Mass Flux Ratio Research Articles

Properties of a Mesoscale Convective System in the Context of an Isentropic Analysis

Abstract Application of an isentropic analysis of convective motions to a simulated mesoscale convective system is presented. The approach discriminates the vertical mass transport in terms of equivalent potential temperature. The scheme separates rising air at high entropy from subsiding air at low entropy. This also filters out oscillatory motions associated with gravity waves and isolates the overturning motions associated with convection and mesoscale circulation. The mesoscale convective system is additionally partitioned into stratiform and convective regions based on the radar reflectivity field. For each of the subregions, the mass transport derived in terms of height and an isentropic invariant of the flow is analyzed. The difference between the Eulerian mass flux and the isentropic counterpart is a significant and symmetric contribution of the buoyant oscillations to the upward and downward mass fluxes. Filtering out these oscillations results in substantial reduction of the diagnosed downward-to-upward convective mass flux ratio. The analysis is also applied to graupel and snow mixing ratios and number concentrations, illustrating the relationship of the particle formation process to the updrafts.

Experimental and numerical investigation of heat transfer from a narrow annulus to supercritical pressure water

Heat transfer characteristics of supercritical pressure water in a narrow annulus with vertically upward and downward flows were investigated experimentally and numerically. The outer diameter of the inner heated rod is 8mm with an effective heated length of 620mm. Experimental parameters covered the pressure of 23–28MPa, mass flux of 400–1000kg/m2s and heat flux on the outer surface of the heated rod from 200 to 1000kW/m2. The general heat transfer behaviors were discussed with respect to various mass fluxes and pressures. According to the experimental data, it was found that the effect of flow direction on heat transfer depends on the heat-flux to mass-flux ratio (q/G). Heat transfer is much improved in the downward flow compared to that of upward flow at high q/G ratios. At the pressure of 25MPa, low-mass-flux deteriorated heat transfer occurred in the upward flow but not in the downward flow. At the same test parameters, however, heat transfer deterioration was observed at both of the two flow directions when the pressure was lowered to 23MPa. The experimental results indicate that buoyancy plays an important role for this type of deterioration, but is not the only mechanism that leads to the heat transfer deterioration. Three turbulence models were assessed against the annulus test data, it was found that the SST k-ω model gives a satisfying prediction of heat transfer deterioration especially for the case of downward flow. The mechanisms for the low-mass-flow heat transfer deterioration were investigated from the viewpoints of buoyancy and property variations of the supercritical water.

Analysis of Droplet Deposition in a Vertical Air-water Dispersed Flow

Droplet deposition in a turbulent vertical air–water dispersed flow onto wall of a tube has been studied theoretically and experimentally. A model for the deposition of large droplets based on the droplet sticking efficiency to the tube wall is proposed. Sticking efficiency is defined as the ratio of the sticking mass flux to the impacting mass flux. The application of the proposed model is illustrated by calculating several quantities of a practical interest for analysis of heat and mass transfer in dispersed flows, namely the deposition coefficient onto dry wall, sticking efficiency onto wall liquid film and the minimum value of the liquid film Reynolds number at which a steady liquid film exist. The proposed model describes the change of the deposition coefficient with droplet concentration and fits the obtained deposition data satisfactorily for a wide range of the gas Reynolds numbers and droplet concentration. The model is useful for analysing of dryout and burnout heat transfer regimes.

A modified integral model for negatively buoyant jets in a stationary ambient

A simple modification is introduced into the integral model (IM) CorJet in an effort to predict better the characteristics of negatively buoyant jets (NBJ) discharged in a stationary ambient. Although this modification was developed for the CorJet model, it can be applied to every IM which employs the entrainment hypothesis. The detrainment of fluid from the main flow is taken into account by inserting a coefficient “p” into the conservation equations of volume, buoyancy and tracer mass flux. This coefficient expresses the ratio of the specific mass flux of the detrained fluid to the net specific mass flux entrained to the NBJ. The value of p is assumed constant along the jet trajectory and up to the maximum jet height, becoming zero thereafter. Results show that the modified CorJet model (MCM) predicts reasonably well experimental data from the literature and data from experiments performed in this work. The optimal value of p and therefore the detrained fluid from the main NBJ flow was found to decrease as the jet initial densimetric Froude number increases.

