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Research of the heat transfer coefficient in different connection schemes for radiators

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Increasing the energy efficiency in the residential and public buildings is an object of observation and impact not only on national level but also on international as well. In the recent years a number of normative documents, measurements for support and financing in this direction have been accepted in Bulgaria. According to Eurostat’s data, the buildings and more especially the residential buildings are the one which have the highest energy consumption in the EU, followed by the transport and industry sectors. The households are the sector with the greatest potential for energy savings in Europe, for them 79% of the total energy consumption is due to the heating and the hot water mainly. The energy savings from building renovations are usually result from improvement of the insulation, heating and cooling systems and electric light. In the present article an experimental study was made to establish the dependence of the heat transfer coefficient in the different schemes of connections on the radiators in order to optimize it and achieving more complete absorption of the supplied heat energy. This research was made within the student’s thesis and to carry it out an operating installation was used in the laboratory of “Heating engineering” at the Faculty of “Technics and Technology” – Yambol. The realized connection schemes of the radiators in the experiments are “up-down” and “down-up”. The methology includes monitoring the ambient temperature, regulating the power of the electric heaters of the heating source, taking into account the inlet and outlet temperatures and the temperature profile of the radiators. Based on the obtained results and done analysis, conclusions for increasing the energy efficiency of a specific radiator by changing the scheme of its connection to the heating network have been formulated.
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RESEARCH ARTICLE | DE CE MB ER 0 7 20 23
Research of the heat transfer coefficient in different
connection schemes for radiators
Vasil Hristov ; Petko Tsankov
AIP Conf. Proc. 2889, 070002 (2023)
https://doi.org/10.1063/5.0172826
20 December 2023 10:16:08
Research of the Heat Transfer Coefficient in Different
Connection Schemes for Radiators
Vasil Hristov1, a) and Petko Tsankov2, b)
1 Faculty of “Technics and Technology, Trakia University, Bulgaria, №38 Graf Ignatiev street, 8600 Yambol,
Bulgaria
2 Faculty of “Technics and Technology”, Trakia University, Bulgaria, №38 Graf Ignatiev street, 8600 Yambol,
Bulgaria
a) Corresponding author: angmar1993@abv.bg
b) ptsankov@abv.bg
Abstract. Increasing the energy efficiency in the residential and public buildings is an object of observation and impact
not only on national level but also on international as well. In the recent years a number of normative documents,
measurements for support and financing in this direction have been accepted in Bulgaria. According to Eurostat’s data,
the buildings and more especially the residential buildings are the one which have the highest energy consumption in the
EU, followed by the transport and industry sectors. The households are the sector with the greatest potential for energy
savings in Europe, for them 79% of the total energy consumption is due to the heating and the hot water mainly. The
energy savings from building renovations are usually result from improvement of the insulation, heating and cooling
systems and electric light. In the present article an experimental study was made to establish the dependence of the heat
transfer coefficient in the different schemes of connections on the radiators in order to optimize it and achieving more
complete absorption of the supplied heat energy. This research was made within the student’s thesis and to carry it out an
operating installation was used in the laboratory of “Heating engineering” at the Faculty of “Technics and Technology”
Yambol. The realized connection schemes of the radiators in the experiments are “up-down” and “down-up”. The
methology includes monitoring the ambient temperature, regulating the power of the electric heaters of the heating
source, taking into account the inlet and outlet temperatures and the temperature profile of the radiators. Based on the
obtained results and done analysis, conclusions for increasing the energy efficiency of a specific radiator by changing the
scheme of its connection to the heating network have been formulated.
I. INTRODUCTION
Human heat comfort is often defined as a state of mind and is expressed as satisfaction with the surrounding
environment, according to a definition given by ASHRAE (The American Society of Heating, Refrigerating and
Air-Conditioning Engineers). Maintaining the thermal comfort is one of the most important objectives of the
engineering design of thermal installations, cooling systems and building envelopes. This heat comfort is determined
by the intensity of energy harvest and the heat transfer to maintain the thermal balance. (Kirov, 2012; Krastev et al.,
1987).
