Thermodynamics is mainly based on a set of four laws that are universally valid when applied to systems that fall within the constraints implicit in each.
The first principle that was established was the second law of thermodynamics, as formulated by Sadi Carnot in 1824. The 1860 already established two "principles" of thermodynamics with the works of Rudolf Clausius and William Thomson, Lord Kelvin. Over time, these principles have become "laws." In 1873, for example, Willard Gibbs claimed that there were two absolute laws of thermodynamics in his graphical methods in fluid thermodynamics.…
Chemical thermodynamics is the study of the interrelation of heat and work with chemical reactions or with physical changes of state within the limits of the laws of thermodynamics.
Chemical thermodynamics involve not only laboratory measurements of various thermodynamic properties, but also the application of mathematical methods for the study of chemical questions and the spontaneity of processes.
The structure of chemical thermodynamics is based on the first two laws of thermodynamics. From the first law of thermodynamics and the second law of thermodynamics, four equations…
Thermodynamics is the branch of classical physics that studies and describes the thermodynamic transformations induced by heat and work in a thermodynamic system, as a result of processes that involve changes in the temperature and energy state variables.
Classical thermodynamics is based on the concept of macroscopic system, that is, a portion of physical mass or conceptually separated from the external environment, which is often assumed for convenience that is not disturbed by the exchange of energy with the system. The state of a macroscopic system that is in equilibrium conditions…
A thermodynamic process is the evolution of certain properties, which are called thermodynamic properties, in relation to a particular thermodynamic system. In order to study a thermodynamic process, it is required that the system be in thermodynamic equilibrium at the initial and final point of the process; that is, that the magnitudes that undergo a variation when passing from one state to another must be completely defined in their initial and final states.
In this way thermodynamic processes can be interpreted as the result of the interaction of one system with another…
Definition of temperature: The temperature is the thermodynamic magnitude that shows the thermal energy of one body in relation to another.
Although the definition of temperature is simple and concise, you can explain what the temperature is in a more extensive way: What is the temperature?
Temperature is a physical quantity of matter that quantifies the common notions of heat and cold. The objects of low temperature perceive them cold, while objects of higher temperatures we consider them warm or hot. This physiological sensation of cold and heat is generated…
A thermodynamic system is a portion of the material space, separated from the rest of the thermodynamic universe (that is, from the external environment) by means of a real or imaginary control surface (or edge), rigid or deformable.
A thermodynamic system can be the seat of internal transformations and exchanges of matter and / or energy with the external environment (that is, everything external to the system that interacts with it). Classification of thermodynamic systems
Within thermodynamics there are three main types of thermodynamic systems: open, closed and isolated.…
Thermodynamics is the branch of physics that studies the effects of changes in temperature, pressure and volume of a physical system (a material, a liquid, a set of bodies, etc.), at a macroscopic level. The term "thermo" means heat and dynamics refers to motion, so thermodynamics studies the movement of heat in a body. Matter is composed of different particles that move disorderly. Thermodynamics studies this disorderly movement.
The practical importance of thermodynamics lies primarily in the diversity of physical phenomena it describes. Knowledge of this diversity has resulted in…
A thermodynamic property is a characteristic or a particularity that allows the changes of the work substance, that is to say, changes of energy.
The thermodynamic properties can be classified as intensive and extensive. They are intensive those that do not depend on the amount of matter of the system (pressure, temperature, composition). Extensive ones depend on the size of the system (mass, volume). Thermodynamic variables
The thermodynamic variables are the magnitudes…
In thermodynamics, a thermodynamic cycle is a circuit of thermodynamic transformations performed on one or more intended devices. The objective of these transformations is to obtain work from two sources of heat at different temperatures, or conversely, to produce through the contribution of work the passage of heat from the source of lower temperature to higher temperature.
Obtaining work from two thermal sources at different temperatures is used to produce movement, for example, in thermal engines or alternators used in the generation of electrical energy. Performance is…
What is entropy? Entropy (S) is a thermodynamic quantity originally defined as a criterion for predicting the evolution of thermodynamic systems.