Experimental study of unsteady wake effect on a film-cooled pitchwise-curved surface

Unsteady wake interactions with the near wall flow field occur when a surface is exposed to fluid flow past upstream rotating bodies. In the case of gas turbines, understanding such interactions are essential to better design cooling schemes on endwalls. In view of this, an experimental study has been conducted to determine the heat transfer coefficient and film cooling effectiveness on a pitchwise-curved surface which is subjected to unsteady passing wakes generated using a wake rod in a wall-normal orientation. The mainstream Mach number was maintained approximately constant at 0.03. A single row of cylindrical film holes with pitch to diameter ratio of 3 and inclined at 35° to the test surface are used for discrete film injection. The coolant to mainstream mass flux ratio (M) is varied between 0.25 and 1. A spoke-wheel type wake generator is used to produce unsteady wakes at two wake Strouhal numbers (S=0.15, 0.3). Measurements are made for (i) steady mainstream flow (S=0) which serves as a baseline case, (ii) mainstream flow with unsteady wakes, (iii) steady mainstream flow with film injection (iv) both (ii) and (iii) combined. The unsteady passing wakes mitigated jet lift-off at high coolant to mainstream momentum flux ratios. The maximum increase in film effectiveness was measured to be ≅16.35% at the jet centerline for M=0.75, S=0.3 at x/D=2. At high coolant to mainstream mass flux ratios, a combination of increasing film jet turbulence and strong interaction with the mainstream, deteriorates film cooling effectiveness but increases the heat transfer coefficient. Heat transfer augmentation increased by ≅7.6% for the highest wake passing frequency (S=0.3) without film injection. A combination of unsteady passing wakes and film injection resulted in a maximum pitch-averaged and centerline heat transfer augmentation of ≅28% and 31.7% respectively.

LES-DPM simulation of turbulent gas-particle flow on opposed round jets

A three-dimensional simulation was performed on the turbulent gas–solid flow in a cylindrical channel with opposed round jets. Large eddy simulation (LES) coupled with discrete phase model (DPM) was employed for carrier gas and laden particles respectively, to investigate the turbulent gas–solid behaviors. Simulations were focused on the effects of particle sizes (dp=5μm, 14μm and 40μm), Stokes numbers (St=0.125, 1 and 8), mass flux ratios (Zm=0.00128, 0.035 and 0.66) and initial gas velocities (U0=15m/s, 25m/s and 35m/s) on the vortex structure evolution, particle motion, time-averaged velocity profiles and turbulence intensity. It was found that the evolutions of vortex structure, including the destruction of large scale coherent structures to tiny vortices and the lateral spreading of vortices at the impingement zone, were augmented when using smaller particles and higher initial gas velocities. In addition, particles followed more closely and were easier to reach quasi-equilibrium state with the decrease of Stokes number (St<1), whereas more particles penetrated the impingement plane when increasing the Stokes number (St>1). And, with the increase of mass flux ratio, the momentum transfer was augmented as well as the turbulence intensity. Moreover, the position (rm) with maximum radial velocity was almost independent of the initial gas velocity on far-spaced opposed round jets.

