Which of the following is not an advantage of fluidisation from transferoperation point of view?(A) Intimate contact of the fluid with all parts of the solid particles(B) Lower fluid pumping power requirement(C) Minimisation of temperature variation(D) Prevention of particle segregation

Which of the following is not an advantage of fluidisation from transferoperation point of view?
(A) Intimate contact of the fluid with all parts of the solid particles
(B) Lower fluid pumping power requirement
(C) Minimisation of temperature variation
(D) Prevention of particle segregation
by

1 Answer

Answer :

(B) Lower fluid pumping power requirement
by

Related questions

A bed of spherical particles (specific gravity 2.5) of uniform size 1500 μm is 0.5 m in diameter and 0.5 m high. In packed bed state, the porosity may be taken as 0.4. Ergun's equation for the above fluid-particle system (in SI units) is given below : Δ P/L = 375 × 10 3 VOM + 10.94 × 10 6 V2 OM (SI units) If water is to be used as the fluidising medium, the minimum fluidisation velocity, VOM is (A) 12 mm/s (B) 16 mm/s (C) 24 mm/s (D) 28 mm/s

Description : A bed of spherical particles (specific gravity 2.5) of uniform size 1500 μm is 0.5 m in diameter and 0.5 m high. In packed bed state, the porosity may be taken as 0.4. Ergun's equation for the above fluid-particle ... fluidisation velocity, VOM is (A) 12 mm/s (B) 16 mm/s (C) 24 mm/s (D) 28 mm/s

Last Answer : (B) 16 mm/s

Minimum fluidisation velocity for a specific system depends upon the (A) Particle size (B) Fluid viscosity (C) Density of both the particle & the fluid (D) All (A), (B) and (C)

Description : Minimum fluidisation velocity for a specific system depends upon the (A) Particle size (B) Fluid viscosity (C) Density of both the particle & the fluid (D) All (A), (B) and (C)

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

With decrease in particle size to be fluidised by a particular fluid, the operating range of fluidisation velocity (A) Widens (B) Squeezes (C) Does not change (D) Unpredictable from the data

Description : With decrease in particle size to be fluidised by a particular fluid, the operating range of fluidisation velocity (A) Widens (B) Squeezes (C) Does not change (D) Unpredictable from the data

Last Answer : (C) Does not change

When larger particles e.g., grains are subjected to fluidisation, the corresponding bed produced is termed as the __________ bed. (A) Spouted (B) Sluggish (C) Boiling (D) Teeter

Description : When larger particles e.g., grains are subjected to fluidisation, the corresponding bed produced is termed as the __________ bed. (A) Spouted (B) Sluggish (C) Boiling (D) Teeter

Last Answer : (A) Spouted

Umf is the minimum fluidisation velocity for a bed of particles. An increase in the superficial gas velocity from 2 Umf to 2.5 Umf results in (all velocities are smaller than the entrainment velocity of the particles) nochange in the(A) Drag on particles(B) Drag on column walls(C) Bed height(D) Bed voidage

Description : Umf is the minimum fluidisation velocity for a bed of particles. An increase in the superficial gas velocity from 2 Umf to 2.5 Umf results in (all velocities are smaller than the entrainment velocity of the particles ... (A) Drag on particles (B) Drag on column walls (C) Bed height (D) Bed voidage

Last Answer : (C) Bed height

In continuous fluidisation (A) Solids are completely entrained (B) The pressure drop is less than that for batch fluidisation (C) There is no entrainment of solids (D) Velocity of the fluid is very small

Description : In continuous fluidisation (A) Solids are completely entrained (B) The pressure drop is less than that for batch fluidisation (C) There is no entrainment of solids (D) Velocity of the fluid is very small

Last Answer : (A) Solids are completely entrained

A streamline is a line in flow field, (A) That is traced by all the fluid particles passing through a given point (B) Along which a fluid particle travels (C) Such that at every point on it, the velocity is tangential to it (D) None of these

Description : A streamline is a line in flow field, (A) That is traced by all the fluid particles passing through a given point (B) Along which a fluid particle travels (C) Such that at every point on it, the velocity is tangential to it (D) None of these

Last Answer : (C) Such that at every point on it, the velocity is tangential to it