Part of this task is to select an appropriate way of connecting the heating bodies to ensure greater energy
efficiency of the heating system used. An important indicator of this is the heat transfer coefficient of the mounted
heaters which is assigned to determine depending on the temperature difference (radiator) - an environment) for
various power heater capacities due to the reason that in this complex process, A determining importance has the
convective heat exchange. It summarizes the influence of all factors on the intensity of the heat flow and is
determined by the heat transfer coefficients on both sides of the wall and from its thermal conductivity. The
International Conference on Technics, Technologies, and Education
AIP Conf. Proc. 2889, 070002-1–070002-11; https://doi.org/10.1063/5.0172826
Published by AIP Publishing. 978-0-7354-4760-8/$30.00
070002-1
20 December 2023 10:16:08
calculation is heavily hampered by the fact that it is necessary to determine the heat transfer coefficients from the
inner and external side of the heater. Complex geometric forms, hydro and aerodynamic flow modes, the presence of
radiation heat exchanges from the outer surface, lead to some insurmountable difficulties or highly simplifying
reception and complex expressions difficult in engineering practice. For the heating body can be demonstrated that
the heat transfer coefficient depends on the temperature operating mode and its geometric characteristics.
This report provides a theoretical and practical task for designing a laboratory stand for simulation of the
operation of electric heating and opportunities for realization of different ways of inclusion of the heating bodies.
The laboratory bench was developed by a diploma project and is located in the Heating Equipment Laboratory at the
Faculty of “Technics and Technology” in Yambol. It can be performed laboratory attempts to determine the heat
transfer coefficient of a heat carrier - water in different types of connections. The implemented binding schemes for
the experiments are "top" and "bottom". The conduct methodology involves monitoring the ambient temperature,
power control of the heating source electric heaters, input temperature and output temperature and the temperature
profile of the heater.
The results obtained proving the connection between the heat transfer coefficient and the temperature operating
mode and the geometric characteristics of the heating bodies.
II. STRUCTURE OF THE LABORATORY BENCH AND A LABORATORY
TEST METHODOLOGY
1. Laboratory Bench - Construction and Principle Scheme
The laboratory bench and the assembly process is shown in Figure 1 and the principle scheme is shown in Figure
2. It is a water-heating system with electrical heating, the heating body connection diagram and consists of a heating
body (panel radiator), three-speed circulation pump, expansion vessel and electric boiler (ELTHERM MM6).
In order to improve the work process of the laboratory bench, new technological elements are installed to serve
and facilitate laboratory tests - manometers (before and after the circulation pump), watt meter (accounting for the
power of the circulating pump), a digital thermometer (environmental temperature measurement ), Autotransformer
(adjusts and takes into account the power of the electric boiler electric heaters), a thermal imaging chamber (taking
the inlet temperature and the output of the heater and shooting the heating dynamics).
FIGURE 1. Laboratory bench
Modernization is also carried out by moving the position of the circulation pump from vertical to the horizontal
position, mounting of the volumetric flowmeter and expanding the tubular network, and connections to the heating
070002-2
20 December 2023 10:16:08
body where different connectivity schemes are carried out, as well as mounting of a new dashboard and connectivity
between it and the control panel and measuring instruments.
2. Test Methology
The methodology for conducting the study consists in determining the heat transfer coefficient by determining
the following quantities (Kostov, 2004; Krastev et al., 1987; Stamov et al., 1990; Stamov et al., 2010; Skanavi et al.,
2008; Jauschowetz, 2004):
temperature of the inlet of the heater -  󰇟󰇠;
temperature of the outlet of the heater -  󰇟󰇠;
temperature of the air in the room - 󰇟󰇠;
mass flow rate - 󰇗 
󰇟
󰇠;
quantity of the heat carrier - V, [dm3];
 - t, [s];
temperature difference of the heat carrier -   
,
[
C];
thermal power of the heater -
󰇗 󰇗   󰇟󰇠;
average surface temperature of the heater -  󰇛󰇜
󰇟󰇠
average area surface temperature measured with a thermal camera -  ,[󰇠
temperature difference (heater, radiator surrounding, premises)
  or 
󰆒

󰆒 󰇟󰇠
area (surface) of the heater -   , [ 󰇠;
heat transfer coefficient of the heater -
󰇛󰇜 or 󰆒
󰇛
󰆓󰇜 󰇟 󰇠

FIGURE 2. Principal scheme of laboratory stand
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20 December 2023 10:16:08
Due to the reason that in this complex process a decisive significance has the convective heat exchange, the heat
transfer factor for this particular heater is determined depending on the temperature difference (heater) for various
power capacities (N 400 ÷ 1000W). It summarizes the influence of all factors on the intensity of the heat flow and is
determined by the heat transfer coefficients on both sides of the wall and from its thermal conductivity. The
calculation is heavily hampered by the fact that it is necessary to determine the heat transfer coefficients from the
inner and external side of the heater.
