Heat Transfer Coefficient Ratio Research Articles

CFD Analysis for the Variation of Velocity inside Different Types of Ribs

Abstract: Heat exchanger is used to accomplish the industrial demand. Heat Exchanger are necessary for nuclear reactors and in chemical engineering, for of large quantity of heat is conveying in a slight space with high heat transmission rates and slight habitation time distributions even it suffers through a disadvantage of larger pressure drop. From my analysis, it is found that the uses of ribs inside the solar heat exchanger increase the heat transfer with increase in Reynolds number. Through analysis, it is also found that the value of heat transfer coefficient increases with increase in Reynolds number, heat transfer coefficient is maximum for rectangular shape rib in both the cases that are during using water and nano fluid as a working fluid. The average heat transfer coefficient ratio graph shows that rib used in the solar heat exchanger with nano fluid flow shows more heat transfer enhancement as compared to a solar heat exchanger with simple water flow. Overall it is found that rectangular shape ribs show more heat transfer coefficient as compared to other rib.

Effects of blowing ratio on surface heat transfer characteristics of a transonic turbine squealer blade tip with a double plenum film cooling supply arrangement

Investigated are the effects of blowing ratio on the surface heat transfer characteristics of a film cooled transonic turbine squealer blade tip with a unique double plenum supply arrangement for the coolant. The present configuration is unique because the forward film cooling holes are supplied by an upstream plenum, while the aft film cooling holes are supplied separately by a second downstream plenum. Considered are varying forward blowing ratios as the aft blowing ratio is maintained constant. Nine total blowing ratio combinations are investigated, such that the forward blowing ratio is varied from 1.89 to 3.07, whereas the aft blowing ratio is varied from 0.96 to 1.45. Surface data are provided along the upper pressure side surface and the squealer tip surface of the turbine blade. Included are spatially-resolved and line-averaged distributions of heat transfer coefficient ratio and adiabatic film cooling effectiveness, which vary in a complex manner as upstream and downstream blowing ratios are altered. Local adiabatic film cooling effectiveness distributions evidence good film coverage along the squealer tip surface for all considered blowing ratios, especially for portions of the trailing edge, recess, and pressure side rim regions. Results indicate that the optimal blowing ratio associated with holes supplied by the upstream plenum depends upon the blowing ratio value associated with holes supplied by the downstream plenum.

Conjugate heat transfer of a turbulent tube flow of water and GaInSn with azimuthally inhomogeneous heat flux

An experimental study of the conjugate heat transfer in a turbulent tube flow with azimuthally homogeneous and inhomogeneous heat flux distribution, where the tube is heated with a constant heat flux only over the half circumference, is presented. Using two fluids with clearly different Prandtl numbers (water and a liquid metal alloy), thermohydraulic effects that occur when fluids with very low Prandtl number are used in contrast to ordinary fluids (e.g. water with Pr≈1) are discussed. The test section is validated with water (Pr=5−7.4) for a Reynolds number in the range of 5·103<Re<4.2·104. The experimental data agree excellently with literature data. The maximum nondimensional temperature at the inner surface of the tube is expressed using a simple relationship based on the efficiency of a fin with an adiabatic tip. A near eutectic alloy of gallium, indium and tin (GaInSn, Pr=0.03) is used for the liquid metal experiments. The Péclet number is varied within the range of 240<Pe<3·103. Based on the experimental data of this work, an adapted correlation for the Nusselt number in a turbulent liquid metal tube flow with azimuthally homogeneous heat flux is provided:Nu=4.364+0.0276·Pe0.803The experimental data underlines, that the azimuthally averaged Nusselt number for an azimuthally inhomogeneous heat flux distribution can also be calculated with this correlation with an acceptable level of accuracy. Remarkably, the ratio of the local convective heat transfer coefficient to the azimuthally averaged value for GaInSn reaches a value up to 0.6 at the location of the maximum wall temperature. This is in strong contrast to water, where this ratio is close to unity.

