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How do I control the negative temperature in an experiment?
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Alan Wu
How do I control the negative temperature in an experiment?
Peltier element
Here's another idea: it's quite practical to pump heat just by passing electrical current through a device, which is usually just a plate with two wires:
I just love these things.
What's especially cool about them is that by simply reversing the current you reverse the heat flow! This just begs for a trivial control loop via thermocouple feedback.
A quick google query reveals commercial offers of heat baths built on this promising whopping 0.01 °C precision of regulation!
The elements are easily available in electronics shops, so with a good power supply it wouldn't be too hard to build your own low-cost precision heat bath.
Here's another idea: it's quite practical to pump heat just by passing electrical current through a device, which is usually just a plate with two wires:
I just love these things.
What's especially cool about them is that by simply reversing the current you reverse the heat flow! This just begs for a trivial control loop via thermocouple feedback.
A quick google query reveals commercial offers of heat baths built on this promising whopping 0.01 °C precision of regulation!
The elements are easily available in electronics shops, so with a good power supply it wouldn't be too hard to build your own low-cost precision heat bath.
Nice answer. I havent seen Peltier modules get down to very low temperatures, especially at sub-zero. They are used a lot with glycol as the cooling medium for home brewing, but it would be nice to experiment with other liquids, and perhaps multistaging to see how far down they could go. Do you know of any low temperature examples?More
Peltiers of ~40-75W (power consumption) are commonly used for portable refrigeration, so are widely available online. Theyre not incredibly efficient but they are effective. Ive also worked with a CCD cooled by a 4-stage Peltier stack, with vacuum insulation, down to ~200K.More
Nice idea, very tempted to give this a go to see how it compares to commercial solutions.More
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The easiest - though not necessarily the cheapest - way to achieve a stable temperature below ambient is to use a refrigerated bath, together with a suitable bath fluid. Ethylene glycol - water mixtures can be used for moderately low temperatures; specialist silicone oils are better but more expensive.
If you can't conveniently immerse your experiment in an open-topped refrigerated bath then you need a circulating bath, which can pump the bath liquid around an external circuit. Cheaper ones have a single pressure pump so the external circuit needs to be closed, e.g. a jacketed vessel; more expensive ones can have balanced output and return pumps so they can circulate to an open container. With an open system you need to be aware of the possibility of siphoning when the circulator is switched off. A circulator should have the facility to connect an external temperature sensor, which could even be inside your reaction vessel, and the instrument will try and maintain the set temperature as measured by the external sensor. You may need to be aware of the possibility of condensation or icing, both on the chilled surfaces and in the bath fluid itself which may accumulate water over time.
Refrigerated baths aren't cheap, but they are fairly common pieces of equipment so if you are on a budget you could try looking for one at used equipment suppliers.
If you already have a temperature-controlled heated water bath or circulator then it may be more cost-effective to use it in combination with an immersion or flow-through chiller, which removes heat at an approximately constant rate allowing you to set a temperature below ambient on the heated bath. For a one-off or relatively short experiment you might be able to achieve a similar effect by running the circulating fluid through a loop immersed in a low-temperature mixture as described by NotNicolau - you'd just have to monitor the temperature of this mixture and top it up with the cold component as necessary.
The easiest - though not necessarily the cheapest - way to achieve a stable temperature below ambient is to use a refrigerated bath, together with a suitable bath fluid. Ethylene glycol - water mixtures can be used for moderately low temperatures; specialist silicone oils are better but more expensive.
If you can't conveniently immerse your experiment in an open-topped refrigerated bath then you need a circulating bath, which can pump the bath liquid around an external circuit. Cheaper ones have a single pressure pump so the external circuit needs to be closed, e.g. a jacketed vessel; more expensive ones can have balanced output and return pumps so they can circulate to an open container. With an open system you need to be aware of the possibility of siphoning when the circulator is switched off. A circulator should have the facility to connect an external temperature sensor, which could even be inside your reaction vessel, and the instrument will try and maintain the set temperature as measured by the external sensor. You may need to be aware of the possibility of condensation or icing, both on the chilled surfaces and in the bath fluid itself which may accumulate water over time.
Refrigerated baths aren't cheap, but they are fairly common pieces of equipment so if you are on a budget you could try looking for one at used equipment suppliers.
If you already have a temperature-controlled heated water bath or circulator then it may be more cost-effective to use it in combination with an immersion or flow-through chiller, which removes heat at an approximately constant rate allowing you to set a temperature below ambient on the heated bath. For a one-off or relatively short experiment you might be able to achieve a similar effect by running the circulating fluid through a loop immersed in a low-temperature mixture as described by NotNicolau - you'd just have to monitor the temperature of this mixture and top it up with the cold component as necessary.
