Need options for improved drying method for finned tubing

[MfgEngineer]

I am looking for options to improve drying of our finned tubing so our tubes may be immediately packaged for shipment. I am looking at blower powered air knives but would like to hear about other options as well. Currently using a venturi type compressor powered blow-off which does not dry the tube completely. Ideally I need to keep the drying unit small, preferably to larger than 11 inches long and 6 inches in diameter so it will fit seamlessly into our production line with no major alterations. We will dry the inside by blowing a plug through it. The improved drying method must completely dry the exterior of the tubes.

Tubing: finned Ti, Cu-Ni, 439, 316, or carbon steel with fin height no greater than 0.050", and O.D. ranging 5/8" to 1". Line speed is between 60 and 120 ft./min.

[JAlberts]

Are you are using heated and/or dehumidified air for this process?

[MfgEngineer]

Are you are using heated and/or dehumidified air for this process?

No. We are using plant air straight from our compressor. In addition, we have no environmental controls in the plant. Much of the year the plant doors are open for ventilation so humidity can be high.

[JAlberts]

What you are describng is an environment with a high dew point and that is a major problem.

There are only two commonly used solutions for drying in this environment. Chilling the air increase its dew point and allow some of its moisture to fallout and be drained off; and, then reheating the air to give it very low dew point so it can draw the moisture from your sheets; or, heating your sheets to a temperature above that of ambient prior to drying.

You posted " We are using plant air straight from our compressor" and that can create a problem of its own if your actually using a compressor rather than a blower to move your air. By initially compressing the air to higher pressure you are actually increasing its relative humidity and then as you expand it through nozzles, or whatever, before flowing it over your sheets the air's relative humidity will drop but the air will also be subject to expansion cooling; and, it will start drawing moisture from your surrounding environment as soon as it leaves the nozzles; and, if the flow velocity through your air delivery system is too high then the discharged air can be entrained with actual moisture droplets as well. Additionally, the cooled air can also cool your product sheets to the point that they will also be subject to collecting moisture from the environment.

I am afraid that, considering the environmental conditions you have described there little chance that your going to find a quick and/or economical solution to your problem

[MfgEngineer]

What you are describng is an environment with a high dew point and that is a major problem.

There are only two commonly used solutions for drying in this environment. Chilling the air increase its dew point and allow some of its moisture to fallout and be drained off; and, then reheating the air to give it very low dew point so it can draw the moisture from your sheets; or, heating your sheets to a temperature above that of ambient prior to drying.

You posted " We are using plant air straight from our compressor" and that can create a problem of its own if your actually using a compressor rather than a blower to move your air. By initially compressing the air to higher pressure you are actually increasing its relative humidity and then as you expand it through nozzles, or whatever, before flowing it over your sheets the air's relative humidity will drop but the air will also be subject to expansion cooling; and, it will start drawing moisture from your surrounding environment as soon as it leaves the nozzles; and, if the flow velocity through your air delivery system is too high then the discharged air can be entrained with actual moisture droplets as well. Additionally, the cooled air can also cool your product sheets to the point that they will also be subject to collecting moisture from the environment.

I am afraid that, considering the environmental conditions you have described there little chance that your going to find a quick and/or economical solution to your problem

Thanks JAlberts,

One thing I could do fairly easily is to heat-up the rinse water in our wash tanks to around 180 F. This would leave the tubes at least 50-60 F warmer than ambient during the air blow-off or air knife drying operation. If that is not sufficient I will consider the other ideas you mentioned

[JAlberts]

Heating the wash tanks is at least a step in the right direction since this will improve water evaporation rates, at least during the period that the water remains above the ambient temperature of the surrounding plant air. There is nothing wrong with taking a step by step route to determine the efficiency each process. This can lead you selecting the most probable element to investigate for enhancement.

At the same time, it will be worthwhile to, while assembling your test results, to try a bit of simple heat transfer analysis. As long as the sheet and drying air temperatures remain above that of the ambient air temperature then moisture will continue to evaporate regardless of the chosen source(s) of heating. By using the initial sheet temperature at the initiation of drying and at the exit of the dryer you can then approximate the amount heat transfer taking place during the drying cycle and extrapolate a general idea of the inital heat input required to complete the process.