Optimizing the shape of PCM container to enhance the melting process

The shape of container influences natural convection inside a latent heat storage with a phase change material (PCM). Often the geometrical design of a PCM container is based on empirical observations. To enhance convection and melting of the PCM, authors propose here new design guidelines for an improved container. Using the so-called Co-factor method as the optimized basis, which is defined as the vector product of the velocity and temperature gradient, the new design method strives to raise the velocity of natural convection in liquid PCM, increase the amount of PCM in the direction of the convective flow, and reduce the amount of PCM far from the heating surface. Following these guidelines and Co factor, an optimized PCM container with an elongated and curved shape is proposed and compared to a rectangular container. Numerical simulations indicated that the total melting time of the PCM in the optimized container could be reduced by more than 20% compared to the rectangular one. The higher natural convection velocity and the better use of it to melt the PCM in the optimized container space attributed to the better performance than that in rectangular container. The results can be used to design more effective PCM storage systems.

Optimal System for Improved Internal Model Control of Argon-Oxygen Decarburization Process Based on the Piecewise Linear Model and Time Constant of Filter Optimization

This paper presents an improved internal model control system to raise the efficiency of refining low-carbon ferrochrome. This control system comprises of a piecewise linearized transfer function and an improved internal model controller based on optimized time constant of the filter. The control system is mainly used to control the oxygen supply rate during the argon-oxygen refining for controlling the smelting temperature. The regulatory performance and servo of two closed-loop control schemes are compared between the improved internal model controller based on the optimized filter time 0000-0002-7606-6546and the internal model controller based on the fixed filter time constant. The simulation analysis shows that the piecewise linearized model and the optimization of the time constant of the filter improves the response time, stability, and anti-interference ability of the controller. Then, the proposed improved internal model controller is used to adjust the gas supply flow in 5 ton AOD furnace to control the smelting temperature. Ten production tests performed the effectiveness of the controlling refining optimal system. The analysis of the experimental data shows that the improved internal model control system can shorten the melting time and improve the melting efficiency. Thus, the application of the improved internal model control system in low-carbon ferrochrome refining is an interesting potential direction for future research.

Correlations for Melting Time and Melt Fraction for Bottom Charged Tube in Tube Phase Change Material Heat Exchanger

Multiple factors govern the Thermo-hydraulic behaviour of Latent heat storage devices. The correlation among these factors varies from case to case. In this work, a concentric tube in tube latent heat storage system is numerically modelled for the bottom charging case. Fixed grid enthalpy porosity approach is adopted to account for phase change. The numerical model’s independence is achieved by testing mesh size, time step, and maximum iterations per time step. The computational approach is validated against the experimental data. Non-dimensional parameters viz Rayleigh Number (3.04x105 to 65.75 x105), Stefan Number (0.2 to 1), Reynolds Number (600 to 3000), and L/D ratio (2 to 15) are varied in the respective ranges mentioned in parenthesis. Stefan number is found to have a major influence on the Melt Fraction and Melting time, compared to Rayleigh Number and Reynolds Number. Correlations are presented for quantifying the melt fraction and dimensionless melting time.

Antioxidant properties, technological and physicochemical characteristics of milk ice cream with addition of camu-camu pulp

Camu-camu is an exotic fruit, known for having high concentrations of vitamin C and bioactive compounds. In order to diversify the consumption of this fruit, this study developed milk ice cream formulations and evaluated the effect of the addition of different concentrations of camu-camu pulp (20 to 26%), sugar (12 to 14%) and defatted dry extract (DDE) (12 to 16%) through a mixture design. Ice creams were evaluated by analyses of overrun, density, melting time, ratio, and cost. Three formulations were defined based on maximum melting time and ratio and minimum cost. The ice creams formulations defined by the experimental design consisted of the following proportions of pulp, sugar and DDE (%): 26:12:12, 20:14:16 and 24:14:12. These formulations were evaluated in relation to their physicochemical and technological characteristics, antioxidant and reducing capacity and sensory acceptance. The results showed that all formulations had high concentrations of antioxidant compounds and vitamin C and the formulation with the addition of camu-camu pulp lower than 24% had greater sensory acceptance. Therefore, it is concluded that the addition of camu-camu pulp in milk ice cream is interesting from a nutritional point of view, as it can increase the content of nutrients and minerals in the final blend.

