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Heat Exchanger for Gas Clothes Dryer

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Question:

I have a very well insullated house.  In addition, the house faces south and i have a lot of south facing windows.  About 40% of my gas bill is for my clothes dryer.  Years ago I saw a heat exchanger that you could put in the exhaust pipe.  It didn’t seem very efficient at the time.  Are there any new models/designs that are availaable?

Response:

You wouldn’t be able to deal with all that humidity unless you have a heat exhanger in the circuit. You will then have a clogging problem from all that clothes lint. Disconnect your dryer outlet for a few laods and see. Keep the duster handy for the next few months.

I have a very well insullated house.  In addition, the house faces south and i have a lot of south facing windows.  About 40% of my gas bill is for my clothes dryer.  Years ago I saw a heat exchanger that you could put in the exhaust pipe.  It didn’t seem very efficient at the time.  Are there any new models/designs that are availaable?

Response:

> You wouldn’t be able to deal with all that humidity unless you have a heat > exhanger in the circuit. You will then have a clogging problem from all that > clothes lint. > Disconnect your dryer outlet for a few laods and see. Keep the duster handy > for the next few months.

DO NOT DISCONNECT THE DRYER OUTLET ON A GAS DRYER. Can you say CO poisoning and death? — Steve Spence Dir., Green Trust, http://www.green-trust.org Contributing Editor, http://www.off-grid.net http://www.rebelwolf.com/essn.html

Response:

Good point!   I haven’t run a gas dryer yet. I do run my gas stove indoors all the time though.

> You wouldn’t be able to deal with all that humidity unless you have a heat > exhanger in the circuit. You will then have a clogging problem from all that > clothes lint. > Disconnect your dryer outlet for a few laods and see. Keep the duster handy > for the next few months.

DO NOT DISCONNECT THE DRYER OUTLET ON A GAS DRYER. Can you say CO poisoning and death? — Steve Spence Dir., Green Trust, http://www.green-trust.org Contributing Editor, http://www.off-grid.net http://www.rebelwolf.com/essn.html

Response:

> I have a very well insullated house.  In addition, the house faces south > and i have a lot of south facing windows.  About 40% of my gas bill is for > my clothes dryer.  Years ago I saw a heat exchanger that you could put in > the exhaust pipe.  It didn’t seem very efficient at the time.  Are there > any new models/designs that are availaable?

A problem I have with my clothes dryer is that the exhaust runs through my attic to an outside wall.  In the winter, the exhaust pipe (4" thin-wall duct) is cooled by the cold air in the attic.  The moisture from the clothing condenses and wets the inside walls.  Then the lint sticks to it like glue. Have to go up there and ‘ram-rod’ the piping each spring to clear out the lint.  This year I layered some extra fiberglass over this (un-faced) to see if that might help the situation. Point is, removing heat from the exhaust will cause some condensation.  And wet lint is troublesome to keep cleared away. daestrom

Response:

– Hide quoted text — Show quoted text -> I have a very well insullated house.  In addition, the house faces south > and i have a lot of south facing windows.  About 40% of my gas bill is > for > my clothes dryer.  Years ago I saw a heat exchanger that you could put in > the exhaust pipe.  It didn’t seem very efficient at the time.  Are there > any new models/designs that are availaable? > A problem I have with my clothes dryer is that the exhaust runs through my > attic to an outside wall.  In the winter, the exhaust pipe (4" thin-wall > duct) is cooled by the cold air in the attic.  The moisture from the > clothing condenses and wets the inside walls.  Then the lint sticks to it > like glue. > Have to go up there and ‘ram-rod’ the piping each spring to clear out the > lint.  This year I layered some extra fiberglass over this (un-faced) to > see if that might help the situation. > Point is, removing heat from the exhaust will cause some condensation. > And wet lint is troublesome to keep cleared away. > daestrom

  Most excellent example. I had not thought of that downside.

Response:

Is the ducting insulated? Insulated ducts are readily available. Or you could always wrap Fibreglass Pink (or whatever) around it..

