scholarly journals Boiling Heat Transfer From an Array of Round Jets With Hybrid Surface Enhancements

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
Matthew J. Rau ◽  
Suresh V. Garimella ◽  
Ercan M. Dede ◽  
Shailesh N. Joshi
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Flat Surface ◽  
Microporous Layer ◽  
Maximum Heat ◽  
Flow Rates ◽  
Pin Fin ◽  
Pin Fins ◽  
Single Jet

The effect of a variety of surface enhancements on the heat transfer achieved with an array of impinging jets is experimentally investigated using the dielectric fluid HFE-7100 at different volumetric flow rates. The performance of a 5 × 5 array of jets, each 0.75 mm in diameter, is compared to that of a single 3.75 mm diameter jet with the same total open orifice area, in single-and two-phase operation. Four different target copper surfaces are evaluated: a baseline smooth flat surface, a flat surface coated with a microporous layer, a surface with macroscale area enhancement (extended square pin–fins), and a hybrid surface on which the pin–fins are coated with the microporous layer; area-averaged heat transfer and pressure drop measurements are reported. The array of jets enhances the single-phase heat transfer coefficients by 1.13–1.29 times and extends the critical heat flux (CHF) on all surfaces compared to the single jet at the same volumetric flow rates. Additionally, the array greatly enhances the heat flux dissipation capability of the hybrid coated pin–fin surface, extending CHF by 1.89–2.33 times compared to the single jet on this surface, with a minimal increase in pressure drop. The jet array coupled with the hybrid enhancement dissipates a maximum heat flux of 205.8 W/cm2 (heat input of 1.33 kW) at a flow rate of 1800 ml/min (corresponding to a jet diameter-based Reynolds number of 7800) with a pressure drop incurred of only 10.9 kPa. Compared to the single jet impinging on the smooth flat surface, the array of jets on the coated pin–fin enhanced surface increased CHF by a factor of over four at all flow rates.

scholarly journals Confined Jet Impingement With Boiling on a Variety of Enhanced Surfaces

2014 ◽  
Vol 136 (10) ◽  
Author(s):  
Matthew J. Rau ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flat Surface ◽  
Jet Impingement ◽  
High Heat ◽  
Microporous Layer ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
Pin Fins

Confined jet impingement with boiling offers unique and attractive performance characteristics for thermal management of high heat flux components. Two-phase operation of jet impingement has been shown to provide high heat transfer coefficients while maintaining a uniform temperature over a target surface. This can be achieved with minimal increases in pumping power compared to single-phase operation. To investigate further enhancements in heat transfer coefficients and increases in the maximum heat flux supported by two-phase jet impingement, an experimental study of surface enhancements is performed using the dielectric working fluid HFE-7100. The performance of a single, 3.75 mm-diameter jet orifice is compared across four distinct copper target surfaces of varying enhancement scales: a baseline smooth flat surface, a flat surface coated with a microporous layer, a surface with macroscale area enhancement (extended square pin fins), and a hybrid surface on which the pin fins are coated with the microporous layer. The heat transfer performance of each surface is compared in single- and two-phase operation at three volumetric flow rates (450 ml/min, 900 ml/min, and 1800 ml/min); area-averaged heat transfer parameters and pressure drop are reported. The mechanisms resulting in enhanced performance for the different surfaces are identified, with a special focus on the coated pin fins. This hybrid surface showed the best enhancement of all those tested, and resulted in an extension of critical heat flux (CHF) by a maximum of 2.42 times compared to the smooth flat surface at the lowest flow rate investigated; no increase in the overall pressure drop was measured.

A Study on Flow Boiling in Microchannel With Piranha Pin Fin

2015 ◽  
Author(s):  
X. Yu ◽  
C. Woodcock ◽  
Y. Wang ◽  
J. Plawsky ◽  
Y. Peles
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Fluid Flow ◽  
Pressure Drop ◽  
Heat Transfer Performance ◽  
Flow Boiling ◽  
Transfer Performance ◽  
Flow Conditions ◽  
Pin Fin ◽  
Flow And Heat Transfer

In this paper we reported an advanced structure, the Piranha Pin Fin (PPF), for microchannel flow boiling. Fluid flow and heat transfer performance were evaluated in detail with HFE7000 as working fluid. Surface temperature, pressure drop, heat transfer coefficient and critical heat flux (CHF) were experimentally obtained and discussed. Furthermore, microchannels with different PPF geometrical configurations were investigated. At the same time, tests for different flow conditions were conducted and analyzed. It turned out that microchannel with PPF can realize high-heat flux dissipation with reasonable pressure drop. Both flow conditions and PPF configuration played important roles for both fluid flow and heat transfer performance. This study provided useful reference for further PPF design in microchannel for flow boiling.

