|
|
| Line 1: |
Line 1: |
| The '''temperature coefficient''' is the relative change of a physical property when the [[temperature]] is changed by 1 [[Kelvin]]. | | The other day I woke up and noticed - I have also been solitary for some time today and after much bullying from friends I today locate myself signed-up for web dating. They guaranteed me that there are a lot of pleasant, normal and enjoyable folks to fulfill, so [http://www.senatorwonderling.com Luke Bryan Live Concert] the pitch is gone by here!<br>I strive to stay as physically healthy as possible coming to the gym several-times weekly. I love my athletics and make an effort to perform or watch as numerous a potential. I'll frequently at Hawthorn fits being wintertime. Notice: Supposing where is the luke bryan concert ([http://lukebryantickets.neodga.com http://lukebryantickets.neodga.com]) that you will considered purchasing an athletics I really don't brain, I have seen the carnage of fumbling fits at stocktake sales.<br>My family and buddies luke bryan schedule 2014 ([http://lukebryantickets.iczmpbangladesh.org http://lukebryantickets.iczmpbangladesh.org]) are awesome and [http://www.sharkbayte.com/keyword/spending+time spending time] with them at pub gigs or dishes is consistently a must. I have never been in to nightclubs as I see you could never get a decent dialog luke bryan tickets 2012 ([http://www.banburycrossonline.com www.banburycrossonline.com]) against the sound. I additionally got two very adorable and definitely cheeky canines who are constantly excited to meet up fresh individuals.<br><br>Here is my blog [http://lukebryantickets.lazintechnologies.com wiz khalifa tickets] |
| | |
| In the following formula, let ''R'' be the physical property to be measured and ''T'' be the temperature at which the property is measured. ''T''<sub>0</sub> is the reference temperature, and Δ''T'' is the difference between ''T'' and ''T''<sub>0</sub>. Finally, '''α''' is the (linear) temperature coefficient. Given these definitions, the physical property is:
| |
| :<math>\operatorname{R}(T) = \operatorname{R}(T_0)(1 + \alpha\Delta T)</math>
| |
| | |
| Here α has the [[dimension]]s of an inverse temperature (1/K or K<sup>−1</sup>).
| |
| | |
| This equation is [[linear]] with respect to temperature. For quantities that vary [[polynomial]]ly or [[logarithm]]ically with temperature, it may be possible to calculate a temperature coefficient that is a useful approximation for a certain range of temperatures. For quantities that vary [[exponential growth|exponentially]] with temperature, such as [[Arrhenius equation|the rate of a chemical reaction]], any temperature coefficient would be valid only over a very small temperature range.
| |
| | |
| Different temperature coefficients are specified for various applications, including nuclear, electrical and magnetic.
| |
| | |
| ==Negative temperature coefficient==
| |
| A '''negative temperature coefficient''' (NTC) occurs when a physical property (such as [[thermal conductivity]] or [[electrical resistivity]]) of a material lowers with increasing temperature, typically in a defined temperature range. For most materials, electrical resistivity will increase with increasing temperature.
| |
| | |
| Materials with a negative temperature coefficient have been used in [[floor heating]] since 1971. The negative temperature coefficient avoids excessive local heating beneath carpets, [[bean bag]] chairs, [[mattress]]es etc., which can damage [[Wood flooring|wooden floors]], and may infrequently cause fires.
| |
| | |
| Most [[ceramic]]s exhibit NTC behaviour, which is governed by an [[Arrhenius equation]] over a wide range of temperatures:
| |
| | |
| :<math>R=A \cdot e^{\frac{B}{T}}</math>
| |
| where ''R'' is resistance, ''A'' and ''B'' are constants, and ''T'' is absolute temperature (K).
| |
| The constant ''B'' is related to the energies required to form and move the [[charge carrier]]s responsible for electrical conduction – hence, as the value of ''B'' increases, the material becomes insulating. Practical and commercial NTC [[resistor]]s aim to combine modest resistance with a value of ''B'' that provides good sensitivity to temperature. Such is the importance of the ''B'' constant value, that it is possible to characterize NTC [[thermistor]]s using the B parameter equation:
| |
| :<math>R = r^{\infty}e^{\frac{B}{T}} = R_{0}e^{-\frac{B}{T_{0}}}e^{\frac{B}{T}}</math>
| |
| where <math>R_{0}</math> is resistance at temperature <math>T_{0}</math>.
