Restricting Pump Flow?

[BreezyBrew]

Hello All,

I recently purchased the 1/8 HP pump from Northern Tool to run hose water through my plate chiller. The issue I believe is that the pump is too strong and the water exits the chiller too fast. The water exiting the hose is still cold (meaning it doesn't have enough time to heat up in the chiller). Would it be possible just to pickup a garden hose connector and restrict the flow so the pass actually gets cooled down? Here's the pump:

http://www.northerntool.com/shop/tools/product_792_792

 

[prandlesc]

I'm missing something here. Don't you have enough water pressure to run hose water through your plate chiller? Why would you add a pump? With the hose water coming from your spigot, you can simply partially close the valve to control the flow.

 

[BreezyBrew]

I'm missing something here. Don't you have enough water pressure to run hose water through your plate chiller? Why would you add a pump? With the hose water coming from your spigot, you can simply partially close the valve to control the flow.

Well I live near Tampa FL and the 80 degree Hose water (last weekend) is a bit warm for pitching temps. I'd like to run the hose until about 100-120 and switch to the recirculation with ice

 

[prandlesc]

You might try a coiled tube wort chiller for your hose water set into an ice bath and run the cooling water through it, then into your wort chiller.

Or to control the flow out of your pump (assuming it goes through a hose on the outlet side of your chiller) your could add a ball valve shut off like this - http://www.homedepot.com/p/Orbit-3-...hut-Off-Coupling-27933/100659291#.UnpJb1OmbyA.

I use a similar valve to control flow out of my plate chiller, as the shut off valve from my house is about 40" from where I brew. It's easier for me to restrict the out flow, and maybe that will work for you, too. So my set up is water into the plate chiller, discharge hose out of the chiller, then the ball valve on the end of the discharge hose. That way I can check the temperature of the water coming out of the hose and adjust the flow at the same point - the end of the hose. Maybe that will work with your pump, too.

 

[mjohnson]

I'm fuzzy on the math, but I don't think you really want the water to be hot coming out. What you should be focusing on is trying to get more wort in contact with the coils. If you can, whirlpool the wort via stirring or recirculating and recycle the cold water back into your chiller water.

I once thought that I needed to restrict the flow through the chiller. But after reading some persuasive posts i came to the conclusion that you want the water to be as cold as possible and moving as fast as possible while maximizing the amount of wort that comes in contact withy the cold surface of the coil.

 

[mpcluever]

If you're just recirculating, you want to be pumping that as fast as you can. You don't want to slow it down such that it's 100 degree water coming out. You want all of those plates as cold as you can get them. The only reason to throttle back your water is so that you're not wasting water down the drain. This is just going back in the bucket.

 

[logdrum]

First off, are you running wort and water in opposite directions? I.e.: your water OUT should be parallel to your wort IN. Assuming they are, you are correct that very little heat exchange is happening if your water is still cold at exit. I run a similar set up with a cheapo Harbor Freight pond pump in a 10gal cooler of ice water. I don't even bother starting with tap water, but direct the initial outflow of HOT water to a bucket for cleanup (about 4 gal.), top off the cooler, then recirculate and fill as many buckets as I need for cleanup-usually about 12 gal total for 5.5 gal. You didn't mention if you are pumping the wort or gravity feeding; I use a Chugger on the wort side & throttle back the outflow, monitoring the wort temp-I actually just bought another Chugger for the water side- strike, sparge, chill-but haven't brewed with it yet; the basic setup will be the same.

If you're just recirculating, you want to be pumping that as fast as you can. You don't want to slow it down such that it's 100 degree water coming out. You want all of those plates as cold as you can get them. The only reason to throttle back your water is so that you're not wasting water down the drain. This is just going back in the bucket.

This is not true, if no heat is removed from the wort (rendering the water coming out hot) the wort stays hot. A heat exchanger (i.e.: plate chiller) passes heat from one medium to another. You should only pump it as fast as the chiller will effectively remove heat.

 

[Brewskii]

To answer your question, yes you can restrict the flow of this centrifugal pump provided you follow a few rules.

Never starve a pump by restricting the flow into it.

Never restrict the flow of a positive displacement pump.

Always flood the pump with liquid prior to starting it.

After flooding the pump, starting the pump with a valve closed on the discharge side will significantly reduce your start up amperage and will reduce wear on your pump greatly.

If you run a pump and need to restrict the flow, the discharge side is the proper place to do so as long as its flooded and has no dual phase flow ( entrained gas/air).

Hope that helps.

 

[Bobby_M]

The best way to limit the flow and pressure is to put a tee inline with the output and then put a valve on the side port of the tee. Basically the more you open that valve, the more pressure is just dumped right back into the icewater bath.

 

[Brewskii]

The best way to limit the flow and pressure is to put a tee inline with the output and then put a valve on the side port of the tee. Basically the more you open that valve, the more pressure is just dumped right back into the icewater bath.

Best? You may reduce pressure on the discharge side with a tee at the pump head discharge but you are causing the pump and motor to run at max flow and therefore max current. It's mechanically harder on the pump and wastes energy.

I see your point about pressure but I wouldn't say it was best especially with a small submersible centrifugal pump, as this is, dangerous pressures on the discharge side are not really feasible.

 

[BreezyBrew]

First off, are you running wort and water in opposite directions?

What the @#$%@@$$#$ I checked today, and I am pretty sure that's what I was inadvertently going on! I had been so focused on getting everything correct with the hose QD's I wasn't paying attention to the "in and out". I can't believe I didn't think of that before.

