Aklilu Tesfamichael Baheta

CFD Analysis of Fouling Effects on Aerodynamics Performance of Turbine Blades

Fouling on gas turbine blades is detrimental to process operation as it may, over a period of time, reduce the blade efficiency and consequently the turbine’s efficiency. With the limitation of today’s technology, experimental study or real-life observation of fouling in a gas turbine is beyond the imagination of maintenance engineers. Hence, the effect of fouling cannot be fully quantified for the engineers to come out with mitigation or intervention plans. Nevertheless, computational fluid dynamics (CFD) may provide a good simulation to understand the phenomena. In this chapter, a recent effort involving CFD study on the influence of fouling on the gas turbine performance is presented. Firstly, the nature of fouling on gas turbine and the general consequences are discussed. This is followed by an elaboration on how CFD study has been conducted by the authors. Finally, the findings from the study are discussed.

Hydrate Formation in Two Phase Flow in Pipe

Hydrate formation occurs in pipelines beyond sea water depth of 3000 ft. with uniform ocean temperature of 38-40oF, and pressure as low as 100 psig. Plugged-up leads to pressure drop and decreased flow rate, disrupting crude oil transportation. This paper reported the detailed investigation of hydrates particles diameters and interfacial area density in relation to the hydrate deposition in deepwater pipeline. The work focused on the pipe bend section where there is an abrupt change of flow momentum. The flow was assumed isothermal and constant mean hydrate particle size. It was found that initial hydrate particulates’ diameter has the most significant impact on the deposition thickness, causing significant increase of thickness in comparison to other factors. It is concluded that the prevention of hydrate plugging should focus primary on controlling the hydrate’s mean particle sizes.

Performance Evaluation of a Variable Geometry Gas Turbine in a CHP Plant

This study is to develop mathematical models and evaluate the performance of a gas turbine with variable geometry compressor working in a CHP plant. A single shaft gas turbine plant can maintain the exhaust gas temperature if the load is not below 50 % of the full load by simultaneously regulating the compressor variable vanes position and fuel flow. For load less than 50% the engine is running to meet the power demand. This is achieved by controlling the fuel flow and air bleed at the downstream of the compressor to avoid surge formation while variable vanes are opened fully. To accommodate change of compressor parameters during variable vanes re-stagger correction coefficients are introduced. A behavior of a 4.2 MW gas turbine performance was evaluated. The effect of variation of load and ambient temperature on the gas turbine specific fuel consumption, temperature, pressure ratio, variable vanes opening and efficiency were examined. Comparison between the field data and simulation results demonstrate good agreement. The off-design calculation was done by in-house developed program in MATLAB environment.

Experimental Investigation of Thermal Conductivity of Paraffin Based Nanocomposite for TES

To maximize and improve utilization of solar collector system, there is need to integrate the system with thermal energy storage (TES), this will increase the over all efficiency of the system and provide continuous supply of energy day and night. The performance of the TES depends on its thermal conductivity and this can be enhanced by introducing nanoparticles. Thus, this paper focus on the thermal conductivity enhancement of Cu and Fe nanoparticles dispersed in paraffin based suspension was investigated experimentally for utilization in solar collector integrated with TES. The enhanced thermal conductivity measurement was performed by transient hot disk sensor technique. The increment in thermal conductivity showed approximately linear progression with increase in percentage of mass concentration of the dispersed metal-nanoparticles. It was observed that the nanoparticle with lower thermal conductivity value (Fe-80 W/mK) at bulk enhanced the polymer matrix higher than the nanoparticle with higher thermal conductivity value (Cu-401 W/mK) at the bulk. The Cu and Fe nanoparticles, at mixing ratio of 1.5% by mass, increased the thermal conductivity of the paraffin based nanocomposites by 20.63% and 51.95%, respectively when compared with the pure paraffin. The experimentally measured thermal conductivities of the Cu and Fe-paraffin nanocomposites were compared with some models and it was observed that they were under predicted. The thermal diffusivity and specific heat showed irregular increase and decrease with varying percentage mass concentration of the nanoparticles. The enhanced nanocomposite will be utilized as heat transfer medium in a solar collector system integrated with TES.

Prediction of Remaining Useful Life for Used Gas Turbine Blades

Used turbine blades are replaced by new once based on manufacturers recommended useful life. However, depending on the turbine operating conditions the blades might have different creep service life. Thus, the aim of this study was to predict the remaining creep life and investigating the microstructure of used gas turbine blades. This was done by using Larson-Miller parameter and Robinson life fraction rules under certain conditions of stress and temperature. The change in microstructure of the materials was analyzed by using the Field Emission Scanning Electron Microscope (FESEM). The result shows that turbine blades suffered from several microstructure changes based on their service life. The method used to predict the remaining useful life of used turbines could be an input to a decision to repair or replace used turbine blades. Keywords: Larson-Miller parameter,life fraction rule, microstructure, creep life, turbine blades.