8/18/2019 Solar Absorption Assignment
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Department: Mechanical Engineering Date: April 2016
Course: Renewable Energy Prof. Adel. Nasser
Course Code: ME 247
Group: 1
Question 1:
In an absorption type refrigerator, the heat is supplied to
NH3
generator by condensing steam at 2 bar and 80% dry. The
temperature in the refrigerator is to be maintained at -4⁰C.
Find the
maximum COP.
If the refrigeration load is 18 tons refrigeration and actual
COP is 72%
of the maximum COP. Find out the mass of steam required per
hour.
Given that the temperature of the atmosphere is 25⁰C.
If a solar collector of area of area 2 m2 has the shown
efficiency curve.
Calculate the required number of this collector to be used to
supply
the absorption generator. The following data has been recorded
for
the collector
Solar
Radiation
Sun
duration/day
Collector
Temperature
Ambient
Temperature
450 W/m2 10 hrs 42⁰C 15⁰C
Question 2:
In 18 tons absorption refrigeration system, the heating in the
generator is carried out using steam at 3bar and
85% dry. The refrigeration temperature is -10⁰C. The
condensation of refrigerant is carried out using cooling
water.
i. Determine the maximum COP.
ii. Determine the mass flow rate of steam required per
hours to run the plant if steam leaves the generator
at the same pressure. Assume relative COP=0.4.
If the heat is supplied to the generator using solar collectors
with the following records, calculate the area
needed for the solar collectors. Given that the solar radiation
is 800 W/m2 for 10 hours a day, the fluid inletand ambient
temperatures are 90⁰C and 20⁰C respectively.
η 0.600 0.530 0.475 0.280 0.210 0.175
(Tin – Ta)/Ic 0.025 0.035 0.060 0.100 0.11
0.13
8/18/2019 Solar Absorption Assignment
2/3
Department: Mechanical Engineering Date: April 2016
Course: Renewable Energy Prof. Adel. Nasser
Course Code: ME 247
Group: 1
Question 3:
Derive an expression for the COP of an ideal vapor absorption
refrigeration system in terms of the generator,
evaporator, condenser and absorber temperatures.
In a simple ideal vapor refrigeration system, following data are
taken.
Generator temperature = 130⁰C.
Condenser/Absorber temperature = 40⁰C.
Evaporator temperature = -10⁰C.
i.
Calculate the maximum COP
ii. If the actual COP is 70% of the maximum COP, determine
the quantity of dry saturated steam supplied to
the generator at 140⁰C for 50 ton capacity if the condensate
leaves the generator at 120⁰C.
Question 4:
In an aqua-ammonia absorption refrigeration system of 9 tons of
refrigeration capacity, the vapor leaving the
generator is 100% pure Nh3 saturated at 40⁰C. The
evaporator, absorber, condenser and generator
temperatures are -10⁰C, 20⁰C, 40⁰C, and 150⁰C respectively. At
absorber exit (strong solution) the
concentration of ammonia is solution χ = 0.3 and enthalpy h = 20
kJ/kg. At generator exit (weak solution
concentration of ammonia is χ = 0.1 and enthalpy h =
695 kJ/kg.
i.
Determine the mass flow rate of ammonia in the evaporator.
ii. Carry out overall mass concentration and mass
concentration of ammonia in absorber to determine mass
flow rate for both weak and strong solution.
iii. Determine the heat rejection in absorber and
condenser, heat supplied to the generator and COP.
iv. If the heat is supplied using solar collectors each
one of 4.1 m2. Given that the collector is tested by ASHRE
method with beam radiation normal to the plane of the collector
and the following information comes
from the test. Find out the number of solar collectors needed to
power the system where the solar
radiation is 700 W/m2 and the collector temperatures are
30⁰C and 60⁰C respectively.
Q u MJ/hr Ic W/m2 Tin⁰C Tout⁰C Tamb⁰C
9.05 864 43 49 10
1.98 894 93 99 10
Consider the mean collector temperature is the mean between
inlet and outlet temperatures.
