Ask me please any question regarding "Theory of absorption Chillers'

[pakblogger2012]

Hi
I am preparing a detailed lecture on "Theory of Absorption chillers" and I hereby request you people to kindly ask me any question related to subject . I would try to answer all questions.
Your questions would definitely help me in better preparation and anticipation of questions from audience.

[nike123]

Good!
I suggest you to first post here your lecture, than we could ask questions! That is how is usually done on lectures.

[pakblogger2012]

Not possible at time to upload lecture file ,Please ask questions in general.

Thanking you in anticipation of your kind guidance and support.

[Segei]

What is energy efficiency of absorption chiller compare to compression chiller?

[pakblogger2012]

Thanks Segei
Energy efficiency of absorption is far less than counterpart compression chillers i.e we have compression chillers with COP (coefficient of performance) more than 5 but absorption has reached the figure of ~ 1.4 for double effect absorption machines.

[The Viking]

What refrigerant is used and how do you safely reclaim it and recharge the system?
How do I know that the charge is right and if there is any leaks?

[pakblogger2012]

In absorption chillers (lithium bromide chillers) water is used as refrigerant and lithium bromide as absorbent.
Cooling capacity is lowered in case of vacuum leakage as evaporating pressure inside evaporator is increased.
2nd most probable cause of low capacity is insufficient quantity of refrigerant .3rd cause may be contamination of refrigerant with lithium bromide.Inside evaporator there should be only refrigerant not any place for lithium bromide.Sampling of refrigerant may also give few hints (like density) about whether there is contamination or not. In case of low capacity I would definitely suspect the required quantity of charge if all other probable culprits are cleared.

[hookster]

Hi pakblogger
How is overcondensing prevented and how is crystallisation rectified.
What would you consider a relative size plant for absorption to be considered a viable option for consideration?

[Peter_1]

adding a a question to Hookster's questions: what is the minimum temperature of the waste heat you need to speak of a efficient system?
What's the banging, knocking noise you often here on these chillers?

[marc5180]

Why does the oil in the purge pump turn milky after it has been changed even on a 'tight' system.

What does your cooling water temp need to be at to prevent crystallization.

What causes cavitation erosion in solution pump?

What causes the cooling capacity to be lower than the setpoint.

[pakblogger2012]

Hi pakblogger
How is overcondensing prevented and how is crystallisation rectified.
What would you consider a relative size plant for absorption to be considered a viable option for consideration?

Overcondensing can lead to crystallization of solution in absorption chillers so best way is to control the equipment that is providing cooling water to chiller.Cooling tower fan can be put on auto or cooling tower bypass path can be used to keep cooling water temperature within range.
Crystallization may be rectified by external heating of relevant location on chiller.Some chiller designs have auto-decrystallization pipe that connects generator to absorber or generator to week solution side.When crystallization takes place ,level of solution in generator increases beacuse of flow bloackage and this rise in level causes the overflow pipe to supply concentrated solution to absorber .In this way hot solution reaches the tube side of heat exchanger and decrystallizes the solution on shell side.Sudden power failure (especially at full load) may cause crystallization quickly.
If you have a very good control on cooling water temperature, proper vacuum in chiller and have arrangement to always put chiller in dilution mode before shutdown then crystallization would never trouble you.

[pakblogger2012]

What causes the cooling capacity to be lower than the setpoint.

Possible reasons for low cooling capacity are as following:

1. The less cooling load from the user
2. Poor vacuum
3. High cooling water inlet temperature.
4. Less cooling water flow.
5. Scale or clogging of heat transfer tubes by foreign matter
6. Inadequate heat supply.
7. Refrigerant water contaminated.
8. Inadequate Ethanol in solution.
9. Less charge of solution.
10. Low chilled water outlet temperature.

[pakblogger2012]

What does your cooling water temp need to be at to prevent crystallization.

.

Cooling water temperature should be maintained in design range(generally 28 ~ 32 deg C) .If the cooling water temperature is too low ,it would decrease the temperature of solution in absorber and this week solution at new reduced temperature may make the hot concentrated solution to cool below its crystallization temperature thus causing crystallization in heat exchanger.

[pakblogger2012]

What causes cavitation erosion in solution pump?

Insufficient head available or low pressure at suction side of solution pump may cause formation of bubbles and vapors. .These bubbles would subsequently implode in pump high pressure side inside pump .The implosion of bubbles may cause erosion in solution pump.