PCM), a novel method is proposed. The method is suitable for either low-temperature PCM or high-temperature PCM whose initial temperature is near the melting point. The deviation fit is smaller than 8% when the time is below 2×104 s. Comparison between the predictions and the reported experimental data of thermal storage time at same conditions is investigated and good agreements have been got. Based on this method, the performance of the thermal storage unit and the role of natural convection are also investigated. Results show a linear relation between the maximum amount of stored heat and thermal storage time, and their ratio increases with the height of the thermal storage unit. As the thickness of the cavity increases, natural convection plays an increasingly important role in promoting the melting behavior of paraffin. When the thickness of the cavity is small, natural convection restrains the melting behavior of paraffin.

Utilization of lauric acid-myristic acid/expanded graphite phase change materials to improve thermal properties of cement mortar

Lauric acid-myristic acid/expanded graphite (LA-MA/EG) composite phase change materials (PCMs) were prepared by absorbing the binary eutectic mixtures into expanded graphite (EG) with high absorbability, in which LA-MA binary eutectic mixtures act as latent heat storage materials while EG serves as the supporting material. LA-MA binary eutectic mixture was prepared according to low eutectic phase transition point theory, which is proper to apply in constructions due to the high latent heat and suitable phase transition temperature. The proper firing technology and absorption content of EG were determined according to the temperature sensibility and the long-term durability. Inner morphology of the prepared LA-MA/EG composite PCMs was observed through scanning electron microscopy (SEM). Alkali resistance, thermal stability and thermal properties of the LA-MA/EG composite PCMs were analyzed through differential scanning calorimeter (DSC), thermogravimetry analysis (TGA) as well as melting point apparatus, respectively. In addition, PCM-based mortar was prepared by mixing LA-MA/EG composites into cement mortar. Thermal performance of PCM-based mortar was studied through temperature simulation, and the temperature fields of thermal control model were performed. Results show that LA-MA/EG composite PCMs, prepared with EG fired at 800°C for 20s, absorbing 600% LA-MA eutectic mixtures, possess the optimal thermal properties. The LA-MA eutectic mixtures can well disperse inside the EG porous structures due to the capillary and surface tension forces. Thermal storage time and thermal release time of LA-MA/EG composite PCMs are shorter than that of LA-MA binary eutectic acids due to the increased heat transfer rate, caused by the combination with the EG that has a high thermal conductivity. The thermal stability of LA-MA/EG composite PCMs improves in comparison with LA-MA eutectic mixtures. The PCM-based mortar shows proper temperature controlling effects, with decreased effective heat value, delayed temperature peak time and larger cooling extent.

Numerical and experimental investigation on latent thermal energy storage system with spiral coil tube and paraffin/expanded graphite composite PCM

For latent thermal energy storage (LTES) systems, performance is limited by the suboptimum structures of heat exchangers and the low thermal conductivities of phase change materials (PCMs). In this work, a rapid charging tube-in-tank LTES system is developed by applying a compact spiral coil tube and paraffin/expanded graphite composite PCM with a high thermal conductivity simultaneously. Numerical simulation coupling heat transfer at the solid-liquid interface is used to investigate the thermal energy storage performance of the LTES system and the results show a good agreement with the experimental data. It is found that heat transfer temperature difference has a great influence on performance of the LTES system, while Reynolds number has a relatively little effect especially when Reynolds number is higher than 8700. Besides, the optimal ratio of the helix radius of the spiral coil tube to the radius of the PCM tank is confirmed to be between 0.53 and 0.64. Moreover, increasing bulk density of the composite PCM can bring about a shorter thermal energy storage time. In summary, the results are valuable for the design of a similar LTES system.

Degradation Analysis of TO-247 Package SiC-MOSFETs Subjected to High Temperature Storage and Heavy Thermal Cycle Test

Abstract Three types of TO-247 package SiC-MOSFETs, denoted as A, B and C and fabricated by different manufacturers, were subjected to thermal cycle tests (TCT) ranging from −40°C to 200°C and a high temperature storage test (HTST) at 200°C in air. Their reliability was continuously investigated based on electrical characterizations, X-ray inspection and scanning acoustic tomography (SAT). Intermittent SAT observation revealed that, regardless of the device type, the epoxy resin (encapsulant) first peeled on the Cu die pad around the outer edge of the SiC power die and then peeling rapidly spread outward as the number of thermal cycles or storage time increased. The number of cycles or storage time differed depending on the device type (manufacturer). Subsequently, further peeling occurred on the SiC die and the devices failed or showed instability. The deterioration pattern tended to differ somewhat between the TCT and HTST. Uplift of the die attachment was observed for device A after thermal storage for 1000 hours.