Gas Transfer of an Implatable Artificial Lung

The water flow characteristics in the implantable artificial lung (IAL) were evaluated by in vitro experiments. The 50-fiber modules were of different lengths but contained well-spaced fibers; and the 300-fiber module had a volume fraction of 0.9. A lower number of tired hollow fibers produce a higher water-side film coefficient of oxygen transfer at a constant velocity of water-side flow. The area of the water flow decreases with increasing hollow fiber packing density, thus if water is induced to flow uniformly in the IAL module, the oxygen transfer rate should monotonously increase with the packing density. The water flow in the IAL is not uniform and depends on the hollow fiber packing density. The stagnation of the water flow occurs in the bundle of the hollow fibers at the water inlet. Intravascular oxygenation represents an attractive, alternative support modality for patients with ARDS. The concept of intravascular oxygenation as an alternative ARDS therapy originated with Mortensen (7), who developed an intravenous oxygenator (IVOX) consisting of a bundle of crimped hollow fiber positioned in the vena cava. In phase I clinical trials, the IVOX provided an average of 28% of basal gas exchange requirements for patients with severe ARDS (8-14). The clinical study, however, concluded that more gas exchange was needed for intravascular oxygenation to be clinically effective in ARDS treatment. We are developing an intravenous membrane oxygenator (IMO) with a design goal of 50% of basal oxygen and carbon dioxide exchange requirements for end-stage ARDS patients. Like the IVOX, the IMO consists of a bundle of manifolded hollow fiber, and is intended for intravenous placement within the superior and inferior vena cava. The target level of gas exchange in the IVOX, and consequently, the IMO, incorporates a polyurethane balloon concentric with the fiber bundle, which rhythmically inflates and deflates to provide active blood mixing, and thus enhances gas exchange. Our current efforts focus on device improvements intended to provide the target levels of gas exchange, given the constraints imposed by intravenous placement on fiber bundle size and hence fiber area for gas exchange. Although critical care techniques have been improved, the high mortality of severe ARDS has not significantly changed (10-15). In an implantable artificial lung (IAL), the greater part of the oxygen transfer resistance is located in the blood-side laminar film (16), and various methods have been attempted to make the laminar film thin and improve the oxygen transfer rate (17, 18). In the present study, the water flow characteristics in the IAL were evaluated by in vitro experiments. The effect of hollow fiber packing fraction on water flow condition was evaluated to produce effective constant of water with the hollow fibers. Oxygen transfer rates were evaluated, and the optimum hollow fiber packing fraction was determined at an outside diameter of hollow fibers of 380 μm. II. THEORYT The Reynolds number (NRe =Lv/υ) characterizes the flow regime and is the ratio of inertial force to viscous force. The Schmidt number (NSc=υ/D), analogous to the Prandtl number in heat transfer, characterizes the fluid properties and is the ratio of momentum transport to diffusive transport. The Peclet number (NPe=Lv/D), which is the product of NRe, characterizes the relative importance of convective and diffusive processes and is the ratio of bulk mass transport to diffusive mass transport. The Sherwood number (NSh=KL/D), also known as the mass transfer Nusselt number, likewise characterizes the relative importance of convective and diffusive transport; it is the ratio of total transport to diffusive transport. The mass transfer Stanton number (NSt=K/v) is proportional to the ratio of the actual mass flux to the mass flux capacity of the flow, i.e. the amount of mass potentially transferable per unit time and cross-sectional area.

Scaling of Film Cooling Performance From Ambient to Engine Temperatures

The present study employs computational fluid dynamics (CFD) to explore the complexities of scaling film cooling performance measurements from ambient laboratory conditions to high temperature engine conditions. In this investigation, a single shaped hole is examined computationally at both engine and near ambient temperatures to understand the impact of temperature dependent properties on scaling film cooling performance. By varying select flow and thermal parameters for the low temperature cases and comparing the results to high temperature flow, the parameters which must be matched to scale film cooling performance are determined. The results show that only matching the density and mass flux ratios is insufficient for scaling to high temperatures. In accordance with convective heat transfer fundamentals, freestream and coolant Reynolds numbers and Prandtl numbers must also be matched to obtain scalable results. By virtue of the Prandtl number for air remaining nearly constant with temperature, the Prandtl number at ambient conditions is sufficiently matched to engine temperatures. However, laboratory limitations can prevent matching both the freestream and coolant Reynolds numbers simultaneously. By examining this trade-off, it is determined that matching the coolant Reynolds number produces the best scalability. It is also found that by averaging the adiabatic effectiveness of two experiments in which the freestream and coolant Reynolds number are matched, respectively, results in significantly better scalability for cases with a separated coolant jet.

Effect of OH depletion on measurements of the mass-to-flux ratio in molecular cloud cores

Abstract The ratio of mass and magnetic flux determines the relative importance of magnetic and gravitational forces in the evolution of molecular clouds and their cores. Its measurement is thus central in discriminating between different theories of core formation and evolution. Here, we discuss the effect of chemical depletion on measurements of the mass-to-flux ratio using the same molecule (OH) both for Zeeman measurements of the magnetic field and the determination of the mass of the region. The uncertainties entering through the OH abundance in determining separately the magnetic field and the mass of a region have been recognized in the literature. It has been proposed however that, when comparing two regions of the same cloud, the abundance will in both cases be the same. We show that this assumption is invalid. We demonstrate that when comparing regions with different densities, the effect of OH depletion, in measuring changes of the mass-to-flux ratio between different parts of the same cloud can even reverse the direction of the underlying trends (for example, the mass-to-flux ratio may appear to decrease as we move to higher density regions). The systematic errors enter primarily through the inadequate estimation of the mass of the region.

