ASHRAE Journal - June 2019 - 22

TECHNICAL FEATURE

FIGURE 2 Airflow patterns at the central plane for isothermal conditions indicate that the discharge velocity has little impact on the distribution of airflow.

a) 200 cfm (94.4 L/s)

c) 600 cfm (283.2 L/s)

A total of four supply airflow rates ranging from 200,
400, 600, and 800 cfm (94.4, 188.8, 283.2, and 377.6 L/s)
corresponding to the discharge face velocities of 25,
50, 75, and 100 fpm (0.13, 0.25, 0.38, and 0.51 m/s),
respectively were analyzed for both isothermal and
non-isothermal cases. In the case of non-isothermal
analyses the cooling capacities of the supply air correspond one, two, three and four times of the sensible
heat load, respectively. The supply air temperature in
all these cases was maintained at 65°F (18.3°C). A standard k-epsilon (k-e) turbulence model was employed to
compute the turbulent viscosity of the air. The predicted
air velocities in each case are normalized by the respective discharge velocities to facilitate the comparison of
results under various test conditions.

Isothermal Analysis
The isothermal analysis was performed without a heat
source for four different supply airflow rates. It indicates
22

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J U N E 2 0 19

b) 400 cfm (188.8 L/s)

d) 800 cfm (377.6 L/s)

that the supply airflow rate or discharge velocity has
little impact on the overall airflow patterns and velocity distribution. Airflow patterns and velocity distribution at the central plane are presented in Figures 2 and
3. The overall airflow patterns exhibit an inverted "Y"
shape. These analyses indicate that the supply airstream
maintains almost unidirectional flow for about 55% of
the distance from the ceiling. Thereafter, the downward
velocity begins to decrease gradually and eventually
reaches to a zero value near the surface of the table.
The main stream of the supply air, as it approaches the
table, splits into two sideward jets which move towards
the exhaust grilles. The velocity distribution indicates
that the high velocity zone remains attached to the
ceiling in the central core of the jet (Figure 3). Also the
sideward jets after separating from the table gain slight
momentum. Such airflow patterns form air recirculation zones above and below the sideward jets, although
the recirculation zones adjacent to the table are formed


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ASHRAE Journal - June 2019

Table of Contents for the Digital Edition of ASHRAE Journal - June 2019

Contents
ASHRAE Journal - June 2019 - Intro
ASHRAE Journal - June 2019 - Cover1
ASHRAE Journal - June 2019 - Cover2
ASHRAE Journal - June 2019 - 1
ASHRAE Journal - June 2019 - Contents
ASHRAE Journal - June 2019 - 3
ASHRAE Journal - June 2019 - 4
ASHRAE Journal - June 2019 - 5
ASHRAE Journal - June 2019 - 6
ASHRAE Journal - June 2019 - 7
ASHRAE Journal - June 2019 - 8
ASHRAE Journal - June 2019 - 9
ASHRAE Journal - June 2019 - 10
ASHRAE Journal - June 2019 - 11
ASHRAE Journal - June 2019 - 12
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ASHRAE Journal - June 2019 - 14
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ASHRAE Journal - June 2019 - 20
ASHRAE Journal - June 2019 - 21
ASHRAE Journal - June 2019 - 22
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ASHRAE Journal - June 2019 - 37
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ASHRAE Journal - June 2019 - Cover3
ASHRAE Journal - June 2019 - Cover4
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