Experimental Study of a Thermal Storage Technique with Phase Change Material Closure for Solar-Biogas Hybrid Fermentation System

It is a key energy policy in China that developing biogas technology is to crack energy short problem in its rural areas. A pilot water thermal storage tank with phase change material insulation closure was developed to collect the daily solar energy for satisfying the heat loading required by biogas fermentation tank which should keep at about 35°C optimum efficient fermentation temperature in each winter day. The thermal performance of the water thermal storage tank was investigated under the different typical local winter air temperatures of 10°C, 5°C and 0°C. Both the numerical and experimental data demonstrate that the phase change material paraffin layer improves the thermal storage time of the tank effectively. This suggests that the proposed water thermal storage tank with phase change material insulation closure could be a promising heat storage device utilized towards solar-biogas hybrid system in rural regions of the middle and lower reaches of Yangtze river.

Effect of microwave power on EPR spectra of thermally sterilized eucerinum anhydricum

Abstract Free radicals formed during thermal sterilization of eucerinum anhydricum – the pharmaceutical base were examined by an X-band (9.3 GHz) spectrometer. Eucerinum anhydricum was sterilized at different physical conditions according to the Polish Pharmacopeia norms. The samples were heated at temperatures: 160°C (120 min), 170°C (60 min), and 180°C (30 min). The aim of this study is to compare free radical concentration and effect of microwave power on EPR spectra of eucerinum anhydricum base thermally sterilized at different temperatures and periods of time. The effect of time storage on the free radicals in the heated samples was tested. Free radical concentrations in the sample stored 15 min strongly decreased with the increasing of sterilization temperature, probably as the result of recombination. Storage caused strong decrease of free radical concentrations in the samples, probably as the result of interactions with oxygen. It was observed to be independent of sterilization conditions from 2 days of storage and longer. Because of the lowest free radical concentration, for eucerinum anhydricum thermal sterilization at 180°C for 30 min is recommended. The sterilized samples should be stored at inert atmosphere without oxygen molecules. Fast spin-lattice relaxation processes existed in sterilized eucerinum anhydricum. The character of changes of amplitudes and linewidths of EPR lines with increasing of microwave power was the same for different storage times. The parameters of thermal sterilization and storage time influenced free radical concentration in eucerinum anhydricum, but magnetic spin-lattice interactions were unchanged. The usefulness of EPR spectroscopy in optimization of thermal sterilization process of eucerinum anhydricum was confirmed.

Thermal analysis of metal foam matrix composite phase change material

In this paper, CPCM (Composite Phase Change Material) was manufactured with metal foam matrix used as filling material. The temperature curves were obtained by experiment. The performance of heat transfer was analyzed. The experimental results show that metal foam matrix can improve temperature uniformity in phase change thermal storage material and enhance heat conduction ability. The thermal performance of CPCM is significantly improved. The efficiency of temperature control can be obviously improved by adding metal foam in phase change material. CPCM is in solid-liquid two-phase region when temperature is close to phase change point of paraffin. An approximate plateau appears. The plateau can be considered as the temperature control zone of CPCM. Heat can be transferred from hot source and be uniformly spread in thermal storage material by using metal foam matrix since thermal storage material has the advantage of strong heat storage capacity and disadvantage of poor heat conduction ability. Natural convection promotes the melting of solid-liquid phase change material. Good thermal conductivity of foam metal accelerates heat conduction of solid-liquid phase change material. The interior temperature difference decreases and the whole temperature becomes more uniform. For the same porosity with a metal foam, melting time of solid-liquid phase change material decreases. Heat conduction is enhanced and natural convection is suppressed when pore size of metal foam is smaller. The thermal storage time decreases and heat absorption rate increases when the pore size of metal foam reduces. The research results can be used to guide fabricating the CPCM.

A comparison study on melting inside the rectangular and curved unit with a vertical heating wall

Efficient and rational use of thermal energy requires the design and development of suitable and cost-effective latent heat storage systems. In this study, a novel curved thermal storage unit is put forward and its thermal behavior has been numerically compared with the traditional rectangular PCM-based thermal storage unit. The solid–liquid interface evolution, liquid flow pattern and temperature distribution are presented. Transient Nu at the heating wall and full melting time are also calculated. The numerical results show the high impact of the enclosure geometry on melting and nature convection. A reduction of 30.6 % in thermal storage time has been achieved by changing the unit from rectangular to curve. Moreover, parametric studies are conducted to assess how thermal performance of the units is affected by the heating wall temperature and PCM thermal conductivity. Correlations encompassing a wide range of parameters are developed in terms of full melting time. Results indicate that proportion of full melting time reduced for the curved unit is almost a constant value and does not vary significantly with these factors. All these may be very helpful for the design of more efficient thermal storage units.

