Experiments were performed to characterize a two-layer oscillating heat pipe in a heat spreading plate heated locally on one side and cooled throughout the other side. The 23-turn oscillating heat pipe with 2 mm hydraulic diameter square channels and interconnected between the layers was charged with a 70 percent fluid loading of degassed DI water. The effect of heating location, operating temperature and orientation were examined. The results showed that the thermal conductance (W/K) of the plate could be increased by more than 100 percent for a heater position near the edge of the plate but less for a central position where conduction through the plate was more effective. The change in the thermal conductance of the oscillating heat pipe path with the effective heat transfer through this path appeared independent of heater position but decreased modestly with operating temperature and for a horizontal plate orientation. The operation of the oscillating heat pipe was correlated using the heated wall superheat and the change in saturation pressure with temperature. The results suggest these were inversely correlated but the boundary delineating the onset of operation depended on orientation. Evidence of hysteresis effects and suppression of oscillation were observed.

The heat generated in the grinding process can result in high temperatures in the grinding contact zone, and result in defects to both the workpiece and the grinding wheel. Typically, coolants are used to transfer heat from the contact zone. This process, however, is not satisfactory as coolants often lose efficacy due to film boiling and can result in adverse health and environment effects. A novel cooling method that incorporates a two phase revolving heat pipe within the annular disk of the grinding wheel has been proposed. In this paper, the heat transfer mechanism in the evaporator section and the condenser section was analyzed using the volume of the fluid (VOF) model in ANSYS/FLUENT. The influence of different evaporator geometry, input heat flux, filling ratio and rotational speed on the heat transfer performance are reported here. In the evaporator, nucleate boiling is suppressed and replaced by laminar convection heat transfer as the rotational acceleration exceeds 1033g. The ideal filling ratio is about 17% with a corresponding heat transfer coefficient of 6091 W/ (m(2).K) and the appropriate heat flux is in the range 2500 to 500,000 W/m(2). Grinding experiments with both revolving heat pipe cooling and coolant cooling are performed, and the results analyzed in terms of grinding temperature and workpiece quality. The average grinding temperature was found to be under 120 degrees C with revolving heat pipe cooling, while temperature spikes as high as 800 degrees C with severe plastic deformation and grain refinement beneath the workpiece surface was found with coolant cooling.

During profile grinding of fir-tree blade slots, a key issue is usually the excessive heat caused by the complex contact zone. Most studies have focused on the cooling efficiency of the coolant; however only few have investigated the heat transfer potency of the grinding wheel matrix. In this study, a new cooling method that incorporates an axially rotating heat pipe (RHP) in the profile grinding wheel has been proposed. The cooling behavior of the new method was analyzed by both simulation and experimental grinding of titanium alloys. The temperature distributions along the RHP and the workpiece surface were monitored using embedded thermocouples. The effects of input heat flux, filling ratio and rotational speed on heat transfer performance were discussed. Comparative profile grinding experiments among RHP cooling, coolant cooling and no cooling demonstrated a great cooling advantage of RHP cooling with the lowest grinding temperature and better workpiece quality. Considering the research gaps of the previous studies, this work is not only deepens the understanding of the cooling behavior in the RHP during profile grinding of turbine blade slots, but also is helpful to provide guidance on the green machining of industrial products with complex profiles.

Defects caused by high grinding temperatures on both workpieces and grinding wheels become more significant with the development of difficult-to-machine materials and creep-feed grinding procedures. The coolants normally used to dissipate heat can cause harm to the environment as well as increase machining costs. A novel idea that incorporates a revolving heat pipe into the grinding wheel has been proposed to enhance heat transfer in the contact zone. In this study, a simulation is performed to investigate the heat transfer mechanism in the evaporator and condenser section of a revolving heat pipe grinding wheel (RHPGW) at a wheel velocity of 45 m/s. The results indicate that natural convection heat transfer and film condensation occur under this condition. The heat transfer and startup performance of the RHPGW are investigated in further experiments with different working fluids, fluid loadings and rotational speeds. Finally, experiments on creep-feed grinding of Inconel 718 are performed using a RHPGW and a grinding wheel without a revolving heat pipe, without application of any coolant. The results show that grinding temperatures can be maintained below 100 degrees C with a RHPGW and both the workpiece and grinding wheel show better quality than those when grinding is performed without a revolving heat pipe. (C) 2016 Elsevier Ltd. All rights reserved.

A hybrid thermal management system for electronics cooling is considered that incorporates a thermoelectric cooler (TEC) based active path in parallel with a conventional heat pipe based passive path. The passive path is used to transport the heat from the chip at moderate thermal conditions keeping the TEC electrically off while the TEC modules are turned on when the conditions become adverse, thus operating at a higher overall system coefficient of performance. An important design parameter is the fraction of the total heat sink area dedicated to each path, which will depend on the rated heat dissipation from the chip, thermal resistance of the entire heat sink and the operational ambient temperature. A thermal resistance network model for the hybrid system that takes into account the governing thermo-physical equations for the TEC is used to investigate the system. Controlled experiments are performed to validate the hybrid thermal management model. The model predictions are in good agreement with the experimental results. The operating envelope of different hybrid thermal management configurations are compared to a heat pipe based passive system and an only TEC system. Parametric studies are performed to analyze the effect of the number of TEC modules and the external thermal resistance.

