Study on the Phase Change Characteristics of Carbon-Based Nanofluids

Abstract

In this study, carbon-based nanofluids (CBNFs) with the minimized carbon materials (MCMs) were prepared using a graphite powder-based heating and cooling processing method (GP-HCPM). In addition, sodium dodecyl benzenesulfonate (SDBS) was added as a dispersant to enhance the stability of the CBNFs. Two methods, one involving fixed heating and cooling rates and the other involving fixed heating and cooling temperatures, were used to measure and analyze the phase change characteristics of the CBNFs and SDBS aqueous solution in order to evaluate the feasibility of employing CBNFs as phase change materials (PCMs) for cold storage applications. Results revealed that SDBS reduced the thermal conductivity (k) and increased the viscosity (μ), density (ρ), and specific heat (c p ) of the samples; the CBNFs tended to increase the k, μ, and ρ values but reduce the c p values of the samples, compared with water. Furthermore, the SDBS aqueous solution and CBNFs significantly reduced the contact angle of droplets, compared with water. Phase change experiments conducted for all samples revealed that the CBNF sample S4 demonstrated the greatest reduction ratios in onset nucleation time, solidification time, and subcooling degree (38.98%, 11.05%, and 35.41%, resp.); thus, S4 was determined to be the most suitable CBNF for use as a PCM in cold storage applications.

Preparation and Experimental Evaluation of Phase-Change Characteristics in Carbon-Based Suspensions

“…The main factors affecting icing heterogeneity nucleation include the morphology and specific surface area of the added material, the interface characteristics between the added material and base fluid, the k of the sample, the dynamic viscosity ( ν = μ / ρ ) of the sample, and the θ of the sample [ 5 , 13 , 14 , 17 , 18 , 19 , 30 ]. The morphology of the added GP and MNCBMs was irregular and the interface characteristics between the added materials and base fluid were not further confirmed.…”

“…Subsequently, 0.4 wt.% SDBS (Sigma-Aldrich, St. Louis, MO, USA) was added to each CBS to improve its stability. SDBS is commonly used to disperse nanocarbon-based materials in water to provide excellent stability [ 14 , 29 , 30 , 31 , 32 ]. The optimum addition concentration of the dispersant was determined by adding different concentrations of SDBS (0.05, 0.1, 0.2, 0.4, and 0.8 wt.%) to 0.25 wt.% CBS.…”

“…The optimum addition concentration of the dispersant was determined by adding different concentrations of SDBS (0.05, 0.1, 0.2, 0.4, and 0.8 wt.%) to 0.25 wt.% CBS. A UV-VIS-NIR spectrometer (V670, Jasco, Tokyo, Japan) was used to measure the changes in absorbance for each CBS with various SDBS addition concentrations before and after standing for 48 h [ 29 , 30 ]. The results revealed that across the range of SDBS addition concentrations, the addition of 0.4 wt.% SDBS to 0.25 wt.% CBSs could achieve optimal suspension performance.…”

“…Next, a DF (Antifoam B Silicone Emulsion, J. T. Baker, Center Valley, PA, USA) at concentration of 35% (0.14 wt.%) of the weight of the added SDBS was added to each CBS to reduce the volume of foam produced from SDBS to complete CBS preparation. The concentration of the added DF was effective in suppressing the foam produced by the 0.4 wt.% SDBS aqueous solution during stirring (stirrer was set at 400 rpm) [ 30 ]. The CBSs with the optimum concentration of SDBS (0.4 wt.%) had been observed for three weeks without any obvious settlement, indicating that the CBSs with the optimum concentration of SDBS had good stability.…”

Study on the Thermal Conductivity of Mannitol Enhanced by Graphene Nanoparticles for Thermoelectric Power Generation

“…The low heat transfer rate has a great impact on the heat transfer process, so it is very important to improve the thermal conductivity of PCMs. The common methods to enhance heat transfer are using fin structure [6], using capsule structure [7,8], using porous medium structure [9,10], and adding high thermal conductivity material [11,12]. Two or more methods can be used to further improve the thermal conductivity, such as mixing paraffin wax with expanded graphite and then adding the nanomixed material to the aluminum foam [13,14].…”