Thermal inductance

Last updated

Thermal inductance refers to the phenomenon wherein a thermal change of an object surrounded by a fluid will induce a change in convection currents within that fluid, thus inducing a change in the kinetic energy of the fluid. [1] It is considered the thermal analogue to electrical inductance in system equivalence modeling; its unit is the thermal henry. [1]

Thus far, few studies have reported on the inductive phenomenon in the heat-transfer behaviour of a system. In 1946, Bosworth demonstrated that heat flow can have an inductive nature through experiments with a fluidic system. [2] [3] He claimed that the measured transient behaviour of the temperature change cannot be explained by merely the combination of the thermal resistance and the thermal capacitance. Bosworth later extended the experiments to study the thermal mutual inductance; however, he did not report on the thermal inductance in a heat-transfer system with the exception of a fluid flow.

Recent studies

In 2013, Ye et al. have a publication of "Thermal Transient Effect and Improved Junction Temperature Measurement Method in High Voltage Light-Emitting Diodes". [4] In their experiments, a high voltage LED chip was directly attached on silicon substrate with thin thermal interface material (TIM). The temperature sensors were fabricated using standard silicon processing technologies which were calibrated ranging from 30 °C to 150 °C. The thickness of the chip and TIM were 153μm and 59μm, respectively. Thus the sensors were very close to the p-n junction. The silicon substrate was positioned and vacuumed on a cumbersome thermal plate with accurate temperature controller in an enclosure. The experimenters applied step-up/step-down currents and measured the characteristics between temperature and forward voltage after 100 ms. In this work, the ‘recovery time’ is defined as the interval from the start of power change to the time at which the temperature became again equal to the initial temperature value. The results show that the junction temperature of LED decreases significantly and immediately (more than 10 °C) when a current from 100 μA to 15 mA is applied. Then, the junction temperature gradually increases. After a recovery time of ~100 ms, the junction temperature reaches the initial value. At the steady state of 15 mA, the applied high current is instantly reduced through a step-down mode to 100 μA. The measured junction temperature increases by 4 °C within 0.1 ms. The sensor temperature simultaneously shows a temperature increase of 2 °C. Subsequently, the junction temperature gradually decreases. After a recovery time of ~100 ms, the junction temperature decrease to their initial values. Then the junction temperature continues to decrease until the system achieves the steady state at room temperature. Notably, the junction temperature changes in opposition to the current change in the chips.

In 2016, there was a further investigation on this phenomenon. [5] Instead of a high-voltage LED chip, a GaN-based low-voltage LED chip was also examined in this case. This chip can withstand a wider range of applied currents and facilitate more precise power change for observing the thermal inductive responses. The chip was mounted on a lead frame and encapsulated with silicone. The chip package was soldered to a metal core printed circuit board and mounted on a thermal plate with controllable temperatures. The transient junction temperature of the LED chip as a function of time was measured with the applied current as different step down functions. They calculated that the junction temperature is equal to 36.2 °C at 350 mA in this situation. The results are consistent with the previous thermal inductive measurement in the GaN-based high-voltage LED chip. As expected, the junction temperatures immediately rise and gradually decrease as the currents are stepped down. And the recovery time is slower for the system with a larger step level decrease. They prove that a rapid changing power through the GaN-based LEDs induces a proportional temperature change, which is opposed to the temperature change expected from the power input. This phenomenon is referred as thermal inductance in the report. The thermal inductive properties could be related to the thermoelectric effect, especially the transient thermoelectric effect. However, rather than considering the specified structure of thermoelectric devices, it is considered that the thermal inductance that occurs in GaN devices with a p–n junction. With the combination of the thermal resistance, the thermal capacitance, and the thermal inductance, it is expected that their assumption can promote the thermal analysis of high-frequency GaN devices. In addition, it is expected that thermal inductance phenomena exist more widely exist in nonhomogeneous materials and in the field of thermal analysis under energy changes in very short duration.

In 2019, an experiment was carried out in which a thermal oscillation was achieved without any external work being done. [6] The device was composed of a Peltier element and an electric inductance switched in series. It was shown that the time derivative of the heat current is proportional to the negative temperature difference across the device, in analogy to an electric inductor where the time derivative of the electric current is proportional to the negative voltage difference. The resulting "thermal self-inductance" allowing for this oscillatory behavior, with the considered objects always being in thermal quasi-equilibrium, was then expressed as a function of electric inductance, Seebeck coefficient of the used thermoelectric material and the operating temperature, and a differential equation was given for the oscillating thermal "LCR" current in the supplementary information section of the publication. Although the reported thermal oscillation was highly damped and the resulting temperature oscillation around the thermal bath temperature was comparably small, the experiment seems to be a valid proof of concept for a working thermal inductance.

