![]() I don't know if an analytic solution exists for this process, but a numeric simulation, and a resulting curve fit, yielded the following for liquid and vapor volumes: Regarding the volume of liquid and vapor, as the liquid expands in a closed container, it takes up more volume than it originally did, so the "liquid" space expands while the "vapor" space contracts. Both liquid and vapor density can be obtained from steam tables, or from a quadratic or cubic curve fit on steam table data. Also, as the temperature goes up, the vapor density goes up, due to the higher vapor pressure of water at the higher temperature. ![]() So, in a nutshell, our case in point is completely determined by: $$U=U_0 \dot Q\Delta t$$ $$V=\mathrm$ then to convert moles water vapor to mass water vapor all you need to do is multiply by the molar mass.Īs the liquid and vapor temperature increases, the liquid density goes down, and the liquid expands. We need only to use the fact that the state of a pure, simple substance is uniquely determined by two independent parameters in order to predict the behavior of your system. note 1 Also, the total volume of your system is constant ( isochoric process). ![]() After leaving the freezer, the vapour returns to the compressor, where it is, of course, compressed (which is why the pump is called the compressor).Are you studying basic thermodynamics? Because your question is exactly what people learn in the first few classes of this subject.įirst Law of Thermodynamics tells us that every joule of energy from the burner will act to increase the system's internal energy. A fan may also distribute the cooled air throughout the rest of the refrigerator. It is then forced through a nozzle into a system of wider pipes (the evaporator) surrounding the freezer, and there it vaporizes, taking heat from the food and from the air in the freezer. Shortly before the fluid reaches the freezer it is in liquid form, moving along some rather narrow pipes. ![]() The fluid is forced around a system of tubes by a pump called the compressor. The exact formula or mixture is doubtless a trade secret. The chlorofluorocarbons have been largely replaced by hydrofluorocarbons, such as C 2H 2F 4, which are believed to be less damaging to the ozone layer. “Freon”, which was a mixture of chlorofluorocarbons, such as CCl 2F 2, was in fashion for a while, but escaping chlorofluorocarbons have been known for some time to cause breakdown of ozone (O 3) in the atmosphere, thus destroying our protection against ultraviolet radiation from the Sun. In industrial refrigerators, the refrigerant may be ammonia, but this is considered to be too dangerous for domestic use. The fundamental principles described in this section do, of course, still apply in the real world! In a real refrigerator, the working substance (the refrigerant) is a volatile fluid which is vaporized in one part of the operation and condensed to a liquid in another part. As mentioned elsewhere in this course, I am not a practical man and I am not suited to describing real, practical machines. Of course the working substance in a real refrigerator (“fridge”) is not an ideal gas, nor does one follow a Carnot cycle – there are too many practical difficulties in the way of achieving this ideal dream. This, of course, can be much greater than 1 – but no refrigerator working between the same source and sink temperatures can have a coefficient of performance greater that that of a reversible Carnot refrigerator. Therefore the coefficient of performance for a Carnot refrigeration cycle can be calculated from \]īy the first law of thermodynamics, the denominator of the expression is Q 2 − Q 1, and for a reversible Carnot cycle, the entropy in equals the entropy out, so that Q 2/ Q 1 = T 2/ T 1.
0 Comments
Leave a Reply. |