In a double pipe heat exchanger, hot fluid (mass flow \(M \mathrm{~kg} / \mathrm{s}\) and specific heat \(\mathrm{C} \mathrm{kJ} / \mathrm{kg}{ }^{\circ} \mathrm{C}\) ) flows inside a pipe and cold fluid (mass flow \(\mathrm{m} \mathrm{kg} / \mathrm{s}\) and specific heat \(\mathrm{c}\) \(\mathrm{kJ} / \mathrm{kg}^{\circ} \mathrm{C}\) ) flows outside in the annular space. The hot fluid enters the heat exchanger at \(T_{h 1}\) and leaves at \(T_{h 2}\) whereas the cold fluid enters at \(T_{c 1}\) and leaves at \(T_{c 2}\). Set up the differential equation to determine the temperature variation (along the heat exchanger) for hot and cold fluids.