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Byju's Answer

Standard XII

Chemistry

Pressure and Temperature

Air is flowin...

Question

Air is flowing steadily in an insulated duct. The pressure and specific volume measurements of the air at two station A and B are

Station A Station B

Pressure 100 kPa 98 kPa

Specific volume 0.81 $m^{3} / k g$ 0.97 $m^{3} / k g$

Take $C_{p} = 1.005 k J / k g K; C_{v} = 0.718 k J / k g K .$ What is direction of air flow in duct?

A to B

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B to A

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Can take place in either direction

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No flow of air takes place

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Solution

The correct option is A A to B
Assume flow takes places from A to B

$S_{B} - S_{A} = C_{v} l n (\frac{P_{B}}{P_{A}}) + C_{p} l n (\frac{V_{B}}{V_{A}})$

$= 0.718 l n (\frac{98}{100}) + 1.005 l n (\frac{0.97}{0.81})$

$= - 0.0145 + 0.181$

$= 0.166 k J / k g K$

Since $Δ S$ is positive,

Therefore. flow takes place from A lo B.

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Similar questions

Q. The specific heat of air at constant pressure is

1.005 k J / k g K

and the specific heat of air at constant volume is

0.718 k J / k g K

.Find the specific gas constant.

Q. In an experimaental set-up, air flows between two stations

P

and

Q

adiabatically. The direction of flow depdns on the pressure and temperature conditions maintained at

P

and

Q

. The conditions at

P

are

150 k P a

and

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. The temperature at station

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300 K

. The following are the properties and relations pertaining to air:
Specific heat at constant pressure,

c_{p} = 1.005 k G / k g K;

Specific heat at constnat volume,

c_{v} = 0.718 k J / k g K;

Characteristic gas constnat,

R = 0.287 k J / k g K

Enthalpy,

h = c_{p} T .

Internal energy,

u = c_{v} T .

If the air has to flow from station

P

to station

Q

, te maximum possible value of pressure in

k P a

at station

Q

is close to

In an experimaental set-up, air flows between two stations $P$ and $Q$ adiabatically. The direction of flow depdns on the pressure and temperature conditions maintained at $P$ and $Q$ . The conditions at $P$ are $150 k P a$ and $35 K$ . The temperature at station $Q$ is $300 K$ . The following are the properties and relations pertaining to air:
Specific heat at constant pressure,
$c_{p} = 1.005 k G / k g K;$
Specific heat at constnat volume,
$c_{v} = 0.718 k J / k g K;$
Characteristic gas constnat,
$R = 0.287 k J / k g K$
Enthalpy, $h = c_{p} T .$
Internal energy, $u = c_{v} T .$

If the pressure at station $Q$ is $50 k P a,$ the change in entropy $(s_{Q} - s_{P})$ in $k J / k g K$ is