Enhanced heat transfer for PCM melting in the frustum-shaped unit with multiple PCMs

Thermal energy storage plays an important role in correcting the disparity between energy supply and demand as well as improving the energy efficiency. The present work numerically investigates the conjugate heat transfer between PCM and heat transfer fluid within the novel and efficient frustum-shaped thermal storage units. A two-dimensional control volume-based numerical model is developed employing the CFD software Fluent. Five units of equal volume but different dimensions are compared to illustrate impacts of geometry on melting, and the optimal geometric design is determined. Then, the multiple PCMs technology is employed to the optimal unit to further enhance the melting heat transfer. Effects of the multiple PCMs arrangement, multiple PCMs’ melting temperature distribution, and type on the melting behavior and heat transfer are investigated. Compared with the frustum-shaped and traditional shell-and-tube unit with a single PCM, predicted results indicate that the five PCMs arrangement in frustum-shaped unit can make the thermal storage time reduced by 21.5 % and 47.5 %, respectively. The great improvement may be of great significance to the optimal design of latent heat storage.

Experimental Study and Numerical Simulation on Thermal Energy Storage Characteristics of Composite Phase Change Materials in Annular Space of Vertical Double-Pipe Heat Exchanger

Experimental system on thermal energy storage characteristics of phase change materials (PCMs) in annular space of a vertical double-pipe heat exchanger was set up. The thermal storage performance of paraffin and paraffin/expanded graphite composite PCM with the mass fraction of 70% paraffin was compared. The Fluent software was used to simulate the temperature field of the composite PCM during the thermal storage process. The results show that, for the paraffin, in the sensible heat storage phase, because the heat transfer process is controlled by the heat conduction, the temperature in paraffin gradually reduces from the inside to the outside of the annular space. But for the phase change thermal storage phase, solid-liquid phase change heat transfer is controlled by natural convection and the effect of buoyancy, the temperature in paraffin reduces from top to bottom, from the inside to the outside of the annular space. For the composite PCM, heat transfer is controlled only by the heat conduction process, both the sensible and latent heat storage process, the temperature in the composite PCM decreases from bottom to top, from inside to outside of the annular space. As the thermal conductivity of composite PCM is 15.65 times of paraffin, the thermal energy storage time is shortened by 86.6% than paraffin. The temperature fields of composite PCM in different time are obtained by numerical simulation method, the measured temperatures and simulation results are in good agreement.

Thermal energy storages analysis for high temperature in air solar systems

In this paper a high temperature thermal storage in a honeycomb solid matrix is numerically investigated and a parametric analysis is accomplished. In the formulation of the model it is assumed that the system geometry is cylindrical, the fluid and the solid thermo physical properties are temperature independent and radiative heat transfer is taken into account whereas the effect of gravity is neglected. Air is employed as working fluid and the solid material is cordierite. The evaluation of the fluid dynamic and thermal behaviors is accomplished assuming the honeycomb as a porous medium. The Brinkman–Forchheimer–extended Darcy model is used in the governing equations and the local thermal non equilibrium is assumed. The commercial CFD Fluent code is used to solve the governing equations in transient regime. Numerical simulations are carried out with storage medium for different mass flow rates of the working fluid and different porosity values. Results in terms of temperature profiles, temperatures fields and stored thermal energy as function of time are presented. The effects of storage medium, different porosity values and mass flow rate on stored thermal energy and storage time are shown.

Effect of Food Stimulated Liquids and Thermocycling on the Monomer Elution from a Nanofilled Composite

The present study was aimed to evaluate the effects of food simulating liquids and thermocycling on the elution of monomers from a nanofilled resin composite in different immersion times. Five Specimen discs were made from a nano-hybrid composite (Supreme 3M) for each group (Total = 180) and immersed in distilled water (control), citric acid, lactic acid, and 75% aqueous ethanol solution. The discs were removed after 24 h, 48 h, 72 h, 1 wk, 4 wk, and 12 wk. Three groups of samples underwent thermocycling for 1000, 2000 and 3000 cycles. The solutes were analyzed with HPLC for detection of eluted monomers. The results showed that the amount of released TEGDMA was significantly higher than that of Bis-GMA; however, there were not any significant differences between the amount of released Bis-GMA and UDMA. Moreover, the highest amount of monomers was released from samples immersed in ethanol solution; samples immersed in citric acid and lactic acid significantly released more monomers than those immersed in distilled water. Furthermore, the immersion time in aqueous ethanol solution had an increasing effect on the release of monomers. In addition, the higher amounts of monomers were release from samples immersed in ethanol and citric acid which underwent a higher number of thermal cycles. In conclusion, food and drink stimulated liquids used in this study increased the amount of some of the monomers released from composite resin. Thermal shocks and storage time are other factors that increased the release of monomers from the composite resin.

