Republic of IraqMinistry of Higher Education

& Scientific Research University of Kufa

By M.Sc. Hyder Mohammed Abdul Hussein

ABSTRACTA theoretical study includes details flow turbulence in air-conditioned spaces with the determination of the boundary conditions depending on the Iraqi Code of cooling is done in this research. Two kinds of two-dimensional and three-dimensional ventilation problems have been considered:(a) isothermal ventilation in simple rooms.(b) non-isothermal ventilation with coupled heat or mass transfer.The investigation has studied the flow and thermal conditions for four different diffusers (displacement, grille, slot, and square diffusers). The dimensions of the of the physical model are (5.16×3.65 m) with (2.43 m high). The supply condition for four diffusers are (displacement (0.0768 kg/s), grille (0.0768 kg/s), slot (0.1410 kg/s), square (0.750 kg/s)) and temperature at supply for all types is (15.0oC), the return considered as the type of diffusers has been imposed zero flow pressure and temperature at (24.0oC).A modified version of a three-dimensional computer program (fluent 6.3.26) by using finite-volume method was used to simulate the complex flow with buoyant inside the model room. They have been investigated numerically by using several turbulence models and the method solution by using k-ε and k-ω models.

A THEORETICAL STUDY OF A COLD AIR DISTRIBTIONSYSTEM WITH DIFFERENT SUPPLY PATTERNS

The Iraqi Code of Cooling limited the outdoor for Baghdad and indoor conditions are listed in Table (1) and Table (2), respectively.

Table (1) Outdoor data for Iraq

RegionDBT in summer

(ºC)

RH %

in summer

The daily

(ºC)

Altitude

(m)

Latitude

N

Longitude

E

Baghdad 47 16 18.7 34.1 33.32 44.33

Table (2) Indoor condit ions

 DBT in summer

(ºC)

RH %

in summer

Air velocity

(m/s)

Human comfort 19 - 24 40 - 60 1.8 – 2

Recommended conditions

inside the office23 - 26 40 - 50 0.13 – 0.23

Four types of diffusers are set in three orientations all south-facing and all cases running as constant wall temperature, but not that all walls of office are exposed to outside. For each type of diffuser three cases are chosen, the first case just eastern and southern walls, the second case is only the southern wall and the third case is the southern and western wall, and the ceiling wall in all cases is included.

University of KufaCollege of EngineeringMechanical Eng. Dept.

Displacement Diffuser

The inlet diffuser is located near the west wall, and the exhaust opening is at the center

of the ceiling

the objects (human, computers, tables, lamps and cabinets) are simulated.

Boundary conditions:

Supply diffuser: mass flow rate of 0.0768 kg/s , turbulence intensity of 4% .

Return: The outlet is specified as pressure outlet.

Thermal conditions:• Computer 1: 171.43 W/m2

• Computer 2: 274.6 W/m2

• Human simulators: 41.9 W/m2

• Lamps: 37.78 W/m2

Turbulence modeling: Applying that the Realizable k-ε and the SST k-ω models.

University of KufaCollege of EngineeringMechanical Eng. Dept.

Computation meshes: (1,480,232) cells.

Numerical schemes: discretized using the second-order upwind scheme. For the

discretization of pressure, the PRESTO! (PREssure STaggering Option) scheme is used. The

SIMPLEC scheme is used for the pressure-velocity coupling.

Summary of boundary condit ions

Table (3) summarize boundary conditions:

Cases OrientationAir supply

ACH (kg/s)

Air velocity

(m/s)

Gross area

Agross

(m2)

Air temp.

supply

(ºC)

Air temp.

return

(ºC)

Case 1Eastern, southern and

ceiling walls

5.0 (0.0768) 0.35 1.1 × 0.53 15 24Case 2 Southern and ceiling wall

Case 3Southern, western and

ceiling wall

University of KufaCollege of EngineeringMechanical Eng. Dept.

Simulation results

E

W

N

S

Fig. (1) Configuration of the displacement ventilation test case.

Fig. (2) The positions of the measuring poles for the displacement ventilation

test case.

University of KufaCollege of EngineeringMechanical Eng. Dept.

a a

b bFig. (3) Distribution of calculat ion air temperature contours

with k-ε , case 1, (a) plane at z=1.825m, (b) plane at z=0.4m.

