High Temperature Gas Turbine Research Articles

Optimizing thermal performance in internal passage cooling with extended rib: Applying response surface method with artificial neural networks

Efficient cooling technology is crucial for high-temperature gas turbines which are significant applications in thermal processes particularly in industries such as power generation aerospace and marine propulsion. Enhancing cooling efficiency in these systems not only improves energy utilization but also plays a critical role in reducing fuel consumption increasing operational reliability and minimizing environmental impacts. This research focuses on optimizing the thermal performance of internal passage cooling channels with extended ribs using a combination of the response surface method and artificial neural networks. By varying the extended rib length and rib width the study aims to enhance heat transfer and minimize flow loss leading to improvements in overall system efficiency. Latin Hypercube Sampling is employed to strategically select variables and automated numerical simulations are conducted to perform a thorough parametric analysis. A steady-state k-ω shear stress transport turbulence model is applied in the simulations and the numerical results are validated against experimental data ensuring accuracy. The combined response surface method–artificial neural network approach integrated with TensorFlow-based modeling allows for the prediction of heat transfer and friction factor ultimately generating a comprehensive response surface to identify the optimal design point. Applying the optimized design leads to a 23.99 % improvement in the thermal performance factor compared to the reference case. The findings of this study highlight a significant enhancement in the thermal performance of the cooling channel structure particularly in high heat flux environments. This research provides valuable insights into the design of more efficient thermal management systems for gas turbines and has broader implications for other high-temperature thermal processes. The proposed optimization methodology offers a reliable approach for improving cooling technologies contributing to the development of the next generation of energy-efficient high-performance gas turbines and other industrial applications where effective thermal management is essential.

Gamma prime formation in nickel-based superalloy IN738LC manufactured by laser powder bed fusion

Complex components for high-temperature gas turbine applications require materials that offer a combination of excellent high-temperature strength and oxidation resistance. Nickel-based superalloys with high gamma prime (γ´) volume fractions are particularly suited for these applications, especially combined with additive manufacturing for intricate geometries. Despite the complex thermal history that these materials experience during laser powder bed fusion (LPBF) processing, γ´formation is suppressed when manufacturing IN738LC, which has a medium equilibrium γ´content of about 40–50 vol%. This study follows γ´formation in LPBF IN738LC during subsequent annealing treatments at temperatures ranging from 745 °C to 865 °C, creating an experimentally determined TTT (temperature-time-transformation) diagram. This diagram is largely based on scanning electron microscopy (SEM) imaging supported by Vickers hardness measurements and scanning transmission electron microscopy (STEM) bright field imaging. Atom probe tomography (APT) of the as-built material indicated nm-sized regions depleted in Cr and enriched in Ni, Al, and Ti, but show no characteristic superlattice patterns in TEM diffraction. APT and TEM diffraction analysis of material annealed at 850 °C for 3 min confirmed the presence of the γ´phase but indicated that γ´had formed through spinodal decomposition instead of precipitation.

Combined effects of blowing ratio and mist diameter with mainstream turbulence intensity in mist-assisted film cooling

Advanced cooling techniques are essential in modern gas turbines to improve the efficiency of the Brayton cycle by raising the turbine inlet temperature. Mist-assisted film cooling offers an innovative solution for cooling high-temperature gas turbine blades. When mist particles with various momenta are injected through the cooling holes, the interplay between mainstream turbulence intensity (Tu) and mist momentum plays a crucial role in mist-assisted film cooling under high Tu conditions. Hence, this numerical study investigates the relationship between mainstream Tu and mist characteristics for the first time, considering the blowing ratio and mist diameter as controlling parameters. Film effectiveness and particle distribution statistics are analysed to understand their correlation. The results demonstrate that mist-assisted film effectiveness follows the trend of air-only film cooling with varying blowing ratios and Tu; however, the magnitude is amplified. The influence of the mist diameter on film effectiveness is determined by the surface-area-to-volume ratio and Stokes number. These factors impact the sensitivity of particles to Tu and subsequently affect film effectiveness. This study provides a novel quantitative analysis of the combined effect of mainstream Tu and mist on film cooling effectiveness, revealing the correlation between mist and mainstream parameters.HighlightsCombined effect of mainstream turbulence intensity (Tu) and mist characteristics is investigated.High mainstream Tu significantly increases the cooling enhancement induced by mist.Mist-assisted film cooling exhibits similar trends to varying mainstream Tu and blowing ratio.Mist diameter significantly influences the response to Tu, governed by surface-area-to-volume ratio and Stokes number.Small particles demonstrate the highest cooling effectiveness and variation by Tu.

