co-current flow in a DX-evaporator

[mrr]

Hi,

I am reading technical and theoretical information about evaporators. Given a DX evaporator, can temperatures be crossed? To my understanding, no. I have not found more information about it in the forum.

However, this link of SWEP says, for a co-current configuration: "At the end of the evaporator, where superheating takes place, the temperatures of the secondary medium and the refrigerant run the risk of crossing each other."

Link: http://www.swep.net/refrigerant-handbook/6.-evaporators/asas6/

Can someone confirm that statement is true?

Regards,

[Grizzly]

Hi mrr.
I am somewhat confused what you are needing explained?
Dx evaporators come in various styles.
The ones being discussed don't refer to a secondary medium. But a secondary fluid!
Ie shell and tube / plate heat exchangers.
Basically the flows of the refrigerant and secondary fluid are specific and if incorrect flows apply.
then cross over can occur!

Grizzly

[frank]

Hi mrr

I think you are talking about a heat exchanger rather than an evaporator where refrigerant is on 1 side and a secondary working fluid is on the other.

There is a calculation that will determine the amount of work done - it's called Log Mean Temperature Difference or LMTD for short.

Here's a link (http://www.enggcyclopedia.com/2011/08/sample-problem-logarithmic-temperature-difference-lmtd-calculation/)where you can read up on the formula but do a search and there are lots of examples which should answer your question

[mrr]

Hi Grizzly and Frank,

I refer specifically to evaporators were phase-change happens, as in Figure 6.13 of the link http://www.swep.net/refrigerant-handbook/6.-evaporators/asas6/

Grizzly, can you explain how can crossover occur? Then the superheated refrigerant would be at higher temperature than the fluid to cool! I do not see how this can happen in a co-current configuration.

Regards,