Entropy is a function of extensive character state. The value of entropy, in an isolated system, grows in the course of a process that occurs naturally. Entropy describes how a thermodynamic system is irreversible.
The meaning of entropy is evolution or transformation. The word entropy comes from the Greek. Entropy in the world of physics
In physics, entropy is the thermodynamic magnitude that allows us to calculate the…
The Kelvin is the temperature unit of the International System. The Kelvin is one of the seven basic units of temperature. Its symbol in the international system of units is K. The Kelvin scale is a thermodynamic (absolute) temperature scale where the absolute zero, the theoretical absence of energy, is zero (0 K). This unit is named after the British physicist, mathematician and engineer William Thomson (1824 - 1907), who was later named Lord Kelvin. Lord Kelvin wrote about the need for a "thermodynamic temperature scale".
To express the temperature difference or the interval, the use…
The third law of thermodynamics, sometimes called Nernst's Theorem or Nernst's Postulate, relates the entropy and the temperature of a physical system.
The third law of thermodynamics states that absolute zero can not be achieved in a finite number of stages. The third law of thermodynamics can also be defined as that when reaching absolute zero, 0 degrees Kelvin, any process of a physical system stops and when reaching absolute zero the entropy reaches a minimum and constant value.
This principle states that the entropy of a system at the absolute zero temperature is a well-defined…
According to the first law of thermodynamics, every process that occurs in a given system must satisfy the principle of conservation of energy, including the flow of heat.
states, in other words, that any process whose sole purpose is to create or destroy energy, is impossible, that is, it denies the existence of a first-class perpetual motion machine.
However, the first law does not tell us anything about the…
The first law of thermodynamics was announced by Julius Robert von Mayer in 1841. It is the principle of conservation of energy.
Definition of the first law of thermodynamics: The total energy of an isolated system is neither created nor destroyed, it remains constant. Energy only transforms from one type to another. When one energy class disappears, an equivalent quantity of another class must be produced.
A body can have a certain speed with what has kinetic energy. If it loses speed, this kinetic energy that it loses becomes another type of energy, whether it is potential energy…
In physics, in particular in thermodynamics, heat is defined as the contribution of transformed energy as a result of a chemical or nuclear reaction and transferred between two systems or between two parts of the same system. This energy is not attributable to a job or a conversion between two different types of energy. Heat is, therefore, a form of transferred energy and not a form of energy contained as internal energy.
As the energy is exchanged, the heat is measured in the International System in joules. In practice, however, it is often still used as the unit of measurement of calories,…
In thermodynamics, the internal energy is the total energy contained in a thermodynamic system.
The internal energy is the energy that is needed to create the system. According to this definition, the energy to displace the environment of the system, any energy related to external force fields (potential energy, gravitational energy, etc.) or any energy associated with the movement (for example, kinetic energy) is excluded from the internal energy. .
The internal energy of a system can be modified by exercising a work on it or by heating it (providing thermal energy). If we look…
In thermodynamics, an isothermal process is a thermodynamic transformation at constant temperature, that is, a variation of the state of a physical system during which the temperature of the system does not change with time. Devices called thermostats can maintain a constant temperature value.
The isothermal transformation of a perfect gas is described by Boyle's law which, in a pressure-volume diagram (or Clapeyron's plane), is represented by a branch of the equilateral hyperbola. Isotherm of a perfect gas Calculation of heat and work exchanged
For isothermal gas…
In engineering a heat exchanger (or simply an exchanger) is an apparatus in which thermal energy is exchanged between two fluids that have different temperatures.
From the thermodynamic point of view, heat exchangers can be assimilated to open systems that work without exchanging work; in other words, they exchange matter and heat with the outside, but they do not exchange jobs.
In the solar thermal industry the heat exchanger is used to transfer the heat captured through the solar radiation that is found from fluid that circulates through the solar collectors to another…
Solar collectors are the elements that capture solar radiation and convert it into thermal energy, into heat. It is a type of solar panel designed for use in solar thermal installations. It is also known as a solar collector.
