Coolant Mass Flux Research Articles

Flow boiling characteristics in a microchannel heat sink with a condensing cover plate

Flow patterns and heat transfer characteristics during flow boiling in a microchannel heat sink with a condensing cover plate have been numerically investigated. The phase-field model is used to analyze the effects of different thermal conditions of the condensing cover plate on the bubble dynamics and heat transfer characteristics. Further, the effects of the wettabilities of the cover plate and the heating surface on the bubble evolution have been studied for different values of coolant mass flux. The condensing cover plate maintained at 50 °C significantly improves heat transfer performance with an enhancement of 23.97 % compared to the condenser plate maintained at 80 °C and a 27.35 % improvement compared to an insulated cover plate. The hydrophobicity of the condensing cover plate facilitates vapor bubble evacuation from nucleation sites, producing maximum heat transfer at a contact angle of 130°. Heat transfer performance decreases beyond the 130° contact angle due to the bubble attachment to the condensing cover plate and impeding subsequent nucleation from the cavity. The maximum heat transfer is observed for the heating surface with a contact angle of 60°. The heat transfer in the microchannel is deteriorated below and above this contact angle. At low coolant mass flux, the heat transfer is controlled by bubble nucleation. After reaching a steady state, the combined effects of bubble nucleation and liquid inertia affect the bubble generation frequency and heat transfer in the microchannel.

A modified local thermal non-equilibrium model of transient phase-change transpiration cooling for hypersonic thermal protection

Aiming to efficiently simulate the transient process of transpiration cooling with phase change and reveal the convection mechanism between fluid and porous media particles in a continuum scale, a new two-phase mixture model is developed by incorporating the local thermal non-equilibrium effect. Considering the low-pressure and high overload working conditions of hypersonic flying, the heat and mass transfer induced by capillary and inertial body forces are analyzed for sub-cooled, saturated and super-heated states of water coolant under varying saturation pressures. After the validation of the model, transient simulations for different external factors, including spatially-varied heat flux, coolant mass flux, time-dependent external pressure and aircraft acceleration are conducted. The results show that the vapor blockage patterns at the outlet are highly dependent on the injection mass flux value and the external pressure, and the reduced saturation temperature at low external pressure leads to early boiling off and vapor blockage. The motion of flying has a large influence on the cooling effect, as the inertial force could change the flow pattern of the fluid inside significantly. The comparison of the results from 2-D and 3-D simulations suggests that 3-D simulation shall be conducted for practical application of transpiration cooling, as the thermal protection efficiency may be overestimated by the 2-D results due to the assumption of an infinite width length of the porous plate.

Multiple hot spot cooling with flow boiling of HFE-7000 in a multichannel pin fin heat sink

Electronics cooling applications require a high cooling performance due to increasing power consumption. Phase change heat transfer is a popular approach for offering high heat flux cooling. Controlling temperature distribution and mitigating boiling instabilities under high heat flux conditions present a significant challenge. While numerous studies investigated the effect of pin fins in a minichannel with single hotspots on boiling enhancement, few research studies are available for minichannels with multiple segmented hotspots. This study's primary objective is to dissipate high heat (1.4 kW) using flow boiling of a dielectric fluid, namely HFE-7000, which has lower thermophysical properties than water, to achieve a uniform temperature distribution, and to suppress boiling instabilities. The boiling performance of a pin fin multichannel heat sink with dimensions of 3 × 14 × 300 mm (H × W × L) subjected to 8 hotspots with uniform heating was investigated in this regard. Flow boiling experiments were performed over a wide range of input heat power from ∼0.1 to ∼1.4 kW with a coolant mass flux of 500 kg/m2 s in the three parallel minichannels having staggered elliptical pin fins with no tip clearance on each hotspot and distribution pins at the inlet. High-speed visualization was used to relate the heat transfer coefficient variations along the channel to flow patterns. The heat transfer performance and flow regimes at different locations were obtained and discussed. Thanks to the mixing effect of elliptical micro pin fins with optimum geometrical parameters along the heat sink, the presence of distribution pin fins at the inlet for suppressing boiling instabilities and early transition to stable annular flow, the temperature uniformity (∼2.3 °C, temperature difference between the inlet and outlet hotspots) could be achieved at the highest heat input. Heat transfer coefficient reduction upto 27 % was reported along the channel when comparing inlet (1st) and outlet (8th) hotspots.