CFD Model of Shell-and-Tube Latent Heat Thermal Storage Unit Using Paraffin as a PCM

This chapter validates the capability of CFD modelling technique to accurately describe processes in the thermal storage system with the PCM. For validation purposes, CFD modelling using FLUENT ANSYS was conducted and the predicted results were compared with the experimental and numerical data from the literature. The comparison between experimental and numerical results was carried out in terms of the temperature distributions and average volume of the PCM liquid fraction. Additionally, the detailed parametric study of the storage system with the PCM was performed and results obtained were discussed with dimensional correlations for the Nusselt number being proposed to be used in the designing process. Finally, a correlation was developed to estimate the total melting time at the thermal storage system.

Melting Enhancement in a Triple-Tube Latent Heat Storage System with Sloped Fins

Due to the potential cost saving and minimal temperature stratification, the energy storage based on phase-change materials (PCMs) can be a reliable approach for decoupling energy demand from immediate supply availability. However, due to their high heat resistance, these materials necessitate the introduction of enhancing additives, such as expanded surfaces and fins, to enable their deployment in more widespread thermal and energy storage applications. This study reports on how circular fins with staggered distribution and variable orientations can be employed for addressing the low thermal response rates in a PCM (Paraffin RT-35) triple-tube heat exchanger consisting of two heat-transfer fluids flow in opposites directions through the inner and the outer tubes. Various configurations, dimensions, and orientations of the circular fins at different flow conditions of the heat-transfer fluid were numerically examined and optimized using an experimentally validated computational fluid-dynamic model. The results show that the melting rate, compared with the base case of finless, can be improved by 88% and the heat charging rate by 34%, when the fin orientation is downward–upward along the left side and the right side of the PCM shell. The results also show that there is a benefit if longer fins with smaller thicknesses are adopted in the vertical direction of the storage unit. This benefit helps natural convection to play a greater role, resulting in higher melting rates. Changing the fins’ dimensions from (thickness × length) 2 × 7.071 mm2 to 0.55 × 25.76 mm2 decreases the melting time by 22% and increases the heat charging rate by 9.6%. This study has also confirmed the importance of selecting the suitable values of Reynolds numbers and the inlet temperatures of the heat-transfer fluid for optimizing the melting enhancement potential of circular fins with downward–upward fin orientations.

Karakteristik Fisikokimia dan Sensoris Es Krim Ubi Jalar Ungu (Ipomoea Batatas L.) Dengan Subtitusi Pemanis Ekstrak Daun Stevia (Stevia Rebaudiana Bertoni M.) dan Berbagai Jenis Stabilizer

This study aims to determine the effect of sweetener concentration, various types of stabilizers and their interactions on proximate, antioxidant and sensory content of ice cream. The study was conducted using a Factorial Completely Randomized Design (CRD) consisting of two factors. The first factor is the comparison of sweetener concentration with 3 levels of 100% sugar sweetener (D1), 50% sugar sweetener: 50% stevia extract sweetener (D2) and 100% stevia extract sweetener (D3) while the second factor is the type of stabilizer with 3 levels namely, agar. - agar (S1), Gelatin (S2) and CMC (S3). The results obtained were analyzed using the F test and followed by the DMRT test with a confidence level of 95%. The results showed that the comparison of sweetener concentration (D) and treatment interaction (DxS) had a significant effect. While the sensory analysis has a significant effect on the texture, taste, overall variables and does not significantly affect the aroma variable. The best treatment in the proximate analysis of sensory analysis is the treatment of using 50% sugar and 50% stevia and agar-agar (D2S1) stabilizer with the organoleptic score of fragrance, texture, taste and preference respectively were 3.80 (normal); 3.60 (slightly soft); 3.80 (good); 4.10 (liked), and the Physicochemical value of overrun, melting time, fibre content, viscosity, antioxidant, and sugar content respectively were 42,5%; 14,06 minutes; 0,3107%; 1,217 cP; 11,65%; 20,33%.

Experimental thermal performance comparison of pure and metal foam-loaded PCMs

The thermal performance of latent heat thermal energy storage (LHTES) systems considerably depends on thermal conductivity of adopted phase change materials (PCMs). To increase the low thermal conductivity of these materials, pure PCMs can be loaded with metal foams. In this study, the melting process of pure and metal-foam loaded phase change materials placed in a rectangular shape case is experimentally investigated by imposing a constant heat flux at the top. Two different paraffin waxes with melting point of about 35°C are tested. The results obtained with pure PCM are compared with those achieved from the use of PCM combined with two different porous metals: a 10 PPI aluminum foam with 96% porosity and a 20 PPI copper foam with 95% porosity. The results demonstrate how metal foams lead to a significant improvement of conduction heat transfer reducing significantly the melting time and the temperature difference between the heater and PCM.