Estimating correlations for the effective thermal conductivity of granular materials

Based on the well-known solution of Maxwell [1] for the thermal conductivity of dilute dispersions of spheres and the improved form of Maxwell’s equation developed by Chiew and Glandt [2], two general correlation for k_eff estimation are proposed. One of them apply to medium dense dispersions (0.15≤φ≥0.85) and the other one for dense porous materials (φ>0.9). Both correlating equations encompass a wide range of phase conductivity ratio values. The comparison with experimental measurements shows very good agreement.     

铜纳米粒子导热增强固-液相变储能材料的性能

使用聚乙烯吡咯烷酮（PVP）和聚乙二醇（PEG）作为钝化剂对铜纳米颗粒进行原位包覆制备了PVP/PEG/Cu复合纳米粒子（CuNP），将其作为导热增强剂引入到PEG中制备了CuNP/PEG固-液相变储能材料（PCMs），并通过FTIR、XRD、DSC以及TGA等表征了CuNP/PEG固-液PCMs的结构及热性能。利用纳米粒子表面的PVP与PEG之间的氢键和空间位阻效应，以及PVP对铜核的保护作用，赋予了铜纳米粒子在PCMs中优异的分散稳定性。结果表明，CuNP的引入能够显著提高复合相变储能材料的导热能力，并能够作为晶核加速材料的结晶行为。当纳米粒子的质量分数为5%时，CuNP/PEG固-液PCMs的相变焓值为157.0 J/g，体系的储热速率、放热速率和结晶速率与纯PEG相比分别提高了34.09%、31.45%和53.33%。     

Speed of sound of ionic liquids: Database,estimation, and its application for thermal conductivity prediction

Speed of sound is an important thermodynamic property of ionic liquids (ILs) and always chosen as a source to determine other properties. A database for the speed of sound of pure ILs created by collecting experimental data from literature covering the period from 2005 to 2013 is presented. The effects of temperature and the alkyl chain length on the speed of sound are discussed and a second‐order corresponding states group contribution method is developed to estimate the speed of sound. An average absolute deviation (AAD) of 2.34% has been obtained. This method offers a simple but reliable approach to estimate the speed of sound of new ILs. Finally, the speed of sound is used to determine the thermal conductivity of ILs based on the Bridgman theory. The calculated values of thermal conductivity show a good agreement with the experimental ones with an AAD of 3.91%. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1120–1131, 2014