Thermodynamic and economic analysis of a revised Graz cycle using pure oxygen and hydrogen fuel

In order to improve the energy efficiency of hydrogen storage for power generation, in this work, an improved Graz cycle (R-Graz cycle) was proposed, which can realize more efficient hydrogen to electricity conversion. The modeling and optimization program of the cycle was developed based on MATLAB, and the thermodynamic properties of the working fluid were obtained by REFPROP. The results show that the R-Graz cycle can reach a net efficiency of 70.98% at the design point, which is about 0.5% higher than that of the Graz cycle with the same input parameters, and much higher than that of the modern gas-steam combined cycle. With the same amount of hydrogen input, the R-Graz cycle can produce 0.34% more electricity than the Graz cycle. At the design point, the levelized cost of electricity (LCOE) of the R-Graz cycle is 156.23 $/MWh, which is 0.22% lower than that of the Graz cycle, and the net present value is also higher. Analysis on the influence of key parameters shows that increasing the inlet temperature and pressure of the high-temperature gas turbine and the inlet temperature of the high-pressure steam turbine as well as reducing the condenser pressure are conducive to improving the R-Graz cycle efficiency, among which the influence of the inlet pressure of the high-temperature gas turbine and condenser pressure is particularly significant. This study also presents the impact of these key parameters on the LCOE. This research can effectively increase the conversion efficiency of electricity-hydrogen-electricity mode, and provides a new path for hydrogen utilization.

Effect of degradation of the thermal barrier coating on the cooling performance of vane in gas turbine

Film cooling and thermal barrier coatings are essential for the thermal protection of high temperature gas turbines. Firstly, the degradation of the coating at the vane surface has been scrutinized under condition of 24,000 equivalent operating hours. In the microstructure analysis of coatings, the thickness of the top coating is diminished by 6.6% on average at the equivalent operating hours compared to pristine condition. Noticeably, an average of 15.7 μm of thermally grown oxide has grown at the interface between the top and bond coatings. Although the thermally grown oxide layer has developed over the entire interface between the coating layers, however, no lamination has been detected. Due to the nature of high thermal conductivity of thermally grown oxide, it is significant to investigate its effect on the cooling performance. In this regard, three-dimensional and numerical simulations have been developed to quantitatively evaluate the degraded cooling performance due to the presence of thermally grown oxide. The simulation results show that the degradation of thermal barrier coating decreases the overall cooling effectiveness by 9.4% in comparison to pristine vane. The resulting temperature rise on the substrate is predicted to 52.2 °C in our numerical simulations.

Stress evaluation of TBCs with inclined film-cooling hole considering CMAS penetration-induced change of thermo-mechanical properties

CaO-MgO-Al2O3-SiO2 (CMAS) penetration is an essential factor leading to the failure of thermal barrier coatings (TBCs), especially around the film-cooling hole structure of high-temperature gas turbine components. The complex temperature distribution and the free-edge effect around the cooling holes aggravate the influence of CMAS penetration on the failure of the TBCs. In this study, a three-dimensional (3D) model of a TBC-film cooling system considering CMAS attack is presented based on the observation of a retired turbine blade. CMAS penetration-induced change of thermo-mechanical properties of the ceramic top coat (TC) was considered. The thermal gradient around a cooling hole and the uneven growth of the thermally grown oxide (TGO) on the stress distribution in TBCs were investigated. The results showed that the thermal insulation performance of TBCs declined considerably under CMAS penetration, and the induced maximum increase in the temperature at the TC/bond coat (BC)interface reached 60 K. CMAS penetration also led to a considerable stress increase in the TBC-film system. We therefore conclude that CMAS penetration accelerates the crack initiation at the TC/TGO and TGO/BC interfaces.

Results of conjugate modeling and analysis of the thermal state of a high-pressure turbine blade

Numerical modeling for the purpose of receiving the temperature field of cooled rotor blades and its improvement is an integral process of modern design of gas turbine engines since the issue of cooling at gas temperature at the combustion chamber outlet over 1800-2000 K is becoming one of the key ones. To ensure the specified parameters of turbine operation during its design, it is necessary to obtain reliable calculation data. The article presents an algorithm for forming a calculation model to determine the thermal state of the working blade of a high-temperature high-pressure gas turbine in the Ansys program. The process of preparation of geometric and grid models is described, the boundary conditions used to set up the project in Ansys CFX Pre are given. A method for determining the cooling efficiency factor using Ansys CFX Post is also presented. The distributions of the temperature field and the coefficient of cooling efficiency over the surfaces of the blade to be cooled are obtained. Integral values of the coefficient of cooling efficiency for the designed blade at various cooling air flow rates were compared with statistical data. On the basis of the comparison a conclusion was made that the working blade considered in the work corresponds to the modern level of cooling efficiency.

