Joule heating

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Joule Heating , also known as Ohm Heating and resistive heating , is a process in which the path of electric current through the conductor generates heat.

Hukum pertama Joule , juga dikenal sebagai hukum Joule-Lenz , menyatakan bahwa kekuatan pemanasan yang dihasilkan oleh konduktor listrik sebanding dengan produk resistansi dan kuadratnya. Sekarang:

${\ displaystyle P \ propto I ^ {2} \ cdot R}  ÂÂ$

Joule heating affects all electrical conductors, unlike the Peltier effect that transfers heat from one electrical connection to another.

Video Joule heating

Histori

James Prescott Joule was first published in December 1840, an abstract in the Proceedings of the Royal Society, indicating that heat can be generated by electric current. Joule immersed a wire in fixed water and measured the temperature rise because a known current flowed through the wire for 30 minutes. By varying the current and length of the wire he concludes that the resulting heat is proportional to the square of the current multiplied by the electrical resistance of the embedded wire.

In 1841 and 1842, subsequent experiments showed that the amount of heat generated was proportional to the chemical energy used in the voltaic pile that produced the current. This led Joule to reject the calorie theory (at that time a dominant theory) supporting the mechanical theory of heat (which he thought heat was another form of energy).

Resistive heating was independently studied by Heinrich Lenz in 1842.

The energy SI unit is then named joule and given the symbol J . The commonly known power unit, watt, is equivalent to one joule per second.

Maps Joule heating

Microscopic description

Joule heating is caused by the interaction between the charge carrier (usually the electron) and the body of the conductor (usually the ion atom).

The voltage difference between the two conductor points creates an electric field that accelerates the load carrier in the direction of an electric field, giving them kinetic energy. When charged particles collide with ions in the conductor, the particles are dispersed; the direction of their motion becomes random rather than aligned with the electric field, which is a thermal movement. Thus, the energy of the electric field is converted into heat energy.

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Loss and power failures

Joule heating is referred to as ohmic warming or resistive heating due to its relationship with Ohm's Law. It forms the basis for a large number of practical applications that involve electrical heating. However, in applications where heating is an unwanted by-product of current use (eg, loss loads in power transformers) energy transfer is often referred to as resistive loss . High voltage usage in electric power transmission systems is specially designed to reduce cable losses by operating at a lower, equivalent current. Ring circuits, or ring mains, used in British homes are another example, where power is delivered to an outlet at a lower current, thereby reducing Joule heating in the wires. Joule heating does not occur in superconducting materials, because these materials have zero electrical resistance in the state of superconductors.

Resistors create electrical noise, called Johnson-Nyquist noise. There is an intimate relationship between Johnson-Nyquist noise and Joule warming, explained by fluctuation-dissipation theorem.

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Formula

Direct current

Rumus yang paling umum dan mendasar untuk pemanasan Joule adalah:

${\ displaystyle P = (V_ {A} -V_ {B}) I}  ÂÂ$

dimana

• P adalah kekuatan (energi per satuan waktu) diubah dari energi listrik menjadi energi panas,
• Saya adalah arus yang bergerak melalui resistor atau elemen lain,
• ${\ displaystyle V_ {A} -V_ {B}}  ÂÂ$ adalah penurunan tegangan pada elemen.

Explanation of this formula ( P = VI ) is:

( Energy lost per unit of time ) = ( Energy lost per charge across the resistor ) Ã,â € "( Overload per unit per unit time )

Ketika hukum Ohm juga berlaku, formula dapat ditulis dalam bentuk lain yang setara:

${\ displaystyle P = IV = I ^ {2} R = V ^ {2}/R}  ÂÂ$

where R is a match.

Flow back and forth

Saat arus bervariasi, seperti halnya di sirkuit AC,

${\ displaystyle P (t) = U (t) I (t)}  ÂÂ$

di mana t adalah waktu dan P adalah kekuatan seketika yang diubah dari energi listrik menjadi panas. Jauh lebih sering, kekuatan rata-rata lebih menarik daripada kekuatan sesaat:

${\ displaystyle P_ {avg} = U_ {\ text {rms}} I _ {\ text {rms}} = I _ {\ text {rms}} ^ {2} R = U_ {\ text {rms}} ^ {2}/R}  ÂÂ$

where "avg" shows average (average) more than one cycle or more, and "rms" denotes the square root of the square.

Rumus ini berlaku untuk resistor ideal, dengan reaktansi nol. Jika reaktansi tidak nol, rumus diubah:

${\ displaystyle P_ {avg} = U_ {\ text {rms}} I _ {\ text {rms}} \ cos \ phi = I _ {\ text {rms}} ^ {2} \ operatorname {Re} (Z) = U_ {\ text {rms}} ^ {2} \ operatorname {Re} (Y ^ {*})}  ÂÂ$

di mana ${\ displaystyle \ phi}  ÂÂ$ adalah perbedaan fasa antara arus dan tegangan, ${\ displaystyle \ operatorname {Re}}  ÂÂ$ berarti bagian nyata, Z adalah impedansi kompleks, dan Y * adalah konjugasi kompleks dari penerimaan (sama dengan 1/ Z * ).

For more details in reactive case, see AC power? 0}

Differential form

Dalam fisika plasma, pemanasan Joule sering perlu dihitung pada lokasi tertentu di ruang angkasa. Bentuk diferensial dari persamaan pemanasan Joule memberikan kekuatan per satuan volume.

