Cooling Curve Method Research Articles

Investigation on solid-liquid equilibrium for binary mixtures of carbon dioxide (R744) and alkanes: Propane (R290) and isobutane (R600a)

The solid-liquid equilibrium (SLE) of binary systems containing carbon dioxide (R744) and alkanes propane (R290) and isobutane (R600a) was experimentally investigated. A novel experimental setup using the cooling curve method was designed, built and verified, enabling SLE measurements at temperatures down to 173 K. The temperature and pressure of the triple point of carbon dioxide (CO2) were measured. The results for R744 and the binary mixture of carbon dioxide and propane were in agreement with the available literature data, demonstrating the accuracy of the experimental setup. Activity coefficients were determined for the binary mixtures studied. The Schröder and Wilson equations were used to calculate solubility over various temperatures and compositions. The Wilson model produced a very accurate correlation for the studied non-ideal binary mixtures, while the Schröder equation did not provide satisfactory results. Determined activity coefficients and SLE curves should be useful for the design of low-temperature refrigeration systems operating on carbon dioxide mixtures with low global warming potential.

Experimental study on freezing point of deep clay under high external load conditions

A rational evaluation of freezing point of deep clay under high pressure is required for artificial freezing construction of deep mining works. The freezing point of deep clay under high external load was measured via a self-designed apparatus with soil temperature monitored by high-precision temperature transducer and external load applied by servo-hydraulic system. The feasibility of the apparatus was verified by comparing the test result to that of the common cooling curve method under no external load. Cooling curves for deep clay sampled from a coal mine at 510–515 m were acquired at six load levels (0.0, 2.0, 4.0, 6.0, 8.0 and 10.0 MPa) and four water contents (25.0%, 30.0%, 34.0% and 38.0%). Results show that the greater the water content, the more pronounced the equilibrium freezing stage. In the absence of external load, equilibrium freezing was observed, whereas temperature jump becomes more noticeable with increasing load. Freezing point and initial nucleation temperature both rise with greater water content, while depress approximately linearly with higher load. A simple model for evaluating the freezing point of deep clay was developed based on the Mizoguchi model, incorporating both matric and pressure potential. The results will provide theoretical evidence for determining the thickness and location of frozen wall during artificial freezing construction in deep strata.

Solid–liquid equilibria of binary systems containing low global warming potential refrigerants

In this study, the solid–liquid equilibria of five binary systems containing refrigerants with low global warming potential, namely carbon dioxide (R744) + 1,1-difluoroethene (R1132a), R1132a + 2,3,3,3-tetrafluoropropene (R1234yf), R1132a + trans-1,3,3,3-tetrafluoropropene (R1234ze(E)), trifluoromethane (R23) + R1234yf, and R23 + R1234ze(E), was experimentally determined. Two experimental setups based on the cooling curve method were employed to measure the samples obtained from different sources. The results obtained using the two setups were in good agreement with the experimental uncertainty. In addition, the experimental data were compared with the values calculated using the Schröder equation, showing limited deviations. The accuracy of the experimental setups was tested by measuring the triple-point temperatures of the components of the studied binary systems, showing good agreement between the experimental data obtained for the pure refrigerants and the data available in the literature.

Studies of eutectic hydrated salt/polymer hydrogel composite as form-stable phase change material for building thermal energy storage

