The performance of membrane humidifier (MH) and enthalpy wheel humidifier (EWH) for a large power proton exchange membrane fuel cell (PEMFC) system is compared using simulations and experiments. The MH model is based on one dimensional diffusion equation and the EWH model is based on the porous media surface diffusion equation. Simulation results agree well with experimental data. According to the results, the effect of intake air temperature has a lower effect on the MH performance than it does on the EWH performance while the air mass flow has a much higher effect on the MH performance than it does on the EWH performance. MH performs better than EWH at a low flow rate but worse at a high flow rate. Vapor transfer mechanism in the humidifiers is also studied.
Aiming at the serious problem of gap leakage between the stator and rotor of the supercritical carbon dioxide compressor, the dry gas seal scheme for centrifugal compressor of small S-CO2 power system is designed in this paper. The sealing characteristics of the single-stage spiral groove dry gas seal in the S-CO2 operating environment are studied by the large-scale commercial CFD numerical analysis software ANSYS CFX. The leakage characteristics of the S-CO2 dry gas seal at different film thicknesses are obtained. The results show that the S-CO2 dry gas seal leakage flow rate increases linearly with the increase of the film thickness. The dry gas seal leakage flow rate under different film thickness is 0.04%∼0.45% of the S-CO2 compressor flow rate, which can meet the leakage requirements of the centrifugal compressor shaft end seal in the small S-CO2 power system.
Floating nuclear power stations are vessels with nuclear reactors, designed to power offshore oil and gas drilling, island development and remote areas. The safety of the facilities is an important issue. The Leak-Before-Break (LBB) assessment is essential to the design and evaluation of nuclear power plants against a sudden double-ended guillotine break of pipes. This paper describes the LBB assessment procedure applicable to the nuclear-class pipe of the floating nuclear power station. The loads considered in the analysis include variation of temperature/pressure, swing and underwater impact. Circumferential cracks are postulated at the dangerous positions of the pipe. The fatigue propagation of the surface crack is predicted based on the fracture mechanics and the finite element method to determine the time that pipe leaking happens. The critical length of the through-wall crack is calculated by the J integral–tearing modulus approach, and then compared with the minimum detectable crack length for the purpose that unstable fracture would not be happened before the leakage detected. According to the results of the analysis it could conclude that the pipe fulfils the LBB requirements.
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