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The present study investigates the local heat (mass) transfer characteristics of flow through perforated plates. Two parallel perforated plates were placed, relative to each other, in either staggered, in line, or shifted in one direction. Hole length to diameter ratio of 1.5, hole pitch to diameter ratio of 3.0, and distance between the perforated plates of 1-3 hole diameters are used at hole Reynolds numbers of 3000 to 14,000. For flows through the staggered layers and the layers shifted in one direction, the mass transfer rates on the surface of the effusion plate increase approximately 50% from impingement cooling alone and are about three to four times that with effusion cooling alone (single layer). The high transfer rate is induced by strong secondary vortices formed between two adjacent impinging jets and flow transition so that heat/mass transfer coefficient in the midway region is as high as stagnation heat/mass transfer coefficient. The mass transfer coefficient for the in-line arrangement is approximately 100% higher on the target surface than that of the single layer case. In overall, the staggered hole arrangement shows better performance than other cases.

The secondary, flows, including passage and other vortices in a turbine cascade, cause significant aerodynamic losses and thermal gradients. Leading edge modification of the blade has drawn considerable attention as it has been shown to reduce the secondary flows. However, the heat transfer performance of a leading edge modified blade has not been investigated thoroughly. Since a fillet at the leading edge blade is reported to reduce the aerodynamic loss significantly, the naphthalene sublimation technique with a fillet geometry is used to study local heat (mass) transfer performance in a simulated turbine cascade. The present paper compares Sherwood number distributions on an endwall with a simple blade and a similar blade having a modified leading edge by adding a fillet. With the modified blades, a horseshoe vortex is not observed and the passage vortex is delayed or not observed for different turbulence intensities. However, near the blade trailing edge the passage vortex has gained as much strength as with the simple blade for low turbulence intensity. Near the leading edge on the pressure and the suction surface, higher mass transfer regions are observed with the fillets. Apparently the corner vortices are intensified with the leading edge modified blade.

The naphthalene sublimation technique is used to investigate the development of Taylor-Gortler vortices over the pressure surface of a simulated high performance turbine blade. In the presence of external disturbances such as high freestream turbulence or a boundary layer trip, no Taylor-Gortler vortices are observed.

Local mass transfer measurements on a simulated high-pressure turbine blade are conducted in a linear cascade with tip clearance, using a naphthalene sublimation technique. The effects of tip clearance (0.86-6.90% of chord) are investigated at an exit Reynolds number of 5.8 X [10.sup.5] and a low turbulence intensity of 0.2%. The effects of the exit Reynolds number (4 - 7 X [10.sup.5]) and the turbulence intensity (0.2 and 12.0%) are also measured for the smallest tip clearance. The effect of tip clearance on the mass transfer on the pressure surface is limited to 10% of the blade height from the tip at smaller tip clearances. At the largest tip clearance high mass transfer rates are induced at 15% of curvilinear distance ([S.sub.p]/C) by the strong acceleration of the fluid on the pressure side into the clearance. The effect of tip clearance on the mass transfer is not very evident on the suction surface for curvilinear distance of [S.sub.s]/C

Local mass transfer measurements were conducted on the tip of a turbine blade in a five-blade linear cascade with a blade-centered configuration. The tip clearance levels ranged from 0.6 to 6.9% of blade chord. The effect of relative motion between the casing and the blade tip was simulated using a moving endwall made of neoprene mounted on the top of the wind tunnel. Data were obtained for a single Reynolds number of 2.7 x [10.sup.5] based on cascade exit velocity and blade chord. Pressure measurements indicate that the effect of endwall motion on blade loading at a clearance of 0.6% of blade chord is to reduce the pressure gradients driving the tip leakage flow. With the introduction of endwall motion, there is a reduction of about 9% in mass transfer levels at a clearance of 0.6% of chord. This is presumably due to the tip leakage vortex coming closer to the suction side of the blade and 'blocking the flow,' leading to reduced tip gap velocities and hence lower mass transfer. [DOI: 10.1115/1.1554411]

An experimental investigation has been performed to measure average and local mass transfer coefficients on the tip of a gas turbine blade using the naphthalene sublimation technique. The heat/mass transfer analogy can be applied to obtain heat transfer coefficients from the measured mass transfer data. Flow visualization on the tip surface is provided using an oil dot technique. Two different tip geometries are considered: a squealer tip and a winglet-squealer tip having a winglet on the pressure side and a squealer on the suction side of the blade. Measurements have been taken at tip clearance levels ranging from 0.6 to 3.6% of actual chord. The exit Reynolds number based on actual chord is approximately 7.2 X [10.sup.5] for all measurements. Flow visualization shows impingement and recirculation regions on the blade tip surface, providing an interpretation of the mass transfer distributions and offering insight into the fluid dynamics within the gap. For both tip geometries the tip clearance level has a significant effect on the mass transfer distribution. The squealer tip has a higher average mass transfer that sensibly decreases with gap level, whereas a more limited variation with gap level is observed for the average mass transfer from the winglet-squealer tip.