Related Research Articles

Diode Electronic component that only allows current to flow in one direction

A diode is a two-terminal electronic component that conducts current primarily in one direction ; it has low resistance in one direction, and high resistance in the other. A diode vacuum tube or thermionic diode is a vacuum tube with two electrodes, a heated cathode and a plate, in which electrons can flow in only one direction, from cathode to plate. A semiconductor diode, the most commonly used type today, is a crystalline piece of semiconductor material with a p–n junction connected to two electrical terminals. Semiconductor diodes were the first semiconductor electronic devices. The discovery of asymmetric electrical conduction across the contact between a crystalline mineral and a metal was made by German physicist Ferdinand Braun in 1874. Today, most diodes are made of silicon, but other semiconducting materials such as gallium arsenide and germanium are also used.

Pyroelectricity Property of certain crystals which are naturally electrically polarized and contain large electric fields

Pyroelectricity is a property of certain crystals which are naturally electrically polarized and as a result contain large electric fields. Pyroelectricity can be described as the ability of certain materials to generate a temporary voltage when they are heated or cooled. The change in temperature modifies the positions of the atoms slightly within the crystal structure, such that the polarization of the material changes. This polarization change gives rise to a voltage across the crystal. If the temperature stays constant at its new value, the pyroelectric voltage gradually disappears due to leakage current. The leakage can be due to electrons moving through the crystal, ions moving through the air, or current leaking through a voltmeter attached across the crystal.

Thermoelectric cooling Uses the Peltier effect to create a heat flux between the junction of two different types of materials

Thermoelectric cooling uses the Peltier effect to create a heat flux at the junction of two different types of materials. A Peltier cooler, heater, or thermoelectric heat pump is a solid-state active heat pump which transfers heat from one side of the device to the other, with consumption of electrical energy, depending on the direction of the current. Such an instrument is also called a Peltier device, Peltier heat pump, solid state refrigerator, or thermoelectric cooler (TEC) and occasionally a thermoelectric battery. It can be used either for heating or for cooling, although in practice the main application is cooling. It can also be used as a temperature controller that either heats or cools.

Thermoelectric effect Direct conversion of temperature differences to electric voltage and vice versa

The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice versa via a thermocouple. A thermoelectric device creates a voltage when there is a different temperature on each side. Conversely, when a voltage is applied to it, heat is transferred from one side to the other, creating a temperature difference. At the atomic scale, an applied temperature gradient causes charge carriers in the material to diffuse from the hot side to the cold side.

Thermoelectric materials Materials whose temperature variance leads to voltage change

Thermoelectric materials show the thermoelectric effect in a strong or convenient form.

The term "thermal diode" is sometimes used for a device which allows heat to flow preferentially in one direction. Or, the term may be used to describe an electrical (semiconductor) diode in reference to a thermal effect or function. Or the term may be used to describe both situations, where an electrical diode is used as a heat pump or thermoelectric cooler.

Thermopile Device that converts thermal energy into electrical energy

A thermopile is an electronic device that converts thermal energy into electrical energy. It is composed of several thermocouples connected usually in series or, less commonly, in parallel. Such a device works on the principle of the thermoelectric effect, i.e., generating a voltage when its dissimilar metals (thermocouples) are exposed to a temperature difference.

A snubber is a device used to suppress ("snub") a phenomenon such as voltage transients in electrical systems, pressure transients in fluid systems or excess force or rapid movement in mechanical systems.

Jean Charles Athanase Peltier French physicist

Jean Charles Athanase Peltier was a French physicist. He was originally a watch dealer, but at the age of 30 began experiments and observations in physics.

Energy harvesting is the process by which energy is derived from external sources, captured, and stored for small, wireless autonomous devices, like those used in wearable electronics and wireless sensor networks.

Inrush current Maximal instantaneous input current drawn by an electrical device when first turned on

Inrush current, input surge current, or switch-on surge is the maximal instantaneous input current drawn by an electrical device when first turned on. Alternating-current electric motors and transformers may draw several times their normal full-load current when first energized, for a few cycles of the input waveform. Power converters also often have inrush currents much higher than their steady-state currents, due to the charging current of the input capacitance. The selection of over-current-protection devices such as fuses and circuit breakers is made more complicated when high inrush currents must be tolerated. The over-current protection must react quickly to overload or short-circuit faults but must not interrupt the circuit when the inrush current flows.

Electronic component Discrete device in an electronic system

An electronic component is any basic discrete device or physical entity in an electronic system used to affect electrons or their associated fields. Electronic components are mostly industrial products, available in a singular form and are not to be confused with electrical elements, which are conceptual abstractions representing idealized electronic components and elements.