On the flow field and heat transfer characteristics of a supercritical CO2-cooled microchannel heat sink under high heat flux conditions

Supercritical CO2 (sCO2) is a suitable choice as a coolant due to its favorable thermodynamic characteristics (lower density and viscosity, and higher specific heat) compared to water. In the current investigation, sCO2 is considered a coolant in a micro heat sink under high heat fluxes 75, 100, 125, and 150 W/cm2 and the operating pressure 8 MPa. The effects of the operating conditions, including the change in coolant mass flux (1250–3125 kg/s-m2), the change in the inlet temperature (305-308 K) under the mentioned heat fluxes on the heat transfer coefficient, thermal resistance, pressure drop, pumping power, and performance evaluation criteria (PEC) are investigated numerically using the finite volume method. Results indicated that thermohydraulic performance of the sCO2-cooled heat sink depends on the inlet coolant temperature and the applied heat flux due to the dramatic variation of the local thermophysical properties. It was found that increase in the heat flux from 75 to 150 W/cm2 results in increase of the pumping power by 48%, diminishing the PEC from 2.35 to 0.5. Overall, sCO2-cooled heat sink performs better than water-cooled heat sink if the mass flow rate is high and the inlet temperature is below the pseudocritical temperature. Otherwise, using sCO2 is not beneficial, especially under higher heat flux conditions.

A multiobjective optimization of 3D - slot jet configuration for enhancement of film cooling in an annular combustor liner

This study reports the results of a combined experimental and numerical investigation of the performance of a three-dimensional film cooling slot configuration and its optimization using an evolutionary-based genetic algorithm. The primary objective of the optimization is to maximize the area-averaged film cooling effectiveness (ηad.avg) and minimize its standard deviation (ση) at a fixed coolant mass flux for a single liner. The experimental study is conducted on flow and heat transfer characteristics to validate the numerical model under laboratory conditions (low temperature and pressure). A design space is created using the Latin hypercube sampling technique, and it is solved using steady-state RANS simulations with the validated numerical model to estimate the ηad.avg and ση under actual engine conditions (high temperature and pressure). A surrogate model is developed using the kriging technique to predict the objective functions with the geometrical parameters of the slot. Following this, the optimum configuration is identified using the genetic algorithm. The geometrical parameters are slot jet diameter (d), slot jet pitch (p), lip taper angle (α), and lip length (L). The numerical results show that the optimum configuration outperforms the two reference configurations of the baseline combustor. At a blowing ratio (BR) of 1, the optimum configuration enhances the ηad.avg by 8% and reduces the ση by 6.6% compared to reference -1 configuration. Similarly, compared to reference -2, the optimum configuration enhances the ηad.avg by 19.8% and reduces the ση by 5.2.%. Furthermore, under actual engine conditions, a numerical study is conducted on a subsequent row of liners to determine the optimum length of the cooling ring. The numerical results show that the optimum slot configuration cools an additional liner length (G/S) of 5.5 compared to the reference-1 slot and results in a reduction of one pair of cooling rings in the combustor, which contributes to a 16.6% less coolant mass flux.

