A sphere of radius 'R_{1}' is enclosed in a sphere of radius 'R_{2}'. The view (or shape) factor for radiative heat transfer of the outer sphere with respect to the inner sphere is

For a laminar flow of fluid in a circular tube, 'h_{1}' is the convective heat transfer co-efficient at velocity 'V_{1}'. If the velocity is reduced by half and assuming the fluid properties are constant, the new convective heat transfer co-efficient is