Hongwu Deng

Visualization Experiments of a Specific Fuel Flow Through Quartz-glass Tubes Under both Sub-and Supercritical Conditions

Abstract The present work is a visualization study of a typical kerosene (RP-3) flowing through vertical and horizontal quartz-glass tubes under both sub- and supercritical conditions by a high speed camera. The experiments are accomplished at temperatures of 300-730 K under pressures from 0.107-5 MPa. Six distinctive two-phase flow patterns are observed in upward flow and the critical point of RP-3 is identified as critical pressure pc=2.33 MPa and critical temperature Tc=645.04 K and it is found that when the fluid pressure exceeds 2.33 MPa the flow can be considered as a single phase flow. The critical opalescence phenomenon of RP-3 is observed when the temperature is between 643.16 K and 648.61 K and the pressure is between 2.308 MPa and 2.366 MPa. The region filled by the critical opalescence in the upward flow is clearly larger than that in the downward flow due to the interaction between the buoyancy force and fluid inertia. Morecover, obvious layered flow phenomenon is observed in horizontal flow under supercritical pressures due to the differences of gravity and density.

Effect of Channel Orientation in a Rotating Smooth Wedge-Shaped Cooling Channel With Lateral Ejection

The effect of channel orientation on heat transfers in a rotating wedge-shaped cooling channel is experimentally investigated in current work. In order to perform a fundamental research, all turbulators are removed away. The classical copper plate technique is employed to measure the regional averaged heater transfer coefficients. The inlet Reynolds number and rotational speed range from 5100 to 21000 and zero to 1000rpm respectively, which results in the inlet Rotation number varies from zero to 0.68. In order to study the effect of channel orientation, five different angles are selected in current study. Furthermore, details such as local bulk temperature calculation and local mass flow rate determination are discussed in current paper. A two-dimensional bulk temperature is measured, and a liner mass flow rate distribution is validated indirectly. Due to the experimental results, the most evident rotation effect on heat transfer happens in 90° configuration. Compared to the non-rotating condition, there is about 35% overall heat transfer enhancement under highest rotation number. However, the greatest leading-to-trailing heat transfer difference happens in 135° or 112.5° configuration which depends on Rotation number. The highest difference is up to 40%. Besides, at the realistic 135° channel orientation, a critical Rotation number is observed after which the decreasing trend of heat transfer is traversed. The inlet Rotation is better than local one to describe this critical point. With the inlet parameter, the critical Rotation number is about 0.3 at all the locations in this channel.

Effect of Channel Orientation on Heat Transfer in Rotating Smooth Square U-Duct at High Rotation Number

The effect of channel orientation on heat transfer in a rotating, two-pass, square channel is experimentally investigated in current work. The classical copper plate technique is employed to measure the regional averaged heat transfer coefficients. The inlet Reynolds number and Rotation number range from 25000 to 35000 and 0 to 0.82, respectively. Five different channel angles (−45°, −22.5°, 0°, 22.5°, 45°) are selected to study the effect of channel orientation on heat transfer.In the radially outward flow channel, the surface average heat transfer in β = 0° channel are higher than those in angled-channel (±22.5°, ±45°) on the trailing surface at all Rotation number ranges (0–0.82). While on the leading surface, surface average heat transfer are lower before a critical Rotation number, and turn higher after the critical point. Channel orientations show less influence on heat transfer in the radially inward flow channel.Compared with their corresponding perpendicular channel orientation values (β = 0° channel), heat transfer in angled-channels decrease on the pressure side and increase on the suction side at a relatively lower Rotation number (Ro 0.4), heat transfer in angled-channel decrease on both the leading and trailing walls in the first pass, and increase on both the leading and trailing walls in the second pass. By considering the effect of channel orientations, the relation between critical Rotation number on the leading surface in the first pass and dimensionless location (X/D) obeys a simple rule: (Roc·X/D)·cosβ = 1.31. The trailing-to-leading heat transfer differences induced by rotation increase with the increasing of Rotation number in angled-channel, and they are larger than β = 0° channel after the critical Rotation number in both passages.Copyright

Effect of Channel Orientation in a Rotating Wedge-Shaped Cooling Channel With Pin Fins and Ribs