Effects of Taper Configurations on Heat Transfer and Pressure Drop in Single-Phase Flows in Microgaps

2020 ◽  
Author(s):  
Debora C. Moreira ◽  
Gherhardt Ribatski ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Single Phase ◽  
Bubble Nucleation ◽  
Low Flow ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Inlet Section ◽  
Flow Rates

Abstract This paper presents a comparison of heat transfer and pressure drop during single-phase flows inside diverging, converging, and uniform microgaps using distilled water as the working fluid. The microgaps were created on a plain heated copper surface with a polysulfone cover that was either uniform or tapered with an angle of 3.4°. The average gap height was 400 microns and the length and width dimensions were 10 mm × 10 mm, resulting in an average hydraulic diameter of approximately 800 microns for all configurations. Experiments were conducted at atmospheric pressure and the inlet temperature was set to 30 °C. Heat transfer and pressure drop data were acquired for flow rates varying from 57 to 485 ml/min and the surface temperature was monitored not to exceed 90 °C to avoid bubble nucleation, so the heat flux varied from 35 to 153 W/cm2 depending on the flow rate. The uniform configuration resulted in the lowest pressure drop, and the diverging one showed slightly higher pressure drop values than the converging configuration, possibly because the flow is most constrained at the inlet section, where the fluid is colder and presents higher viscosity. In addition, a minor dependence of pressure drop with heat flux was observed due to temperature dependent properties. The best heat transfer performance was obtained with the converging configuration, which was especially significant at low flow rates. This behavior could be explained by an increase in the heat transfer coefficient due to flow acceleration in converging gaps, which compensates the decrease in temperature difference between the fluid and the surface due to fluid heating along the gap. Overall, the comparison between the three configurations shows that converging microgaps have better performance than uniform or diverging ones for single-phase flows, and such effect is more pronounced at lower flow rates, when the fluid experiences higher temperature changes.

Two-Phase Performance of a Hybrid Jet Plus Multipass Microchannel Heat Sink

2019 ◽  
Vol 12 (1) ◽  
Author(s):  
Shailesh N. Joshi ◽  
Danny J. Lohan ◽  
Ercan M. Dede
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Rate ◽  
Heat Sink ◽  
Maximum Pressure ◽  
Microchannel Heat Sink ◽  
Large Area ◽  
Two Phase ◽  
Maximum Heat ◽  
Flow Rates

Abstract The heat transfer and fluid flow performance of a hybrid jet plus multipass microchannel heat sink in two-phase operation is evaluated for the cooling of a single large area, 3.61 cm2, heat source. The two-layer branching microchannel heat sink is evaluated using HFE-7100 as the coolant at three inlet volumetric flow rates of 150, 300, and 450 ml/min. The boiling performance is highest for the flow rate of 450 ml/min with the maximum heat flux value of 174 W/cm2. Critical heat flux (CHF) was observed at two of the tested flow rates, 150 and 300 ml/min, before reaching the maximum operating temperature for the serpentine heater. At 450 ml/min, the heater reached the maximum allowable temperature prior to observing CHF. The maximum pressure drop for the heat sink is 34.1 kPa at a heat flux of 164 W/cm2. Further, the peak heat transfer coefficient value of the heat sink is 28,700 W/m2 K at a heat flux value of 174 W/cm2 and a flow rate of 450 ml/min. Finally, a validated correlation of the single device cooler is presented that predicts heat transfer performance and can be utilized in the design of multidevice coolers.

Influence of Rib Turbulators on Pin-Fin Heat Transfer in the Trailing Region of Gas Turbine Vane: A Numerical Study

2006 ◽  
Author(s):  
N. Kulasekharan ◽  
B. V. S. S. S. Prasad
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Numerical Study ◽  
Pressure Ratio ◽  
Constant Heat Flux ◽  
Transfer Coefficients ◽  
Flux Boundary Condition ◽  
Pin Fin ◽  
Pin Fins ◽  
Rib Turbulators

A numerical investigation is carried out for estimating the influence of rib turbulators on heat transfer and pressure drop of staggered non-uniform pin-fin arrays of different shapes, in a simulated cambered vane trailing region. Pin-fins of square, circular and the diamond shapes, each of two sizes (d) were chosen. The ratio of span-wise pitch to longitudinal pitch is 1.06 and that to the pin size are 4.25 and 3.03, for all pin shapes. A constant heat flux boundary condition is assumed over the coolant channel walls, rib surfaces and circumferential faces of the pin-fins. Reynolds number is varied (20,000<ReD<40,000) by changing the coolant outlet to inlet pressure ratio. Pin end-wall and pin surface averaged heat transfer coefficients and Nusselt numbers are estimated and detailed contours of heat transfer coefficient on both the pressure and suction surfaces are presented. Whilst there is an enhancement in heat transfer and pressure drop with ribs for all the pin shapes, diamond pins have shown the highest enhancement values for both ribbed and non-ribbed configuration.

