FREE-CONVECTION HEAT-TRANSFER FROM ARRAYS OF VERTICALLY SEPARATED HORIZONTAL CYLINDERS AT LOW RAYLEIGH NUMBERS

Steady state free convection heat transfer from horizontal isothermal cylinders in vertical arrays of two to eight, at low Rayleigh numbers, is studied, experimentally. Effects of Rayleigh number and cylinder to cylinder separation distance on the heat transfer behavior of the cylinders are investigated. Heat transfer from the bottom cylinder remains the same as that of a single cylinder. However, for other cylinders we may have either reduction or improvement of heat transfer which depends on their location in the array and the geometry of the array. Results show that there is an optimum separation distance for the best overall convection heat transfer of each array. A correlation is presented to calculate the array Nusselt number in terms of Rayleigh number, cylinder spacing to diameter ratio and number of cylinders in the array.