EFFECTS OF ADDITIVELY MANUFACTURED SURFACE ROUGHNESS ON SMALL DIAMETER PLENUMS WITH MULTIPLE SIDE DISCHARGES FOR HIGH TEMPERATURE GAS TURBINE BLADE COOLING APPLICATIONS

Combined heat and power (CHP) applications have significant environmental and economic benefits that are consistent with the goals of the U.S. Department of Energy (DOE). One area that is currently being studied includes the potential benefits of CHP turbine operation at higher turbine inlet temperatures. Internal cooling concepts enabled by additive manufacturing (AM) are of primary interest. The effectiveness of internal cooling is hindered by many factors such as velocity distribution of the cooling air to the hot surface considering impingement cooling. To simulate cooling air exiting from a series of orifices for internal cooling in an airfoil, a straight smooth wall tubing with multiple side discharging orifices is used and compared to additively manufactured tubing (Ti6Al4V Grade 23) with orifice size and spacing as well as inner and outer diameters identical to the smooth wall tubing. Similar to flow discharging form perforated pipes, the flow discharged from individual orifices along the tubes in this study is found to be nonuniformly distributed, and the horizontal (axial direction) momentum can be observed from the experimental data. Discharge velocities have been measured with two-dimensional (2D) particle imaging velocimetry (PIV) and single element hot wire anemometry. Numerical analysis has also been conducted to predict the velocity distributions along the orifices in the smooth wall and additive manufacturing (AM) tubing, which are inherited with surface roughness. Numerical and measured results in this study are compared, presented, and discussed.

Asymmetric Method of Heat Transfer Intensification in Radial Channels of Gas Turbine Blades

Loop and semi-loop cooling schemes are widely used for the high-temperature gas turbine blades. In such schemes, the mid-chord airfoil parts are traditionally cooled by radial channels with ribbed walls. The blades with a small specific span, or “short” blades, have different heat flux amounts on pressure and suction sides, which results in a temperature difference in these sides of 100–150 °K. This difference causes thermal stresses and reduces the long-term strength margins. This paper presents a new method of heat transfer intensification in the ribbed radial cooling channels. The method is based on air streams’ injection through holes in the ribs that split channels. The streams are directed along the walls into the stagnation zones behind the ribs. The results of a 3D coolant flow simulation with ANSYS CFX code show the influence of the geometry parameters upon the channel heat transfer asymmetry. In the Reynolds number within a range of 6000–20,000, the method provides the heat transfer augmentation difference by up to 40% on the opposite channel walls. Test results presented in the criteria relations form allow for the calculation of mean the heat transfer coefficient along the channel length.

A Comprehensive Study of Ceramic Matrix Composites for Space Applications

Ceramic matrix composites (CMCs) have grown in popularity as a material for a range of high as well as protection components, increasing the need to better understand the impacts of multiple machining methods. It is primarily composed of ceramic fibers embedded in the matrix. Ceramic materials, especially carbon fibers and carbon were used to create the matrix and fibers. These ceramics include a huge variety of non-metallic inorganic materials that are regularly utilized under high temperatures. The aircraft industry became revolutionized by this unique combination of materials, which made parts better resistant under extreme conditions as well as lighter than the earlier technology. The development, properties, and production of ceramic matrix composites, as well as space applications, are discussed in this article. Ceramic materials have an interesting set of properties, including great strength and stiffness under extremely high temperatures, chemical inertness, low density, etc. In CMC, ceramics are used in the matrix as well as reinforcement. The matrix material keeps things running smoothly while the reinforcement delivers unique special properties. Ceramic matrix composites are developed for applications that required high thermal and mechanical characteristics, which include nuclear power plants, aircraft, chemical plants, space structures, and transportation services. Even though advanced aircraft relies on high-performance propulsion systems, improving the total impulses over the total mass ratio for rocket engines becomes essential for improving their performance that demands reduced engine structural weight as well as higher component heat resistance. The evolution of new ultra-high-temperature composites having high-temperature resistance as well as low density that a substitute super alloy and refractory metal material has become so essential and laid the foundation for high-performance engine design. The benefits of continuous fiber- reinforced CMC with high-temperature engine designs have long been recognized as a better measure of a country’s ability to design and produce spacecraft, modern aircraft, and weapons. Ceramic matrix composites materials are used in various aircraft type engines, aircraft brake disks, high-temperature gas turbines components, slide bearing components, hot gas duct, flame holders and components for burners are made by using oxide CMCs.