For temperatures below room temperature cooling baths are used.
These baths consist of a solvent + something that has a low temperature already (ice, dry ice, or liquid nitrogen). A comprehensive list is given below:
Although all of these temperatures are technically achievable, in practice we rarely prepare most of them due to either cost (acetonitrile is quite expensive to be using for a cooling bath), toxicity (a benzene/CO2 bath is not ideal) or difficulty (a methanol/LN2 bath forms a very thick slurry which is difficult to work with).
Most reactions below room temperature are therefore conducted at 0 (ice/water) or at -78 (dry-ice/acetone), with in-between temperatures achieved by adding dry ice slowly to acetone until the desired temperature is reached.
In addition to using this kind of cooling baths, there are machines that will allow you to dial up a given temperature and they will cool the solvent to within a few degrees. These are incredibly useful but their size and cost restricts them from everyday use (most labs don't have one, and those that do won't have enough for everyone to use one everytime they need cryogenic conditions)
For temperatures below room temperature cooling baths are used.
These baths consist of a solvent + something that has a low temperature already (ice, dry ice, or liquid nitrogen). A comprehensive list is given below:
Although all of these temperatures are technically achievable, in practice we rarely prepare most of them due to either cost (acetonitrile is quite expensive to be using for a cooling bath), toxicity (a benzene/CO2 bath is not ideal) or difficulty (a methanol/LN2 bath forms a very thick slurry which is difficult to work with).
Most reactions below room temperature are therefore conducted at 0 (ice/water) or at -78 (dry-ice/acetone), with in-between temperatures achieved by adding dry ice slowly to acetone until the desired temperature is reached.
In addition to using this kind of cooling baths, there are machines that will allow you to dial up a given temperature and they will cool the solvent to within a few degrees. These are incredibly useful but their size and cost restricts them from everyday use (most labs don't have one, and those that do won't have enough for everyone to use one everytime they need cryogenic conditions)
I disagree with Acetonitrile being too expensive. Any lab that does HPLC will have enough acetonitrile standing around that half a litre can be stolen quietly without anyone noticing ;) Whoops, did I just give myself away …?More
You place your reaction flask inside the cooling bath (i.e. so just the top of the flask is poking out). Ideally the thing you make the cooling bath in is insulated (a dewar) to prevent it warming up too fast. Also be aware that at low temperatures moisture condenses so if your reaction is in any way sensitive it needs to be tightly sealedMore
Well, most labs have acetone that isnt >99% stuff for doing their washing up etc. The MeCN we use for HPLC is ultra high grade and quite pricey (Im sure you can get cheap stuff, we just dont, and there is something a bit strange about the pricing/availability/market for MeCN) admittedly its fine for a reaction in a 50mL flask, but repeatedly making up large baths gets expensive quickly (MeCN/CO2 baths also seem a bit crap anyway).More
Peltier element
Here's another idea: it's quite practical to pump heat just by passing electrical current through a device, which is usually just a plate with two wires:
I just love these things.
What's especially cool about them is that by simply reversing the current you reverse the heat flow! This just begs for a trivial control loop via thermocouple feedback.
A quick google query reveals commercial offers of heat baths built on this promising whopping 0.01 °C precision of regulation!
The elements are easily available in electronics shops, so with a good power supply it wouldn't be too hard to build your own low-cost precision heat bath.
Hope that helps!
Peltier element
Here's another idea: it's quite practical to pump heat just by passing electrical current through a device, which is usually just a plate with two wires:
I just love these things.
What's especially cool about them is that by simply reversing the current you reverse the heat flow! This just begs for a trivial control loop via thermocouple feedback.
A quick google query reveals commercial offers of heat baths built on this promising whopping 0.01 °C precision of regulation!
The elements are easily available in electronics shops, so with a good power supply it wouldn't be too hard to build your own low-cost precision heat bath.
Hope that helps!
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The easiest - though not necessarily the cheapest - way to achieve a stable temperature below ambient is to use a refrigerated bath, together with a suitable bath fluid. Ethylene glycol - water mixtures can be used for moderately low temperatures; specialist silicone oils are better but more expensive.
