For a certain two-dimensional incompressible flow, velocity field is given by $$2xy\widehat i - {y^2}\widehat j.$$ The streamlines for this flow are given by the family of curves

Steady one-dimensional heat conduction takes place across the faces $$1$$ and $$3$$ of a composite slab consisting of slabs $$A$$ and $$B$$ in perfect contact as shown in the figure, where $${k_A},\,\,{k_B}$$ denote the respective thermal conductivities. Using the data as given in the figure, the interface temperature $${T_2}$$ $$\left( {in\,{\,^ \circ }C\left. \, \right)} \right.$$ is ______________.

A cylindrical steel rod, $$0.01$$ $$m$$ in diameter and $$0.2$$ $$m$$ in length is first heated to $${750^ \circ }C$$ and then immersed in a water bath at $${100^ \circ }C.$$ The heat transfer coefficient is $$250\,W/{m^2}$$-$$K.$$ The density, specific heat and thermal conductivity of steel are $$\rho = 7801\,\,kg/{m^3},$$ $$c = 473$$ $$J/kg$$-$$K,$$ and $$k = 43$$ $$W/m$$-$$K,$$ respectively. The time required for the rod to reach $${300^ \circ }C$$ is ________ seconds.

Grashof number signifies the ratio of