The inorganic phase change material (PCM) is a promising energy storage material in the construction field because of their characteristics, such as high latent heat, low price and nonflammability. However, from the perspective of construction engineering applications, conventional inorganic phase change materials have some inherent performance defects, such as high phase change temperature, phase separation and leakage. To overcome these performance deficiencies, a novel eutectic hydrated salt/polymer hydrogel composite form-stable phase change material (HP-FSPCM) suitable for building thermal storage was developed, which used Na2SO4·10H2O–Na2CO3·10H2O eutectic salt (SCES) as PCM, sodium polyacrylate (PAAS) as thickener and packaging material, borax as nucleating agent and flake graphite as thermal conductivity enhancer. The phase change temperature and crystal structure characteristics of SCES were analyzed by means of step cooling curve method and X-ray diffraction technique (XRD). The microstructure and thermal properties of HP-FSPCM were tested and analyzed by scanning electron microscopy (SEM), differential scanning calorimeter (DSC) and transient planar thermal conductivity instrument. The test results showed that the cross-linked network formed by PAAS can eliminate the phase separation and leakage of SCES, and the latent heat value, melting temperature and crystallization temperature of HP-FSPCM were 165.5 J/g, 22.4 °C and 13.8 °C, respectively. The thermal cycle reliability of HP-FSPCM was tested, the latent heat loss of HP-FSPCM was only 2.2% after 300 thermal cycles.

Study on Performance Improvement of Sodium Acetate Trihydrate in Thermal Energy Storage System by Disturbance

Phase change materials (PCM) have been widely used in Thermal Energy Storage (TES) Systems. Considering the energy efficiency and the use of domestic hot water, the melting temperature range of phase change materials is considered to be optimal in the range of 50–60 °C. The most commonly used is sodium acetate trihydrate-based phase change material, which has the advantages of high latent heat and low price, but its high supercooling, low thermal conductivity, and phase separation affect its application. Therefore, this paper used sodium acetate trihydrate, disodium hydrogen phosphate dodecahydrate (DSP), and expanded graphite (EG) as raw materials to prepare composite phase change materials (CPCM) and used physical disturbance to further improve their properties. Firstly, their thermophysical properties were investigated by the step cooling curve method, differential scanning calorimetry (DSC), and x-ray diffraction (XRD). Secondly, in order to further evaluate the effect of physical disturbance on CPCM crystallization, further experimental studies were carried out by adjusting the rotor mass and rotational speed. The experimental results showed that when 1.5 wt.% DSP, 1.5 wt.% EG and physical perturbation work together, the CPCM phase transition temperature is 56.7 °C, and the latent heat is as high as 258.98 kJ/kg. At this time, its thermal conductivity increased from 0.62 w/m·k to 1.1625 w/m·k, and its subcooling degree decreased from above 20 °C to less than 0.5 °C, and no phase separation occurred. The greater the disturbance momentum (the greater the rotor mass or the greater the rotational speed), the shorter the induction time, which is more conducive to the crystallization of CPCM. The results obtained in this paper are instructive for the preparation of efficient new CPCMs.

Preparation and characterization of phase change energy storage gypsum

The thermophysical properties of binary phase change materials with different ratios of capric acid and palmitic acid were studied by step cooling curve method and differential scanning calorimetry in this paper. Furthermore, the best adsorption materials and coating materials were selected by testing their mass adsorption rate and mass loss rate. Finally, the specific heat capacity, thermal conductivity coefficient, and compressive strength of phase change energy storage gypsum was determined, respectively, and the energy-saving effect of the phase change energy storage gypsum in the wall is evaluated. The results show that the binary phase change materials can form a eutectic system. When the mass ratio of capric acid to palmitic acid is 7:3, the low eutectic point of the binary system is formed, and the crystallization temperature of system is 26?C. The adsorption capacity of expanded perlite is much larger than that of ceramsite, and the mass loss rate of the material coated by styrene acrylic emulsion is lower than that of ethylene vinyl acetate. The specific heat capacity of phase change energy storage gypsum is about twice that of ordinary gypsum. With the addition of phase change materials, the thermal conductivity coefficient of phase change energy storage gypsum decreases gradually, and the compressive strength of phase change energy storage gypsum decreases gradually at the same time. Compared with ordinary gypsum, phase change energy storage gypsum has better energy-saving performance.