Complex external geometric forms, hydro and aerodynamic flow modes, the presence of radiation heat
exchanges from the outer surface, lead to certain insurmountable difficulties or highly simplified reception and
complex expressions difficult to use in engineering practice. For the heater can be demonstrated that the heat
transfer coefficient depends on the temperature operating mode and its geometric characteristics.
In Figure 2 is shown the construction scheme of the laboratory bench. The system is filled with water directly
from the central water supply network through the control valve (CV-009) to achieve a certain pressure allowing the
rapid course of the experiment (150 kPA). After filling the system, adjustable cranes are adjusted (CV - 001 ... 008)
to achieve a specified connection scheme (Table 1). After selecting the desired connection schedule, the circulating
pump (P-001) is started. By means of the automatic deaerator (AD-001), air from the system is removed. When
there is no air in the system the electrical boiler (B-001) is started. By means of the mounted manometers before and
after the circulation pump (M-001 and M-002), the pressure in the system is monitored and the flow rate is read with
a volume flowmeter (FM-001). In the event that the pressure in the system increases, the safety valve (SV - 001) set
to 250kpa opens and discharges the network. The power of the circulating pump is monitored by the control panel
(CP-002) to which an energy meter (wattmeter) is fitted and the power of the electric heaters is monitored and
manually set by autotransformer (AT-001).
TABLE 1. Control valves positions in different heating body connection schemes
Scheme
top-bottom
(diagonal)
top-bottom
(unilaterally)
bottom-top
(diagonal)
top-top
bottom-
bottom
CV 001
closed
closed
opened
opened
closed
CV 002
opened
closed
closed
closed
opened
CV 003
opened
opened
closed
opened
closed
CV 005
closed
opened
opened
closed
opened
CV 006
closed
opened
closed
closed
closed
CV 007
closed
closed
opened
closed
opened
CV - 008
opened
opened
closed
opened
closed
3. Terms and Test Modes
The course of the experiments to determine the heat transfer coefficient was carried out as follows:
1. Select the connection scheme of the heater and fill the system with water;
2. Starting the P-001 (circulation pump) and deaeration of the installation;
3. Turning on the boiler heaters;
4. Adjusting the power of the electric heaters and measuring with watt-pliers for confirmation;
5. Measurement of the volumetric flow of the heat carrier with a volumetric flow meter FM-001 and with a
stopwatch;
6. Reporting the environmental temperature and the time pause for temperature balancing (settlement of
constant temperatures);
7. Reporting of the input and output temperatures of the heater at a temperature-based balanced system;
8. Monitoring the process by means of a thermal imaging camera and recording the temperature profile of
the heater;
For each subsequent experiment, the points from 4 till 8 are repeated. The first experiments were accomplished
when connecting the heater in the "top-bottom" scheme, with the total number of all experiments being 24.
070002-4
20 December 2023 10:16:08
Before switching to the system of the next experiment, which was selected, namely "bottom-top" the boiler
heaters were turned off, the exhaust (drainage) valve (CV-004) was manually opened, the circulating pump was
switched on to the highest rate in view of the water continuously to circulate in the system and simultaneously
supply water from the central network. After lowering the temperature in the system, the drain valve closes and the
points 1 ÷ 8 were followed.
III. RESEARCH RESULTS
During the laboratory experiments, the following connection schemes "inlet - outlet" of the heater were
researched - "top-bottom" (diagonal), "bottom-top" (diagonal), "top-bottom" (unilaterally) and "bottom-top" -
"(unilaterally) in different thermal capacities of the heat carrier - the results are presented in Table 2 (Maragkos and
Beji, 2021; Teskeredzic and Blazevic, 2018). The variable environmental temperatures are reported - environment
premise (tп = 28…310С); the variable density of the heat carrier - water (r(t) = 997…975 kg/m³). During each of the
experiments, the dynamics of the heating character was shot with a thermal imaging camera, and the results were
processed using the thermal imaging camera software in view of more accurate measurement of technical
parameters and compiling histograms and temperature profiles (Figure 3, Figure 4). The final results for each
laboratory experience were processed by Excel and represented by summary graphs describing the dependence of
the heat transfer ratio "k" and the temperature difference "heater (radiator) room”– Dtот-п (Mižáková and Pitel,
2017; Petrik et al., 2019).