Thermal-hydraulic performance of a plate heat exchanger with grooved copper foam

This study proposes a plate heat exchanger (PHE) partially filled with metal foam having checkered pattern grooves. The study presents new experimental data obtained from PHE with grooved copper foam that elucidates the effect of mass flux, copper foam groove width, and pore density on the heat transfer coefficient (HTC) and pressure drop (ΔP). The testing is conducted with a water mass flux ranging from 120 to 320 kg/m2s, a groove width ranging from 2 to 6 mm, and a pore density of 30 pores per inch (PPI) and 50 PPI. The results demonstrate that HTC and ΔP increase as the copper foam groove width is reduced. Considering the impact of copper foam groove width on the filling rate, the HTC ratio increases significantly at a filling rate between 50 and 75%. Furthermore, an increase in pore density enhances HTC and ΔP. The plate heat exchanger inserted with copper foam (PHE_CF) provides the optimum thermal-hydraulic performance (TP). However, at a low Reynolds number, the results show that TP of PHE with grooved copper foam with a groove width of 2 mm is similar to PHE_CF. New correlations are also proposed to predict ΔP and HTC in the practical applications.

Numerical study of leakage characteristics of hydrogen-blended natural gas in buried pipelines

Pipeline transportation of hydrogen-blended natural gas is susceptible to leakage or rupture accidents caused by pipeline construction, corrosion, and hydrogen embrittlement, posing significant threats to the environment, human safety, and property. This paper improves the model of non-adiabatic pipeline leakage to study the flow characteristics of hydrogen-blended natural gas leakage, and its accuracy is validated using OLGA software and experiment data. The impact of the heat transfer coefficient, initial pressure and hydrogen blending ratio on the leakage flow characteristics is also analyzed. The findings indicate that the initial pressure in the pipe increases linearly at 0.5 MPa and the mass leakage velocity decreases linearly at a rate of nearly 9 kg/s; meanwhile, the temperature drop in the pipe and the overall leakage time increase. An increased hydrogen blending ratio corresponds to lower mass leakage velocity and shorter leakage time. The maximum dangerous distance of pure methane pipeline leakage is greater than that of a pure hydrogen pipeline. Furthermore, changes in the heat transfer coefficient predominantly affect the temperature inside the pipe.

Analysis of transport phenomena on cooling a flat surface using swirl jet impingement with crossflow

Enhancing airside convective heat transfer is a challenging problem due to the poor thermal properties of air and the high thermal resistance of the thermal boundary layer. This study presents an innovative method to improve the convective heat transfer of cross airflow over a flat plate using a Swirl jet to suppress the boundary layer thus reducing the thermal resistance. A three-dimensional numerical analysis was performed to study the transport phenomena that occur when a swirl air jet is issued perpendicular to a crossflow of air flowing over a hot flat plate. The finite element method with SST k-ω turbulence model was employed for this numerical study after validation with experimental data from the literature. A parametric study was performed by varying Reynolds number of the jet, Rej(2500−10000), dimensionless jet to plate spacings, Z/D(1−2), swirl number, SW(0.3−0.9), and blockage ratios, BR(0.4−0.6). The thermal performance was assessed by the average heat transfer coefficient, h‾j, in addition to the ratio of heat transfer coefficient between the proposed setup involving crossflow with jet to the reference case of crossflow without jet, h‾j/h‾woj, thus, a correlation is obtained for the average heat transfer coefficient. The friction factor, f, and the pumping power were used to evaluate hydraulic performance. The performance evaluation coefficient, PEC, was chosen to identify the best possible thermal and hydraulic performance. Results show that for all the cases under study, there is a clear enhancement of the heat transfer coefficient when employing a combination of swirl jet with crossflow over a flat plate compared to the case of crossflow without jet. The maximum value of PEC was 1.8 occurring at Reynolds number, Rej, of 10000, swirl number of 0.9, blockage ratio of 0.6, and jet-to-plate spacing of 2D.

Bifurcated divergent microchannel heat sinks for enhanced micro-electronic cooling

The thermal performance of microchannel heat sinks (MHSs) can be enhanced by utilizing extended surfaces such as pin fins, ribs, and bifurcation plates. Extended surfaces, however, adversely affect the hydraulic performance of the MHSs. Divergent microchannels, on the other hand, offer higher hydraulic performances but lower thermal performances than parallel microchannels. Here, bifurcated divergent MHSs are studied to examine the opposing effects of bifurcation and divergence on the thermo-hydraulic performance. Bifurcation plates with constant cross-section, variable width, and variable height are considered. Results showed that the pressure drop penalty and average heat transfer coefficient of bifurcated divergent MHSs are lower than the parallel MHSs. Considering the performance index (PI) defined as the ratio of heat transfer coefficient to pressure drop penalty, the bifurcated divergent microchannels outperform the parallel MHSs. Results also revealed that increasing the width of the bifurcation plate in the flow direction decreases the overall performance of the bifurcated divergent microchannels. The divergent bifurcation microchannels with a variable height bifurcation plate outperform the ones with a constant cross-section bifurcation plate. This study confirms the advantage of bifurcated divergent microchannels for increasing the cooling performance of the MHSs.

