Direct expansion ammonia evaporator/condenser
Direct expansion ammonia evaporator/condenser
(OP)
Hello!
Perhaps somebody of you has little information and/or experience about the following cascade heat exchanger application:
Because of low space we want to use a plate heat exchanger for condensing ammonia at -38°C (-36.4F) by evaporating ammonia at about 4K colder on the other side of the heat exchanger. Here are my questions:
1) What type of plate heat exchanger should we use and why? How should we install it? We think about direct expansion installation in order not to have to install a separator. (There are no problems with droplets because of ammonia absorption refrigeration system)
2) What additional problems we should take into account and consider concerning this application? (In general we are familiar with this application)
Of course we have some information of potential suppliers but I would like to learn something from you.
Kind regards
virk
Perhaps somebody of you has little information and/or experience about the following cascade heat exchanger application:
Because of low space we want to use a plate heat exchanger for condensing ammonia at -38°C (-36.4F) by evaporating ammonia at about 4K colder on the other side of the heat exchanger. Here are my questions:
1) What type of plate heat exchanger should we use and why? How should we install it? We think about direct expansion installation in order not to have to install a separator. (There are no problems with droplets because of ammonia absorption refrigeration system)
2) What additional problems we should take into account and consider concerning this application? (In general we are familiar with this application)
Of course we have some information of potential suppliers but I would like to learn something from you.
Kind regards
virk





RE: Direct expansion ammonia evaporator/condenser
My experience with plate and frame heat exchangers in ammonia applications is limited to using them as either flooded or liquid overfeed evaporators for chilling glycol. In this case many people want to use the completely welded type with no gaskets since ammonia leaks now have to be reported. I have not used a plate and frame on a DX system and I think that it would be a waste of the advantages of the plate and frame system that you are trying to obtain (limited space and heat transfer area) since the superheat in a DX system reduces your heat transfer.
Sorry that I couldn't be much help but I don't know much about the application only the heat exchanger.
RE: Direct expansion ammonia evaporator/condenser
As for the exchanger, I'd look at something in a nickel brazed plate type over a gasketed plate and frame. Try www.flatplate.com for a US supplied.
If you do go with a DX design, use an electronic expansion valve.
Ken
KE5DFR
RE: Direct expansion ammonia evaporator/condenser
Ken, why do you suggest not to use DX-evaporation below 0 dF and why should we use an electronic expansion valve.
(We plan to use AlfaNova from company AlfaLaval) In case of DX-system we can do without a separator, which saves money and space.
Kind regards
virk
RE: Direct expansion ammonia evaporator/condenser
RE: Direct expansion ammonia evaporator/condenser
I do know that i had to work on one DX NH3 glycol chiller at a -15 dF ET and it would not work well. We finally wound up converting the DX chiller with new heads and a thermosiphon drum. Never changed the surface area, just a single pass thermosiphon design and it worked fine.
Ken
Ken
KE5DFR
RE: Direct expansion ammonia evaporator/condenser