Encyclopedia of Science

[fahad20]

Q)the chilling room of a meat plant is 15mx18mx5.5m in size and has a capacity of 350 beef carcasses.the power consumed by the fans and the lights in the chilling room are 22 and 2kw respectively,and the room gains heat thru its envelope at a rate of 11kw.the carcasses have an average mass of 280kg,and enter the chilling room at 35 degree celcius after they are washed to facilitate evaporative cooling and are cooled to 16 degree celcius in 12hours.the air enters the chilling room at -2.2 degreecelsius and leaves at 0.5degreecelsius.

determine(a)the refrigeration load of the chilling room(b)the volume flow rate of air.the average specific heats of beef carcasses and air are 3.14 and 1.0kj/(kg.degree celcius) respectively.also the density of air can be taken to be 1.28 kg/cubic meter.


solution....

i have been able to come up with the following ..please help me with further solving...

analysis=there r 2 inlets from where beef and air is entering the control volume.....only 1 outlet for air...

taking the room as the control volume

volume=15*18*5.5=14850 cubic meters.

total mass entering the control volume=350*280=98000kg

now calculating Q(net)

as beef is losing heat and cooling down at a rate...so

Qbeef=mcdelta T
-----------
delta time

=98000*3.14*(35-16)
-------------------------
12*60*60
=135.34kw

as given....

Q(heat gained)=11kw

do i need to calculate the heat gained by air??isnt it equal to the heat lost by beef?.

now calculating net work.

W(net)=-2-22=-24kw (minus because work being done on the system)

now here is the biggest problem..is this a steady flow or unsteady flow?

if i take it as a unsteady flow then its equation is...

. . . 2 . 2
Q- W=sumation m(e)[h(e)+v(e)/2 +gz(e)] -sumation m(i)[h(i)+v(i)/2+gz(i)] + .
delta energy

note=the dots over the variables represent time..i.e rate of work or rate of energy transfer..or rate of mass/flow of mas with respect to time.

now how to apply this equation?...this is confusing...

also m(in)-m(out)=m(2)-m(1)
=delta mass system
1=initial state
2=final state
please help..i have 1 day to submit this assignment..

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