Effects of dusting film cooling placement and configuration on surface heat transfer characteristics of a transonic turbine squealer blade tip

Investigated are the effects of dusting hole film cooling placement and configuration on the surface heat transfer characteristics of a transonic turbine squealer blade tip. Three different blade tip arrangements are investigated, which are denoted C1, C2, and C3. Data are provided which include spatially-resolved and line-averaged distributions of heat transfer coefficient ratio and adiabatic film cooling effectiveness. The University of Alabama in Huntsville SS/TS/WT (supersonic/transonic/wind tunnel) blow down facility is employed with a transonic test section containing a five blade linear cascade for the investigation. Spatially-resolved surface heat transfer characteristics are measured using time- and spatially-resolved infrared thermography, in conjunction with an impulse response transient measurement procedure. Film coolant is supplied with a carbon dioxide injection system. Results indicate that heat transfer coefficient and adiabatic film cooling effectiveness distributions vary significantly as dusting hole placement and configuration are altered. For example, heat transfer coefficients for the C1 and C2 blade configurations are substantially lower, compared to baseline values with no film cooling, within the squealer recess region downstream of the dusting holes. Smaller heat transfer coefficient deviations, relative to baseline values, are present when the C3 configuration is employed. In general, distributions and magnitudes of local adiabatic film cooling effectiveness indicate that all three dusting hole configurations provide reasonably good film coverage within portions of squealer recess regions. For downstream portions of the blades, the C1 and C3 configurations both provide good surface protection which are indicated by film cooling effectiveness values, whereas coverage provided by the C2 arrangement ends abruptly at the location of a structural rib which is located within the squealer recess region.

Effects of pressure side film cooling hole placement and condition on surface heat transfer coefficients along a transonic turbine blade tip

Considered is thermal performance for the squealer blade tip of four film cooling configurations, B1, B2, B3 and B4, with hole exits for each arrangement positioned along a different portion of the upper pressure side of a transonic turbine blade. Each upper pressure side configuration includes five film cooling holes, such that each hole has a compound angle of 45° with respect to the circumferential/axial plane, also with an angle orientation of 40° relative to the plane tangent to the exit cross sectional area of each hole. Results are given for blowing ratios ranging from 0.42 to 3.20 in the form of spatially-resolved and spatially-averaged surface distributions of heat transfer coefficients and heat transfer coefficient ratios. In regard to tip surface variations, surface heat transfer coefficient ratios distributions are a consequence of the manner in which the film coolant collects in a substantial manner along the pressure side rim and then advects above and across the squealer recess with little to no coolant collecting within the cavity, or along the recess surface, to then collect in a substantial manner further downstream along the suction side rim. Such flow characteristics affect heat transfer coefficient ratio variations for all four film cooling configurations, but are especially influential for the B3 arrangement. Considering local heat transfer coefficient ratio distributions along the upper pressure side surface, the most significant local variations in the vicinity of a film cooling hole exit locations. Here, heat transfer coefficient ratio distributions for the B1 and the B4 configurations, in particular, show evidence of a horseshoe-shaped vortex which forms around each emerging coolant concentration. The two downstream legs of each vortex are associated with a pair of locally augmented heat transfer coefficient streaks, often with a streak of locally-lower coefficient ratios positioned between. Local and line-averaged heat transfer coefficient ratios along the upper pressure side also vary significantly with blowing ratio, with additional periodic variations as the normalized circumferential/axial coordinate varies. Within the resulting distributions, local heat transfer coefficient ratio increases are associated with locally augmented mixing and turbulent transport, which are especially present near the exits of different film cooling hole locations.

Condensation characteristics of air–water vapor mixture on the surface of vertical flat plate

The condensation heat transfer of air–water mixed vapor is an important heat transfer phenomenon in production life. An experimental system for condensation heat transfer of the air–water vapor mixed vapor is built in this paper. The condensation characteristics of the mixed vapor and the double boundary layer structure characteristics were investigated. The study mainly discussed the influence of flow velocity on the condensation performance of mixed vapor and summarized the experimental correlation equations considering flow velocity. Results indicate that the condensation performance decreases significantly as the air concentration increases. The mixed vapor flow velocity was increased from 1 to 3 m/s, and the condensation heat transfer coefficient was increased by 34.9–121.0%. The enhanced effect of flow velocity was also observed at high air concentration and low subcooling. The ratio of convective and condensation heat transfer coefficients increases with the rise in air concentration, reaching a maximum of 0.12. The proportion of convective heat transfer can be reduced by increasing the mixed vapor flow velocity. The gas film thickness is substantially higher than the liquid film thickness in mixed vapor condensation, and the gas/liquid film thermal resistance ratio can be more than 30 times. And increasing the flow velocity can significantly reduce the gas film/liquid film thermal resistance ratio. A new experimental correlation equation is fitted based on the experimental results, and this equation can be used as a reference for the design of related heat exchangers.

