Effect Of Main And Exit Channels’ Diameters on Exit

For this purpose, the first channel, determined previously that has 150 mm main and 50 mm exit channel diameters was analyzed.

Area weighted average exit velocity and mass flow rate values obtained from the analyses of the first channel having 150 mm main and 50 mm exit channel diameters are tabulated in Table 4.18 and graphed in Figure 4.26 and 4.27 respectively.

Table 4.18. Results obtained form analysis of 150/50 channel

Exit

Area Weighted Average Exit Velocities of Channel 150/50

Area Weighted Average Exit Velocity (m/s)

150/50

Figure 4.26. Graphic of area weighted average exit velocities of 150/50 channel

Mass Flow Rate of Channel 150/50

0,01

Figure 4.27. Graphic of mass flow rate of 150/50 channel

In order to see the effect of change of main channel diameter on exit velocities and mass flow rates, a controlled test study was conducted by keeping the all properties of the channel and analyses are the same and only chancing the main

channel diameter from 150 mm to 130 mm. Area weighted average exit velocity and mass flow rate values obtained from the analyses are tabulated in Table 4.19 and graphed in Figure 4.28 and 4.29 respectively.

Table 4.19. Results obtained form analysis of 130/50 channel

Exit

Figure 4.28. Graphic of area weighted average exit velocities of 130/50 channel

Mass Flow Rate of Channel 130/50

Figure 4.29. Graphic of mass flow rate of 130/50 channel

As the results obtained from the first 2 analyses were compared, it is seen that decreasing the main channel diameter has a negative effect on exit velocity and mass flow rate stability. Because when a standard deviation value was calculated by employing the following equation, it is seen that standard deviation for the channel having 150 mm is 14,1%, while 17,3% for 130 mm main channel.

n

i X Xİ

n ₁( )² 1

With a similar approach, in order to see the effect of change of exit channel diameter on exit velocities and mass flow rates, a controlled test study was conducted again by keeping the main channel diameter 130 mm and chancing the exit channel diameter from 50 mm to 30 mm.

Area weighted average exit velocity and mass flow rate values obtained from the analyses of 130/30 channel are tabulated in Table 4.20 and graphed in Figure 4.30 and 4.31 respectively.

Table 4.20. Results obtained form analysis of 130/30 channel

Area Weighted Average Exit Velocities of Channel 130/30

24

Area Weighted Average Exit Velocity (m/s)

130/30

Figure 4.30. Graphic of area weighted average exit velocities of 130/30 channel

Mass Flow Rate of Channel 130/30

Figure 4.31. Graphic of mass flow rate of 130/30 channel

Results obtained from the analyses of the channels 150/50, 130/50 and 130/30 are compared in Figures 4.32 and 4.33 collectively.

Area Weighted Average Exit Velocities

6

Area Weighted Average Exit Velocity (m/s)

150/50 130/50 130/30

Figure 4.32. Graphic of area weighted average exit velocities of the channels

Exit Mass Flow Rate

Figure 4.33. Graphic of mass flow rates of the channels

Subtractions gained from the evaluations of the results of the first 3 analyses are as follows;

As the main channel diameter decreased, exit velocity and consequently mass flow rate of the exit 1, which is positioned parallel to the flow direction, increased.

Similarly an increase in velocity and mass flow rate of Exit 6 and 7, which are located close to the inlet region, was observed. Velocity and mass flow rate of rest of the exits has a small amount of decrease.

As the exit channel diameter decreased, velocity magnitude of all exits increased drastically. While the average exit velocity of the channel having 150 mm main and 50 mm exit diameter is approximately 10 m/s, average velocity of the channel having same main channel diameter (150mm) and 30 mm exit channel is about 27 m/s.

On the other hand, decreasing the exit channel diameter decreases the deviation of the mass flow rate and provides a graphic near to flat. The minimum standard deviation value of mass flow rate was found with the channel having 130 mm main and 30mm exit channel diameter as 4,6 %.

By evaluating all these results and subtractions, it is predicted that, the channel having larger main diameter and smaller exit channel diameter would provide the minimum deviation. And consequently a channel having 150 mm main and 30 mm exit channel diameter was designed and re-analyzed again under the specified conditions.

Area weighted average exit velocity and mass flow rate values obtained from the analyses of 150/30 channel are tabulated in Table 4.21 and graphed in Figure 4.34 and 4.35 respectively.

Table 4.21. Results obtained form analysis of 150/30 channel

Exit

Area Weighted Average Exit Velocities of Channel 150/30

Area Weighted Average Exit Velocity (m/s)

150/30

Figure 4.34. Graphic of area weighted average exit velocities of 150/30 channel

Mass Flow Rate of Channel 150/30

0,01

Figure 4.35. Graphic of mass flow rate of 150/30 channel

As it was predicted, as the main channel diameter was increased and the exit channel diameter was decreased, deviation of exit mass flow rates decreased to approximately 2 %.

Collective results obtained from the analyses of the channels 150/50, 130/50, 130/30 and 150/30 are showed and compared in Figures 4.36 and 4.37.

Area Weighted Average Exit Velocities

6

Area Weighted Average Exit Velocity (m/s)

150/50 130/50 130/30 150/30

Figure 4.36. Graphic of area weighted average exit velocities of the channels

Exit Mass Flow Rate

Figure 4.37. Graphic of mass flow rates of the channels

However, although the 150/30 channel has minimum deviation and fluctuation on both velocity and mass flow rate theoretically, in the application to the vehicle the channel 150/30 has some problems;

Maximum main channel diameter was restricted by the vehicle construction (i.e. Roof structure and luggage rack profile). So the main channel diameter cannot be increased anymore. Also decreasing the exit channel diameter, increases the exit velocity extremely and consequently the internal noise, which is the one of the most important parameter affecting passenger comfort. In the current study, by considering all these subtractions and situations, it was tried to design the air channel that would provide homogenous air distribution with suitable noise level.