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Old 08-10-2015, 17:29   #361
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Re: Why no Residential Fridges?

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Originally Posted by sailorchic34 View Post
I oddly agree with what your saying. But to get a Flow rate, we need a bit more information.

From Wikipedia,
"Volumetric flow rate

In physics and engineering, in particular fluid dynamics and hydrometry, the volumetric flow rate, (also known as volume flow rate, rate of fluid flow or volume velocity) is the volume of fluid which passes per unit time;



Fundamental definition Volumetric flow rate is defined by the limit:[1]


I.e., the flow of volume of fluid V through a surface per unit time t.
Since this is only the time derivative of volume, a scalar quantity, the volumetric flow rate is also a scalar quantity. The change in volume is the amount that flows after crossing the boundary for some time duration, not simply the initial amount of volume at the boundary minus the final amount at the boundary, since the change in volume flowing through the area would be zero for steady flow."


So while I agree with what your saying, we also can know the weight of the fluid per unit time. The question asked was "What is the weight of a GPH" To know what GPH is we must know the volume of the fluid. If we know the volume and fluid type we also know the weight of the fluid flowing allowing for temperature density changes. So yes we can know the weight of a GPH.
Wrong, you can't get the volume of fluid directly from GPH as there is no defined volume for that unit as it depends on how long the flow lasts. Without a volume you can't define the weight.

I believe what you are trying to say is you can create an correlary unit to GPH of Pounds per Hour but again, without knowing how many hours, 8lb/hr has no defined weight since you don't know if the flow has been going for 1 sec, 1 hour, 1 year, etc...
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Old 08-10-2015, 17:32   #362
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Re: Why no Residential Fridges?

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Wrong, you can't get the volume of fluid directly from GPH as there is no defined volume for that unit as it depends on how long the flow lasts. Without a volume you can't define the weight.
Of course the main factor is TIME.

GPH * time = gallons

Weight per gallon * number of gallons = weight
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Old 08-10-2015, 17:37   #363
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Re: Why no Residential Fridges?

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Of course the main factor is TIME.

GPH * time = gallons

Weight per gallon * number of gallons = weight
Exactly and looping it back around to the battery discussion.

Amps by itself doesn't tell you how much electricity was used.

Amp * Hr gives you the amount used (assuming a single voltage and ignoring losses in the system)

(the question about the weight was just to help her understand the difference between Gallon and GPH).
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Old 08-10-2015, 17:58   #364
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Re: Why no Residential Fridges?

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Originally Posted by valhalla360 View Post
Wrong, you can't get the volume of fluid directly from GPH as there is no defined volume for that unit as it depends on how long the flow lasts. Without a volume you can't define the weight.

I believe what you are trying to say is you can create an correlary unit to GPH of Pounds per Hour but again, without knowing how many hours, 8lb/hr has no defined weight since you don't know if the flow has been going for 1 sec, 1 hour, 1 year, etc...
GPH is GPH. If you want the amount I/2hr. divide by two, Two hours multiply by two, If you want the height multiply by the weight of the specific gravity of the fluid in question. salt and fresh water have different weights as does BS.
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Old 08-10-2015, 19:41   #365
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Re: Why no Residential Fridges?

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You are absolutely correct.

It's a rough approximation based on the critical factors:

Amount to be cooled (Amt): One approx 330 mil can.
Degrees to cool (Deg): quoted 8- 10 degrees C.
Carnot efficiency of the unit (Car): 5-8% assumed.

These three factors are sufficient to get a reasonable approximation of the Watt hrs required: Required: Amt x Deg * Car * K where K is the (dimensionless) conversion factor from whatever units you did the calculation in to Watt hours.

USB power supply: approx 2 Amps at 5 Volts maximum for the vast majority of USB sources. Avail= 2 x 5 = 10 Watts

That is sufficient to get a reasonable approximation of the Watts deliverable.

Time = Required/Avail (to the nearest order of magnitude )

Note, as long as it can accept the available 10 Watts. it doesn't matter how big the Peltier unit is. That is all the power that will be available.

"Ye cannae change the laws of physics, Jim"
Interesting reference to star trek however my name is rob and I'm more of Scottie not kirk
Now on the fridge it will do its stated job just fine the description says it willkeep a beverage cold implying it was pper chilled in a standard refer .
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Old 08-10-2015, 19:55   #366
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Re: Why no Residential Fridges?

Here's an interesting article on pielter plates and voltage seems if you run a 1 volt nominal pielter unit on 5 volts I seems to significantly increase the efficiency coefficient ( will try it myself ) that idea sounds like its worth a try. Here's the posting on this study.
http://www.fieldlines.com/index.php?topic=144978.0
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Old 08-10-2015, 20:53   #367
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Re: Why no Residential Fridges?

One interesting snippet from that link that I hadn't though about:

"another issue is that when you turn it off, the heat in the heat sink is back fed into the fridge, at half the maximum rate you can remove it"
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Old 08-10-2015, 21:20   #368
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Re: Why no Residential Fridges?

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Wrong, you can't get the volume of fluid directly from GPH as there is no defined volume for that unit as it depends on how long the flow lasts. Without a volume you can't define the weight.
LOL. You are of course correct that you can't know volume from GPH. That's not what I said. In order to know what GPH is, you MUST first know what the volume of the flow rate is. You can not calculate a flow rate number without it.

Here's the formula again



V being volume, Q=flow rate, t = time and d being diameter or wetted surface in a channel. Of course this is a simplistic formula and it would be different for gravity flow and pressurized flow rates.

