Understanding Motor Controls
4th Edition
ISBN: 9781337798686
Author: Stephen L. Herman
Publisher: Delmar Cengage Learning
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Chapter 25, Problem 1RQ
To determine
Identify why it is desirable to disconnect the autotransformer from the circuit hen the motor reaches the run stage.
Expert Solution & Answer
Explanation of Solution
The autotransformer is used to reduce the amount of inrush current by reducing the voltage applied to the motor at the time of starting. When the motor reaches 75% of the normal speed it is said to have reached run state.
After reaching the run state, full voltage can be supplied to the motor. The use of autotransformer to provide full voltage to the motor is a waste of energy as the same can be applied directly.
Hence, it is desirable to disconnect the autotransformer after the motor reached the run state to save energy and extend the life if the autotransformer.
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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.
Example(2):
Double effect evaporator is used for
concentrating a certain caustic soda
solution 10000kg/hr from 9wt% to
47wt%. The feed at 30°C enters the
first evaporator. Backward arrangement
evaporators are used. steam is available at
167.7°C and the vapor space in the second
effect is 14.6Kpa.
The overall heat transfer coefficients of
the two effects are 8380 and 6285kcal/
W.CH
ork
-conce
-SOLFFF
and-ans..
112.1
а
DiD
3
respectively and the specific heat capacity
of all caustic soda solution 3.771 KJ/Kg.
°C, determine the heat transfer area of
each effect
معدلة 5:48 م
O
give me solution math not explin
Chapter 25 Solutions
Understanding Motor Controls
Ch. 25 - Prob. 1RQCh. 25 - Explain the differences between open and closed...Ch. 25 - Prob. 3RQCh. 25 - Refer to the circuit shown in Figure 252. Assume...Ch. 25 - Prob. 5RQCh. 25 - Prob. 6RQCh. 25 - Prob. 7RQCh. 25 - Refer to the circuit shown in Figure 255. Explain...Ch. 25 - Prob. 9RQCh. 25 - Refer to the circuit shown in Figure 25–5. Assume...
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- give me solution math not explinarrow_forwarduse Q Strips of material 10 mm thick are dried under constant drying conditions from 28 to 13 per cent moisture in 25 ks. The equilibrium moisture content is 7 per cent. The relation between E, the ratio of the final free moisture content at time t to the initial free moisture content, and the parameter J is given by: E 1 0.64 0.49 0.38 0.295 0.22 0.14 J 0 0.1 0.2 0.3 0.5 0.6 العنوان 0.7 It may be noted that J = kt/12, where, k = constant, t = time (ks) 1 = thickness/2 of the sheet of material (mm) a. Based on the given data, plot a graph of E against J b. Determine the time taken to dry 60 mm planks from 22 to 10 per cent moisture under the same conditions assuming no loss from the edges? ina östler ۲/۱arrow_forward14.25.2.5 kg/s of a solution at 288 K containing 10 per cent of dissolved solids is fed to a forward-feed double-effect evaporator, operating at 14 kN/m² in the last effect. If the product is to consist of a liquid containing 50 per cent by mass of dissolved solids and dry saturated steam is fed to the steam coils, what PROBLEMS 1179 should be the pressure of the steam? The surface in each effect is 50 m² and the coefficients for heat transfer in the first and second effects are 2.8 and 1.7 kW/ m² K, respectively. It may be assumed that the concentrated solution exhibits a boiling-point rise of 5 deg K, that the latent heat has a constant value of 2260 kJ/kg and that the specific heat capacity of the liquid stream is constant at 3.75 kJ/kg K Oarrow_forward
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