Experimental Investigation of Flow Boiling Performance of Open Microchannels With Uniform and Tapered Manifolds (OMM)

2013 ◽  
Author(s):  
Ankit Kalani ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Flow Boiling ◽  
Heat Removal ◽  
Medium Effect ◽  
Maximum Pressure ◽  
Successful Implementation ◽  
Efficient Operation ◽  
Maximum Heat ◽  
Fluid Medium

Boiling can provide orders of magnitude higher cooling performance than a traditional air cooled system especially related to electronics cooling application. It can dissipate large quantities of heat while maintaining a low surface temperature difference. Flow boiling with microchannels has shown a lot of potential due to its high surface area to volume ratio and latent heat removal. Flow instabilities and early critical heat flux have however prevented its successful implementation. A novel flow boiling design is experimentally investigated to overcome the above mentioned disadvantages while presenting a very low pressure drop. The design uses open microchannels with a tapered manifold (OMM) to provide stable and efficient operation. Distilled, degassed water at atmospheric pressure is used as the fluid medium. Effect of tapered block with varied dimension is investigated. Heat transfer coefficient and pressure drop data for uniform and tapered manifolds for plain and microchannel chips are presented. A maximum heat flux of 281.2 W/cm2 at 10.1 °C wall superheat is obtained with microchannel chips using a tapered manifold. The CHF was not reached as the performance exceeded the heater capacity. The maximum pressure drop obtained for the above mentioned configuration was only 3.3 kPa.

Evaluation of Pressure Drop Performance During Enhanced Flow Boiling in Open Microchannels With Tapered Manifolds

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
Ankit Kalani ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
High Surface ◽  
Heat Removal ◽  
Electronics Cooling ◽  
Successful Implementation ◽  
Efficient Operation

Boiling can provide several orders of magnitude higher performance than a traditional air cooled system in electronics cooling applications. It can dissipate large quantities of heat while maintaining a low surface temperature difference. Flow boiling with microchannels has shown a great potential with its high surface area to volume ratio and latent heat removal. However, flow instabilities and low critical heat flux (CHF) have prevented its successful implementation. A novel flow boiling design is experimentally investigated to overcome the above-mentioned disadvantages while presenting a very low pressure drop. The design uses open microchannels with a tapered manifold (OMM) to provide stable and efficient operation. The effect of tapered manifold block with varied dimension is investigated with distilled, degassed water at atmospheric pressure. Heat transfer coefficient and pressure drop results for uniform and tapered manifolds with plain and microchannel chips are presented. The OMM configuration yielded a CHF of over 500 W/cm2 in our earlier work. In the current work, a heat transfer coefficient of 277.8 kW/m2 °C was obtained using an OMM design with an inlet gap of 127 μm and an exit gap of 727 μm over a 10 mm flow length. The OMM geometry also resulted in a dramatic reduction in pressure drop from 158.4 kPa for a plain chip and 62.1 kPa for a microchannel chip with a uniform manifold, to less than 10 kPa with the tapered OMM design. A tapered manifold (inlet and exit manifold heights of 127 and 727 μm, respectively) with microchannel provided the lowest pressure drop of 3.3 kPa.

Enhanced Flow Boiling Using Radial Open Microchannels With Manifold and Offset Strip Fins

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Alyssa Recinella ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Flow Rate ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Valuable Insight ◽  
Reduced Pressure ◽  
Maximum Heat ◽  
Wall Superheat ◽  
Maximum Heat Flux

The increasing demand for designing effective cooling solutions in high power density electronic components has resulted in exploring advanced thermal management strategies. Over the past decade, phase-change cooling has received widespread recognition due to its ability to dissipate large heat fluxes while maintaining low temperature differences. In this paper, a radial flow boiling configuration through a central inlet was studied. This configuration is particularly suited for chip cooling application. Two heat transfer surfaces with (a) radial microchannels, and (b) offset strip fins were fabricated and their flow boiling performance with distilled water was obtained. Furthermore, the effect of the liquid flow rate on the boiling performance and enhancement mechanisms was also investigated in this study. At a flow rate of 240 mL/min, a maximum heat flux of 369 W/cm2 at a wall superheat of 49 °C and a pressure drop of 59 kPa was achieved with the radial microchannels, while the offset strip fins achieved a maximum heat flux of 618 W/cm2 at a wall superheat of 20 °C. Increasing the flow rate to 320 mL/min resulted in a heat flux of 897 W/cm2 demonstrating the potential of using a radial configuration for enhancing the boiling performance. The increase in flow cross-sectional area was shown to be responsible for the reduced pressure drop when compared to straight microchannel configurations. The high-speed imaging incorporated in each test provided valuable insight and understanding into the flow patterns and underlying mechanism in these geometries. With the ease of implementation, highly stable flow, and further optimization possibilities with different microchannel and taper configurations, the radial geometry is expected to provide significant performance enhancement well beyond a critical heat flux (CHF) of 1 kW/cm2.

