Illustration 6.1

Saturated steam at 70.14 kPa is condensing on a vertical tube 0.5 m long having an outer diameter of 2.5 cm and a surface temperature of 80^oC. Calculate the average heat-transfer coefficient.

Solution 6.1

It is a problem of condensation on a vertical plate, thus eq.6.10b can be used,

where, different liquid and steam properties are evaluate at average film temperature,

Using steam table, the temperature of the steam corresponding to 70.14kPa pressure is 90^oC. The average film temperature will then be the average of 80 ^oC and 90 ^oC and it comes out to be 85 ^oC,

Using given data the different properties can be found using steam table and other relevant tables given in the standard literature. The data is tabulates below at 85^oC,

On putting the above values in the above equation,

h_av = 1205.2 W/m² °C