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ETASR - Engineering, Technology & Applied Science Research Vol. 3, �o. 3, 2013, 424-428 424
www.etasr.com Kardjilova et al.: Influence of Temperature on Energetic and Rheological Characteristics…
Influence of Temperature on Energetic and
Rheological Characteristics of PLANTOHYD Bio
Lubricants – a Study in the Laboratory
Krassimira Kardjilova
Department of Physics
Technical University
of Varna
Varna, Bulgaria
kardjilova@yahoo.com
Vlasta Vozarova
Department of Physics
Slovak University of Agriculture
of Nitra
Nitra, Slovak Republic
vlasta.vozarova@uniak.sk
Mihal Valah
Department of Physics
Slovak University of Agriculture
of Nitra
Nitra, Slovak Republic
michal.valach@uniag.sk
Abstract — This article presents the results of measuring the
calorific value and the rheological characteristics of Plantohyd
bio lubricants. Measurements were conducted under
laboratory conditions with an IKA C5000 calorimeter and a
DV-3P Anton Paar digital viscometer. Results are presented
graphically. It is shown that the physical interpretation of
energy values results and the dependence of rheological
properties on temperature can be used to assess the quality of
lubricants.
Keywords: Plantohyd; calorific value; rheological
characteristics; quality of lubricants.
I. INTRODUCTION
Biofuels and bio lubricants are widely entering the
market, especially the liquid fuel market. Biofuels and bio
lubricants are compatible with existing engines and vehicles,
but produced from organic material (waste agricultural
products, sunflower, rapeseed oil, etc.). Therefore, they are
far more environment-friendly, whereas they are capable of
producing similar energy values with ordinary fuels.
Plantohyd lubricants are products based on synthetic
esters, providing an alternative to petroleum-based hydraulic
oils (e.g. [1]).
The main advantages of these lubricants are:
• Excellent composting - 90% for 14 days;
• Excellent resistance to aging and oxidation;
• Good viscosity–temperature dependence.
Plantohyd hydraulic lubricants are suitable for all mobile
and stationary hydraulic equipment in vehicles and industry.
Their use is recommended especially when there is a danger
of leakage of hydraulic and lubricating oisl in soil,
groundwater or surface water.
To maintain their production properties, they must be
used independently and not in combination with petroleum-
based oils. They can be applied in a wide temperature range
from -35
o
C to +90
o
C, covered by different Plantohyd types.
There is little information for the energetic values of
different lubricants. Changing other characteristics of
the lubricants depending on temperature, pressure
during use and storage conditions has also met limited
investigation.
Measurements were conducted in the scientific laboratory of
the Department of Physics of the Slovak University of
Agriculture in Nitra. We measured the specific heat of
combustion of three Plantohyd samples and of the
dependence of rheological characteristics-dynamic
viscosityη , kinematic viscosity ν , fluidity φ and density
ρ on temperature .t Measurement methods of thermo-
physical properties and their theoretical principles can be
found in [2-5]
II. THEORETICAL BASE
Basic physical processes that can be used to measure the
influence of temperature on physical properties of lubricants
are the hot wire method [2] and thermal analysis methods [6].
Among the most common methods of thermal analysis are
the thermo gravimetric analysis, the differential thermal
analysis and the calorimetric differential compensatory
difference.
The main quantity studied in thermal analysis methods is
the change in enthalpy H∆ [3, 7].
A. Specific enthalpy (calorific value of fuels)
The amount of energy generated when a unit mass of fuel
is burned completely is known as the calorific value of the
fuel. Enthalpy is a measure of the energy content in a
thermodynamic (TD) system. For each balance state of the
TD system, specific enthalpy has a specific value. The value
of enthalpy and its change depend on the initial and final
state of the TD system, rather than the intermediate states [4].
Specific enthalpy is the enthalpy per unit mass[ ]
kJ
h
kg
= .
The change of specific enthalpy determines the heat
released from the system at a fixed process. The release
during the combustion of fuel energy transfers the products
of combustion, which leads to a change in its enthalpy.
Enthalpy of combustion is defined as the difference
between the enthalpy of the products and the enthalpy of
ETASR - Engineering, Technology & Applied Science Research Vol. 3, �o. 3, 2013, 424-428 425
www.etasr.com Kardjilova et al.: Influence of Temperature on Energetic and Rheological Characteristics…
reagents when complete combustion occurs at a given
temperature and pressure [4].
In the combustion, the calorimeter technique is adopted to
determine the enthalpy of combustion products that result
from the fuel unit.
Enthalpy-energy diagrams, with graphical interpolation
for intermediate values, can be used to determine the
enthalpy of combustion products at different temperatures,
excess air in the construction of thermal balance and the
related thermo calculations of combustion.