A special naphthalene sublimation technique is used to study the film cooling performance downstream of one row of holes of 35 deg inclination angle with 3d hole spacing and relatively small hole length to diameter ratio (L/d= 6.3). Both film cooling effectiveness and mass/heat transfer coefficient are determined for blowing rates from 0.5 to 2.0 with density ratio of 1.0. The mass transfer coefficient is measured using pure air film injection, while the film cooling effectiveness is derived from comparison of mass transfer coefficients obtained following injection of naphthalene-vapor-saturated air with those from pure air injection. This technique enables one to obtain detailed local information on film cooling performance. The laterally averaged and local film cooling effectiveness agree with previous experiments. The difference between mass/heat transfer coefficients and previous heat transfer results indicates that conduction error may play an important role in the earlier heat transfer measurements.

The naphthalene sublimation technique is used to investigate the influence of high free-stream turbulence with large length scale on the heat/mass transfer from a turbine blade in a highly accelerated linear cascade. The experiments are conducted at four exit Reynolds numbers, ranging from 2.4 x [10.sup.5] to 7.8 x [10.sup.5], with free-stream turbulence of 3, 8.5, and 18 percent and corresponding integral length scales of 0.9 cm, 2.6 cm, and 8 cm, respectively. On the suction surface, the heat/mass transfer rate is significantly enhanced by high free-stream turbulence due to an early boundary layer transition. By contrast, the transition occurs very late, and may not occur at very low Reynolds numbers with low free-stream turbulence. In the turbulent boundary layer, lower heat/mass transfer rates are found for the highest free-stream turbulence level with large length scale than for the moderate turbulence levels with relatively small scales. Similar phenomena also occur at the leading edge. However, the effect of turbulence is not as pronounced in the laminar boundary layer.

Convective heat/mass transfer near and within the entrance region of film cooling holes supplied with air from an internal duct (plenum) behind the cooling holes has been measured using a naphthalene sublimation technique. The experiments are conducted for duct Reynolds number, based on the duct inlet flow condition, of 1800 to 13,500, which results in a range of hole Reynolds numbers of 8000 to 30,000, close to actual engine operating conditions. The flow entering the hole can be considered a combination of flow along a 90 deg tube bend and a sudden contraction duct flow. The flow separates at the inner corner and a secondary flow is induced by the centrifugal force associated with the streamline curvature. The mass transfer coefficient for the duct wall (surface of film-cooled plate) with a cooling hole is three to five times higher than for a fully developed duct flow. With a smaller duct, the overall transfer coefficient on the hole entrance surface increases due to the higher duct Reynolds numbers, but the flow has less secondary flow effects within the smaller space. Generally, transfer coefficients on the hole entrance surface are largely Unaffected by the duct end presence, but the transfer coefficient is larger downstream for a short distance from the center of the last hole to the duct end. In tests with multiple film cooling holes, the flow at the first hole is more of a curved duct flow (strong secondary flow) and the flow at the last hole is more of a sink-like flow. At the middle hole, the flow is a combination of both flows. The mass transfer rates on the inner hole surfaces are found to be the same for holes with corresponding positions relative to the duct end, although the total number of open holes is different.

Film cooling effectiveness data are presented against a backdrop of ammonia-diazo flow visualizations for row-of-holes injection along a convex wall and a concave wall at angles of 15, 25, and 45 deg to the mainstream and at density ratios of approximately one and two. Injection angle effects vary with the rate of injection: At low blowing rates the injection angle is unimportant, at moderate blowing rates the shallower angles provide better effectiveness, and at high blowing rates a steeper injection angle sometimes provides better effectiveness. The condition of the local boundary layer, the severity of jet lift-off, and the strength of vortex interactions among the bound vortices of neighboring jets are key considerations in interpreting the data.

A critical vent area below, where ventilation is poor below and air flow is minimal above, exists in the air venting system in pressure die casting. Geometry and the filling time determine such critical area. The critical area is also a tool to 'combine' the actual vent area with the resistance in the vent to the air flow, with the compressibility of the gas flow factored in.

The present study investigates heat/mass transfer for flow through perforated plates for application to combustor wall and turbine blade film cooling. The experiments are conducted for hole length-to-diameter ratios of 0.68 to 1.5, for hole pitch-to-diameter ratios of 1.5 and 3.0, for gap distance between two parallel perforated plates of 0 to 3 hole diameters, and for Reynolds numbers of 60 to 13,700. Local heat/mass transfer coefficients near and inside the cooling holes are obtained using a naphthalene sublimation technique. Detailed knowledge of the local transfer coefficients is essential to analyze thermal stress in turbine components. The results indicate that the heat/mass transfer coefficients inside the hole surface vary significantly due to flow separation and reattachment. The transfer coefficient near the reattachment point is about four and half times that for a fully developed circular tube flow. The heat/mass transfer coefficient on the leeward surface has the same order as that on the windward surface because of a strong recirculation flow between neighboring jets from the array of holes. For flow through two in-line layers, the transfer coefficient affected by the gap spacing is approximately 100 percent higher on the windward surface of the second wall and is about 20 percent lower on the inside hole surface than that with a single layer. The transfer coefficient on the leeward surface is not affected by upstream flow conditions due probably to strong recirculation in the wake flow.