A problem I have with my clothes dryer is that the exhaust runs through my attic to an outside wall.  In the winter, the exhaust pipe (4" thin-wall duct) is cooled by the cold air in the attic.  The moisture from the clothing condenses and wets the inside walls.  Then the lint sticks to it like glue. Have to go up there and ‘ram-rod’ the piping each spring to clear out the lint.  This year I layered some extra fiberglass over this (un-faced) to see if that might help the situation. Point is, removing heat from the exhaust will cause some condensation.  And wet lint is troublesome to keep cleared away. daestrom

Response:

> Is the ducting insulated? Insulated ducts are readily available. Or you > could always wrap Fibreglass Pink (or whatever) around it..

No insulation, that was my point.  The only insulated ducts I could find are of that ’spiral’ wire & plastic crap.  And I figured the spirals would be a lot harder to clean than a smooth bore metal duct.  As I said, I put some fibreglass batting over/along/around it this year, so next spring I guess we’ll see how that worked out. daestrom

Response:

> Is the ducting insulated? Insulated ducts are readily available. Or you > could always wrap Fibreglass Pink (or whatever) around it.. > No insulation, that was my point.  The only insulated ducts I could find > are of that ’spiral’ wire & plastic crap.  And I figured the spirals would > be a lot harder to clean than a smooth bore metal duct.  As I said, I put > some fibreglass batting over/along/around it this year, so next spring I > guess we’ll see how that worked out. > daestrom

  The spirals are hard to clean. I have done it. The orignial post was to use a heat exchanger to tap heat from the dryer outlet. Taking heat brings it closer to condensation. I suppose after you take out some heat with an exchanger you would want to insulate as much as possible.

Response:

– Hide quoted text — Show quoted text ->> Is the ducting insulated? Insulated ducts are readily available. Or you >> could always wrap Fibreglass Pink (or whatever) around it.. > No insulation, that was my point.  The only insulated ducts I could find > are of that ’spiral’ wire & plastic crap.  And I figured the spirals > would be a lot harder to clean than a smooth bore metal duct.  As I said, > I put some fibreglass batting over/along/around it this year, so next > spring I guess we’ll see how that worked out. > daestrom >  The spirals are hard to clean. I have done it. > The orignial post was to use a heat exchanger to tap heat > from the dryer outlet. Taking heat brings it closer to condensation. > I suppose after you take out some heat with an exchanger you would > want to insulate as much as possible.

But since the exhaust is very nearly at 100% RH, any heat removal via a heat exchanger would undoubtedly lead to some condensation on the heat exchanger surface. Now, on the one hand, recovering the latent heat of vaporization from the water vapor driven out of the clothing would be a great energy source. (~1100 BTU/lbm of water, as opposed to just 30 BTU/lbm to cool it 60 degreesF).  So there *is* a lot of energy there to be reclaimed. But the issue I was wondering is just *how* to keep the lint from collecting all over the heat exchanger’s wet surface and requiring tedious/frequent cleaning?  My own experience with straight metal ducting in my attic suggests that the lint will very quickly build up to 1/4 inch thick layer on the leading surfaces of the heat exchanger. Disconnecting, disassembling and cleaning the lint from something with a lot of fins on it every month or two sounds like a royal pain in the arse. Yet, a lot of energy to be recovered…… daestrom – Hide quoted text — Show quoted text –

Response:

- Hide quoted text — Show quoted text ->>>Is the ducting insulated? Insulated ducts are readily available. Or you >>>could always wrap Fibreglass Pink (or whatever) around it.. >>No insulation, that was my point.  The only insulated ducts I could find >>are of that ’spiral’ wire & plastic crap.  And I figured the spirals >>would be a lot harder to clean than a smooth bore metal duct.  As I said, >>I put some fibreglass batting over/along/around it this year, so next >>spring I guess we’ll see how that worked out. >>daestrom > The spirals are hard to clean. I have done it. >The orignial post was to use a heat exchanger to tap heat >from the dryer outlet. Taking heat brings it closer to condensation. >I suppose after you take out some heat with an exchanger you would >want to insulate as much as possible. > But since the exhaust is very nearly at 100% RH, any heat removal via a heat > exchanger would undoubtedly lead to some condensation on the heat exchanger > surface. > Now, on the one hand, recovering the latent heat of vaporization from the > water vapor driven out of the clothing would be a great energy source. > (~1100 BTU/lbm of water, as opposed to just 30 BTU/lbm to cool it 60 > degreesF).  So there *is* a lot of energy there to be reclaimed. > But the issue I was wondering is just *how* to keep the lint from collecting > all over the heat exchanger’s wet surface and requiring tedious/frequent > cleaning?  My own experience with straight metal ducting in my attic > suggests that the lint will very quickly build up to 1/4 inch thick layer on > the leading surfaces of the heat exchanger. > Disconnecting, disassembling and cleaning the lint from something with a lot > of fins on it every month or two sounds like a royal pain in the arse. > Yet, a lot of energy to be recovered…… > daestrom

