Cooling Tower

Cooling Tower:
                                                                             
Cooling Tower is used to cool the hot water coming from different units of a process plant and after cooling it is sent back to units. cooling tower is of the following types:
Natural Draft
Force Draft
Balance Draft
Natural Draft cooling tower
It works based on the natural flow of air. dry air from atmosphere is entering into the bottom inlet section of tower and flows up.hot water from different process units is collected and fed at the top of the cooling tower. hot water and dry air comes in contact in counter current manner and evaporative cooling occurs. some water droplets evaporate with upflowing air and latent heat required for evaporation is taken from hot water. so temperature of the cooling water reduce. 


packing fill is used inside the cooling tower to get intimate contact and higher residence time between hot water and air.demister pad is used above the packing to minimize entrainment of water droplets.

The shape of a Natural Draft cooling tower is hyperbolic. hyperbolic shape helps to increase the velocity of moist air after coming out from the packed section.

The efficiency of a Natural Draft cooling tower is less in compare to Force Draft and Balance Draft cooling tower. moist air coming out from top of the tower may mix and recirculate with atmospheric air to enter into tower and hence reduce the efficiency of tower.so long structure is needed to reduce back mixing of moist air with atmospheric air. 

Solid-Fluid System

When a solid particle moves through fluid then three force acting on the solid particle along with. these three forces are :

1. Gravitational force
2. Buoyancy force
3. Drag force 

Gravitational force is due to the weight of the particle acting downward. buoyancy force due to the weight of the displaced fluid by the solid body.buoyancy force acting upwards exactly opposite to the gravitational force. drag force is the force which acts due to the movement of solid through the fluid or movement of fluid over the solids.the direction of drag force is opposite to the solid movement.

The drag force consists of two. these are friction drag and pressure drag.

total drag =friction drag + pressure drag

total drag is given by 
                         

Chemical Reactor

There has generally two types of chemical reactors.

Batch Reactor and Flow Reactor

                                       Batch Reactor: 

It is used only for small scale operation like new process reaction which is not even industrially scaled up but can be used to test the feasibility of the reaction.In the laboratory testing batch reactor is normally used.

                                           

Flow Reactor: 

 flow reactor are of two types: continuous stirred tank reactor and plug flow reactor.In CSTR the composition of fluid mixture inside the tank is same as that of outlet flow and there has perfect backmixing between fluid particles.