alternative defrost systems

[mystry]

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]

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 0°C; 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]

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]

What sort of 'different' systems are you looking for ?
Also what is wrong with the current types that you are unhappy with?

[US Iceman]

i find warm liquid defrosting for supermarket refrigeration

What in the world is warm liquid defrosting?

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]

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]

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]

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

[US Iceman]

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]

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]

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.

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