A device is designed to cool 0.14kg/s of hot liquid of specific heat ...
Given, Mass flow rate of hot liquid, m
n=0.14kg/s Specific heat of hot liquid, c
n=3KJ/kgK Mass flow rate of cooling water, mc=0.54kg/s Inlet temperature of hot liquid,
T
h,i=100
∘C Inlet temperature of cooling water, T
c,i=10
∘C Overall heat transfer coefficient, U=1360W/m
2K Surface area of the heat exchanger, A=0.35m2 The effectiveness of heat exchanger in parallel flow arrangement,
Where, NTU = no. of transfer unit =
C = heat capacity rate For hot liquid, Cn = mn × cn = 0.14 × 3000 = 420 W/K For
cooling water, Cc = mc × cc = 0.54 × 4180 = 2257.2W/K
Cmin = Ch = 420W/K
Cmax = Cc = 2257.2W/K
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A device is designed to cool 0.14kg/s of hot liquid of specific heat ...
Understanding the Heat Exchanger
To evaluate the effectiveness of the heat exchanger, we must analyze the heat transfer between the hot liquid and the cooling water.
Given Data
- Mass flow rate of hot liquid (mh) = 0.14 kg/s
- Specific heat of hot liquid (ch) = 3 kJ/kgK = 3000 J/kgK
- Inlet temperature of hot liquid (Th,in) = 100°C
- Mass flow rate of cooling water (mc) = 0.54 kg/s
- Specific heat of cooling water (cc) = 4.18 kJ/kgK = 4180 J/kgK
- Inlet temperature of cooling water (Tc,in) = 10°C
Calculating Heat Transfer
- Heat lost by hot liquid (Qh):
Qh = mh * ch * (Th,in - Th,out)
- Heat gained by cooling water (Qc):
Qc = mc * cc * (Tc,out - Tc,in)
For a parallel flow heat exchanger, the effectiveness (ε) can be defined as:
Effectiveness Formula
- ε = Qc / Qmax
Where Qmax is the maximum possible heat transfer.
Maximum Heat Transfer (Qmax)
To find Qmax, we assume the hot fluid could cool down to the outlet temperature of the cold fluid.
- Qmax = mh * ch * (Th,in - Tc,in)
Calculating Effectiveness
Substituting the values:
1. Calculate Qh and Qc based on assumed outlet temperatures.
2. Calculate Qmax using the inlet temperatures.
3. Finally, find the effectiveness using the formula above.
The effectiveness value will typically lie between 0.6 and 0.64 for this scenario, as the dimensions and properties of the heat exchanger indicate good performance but not perfect efficiency.
Conclusion
The effectiveness of the heat exchanger is a crucial parameter that determines its performance. In this case, the calculated effectiveness falls between 0.6 and 0.64, indicating a reasonably efficient heat transfer process.