Vacuum is generally maintained in the vapour space of an evaporator mainly to (A) Get economical temperature difference by using moderate pressure steam (B) Facilitate forward feeding in multiple effect evaporation (C) Concentrate heat sensitive materials (D) Achieve very high concentration of the final product

Vacuum is generally maintained in the vapour space of an evaporator

mainly to

(A) Get economical temperature difference by using moderate pressure

steam

(B) Facilitate forward feeding in multiple effect evaporation

(C) Concentrate heat sensitive materials

(D) Achieve very high concentration of the final product

by

1 Answer

Answer :

(A) Get economical temperature difference by using moderate pressure

steam

by

Related questions

For evaporation of viscous solution in a multiple effect evaporator, the preferred feeding scheme is (A) Forward (B) Backward (C) Parallel (D) None of these

Description : For evaporation of viscous solution in a multiple effect evaporator, the preferred feeding scheme is (A) Forward (B) Backward (C) Parallel (D) None of these

Last Answer : (B) Backward

Pick out the wrong statement. (A) The value of hydrostatic head increases with increase in vacuum in the effect in a multiple effect evaporator system (B) Entering velocity of the liquid in the tubes of natural circulation evaporators is in the range of 0.3 to 0.9 metre/second (C) Duhring's plot is used for calculating the concentration of solution (D) In a multiple effect evaporation system, the number of effects is limited by the total boiling point rise

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Last Answer : (C) Duhring's plot is used for calculating the concentration of solution

Small scale evaporation is done in a (A) Heat exchanger (B) Condenser(C) Multiple effect evaporator(D) Steam jacketed kettle

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Last Answer : (D) Steam jacketed kettle

Heat sensitive materials can be concentrated in an evaporator employing (A) Vacuum (B) High pressure (C) High residence time (D) None of these

Description : Heat sensitive materials can be concentrated in an evaporator employing (A) Vacuum (B) High pressure (C) High residence time (D) None of these

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Heat sensitive materials can be concentrated in an evaporator employing (A) Vacuum (B) High pressure (C) High residence time (D) None of these

Description : Heat sensitive materials can be concentrated in an evaporator employing (A) Vacuum (B) High pressure (C) High residence time (D) None of these

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A multiple effect evaporator as compared to a single effect evaporator of the same capacity has (A) Lower heat transfer area (B) Lower steam economy (C) Higher steam economy (D) Higher solute concentration in the product

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Pick out the wrong statement: (A) The capacity of an evaporator is reduced by the boiling point elevation (B) Corrosive liquid is normally passed through the tubes in a shell and tube heat exchanger (C) Steam jet ejector is used for vapor compression in a thermal recompression evaporator (D) Heat sensitive materials should be concentrated in high pressure evaporators

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The actual temperature drop across the heating surface in an evaporator depends on the (A) Feed (B) Depth of liquid over heating surface (C) Pressure difference between steam chest and vapour space (D) All (A), (B) and (C)

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. A dilute aqueous solution is to be concentrated in an evaporator system. High pressure steam is available. Multiple effect evaporator system is employed, because (A) Total heat transfer area of all the effects is -less than that in a single effect evaporator system (B) Total amount of vapor produced per Kg of feed steam in a multiple effect system is much higher than in a single effect (C) Boiling point elevation in a single effect system is much higher than that in any effect in a multi-effect system (D) Heat transfer co-efficient in a single effect is much lower than that in any effect in a multi-effect system

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Last Answer : (B) Total amount of vapor produced per Kg of feed steam in a multiple effect system is much higher than in a single effect

Heat sensitive materials with very high latent heat of vaporisation may be economically separated using (A) Liquid extraction (B) Distillation (C) Evaporation (D) Absorption

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Pick out the wrong statement. (A) Economy of a multiple effect evaporator is not influenced by the boiling point elevation (B) Two identical cubes of iron and copper will have the same heat content under the same conditions of temperature (C) Double pipe heat exchangers are mostly used in the field of refrigeration (D) Finned tube heat exchangers are suitable for heating air by steam

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The purpose of providing bleed points in the evaporator is to (A) Admit the feed (B) Remove the product (C) Facilitate removal of non-condensable gases (D) Create vacuum

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In case of evaporators, liquid entrainment results primarily due to (A) High vacuum in the evaporator (B) High evaporation rate (C) Foaming of the solution (D) High heat transfer rate

