turbulent flow of water

Don't know about the 30% thing but turbulent or laminar flow is not really a function of pressure. It is related to the velocitly of the fluid in the pipe the density and dynamic viscosity of the fluid.

I'm not going to get into the theory of it mainly cos I can't remember the equations of the top of my head but you will need to work out the Reynolds number and this will tell you if the flow is turbulent or laminar. I think if its greater than 4000 then it is turbulent but dont take that as gospel. Generally though in practice you will find most flows are turbulent.

Any fluid dynamics book or the internet will give you the equations you need.

As MACA said, flow is turbulent if Reynolds No. is > 4000. (Laminar if < 2300, transitional in between). Sorry if it's stating the obvious but it has to be turbulent in the pipe where the cooling occurs (hot fluid outside the pipe) not just the supply pipe. Also better to be turbulent on the hot side as well if possible.

Reynolds No. = V x D x ρ/μ where V = velocity, D = dia., ρ = density, μ = dynamic viscosity. Reynolds No. is dimensionless so same in any consistent set of units. In SI units, ρ/μ ~ 10⁶, so in 1/2" pipe V needs to be > 0.3 m/s (1 ft/s), in 1" pipe > 0.15 m/s (0.5 ft/s).

Codey

I work for a manufacturer of automotive heat exchangers. In order to create turbulation of the fluid being cooled we coin dimples into the tubes of the heat exchanger. This means that the fluid has a series of obstacles to get past therefore causing eddys in the fluid.

Al

The surest way to get turbulent flow is to try and design it with laminar....

Hello Del - amusing comment, but I don't think that's right. As I understand it, in pipe flow, for Reynolds No. < 2300 flow cannot be turbulent, as there is insufficient energy available. But with special attention to pipe layout, flow straightening etc flow can be laminar when Re > 2300, although flow is unstable and a disturbance is likely to set turbulence off.

Codey

My thoughts exactly!!

As the other replies indicated the main thing to get to the turbulent flow regime is finding the Reynolds Number. Since you could find the flow rate through your pipes (1" and 1/2") easily just by timing the amount of the water spent (say 36 liter) in certain time (say 10 second) you have flow rate (Q=flow/time)of 36x10^-3 m³/s so dividing this value by you pipe cross-section area with I.D=1/2 " = 12.5mm A=1.227 m² Then velocity V=Q/A

V = 36x10^-3/1.227= 0.029 m/s

Reynolds number = (1000x 0.029 x12.5/1000)/1.002x10^-3 = 361

since your R <2000-2300 so the flow is not turbulent.

by reducing the pipe diameter since Q=VxA and having a constant flow you will increase your velocity and as a result you will get R value greater than 2500 -4000 which gets you to turbulent regime.

I'll be happy if I could be more help to you.

Hamid

There's something awry with your calculation there. Your example 36 litre in 10 sec = 3.6 litre/sec = 3.6x10^-3 m³/s, not 36x10^-3. Then 1/2" pipe has somewhat smaller area than 1.227 m² ! Velocity comes to 29 m/s and I don't need to calculate Re to know that's turbulent! tho obviously much too high to be practical.

In any case original question implies it's an existing setup so easier to alter the cooling water flow than the pipe size (assuming pipe is where the cooling happens - see #2).

Cheers...Codey

http://www.immnet.com/articles=?article=2901

This article should help. However as a general rule the location and number of waterlines makes as much difference in a mold. The thermal conductivity and the proximity to the molding surface are critical as well as the amount of heat (BTU's) to be removed from the molding steel.

If you have access to an IR camera this sheds a lot of light to your process.

You can use textbooks to design for turbulent flow. Turbulent is better than laminar for cooling because of higher velocity near the walls. If you can adjust the flow rate, I suggest you increase it until the temperature of the cooling water is maximum. This will indicate maximum cooling of your system.

I think you want the turbulent flow in the mold chamber, not in the piping leading to the mold. As previous posters have noted, this is a function of velocity not pressure. Increase the flow rate until you get acceptable cooling.

First question should be how much heat do you want to reject. How fast do you want to reject the heat. Then ask what is maximum temperature of cooling water that you can tolerate. At that point you can calculate how many GPM you need to pump through the mold. If you have a variety of different molds with different heat requirements, add a temp control if you want to be fancy and try to reduce pump costs.

There was an extrusion blow molder in Richmond, Spentech Plastics, now a part of Captive plastics. They had great efficiency gains using turbulent flow to cool their blow molds. Perhaps you may be able to network with the engineers at this company or gain a lead to the mold makers.

Captive has great experience in injection molding parts for HBA, Food/Beverage. Perhaps if you are not in competing fields, you can open a dialog with the home office in Piscataway New Jersey.

Turbulation inside any conductive "pipe" is simply accomplished by making the water flow in a ROTATIONAL screw flow method...thereby altering the parasitic drag velocity differential of the cross section of the flow.

Easily accomplished by drag installing a small wire diameter spring...stretched....through the heat transfer area. Stretch to a 2/1 ratio of land length over diameter. Old blacksmiths trick for creating turbulation. Choose spring about 10% larger OD than pipe....stretching it will reduce the spring OD.

On straight pipe/carrier I've used a twisted piece of thin sheet metal in stead of a stretched spiring.......wound it in a lathe.... The spring will get you around bends if you are careful and noit too stiff..

Is that 1 " and .5" as in two separate flow areas....or 1.5" pipe in transfer area?

MR. GUY

I would think that putting small metal parts in your water flow would create issues with mineral build up. Over time that wire breaks then you have a problem blowing those water lines clean.

It has to do with the interior surface of the lines and their configuration through the tool.

the turbulence allows increased water flow. better cooling. more efficient cycles.

There was another post on CR4 recently on this subject.

There is a correlation between turbulence and heat transfer, the one increasing with the other, though the relationship is not linear. Other posts have indicated, quite correctly, the crossover point being in the Reynolds Number range of 2300-4000. For 1" pipes on water at ambient temperatures the velocity required is quite low and the flow is probably turbulent now, otherwise the pipe is considerably oversized.

Turbulence in pipes is a function of velocity, diameter, viscosity and density. Pressure is largely irrelevant.

The velocity used in the extrusion molds was high. with out the turbulent flow through the tool, I believe laminar flow through the cooling system reduced the cooling effect. The turbulence would ensure a good mix of the coolant through the water lines.

The turbulence also allowed for higher velocity

Quite. So it's not really worth worrying about.

If u want a turbulent flow in the pipe then think of the inverse of pressure that is velocity. If u increase the velocity the Re. Number increases and the pressure decreases. So u have calculate velocity of fluid from Re. numbers formula since u know u have turbulent flow.