Experiments are preformed to investigate the effect of channel orientation in a rotating wedge-shaped cooling channel with lateral flow extraction. The test section bears the following characteristics. Staggered ribs are arranged in the inner wide region of the channel, while the pin-fins are located in the outer narrow region. The regionally averaged heat transfer coefficients are obtained to study the characteristics of heat transfer variations in this channel under rotating and non-rotating conditions. The experiments are conducted under four inlet Reynolds numbers (6100, 15000, 25100, 33000), five rotational speeds (0, 300, 500, 800, 1000rpm) and three channel orientations (90°, 135°, 180° angle from the channel symmetry plan to the rotating plan). The inlet rotation number ranges from zero to 0.62. Finally, the experimental data demonstrates that the streamwise heat transfer variations under rotating condition are strongly affected by channel orientation in this configuration. Furthermore, compared with the data under two channel orientation 90° and 180° (the direction of rotation is perpendicular and parallel to the channel symmetry plan), the heat transfer characteristics under 135° configuration, which is regarded as the typical trailing edge orientation, approaches to the 180° one in this rotating channel. An evident critical rotation number, after which the nature of heat transfer changes abruptly, exists under 180° and 135° configuration but not under 90° one.© 2012 ASME

Flow and Heat Transfer in a Rotating and Non-Rotating Wedge-Shaped Cooling Passage with Ribs and Pin Fins

Cooling the trailing edge of a gas-turbine vane/blade typically involves an embedded wedge-shaped duct in a very confined volume, where coolant enters the duct radially and then directed to flow axially by ribs and pin fins to cool the entire trailing-edge region as efficiently and uniformly as possible. CFD simulations based on steady RANS – compressible formulation with temperature-dependent properties closed by the shearstress transport turbulence model – were performed to study the flow and heat transfer in a wedge-shaped duct with ribs and pin fins under rotating and non-rotating conditions. The objective of this study is twofold. The first is to understand the flow mechanisms by which ribs and pin fins turn radially outward flow to flow in the axial direction. The second is to understand what features of the flow and heat transfer obtained under laboratory conditions – where measurements have been made to validate this computational study – can be extrapolated to engine-relevant operating conditions. Results obtained show pin fins judiciously placed around the turn of the wedge-shaped duct to greatly reduce the size of the separated region when the coolant jets radially into the wedge-shaped duct. Also, pin fins provide flow resistance to control the flow direction, and the uniformity of the flow along the cross section of the wedge-shaped duct in addition to enhancing surface heat transfer via horseshoe vortices about each pin fin. The staggered array of ribs along the radial direction of the wedge-shaped duct was found to create up to three sets of recirculating flows that cause the flow entering the duct in the radial direction to spiral towards the axial direction with one created by the stagnation region upstream of each rib, one by the separation at the downstream edge of each rib, and one by the cavity-like flow between the aforementioned recirculating flows. When there is rotation, the staggered array of ribs was found to minimize the adverse effects of centrifugal buoyancy by confining flow separation to be between the ribs on the leading face. On what could be learned under laboratory condition that are meaningful for engine-relevant conditions, all of the aforementioned flow mechanisms are the same and the flow features are qualitatively similar. The exception is the size of the separated region at the tip of the wedge-shaped duct under non-rotating conditions, which is very large for the laboratory condition and very small for the engine-relevant condition.

Interaction of Secondary Flow With Developing, Turbulent Boundary Layers in a Rotating Duct

Investigations of the interaction of secondary flow with developing, turbulent boundary layer in a rotating square-section straight channel have been done in a new rotating facility with normal hot wire anemometry. The measurements are performed with Re=18391 and Ro=0, 0.116, 0.232, respectively, characterized by the channel hydraulic diameter of 80 mm and the bulk mean velocity. Measurements at five stations distributed in the streamwise direction have been done to study the turbulent boundary layer streamwise development. The mean velocity profiles in both ordinary and semi-logarithm coordinates and skin shear velocities at these test stations are obtained. On the leading side, the skin shear velocity firstly decreases, and then increases in the streamwise direction. This phenomenon is analogous to the critical rotation number phenomenon revealed in previous work with heat transfer. Based on this analogy, a new possible explanation of the critical rotation number phenomenon is given here. The semi-logarithm mean velocity profile is found to not obey the traditional log-law linear rotation correction. This suggested the need of a secondary flow strength correction of the log law with system rotation.Copyright

Heat Transfer and Pressure Drop in a Rotating Two-Pass Square Channel With Different Ribs at High Rotation Numbers