Hi, How about putting a filter in ahead of the heat exchanger and in a convenient place (like in the laundry room) where it can be cleaned easily and frequently?  Maybe a filter with quite a bit of cross sectional area and washable? — Gary www.BuildItSolar.com "Build It Yourself" Solar Projects

Response:

– Hide quoted text — Show quoted text ->>> Is the ducting insulated? Insulated ducts are readily available. Or you >>> could always wrap Fibreglass Pink (or whatever) around it.. >> No insulation, that was my point.  The only insulated ducts I could find >> are of that ’spiral’ wire & plastic crap.  And I figured the spirals >> would be a lot harder to clean than a smooth bore metal duct.  As I >> said, I put some fibreglass batting over/along/around it this year, so >> next spring I guess we’ll see how that worked out. >> daestrom >  The spirals are hard to clean. I have done it. > The orignial post was to use a heat exchanger to tap heat > from the dryer outlet. Taking heat brings it closer to condensation. > I suppose after you take out some heat with an exchanger you would > want to insulate as much as possible. > But since the exhaust is very nearly at 100% RH, any heat removal via a > heat exchanger would undoubtedly lead to some condensation on the heat > exchanger surface. > Now, on the one hand, recovering the latent heat of vaporization from the > water vapor driven out of the clothing would be a great energy source. > (~1100 BTU/lbm of water, as opposed to just 30 BTU/lbm to cool it 60 > degreesF).  So there *is* a lot of energy there to be reclaimed. > But the issue I was wondering is just *how* to keep the lint from > collecting all over the heat exchanger’s wet surface and requiring > tedious/frequent cleaning?  My own experience with straight metal ducting > in my attic suggests that the lint will very quickly build up to 1/4 inch > thick layer on the leading surfaces of the heat exchanger. > Disconnecting, disassembling and cleaning the lint from something with a > lot of fins on it every month or two sounds like a royal pain in the arse. > Yet, a lot of energy to be recovered…… > daestrom

  I have thought that reclaiming latent heat with a desicant might be interesting.

Response:

– Hide quoted text — Show quoted text ->>>>Is the ducting insulated? Insulated ducts are readily available. Or you >>>>could always wrap Fibreglass Pink (or whatever) around it.. >>>No insulation, that was my point.  The only insulated ducts I could find >>>are of that ’spiral’ wire & plastic crap.  And I figured the spirals >>>would be a lot harder to clean than a smooth bore metal duct.  As I >>>said, I put some fibreglass batting over/along/around it this year, so >>>next spring I guess we’ll see how that worked out. >>>daestrom >> The spirals are hard to clean. I have done it. >>The orignial post was to use a heat exchanger to tap heat >>from the dryer outlet. Taking heat brings it closer to condensation. >>I suppose after you take out some heat with an exchanger you would >>want to insulate as much as possible. > But since the exhaust is very nearly at 100% RH, any heat removal via a > heat exchanger would undoubtedly lead to some condensation on the heat > exchanger surface. > Now, on the one hand, recovering the latent heat of vaporization from the > water vapor driven out of the clothing would be a great energy source. > (~1100 BTU/lbm of water, as opposed to just 30 BTU/lbm to cool it 60 > degreesF).  So there *is* a lot of energy there to be reclaimed. > But the issue I was wondering is just *how* to keep the lint from > collecting all over the heat exchanger’s wet surface and requiring > tedious/frequent cleaning?  My own experience with straight metal ducting > in my attic suggests that the lint will very quickly build up to 1/4 inch > thick layer on the leading surfaces of the heat exchanger. > Disconnecting, disassembling and cleaning the lint from something with a > lot of fins on it every month or two sounds like a royal pain in the > arse. > Yet, a lot of energy to be recovered…… > daestrom > Hi, > How about putting a filter in ahead of the heat exchanger and in a > convenient place (like in the laundry room) where it can be cleaned > easily and frequently?  Maybe a filter with quite a bit of cross > sectional area and washable?