I recirculate with a chugger pump. I measured the wort coming out of the plate chiller gong back into the kettle and it was about 61. If I hook it up properly, I do believe that will drop the temp significantly. I have included a brief pic of my setup, just realized I don't have any with all of the connections, but I think you get the idea.

If the flow from the hose pump is still moving to fast, i'll think about restricting, it but first I need to double check that the connections were correct. Good news that I can actually restrict the flow, I thought it may put too much wear on the pump and burn it up in just a few uses.

 

[logdrum]

Wow, that is a monster of a chiller, what are the specs?

 

[BreezyBrew]

Wow, that is a monster of a chiller, what are the specs?

Thanks man! http://www.dudadiesel.com/choose_item.php?id=HX3630BWGH

It's the B3 36A 30 plate chiller. Less money than the terminator and way more surface area. I thought something was up when it it took about 25 min to chill a 6 gallon batch.

 

[dyqik]

This is not true, if no heat is removed from the wort (rendering the water coming out hot) the wort stays hot. A heat exchanger (i.e.: plate chiller) passes heat from one medium to another. You should only pump it as fast as the chiller will effectively remove heat.

This is completely wrong in this situation. The chiller will move heat from the hot side to cold in side at a rate proportional to the temperature difference across the plates, and the removed heat is proportional to the temperature difference of the coolant inlet and outlet times the flow rate. If the cooling water is coming out cold* at a high rate, it will be removing more heat than if it's coming out warm at a low rate, everything else being equal (thermal resistance of the chiller plates, flow rate of wort). By having a higher flow and cooler outlet coolant, you have a higher average temperature difference in the chiller, and hence a higher heat transfer.

If you have no restrictions on the coolant flow rate (i.e. you are recirculating and hence not wasting water), and the chiller heat transfer rate is your limiting factor, then you should pump the coolant as fast as possible. Only if the coolant or pumping costs you a lot of energy or money should you restrict the flow.

* the output will still be hotter than the inlet temperature, in all cases.

 

[logdrum]

This is completely wrong in this situation. The chiller will move heat from the hot side to cold in side at a rate proportional to the temperature difference across the plates, and the removed heat is proportional to the temperature difference of the coolant inlet and outlet times the flow rate. If the cooling water is coming out cold* at a high rate, it will be removing more heat than if it's coming out warm at a low rate, everything else being equal (thermal resistance of the chiller plates, flow rate of wort). By having a higher flow and cooler outlet coolant, you have a higher average temperature difference in the chiller, and hence a higher heat transfer.

If you have no restrictions on the coolant flow rate (i.e. you are recirculating and hence not wasting water), and the chiller heat transfer rate is your limiting factor, then you should pump the coolant as fast as possible. Only if the coolant or pumping costs you a lot of energy or money should you restrict the flow.

* the output will still be hotter than the inlet temperature, in all cases

That's what I said. Water entering @ 75ºF & exiting @ 85ºF at a rate of 15 gpm = a coefficient of 150; water entering @ 75ºF & exiting @ 175ºF at a rate of 3 gpm = a coefficient of 300, better results.

 

[logdrum]

Of course your are correct, there are diminishing returns,; someone should chart a coolant curve.

 

[logdrum]

Of course your are correct, there are diminishing returns,; someone should chart a coolant curve.

Next best thing:

http://www.dudadiesel.com/files/beerwortchart.pdf

 

[dyqik]

That's what I said. Water entering @ 75ºF & exiting @ 85ºF at a rate of 15 gpm = a coefficient of 150; water entering @ 75ºF & exiting @ 175ºF at a rate of 3 gpm = a coefficient of 300, better results.

However you can't achieve those figures for the same CFC at the same temperature difference in the wort. The highest possible heat transfer rate occurs when the coolant flow rate is high, and the temperature difference of the coolant is lowest. This is inefficient use of the coolant, but that is not a problem if the coolant is being recirculated and chilled by mixing with ice.

In each section of CFC, the heat flow rate is

, where delta T is the temperature difference between the two flows. The integral of the heat flow rate is higher for higher temperature differences between the flows, and so the total heat transfer rate is highest when the coolant outlet temperature is cooler.

To illustrate this, the equation for the total rate of heat exchanged for a given heat exchanger (with the flow rates cancelled out) is

.
If we set the input wort temperature (Ta1) to 210, the output wort temperature (Ta2) to 60, and the inlet water temp (Tb1) to 35, then we can use Wolfram Alpha to plot the rate of heat exchange as a function of outlet water temperature.



As you can see, the rate of heat transfer increases with decreasing outlet temperature. This means that you can maintain a higher wort flow rate for a given wort temperature difference as the outlet temperature decreases. However, as you say, diminishing returns kicks in pretty quickly as you increase the flow rate, which is where the inefficiency in use of coolant could become an issue. However, for the OP, there's no reason to restrict the flow on recirculation pump for CFC coolant unless the ice can't cool the coolant fast enough.

You can also go here to play with an online calculator for a CFC.

In addition, a higher coolant flow is more turbulent which also helps keep the heat transfer rate per unit length in the CFC high.

Yes, I am this bored this morning, waiting for my strike water to heat up...

 

[Brewskii]

.

 

[logdrum]

"However, as you say, diminishing returns kicks in pretty quickly as you increase the flow rate, which is where the inefficiency in use of coolant could become an issue. However, for the OP, there's no reason to restrict the flow on recirculation pump for CFC coolant unless the ice can't cool the coolant fast enough."

This has been my experience, which is why I'll redirect my initial outflow & top off w tap water.

 

[logdrum]

.

Thanks for pointing that out : )

 

[Brewskii]

Thanks for pointing that out : )

Didn't even try to read that post. Just thought it was funny. My water is cheap and my wort is cold.