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Numerical Heat Transfer, Part A: Applications
An International Journal of Computation and Methodology
Volume 70, 2016 - Issue 1
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Original Articles

Rapid prediction of exergy destruction in data centers due to airflow mixing

, , &
Pages 48-63 | Received 23 Sep 2015, Accepted 03 Dec 2015, Published online: 02 May 2016
 

ABSTRACT

A novel lumped parameter approach is introduced to predict data center exergy destruction due to airflow mixing, resulting in a speedup of several orders of magnitude compared to detailed computational fluid dynamics (CFD) simulations. Both lumped parameter and detailed CFD methods agree within 8.5% for 11 test cases on an example data center. A significant time-saving design strategy is also introduced using two detailed CFD simulations to predict bulk flow parameters, and then applying lumped parameter analysis on flow-independent design parameters. The strategy shows agreement within 0.39% when computer room air conditioner (CRAC) supply temperature is varied from 12–20°C.

Nomenclature

A=

area, m2

CFM=

cubic feet per minute, ft3/min

cp=

mass-based heat capacity, J/kg K

Dh=

hydraulic diameter, m

err=

error, dimensionless

f=

Darcy friction factor, dimensionless

fB=

flow bypass factor, dimensionless

F=

open area fraction, dimensionless

g=

gravitational acceleration, m/s2

h=

specific enthalpy, J/kg

K=

minor loss factor, dimensionless

L=

length, m

=

mass flow rate, kg/s

N=

quantity

p=

pressure, Pa

P=

perimeter, m

Q=

flow rate, m3/s

=

heat flow, W

R=

flow resistance, Pa-s2/m6

=

mass-based ideal gas constant, J/kg K

=

thermal resistance, K/W

s=

specific entropy, J/kg K

S=

entropy, J/K

SHI=

supply heat index, dimensionless

V=

speed, m/s

=

mechanical work, W

z=

elevation, m

α=

thermal diffusivity, m2/s

Δp=

pressure drop, Pa

=

pressure gain, Pa

ε=

turbulent dissipation, J/kg s

ρ=

mass density, kg/m3

ψ=

specific exergy, J/kg

=

exergy destruction, W

=

nondimensionalized exergy destruction, dimensionless

Subscripts=
c=

cold aisle

ch=

cold aisle to hot aisle through row of racks

cr=

cold aisle to return plenum

DC=

data center

e=

exit

eq=

equivalent

f=

fan

gen=

generation

h=

hot aisle

hc=

hot aisle to cold aisle (recirculation)

hr=

hot aisle to return plenum

i=

inlet

j=

rack designation

k=

server designation

l=

row designation

mix=

airflow mixing

n=

nonserver equipment on rack

nre=

nonrack equipment

r=

return plenum

rack=

rack

row=

row-based

s=

supply plenum

sc=

supply plenum to cold aisle

sh=

supply plenum to hot aisle

S=

surface

sv=

server

t=

turbulent

th=

thermal

x, y, z=

coordinate direction-based

0=

reference condition

Nomenclature

A=

area, m2

CFM=

cubic feet per minute, ft3/min

cp=

mass-based heat capacity, J/kg K

Dh=

hydraulic diameter, m

err=

error, dimensionless

f=

Darcy friction factor, dimensionless

fB=

flow bypass factor, dimensionless

F=

open area fraction, dimensionless

g=

gravitational acceleration, m/s2

h=

specific enthalpy, J/kg

K=

minor loss factor, dimensionless

L=

length, m

=

mass flow rate, kg/s

N=

quantity

p=

pressure, Pa

P=

perimeter, m

Q=

flow rate, m3/s

=

heat flow, W

R=

flow resistance, Pa-s2/m6

=

mass-based ideal gas constant, J/kg K

=

thermal resistance, K/W

s=

specific entropy, J/kg K

S=

entropy, J/K

SHI=

supply heat index, dimensionless

V=

speed, m/s

=

mechanical work, W

z=

elevation, m

α=

thermal diffusivity, m2/s

Δp=

pressure drop, Pa

=

pressure gain, Pa

ε=

turbulent dissipation, J/kg s

ρ=

mass density, kg/m3

ψ=

specific exergy, J/kg

=

exergy destruction, W

=

nondimensionalized exergy destruction, dimensionless

Subscripts=
c=

cold aisle

ch=

cold aisle to hot aisle through row of racks

cr=

cold aisle to return plenum

DC=

data center

e=

exit

eq=

equivalent

f=

fan

gen=

generation

h=

hot aisle

hc=

hot aisle to cold aisle (recirculation)

hr=

hot aisle to return plenum

i=

inlet

j=

rack designation

k=

server designation

l=

row designation

mix=

airflow mixing

n=

nonserver equipment on rack

nre=

nonrack equipment

r=

return plenum

rack=

rack

row=

row-based

s=

supply plenum

sc=

supply plenum to cold aisle

sh=

supply plenum to hot aisle

S=

surface

sv=

server

t=

turbulent

th=

thermal

x, y, z=

coordinate direction-based

0=

reference condition

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