In many cases however, the enthalpy of combustion,
which can be experimentally determined, is used for
energetic analysis when the enthalpy formation data are not
directly accessible
Fast and precise enough measurement of the specific
enthalpy (calorific value of fuels) can be acquired with a
C5000 calorimeter.
B. Rheological characteristics
Rheology is a branch of physics, which deals with the
ways in which materials and fluids deform in response to
applied forces or stress [8]. Newton formulated the law for an
ideal fluid: shear stress between layers is proportional to the
velocity gradient, ∂u/∂y, in a direction perpendicular to the
layers, in other words, the relative movement of layers.
u
y
τ η
∂
=
∂
(1)
Here, the constant η is the coefficient of viscosity
(viscosity) or dynamic viscosity.
Many fluids, such as water, satisfy Newton's criterion and
are known as Newtonian fluids. Non-Newtonian fluids
exhibit a more complex relationship between shear stress and
velocity gradient. In some cases, the ratio of inertial
resistance is calculated using fluid density ρ. Kinematic
viscosity is determined by:
η
ν
ρ
= (2)
Reciprocal value of viscosity determines the fluidity
1
η
ϕ = (3)
It is known that dynamic viscosity changes with
temperature, which means that this impact will also occur in
kinematic viscosity and fluidity.
Theoretical and experimental studies show that this
dependence is exponentially or linearly decreasing for η and
ν and linearly or exponentially increasing for φ [8, 9].
The dependencies are determined by the kind of the
substance and the manner of processing and storage. This
means that many different fluids are required in order to
investigate the dependency of rheological properties on
temperature.
III. MODEL AND METHOD OF MEASUREMENT
Three samples of Plantohyd (15S, 46S and 40N) were
examined.
Measurements were made under laboratory conditions in
air temperature t=21
o
C, atmospheric pressure and normal
humidity ω=56%.
All calorie values are measured two times and all
rheological three times. The presented results are average
values.
A. Measurement of energy values
Measurements are performed with an IKA Calorimeter
system C5000 control (C5040 CalWin) [3, 7]. The selected
operating condition is adiabatic. Calibration of the apparatus
is conducted before the measurement, in order to achieve a
high degree of precision and accuracy
The masses of the samples are measured with a digital
balance accurate to 0.0001 g and then the samples are placed
in a calorimetric bomb in which the combustion process
takes place, under certain conditions. The specific heat of
combustion is calculated based on data obtained for the mass
of the samples, the heat capacity of the calorimeter and the
temperature rise of the water in the calorimeter.
B. Measurement of rheological values
Measurements are made with a DV-3P Anton Paar digital
viscometer, which is a rotational viscometer [8]. It holds and
operates on the principle of measuring the torsion force as a
function of resistance, which has a model for the rotation of
the cylinder or spindle immersed in the sample. Viscosity is
calculated from the measured values. The combination of
spindles (R2, R3) and speed allows an optimal choice for
measuring viscosity.
Measurements of viscosity should be conducted in
laminar flow, which requires a specific time (in our case 2
minutes). There should be no air bubbles in the model. It
should have a uniform texture and should be free of
mechanical impurities. The temperature must be constant
throughout the volume of the sample. Only under these
conditions, the measured value of viscosity can be considered
correct. The density of the samples is measured using the
pycnometric method and a calibrated pycnometer with a
volume of 50 ml.
The dynamic viscosity of the three samples was measured
at different temperatures. For the same temperature range, we
measured the densities of the samples and calculated
kinematic viscosity and fluidity.
IV. RESULTS
The energetic values of the three Plantohyd samples are
shown in Table I.
The kinematic viscosity and fluidity are calculated from
the measured dynamic viscosity and density of the three
samples.
Graphs are constructed using the Grafer software, and the
mode of the functional dependence and the coefficient of
determination are calculated. The results are presented in
Table II to VIII and in Figures 1 to 4.