Experimental investigation on pressure oscillation frequency for submerged sonic/supersonic steam jet

Experimental investigations and analysis on the pressure oscillation frequency for sonic and supersonic steam injected into subcooled water have been performed. The effects of steam mass flux, water temperature and pressure ratio on the oscillation frequency are discussed. The penetration length increases and the frequency decreases with the increasing steam mass flux and water temperature for both sonic and supersonic steam injection. The frequency first increases and then decreases with the decreasing pressure ratio for supersonic steam injected into subcooled water. When the flow pattern changes from under-expanded jet to over-expanded jet with the decreasing pressure ratio, the frequency reaches a maximum and will be at the safest value. The safest pressure ratio is about 0.2 for supersonic steam injection. The correlation reported by previous scholars cannot be directly used to predict the frequency of supersonic steam injected into subcooled water. Based on our experimental data, penetration length and expansion coefficient correlations which are appropriate for the supersonic steam injection have been given. Using the given penetration length and expansion coefficient correlations, the correlation of Hong can be used to predict the oscillation frequency for supersonic steam injection. The predictions agree well with the present experimental data, the discrepancies are within −20%∼20%.

A study on the flow characteristics of refrigerant and oil mixture in compressor suction line

Abstract This paper discusses the experimental results of oil retention amount and pressure drop in the gas line of refrigerant. R410A and polyvinylether oil were used as refrigerant and lubricant, respectively. The experiment was conducted under various pipe inner diameters of 14.1, 17.3 and 26.0 mm, and refrigerant mass flux and oil circulation ratio (OCR) were varied from 40 to 250 kg m −2 s −1 and 0.5–4.0%, respectively. The oil retention amount tends to increase as refrigerant mass flux decreases and OCR increases. The oil retention amount in vertical pipe was higher than that in horizontal pipe. The empirical expressions for predicting the oil retention amount and pressure drop were suggested. The mean absolute percentage errors of each expression for predicting the oil retention amount in horizontal and vertical pipes were 18.1% and 14.1%, respectively, and those for predicting the pressure drop in horizontal and vertical pipes were 22.2% and 20.1%, respectively.

Sorption and pervaporation of methanol/water mixtures with poly(3-hydroxybutyrate) membranes

In this contribution, poly(3-hydroxybutyrate) (PHB) membranes were evaluated in sorption and pervaporation experiments for methanol/water separation. Single component sorption tests showed that PHB membranes have higher affinity toward methanol than water: at 40°C the sorption degree was 18.4 and 1.1%, respectively. This was in agreement with contact angle measurements, performed with both liquids, and Hansen solubility parameter. PHB sorption degree in the whole methanol/water composition range and three temperature levels were determined, showing an anomalous behavior (sigmoid like curves). A simple technique, named by us “Desorption by Dissolution”, was developed to determine sorbed mixture composition. It basically consists on dissolving the polymer after sorption equilibrium in the mixture has been reached, to completely extract the mixture. Then, chromatographic analysis is used to determine solution composition. It does not require adapting equipment or using vacuum devices neither cold traps. When both components were present, methanol grams sorbed in the membrane were always lower than the mixture in which they were immersed, while water sorption was enhanced due to methanol presence. Very low standard deviation values were registered (<0.84) confirming the technique reliability. Single component fluxes and mass flux ratio in pervaporation increased with temperature: methanol flux was 3.5×10−5kgm−2s−1 at 25°C, whereas at 50°C exceeded 7×10−5kgm−2s−1; water flux increased from 1.8×10−5kgm−2s−1 at 30°C to 2.2×10−5kgm−2s−1 at 50°C. Since permeances decreased, the increase in fluxes with temperature can be attributed to the increase in vapor pressure driving forces. Mixture pervaporation results showed similar behavior, highlighting the fact that separation factor increased with temperature as well: 3.5 at 30°C and 3.8 at 50°C. Selectivities were higher than 12 for 10wt% water/methanol+water mixtures. Results were discussed in terms of polymer crystallinity, solubility parameters, component size, activation energies and cluster formation.

Mixing of cold and hot particles in a pre-lifting scheme with two strands of catalyst inlets for FCC riser

The paper presents a pre-lifting scheme for an FCC riser with two strands of catalyst inlets. The solid volume fraction, particle velocity and the mixing of cold and hot particles in the pre-lifting zone are investigated using optical-fiber and a thermal technique in a large cold Plexiglas model. The heat exchange uniformity is used to quantify the mixing of cold and hot particles under different operating conditions. The whole pre-lifting zone is divided into four regions. The flow characteristics are different in each region, indicating that the particles are redistributed in this proposed pre-lifting scheme. The distribution of heat exchange uniformity shows that the mixing extent of cold and hot particles decreases in the following sequence: the riser entrance region>the central tube region>the bottom region. This may be due to the fact that the cold and hot particles have mixed completely and intensely in the proposed pre-lifting scheme. The mixing of cold and hot particles is quite desirable when the mass flux ratio of cold particles to hot particles is 3:2.