But in all cases, you need to know volume of flow to calculate a flow rate. If you have the volume, you can also calculate pounds of flow. So so simple.

Oh you can read a flow rate from a manufactures date sheet or engine spec sheet, etc. But in order for someone down the line to have printed that information, they would have needed to know the volume of the fluid to calculate a flow rate.
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Old 08-10-2015, 21:47   #369
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Re: Why no Residential Fridges?

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(the question about the weight was just to help her understand the difference between Gallon and GPH).
LOL, after designing plumbing, steam, chilled water, gas, etc for over 35 years in buildings up to $1.3 billion in cost, where I was senior project engineer, I can appreciate your training that you think I need. But I'm pretty sure I understand Gallons and GPH and a whole bunch of other thingys too. But I thank you for your effort. I am after all a woman.

Mind you, I have no formal training in engineering, So I missed out on all that dreadful uni theory. Alas, I'm an Autodidactic, which basically means I read a bit.
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Old 08-10-2015, 22:24   #370
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Re: Why no Residential Fridges?

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Originally Posted by StuM View Post
One interesting snippet from that link that I hadn't though about:

"another issue is that when you turn it off, the heat in the heat sink is back fed into the fridge, at half the maximum rate you can remove it"
Hence the need for a cooling fan to remove the heat so the temperature differential is lower when the plate turns off thermostatically
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Old 08-10-2015, 22:29   #371
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Re: Why no Residential Fridges?

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Hence the need for a cooling fan to remove the heat so the temperature differential is lower when the plate turns off thermostatically
But the problem is that even when the external heat sink has returned to ambient temperature, it is hotter than the interior and so you get heat fed back into the fridge. It is defeating the insulation.
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Old 08-10-2015, 23:01   #372
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Re: Why no Residential Fridges?

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But the problem is that even when the external heat sink has returned to ambient temperature, it is hotter than the interior and so you get heat fed back into the fridge. It is defeating the insulation.
True however everything is a tradeoff somewhere nothing is 100% efficient except electric heat
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Old 09-10-2015, 00:34   #373
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Re: Why no Residential Fridges?

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GPH is GPH. If you want the amount I/2hr. divide by two, Two hours multiply by two, If you want the height multiply by the weight of the specific gravity of the fluid in question. salt and fresh water have different weights as does BS.
Sure but she was claiming GPH is a volume and that it has a defined weight. Likewise she was making the same mistake with amps.

By itself, GPH has no weight. If you say the water pump on my boat generates a flow of 5GPH, you have no idea how many gallons were moved. Same as when she claims that if you say you used 50amps, you have no idea if that ran down the fully charged batteries you started with until you define how long the 50 amp draw lasted.

We already addressed the fresh/salt water issue a while back (search for a post with grape juice). Unless you have taken up drinking salt water, when talking of fresh water systems, it's the unit weight of fresh water. Likewise if you are talking about your diesel fuel system, it's the unit weight of diesel. We also covered minor variations due to temperature expansion, relativity and a few other things. We didn't cover the effects of gravity on another planet but it's not hard and as soon as you get a sailboat to float on mars we can run the math for you.
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Old 09-10-2015, 00:47   #374
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Re: Why no Residential Fridges?

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LOL, after designing plumbing, steam, chilled water, gas, etc for over 35 years in buildings up to $1.3 billion in cost, where I was senior project engineer, I can appreciate your training that you think I need. But I'm pretty sure I understand Gallons and GPH and a whole bunch of other thingys too. But I thank you for your effort. I am after all a woman.

Mind you, I have no formal training in engineering, So I missed out on all that dreadful uni theory. Alas, I'm an Autodidactic, which basically means I read a bit.
You are doing an excelent job fooling us on your expertise then. I've tried to keep this civil but your insistence on getting this simple matter flat out wrong is amazing.

Not sure why you are beating yourself up over being a woman. My boss and my boss's boss are women and they are excelent engineers. My boss's boss is the one who recruited me to my current position 10yrs ago. I take no issue with your gender. I take issue with you getting the facts wrong so please don't trot out the downtrodden woman card. No one has brought it up but you.

It is ironic that you claim to have missed out on theory but you seem to be dodging the issue by trying to make it as theoretical as possible in recent posts when it's really a very simple concept.

But back to our recent discussion, I'm still waiting for a source that provides lists volume in GPH or can define weight based on GPH without providing a duration or other
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Old 09-10-2015, 08:23   #375
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Re: Why no Residential Fridges?

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Sure but she was claiming GPH is a volume and that it has a defined weight. Likewise she was making the same mistake with amps.

By itself, GPH has no weight. If you say the water pump on my boat generates a flow of 5GPH, you have no idea how many gallons were moved. Same as when she claims that if you say you used 50amps, you have no idea if that ran down the fully charged batteries you started with until you define how long the 50 amp draw lasted.

We already addressed the fresh/salt water issue a while back (search for a post with grape juice). Unless you have taken up drinking salt water, when talking of fresh water systems, it's the unit weight of fresh water. Likewise if you are talking about your diesel fuel system, it's the unit weight of diesel. We also covered minor variations due to temperature expansion, relativity and a few other things. We didn't cover the effects of gravity on another planet but it's not hard and as soon as you get a sailboat to float on mars we can run the math for you.
Actually don't need to have a boat float on mars to do that math once you have a specific weight defined by gravity on the surface of the earth at sea level. Mars is .38 earth gravity but I'm not going to mars anytime soon so doesn't matter to me. Now my tohatsu outboard uses 5 gph of gasoline so I know I can run it for 7.5 hours with the available fuel capacity on my boat. Don't care what it weighs .
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