If you can't conveniently immerse your experiment in an open-topped refrigerated bath then you need a circulating bath, which can pump the bath liquid around an external circuit. Cheaper ones have a single pressure pump so the external circuit needs to be closed, e.g. a jacketed vessel; more expensive ones can have balanced output and return pumps so they can circulate to an open container. With an open system you need to be aware of the possibility of siphoning when the circulator is switched off. A circulator should have the facility to connect an external temperature sensor, which could even be inside your reaction vessel, and the instrument will try and maintain the set temperature as measured by the external sensor. You may need to be aware of the possibility of condensation or icing, both on the chilled surfaces and in the bath fluid itself which may accumulate water over time.
Refrigerated baths aren't cheap, but they are fairly common pieces of equipment so if you are on a budget you could try looking for one at used equipment suppliers.
If you already have a temperature-controlled heated water bath or circulator then it may be more cost-effective to use it in combination with an immersion or flow-through chiller, which removes heat at an approximately constant rate allowing you to set a temperature below ambient on the heated bath. For a one-off or relatively short experiment you might be able to achieve a similar effect by running the circulating fluid through a loop immersed in a low-temperature mixture as described by NotNicolau - you'd just have to monitor the temperature of this mixture and top it up with the cold component as necessary.
The easiest - though not necessarily the cheapest - way to achieve a stable temperature below ambient is to use a refrigerated bath, together with a suitable bath fluid. Ethylene glycol - water mixtures can be used for moderately low temperatures; specialist silicone oils are better but more expensive.
If you can't conveniently immerse your experiment in an open-topped refrigerated bath then you need a circulating bath, which can pump the bath liquid around an external circuit. Cheaper ones have a single pressure pump so the external circuit needs to be closed, e.g. a jacketed vessel; more expensive ones can have balanced output and return pumps so they can circulate to an open container. With an open system you need to be aware of the possibility of siphoning when the circulator is switched off. A circulator should have the facility to connect an external temperature sensor, which could even be inside your reaction vessel, and the instrument will try and maintain the set temperature as measured by the external sensor. You may need to be aware of the possibility of condensation or icing, both on the chilled surfaces and in the bath fluid itself which may accumulate water over time.
Refrigerated baths aren't cheap, but they are fairly common pieces of equipment so if you are on a budget you could try looking for one at used equipment suppliers.
If you already have a temperature-controlled heated water bath or circulator then it may be more cost-effective to use it in combination with an immersion or flow-through chiller, which removes heat at an approximately constant rate allowing you to set a temperature below ambient on the heated bath. For a one-off or relatively short experiment you might be able to achieve a similar effect by running the circulating fluid through a loop immersed in a low-temperature mixture as described by NotNicolau - you'd just have to monitor the temperature of this mixture and top it up with the cold component as necessary.
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For temperatures below room temperature cooling baths are used.
These baths consist of a solvent + something that has a low temperature already (ice, dry ice, or liquid nitrogen). A comprehensive list is given below:
Although all of these temperatures are technically achievable, in practice we rarely prepare most of them due to either cost (acetonitrile is quite expensive to be using for a cooling bath), toxicity (a benzene/CO2 bath is not ideal) or difficulty (a methanol/LN2 bath forms a very thick slurry which is difficult to work with).
Most reactions below room temperature are therefore conducted at 0 (ice/water) or at -78 (dry-ice/acetone), with in-between temperatures achieved by adding dry ice slowly to acetone until the desired temperature is reached.
In addition to using this kind of cooling baths, there are machines that will allow you to dial up a given temperature and they will cool the solvent to within a few degrees. These are incredibly useful but their size and cost restricts them from everyday use (most labs don't have one, and those that do won't have enough for everyone to use one everytime they need cryogenic conditions)
For temperatures below room temperature cooling baths are used.
These baths consist of a solvent + something that has a low temperature already (ice, dry ice, or liquid nitrogen). A comprehensive list is given below:
Although all of these temperatures are technically achievable, in practice we rarely prepare most of them due to either cost (acetonitrile is quite expensive to be using for a cooling bath), toxicity (a benzene/CO2 bath is not ideal) or difficulty (a methanol/LN2 bath forms a very thick slurry which is difficult to work with).
Most reactions below room temperature are therefore conducted at 0 (ice/water) or at -78 (dry-ice/acetone), with in-between temperatures achieved by adding dry ice slowly to acetone until the desired temperature is reached.
In addition to using this kind of cooling baths, there are machines that will allow you to dial up a given temperature and they will cool the solvent to within a few degrees. These are incredibly useful but their size and cost restricts them from everyday use (most labs don't have one, and those that do won't have enough for everyone to use one everytime they need cryogenic conditions)
More
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