Home Thermodynamics

# Thermodynamics

### Flow work in open systems

The work which is required to maintain the flow against the different static pressures between inlet and outlet of an open system is referred to as flow work. Introduction Many thermodynamic processes take...

### Reversibility of thermodynamic processes (entropy)

In thermodynamics, reversible processes are processes which are reversible from an energetic point of view! Introduction The free adiabatic expansion of an ideal gas in a vacuum showed that this thermodynamic process cannot...

### What is the Joule-Thomson effect?

The Joule-Thomson effect describes the decrease in temperature of real gases when they expand against a lower pressure! In the article Free expansion of an ideal gas in a vacuum it was...

### Free adiabatic expansion of an ideal gas in a vacuum

The expansion of an ideal gas against a vacuum in an adiabatic system is an isothermal process! In the article on the isentropic process it was already indicated that the often used...

### Polytropic process in a closed system

Learn more about polytropic thermodynamic processes in closed systems in this article. Particular processes shown in a volume-pressure diagram The figure below shows the course of the pressure as a function of the...

### Derivation of the formulas for work and heat of a polytropic process

In this article you will learn more about the derivation of the formulas for calculating work, heat and change of internal energy for polytropic processes. Polytropic equations In the article Polytropic Process in...

### Isentropic (“adiabatic”) process in a closed system

An isentropic process is a reversible process of an adiabatic system. Definition Whereas in an isochoric process no pressure-volume work is done by the system or on the system (Wv=0) and in an...

### Isothermal process in a closed system

In this article, learn more about the calculation of pressure, volume, work and heat in an isothermal process in a closed system. A change of state of a gas in which the...

### Isobaric process in a closed system

In this article, learn more about the calculation of volume, temperature, work, and heat in an isobaric process in a closed system. A change of state of a gas in which the...

### Isochoric process in a closed system

In this article, learn more about the calculation of pressure, temperature, work and heat in an isochoric process in a closed system. A change of state of a gas in which the...

### Explanation of liquefaction using the Van der Waals equation

In this article, learn how the Van der Waals equation can be used to explain the liquefaction of gases at high pressures. Van der Waals equation The ideal gas law describes the behavior...

### What is meant by dissipation of energy?

Dissipation is the (partial) conversion of a certain form of energy into thermal energy that cannot be fully converted back into the original form of energy. Definition Dissipation of energy means that when...

### Concept of pressure-volume work (displacement work)

The pressure-volume work (displacement work) is the work don on the gas or by the gas due to the acting gas pressure during a change in volume. Heat engines and heat pumps Gases...

### Dissipation of energy in closed systems

Learn in this article why, in thermodynamic processes with dissipation of energy, the pressure-volume work of the gas does not correspond to the work done by the system. Pressure-volume work (displacement work) In...

### Derivation of the pressure-volume work (displacement work)

Learn in this article why the area under the curve in a volume-pressure diagram corresponds to the pressure-volume work (displacement work). In the article concept of pressure-volume work, it was said without...

0

### Why does water boil faster at high altitudes?

0
Due to the lower pressure, the boiling point of water decreases and the water boils earlier at high altitudes. Cooking on Mount Everest With increasing altitude above sea level, the air pressure decreases...

### Difference between latent heat of vaporization and enthalpy of vaporization

0
For isobaric vaporization, the added heat of vaporization (process quantity) leads to a change in the enthalpy of the substance (state variable). Increase in volume during vaporization In the article Specific latent heat...

### Vineyard Frost Protection (sprinkling with water)

0
With sprinklers for frost protection, the crop stays protected from low temperatures by the heat of solidification released when the water freezes. If growing fruits are exposed to sub-zero temperatures (frost) on...

### Why steam burns are more dangerous than water burns?

0
Steam burns are more dangerous than water burns because more heat is transferred due to the additional release of latent heat of condensation. To vaporize a liquid, energy as heat must be...

