A High-Accuracy Thermal Conductivity Model for Water-Based Graphene Nanoplatelet Nanofluids

High energetic efficiency is a major requirement in industrial processes. The poor thermal conductivity of conventional working fluids stands as a limitation for high thermal efficiency in thermal applications. Nanofluids tackle this limitation by their tunable and enhanced thermal conductivities compared to their base fluid counterparts. In particular, carbon-based nanoparticles (e.g., carbon nanotubes, graphene nanoplatelets, etc.) have attracted attention since they exhibit thermal conductivities much greater than those of metal-oxide and metallic nanoparticles. In this work, thermal conductivity data from the literature are processed by employing rigorous statistical methodology. A high-accuracy regression equation is developed for the prediction of thermal conductivity of graphene nanoplatelet-water nanofluids, based on the temperature (15–60 °C), nanoparticle weight fraction (0.025–0.1 wt.%), and graphene nanoparticle specific surface area (300–750 m2/g). The strength of the impact of these variables on the graphene nanoplatelet thermal conductivity data can be sorted from the highest to lowest as temperature, nanoparticle loading, and graphene nanoplatelet specific surface area. The model developed by multiple linear regression with three independent variables has a determination coefficient of 97.1% and exhibits convenience for its ease of use from the existing prediction equations with two independent variables.

Experimental And Numerical Invetigation Of Dependence Of Soil Thermal Conductivity On Temperature Water Content, And Soil Texture

Comprehensive set of thermal conductivity data for a loam soil was generated, for temperature variations from 5ºC to 92ºC and water content variations from dry to saturation, and compared to two other soil textures. The results exhibited similar characteristics as those of the other textures, where a significant change in soil thermal conductivity was. Using the thermal conductivity data sets, a model representing heat and mass transfer in soil was used to study the apparent thermal conductivity due to vapour migration. In addition, a computer simulation of a ground source heat pump system was developed, where the experimental data was used to investigate the impact of water content and soil texture variation on the GSHP performance. It was observed that the GSHP energy consumption varied more prominently when the soil wetness varied from dryness to full saturation and less significantly when the soil type varied from coarse to finer texture.

Experimental And Numerical Invetigation Of Dependence Of Soil Thermal Conductivity On Temperature Water Content, And Soil Texture

Comprehensive set of thermal conductivity data for a loam soil was generated, for temperature variations from 5ºC to 92ºC and water content variations from dry to saturation, and compared to two other soil textures. The results exhibited similar characteristics as those of the other textures, where a significant change in soil thermal conductivity was. Using the thermal conductivity data sets, a model representing heat and mass transfer in soil was used to study the apparent thermal conductivity due to vapour migration. In addition, a computer simulation of a ground source heat pump system was developed, where the experimental data was used to investigate the impact of water content and soil texture variation on the GSHP performance. It was observed that the GSHP energy consumption varied more prominently when the soil wetness varied from dryness to full saturation and less significantly when the soil type varied from coarse to finer texture.

Thermal conductivity of transition metal containing type-I clathrates

ABSTRACTConcerning a materials ability to convert heat to electrical energy, the electrical power factor S2/ρ as well as the thermal conductivity at elevated temperatures are of special interest. Since Flash experiments measure the thermal diffusivity and standard steady-state heat-flow experiments are inaccurate at elevated temperatures due to radiation errors inherent to this technique, direct and accurate thermal conductivity data on type-I clathrate single crystals at elevated temperatures are scarce in literature. Here we report 3ω thermal conductivity data on single crystalline Ba8Cu5.09Ge40.91 (BCG), La1.23Ba6.99Au5.91Si39.87, and Ce1.06Ba6.91Au5.56Si40.47 in the temperature range between 80 and 330 K, and specific heat data on BCG between 2 and 300 K. The comparison of our room temperature phonon thermal conductivity data (κph) to results on transition metal (TM) free type-I clathrates in terms of the guest free space (Rfree) suggests a stronger dependence of κph on Rfree for the clathrates containing TM elements.

Experimental Determination of Temperature-Dependent Thermal Conductivity of Solid Eicosane-Based Nanostructure-Enhanced Phase Change Materials

The effective thermal conductivity of composites of eicosane and copper oxide nanoparticles in the solid state was measured experimentally by using the transient plane source technique. Utilizing a controllable temperature bath, measurements were conducted at various temperatures between 10 and 35°C for the solid samples. In the course of preparation of the solid specimen, liquid samples (0, 1, 2, 5 and 10 wt%) were poured into small diameter molds and were degased within a vacuum oven. The molds were then subjected to either ambient solidification or ice-water bath freezing method. Measured thermal conductivity data of the composites were found to be nearly independent of the measurement temperature for a given loading of CuO nanoparticles regardless of the solidification procedure. Irrespective of the solidification method, as the melting temperature was approached, thermal conductivity data of the solid disks rose sharply for both sets of experiments. The composites prepared using the ice-water bath solidification scheme consistently exhibited lower values of thermal conductivity when compared to the samples which prepared under ambient solidification method. This behavior might be due to the greater void percentage of ice-water bath samples and/or crystal structure deviations due to phase transition method.