Film cooling improvement of dovetail hole compared to cylindrical hole at different hole row locations on nozzle guide vane

The profile curvature and boundary layer flow pattern at different positions of nozzle guide vane of aero engine resulted in the improvement differences in the film cooling performance of the shaped hole. In this paper, the two-dimensional distributions of temperatures of wall surface downstream single row of dovetail hole and cylindrical hole were examined at four typical locations by infrared thermal imaging technology in the linear cascade. The film effectiveness, heat transfer coefficient and heat flux ratio were analyzed. The results show that the improvements of spanwise averaged film effectiveness become small in the main-stream direction. At blowing ratios of 1.0–2.0, the improvements of film effectiveness are 92.3%–177.8% at SS1 location, 53.8%–75.1% at SS2 location, 42.6%–79.2% at PS1 location and 206.4%–388.4% at PS2 location, respectively. Heat transfer coefficients reduced by film cooling are found near the hole on the suction side. Heat transfer coefficient ratios increase on the suction side and slightly decrease on the pressure side in the mainstream direction. The maximum improvement based on film effectiveness occurs at the PS2 position, while the most effective improvement based on the heat flux ratio occurs at the SS1 position.

Effect of Heat Transfer Medium and Rate on Freezing Characteristics, Color, and Cell Structure of Chestnut Kernels

This paper compared the effects of air and nitrogen on the freezing characteristics, color, and cell structures of chestnut kernels at different rates of heat transfer and adopted liquid nitrogen spray quick-freezing (NF-40 °C/-60 °C/-80 °C/-100 °C) and still air freezing (AF-20 °C/-40 °C) as the freezing methods. The ratio of heat transfer coefficients in N2 groups was two times as high as those in air groups, and NF-100 °C and NF-80 °C showed better freezing characteristics, good protection for cytoskeletons, and the color was similar to those of the fresh group. Taking both Multivariate Analysis of Variance (Principal Components Analysis and Cluster Analysis) and economic factors, NF-80 °C can be used as a suitable method for chestnut kernel freezing. When the ambient freezing temperature was lower than Tg, both NF and AF treatment groups presented poor quality. The rate and medium of heat transfer jointly influenced the freezing characteristics and quality. The former had a greater effect than the latter, however.

Experimental study on suppressing heat transfer deterioration of supercritical CO2 in vertical tubes based on Helmholtz oscillator

Heat transfer deterioration of supercritical CO2 (S-CO2) heated in gas heaters influences the efficiency and safe operation of the trans-critical CO2 system due to local high temperatures. To suppress the heat transfer deterioration of S-CO2, three Helmholtz oscillators with different nozzle diameters are designed and applied to the inlet of the heated vertical tube. The heat transfer characteristics of S-CO2 heated in the smooth tube and the smooth tube with Helmholtz oscillators are investigated at the mass fluxes from 144 to 750 kg/(m2·s), the heat fluxes from 23.0 to 128.1 kW/m2, the inlet temperatures of 15.0 and 25.0 °C, and the fixed pressure of 8.0 MPa. The results show that the heat transfer deterioration observed in the smooth tube is significantly inhibited by the Helmholtz oscillator. At G ≥ 400 kg/(m2·s), the ratio of local heat transfer coefficient and the thermal performance evaluation factor can be up to 9.86 and 3.09, respectively. The pulsating flow generated by the Helmholtz oscillator strengthens the mutual disturbance between near-wall fluid and the core fluid, resulting in more uniform thermophysical properties of S-CO2 in the radial direction and a much weaker buoyancy effect. In addition, the influence of the downstream nozzle diameter on the heat transfer characteristics of S-CO2 is more significant than that of the upstream nozzle diameter in the present study. Finally, a new empirical heat transfer correlation of S-CO2 in the smooth tube with Helmholtz oscillator is proposed, which takes into account the effect of the thermophysical properties of CO2 and the structure parameters of the Helmholtz oscillators with an accuracy of ±20 %.