Impingement Jet Cooling With Ribs and Pin Fin Obstacles in Co-Flow Configurations: Conjugate Heat Transfer Computational Fluid Dynamic Predictions

2016 ◽  
Author(s):  
Abubakar M. El-Jummah ◽  
Gordon E. Andrews ◽  
John E. J. Staggs
Keyword(s):  
Heat Transfer ◽  
Pressure Loss ◽  
Conjugate Heat Transfer ◽  
Coolant Flow ◽  
Experimental Results ◽  
Hole Density ◽  
Flow Rates ◽  
Pin Fin ◽  
Impingement Jet ◽  
Pin Fins

Conjugate heat transfer (CHT) computational fluid dynamics (CFD) predictions were carried out for impingement heat transfer with obstacle (fins) walls on the target surface midway between the impingement jets and aligned in the direction of the crossflow (direction of outflow of the impingement cooling air) to minimise the pressure loss increase due to the fins. A single sided flow exit was used in a geometry that was applicable to reverse flow cooling of low NOx combustors, but was also relevant to turbine blade and nozzle cooling. A 10 × 10 row of impingement jet holes (hole density n of 4306 m−2) was used, which had ten rows of holes in the cross-flow direction. One heat transfer enhancement obstacle per impingement jet was investigated and compared with previously published experimental results, for Nimonic 75 metal walls, for flow pressure loss and surface averaged heat transfer coefficients. Two different shaped obstacles were investigated with an impingement gap, Z, of 10mm: a continuous rectangular rib 4.5mm high (H) and 3.0 mm thick and a rectangular pin-fin rib with ten 8mm high (H) pins that were 8.6mm wide and 3.0 mm thick. The obstacles were equally spaced on the centreline between each row of impingement jets aligned with the crossflow. The impingement jet pitch to diameter X/D and gap to diameter Z/D ratios were kept constant at 4.66 and 3.06 for X, Z and D of 15.24, 10.00 and 3.27 mm, respectively. The two obstacles investigated had obstacle height to diameter ratio H/D of 1.38 and 2.45. The computations were carried out for three different air coolant mass fluxes G of 1.08, 1.48 and 1.94 kg/sm2bar. The pressure loss ΔP/P and surface average heat transfer coefficient (HTC) h predictions for all three G showed good agreement with the experimental results. The predicted results were also compared with the impingement jet single exit flow, for a smooth target wall of the same impingement hole configuration. A significant increase in the overall surface averaged heat transfer was predicted and measured for the co-flow configuration with rectangular pin-fins. This was a 20% improvement at low coolant flow rates for the rectangular pin fin obstacles and 15% for the ribs. At high coolant flow rates the improvement was smaller at 5% for the rectangular pin fins and 1% for the rectangular ribs.

scholarly journals Investigation of Enhanced Surface Spray Cooling

2004 ◽  
Author(s):  
Eric A. Silk ◽  
Jungho Kim ◽  
Ken Kiger
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flat Surface ◽  
Spray Cooling ◽  
Chamber Pressure ◽  
Working Fluid ◽  
Sectional Area ◽  
Cross Sectional ◽  
Pin Fins ◽  
Enhanced Surface

Experiments were conducted to study the effects of enhanced surfaces on heat transfer during spray cooling. The surface enhancements consisted of cubic pin fins, pyramids, and straight fins (uniform cross sectional straight fins) machined on the top surface of copper heater blocks. Each had a cross-sectional area of 2.0 cm2. Measurements were also obtained on a heater block with a flat surface for baseline comparison purposes. A 2×2 nozzle array was used with PF-5060 as the working fluid. Thermal performance data was obtained under nominally degassed (chamber pressure of 41.4 kPa) and gassy conditions (chamber with N2 gas at 101 kPa). The results show that the straight fins had the largest enhancement in heat flux. Critical heat flux (CHF) for this surface showed an increase of 55% in comparison to the flat surface for the nominally degassed condition. The cubic pin finned and pyramid surfaces provided slightly more than half the heat flux enhancement (30%–40% greater than the flat surface) of the straight fins. The gassy case showed that the straight fins again provided the largest enhancement (48%) in CHF relative to the flat surface. This was followed by the cubic pin fins, and pyramids which had increases of 31% and 18% respectively. No significant effect was observed in the surface temperature at which CHF occurs for either portion of the study.

