A wide variety of pin-fins have been used to enhance heat transfer in internal cooling channels. However, due to their large blockage in the flow direction, they result in an undesirable high pressure drop. This experimental study aims to reduce pressure drop while increasing the heat transfer surface area by utilizing strip-fins in converging internal cooling channels. The channel is designed with a trapezoidal cross-section, converges in both transverse and longitudinal directions, and is also skewed β = 120° with respect to the direction of rotation in order to model a trailing edge cooling channel. Only the leading and trailing surfaces of the channel are instrumented, and each surface is divided into eighteen isolated copper plates to measure the regionally averaged heat transfer coefficient. Utilizing pressure taps at the inlet and outlet of the channel, the pressure drop is obtained. Three staggered arrays of strip-fins are investigated: one full height configuration and two partial fin height arrangements (S z = 2mm and 1mm). In all cases, the strip fins are 2mm wide (W) and 10mm long (L f ) in the flow direction. The fins are spaced such that S y /L f = 1 in the streamwise direction. However, due to the convergence the spanwise spacing S x /W, was varied from 8 to 6.2 along the channel. The rotation number of the channel varied up to 0.21 by ranging the inlet Reynolds number from 10,000 to 40,000 and rotation speed from 0 to 300rpm. It is found that the full height strip-fin channel results in a more non-uniform spanwise heat transfer distribution than the partial height strip-fin channel. Both trailing and leading surface heat transfer coefficients are enhanced under rotation conditions. The 2mm height partial strip-fin channel provided the best thermal performance, and it is comparable to the performance of the converging channels with partial length circular pins. The strip-fin channel can be a design option when the pressure drop penalty is a major concern.

High temperature operation limits the life of fluid film bearings; hence the need to quantify the effect of pad material on the performance of tilting pad journal bearings (TPJBs). The paper presents measurements of performance conducted on a copper-pads bearing (C-PB) and a steel-pads bearing (S-PB). Both bearings have the same geometry and differ on the pads’ backing material, copper vs. steel, and slightly in the assembled cold clearance. The journal diameter D = 102 mm, and a bearing has five pads with length L = 0.4 D , nominal radial clearance 0.064 mm, and pad preload of 0.42. The pads are 12.3 mm in thickness and have a 50% offset pivot, ball-in-socket type. The bearings operate at four shaft speeds ranging from 6 krpm (32 m/s surface speed) to 14 krpm (74 m/s) and under multiple specific loads ranging from 0.17 MPa to 2.1 MPa. ISO VG 32 oil, at a supply temperature of 49 °C, lubricates a test bearing configured with end seals (flooded bearing). At the highest load (on pad) and low shaft speed, the S-PB static eccentricity is up to 37% higher than that for the C-PB. The oil exit temperature rise is similar for both bearings, the maximum difference reaches 6 °C. For all operating conditions, the pads’ peak temperature rise, having a maximum difference of 5 °C to 16 °C, is larger for the S-PB. The S-PB produces a ∼ 5% lower drag power loss than that in the C-PB. Drag power in both bearings increases with shaft speed and is largely independent of applied load. From dynamic load tests with multiple excitation frequencies to 250 Hz, the C-PB direct stiffness K YY (along the load direction) is up to 30% higher than the S-PB stiffness, while the difference in K XX between the C-PB and the S-PB ranges from 60% to 90%. Similar to the stiffness results, the C-PB produces larger direct damping coefficients; C YY and C XX are up to 25% and 40% larger than those for the S-PB. Both bearings, however, show symmetry in the damping coefficients, i.e., C XX ∼ C YY . Virtual mass coefficients ( M XX , M YY ) are significant in magnitude though having a large uncertainty. A computational physics model predicts the TPJB performance under identical conditions. The exhaustive comparison conducted with a sound dimensional characterization of parameters reveals that predictions agree well with measurements of journal eccentricity, oil exit temperature, pad surface temperatures, and stiffness and damping force coefficients. The differences amount to 20% or less. The model relies on specifying the material properties for pads and pivots and the operating (hot) clearance to produce accurate thermo-mechanically induced deformations that affect bearing performance at high loads and high surface speed operation.