Fig. (4) Distr ibut ion of calculation air temperature contours with k-ω , case 1,

(a) plane at z=1.825m, (b) plane at z=0.4m.

a a

b bFig. (5) Distribution of calculat ion air temperature contours

with k-ε , case 1, (a) plane at z=1.825m, (b) plane at z=0.4m.

Fig. (6) Distr ibut ion of calculation air temperature contours with k-ω , case 1,

(a) plane at z=1.825m, (b) plane at z=0.4m.

a a

b b

a

Fig. (7) Distr ibut ion of calculat ion air temperature contours with k-ε , case 2,

(a) plane at z=1.825m, (b) plane at z=0.4m.

Fig. (8) Distr ibution of calculat ion air temperature contours with k-ω , case 2,

(a) plane at z=1.825m, (b) plane at z=0.4m.

a a

b bFig. (9) Distr ibut ion of calculat ion air temperature

contours with k-ε , case 2, (a) plane at z=1.825m, (b) plane at z=0.4m.

Fig. (10) Distribution of calculat ion air temperature contours with k-ω , case 2,

(a) plane at z=1.825m, (b) plane at z=0.4m.

a a

b b

Fig. (11) Distr ibut ion of calculat ion air temperature contours with k-ε , case 3,

(a) plane at z=1.825m, (b) plane at z=0.4m.

Fig. (12) Distr ibut ion of calculat ion air temperature contours with k-ω , case 3,

(a) plane at z=1.825m, (b) plane at z=0.4m.

a a

b b

Fig. (14) Distr ibut ion of calculat ion air temperature contours with k-ε , case 3,

(a) plane at z=1.825m, (b) plane at z=0.4m.

Fig. (15) Distr ibut ion of calculat ion air temperature contours with k-ω , case 3,

(a) plane at z=1.825m, (b) plane at z=0.4m.

Fig. (16) Effect draft temperature for k-ε and k-ω models, (a) case1, (b) case 2, (c) case

3.

a b

c

Gril le DiffuserBoundary conditions:

Supply diffuser: mass flow rate of 0.0768 kg/s , turbulence intensity of 4% .

Return: The outlet is specified as pressure outlet.

Thermal conditions:• Computer 1: 171.43 W/m2

• Computer 2: 274.6 W/m2

• Human simulators: 41.9 W/m2

• Lamps: 37.78 W/m2

Turbulence modeling: Applying that the Realizable k-ε and the SST k-ω models.Computation meshes: (499,952) cells.

Numerical schemes: discretized using the second-order upwind scheme. For the discretization of

pressure, the PRESTO! (PREssure STaggering Option) scheme is used. The SIMPLEC scheme is used

for the pressure-velocity coupling.

University of KufaCollege of EngineeringMechanical Eng. Dept.

Summary of boundary condit ions

Table (4) summarize boundary conditions:

Cases OrientationAir supply

ACH (kg/s)

Air velocity

(m/s)

Gross area

Agross

(m2)

Air temp.

supply

(ºC)

Air temp.

return

(ºC)

Case 1Eastern, southern and

ceiling walls

5.0 (0.0768) 2.7 0.28 × 0.18 15 24Case 2 Southern and ceiling wall

Case 3Southern, western and

ceiling wall

University of KufaCollege of EngineeringMechanical Eng. Dept.

Simulation results

Fig. (17) Configuration of grille ventilation test case

Fig. (18) The positions of the measuring poles for the grille ventilation test case [13].

E

W

N

S

University of KufaCollege of EngineeringMechanical Eng. Dept.

a a

b bFig. (19) Distr ibut ion of calculat ion air temperature

contours with k-ε , case 1, (a) plane at z=1.825m, (b) plane at z=0.4m.

Fig. (20) Distr ibut ion of calculation air temperature contours with k-ω , case 1,

(a) plane at z=1.825m, (b) plane at z=0.4m.

a a

b bFig. (21) Distr ibut ion of calculat ion air temperature

contours with k-ε , case 1, (a) plane at z=1.825m, (b) plane at z=0.4m.

Fig. (22) Distr ibut ion of calculation air temperature contours with k-ω , case 1,

(a) plane at z=1.825m, (b) plane at z=0.4m.

a a

b bFig. (23) Distr ibut ion of calculat ion air temperature

contours with k-ε , case 2, (a) plane at z=1.825m, (b) plane at z=0.4m.

