Measuring the efficiency of Heat exchangers

[david358]

Hello all, I would be grateful if someone could provide me with a little insight.

I am tasked with writing some software to do calculations and control a system to measure the efficiency of heat exchange systems.

My problem is that I am from a chemistry background, and I strongly feel that the design of the experiment is flawed; it is not my area and the engineers that have designed the system have dispelled my concerns.

My chief concern is that the system draws air from the external environment, and the relative constituents of the air is not measured; it is my assertion that moisture or other emissions from neighbouring business will be able to significantly alter the specific heat capacity of the air in a system with a large volume of air; and thus invalid any comparisons made with the system.

Does anyone have any experience in this area? Are my concerns well founded?

I just want to fit a GC machine and only operate the machine within certain parameters...I figure buying in a huge volume of compressed air would be preclusively expensive.

 

[StoneCold]

As a first pass at this, I would just measure the incoming temperature, flow rate and relative humidity, then the outlet temperature. Then based on heat capacity of stanadard air at a given humidity you can get a heat load on the exchanger. No GC involved. Now if you are condensing out water or sucking water off of tanks you will have to modify the number of parameters you are measuring to creat a more complex mass balance. I doubt that the emissions of your neighbors are going to effect the heat capacity of your air. If it would, you should really be worried about breathing it.

Regards
StoneCold

 

[IRstuff]

I would concentrate only on RH, temperature, pressure, velocity, which can be measured with the usual instrumentation. Anything other gases that rise to that level, you'd be worried about dying rather than the efficiency of the exchanger. GC would be a complete waste of money.

Is this for school?

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[dcasto]

Compare the properties of these two gases

CP BTU/LBMOL/R 6.9697
CP BTU/LB/R 0.2416
CV BTU/LBMOL/R 4.9737
CV BTU/LB/R 0.1724
CP/CV 1.4013
DENSITY LB/FT3 0.074333


CP BTU/LBMOL/R 6.9991
CP BTU/LB/R 0.2450
CV BTU/LBMOL/R 5.0022
CV BTU/LB/R 0.1751
CP/CV 1.3992
DENSITY LB/FT3 0.073607

The top is bone dry air, the bottom is 100% saturated air both at 72F and 14.696 psia.

CP BTU/LBMOL/R 6.9688
CP BTU/LB/R 0.2415
CV BTU/LBMOL/R 4.9735
CV BTU/LB/R 0.1724
CP/CV 1.4012
DENSITY LB/FT3 0.069272

Here is the same dry air only with a filter having a 1 psi pressure drop

The pressure has a larger effect than the humidity.

put your money on measuring the T&P and forget the composition.