List of top Heat Transfer Questions asked in GATE CH

In a double pipe cocurrent heat exchanger, operating at steady state, oil (specific heat capacity = \(2100\ \mathrm{J\,kg^{-1}\,^\circ C^{-1}}\)) entering at \(7\ \mathrm{kg\,s^{-1}}\) at \(100^\circ\mathrm{C}\) is used to heat water (specific heat capacity = \(4200\ \mathrm{J\,kg^{-1}\,^\circ C^{-1}}\)) flowing at \(3.5\ \mathrm{kg\,s^{-1}}\) from \(20^\circ\mathrm{C}\) to \(50^\circ\mathrm{C}\). If the overall heat transfer coefficient is \(291\ \mathrm{W\,m^{-2}\,^\circ C^{-1}}\), the required heat transfer area (in \(\mathrm{m^2}\)) is ______ (rounded off to one decimal place).

A pipe with an outer diameter of \(0.02\ \mathrm{m}\) carries hot water. The temperature at the outer surface of the pipe is \(70^\circ\mathrm{C}\). This pipe is covered with two concentric layers of insulation, each having a thickness of \(0.01\ \mathrm{m}\). The first layer (adjacent to the pipe) is made up of felt material (thermal conductivity \(k_f = 0.12\ \mathrm{W\,m^{-1}\,^\circ C^{-1}}\)), and the next layer is made up of asbestos (thermal conductivity \(k_{as} = 0.15\ \mathrm{W\,m^{-1}\,^\circ C^{-1}}\)). The insulated pipe is exposed to ambient air at \(20^\circ\mathrm{C}\). The convection heat transfer coefficient at the outer insulation layer is \(3\ \mathrm{W\,m^{-2}\,^\circ C^{-1}}\). At steady state, neglecting heat transfer due to radiation, the heat loss at the outer insulation layer (in \(\mathrm{W\,m^{-1}}\)) is ______ (rounded off to two decimal places).