Thermal Characterization of Lauric Acid and Stearic Acid Binary Eutectic Mixture in Latent Heat Thermal Storage Systems with Tube and Fins

In order to obtain the suitable phase change material（PCM） with low phase change temperature and improve its heat transfer rate, experimental investigation was conducted. Firstly, different mass ratios of lauric acid（LA） and stearic acid（SA） eutectic mixtures were prepared and characterized by differential scanning calorimetry（DSC）. Then, the performance of eutectic mixture during charging process under different fin widths in vertical condition, and performance during charging and discharging processes under different inlet temperature heat transfer fluid（HTF） in horizontal condition were investigated, respectively. The results revealed that the LA-SA eutectic mixture had the suitable phase change temperature and desired latent heat for low-temperature water floor heating system. Wide fins and high inlet temperature HTF significantly enhanced the transfer rate and decreased the melting time.

Temperature-Dependent Rheological Behaviors of Binary Eutectic Mixtures of Sugar Alcohols for Latent Heat Storage:A Comparative Study with Pure Sugar Alcohols

The temperature-dependent rheological behaviors of five selected binary eutectic mixture sugar alcohols,with great potential for latent heat storage in the range of 353.15 K to 523.15 K,were investigated.It was found that the rheological behaviors of the mixture sugar alcohols depend on those of the pure compounds as well as their molar ratios.The two mixtures of xylitol(75 mol%)+erythritol and erythritol(84 mol%)+d-mannitol behave like pseudoplastic fluids with typical non-Newtonian shear-thinning behaviors,as indicated by the power law index of 0.99(<1).The mixture of d-mannitol(70 mol%)+d-dulcitol is a nonlinear Bingham fluid,exhibiting a slight yield stress(0.001 Pa to 0.01 Pa)at low shear rates.The rest two mixtures containing the cyclic-structured inositol behave like Herschel-Bulkley fluids.The infinite shear viscosities of the eutectic mixtures over the entire temperature range appear to be higher than those of their respective pure compounds,except for inositol.The mixture of xylitol(75 mol%)+erythritol at its melting point shows higher dynamic viscosity of about 0.546 Pa·s than the values of about 0.396 Pa·s and 0.035 Pa·s for xylitol and erythritol,respectively.In addition,the activation energies of viscous flow of the mixtures,as determined by fitting the dynamic viscosity-temperature curves using the Arrhenius model,also exhibit higher values than those of their pure compounds.The activation energy of viscous flow of the mixture xylitol(75 mol%)+erythritol was determined to be about 92400 J/mol in the supercooled liquid state,while the supercooled liquid xylitol and erythritol have much lower values of 83500 J/mol and 51900 J/mol,respectively.Both the increased dynamic viscosities and activation energies of viscous flow can result in deteriorated crystallization performance during latent heat retrieval.

Ionothermal Synthesis and Structural Characterization of a Novel Open Framework Zinc Diphosphonate with Carboxylate-like Linker

A novel crystalline zinc diphosphonate, （CH3NH3）4Zn2（xbp）2·H2O, denoted as compound 1, was ionothermally synthesized from tetraethyl-p-xylylenebisphosphonate （Yexbp） and Zn（OAc）2 in a protic eutectic mixture with urea/methylamine hydrochloride. Its structure was determined by single-crystal X-ray diffraction data and had a special three-dimensional open framework with rhombic channels. Compound 1 belongs to the monoclinic system （space group C2/c）, with lattice parameters a=22.6876（19）A, b=8.7376（7）A, c=8.1673（9）A, β= 108.146（2）°, V= 1538.5（2） A^3, Z=2. Its structure is totally different from the typical organic pillared structure, only two oxygens of the phosphonate group are coordinated with zinc atoms, and the third oxygen exists in the terminal form, which is similar to the popular dicarboxylate linkers in MOFs. The organic cations [CH3NH3]^＋ of the eutectic mixture played a structure-directing role for constructing this framework and were confined in the pore channels to balance the negative charges resulting from the zinc phosphonate inorganic chains.