The Effect of Wall Thermal Boundary Condition on Natural Convective Shutdown Cooling in a Gas Turbine

As a civil gas turbine cools down, asymmetric natural convective heat transfer causes the bottom sector of the rotor to cool faster than the top; this circumferential thermal gradient can potentially cause the shaft to deflect – a phenomenon called thermal or rotor bow. Rotor bow is tremendously difficult to predict due to its dependence on a number of engine design parameters, in addition to the complex nature of natural convective flows. A novel experimental facility has been developed to gain further understanding into shutdown cooling of a gas turbine. The scope of this paper is to quantify the effect of basic design features on natural convective cooling in an engine annulus during shut-down. In addition to this, a low-cost, robust thermocouple probe has been developed and validated, which allows for accurate temperature measurements in a natural convective boundary layer. An extensive experimental campaign has been completed. The key finding is that the local radial wall temperature difference was found to be the most influential parameter on the local heat transfer. Non-isothermal walls did not alter the overall distribution of the inner wall equivalent conductivity. This was true for both cylindrical and conical sections. Therefore, the mean surface heat transfer for non-isothermal inner and outer profiles, within the range −0.4<Ra/RaLc <0.4, where the thermal gradient is negative in the clockwise from top-dead- centre, can be predicted using isothermal correlations for RaLc < 5.0 × 105 and Dr < = 1.5.

Temperature Stability and Effectiveness of Plasma-Activated Liquids over an 18 Months Period

Non-buffered plasma-activated liquids such as water and saline have shown bactericidal effects. In the present study, we investigated the anti-bacterial efficacy and stability of plasma-activated water (PAW) and plasma-activated saline (PAS), generated using a high voltage dielectric barrier discharge system. This study compares the potential of non-buffered plasma-activated liquids (PAL) for the inactivation of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) after storage of the solutions at five different temperatures for a storage time up to 18 months after their generation. The temperatures used were room temperature, 4 °C, −16 °C, −80 °C, −150 °C. Both PAW and PAS achieved 6 log reduction for both bacteria on the first day of their generation after 60 min contact time and they retained these effects after 18 months when stored at the lowest temperatures. Chemical analysis of PAL showed that plasma caused a drop in pH, generation of reactive oxygen species and nitrates, whereas no nitrites are detected in the system used. The concentrations of chemical species were affected by the storage at different temperatures and a thermocouple probe was used to investigate the freezing behaviour of the PAL.

Towards Quantitative Wall Shear Stress Measurements: Calibration of Liquid Crystals

The wall shear stress distribution on an aerodynamically loaded component is of both practical and fundamental importance. Significant examples are the improvement of the performance of a vehicle, e.g. drag reduction, and more basic problems, such as the characterization of surface flows, e.g. with respect to flow control. The liquid crystal technique represents a promising diagnostics for measuring wall shear stress magnitude and orientation. In contrast to most other techniques, the direct measurement of two-dimensional wall shear stress distributions is straightforward. In order to establish quantitative measurements of wall shear stress using the liquid crystal technique, an in-depth understanding of the influencing parameters is required. For their investigation, a novel generic flat plate test section was designed. The experiments are performed in such a way that a turbulent boundary layer is triggered at a corresponding Reynolds number within the test section. Due to the generic test case, precise and well-known flow boundary conditions can be established, which in turn are validated by probe measurements. Velocity and temperature profiles are recorded with high spatial resolution using a miniaturized combined Pitot-thermocouple probe. Furthermore, the operational range of the new test rig is presented. Preliminary wall shear stress measurements confirm the well-defined flow conditions in the test section and the potential of the measurement technique.

Indium Tin Oxide Thin-Film Thermocouple Probe Based on Sapphire Microrod

Indium tin oxide (ITO) thin-film thermocouples monitor the temperature of hot section components in gas turbines. As an in situ measuring technology, the main challenge of a thin-film thermocouple is its installation on complex geometric surfaces. In this study, an ITO thin-film thermocouple probe based on a sapphire microrod was used to access narrow areas. The performance of the probe, i.e., the thermoelectricity and stability, was analyzed. This novel sensor resolves the installation difficulties of thin-film devices.

Numerical Investigation on Metrological Fidelity of a Shielded Thermocouple Probe and the Effects of Geometrical Parameters

Proper design optimization and precise error characterization of temperature sensing-elements are rudimentary in the field of high accuracy gas temperature measurements. The intricate flow structures and heat transfer mechanisms related to a shielded thermocouple probe are studied in this paper using computational fluid dynamics and conjugate heat transfer (CFD/CHT) simulation tools. Owing to the probe’s novel geometry, it was a pre-requisite to characterize the metrological fidelity of the probe and the steady-state errors were determined from the simulations. The influence of certain geometrical parameters on the error characteristics of the probe was also investigated. The characteristic variation of the metrological fidelity of the probe with respect to those geometrical parameters should facilitate the optimization of the probe design.

Пространственное распределение температуры газа в воздушной плазменной струе тлеющего микроразряда постоянного тока

The spatial distribution of gas temperature in air plasma jet of dc glow microdischarge has been determined. The temperature field was measured by a thermocouple probe and compared to schlieren images. The jet can be separated in the radial direction into three characteristic regions with clearly pronounced boundaries. The central region represents a narrow hot zone corresponding to the visible plasma plume, in which the gas temperature varies from 50 to 200°C depending on the air flow rate and distance from the anode. This zone is surrounded by a warm “coat” of ~1-cm diameter and a temperature within 30–50°C. The outer region represented ambient air at room temperature. The zone of temperatures above 50°C did not extend to a distance above 3 cm from the output nozzle of the discharge cell.