### Why does water extinguish fire?

0
By absorbing a very large amount of heat during vaporization, water draws energy from the fire site and thus cools it down until the fire goes out! The simple answer to this...

### Specific latent heat of solidification (enthalpy of solidification)

0
Specific heat of solidification is the heat energy to be released for solidification of a liquid per kilogram of the substance! Melting and solidification In the article on specific latent heat of fusion,...

### Specific latent heat of fusion (enthalpy of fusion)

0
The specific latent heat of fusion (enthalpy of fusion) is the amount of heat required to melt a solid substance! Process of melting If a solid is heated more and more, then at...

### Specific latent heat of condensation

0
Specific heat of condensation is the heat energy to be released for condensation of a gas per kilogram of the substance! Vaporization and condensation In the article on specific latent heat of vaporization,...

### Specific latent heat of vaporization

0
The specific latent heat of vaporization (enthalpy of vaporization) is the amount of heat required to vaporize a liquid substance! Process of vaporization If a liquid is heated more and more, then at...

### Van der Waals equation (gas law for real gases)

The Van der Waals equation describes the relationship between pressure, volume and temperature for real gases. Ideal gas law In thermodynamic processes, gases are often considered as ideal gases for simplicity. Depending on...

### Why does the temperature remain constant during a change of state (phase transition)?

0
During a change of the state of matter, the supplied energy is not used to increase the kinetic energy of the molecules, but to change the binding energies. Therefore, the temperature...

### Final temperature of mixtures (Richmann’s law)

0
Richmann's law of mixtures describes the final temperature resulting in thermodynamic equilibrium when two bodies with different initial temperatures are brought into contact. Adiabatic mixing If two bodies with different initial temperatures are...

### Heating and cooling of several objects

0
Learn more about calculating the final temperature of several objects with different temperatures in this article. Heating of several objects In practice, when heating or cooling objects, one usually has to deal with...

### Heat capacity of objects

0
Heat capacity is the amount of heat required to raise the temperature of an object by 1 Kelvin (1 °C). Learn more about it in this article. Specific heat capacity of substances The...

### Calorimeter to determine the specific heat capacities of liquids

0
Calorimetry deals with the measurement of heat energy.These measurements are based on temperature changes, which are used to determine the amount of heat involved. Test setup The experimental setups used in calorimetry are...

### Specific heat capacity of gases (at constant volume or pressure)

0
Due to compressibility of gases, a distinction must be made between the isobaric and the isochoric specific heat capacity. Differentiation between isochoric and isobaric heat transfer Unlike liquids or solids, gases are special...

### Specific heat capacity of water

0
The specific heat capacity of water depends on the temperature and is strongly dependent on the state of matter. The specific heat capacity is not a material constant for a substance, but...

### Specific heat capacity of selected substances

0
In this article, learn more about the specific heat capacity of different materials and how it affects the change in temperature over time during a heat transfer. Definition of the specific heat...

### Important remarks on the specific heat capacity

0
Definition of the specific heat capacity The specific heat capacity c describes the relationship between a transfer of heat Q and the associated temperature change ΔT of a substance of mass m: begin{align}label{q}&...

### Specific heat capacity (derivation and definition)

0
The specific heat capacity indicates how much heat must be absorbed by a substance of mass 1 kg in order to increase its temperature by 1 K (1 °C). Introduction The temperature of...

### Internal energy of ideal gases

In ideal gases, the change in internal energy is directly related to the change in temperature. Learn more about the relationships in this article. Simplified assumptions for ideal gases In thermodynamics, gases play...

### Calculation of the internal energy for ideal gases

Learn more about calculating the internal energy for ideal gases in this article. First law of thermodynamics In the article Internal energy of ideal gases it was explained in detail that in ideal...

### Law of Gay-Lussac for ideal gases (Charles’s law)

The law of Gay-Lussac describes the relationship between an increase in temperature and the resulting increase in volume at constant pressure (isobaric process). Isobaric process If a thermodynamic process takes place at constant...

