S. M. Guo

A Converging Slot-Hole Film-Cooling Geometry—Part 1: Low-Speed Flat-Plate Heat Transfer and Loss

This paper presents experimental measurements of the performance of a new film cooling hole geometry - the Converging Slot-Hole or Console. This novel, patented geometry has been designed to improve the heat transfer and aerodynamic loss performance of turbine vane and rotor blade cooling systems. The physical principles embodied in the new hole design are described, and a typical example of the console geometry is presented. The cooling performance of a single row of consoles was compared experimentally with that of typical 35° cylindrical and fan-shaped holes and a slot, on a large-scale, flat-plate model at engine representative Reynolds numbers in a low speed tunnel with ambient temperature main flow. The hole throat area per unit width is matched for all four hole geometries. By independently varying the temperature of the heated coolant and the heat flux from an electrically heated, thermally insulated, constant heat flux surface, both the heat transfer coefficient and the adiabatic cooling effectiveness were deduced from digital photographs of the colour play of narrowband thermochromic liquid crystals on the model surface. A comparative measurement of the aerodynamic losses associated with each of the four film-cooling geometries was made by traversing the boundary layer at the downstream end of the flat plate. The promising heat transfer and aerodynamic performance of the console geometry have justified further experiments on an engine representative nozzle guide vane in a transonic annular cascade presented in Part 2 of this paper [1].

The development of a new direct-heat-flux gauge for heat-transfer facilities

A new type of direct-heat-flux gauge (DHFG) comprising an insulating layer mounted on a metal substrate has been developed. The gauge measures the heat flux across the insulating layer by measuring the top surface temperature employing a sputtered thin-film gauge (TFG) and the metal temperature using a thermocouple. The TFGs are platinum temperature sensors with physical thickness less than 0.1 µm. They are instrumented on the insulating layer. The thermal properties and the ratio of the thickness over the thermal conductivity of the insulating layer have been calibrated. A detailed method of analysis for calculating the surface heat flux from DHFG temperature traces is presented. The advantages of the DHFG include its high accuracy, its wide range of frequency response (from dc to 100 kHz) and, most significantly, that there is no requirement for knowledge of the structure of the metal substrate. Since the metal substrate is of high conductivity, few thermocouples are required to monitor the small spatial variation of the metal temperature, whereas multiple thin-film gauges may be employed. The DHFGs have been applied to a gas turbine nozzle guide vane and tested in the Oxford Cold Heat Transfer Tunnel successfully.

A Converging Slot-Hole Film-Cooling Geometry: Part 2 — Transonic Nozzle Guide Vane Heat Transfer and Loss

This paper presents the first experimental measurements on an engine representative nozzle guide vane, of a new film-cooling hole geometry, a convergingslot-hole or console. The patented console geometry is designed to improve the heat transfer and aerodynamic performance of turbine vane and rotor blade cooling systems. These experiments follow the successful validation of the console design in low-speed flat-plate tests described in Part 1 of this paper. Stereolithography was used to manufacture a resin model of a transonic, engine representative nozzle guide vane in which seven rows of previously tested fan-shaped film-cooling holes were replaced by four rows of consoles. This vane was mounted in the annular vane ring of the Oxford cold heat transfer tunnel for testing at engine Reynolds numbers, Mach numbers and coolant to mainstream momentum flux ratios using a heavy gas to simulate the correct coolant to mainstream density ratio. Heat transfer data were measured using wide-band thermochromic liquid crystals and a modified analysis technique. Both surface heat transfer coefficient and the adiabatic cooling effectiveness were derived from computer-video records of hue changes during the transient tunnel run. The cooling performance, quantified by the heat flux at engine temperature levels, of the console vane compares favourably with that of the previously tested vane with fan-shaped holes. The new console film-cooling hole geometry offers advantages to the engine designer due to a superior aerodynamic efficiency over the fan-shaped hole geometry. These efficiency measurements are demonstrated by results from midspan traverses of a four-hole pyramid probe downstream of the nozzle guide vane.

