The relationship between the parameters of humid air is graphically represented, and the enthalpy-humidity diagram is drawn, which is very convenient to apply. A wet air system with a certain mass of dry air may also have a change in steam content, which has one more degree of freedom of state change than a simple compressible system, so the state of wet air is determined by three independent parameters.
There are only two independent parameters in the state point on the plane, so the humidity chart is often made under the condition of constant total pressure, and then two independent parameters are selected as coordinates. There are many choices of coordinates, such as d-t diagram with water content and dry bulb temperature as coordinates, and h-d diagram with enthalpy and water content as coordinates.
Extended data:
Application of enthalpy-humidity diagram
(1) It is known that two kinds of air are mixed in proportion, and the parameters of mixing state are found.
There are two states of air: A and B. The temperature and humidity of air A are 25℃ and 55% respectively, and the air volume MA is 3 kg/s; The dry and wet bulb temperatures of air B are 30℃ and 25℃ respectively, and the air volume MB = 2 kg/s; The local atmospheric pressure is 10 1.3kPa, and the parameters of the mixed state point are obtained.
(2) Knowing one state point and heat-humidity ratio, find another state point.
Air conditioners often need to be ventilated according to the set process. For example, given the air state A: 25℃, 55%, along the process line of heat and humidity ratio ε= 10000kJ/kg, find another air state line that reaches the known state point A.
A straight line parallel to the straight line of heat-humidity ratio 10000kJ/kg can be drawn in the lower right corner of the enthalpy-humidity diagram, and any point on the process line can become state A. There is no definite solution to this problem and supplementary conditions are needed. If the supplementary condition is that the air state is close to saturation, the hydrograph can be extended to? =95% equal relative humidity lines intersect.
Baidu encyclopedia-enthalpy and humidity chart