Solidification Behaviour of Sn-40Pb Lead Solder and Sn-0.7Cu Lead-free Solder

Lead-free solder, especially Sn-0.7Cu has been evolving due to the restriction of the lead solder usage which is environmental and health unfriendly. However, most of the lead solder properties show a better result compared to the lead-free solder. To further improve the properties of lead-free solder, the solidification state of Sn-40Pb and Sn-0.7Cu, which is one of the important behaviour in thermal analysis that affects the solder properties and performance, was investigated and compared in this study by natural cooling curve method. The result showed that Sn-40Pb has two nucleation phase while Sn-0.7Cu has only one during the solidification. The primary lead-rich phase was first nucleated in Sn-40Pb following by the secondary tin-rich phase when cooling; while the phase of Cu6Sn5 was nucleated in Sn-0.7Cu. In addition, it is found that the undercooling of Sn-40Pb is lower than Sn-0.7Cu in the cooling curve.

Study on Liquidus Temperature of NaF-KF-LiF-AlF3 System with Low Cryolite Ratio

Development of an energy-efficient method for aluminum manufacturing is the current research trend in the aluminum electrolysis industry. A low-temperature electrolysis process is an appropriate choice for aluminum electrolysis. The NaF-KF-LiF-AlF3 system with its low cryolite ratio may be a suitable candidate electrolyte system because of its reduced liquidus temperature. In this paper, the liquidus temperature of NaF-KF-LiF-AlF3 system with cryolite ratios of 1.3 and 1.4 is investigated via the cooling curve method and the differential thermal analysis method. The effects of both potassium fluoride and lithium fluoride on the NaF-KF-LiF-AlF3 system are studied. The liquidus curves of systems containing potassium fluoride and lithium fluoride are different and depend on the KF/(NaF+KF+LiF) and LiF/(NaF+KF+LiF) ratios. Part of the (NaF-LiF-AlF3)-KF pseudo-binary phase diagram with fixed LiF concentration is plotted according to the data of liquidus temperature and the compositions of the phase diagram containing potassium fluoride and lithium fluoride with a cryolite ratio of 1.3 are analyzed. The change trend of the compositions is similar to the NaF-KF-AlF3 system with a low cryolite ratio. LiF hardly participate in the formation of the compounds at equilibrium state except for the fact that chiolite is the main composition of molten salt.

Study on performance optimization of sodium sulfate decahydrate phase change energy storage materials

In this paper, sodium sulfate decahydrate (SSD) with a phase transition temperature of 32 °C was selected as the phase change energy storage material. However, SSD has the problems of large degree of supercooling, obvious phase stratification, and low thermal conductivity. To address these issues, a new SSD composite phase change energy storage material was synthesized by adding certain amounts of nucleating agents, thickeners, and high thermal conductivity agent to SSD. The results showed that when the addition of nucleating agent Na2B4O7·10H2O and thickener carboxymethyl cellulose (CMC) reached an optimal formulation ratio of SSD:Na2B4O7·10H2O:CMC = 100:5:3, the supercooling degree of the SSD composite phase change material was only 1.5 °C. Moreover, the heat release time of the phase change process was 25 min, and no phase stratification occurred. When expanded graphite with high thermal conductivity was added with the mass ratio of 9%, the effect on the supercooling degree of the SSD composite energy storage material was small, and the thermal conductivity increased by 3.9 times, reaching 2.13 W m−1 K−1. Differential scanning calorimetry method and step cooling curve method were used to test the decay rate of the thermal properties of the new composite phase change energy storage material, and the results were relatively close.

KF-NaF-AlF3 System: Liquidus Temperature and Phase Transition

The development of low-temperature aluminum electrolysis makes it possible to reduce energy consumption and greenhouse gas emissions. The KF-NaF-AlF3-based electrolyte is a promising low-temperature electrolyte for aluminum reduction. The liquidus temperatures of KF-NaF-AlF3 electrolytes with a total cryolite ratio (CRt) fixed at 1.3–2.0, and with different concentrations of NaF (with a step change of 5 mol.%), were investigated by the cooling curve method. The results showed that the liquidus temperature of KF-NaF-AlF3 mixtures increases with the increase of the CRt, which has a bigger influence on the liquidus temperature than the traditional NaF-AlF3 electrolyte currently used in aluminum smelters. When the content of NaF is 10–20 mol.%, the curves of the liquidus temperature vs. NaF content reach a peak. When the NaF content ranges from 30 to 40 mol.%, the liquidus temperature is relatively low (695–900°C). The precipitated order of the compounds in molten KF-NaF-AlF3 electrolytes with a CRt of 1.3 is as follows: K2NaAlF6 (or K3AlF6) → Na3Al5F14 → K2NaAl3F12 → KAlF4.