Effect of pasteurization and storage on bioactive components of Aloe vera gel

PurposeAloe vera gel has nutritional and therapeutic properties due to presence of bioactive components. The aim of this study is to investigate the effect of pasteurization and storage time at different temperatures on some bioactive components of Aloe vera gel juice.Design/methodology/approachAloe vera gel juice (Aloe barbadensis Miller) was pasteurized at 90°C for 1 min and stored up to 30 days at 4 and 25°C. The effect of pasteurization and storage time on glucomannan, vitamin C, DPPH inhibition (percent) and color of the juice was evaluated.FindingsThe results showed that pasteurization reduced vitamin C content and antioxidant activity 16% and 57%, respectively. During storage at 4 and 25°C, vitamin C and glucomannan contents reduced from 84.47 to 54.96 and 46.82 mg vitamin C/100 g dm and from 2.11 to 1.77 and 1.71 g/L, respectively. DPPH inhibition (percent) and Browning index (BI) increased significantly at both storage temperatures, which was more intensive at 25 than 4°C.Originality/valueThis paper is believed to be the only one which investigates the effect of thermal pasteurization and storage time at different temperatures on some bioactive components of Aloe vera gel juice.

Thermal Storage and Release Properties of Aluminum Foam - Paraffin Composite Phase Change Materials

Aluminum foam-Paraffin Composite Phase Change Materials (APCPCMs) were fabricated by aluminum foam and paraffin, and the thermal storage and thermal release properties of the composites have been studied. The results are shown as follows. (1) When the volume ratio between APCPCM and water is 1:4, the time for the temperature changing of APCPCMs with aluminum foam porosity being 54.81%, 60.52%, 64.37% and 69.74%, from 24°C to 66°C, is 190s, 305s, 380s and 395s respectively. The thermal release time of these APCPCMs is 270s, 355s, 540s and 600s after being put into 24°C water, and resulting in a water temperature increase by 8.2°C, 8.7°C, 9.4°C and 10.1°Crespectively. (2) APCPCM with aluminum foam porosity 60.52% is compared with aluminum foam and paraffin, the thermal storage time of these three kinds of materials is 305s, 60s, 870s, and the thermal release time is 355s, 30s, 1470s respectively. (3) The equivalent thermal conductivity coefficient of the APCPCMs with aluminum foam porosity ranging form 69.74% to 54.81% is between 61.16 W•m-1•k-1 to 91.4W•m-1•k-1.

Effect of Food Stimulated Liquids and Thermocycling on the Monomer Elution from a Nanofilled Composite

The present study was aimed to evaluate the effects of food simulating liquids and thermocycling on the elution of monomers from a nanofilled resin composite in different immersion times. Five Specimen discs were made from a nano-hybrid composite (Supreme 3M) for each group (Total = 180) and immersed in distilled water (control), citric acid, lactic acid, and 75% aqueous ethanol solution. The discs were removed after 24 h, 48 h, 72 h, 1 wk, 4 wk, and 12 wk. Three groups of samples underwent thermocycling for 1000, 2000 and 3000 cycles. The solutes were analyzed with HPLC for detection of eluted monomers. The results showed that the amount of released TEGDMA was significantly higher than that of Bis-GMA; however, there were not any significant differences between the amount of released Bis-GMA and UDMA. Moreover, the highest amount of monomers was released from samples immersed in ethanol solution; samples immersed in citric acid and lactic acid significantly released more monomers than those immersed in distilled water. Furthermore, the immersion time in aqueous ethanol solution had an increasing effect on the release of monomers. In addition, the higher amounts of monomers were release from samples immersed in ethanol and citric acid which underwent a higher number of thermal cycles. In conclusion, food and drink stimulated liquids used in this study increased the amount of some of the monomers released from composite resin. Thermal shocks and storage time are other factors that increased the release of monomers from the composite resin

Energy storage and solidification of paraffin phase change material embedded with graphite nanofibers

Phase change materials (PCMs) are known to be excellent candidates for thermal energy storage in transient applications. However, enhancement of the thermal conductivity of a paraffin-based PCM is required for effective performance, particularly during solidification where diffusion is the dominant heat transfer mode. This study experimentally examines the effect that graphite nanofibers (GNFs), aspect ratio and power density have on both thermal storage and solidification time of a PCM which is embedded between two sets of aluminum fins. Additionally, a figure of merit is introduced in order to quantify the effectiveness of each of these three parameters with respect to solidification time. GNF enhancement was shown to reduce the maximum temperature in the thermal containment unit (TCU) by 48%. It was also found that for aspect ratios of 1, the GNF enhancement shortens solidification time by as much as 61% over the paraffin samples. This research indicates that GNF impregnation into phase change materials is an effective method for the enhancement of the thermal energy storage and the solidification of paraffin-based phase change materials.