Numerical study on transient response of transpiration cooling with hydrocarbon fuel as coolant

A transient non-thermal equilibrium model was established to solve the transient process of transpiration cooling, which considers the influence of cracking reaction. The occurrence of cracking reaction leads to the increase of inlet pressure, thermal diffusion coefficient and heat transfer coefficient and effectively reduces the temperature of porous matrix. In the absence of external oscillation excitation, the change rate of porous matrix temperature and fluid temperature with heating time gradually decreases. In the case of unsteady heat flux, the oscillation amplitude of fluid parameters near the outlet of porous media is larger. The increase of thermal conductivity of solid matrix can effectively restrain the temperature oscillation caused by external heat flux, but the amplitude of coolant supply pressure increases with the increase of thermal conductivity, which is not conducive to the supply of coolant. The amplitude of reaction heat is the smallest when the frequency of coolant mass flux and heat flux is the same. The greater inlet pressure oscillation is formed when the coolant supply cycle period is lower than the cycle period of heat flux.

A hydrophobic porous substrate-based vapor venting technique for mitigating flow boiling instabilities in microchannel heat sink

With the onset of nucleation, flow boiling in microchannels is susceptible to undesirable flow instabilities resulting in fluctuating wall temperature and large pressure drops. It is imperative to develop a passive technique to mitigate flow boiling instabilities and enhance the thermo-hydraulic performance of the heat sink without additional pressure drops. The present work explores a hydrophobic porous polydimethylsiloxane (PDMS) substrate-based vapor venting technique to mitigate flow boiling instabilities in microchannels. The hydrophobic porous substrate fitted at the channel exit manifold attracts the vapor plug, assists in vapor venting, and thus facilitates the easy evacuation of the bubbles from the channel. Flow boiling experiments are performed with deionized water in rectangular cross-section microchannels for a heat flux range of 10–260 W/cm2 and the coolant mass flux range of 206–335.49 kg/m2s. Heat transfer and pressure drop characteristics of the proposed configuration are compared with those of the conventional configuration. The proposed design suppresses the wall temperature oscillation and pressure oscillations. It produces a 32 % enhancement in heat transfer coefficient and a 63 % reduction in pressure drop compared to the conventional outlet configuration. The new configuration significantly reduces the bubble ebullition cycle, resulting in an efficient bubble evacuation from the channels. Further, frequent flushing of the vapor slug in the new design reduces the temperature fluctuations and enhances the heat transfer coefficient. The heat transfer augmentation is more pronounced at higher heat flux with more vapor generation rates.

Critical heat flux on zircaloy and accident tolerant fuel cladding under prototypical conditions of pressurized and boiling water reactors

First of a kind high spatial and temporal resolution temperature measurements of Pressurized Water Reactor and Boiling Water Reactor simulated fuel pins (high heat flux cosine profile heaters) in annular rod type geometry during nucleate boiling, departure from nucleate boiling and re-wetting has been performed. Distributed fiber optic measurements of the cladding axial temperature with spatial resolutions down to 2.5 mm axially at up to three equally spaced azimuthal locations per rod have demonstrated the similarities and differences of the different accident tolerant fuel cladding materials. These experiments show the performance of accident tolerant cladding with a precise measurement of the location and evolution of dryout followed by the re-wetting phenomena (see supplementary time history of a critical heat flux event). Experimental parameters varied coolant mass fluxes from 1695 to 2712 kg/m2s, pressures from 10 to 20 MPa, and inlet subcooling from 10 to 55 °C. It was found that the coatings and different material have little effect on the value of the critical heat flux. Any discrepancies between the local critical heat flux verified among the cladding material are attributed to different departure from nucleate boiling phenomena captured during the experiment with the high-resolution optical fiber temperature data. Substantial differences in the performance of the different cladding material to survive a critical heat flux event were however observed by post-test X-ray and optical inspection. External evident damage and internal cracks to the simulated fuel pin having the bare zircaloy cladding were observed in regions associated with the occurrence of the critical heat flux for longer periods. Such damages were associated with zirconium oxidation, and not noticed on the Cr coated zircaloy or FeCrAl claddings. These results indicate that the use of FeCrAl or a Cr coated zircaloy as cladding in Pressurized Water Reactor and Boiling Water Reactor may increase the survivability of the cladding material for short transients.

