Power dissipated, maximum

The power dissipated in an AC circuit with current of maximum amplitude flowing through a resistance is less than the power produced by a constant DC current of magnitude flow ing through the same resistance. For a sinusoidal AC current, the root mean square (rms) value of current I is the magnitude of the DC current producing the same power as the AC current with maximum amplitude I. The rms value I is given by... 

The optimization procedure must take into account constraints such as maximum admissible local power dissipation and maximum tolerable magnetic field inhomogeneity. In this way, such constraints influence, often quite seriously, the final performance of the magnet. 

One problem, or should we say challenge, in designing this type of circuit is to ensure that the Darlington pair transistors are not overstressed by causing them to dissipate too much power. The maximum power the transistor can dissipate decreases with increasing collector-emitter voltage. 

The maximum ratings of temperature, collector current Ic, base current fB, emitter-to-collector voltage VCe> and power dissipation IcVqe should not be exceeded. 

Fill factor — The current versus potential I(U) characteristics of a —> power source, contrarily to those of power dissipation devices, is not limited to the first and third quadrant. In this case the I(U) curve crosses the U and I axes at values different from zero. The value of I at U = 0 is denoted -+ short-circuit current, Jsc, and the value of U at I = 0 is denoted open-circuit potential, Uoc. The maximum power output, Pmax> from a power source depends on the shape of the I(U) curve and is given by Tmax = ( 7) max> excluding first and third quadrant points. The fill factor FF is given by FF = yfff-... 

In the context of resonant acoustic devices, Q =fiJBW, where fn is the resonant frequency and BW is the bandwidth it can equivalently be defuied as loU Pj, where o> is the angular frequency. Up is the peak total energy present in the device, and is the power dissipated by the device. For resonant systems, BW is the range of frequencies over which the reflected power is within 3 dB (a factor of two) of its minimum value, attained at fit, for non-resonant systems (e.g., delay lines), BW is the range of iiequencies over which the transmitted power is within a factor of two of its maximum value. 

SOLUTION Four identical power transistors arc attached on a copper plate. For a maximum case temperature of 70°C, the maximum power dissipation and the temperature jump at the interface are to be determined. 

Using EES (or other) software, investigate the effects of air velocity at (lie inlet of the channel and (he maximum surface temperature on the maximum total power dissipation of electronic components. Let the air velocity vary from I m/s to lO m/s and the surface temperature from 30°C to 90 C. Plot the power dissipation as functions of air velocity and surface temperature, and discuss the results. 

Contact a manufacturer of aluminum heal sinks and obtain their product catalog for cooling electronic components by natural convection and radiation. Write an essay on how to select a suitable heal sink for an electronic component when its maximum power dissipation and maximum allowable surface temperature are specified. 

A piece of rubber is used to damp the mechanical vibration of a structural mechanism. Determine the power dissipated by this rubber when it is subjected to shear vibrations of maximum amplitude 2 x 10 and frequency m = 12000 rpm. The viscoelastic characteristics of the rubber are <7 = 2 MPa and tan 5 = 0.5. 

Maximum stable drop diameter, m Impeller diameter, m Diffusivity of dissolved component or reactant in liquid, m /s Gravitational acceleration, m/s Height of liquid in vessel, m Mass transfer coefficient, m/s Mass transfer coefficient for a single spherical droplet immersed in a liquid flowing at constant velocity past the droplet, m/s Mass of liquid, kg Rate of mass transfer of solute or reactant, kg/s Impeller speed, rotations/s Minimum speed to just suspend solid particles in vessel, rotations/s Minimum impeller speed to completely incorporate dispersed phase into continuous phase in liquid-liquid systems, rotations/s Power dissipation, W Time, s... 

High-voltage electric power transmitted to a city is dropped to a low voltage in a transformer before use. To keep the transformer at a steady temperature, Joulean power dissipation (recall El — I2R) needs to be transferred to an ambient Assume the transformer to be a vertical cylinder (D = 0.4 m, L = 1 m) whose walls are kept at 90 °C in a stagnant water bath at 15 C. Determine the maximum allowable power dissipation. 

In both these regimes of wear, high rates of power dissipation in the contact first lead to surface and then subsurface thermal softening. These thermal effects generally limit the maximum PV (pressure-velocity) product of polymeric contacts. Furthermore,... 

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