what is suitable water flow velocity in Evaporator?

[chistine]

we are dealing with Hstars Brand heat exchangers, our water flow velocity in evaporator is about 2m/s, however, one of our customer told us that the speed is too much, that will cause cooper vibration, he told me a good and easy solution to reduce velocity at inlets is to increase the nozzle size.

However, I donot think 2m/s is too fast, anyone tell me what is the right velocity of flow rate?

[NoNickName]

2 m/s is not too fast. Ask the customer what speed he's fine with, and sell that evaporator to him, under written acceptance of responsibility.

[Samarjit Sen]

HELLO CHISTINE,

We meet again. The velocity of 2 m/s is within the admissable limit. The velocity will also depend on the flow rate. The user has to maintain the parameters. I do not think that there is any need to make any changes to your heat exchangers.

[US Iceman]

...he told me a good and easy solution to reduce velocity at inlets is to increase the nozzle size.

Are you talking about the tube velocity or the nozzle velocity?

[Josip]

Hi,

Suitable velocities of water in pipes for various types of installation:

Water:
- city supply 0,6-1,5 m/s
- general supply 1,5 - 3,0 m/s
- boiler supply 2,0 - 3,0 m/s
- supply of suction pumps
and disposl pipe-lines 0,75 - 1,5 m/s
- hydraulic fluid up to 12 m/s

Hope this will help

Best regards, Josip

[patrickj]

Hi My Friend,
The water velocities are clearly defined in the Carrier Air Conditioning Design hand book chapter 3-21.
Max. water vel. to minimise erosion

operation Velocity
hr/year fps

1500 15
2000 14
3000 13
4000 12
6000 10
8000 08

So 2 m/sec. is not so high (6.6 fps)

patrickj

[chistine]

Hi, Samarjit Sen,nice to see you here, and thank you Nonickname and partrikj, Thank you all,now I am clear about the water velocity in the Evaporator,however, Mr iceman, I mean the tube velocity,and I actually, want to listen to your opion about the difference about the tube velocity and nozzle velocity.

[US Iceman]

The nozzle velocity is wht you find in the water inlet & outlet nozzles to the heat exchanger. On a DX chiller the nozzle velocity may also impact (literally) the tubes. In some designs you may find an impingement plate to provide some protection of the tubes from this.

Likewise, the tube velocity has several considerations; erosion, keeping the tube clean, or vibration.

Part of the issue with vibration related issues may be due to the tolernaces of the tubes in the baffles or tube supports too.

Needless to say there is a lot more more to shell & tube exchanger design than film coefficients or pressure drop.

Heat transfer is only one function. The mechanical design is a second criteria.