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An experimental and numerical investigation of particles fluid dynamic flow and energy transfer in a heat exchanger. Part 1. An experimental and numerical granular material flowability study

Khumalo Samkelo M., Cieslakiewicz Waldemar F., Madyira Daniel M., Scholtz Dewald, Serfontein Jan

Technical Sciences / University of Warmia and Mazury in Olsztyn

2025

Vol. 28

35--63

Flowability is of great importance to a lot of processes especially granular material handling and heat transfer. In the industry achieving the highest heating efficiency of granular material heat exchanger is the most important factor. Heating/cooling area size is one of the critical factors in heat transfer processes and is highly dependent on flowability. The complexity of optimizing flowability can only be solved in two ways, either through experiment or computational modelling. However, the simulation technique is more time efficient and cost effective compared to the experimental analysis technique. Nonetheless, the CFD methodology requires prior validation of the model with the experiment. This study comprises of the experimental and numerical analysis of granular material flowability, and it aims at establishing a balanced flow of spherical silicon particles in a heat exchanger and developing a validated model that can be used for design optimisation. A Discrete Element Method (DEM) is employed in Simcenter STAR CCM+ to analyse the flow behaviour and is validated qualitatively and quantitatively from the experimental data. The results from both the simulation and the experiment exhibit a similar trend, indicating consistency between the two approaches. In both cases, the particle velocities are not uniform within the heat exchanger, as variations are observed across different regions, from 2 mm/s to 9 mm/s. Specifically, particles near the heat exchanger walls experience lower velocities due to higher frictional resistance, while those in the central flow stream, especially close to the outlet, move at relatively higher speeds. Quantitatively, the percentage difference between the simulation and experimental results is 9.53% for particle velocity and 5.61% for mass flow rate, which falls within an acceptable range for computational modelling of granular flow. This level of accuracy indicates that the simulation effectively captures the key flow dynamics within the heat exchanger, making it a reliable tool for further analysis. The study shows convincingly that the model was validated successfully, however investigated heat exchanger is highly inefficient but using the validated model can be optimized. The study comprises two parts. The first one presents the experimental and numerical particles flow analysis of the fluid (granular material), while the second one focuses on the experimental and numerical energy transfer (heating/cooling) analysis.

Exergy Analysis of Titanium Dioxide (TiO2) Suspended with R290/R600 as a Substitute for R134a

Madyira Daniel M., Babarinde Taiwo Oluwafemi

Archives of Metallurgy and Materials

2024

Vol. 69, iss. 1

237--243

Synthetic refrigerants are being phased out gradually in accordance with international environmental protection protocols because of global warming and ozone layer depletion. Adopting R290/R600 refrigerant, an environmentally friendly refrigerant, to replace R134a, a high global warming potential refrigerant, provides one of the solutions. In this study, exergy analysis of R134a and TiO2 suspended with lubricant and R290/R600 with a composition of 60% R290 and 40% R600 (60:40) was investigated in vapour compression system (VCRS) using R290/R600 in TiO2 nanomixture lubricant and compared with R134a and R290/R600 in pure lubricant. At the inlets and outlets, the main components of the VCRS are connected to temperature and pressure sensors to measure the inlet and outlet temperatures and pressures. The results obtained were used to analyses the exergy losses at various VCrR components (compressor, condenser, evaporator, expansion valve) were investigated to determine the refrigerator’s total exergy destruction (Exdest.Total) and efficiency (ηex). The Exdest.Total of R290/R600 in pure lubricant and R290/R600 TiO2 nanomixture lubricant was reduced by 26.9% and 42.3%, respectively, and system ηex increased by 27.7% and 38.9% respectively when compared to R134a in the system. Hence, TiO2 suspended with R290/R600 is potential a substitute for R134a.