### Law of Amontons for ideal gases

The law of Amontons describes the relationship between an increase in temperature and the resulting increase in pressure at constant volume (isochoric process). Isochoric process If a thermodynamic process takes place at constant...

### Law of Boyle-Mariotte for ideal gases

The law of Boyle-Mariotte describes the relationship between a decrease in volume and the resulting increase in pressure at constant temperature (isothermal process). Isothermal process If a thermodynamic process takes place at constant...

### Why does ice form on the top of a lake?

0
Learn in this article why ice form always on top of a lake in winter. The negative thermal expansion of water (density anomaly) has an existential importance for life on earth. More...

### Gulf Stream & global ocean conveyor belt

0
The Gulf Stream is an ocean current in the Atlantic Ocean which, as part of the earth's global conveyor belt, has a decisive influence on the climate in Northern and Western...

### Difference between thermal conductivity, diffusivity, transmittance, resistance and heat transfer coefficient

0
Learn more in this article about the differences and importance of thermal conductivity, thermal diffusivity, heat transfer coefficient, thermal transmittance and thermal resistance, etc. Thermal conductivity Thermal conductivity (lambda) describes the heat transfer...

### Why are radiators usually located under a window?

0
Learn in this article, why radiators are usually located under a window? Central heating systems use the principle of thermal convection. The water is heated by a central heater and then transferred...

### Viscosity of an ideal gas

0
The viscosity of ideal gases is mainly based on the momentum transfer due to diffusion between the fluid layers. Definition of viscosity In the article Viscosity, the cause of viscosity was mainly attributed...

### Dimensionless numbers of the boundary layers (Prandtl, Schmidt and Lewis number)

0
To describe the heat and mass transport, dimensionless numbers are introduced to describe the processes within the boundary layers. Between a flowing fluid and a solid surface, different boundary layers are formed,...

### Thermal and concentration boundary layer

0
In addition to the hydrodynamic boundary layer, the thermal boundary layer and the concentration boundary layer also have a decisive influence on the entire heat and mass transport in a flow. Temperature...

### Prandtl number

0
The Prandtl number is a dimensionless similarity parameter to describe the transport of heat and momentum. Definition In the article on the different boundary layers, the importance of these boundary layers with respect...

### Lewis number

0
The Lewis number is a dimensionless similarity parameter to describe heat and mass transport. The Lewis number always comes into play when a flowing fluid is transferring both heat by conduction and...

### Calculation of the Nusselt numbers for forced flows over plates and in pipes

0
In this article you will find formulas for calculating the local and average Nusselt numbers for forced flows over plates and in pipes with circular cross sections. Nusselt number The definition and importance...

### Heat transfer coefficient for thermal convection

0
The heat transfer coefficient describes the convective heat transfer from a solid to a flowing fluid and vice versa! Introduction The heat transfer coefficient describes the convective heat transfer from a solid to...

### Hydrodynamic boundary layer

0
The hydrodynamic boundary layer of a flow has a decisive influence on heat and mass transport. Introduction In this article we take a closer look at the boundary layers between a solid surface...

### Nusselt number to describe convective heat transfer

0
The Nusselt number is a dimensionless similarity parameter to describe convective heat transfer, independent of the size of the system. Introduction Convective heat transfer describes the heat transport between a solid surface and...

### Temperature profiles and heat flows through different geometries

0
In this article we discuss temperature curves and heat flows through a plane wall, through a cylindrical pipe and through a hollow sphere. Introduction Temperature differences cause heat flows. These heat flows, in...

### Thermal conduction in solids and ideal gases

0
The thermal conductivity in crystalline, non-metallic solids first increases and then decreases again with increasing temperature. Phonons: Quasiparticles of the lattice vibrations Thermal conduction refers to the transfer of thermal energy through a...