Shower Head and Trailing Edge Cooling Influence on Transonic Vane Aero Performance

An experimental investigation on a cooled nozzle guide vane (NGV) has been conducted in an annular sector to quantify aerodynamic influences of shower head (SH) and trailing edge (TE) cooling. The investigated vane is a typical high pressure gas turbine vane, geometrically similar to a real engine component, operated at a reference exit Mach number of 0.89. The investigations have been performed for various coolant-to-mainstream mass–flux ratios. New loss equations are derived and implemented regarding coolant aerodynamic losses. Results lead to a conclusion that both TE cooling and SH film cooling increase the aerodynamic loss compared to an uncooled case. In addition, the TE cooling has higher aerodynamic loss compared to the SH cooling. Secondary losses decrease with inserting SH film cooling compared to the uncooled case. The TE cooling appears to have less impact on the secondary loss compared to the SH cooling. Area-averaged exit flow angles around midspan increase for the TE cooling.

Computational Fluid Dynamics Evaluations of Unconventional Film Cooling Scaling Parameters on a Simulated Turbine Blade Leading Edge

While it is well understood that certain nondimensional parameters, such as freestream Reynolds number and turbulence intensity, must be matched for proper design of film cooling experiments; uncertainty continues on the ideal method to scale film cooling flow rate. This debate typically surrounds the influence of the coolant to freestream density ratio (DR) and whether mass flux ratio or momentum flux ratio properly accounts for the density effects. Unfortunately, density is not the only fluid property to differ between typical wind tunnel experiments and actual turbine conditions. Temperature differences account for the majority of the property differences; however, attempts to match DR through the use of alternative gases can exacerbate these property differences. A computational study was conducted to determine the influence of other fluid properties besides density, namely, specific heat, thermal conductivity, and dynamic viscosity. Computational fluid dynamics (CFD) simulations were performed by altering traditional film cooling nondimensional parameters as well as others such as the Reynolds number ratio, Prandtl number ratio, and heat capacity ratio (HCR) to evaluate their effects on adiabatic effectiveness and heat transfer coefficient. A cylindrical leading edge with a flat afterbody was used to simulate a turbine blade leading edge region. A single coolant hole was located 21.5 deg from the leading edge, angled 20 deg to the surface and 90 deg from the streamwise direction. Results indicated that thermal properties can play a significant role in understanding and matching results in cooling performance. Density effects certainly dominate; however, variations in conductivity and heat capacity can result in 10% or higher changes in the resulting heat flux to the surface when scaling ambient rig configurations to engine representative conditions.

Numerical Investigation of Heat and Mass Flux Effects on Heat Transfer Characteristics of Supercritical Water in an Upward Flow Vertical Tube

In the present work, the heat transfer characteristics of supercritical pressure water are numerically investigated in an upward flow vertical smooth tube. The numerical simulations are carried out by using Ansys-Fluent solver. The objective of the present work is to investigate the effect of heat flux and mass flux on heat transfer characteristics in supercritical water. In order to perform numerical simulation, experimental data of Mokry et al. [2] is considered. Various simulations were carried out for the inlet parameters of temperature 350°C, pressure 240bar; heat flux values ranging from 190 to 884kW/m2 and mass flux values ranging from 498 to 1499kg/m2s. Based on the available parameters of heat flux and mass flux, they are segregated as groups with heat flux to mass flux ratios of 0.39 and 0.67. According to computational data, the heat transfer enhancement and heat transfer deterioration phenomenon of supercritical water were analyzed and based on the comparison with experimental data; their occurrence and mechanism were addressed.

