Last Updated on April 8, 2023 by Tabraiz
When a fuel like cooking gas, methane, or coal burns in the air, the chemical energy stored by molecules can be released during chemical reactions as heat. When fuel burns in an engine, the chemical energy can also be used to do mechanical work or to provide electrical energy via a galvanic cell such as a dry cell. Thus, different types of energy are interconnected, and under certain conditions, they can be transformed from one type to another. The study of these energy transformations is what thermodynamics is all about.
A psychrometer is a device that measures the relative humidity or water vapour content in the air. It is made up of two identical thermometers:
Wet-bulb thermometer: It measures temperature by dipping the bulb in liquid. The bulb is protected by a muslin cloth jacket that can be saturated with distilled water.
Dry-bulb thermometer: It measures temperature by exposing it to air. There are two kinds of psychrometers:
Sling psychrometer: Thermometers are attached to a grip or span of rope and spun in the air for a period of time in this type of psychrometer. It is rarely used in field computations. It has now been replaced by more appropriate electronic sensors.
Whirling psychrometer – Two thermometers are joined together to form an instrument that resembles a ratchet or football rattle in a whirling psychrometer.
In some ships, electric psychrometers are used as the primary wet bulb temperature measuring device. It serves as a backup for the automatic air temperature and dew point sensors.
Psychrometers are attached to musical instruments, such as pianos, guitars, and violins, which can be damaged by excessive humidity.
Thermal conductivity is defined as the ability of a material to inherently conduct or transfer heat. It is denoted by k, or 𝛌 . Thermal conductivity is one of three heat transfer methods, the others being radiation and convection. Heat transfer processes can be mathematically expressed using appropriate equations of rate. In this heat transfer mode, the rate equation is based on Fourier’s law of heat conduction.
Fourier’s law of heat conduction differential form can be expressed as follows: q = -k.∇T
∇T denotes the temperature gradient, q is the thermal flux or heat flux, and k is the thermal conductivity of the material in the question.
The SI unit of this quantity is watts per metre-Kelvin or Wm-1K-1.
Factors Affecting Thermal Conductivity
Since molecular movement is the foundation of thermal conductance, a material’s temperature has a large influence on its thermal conductivity. Because molecules move faster at higher temperatures, heat is transferred through the material at a faster rate. This means that the thermal conductivity of the same sample can change dramatically as the temperature rises or falls.
The Maggi-Righi-Leduc effect describes the change in the thermal conductivity of a conductor when placed in a magnetic field. When magnetic fields are applied, an orthogonal temperature gradient is observed.
Thermal conductivity is highly dependent on material density. The thermal conductivity increases as density increases.