The area of the heater is:
   (1)
The specificity of this experiment is characterized by the following features:
The process should be stationary, which requires continuous waiting of the measured temperatures to be
settled;
The environment temperature was relatively high -  °C, which further impedes heat exchange
and reduces the temperature difference - ;
A small temperature difference in the heater (  ) 1 ÷ 4 °С, one of the possible solutions
is to increase the temperature difference by significantly reducing (2- 3 times) the mass flow through the
heater;
Results of the experiments are brought into tables and presented as graphical dependence - „k Dtот-п”;
FIGURE 3. Dynamics of “thermal infilling” of the heater with a connection scheme “top-bottom” (diagonal)
070002-5
20 December 2023 10:16:08
FIGURE 4. Dynamics of “thermal infilling” of the heater with a connection scheme “bottom-top” (diagonal)
TABLE 2. Research results and comparative calculations for average temperatures: computing temperature -  and
temperature from thermal imaging- 
N
W
τ
󰇗
tвх
tизх
Δt
󰇗
tот
k


k'

󰆒
W
l
s
kg/s
°C
°C
°C
W
°C
W/m2K
°C
°C
W/m2K
°C
"top-bottom" (diagonal)
400
1
18,1
0,055
49,2
47,5
1,7
392
48,35
15,89
18,35
47,9
16,29
17,9
750
1
15,37
0,065
59,3
56,7
2,6
706
58
18,76
28
56,6
19,75
26,6
1000
1
15,62
0,064
65,1
61,6
3,5
935
63,35
20,86
33,35
62,4
21,48
32,4
"bottom-top" (diagonal)
400
1
17,92
0,056
47,9
46,3
1,6
372
47,1
16,60
16,7
44,2
20,09
13,8
750
1
18,27
0,055
59,4
56,3
3,1
708
57,85
19,19
27,45
53,2
23,11
22,8
1000
1
18,15
0,055
66,4
62,3
4,1
942
64,35
20,66
33,95
58,2
25,23
27,8
"top-bottom" (unilaterally)
400
1
18,91
0,053
42,7
41
1,7
375
41,85
20,16
13,85
41,85
20,16
13,85
750
1
18,31
0,054
53,5
50,4
3,1
706
51,95
21,95
23,95
51,95
21,95
23,95
1000
1
18,48
0,054
60,3
56,2
4,1
926
58,25
22,78
30,25
58,25
22,78
30,25
"bottom-top" (unilaterally)
400
1
18,57
0,054
48,6
46,9
1,7
382
47,75
14,92
19,05
40
25,16
11,3
750
1
18,63
0,054
56,8
53,6
3,2
717
55,2
20,13
26,5
48
27,64
19,3
1000
1
18,52
0,054
73,6
69,4
4,2
946
71,5
16,45
42,8
53
28,98
24,3
In the heat flow studies of the radiator, the temperatures of the heat carrier are measured:
The temperatures of the inlet and outlet of the radiator are measured  и  , and then for an
average temperature of the heater (radiator) is taken the average-arithmetic “inlet-outlet” - 
󰇛 󰇜
;
The average temperature of the heater is measured  , and defined as an average area temperature -
derived from a thermal imaging picture (with the thermal camera: testo 885-2) and processed using the
IRSOFT software;
Table 2 presents the results from the heat transfer coefficient of the heating body (radiator) in different: heat flow
capacities 󰇗, with different radiator connection schemes, in different methods of reading the average temperature of
the heating unit - by  and . The graphic dependencies of the heat transfer coefficient depending on the
070002-6
20 December 2023 10:16:08
temperature difference "heater-premises"-k - Dtот-п и k Dtот-п for  and  are represented in
Figure 5 and Figure 6.