In Newton's law range, the terminal velocity of a solid spherical particle falling through a stationary fluid mass varies as the __________ of its diameter. (A) Inverse (B) Square root (C) Second power (D) First power

Description : In Newton's law range, the terminal velocity of a solid spherical particle falling through a stationary fluid mass varies as the __________ of its diameter. (A) Inverse (B) Square root (C) Second power (D) First power

Last Answer : (B) Square root

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

For motion of spherical particles in a stationary fluid, the drag co￾efficient in hindered settling compared to that in free settling is (A) More (B) Less (C) Equal (D) More or less, depending on the type of particle

Description : For motion of spherical particles in a stationary fluid, the drag co￾efficient in hindered settling compared to that in free settling is (A) More (B) Less (C) Equal (D) More or less, depending on the type of particle

Last Answer : (A) More

A bed of spherical particles (specific gravity 2.5) of uniform size 1500 μm is 0.5 m in diameter and 0.5 m high. In packed bed state, the porosity may be taken as 0.4. Ergun's equation for the above fluid-particle system (in SI units) is given below: Δ P/L = 375 × 10 3 VOM + 10.94 × 10 6 V2 OM (SI units) If water is to be used as the fluidising medium, in actual operation, the above bed has a height = 1 m. What is the porosity of the fluidised bed? (A) 0.2 (B) 0.5 (C) 0.7 (D) 0.8

Description : A bed of spherical particles (specific gravity 2.5) of uniform size 1500 μm is 0.5 m in diameter and 0.5 m high. In packed bed state, the porosity may be taken as 0.4. Ergun's equation for the above fluid-particle system ... What is the porosity of the fluidised bed? (A) 0.2 (B) 0.5 (C) 0.7 (D) 0.8

Last Answer : (C) 0.7

For the non catalytic reaction of particles with surrounding fluid, the same needed to achieve the same fractional conversion for particles of different unchanging sizes is proportional to the particle diameter, when the __________ is the controlling resistance. (A) Film diffusion (B) Diffusion through ash layer (C) Chemical reaction (D) Either (A), (B) or (C)

Description : For the non catalytic reaction of particles with surrounding fluid, the same needed to achieve the same fractional conversion for particles of different unchanging sizes is proportional to the particle diameter, when the ... through ash layer (C) Chemical reaction (D) Either (A), (B) or (C)

Last Answer : (C) Chemical reaction

For the non-catalytic reaction of particles with surrounding fluid, the time needed to achieve the same fractional conversion for particles of different but unchanging sizes is proportional to the square of particle diameter, when the __________ is the controlling resistance. (A) Film diffusion (B) Diffusion through ash layer (C) Chemical reaction (D) Either (A), (B) or (C)

Description : For the non-catalytic reaction of particles with surrounding fluid, the time needed to achieve the same fractional conversion for particles of different but unchanging sizes is proportional to the square of particle diameter, ... through ash layer (C) Chemical reaction (D) Either (A), (B) or (C)

Last Answer : (B) Diffusion through ash layer

Fluid motion in the natural convection heat transfer between a solid surface and a fluid in contact with it, results from the (A) Existence of thermal boundary layer (B) Temperature gradient produced due to density difference (C) Buoyancy of the bubbles produced at active nucleation site (D) None of these

Description : Fluid motion in the natural convection heat transfer between a solid surface and a fluid in contact with it, results from the (A) Existence of thermal boundary layer (B) Temperature gradient produced ... difference (C) Buoyancy of the bubbles produced at active nucleation site (D) None of these

Last Answer : (D) None of these

Pick out the wrong statement. (A) Gape is the greatest distance between the crushing surfaces or the jaws (B) The angle of nip (2α) is the angle between roll faces at the level where they will just take hold of a particle and draw it in the crushing zone (C) Crushing efficiency is the ratio of the energy absorbed by the solid to the surfaces energy created by crushing (D) Reduction ratio is the ratio of the maximum size of the particles in the feed to that in the product

Description : Pick out the wrong statement. (A) Gape is the greatest distance between the crushing surfaces or the jaws (B) The angle of nip (2α) is the angle between roll faces at the level where they will ... Reduction ratio is the ratio of the maximum size of the particles in the feed to that in the product