| |
| Therefore, many materials that produce acceptable values of <math>R_{0}</math> include materials that have been alloyed or possess variable [[cation]] valence states and thus contain a high natural defect center concentration. The value of ''B'' strongly depends on the energy required to dissociate the charge carriers that are used for the electrical conduction from these defect centers.
| |
| | |
| ==Reversible temperature coefficient==
| |
| Residual magnetic flux density or [[Magnetic field#B and H|Br]] changes with temperature and it is one of the important characteristics of magnet performance. Some applications, such as inertial [[gyroscope]]s and [[traveling-wave tube]]s (TWTs), need to have constant field over a wide [[temperature range]]. The '''reversible temperature coefficient''' (RTC) of Br is defined as:
| |
| :<math>RTC = \frac{\Delta Br}{Br \Delta T} \times 100</math>
| |
| | |
| To address these requirements, temperature compensated magnets were developed in the late 1970s.<ref>{{cite web |url=http://www.electronenergy.com/about-us/about-us.htm |title=About Us |publisher=Electron Energy Corporation}}</ref> For conventional [[Samarium–cobalt magnet|SmCo magnets]], Br decreases as temperature increases. Conversely, for GdCo magnets, Br increases as temperature increases within certain temperature ranges. By combining [[samarium]] and [[gadolinium]] in the alloy, the temperature coefficient can be reduced to nearly zero.
| |
| | |
| ==Temperature coefficient of electrical resistance==
| |
| {{see also|Resistivity#Resistivity of various materials|l1=Table of materials' resistivities}}
| |
| | |
| The temperature dependence of [[electrical resistance]] and thus of electronic devices ([[wire]]s, resistors) has to be taken into account when constructing devices and [[electrical network|circuits]]. The temperature dependence of [[Electrical conductor|conductors]] is to a great degree linear and can be described by the approximation below.
| |
| | |
| :<math>\operatorname{\rho}(T) = \rho_{0}[1 + \alpha_{0}(T-T_{0})]</math>
| |
| where
| |
| :<math>\alpha_{0}=\frac{1}{\rho_{0}}\left [ \frac{\delta \rho}{\delta T}\right ]_{T=T_{0}}</math> | |
| <math>\rho_{0}</math> just corresponds to the specific resistance temperature coefficient at a specified reference value (normally ''T'' = 0 °C)<ref>{{cite book |first=S. O. |last=Kasap |title=Principles of Electronic Materials and Devices |edition=Third |publisher=Mc-Graw Hill |year=2006 |page=126}}</ref>
| |
| | |
| That of a [[semiconductor]] is however exponential:
| |
| | |
| :<math>\operatorname{\rho}(T) = S \alpha^{\frac{B}{T}}</math>
| |
| where <math>S</math> is defined as the cross sectional area and ''<math>\alpha</math>'' and ''<math>b</math>'' are coefficients determining the shape of the function and the value of resistivity at a given temperature.
| |
| | |
| For both, ''<math>\alpha</math>'' is referred to as the resistance temperature coefficient.<ref>{{cite book|last=Alenitsyn|first=Alexander G.|coauthors=Butikov, Eugene I.; Kondraryez, Alexander S.|title=Concise Handbook of Mathematics and Physics|publisher=CRC Press|year=1997|pages=331–332|isbn=0-8493-7745-5}}</ref>
| |
| | |
| This property is used in devices such as thermistors.
| |
| | |
| ===Positive temperature coefficient of resistance===
| |
| A '''positive temperature coefficient''' (PTC) refers to materials that experience an increase in electrical resistance when their temperature is raised. Materials which have useful engineering applications usually show a relatively rapid increase with temperature, i.e. a higher coefficient. The higher the coefficient, the greater an increase in electrical resistance for a given temperature increase.
