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Homework Help: Themo Problem

  1. Nov 18, 2004 #1
    Here's my problem:
    For each kW of power input to an icemaker at steady state, determine the maximum rate that ice can be produced in kg/h, from liquid water at 0 C. Assume that 333 kJ/kg of energy must be removed by heat transfer to freeze water at 0 C, and that the surroundings are at 20 C.

    I know that W = 1 kw, Tc = 0C=273 K, Th = 20C=293 K.
    Since the device operates at steady state, W = Qh - Qc.
    I also know that W/Qh is less than or equal to (1- Tc/Th)

    Could someone give me a hint on where to start with this one? What is the 333 kJ/kg?

    Thanks!
     
  2. jcsd
  3. Nov 19, 2004 #2
    The answer is [tex]14.76kgh^{-1}[/tex], is it?

    My working is as follow:
    [tex]Q_c=mL_f=m(333\times10^3)[/tex]
    [tex]\frac{Q_c}{Q_h}=\frac{T_c}{T_h}[/tex]
    [tex]\Rightarrow Q_h=m(357.4\times10^3)[/tex]
    [tex]W=Q_h-Q_c=m(24.4\times10^3)[/tex]
    [tex]1\times10^3=\frac{m(24.4\times10^3)}{t}[/tex]
    [tex]\frac{m}{t}=40.98\times10^{-3}kgs^{-1}=147.54kgh^{-1}[/tex]
     
    Last edited: Nov 19, 2004
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