Line Fabric through the oven

Fabric GSM g/m2

Working Width m

Line Speed m/min

Wet Pick-Up %

Liquor carried out of the mangle, on dry fabric weight

Temperatures What has to be heated, and to what

Fabric Inlet Temperature degC

Cure Temperature degC

Thermal Constants & Cost Properties and plant efficiency

Specific Heat of Water kJ/kg.K

Latent Heat of Evaporation kJ/kg

At atmospheric pressure. This term dominates everything

Specific Heat of Fabric kJ/kg.K

Oven Thermal Efficiency %

Useful heat as a share of fuel energy, after exhaust and shell losses

Energy Cost cost/kWh

Burner Duty Required

— kW

Fuel energy per hour, after oven efficiency

Heat Balance

Fabric Throughput: — kg/h
Water to Evaporate: — kg/h
Heating the Water: — kJ/h
Boiling the Water: — kJ/h
Heating the Cloth: — kJ/h
Latent Share of Useful Heat: — %
Useful Heat: — kJ/h
Fuel Energy Required: — kJ/h
Energy per kg of Fabric: — kJ/kg
Energy per kg of Water: — kJ/kg
Energy Cost: — cost/h
Saved by 5 Points Less Pick-Up: — cost/h

The balance is steady-state and counts only what leaves in the fabric and the vapour; it does not model the air actually moved through the oven, which is where a badly set exhaust throws away far more than any of these terms. Energy per kilogram of water is the number to benchmark against, and a well-run stenter sits near 3,000 to 3,500 kJ per kilogram evaporated - a figure well above that points at exhaust humidity rather than at anything in this calculation, because an oven exhausting drier air than it needs to is heating fresh air for no purpose. Oven efficiency is therefore doing a great deal of work as a single input and should be measured rather than assumed. Cure is treated as a temperature to reach rather than a time to hold, so a resin needing dwell at temperature will need a longer oven than the heat balance alone suggests. The pick-up sensitivity assumes the same efficiency at the lower loading, which is slightly conservative: a stenter with less water to remove usually runs at a better exhaust setting as well, so the real saving tends to exceed the figure shown.

Pad-Dry-Cure Thermal Load & Pick-Up Sensitivity — free, with the formula and a worked example, at Textile School.