Graded Approach Establishment for the HTGR Maintenance Activities Using Modified Fuzzy FMEA & Expert Judgement Methodology

Grading is an important step of the Nuclear Power Plant (NPP) operation & maintenance activities. However, there are several grading difficulties for the High Temperature Gas Reactor (HTGR) as well as the other type of NPPs causing by the lack of operational experiences and availability of the reliability data. Failure Mode & Effects Analysis (FMEA) is one of the mature techniques that are commonly used to solve such kinds of difficulties. Nevertheless, traditional FMEA has several issues and possibly become an obstacle in the grading process. The modified FMEA by utilizing expert judgment elicitation techniques combined with the fuzzy logic theory is proposed to solve those issues. As a study practice, the proposed methodology is applied by examining Japanese’s HTGR, Gas Turbine High Temperature Reactor 300 for Cogeneration (GTHTR300C) design carefully. This study establishing good practice especially for the future advanced NPP maintenance activities development.

Multi-objective materials bayesian optimization with active learning of design constraints: Design of ductile refractory multi-principal-element alloys

Bayesian Optimization (BO) has emerged as a powerful framework to efficiently explore and exploit materials design spaces. To date, most BO approaches to materials design have focused on the materials discovery problem as if it were a single expensive-to-query ‘black box’ in which the target is to optimize a single objective (i.e., material property or performance metric). Also, such approaches tend to be constraint agnostic. Here, we present a novel multi-information BO framework capable of actively learning materials design as a multiple objectives and constraints problem. We demonstrate this framework by optimally exploring a Refractory Multi-Principal-Element Alloy (MPEA) space, here specifically, the system Mo-Nb-Ti-V-W. The MPEAs are explored to optimize two density-functional theory (DFT) derived ductility indicators (Pugh’s Ratio and Cauchy pressure) while learning design constraints relevant to the manufacturing of high-temperature gas-turbine components. Alloys in the BO Pareto-front are analyzed using DFT to gain an insight into fundamental atomic and electronic underpinning for their superior performance, as evaluated within this framework.

Образование сварных твердофазных соединений проволок при изготовлении пористых сетчатых материалов из стали 12Х18Н10Т

The experience of using turbine blade shells based on porous mesh materials in aerospace products and high-temperature gas turbines has shown that they are subject to destruction when under the influence of pressure fluctuations. So, first of all, fatigue failure occurs, in those permeable shells where there are no high-quality connections of structure-forming elements. It has been established that in diffusion welding and rolling welding, the strength of welded bonds increases with an increase in the process temperature, as well as in the vacuum depth and deformation time in diffusion welding. Research findings show that at strain rates of 10–2…1.0 s–1, the low quality of welded joints is explained by the high deformation resistance of microroughnesses on the contact surfaces of the wires and the low rate of diffusion mass transfer in the connection zone. The study establishes that under the conditions of diffusion and impact welding in vacuum, the formation of a solid-phase joint is possible on the entire surface of the macrocontact. At the same time, in percussion welding, the influence of the temperature value in the investigated interval on the quality of welded bonds is much lower than that for processes with lower loading rates. Practical recommendations are given for determining the optimal modes of wire mesh welding in the manufacture of porous mesh materials made of 12Kh18N10T steel.

Efficiency of chemically recuperated gas turbine fired with methane: Effect of operating parameters