The application of thin-film technology to measure turbine-vane heat transfer and effectiveness in a film-cooled, engine-simulated environment

Abstract Thin-film technology has been used to measure the heat transfer coefficient and cooling effectiveness over heavily film cooled nozzle guide vanes (NGVs). The measurements were performed in a transonic annular cascade which has a wide operating range and simulates the flow in the gas turbine jet engine. Engine-representative Mach and Reynolds numbers were employed and the upstream free-stream turbulence intensity was 13%. The aerodynamic and thermodynamic characteristics of the coolant flow (momentum flux and density ratio between the coolant and mainstream) have been modelled to represent engine conditions by using a foreign gas mixture of SF 6 and Argon. Engine-level values of heat transfer coefficient and cooling effectiveness have been obtained by correcting for the different molecular (thermal) properties of the gases used in the engine-simulated experiments to those which exist in the true engine environment. This paper presents the best combined heat transfer coefficient and effectiveness data currently available for a fully cooled, three-dimensional NGVs at engine conditions.

Senary refractory high entropy alloy MoNbTaTiVW

Abstract The design approach and validation of a single phase senary refractory high entropy alloy (HEA) MoNbTaTiVW was presented in the present study. The design approach was to combine phase diagram inspection of available binary and ternary systems and Calculation of Phase Diagrams prediction. Experiments using X-ray diffraction and scanning electron microscopy techniques verified a single phase microstructure in body centred cubic lattice for MoNbTaTiVW. The observed elemental segregation agrees well with the solidification prediction using the Scheil model. The lattice constant, density and microhardness were measured to be 0.3216 nm, 4.954 GPa and 11.70 g cm− 3 respectively. The atomic size difference, the Ω parameter, enthalpy of mixing and entropy of mixing for MoNbTaTiVW HEA are 3.1%, 11.1, − 3.4 kJ mol− 1 and +13.39 J K− 1 mol− 1 respectively.

Senary Refractory High-Entropy Alloy HfNbTaTiVZr

Discovery of new single-phase high-entropy alloys (HEAs) is important to understand HEA formation mechanisms. The present study reports computational design and experimental validation of a senary HEA, HfNbTaTiVZr, in a body-centered cubic structure. The phase diagrams and thermodynamic properties of this senary system were modeled using the CALPHAD method. Its atomic structure and diffusion constants were studied using ab initio molecular dynamics simulations. The microstructure of the as-cast HfNbTaTiVZr alloy was studied using X-ray diffraction and scanning electron microscopy, and the microsegregation in the as-cast state was found to qualitatively agree with the solidification predictions from CALPHAD. Supported by both simulation and experimental results, the HEA formation rules are discussed.

Influence of Surface Roughness on Heat Transfer and Effectiveness for a Fully Film Cooled Nozzle Guide Vane Measured by Wide Band Liquid Crystals and Direct Heat Flux Gauges

The influence of surface roughness on heat transfer coefficient and cooling effectiveness for a fully film cooled 3D nozzle guide vane (NGV) has been measured in a transonic annular cascade using wide band liquid crystal and direct heat flux gauges (DHFGs). The liquid crystal methods were used for rough surface measurements and the DHFGs were used for the smooth surfaces. The measurements have been made at engine representative Mach and Reynolds numbers and inlet freestream turbulence intensity. The aerodynamic and thermodynamic characteristics of the coolant flow have been modelled to represent engine conditions by using a heavy “foreign gas” (30.2% SF6 and 69.8% Ar by weight). Two cooling geometries (cylindrical and fan-shaped holes) have been tested. The strategies of obtaining accurate heat transfer data using a variety of transient heat transfer measurement techniques under the extreme conditions of transonic flow and high heat transfer coefficient are presented.The surfaces of interest are coated with wide-band thermochromic liquid crystals which cover the range of NGV surface temperature variation encountered in the test. The liquid crystal has a natural peak-to-peak roughness height of 25 μm creating a transitionally rough surface on the NGV. The time variation of colour is processed to give distributions of both heat transfer coefficient and film cooling effectiveness over the NGV surface. The NGV was first instrumented with the DHFGs and smooth surface tests preformed. Subsequently the surface was coated with liquid crystals for the rough surface tests. The DHFGs were then employed as the means of calibrating the liquid crystal layer. The roughness of 25 μm, which is the typical order of roughness for the in service turbine blades and vanes, increases the heat transfer coefficient by up to 50% over the smooth surface level. The film cooling effectiveness is influenced less by the roughness.Copyright

Influence of Surface Roughness on Heat Transfer and Effectiveness for a Fully Film Cooled Nozzle Guide Vane Measured by Wide Band Liquid Crystals and Direct Heat Flux Gages

