First some basics HERE

Then SELECT

Thanks I don't to buy control valve. i just want to fix flow by manually opening or closing valve at some value. It will restrict the flow and flow rate will change.

Why is there a need to restrict the coolant flow to some value below its maximum?

Gate valves will give a lousy adjustment. Go for either a globe or a needle for the application, depending on line size.

Since the hole in copper conductor is of d=3.5 mm2, the pipe size will be near this.

pump can deliver min 5 L/min, requirement is minimum 3 L/min, but in case we have to work on 3 L /min then perhaps has to reduce the flow.

Go for a needle valve for this particular application.

_{<unsubscribes>}

Was I trying to sell you any valve? I was only trying to help you, in selecting a suitable valve yourself, for your application.

The diameter could be 3.5 mm, but not 3.5 mm². A needle valve will be best.

VFD. If the pump volume is more then you need control that flow. In doing so you cut energy cost. Restricting the flow will increase energy cost.

What makes you think that you will need any restriction? You say you have 15 bar pressure drop across the tubing.

Without knowing what the pump will produce, nobody here can make an intelligent suggestion.

The velocity through the tubing is higher than economic for pipe flow by ~+75%.

Flow through the copper winding is laminar, according to those figures. Increasing the diameter of the winding would lead to turbulent flow at a lower velocity, and better heat transfer.

...oh, and a lower pressure drop through the coil, giving more controllability at the valve.

Kazengg,

First of all you need to indicate whether or not you want modulating control or on-off, next, you need to size the valve for the smallest realistic pressure drop across it, such that it does not make the valve too big yet does not affect your system pressure.

Also you need to define the loop precision and what percentage of deviation is acceptable for your system.

Finally the choice between plug, angle, needle, globe will be an economic criteria since most of these would be applicable for your needs.

Now then sizing the valve most manufacturers will supply the programs, but if it is on-off service, you could take the Cv supplied for each valve and based on calculating the required Cv you could select the appropriate vale.

Finally the actuator, which could be pneumatic, electric solenoid or other, since you have not indicated the function or selection criteria more in detail I would assume that maybe an electric solenoid with a plug valve may work, if you want modulating control I would suggest a globe valve with a small pneumatic actuator.

See #2.

Thanks a lot