A computational fluid dynamics (CFD) study was conducted to analyse the flow structure and the effect of varying the coil pitch on the coil friction factor and wall shear stress, through utilising different models’ configurations. Three coils were tested, all of them having the same diameter and coil diameter: 0.005m and 0.04m respectively. Pitch variations began with 0.01, 0.05, 0.25 m for the first, second and third model respectively. Two turbulence models, STD(k-ϵ) and STD(k-w), were utilised in this simulation in order to determine the turbulence model which could capture most of the flow characteristics. A comparison was made between the STD(k-ϵ) and STD(k-w) models in order to analyse the pros and cons of each model. The results were validated with Ito’s equation for turbulent flow and compared with Filonenko’s equation for a straight pipe. The governing equations were discretized using finite volumes method and the SIMPLE algorithm was used to solve the equations iteratively. All the models were simulated using the ANSYS Fluent solver CFD commercial code. The results showed that in turbulent flows, Dean number had a stronger effect on reducing coil friction factor than the increment in pitch dimension.
Experimental investigations of the flows inside helically coiled pipe are difficult and may also be expensive, particularly for small diameters. Computational fluid dynamics (CFD) packages, which can easily construct the geometry and change the dimensions with 100% of accuracy, provide an alternative solution for the experimental difficulties and uncertainties. Therefore, a computational fluid dynamics (CFD) study was conducted to analyse the flow structure and the effect of varying the coil pitch on the coil friction factor, through utilising different models' configurations. Two coils were tested, all of them sharing the same pipe and coil diameter: 0.005m and 0.04m respectively. Pitch variations began with 0.01 and 0.05 m for the first, second model respectively. In this study, the velocity was analysed, and the effects of this reduction on coil friction factor were also examined using laminar flow. The results were validated by Ito's equation for the laminar flow.
In a standing wave thermoacoustic refrigerator, heat transport from the "cold" to the "ambient" end of a stack is achieved by means of an oscillatory motion of a compressible fluid undergoing cyclic compression and expansion. However, the stacks can be both costly and impractical to fabricate due to material and assembly costs, which limits the cost benefits of thermoacoustic systems. Some of these problems could be solved by the application of stacks that have irregular geometries, for instance stacks made of "random" materials from metal machining (swarf), which are often considered as waste. In this paper, the thermal performance of stacks made of a few selected materials is determined by carrying out experiments in a standing wave thermoacoustic refrigerator. The reported results will be beneficial for developing low-cost thermoacoustic refrigerators or heat pumps for both domestic and commercial applications.
Free convection of various nanofluids inside concentric and eccentric annular cavity with internal heat flux, fully filled with porous media is studied numerically and its heat transfer rate and pressure drop are examined. The impact of inner cylinder inclination angles (βecc = 45°, 135°, 225°, and 270°) and nanofluids (Al2O3/water, CuO/water and SiO2/water) for different heat flux (1000, 2000, 3000, and 4000 w/m2) on the heat transfer rate are evaluated. Initially, a validation process has been implemented to ensure that the predicted results obtained from this model are accurate. Results indicate that Al2O3 Nanofluid provides a better enhancement in the heat transfer rate when compared to SiO2 and Cu Nanofluids. Furthermore, the heat transfer coefficient increased with the inclination angle of βecc = 225°, and maximum heat transfer occurred at a heat flux of 4000 W/m2, which was roughly 6% greater than the concentric annular cylinder. The findings also indicated that while increasing the eccentricity has a minor impact on the heat transfer rate for convection-dominated flows (high heat flux), on the other hand, it has a significant impact on the heat transfer rate for conduction-dominated flows (low heat flux).
Ordinary refrigeration systems such as vapor-compression refrigerators are the commonly used devices in industry, mostly for their high efficiencies. However, they make a significant contribution to the depletion of Ozone and global warming due to their operational refrigerants. Hence, thermoacoustic refrigeration can be a great alternative candidate which uses inert gases such as air, helium and nitrogen as the primary refrigerant. Thermoacoustic refrigerators convert the acoustic power (sound waves) into a thermal effect (cooling power). Thermoacoustics can be counted as a new technology that has a strong potential toward the development of the thermal applications. This study aims to design and fabricate miniaturized traveling wave thermoacoustic refrigerator which can be driven by an ordinary loudspeaker. The optimized numerical design of the refrigerator shows an overall efficiency (cooling power over input electricity) of nearly 66% at a temperature difference of 25[Formula: see text]K (between cold and ambient heat exchangers). The maximum estimated cooling power is 65[Formula: see text]W at coefficient of performance (COP) of 2.65.
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