Thermal analysis on the evaporation of fluid covered by porous media subjected to ultrasound and air jet impingement

The porous layer subjected to air jet is set above fluid passing through heating surface to control its thickness and avoid drying up, as well as ultrasound is introduced at upstream to enhance convection in flowing channel, in which heat flux can be dispersed in convection between fluid and heating surface as well as evaporation on the outside surface of porous cover to the outside. Local thermal equilibrium (LTE) occurs in porous cover, and the effect of sound pressure from ultrasound on liquid fluid is introduced according to acoustic theory. Brinkman–Forchheimer extended Darcy equations and k-ε turbulent model together with the above formulas are employed to describe the heat transfer in fluid covered by porous media subjected to ultrasound and air jet impingement. The effects of ultrasound power and frequency, fluid layer thickness as well as porosity and particle size in porous cover on heat transfer are investigated. The performance evaluation criteria (PEC) is defined to evaluate thermal characteristics in the cases with ultrasound than those without. The 35.7% rise ratio of heat transfer coefficient in the mode with ultrasound power of 50 W happens than that without. The higher ultrasound power and lower frequency of ultrasound cause lower heating surface temperature and larger heat transfer coefficient. The simulations agree with available published experiment data. All results of this study can be considered into utilization of ultrasound and porous layer to enhance heat transfer in flowing channel.

Effect of plate spacing and inclination angle over the thermal performance of plate heat exchanger working with novel stabilized polar solvent-based silicon carbide nanofluid

In this work, the overall thermal performance of a commercial corrugated plate heat exchanger has been conducted for the first time by varying the three different plate corrugated angles (30°, 45°, 60°) and variable plate spacing (from 5 mm to 20 mm) working with polar solvent-based novel Silicon carbide (SiC)/DI Water nanosuspension as a coolant by focusing potential industrial application. This study aimed to identify the enhancement in thermal performance of plate heat exchanger by evaluating its overall heat transfer coefficient, pressure drop, pumping power, and exergetic efficiency by utilizing SiC/DI water nanofluid of varying volume concentration (0.20 %, 0.40 %, 0.60 %, 0.80 %, 1.00 %, 1.20 %, and 1.40 %) at ambient condition (T0 = 27 ° C), and fixed volumetric flow rate (3 L/min) for both (nanofluid and milk) sides. From the experimental results, the optimum volume concentration for the coolant was found as 0.60 %, which yields a significant enhancement in the overall heat transfer coefficient ratio by approximately 51 %, 42 %, and 38 % for 60°, 45°, and 30° corrugated plate angle respectively. The significant enhancement for 0.6 % of optimum volume concentration and 5 mm plate spacing has been reported as the best possible option at which the pumping power ratio, performance index ratio, and exergetic efficiency ratio attained the highest enhancements.

Study of the Technologies for Freeze Protection of Cooling Towers in the Solar System

A cooling tower is an important guarantee for the proper operation of a solar system. To ensure proper operation of the system and to maintain high-efficiency points, the cooling tower must operate year-round. However, freezing is a common problem that degrades the performance of cooling towers in winter. For example, the air inlet forms hanging ice, which clogs the air path, and the coil in closed cooling towers freezes and cracks, leading to water leakage in the internal circulation. This has become an intractable problem that affects the safety and performance of cooling systems in winter. To address this problem, three methods of freeze protection for cooling towers are studied: (a) the dry and wet mixing operation method—the method of selecting heat exchangers under dry operation at different environments and inlet water temperatures is presented. The numerical experiment shows that the dry and wet mixing operation method can effectively avoid ice hanging on the air inlet. (b) The engineering plastic capillary mats method—its freeze protection characteristics, thermal performance, and economics are studied, and the experiment result is that polyethylene (PE) can meet the demands of freeze protection. (c) The antifreeze fluid method—the cooling capacity of the closed cooling towers with different concentrations of glycol antifreeze fluid is numerically studied by analyzing the heat transfer coefficient ratio, the air volume ratio, the heat dissipation ratio, and the flow rate ratio. The addition of glycol will reduce the cooling capacity of the closed cooling tower.

