After applying vacuum in mixing vessel Temperature decreased??

jeevan.tp · Jul 24, 2017

HI,

In a mixing vessel tank, it was maintained with a product temperature of 70 degree.
When vacuum applied to the tank, the product and jacket temperature started decreasing..??? why it happened
Is it under vacuum condition can't we measure the temperature??

Thank you

cardosocea · Jul 24, 2017

Is the probe in the product? Or is there a layer of "air" between the probe and product?

jeevan.tp · Jul 24, 2017

cardosocea said:
Is the probe in the product? Or is there a layer of "air" between the probe and product?

Yess,,probe is in product.
Hot water circulation through jacket is provided.

gripster · Jul 24, 2017

Is this not basic physics, as you apply the vacuum the pressure will drop then return as it is heated to 70 deg? T2= (P2xT1)/P1

Andybr · Jul 24, 2017

The boiling point of water reduces with atmospheric pressure and will be much less than 70C in anything approaching a vacuum. Your energy is providing latent heat to boil the water.

Negatronic · Jul 24, 2017

You're pulling gasses out of the tank. With those gasses goes the thermal energy. Just like when a how a propane or CO2 tank gets cold when you dispense it. If this is a problem, you will just have to pull the vacuum slower, or apply heat to the tank or live with it.

geniusintraining · Jul 24, 2017

They also do this a lot with food... if you use a vacuum chamber you can freeze or just lower the temperature of the product much faster than at atmospheric pressure, a lot of vegetables need to be lowered to less than 40 deg once picked so they stay fresh

jeevan.tp · Jul 24, 2017

Okay,,let me tell you exactly
Actually with some product and water(extra 30 ltr) added to the mixing vessel later after some time i applied the vacuum to remove the excess of water(30 ltr). In this process the temperature of the mixing product was 70 and jacket temperature was around 75. when we applied vacuum it temperature started decreasing.
My question is how the product temperature reduces?? whether applying vacuum makes the vessel cool ??

Negatronic · Jul 24, 2017

jeevan.tp said:
Okay,,let me tell you exactly
Actually with some product and water(extra 30 ltr) added to the mixing vessel later after some time i applied the vacuum to remove the excess of water(30 ltr). In this process the temperature of the mixing product was 70 and jacket temperature was around 75. when we applied vacuum it temperature started decreasing.
My question is how the product temperature reduces?? whether applying vacuum makes the vessel cool ??

I just told you that, man. This is how air conditioners work, by compressing and decompressing gasses in a continual loop. Picture two pressure vessels. You move the gasses back and forth between them, but never outside the system. As you evacuate one vessel, it cools. The other one heats up because it has all it's thermal energy, plus the newly added thermal energy forced into the same area. Higher concentration of thermal energy = higher temperature. After some time, the hot tank will disperse this energy through the wall of the tank and into the air, and the cold tank will absorb.

LoganB · Jul 24, 2017

Do you mean that you have a completely closed environment, and you are reducing the pressure by removing liquid/gas CREATING a semi-vacuum environment?

Or is it an open environment and in this case you mean vacuum like the appliance where you are removing water but air is free to take the place of the liquid you are removing (therefore keeping pressure ~1 atm).

If it's the former, I think the question has already been answered.

jeevan.tp · Jul 24, 2017

Yes, its a completely Closed environment.Am applying vacuum to remove the liquid.

LoganB · Jul 24, 2017

Then yes, applying a vacuum to a closed environment by removing matter (which takes heat energy with it when removed) will cool the environment.

keithkyll · Jul 24, 2017

Andybr said:
The boiling point of water reduces with atmospheric pressure and will be much less than 70C in anything approaching a vacuum. Your energy is providing latent heat to boil the water.

+1.
The water evaporates. Boils. Changes from a liquid to a gas. As the molecules expand, they take heat.

Put water on your hand. Blow on it. It's cold, because you increased the rate of evaporation. Same thing is happening inside your vacuum chamber.

shooter · Jul 24, 2017

Put a cooler before the vacuum pump and you will have a better efficiency

for example sugar is made this way, they boil out the water, by putting energy in and vacuum to reduce the boilingtemperature.

With a cooler you only need a small pump, as it is only used to take out the non condensable gasses.

Negatronic · Jul 24, 2017

This really doesn't have anything to do with boiling. You would see the same cooling effect by pulling a vacuum on a vessel that is all gas and no liquid. But yes, liquids are more dense and hold more thermal energy. They evaporate at room temperature in a vacuum an get sucked out as gas, taking that heat with them.

After applying vacuum in mixing vessel Temperature decreased??

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