(a)
(b)
(c)
(d)
FIGURE 5. Graphic dependencies of the heat transfer coefficient depending on the temperature difference "heater-premises"
(average-arithmetic) - k Dtот-п” in different connection schemes: (а) top-bottom (diagonal), (b) bottom-top (diagonal), (c)
top-bottom “(unilaterally), (d)bottom-top “(unilaterally)
(a)
(b)
y = 0,3273x + 9,8154
R² = 0,9943
0
10
20
30
010 20 30 40
к, (W/ м2.К)
𝑡
от-п
, 0С
k - Dtот-п
k-T
y = 0,236x + 12,681
R² = 0,9997
0
10
20
30
010 20 30 40
к, (W/ м2.К)
𝑡
от-п
, 0С
k - Dtот-п
k-T
y = 0,1614x + 17,971
R² = 0,9939
0
10
20
30
010 20 30 40
к, (W/ м2.К)
𝑡
от-п
, 0С
k - Dtот-п
k-T
y = -0,0389x2+ 2,4715x - 18,033
R² = 1
0
10
20
30
020 40 60
к, (W/ м2.К)
𝑡
от-п
, 0С
k - Dtот-п
k-T
y = 0,3606x + 9,9338
R² = 0,9944
10
15
20
25
30
010 20 30 40
к', (W/ м2.К)
𝑡
от-п
, 0С
k' -Dt'
от-п
k-T
y = 0,3635x + 15,012
R² = 0,996
10
15
20
25
30
010 20 30
к', (W/ м2.К)
𝑡
от-п,
0С
k' -Dt'от-п
k-T
070002-7
20 December 2023 10:16:08
(c)
(d)
FIGURE 6. Graphic dependencies of the heat transfer coefficient depending on the temperature difference "heater-premises"
(average area temperature derived from a thermal image camera) k Dtот-п in different connection schemes: (a) top-
bottom (diagonal), (b) bottom-top (diagonal), (c) top-bottom(unilaterally), (d) bottom-top(unilaterally)
IV. CONCLUSION
In the methodology for determining the heat transfer coefficient of the radiator K is used the temperature
difference of the average temperature (radiator) and the environment (in the room) - . Simultaneously, this
temperature difference can be determined on two average temperatures - the average-arithmetic calculated at the
"inlet-outlet" temperatures -  and the average measurement with the thermal imaging camera (average area) -
. When asked whether there is a difference in these temperatures and which results are reliable, we can conclude
that:
1. There is a difference in the determination of the average temperature in the radiator in both ways -
comparison of these temperatures in the various connections and capacities are given in Table 3.
TABLE 3. Comparison of the average temperatures  и  in various connections and capacities
Connection
scheme
Top-bottom
(diagonal)
Bottom-top
(diagonal)
Top-bottom
(unilaterally)
Bottom-top
(unilaterally)
Capacity (W)
400
750
1000
400
750
1000
400
750
1000
400
750
1000

48,4
58
63,4
47,1
57,9
64,4
41,9
52
58,3
47,8
55,2
71,5

47,9
56,6
62,4
44,2
53,2
58,2
41,6
51,9
58
40
48
53
t
0,5
1,4
1
2,9
4,7
6,2
0,3
0,1
0,3
7,8
7,2
18,5
When there is top submission of the heat carrier ("top-bottom" (diagonal) or "top-bottom” (unilaterally")) this
difference (on Table 3) t is less, but at the bottom submission of the heat carrier (“bottom-top” (diagonal) “or
“bottom-top (unilaterally)) the temperature difference increases slightly - t = 3 8 °С, and for cases where the
capacity is high - t = 18,5 °С. In Figure 7 is depicted the physical explanation of the specific laboratory
experiments.
Submission of the heat carrier to the heating body "top" and its downward movement is mixing" more
intensively the hot carrier which is raising up by the convective flows. This results in a more even temperature field
along the entire surface of the heater. Then the average temperatures defined as: the average-arithmetic "inlet-outlet"
 and the average area surface temperature measured with a thermal camera  are almost the same (the deviation
is only t = 0,31 °С). The physical effect is more important - even heating of the radiator and a uniform
temperature field in which there are no overheating and reduced temperatures and the temperature of the entire
heater is almost constant. - tср-п const. (Figure.7 (a) and (b)).