Dusting Hole Film Cooling Heat Transfer on a Transonic Turbine Blade Tip

Investigated is a transonic turbine blade tip with a squealer rim and a squealer recess, with a single dusting film cooling hole contained within the leading edge region of the squealer recess. Data are provided for transonic flow conditions for a range of film cooling blowing ratios for two tip gap values, using a linear cascade, with no relative motion between the blade and the casing. Surface heat transfer characteristics are measured using the transient impulse-response measurement approach, employed with infrared thermography. Line-averaged adiabatic film cooling effectiveness values, for the 1.4 mm tip gap, are generally very small along the pressure side rim, with only small, locally increased values along the suction side rim. For the 0.8 mm tip gap, line-averaged adiabatic film cooling effectiveness values are generally somewhat higher along the pressure side rim and along the suction side rim. In general, effectiveness values for both tip gap values, for these locations, and for the recess region, increase as the blowing ratio increases. As the tip gap decreases from 1.4 mm to 0.8 mm, line-averaged adiabatic film cooling effectiveness generally increases on the rims and downstream regions of the recess, with increased magnitudes which are spread over larger spatial surface areas. For tip gaps of 0.8 mm and 1.4 mm, for regions where the line-averaged heat transfer coefficient ratio deviates significantly from 1.00, values generally decrease as the blowing ratio increases. Across every region of the blade, line-averaged heat transfer coefficient ratios either decrease or remain approximately invariant, as the tip gap value decreases from 1.4 mm to 0.8 mm.

Heat transfer and pressure drop correlations for a gas flow in unidirectional porous copper tubes

In this study, to develop a heat exchanger having small-scale and high performance, the heat transfer performance and the pressure drop in a gas flow are evaluated for six types of unidirectional porous copper tubes fabricated by explosive compaction. Furthermore, correlation equations for the effective heat transfer coefficient and the friction factor are constructed. The maximum enhancement ratio of the effective heat transfer coefficient in the porous copper tubes is four times as high as a swirl tube, which is a typical heat transfer promoter. The performance of these porous tubes becomes high with increasing the Reynolds number based on the superficial velocity. The correlation equation for effective heat transfer coefficient can predict with the error within ±10% regarding 70% of obtained experimental data, that for the friction factor is high accuracy regarding when the number of pores is relatively small and the pore diameter is relatively large.

Surface film cooling characteristics of rectangular holes along the trailing edge of a transonic turbine blade tip

The present study investigates film cooling in the trailing edge region of a transonic turbine blade tip, with an arrangement which is significantly different from all previous blade tip investigations. In particular, five rectangular film cooling holes, located along the tip near the blade trailing edge and positioned downstream of a squealer recess region, are employed. Each film cooling hole is oriented at a 45° angle relative to the blade tip surface. Heat transfer coefficient ratio data, and adiabatic film cooling effectiveness data are provided for two tip gaps over a range of blowing ratios. Tip gap magnitudes are 1.4 mm and 0.8 mm, which correspond to 1.16% and 0.66% of the true blade span, respectively. Surface heat transfer characteristics are measured using a transient impulse-response approach with infrared thermography. Along most of the trailing edge tip surface, adiabatic film cooling effectiveness values are locally augmented for all blowing ratios BR and for both tip gaps considered, which evidences substantial film coolant concentrations near the blade tip surface. Local values of adiabatic film cooling effectiveness often increase with increasing blowing ratio and are consistently higher for the smaller tip gap. In general, only minor differences between the 0.8 mm and 1.4 mm tip gap heat transfer coefficient ratio data sets are present, with marginally higher values of heat transfer coefficient ratios for the smaller tip gap. Together, heat transfer coefficient ratio and adiabatic film cooling effectiveness data suggest that the thermal protection offered by the 0.8 mm tip gap along the trailing edge tip region is superior to that of the 1.4 mm tip gap for a range of blowing ratios.

Investigation on overall performance of double-jet film cooling holes with various spanwise distance

The overall film cooling performances of double-jet film cooling (DJFC) holes on a flat plate were evaluated experimentally and numerically including the film cooling effectiveness (η), heat transfer coefficient (HTC) ratio, as well as the net heat flux reduction (NHFR) parameter. The spanwise distance (p/d) varied as 0.5, 1.0, 1.5, and the streamwise distance (s/d) was kept as 3.0. Results show that p/d = 0.5 has the highest cooling effectiveness and the highest net heat flux reduction parameter among all configurations. When the blowing ratio is low, all the DJFC configurations have high film cooling effectiveness and positive NHFR values. However, the NHFR becomes negative for the cases of p/d = 1.0, 1.5 at high blowing ratios, which means the increased heat flux is larger than the case without film cooling. From the flow field, film effectiveness distribution is largely affected by the anti-kidney vortex which is relevant to p/d and blowing ratios (M). The heat transfer coefficient ratio profile is mainly connected to the turbulent kinetic energy (TKE) enhanced by the jet interaction.