Search results
Results From The WOW.Com Content Network
In thermal engineering, the logarithmic mean temperature difference (LMTD) is used to determine the temperature driving force for heat transfer in flow systems, most notably in heat exchangers. The LMTD is a logarithmic average of the temperature difference between the hot and cold feeds at each end of the double pipe exchanger.
The RMS value of an alternating current is also known as its heating value, as it is a voltage which is equivalent to the direct current value that would be required to get the same heating effect. For example, if 120 V AC RMS is applied to a resistive heating element it would heat up by exactly the same amount as if 120 V DC were applied.
In electronics and electrical engineering, the form factor of an alternating current waveform (signal) is the ratio of the RMS (root mean square) value to the average value (mathematical mean of absolute values of all points on the waveform). [1] It identifies the ratio of the direct current of equal power relative to the given alternating ...
LMTD is just the mean temperature difference (ie, just an arithmetic mean), it just turns out the arithmetic mean using infinitesimal steps has a log in it (see the derivation section)! Calling it a logarithmic mean just confuses the issue and makes it appear more abstract than it actually is. 'F' is a 'correction factor'.
Angle notation can easily describe leading and lagging current: . [1] In this equation, the value of theta is the important factor for leading and lagging current. As mentioned in the introduction above, leading or lagging current represents a time shift between the current and voltage sine curves, which is represented by the angle by which the curve is ahead or behind of where it would be ...
The abbreviations AC and DC are often used to mean simply alternating and direct, respectively, as when they modify current or voltage. [ 1 ] [ 2 ] The usual waveform of alternating current in most electric power circuits is a sine wave , whose positive half-period corresponds with positive direction of the current and vice versa (the full ...
The average of a symmetric alternating value is zero and it is therefore not useful to characterize it. Thus the easiest way to determine a quantitative measurement size is to use the average rectified value. The average rectified value is mainly used to characterize alternating voltage and current.
To measure alternating current, which changes up and down repeatedly, a rectifier is inserted in the circuit so that each negative half cycle is inverted; the result is a varying and nonzero DC voltage whose maximum value will be half the AC peak to peak voltage, assuming a symmetrical waveform.