The function of solar thermal energy is to take advantage of solar energy to obtain heat, to heat a fluid. Unlike photovoltaic solar energy whose function is to generate electricity.
Solar collectors are those with flat plates, evacuated tubes and absorber collectors without protection or isolation. The flat (or flat plate) collection…
Enthalpy is a term linked to the field of thermodynamics. The enthalpy symbol is H.
Enthalpy is also known as absolute enthalpy or amount of heat.
We define enthalpy as a physical quantity defined in the field of classical thermodynamics so that it measures the maximum energy of a thermodynamic system theoretically capable of being eliminated from it in the form of heat or thermal energy.
Enthalpy is particularly useful in the understanding and description of isobaric processes: the constant pressure, the enthalpy change are directly associated with the energy received…
Passive solar energy is based on the use of solar energy without the need to use external support mechanisms. By these mechanisms we refer to the use of electric motors to orient solar panels or similar systems.
The objective is to obtain personal thermal comfort. Personal thermal comfort is a function of personal health factors (medical, psychological, sociological and situational), ambient air temperature, average radiant temperature, air movement (thermal sensation, turbulence) and relative humidity (which affects human evaporative cooling).
To use passive solar energy…
An adiabatic process is a thermodynamic process in which the system does not exchange heat with its surroundings. An adiabatic process may also be isentropic, which means that the process may be reversible.
The adiabatic process provides a rigorous conceptual basis for the theory used to expose the first law of thermodynamics and, as such, is a key concept in thermodynamics.
The term adiabatic refers to elements that impede the transfer of heat with the environment. An isolated wall is quite close to an adiabatic limit. Hence the adiabatic wall term appears.
A process that…
Thermal temperature is the absolute measure of temperature and is one of the main parameters of thermodynamics. Its unit of measure in the international system of measures is the Kelvin.
This is an "absolute" scale because it is the measure of the fundamental property of temperature: its zero value, or absolute zero, is the lowest possible temperature. There is nothing that can have a temperature below absolute zero. The absolute zero of the thermodynamic temperature, transformed in the Celsius scale would be equal to 273,5ºC. This characteristic is defined by the third law of thermodynamics…
The efficiency of photovoltaic cells is one of the elements that determine the production of a photovoltaic solar energy installation. The other factors that determine the performance of a solar plant are latitude and climate.
The conversion efficiency value of a photovoltaic cell depends on several factors. When we refer to conversion efficiency, we refer implicitly to the thermodynamic efficiency, to the separation efficiency of the load carrier, to the reflectance efficiency and to the values of conduction efficiency. These parameters are difficult to measure…
A solar thermal power plant or thermosolar power plant is an industrial facility in which solar radiation is used to generate electricity. Solar radiation is used to heat a fluid. Using fluid, taking advantage of the laws of thermodynamics, the necessary power is produced to move an alternator to generate electrical energy as in a classic thermoelectric power station. Operation of a solar thermal power station
The operation of a solar thermal power plant is based on obtaining heat from solar radiation and transferring it to a heat carrier medium. This heat carrier is usually water.…
In general, both photovoltaic solar energy and, above all, solar thermal energy has a very good acceptance in society. However, it is convenient to know the advantages and disadvantages of solar energy to reinforce or contrast our opinion.
When we talk about energy sources, most people are positioned in favor or against a certain type (solar energy, nuclear energy, wind power, etc.). The arguments for positioning are varied: energy efficiency, pollution, safety, cost ... Therefore, we will try to analyze the advantages and disadvantages of solar energy in the most objective way possible.…
In thermodynamics, an isobaric process is a change in the state of a certain amount of matter in which the pressure does not change, but one or more of its state variables. An example of this is air in a cylinder with a freely movable piston to which heat is supplied. Due to the increase in temperature, the volume will increase, but the pressure will remain constant.
The isobaric process is governed by Charles's law. The Frenchman Jacques A. Charles (1742-1822) was the first to make measurements about gases that expand when their temperature increases. Examples of isobaric processes…