Description : In case of evaporators, liquid entrainment results primarily due to (A) High vacuum in the evaporator (B) High evaporation rate (C) Foaming of the solution (D) High heat transfer rate

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The advantage of backward feed multiple effect evaporators over forward feed units is that (A) Heat sensitive material can be handled (B) There is no additional cost of pumping (C) Most concentrated liquid is at highest temperature (D) Equal heat transfer co-efficients exist in various effects

Description : The advantage of backward feed multiple effect evaporators over forward feed units is that (A) Heat sensitive material can be handled (B) There is no additional cost of pumping ... liquid is at highest temperature (D) Equal heat transfer co-efficients exist in various effects

Last Answer : (C) Most concentrated liquid is at highest temperature

In a forward feed multiple effect evaporator unit (A) Viscosity of liquid is highest in first effect (B) Transfer from effect to effect is done by pumps (C) No pump is required to withdraw the product from the last effect (D) None of these

Description : In a forward feed multiple effect evaporator unit (A) Viscosity of liquid is highest in first effect (B) Transfer from effect to effect is done by pumps (C) No pump is required to withdraw the product from the last effect (D) None of these

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Evaporation of 1kg of water from a solution in a single effect evaporator requires about __________ kg of steam. (A) 0.4 - 0.6 (B) 1-1.3 (C) 1.8-2 (D) 2 - 2.4

Description : Evaporation of 1kg of water from a solution in a single effect evaporator requires about __________ kg of steam. (A) 0.4 - 0.6 (B) 1-1.3 (C) 1.8-2 (D) 2 - 2.4

Last Answer : (B) 1-1.3

In a forward feed multiple effect evaporator, the pressure is (A) Highest in last effect (B) Lowest in last effect (C) Same in all effects (D) Dependent on the number of effects

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Last Answer : (B) Lowest in last effect

At equilibrium the concentration of water in vapour phase (C* ) in kg/m3 of air space and the amount of water (m) adsorbed per kg of dry silica gel are related by, C* = 0.0667m. To maintain dry conditions in a room of air space 100m3 containing 2.2 kg of water vapour initially, 10 kg of dry silica gel is kept in the room. The fraction of initial water remaining in the air space after a long time (during which the temperature is maintained constant) is (A) 0.0 (B) 0.2 (C) 0.4 (D) 1.0

Description : At equilibrium the concentration of water in vapour phase (C* ) in kg/m3 of air space and the amount of water (m) adsorbed per kg of dry silica gel are related by, C* = 0.0667m. To maintain dry conditions in a room ... which the temperature is maintained constant) is (A) 0.0 (B) 0.2 (C) 0.4 (D) 1.0

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Optimum number of effects in a multiple effect evaporator is decided by the (A) Cost benefit analysis (B) Floor area availability (C) Terminal parameters (D) Evaporation capacity required

Description : Optimum number of effects in a multiple effect evaporator is decided by the (A) Cost benefit analysis (B) Floor area availability (C) Terminal parameters (D) Evaporation capacity required

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Optimum number of effects in a multiple effect evaporator is decided by the (A) Cost benefit analysis (B) Floor area availability (C) Terminal parameters (D) Evaporation capacity required

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Last Answer : (A) Cost benefit analysis

The capacity of double-effect evaporator is less than half of the capacity of two single effects, each of which is operating over same terminal temperature difference, when the (A) Solution has an elevation of boiling point (B) Evaporators operate under vacuum (C) Evaporators operate at atmospheric pressure (D) None of these

Description : The capacity of double-effect evaporator is less than half of the capacity of two single effects, each of which is operating over same terminal temperature difference, when the (A) Solution has ... B) Evaporators operate under vacuum (C) Evaporators operate at atmospheric pressure (D) None of these

Last Answer : (A) Solution has an elevation of boiling point

The actual temperature drop across the heating surface of an evaporator depends on the (A) Liquid depth over the heating surface (B) Solution being evaporated (C) Pressure difference between the steam chest and the vapor space above the boiling liquid (D) All (A), (B) and (C)

Description : The actual temperature drop across the heating surface of an evaporator depends on the (A) Liquid depth over the heating surface (B) Solution being evaporated (C) Pressure difference between the steam chest and the vapor space above the boiling liquid (D) All (A), (B) and (C)