Numerical investigation on the transient transport and heat transfer characteristics of transpiration cooling with liquid phase change during coolant adjustment

• A new transient model is proposed for phase-change transpiration cooling. • Dynamic fluid–solid coupling heat transfer during coolant adjustment is studied. • Dramatic variation of injection pressure with coolant mass flux is simulated. • Influence of coolant phase change location on transport characteristic is analyzed. Aimed at learning the variation law of injection pressure with coolant mass flux and promoting the active control of phase-change transpiration cooling, this study proposes a new transient mathematical model by simplifying the two-phase mixture model (TPMM) with the introduction of modified mixture enthalpy and enthalpy ratio. The smooth change with time of mixture enthalpy and enthalpy ratio improves the convergence and stability of TPMM. Experiment is first carried out to verify the accuracy of the new model. Then the two-phase flow and corresponding fluid–structure coupling heat transfer processes of transpiration cooling are studied with the new model under both steady and transient conditions. Besides, the relationship link from coolant adjustment, corresponding pressure and mass flux to the cooled wall temperature is discussed. The steady results show that injection pressure is closely related with phase change location, and the huge change of fluid kinematic viscosity and pumping effect of capillary force induces the non-linear variation of injection pressure with coolant mass flux. The transient results reveal that injection pressure changes with different laws when the mass flux increases and decreases. The changing speed of mass flux and scale of external heat flux also have a vital influence on the fluctuation of injection pressure, the faster the mass flow rate changes and the greater the heat flux is, more tempestuously the injection pressure varies.

Multiphysics Investigation on Coolant Thermohydraulic Conditions and Fuel Rod Behavior During a Loss-of-Coolant Accident

This article simulates the multiphysics coolant thermohydraulic conditions and fuel performance of a pressurized water reactor (PWR) during a loss-of-coolant accident (LOCA). In the coolant channel of a PWR, the coolant undergoes a series of different boiling regimes along the axial direction. At the inlet of the coolant channel, heat exchange between the cladding wall and coolant is based on single-phase forced convection. As the coolant flow distance increases, the boiling regime gradually converts to nucleate boiling. When a LOCA occurs, on the one hand, the coolant flux and coolant pressure decrease sharply; on the other hand, the heat flux at the cladding wall decreases relatively slowly. They both contribute to a swift increase in coolant temperature. As a consequence, a boiling crisis may occur as critical heat flux (CHF) decreases. In this article, the void fraction along the length of coolant channel in a reactor and mechanical performance of Zr cladding enwrapping UO2 fuel are investigated by establishing a fully coupled multiphysics model based on the CAMPUS code. Physical models of coolant boiling regimes are implemented into the CAMPUS code by adopting different heat transfer models and void fraction models. Physical properties of the coolant are implemented into the CAMPUS code using curve-fitting results. All physical models and parameters related to solid heat transfer are implemented into the CAMPUS code with a 2D axisymmetric geometry. The modeling results help enhance our understanding of void fraction along the length of the coolant channel and mechanical performance of Zr cladding enwrapping UO2 fuel under different coolant pressure and mass flux conditions during a LOCA.

Analytical solution of flows in porous media for transpiration cooling applications

Abstract

Flow boiling characteristics in different configurations of stepped microchannels

Geometrical modifications in microchannel geometry intended towards mitigation of flow instabilities generally results in increased pressure drop across the microchannel heat sink. To overcome this, stepped microchannels configurations with combination of narrow bottom (aspect ratio: AR = depth/width > 1) and wider top (AR < 1) part are investigated and their flow boiling performances have been compared with rectangular cross-section microchannels (RMC) having same hydraulic diameter (350 μm). The effect of varying wider cross-section on flow boiling instability and heat transfer performance have been explored for three configurations of stepped microchannels namely: stepped straight microchannels (SMC), stepped converging microchannels (SCMC) and stepped diverging microchannels (SDMC). These geometrical variants are fabricated on a 10 × 10 mm2 copper block having nine parallel microchannels. Flow boiling experiments have been conducted using de-ionized (DI) water as coolant for an inlet subcooling of 20 °C, coolant mass fluxes ranging from 327.6 to 777.54 kg/m2s and for wide range of heat fluxes. Combination of narrow and wider converging/diverging flow passage improves flow stability by allowing bubbles in the confined narrow bottom to grow and expand in the wider top section thus reducing their evaporative momentum. Different flow regimes govern the heat transfer and pressure drop mechanisms while the compressible volume-liquid interaction dictates flow instability. Favorable surface tension gradient in SDMC alleviates flow instability whereas reduced flow resistance at the inlet in SCMC resulted in smooth rewetting during dry out. Amplitude and fluctuation of pressure drop is found to be minimum in SCMC among all geometric configurations, while better heat transfer performance has been observed in SDMC configuration.

