Chapter 13 (HTRN) Flashcards
One of the reasons for insulating the pipes is
Heat loss from the surface is minimized
The rate of radiant energy, that is emitted by a surface at any temperature and in small wavelengths is found from the known rate of energy, that under the same conditions will be emitted from a black surface, by multiplying with the absorptivity. The above enunciation is called:
Kirchoff’s Law
Which of the following is generally used to measure the temperature inside the furnace?
Optical Pyrometer
All heat transfer processes:
involve temperature difference between the bodies
What is thermal diffusivity ?
a physical property of the material
Which of the following is a unit of thermal diffusivity?
m²/hr
Non isotropic conductivity is shown by which of the following?
wood
For glass wool thermal conductivity changes from sample to sample due changes in:
structure, density, composition (all of the above)
Which of the following is the SI unit of thermal conductivity?
W/ m°K
What is the value if the Prandt’l number for air?
0.7
According to Prevost Theory of heat exchange;
all bodies absolute zero emit radiation
Thermal conductivity of wood depends in which of the following?
moisture, temperature, density
A fur coat on an animal will help the animal to remain:
warm in winter
The nature of flow of a fluid inside s tube, whether it is turbulent or laminar, can be ascertained by:
Reynolds number
Which of the following modes of heat transfer is the Stefan-Boltzmann law applicable?
Radiation
At all wave lengths and temperatures the monochromatic emissivity of a white body is equal to:
zero
The radiation from flames is having:
all of the above
The statement that the emissivity and absorptivity of a surface is surrounded by its own temperature are the same for both monochromatic and total radiation is called:
Kirchoff’s Law
A reservoir that supplies energy in the form of heat is called:
source
In regenerator type heat exchanger, heat transfer occurs by:
flow of hot and cold fluids alternately over surface
Least value of Prandt’l number can be expected in case of:
liquid metals
“The boiling point of a solution is a linear function of water at the same pressure.” The above statement is called
Dubring’s Rule
Floating heads are provided in heat exchangers to
avoid deformation of tubes because of thermal expansion
What do you call the first page of crystal formation?
nucleation
In heat exchanger design, one transfer unit implies:
condition when the change in temperature of one steam is numerically equal to the average driving force
Dritus Boelter equation can be applied in case of fluids flowing in:
turbulent region
In sugar mills can just is evaporated in:
long vertical tube evaporators
A 1-3 heat exchanger refers to which of the following?
single pass on shell side and double pass on tube side
A correction of LMTD is essential in case of:
cross flow heat exchanger
Which of the following is used as entrainer in acetic acid water separation?
Butyl acetate
A type of radiation consisting of singly charged particles that generate to intermediate distances
Beta radiation
An electrically charged atom or radical which carries electricity through an electrolyte is called:
ion
The energy of a body that can be transmitted in the form if heat
thermal energy
In an isometric process, the heat transferred is equal to:
change in internal energy
A substance that is able to absorb liquids ir gases and is used for removing them from a given medium or region
Absorbent
Radiant heat transfer is described by
Kirchoff’s Law
A reservoir that absorbs energy in the form of heat is called
sink
When the entire heat exchanger is selected as control volume, heat becomes
zero
Heat is conducted in the direction of
decreasing temperature
The heat transfer term in the first law of thermodynamics may be due to any of the following except:
internal heat generation (e.g., chemical reaction)
All heat transfer processes require a medium of energy exchange except:
radiation
Thermal conduction is described by
Fourier’s Law
Convection is described by which if the following laws?
Newton’s Law
Radiation heat transfer is described by
Kirchoff’s Law
The equivalent of ratio of emissive power to absorptivity for bodies in thermal equilibrium is described by:
Kirchoff’s Law
The temperature potential between temperature at the two ends of a heat exchanger are given by
the logarithmic mean temperature difference
The function of a heat exchanger is to
transfer heat from one fluid to another
The function of a superheater is to
exhange heat ti increase energy to the flow
A theoretical body which when heated to incandescence would emit a continuous light gray spectrum
Black body
Which of the following is the reason for insulating the pipes?