Fluids in motion can separate into regions of higher and lower energy (temperature); this is called 'energy separation.' The present study concerns the mechanism of energy separation in a free, circular, air jet, including the effects of acoustic excitation. Starting with the initial energy separation occurring in the boundary layer inside the nozzle, the energy separation in a jet begins to be affected by the action of vortices from an axial location, measured from the jet exit, of about 0.3D (D is the diameter of nozzle exit), becomes intensified at about 0.5D, begins to be diffused from about 1D, and there is no discernible energy separation at about 14D. The entrainment of the ambient fluid considerably affects the energy separation, and its effects appear at axial locations between about 6D and 8D. The present definition of the energy separation factor renders its distribution independent of the jet Reynolds number; except for axial locations between about 0.3D and 4D. The development of energy separation in the region close to the nozzle exit is faster when the jet Reynolds number is higher. Acoustic excitation not only enhances the energy separation, but also accelerates its diffusion. This effect is greatest for axial locations between about 1D and 4D. The fact that the acoustic excitation has a strong effect on the vortex structure and the energy separation provides good evidence that the convective movement of vortices is the cause of energy separation in jets.

Multifunctional characteristics of die casting parts are significantly compromised by the presence of voids, which can result in a substantial decrease in the elastic moduli and thermal conductivity. Gas/air porosity constitutes a large part of the total porosity. To reduce the porosity due to the gas/air entrainment, a vacuum can be applied to remove the residual air in the die. In some cases vacuum castings have low porosity, while in other cases the results are not satisfactory. These differing results can be explained in some instances by an analysis of the vent area. A simple model is proposed based on conservation laws which describes the relationship between vent area and pressure variation in the die. The analysis of vacuum venting indicates that there is a critical/optimum vent area below which the ventilation is poor and above which the resistance to the air flow is minimal. The model yields a simple equation to select the optimum area which is a function of the duct resistance, the evacuated volume, and the filling time. This result should be useful to the design engineer. The result also provides a tool to 'measure' the vent size for numerical simulations of the cavity filling, taking into account the compressibility of the gas.

Convection in a thick, initially uniform, horizontal fluid layer, subjected to constant flux from below, starts at a constant critical Rayleigh's number. The critical wavenumber is 2.2. The turbulent convection bears a definite structure, with a permanent boundary layer. Convection at the heated surface begins with a cellular pattern similar to Benard cells. Ultimately, a quasi-steady state forms, in which the cell pattern breaks down and only the slow moving warm lines remain. These lines are the source of plumes and thermals, which break away from plumes at higher heat fluxes.

An experimental evaluation of the flow patterns and mass transfer through a rectangular cylinder array reveals that the flow pattern is asymmetric and that mass transfer on the short wake cylinders is less than that on the leeward surface of the long wake cylinders. The arrangement of the long and short wakes is even and periodic, and their position is changeable in each cylinder. The air flow on the side surfaces of short wake cylinders detaches and reattaches, causing a high mass transfer.

A naphthalene sublimation technique is employed to study the mass transfer distribution on the suction (convex) surface of a simulated turbine blade. Comparison with a heat transfer study shows good agreement in the general trends in the region of two-dimensional flow on the blade. Near the endwall, local convective coefficients on the suction surface are obtained at 4608 locations from two separate runs. The secondary flows in the passage significantly affect the mass transfer rate on the suction surface and their influence extends to a height of 75 percent of the chord length, from the endwall, in the trailing edge region. The mass transfer rate in the region near the endwall is extremely high due to small but intense vortices. Thus, a large variation in the mass transfer distribution occurs on the suction surface, from a mass transfer Stanton number of 0.0005 to a maximum of 0.01. In the two-dimensional flow region, the mass transfer distributions at two different Reynolds numbers are presented.

Metoprolol is a drug that affects heart function and is used to treat high blood pressure. It has been made available in a slow-release system, OROS (oral osmotic system), which looks like a normal tablet and is taken once daily. Metoprolol OROS is medically effective and provides less variable blood levels of the drug than conventional oral doses. The safety and tolerability of metoprolol in doses from 100 to 600 milligrams daily have been investigated in 114 people with mild to moderate hypertension, 66 of whom were men. The medication was effective; 85 percent of patients had their hypertension controlled with doses of 100 to 400 milligrams. Side effects, generally mild, were experienced by 29 percent of patients. Patients who withdrew from the study were receiving different doses of the drug, so that adverse effects were apparently not dose-related. Side effects included nausea, dizziness, fatigue, headache, edema (water retention), and insomnia, which are common with this type of drug. The study indicates that metoprolol OROS is safe and well-tolerated during the treatment of hypertension. (Consumer Summary produced by Reliance Medical Information, Inc.)