A counter flow double pipe heat exchanges using a Super heated steam i...
Heat Transfer Rate Calculation
To calculate the heat transfer rate (\(Q\)) in the counter flow double pipe heat exchanger, we can use the formula:
\[
Q = \dot{m} \cdot C_p \cdot \Delta T
\]
Where:
- \(\dot{m}\) = mass flow rate of water (kg/s)
- \(C_p\) = specific heat capacity of water (approximately \(4.186 \, \text{kJ/kg°C}\))
- \(\Delta T\) = temperature change of water (°C)
First, convert the mass flow rate from kg/hr to kg/s:
\[
\dot{m} = \frac{10,500 \, \text{kg/hr}}{3600 \, \text{s/hr}} \approx 2.9167 \, \text{kg/s}
\]
Calculate \(\Delta T\):
\[
\Delta T = 80°C - 30°C = 50°C
\]
Now, substituting into the formula:
\[
Q = 2.9167 \, \text{kg/s} \cdot 4.186 \, \text{kJ/kg°C} \cdot 50°C \approx 609.93 \, \text{kW} \approx 610 \, \text{kW}
\]
Area Calculation for Parallel Flow
In a parallel flow configuration, the temperature difference between the two fluids is less effective compared to counter flow. The heat transfer rate can be recalculated using the logarithmic mean temperature difference (LMTD):
\[
\text{LMTD} = \frac{\Delta T_1 - \Delta T_2}{\ln{\left(\frac{\Delta T_1}{\Delta T_2}\right)}}
\]
Where:
- \(\Delta T_1 = T_{steam, in} - T_{water, out} = 180°C - 30°C = 150°C\)
- \(\Delta T_2 = T_{steam, out} - T_{water, in} = 130°C - 80°C = 50°C\)
Calculate LMTD:
\[
\text{LMTD} = \frac{150 - 50}{\ln{\left(\frac{150}{50}\right)}} \approx 81.87°C
\]
Now, we calculate the required area (\(A\)) using:
\[
Q = U \cdot A \cdot \text{LMTD}
\]
Thus,
\[
A = \frac{Q}{U \cdot \text{LMTD}} \approx \frac{610,000 \, W}{814 \, W/m^2°C \cdot 81.87°C} \approx 9.05 \, m^2
\]
The increase in area when switching from counter flow to parallel flow generally leads to a larger area requirement, given the less effective heat transfer in the parallel configuration.
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