Thermal Impulse Response in Porous Media for Transpiration-Cooling Systems

A solution of the coupled differential equations for fluid and solid phases in a one-dimensional porous medium in thermal nonequilibrium is presented using the concept of analyzing the impulse response. The impulse response is shown to be sensitive to the volumetric heat transfer coefficient and the coolant mass flux. Experimental data obtained from surface heating of transpiration-cooled porous zirconium di-boride () samples are compared to a newly developed theoretical model. The surface and backside temperatures of the solid are measured using thermographic imaging and thermocouple instrumentation. The noninteger system identification approach is used to experimentally obtain the thermal impulse response, which is then compared to the model prediction. Good agreement is found between the simulated and experimental data with average deviations below 10%. The developed model provides the basis for inverse heat transfer measurements and further analysis of transpiration-cooled materials.

Influences of large fillets on endwall flows in a vane cascade with upstream slot film-cooling

Investigations in cascade employ filleted blades to influence the near endwall secondary flows and total-pressure losses. The secondary flows aggravate the aerodynamic losses and endwall thermal stresses in the gas turbine passages. Investigations of different configurations of the slot-bleed flow from the endwall of cascade upstream show significant influences on the near endwall flows. In the present paper, the near endwall flow-field in a linear cascade employing filleted vanes and bleed flow from the upstream endwall slots is measured experimentally. Two fillet profiles are tested, one is larger than the other. The objectives are to quantify the combined effects of endwall fillet, fillet profiles, and film-cooling flow on the endwall region flow-field. The fillet covers the junction of vane and endwall upstream of the cascade throat region. The discontinuous bleed-slots near the cascade entrance provide the film-cooling flow on endwall and simulate the gaps between combustor/nozzle-vane discs or stator/rotor discs in the gas turbine. The inlet Reynolds number of 2.0E+05 is based on the chord length of vane profile. The density and temperature ratios of the coolant flow to mainstream are both about 1.0. The inlet blowing ratio of the film-cooling flow varies between 1.0 and 2.8. The flow-field is measured through the distributions of flow temperature, yaw angle, axial vorticity, and total-pressure losses along the vane passage. The effects on the flow-field are then presented by comparing the cases of filleted vanes with the cases of un-filleted vanes. The results of flow yaw angle and axial vorticity in the filleted passage are smaller than those in the passage without the fillet. The yaw angles responsible for the endwall secondary flows are the smallest for the smaller fillet (Fillet-2). The temperature field indicates the pitchwise distributions of the coolant on endwall specially near the pressure side are better when the smaller fillet is employed. Also, the weakened passage vortex of the endwall secondary flows in the filleted passage reduces the total-pressure losses. Although the total-pressure losses decrease at very high coolant mass flux with and without the fillet, the losses are always smaller for the filleted passage than for the un-filleted passage. The present investigation is beneficial for improving and optimizing the endwall film-cooling in the gas turbine passage.

