Evaluating the conservation of energy variables in simulations of deep moist convection

It is often assumed in parcel theory calculations, numerical models, and cumulus parameterizations that moist static energy (MSE) is adiabatically conserved. However, the adiabatic conservation of MSE is only approximate because of the assumption of hydrostatic balance. Two alternative variables are evaluated here: MSE −IB and MSE +KE, wherein IB is the path integral of buoyancy (B) and KE is kinetic energy. Both of these variables relax the hydrostatic assumption and are more precisely conserved than MSE. This article quantifies the errors that result from assuming that the aforementioned variables are conserved in large eddy simulations (LES) of both disorganized and organized deep convection. Results show that both MSE −IB and MSE +KE better predict quantities along trajectories than MSE alone. MSE −IB is better conserved in isolated deep convection, whereas MSE −IB and MSE +KE perform comparably in squall line simulations. These results are explained by differences between the pressure perturbation behavior of squall lines and isolated convection. Errors in updraft B diagnoses are universally minimized when MSE−IB is assumed to be adiabatically conserved, but only when moisture dependencies of heat capacity and temperature dependency of latent heating are accounted for. When less accurate latent heat and heat capacity formulae were used, MSE−IB yielded poorer B predictions than MSE due to compensating errors. Our results suggest that various applications would benefit from using either MSE −IB or MSE +KE instead of MSE with properly formulated heat capacities and latent heats.

Polymers in Molten Inorganic Salt Hydrates Phase Change Materials: Solubility and Gelation

Inorganic salt hydrates are of interest as phase change materials (PCMs) for thermal energy storage because of their unique properties such as high latent heats of fusion, moderate melting temperatures,...

System Simulation of an Elastocaloric Heating and Cooling Device Based on SMA

Elastocaloric (EC) cooling uses solid-state NiTi-based shape memory alloy (SMA) as a non-volatile cooling medium and enables a novel environment-friendly cooling technology. Due to the high specific latent heats activated by mechanical loading/unloading, substantial temperature changes are generated in the material. Accompanied by a small required work input, a high coefficient of performance is achievable. Recently, a fully functional and illustrative continuous operating elastocaloric air cooling system based on SMA was developed and realized. To assist the design process of an optimized device with given performance and efficiency requirements, a fully coupled thermo-mechanical system-level model of the multi-wire cooling unit was developed and implemented in MATLAB. The resulting compact simulation tool is qualified for massively parallel computation, which allows fast and comprehensive parameter studies. In this work, the influence of different SMA diameters, rotation frequencies, and airflow rates is investigated. The results are analyzed to find the suited parameter for high efficiency (COP) and temperature span.

Joseph Black and the rise of heat capacity

By developing the science of calorimetry and the doctrines of sensible and latent heats, Joseph Black separated temperature from heat. Subsequent research by others on the concept of heat capacity led to the Dulong–Petit Law, which can be understood based on the atomic theory of matter.

Sugar-alcohol@ZIF nanocomposites display suppressed phase-change temperatures

The synthesis and characterization of phase change materials infused into metal–organic framework crystals to demonstrate high latent heats with suppressed phase change temperatures.

The Effect of Electrode Gap on the Nucleation of CaCl2.6H2O by using Sharp End Copper Electrode

The performance of the calcium chloride hexahydrate (CaCl2.6H2O) to store the sensible and latent heats is mainly determined by its nucleation or liquid to the solid phase transition. This is due to the barrier that has to be overcome when the material undergoes the nucleation process with a reduction in the entropy value. This material, with melting temperature around 29.8 °C, can be used as the thermal energy storage for building applications in tropical areas such as Indonesia, in order to reduce the electrical energy for aircond (AC) machines. In this paper, we report the results of an experimental study for the effect of the electrical field to the supercooling degree and time period for a phase transition. The variation in the magnitude of the electrical field was achieved by variation in the gap of the electrode for sharp end electrodes (cathode and anode), for the commonly sold copper electrode.

Fabrication and characterization of conductive microcapsule containing phase change material

Microencapsulated phase change materials (MicroPCMs) were fabricated using n-octadecane as PCM and melamine-formaldehyde as shell via in situ polymerization. They were coated with polypyrrole (PPy) to fabricate conductive microcapsules. The structure, morphology, thermal properties and the electrical conductivity of the microcapsules were characterized using the scanning electron microscope (SEM), the Fourier transformed infrared spectroscopy (FTIR), the thermo gravimetric analysis (TGA), the differential scanning calorimetry (DSC) and the standard four-probe method. The results show that, n-octadecane is well encapsulated in rough and compact spherical composites. The melting and freezing the composites latent heats are 90.2 and 92.0 J/g, respectively, while the mass percentage of the n-octadecane in the composites is 49.7%. The melting and crystallizing peak temperature of PPy/MicroPCMs is 24.6°C and 17.9°C, respectively. The addition of PPy improves the thermal stability of the composites. The conductivity of the PPy/MicroP-CMs increases from 0.1 S‧cm–1 to 0.33 S‧cm–1 as the PPy concentration increases from 3 to 10 wt%.

Neopentyl Glycol as Active Supporting Media in Shape-Stabilized PCMs

The present work explores the feasibility of using polyalcohols with solid-solid phase transition as active supporting matrix of n-alkanes in shape-stabilized phase change materials (SSPCMs). It is well-established that the use of SSPCM avoids leakage and increases stability and easy handling of solid-liquid PCMs. Nevertheless, the resulting composite exhibits a loss of heat storage capacity due to the volume occupied by the supporting material, which does not contribute to latent heat storage. Therefore, the objective of this work is to combine solid-liquid PCMs (alkanes) with solid-solid PCMs (polyalcohols), both exhibiting a phase transition in the same range of temperature, to obtain high energy density SSPCMs. Towards that goal, the performance of Neopentyl Glycol (NPG) and Docosane as a new energetic SSPCM has been proved. The NPG-Docosane chemical compatibility and its outstanding wettability facilitate the propitious association of both materials. The higher capillary forces obtained by decreasing the NPG crystal size together with the addition of expanded graphite (EG) allowed to obtain a maximum Docosane content of 60 wt%. The addition of EG improves the shape stability at the time that increases the heat transfer properties of the composites. The analysis showed that the components of the obtained SSPCMs are able to combine their latent heats, achieving a maximum value of 210.74 J/g for the highest Docosane content. This value is much higher than those latent heats exhibited by existing SSPCMs in the same working temperature range.