Sulfur oxides, abbreviated to SOx, refer to both sulfur dioxide (SO 2 ) and sulfur trioxide (SO 3 ) that are gaseous pollutants emitted by the combustion of low-grade fuels, including heavy oils, sour gases and coal. Current Flue Gas Desulfurization (FGD) technologies mainly use limestone or CaO (quicklime) as sulfur scavenger. They consume water and produce significant stocks of calcium sulfate, a non-regenerable solid that has limited market outlets and is sometimes considered as waste. To tackle this problem, a multi-partner team has launched a two-phase program in order to develop a new, regenerative FGD concept. This partnership includes a GE Power team (Belfort, France), three research laboratories (IS2M-MPC, LGRE from University of Haute Alsace, Mulhouse and ICB-UTBM-LERMPS, Belfort), a ceramic material testing center (ICAR, Moncel les Luneville, France) and a consultancy organization skilled in materials (Zephir Alsace, Mulhouse). The main objective was to design a regenerable adsorbent that would not release any solid waste but would allow instead the recovery of sulfur in the form of H 2 SO 4 (sulfuric acid) which is a valuable chemical commodity. A first subprogram, executed from September 2012 through March 2015 and called “DeSOx New Gen”, enabled the different partners to identify and test at lab scale a regenerable and durable adsorbent. This adsorbent, used initially in powder form, involved an organized mesoporous silica (SiO 2 ), which was used as a support and was impregnated with copper oxide (CuO) likely to undergo reversible sulfation. Such binary system proved capable of achieving large numbers of successive adsorption/regeneration cycles (more than fifteen attained in the lab) without undergoing substantial activity loss. A second subprogram, initiated in September 2017 and called “AdSOx”, aimed to obtain and test a bead-shaped form of the previously developed adsorbent in view of industrial applications. This product in bead-shaped adsorbent was then evaluated in 2019 in a pilot combustion rig, the flue gases of which were representative of a real industrial combustion installation in terms of SOx, NOx, CO, CO 2 , H 2 O and PM (particulate matter). In these rig tests, the performances of the adsorbent for the capture of SOx, including its capability to be regenerated for multi-cyclic use, have been assessed in fluidized bed and most recently in fixed bed conditions. This paper outlines the most significant steps and outcomes of this collaborative two-phase development program. It also illustrates the interesting capabilities of mesoporous materials for the design of highly active sorption and catalytic systems.

The heat transfer and pressure drop characteristics of a rotating cooling channel that has an angled trapezoidal cross-section and converges from the hub to tip in both the streamwise and spanwise directions are experimentally investigated. The channel is oriented 120° with respect to the direction of rotation to model the geometry of an internal, trailing edge cooling passage. Both the leading and trailing sides of the channel are divided into three and six regions in the spanwise and streamwise directions, respectively. The copper plate method is used to obtain regionally averaged heat transfer coefficients. The pressure drop is measured utilizing pressure taps placed at the inlet and outlet of the channel. Experiments were conducted with the inlet Reynolds number ranging from 10,000 to 40,000. The rotational speed varies from 0 rpm to 300 rpm, resulting in the highest rotation number of 0.21. The effects of full pin-fins on the heat transfer and pressure drop characteristics are obtained and compared to the smooth surface converging channel results. The impact of the convergence, which causes variations of flow and geometric parameters through the passage, such as aspect ratio, Reynolds number, and rotation number, on the heat transfer coefficients and pressure drop are addressed. Results show that due to the 120° channel orientation, rotation has a positive impact on the leading and trailing surface heat transfer. Furthermore, the convergence decreases the aspect ratio while increasing Reynolds number. The convergence significantly enhances heat transfer on both the leading and trailing surfaces along the streamwise and spanwise directions. The convergence also reduces the rotation effect in the streamwise direction for a given mass flow rate.

Aerothermal performance of an asymmetrical-profile, leading-edge jet impingement array is studied using numerical and experimental techniques. This array consists of a single row of 9 jets impinging on a leading edge of diameter ratio D/d = 2, and a distinct suction side/pressure side akin to that of an actual turbine blade. Two different jet-to-target heights are tested, while the jet spacing of 4 jet diameters is kept constant. A range of jet-averaged Reynolds numbers between 20k – 80k are tested. The mean flow field of the mid-jet plane is quantified experimentally, through a non-intrusive experimental method of Particle Image Velocimetry (PIV), while area-averaged heat transfer is measured by the constant temperature copper block technique. The target surface is divided into several copper blocks to investigate the area-averaged heat transfer at each jet. The numerical portion of the presented work serves to investigate the fidelity of the Reynolds Averaged Navier-Stokes (RANS) k-ω turbulence model and how well it can predict the flow field within the geometrical domain of the leading edge.

