mulcho Flashcards
Begin with an end in mind. Goodluck!
True or False
True
The product of the Grashof number and the Prandtl number is another
dimensionless number referred to as _______ ?
Rayleigh
_____ number is equivalent to the product of the Reynolds number and
the Prandtl number.
Peclet
_______ is a dimensionless number in fluid dynamics and heat transfer
which approximates the ratio of the buoyancy to the viscous force
acting on a fluid. It frequently arises in the study of situations involving
natural convection.
Grashof
The dimensionless expression is DG/mu is
Reynold’s Number
A dimensionless group that is directly proportional to the specific
heat and viscosity but inversely proportional to the conductivity of
a material is called _____
Prandtl Number
The Fourier’s Law of heat conduction states that the heat flux is
_____________the temperature gradient.
directly proportional to
The temperature inside a sphere of material has uniform heat
generation per unit volume and uniform thermal conductivity.
Which of the following is the correct expression for temperature
profile where a and b are constants and r is the radius measured
from the centerline.
I. T = a - br
II. T = a - b/r
III. T = a - br^2
IV. T = a - b ln(r)
III (yung br^2)
When two substances are in thermal contact, which of the
following statement(s) is/are true
I. heat flows from higher temperature to lower temperature
II. the heat flows in the direction of temperature decrease
III. heat may flow by conduction, convection, and/or radiation
I, II, III ; LAHAT
The rate of heat flow by conduction through layers of insulation in
series
a) increases across each layer
b) decreases across each layer
c) directly proportional to the number of layers
d) none
e) are equal
e) are equal
The mean transport area in one-dimensional steady-state radial
heat conduction in a cylindrical wall is
logarithmic mean area
The local individual coefficient of convection heat transfer for
gases flowing inside long straight tubes is inversely proportional
to the ___
viscosity of the gas
Which of the following is/are used to increase the effective surface
area for convective heat transfer in heat exchangers, internal
combustion engines, electrical components, among others?
A. Fin
B. Extended Surface
C. Radiator
A & B
In forced convection inside a pipe, if the velocity of the fluid
increases, the convective heat transfer coefficient of the fluid
normally
increases
The heat transfer coefficient of a condensing fluid due to film
condensation in the outer surface of a horizontal tube is generally
________ that of a vertical tube of the same length.
greater than
The equation Nu = 0.023(Re^0.80)(Pr^n) is used for forced
convection where “n” is ____ when the fluid is being heated.
0.4 (Dittus-Boetler Eqn)
Which empirical equation to estimate convective heat transfer
coefficient is used when the flow of fluids in long horizontal
straight pipes is turbulent and the fluid is highly viscous?
Sieder-Tate
The film coefficient of a fluid flowing inside a tube is ______
when the viscosity is decreased.
increased
It is the dimensionless number that describes the ratio of convection at
the surface of the body to the conduction within the body
Biot Number
The lump analysis method can be used to solve the one-dimensional
transient heat conduction in any of the following conditions except:
a) solids with very high thermal diffusivity
b) when temperature gradient within the solid is small
c) if the thermal resistance within the solid is very small compared to the external thermal resistance
d) none of the choices
e) if the biot number is less than 0.1
It is an idealized surface that absorbs all incident radiation,
regardless of wavelength and direction, and is also considered to
be a perfect emitter.
black body
It is defined as the ratio of the radiation emitted by the surface to
the radiation emitted by a blackbody at the same temperature.
emissivity
Which of the following bare steam pipe (containing saturated
steam at 100 psig) would provide most likely the largest heat loss
to the surrounding (given the same pipe dimension and ambient
condition)?
a) oxidized steel pipe
b) polished stainless steel pipe
c) 304 stainless steel pipe
d) insufficient information
a) oxidized steel pipe
It states that the amount of radiation emitted in all directions and
overall wavelengths by a perfect emitter is proportional to the
fourth power of the absolute temperature of the emitter.
Stefan-Boltzmann Law