Last Answer : (C) Crushing efficiency is the ratio of the energy absorbed by the solid to the surfaces energy created by crushing

Number of particles in a crushed solid sample is given by (where, m = mass of particles in a sample, Vp = volume of one particle, ρ= density of particles) (A) m/ρ . Vp (B) m . ρ/Vp (C) m . Vp /ρ (D) Vp /m . ρ

Description : Number of particles in a crushed solid sample is given by (where, m = mass of particles in a sample, Vp = volume of one particle, ρ= density of particles) (A) m/ρ . Vp (B) m . ρ/Vp (C) m . Vp /ρ (D) Vp /m . ρ

Last Answer : (A) m/ρ . Vp

Pick out the wrong statement. (A) The binary diffusivity in liquids is of the order of 10 -5 cm2 /sec (B) Molecular diffusion in solid is much faster than that in liquids (C) Particles movement from higher concentration to lower concentration takes place in diffusion process (D) According to Poiseuille's law, the permeability decreases with increase in temperature for flow of a gas through a given capillary

Description : Pick out the wrong statement. (A) The binary diffusivity in liquids is of the order of 10 -5 cm2 /sec (B) Molecular diffusion in solid is much faster than that in liquids ( ... Poiseuille's law, the permeability decreases with increase in temperature for flow of a gas through a given capillary

Last Answer : (B) Molecular diffusion in solid is much faster than that in liquids

A manufacturer has decided to improve its inventory management by maintaining low inventory levels and waiting to purchase materials until right before they are needed in production. This inventory management technique is called A)just -in -time (JIT). B)inventory minimisation. C)economic order quantity.D)reorder point maximisation.

Description : A manufacturer has decided to improve its inventory management by maintaining low inventory levels and waiting to purchase materials until right before they are needed in production. This inventory ... time (JIT). B)inventory minimisation. C)economic order quantity.D)reorder point maximisation.

Last Answer : D)reorder point maximisation.

. A 0.5 m high bed made up of a 1 mm dia glass sphere (density 2500 kg/m3 ) is to be fluidised by water (density 1000 kg/m3 ). If at the point of incipient fluidisation, the bed voidage is 40%, the pressure drop across the bed is (A) 4.4 KPa (B) 2.94 KPa (C) 3.7 KPa (D) None of these

Description : . A 0.5 m high bed made up of a 1 mm dia glass sphere (density 2500 kg/m3 ) is to be fluidised by water (density 1000 kg/m3 ). If at the point of incipient fluidisation, the bed voidage is 40%, the pressure drop across the bed is (A) 4.4 KPa (B) 2.94 KPa (C) 3.7 KPa (D) None of these

Last Answer : (A) 4.4 KPa

In the Newton's law range, the terminal velocity of a solid spherical particle falling through a stationary fluid mass is __________ the fluid viscosity. (A) Directly proportional to (B) Inversely proportional to (C) Inversely proportional to the square root of (D) Independent of

Description : In the Newton's law range, the terminal velocity of a solid spherical particle falling through a stationary fluid mass is __________ the fluid viscosity. (A) Directly proportional to (B) Inversely proportional to (C) Inversely proportional to the square root of (D) Independent of

Last Answer : (B) Inversely proportional to

The terminal velocity of a solid spherical particle falling through a stationary fluid mass in the Stoke's law range is proportional to the (A) Inverse of fluid viscosity (B) Square of particle size (C) Difference in the densities of the particle & fluid (D) All (A), (B) and (C)

Description : The terminal velocity of a solid spherical particle falling through a stationary fluid mass in the Stoke's law range is proportional to the (A) Inverse of fluid viscosity (B) Square of particle size (C) Difference in the densities of the particle & fluid (D) All (A), (B) and (C)

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

The main factor on which the behaviour of a mass of fluidised solid depends mainly is the (A) Fluid characteristics (B) Particle size (C) Both (A) and (B) (D) Neither (A) nor (B)

Description : The main factor on which the behaviour of a mass of fluidised solid depends mainly is the (A) Fluid characteristics (B) Particle size (C) Both (A) and (B) (D) Neither (A) nor (B)