Heat loss from the surface is minimized
Heat transfer due to density differential
Convection
The term “exposure” in radiological effects is used as a measure of a gamma ray or an x ray field in the surface of an exposed object. Since this radiation produces ionization of the sir surrounding the object, the exposure is obtained as
number of ions produced per mass of air x coulumbs per kg
The passing of heat energy from molecule to molecule through a substance
conduction
The radiant heat transfer depends on
heat rays
What kind of heat exchanger where water is heated to a point that dissolved gases are liberated?
Deaerator
Heat transfer processes which include a change of phase of a fluid are considered
convection
A hot block is cooled by blowing cool air over its top surface. The heat is first transferred to the air layer close to the block is by conduction. It is eventually carried away from the surface by
convection
A body that is hot compared to its surroundings illuminates more energy than it receives, while its surrounding absorbs more energy than they give. The heat is transferred from one to another by energy eave motion. What is the mode of heat transfer?
Radiation
What is the density due to density differential?
Convection
The transmission of heat from one place to another by fluid circulation between the spots of different temperatures is called
convection
Which of the following requires the greatest amount of heat per kilogran for a given increase in temperature?
Water
What do you call the effectiveness of a body as a thermal radiator at a given temperature?
Emissivity
The natural direction of the heat flow between two reservoirs is dependent on which of the following?
Their temperature difference
Why are metals good conductors of heat?
Because they contain free electrons
In natural convection a heated portion of a fluids moves because
Their density is less than that of the surrounding fluid
In order to emit electromagnetic radiation, an object must be at a temperature:
above 0 K
The rate at which an object radiates electromagnetic energy does not depend on its
mass
Sublimation refers to
the vaporization of a solid without becoming liquid
In the process if freeze drying, ice goes directly into water vapor. What is the temperature at which this process can take place?
Below the triple point of water
What usually happen when a vapor condenses into a liquid?
It evolves heat
In cooling tower, the water is cooled mainly by:
evaporation
How do you classify a body that has an emissivity factor of 0.7?
Gray body
At what particular condition that no more heat can that be removed from a substance and the temperature can no longer be lowered?
Absolute zero
What refers to heat transfer wherein the heat is transferred from one point to another by actual movement of substance?
Convection
The ratio of the radiation of actual body to the radiation of a blackbody is known as
emittance
Which of the following is the actual geometric view factor for a black body?
One
What happens to the heat transferred radially across insulated pipe per unit area?
Decrease from pipe wall to insulated surface
What do you call a change of phase directly from vapor to solid without passing through the liquid state?
Deposition
Which of the following is the Stefan-Boltzmann constant?
5.67 x 10^-8 W/m² K⁴
What is the usual value of transmissivity for opaque materials?
0
A body whose emissivity is less than 1 as known as a real body. What is the other tetm for real body?
Gray body
What refers to an ideal body that absorbs all of the radiant energy that intrudes on it and also emits the maximum possible energy when acting as a source?
Black body
The thermal resistance for one dimensional steady conduction heat transfer through cylindrical wall in the radial direction is expressed in which of the following functions?
Logarithmic
The law which states that “the ratio of the emissive powers to absorptivities are equal when the two bodies are in thermal equilibrium” is known as
Kirchoff’s Law of Radiation
It refers to the ratio of the internal thermal resistance of a solid to the boundary layer thermal resistance (or external resistance of the body?
Biot number
It refers to the ratio of the heat transferred by conduction to the rate of energy stored
Fourier number
It is the term used to describe the energy of a body that can be transmitted in the form of heat
thermal energy
Which of the following is the equivalent heat transferred of a gas undergoing isometric process?
Change in internal energy
What do you call a substance ttat is able to absorb liquids or gases and is usually used for removing liquids or gases from a given medium or region?
Absorbent
In which direction that heat is transferred through conduction
Decreasing temperature
Which of the following statements is based on Prevost theory of heat exchange?
All bodies have absolute zero emit radiation
Which of the following is the emissivity of white body?
Zero
The mechanism of heat transfer in which there is no medium (i.e. water, air, solid concrete) required for the heat energy to travel is:
Radiation
The temperature potential between temperature at the two ends of a heat exchanger are given by:
the logarithmic mean temperature difference
Which of the following best describe function of heat exchanger?
Transfer heat from one fluid to another
What refers to a form of energy associated with the kinetic random energy motion of large numbers of molecules
Heat
How much air is the part light that is absorbed by the body that transmits and reflects 80% and 10% respectively?
