Thermos flask

Cryogenics We use several types of evacuated stainless steel cryostats of about 1 htre capacity to provide the 77 K cooling with hquid nitrogen. The simplest, best valued and easiest to handle one is a ordinary thermos flask available from the supermarket (see fig.3). It is sufficient for a measurement period of more than 12 hours. A specially designed stainless steel vessel gains cooling periods of 30 hours. 

C06-0051. A stainless steel spoon weighs 24.7 g and is at a temperature of 18.5 °C. It is immersed in 85.0 mL of hot coffee (T — 84.0 ° C) in a Thermos flask. What is the final temperature of spoon + coffee (Assume that the heat capacity of the spoon is the same as that of pure iron and that the heat capacity of the coffee is the same as that of pure water.)... 

C06-0128. A 9.50-g copper block, initially at 200.0 °C, is dropped into a Thermos flask containing 200 mL of water initially at 5.00 °C. What is the final temperature of the Thermos flask contents ... 

C06-0139. Suppose 100.0 mL of 1.00 M HCl and 100.0 mL of 1.00 M NaOH, both initially at 25.0 °C, are mixed in a Thermos flask. When the reaction is complete, the temperature is 31.8 °C. Assuming that the solutions have the same heat capacity as pure water, compute the heat released. Use this value to evaluate the molar heat of the neutralization reaction H3 O (a q) + 0H ((3 q) 2H2 0(/)... 

A. 1,4-Diphenyl-5-amino-l,2,3-triazole. A 500-ml. three-necked flask is equipped with a sealed stirrer, a thermometer well, and a dropping funnel which is protected by a drying tube and has a pressure-equalizing side arm. A mixture of 35.7 g. (0.3 mole) of phenyl azide (Note 1) and 38.6 g. (0.33 mole) of phenylacetonitrile (Note 2) is placed in the flask. The flask is immersed in an ice-water mixture contained in a 1-gal. Thermos flask. After the reaction mixture has cooled to about 2°, a solution of 24.3 g. (0.45 mole) of sodium methoxide (Note 3) in 150 ml. of absolute ethanol is added dropwise during the course of 2 hours. The reaction mixture is then stirred at 2-5° in the ice-water bath for a period of 48 hours (Note 4). After the cooling bath has been removed and the flask allowed to warm spontaneously to room temperature, the mixture is filtered by suction on a sintered glass funnel, and the col-... 

ISOLATED SYSTEM - neither material nor energy exchange with the surroundings (e.g. thermos flask). 

In the example of balloon above, as long as we keep blowing in the gas, it is an open system and when we seal the mouth of balloon it becomes a closed system. But it is not an isolated system since the gas inside can get heated or cooled due to the condition of its surroundings. When we carry ice or hot tea in a thermo-flask we try to create an isolated system. 

The ovaries were delivered to the laboratory within 4hrs of collection in a PBS or saline media and at 35-37°C temperatures. The ovaries were collected between 06.30-08.30 hrs, placed in a thermos flask containing Dulbecco s phosphate buffered saline that was supplemented with 0.5ml/L of penicillin (250,000 lU) and streptomycin (0.25g) (Dulbecco s PBS+), pre-heated to 39°C. 

Having switched on the apparatus, it should be allowed to equilibrate for about half an hour, so that the electronic system warms up and the conditions settle. During this period the zero mass reading of the balance is likely to drift. The measuring thermocouple system and furnace thermocouples may require reference junctions. If the instrument uses a cold junction reference, at this point the thermos flask should be filled with fresh ice and the sheathed thermocouples inserted. This allows them to cool to 0°C. 

Heat transfer to the surroundings is reduced to a minimum the walls of the vessel consist of two thin layers of glass (or, in large vessels, steel) separated by a vacuum to reduce conduction and convection the inner surface of a glass vessel is silvered to reduce radiation and the vessel is stoppered to prevent evaporation. It was devised around 1872 by Sir James Dewar and is also known by its first trade name Thermos flask. See also cryo-... 

Experimentally, particularly with the McBain spring balances, some difficulties may be experienced. The tube containing the sample must be well immersed in the liquid nitrogen. Thermal transpiration effects can operate when radiation from the equipment above the sample can radiate energy and raise the temperature of the sample. Similarly, as the containing tube has the characteristics of a Dewer vessel (thermos flask) sufficient time should be allowed for thermal equilibration. The carbon sample may never reach 77 K but is a litde higher as experimental limitations become controlling factors. 

Dewar flask A container used for storing hot or cold liquids that are able to maintain their temperature independently from their surroundings. The heat loss is kept to a minimum by using a container held within a container separated by a vacuum. The thin walls of the inner container are made of glass (or steel in the case of bigger containers). The irmer surface of the glass vessel is silvered to reduce loss through radiation. It was devised around 1872 by Sir James Dewar, and is also known by its trade name Thermos flask. 

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