The large scale ∞ow structures in an ofiset attaching jet with an ofiset height equal to the jet height and Re = 44 000 were studied using simultaneous measurements of the ∞uctuating wall pressure along the streamwise direction and the ∞uctuating velocity fleld estimated using a spectral linear stochastic estimation (LSE) technique. Box fllters were used to examine the ∞ow structures with difierent characteristic frequencies. The results showed evidence of difierent dominant ∞ow structures in the ∞ow. The instantaneous distributions of the estimated velocities and vorticity were examined for periods when difierent modes were prominent and showed difierences in the behavior of the ∞ow structures in the ∞ow. Ofiset jets with modest ofiset distances are used in a range of difierent cooling applications. The ofiset jets produce a local maximum in the heat transfer where they attached to the wall. The magnitude of the heat transfer at this point decreases as the ofiset distance of the jet (Hs) increases even for jets with Hs=Hj • 1 despite an increase in the turbulence level in the ∞ow near this point. This suggest there may be a change in the way the ∞ow structures interact with the wall as Hs changes even for Hs=Hj • 1. Recently, Gao and Ewing 4 studied the ∞ow structures in ofiset attaching jet with Hs=Hj • 1 using the correlation between the ∞uctuating wall pressure and the ∞uctuating velocities, and found features near the reattachment point similar to other reattaching shear layer ∞ows such as ∞ow over a backward facing step or ∞ow separated from a blufi body. 2,9,10 In particular, there were shedding mode motions with a frequency of fXr=Uj … 0:5 to 1 and a low frequency ∞apping instability with fXr=Uj < 0:2. Here, Xr is the mean reattachment length. The structures formed in the inner shear layer then developed downstream and appeared to merge with the structures in the outer shear layer of the jet. The outer shear layer structures grew in size while the jet was attaching to the wall and eventually became similar to the structures in a planar wall jet with a frequency fHj=Uj < 0:1. Gao and Ewing 5 studied the coherence of the ∞uctuating pressure and velocity in an ofiset jet with Hs=Hj = 1 and the propagation velocity of the structures in this ∞ow by considering the change in the phase of the cross-spectra of the ∞uctuating pressure along the wall and the cross-spectra of the ∞uctuating wall pressure and ∞uctuating velocity throughout the ∞ow. They found that the propagation speed of these motions varied with frequency. In particular, they found evidence of two modes in the inner shear layer, 0:6 . fXr=Uj . 0:9 and 0:9 . fXr=Uj . 1:4, that had difierent propagation velocities. They also found evidence that motions with 0:3 . fXr=Uj . 0:6 propagated downstream slower than the higher frequency motions. These slower motions appear to be associated with the structures that eventually form the wall jet structures travelled slower than the inner shear layer structures. The propagation velocity for the motions with fXr=Uj < 0:3 varied linearly with frequency and was consistent with a ∞apping motion. The objective of this investigation was to examine if the dynamics and interactions of difierent structures can be captured in the instantaneous ∞uctuating velocities estimated using a spectral linear stochastic estimation technique. 3 In this approach, the instantaneous velocity fleld is estimated from simultaneous time resolved measurements of the ∞uctuating wall pressure using coe‐cients that depend on the pressure velocity cross-spectra. Tinney et al. 12 and Hall and Ewing 6 found that the spectral LSE produced better estimations

An experimental investigation was performed to characterize the development of planar jets initially issuing parallel to an adjacent wall with offset distances of up to 1 jet height and Reynolds number of 44,000. The results showed that the initial development of the mean flow field in the planar offset jets could be divided into five regions; three associated with the jet attaching to the wall similar to other reattaching shear layer flows and two associated with the resulting planar wall jet flow. The transition from the reattaching flow to the wall jet flow was also characterized by a significant change in the characteristic frequency, size, and convection velocity of the large-scale structures in the flows.

An experimental investigation was performed to characterize the large scale structures present in turbulent offset attaching jets with a lower velocity co-flowing jet. The results showed that the nature of the structures present in the jets changed as the ratio of the lower jet velocity to the upper jet velocity changed. When the lower jet velocity was small, the lower jet was entrained into the upper jet before it attached to the surface. In these cases, the structures that developed in the inner shear layer were most prominent near the reattachment point, before a lower frequency motion that may be related to the outer shear layer of the jet became dominant. When the lower jet velocity was higher, there was a significant periodic motion in the near field that seemed to be associated with a flapping of the inner shear layer of the upper jet. This significantly increased the vertical fluctuating velocity in this region, but the fluctuations seemed to be damped as the inner shear layer approached the wall and did not have a large impact on the heat transfer or fluctuating pressure in this region where the upper jet interacted with the wall.

