Analysis on the Improvement of Thermal Performance of Phase Change Material Ba (OH)2·8H2O

Benefitting from the characteristics of a high latent heat capacity and stable phase change behavior, phase change materials have widely received concerns in the field of thermodynamic management. Ba(OH)2·8H2O is an ideal phase change material (PCM) in the mid-to-low temperature range, but its large-scale application is still limited by severe supercooling during the nucleation process. In this paper, the experimental analysis and comparison are performed via an Edisonian approach, where Ba(OH)2·8H2O is adopted as an original substrate; BaCO3, CaCl2, NaCl, KH2PO4, and NaOH are selected as nucleating agents; and graphite is used as a heat-conducting agent. The results show that Ba(OH)2·8H2O containing 1.2% BaCO3 and 0.2% graphite powder has the best performance. Compared with pure Ba(OH)2·8H2O, the supercooling degree is reduced to less than 1 °C, the phase change latent heat duration is extended, and the thermal conductivity is significantly improved. Therefore, this study not only provides a reference for the application of Ba(OH)2·8H2O, but can also be used as a guidance for other material modifications.

Improvement the performance of composite PCM paraffin-based incorporate with volcanic ash as heat storage for low-temperature application

Paraffin is well known thermal energy storage with the high latent heat of fusion. Unfortunately, low thermal conductivity and low melting temperature inhibit large-scale applications for lower temperature applications like solar water heaters and desalination. The addition of high thermal conductivity material can increase the thermal conductivity of paraffin and increase the melting temperature of paraffin. In this study, a new approach is taken by using volcanic sand as thermal conductivity enhancement material. The properties of the sand are examined. The chemical composition of the sand is dominated by Fe (51.23 %), Fe2O3 (23.24 %) and SiO2 (11 %), which are known as good thermal conductivity materials. Six different compositions of paraffin/sand (weight ration) are tested to observe the melting and vapor temperature of the composite. Adding sand (with granule size of 44 µm) by 30 wt % can accelerate the charging rate by 25 % compared to pure paraffin, where the discharging rate is increased significantly by 17.8 %. The supercooling degree of the composite is only 1 °C, where pure paraffin has a supercooling degree by 8 °C. The charging and discharging characteristics for each sample are discussed in detail within the article. Overall, the addition of volcanic sand improves paraffin's charging and discharging rate, reducing the supercooling degree and can be considered a convenient method to improve the paraffin performance as latent heat storage

Synthesis and Properties of Inositol Nanocapsules

Sugar alcohols are phase−change materials with various advantages but may suffer from leakage during applications. In this study, inositol nanocapsules were synthesized at various conditions, including the amount of precursors and the time for adding the precursors. The effects of synthesis conditions on the properties of the nanocapsules were studied. The morphology, chemical composition, microstructure, phase−change characteristics and size distribution of the nanocapsules were investigated by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT−IR), transmission electron microscope (TEM), differential scanning calorimeter (DSC) and a zeta potential analyzer. The results confirm that inositol was well−encapsulated by an SiO2 shell. The shell thickness increased, while the supercooling degree of the nanocapsules decreased with increasing time for adding the precursors. In order to obtain nanocapsules with good morphology and phase−change characteristics, the time for adding the precursors should increase with the amount of precursors. The nanocapsules with the best properties exhibited high melting enthalpy, encapsulation ratio and energy storage efficiency of 216.0 kJ/kg, 83.1% and 82.1%, respectively. The size of the nanocapsules was remarkably affected by the triethoxysilane (TES) amount.

Experimental Study on Supercooling Phenomenon and Supercooling Degree of Nanofluids

In recent years, nanofluid has gradually entered people's field of vision due to its unique cold storage performance. Hybrid nanofluid has a more prominent effect. In order to reduce the supercooling degree of the nanofluid and obtain a practical and effective method to reduce the supercooling degree, the nano-particle graphene oxide and Al2O3 are added into deionized water ultrasonically to configure the nanofluid, and then the temperature is cooled. The effect of nanofluid concentration and different initial fluid temperature on the nanofluid subcooling degree is obtained when the ultrasonic time is 120min; when the nanofluid concentration is 0.15%wt, the nanofluid subcooling degree is the lowest, and the nanofluid is supercooled at this time The temperature is 2.8°C, which is the optimal condition for undercooling research.

