Creep-Fatigue Interaction Effects On Pressure-Reducing Valve Under Cyclic Thermo-Mechanical Loadings Using Direct Cyclic Method

Supercritical boiler system has been widely used to increase efficiency of electricity generation in power plant industries. However, the supercritical operating condition can seriously affect structural integrity of power plant components due to high temperature that causes degradation of material properties. Pressure reducing valve is an important component being employed within a main steam line of the supercritical boiler, which occasionally thermal-fatigue failure being reported. This research has investigated creep-cyclic plastic behaviour of the pressure reducing valve under combined thermo-mechanical loading using a numerical direct method known as extended Direct Steady Cyclic Analysis of the Linear Matching Method Framework (LMM eDSCA). Finite element model of the pressure-reducing valve is created based on a practical valve dimension and temperature-dependent material properties are applied for the numerical analysis. The simulation results demonstrate a critical loading component that attributes creep-fatigue failure of the valve. Parametric studies confirm the effects of magnitude of the critical loading component on creep deformation and total deformation per loading cycle. With these comprehensive numerical results, this research provides engineer with an insight into the failure mechanism of the pressure-reducing valve at high temperature.

Analysis of Retention Time and Steam Pressure Variations in the Conditioning Process on the Moisture Content of Feed in the Packaging Process

Pellets are compressed feed, compacted through a mechanical process. Pellets can be molded in the form of lumps and small cylinders with different diameters, lengths, and levels of strength. The right moisture content value will maximize the quality of the pellets and increase the value of the Pellet Durability Index(PDI). Many factors affect the moisture content in the feed such as changing the steam pressure configuration, adding moisture to the mixing process, changing the retention time configuration, and other methods. The method tested was to provide variations on the configuration of retention time and steam pressure on the Pressure Reducing Valve (PRV) which aims to determine the increase in moisture content in the feed. Variations of retention time configuration tested were 50 seconds, 55 seconds, 60 seconds, 65 seconds, 70 seconds with variations in the Steam pressure configuration in the test were 1.4 bar and 1.6 bar. The test results prove that the retention time of 65 seconds with a steam pressure of 1.4 bar is the best configuration with an increase in moisture content of 2.67% with a difference in moisture content of bagging to the mixing of -0.46.

Similarity model for predicting the performance of an R718 compressor

A general compression refrigeration system consists of a compressor, condenser, pressure-reducing valve, and evaporator to induce phase changes in the refrigerant. The performance of the compression refrigeration system strongly depends on the type and characteristics of the refrigerant. However, synthetic refrigerants such as chlorofluorocarbon, hydrochloro-fluorocarbon, and hydrofluorocarbon directly affect the environment as greenhouse gases and indirectly affect the environment by generating substances as they decompose. Thus, researchers have been focusing on developing refrigerants with a low or zero global warming potential. R718 (i.e. water) is an ecofriendly refrigerant, but its specific volume rapidly changes between the liquid and gas phases. This requires making the components of the compression refrigeration system larger than normal to accommodate these volume changes, which is inefficient for manufacturing prototypes. In this study, an alternative refrigerant was applied to the design of a centrifugal compressor that uses R718 as the working fluid. To address the volume change of R718, a numerical analysis was conducted by using the similarity method, where the size of the impeller was reduced and the rotational speed was controlled. To ensure the reliability of the similarity model, its results were compared against the experimental data of the original model for verification.