Previously, a set of optimistic studies have been published to show the efficiency of chemically recuperated gas turbines (CRGT) based on steam methane reforming. The thermodynamic efficiency of such turbines is depending not only on temperature and pressure in a cycle but also on temperature, pressure and steam-to-methane ratio in a recuperation system. In this paper, the effect of operational parameters (temperature, pressure, steam-to-methane ratio) on the efficiency of CRGT was determined. Exhaust heat recuperation in CRGT is taking place due to methane reforming, steam-methane mixture heating, and steam generation. A thermodynamic enthalpy of steam methane reforming process was determined via Gibbs free energy minimization method. The thermodynamic analysis of CRGT was performed in Aspen HYSYS. The efficiency of CRGT was determined for a wide range of operational parameters (gas turbine inlet temperature of 800–1500 °C, pressure of 5–25 bar, steam-to-methane ratio of 1...3). Based on the analysis it was confirmed that the efficiency of CRGT and thermochemical exhaust heat recuperation system is increasing with an increase in temperature. An increase in temperature and steam-to-methane ratio leads to an increase in a share of recuperated heat in a reformer. The heat recuperation rate is up to 0.63 for a high-temperature gas turbine and a steam-to-methane ratio of 3. The efficiency of CRGT is up to 49% for gas turbines with inlet gas temperature of 1500 °C which is an available level in modern gas turbines from Mitsubishi, Siemens, Alstom, etc.

Investigation of the effect of pulsed surfacing on the state of a heat-resistant single-crystal alloy

The article is devoted to the study of elemental and phase compositions, microstructure and mechanical properties of heat-resistant single-crystal intermetallic alloy used in the manufacture of cooled blades of high-temperature gas turbines of power equipment. State of monocrystal alloy after carrying out comparative experiments by methods of pulsed build-up and argon-arc build-up is investigated. It has been found that the pulsed build-up does not result in the formation of a zone of thermal influence and changes in the state of the base material. This method is recommended to restore defective areas and geometric dimensions of parts as part of resource-saving technologies.

Storage-Coupled Nuclear Combined Cycle

AbstractA new design paradigm for nuclear power plants is needed to complement the increasing adoption of low marginal cost variable renewable energy resources. The situation is reflected in the wholesale electricity price–duration curve with four distinct economic opportunities: (a) a hundred or so hours per year of high-value peaking power; (b) about 4000–5000 h of moderate electric prices; (c) about 2000 h per year when renewables set the marginal price at or near zero; and (d) about 1000 h of flexible ramping between the b and c regions. The current approach to the low-carbon energy transition reduces the need for baseload power and requires curtailment of conventional, nuclear, and even renewable generation, decreasing their capacity factors and increasing their fixed charges for electricity generation. Flexible low-carbon dispatchable power plants capable of daily cycling along with storage and time shifting of low-cost nondispatchable renewable power will be needed. Although nuclear power plants have demonstrated load-following capability, cycling can be limited by reactor kinetics (xenon poisoning) as well as by thermal stresses and fatigue considerations in the steam cycle. Storage of nuclear heat is hampered by the relatively low operating temperatures of existing nuclear reactors (but not advanced reactors) that lowers thermal to electric conversion efficiency, which in turn increases the required quantity of storage medium and the cost of storage. The quantity of storage medium can be reduced by integration of thermal energy storage with high-grade heat as in the liquid salt combined cycle (LSCC). The LSCC uses high-temperature gas turbine exhaust heat to increase the electricity output per unit of storage medium, uses the stored energy to add operating flexibility to a bottoming steam cycle, and substantially reduces the fuel heat rate. The low fuel heat rate improves economic competitiveness compared to alternative gas turbine-based power plants, especially when burning expensive fuels such as hydrogen. LSCC could be coupled to a nuclear power plant for time shifting both nuclear and renewable electricity and could support high utilization of a co-located hydrogen electrolysis plant. Further cost reduction could be achieved by using solid media for thermal energy storage, with the liquid salt used as a heat transfer medium.

Effect of nuclear heat caused by the 6Li(n,α)T reaction on tritium containment performance of tritium production module in High-Temperature Gas-Cooled reactor for fusion reactors

Tritium is required for research and development activities for the deuterium–tritium (DT) fusion reactor and fueling the DEMOnstration Power Station (DEMO). However, tritium is a very rare nuclide and must be produced artificially. Tritium production by loading Li compounds (Li rods) into burnable poison holes of a high-temperature gas-cooled reactor (HTGR) has been proposed (H. Matsuura, et al., Nucl. Eng. Des. 243 (2012) 95–101.). Al2O3 and Zr are used to prevent tritium leaks. Nuclear reaction heat caused by the nuclear reaction (e.g., 6Li(n,α)T reaction) can cause a spatial temperature profile in the Li rods and may change its tritium containment performance, because Al2O3 and Zr performance strongly depend on these temperatures. The effect of nuclear reaction heat by the 6Li(n,α)T reaction on the tritium containment performance of the Li rods was evaluated by simulation. The temperatures of the Li rods for the high-temperature engineering test reactor (HTTR) and gas turbine high-temperature reactor 300 (GTHTR300) increased by 36 K and 46 K, and the leaked tritium decreased by 32% and 37% via nuclear reaction heat, respectively.

