fedri

10-05-2006, 08:24 AM

Hi, i want to know about formulas to calculate pressure and temperature drops in evaporator. :D

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fedri

10-05-2006, 08:24 AM

Hi, i want to know about formulas to calculate pressure and temperature drops in evaporator. :D

US Iceman

10-05-2006, 02:55 PM

The temperature drop is based on the differences in pressures due to the saturation temperatures of the specific refrigerant.

The pressure drop is very complex as it is a two phase (liquid and vapor) flow problem. The pressure losses are normally limited to reduce the temperature penalty to a minimum so the heat exchanger performance is not drastically affected.

The design value changes for the operating evaporating temperature and liquid feed type (DX, flooded, or liquid overfeed).

The pressure drop is very complex as it is a two phase (liquid and vapor) flow problem. The pressure losses are normally limited to reduce the temperature penalty to a minimum so the heat exchanger performance is not drastically affected.

The design value changes for the operating evaporating temperature and liquid feed type (DX, flooded, or liquid overfeed).

Lc_shi

11-05-2006, 02:02 AM

It's too general question:).

The pressure drop affect directly the temp drop across the evaporator. It's needed to optimize the heat exchanger size and the pressure drop. I think you can get the formula based on the specified type of HX. There is no universal formula for it.:p

rgds

LC

The pressure drop affect directly the temp drop across the evaporator. It's needed to optimize the heat exchanger size and the pressure drop. I think you can get the formula based on the specified type of HX. There is no universal formula for it.:p

rgds

LC

US Iceman

11-05-2006, 04:42 AM

If you want an estimated value without too much trouble do this....

Figure the mass flow through the evaporator as all vapor.

Find the refrigerant velocity through a single tube circuit.

Find the Reynolds number of the flow through the circuit tube.

Find the friction factor for the tube and inside surface of the circuit tube. You can find the friction factor by using the Moody diagram or the Colebrook equation.

http://www.cheresources.com/colebrook1.shtml

Find the pressure loss using the Darcy-Weisbach equation.

http://arash.dejkam.com/software/pressure_loss/methods.php

To find the temperature loss find the saturation temperature for the entering pressure to the circuit.

Also find the saturation temperature for the outlet pressure of the circuit.

The difference in saturation temperatures is the temperature loss due to flow.

Figure the mass flow through the evaporator as all vapor.

Find the refrigerant velocity through a single tube circuit.

Find the Reynolds number of the flow through the circuit tube.

Find the friction factor for the tube and inside surface of the circuit tube. You can find the friction factor by using the Moody diagram or the Colebrook equation.

http://www.cheresources.com/colebrook1.shtml

Find the pressure loss using the Darcy-Weisbach equation.

http://arash.dejkam.com/software/pressure_loss/methods.php

To find the temperature loss find the saturation temperature for the entering pressure to the circuit.

Also find the saturation temperature for the outlet pressure of the circuit.

The difference in saturation temperatures is the temperature loss due to flow.

autt

16-05-2006, 02:20 PM

Hi guys,

There is not only friction factor, but also a acceleration caused pressure drop, which is produced by gas velocity increasing. see this file

http://fire.nist.gov/bfrlpubs/build01/PDF/b01078.pdf

Then two phase outlet temperature got by its corresponding saturated pressure.

There is not only friction factor, but also a acceleration caused pressure drop, which is produced by gas velocity increasing. see this file

http://fire.nist.gov/bfrlpubs/build01/PDF/b01078.pdf

Then two phase outlet temperature got by its corresponding saturated pressure.

md.tanwir

08-07-2006, 08:59 PM

Hello. I am new to this site and I want to know how and where to write your messages. Plz. provide complete information.

Thanks.

Thanks.

md.tanwir

08-07-2006, 09:14 PM

Any body who can clear my doubts in NPSH calculation for the pumps in reverse return system. Plz. see the attachment.

Tanwir

Tanwir

autt

09-07-2006, 03:44 PM

Hello. I am new to this site and I want to know how and where to write your messages. Plz. provide complete information.

Thanks.

From this page,

http://www.refrigeration-engineer.com/forums/index.php

Select a forum, when new page appears press "New thread" on top left of list table to post you messages.

I have seen your file, may be you can calculate every duct loss by its design flow and diameter, include fittings as bends, tee branches, valves and equipments etc, select the maximal loss for each parallel flows, so that to get the total loss, finally plus spare capacity to determine the pump head.

Thanks.

From this page,

http://www.refrigeration-engineer.com/forums/index.php

Select a forum, when new page appears press "New thread" on top left of list table to post you messages.

I have seen your file, may be you can calculate every duct loss by its design flow and diameter, include fittings as bends, tee branches, valves and equipments etc, select the maximal loss for each parallel flows, so that to get the total loss, finally plus spare capacity to determine the pump head.

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