Global Journal of Engineering Sciences (GJES)
Air
Conditioning Booster
Authored by Ehab Nader Tuffaha
Abstract
The
study trying to utilize and allows to harness the natural and free solar energy
gotten from the sun by converting the additional free enthalpy gotten as
thermal and kinetic energy likewise into useful power; on other words the main
concern is increasing the COP.
This
type of AC will use as much solar energy as is available and convert the solar
energy directly to replace the equivalent amount of AC power from the mains
provider. Under optimum conditions, this can save up to 25% – 45 % of your
mains power usage during the summer.
This
will be most recent innovation in standalone power saving which is partially
free of charge by the Sun.
The
study aims to renovate the traditional refrigeration system which is normally
known as compression refrigeration cycle everywhere in our buildings, so that
it can be developed to take advantage of the free solar energy without
complicated changes neither a completely demolishing.
Keywords: HVAC; Solar radiation; R 134a;
Thermodynamics; Momentum
Introduction
Jordan
is among of the most enthusiastic developing country to promote utilization of
renewable energy, as very well known the solar radiation in Jordan average
within 4500 Wh/m2 to8000 Wh/ m2.
More
than 300 sunny days in Jordan driving us to think more seriously in renewable
energy resources and somehow reduce dependence on oil consumption.
Basic
thermodynamics statement that as a greater temperature difference between
substances the faster heat flow, so once the refrigerant gas temperature
increased then a heat rejection is higher; same what happened when the ambient
temperature increases, less heat can be rejected from the air-cooled condenser
to the hotter ambient.
Adding
an extra heat to the cycle in order to increase ΔT between condenser and
surrounding environment. Not quite, but the future will be for renewable
energy, however the first step should be renovating the transition phase of the
hybridized types by paving the way for the renewable sources, as there is no
doubt that renewable energy does not match in any way the traditional energy
that we are accustomed to in term of cost neither the required efficiency.
Methodology
Heat transferee calculations:
a) Qh = mh x Cph (Thou t-Thin)
Versus b) Qc = mc x Cpc (Tc out-T c in)
Equation a here represent
water system versus equation b for refrigeration cycle.
Where Q = heat energy (Joules,
J) m = mass of a substance (kg) c = specific heat (unit’s J/kg∙K) Δt is a
symbol meaning “the change in” temperatures
Tcout = Outlet refrigeration temperature from heat exchanger.
Tcin = Inlet refrigeration temperature from heat exchanger.
Thin = Water Inlet temperature from the solar collector to heat
exchanger.
Mpemba Effect on the Refrigeration Cycle
The basic advantage is a
quicker phase change from gas to liquid leading to a better sub cooling and
that to less flash gas then more cooling capacity at the evaporator and with
the control of the unit then to the original cooling capacity at the evaporator
but with less compressor work. All the known formulas in thermodynamics can’t
explain, because there is really none for the phase change except the amount of
heat transferred at phase change.
We gain here 15 KW using our
selected heat exchanger); Now a gas coming from a higher temperature has a much
higher kinetic energy of the molecules and they kick much more into them as a
result they can develop much quicker the interconnecting Vander Waals forces
and as a result they liquefy quicker. Since the gas gets quicker liquid, the
remaining way in the condenser is used to cool down the fully liquid further.
Where a & b are
dimensions to be experimentally found. p = pressure, n= number of moles, T =
temperature, V = volume and R = universal gas constant. Hence Its value will be
nearby to general gas equation the given gas is at low pressure and high
temperature.
PV = nRT; V = As x L, as the
selected exchanger is 0.311m height,
P @ 90 C = 10 bar = 9.9 atm;
V= 0.5 m3
R = 0.082 lt. atm /deg.k.mole
10 x 0.5= n x 0.082x 363
So n= 0.2
However as very known from
P1V = n1RT …;
P2V = n2RT … Considering the volume is constant (Isochoric) as the heat
exchanger is a small closed tank so: P2 X 0.5= 0.2 x 0.082 x 363 k ; So P2 =12
bar
Discussions and Ideas
Based on the below equations
and numbers, a rapidly increasing in momentum during of heating the refrigerant
gas R 134a:
As an estimation each pressure
drop in heat exchanger 4m/ 100m and we have a 10 meters pipes so we have a 0.4
bar =4079 kgf/m2 (kg per sq. meter); let us multiply the factors as below:
0.2 kg/s (refrigerant flow
rate) x 4079 kg/m2 x 0.02 m3/kg (specific volume @ 40 c & 2 bar) = 16
kg.m/s
This unit is a momentum, so
let us try to get the momentum @ 90 c & 10 bar:
0.2 kg/s (refrigerant flow
rate) x 4079 kg/m2 x 0.3m3/kg (specific volume @ 90 c & 10 bar) = 245
kg.m/s.
This is mean each change in
momentum is a new specific impulse on other words this is producing a thrust
force which is also a gain for the cycle.
Conclusion
• The system clearly shows
that COP is increased from 4.3 to 5.5, by converting solar thermal energy to
sub cooling additional for the refrigeration cycle.
• The system adds more 2 bars
to the refrigeration cycle consequently increasing in the entropy as mean a
quicker phase change due to quicker set-up of intermolecular bindings because
of v Van der Waals forces yielding additional sub-cooling.
• The most important is we
don’t have to increase condenser surface. It is very well capable to remove the
additional heat, the Formula Q = alpha X surface x delta T. Alpha is heat
transfer coefficient and does not change, If Delta T increases due to higher
temperature of the refrigerant entering the condenser, the condenser just
transfers more heat. The environment as the heat absorbing media is capable of
taking up that additional heat. For more explanation, let say what happened
with radiators: if you flush water with a temperature of 45 °C through the
radiator, it does not provide that much heat as if you flush water through with
a temperature of 90 °C so the radiator is capable of doing the job.
Basically W (KJ/Kg) = ∫p*dv,
however the dv in heat exchanger considered zero by other words it’s an
Isochoric Work When V is held constant and P changes W = 0 Because gas is not
doing any work but as surrounding adds energy to internal energy of gas That’s
why Cp is always greater than Cv Specific heat capacity at constant pressure is
always greater than Specific heat capacity at constant volume, now once the gas
goes through the condenser a quicker phase change occurred there cause When gas
expands it has to do work to push environment to create space for its expansion
by spending energy from its internal energy that’s why suddenly Gas cools down.
Addendum
Data Analysis
The below study shows if
reduce refrigerant up to certain limit could be useful for COP, however should
we not reach to the maximum temperature of 120 c which is the critical
temperature, however power consumption is reduced accordingly (Table 1).
The below are a figure out and illustrations using Mollier diagrams which is a very common for systems with fixed compressor speed = fixed mass flow. DC Inverter units with variable mass flows and many changes in circuit offer wide range of mollier diagrams will be a high improvement for the proposed system .
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