Mullite Stabilized Palmitic Acid as Phase Change Materials for Thermal Energy Storage

In this paper, mullite was adopted in order to absorb Palmitic Acid (PA) via a direct impregnation method. The prepared PA/mullite form-stable phase change materials (FSPCM) were systematically characterized by the Leakage Test (LT), Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), Differential Scanning Calorimeter (DSC), Thermogravimetry (TG) and Cooling Curve Method (CCM). The results indicated that, among these composites with different mass fractions of PA, the sample with the 32 wt % Palmitic Acid has the best properties without any leakage. The enthalpy of 32%PA/68%mullite FSPCM is 50.8 J/g for melting process, and 58.3 J/g for solidifying process. The phase change point of 32%PA/68%mullite FSPCM is 64.1 °C for melting and 58.7 °C for solidifying. The heat storage efficiency of the PA/mullite FSPCM was enhanced considerably by adding mullite. The leakage and thermal properties of PA/mullite FSPCM were discussed and the performance of the FSPCM has been apparently improved.

Study on Modification of Phase Change Energy Storage Materials Suitable for Biogas Fermentation

In this study, the problems of supercooling and phase separation of inorganic hydrated salts as phase change energy storage materials when applied to biogas generating devices were investigated. In the experiment, two common hydrated salts of zinc nitrate hexahydrate and disodium hydrogen phosphate dodecahydrate were selected as phase change materials, and tested at room temperature. Recording temperature and drawing the step cooling curve method, by adding different proportions of nucleating agent and dye to improve the supercooling and phase separation of the phase change materials, so that the reaction temperature of the biogas plant was always maintained at a suitable temperature (20-30 °C) to ensure the activity of microorganisms. The experimental results showed that sodium tetraborate decahydrate can effectively reduce the subcooling degree of zinc nitrate hexahydrate, and the azo (-N = N-) dye not only improved the solar absorption rate but also weakened the phase separation of phase change materials to some extent. This study proposed a possible reaction mechanism and provided reference for the development and application of other solar energy storage materials for bioreactors.

A Modified Single Pulse Method for Transient Thermal Impedance (TTI) Measurement of VDMOSFET Relates Gate Bias to the TTI Results

Transient thermal impedance plays a critical role in thermal design of power device. Welldesigned packaging and circuit board insure the continuous cooling performance although the temperature raise in junction under pulse with high power in short time scale relates to the structure of chips. A modified TTI(Transient Thermal Impedance) measurement method has been proposed which simulates the pulse applying in channel of trench-gate MOSFET and the calculated TTI value has 30% difference between the single pulse method and the cooling curve method. The discrepancy of results can be attributed to the influences brought by microstructure inside cells. Experiments prove that the gate bias is related to the tested TTI value. Analysis has indicated that the mechanism is due to the electrical resistance distribution in cells which is dominated by gate bias, electrical character of channel, accumulation layer, drift region, substrate and structure of cell.

Experimental study on freezing point of saline soft clay after freeze-thaw cycling

The brine leakage is a tough problem in artificial freezing engineering. This paper takes the common soft clay in Wujiang District as the study object, and calcium chloride solutions with six salinity levels were considered. The \'classic\' cooling curve method was employed to measure the freezing point of specimens after freeze-thaw. Results indicate that four characteristic stages can be observed including supercooling, abrupt transition, equilibrium and continual freezing, strongly dependent on the variation of unfrozen water content. Two characteristic points were found from the cooling curves, i.e., freezing point and initial crystallization temperature. A critical value for the former exists at which the increment lowers. The higher the saline content approximately linearly, lower the freezing point. In the initial five cycles, the freezing point increases and then stabilizes. Besides, the degree of supercooling was calculated and its correlations with water, salt and freeze-thaw cycles were noted. Finally, an empirical equation was proposed for the relationship of freezing point and three main factors, i.e., water content, saline content and freeze-thaw cycles. Comparison of calculated and measured data proves that it is reliable and may provide guidance for the design and numerical analysis in frozen soil engineering.

