In the thin wall tube-in-tube heat exchanger oil flows in the gap and water flows through the inner tube with walls heated by electrical current at a constant heat flux. The flow of the oil is one-dimensional and can be described by the z component of the momentum balance (Eq. 1). Eq. 2 gives general thermal energy balance for oil. (tvz+vrrvz+rvvz+vzzvz)=zp+[r1r(rrvz)+r2122vz+z22vz]+gztT+vrrT+rvT+vzzT=cpk[r1r(rrT)+r2122T+z22T]+cps (c) The oil velocity distribution can be approximated by the following semiempirical equation: vz(r)=5.95(1.0400r2+1.08lnr0.05) where vz[ms1],r[m] Comment on the accuracy of this approximation by checking the boundary conditions and calculate pressure drop per unit length of the outer tube. DATA [35\%] Physical properties of oil: =950kgm3,=2.5Pas,cp=800Jkg1K1,k=0.85Wm1K1 Diameters of the pipes: d1=0.05m,d2=0.10m