High flux boiling in low flow rate, low pressure drop mini-channel and micro-channel heat sinks

At the present time, thermal power plants and combined heat and power plants operate in highly manoeuvrable modes with almost daily deep unloading, shutdowns on weekends and holidays followed by launches from various thermal conditions. During start-ups, the operation at partial modes and shutdowns, the turbine flow path operates at low-flow rate modes and, as a result, varying tear-off phenomena appear — depending on a relative volumetric flow rate of steam Gv2 in the low-pressure cylinder starting from the last stage. This is especially true for the operation of the low-pressure path for cogeneration turbines. Under low-flow rate modes a change in the flow structure occurs accompanied by the appearance of the bushing tear-off, the rotating vortex in the gap between stator blades and rotor blades, and an increase in pressure in the main flow when switching to the operation at the compressor mode. The formation of the tear-off area is accompanied by a significant increase in the temperature of steam during its overheating due to ventilation losses created by vortex structures in the areas of tear-off. The temperature change along the working blade length is considered, the characteristic points of this change depending on the relative volumetric flow rate of steam are highlighted. The boundaries of transition from the wet steam to the su— perheated steam with decreasing Gv2 are determined. The power consumption for the operation of the stage with a decrease in the flow rate of steam and a change in the flow structure is considered.

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Two-Phase Electronic Cooling Using Mini-Channel and Micro-Channel Heat Sinks: Part 2—Flow Rate and Pressure Drop Constraints

Journal of Electronic Packaging ◽

10.1115/1.2905701 ◽

1994 ◽

Vol 116 (4) ◽

pp. 298-305 ◽

Cited By ~ 71

Author(s):

M. B. Bowers ◽

I. Mudawar

Keyword(s):

Pressure Drop ◽

Flow Rate ◽

Heat Dissipation ◽

Flow Boiling ◽

Phase Region ◽

Heat Fluxes ◽

Heat Sinks ◽

Micro Channel ◽

Two Phase ◽

Channel Geometry

Increased rate of heat dissipation from electronic chips was explored by the application of flow boiling in mini-channel (D = 2.54 mm) and micro-channel (D = 510 μm) heat sinks with special emphasis on reducing pressure drop and coolant flow rate. A pressure drop model was developed that accounts for the single-phase inlet region, the single- and two-phase heated region, and the two-phase unheated outlet region. Inlet and outlet losses associated with the abrupt contraction and expansion, respectively, were also accounted for, and so were the effects of compressibility and flashing within the two-phase region. Overall, the major contributor to pressure drop was the acceleration caused by evaporation in the channels; however, compressibility effects proved significant for the micro-channel geometry. Based upon practical considerations such as pressure drop, erosion, choking, clogging, and manufacturing ease, the mini-channel geometry was determined to offer inherent advantages over the micro-channel geometry. The latter is preferred only in situations calling for dissipation of high heat fluxes where minimizing weight and liquid inventory is a must.

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Characteristics of the critical heat flux for downward flow in a vertical tube at low-flow rate and low-pressure conditions

Experimental Thermal and Fluid Science ◽

10.1016/0894-1777(93)90241-a ◽

1993 ◽

Vol 7 (2) ◽

pp. 159 ◽

Cited By ~ 3

Author(s):

S.W. Ruan ◽

G. Bartsch ◽

S.M. Yang

Keyword(s):

Heat Flux ◽

Critical Heat Flux ◽

Flow Rate ◽

Low Pressure ◽

Vertical Tube ◽

Low Flow ◽

Downward Flow ◽

Low Flow Rate

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Characteristic Study on the Optimization of Pin-Fin Micro Heat Sink

Volume 9: Heat Transfer, Fluid Flows, and Thermal Systems, Parts A, B and C ◽

10.1115/imece2009-11816 ◽

2009 ◽

Cited By ~ 3

Author(s):

T. J. John ◽

B. Mathew ◽

H. Hegab

Keyword(s):

Pressure Drop ◽

Thermal Resistance ◽

Flow Rate ◽

Heat Sink ◽

Heat Dissipation ◽

Heat Sinks ◽

Low Flow ◽

Pumping Power ◽

Flow Rates ◽

Pin Fin

The need for dissipating heat from microsystems has increased drastically in the last decade. Several methods of heat dissipation using air and liquids have been proposed by many studies, and pin-fin micro heat sinks are one among them. Researchers have developed several effective pin-fin structures for use in heat sinks, but not much effort has been taken towards the optimization of profile and dimensions of the pin-fin. In this paper the authors studied the effect of different pin-fin shapes on the thermal resistance and pressure drop in a specific micro heat-sink. Optimization subjected to two different constraints is studied in this paper. The first optimization is subjected to constant flow rate and the second one is subjected to constant pressure drop. Both optimization processes are carried out using computer simulations generated using COVENTORWARE™. Two of the best structures from each of these optimization studies are selected and further analysis is performed for optimizing their structure dimensions such as width, height and length. A section of the total micro heat-sink is modeled for the initial optimization of the pin-fin shape. The model consists of two sections, the substrate and the fluid. Six different shapes: square, circle, rectangle, triangle, oval and rhombus were analyzed in the initial optimization study. Preliminary tests were conducted using the first model described above for a flow rate of 0.6ml/min. The non dimensional overall thermal resistance of the heat sink, and the nondimensional pumping power was calculated from the results. A figure of merit (FOM) was developed using the nondimensional thermal resistance and nondimensional pumping power for each structure with different pin-fin shapes. Smaller the value of FOM better the performance of the heat sink. The study revealed that the circle and ellipse structures have the best performance and the rectangle structure had the worst performance at low flow rates. At high flow rates rectangular and square structures have the best performance.

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