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

Which of the following factors control the design of a fluid-solid reactor? (A) Reaction kinetics for single particle (B) Size distribution of solids being treated (C) Flow patterns of solids and fluid in the reactor (D) All (A), (B) and (C)

Description : Which of the following factors control the design of a fluid-solid reactor? (A) Reaction kinetics for single particle (B) Size distribution of solids being treated (C) Flow patterns of solids and fluid in the reactor (D) All (A), (B) and (C)

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

A change in genetic constitution, which arises suddenly and not to segregation and recombination of genes in sexual reproduction is called as: a. Hybridization b. Bud variation c. Mutation d. Non of them

Description : A change in genetic constitution, which arises suddenly and not to segregation and recombination of genes in sexual reproduction is called as: a. Hybridization b. Bud variation c. Mutation d. Non of them

Last Answer : Mutation

The rate of solid-liquid extraction is limited by the (A) Phase change of the solute as it dissolves in the solvent (B) Diffusion of the solute through the solvent in the pores to the outside of the particle (C) Diffusion of the solute from the solution in contact with the particle to the main bulk of the solution (D) All 'a', 'b' & 'c'

Description : The rate of solid-liquid extraction is limited by the (A) Phase change of the solute as it dissolves in the solvent (B) Diffusion of the solute through the solvent in the pores to the outside of the particle (C) ... contact with the particle to the main bulk of the solution (D) All 'a', 'b' & 'c'

Last Answer : (D) All 'a', 'b' & 'c'

From the point of view of international business, an organization that enjoys competitive advantage in an industry has done so by: A. Focusing on long-term profit. B. Charging lower prices than competition. C. Creating superior value for customers. D. Constantly enlarging its marketing activities.

Description : From the point of view of international business, an organization that enjoys competitive advantage in an industry has done so by: A. Focusing on long-term profit. B. Charging lower prices than competition. C. Creating superior value for customers. D. Constantly enlarging its marketing activities.

Last Answer : Creating superior value for customers.

A globe valve is the most suitable for applications, in which (A) Fluid flow control is required (B) Fluid contains dispersed solid particles (C) Valve is required to be either fully open or fully closed (D) One way flow is required

Description : A globe valve is the most suitable for applications, in which (A) Fluid flow control is required (B) Fluid contains dispersed solid particles (C) Valve is required to be either fully open or fully closed (D) One way flow is required

Last Answer : (A) Fluid flow control is required

At the point of boundary layer separation in fluid flow, the (A) Shear stress is maximum (B) Velocity gradient is flat (C) Density variation is maximum (D) Shear stress is zero

Description : At the point of boundary layer separation in fluid flow, the (A) Shear stress is maximum (B) Velocity gradient is flat (C) Density variation is maximum (D) Shear stress is zero

Last Answer : Option A

Heat transfer efficiency leading of energy conservation in a heat exchanger can be achieved by (A) Keeping the heat transfer surface clean (B) Enhancing the fluid pumping rate (C) Increasing the tube length (D) None of these

Description : Heat transfer efficiency leading of energy conservation in a heat exchanger can be achieved by (A) Keeping the heat transfer surface clean (B) Enhancing the fluid pumping rate (C) Increasing the tube length (D) None of these

Last Answer : (A) Keeping the heat transfer surface clean

When the head pumped against is less than the head of the fluid used for pumping, the usual device is a/an (A) Ejector (B) Blower (C) Injector (D) Airlift

Description : When the head pumped against is less than the head of the fluid used for pumping, the usual device is a/an (A) Ejector (B) Blower (C) Injector (D) Airlift

Last Answer : (D) Airlift

For a given fluid, as the pipe diameter increases, the pumping cost (A) Decreases (B) Increases (C) Remains the same (D) May increase or decrease, depending upon whether the fluid is Newtonian or non-Newtonian

Description : For a given fluid, as the pipe diameter increases, the pumping cost (A) Decreases (B) Increases (C) Remains the same (D) May increase or decrease, depending upon whether the fluid is Newtonian or non-Newtonian

Last Answer : (A) Decreases

Optimum economic pipe diameter for fluid is determined by the (A) Viscosity of the fluid (B) Density of the fluid (C) Total cost considerations (pumping cost plus fixed cost of the pipe) (D) None of these

