An air refrigeration system works on Bell – Coleman cycle. It draws air at the rate of 1 kg/s from the cold chamber at 1 bar and 5°C. Air is compressed to 7 bar and then is cooled to 25°C before sending it to the expansion cylinder. Given γ = 1.4 c_p = 1.005 kJ/kg-K and 7^0.286 = 1.745. The refrigeration effect for this system in tonne per hour, is:

Concept:

Bell Coleman or Reversed Brayton cycle: there are two isobaric and two isentropic process in this cycle which are as follows:

• 1-2 Isentropic compression
• 2-3 Constant pressure heat rejection
• 3-4 isentropic expansion
• 4-1 Constant pressure heat additionThe pressure at point 1 and 2 are equal ⇒ P₁ = P₄

The pressure at point 3 and 4 are equal ⇒ P₂ = P₃ 

In isentropic process : , ,  

Refrigeration effect (RE) = C_p (T1 - T4) kJ/Kg

Refrigeration capacity  kW

1 Tonne Refrigeration per hour  = 3.5 kW

Calculation:

Given:

P₁ = P₄ = 1 bar , P₂ = P3 = 7 bar, T₁ = 5 °C = 5 + 273  = 278 K, T₃ = 25 °C = 25 + 273 = 298 K

 , γ = 1.4 cp = 1.005 kJ/kg-K,  70.286 = 1.745

(RE) = Cp (T1 - T₄)

Apply isentropic relation between 3 & 4

 ⇒  

T₄ = 170.77 K

RC = 1 x 1.005 (278 - 170.77) = 107.76 KW

Since 1TR = 3.5 kW

Hence the nearest answer is an option (2) 30.6 TR