ETASR - Engineering, Technology & Applied Science Research Vol. 3, �o. 3, 2013, 424-428 426
www.etasr.com Kardjilova et al.: Influence of Temperature on Energetic and Rheological Characteristics…
TABLE I. MEASURED ENERGETIC VALUES OF THREE PLANTOHYD
SAMPLES
Type ( )m g ( / )H J g / )(H MJ kg
0.2363 37511
Plantohyd 15S
0.5100 37345
37.428
0.2667 39521
Plantohyd 46S
0.5554 39457
39.483
0.3334 39466
Plantohyd 40N
0.5963 39378
39.417
TABLE II. MEASURED VALUES OF , , ,η ν ϕ ρ - PLANTOHYD 15S
( )
o
t C
ρ
3
( / )kg m
η
( )mPa s⋅
ν
2 6( / 10 )m s
−
⋅
φ
1 1
( )Pa s
− −
⋅
-10 939.974 79.3 84.41 12.61
-5 937.897 75.8 80.87 13.19
0 934.776 62.4 66.77 16.03
5 931.656 57.1 61.26 17.51
10 928.537 51.2 55.17 19.53
20 922.298 45.9 49.79 21.79
30 913.980 35.5 38.84 28.17
40 908.781 24.0 26.41 41.67
50 902.542 21.7 23.99 46.08
TABLE III. MEASURED VALUES OF , , ,η ν ϕ ρ - PLANTOHYD 46S
( )
o
t C ρ
3
( / )kg m
η
( )mPa s⋅
ν
2 6( / 10 )m s
−
⋅
φ
1 1
( )Pa s
− −
⋅
-10 927.497 216.4 233.30 4.62
-5 926.457 166.3 179.50 6.01
0 925.417 122.5 132.37 8.16
5 924.378 102.2 110.55 9.78
10 922.298 84.6 91.70 11.81
20 913.980 61.2 66.95 16.34
30 907.741 50.9 56.05 19.65
40 900.462 43.2 48.01 23.15
50 896.303 37.6 41.95 26.59
TABLE IV. MEASURED VALUES OF , , ,η ν ϕ ρ - PLANTOHYD 40N
( )
o
t C ρ
3
( / )kg m
η
( )mPa s⋅
ν
2 6
( / 10 )m s
−
⋅
φ
1 1
( )Pa s
− −
⋅
-10 934.776 233.7 239.30 4.28
-5 937.696 174.7 186.30 5.37
0 930.616 132.3 142.16 7.56
5 926.457 93.7 10109 10.67
10 922.298 69.8 75.73 14.33
20 918.139 54.9 59.79 18.21
30 906.701 47.5 52.39 21.05
40 904.621 39.3 43.45 25.45
50 897.343 36.2 40.38 27.62
TABLE V. RESULTS FOR FUNCTIONAL DEPENDENCE AND COEFFICIENT
OF DETERMINATION FOR DENSITY ( )f tρ =
Type Equation Association coefficient
15S Y= -0.642x + 934.4 R
2
= 0.997
46S Y= -0.566x + 924.8 R
2
= 0.974
40N Y= -0.675x + 930.3 R
2
= 0.976
TABLE VI. RESULTS FOR FUNCTIONAL DEPENDENCE AND COEFFICIENT
OF DETERMINATION FOR DYNAMIC VISCOSITY ( )f tη =
Type Equation Association coefficient
15S
Y= -0.000x
3
+ 0.015x
2
- 1.369x +
64.87
R
2
= 0.986
46S
Y = -0.001x
3
+0.181x
2
- 6.447x +
129.4
R
2
= 0.997
40N
Y= -0.002x
3
+ 0.236x
2
- 7.761x +
129.8
R
2
= 0.997
TABLE VII. RESULTS FOR FUNCTIONAL DEPENDENCE AND COEFFICIENT
OF DETERMINATION FOR KINEMATIC VISCOSITY ( )f tν =
Type Equation
Association
coefficient
15S
Y= -1E-10x
3
+ 2E-08x
2
- 1E-06x +
7E-05
R
2
= 0.985
46S
Y = -2E-09x
3
+ 2E-07x
2
- 7E-06x +
0.000
R
2
= 0.997
40N
Y= -2E-09x
3
+ 2E-07x
2
- 8E-06x +
0.000
R
2
= 0.997
TABLE VIII. RESULTS FOR FUNCTIONAL DEPENDENCE AND COEFFICIENT
OF DETERMINATION FOR FLUIDITY ( )f tϕ =
Type Equation Association coefficient
15S Y = 15.35e
0.022x
R
2
= 0.983
46S Y = 0.374x + 8.184 R
2
= 0.998
40N Y = 0.411x + 8.547 R
2
= 0.984
Fig. 1. Dependence of density on temperature.
Fig. 2. Dependence of dynamic viscosity on temperature.
ETASR - Engineering, Technology & Applied Science Research Vol. 3, �o. 3, 2013, 424-428 427
www.etasr.com Kardjilova et al.: Influence of Temperature on Energetic and Rheological Characteristics…
Fig. 3. Dependence of kinematic viscosity on temperature.
Fig. 4. Dependence of fluidity on temperature.
A. Analysis of results
The results for the energetic values show that they are
very close for both Plantohyd 46S and 40N and lower for
15S.
Constructed graphs of the dependence of density on
temperature show a linear decreasing function for all three
samples.
Dependence is:
( )tBA −=ρ (4)
where A and B are constants that depend on the type of
substance.
The values of densities fall in the following ranges:
• Plantohyd 15S: from 939.97 kg/m
3
at -10
0
C to
902.54 kg/m
3
at +50
0
C.