10%
In convection heat transfer, what happens to the heat transfer coefficient if the viscosity of the fluid increases
The heat transfer coefficient will decrease
How do you call a phenomenon wherein the heat is transferred by motion of fluid under the action of mechanical device?
Forced convection
In conduction heat transfer, what happens to the heat transfer per unit time when the termsl conductivity decreases?
The heat flow will decrease
Which of the following is the driving force in heat transfer?
Temperature gradient
Which of the following is the measure of the relative effectiveness of momentum and energy transport by diffusion in the velocity snf thermal boundary layer?
Prandt’l number
Which of the following property of the solid that provides the measure of the rate of heat transfer to the energy storage?
Thermal diffusivity
Two metals were kept together at room temp. and it was found out that one is colder than the other. Which of the following is the best reason why one metal is colder than the other?
The thermal conductivity of one metal is high as compared to the other
In convection heat transfer, what happens to the heat transfer coefficient if the viscosity of the fluid decreases?
The heat transfer coefficient also increases
A body that is hot compared to its surroundings illuminates more energy than it receives, while its surrounding absorbs more energy than they give. The heat us transferred from one to another by energy if eave motion. What is this mode of heat transfer?
Radiation
What do you call a theoretical body where absorptivity and emissivity are independent of the wavelength over the spectral region of the irradiation and the surface emission?
Transparent body
Which of the following is the structure designed to prevent the spread of fire having a fire resistance rating of not less than four hours?
Fire wall
Which of the following heat exchange device used to privide heat transfer between the exhaust gases and air prior to the entrance of a combustor?
Regenerator
Which of the following transfer of heat is involved in the changing of boiling water at 100°C to vapor at the same temperature?
Convection
Which of the following is the science of low temperatures?
Cryogenics
Which of the following thermal state of the body considered as reference to communicate heat to the other bodies?
Temperature
The true mean temperature difference is also known as
The logarithmic mean temperature difference
Which of the following can be a geometric view factor of a gray body?
Greater than zero but less than one
The heat transferby conduction occurs in which of the following?
In solids, liquids, and gases
Which of the following reasons why one gram of steam at 100°C causes more serious burn than 1 gram of water at 100°C?
Steam contains more internal energy
What usually happens when vapor condenses into liquid?
It rejects heat
Which of the following has the highest thermal conductivity?
Mercury
Which of the following is the requirement of the temperature of a body for it to emit radiation?
Above zero kelvin
Which of the following is the color of iron when it is heated to a highest temperature?
White
Which of the following is the reason why metals are good conductors of heat?
Metals contain free electrons
The rate at which heat flows through a slab of some material does not depend on which of the following?
The specific heat of material
Which of the following is the primary fucntion of a thermal radiator?
To transfer heat with or without a medium
What is the reason why styrofoam is a good insulating material?
Because it contains many tiny pockets of air
What usually happens to the surrounding whrn water wapor condenses
It warms the surrounding
The rate of radiation does not depend on which of the following
The thickness of the radiating body
Which of the following is not a good conductor of heat?
Asbestos
Which of the following is not a unit of the rate of heat transfer?
Btu/HP-hr
The thermal conductivity does not depend on which of the following?
Gravitational pull
In Maxwell’s theory for thermal conductivity of gases snd vapors, which of the followibg is the value of “a” for triatomic gases?
1.7
Which of the following conductivities where Sutherland equation is used?
Thermal conductivities of gases
For pure metals, what happens to the thermal conductivity if the temperature is extremely high?
Almost constant except for ferromagnetic materials
Which of the following liquids that has the highest thermal conductivity?
Water
Which of the following is not a heat exchanger?
Water hammer
Which of the following heat exchangers where fluid flow in the dsme direction and both are of changing temperatures?
Parallel flow
What happens to the thermal conductivity of diatomic gases if the temperature is increased?
The thermal conductivity will also increase
What device is used to measure the amount of infrared radiation in each portion of a person’s skin that is emitted?
Thermograph
The heat transfer by convection occurs in which of the following?
Only in gases and liquids
In convection heat transfer, what mechanism heat transfer where the fluid moves due to the decrease in its density caused by increase in temperature?
Natural convection
