COOLING PLANTS AND TOWERS
.1 Evaporating Cooling :
The atmosphere may be a mixture of air and vapor, in proportions represented by the term wetness. It seldom contains all the vapour it's capable of holding and once it will, its vapour holding capability will be any accumulated by warming it. In any method whereby additional water is volatilised into the air the heat of transformation of evaporation should be provided from some supply. underneath sure conditions this supply will be internal energy of the liquid water from that the vapour is being made. What liquid stay when the vapour has befell is found to be significantly cooled.
The practical application of this to the ability plant or associate industrial advanced is puzzled out {in a|during a|in associate exceedingly|in a very} cooling equipment that is meant to reveal an oversized surface of heat water to an air flow, thereby humidifying the air and cooling the remaining water.
The different varieties of this equipment are :
1. Cooling Ponds 2. Spray Ponds 3. Cooling Towers.
1.2 Cooling Towers and its main elements.
The cooling is an interior device for the state change cooling of water by contact with air.
A typical tower with its main elements is explained here.
The main elements ar :
1. Casing : Encloses heat transfer method and supports different things
2. Fans : For movement of air.
3. Fills or packing : to extend in area of the water.
4. Drift eliminators : it's close to the air outlet and prevents droplets of water being frantic (carryover loss).
5. Water distribution system : To unfold water equally within the system by use of nozzles, troughs and weirs.
6. Sump or basin : At base of the tower to gather cooled water.
1.3 Operative Terms :
1. Cooling vary : distinction between the temperatures of the water coming into and feat the tower.
2. Approach : distinction between the temperature of water feat the tower and also the wet bulb temperature of air coming into the tower.
3. Heat Load : quantity of warmth dissipated within the cooling in B.T. US/min. = Weight of water/min. x cooling vary.
4. structure : Some water is lost by manner of evaporation and a few frantic by the air. thus concerning 100 percent structure water is needed to fill again this lost water.
1.4 Fundamental Principles.
Consider a drop of water within the tower. because the air passes past the water, the warmth is transferred by 3 ways :
1. Radiation : From the surface of the water driblet.
2. Convection and physical phenomenon : From the surface of driblet. Proportional to the temperature distinction between air and water.
3. Evaporation : Caused by the distinction of pressure of vapor at surface of water and in air. There {vapour pressure|vapor pressure|pressure|pressure level|force per unit ara} are functions of water temperature and degree of saturation of air.
a) By radiation from the surface of water driblet. – Negligible
b) By physical phenomenon and convection between water and air.
– About ¼ to 1/3.
c) By evaporation – About ¾ to 2/3
Some wise heat is transferred from water to air within the tower, however the most recent heat of evaporation of the water volatilised is that the main supply of warmth transfer. The degree of cooling action is restricted by the vapour which will be absorbed before the air reaches saturation wetness at it’s feat temperature.
1.4.1Ways to increase cooling capacity Five ways of increasing the cooling capacity of the tower :-
1. Increase velocity of air.
2. Increase surface area of water.
3. Lower the atmosphere pressure.
4. Raise the entering water temperature.
5. Reduce vapour content of the inlet air.
1.5 Cooling Towers :
Cooling towers are classified by 2 ways.
1. Natural Draft : i) Spray filled
ii) Chimney or hyperbolic tower.
2. Mechanical Draft : i) Forced draft
ii) Induced draft
iii) Cross flow type.
The various types of cooling towers along with their merits and demerits are discussed briefly.
1.5.1 Natural Draft Tower :
i) Spray filled tower :
Used for small refrigeration, air conditioning and engine jacked cooling water installations. Compact, less expensive, suitable for roof top installation thus saving floor space.
ii) Frequent clogging of nozzles
iii) High windage losses.
ii) Chimney or Hyper Tower :
Advantages : i) Produce cooling effects similar to those provided by MD tower but without the mechanical parts and power to run them.
ii) Low maintenance cost.
iii) Require small ground area.
Disadvantages : i) Height needed to produce draft.
ii) Control of water temperature difficult to achieve as performance depends upon wind movements.
iii) Capital costs very high.
1.5.2 Mechanical Draft Tower :
i) Forced Draft Tower :
In this type of the tower, fan is at the air inlet side of the tower and velocities of air and water are 180O out of phase.
Advantages : i) Less vibration as fan is located near the ground.
ii) More life for the mechanical assembly as it is in the dry air side.
Disadvantages : i) Chances of hot humid air recirculation.
ii) Chances of ice formation on air fan blades in winter.
iii) Fan size limited, hence more fans needed.
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