Ang Thermal Conductivity sa mga Metal: Kung Paano Ang Pagtumakbo sa Kalibutan Sa Mga Naang Material
Ang thermal conductivity mao ang katangian nga midaog kung unsa ka maayo ang materyales sa pagpuyo og heat gikan sa usa ka punto ngadto sa lain laing punto walay paggalilid sa materyales mismo. Depende kini sa mga factor sama sa structure, composition, ug temperature sa materyales. Sa suga, atong ibutang ang atensyon sa thermal conductivity of metals, nga mao ang mga solid nga may high electrical ug thermal conductivity, ug high density.
Unsa ang Metal?
Ang metal mao ang solid material nga may crystalline structure, diin ang atoms gibulag sa regular pattern. Ang atoms consist sa nuclei uban sa ilang surrounding shells of core electrons, nga tightly bound sa nuclei. Pero ang pipila ka outermost electrons libre sa pag-move sa tanang bahin sa metal, forming a sea of electrons nga makapuyo electric current ug heat energy.
Ang metals adunay daghang useful properties, sama sa high strength, ductility, malleability, luster, ug reflectivity. Sila usab maayo nga conductors of electricity ug heat, nga nangahiusa sila makapuyo niini nga mga form sa energy efficiently ug quickly.
Unsaon ang Heat Transfer sa Metals?
Ang heat transfer mao ang proseso sa pagpuyo og thermal energy gikan sa rehiyon sa mas taas nga temperatura ngadto sa rehiyon sa mas baba nga temperatura. Adunay tulo ka main modes sa heat transfer: conduction, convection, ug radiation.
Conduction mao ang mode sa heat transfer nga nahitabo sa solids, diin ang heat flows through direct contact between atoms or molecules. Convection mao ang mode sa heat transfer nga nahitabo sa fluids (liquids or gases), diin ang heat flows through the movement of fluid particles. Radiation mao ang mode sa heat transfer nga nahitabo through electromagnetic waves, sama sa light o infrared radiation.
Sa metals, ang heat transfer mainly occurs by conduction, tungod kay ang metals mao ang solids ug adunay daghan nga free electrons. Ang free electrons makamove randomly throughout the metal ug collide with other electrons or atoms, transferring kinetic energy ug thermal energy. The more free electrons a metal has, the higher its thermal conductivity.
Unsa ang Factors Affect the Thermal Conductivity of Metals?
The thermal conductivity of metals depends on several factors, such as:
The type and number of free electrons: Metals with more free electrons have higher thermal conductivity since they can carry more heat energy. For example, silver has the highest thermal conductivity among metals, followed by copper and gold.
The atomic mass and size: Metals with heavier and larger atoms have lower thermal conductivity since they vibrate more slowly and hinder the movement of free electrons. For example, lead has a low thermal conductivity among metals.
The crystal structure and defects: Metals with a more regular and compact crystal structure have higher thermal conductivity since they have less resistance to electron flow. For example, metals with a cubic structure have higher thermal conductivity than metals with a hexagonal structure. Defects such as impurities, vacancies, or dislocations can also reduce the thermal conductivity of metals by scattering electrons.
The temperature: The thermal conductivity of metals varies with temperature in different ways depending on the dominant mechanism of heat transfer. For pure metals and alloys, heat transfer is mainly due to free electrons (electronic conduction). As temperature increases, both the number of free electrons and lattice vibrations increase. Thus, the thermal conductivity of metals decreases slightly with increasing temperature. For insulators and semiconductors, heat transfer is mainly due to lattice vibrations (phononic conduction). As temperature increases, lattice vibrations increase significantly and scatter electrons more frequently. Thus, the thermal conductivity of insulators and semiconductors increases rapidly with increasing temperature.
Unsa ang Wiedemann-Franz Law?
Wiedemann-Franz law mao ang relation nga nagconnect sa electrical conductivity ug thermal conductivity sa metals sa given temperature. Nagsulti kini nga:
σK=LT
Diin,
K mao ang thermal conductivity in W/m-K
σ mao ang electrical conductivity in S/m
L mao ang Lorenz number, nga mao ang constant equal to 2.44 x 10^-8 W-ohm/K^2
T mao ang absolute temperature in K
This law implies that metals that have high electrical conductivity also have high thermal conductivity since both properties depend on the free electrons. It also implies that the ratio of thermal conductivity to electrical conductivity is proportional to the temperature of metals.
However, this law has some limitations. It only applies to pure metals and alloys at very high or very low temperatures. It does not apply to insulators or semiconductors, where phononic conduction dominates over electronic conduction. It also does not apply to some metals, such as beryllium or pure silver, which deviate from this.
Unsa ang Thermal Conductivity Values of Some Common Metals?
The thermal conductivity of metals varies widely depending on the type and purity of the metal. The table below shows some examples of thermal conductivity values for some common metals at room temperature (25°C).