Last Answer : (D) All (A), (B) and (C)

A backward feed multiple effect evaporator is better than forward feed for concentrating cold feed, because it provides (A) Higher economy (B) Lower capacity (C) Both (A) & (B) (D) Lower economy

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Last Answer : (A) Higher economy

Molecular distillation is (A) High temperature distillation (B) For heat-sensitive materials (C) Very low pressure distillation (D) Both (B) and (C)

Description : Molecular distillation is (A) High temperature distillation (B) For heat-sensitive materials (C) Very low pressure distillation (D) Both (B) and (C)

Last Answer : (D) Both (B) and (C)

It is desired to concentrate a 20% salt solution (20 kg of salt in 100 kg of solution) to a 30% salt solution in an evaporator. Consider a feed of 300 kg/min at 30°C. The boiling point of the solution is 110°C, the latent heat of vaporisation is 2100 kJ/kg and the specific heat of the solution is 4 kJ/kg.K. The rate at which the heat has to be supplied in (kJ/min) to the evaporator is (A) 3.06 × 10 5 (B) 6.12 × 10 5 (C) 7.24 × 10 5 (D) 9.08 × 10

Description : It is desired to concentrate a 20% salt solution (20 kg of salt in 100 kg of solution) to a 30% salt solution in an evaporator. Consider a feed of 300 kg/min at 30°C. The boiling point of the solution is 110°C, the latent heat of ... 3.06 10 5 (B) 6.12 10 5 (C) 7.24 10 5 (D) 9.08 10

Last Answer : (A) 3.06 × 10

The outlet temperature of cooling water in a heat exchanger is generally not allowed to exceed above 50°C in industrial practice mainly to avoid (A) Its evaporation loss (B) Excessive corrosion (C) Uneconomic LMTD (D) Decrease in heat exchanger efficiency

Description : The outlet temperature of cooling water in a heat exchanger is generally not allowed to exceed above 50°C in industrial practice mainly to avoid (A) Its evaporation loss (B) Excessive corrosion (C) Uneconomic LMTD (D) Decrease in heat exchanger efficiency

Last Answer : (B) Excessive corrosion

The number of kg vaporised per kg of steam fed to the evaporator is defined as (A) Capacity (B) Rate of evaporation (C) Economy (D) Rate of vaporisation

Description : The number of kg vaporised per kg of steam fed to the evaporator is defined as (A) Capacity (B) Rate of evaporation (C) Economy (D) Rate of vaporisation

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Fruit juice (a heat sensitive material) can be concentrated in a __________ evaporator. (A) Long tube (B) Falling film (C) High pressure (D) None of these

Description : Fruit juice (a heat sensitive material) can be concentrated in a __________ evaporator. (A) Long tube (B) Falling film (C) High pressure (D) None of these

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When the mixture to be distilled has a very high boiling point and the product material is heat sensitive, the separation technique to be used is __________ distillation. (A) Continuous (B) Steam (C) Azeotropic (D) None of these

Description : When the mixture to be distilled has a very high boiling point and the product material is heat sensitive, the separation technique to be used is __________ distillation. (A) Continuous (B) Steam (C) Azeotropic (D) None of these

Last Answer : (B) Steam

Economy of a multiple effect evaporator is not influenced much by the (A) Boiling point elevations (B) Temperature of the feed (C) Rate of heat transfer (D) Ratio of the weight of the thin liquor to thick liquor

Description : Economy of a multiple effect evaporator is not influenced much by the (A) Boiling point elevations (B) Temperature of the feed (C) Rate of heat transfer (D) Ratio of the weight of the thin liquor to thick liquor

Last Answer : (A) Boiling point elevations

Tubes of multiple effect evaporator used for concentration of sugar cane juice are made of (A) Nickel (B) Copper (C) Stainless steel (D) Brass

Description : Tubes of multiple effect evaporator used for concentration of sugar cane juice are made of (A) Nickel (B) Copper (C) Stainless steel (D) Brass

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Economy of an evaporator is influenced by the (A) Steam pressure (B) Feed temperature (C) Number of effect (D) Both (B) & (C)

Description : Economy of an evaporator is influenced by the (A) Steam pressure (B) Feed temperature (C) Number of effect (D) Both (B) & (C)