Comparison of experimental and simulated critical heat flux tests with various cladding alloys: Sensitivity of iron-chromium-aluminum (FeCrAl) to heat transfer coefficients and material properties

In this work we analyze the differences between previous transient critical heat flux (CHF) experiments using iron-chromium-aluminum (FeCrAl), Inconel 600, and stainless steel 316 (SS316) alloy test sections and best-estimate modeling results from widely-used nuclear engineering systems and subchannel analysis tools. FeCrAl is an Accident Tolerant Fuel (ATF) candidate cladding material. The thermal hydraulic performance and safety characteristics of FeCrAl are being evaluated to determine viability as a cladding material in Light Water Reactors (LWRs). In this study, the results of the CHF experiments conducted at atmospheric pressure and fixed inlet coolant temperature and mass flux are compared to models built in the fifth version of the Reactor Excursion and Leak Analysis Program (RELAP5-3D) and CTF, the modernized version of COBRA-TF developed by the Consortium for Advanced Simulation of LWRs (CASL). Results from RELAP5-3D and CTF showed differences from the experiments and from each other in predicting CHF. In the Inconel 600 case, both computational tools overpredicted CHF, which led to an underprediction in the tube outer surface temperature. In the SS316 and FeCrAl cases, CHF was underpredicted by the codes, leading to an overprediction of the tube outer surface temperature.To understand the discrepancies in CHF and post-CHF predictions, studies were performed using RELAP5-3D and RAVEN to determine the sensitivity of CHF and peak test section temperature, an analog to peak cladding temperature (PCT), to heat transfer coefficients, a CHF multiplier, and uncertainties in the thermal conductivity and volumetric heat capacity. We found that CHF depends most strongly on the CHF multiplier and thermophysical properties. A combination of these factors that produced the best match to the experiment based on CHF, PCT, and the total energy deposited into the tube was determined. The best match parameters were able to provide best-estimate predictions of the CHF and integral heat flux, but were still conservative when predicting the PCT. The best match set of parameters developed in this paper are intended only as a demonstration of an approach that could be applied in the future with a larger set of experiments to produce more accurate models of CHF and post-CHF behavior.

Flat Plate and Turbine Vane Film-Cooling Performance with Laid-Back Fan-Shaped Holes

Shaped holes are considered as an effective solution to enhance gas turbine film-cooling performance, as they allow to increase the coolant mass-flux, while limiting the detrimental lift-off phenomena. A great amount of work has been carried out in past years on basic flat plate configurations while a reduced number of experimental works deals with a quantitative assessment of the influence of curvature and vane pressure gradient. In the present work PSP (Pressure Sensitive Paint) technique is used to detail the adiabatic effectiveness generated by axial shaped holes with high value of Area Ratio close to 7, in three different configurations with the same 1:1 scale: first of all, a flat plate configuration is examined; after that, the film-cooled pressure and suction sides of a turbine vane model are investigated. Tests were performed varying the blowing ratio and imposing a density ratio of 2.5 . The experimental results are finally compared to the predictions of two different correlations, developed for flat plate configurations.

Numerical investigation on the characteristics of coolant flow, heat absorption and phase change in transpiration cooling process

Transpiration cooling using liquid water as coolant has been confirmed as a promising thermal protection method due to the huge phase change latent heat. A multi-region numerical strategy is developed and presented in this paper, to simulate directly the liquid transpiration cooling process within a wedge-shaped porous cone. An experiment was conducted to validate the numerical strategy. Using the validated strategy, five series of numerical simulations under different coolant mass fluxes were carried out. The numerical results revealed some interesting and valuable characteristics of fluid flow, heat absorption and phase change of liquid coolant in the porous cone and on the impermeable surface. When the liquid coolant is vaporized incompletely in the porous region, one can find two interesting phenomena: 1) A large amount of coolant flow towards the end of the porous cone, while only a small part of coolant can be transferred into the leading edge region; 2) An increase in inlet coolant mass flux causes a decrease of the coolant ejected from the leading edge. However, these phenomena are absent when the liquid coolant is vaporized completely in porous region. Another important phenomenon demonstrated in this work is an additional thermal protection effect on the downstream impermeable surface. This additional thermal protection effect increases with the inlet coolant mass flux, but at the price of a larger wastage of coolant phase change latent heat.

