WorksheetsVapor Power Cycle
Total questions: 22
Worksheet time: 11mins
What should be the critical temperature of working fluid for maximum efficiency of vapour power cycle?
the working fluid should have critical temperature as low as possible
the working fluid should have critical temperature as high as possible
the critical temperature does not affect the efficiency of the vapour power cycle
none of the above
What is the drawback of the steam as a working substance in a power cycle?
in a vapour power cycle, maximum temperature which can be obtained with best available material is more than the critical temperature of water and requires large superheating
it allows only small amount of heat addition at the highest temperature
it requires reheat and reheater tubes are costly
all of the above
The below diagram is the T-s diagram of the Rankine cycle with reheat. Which process represents the reheat?
process 1 – 2
process 2 – 2 ′
process 2 ′ – 2 ″
process 2 – 3 ′
How are the effect of reheat and effect of regeneration on the efficiency of steam power plant compared?
effect of reheat is greater that the effect of regeneration on plant efficiency
effect of regeneration is greater that the effect of reheat on plant efficiency
both the reheat and regeneration have same effect on efficiency of steam power plant
cannot say
Which among the following has the lowest efficiency than the others, when they are operated between same pressures?
Ideal Rankine cycle
Ideal regenerative cycle
Carnot cycle
None. All of the above have same efficiency
The mean temperature of heat addition ( TH ) in the Rankine cycle can be increased by
reheating the steam
increasing superheat
increasing pressure ratio between which the cycle works
all of the above
The reheat cycle allows steam power plant -
to use higher pressure ratio
to maintain required quality of steam at the exit of the turbine
to increase the turbine work
all of the above
What is the effect of superheated steam on efficiency of Rankine cycle?
efficiency of Rankine cycle decreases with increase in superheat of the steam
efficiency of Rankine cycle increases with increase in superheat of the steam
efficiency of Rankine cycle is not affected by change in superheat of the steam
none of the above
The maximum efficiency of Rankine cycle (ηRankine) is the function of
the mean temperature of heat addition (Tm) only
the mean temperature of heat addition (Tm) and temperature of steam at the exit of the turbine
the mean temperature of heat addition (Tm) and temperature of steam at the entry of the turbine
the mean temperature of heat addition (Tm) and temperature of steam at exit of the condenser
What is the relation between efficiencies of Rankine cycle and Carnot cycle for the same pressure ratio?
(ηRankine) = (ηCarnot)
(ηRankine) > (ηCarnot )
(ηRankine) < (ηCarnot )
none of the above
How can we differentiate Rankine cycle from Carnot cycle?
Heat addition process of Rankine cycle is reversible isothermal whereas heat addition process of Carnot cycle is reversible isobaric
Heat addition process of Rankine cycle is reversible isobaric whereas heat addition process of Carnot cycle is reversible isothermal
Heat addition process of Rankine cycle is reversible isentropic whereas heat addition process of Carnot cycle is reversible isothermal
both cycles are identical except the working fluid used
Considering only heat loss (Qloss) in the expansion process at the turbine, what is the correct relation among enthalpies of steam entering and leaving the turbine (h1 and h2 respectively), turbine work (WT) and heat loss (Qloss)
h1 = h2 – WT – Qloss
h1 = h2 + WT – Qloss
h1 = h2 + WT + Qloss
none of the above
Which loss does present in actual vapour power cycle at the exit of the boiler and at the entry of the turbine?
friction loss
constant pressure heat loss
both a. and b.
none of the above
To maximize the work output at turbine, the specific volume of working fluid should be -
as small as possible
as large as possible
constant throughout the cycle
none of the above
What is the highlighted area (area enclosed by 1234) in the following T-s diagram of vapour power cycle indicate?
heat added in cycle
work produced by turbine
net work produced by cycle
heat rejected from cycle
How is the capacity of vapour power plant expressed?
in terms of heat rate
in terms of steam rate
in terms of work output
none of the above
In the following T-s diagram of Rankine cycle, process (1-2) is heat addition in boiler, process (2-3) is an expansion at turbine, process (3-4) is a condensation process and process (4-1) is a pumping process at feed pump. What is the formula for efficiency of Rankine cycle?
ηRankine = ((h2 – h3) + (h1 – h4)) / (h2 – h1)
ηRankine = ((h2 – h3) – (h1 – h4)) / (h2 – h1)
ηRankine = (h2 – h3) / (h2 – h1)
none of the above
In the T-s diagram of vapour power cycle, what is the condition of stem at the starting of turbine expansion?
wet with dryness fraction 0.8
wet with dryness fraction 0.99
dry saturated
superheated
Which ideal process is carried out at the turbine in vapour power cycle?
reversible adiabatic compression
reversible adiabatic expansion
reversible constant pressure heat addition
reversible constant pressure heat rejection
At ideal condition of vapour power cycle, reversible constant pressure heat rejection is carried out at -
boiler
turbine
condenser
feed pump
What is the formula for efficiency of vapour power cycle?
ηcycle = Wnet / Qin
ηcycle = (WT – WP) / Qin
ηcycle = (Qin – Qout) / Qin
all of the above
What will be the net change in internal energy of working fluid of power cycle over the complete cycle?
net change in internal energy of working fluid will be positive
net change in internal energy of working fluid will be negative
no any net change in internal energy of working fluid
none of the above