An Experimental Study on the Formation of Natural Gas Hydrate With Thermodynamic Inhibitors

Gas hydrates formed in the conditions of high pressure and low temperature in deep sea and in the process of oil and gas transportation, natural gas hydrate (NGH), will seriously affect the safety of drilling and completion operations and marine equipment and threaten the safety of drilling platform. How to prevent the hydrate formation in the process of oil and gas production and transportation has become an urgent problem for the oil and gas industry. For this reason, in view of the formation of NGH in the process of drilling and producing marine NGH, the phase equilibrium calculation research of NGH formation was carried out, the mathematical model of gas hydrate formation phase equilibrium condition was established, and the experimental research on NGH formation was carried out through adding different thermodynamic inhibitors. The experimental phenomena show that, first, the stirring speed has little effect on the inhibition of hydrate formation. Second, when the pressure is 10 MPa and the volume concentration of inhibitor is 1, 3, 5, and 7%, the supercooling degree of hydrate formation is 1.81, 8.89, 11.09, and 9.39°C, respectively. Third, when the volume concentration of inhibitor is 1, 3, 5, and 7%, the induction time of hydrate formation is 10328, 14231, 19576, and 24900 s, respectively. As the polymer molecules in the inhibitor reduce the activity of water in the system and fill the cavity structure of the hydrate, they reduce the generation conditions of NGH and break the original phase equilibrium conditions when NGH is generated, thus forming NGH at a lower temperature or higher pressure.

The Effect of Static Electric Field and Nucleator Agent on the Solidification of CaCl2·6H2O and Ca(NO3)2·4H2O

The addition of energy from the electric field is one way in the active method to overcome the nucleation barriers of inorganic phase change materials (PCM) e.g. salt hydrate. The effort is to aim at improving the performance of PCM as a thermal energy storage system. Moreover, the passive method commonly uses a chemical substance called nucleator agent to induce the nucleation and to reduce the phase separation that typically occurs during the freezing-thawing cycle of salt hydrate PCM. In this paper, we report an experimental study to conduct the effect of the static electric field (DC voltage) and nucleator agent as a combination of passive and active methods on the nucleation of salt hydrates consisting of CaCl2·6H2O and Ca(NO3)2·4H2O. In general, the nucleation temperature of CaCl2·6H2O and CaCl2·6H2O+BaSO4 (0.1 wt%) become higher with the increase of the intensity of the electric field, leading to the decreases of supercooling degree. Besides that, the electric field also induces the increase in the nucleation rate, as measured by the shorter induction time. Meanwhile, the case for Ca(NO3)2·4H2O and Ca(NO3)2·4H2O+Ba(OH)2·8H2O (1 wt%) show that the nucleation temperature tends to become smaller with increase the intensity of the electric field, leading to increases the supercooling degree. However, the addition of the nucleator agent, Ba(OH)2·8H2O (1 wt%) to Ca(NO3)2·4H2O has not provided a significant result in terms of nucleation probability.

Effect of high-voltage electrostatic field on cryopreservation of human epidermal melanocytes

The objective of this research was to evaluate the influence of high-voltage electrostatic field (HVEF) on the freezing of human epidermal melanocytes (HEM) with respect to the degree of cell deformation, survival and proliferation rate after cell resuscitation. As a result, the degree of supercooling is increased by enhancing the strength of the static electric field in the range of 15 kV/m, and the maximum supercooling degree is 7.83±0.05 °C at 15 kV/m. By contrast, the morphology of the electric field assisted freezing cell after resuscitation was significantly improved, and the best electric field strength for cryopreservation is 15 kV/m. The survival rate of human epidermal melanocytes recovered was 88.03%, which was higher than that of the control group. The proliferation rate at 24, 48 and 72 hours are 17%, 28% and 25%, respectively, which are higher than that of the control cells. These findings demonstrate that the freezing HVEF can protect the cell physiological activity, and reduce the freezing damage. Therefore, the optimal HVEF cryopreservation technology be of great significance for the research of tissue engineering in repairing wounds, infections, and promote the development of food, medicine and other fields.

Effect of Copper Electrode Geometry on Electrofreezing of the Phase-Change Material CaCl2·6H2O

The development of effective active thermal energy storage systems requires an understanding of how electrode geometry affects the electrofreezing process. This study aimed to observe the nucleation behavior of an inorganic phase-change material, CaCl2·6H2O, using a DC electric field and various copper electrode geometries. The effects of both the electrode diameter (d=0.5 and 0.7 mm) and the tip shape (flat and sharp end surfaces) were investigated. Data analysis was performed to reveal the nucleation temperature, freezing temperature, supercooling degree, supercooling time, and crystallization time period. The copper electrode with the larger diameter was found to result in a higher nucleation temperature, a smaller supercooling degree, faster nucleation, and a shorter crystallization time period. Moreover, changing from a flat tip to a sharp tip decreased the nucleation temperature and increased the supercooling degree. This study showed that the electrode geometry plays an important role in the phase-change behavior of CaCl2·6H2O.