The purpose of this problem is to investigate the influence of flow gross maldistribution on an…

The purpose of this problem is to investigate the influence
of flow gross maldistribution on an air-cooled air-conditioning condenser with
round tubes and flat fins (Fig. P7.18). Because of the specific packaging
arrangement, the condenser’s face area is blocked by 50%, as shown in Fig.
P7.18b. Assume that the total airflow rate over the partially blocked condenser
of Fig. P7.18b is the same as the airflow rate over the unblocked condenser of
Fig. P7.18a. The Nusselt number and friction factor correlations for the
airside surface are as follows:

Determine the following, mentioning
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The purpose of this problem is to investigate the influence
of flow gross maldistribution on an air-cooled air-conditioning condenser with
round tubes and flat fins (Fig. P7.18). Because of the specific packaging
arrangement, the condenser’s face area is blocked by 50%, as shown in Fig.
P7.18b. Assume that the total airflow rate over the partially blocked condenser
of Fig. P7.18b is the same as the airflow rate over the unblocked condenser of
Fig. P7.18a. The Nusselt number and friction factor correlations for the
airside surface are as follows:

Determine the following, mentioning clearly any additional
assumptions that you may make for the solution during each step.

(a) Percentage increase or decrease in the air-side heat
transfer coefficient due to blockage of the face area.

(b) Percentage increase or decrease in the air-side pressure
drop.

(c) Percentage increase or decrease in   ohA on the air
side. Here assume that    o is sufficiently high that it changes negligibly
with the change in h.

(d) The total thermal resistance for the unblocked condenser
in terms of the airside thermal resistance assuming negligible fouling and wall
resistances. For this case, the ratio ohA on the air side to hA
on the refrigerant side is 1

3. Note that there are no fins on the refrigerant side.
Hint: Use Eq. (3.24).

(e) The total thermal resistance of the partially blocked
condenser in terms of its air-side thermal resistance, again neglecting fouling
and wall resistances. Note that the refrigerant-side heat transfer coefficient
for unblocked and partially blocked condensers remains the same (since the
refrigerant passages are not blocked); only its heat transfer surface area is
affected.

(f ) The NTU of the partially blocked condenser, assuming
the NTU of the unblocked condenser to be 0.5 and UA’s known from parts (d) and
(e).

(g) Finally, determine the reduction in the heat transfer
rate of the condenser assuming that C* = 0 and the same inlet temperature
difference Tmax.

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