A series of sweeping jet-impingement experiments are conducted over a circular heated surface, with a main objective of understanding the impact of the unique flow field on the resulting heat transfer. The sweeping motion of the fluidic oscillator is influenced by the sweeping frequency and sweeping angle where each is directly dependent on the geometric design (i.e. internal feedback loops, mixing chamber, etc.). The target surface consists of a heated copper disk, where heater power is supplied to the bottom surface of the disk and adjusted until a differential of 30°C is obtained between the jet and target surface temperatures. An energy balance over the target surface temperatures provides a means for calculating area-averaged heat transfer rate, hence Nusselt number. An increase in the sweeping jet’s thermal inertia initiates an augmentation in heat transfer due to sweeping motion of the jet across the target surface. PIV data was acquired for two jet configurations, confined and unconfined, so that the recirculation behavior can be determined. The fluidic oscillator is found to improve only at a low z/d. At large z/d (greater than 4 in this study), the fluidic oscillator adversely affects the heat transfer.

This paper presents developing secondary flow and heat transfer measurements in a ribbed cooling channel. Experiments are carried out for Reynolds number ranging from 25,000–140,000. Regionally averaged local heat transfer measurements are conducted using heated copper segments. Flow measurements are carried out using a miniature five-hole pressure probe and presented for cross sections at intervals of 1.8 hydraulic diameters d h in flow direction. Results are compared to numerical simulations using explicit algebraic Reynolds stress and turbulent heat transfer models. The paper focuses on the entrance region where secondary flow structure has not emerged yet. The findings show that the well-known secondary flow structure of the crossed rib configuration, consisting of one large single rotating secondary flow, is not established until approximately 6–7 d h in main flow direction. Instead two opposed vortices are identified which dominate the flow characteristics and provide an increase in heat transfer of up to 15–20% when compared to the periodically developed flow condition. Thus, for the first time to the author’s knowledge, the paper describes in detail the developing secondary flow in a crossed rib arrangement and links it to the heat transfer distribution observed. In summary, this paper stresses the importance of the developing flow region for the design process in convection cooled gas turbines, especially for short channels of high pressure blades and vanes, as it has a significant effect on cooling channel heat transfer performance.

Flow structures in lattice cooling channels are investigated experimentally by measuring three-dimensional velocity components over entire duct. The lattice cooling structure is formed by crossing two sets of parallel inclined ribs. Heat transfer is enhanced when coolant flows through the narrow sub-channels between the ribs. According to the past literature, longitudinal vortex structures are formed inside the sub-channels due to interactions between crossing flows. In this study, three-dimensional velocity field measurement is performed using MRI scanner to clarify the flow mechanism. The rib inclination angle is varied from 30 to 60 degrees. Reynolds number is set at approximately 8,000 based on the whole duct inlet hydraulic diameter and bulk velocity. Working fluid is 0.015mol/L copper sulfate aqueous solution. Measured results show that coolants in the upper and lower sub-channels interact not only at the both ends of the duct, but also at diamond-shaped openings formed by opposite sub-channels. The exchange of momentum between the upper and lower sub-channels occurs at the openings, leading to sustained longitudinal vortex in each sub-channel as mentioned in the literature. When the ribs are arranged with obtuse angle, a large vortex spreads across the contact surface, while the vortex structure independently stays in each sub-channel for acute rib angle. The measured velocity fields are compared with numerically-simulated ones using a RANS solver. Overall flow pattern is captured, but flow interaction between the upper and lower sub-channels is underestimated.