Rotation effects on heat transfer and pressure drop in a rotating two-pass square channel with ribs is experimentally investigated. The cooper plate heating technique is applied to obtain the regional average heat transfer coefficients. The Reynolds number and rotation number varies from 10000 to 60000, and 0 to 2.0, respectively. Rib turbulators are placed on the leading and trailing walls of the channel at an angle of 90 deg or 45 deg to the flow direction. The rib pitch-to-height (P/e) ratio is 10 and the height-to-hydraulic diameter (e/Dh) ratio is 0.1 for all tests.The detailed comparisons between smooth wall case and ribbed wall cases are presented. At stationary, increasing the Reynolds number decreases heat transfer and thermal performance ratios, but raises the friction factor ratios dramatically. Rotation shows the strongest effect on heat transfer in smooth case, and then 90 deg rib case, and the least in 45 deg rib case. Channel friction in smooth case is increased by rotation monotonously, but decreases with Ro in ribbed case when Ro increases up to 0.5. The similar thermal performances trends are observed for smooth and ribbed cases at rotation but with different peak point. The 45 deg rib channel has the superior thermal performance because it incurs the highest heat transfer and moderate pressure penalty.Copyright

Experimental Study on Heat Transfer Characteristics to Supercritical Hydrocarbon Fuel in a Horizontal Micro-Tube

Supercritical hydrocarbon fuel experimental loop was constructed at Beihang University to study the heat transfer characteristics to supercritical hydrocarbon fuel. The test section, a stainless tube (1.86mm I.D., 2.26mm O.D., 1Cr18Ni9Ti) with the length of 300mm, was placed horizontally above the ground and the local heat transfer coefficients of the test section were systematically measured at fixed supercritical pressure of 5MPa. The mass flux varied from 786.5 to 1573 kg/ (m2 ·s), with the uniform heat flux from 180 to 450kW/m2 and the inlet fuel temperature ranged from 373 to 673K. The experimental investigation was confined to supercritical flows with heat addition only. Hence, heat losses were measured to be taken into consideration for every experimental condition.The experimental results were analyzed that heat transfer enhances at the reduced temperature Tb/Tpc rising from 0.95 to 1.04 and deteriorates when Tb/Tpc is larger than 1.04. The criterions of Shitman and Jackson were selected to judge the heat transfer characteristics in a horizontal micro-tube. The results indicated that buoyancy effects are ignored as the K<0.01 for the micro-scale tube and thermal acceleration is the main factor for the heat transfer characteristics. By direct comparison with an assortment of experimental data, a new correlation was proposed to be more accurate than others in predicting heat transfer phenomena for Chinese RP-3 hydrocarbon fuel in a horizontal micro-tube.Copyright

Coke Deposition Effect on the Flow Distribution Characteristics of Kerosene Under Supercritical Pressure

Performed experiments have studied the effect of coke deposition on the characteristics of flow distribution of aviation kerosene RP-3 at supercritical pressure. The whole experiment is divided into two steps: 1) making a coke tube; 2) paralleling the coked tube and a regular one with the same scale and observing the flow distribution status in different system pressure and total mass flow rate. The experimental results indicated that the deposition of coke made a great difference on the flow distribution of fuel.Based on experimental results, it’s demonstrated that the percentage of total mass flow rate in coke-free tube increases to 68.5%. Further analyses reveal the fact that the total mass flow rate has nearly no impact on flow distribution and the system pressure also influence the distribution very little. What’s more, the amount of coke vs axial position and total amount of coke in coked tube are mentioned in this paper, which is benefit in analysis of flow distribution.Copyright

Vibration Effects on Surface Coke Deposition of Hydrocarbon Fuel at Supercritical Pressure Condition in Micro-Tubes

Experiments are performed to study vibration effects on surface coke deposition of aviation hydrocarbon RP-3 under supercritical pressure. The flowing RP-3 kerosene is stressed to 5MPa, and heated up from 127°C to 450°C in a stainless tube (1.8mm I.D., 2.2mm O.D., 1Cr18Ni9Ti) with a constant heat flux, and the mass flow rate is 3g/s. The working fluids flow downward through an 1800mm long tube. The vibration frequency is set from 100Hz to 600Hz, covering the main frequencies of the combustion chamber vibration when it works. Compared with stable condition, vibration effects have a distinct impact on the flow resistance and heat transfer.The amount of coke deposition reduced under all different frequencies with the maximize decline of 40.46%. Moreover, restraining efficiency is proportional to the vibration energy. Besides, vibration enhanced the heat transfer, the coefficient of which comes to a wave crest at the zone of second-order modes of response to the peak area with the biggest vibration energy.© 2013 ASME