The distributions of the wall shear stress and the Stanton number for an offset attaching planar jet with a Reynolds number of 43000 and a co-flowing jet was measured experimentally using thin oil film interferometry and a heated thin foil. The flow fields, static wall pressure and the fluctuating wall pressure were also measured to examine the effect of the velocity ratio had on the development of the jets. It was found that the lower jet was entrained into the upper jet for low velocity ratios and the two jets seem to develop parallel to each other for larger velocity ratios. The change in the skin friction was found to be associated with the mean flow and the static wall pressure, while the change in the heat transfer seemed more closely related to the turbulence in the shear layer.

The development of the large-scale vortical structures in the three-dimensional turbulent wall jet formed by a rectangular channel with aspect ratio of Ar = 4 was investigated using measurements of the fluctuating wall pressure and the turbulent velocity field in the near and intermediate regions. Contours of the turbulence intensity and one component of the mean streamwise vorticity on either side of the jet centreline indicate that there are two regions of counter-rotating mean vorticity associated with the edges of the lateral shear layers that cause the mean flow to be driven down and outward. The inner vortices remain at approximately the same lateral position as the flow evolves downstream, while the outer regions move away from the wall and outward. The application of the proper orthogonal decomposition (POD) to the fluctuating pressure measurements and a temporal reconstruction revealed that the majority the flow energy was approximately equally divided between an symmetric and an antisymmetric mode. Pressure velocity correlations reveal that the passage of the coherent structure is more complicated that earlier models of this flow would suggest.

The development of three-dimensional turbulent wall jets were formed using rectangular channels of moderate aspect ratios from Ar = 1 to 8 have been investigated using profiles and contours of the turbulent velocities in the region x/h = 3 to 60. The decay of the streamwise velocity and the lateral and vertical growth of the jet half widths could be collapsed by scaling by the square root of area and normalizing by the initial width and height of the jet. Although this scaling collapses the mean flow contours, the Reynolds stresses and the streamwise vorticity differ indicating that the physics of the flow is different.

Experiments were performed to characterize the development of the large-scale structures in the stagnation and wall-jet regions of a turbulent impinging jet with a nozzle-to-plate spacing of 2 diameters and a Reynolds number of 20000. In particular, the instantaneous pressure was measured at 137 points on the wall using 6 concentric rings of pressure taps located 0.25, 0.5, 1.0, 1.5, 2.0 and 2.5 pipe diameters from the jet centreline. The 6 rings respectively contained 8, 16, 16, 32, 32 and 32 equally spaced taps as well as a single pressure tap placed at the jet centerline. The fluctuating pressure was decomposed into azimuthal modes and it was found that a significant portion of the field was contained in azimuthal mode 0 associated with the axisymmetric ring structures and azimuthal mode 1, often associated with jet precessing. The instantaneous pressure was filtered so that only azimuthal modes 0, 1 and −1 remained, and the dynamics of the large-scale structures associated with these modes was examined. These structures were found to be convected radially outward, were highly intermittent, and found to not rotate in a preferred direction.

The flow field of a dual-lip air ring used in the blow film manufacturing process was studied experimentally. The static pressure distributions on a model bubble was measured using manometers while the fluctuating pressure was measured using microphones. The flow field caused by the air ring was measured using single and cross-wire probes. It was found that the pressure distribution below the forming cone was determined by the lower jet velocity. The flow and the pressure distribution on the bubble above the forming cone was determined by the ratio of the upper and the lower jet velocities where two jets interact and by the upper jet after the upper jet attached to the bubble.

The development of the large-scale structures in the intermediate region of the three-dimensional wall jet was examined using measurements of the mean streamwise vorticity and the two-point, two-time correlations of the streamwise fluctuating velocity in the vertical and lateral directions. It was found that a dominant large-scale double horse-shoe structure persisted to 40 diameters downstream of the jet exit. It was also found that the structure continued to evolve throughout the intermediate field. In particular, the inner horse-shoe vortex was induced toward the wall, while the position of the outer horseshoe vortex relative to the half-width moved toward the centerline. The inclination of this structure relative to the wall also increased as the flow evolved downstream. These changes in the structure combined to cause the lateral spread rate of the jet to aprroximately double in the intermediate field.

One of the most widely accepted ideas in turbulence theory is that the large-scale structures in turbulent shear flows forget how they are generated so that all flows of a particular type asymptotically evolve to a single universal state. It is shown here, usingthe temporally evolvingw ake as an example, that the governing equations for the two-point velocity correlations have self-similar solutions indicating the large-scale structures asymptotically evolve in an equilibrium manner. It is further shown these equations do not have unique solutions so the notion of a single ‘universal’ solution is not necessarily consistent with the governing equations.

The data base measured by Citriniti (1996) is used to examine the accuracy of using Linear Stochastic Estimation to estimate the velocity field in the annular mixing layer. In the first case, the velocity information is estimated using information from a single instant in time on two radii. In the second approach, the signal is Fourier transformed in time and the frequency dependent coefficients are estimated using coefficients measured on two radii, thus effectively incorporating information from all points in time into the estimate. The estimated velocity fields are then used with the Proper Orthogonal Decomposition to yield low-dimensional reconstructions of the flow. It is found that both estimated fields are capable of accurately reproducing the gross features of both the ring structures and the inter-ring regions found in the shear layer, however, the single-time method does not accurately reproduce the amplitude of the fluctuating velocity.