| |
| | |
| ==Temperature coefficient of elasticity==
| |
| The [[elastic modulus]] of elastic materials varies with temperature, typically decreasing with higher temperature.
| |
| | |
| ==Temperature coefficient of reactivity==
| |
| In [[nuclear engineering]], the temperature coefficient of reactivity is a measure of the change in reactivity (resulting in a change in power), brought about by a change in temperature of the reactor components or the reactor coolant. This may be defined as
| |
| | |
| :<math>\alpha_{T}=\frac{\partial \rho}{\partial T}</math> | |
| | |
| Where <math>\rho</math> is [[Nuclear chain reaction#Effective neutron multiplication factor|reactivity]] and ''T'' is temperature. The relationship shows that <math>\alpha_{T}</math> is the value of the [[partial differential]] of reactivity with respect to temperature and is referred to as the "temperature coefficient of reactivity". As a result, the temperature feedback provided by <math>\alpha_{T}</math> has an intuitive application to [[passive nuclear safety]]. A negative <math>\alpha_{T}</math> is broadly cited as important for reactor safety, but wide temperature variations across real reactors (as opposed to a theoretical homogeneous reactor) limit the usability of a single metric as a marker of reactor safety.<ref>Duderstadt & Hamilton 1976, pp. 259–261</ref>
| |
| | |
| In water moderated nuclear reactors, the bulk of reactivity changes with respect to temperature are brought about by changes in the temperature of the water. However each element of the core has a specific temperature coefficient of reactivity (e.g. the fuel or cladding). The mechanisms which drive fuel temperature coefficients of reactivity are different than water temperature coefficients. While water expands [[Water (properties)#Density of water and ice|as temperature increases]], causing longer neutron travel times during [[Neutron moderator|moderation]], fuel material will not expand appreciably. Changes in reactivity in fuel due to temperature stem from a phenomenon known as [[doppler broadening]], where resonance absorption of fast neutrons in fuel filler material prevents those neutrons from thermalizing (slowing down).<ref>Duderstadt & Hamilton 1976, pp. 556–559</ref> {{Further|Fuel temperature coefficient of reactivity}}
| |
| | |
| ==Units==
| |
| | |
| The thermal coefficient of [[Electrical_network|electrical circuit]] parts is sometimes specified as [[Parts per notation|ppm]]/°[[Celsius|C]]. This specifies the fraction (expressed in parts per million) that its electrical characteristics will deviate when taken to a temperature above or below the [[operating temperature]].
| |
| | |
| ==References==
| |
| {{reflist}}
| |
| | |
| ==Bibliography==
| |
| *{{cite book|last=Duderstadt|first=Jame J.|authorlink=James Johnson Duderstadt|coauthors=Hamilton, Louis J.|title=Nuclear Reactor Analysis|publisher=Wiley|year=1976|isbn=0-471-22363-8}}
| |
| | |
| [[Category:Electric and magnetic fields in matter]]
| |
| [[Category:Electrical engineering]]
| |
| [[Category:Nuclear physics]]
| |
The other day I woke up and noticed - I have also been solitary for some time today and after much bullying from friends I today locate myself signed-up for web dating. They guaranteed me that there are a lot of pleasant, normal and enjoyable folks to fulfill, so Luke Bryan Live Concert the pitch is gone by here!
I strive to stay as physically healthy as possible coming to the gym several-times weekly. I love my athletics and make an effort to perform or watch as numerous a potential. I'll frequently at Hawthorn fits being wintertime. Notice: Supposing where is the luke bryan concert (http://lukebryantickets.neodga.com) that you will considered purchasing an athletics I really don't brain, I have seen the carnage of fumbling fits at stocktake sales.
My family and buddies luke bryan schedule 2014 (http://lukebryantickets.iczmpbangladesh.org) are awesome and spending time with them at pub gigs or dishes is consistently a must. I have never been in to nightclubs as I see you could never get a decent dialog luke bryan tickets 2012 (www.banburycrossonline.com) against the sound. I additionally got two very adorable and definitely cheeky canines who are constantly excited to meet up fresh individuals.
Here is my blog wiz khalifa tickets