In the internal cooling passages of the first stage turbine blade in the modern advanced gas turbines, the dense bleeding holes are arranged in order to supply the cold air for the external film cooling. The fluid extractions dramatically vary the flow field and convective heat transfer in the internal channels. In the current work, the flow and heat transfer in a high aspect ratio channel (AR = 4) with the side wall bleeding slots are investigated. Unlike the traditional single inlet channel, the cooling air is supplied into the channel from two entrances located at the both ends of the long straight channel. Therefore, a counteractive flow pattern is generated. The effects of the flow rate ratio of the two streams (MR = ṁ 2 /ṁ 1 ) on the flow and heat transfer inside the channel are investigated, where ṁ 1 and ṁ 2 , are the flow rate of the two streams at the two entrances. The local heat transfer is found to be zigzagging with an increase in the flow rate ratio. Interestingly, once a local flow ratio, MR x , is defined, which is based on the predicted local flow rate, all the data at different locations are converged to the same trend in the Nu/Nu 0 - MR x space, where Nu is the measured local Nusselt number normalized with the Dittus-Boelter correlation, Nu 0 . Based on the numerical simulations, the detailed flow structure is analyzed and reported. The thermal boundary conditions in the simulations mimic the heating scheme in the experiments, where the channel wall is segmented into a matrix of copper plates which are separated by the insulations. It shows that the segmental heating scheme influences the heat transfer significantly.

The heat transfer characteristics in a rotating pin-fin roughened rectangular channel with an aspect ratio of 4:1 is investigated, simulating a rotor blade trailing edge. The copper plate regional average method is used to determine the heat transfer coefficient. A second inlet is added at the inner top corner of the traditional one-inlet cooling channel to improve heat transfer in the high radius region. Coolant from these two inlets mixes in the middle of the channel, and then exits through eight sidewall slots. The channel is assembled in a rotating facility, and the symmetrical plane of the rectangular channel is orientated at an angle of 135° with respect to the rotation plane. The mass flow rate of the bottom inlet is kept at a constant ( Re 1 = 20,000), whereas the inlet mass flow rate ratio ( MR , second inlet mass flow rate/bottom inlet mass flow rate) changes from 0 to around 0.55. Results show that the second inlet improves the heat transfer in the proximity of the second inlet extensively, but the overall averaged heat transfer is decreased a bit compared to the one inlet channel. Moreover, with the local MR , the heat transfer data at different locations converge into the same trend, indicating that the local MR should be a good parameter in describing the flow in this pin-fin cooling channel. In the rotating one-inlet channel ( MR = 0), a critical Ro phenomenon is observed. After the critical point, rotation stops decreasing heat transfer and starts to elevate it. A lower critical Ro is observed at higher radius location but the corresponding local Ro is a constant at around 1.0. In rotating two-inlet channel, the overall heat transfer enhancement caused by rotation is almost in the same level with different MR , indicating that high MR cases ( MR > 0.2) is not recommended because the coolant from the second inlet is not efficiently used.

Oil-free micro turbomachinery (OFT) implements compliant foil bearings because of their minute drag and ability to operate in extreme (high or low) temperature. Prominent to date, bump-type foil bearings integrate an underspring thin metal structure that provides resilience and material damping; and while the rotor is airborne, acts in series with the stiffness and damping of the gas film. The design and manufacturing of foil bearings remains costly as it demands of extensive engineering and actual experience. Alternative foil bearing configurations, less costly and easier to manufacture, are highly desirable to enable widespread usage of OFT. This manuscript details the design and manufacturing of a novel Rayleigh-step metal mesh foil thrust bearing (MMFTB) as well as its testing on a dedicated rig. Metal mesh structures offer significant material structural damping and can be easily procured at a fraction of the cost of a typical bump foil strip layer. The MMFTB consists of a solid carrier, a number of stacked annular Copper mesh sheets (wire diameter = 0.25, 0.3 and 0.41 mm), and a steel top foil (0.127 mm thick) that makes six pads (ID = 50.8 mm, OD = 2 ID), each 45° in extent. A 3 μm polymer coats each pad and a photo-chemical process etches a step 20 μm in height. Static and dynamic load measurements (without rotor speed) demonstrate the MMFTB has structural stiffness and material damping similar to that of a publicized bump-type foil thrust bearing. A maiden test of the MMFTB with rotor speed of Ω = 15 krpm (∼80 m/s at bearing outer diameter) proved briefly the bearing operation when applying a tiny thrust load. Further tests with ambient air, a rotor speed of 40 krpm (∼212 m/s at bearing OD), and a very light load/area < 7 kPa failed several of the prototype bearings, all exhibiting significant wear on one or more pads. The source of the failure is the inherent unevenness of the metal mesh stacked substructures, thus causing the pads to bulge towards the rotor collar surface before a load applies. A deficient anchoring method exacerbates the unevenness. Incidentally, a high rotor speed induced large windage that lifted the top foils pushing them against the spinning collar. As the bearing moved towards the rotating collar to begin applying thrust, the local high spots rubbed against the collar, before a hydrodynamic wedge could form to separate the surfaces. Without a robust sacrificial coating, metal-to-metal contact quickly disfigured the contacting top foil pads, erasing the etched step, and leading to failure. In concept, and on paper, the mesh sheets and the top foil lay flat against the bearing carrier, giving a false sense of uniformity in the design process. In actuality, a designer must consider the manufactured states of the individual components and how they assemble. A redesign of the bearing intends to overcome the existing flaws (highlighted herein) by incorporating a thicker top foil that is well anchored (to better withstand the effects of windage), a robust sacrificial coating, and a hydrodynamic wedge accomplished via a circumferential taper on each pad.

