Abstract
Air psychrometric properties are important in several areas of agricultural engineering, such as calculation of evaluation of the animal environment and air control in grain storage units. Due to their relevance and the complexity and the uncertainties in the use of psychrometric charts, the objective of this paper was to develop the software, PsyCalculator, which stands out for the automated function that allows presenting the data acquired through sensors and the respective psychrometric properties of the air, either in graph or tables. The automatic data acquisition system consists of a microcontroller that performs readings of sensors that measure the dry bulb temperature and another variable, which may be: wet bulb temperature, relative air humidity or dew point temperature. Then, the values are sent to the PsyCalculator software system. In addition to the values of dry bulb temperature, the software system presents wet bulb temperature and dew point temperature, values of saturation vapor pressure, vapor pressure, mixing ratio, specific volume, enthalpy and degree of saturation. Among the psychometric variables analyzed, the software developed in the study presented a maximum error of 2.14% for the calculation of dew point temperature. The developed software allows the automation of systems that depend on the psychrometric parameters in a friendly and precise fashion.
Highlights
Psychrometry is the study of the thermodynamic properties of the vapor-gas mixtures
The following properties of humid air may be related to the amount of water vapor: vapor pressure, mixing ratio, absolute humidity, relative air humidity, specific humidity and degree of saturation
Those directly related to temperature are the dry bulb temperature, wet bulb temperature and dew point temperature
Summary
Psychrometry is the study of the thermodynamic properties of the vapor-gas mixtures. It is an indispensable science for the calculation of energy in the drying and cooling of agricultural products, humidity and temperature control in storage units, evaluation of animal environments, meteorological calculations, cooling towers, human comfort and evapotranspiration calculations among others. The following properties of humid air may be related to the amount of water vapor: vapor pressure, mixing ratio, absolute humidity, relative air humidity, specific humidity and degree of saturation Those directly related to temperature are the dry bulb temperature, wet bulb temperature and dew point temperature. As an alternative to the traditional methods, such as the table, the psychrometric chart and semi-empirical mathematical models (AGRAWAL & RAO, 1974), researchers have been developing computer programs and even web pages (ASHRAH , 2018), where it is possible to calculate the psychrometric properties of air. The automated methods allow calculating the psychrometric values with greater precision
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