Understanding Motor Controls
3rd Edition
ISBN: 9781305498129
Author: Stephen L. Herman
Publisher: Cengage Learning
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Question
Chapter 27, Problem 1RQ
To determine
Identify why and which voltage must be used for the dual voltage motor to be used for part winding starting.
Expert Solution & Answer
Explanation of Solution
If a dual voltage 240/480V motor is used for a part winding starting, then the low voltage setting must be used. This is because, since only one winding is connected to the power line, the high current due to high voltage supplied causes overheating of the windings.
Hence, 240V must be used for part winding starting.
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seoni
4) 1 Mg (dry weight) of a non-porous
solid is dried under constant drying
conditions with an air
velocity of 0.75 m/s parallel to the drying
surface. The area of drying surface is 55
m2
If initial
rate of drying is 0.3 g/m2
s, how long it will take to dry a material
from 0.15 to 0.025 kg water/kg
dry solid? The critical moisture content
is 0.125 and the equilibrium moisture is
negligible.
The falling rate of drying is linear
in moisture content. If air velocity
increases to 4 m/s, what
will be the anticipated saving in drying
time?
0
osther
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.
O
O
5) A 100 kg batch of granular solids
containing 30% moisture is to be dried in
a tray drier to
15.5% by passing a current of air at 350
K tangentially across its surface at a
velocity of 1.8
m/s. If the constant rate of drying under
these conditions is 0.7 g/s m2
and the critical moisture
content is 15%, calculate the
approximate drying time. Assume the
drying surface to be 0.03
m2
/kg dry mass.
O
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Understanding Motor Controls
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