The influence of surface roughness on heat transfer coefficient and cooling effectiveness for a fully film cooled three-dimensional nozzle guide vane (NGV) has been measured in a transonic annular cascade using wide band liquid crystal and direct heat flux gages (DHFGs). The liquid crystal methods were used for rough surface measurements and the DHFGs were used for the smooth surfaces. The measurements have been made at engine representative Mach and Reynolds numbers and inlet free-stream turbulence intensity. The aerodynamic and thermodynamic characteristics of the coolant flow have been modeled to represent engine conditions by using a heavy foreign gas (30.2 percent SF 6 and 69.8 percent Ar by weight). Two cooling geometries (cylindrical and fan-shaped holes) have been tested. The strategies of obtaining accurate heat transfer data using a variety of transient heat transfer measurement techniques under the extreme conditions of transonic flow and high heat transfer coefficient are presented. The surfaces of interest are coated with wide-band thermochromic liquid crystals, which cover the range of NGV surface temperature variation encountered in the test. The liquid crystal has a natural peak-to-peak roughness height of 25 μm creating a transitionally rough surface on the NGV. The time variation of color is processed to give distributions of both heat transfer coefficient and film cooling effectiveness over the NGV surface. The NGV was first instrumented with the DHFGs and smooth surface tests preformed, Subsequently the surface was coated with liquid crystals for the rough surface tests. The DHFGs were then employed as the means of calibrating the liquid crystal layer. The roughness of 25 μm, which is the typical order of roughness for the in-service turbine blades and vanes, increases the heat transfer coefficient by up to 50 percent over the smooth surface level. The film cooling effectiveness is influenced less by the roughness.

The Application of Thin Film Gauges on Flexible Plastic Substrates to the Gas Turbine Situation

Thin film heat transfer gauges have been instrumented onto flexible plastic substrates which can be adhesively bonded to plastic or metal models. These new gauges employ standard analysis techniques to yield the heat flux to the model surface and have significant advantages over gauges fired onto machinable glass or those used with metal models coated with enamel. The main advantage is that the construction of the gauges is predictable and uniform, and thus calibration for thickness and geometric properties is not required.The new gauges have been used to measure the heat transfer to an annular turbine nozzle guide vane in the Oxford University Cold Heat Transfer Tunnel. Engine-representative Mach and Reynolds numbers were employed and the free-stream turbulence intensity at NGV inlet was 13%.The vanes were either precooled or preheated to create a range of different thermal boundary conditions. The gauges were mounted on both perspex and aluminium NGVs and the heat transfer coefficient was obtained from the surface temperature history using either a single layer analysis (for perspex) or double layer (for aluminium) analysis. The surface temperature and heat transfer levels were also measured using rough and polished liquid crystals under similar conditions. The measurements have been compared with computational predictions.Copyright

Proton Exchange Membrane Fuel Cell High Carbon Monoxide Tolerance Operation Using Pulsed Heating and Pressure Swing

Proton exchange membrane fuel cells (PEMFCs) are attractive power plants for use in many applications, including portable power sources, electric vehicles, and on-site combined power/heat plants. Despite the advantages, one of the significant obstacles to PEMFC commercialization is the low tolerance to carbon monoxide (CO). Ideally, PEMFCs should use pure hydrogen fuel. However, because of the difficulties inherent in storing hydrogen onboard, there is an increasing interest in using hydrogen-rich gases produced by reforming hydrocarbon fuels. Fuel reformer produces hydrogen containing a small amount of CO. PEMFC performance degrades when CO is present in the fuel gas, referred to as CO poisoning. This paper presents the results of a novel PEMFC performance study using a pulsed heating device and the feeding channel pressure swing method to mitigate the CO poisoning problem. The effectiveness of these strategies is demonstrated through simulation and experimental work on a single cell. By applying a transient localized heating to the catalyst layer while maintaining the PEMFC membrane at a normal temperature (below 80° C) and by using the feeding channel pressure swing, significant enhancement in the carbon monoxide tolerance level of PEMFCs was found. These approaches could potentially eliminate the need for an expensive selective oxidizer. The CO poisoning process is generally slow and reversible. After applying pulsed heating, the transient high temperature in the catalyst layer could help the recovery of the PEMFC from CO poisoning. By using feeding channel pressure swing, oxygen can easily diffuse into the membrane electrode assembly (MEA) from the outlet port and promote a quick recovery. Using these operational strategies, a PEMFC could operate continually using a high CO concentration fuel.