Enhanced Specific Heat of Molten Salt Nano-eutectic via Nanostructural Change

In this study, the specific heat of molten salt nano-eutectic (Li2CO3-K2CO3 doped with SiO2 nanoparticles) was theoretically and computationally investigated. According to the proposed theory in the literature [1], the effective specific heat of a nano-eutectic can be significantly enhanced by the formation of needle-like nanostructures by salt eutectic. To investigate the effect of the formed nanostructure, its specific heat was theoretically calculated by the model used by Wang and other researchers [2-4]. The mass fraction of the formed nanostructure was estimated by MATLAB using the reported material characterization studies [1, 5, 6]. The theoretical prediction made a good agreement with the measured specific heat values from the literature with an error less than 3 %. Additional verification of the proposed model was performed by a molecular dynamics simulation study. The simulated specific heat of pure molten salt eutectic made a good agreement with the literature value (1.6 kJ/kg°C with an error less than 1.7 %). The simulated specific heat of nano-eutectic was 2.017 kJ/kg°C. The error between the theoretical prediction and the simulation is only 3.4 % and the value made a good agreement with the experiment (1.9 % max. error). The result shows the enhanced specific heat of a nano-eutectic can be explained by the contribution of the formed nanostructures.

Determination of effective specific heat capacity of interior plaster containing phase change materials

A precise technique for determination of effective specific heat capacity of building materials is presented within this paper. The applicability of the technique is demonstrated on a PCM-enhanced plaster, being characterized by a phase change between 15 and 30 °C. The effective specific heat capacity is determined by means of inverse analysis of calorimetric data using computational model of the device. The identified effective specific heat capacity values reached up to 1890 J·kg-1·K-1 when cooled and 1580 J·kg-1·K-1 when heated. Using this quantity in simulation of thermal performance, the PCM-enhanced plaster showed to have a promising potential to be used in buildings’ interiors as a thermal regulator to stabilize inner environment as it contributed to a thermal oscillation decrease by up to 2.5 °C

Enhanced Heat Capacity of Salt Hydrate by In-Situ Formed Nanostructure

Silica nanoparticles and polyethylene-block-poly were doped in sodium acetate trihydrate to in-situ synthesize stelliform nanostructure to enhance the effective specific heat capacity of sodium acetate trihydrate. Sodium dodecyl sulfate and methanol were also used in the synthesis to help the dispersion. A modulated differential scanning calorimeter was employed to characterize the specific heat capacity of pure sodium acetate trihydrate and their nano samples. The measurement was repeated multiple times on different days to confirm the repeatability of the measurement. The result shows the specific heat capacity was enhanced by 11% in comparison with pure sodium acetate trihydrate. The conventional effective specific heat capacity model was compared with the experimental result.

A Comparison of Input Data Used to Represent Phase Transformations during the Quenching of a Large Nuclear Forging

The present work explores the importance of model parameters and input variables when simulating the quenching of thick sectioned nuclear forgings. The modelling approach adopted uses values of specific heat capacity, containing latent heat release, to simulate cooling curves; rather than calculating transformation kinetics based upon a mathematical model. Termed the effective specific heat (Cpeff), two different methods were used to establish values: differential scanning calorimetry (DSC) and thermos dynamic predictive software. Values were then included in finite element (FE) models to simulate the characteristic cooling at the mid-wall position in a thick section forging and were validated against production thermocouple data. The investigation found that the formation of ferrite, bainite and martensite or lower bainite were all represented by the data established using DSC and critical formation temperatures were comparable with others in the literature. Conversely, values calculated using the thermodynamic software failed to represent ferrite formation and predicted different critical transformation temperatures for bainite. The simulated cooling curve that used the software predicted Cpeff data was comparable to the thermocouple data either side of the bainite transformation, however during the transformation the effects of latent heat on cooling rate were over predicting leading to disparities. The equivalent DSC cooling curves produced a near exact match.

Modelling of the 1D Convective Heat Exchange between Logs Subjected to Freezing and to Subsequent Defrosting and the Surrounding Environment/ Egydimenziós konvektív hővezetés modellezése fagyott és normál állapotú rönk és környezte között

A 1D mathematical model for the computation of the temperature on the surface of cylindrical logs, tsr, and the non-stationary temperature distribution along the radiuses of logs subjected to freezing and subsequent defrosting at convective exponentially changing boundary conditions has been suggested. The model includes mathematical descriptions of the thermal conductivity in radial direction, λr, the effective specific heat capacity, ce, and the density, ρ, of the non-frozen and frozen wood, and also of the heat transfer coefficient between the surrounding air environment and the radial direction of horizontally situated logs, αr. With the help of the model, computations have been carried out for the determination of αr, tsr, λsr, and 1D temperature distribution along the radiuses of beech logs with diameters of 0.24 m, initial temperature 20 °C, and moisture content 0.4 kg·kg-1, 0.8 kg·kg-1, and 1.2 kg·kg-1, during their freezing at -20 °C, and during subsequent thawing at 20 °C.

Experimental Study of Phase-Changeable Water/Polyalphaolefin Nanoemulsion Fluids

In this work, thermal properties especially phase change heat transfer properties of one new type of nanostructured heat transfer fluid: Water/Polyalphaolefin (PAO) nanoemulsion fluid are investigated. Water is added into PAO fluid to form nanoemulsion fluids in which dispersed water nanodroplets are formed by self-assembly. The liquid-to-vapor phase change results, expressed in terms of surface heat flux and heater temperature, have shown that the presence of water nanodroplets has a drastic impact on the liquid-to-vapor phase change behavior of the nanoemulsion fluid studied: the water nanodroplet formed inside can enhance its heat transfer coefficient by over 300% after the incipience of its phase change. In addition to that, the vaporization of the water nanodroplet inside is found to be different depending on the concentration of water inside, which happens to coincide with the structure change with different water concentrations as observed in SANS measurement. On the other hand, the effective specific heat is also found to increase with higher water concentration until reaching a maximum value which also happens to coincide with the structure transition from spherical to cylinder shape with the increasing of water concentrations as observed from SANS measurement. More study is still needed to understand the mechanism behind these phenomena.