Channel temperature measurement in hermetic packaged GaN HEMTs power switch using fast static and transient thermal methods

A GaN-based power device is a superior component for high-frequency and high-efficiency applications and especially for applications that involve megahertz power conversion. In this work, a fast process of static thermal resistance (R th) and transient thermal impedance (Z th) measurements are made and analyzed to determine the thermal characteristics of the channel temperature of a hermetically packaged GaN power device. Five temperature-sensitive parameters (TSPs) are measured at temperatures from 20 to 160 °C. Measurements and statistical analyses included variations with temperature of on-resistance (R on), saturation drain current (I Dsat), drain conductance (g d), threshold voltage (V th), and knee voltage (V knee). The statistical analyses revealed the relationships between the heating curve parameter (R on) and the cooling curve parameters (V knee, I Dsat, g d, and V th). The average thermal resistance values are extracted as follows: Maximum R th is 2.99 °C W−1, minimum R th is 2.92 °C W−1, and the variation among the five TSPs is <3%. Conventional optical-based techniques such as infrared (IR) and micro-Raman thermography are destructive to packaged devices. Therefore, this study developed the two reliable and fast non-destructive methods for estimating channel temperature with the following features: (1) They elucidate static and transient characteristics; (2) they involve heating and cooling; and (3) they evaluate transient thermal impedance (TTI) and safe operating area (SOA). The heating curve method has advantages over cooling curve method in terms of capturing time (40 vs. 400 s, respectively), and a lower power excitation is required to obtain the transient channel temperature response.

Storage of fresh-cut swede and turnip: Effect of temperature, including sub-zero temperature, and packaging material on sensory attributes, sugars and glucosinolates

Freezing point of fresh-cut swede (Brassica napus L. var. napobrassica Rchb.) and turnip (Brassica rapa L. ssp. rapifera Metzg.) dice was measured by the cooling curve method, and mean equilibrium freezing points were found to be −2.67 and −1.97°C, respectively. This indicates that storage of fresh-cut swede and turnip at temperatures below 0°C is possible. Fresh-cut swede and turnip were packed in pouches made of biaxially oriented polypropylene film, and a film based on polylactic acid, and stored for 10 d at −2, 0, 5 and 10°C. One sample of each vegetable was stored at −2°C for 5 d, followed by 5 d of storage at 5°C. Differences in sensory quality between storage at −2°C and 0°C were found in appearance attributes only. Both swede and turnip had higher evenness of colour at −2°C than at 0°C. Storage at −2°C vs. 0°C gave lower whiteness for swede but higher for turnip, and lower intensity of hue for turnip only. Increased storage temperature from 0°C to 5 or 10°C did not change appearance in swede, but in turnip hue and colour intensity increased, and colour evenness and whiteness decreased. Differences in odour, taste and flavour during storage at 5 or 10°C vs. 0°C were prominent for turnip: decreased sour odour and flavour, green odour and flavour, sulphurous odour and sweet taste, and increased muddy odour and cloying odour and flavour for 5°C or 10°C. For swede, higher storage temperature gave only increased intensity of sulphurous odour and pungent odour. Texture changed for turnip only with decreased juiciness with increased temperature. The lowest temperature (−2°C) gave the highest sucrose content in both swede and turnip, the highest total sugar content in turnip and the lowest glucose content in swede. Higher storage temperature resulted in higher content of total indolic glucosinolates in both fresh-cut swede and turnip, but a lower content of total aliphatic glucosinolates in turnip only. Increased contents with increased storage temperature were found for glucobrassicin and 4-methoxyglucobrassicin in both vegetables, and decreased contents for glucobrassicanapin and gluconapin in turnip and glucoalyssin in swede. Storage in polylactic acid film resulted in higher weight loss than the biaxially oriented polypropylene film in both vegetables.

