Water flows through a cast steel pipe (k = 50 W/mK) with an outer diameter of 104 mm and 2 mm wall thickness. Consider a constant water temperature of 15 ⁰C inside the pipe (h = 30,000 W/m² K), exposed to an outside air temperature of -10 ⁰C and an outside heat transfer coefficient of 20 W/m²K.

a. Calculate the heat loss by convection and conduction per metre length of uninsulated pipe.

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Answer:

Let's calculate the values step by step.

Given:

- \( k = 50 \, \text{W/mK} \)

- \( h = 30,000 \, \text{W/m}^2\text{K} \)

- \( T_{\text{in}} = 15 \, \text{°C} \)

- \( T_{\text{out}} = -10 \, \text{°C} \)

- \( D_{\text{out}} = 104 \, \text{mm} \)

- \( \text{Wall thickness} = 2 \, \text{mm} \)

First, calculate \( D_{\text{in}} \):

\[ D_{\text{in}} = D_{\text{out}} - 2 \times \text{Wall thickness} \]

\[ D_{\text{in}} = 104 \, \text{mm} - 2 \times 2 \, \text{mm} = 100 \, \text{mm} \]

Convert \( D_{\text{in}} \) to meters: \( D_{\text{in}} = 0.1 \, \text{m} \)

Now, calculate \( Q_{\text{cond}} \):

\[ Q_{\text{cond}} = \frac{2\pi k L (T_{\text{in}} - T_{\text{out}})}{\ln\left(\frac{D_{\text{out}}}{D_{\text{in}}}\right)} \]

\[ Q_{\text{cond}} = \frac{2 \times \pi \times 50 \times L \times (15 - (-10))}{\ln\left(\frac{0.104}{0.1}\right)} \]

Now, calculate \( Q_{\text{conv}} \):

\[ Q_{\text{conv}} = h \times 2\pi L (T_{\text{in}} - T_{\text{out}}) \]

\[ Q_{\text{conv}} = 30,000 \times 2 \times \pi \times L \times (15 - (-10)) \]

Please provide the length (\( L \)) of the pipe so that we can calculate the numerical values.