4. At steady state, a new power cycle is claimed by its inventor to develop power at a rate of (a) 90 hp, (b) 100 hp, (c) 110 hp for a heat rejection rate of 5.1 x 105 BTU/hr while operating between hot and cold reservoirs at 1000K and 500 K. Evaluate each claim. Is it impossible, reversible or irreversible

Respuesta :

Answer:

a) Possible

b) Possible

c) Possible

Explanation:

Given:

temperature of hot reservoir, [tex]T_H=1000\ K[/tex]

temperature of the cold reservoir, [tex]T_C=500\ K[/tex]

heat rejected to the colder reservoir, [tex]Q_C=5.1\times 10^5\ btu.hr^{-1}[/tex]

We know that:

[tex]1\ hp=2544.43\ Btu.h^{-1}[/tex]

so,

[tex]Q_C=200.438\ hp[/tex]

a)

power rate developed by the power, [tex]W=90\ hp[/tex]

Now the Carnot efficiency of the cycle:

[tex]\eta_c=1-\frac{T_C}{T_H}[/tex]

[tex]\eta_c=1-\frac{500}{1000}[/tex]

[tex]\eta_c=0.5[/tex] .........................(1)

Now the actual efficiency of the cycle:

[tex]\rm \eta=\frac{desired\ effect}{energy\ consumed}[/tex]

[tex]\eta=\frac{W}{Q_C+W}[/tex]

[tex]\eta=\frac{90}{90+200.438}[/tex]

[tex]\eta=0.31[/tex]

Since [tex]\eta_c>\eta[/tex] therefore the cycle is possible

b)

power rate developed by the power, [tex]W=100\ hp[/tex]

Now the actual efficiency of the cycle:

[tex]\rm \eta=\frac{desired\ effect}{energy\ consumed}[/tex]

[tex]\eta=\frac{W}{Q_C+W}[/tex]

[tex]\eta=\frac{100}{100+200.438}[/tex]

[tex]\eta=0.33[/tex]

Since [tex]\eta_c>\eta[/tex] therefore the cycle is possible

c)

power rate developed by the power, [tex]W=110\ hp[/tex]

Now the actual efficiency of the cycle:

[tex]\rm \eta=\frac{desired\ effect}{energy\ consumed}[/tex]

[tex]\eta=\frac{W}{Q_C+W}[/tex]

[tex]\eta=\frac{110}{110+200.438}[/tex]

[tex]\eta=0.35[/tex]

Since [tex]\eta_c>\eta[/tex] therefore the cycle is possible