2.2.3 Longitudinal Mixing Effects on Recirculated Cooling Pond
Performance
In addition to dissipating heat from water flowing from an industrial process, the
lowest possible intake temperature of the water re-entering the process is a prime
objective of proper operation of the pond if that water is to be reused in the process.
Dissipating heat and lowering the temperature of the water recirculated back to the
process are not necessarily complementary objectives.
Pond exit temperature (process intake temperature) at a given set of weather
conditions is directly related to the amount of longitudinal mixing that takes place
within the cooling pond. Also affecting this temperature is the uniformity of flow
through the pond. Short circuit flows of water within the pond will result in direct
transport of warm water entering the pond to the pond discharge point. Such short
circuit flow will return water to the process at elevated temperature.
If insufficient longitudinal mixing occurs, a number of techniques are available to
alleviate the condition. Transverse baffles placed in the pond will increase the length
of the flow path of water in the pond. Vertical skimmer walls may be placed in the
pond to minimize wind-driven short circuits. This effect of wind-driven water
currents is also minimized by a high length to width ratio of pond size. Relatively
shallow pond design will minimize vertical water current formation in the pond.
Fig. 5.2 Values of heat transfer coefficients in terms of wind speed and average temperature
206
Y.-T. Hung et al.
Performance
In addition to dissipating heat from water flowing from an industrial process, the
lowest possible intake temperature of the water re-entering the process is a prime
objective of proper operation of the pond if that water is to be reused in the process.
Dissipating heat and lowering the temperature of the water recirculated back to the
process are not necessarily complementary objectives.
Pond exit temperature (process intake temperature) at a given set of weather
conditions is directly related to the amount of longitudinal mixing that takes place
within the cooling pond. Also affecting this temperature is the uniformity of flow
through the pond. Short circuit flows of water within the pond will result in direct
transport of warm water entering the pond to the pond discharge point. Such short
circuit flow will return water to the process at elevated temperature.
If insufficient longitudinal mixing occurs, a number of techniques are available to
alleviate the condition. Transverse baffles placed in the pond will increase the length
of the flow path of water in the pond. Vertical skimmer walls may be placed in the
pond to minimize wind-driven short circuits. This effect of wind-driven water
currents is also minimized by a high length to width ratio of pond size. Relatively
shallow pond design will minimize vertical water current formation in the pond.
Fig. 5.2 Values of heat transfer coefficients in terms of wind speed and average temperature
206
Y.-T. Hung et al.