Effects of Thermal Storage and Cu Addition on Adhesive Strength and Microstructure of Sn-3.0 mass% Ag-1.5 mass% Sb-<I>x</I>Cu Solder Joints

This paper examines the effects of the thermal storage time and Cu addition on the adhesive strength and microstructure of lead-free Sn3.0 mass% Ag-1.5 mass% Sb-xCu solder joints. The experimental results show that the adhesive strength of the as-soldered specimens increases with increasing Cu addition and increasing strain rate. Meanwhile, for the aged specimens, the adhesive strength increases with increasing strain rate, but decreases with increasing storage time or with increasing Cu addition beyond 1.0 mass%. The microstructures and fracture morphologies of the solder specimens are analyzed by optical microscopy (OM) and scanning electron microscopy (SEM). The observations reveal that the Cu6Sn5 and Ag3Sn particles within the solder microstructure coarsen following high temperature storage and thus reduce the adhesive strength of the solder. Finally, it is found that the prolonged aged specimens with a Cu addition of 0.5 mass% or 1.0 mass% fracture in a combined brittle and ductile failure mode, while those with a Cu addition of 1.5 mass% fail as a result of cleavage after following 200 hours of thermal storage and a strain rate of over 1 s � 1 , but otherwise these fracture in a combined brittle and ductile failure mode.

Effect of various parameters on detection of irradiated fish and oregano using the ESR and PSL methods

Control of irradiated food on the market is a requirement of EU regulations. In order to improve checks of irradiated food in Greece, electron spin resonance (ESR) and photostimulated luminescence (PSL) were tested to detect electron beam radiation treatment of representative samples, namely fish (herring) and aromatic plant (oregano). The absorbed irradiation doses for both food samples were 1, 4 and 10 kGy. The effect of thermal treatment and storage time of fish samples on the sensitivity of ESR method as well as the effect of light exposure (after irradiation treatment) and storage time of oregano samples on the sensitivity of PSL method was studied. In addition, the suitability of both methods for two food samples was studied. For fish samples, the detection of irradiation treatment was based on ESR or PSL signal of fish bones. The results showed that PSL is a sensitive detection method for irradiated oregano samples allowing verification of irradiation treatment for all absorbed doses but this is not a sensitive detection method for irradiated herring containing bones. In contrast, ESR allowed verification of the irradiation treatment of fish bone samples but this is not a sensitive method for irradiated oregano samples. Daylight exposure of oregano samples (10 klux, 9 h) produced a strong effect on the PSL signal of all irradiated samples decreasing or disappearing the irradiation signal, while the thermal treatment (100 ± 1 °C, 1 h) of fish bones was produced a clear decreasing effect on the ESR signal of irradiated samples mainly for the higher dose of 10 kGy. The storage time strongly affected the PSL signal intensity of oregano samples as well as the ESR signal intensity of herring bone samples but the samples could be correctly identified as irradiated after a storage time of seven months.

Adhesive strength and tensile fracture of Ni particle enhanced Sn–Ag composite solder joints

This study forms composite solders by adding 0.5–3 wt% of Ni particles in situ to Sn–3.5 wt%Ag lead-free solder. Cu/solder/Cu specimens are prepared by dipping two Cu rods into a solder bath to produce a solder joint. Some of the joint specimens are retained in the as-soldered condition, while the others are aged at 150 °C for 100, 200, 400, or 500 h, respectively. The experimental results reveal that the addition of Ni to the molten Sn–Ag solder leads to the formation of in situ Ni 3Sn 4 dispersoids. The adhesive strength of the joint is found to increase with increasing Ni content in the as-soldered specimens. In general, the strength of the thermally processed specimens reduces as the thermal storage time increases. The Sn–Ag–0.5 wt%Ni joints show a mixture of ductile and brittle fracture, whereas the joints containing more than 1 wt% of Ni show mainly brittle fracture with solder residue at the exposed (Cu,Ni) 6Sn 5 IMC layer.