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Open vessels containing heated fluids should be covered to minimize losses.

Open vessels that contain heated liquids often have a high loss due to surface evaporation. An open surface of area 50m2 loses 14940Kcal of energy per hour! Both energy and liquid losses are reduced by covering open vessels with insulated lids. Though this is a commonly known solution, it is often not implemented on the plant floor.

The table below shows the amount of heat lost per m2 of open surface in Kcal/hr. The losses are dependent on the difference between the ambient temperature and the liquid temperature.

heat loss table


A tank 5m wide and 10m long, is maintained at a constant temperature of 65°C. The evaporative heat loss from the tank if ambient temperature is 30°C would be:

Area of evaporating surface = 5m x 10m = 50m2

Total heat loss for uncovered liquid surface = 298.8Kcal/hr/m2 x 50m2 = 14940Kcal/hr = 5.4KL of FO / yr