PDF Publication Title:
Text from PDF Page: 004
M.M. Kenisarin, et al. Journal of Energy Storage 27 (2020) 101082 sphere is caused by natural convection, which determined by the buoyancy forces (the difference between densities of PCM in solid and liquid phases). Tan [48] carried out the experimental study of constrained and unconstrained melting of PCM inside a spherical enclosure. N-octade- cane was used as the PCM for investigations. The spherical flask with a diameter of 101.66 mm and a volume of 550 cm3 was filled with the molten PCM. For constrained melting, three experiments were per- formed at three different initial sub-cooling levels of 1, 10, and 20 °C for a constant temperature of 40 °C at the surface of the sphere. The typical experimental results for the constrained melting are presented in Fig. 3. In experiments with the initial sub-cooling level of −10 °C, it was ob- served that the natural convection starts to play a dominant role in the heat transfer process after 30 min from the beginning of the experi- ment. This period corresponds to t* ≈ 0.046 (our estimation), which is significantly higher than 0.0164, obtained in [47]. The contours of melting process shown in photographs in [47] and [48], also sig- nificantly differ. It is worth noting that under the same experimental conditions, the unconstrained melting inside the sphere occurs at a faster rate than during constrained melting. Thus, the time required for constrained melting was 130 min, whereas only 80 min were required for the unconstrained melting. During the constrained melting, heat conduction plays a role only at the beginning of melting process. This effect causes the PCM to melt inwards in almost concentric manner. An oval shape-melting pattern is formed at the top half of the solid PCM but the profile at the bottom remains relatively unchanged. The oval shape phase front is caused by the natural convection when the liquid layer increases. Natural convection occurs because of the warm liquid PCM rises along the hot wall while the cooler liquid in the center flows down to replace the warmer fluid. This creates an unstable fluid cir- culation inside the sphere, known as buoyancy-driven convection. The top part of PCM melts at a faster rate than its bottom half. Natural convection also occurs at the bottom half of the vessel, thus resulting in the wavy profile of the bottom part of PCM. Tan with colleagues [49] conducted a comparative study of ex- perimental results, presented in [46], and numerical simulations on the constrained melting of PCM. Fig. 4 shows the instantaneous values of the liquid fraction within the spherical capsule found numerically and experimentally. It can be seen, that the computational technique pre- dicts a faster rate of constrained melting. Experimental data was ob- tained using the digitalization of the photographs with the solid-liquid interface (similar to those in Fig. 3). Three-dimensional melting effects, which were not accounted for in the modeling, cause the observed differences in sets of results. Khot et al. [50] carried out an experimental investigation of con- strained and unconstrained melting of paraffin wax inside a spherical capsule. In the study, the sample of paraffin wax was used with the melting point of 59.8 °C and the heat of fusion of 190 J/g. The bor- osilicate glass spherical capsules with a diameter of 85 mm was used for Fig. 4. Computational and experimental variation of the liquid fraction as a function of time [49]. melting process observation. Preliminarily, capsules were maintained at a constant initial temperature of 27 °C. When the water reached the required temperature, the capsules were placed into the test water tank, and the melting process was started. A digital camera captured the process of melting by taking photos with 10 min intervals. The tests were conducted for four HTF temperatures of 62, 70, 75 and 80 °C for both constrained and unconstrained melting of the PCM inside the capsule. Fig. 5 presents the instantaneous photographs of wax melting during one of the experiments. The effect of Stefan number on forming molten fraction during the constrained melting was studied. At the Stefan number of 0.227, paraffin wax completely melted within 55 min compared to 60, 80, and 115 min for Stefan numbers equal to 0.171, 0.114, and 0.024, respectively. The higher Stefan number (i.e. higher ΔT) results in, the shorter time, required for complete melting in both constrained and unconstrained modes of melting. It is easy to note that the contours of the solid-liquid interface observed in [45] differ from those presented in [46]. In 2015, Galione et al. [51] presented the results of the fixed-grid numerical modeling of melting of n-octadecane inside a spherical capsule. A comparison of predicted values with data of Tan et al. in [49] demonstrated that only three-dimensional simulations provide a close approximation to the experiment, see Fig. 6. Li et al. [52] reported results of another numerical study on the constrained melting of PCM inside a spherical capsule. For validation of the mathematical model, the experimental observation of the con- strained melting of paraffin wax inside the spherical glass flask was Fig. 3. Constrained melting phase fronts at 40 °C with the initial sub-cooling of 10 °C [48]. 4PDF Image | Journal of Energy Storage 27
PDF Search Title:
Journal of Energy Storage 27Original File Name Searched:
tes-spherical-ball-storage-paraffin.pdfDIY PDF Search: Google It | Yahoo | Bing
Turbine and System Plans CAD CAM: Special for this month, any plans are $10,000 for complete Cad/Cam blueprints. License is for one build. Try before you buy a production license. More Info
Waste Heat Power Technology: Organic Rankine Cycle uses waste heat to make electricity, shaft horsepower and cooling. More Info
All Turbine and System Products: Infinity Turbine ORD systems, turbine generator sets, build plans and more to use your waste heat from 30C to 100C. More Info
CO2 Phase Change Demonstrator: CO2 goes supercritical at 30 C. This is a experimental platform which you can use to demonstrate phase change with low heat. Includes integration area for small CO2 turbine, static generator, and more. This can also be used for a GTL Gas to Liquids experimental platform. More Info
Introducing the Infinity Turbine Products Infinity Turbine develops and builds systems for making power from waste heat. It also is working on innovative strategies for storing, making, and deploying energy. More Info
Need Strategy? Use our Consulting and analyst services Infinity Turbine LLC is pleased to announce its consulting and analyst services. We have worked in the renewable energy industry as a researcher, developing sales and markets, along with may inventions and innovations. More Info
Made in USA with Global Energy Millennial Web Engine These pages were made with the Global Energy Web PDF Engine using Filemaker (Claris) software.
Sand Battery Sand and Paraffin for TES Thermo Energy Storage More Info
CONTACT TEL: 608-238-6001 Email: greg@infinityturbine.com (Standard Web Page)