Fig. (24) Distribution of calculat ion air temperature contours with k-ω , case 2,

(a) plane at z=1.825m, (b) plane at z=0.4m.

a a

b bFig. (25) Distr ibut ion of calculat ion air temperature

contours with k-ε , case 2, (a) plane at z=1.825m, (b) plane at z=0.4m.

Fig. (26) Distribution of calculat ion air temperature contours with k-ω , case 2,

(a) plane at z=1.825m, (b) plane at z=0.4m.

a a

b b

Fig. (27) Distr ibut ion of calculat ion air temperature contours with k-ε , case 3,

(a) plane at z=1.825m, (b) plane at z=0.4m.

Fig. (28) Distr ibut ion of calculat ion air temperature contours with k-ω , case 3,

(a) plane at z=1.825m, (b) plane at z=0.4m.

a a

b b

Fig. (29) Distr ibut ion of calculat ion air temperature contours with k-ε , case 3,

(a) plane at z=1.825m, (b) plane at z=0.4m.

Fig. (30) Distr ibut ion of calculat ion air temperature contours with k-ω , case 3,

(a) plane at z=1.825m, (b) plane at z=0.4m.

a b

c

Fig. (31) Gri l le effect draft temperature for k-ε and k-ω models, (a) case1, (b) case 2, (c)

case 3.

Slot DiffuserBoundary conditions:

Supply diffuser: mass flow rate of 0.1410 kg/s , turbulence intensity of 5% .

Return: The outlet is specified as pressure outlet.

Thermal conditions:• Computer 1: 171.43 W/m2

• Computer 2: 274.6 W/m2

• Human simulators: 41.9 W/m2

• Lamps: 37.78 W/m2

Turbulence modeling: Applying that the Realizable k-ε and the SST k-ω models.Computation meshes: (1,071,118) cells.

Numerical schemes: discretized using the second-order upwind scheme. For the discretization of

pressure, the PRESTO! (PREssure STaggering Option) scheme is used. The SIMPLEC scheme is used

for the pressure-velocity coupling.

University of KufaCollege of EngineeringMechanical Eng. Dept.

Summary of boundary condit ions

Table (5) summarize boundary conditions:

Cases OrientationAir supply

ACH (kg/s)

Air velocity

(m/s)

Gross area

Agross

(m2)

Air temp.

supply

(ºC)

Air temp.

return

(ºC)

Case 1Eastern, southern and

ceiling walls

9.2 (0.1410) 3.9 1.15 × 0.10 15 24Case 2 Southern and ceiling wall

Case 3Southern, western and

ceiling wall

University of KufaCollege of EngineeringMechanical Eng. Dept.

Simulation results

Fig. (32) Configuration of slot ventilation test case.

Fig. (33) The positions of the measuring poles for the ceiling slot ventilation test

case, [13].

E

W

N

S

University of KufaCollege of EngineeringMechanical Eng. Dept.

a a

b bFig. (34) Distr ibut ion of calculat ion air temperature

contours with k-ε , case 1, (a) plane at z=1.825m, (b) plane at z=0.4m

Fig. (35) Distr ibut ion of calculation air temperature contours with k-ω , case 1,

(a) plane at z=1.825m, (b) plane at z=0.4m

a a

b bFig. (36) Distr ibut ion of calculat ion air temperature

contours with k-ε , case 1, (a) plane at z=1.825m, (b) plane at z=0.4m

Fig. (37) Distr ibut ion of calculation air temperature contours with k-ω , case 1,

(a) plane at z=1.825m, (b) plane at z=0.4m

a a

b bFig. (38) Distr ibut ion of calculat ion air temperature

contours with k-ε , case 2, (a) plane at z=1.825m, (b) plane at z=0.4m.

Fig. (39) Distribution of calculat ion air temperature contours with k-ω , case 2,

(a) plane at z=1.825m, (b) plane at z=0.4m.

a a

b bFig. (40) Distr ibut ion of calculat ion air temperature

contours with k-ε , case 2, (a) plane at z=1.825m, (b) plane at z=0.4m.

Fig. (41) Distribution of calculat ion air temperature contours with k-ω , case 2,

(a) plane at z=1.825m, (b) plane at z=0.4m.

a a

b b

Fig. (42) Distr ibut ion of calculat ion air temperature contours with k-ε , case 3,

(a) plane at z=1.825m, (b) plane at z=0.4m.

