# Heat Exchanger Capacity

1. Dec 22, 2007

### plucker_08

is there such thing as condenser/evaporator capacity of an aircon?
how to compute for that?

thanks!

2. Dec 22, 2007

### ray b

they are rated in BTU at a given temp and fan speed for air flow
but capacity can change at extream temps

3. Dec 23, 2007

### Staff: Mentor

There is a theoretical maximum capacity of any heat exchanger, based on the delta-T and flow rates of the fluids on each side of it.

4. Dec 24, 2007

### plucker_08

any exact formula?

5. Dec 24, 2007

### machinest

well,for the evaporator as a heat exchanger,the two fluids are the air and the refrigerant,which exchange the heat between eachother,to calculate the evaporating capacity"cooling capacity":
Qref=c.c=Mref*delta h(enthalpy difference)
where:Mref:refrigerant mass flow rate,h:the enthalpy at two different points from the (p-h)chart.
for the air:
Q=(Mair*Cair*delta-T)
both Q are equaled.
for the condenser:
Qrej=(Mref*delta-h) which is equal=(Mair*Cair*delta-T) for air cooled condenser.
=(Mw*Cw*delta-T) for water cooled condenser.
also google the (p-h) chart,for a vapor compression cycle,to get the delta-h in each case for the evaporator capacity and condenser capacity.
and thats all about capacities for evap.and condenser,but for a simple vapor compression cycles,improved cycles may differe a bit,so if u told us more detail it would help us to help you if we can.
hope that helped.
thanks.
machinest.

Last edited: Dec 24, 2007
6. Dec 25, 2007

### momentum_waves

Heat transfer design of basic heat-exchangers, can be learned by reading a number of basic heat-transfer books.

Evaporator & condenser design will require you to read a fair amount on the physical mechanisms involved. Try Collier & Thome, 'Convection boiling & condensation'. You could also try Webb & Kim, "Principles of enhanced heat transfer".

There is no simple formula, but rather a mountain of information & plethora of formulae you will need to wade though.

mw...

7. Dec 25, 2007

### Staff: Mentor

The theoretical maximum performance of a non-phase change heat exchanger is the approach temperature times the flow rate times the specific heat capacity of the fluid with the lower specific heat*flow. The real performance is just that times an efficiency factor.

For one with a phase change, you just add a term for the heat of vaporization times flow rate.

To actually calculate the real performance of a heat exchanger completely from scratch is extremely complicated. In reality, it is done through testing.

8. Dec 26, 2007

### plucker_08

my task is to design a heat exchanger testing facility (condenser and evaporator of an air con...

its objective is to test the capacity of both condenser and evaporator...

using simple tools like flow meter, thermocouples, etc...

9. Dec 27, 2007

### plucker_08

up......

10. Dec 31, 2007

### plucker_08

how can i measure the pressure inside the inlet of a tube?

11. Dec 31, 2007

### stewartcs

With a pressure transducer.

12. Jan 2, 2008

### plucker_08

do i have to bore the tube or just place the transducer around the pipe.?

13. Jan 2, 2008

### plucker_08

what values will i use for the effeciencies? should i assume values?

tnx!

14. Jan 2, 2008

### momentum_waves

Plucker_08, if this is an industrial application, then I'd suggest that you employ the services of a professional consultant.

If this a student project, then you will have a lot of reading to do.

These are simple facts of life. Some consultants have spent years researching & applying the principles in practice. This comes at a price, unfortunately - time <=> money.

15. Jan 2, 2008

### Staff: Mentor

You solder a coupling with a pressure port onto the tube.

16. Jan 2, 2008

### plucker_08

this is a student project sir.

17. Jan 2, 2008

### plucker_08

the situation is this

for e.g. an owner wants to test the capacity of the condenser/evaporator inside the aircon she bought..

what if there is no pressure port? do i have to create one?

18. Jan 3, 2008

### momentum_waves

Do you have a complete working HVAC system available for your test?

In other words, could you make a test chamber for the system & test it's capacity under controlled conditions? If that's the case, then you could read up on how companies test HVAC systems.

Testing each heat-transfer component separately can become rather complex, & subject to error.

19. Jan 3, 2008

### plucker_08

does the maximum capacity of evaporator/condenser changes with different room volume or outside temperature?

20. Jan 3, 2008

### momentum_waves

The maximum achievable capacity of the HVAC&R system as a whole, based on initial set-up conditions, charge volume & so forth - would be affected if the load & sink values were changed.

Most domestic hvac's have a rated capacity before they are installed. The technician then comes along, installs the system, charges it with refrigerant, runs a test & then leaves. Whether the system ever reaches the rated capacity would have to tested/simulated.

The operating capacity of each exchanger in the system will certainly be affected by the prevailing local conditions eg. room volume/temp, or outside temperature. This occurs via LMTD changes - affecting unit capacity.

Have a look at the Webb reference I mentioned earlier. He reviews this aspect fairly well.