20th June 2011 1Enrico Da Riva , V. Rao

Project Request and Geometry constraints

June 20th 2011Bdg 298

Enrico Da Riva,Vinod Singh Rao

CFD-2011-03-GTKNA-62(Microchannel)

20th June 2011 2Enrico Da Riva , V. Rao

The goal of the Project is to improve the fluid distribution and reduce the pressure

drop across the manifold of the micro channel heat exchanger used for the

cooling of the pixels sensors of the NA62 Giga tracker (GTK).

PROJECT GOAL

20th June 2011 3Enrico Da Riva , V. Rao

A single phase heat exchanger is to be designed for the cooling of silicon pixels sensors of NA62 GTK. The heat load is approximately 32 W distributed over a rectangular domain of 60 mm x 40 mm. Perfluorohexane (C6F14) is used as the working fluid. The geometry of the microchannels is fixed in the initial prototype and the CFD simulation is aimed to improve the design of the inlet and outlet manifolds.

Description of the problem

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Approximate Heat load:- 32 WHeating Area :- 60x40 mm2

Problem Documentation

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Microchannels display square cross-section: 100 μm X 100 μm

Problem Documentation

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Problem Documentation

The thickness of the central must be ≤ 100 μm

20th June 2011 7Enrico Da Riva , V. Rao

Description of the problem

The major objectives of the simulation are:- Improve the refrigerant flow distribution. Reduce the pressure drop through the manifold. Reduce the pressure drop through the micro-channels. Improve the heat transfer coefficient.

Major design parameters:- Shape of the manifold. Thickness of the manifold.

(Shape of the micro-channels)

The results required are:- Compute the refrigerant flow in order to check distribution and pressure drop. Compute the local temperature distribution.

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Problem Documentation

Thickness of the silicon wafer: 380 µm Thermal conductivity of silicon: ???? Diameter of the silicon wafer: 90 mm Diameter of the inlet : 1.4 mm Thickness(Depth) of channels: 100 µm Width of channels: 100 µm

Working fluid: Perfluorohexane (C6F14) @ -25°C Design mass flow rate : 7 gm sec-1

Density : 1805.25 kg m-3 @ -25 °C Kinematic Viscosity: 0.8 cSt @ -25 °C Thermal Conductivity: 0.05999 W m-1 °C-1 @ -25 °C Liquid Specific Heat: 975.15 J kg-1 °C-1 @ -25 °C

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Problem Documentation

Variation of Properties with temperature:-Specific Heat (J kg-1 °C-1) = 1014 + 1.554 (T, °C)Thermal Conductivity (W m-1 °C-1) = 0.060 – 0.00011 (T, °C) Density (kg m-3) = 1740 – 2.61 (T, °C)  

Constraints :-•Since the radiations have to pass through the detector, the thickness(depth) of the micro channel can not be more than 100 µm . Although the thickness of the manifolds can be increased.•For a refrigerant temperature drop of approximately 5 °C , the mass flow rate is fixed to 7 gm/sec for the given heat load and fluid used . So, the mass flow rate can not be decreased any further.•Breakdown of the Pyrex layer at the inlet manifold (and sometimes of the wafer itself) was observed during experimental tests: pressure drop must be decreased and the gap between the bonds cannot be too large (e.g. the size of the manifold cannot be increased too much). •The inlet and outlet have to be normal to the plane of the channels for proper integration in the over all system.

EXPERIMENTAL DATA: PRESSURE DROP

• “Corrected pressure drop” takes into account Δp in the inlet/outlet piping (L=0.5 m, D=1.4mm)• Experimental tests are performed at 15°C, but the design working temperature is -25°C

(kinematic viscosity is the double at -25°C as compared to 15°C → around double Δp for laminar flow)

• Q = m cp ΔT, Q = 32 W, cp = 975 J kg-1 K-1

• Design mass flow rate: m = 0.007 kg/s → ΔT = 4.7 K

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Problem Documentation

Possible solutions:-• Modification in the shape of the channels to reduce the

pressure drop in the micro channels.• Redefining the geometry of the manifolds i.e. by introducing

multiple inlet-outlet or multiple inlet – single outlet etc. • Modification in the shape of manifolds in terms of curvature

and its conicity .• If possible , using a different fluid with higher heat capacity so

the mass flow rate can be decreased.

20th June 2011 11Enrico Da Riva , V. Rao

“Roll-bond” solar collectors

20th June 2011 12Enrico Da Riva , V. Rao