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Journal of Thermal Spray Technology

, Volume 28, Issue 1–2, pp 144–160 | Cite as

Pin Fin Array Heat Sinks by Cold Spray Additive Manufacturing: Economics of Powder Recycling

  • J. PerryEmail author
  • P. Richer
  • B. Jodoin
  • E. Matte
Peer Reviewed
  • 117 Downloads

Abstract

As a result of the rise in processing power demands of today’s personal computers, water-cooled pin fin heat sinks are increasingly being employed for the cooling of graphical processing units. Currently, these high-performance devices are manufactured through high-cost, high-waste processes. In recent years, a new solution has emerged using the cold gas dynamic spray process, in which pin fins are manufactured onto a base plate by spraying metallic powder particles through a mask allowing for a high degree of adaptability to different graphics processing unit shapes and sizes. One drawback of this process is reduced deposition efficiency, resulting in a fair portion of the feedstock powder being wasted as substrate sensitivity to heat and mechanical residual stresses requires the use of reduced spray parameters. This work aims to demonstrate the feasibility of using powder recycling to mitigate this issue and compares coatings sprayed with reclaimed powder to their counterparts sprayed with as-received powder. The work demonstrates that cold gas dynamic spray is a highly flexible and economically competitive process for the production of pin fin heat sinks when using powder recycling. The heat transfer properties of the resulting fins are briefly addressed and demonstrated.

Keywords

cold spray economics heat sink pin fin powder recycling 

List of symbols

ΔT1

Inlet temperature difference (°C)

ΔT2

Outlet temperature difference (°C)

ΔTlm

Log-mean temperature difference (°C)

ηf

Fin efficiency

ηo

Surface efficiency

θ

Fin base angle (°)

μ

Dynamic viscosity (Pa s)

ρ

Density (kg/m3)

A*

Nozzle throat area (m2)

Afin

Fin area (m2)

Atot

Total heat transfer area (m2)

Aun-fin

Un-finned area (m2)

B

Transverse fin base width (m)

Bs

Side fin base width (m)

CCu

Cost of copper ($/kg)

Celectricity

Cost of electricity ($/kW-h)

Clabor

Cost of labor ($/h)

CN2

Cost of nitrogen ($/kg)

CpN2

Specific heat of nitrogen (kJ/kg K)

D

Linear spray distance (m)

Dh

Hydraulic diameter (m)

DEmask

Mask deposition efficiency

DEsubstrate

Substrate deposition efficiency

EC

Total electricity cost ($)

GC

Total gas cost ($)

H

Fin height (m)

h

Convection coefficient (W/m2 K)

I1

First-order modified Bessel function

I2

Second-order modified Bessel function

k

Specific heat ratio

kCu

Conductivity of copper (W/m K)

L

Length of the finned area (m)

LC

Total labor cost ($)

m

Fin parameter (m−1)

\(\dot{m}_{{N}2}\)

Mass flowrate of nitrogen (kg/s)

\(\dot{m}_{{\rm water}}\)

Mass flowrate of water (kg/s)

Nfins,w

Number of fins widthwise

P*

Pressure at the nozzle throat (Pa)

Pflow

Perimeter of the flow area (m)

Po

Stagnation pressure (Pa)

PC

Total powder cost ($)

PCmask

Total powder cost lost on the mask ($)

PCsubstrate

Total powder cost lost on the substrate ($)

PCun-deposited

Total powder cost un-deposited ($)

PFR

Powder feed rate (kg/s)

\(\dot{Q}_{\text{Cu}}\)

Heat rate through copper (W)

QN2

Total heat into nitrogen (J)

\(\dot{Q}_{N2}\)

Heat rate into nitrogen (W)

\(\dot{Q}_{\text{water}}\)

Heat rate into water (W)

R

Ideal gas constant (J/mol-K)

RCu

Resistance of copper (K/W)

Req

Equivalent resistance (K/W)

Rfin

Resistance of fins (K/W)

RTC

Thermal contact resistance (K/W)

Run-fin

Resistance of un-finned area (K/W)

Re

Reynolds number

S

Distance between fins (m)

t

Time of spray (s)

T*

Temperature at nozzle throat (°C)

T1

Inlet temperature of nitrogen (°C)

T2

Outlet temperature of nitrogen (°C)

Tblock

Temperature of the block (°C)

To

Stagnation temperature (°C)

Ts

Surface temperature (°C)

Twater,in

Water inlet temperature (°C)

Twater,out

Water outlet temperature (°C)

UA

Thermal conductance (W/K)

Vmax

Maximum flow velocity (m/s)

VT

Traverse velocity (m/s)

W

Width of the finned area (m)

Notes

Acknowledgments

The authors would like to acknowledge the financial support of NSERC.

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Copyright information

© ASM International 2018

Authors and Affiliations

  1. 1.University of Ottawa Cold Spray Research LaboratoryOttawaCanada
  2. 2.Ironside Engineering Inc.OttawaCanada

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