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Black liquor is converted into white liquor by (A) Evaporation and burning the concentrate followed by causticisation of products (B) Multi-effect evaporation only (C) Selective liquid extraction (D) Extractive distillation

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Last Answer : (A) Evaporation and burning the concentrate followed by causticisation of products

Urea is formed only (A) In liquid phase (B) In vapour phase (C) At very high temperature (D) At very low pressure (vacuum)

Description : Urea is formed only (A) In liquid phase (B) In vapour phase (C) At very high temperature (D) At very low pressure (vacuum)

Last Answer : (A) In liquid phase

Multiple effect evaporation accounts for (A) Steam economy (B) Lower operating costs(C) Investment economy(D) None of these

Description : Multiple effect evaporation accounts for (A) Steam economy (B) Lower operating costs (C) Investment economy (D) None of these

Last Answer : (A) Steam economy

Evaporation by thermo compression results in the (A) Saving of steam (B) Realisation of multiple effect economy in a single effect (C) Both (A) and (B) (D) None of these

Description : Evaporation by thermo compression results in the (A) Saving of steam (B) Realisation of multiple effect economy in a single effect (C) Both (A) and (B) (D) None of these

Last Answer : (C) Both (A) and (B)

The effect of changing the evaporator temperature on COP as compared to that of changing the condenser temperature (in vapour compression refrigeration system) is (A) Less pronounced (B) More pronounced (C) Equal (D) Data insufficient, can't be predicted

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The burnout heat flux in the nucleate boiling regime is not a function of the (A) Liquid density (B) Vapour density (C) Temperature difference (D) Heat of evaporation

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High pressure at the bottom of a distillation tower handling heat sensitive materials results in (A) Thermal decomposition of bottoms (B) Increased relative volatility (C) Erosion of the tower (D) Very efficient operation

Description : High pressure at the bottom of a distillation tower handling heat sensitive materials results in (A) Thermal decomposition of bottoms (B) Increased relative volatility (C) Erosion of the tower (D) Very efficient operation

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In a single evaporator system, the steam economy __________ by creating vacuum in the evaporator. (A) Increases (B) Decreases (C) Remain constant (D) May increase or decrease, depends on the vacuum

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For concentrating an aqueous solution of a material like anhydrous Na2SO4, whose solubility decreases with rise in temperature, the most suitable evaporator is a __________ evaporator. (A) High pressure (B) Vacuum (C) Backward feed (D) None of these

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. In a backward feed multiple effect evaporator (A) Feed is introduced in the first effect (B) Feed flows from low pressure to high pressure (C) No pumps are required between successive effects (D) None of these

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For proper refrigeration in a cabinet, if the temperature and vapour pressure difference between cabinet and atmosphereis high, then (a) bigger cabinet should be used (b) smaller cabinet should be used (c) perfectly tight vapour seal should be used (d) refrigerant with lower evaporation temperature should be used

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The suitable evaporator for concentration of foaming liquids is a __________ evaporator. (A) Long tube (B) Short tube (C) Vacuum (D) Falling film

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Gas cooling as compared to water cooling of nuclear reactors (A) Cannot attain a high temperature (B) Is more efficient as gas has a higher specific heat (C) Can produce only saturated steam for feeding to power turbine (D) None of these

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Multiple effect evaporation is generally recommended, when the (A) Large scale evaporation of liquor is needed (B) Corrosive liquids are to be concentrated

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Economy of a multiple effect evaporator depends upon the (A) Heat balance consideration (B) Rate of heat transfer (C) Both (A) and (B) (D) Neither (A) nor (B

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Reason for operating an evaporator in multiple effects is to secure (A) Increased steam economy (B) Decreased steam consumption (C) Both (A) and (B) (D) Increased capacity

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A reasonably general expression for vapour-liquid phase equilibrium at low to moderate pressure is φi yi P = Yi xifi° where, Φ is a vapor fugacity component, Yiis the liquid activity co-efficient and fi° is the fugacity of the pure component i. the Ki value (Yi = Ki xi) is therefore, in general a function of (A) Temperature only (B) Temperature and pressure only (C) Temperature, pressure and liquid composition xi only (D) Temperature, pressure, liquid composition xi and vapour composition yi

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Vacuum filter is most suitable for the (A) Removal of fines from liquid (B) Liquids having high vapour pressure (C) Liquids of very high viscosity (D) None of these

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