Yeah, I was thinking that too.  Need much better filtration than what the ’standard’ dryer outlet has.  And to keep the backpressure at a minimum, yes a larger area.  Maybe even a furnace filter (a washable version). Might have to run some numbers and see how much heat we’re talking about, see what it’s worth to me ;-) daestrom

Response:

My electric dryer runs 4800 watts input plus the motor on a cyclic basis. There should be a way to extract some heat and/or moisture out of it.  The moisture may be hard to get rid of though.

– Hide quoted text — Show quoted text ->>>>Is the ducting insulated? Insulated ducts are readily available. Or you >>>>could always wrap Fibreglass Pink (or whatever) around it.. >>>No insulation, that was my point.  The only insulated ducts I could find >>>are of that ’spiral’ wire & plastic crap.  And I figured the spirals >>>would be a lot harder to clean than a smooth bore metal duct.  As I >>>said, I put some fibreglass batting over/along/around it this year, so >>>next spring I guess we’ll see how that worked out. >>>daestrom >> The spirals are hard to clean. I have done it. >>The orignial post was to use a heat exchanger to tap heat >>from the dryer outlet. Taking heat brings it closer to condensation. >>I suppose after you take out some heat with an exchanger you would >>want to insulate as much as possible. > But since the exhaust is very nearly at 100% RH, any heat removal via a > heat exchanger would undoubtedly lead to some condensation on the heat > exchanger surface. > Now, on the one hand, recovering the latent heat of vaporization from the > water vapor driven out of the clothing would be a great energy source. > (~1100 BTU/lbm of water, as opposed to just 30 BTU/lbm to cool it 60 > degreesF).  So there *is* a lot of energy there to be reclaimed. > But the issue I was wondering is just *how* to keep the lint from > collecting all over the heat exchanger’s wet surface and requiring > tedious/frequent cleaning?  My own experience with straight metal ducting > in my attic suggests that the lint will very quickly build up to 1/4 inch > thick layer on the leading surfaces of the heat exchanger. > Disconnecting, disassembling and cleaning the lint from something with a > lot of fins on it every month or two sounds like a royal pain in the > arse. > Yet, a lot of energy to be recovered…… > daestrom > Hi, > How about putting a filter in ahead of the heat exchanger and in a > convenient place (like in the laundry room) where it can be cleaned > easily and frequently?  Maybe a filter with quite a bit of cross > sectional area and washable?

Yeah, I was thinking that too.  Need much better filtration than what the ’standard’ dryer outlet has.  And to keep the backpressure at a minimum, yes a larger area.  Maybe even a furnace filter (a washable version). Might have to run some numbers and see how much heat we’re talking about, see what it’s worth to me ;-) daestrom

Response:

– Hide quoted text — Show quoted text -> My electric dryer runs 4800 watts input plus the motor on a cyclic basis. > There should be a way to extract some heat and/or moisture out of it. > The moisture may be hard to get rid of though. >>>>>Is the ducting insulated? Insulated ducts are readily available. Or >>>>>you >>>>>could always wrap Fibreglass Pink (or whatever) around it.. >>>>No insulation, that was my point.  The only insulated ducts I could >>>>find >>>>are of that ’spiral’ wire & plastic crap.  And I figured the spirals >>>>would be a lot harder to clean than a smooth bore metal duct.  As I >>>>said, I put some fibreglass batting over/along/around it this year, so >>>>next spring I guess we’ll see how that worked out. >>>>daestrom >>> The spirals are hard to clean. I have done it. >>>The orignial post was to use a heat exchanger to tap heat >>>from the dryer outlet. Taking heat brings it closer to condensation. >>>I suppose after you take out some heat with an exchanger you would >>>want to insulate as much as possible. >> But since the exhaust is very nearly at 100% RH, any heat removal via a >> heat exchanger would undoubtedly lead to some condensation on the heat >> exchanger surface. >> Now, on the one hand, recovering the latent heat of vaporization from >> the >> water vapor driven out of the clothing would be a great energy source. >> (~1100 BTU/lbm of water, as opposed to just 30 BTU/lbm to cool it 60 >> degreesF).  So there *is* a lot of energy there to be reclaimed. >> But the issue I was wondering is just *how* to keep the lint from >> collecting all over the heat exchanger’s wet surface and requiring >> tedious/frequent cleaning?  My own experience with straight metal >> ducting >> in my attic suggests that the lint will very quickly build up to 1/4 >> inch >> thick layer on the leading surfaces of the heat exchanger. >> Disconnecting, disassembling and cleaning the lint from something with a >> lot of fins on it every month or two sounds like a royal pain in the >> arse. >> Yet, a lot of energy to be recovered…… >> daestrom > Hi, > How about putting a filter in ahead of the heat exchanger and in a > convenient place (like in the laundry room) where it can be cleaned > easily and frequently?  Maybe a filter with quite a bit of cross > sectional area and washable? > Yeah, I was thinking that too.  Need much better filtration than what the > ’standard’ dryer outlet has.  And to keep the backpressure at a minimum, > yes > a larger area.  Maybe even a furnace filter (a washable version). > Might have to run some numbers and see how much heat we’re talking about, > see what it’s worth to me ;-) > daestrom

