The Sous Vide cooker is overkill. A cheap ($20) rice cooker will boil water, and automatically shuts off when the weight gets low (there's a spring-loaded switch under the pot that turns the power off). Plain water just boils, it doesn't "boil over", as there is nothing to make foam from.
If you want to store something cold overnight, put it in the fridge.
There are two groups of people interested in thermocyclers: those that want a compact, reliable, neat, clean, piece of laboratory equipment so they can get their real job done, and those of us who like building gadgets. I am sometimes in each category -- for example, I love Cathal's Dremelfuge, but when I found I needed a centrifuge, I just bought one (they're cheap) and I have a nice appliance sitting next to the microscope that is convenient and easy. The hot and cold water method will never be a convenient appliance sitting on a lab bench, but it will be fun to design and build, and work the kinks out of. Let's keep looking into ways to make the convenient appliance as well.
On Tue, Feb 16, 2016 at 3:45 PM, William Beeson <beesonwt@gmail.com> wrote:
I like the idea of just directly controlling the flow rate of two pumps instead of requiring a switching valve. If you can adjust the flow by just adjusting the voltage/current to the pump in a feedback loop with a temperature sensor that is probably the cheapest. I was originally thinking of using a calculation to determine theoretically what ratio should be mixed together. It is probably a lot easier to just control the circuit (apply more voltage to one pump and less to the other until T is reached).--I think the advantage to using something like a sous vide (homemade or bought on amazon for $180) is the safety aspect. If you have boiling water that probably requires an external heat source and the potential that the water could boil over or evaporate entirely if left unattended. If you hold the temperature just below boiling and keep the top covered you can maintain the high temperature indefinitely without a risk of running out of liquid or overheating. I think the commercial sous vide also have auto-shutoff safety features. I see the point about using cold tap water. Advantage of ice water is then you can store the reactions overnight at low temperature if desired. I think a good igloo cooler can keep ice overnight.Could this really be built pretty easily? I already have the sous vide and a MiniPCR (for direct comparison).
On Tuesday, February 16, 2016 at 1:13:07 PM UTC-5, Simon Field wrote:You can get small submersible fountain pumps for $4.31.Keep one pot boiling (don't bother to even monitor the temperature).Keep another pot full of cold water from the tap (don't bother to cool it, or monitor the temperature).Put a battery powered pump in each pot, controlled by a cheap Arduino Nano for $1.83.Put a digital temperature sensor in one or more of the 96 tubes in the rack.Pump boiling water into the bath the rack is sitting in.Use PID control software to tell when to stop pumping hot water and start pumping cold water.Now you have a simple fast ramp thermocycler that can only cycle (it can't hold an intermediate temperature).To get intermediate temperatures, the PID control software will control the speed of each pump.No valves needed (they are five times the cost of the pumps).No Sous Vide cooker needed -- the Arduino is perfectly capable of doing the temperature control, even if you are using household AC current to build your own Sous Vide cooker.On Mon, Feb 15, 2016 at 4:52 PM, William Beeson <bees...@gmail.com> wrote:To view this discussion on the web visit https://groups.google.com/d/msgid/diybio/5633208b-80f3-4a10-adb9-0e6a47fd98f9%40googlegroups.com.Why couldn't a system like the following work:--Two large temperature reservoirs: Ice water and sous vide at 99CA programmable valve that controls the proportion of flow from each sourceA peristaltic pump that flows at >100 ml/min3D printed and insulated incubation chamber (10 mL working volume)The temperature reservoirs could actually be hooked up to many "pcr" machines and all you need is the arduino controlled valve. The "low" cost PCR machines are in the $600-700 range, but they can only handle a small number of tubes. An advantage of this approach is that it would be scalable to much larger numbers of reactions -- which is useful if you want to do larger scale genotyping. The tubing, valves, and peristaltic pump aren't very expensive. Sous vide immersion heater is less than $200. I know the sous vide can hold temperature accurately to +/- 0.5 C and ice saturated water is very constant at ~0C. So long as the peristaltic pump and valves work reliably it should be very easy to calculate the mixture rate to get a given temperature so long as the tubing and reaction chamber is adequately insulated.
On Monday, February 15, 2016 at 3:35:19 PM UTC-5, Simon Field wrote:The time to notice a spot that is boiling might be short.I can insert my soldering iron into water and get to a boil very quickly.The time to get all of the water to 99 degrees Celsius should be about the same in aluminum or titanium, for quantities of 100 ml or more.On Mon, Feb 15, 2016 at 8:47 AM, John Griessen <jo...@industromatic.com> wrote:On 02/15/2016 07:57 AM, Alex D wrote:
t it boils water definitely twice faster then any Al cups ive had.
anyone can clarify on that?
It is probably because of the extreme thinness of the strong Ti sheet the pan is made of.
So you can probably see the flame pattern in the boiling on the pans bottom -- very little heat spreading, mostly flowing through the thin sheet and transferring to the liquid.
Pan thinness of Ti pans is usually about 1/2 that of aluminum that I have seen. And conductivity is 10X different Ti less than Al. The thinness is not all of it. The fire is much hotter than boiling is another thing. Even though the conductivity of a half as thick ti pan might be 5X less than aluminum, there is still plenty of temperature difference to get heat flowing to
the boiling water. Maybe the formation of hot spots helps speed the boil? Hot spots would be causing early boiling that stirs the water well and speeds heat up. Could the thicker aluminum pan be so much more even that laminar layers of hot/warm/cool water form from the bottom up in the pan without stirring much for a several minutes, while the Ti pan is already stirring like mad because of one spot boiling early?
I've seen a neato product for camping called a turbo rocket boil something that advantages Titanium. It has insulating sleeve around a shell separated by corrugated metal from an inner pot such that the flow of propane flames goes along the sides of the boiling pot effectively. That pot boiler has a vertical shape, compact, protected from dings by having the two layers. I bet its inner pot is really thin and that is its trick.
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