Performance of Cooling Towers

Higher summer temperatures and Humidity. Solution, more bays.

I don't know if salt content of the water has anything to do with evaporation. Maybe someone knows. I seem to remember that it is detrimental to cooling.

The salt content of the water has an effect in that with rising total dissolved solids [TDS], there are increasing opportunities for the dissolved solids to precipitate onto heat exchange surfaces, both in the tower and the utility user's equipment.

The usual ways of counteracting this are to 'blow-down' the towers at predetermined levels of TDS (measurable using a conductivity instrument) and making-up with purer water, and dosing antiscalants, disinfectants and antifoulants to the water so that there is less tendency for precipitation and bio-fouling.

Probably the heat load calculations were not done properly or season temperature swings not taken into account resulting in an undersized cooling tower. Try increasing the fan blade pitch to move more air.

There is some risk that air velocities will rise to the point where, beyond a critical point, cooling water droplets are blown out the top of the tower and onto the surrounding area, which needs to be taken into account in determining the optimum fan pitch.

Quite so. Thanks for the insight. Our friend in need shall require a clinometer to get the nominal pitch angle and then adjust in small increments while monitoring motor current draw and mist coming out of the tower.

Assuming the word 'performance' is being used to describe minimum temperature, then the minimum achievable temperature of the cooling water is the wet-bulb temperature of the air passing through it at any instant. The amount of evaporation within the tower determines the heat to be removed from the cooling water and the cooling effect achievable. As the cooling water passes down the tower, its temperature drops. The driving force for evaporation, the difference between the spot temperature of the water and the wet-bulb temperature of the air, drops away. When the water temperature reaches the wet-bulb temperature, the driving force is zero, so the wet-bulb temperature of the air passing through it is the minimum cooling water temperature that can be achieved.

As a consequence of air humidity changes with the seasons, spot circulating cooling water supply temperatures are likely to be higher in summer than in winter, and higher during the summer day compared to during the summer night.

If a utility user requires lower temperatures to be achieved than the cooling water system is able to provide in summer periods, then refrigeration to produce a chilled service is required as an intermediate process between the cooling tower and the utility user.

Sometimes, the potential of an uncomfortable investment in refrigeration and the user disruption can be avoided by making other process and operational changes of a lower value at the user's facility.

Air temperature and humidity measurements and the use of psychrometric charts are valuable tools for predicting cooling tower performance.

First, you have to check the equipment datasheet and cooling requirements for the process. Compare the need vs tower capacity. It is very possible that the cooling tower has been designed taking into account just winter season, but maybe other factors that are important not to ignore.

As PWSlack has pointed, you have to consider the wet-bulb temperature and humidity used in the tower design, the real values varies with season. In theory, the wet-bulb temperature is the minimum temperature the tower will delivery, but in practice this figure is related to the approach and consequently will be higher.

You could try starting on more cells, if apply.

What part of the world are you in?

Outside temp and humidity are your biggest factors.

Thanx every1 for ur suggestions, definitely they will help me a lot. But, please help me with just one more thing... There are 2 evaporators. The outlet from the condensors of these evaporators are fed to cooling tower through 1 line. Now, when I switch one evaporator from production to CIP, while other evaporator still in production phase, then the problem starts. Actually the switching is causing problem...so what you guyz say now??

So the problem only occurs when you shutdown one of the condensers for cleaning, meaning that with two condensers in line (and higher thermal load) no such trouble occurs. It doesn´t seem logical. Perhaps we can get to the bottom of this if you´d care to elaborate.

Few questions:

- which kind of evaporators?

- which kind of products?

- which kind of chemicals for CIP?

- which conditions of steam at 1st effect on both of them, during production?

- when you switch one evaporator to CIP, what about the steam at 1st effect?

I designed evaporating plants during the past 20 years, perhaps I could give you some answer to your problem.

I repeat after registration:

Few questions:

- which kind of evaporators?

- which kind of products?

- which kind of chemicals for CIP?

- which conditions of steam at 1st effect on both of them, during production?

- when you switch one evaporator to CIP, what about the steam at 1st effect?

I designed evaporating plants during the past 20 years, perhaps I could give you some answer to your problem.

After reading all replies and your second part of question(problem) which should be addressed in first place. Based on my experience you should completely isolate the piping system of the evaporator and shut the valves of off-line cooling tower, because in my opinion, the water from second evaporator when pumped through the system, does not run through the longest run and selects the shortest run which in this case is the evaporator of the switched off one. Be sure that all the valve are shut off completely.

Good luck,

The performance of a Cooling Tower is measured the amount of it dissipates the heat and make the wider difference from hot water falling from distribution deck to the water at the end of the fall i.e. cold water basin, so Wider delta T better is the performance. Again it dependes on whether you have forced darft, induced draft or telescopic gravity high rise towers. I am not aware about the design you are in. The effect of ambient air plays important role to evaporate the finer water droplets to take away the heat from the water droplets and again the size of the droplets with the location of the tower and wind direction change during the year around.. So you will appericiate, certain engineering parameters are to be known, before we can come forward to help you.

The question that comes to mind other than the obvious one about the difference in temperatures and humidities between summer and winter is how far from the towers are the actual tanks or whatever you are trying to cool? Are the lines insulated? Just a thought...

Regards,

Keywalker

did you consider the cooling load required in summer and winter , I mean the cooling tower performance direct related to the ambient tempressure max. diff race between the ambient temp. and cooling water temp. is around 8-10 c. for example if the ambient is around 45c the min. temp. you can achieve is around 35c,and make sure that the air flow for the cooling tower is not restricted by walls(close high),roofs. you can try to shade the cooling tower

You need to know Delta T &,Flow rate estimatwed across your heatexchanger selected cooling water pump flow rate and dischargehead and designed head for the pump, Your cooling tower approch and range.Its very essential to know your ambient wet bulb temperature and match these parameters with your cooling tower Data sheet then you can solve your over heating problem

goodluck

crm

As Dr. G .H. Thanki pointed, it will help if you give more information about the system you are handling with. Engineering is based on facts and data, so try to explain as deep as possible for you to get the help you need. Could you tell how is the normal operation logic of the evaporators (one operating / one in standby)? What is exactly the problem (lower outlet temperature, flow goes down)? Have the evaporators the same size, duty? Has the process being afected or just the cooling tower loop?

I am sure we are going to solve this issue.

BSChE.

Sorry, I forgot to log in, so my comment (#15) appears as a Guest. Here comes again:

As Dr. G .H. Thanki pointed, it will help if you give more information about the system you are handling with. Engineering is based on facts and data, so try to explain as deep as possible for you to get the help you need. Could you tell how is the normal operation logic of the evaporators (one operating / one in standby)? What is exactly the problem (lower outlet temperature, flow goes down)? Have the evaporators the same size, duty? Has the process being afected or just the cooling tower loop?

I am sure we are going to solve this issue.

BSChE.

Dear all,

In my country, at night the air temperature is around 24oC but the air humidity is very high (> 90%). I intend to stop the cooling tower fan, could I ?

How exactly do you measure cooling tower performance? By measuring temperature difference or by measuring differential flow rate?