S1 Flashcards
Crystal size in a continuous crystallizer depend upon the
**All a, b,c **
A. Rate of heat transfer
B. Degree of turbulence
C. Degree of supersaturation
Heat waves
Both b and c
B. Travel in straight line
C. Can be reflected by mirror
Air is best heated with steam in a heat exchanger of
**Double pipe type with fin on air side **
Which of the following is generally considered as opaque surface towards radiations?
**Both b and c **
B. Solids
C. Liquids
Black liquor generated during paper manufacture is concentrated in a
**Multiple effect evaporator **
When vaporization takes place directly at the heating surface, it is called
**Nucleate boiling **
Steam consumption in kg/hr in case of an evaporator is given by
**C/E **
Reynold’s analogy states that
**Nst α f **
With increase in temperature, the thermal conductivity of non-metallic amorphous solids
**Increases **
Fourier’s law applies to the heat transfer by
Conduction
Shell side pressure drop in a shell and tube heat exchanger does not depend upon the
None of these
In the equation Q=UAdeltaT, delta T is
**Logarithmic mean temperature difference **
With increase in porosity, the thermal conductivity of a solid substance
**Decreases **
For an ideal black body,
** Absorptivity=1 **
In Joule’s experiment, an insulated container contains 20 kg of water initially at 25°C. It is stirred by an agitator, which is made to turn by a slowly falling body weighing 40 kg through a height of 4 m. The process is repeated 500 times. The acceleration due to gravity is 9.8 ms-2. Neglecting the heat capacity of agitator, the temperature of water (in °C) is
**34.4 **
Fouling factor
accounts for additional resistances to heat flow
In case of vertical tube evaporator, with increase in liquor level, the overall heat transfer coefficient
**decreases **
The steam ejector is used to
**create vacuum **
For shell and tube heat exchanger, with increasing heat transfer area, the purchased cost per unit heat transfer area
**passes through a maxima **
The thermal efficiency of a reversible heat engine operating between two given thermal reservoirs is 0.4. The device is used either as a refrigerator or as a heat pump between the same reservoirs. Then the coefficient of performance as a refrigerator (COP)R and the co-efficient of performance as a heat pump (COP)HP are
(COP)R= 1.5; (COP)HP= 2.5
Hot water (0.01 m3 /min) enters the tube side of a counter current shell and tube heat exchanger at 80°C and leaves at 50°C. Cold oil (0.05 m3/min) of density 800 kg/m3 and specific heat of 2 kJ/kg.K enters at 20°C. The log mean temperature difference in °C is approximately
**32 **
In a heat exchanger, floating head is provided to
**relieve stress caused by thermal expansion **
Leidenfrost point is a term concerned with the
**boiling of a liquid on a hot surface **
A process stream of dilute aqueous solution flowing at the rate of10 Kg.s-1 is to be heated. Steam condensate at 95°C is available for heating purpose, also at a rate of 10 Kg.s-1. A 1 - 1 shell and tube heat exchanger is available. The best arrangement is
**counter flow with process stream in shell side **
Heat produced when a steady state current passes through an electrical conductor having resistance, ‘R’ is
I^2R
Pick out the wrong statement.
**Orifice baffles are never used in a shell and tube heat exchanger **
Convective heat transfer coefficient in case of fluid flowing in tubes is not affected by the tube length/diameter ratio, if the flow is in the ______ zone.
**highly turbulent **
The actual temperature drop across the heating surface in an evaporator depends on the
All a,b, and c
A. Feed
B. Depth of liquid over heating surface
C. Pressure difference between steam chest and vapor space
Which of the following is not used as a medium for high temperature heating?
**Mercury **
Presence of non-condensing gas in a condensing vapor
None of these
Kirchoff’s law applies to ______ radiation.
**Both a and b **
A. Total
B. Monochromatic
With the increase of temperature, the Col-burn jH factor
**increases **
In case of evaporators, liquid entrainment results primarily due to
**foaming of the solution **
Baffles in the shell side of a shell and tube heat exchanger
**increase the shell side heat transfer coefficient **
Air is to be heated by condensing steam. Two heat exchangers are available (i) a shell and tube heat exchanger and (ii) a finned tube heat exchanger. Tube side heat transfer area are equal in both the cases. The recommended arrangement is
**finned tube heat exchanger with air outside and steam inside **
The unit of heat transfer coefficient in SI unit is
**W/m^2K **
The number of kg vaporized per kg of steam fed to the evaporator is defined as
**economy **
Pick out the wrong statement.
**The equivalent diameter of heat transfer for a duct of square cross-section (having each side as x) is equal to 4x. **
Economy of a multiple effect evaporator is not influenced much by the
**boiling point elevations **
Increasing the liquor level in the evaporator results in the
**decreased capacity **
The equivalent diameter for pressure drop is _______ that for heat transfer
smaller than
Controlling heat transfer film coefficient is the one, which offers _____ resistance to heat transfer.
**the largest **
The heat flux (from outside to inside) across an insulating wall with thermal conductivity, K= 0.04 W/m.°K and thickness 0.16m is 10 W/m2. The temperature of the inside wall is - 5°C. The outside wall temperature is
**35degC **
Thermal conductivity of a conducting solid material depends upon its
**Both a and b **
A. Temperature
B. Porosity
Pick out the wrong statement.
**In case of a 1-2 shell and tube heat exchanger, the LMTD correction factor value increases sharply, when a temperature cross occurs. **
The average heat transfer coefficient for laminar film condensation on a vertical surface is inversely proportional to
**(deltaT)^1/4 **
Bulk of the convective heat transfer resistance from a hot tube surface to the fluid flowing in it, is
**mainly confined to a thin film of fluid near the surface **
Which of the following is concerned with both heat and mass transfer?
**Lewis relationship **
A backward feed multiple effect evaporator is better than forward feed for concentrating cold feed, because it provides
**higher economy **
A 10 cm dia steam pipe, carrying steam at 180°C, is covered with an insulation (conductivity = 0.6 W/m.°C). It losses heat to the surroundings at 30°C. Assume a heat transfer co-efficient of 0.8 W/m2.°C for heat transfer from surface to the surroundings. Neglect wall resistance of the pipe and film resistance of steam. If the insulation thickness is 2 cms, the rate of heat loss from this insulated pipe will be
**less than that of the uninsulated steam pipe*
