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Liquefied natural gas (LNG) serves as a crucial alternative fuel for ships, yet the potential for jet fires arises when compressed natural gas (CNG) is accidently released in a ship engine room. Taking the pipe as the typical cylindrical obstacle, this study conducted a numerical investigation on flame shape characteristics resulting from a vertical jet fire impinging on a horizontal pipe. It is found that both the vertical flame length above the pipe and the horizontal extension flame length underneath it increases with a higher gas leakage velocity. Additionally, a larger pipe diameter was found to suppress the vertical flame length above the pipe while contributing to the horizontal extension length underneath it. Moreover, as increase in the nozzle-pipe distance led to a decrease in both the vertical flame length above the pipe and the horizontal extension flame length. With smaller pipe-nozzle distances and higher gas leakage velocities, more flame spikes were observed above the pipe. To quantify these phenomena, new dimensionless models were developed for the vertical flame length above pipe and the horizontal extension flame length. These models were validated against experimental results, demonstrating deviations within 12.5%. The outcomes of this research can offer an essential reference for fire prevention design, fire risk assessment and fire science research in the engine room of LNG-powered ships.
The diaphragm compressor is the essential component of a hydrogen refueling station, but the traditional design method results in low cavity volumetric efficiency and high refilling oil pressure. This study proposes a design method using a free moving oil piston to optimize the cavity volume. This method allows the cavity volume to be utilized to the maximum, and a “zero pressure” stage occurs at the end of the suction process, which greatly improves the cavity volumetric efficiency and reduces the refilling oil pressure. To further examine and verify the superiority of this method, 90 MPa and 200 MPa diaphragm compressors were designed and produced for comparison, and their simulation study was conducted simultaneously. The results demonstrate that this proposed design method can raise the cavity volumetric efficiency of the 90 MPa diaphragm compressor in the experimental case from 0.37 to 0.66. Additionally, the benefit increases with the compressor pressure. For the case of a 200 MPa diaphragm compressor, the cavity volumetric efficiency increases from 0.19 to 0.64.
To ensure that the rectangular thermal energy storage unit (RTESU) can heat more cold outdoor air for practical applications, three kinds of storage units with air flow rates of 60 m3/h, 120 m3/h, and 180 m3/h for heights of 150 mm, 300 mm, and 450 mm are proposed, respectively. Besides, the effect of natural convection (NC) on the charging and discharging process is examined during the modular expansion of the RTESU. The melting performance including melting duration and phase change process is numerically investigated by varying the configurations such as height, uniform, non-uniform, and eccentric tube arrangements. The results show that NC has a significant impact on the charging process. It is further demonstrated that the charging process can be enhanced by about 14.58% and 13.61% when non-uniform and eccentric tube arrangements are implemented, respectively, as they both can increase the area dominated by NC. However, there is an opposite trend in the effect of enhanced heat transfer between the two methods for different heights in general. It is worth noting that the Nusselt number ( [[EQUATION]] ) is introduced for examining the heat transfer performance during the melting process with different unit configurations. And the correlation between the dimensionless numbers is applied to predict the variation of a liquid fraction under different configurations. For the heat release process, the performance including air outlet temperature, heat extraction, and heat release efficiency of the modular RTESU is evaluated. It is found that the NC has a negligible effect on the discharging process, which is dominated by heat conduction. With the modular expansion, an increase in air flow rate and improvement in the charging process as well as the maintenance of a higher heat release efficiency of about 84.5% can be achieved in the RTESU.
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