### Thermodynamic derivation of the Stefan-Boltzmann Law

0
In this article the Stefan-Boltzmann-Law is to be derived using the laws of thermodynamics. Introduction In this article, the Stefan-Boltzmann Law is to be derived with the laws of thermodynamics. In order to...

### Different forms of Planck’s law

0
Planck's law of radiation can be expressed in different forms. The most important ones are discussed in this article. Introduction Planck's law of radiation describes the radiation emitted by black bodies. However, there...

### Planck’s law and Wien’s displacement law

0
Planck's law describes the radiation emitted by black bodies and Wien's displacement law the maximum of the spectral intensity of this radiation. Blackbody radiation The emitted wavelength spectrum of a blackbody as shown...

### Laser-Flash method for determining thermal conductivity (LFA)

0
With the Laser-Flash method (Laser Flash Analyser, LFA), the thermal conductivity is determined by the temperature rise in a test sample that is heated by a short laser pulse from one...

### Transient-Hot-Wire method method for determining thermal conductivity (THW)

0
With the Transient-Hot-Wire method (THW), the thermal conductivity is determined by the change in temperature over time at a certain distance from a heating wire. Design With the transient-hot-wire method, the thermal conductivity...

### Heat-Flow-Meter method for determining thermal conductivity (HFM)

0
With the Heat-Flow-Meter method (HFM) the thermal conductivity is determined by comparative measurement of the heat flow using a reference sample. Thermal conductivity Thermal conductivity is a measure of how well or poorly...

### Guarded-Hot-Plate method for determining thermal conductivity (GHP)

0
With the Guarded-Hot-Plate method (GHP) the thermal conductivity is determined by the electrical power output of a hot plate with guided heat conduction. Thermal conductivity Thermal conductivity is a measure of how well...

### Derivation of heat equation (diffusion equation)

0
The heat equation describes the temporal and spatial behavior of temperature for heat transport by thermal conduction. Derivation of the heat equation We first consider the one-dimensional case of heat conduction. This can...

### Thermal conductivity of gases

0
The thermal conductivity of ideal gases is not dependent on pressure for gases that are not too strongly diluted. This is no longer the case for gases with low pressure. Introduction In the...

### Experimental setup for determining thermal conductivity

0
In this article you can learn more about the experimental determination of the thermal conductivity of materials using steam and ice. Thermal conductivity Thermal conductivity is a measure of how well or poorly...

### Thermal transmittance (U-value)

0
The thermal transmittance (U-value or U-factor) describes the heat transfer through a solid object, which is located between two fluids (gas or liquid) with different temperatures. Definition and unit of the U-value The...

0

### Heat transfer by thermal radiation

0
With thermal radiation, heat is transferred by electromagnetic waves without the presence of a substance! The mechanisms of thermal convection and thermal conduction explained in separate articles have one thing in common:...

### Heat transfer by thermal convection

0
With heat transfer by thermal convection, heat is transported with a flowing substance. Convection only occurs in fluids, i.e. gases and liquids. Introduction One possibility of heat transfer is that hot substances flow...

### Heat transfer by thermal conduction

0
Heat transfer by thermal conduction means that heat is conducted through a material. Heat energy is transferred from molecule to molecule at the atomic level. Introduction The principle of thermal convection can basically...

### Rate of heat flow: Definition and direction

0
The rate of heat flow refers to the heat energy transferred per unit of time (heat output). The drive for the heat flow is a temperature difference. Direction of the heat flow If...

### Thermal conductivity (Fourier’s law)

0
Thermal conductivity is a measure of how well or poorly a material conducts heat energy (measure of the strength of heat conduction)! Thermal conduction In general, heat can be transferred in three different...

### Heat and thermodynamic equilibrium

0
In thermodynamics, heat is the transport of energy due to a temperature difference. Heat in this respect is never "contained" in an object! Equalization of temperature of two substances Everyday experience shows that...