Numerical investigation on transpiration cooling with coolant phase change under hypersonic conditions

Owing to the huge phase-change latent heat, transpiration cooling using liquid coolant has been widely recognized as an effective thermal protection approach for hypersonic vehicles. This paper presents a modified local thermal non-equilibrium two-phase mixture model (LTNE-TPMM), and develops a multi-region numerical strategy to solve the coupled problems of internal heat and mass transfer in a porous cone with the external aerodynamic heat/force. The modified LTNE-TPMM and numerical strategy are validated by the experimental data obtained under a supersonic condition. Using the validated model and numerical strategy, numerical simulations are carried out under the condition of flight Mach number 7.0 and altitude 26.5 km, to study the mechanisms and analyze the performances of the transpiration cooling with liquid phase-change in a porous wedge-shaped nose cone. The numerical results revealed some interesting, valuable phenomena generated in liquid phase-change process, including the coolant movement and the distributions of temperature, pressure, saturation within the porous cone. The coolant mass flux along the radial direction of the cone decreases gradually in the vapor region, and then decreases rapidly at the beginning of two-phase region, but increases in the liquid region. Another important discovery is that the relation between coolant injection pressure and mass flow rate is not one-to-one. One injection pressure may correspond to multiple mass flow rates.

Numerical study on flow and heat transfer behavior of vortex and film composite cooling

The complete vortex and film composite cooling model is established to study the flow and heat transfer behavior. Influences of coolant Reynolds number, film hole diameter and inject angle on vortex and film composite cooling property are thoroughly discussed. Results show that the vortex nozzle coolant mass flux increases along the vortex chamber axial direction, while the film hole coolant mass flux and blowing ratio decrease along the vortex chamber axial direction. The internal heat transfer intensity will increase along the vortex chamber axial direction. The adiabatic film cooling efficiency decreases downstream due to counter rotating vortex pairs (CRVP) lift off wall effects. The coolant rotational velocity in vortex chamber increases with the increasing Reynolds number, thus leading to obvious heat transfer enhancement. An increase in Reynolds number results in an increase in CVRP intensity, hence the adiabatic film cooling efficiency will turn lower. The coolant rotational velocity and internal heat transfer intensity will decrease with the increase of film hole diameter. The CRVP intensity and film hole jet coolant mass flux increases with the increasing film hole diameter, leading to an increase in adiabatic film cooling efficiency. The rotational coolant flow and heat transfer intensity are not sensitive to inject angle. As the inject angle increases, the CRVP intensity changes little and the inject coolant owns larger inclined angle with gas mainstream flow, therefore the adiabatic film cooling efficiency will increase.

An Investigation of Coolant Within Serpentine Passages of a High-Pressure Axial Gas Turbine Blade

Cooling flow behavior is investigated within the multiple serpentine passages with turbulators on the leading and trailing walls of an axial gas turbine blade operating at design-corrected conditions with accurate external flow conditions. Pressure and temperature measurements at midspan within the passages are obtained using miniature butt-welded thermocouples and miniature Kulite pressure transducers. These measurements, as well as airfoil surface pressure field data from a full computational fluid dynamics (CFD) simulation, are used as boundary conditions for a model that provides quantitative values of film-cooling blowing ratio for each film-cooling hole on the blade. The model accounts for the continuously changing cross-sectional area and shape of the channels, frictional pressure loss, convective heat transfer from the solid portion of the blade, massflow reduction as coolant bleeds out through film-cooling or impingement holes, compressibility effects, and the effects of blade rotation. The results of the model provide detailed coolant ejection information for a film-cooled rotating turbine airfoil operating at design-corrected conditions and also account for the highly variable freestream conditions on the airfoil. While these values are commonly known for simpler experimental geometries, they have previously either been unknown or estimated crudely for full-stage experiments of this nature. The better-quantified cooling parameters provide a bridge for better comparison with the wealth of film-cooling work already reported for simplified geometries. The calculation also shows the significant range in blowing ratio that can arise even among a single row of cooling holes associated with one of the turbulated passages, due to significant changes in both coolant and local freestream massfluxes.