Description : Optimum economic pipe diameter for fluid is determined by the (A) Viscosity of the fluid (B) Density of the fluid (C) Total cost considerations (pumping cost plus fixed cost of the pipe) (D) None of these

Last Answer : (C) Total cost considerations (pumping cost plus fixed cost of the pipe)

Intimate contact occurs between the food or package and the refrigerant with ____ freezing. a. blast c. cold b. pressure d. immersion

Description : Intimate contact occurs between the food or package and the refrigerant with ____ freezing. a. blast c. cold b. pressure d. immersion

Last Answer : d. immersion

OES Office Systems' use of fax machines to carry its advertising messages to customers is which component of the communication process? A)Medium of transmission. B)Decoding process. C)Coding process. D)Sharing of meaning. E)Noise minimisation.

Description : OES Office Systems' use of fax machines to carry its advertising messages to customers is which component of the communication process? A)Medium of transmission. B)Decoding process. C)Coding process. D)Sharing of meaning. E)Noise minimisation.

Last Answer : A)Medium of transmission.

For a minimisation Transportation Problem, the objective is to minimise: a. Profit b. Cost c. Solution d. None of these

Description : For a minimisation Transportation Problem, the objective is to minimise: a. Profit b. Cost c. Solution d. None of these

Last Answer : b. Cost

A minimisation problem can be connected into maximisation problem by changing the signs of coefficients in the ........................... a. Constraints b. Objectives c. Both a and b d. None of these

Description : A minimisation problem can be connected into maximisation problem by changing the signs of coefficients in the ........................... a. Constraints b. Objectives c. Both a and b d. None of these

Last Answer : b. Objectives

Minimum porosity for fluidisation is(A) That corresponding to static bed (B) That corresponding to completely fluidised bed (C) The porosity of the bed when true fluidisation begins (D) Less than that of the' static bed

Description : Minimum porosity for fluidisation is (A) That corresponding to static bed (B) That corresponding to completely fluidised bed (C) The porosity of the bed when true fluidisation begins (D) Less than that of the' static bed

Last Answer : (C) The porosity of the bed when true fluidisation begins

What is the most common cause of solid size segregation in bulk solid systems?

Description : What is the most common cause of solid size segregation in bulk solid systems?

Last Answer : Many engineers usually point directly to the pneumatic conveying system as a source of such a problem. The truth is that in most cases, segregation occurs because of the differences in ... problem is occurring. Reference: Richard Farnish, the Wolfson Centre for Bulk Solids Handling Technology

Bond crushing law (A) Calls for relatively less energy for the smaller product particles, than does the Rittinger law (B) Is less realistic in estimating the power requirements of commercial crushers (C) States that the work required to form particle of any size from very large feed is proportional to the square root of the volume to surface ratio of the product (D) States that the work required for the crushing is proportional to the new surface created

Description : Bond crushing law (A) Calls for relatively less energy for the smaller product particles, than does the Rittinger law (B) Is less realistic in estimating the power requirements of commercial crushers ( ... (D) States that the work required for the crushing is proportional to the new surface created

Last Answer : (A) Calls for relatively less energy for the smaller product particles, than does the Rittinger law

In case of steam distillation, the steam leaving the liquid is not completely saturated with distillate vapour, because(A) Temperature is less(B) Total pressure is less(C) Mixing of steam with the material being vaporised is not so intimate asto result in equilibrium condition(D) Saturated steam is used for steam distillation

Description : In case of steam distillation, the steam leaving the liquid is not completely saturated with distillate vapour, because (A) Temperature is less (B) Total pressure is less (C) Mixing of steam ... not so intimate as to result in equilibrium condition (D) Saturated steam is used for steam distillation

Last Answer : (C) Mixing of steam with the material being vaporised is not so intimate as to result in equilibrium condition

The purpose of lubrication in an antifriction bearing is (a) to reduce the friction between balls and races (b) dissipation of frictional heat prevention of corrosion (c) protection of the bearing from dirt and other foreign particles (d) all of the mentioned

Description : The purpose of lubrication in an antifriction bearing is (a) to reduce the friction between balls and races (b) dissipation of frictional heat prevention of corrosion (c) protection of the bearing from dirt and other foreign particles (d) all of the mentioned