### Heat transfer (heat transport)

0
Heat transfer is the transport of thermal energy from a warmer object to a cooler object. A distinction is made between convection, conduction and radiation. Example 1: Building The figure below shows a...

### The process quantities: Heat and work

Work and heat are process quantities that describe the process of a supply of energy ("energy in transit")! Learn more about it in this article. Work and heat transferred to a substance Energy...

### Internal energy & first law of thermodynamics

Internal energy is the sum of the different forms of energy on a microscopic level inside a substance. Learn more about it in this article. Energy transfer as heat and as work In...

### Thermodynamic systems

A thermodynamic system is a confined space of matter (e.g. gas) within which thermodynamic processes take place. The system boundary separates the system from the environment. Definition of the term thermodynamic system In...

### Stefan-Boltzmann law & Kirchhoff’s law of thermal radiation

0
The Stefan-Boltzmann law states that the radiant power of an object in thermal equilibrium is proportional to the fourth power of temperature and directly proportional to its surface! Introduction In the article Blackbody...

### Mean free path & collision frequency

The mean free path is the average distance a particle travels without colliding with other particles! Introduction In the article Maxwell-Boltzmann distribution it was shown that the mean speed (average speed) of the...

### Derivation of the Maxwell-Boltzmann distribution function

The Maxwell-Boltzmann distribution function of the molecular speed of ideal gases can be derived from the barometric formula. Introduction For ideal gases, the distribution function f(v) of the speeds has already been explained...

### Equipartition theorem

The equipartition theorem states that the kinetic energy of the gas molecules is equally divided along all three spatial directions! Equipartition theorem In the article Pressure and temperature the following equation was derived...

### Ideal gas law (explained and derived)

The ideal gas law describes the relationship between pressure, volume, mass and temperature of ideal gases. Parameters influencing the gas pressure The figure below shows a gas-filled cylinder closed with a piston. If...

### How does a thermal imaging camera work?

0
Thermal imaging cameras are based on the same principle as the pyrometer. These cameras capture the radiation spectrum of an object, which then allows conclusions to be drawn about the temperature...

### How does a infrared thermometer (pyrometer) work?

0
Pyrometers (infrared thermometers) use the heat radiation of objects invisible to the human eye to determine the temperature! The thermometers presented in the previous articles must directly touch the object from which...

### How does a thermocouple work?

0
Seebeck effect A thermocouple uses the phenomenon that a voltage is caused by the presence of a temperature gradient along an electrical conductor. The cause of this thermoelectric effect lies in the metallic...

### How does a resistance temperature detector (resistance thermometer) work?

0
In resistance thermometers the dependence of the electrical resistance on the temperature is used to determine the temperature! Operating principle A further measuring principle for determining the temperature is the change in the...

### How does a vapor pressure thermometer (vapor-in-metal) work?

0
Vapor pressure thermometers use the temperature-dependent vapor pressure of a liquid as the measuring principle. The less popular vapour pressure thermometers work according to the same principle as liquid-in-metal thermometers or gas-in-metal...

### How does a gas filled thermometer (gas-in-metal) work?

0
In gas thermometers, the pressure rise connected with a temperature increase is used for measuring the temperature! In gas filled temperature gauges (also called gas thermometers or gas-in-metal thermometers), a gas is...

### How does a liquid filled thermometer (liquid-in-metal) work?

0
Liquid-in-metal thermometers use the pressure rise of a liquid that comes along with an increase in temperature, if the volume is kept constant! In liquid-in-metal thermometers (also referred to as liquid filled...

### How does a bimetallic strip thermometer work?

0
In bimetallic strip thermometers the different rates of expansion of metals when heated is used to measure the temperature! Operating principle Temperatures can be meassured based on the principle of different thermal expansion...

### How does a liquid-in-glass thermometer work?

0
In liquid-in-glass thermometers, the thermal expansion of liquids is used for measuring the temperature! Operating principle Liquid-in-glass thermometers are based on the principle of thermal expansion of substances. A liquid in a glass...