• Plantohyd 46S: from 927.50 kg/m
3
at -10
0
C to
896.30 kg/m
3
at +50
0
C.
• Plantohyd 40N: from 934.78 kg/m
3
at -10
0
C to
897.34 kg/m
3
at +50
0
C.
It can be seen from the graphs that Plantohyd 46S and
40N have slightly different densities after +400C, and that
Plantohyd 15S has the highest density values.
Our results for Plantohyd densities are comparable to
results given in reference books (for Plantohyd 46S: 921
kg/m
3
, for Plantohyd 40N: 922 kg/m
3
, data for Plantohyd 15S
were not found, but for Plantohyd 32S density is 921 kg/m
3
).
The results for η show that dependence on t is not
exponential and not linear. It rather follows a cubic decrease.
Dependence is:
( ) ( ) ( )
2 3
C D t I t F tη = − + − (5)
where C, D, F and I are constants that depend on the type of
substance.
The values of dynamic viscosity for Plantohyd 46S and
40N are close:
• Plantohyd 46S: 216.4 mPa·s at -10
0
C to 37.6 mPa·s
at +50
0
C.
• Plantohyd 40N: 233.7 mPa·s at -10
0
C to 36.2 mPa·s
at +50
0
C.
Significantly, lower values of dynamic viscosity are
for Plantohyd 15S: 79.3 mPa·s at -10
0
to 21.7 mPa·s at +50
0
C.
Similar results can be seen for the dependence of
kinematic viscosity on temperature. Decreasing dependence
is cubic.
Dependence is
( ) ( ) ( )
2 3
G H t M t * tν = − + − (6)
G, H, M and * are constants that depend on the type of
substance.
Values for 46S and 40N are relatively close, and those for
15S are smaller. The results are as follows:
• Plantohyd 46S: 233.3·10
-6
m
2
/s at -10
0
C and 41.9·10
-
6
m
2
/s at +50
0
C.
• Plantohyd 40N: 239.3·10
-6
m
2
/s at -10
0
C and
40.4·10
-6
m
2
/s at +50
0
C.
• Plantohyd 15S: 84.4·10
-6
m
2
/s at -10
0
C and 23.9·10
-6
m
2
/s at +50
0
C.
Comparison of the results can be made with the given
values of kinematic viscosity characteristics of those
lubricants at 40
0
C.
• Plantohyd 46S: 48.8·10
-6
m
2
/s – our calculatted value
is 48.01·10
-6
m
2
/s.
• Plantohyd 40N: 42·10
-6
m
2
/s - our calculatted value is
43.4·10
-6
m
2
/s.
• Plantohyd 15S: no evidence for kinematic viscosity.
The dependence of fluidity on temperature is a linearly
increasing function of Plantohyd 46S and Plantohyd 40N.
Dependence is:
( )K L tϕ = + (7)
Dependence for Plantohyd 15S is:
( )expK L tϕ = (8) ,
K and L are constants that depend on the type of substance.
These functions are not differing significantly at
temperatures from -10
0
C to +10
0
C. The obtained values for
fluidity are:
ETASR - Engineering, Technology & Applied Science Research Vol. 3, �o. 3, 2013, 424-428 428
www.etasr.com Kardjilova et al.: Influence of Temperature on Energetic and Rheological Characteristics…
• Plantohyd 46S: from 4.62 Pa
-1
·s
-1
at -10
0
C to 26.59
Pa
-1
·s
-1
at +50
0
C.
• Plantohyd 40N: from 4.28 Pa
-1
·s
-1
at -10
0
C to 27.62
Pa
-1
·s
-1
at +50
0
C.
The dependence of fluidity on temperature for Plantohyd
15S is an exponentially increasing function.
The obtained values for fluidity are from 12.61 Pa
-1
·s
-1
at
-10
0
C to 46.08 Pa
-1
·s
-1
at +50
0
C.
V. CONCLUSION
Lubricants are classified by their two main
characteristics: viscosity and operational level - the kinematic
viscosity. The physical interpretation of the results of energy
values and the dependence of rheological properties on
temperature can be used to assess the quality of lubricants.
Using bio lubricants helps to lubricate the engine, providing
longer engine and segment life. Suitability for use of a bio
lubricant is estimated with the help of certain criteria. As one
of the roles of fuel and lubrication is its function, the change
of its viscosity and its density are indicative of a change in
quality. The viscosity values show the ability to withstand
and protect against wear and corrosion. The results presented
in this paper can be useful for manufacturers of similar
synthetic oils and could be used by the automotive and
mechanical engineering industry, which uses similar
lubricants. Further, the data obtained can be used in
technological processes as well as for studying the physical
properties of biо lubricants which would allow the
development of new technologies using bioenergetics
conversion and use of bio lubricants with better performance.
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