Cryogenic particle detectors operate at very low temperature, typically only a few degrees above absolute zero. These sensors interact with an energetic elementary particle and deliver a signal that can be related to the type of particle and the nature of the interaction. While many types of particle detectors might be operated with improved performance at cryogenic temperatures, this term generally refers to types that take advantage of special effects or properties occurring only at low temperature.

Thermal management (electronics) Regulation of the temperature of electronic circuitry to prevent inefficiency or failure

All electronic devices and circuitry generate excess heat and thus require thermal management to improve reliability and prevent premature failure. The amount of heat output is equal to the power input, if there are no other energy interactions. There are several techniques for cooling including various styles of heat sinks, thermoelectric coolers, forced air systems and fans, heat pipes, and others. In cases of extreme low environmental temperatures, it may actually be necessary to heat the electronic components to achieve satisfactory operation.

A resonant-tunneling diode (RTD) is a diode with a resonant-tunneling structure in which electrons can tunnel through some resonant states at certain energy levels. The current–voltage characteristic often exhibits negative differential resistance regions.

Thermoelectric generator

A thermoelectric generator (TEG), also called a Seebeck generator, is a solid state device that converts heat flux directly into electrical energy through a phenomenon called the Seebeck effect. Thermoelectric generators function like heat engines, but are less bulky and have no moving parts. However, TEGs are typically more expensive and less efficient.

Junction temperature, short for transistor junction temperature, is the highest operating temperature of the actual semiconductor in an electronic device. In operation, it is higher than case temperature and the temperature of the part's exterior. The difference is equal to the amount of heat transferred from the junction to case multiplied by the junction-to-case thermal resistance.

Thermal management of high-power LEDs

High power light-emitting diodes (LEDs) can use 350 milliwatts or more in a single LED. Most of the electricity in an LED becomes heat rather than light. If this heat is not removed, the LEDs run at high temperatures, which not only lowers their efficiency, but also makes the LED less reliable. Thus, thermal management of high power LEDs is a crucial area of research and development. It is necessary to limit both the junction and the phosphor particles temperatures to a value that will guarantee the desired LED lifetime.

Thermal copper pillar bump

The thermal copper pillar bump, also known as the "thermal bump", is a thermoelectric device made from thin-film thermoelectric material embedded in flip chip interconnects for use in electronics and optoelectronic packaging, including: flip chip packaging of CPU and GPU integrated circuits (chips), laser diodes, and semiconductor optical amplifiers (SOA). Unlike conventional solder bumps that provide an electrical path and a mechanical connection to the package, thermal bumps act as solid-state heat pumps and add thermal management functionality locally on the surface of a chip or to another electrical component. The diameter of a thermal bump is 238 μm and 60 μm high.

Transition-edge sensor

A transition-edge sensor (TES) is a type of cryogenic energy sensor or cryogenic particle detector that exploits the strongly temperature-dependent resistance of the superconducting phase transition.

References

  1. 1 2 Jerrard HG (2012). A Dictionary of Scientific Units: Includingusiness Media. p. 142. ISBN   9789400941113.
  2. ↑ Bosworth RC (31 August 1946). "Thermal Inductance". Nature. 158 (4009): 309. Bibcode:1946Natur.158R.309B. doi: 10.1038/158309b0 .
  3. ↑ Bosworth RC (31 January 1948). "Thermal Mutual Inductance". Nature. 161 (4083): 166–167. Bibcode:1948Natur.161..166B. doi:10.1038/161166a0. S2CID   4098892.
  4. ↑ Ye H, Chen X, van Zeijl H, Gielen AW, Zhang G (September 2013). "Thermal Transient Effect and Improved Junction Temperature Measurement Method in High Voltage Light-Emitting Diodes". IEEE Electron Device Letters. 34 (9): 1172. Bibcode:2013IEDL...34.1172Y. doi:10.1109/LED.2013.2274473. S2CID   38718418.
  5. ↑ Ye H, Leung SY, Wong CK, Lin K, Chen X, Fan J, Kjelstrup S, Fan X, Zhang G (2016). "Thermal Inductance in GaN Devices". IEEE Electron Device Letters. 37 (11): 1473. Bibcode:2016IEDL...37.1473Y. doi:10.1109/LED.2016.2612243. S2CID   45941309.
  6. ↑ Schilling A, Zhang X, Bossen O (April 2019). "Heat flowing from cold to hot without external intervention by using a "thermal inductor"". Science Advances. 5 (4): eaat9953. arXiv: 1804.06405 . Bibcode:2019SciA....5.9953S. doi:10.1126/sciadv.aat9953. PMC   6474763 . PMID   31016235.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.