The effects of mixing on age of air

Mean age of air (AoA) measures the mean transit time of air parcels along the Brewer-Dobson circulation (BDC) starting from their entry into the stratosphere. AoA is determined both by transport along the residual circulation and by two-way mass exchange (mixing). The relative roles of residual circulation transport and two-way mixing for AoA, and for projected AoA changes are not well understood. Here effects of mixing on AoA are quantified by contrasting AoA with the transit time of hypothetical transport solely by the residual circulation. Based on climate model simulations, we find additional aging by mixing throughout most of the lower stratosphere, except in the extratropical lowermost stratosphere where mixing reduces AoA. We use a simple Lagrangian model to reconstruct the distribution of AoA in the GCM and to illustrate the effects of mixing at different locations in the stratosphere. Predicted future reduction in AoA associated with an intensified BDC is equally due to faster transport along the residual circulation as well as reduced aging by mixing. A tropical leaky pipe model is used to derive a mixing efficiency, measured by the ratio of the two-way mixing mass flux and the net (residual) mass flux across the subtropical boundary. The mixing efficiency remains close to constant in a future climate, suggesting that the strength of two-way mixing is tightly coupled to the strength of the residual circulation in the lower stratosphere. This implies that mixing generally amplifies changes in AoA due to uniform changes in the residual circulation.

An experimental study of density ratio effects on the film cooling injection from discrete holes by using PIV and PSP techniques

An experimental study was conducted to investigate the performance of film cooling injection from a row of circular holes spaced laterally across a flat test plate. While a high-resolution Particle Image Velocimetry (PIV) system was used to conduct detailed flow field measurements to quantify the dynamic mixing process between the coolant jet stream and the mainstream flows, Pressure Sensitive Paint (PSP) technique was used to map the corresponding adiabatic film cooling effectiveness on the surface of interest based on a mass-flux analog to traditional temperature-based cooling effectiveness measurements. The cooling effectiveness data of the present study were compared quantitatively against those derived directly from the temperature-based measurements under the same or comparable test conditions in order to validate the reliability of the PSP technique. The effects of the coolant-to-mainstream density ratio (DR) on the film cooling effectiveness were investigated by performing experiments at fixed blowing ratios by using either Nitrogen (DR=0.97) or CO2 (DR=1.53) as the coolant streams for the PSP measurements. An accompanying analysis of scaling quantities, such as the coolant-to-mainstream momentum flux ratio, I, and bulk coolant-to-mainstream velocity ratio, VR, in addition to the most-commonly used blowing ratio (i.e., the coolant-to-mainstream mass flux ratio), M, was also conducted to illuminate the extent to which the flow scenario can be described using purely kinematic or dynamic means. It was found that the scaling quantities that give more weight to density ratio (i.e., blowing ratio, M, and then momentum ratio, I) have more success to collapse measurement data from varying density ratio of the coolant flows for the cases with relatively low coolant flow rates, while the coolant-to-mainstream bulk velocity ratio, VR, may be used with some success to scale the film cooling effectiveness for the cases with higher coolant flow rates.

Optimal design of impinging jets in an impingement/effusion cooling system

To design an impingement/effusion cooling system that realizes the lowest thermal stress in an impingement/effusion cooling system, we conducted thermal analysis and optimization using a second-order response surface method. The optimal impinging jet system was based on four design variables: the spacing between the impinging jets and effusion holes (1.0 ≤ Sp ≤ 5.0), the channel height from impinging jet to effusion surface (1.0 ≤ Ht ≤ 3.0), the mass flux ratio of the crossflow to the impinging jet flow (0.1 ≤ G∗ ≤ 1.3, −1.3 ≤ G∗ ≤ −0.1), and the main flow temperature (1100 K ≤ Tm ≤ 1800 K). We considered several cases involving inlined and staggered jets, and two cooling flow direction: the same direction and reverse direction. Response surface functions were constructed to determine the impinging jet system with the lowest value among the maximum stresses calculated within the design ranges. In each case, the response surface function for determining the maximum stress was composed of combinations of the four design variables. These functions can be used to find the optimum design point that achieves the lowest stress around film cooling holes in hot components of a gas turbine.

Ultra Fast Cooling and Its Effect on the Mechanical Properties of Steel

The objective of this work is to study about the ultrafast cooling of a hot static 6 mm thick steel plate (AISI-1020) by air assisted spray cooling. The study covers the effect of air flow rate and the water impingement density on the cooling rate. The initial temperature of the plate, before the cooling starts, is kept at 900 °C. The spray was produced from a full cone high mass flux and low turn down ratio air atomizer at a fixed nozzle to plate distance. The cooling rate shows that low turn down ratio air atomized spray can generate ultra fast cooling (UFC) rate for a 6 mm thick steel plate. After cooling, the tensile strength and hardness of the cooled steel plate were examined. The surface heat flux and surface temperature calculations have been performed by using INTEMP software. The result of this study could be applied in designing of fast cooling system especially for the run-out table cooling.