Heat Transfer in Rotating, Trailing Edge, Converging Channels With Partial Length Pin-Fins

2021 ◽  
Vol 143 (6) ◽  
Author(s):  
Izzet Sahin ◽  
I-Lun Chen ◽  
Lesley M. Wright ◽  
Je-Chin Han ◽  
Hongzhou Xu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Slight Reduction ◽  
Transfer Coefficients ◽  
Trailing Edge ◽  
Pin Fin ◽  
Heat Transfer Coefficients ◽  
Partial Length ◽  
Pin Fins ◽  
Cooling Passage

Abstract In the current study, the heat transfer and pressure drop characteristics of a rotating, partial pin-finned, cooling channel that has a trapezoidal cross section and converges from the hub to tip in both the streamwise and spanwise directions are experimentally investigated. To model the geometry of an internal trailing edge cooling passage, the channel is oriented with respect to the direction of rotation (β = 120 deg). Isolated copper plates are used to obtain regionally averaged heat transfer coefficients on the leading and trailing surfaces. Pressure drop is measured using pressure taps placed at the inlet and outlet of the channel. Utilizing Dp = 5 mm diameter pins, a staggered array is created. For this array, the streamwise pin-spacing, Sy/Dp = 2.1, was kept constant; however, the spanwise pin-spacing, Sx/Dp, was varied from the hub to tip between 3 and 2.6 due to the channel convergence. Experiments were conducted for two partial pin-fin sets having pin length-to-diameter ratios of Sz/Dp = 0.4 and 0.2. The rotation number was varied from 0 to 0.21 by ranging the inlet Reynolds number from 10,000 to 40,000 and rotation speed from 0 to 300 rpm. A significant decrease in pressure loss and a slight reduction in heat transfer enhancement are observed with the use of partial pin-fins compared with the previously reported full pin-fin converging channel study. This provides better thermal performances of the partial pin-fin arrays compared with the full pin-fin array, in the converging channels.

scholarly journals Numerical Research on Thermal Variations along SSF Pin Fins Shaped with SSM Processing

2019 ◽  
Vol 8 (12) ◽  
pp. 504-507
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Flux ◽  
Stainless Steel ◽  
Heat Dissipation ◽  
Heat Sinks ◽  
Pin Fin ◽  
Temperature Distributions ◽  
Pin Fins ◽  
Numerical Research

Fins or heat sinks are meant for boosting heat transfer. Therefore, planned computations remain fortified for examining the impacts of SSF pin fin on thermal dispersal concerning constant thermal value 6 W/cm2 . For that SSF pin fins materials of stainless steel and aluminum are preferred. Usual convective equations are solved to foretell thermal apprehensions. As anticipated, for both the stated SSF pin fins, temperature and heat flux declines for increasing length scales. Additionally, temperature distributions on SSF aluminum pin fin lays beneath SSF stainless steel pin fin. Hence, heat dissipation from SSF aluminum pin fin is relatively higher. Obviously, it may be owing to quite higher thermal conductivity of SSF aluminum pin fin. Consequently, it delivers higher, gregarious and remarkable thermal behaviors. Nevertheless, both simulation forecasts remain analogous with one another.

Liquid Single-Phase Flow in an Array of Micro-Pin-Fins—Part II: Pressure Drop Characteristics

2008 ◽  
Vol 130 (12) ◽  
Author(s):  
Weilin Qu ◽  
Abel Siu-Ho
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Friction Factor ◽  
Single Phase ◽  
Cast Aluminum ◽  
Pin Fin ◽  
Pin Fins ◽  
Friction Factor Correlation ◽  
Micro Pin Fins ◽  
Pin Fin Arrays

This Technical Brief is Part II of a two-part study concerning water single-phase pressure drop and heat transfer in an array of staggered micro-pin-fins. This brief reports the pressure drop results. Both adiabatic and diabatic tests were conducted. Six previous friction factor correlations for low Reynolds number (Re<1000) flow in conventional and micro-pin-fin arrays were examined and found underpredicting the adiabatic data except the correlation by Short et al. (2002, “Performance of Pin Fin Cast Aluminum Coldwalls, Part 1: Friction Factor Correlation,” J. Thermophys. Heat Transfer, 16(3), pp. 389–396), which overpredicts the data. A new power-law type of correlation was developed, which showed good agreement with both adiabatic and diabatic data.

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