Fig. (43) Distr ibut ion of calculat ion air temperature contours with k-ω , case 3,

(a) plane at z=1.825m, (b) plane at z=0.4m.

a a

b b

Fig. (44) Distr ibut ion of calculat ion air temperature contours with k-ε , case 3,

(a) plane at z=1.825m, (b) plane at z=0.4m.

Fig. (45) Distr ibut ion of calculat ion air temperature contours with k-ω , case 3,

(a) plane at z=1.825m, (b) plane at z=0.4m.

a b

c

Fig. (46) Slot effect draft temperature for k-ε and k-ω models, (a) case1, (b)

case 2, (c) case 3.

Square Diffuser

Boundary conditions:

Supply diffuser: mass flow rate of 0.750 kg/s , turbulence intensity of 5% .

Return: The outlet is specified as pressure outlet.

Thermal conditions:• Computer 1: 171.43 W/m2

• Computer 2: 274.6 W/m2

• Human simulators: 41.9 W/m2

• Lamps: 37.78 W/m2

Turbulence modeling: Applying that the Realizable k-ε and the SST k-ω models.Computation meshes: (1,751,500) cells.

Numerical schemes: discretized using the second-order upwind scheme. For the discretization of

pressure, the PRESTO! (PREssure STaggering Option) scheme is used. The SIMPLEC scheme is used

for the pressure-velocity coupling.

University of KufaCollege of EngineeringMechanical Eng. Dept.

Summary of boundary condit ions

Table (6) summarize boundary conditions:

Cases OrientationAir supply

ACH (kg/s)

Air velocity

(m/s)

Gross area

Agross

(m2)

Air temp.

supply

(ºC)

Air temp.

return

(ºC)

Case 1Eastern, southern and

ceiling walls

4.9 (0.750) 5.2 0.3 × 0.3 15 24Case 2 Southern and ceiling wall

Case 3Southern, western and

ceiling wall

University of KufaCollege of EngineeringMechanical Eng. Dept.

Simulation results

Fig. (47) Configuration of ceiling slot ventilation test case.

Fig. (48) The positions of the measuring poles for the ceiling slot ventilation test

case, [13].

E

W

N

S

Fig. (49) modeling of the square diffuser.

a a

b bFig. (50) Distr ibut ion of calculat ion air temperature

contours with k-ε , case 1, (a) plane at z=1.825m, (b) plane at z=0.4m.

Fig. (51) Distr ibut ion of calculation air temperature contours with k-ω , case 1,

(a) plane at z=1.825m, (b) plane at z=0.4m.

a a

b bFig. (52) Distr ibut ion of calculat ion air temperature

contours with k-ε , case 1, (a) plane at z=1.825m, (b) plane at z=0.4m.

Fig. (53) Distr ibut ion of calculation air temperature contours with k-ω , case 1,

(a) plane at z=1.825m, (b) plane at z=0.4m.

a a

b bFig. (54) Distr ibut ion of calculat ion air temperature

contours with k-ε , case 2, (a) plane at z=1.825m, (b) plane at z=0.4m.

Fig. (55) Distribution of calculat ion air temperature contours with k-ω , case 2,

(a) plane at z=1.825m, (b) plane at z=0.4m.

a a

b bFig. (56) Distr ibut ion of calculat ion air temperature

contours with k-ε , case 2, (a) plane at z=1.825m, (b) plane at z=0.4m.

Fig. (57) Distribution of calculat ion air temperature contours with k-ω , case 2,

(a) plane at z=1.825m, (b) plane at z=0.4m.

a a

b b

Fig. (58) Distr ibut ion of calculat ion air temperature contours with k-ε , case 3,

(a) plane at z=1.825m, (b) plane at z=0.4m.

Fig. (59) Distr ibut ion of calculat ion air temperature contours with k-ω , case 3,

(a) plane at z=1.825m, (b) plane at z=0.4 m.

a a

b b

Fig. (60) Distr ibut ion of calculat ion air temperature contours with k-ε , case 3,

(a) plane at z=1.825m, (b) plane at z=0.4m.

Fig. (61) Distr ibut ion of calculat ion air temperature contours with k-ω , case 3,

(a) plane at z=1.825m, (b) plane at z=0.4 m.

a b

c

Fig. (62) Slot effect draft temperature for k-ε and k-ω models, (a) case1, (b)

case 2, (c) case 3.