PTC Thermistors
There are three types of PTC or positive temperature coefficient thermistors.
• Ceramic Switching PTC Thermistors
• Silistor Silicon PTC Thermistors
• Polymer PPTC Thermistors
Change in the resistance of a PTC thermistor can be brought about either by a change in the ambient temperature or internally by self-heating resulting from current flowing through the device.
Manufacturing process
The manufacturing process for PTC thermistors begins by mixing selected material with a binding agent. Next; the mixture is pressed and sintered into wafer form. The mix of raw material will vary depending on the specific type of PTC thermistor being manufactured
General PTC Thermistor Applications
• Time Delay
• Degaussing
• Motor Starting
•
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Because they possess positive coefficient characteristics, they exhibit a trace amount of negative temperature coefficient until they reach a critical temperature point known as a “curie” or transition state. At which point, the device begins to exhibit a positive temperature coefficient along with a significant increase in resistance.
Manufacturing Material
Ceramic Switching PTC thermistors are made from a polycrystalline ceramic material that contains barium titanate. This mix of material when doped with rare earth metals is what gives them their positive temperature coefficient characteristics.
Applications
• Over-current protection:
• Time Delay:
Benefits
To demonstrate the versatility of the PTC thermistor; below are some examples where their use as an Inrush Current Limiter is the optimal choice.
• Ambient temperature is greater than 65 °C.
• Ambient temperature is less than Zero °C.
• Reset time needs to be near zero °C.
• Short circuit concerns.
Configurations
• Radial Leaded
• Surface Mount
On the other hand, the active magnetic refrigeration cycle is similar to the ADR cycle, but heat addition and rejection occurs at a constant magnetic field rather than at constant temperature. Isothermal heat rejection and addition is impractical to implement since the applied magnetic field must be modulated to match the temperature with the heat rejection rate [13],
"Production of Refractory Metal Powders," in Powder Metal Technologies and Applications, vol. 7, 1998, pp. 188-201.
... : The difference in slope is positively correlated with a lower temperature. This slope becomes apparent
This study will explore the shape and scope of the Manhattan Project scientists’ political movement between 1942 and 1945. It will examine the messages they brought into the political realm and investigate how they approached political questions. It will further examine why the scientists were unable to influence wartime policy regarding the use of nuclear weaponry.
The objective of this experiment was to identify a metal based on its specific heat using calorimetry. The unknown metals specific heat was measured in two different settings, room temperature water and cold water. Using two different temperatures of water would prove that the specific heat remained constant. The heated metal was placed into the two different water temperatures during two separate trials, and then the measurements were recorded. Through the measurements taken and plugged into the equation, two specific heats were found. Taking the two specific heats and averaging them, it was then that
Superconductivity, a similar phenomenon, was discovered in 1911 by Dutch physicist Heike Kamerlingh Onnes. When he cooled some mercury down to liquid helium temperatures, it began to conduct electricity with no resistance at all. People began experimenting with other metals, and found that many tranisition metals exhibit this characteristic of 0 resistance if cooled sufficiently. Superconductors are analagous to superfluids in that the charges within them move somewhat like a superfluid - with no resistance through sections of extremely small cross-sectional area. Physicists soon discovered that oxides of copper and other compounds could reach even higher superconducting temperatures. Currently, the highest temperature at wich a material can be superconductive is 138K, and is held by the compound Hg0.8Tl0.2Ba2Ca2Cu3O8.33.
- Temperature was measured after and exact time i.e. 1 minute, 2 minutes, 3 minutes.
The change in temperature upon adding Zinc in a perfect situation, where no heat is lost. The gradient shows that temperature decreases when Zinc was added in it. Very steep gradient line shows the speed of the reaction at which temperature was decreasing.
Answer: The term thermiionic emission comes from the phenomena of quantumm mechanical tunneling which takes place in some special circumstances. It sometimes happens that electrons with energy less than the barrier height to cross the barrier passing through it instead of over is called tunnneling effect. In semi conductors we can see this in heavily doped material where the current in the forward direction arises due to tunneling of the charged particles with energies close to the Fermi level but not the actual barrier height. This kind of emission due to tunneling is called field emission. Now if we increase the forward bias voltage, the electrons acquire enough energy to tunnel through the thin depletion region. To avoid this kind of tunneling and get a pure current flow we raise the temperature to a certain point such that the electrons get enough energy to cross the barrier and no longer tunnel through it. This temperature generated effect is called pure thermionic emission.
The worst accident in the history of this nuclear power generation occurred on the morning of April 26, 1986. It was at the Chernobyl (Ukraine) nuclear power station in the Soviet Union. At 1:32AM Lieutenant Colonel Leonid Telyatnikov received a telephone call and was told that there was a fire at the nuclear power plant. There were many reasons their plant had backfired. These reasons included human error and poor plant design due to the cold war. Chernobyl was located in the former Soviet Union in what is now Ukraine. The area in and around Chernobyl is now a nuclear wasteland. People are not supposed to live in these areas, yet they still do, even with the danger of mutations and radiation sickness. For the people and countries affected by the radiation, this was a horrible, terrifying and angering experience. Villages were evacuated late and not many things were done in time to save lives and prevent more damages.
Chernobyl was the largest uncontrolled radioactive release ever recorded in history. Chernobyl was an accident that occurred while running routine checks on the Chernobyl 4 reactor on April 26, 1986. The explosion released all of its xenon gas, and about half of its iodine-131 and caesium-137 into the atmosphere. This accident resulted in tens of thousands of deaths and millions left with radiation poisoning. Chernobyl used to be prospering with a population of about 14,000; however, today it's a ghost town with a population hovering around 150 residents. Almost all the population chose to evacuate, while others took the risk in order to hold onto their memories of the once thriving town. The radiation still hovers around in the air today, still at very powerful and dangerous levels; 600,000 workers have attempted to contain the radiation levels. Chernobyl still has lasting effects today; it released record amounts of radiation, affected millions of lives, called for thousands of abortion requests, destroyed wild life, and it was a key turning point in history for nuclear safety.
At this point the desirable crystalline structure of the metal has been reached but it must not be allowed to be heated further as the solution will begin to melt.
1995A lost foam vaccum casting process to produce stainless steel with low carbon content .some of members like OH Babcock,Wilcox got the patent for this.
Superconductors consist of an element, inter-metallic alloy, or compound that will conduct electricity without resistance (loss of energy flowing through the material) below a certain temperature. Once in motion, electrical current will flow forever in a closed loop of superconducting material, hence the high demand of such a product.
Process bc : This high pressure and high temperature vapour then enters a condenser where the temperature of the vapour first drops to saturation temperature and subsequently the vapour refrigerant condenses to liquid state .