Heat transfer in a rotating two-pass trapezium-shaped channel, with staggered 90-deg ribs on both leading and trailing surfaces is experimentally investigated. The hydraulic diameter of the first and second pass is 24.5 mm and 16.9 mm, respectively. The inlet Reynolds number and rotational speed range from 10000 to 50000 and zero to 1000 rpm, respectively, which results in the inlet rotation number varying from zero to 1.0. The heated copper plate technique is employed to measure the regional averaged heater transfer coefficients. Pressure drops are measured by newly designed rotating pressure measurements module. Both ribbed cases and smooth cases are compared to present rib enhancement effect. For non-rotating result, the results show that the trailing surface presents much higher heat transfer than other cases due to the special wedge-shaped geometry. The ribbed wedge-shaped achieves enhanced regional heat transfer performances than the smooth case at all locations. Compared with the non-rotating results in the first pass, heat transfer on both trailing and leading surfaces is enhanced except for the position near the turn region, but weakened on outer surface in stream-wise direction. And at high rotation numbers, the highest maximum heat transfer on railing surface happens at a location of approximately X/D = 10. In the first pass, rotation always enhances heat transfer on the trailing surface as rotation number increases and the rotation-to-stationary Nusselt number ratio reaches to 2.0 at the rotation number of 0.5. The leading and outer surfaces both have a critical rotation number located at Ro c = 0.05.

In the continuous demand of increasing cooling efficiency for novel combustor liners, it is necessary to have a comprehensive understanding of the interaction of hot gases with coolant flows. The aim of the present study is the experimental characterization of the flow field and the measurement of liner heat transfer coefficient in a combustion chamber model equipped with an axial swirler and a liner slot cooling scheme. The test rig geometry consists in a linear three sector chamber fed by an open loop blower. The system is operated at isothermal conditions. A highly swirled main stream flow is achieved by considering an injector geometries that produce flow structures which interact with film cooling flow delivered by a simplified slot at the inner wall of the liner. To study the effects of this mutual interaction, the flow field and the liner heat transfer are investigated at different slot cooling and injector flow rates. A 2D PIV (Particle Image Velocimetry) technique is employed to investigate the test section flow field on two different planes. An experimental campaign focused on liner heat transfer measurement is carried out using a TLC (Thermochromic Liquid Crystals) steady state technique with a thin Inconel heating foil fed by two copper bus bars. Results obtained indicate an appreciable role of film cooling flow on both swirler aerodynamics and the liner heat transfer coefficient. When the slot cooling flow rate is increased, the observed peak of heat transfer coefficient, due to liner-swirl flow interaction, gradually reduces. This is a consequence of a reduction in swirling jet expansion when slot cooling is increased, which also affects the amount of flow recirculation due to vortex breakdown.

A laboratory scale test facility has been developed to investigate deposition in steam turbines under conditions that are representative of those in steam power generation cycles. The facility is an advanced two-reactor vessel test arrangement, which is a more flexible and more accurately controllable refinement to the single reactor vessel test arrangement described previously in ASME Paper No. GT2014-25517 [1]. The commissioning of the new test facility is described in this paper, together with the results from a series of tests over a range of steam conditions, which show the effect of steam conditions (particularly steam pressure) on the amount and type of deposits obtained. Comparisons are made between the test results and feedback/experience of copper fouling in real machines.

