0- Editor's note

Suzhou Techinno New Material Technologies Co., Ltd.will launch basic knowledge, principles and latest research progress in the field of thermal management materials from time to time, In order to better popularize the knowledge related to thermal management, enhance the public and industry personnel’s understanding of the industry. In the first issue we start with what is "heat".

1-Introduction

Without explaining too much everyone knows what "heat" is. However, do you really know what "heat" is? What is the nature of "heat"? What are the key indicators of "heat" in the electronics industry? With these questions, let's take a look at the true face of "heat" today.

2-The nature of heat

In ancient China's Five Elements Theory, fire is considered to be the same material as metal, wood, water, and earth. Aristotle (384 BC-322 BC, ancient Greek philosopher and scientist) held a similar view and put forward the theory of four elements. In the 17th century, German chemists Becher and Stahl (1659-1734) put forward the "phlogiston theory", thinking that heat is an element. In 1770, Priestley (1733-1804, British chemist, discoverer of oxygen) put forward the "thermal mass theory", believing that "thermal mass" is a massless gas that cannot be produced or destroyed. The temperature of an object will rise after absorbing thermal mass, and the heat will flow from objects with a higher temperature to ones with a lower temperature. In 1772, Lavoisier (1743-1794, French chemist, father of modern chemistry) overthrew the phlogiston theory with experiments, and Lavoisier's "Basics of Chemistry" listed heat among the basic substances. In 1799, Humphrey Davy (1778~1829, British chemist) confirmed the absence of heat and mass through the ice friction experiment, and believed that heat was the vibration of object particles, but his experiment did not receive attention at that time. In 1840, Joule through the conductor heating experiment, found that the calorific value is proportional to the square of the current, and p

High temperature: particles fast movement
Low temperature: particles slow movement
Heat transfer

3- The physical quantity of "heat".

Temperature: Temperature is a physical quantity that expresses how hot or cold an object is. The more commonly used temperature scales are Celsius (℃) and Fahrenheit (°F). In 1724, the German Garbriel Daniel Fahrenheit (Garbriel Daniel Fahrenheit, 1686-1736) formulated the Fahrenheit temperature scale. He set the temperature at which a certain concentration of salt water solidifies as 0°F and his wife's body temperature at 100°F. In order to be rigorous, he set the freezing point temperature of pure water as 32°F, and the boiling point temperature of water under standard atmospheric pressure as 212°F. The middle is divided into 180 equal parts, one representing 1 degree. The 18th-century Swedish astronomer Anders Celsius (1701-1744) proposed that under standard atmospheric pressure, the temperature of the ice-water mixture is 0 ℃, the boiling point of water is 100 ℃, and the middle is divided into 100 equal parts, Each aliquot is 1℃. Both the Celsius (℃) and Fahrenheit (°F) scales are man-made. In 1848, William Thomson (1824-1907), Baron Kelvin, defined absolute zero, the temperature of matter when the kinetic energy of particles is as low as the lowest point of quantum mechanics, which only exists in the lower limit of the theory. The thermodynamic temperature scale is written as K, which is equal to the Celsius temperature scale - 273.15℃.

Heat and calorific value: Heat refers to the energy transferred due to temperature difference, that is to say, the heat is digitized. Between objects with different temperatures, heat is always transferred from a high-temperature object to a low-temperature object, which is the internal energy changed in the process of energy transfer or transformation. The symbol is Q, and the unit is J (joule). Calorific value refers to the amount of heat generated or transferred per unit time. The unit of heat is the joule (J), and the calorific value is mainly used in watts (W). Watts are defined by joules and time (seconds). W=J/s (W calorific value; J calorific value, s time (second)). By the way, although "Caloric Theory" is considered to be wrong, its name "Calorie" has been retained. As one of the units of heat, the basic definition is "1g of water temperature at standard atmospheric pressure Calories required to raise 1°C", 1 calorie = 4.184J.

Specific heat capacity and heat capacity: Specific heat capacity refers to the amount of heat required to raise the temperature of 1g of a substance by 1K. The symbol is C, and the unit is J/K·g. (K: absolute temperature (+1°C = +1K)). Each substance has a different specific heat capacity. Heat capacity refers to the amount of heat required to raise the temperature of a certain amount of material by 1K. The symbol is C, which is the value obtained by multiplying the specific heat capacity of the material by the number of grams.

4-Form of heat transfer

Heat transfer and heat balance: Heat transfer (also known as heat conduction) means that when there is a temperature difference between different objects or within the same object, energy transfer occurs through the microscopic vibration, displacement and mutual collision of molecules, atoms and electrons. The only condition for heat transfer to occur is the existence of a temperature difference, regardless of the state of the objects, whether they are in contact or not. When the temperature of the two is equal, heat transfer no lon

Thermal Convection: Thermal convection refers to the phenomenon in which heat is transferred through the movement of a fluid (gas or liquid) due to a temperature difference. When the temperature rises, gases and liquids expand become less dense and lighter and gradually rise. Conversely, gases and liquids become heavier when the temperature decreased and drop gradually.

Thermal radiation: Thermal radiation refers to the phenomenon that objects radiate electromagnetic waves due to their temperature. Not only can heat transfer through matter, but also through radiation, heat transfer is possible even in a vacuum. The heat from the sun is transferred to the earth by thermal radiation.

Thermal Conduction and Thermal Conductivity: Thermal conduction refers to the phenomenon of heat transfer through matter by the propagation of lattice vibrations of atoms or molecules and the movement of free electrons. According to the characteristics of heat, heat is conducted from the high temperature side to the low temperature side. The ease with which this heat transfer is expressed numerically is called Thermal Conductivity. When there is a temperature difference of 1°C per 1m long, thermal conductivity represents the amount of heat that moves 1m2 of unit cross-sectional area in unit time (1 second), and the unit is (W/m·K).

This means that the larger the value of thermal conductivity, the easier the heat transfer. Thermal conductivity varies according to substance and form. Generally, the thermal conductivity is in the order of gas<liquid<solid from low to high. The thermal conductivity of air is only 0.023 W/m·K. The thermal conductivity in solids also varies depending on the species. The thermal conductivity of various materials is listed below. This is very important for the thermal management and thermal design of electronic products, and it is also one of the key parameters of thermal interface material design.

Heat conduction, heat convection, and heat radiation all play a key role in the cooling of electronic equipment. This figure briefly lists the relationship between heat conduction, heat convection, and heat radiation and the cooling of equipment or components. The heat emitted by the electronic components is transferred to the heat sink in the form of thermal conduction through the thermal interface material, and at the same time, the heat is conducted and dispersed to the substrate in the form of thermal conduction. Due to the heat of the heat sink, thermal convection is caused, and the surrounding temperature is averaged, and the temperature decreases accordingly.

5-Summary

Here we focus on the history, basic characteristics, physical quantities and terminology of the study of thermal nature. Next time, we will talk about why chips, automotive electronics, etc. are so "hot".