Optimization of a radiant system for hydrothermal performance using Taguchi and utility concept

2021 ◽  
pp. 1-29
Author(s):  
Ratnadeep Nath ◽  
Vikas Verma ◽  
Rahul Tarodiya
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Temperature Difference ◽  
Wall Temperature ◽  
Thermal Parameters ◽  
Conventional Heating ◽  
Geometrical Parameters ◽  
Maximum Heat ◽  
Utility Concept ◽  
Heating Mode

Abstract Radiant floor panel technology is gaining popularity as an alternative system over conventional heating, ventilation and, air conditioning system (HVAC) to maintain the room temperature for the desired comfort. This research paper aims to optimize the hydrothermal performance of a radiant system by implementing the Taguchi technique and utility concept for cooling and heating mode of operation. Five geometrical and thermal parameters such as pipe diameter, pipe spacing, concrete layer thickness, wall temperature, and inlet and outlet water temperature difference with three levels are chosen as controlling factors to perform optimization. Considering five parameters and three levels, a total of 27 trial runs (L27) are constructed and computed by mathematical calculation. Two different sets of optimum parameters are obtained for maximizing heat flux and minimizing pressure drop. Further, the utility concept is employed to get a single set of parameters to achieve maximum utilization of the radiant system. Taguchi analysis revealed that thermal parameters like temperature difference and wall temperature are the most influential parameters to reach maximum heat transfer and minimum pressure drop followed by geometrical parameters like pipe spacing and diameter for heat flux and pressure drop, respectively. Providing more weightage to heat flux than pressure drop, utility analysis showed 32% and 42% augmentation in heat flux for cooling and heating mode respectively, at the cost of an increase in pressure drop.

Heat Transfer Enhancement in Compact Phase Change Microchannel Heat Exchangers for High Flux Laser Diodes

2018 ◽  
Author(s):  
Jensen Hoke ◽  
Todd Bandhauer ◽  
Jack Kotovsky ◽  
Julie Hamilton ◽  
Paul Fontejon
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Phase Change ◽  
Flow Boiling ◽  
Laser Diodes ◽  
High Heat ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Maximum Heat ◽  
Average Maximum

Liquid-vapor phase change heat transfer in microchannels offers a number of significant advantages for thermal management of high heat flux laser diodes, including reduced flow rates and near constant temperature heat rejection. Modern laser diode bars can produce waste heat loads >1 kW cm−2, and prior studies show that microchannel flow boiling heat transfer at these heat fluxes is possible in very compact heat exchanger geometries. This paper describes further performance improvements through area enhancement of microchannels using a pyramid etching scheme that increases heat transfer area by ∼40% over straight walled channels, which works to promote heat spreading and suppress dry-out phenomenon when exposed to high heat fluxes. The device is constructed from a reactive ion etched silicon wafer bonded to borosilicate to allow flow visualization. The silicon layer is etched to contain an inlet and outlet manifold and a plurality of 40μm wide, 200μm deep, 2mm long channels separated by 40μm wide fins. 15μm wide 150μm long restrictions are placed at the inlet of each channel to promote uniform flow rate in each channel as well as flow stability in each channel. In the area enhanced parts either a 3μm or 6μm sawtooth pattern was etched vertically into the walls, which were also scalloped along the flow path with the a 3μm periodicity. The experimental results showed that the 6μm area-enhanced device increased the average maximum heat flux at the heater to 1.26 kW cm2 using R134a, which compares favorably to a maximum of 0.95 kw cm2 dissipated by the plain walled test section. The 3μm area enhanced test sections, which dissipated a maximum of 1.02 kW cm2 showed only a modest increase in performance over the plain walled test sections. Both area enhancement schemes delayed the onset of critical heat flux to higher heat inputs.

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.