Measurement of freezing point of tilapia fish burger using differential scanning calorimetry (DSC) and cooling curve method

The aim of this work was to determine the freezing point (Tf) of tilapia (Oreochromis niloticus) fish burger using the cooling curve and differential scanning calorimetry (DSC) method. Cooling curves were obtained for two household refrigerators, a freezer with no quick freeze function and another one equipped with a quick freeze compartment. Freezing point, freezing time and freezing rates were determined from the cooling curves. The freezers showed slow freezing rates ranging from 0.10 to 0.40cm/h. The quick freeze function improved the freezing process, as it significantly reduced the freezing times by significantly increasing freezing rates. Tf of the tilapia fish burger was (−2.7±0.1) °C and no significant difference between freezing rates and the DSC method was observed. This investigation demonstrated that the cooling curve method using a simple experimental apparatus and domestic refrigerators can be used to measure freezing point of high moisture foods.

Measurement of binary phase diagram of Cu2S–MoS2 system

A novel method, bath smelting process, was developed to treat molybdenite concentrate aiming at the existing problems of traditional process. To understand the dissolving behavior of MoS2 in white matte, the binary phase diagram of Cu2S–Mo2S was measured by the cooling curve method. The result shows that this system is a simple binary eutectic with a eutectic temperature of (1117.0±3.0) °C and a eutectic composition of (1.70±0.20)% MoS2 in mass fraction. When the MoS2 addition exceeds 4.48%, MoS2 and Cu2S can form the ternary compound containing CuMo2S3 or Cu2Mo6S8. In the temperature range of copper smelting, 1200–1300 °C, molybdenite can dissolve in the cuprous sulfide. At 1200 °C, the solubility of molybdenite can reach 14.8%.

Research on the Thermo Physical Properties of Lauric Acid-Capric Acid Binary Mixture Phase Change Materials

Lauric acid(LA) and capric acid(CA) were mixed into binary mixture, whose melting temperature was predicted with Schroder’s equation and tested in step cooling curve method. Then latent heat was tested by DSC, and T-history method was used to test thermal conductivity of binary mixtures, heating and cooling characteristics were studied through expanded perlite(EP) adsorption of binary mixtures. Results show that Schroder’s equation can be used to predict melting temperature of fatty acid, and binary mixture prepared of 6:4 molar ratio has a high latent heat and its temperature is within a range that meets indoor comfort temperature. Thermal conductivity and the heating and cooling characteristics of the mixtures reveals that the thermal conductivity of fatty acid phase change material(PCM) is low, which restricts its latent heat release rate.

Preparation and Performance Study of Fatty Acid Diatomite Composite Phase Change Materials and Light Weight Phase Change Gypsum Wall Materials

Fatty acid phase change materials(PCMs) and composite diatomite PCMs were prepared in this study, the phase change temperature of different mole ratio lauric acid(LA) and capric acid(CA) PCMs were tested by step cooling curve method, thermal physical performance of the prepared PCMs were tested by differential scanning calorimeter (DSC). A new type of lightweight phase change gypsum wallboard incorporated with LA-CA/diatomite composite PCMs was prepared, and the thermal performance of this material was studied. The results showed that the LA and CA could form an eutectic mixture. DSC results indicated that the phase change temperature of the PCMs and composite diatomite PCMs are both 26.7°C, the latent heat of the PCMs are 142.2J/g and 73.5J/g, respectively. Thermal performance test of the gypsum wallboard indicated that the temperature difference of the phase change gypsum wallboard at different moment is lower than the blank gypsum wallboard, which showed a better energy storage function of the phase change gypsum wallboard.