${\ displaystyle \ mathrm {d} P/\ mathrm {d} V = \ mathbf {J} \ cdot \ mathbf {E}}  ÂÂ$

Di sini, ${\ displaystyle \ mathbf {J}}  ÂÂ$ adalah kerapatan saat ini, dan ${\ displaystyle \ mathbf {E}}  ÂÂ$ adalah medan listrik. Untuk plasma netral tidak dalam medan magnet dan dengan konduktivitas ${\ displaystyle \ sigma}  ÂÂ$ , ${\ displaystyle \ mathbf {J} = \ sigma \ mathbf {E}}  ÂÂ$ dan karenanya

${\ displaystyle \ mathrm {d} P/\ mathrm {d} V = \ mathbf {J} \ cdot \ mathbf {E} = \ mathbf {J} \ cdot \ mathbf {J}/\ sigma = J ^ {2} \ rho}  ÂÂ$

di mana ${\ displaystyle \ rho = 1/\ sigma}  ÂÂ$ adalah resistivitas. Ini secara langsung menyerupai " ${\ displaystyle I ^ {2} R}  ÂÂ$ "dari bentuk makroskopik.

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Pembangkit listrik arus bolak-balik tegangan tinggi

Overhead power lines transfer electrical energy from power producers to consumers. The power line has a non-zero resistance and is therefore subject to Joule heating, which causes transmission losses.

The distribution of power between the transmission loss (Joule heating in the transmission line) and the load (useful energy delivered to the consumer) can be approximated by a voltage divider. To minimize transmission losses, line resistance should be as small as possible compared to load (consumer equipment resistance). Line resistance is minimized by the use of copper conductors, but the resilience and specifications of the consumer electrical equipment supply have been improved.

Typically, a transformer is placed between the line and consumption. When the voltage is high, the low-intensity current in the primary circuit (before the transformer) is converted to low voltage, high-intensity current in the secondary circuit (after the transformer), the secondary circuit equivalent resistance becomes higher. and the loss of transmission is proportionally reduced.

During the Flow War, the AC installation can use a transformer to reduce line loss by Joule heating, with higher voltage costs in transmission lines, compared to a DC installation.

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Apps

Joule-heating or resistive-heating is used in many industrial devices and processes. The part that turns electricity into heat with Joule heating is called heating element .

There are many practical uses for Joule warming:

• An incandescent bulb lights up when the filament is heated by a Joule heater, due to thermal radiation (also called black radiation).
• The electric fuse is used as a safety, damaging the circuit by melting if the current flow is sufficient to melt it.
• Electronic cigarettes evaporate propylene glycol and vegetable glycerin with Joule heating.
• Some heating devices use Joule heaters, such as electric stoves, electric heaters, soldering irons, cartridge heaters.
• Some food processing equipment can use Joule heating: running current through foodstuffs (which serve as electrical resistors) causes heat release in the food. Alternating electric current coupled with food resistance causes heat generation. Higher resistance increases the heat generated. Ohmik heating enables warming up of food products quickly and uniformly, which maintains high quality in food. Products with heat particles are faster in Ohmic heating (compared to conventional heat processes) due to higher resistance.

Food Processing

Joule Heating is flash pasteurization (also called "short-time high temperature process" (HTST)) that runs 50-60 Hz alternating current through food. Heat is generated through the electrical resistance of food. As the product heats up, the electrical conductivity increases linearly. Higher electric current frequency is best because it reduces oxidation and metal contamination. This heating method works best for foods containing suspended particles in mediums containing weak salts because of their high resistance properties. Ohmik heating enables the quality of food that is maintained due to uniform heating that decreases deterioration and excess food processing.

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Heating efficiency

As a heating technology, Joule heaters have a performance coefficient of 1.0, which means that each joule of electric energy supplied produces one hot joule. In contrast, the heat pump can have a coefficient of more than 1.0 as it propels additional heat energy from the environment to the hot object.

The definition of the efficiency of the heating process requires the determination of the system boundary to be considered. When heating a building, overall efficiency differs when considering the heating effect per unit of electrical energy delivered on the customer side of the meter, compared to overall efficiency when also considering losses on power generation and power transmission.

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Hydraulic equivalents

Dalam keseimbangan energi aliran air tanah, setara hidrolik hukum Joule digunakan:

${\ displaystyle {dE \ over dx} = {v_ {x} ^ {2} \ over K}}  ÂÂ$

dimana:

${\ displaystyle dE/dx}  ÂÂ$ = kehilangan energi hidraulik ( ${\ displaystyle E}  ÂÂ$ ) karena gesekan aliran dalam ${\ displaystyle x}  ÂÂ$ -direction per unit waktu (m/hari) - sebanding dengan ${\ displaystyle P}  ÂÂ$

${\ displaystyle v_ {x}}  ÂÂ$ = kecepatan aliran dalam ${\ displaystyle x}  ÂÂ$ -direction (m/day) - sebanding dengan ${\ displaystyle I}  ÂÂ$

${\ displaystyle K}  ÂÂ$ = konduktivitas hidrolik tanah (m/hari) - konduktivitas hidrolik berbanding terbalik dengan resistansi hidraulik yang dibandingkan dengan ${\ displaystyle R}  ÂÂ$

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Lihat juga

• Kawat tahanan
• Elemen pemanas
• Nichrome
• Tungsten
• Disilicide Molibdenum
• Panas berlebih (listrik)
• Manajemen termal (elektronik)

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Referensi

Source of the article : Wikipedia