  They make desiccant wheels for dehumidification. If you could somehow use the dry side of the wheel to capture the filtered hot moist air and dry it with the hot dry furnace air, maybe you would recapture some of that latent heat. That would mean only drying clothes when you needed the heat though. http://www.semcoinc.com/Products.nsf/o/74FE22C4499EB0AB86256DC700649A…

Response:

> My electric dryer runs 4800 watts input plus the motor on a cyclic basis. > There should be a way to extract some heat and/or moisture out of it. >  The moisture may be hard to get rid of though.

   When we first bought our house, it had an electric dryer which had a heat exchanger at the bottom. It was a series of 1" vertical aluminum tubes where the warm moist air went through and a drip pan under these. the inlet air flowed over the outside of the tubes. The condensed water trapped the lint.    My wife always forgot to empty the pan after every load and it often overflowed, so her mother bought a conventional dryer for us. Bad move in hindsight. – Hide quoted text — Show quoted text ->>>>>Is the ducting insulated? Insulated ducts are readily available. Or you >>>>>could always wrap Fibreglass Pink (or whatever) around it.. >>>>No insulation, that was my point.  The only insulated ducts I could find >>>>are of that ’spiral’ wire & plastic crap.  And I figured the spirals >>>>would be a lot harder to clean than a smooth bore metal duct.  As I >>>>said, I put some fibreglass batting over/along/around it this year, so >>>>next spring I guess we’ll see how that worked out. >>>>daestrom >>>The spirals are hard to clean. I have done it. >>>The orignial post was to use a heat exchanger to tap heat >>>from the dryer outlet. Taking heat brings it closer to condensation. >>>I suppose after you take out some heat with an exchanger you would >>>want to insulate as much as possible. >>But since the exhaust is very nearly at 100% RH, any heat removal via a >>heat exchanger would undoubtedly lead to some condensation on the heat >>exchanger surface. >>Now, on the one hand, recovering the latent heat of vaporization from the >>water vapor driven out of the clothing would be a great energy source. >>(~1100 BTU/lbm of water, as opposed to just 30 BTU/lbm to cool it 60 >>degreesF).  So there *is* a lot of energy there to be reclaimed. >>But the issue I was wondering is just *how* to keep the lint from >>collecting all over the heat exchanger’s wet surface and requiring >>tedious/frequent cleaning?  My own experience with straight metal ducting >>in my attic suggests that the lint will very quickly build up to 1/4 inch >>thick layer on the leading surfaces of the heat exchanger. >>Disconnecting, disassembling and cleaning the lint from something with a >>lot of fins on it every month or two sounds like a royal pain in the >>arse. >>Yet, a lot of energy to be recovered…… >>daestrom >Hi, >How about putting a filter in ahead of the heat exchanger and in a >convenient place (like in the laundry room) where it can be cleaned >easily and frequently?  Maybe a filter with quite a bit of cross >sectional area and washable? > Yeah, I was thinking that too.  Need much better filtration than what the > ’standard’ dryer outlet has.  And to keep the backpressure at a minimum, yes > a larger area.  Maybe even a furnace filter (a washable version). > Might have to run some numbers and see how much heat we’re talking about, > see what it’s worth to me ;-) > daestrom

