Optimal eccentric annuli (Containing atmospheric-pressure air) for thermally insulating, horizontal, relatively cold pipes

The geometrical configurations of those air-filled, horizontal eccentric annuli, that provide maximum thermal insulation corresponding to various imposed temperature conditions have been identified. For the concentric system, a simple correlation is presented which will permit the calculation of the associated steady-state rates of convective/conductive heat leak through the air annulus to the horizontal pipe conveying a chilled fluid. The conclusions and recommendations should be of use to designers, especially of district-cooling networks.