Answer / alok prabhu

Natural draught cooling towers use very tall concrete
chimneys to introduce air through the media.Due to large
size of these towers they are generally used for flow rates
above 45,000m^3/hr.These types are used only by utility
power stations.It is used where WET BULB TEMP is
low.Temperature difference achieved is 6-8deg C.

Induced draught/Mechanical draught cooling towers used
large fans to force air through circulating water.The water
falls downwards over fill surfaces which helps increase
contact time between water and air.cooling rate depends
upon fan diameter and speed of operation.It is used where
WBT is more.Used for critical applications.Temp difference
achieved can be 2-15deg C.When fan is switched off it works
as a natural draught cooling tower.

Answer / abdul

The basic criteria is WET BULB TEMPERATURE (WBT).Where WBT is low, NDCT shall be used and where WBT is high, IDCT shall be used. Moreover, NDCT is not very suitable for very dry climates with high dry bulb and low relative humidity, on the other hand IDCT is suitable for all weather conditions.

Answer / suresh sarma

Major factors are :
1. type of Load:- NDCT need consistent load and are not very suitable for part load since the draft is a function of exit air temperature which is a function of hot water. hence mostly used in power plants.
2. NDCT need higher pumping head to provide a proper D/H ratio.
3. NDCT size becomes bigger in dry climate because of low RH. NDCT operate on principle of buoyancy or chimney effect and hence dry and hot weather are much less suitable for it and increase the required size and cost.
4. Time of construction is much more than an IDCT.
5. They are more suitable for larger Ranges and longer approaches.
6. Is generally a concrete structure and requires special equipment and manpower.
7. NDCT performance is directly badly effected by wind speed.
many other finer parameters are there. please read difference between NDCT and IDCT IN https://www.gtpl.co.in/files/Comparison%20between%20Natural%20Draft%20Cooling%20Tower%20and%20Induced%20Draft%20Cooling%20Tower.pdf

Answer / kapil

The selection criteria also depends upon the cost economics. The capital cost of NDCT is more than IDCT.Hence in calculating the tariff the loading of NDCT capital cost w.r.t coal transportation factor is also considered. Normally sea water application favor NDCTs.

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