High-Efficiency Combined Heat and Power through a High-Temperature Polymer Electrolyte Membrane Fuel Cell and Gas Turbine Hybrid System

High-temperature proton-exchange membrane fuel cells are a promising technology for distributed power generation thanks to their high-power density, high efficiency, low emissions, fast start-up, and excellent dynamic characteristics, together with their high tolerance to CO poisoning (i.e., CO in the feed up to 3%). In this paper, we present an innovative, simple, and efficient hybrid high-temperature proton-exchange membrane fuel cell gas turbine combined heat and power system whose fuel processor relies on partial oxidation. Moreover, we demonstrate that the state-of-the-art fuel processors based on steam reformation may not be the optimal choice for high-temperature proton-exchange membrane fuel cells’ power plants. Through steady-state modeling, we determine the optimal operating conditions and the performance of the proposed innovative power plant. The results show that the proposed hybrid combined heat and power system achieves an electrical efficiency close to 50% and total efficiency of over 85%, while a state-of-the-art system based on steam reformation has an electrical efficiency lower than 45%. The proposed innovative plant consists of a regenerative scheme with a limited power ratio between the turbine and fuel cell and limited optimal compression ratio. Therefore, micro-gas turbines are the most fitting type of turbomachinery for the hybrid system.

Tailoring microstructure of double-layered thermal barrier coatings deposited by suspension plasma spray for enhanced durability

Gadolinium zirconate (GZ)-based TBCs comprising GZ as the top layer and yttria stabilized zirconia (YSZ) as the base layer, are attractive double-layered thermal barrier coatings (TBCs) for high temperature gas turbine engine application. This work attempts to understand the influence of individual layer microstructure on the durability of GZ/YSZ double-layered TBCs processed by suspension plasma spray (SPS). Two different spray parameters were chosen to obtain a combination of three microstructurally distinct GZ/YSZ double-layered TBCs i.e. GZ porous (P)/YSZ porous (P), GZ dense (D)/YSZ porous (P) and GZ dense (D)/YSZ dense (D). Thermal diffusivity of the as-deposited coatings was measured using Laser Flash Analysis (LFA) technique and the thermal conductivity of the TBCs was calculated. The GZ/YSZ double-layered TBC specimens were subjected to two different durability tests, i.e. thermal cyclic fatigue (TCF) and burner rig test (BRT). Sintering behavior of the individual layer TBC microstructures was evaluated by comparing the porosity evolution in as-deposited and TCF tested TBCs. Fracture toughness measurements performed on each layer of the double-layered TBCs were correlated with the durability results. Thermal cycling results amply demonstrate that the individual layer microstructure of GZ/YSZ double-layered TBC influenced its durability. Detailed failure analysis of the TCF and BRT failed specimens revealed similar failure modes for GZ (P)/YSZ (P), GZ (D)/YSZ (P) and GZ (D/YSZ (D) TBCs under identical thermal cyclic test conditions. However, failure modes differed when subjected to different thermal cyclic test conditions (TCF and BRT) and the probable causes are discussed. Findings from this work provide key insights on designing durable GZ/YSZ double-layered TBCs.

Numerical Investigation of a Radially Cooled Turbine Guide Vane Using Air and Steam as a Cooling Medium

Gas turbine performance is closely linked to the turbine inlet temperature, which is limited by the turbine guide vanes ability to withstand the massive thermal loads. Thus, steam cooling has been introduced as an advanced cooling technology to improve the efficiency of modern high-temperature gas turbines. This study compares the cooling performance of compressed air and steam in the renowned radially cooled NASA C3X turbine guide vane, using a numerical model. The conjugate heat transfer (CHT) model is based on the RANS-method, where the shear stress transport (SST) k−ω model is selected to predict the effects of turbulence. The numerical model is validated against experimental pressure and temperature distributions at the external surface of the vane. The results are in good agreement with the experimental data, with an average error of 1.39% and 3.78%, respectively. By comparing the two coolants, steam is confirmed as the superior cooling medium. The disparity between the coolants increases along the axial direction of the vane, and the total volume average temperature difference is 30 K. Further investigations are recommended to deal with the local hot-spots located near the leading- and trailing edge of the vane.