2.4. Heat transfer between cold vapour and neck wall is extremely good. Moreover, heat transfer from a heater
element mounted in the cold vapour is shared across the whole vapour column by a spontaneous process of
horizontal convection, via the density stratification in the vapour. Measurements have indicated that the effective
heat transfer coefficient is enhanced by up to 10 fold.
Thus, it has been found that horizontal vapour cooled radiation shields in the neck can absorb infra-red radiation
heat flows down the neck very efficiently. With optimum positioning, they can totally absorb the radiation heat
flow, with almost zero radiation heat flow into the liquid.