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MindTap for Herman's Understanding Motor Controls, 4th Edition [Instant Access], 2 terms
4th Edition
ISBN: 9781337798754
Author: Herman; Stephen L.
Publisher: Cengage Learning US
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Textbook Question
Chapter 43, Problem 1RQ
What are the disadvantages of low-speed, directly coupled induction motors?
Expert Solution & Answer
To determine
The disadvantages of low-speed, directly coupled induction motor.
Explanation of Solution
The directly coupled induction motors are rarely used in the applications where the required speed is below 500rpm. The induction motor take very less current from the supply main.
The vector sum of load current and magnetizing current lags voltage by around 75-80 degrees and hence, the power factor is low. Due to high magnetizing current, the copper losses of the motor increase. This in turn leads to decrease in the efficiency of the motor.
Thus Disadvantage of low-speed, directly coupled induction motors are low power factor and low efficiency.
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Example 8: 900 Kg dry solid per hour is
dried in a counter current continues dryer
from 0.4 to 0.04 Kg H20/Kg wet solid
moisture content. The wet solid enters the
dryer at 25 °C and leaves at 55 °C. Fresh
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mixed with a part of the moist air leaving
the dryer and heated to a temperature of
130 °C in a finned air heater and enters the
dryer with 0.025 Kg/Kg alry air. Air leaving
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0.055 Kg vaper/Kg dry air. At equilibrium
the wet solid weight is 908 Kg solid per
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*=0.0088
Calculate:- Heat loss from the dryer and
the rate of fresh air.
Take the specific heat of the solid
and moisture are 980 and 4.18J/Kg.K
respectively,
A. =2500 KJ/Kg.
Humid heat at 0.01 Kg vap/Kg dry=1.0238
KJ/Kg. "C. Humid heat at 0.055 Kg/Kg
1.1084 KJ/Kg. "C
2.8
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العنوان
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Jon
14.23. A double-effect forward-feed
evaporator is required to give a product
consisting of 30 per cent crystals and a
mother liquor containing 40 per cent by
mass of dissolved solids. Heat transfer
coefficients are 2.8 and 1.7 kW/m² K in the
first and second effects respectively. Dry
saturated steam is supplied at 375 kN/m²
and the condenser operates at 13.5 kN/
m².
(a) What area of heating surface is
required in each effect assuming the
effects are identical, if the feed rate is 0.6
kg/s of liquor, containing 20 per cent by
mass of dissolved solids, and the feed
temperature is 313 K?
(b) What is the pressure above the boiling
liquid in the first effect?
The specific heat capacity may be
taken as constant at 4.18 kJ/kg K. and
the effects of boiling-point rise and of
hydrostatic head may be neglected.
Chapter 43 Solutions
MindTap for Herman's Understanding Motor Controls, 4th Edition [Instant Access], 2 terms
Ch. 43 - What are the disadvantages of low-speed, directly...Ch. 43 - Prob. 2RQCh. 43 - What three alignment checks should be made to...Ch. 43 - Prob. 4RQCh. 43 - Induction motors should not be used below a...Ch. 43 - What is the primary reason for using a pulley...Ch. 43 - How tightly should V-belts be adjusted?Ch. 43 - Refer to Figure 436 and assume the motor is to...Ch. 43 - A machine delivered for installation has a 2-inch...
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