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mystry
23-06-2006, 12:25 PM
hello!
first of all, im studying mechanical eng. and i'm searching about the alternative defrost systems for the refrigerature and when i'm searching, i find this site. so i know anybody help me. anybody know what are the alternative defrost systems?

thanks for helper and site's admin and mods.

Brian_UK
23-06-2006, 11:16 PM
Hi Mystry and welcome to the forum.

There are three main types of defrost and each is used depending on the system itself.

1. Natural Defrost - Switch off the compressor and allow the coil to defrost on it's own. This will only work if the evaporator is about 0C; like you home refrigerator..

2. Electric defrost - Here there are electric heater elements fitted to the cooling coil which are heated after the compressor is switched off.

3. Hot Gas Defrost - With the compressor still running a reversing valve is utilised to begin pumping the hot compressor discharge gas around the cooling coil forcing any ice build up to melt.

Items 2 and 3 require specilised time clocks to control the defrost event.

mystry
26-06-2006, 07:04 AM
thanks ur post but i'm looking for new defrost systems. i searched in net and i find warm liquid defrosting for supermarkets refrigerations. but i want to find different systems.

Brian_UK
26-06-2006, 06:55 PM
What sort of 'different' systems are you looking for ?
Also what is wrong with the current types that you are unhappy with?

US Iceman
26-06-2006, 08:59 PM
i find warm liquid defrosting for supermarket refrigeration


What in the world is warm liquid defrosting? :confused:

It sounds like water defrost.

Are looking at a chilled glycol system for cooling the evaporators, and then when defrosting is required a warm glycol is pumped through the coil (or over the coil) for defrosting?

My next question is the same as Brian's. What is wrong with the normal defrost systems?

mystry
28-06-2006, 09:47 AM
There isn't wrong anything these systems. I just search the defrost systems, which are organising different. Warm liquid is different form others. I know it has some advantages form electric defrost. It requires low energy then ED, but defrost termination time is longer than ED. Like this, i want to learn other systems. For example, reverce cycle defrost system. Is this alternative system for defrosting? Or Iceman's chilled glycol system, is this alternative? I have to search information about it.

Thank you.

RapidRun
03-10-2006, 07:24 PM
Reverce cycle defrost is the same in principle as hot gas defrost mentioned earlier. In some systems you can probably use the liquid from the condenser/reciever as heat source for defrosting. That would be warm liquid defrost.

I believe brians list + liquid line defrost covers it all.

nh3wizard
03-10-2006, 08:20 PM
thanks ur post but i'm looking for new defrost systems. i searched in net and i find warm liquid defrosting for supermarkets refrigerations. but i want to find different systems.

He might be referring to a glycol based soulution sprayed
over the coils, I believe "Dan" mentioned it in anotgher thread:confused:

US Iceman
03-10-2006, 09:14 PM
Well, I can think of two types of warm liquid defrosting systems.

1) Cold glycol is pumped to the coils for cooling. When defrost is required, a warm glycol solution is pumped through the coil for defrosting. Josip is working on one of these systems now.

2) This is a more exotic. This type of system uses a glycol solution which is pumped over the coil all of the time. The glycol absorbs the frost from the coil. The glycol solution becomes diluted and needs to be re-concentrated. The trade name for this method is the Niagra No-Frost.

en9ech
21-03-2007, 10:15 PM
Reverce cycle defrost is the same in principle as hot gas defrost mentioned earlier. In some systems you can probably use the liquid from the condenser/reciever as heat source for defrosting. That would be warm liquid defrost.

I believe brians list + liquid line defrost covers it all.


I have heard of liquid being drawn from the receiver and termed a "warm liquid" defrost too.

What is the aim of your study? There has been a lot of research done into defrost strategies and huge energy savings can be made by simply defrosting only when needed. There are a lot of papers out there researching new strategies. Try searching for work by S A Tassou and D Datta of brunel university. If you can't find anything email me and I'll send you a chunk of my lit review. (edwardchammond@yahoo.co.uk)

Ed

nh3simman
24-03-2007, 02:23 PM
This is just speculation but he did say he wanted new systems.

de-superheater defrost
How about a few condenser tubes in the evaporator. To defrost, trigger solenoid to bypass some discharge gas to these tubes.

:cool:.....