Textile Dye-Bath Heat Recovery Simulator

Dye-Bath Discharge

Hot wastewater in T_h,in 70 °C

Fresh mains water in T_c,in 15 °C

Heat Exchanger

Flow rate (both streams) 20 L/min

Exchanger size (UA) 2000 W/K

Live Readouts

Heat recovered Q

0.0 kW

Preheated water out T_c,out

0.0 °C

Dye-bath heating energy saved

0 %

■ hot wastewater (draining out) ■ fresh water (preheating in)
Counter-flow: the two streams move in opposite directions through the exchanger core.

How it works

A counter-flow heat exchanger routes hot dye-bath wastewater one way and incoming fresh mains water the other way through a shared thermal core, so the fresh water leaves already warm — cutting the energy the next dye bath needs from its heater. This uses the effectiveness–NTU method with balanced flow (equal mass flow, equal specific heat c_p on both sides, so C_r = 1):

C = ṁ·c_p            (thermal capacity rate, W/K)
NTU = UA / C          (number of transfer units)
ε = NTU / (1 + NTU)   (effectiveness, balanced counter-flow)
Q = ε·C·(T_h,in − T_c,in)
T_c,out = T_c,in + Q/C
T_h,out = T_h,in − Q/C

A special feature of the balanced counter-flow case (C_r=1): the temperature difference between the two streams stays constant along the entire length of the exchanger, so both temperature profiles are straight lines running in opposite directions — that's exactly what the two colored tubes show.

T_h,in — how hot the dye-bath discharge is (higher-temperature dye processes recover more).
T_c,in — incoming mains water temperature (colder mains → bigger possible gain).
Flow rate — raising it raises C, which lowers NTU and effectiveness ε, but each liter still carries more heat — a real design trade-off.
Exchanger size (UA) — a bigger/better plate exchanger raises UA, raising NTU and effectiveness, at higher capital cost.

Real mills routinely recover 40–60% of dye-bath heating energy this way, since dyeing and rinsing baths are drained hot (60–90 °C) and immediately refilled with cold mains water for the next batch.

Hot wastewater Fresh preheated water

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