Coolant is one of the important factors affecting the overall performance of the intercooler for the intercooled cycle marine gas turbine. Conventional coolants such as water and ethylene glycol have lower thermal conductivity which can hinder the development of highly effective compact intercooler. Nanofluids that consist of nanoparticles and base fluids have superior properties like extensively higher thermal conductivity and heat transfer performance compared to those of base fluids. This paper focuses on the application of two different water-based nanofluids containing aluminum oxide (Al 2 O 3 ) and copper (Cu) nanoparticles in intercooled cycle marine gas turbine intercooler. The effectiveness-number of transfer unit method is used to evaluate the flow and heat transfer performance of intercooler and the thermophysical properties of nanofluids are obtained from literature. Then the effects of some important parameters such as nanoparticle volume concentration, coolant Reynolds number, coolant inlet temperature and gas side operating parameters on the flow and heat transfer performance of intercooler are discussed in detail. The results demonstrate that nanofluids have excellent heat transfer performance and need lower pumping power in comparison with base fluids under different gas turbine operating conditions. Under the same heat transfer, Cu-water nanofluids can reduce more pumping power than Al 2 O 3 -water nanofluids. It is also concluded that the overall performance of intercooler can be enhanced when increasing the nanoparticle volume concentration and coolant Reynolds number and decreasing the coolant inlet temperature.

This paper describes a test program undertaken by the Navy to determine the causes of two problems in the fuel-oil systems of gas turbine engines. The first problem concerns short filter life; the second, copper deposits that cause clogging of fuel-oil nozzles. Results are given for operating experience with va-ious filter units from both laboratory tests and fleet experience. The effect of copper deposits on thermal stability is discussed. The author concludes with a review of remedial actions being taken to solve these problems.

A high pressure fuel coking test apparatus was designed and developed and was used to evaluate thermal decomposition (coking) limits and carbon deposition rates in heated copper tubes for two hydrocarbon fuels, RP-1 and commercial-grade propane. Tests were also conducted using JP-7 and chemically-pure propane as being representative of more refined cuts of the baseline fuels. A parametric evaluation of fuel thermal stability was performed at pressures of 136 atm to 340 atm, bulk fuel velocities in the range 6–30 m/s and tube wall temperatures in the range 422–811 K. In addition, the effect of the inside wall material on deposit formation was evaluated in selected tests which were conducted using nickel-plated tubes. The results of the tests indicated that substantial deposit formation occurs with RP-1 fuel at wall temperatures between 600 and 800 K, with peak deposit formation occurring near 700 K. No improvements were obtained when deoxygenated JP-7 fuel was substituted for RP-1. The carbon deposition rates for the propane fuels were generally higher than those obtained for either of the kerosene fuels at any given wall temperature. Finally, plating the inside wall of the tubes with nickel was found to significantly reduce carbon deposition rates for RP-1 fuel.

Commercially available elements of a composite consisting of a plastic sheet coated with liquid crystal, another sheet with a thin layer of a conducting material (gold or carbon), and copper bus bar strips were evaluated and found to provide a simple, convenient, accurate, and low-cost measuring device for use in heat transfer research. The particular feature of the composite is its ability to obtain local heat transfer coefficients and isotherm patterns that provide visual evaluation of the thermal performances of turbine blade cooling configurations. Examples of the use of the composite are presented.

In an attempt to reduce the cost of testing many configurations of short pin fins in a rectangular channel, a technique has been identified whereby the pins are epoxied to the end wall and can be easily removed to form a new configuration at the end of a test. Analytical and experimental results indicate that the temperature drop across a thin layer of epoxy (∼.005–.006 cm) (K = 22.5 W/m°C) with copper pin and endwalls was less than 1% of the heat transfer surface temperature. The technique was then used to test 4 pin fin configurations of height to diameter ratio of about unity. The heat transfer results showed excellent agreement with earlier published data, thus confirming the validity of this technique.

Turbine compressor coatings are evaluated for use in acidified environments. In such environments, field performance shows poor correlation to results of neutral salt spray tests (ASTM B117). Tests which might better describe these low pH atmospheres are described and the copper accelerated acetic acid salt spray (ASTM B368) is selected as the most useful development tool. In addition, combining CASS exposure with thermal cycling is shown to be a useful procedure to further differentiate coatings for use in acidic environments. It is shown that, unlike the neutral salt spray, in CASS, highly sacrificial (i.e., galvanic) aluminum-filled ceramic overlay coatings fail more rapidly than do non sacrificial materials. Conventional barrier films represented by high performance polymeric coatings are prone to severe blistering in these acidic conditions. Preferred acid resistant coatings are described.