Response:

– Hide quoted text — Show quoted text -> My electric dryer runs 4800 watts input plus the motor on a cyclic basis. > There should be a way to extract some heat and/or moisture out of it. >  The moisture may be hard to get rid of though. >   When we first bought our house, it had an electric dryer which had a > heat exchanger at the bottom. It was a series of 1" vertical aluminum > tubes where the warm moist air went through and a drip pan under these. > the inlet air flowed over the outside of the tubes. The condensed water > trapped the lint. >   My wife always forgot to empty the pan after every load and it often > overflowed, so her mother bought a conventional dryer for us. Bad move in > hindsight. >>>>>>Is the ducting insulated? Insulated ducts are readily available. Or >>>>>>you >>>>>>could always wrap Fibreglass Pink (or whatever) around it.. >>>>>No insulation, that was my point.  The only insulated ducts I could >>>>>find >>>>>are of that ’spiral’ wire & plastic crap.  And I figured the spirals >>>>>would be a lot harder to clean than a smooth bore metal duct.  As I >>>>>said, I put some fibreglass batting over/along/around it this year, so >>>>>next spring I guess we’ll see how that worked out. >>>>>daestrom >>>>The spirals are hard to clean. I have done it. >>>>The orignial post was to use a heat exchanger to tap heat >>>>from the dryer outlet. Taking heat brings it closer to condensation. >>>>I suppose after you take out some heat with an exchanger you would >>>>want to insulate as much as possible. >>>But since the exhaust is very nearly at 100% RH, any heat removal via a >>>heat exchanger would undoubtedly lead to some condensation on the heat >>>exchanger surface. >>>Now, on the one hand, recovering the latent heat of vaporization from >>>the >>>water vapor driven out of the clothing would be a great energy source. >>>(~1100 BTU/lbm of water, as opposed to just 30 BTU/lbm to cool it 60 >>>degreesF).  So there *is* a lot of energy there to be reclaimed. >>>But the issue I was wondering is just *how* to keep the lint from >>>collecting all over the heat exchanger’s wet surface and requiring >>>tedious/frequent cleaning?  My own experience with straight metal >>>ducting >>>in my attic suggests that the lint will very quickly build up to 1/4 >>>inch >>>thick layer on the leading surfaces of the heat exchanger. >>>Disconnecting, disassembling and cleaning the lint from something with a >>>lot of fins on it every month or two sounds like a royal pain in the >>>arse. >>>Yet, a lot of energy to be recovered…… >>>daestrom >>Hi, >>How about putting a filter in ahead of the heat exchanger and in a >>convenient place (like in the laundry room) where it can be cleaned >>easily and frequently?  Maybe a filter with quite a bit of cross >>sectional area and washable? > Yeah, I was thinking that too.  Need much better filtration than what the > ’standard’ dryer outlet has.  And to keep the backpressure at a minimum, > yes > a larger area.  Maybe even a furnace filter (a washable version). > Might have to run some numbers and see how much heat we’re talking about, > see what it’s worth to me ;-) > daestrom

  Condensed water on a screen sounds like it would make a good filter. Tou would have to clean it regularly, but you do with the link filter in the dryer also. So, that brings us back to the double wall air to air heat exchanger that has saturated warm air and would condense if you exchanged heat out of it. No problem. use the condensation on a screen as a lint after filter. I used to get lots of lint in my garage even though there was an in dryer filter. I had to sweep and vaccum it up before it bacame a fire hazard.

Response:

My folks had a sink next to their washer/dryer.  They ran the dryer output through and old panty hose leg, in the sink.  If you don’t have a drain, use a large bucket or tub to catch the the moisture.  Instant heat capture, moisture collection, and lint filter.

Response:

> My folks had a sink next to their washer/dryer.  They ran the dryer > output through and old panty hose leg, in the sink.  If you don’t have > a drain, use a large bucket or tub to catch the the moisture.  Instant > heat capture, moisture collection, and lint filter.

You don’t do this with a propane dryer. Electric you can …. — Steve Spence Dir., Green Trust, http://www.green-trust.org Contributing Editor, http://www.off-grid.net http://www.rebelwolf.com/essn.html

Response:


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