Last Answer : (d) all of the mentioned

. In case of turbulent flow of fluid through a circular pipe, the (A) Mean flow velocity is about 0.5 times the maximum velocity (B) Velocity profile becomes flatter and flatter with increasing Reynolds number (C) Point of maximum instability exists at a distance of 2r/3 from the pipe wall (r = pipe radius) (D) Skin friction drag, shear stresses, random orientation of fluid particles and slope of velocity profile at the wall are more

Description : . In case of turbulent flow of fluid through a circular pipe, the (A) Mean flow velocity is about 0.5 times the maximum velocity (B) Velocity profile becomes flatter and flatter with ... , shear stresses, random orientation of fluid particles and slope of velocity profile at the wall are more

Last Answer : (D) Skin friction drag, shear stresses, random orientation of fluid particles and slope of velocity profile at the wall are more

Dean number is concerned with the (A) Fluid-particle interaction (B) Fluid flow through helical pipes (C) Power consumption in agitated vessels (D) Psychrometry

Description : Dean number is concerned with the (A) Fluid-particle interaction (B) Fluid flow through helical pipes (C) Power consumption in agitated vessels (D) Psychrometry

Last Answer : (B) Fluid flow through helical pipes

Vibration measuring instruments are classified on the basis of ____________. (A) contact between the vibrating system and measuring instrument (B) the requirement of power source (C) method of measurements (D) all of the above

Description : Vibration measuring instruments are classified on the basis of ____________. (A) contact between the vibrating system and measuring instrument (B) the requirement of power source (C) method of measurements (D) all of the above

Last Answer : (D) all of the above

Black cotton soil is unsuitable for foundations because its (A) Bearing capacity is low (B) Permeability is uncertain (C) Particles are cohesive (D) Property to undergo a volumetric change due to variation of moisture content

Description : Black cotton soil is unsuitable for foundations because its (A) Bearing capacity is low (B) Permeability is uncertain (C) Particles are cohesive (D) Property to undergo a volumetric change due to variation of moisture content

Last Answer : Answer: Option D

Which among the following constitutes “sexual harassment” according to the Sexual Harassment at Workplace (Prevention, Prohibition and Redressal) Act, 2013? a) Unwelcome physical contact and advances, or unwelcome sexually colored remarks b) Trafficking c) Acid attack

Description : Which among the following constitutes “sexual harassment” according to the Sexual Harassment at Workplace (Prevention, Prohibition and Redressal) Act, 2013? a) Unwelcome physical contact and advances, or unwelcome sexually colored remarks b) Trafficking c) Acid attack 

Last Answer : a) Unwelcome physical contact and advances, or unwelcome sexually colored remarks  

The frictional resistance in laminar flow does not depend on the (A) Area of surface in contact (B) Flow velocity (C) Fluid temperature (D) Pressure of flow

Description : The frictional resistance in laminar flow does not depend on the (A) Area of surface in contact (B) Flow velocity (C) Fluid temperature (D) Pressure of flow

Last Answer : (A) Area of surface in contact

Energy requirement (per unit mass of material crushed/ground) is highest for (A) Jaw crusher (B) Rod mill (C) Ball mill (D) Fluid energy mil

Description : Energy requirement (per unit mass of material crushed/ground) is highest for (A) Jaw crusher (B) Rod mill (C) Ball mill (D) Fluid energy mil

Last Answer : (D) Fluid energy mil

An advantage of DC motors over AC motors is that they _____________. A. are less expensive B. require less maintenance C. offer infinite speed variation D. all of the above

Description : An advantage of DC motors over AC motors is that they _____________. A. are less expensive B. require less maintenance C. offer infinite speed variation D. all of the above

Last Answer : Answer: C

Viscosity index of a lubricating oil (A) Is the measure of its flash point (B) Is the measure of variation of viscosity with temperature (C) Should be low (D) None of these

Description : Viscosity index of a lubricating oil (A) Is the measure of its flash point (B) Is the measure of variation of viscosity with temperature (C) Should be low (D) None of these

Last Answer : (B) Is the measure of variation of viscosity with temperature