High Heat Flux Subcooled Flow Boiling of Methanol in Microtubes

2015 ◽  
Author(s):  
Farzad Houshmand ◽  
Hyoungsoon Lee ◽  
Mehdi Asheghi ◽  
Kenneth E. Goodson
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Flow Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Two Phase ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow ◽  
Inner Diameter ◽  
Phase Pressure

As the proper cooling of the electronic devices leads to significant increase in the performance, two-phase heat transfer to dielectric liquids can be of an interest especially for thermal management solutions for high power density devices with extremely high heat fluxes. In this paper, the pressure drop and critical heat flux (CHF) for subcooled flow boiling of methanol at high heat fluxes exceeding 1 kW/cm2 is investigated. Methanol was propelled into microtubes (ID = 265 and 150 μm) at flow rates up to 40 ml/min (mass fluxes approaching 10000 kg/m2-s), boiled in a portion of the microtube by passing DC current through the walls, and the two-phase pressure drop and CHF were measured for a range of operating parameters. The two-phase pressure drop for subcooled flow boiling was found to be significantly lower than the saturated flow boiling case, which can lead to lower pumping powers and more stability in the cooling systems. CHF was found to be increasing almost linearly with Re and inverse of inner diameter (1/ID), while for a given inner diameter, it decreases with increasing heated length.

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.

Effect of Inlet Restriction on Flow Boiling Heat Transfer in a Horizontal Microtube

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
YanFeng Fan ◽  
Ibrahim Hassan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Critical Heat Flux ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Mass Fluxes ◽  
Flow Boiling Heat Transfer ◽  
Low Mass

Flow boiling heat transfer in a horizontal microtube with inlet restriction (orifice) under uniform heating condition is experimentally investigated using FC-72 as working fluid. A stainless steel microtube with an inner diameter of 889 μm is selected as main microtube. Two microtubes with smaller diameters are assembled at the inlet of main microtube to achieve the restriction ratios of 50% and 20%. The experimental measurement is carried out at mass fluxes ranging from 160 to 870 kg/m2·s, heat fluxes varying from 6 to 170 kW/m2, inlet temperatures of 23 and 35 °C, and saturation pressures of 10 and 45 kPa. The effects of the orifices on two-phase pressure drop, critical heat flux (CHF), and flow boiling heat transfer coefficient are studied. The results show that the pressure drop caused by the orifice takes a considerable portion in the total pressure drop at low mass fluxes. This ratio decreases as the vapor quality or mass flux increases. The difference of normal critical heat flux in the microtubes with different orifice sizes is negligible. In the aspect of flow boiling heat transfer, the orifice is able to enhance the heat transfer at low mass flux and high saturation pressure, which indicates the contribution of orifice in the nucleate boiling dominated regime. However, the effect of orifice on flow boiling heat transfer is negligible in the forced convective boiling dominated regime.

Experimental Investigation on Flow Instability in a Single Vertical Microtube

2015 ◽  
Author(s):  
Qian You ◽  
Ibrahim Hassan ◽  
Lyes Kadem
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Mass Flux ◽  
Flow Instability ◽  
Flow Boiling ◽  
Flow Direction ◽  
Density Wave ◽  
Mass Fluxes ◽  
Flow Oscillations ◽  
Flow Directions

The experiments are conducted to study the flow boiling instability in a single microtube with 0.889 mm hydraulic diameter in vertical upward and downward flow directions (VU and VD). The subcooled dielectric liquid FC-72 is driven at mass fluxes varying from 700 to 1400 kg/m2·s, and the heat flux uniformly applied on the microtube surface is up to 9.6 W/cm2. The onsets of flow oscillations (OFIs) in both flow directions are observed. Their oscillation types and characteristics are presented as well. The effects of mass flux and heat flux on flow instability in vertical flow directions are discussed. The results show that as the mass flux increases, the OFI occurrence is postponed, and the compounded oscillation types (Ledinegg, pressure drop and density wave oscillations) turn to pressure drop type dominant. At low mass fluxes, the OFI appears earlier in VD than in VU due to the buoyancy force impeded the bubble discharging. As the mass flux increases, the OFI appearance in VD is close to the ones in VU and its flow oscillations tend to be re-stabilized. After OFIs appeared at a given mass flux, with more heat flux added, the density wave oscillation type in VU becomes more active. However, at a constant mass flux, as the heat flux increases, the flow instability in VD becomes “stable” which may be due to the rapid flow pattern change, and this kind of “stable” is not expected because the local dryout may accompany. Hence, the microtube with vertical upward flow direction (VU) performs better from flow boiling instability point of view.

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