Chilling chickens. Chickens with an average mass of 2.2 kg each and average spec

Question

Chilling chickens. Chickens with an average mass of 2.2 kg each and average specific heat of 3.54 kj/kg. degree C are to be cooled by chilled water that enters a continuous-flow-type immersion chiller at 0.5 degree C. Chickens are dropped into the chiller at a uniform temperature of 15 degree C at a rate of 500 chickens per hour and are cooled to an average temperature of 3 degree C before they are taken out. The chiller gains heat from the surroundings at a rate of 210 kj/min. Determine (a) the rate of heat removal from the chicken, in kW, and (b) the mass flow rate of water, in kg/s, if the temperature rise of water is not to exceed 2 degree C.

Explanation / Answer

m = 2.2 kg

Cp = 3.54 kJ/kgC

Ti = 0.5°C

Tc = 15°C

n = 500 chicken per hour

Tf = 3 °C

Rate = 210 kJ/min

a)

rate of heat removal from chicken in kW

N = 500 chicken / min = 500/60 = 8.333 chicken/s

Qchicken = N*m*C*(Tf-Ti) = 8.333 chicken/s * 2.2 kg /chicken* 3.54 kJ/kg * (3-15)°C = -778.76 kJ/s = -778.76 kW

b)

mass required for water

Qgain = Qlost

Qwater = 778.76 kW

Qwater = m*C*(Tf-Ti)

778.76 kW/s = m * 4.184 kJ/kg*C * (2-0.5)°C

m = 778.76/4.184 (2-0.5) = 279.192 kg/s

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