y = 0,1481x + 18,503
R² = 0,9992
10
15
20
25
30
010 20 30 40
к', (W/ м2.К)
𝑡
от-п
, 0С
k' -Dt'от-п
k-T
y = 0,2956x + 21,854
R² = 0,9986
10
15
20
25
30
010 20 30
к', (W/ м2.К)
𝑡
от-п
, 0С
k'-Dt'от-п
k-T
070002-8
20 December 2023 10:16:08
Conversely: the submission of the heat carrier in the heating body "bottom" and its leakage "top" refers naturally,
caused by the convective flow where the hotter upper layer of the heat carrier moves directly towards to the outlet of
the heating body. This worsens the heat exchange in it by creating areas with different temperatures, significantly
increases the differences in the medium temperature of the heating unit as defined as  and - or the real
temperature in the heating body in different areas is different from the average - tср-п  ( Figure.7 (c) and
(d)).
FIGURE 7. Scheme of fluid and thermal streams at different heating body connections
2. True, more credible for use in further calculations is the average temperature , determined by the average
thermal imaging indication for the whole heating body. This is because the heating is from the entire surface
of the heater, including from a higher or lower temperature zones. In Figure 8 are shown the thermal
imaging pictures of extremely established heating of a heating body in different connection schemes which
are very well outlined:
The even distribution of the radiator's surface temperature in schematic: "top-bottom" (diagonal)
(Figure 8 (a)) and "top-bottom" (unilaterally) (Figure 8 (c));
The uneven distribution of the surface temperature of the radiator in schematic: "bottom-top" (diagonal)
(Figure 8 (b)) and "bottom-top" (unilaterally) (Figure 8 (d));
FIGURE 8. Thermal images of extremely established heat transfer of a heating body in different binding schemes
3. The average heating body temperature  is influencing the heat transfer coefficient of the radiator :
󰆒
󰆓 , 
(2)
070002-9
20 December 2023 10:16:08
Figure 9 represents the dependence of the heat transfer coefficient of the radiator  at different connection
scheme and temperature differences . In the case of more correct reading of the average temperature of the
radiator by  the studies show that the heat transfer ratio of the radiator is greater when applying the heat carrier
under the "bottom" scheme. The summary results are also given in Table 4.
FIGURE 9. Dependence of the heat transfer coefficient of a heating body at different connections
TABLE 4. Values of  and k at different connections of the heating body
Connection
scheme and
power capacity
Top-bottom
(diagonal)
Bottom-top
(diagonal)
Top-bottom
(unilaterally)
Bottom-top
(unilaterally)
400
750
1000
400
750
1000
400
750
1000
400
750
1000
 (0С)
47,9
56,6
62,4
44,2
53,2
58,2
41,6
51,9
58
40
48
53
k' , (W / m2.K)
16,3
19,8
21,5
20,1
23
25,2
20,5
22
23
25,2
27,6
29
The results for the larger values of the heat transfer coefficient in the "bottom" connection schemes of the
radiator should not deceiving. The uneven heating of the heating body when the connecting scheme is „bottom “,
also has a very uneven heat transfer coefficient in different radiator zones. Parts of the heater have a very high heat
flow temperature and others with a significantly lower one. The majority of the heating body has reduced
temperature indicators, resulting in an average higher heat transfer coefficient factor for the whole heating body.
4. From the graphical depiction of the experimental results, it is clearly visible that the heat transfer ratio
(regardless of the mode of connection) is increasing linearly with the heating of the heating body. In this, the
inclination of these linear dependencies is the same because the researched heating body is one.
5. In the research where the thermal imaging camera was used, dynamic studies of the initial heating process
("thermal filling") of the heater were made. The received videos give a very visual and accurate picture of:
Possible areas of non-compliant or degraded heat - "air pockets" or for various reasons "dead zones";
Different temperature zones at the beginning of the process or zones of substantial temperature differences
(t) caused by low heat carrier circulation;
Time for full or terminal tempering - establishing a permanent, constant over time temperature at different
points of the test radiator;
y = 0,3418x + 9,7497
R² = 0,9993
y = 0,3635x + 15,012
R² = 0,996
y = 2,9923ln(x) + 12,673
R² = 0,9852
y = 0,2956x + 21,854
R² = 0,9986
0
5
10
15
20
25
30
35
0 5 10 15 20 25 30 35
k', (W/ м2.К)
D
t'от-п,0С
k' -𝑡'от-п
Top-bottom (diagonal) Bottom-top (diagonal)
Top-bottom (unilaterally) Bottom-top (unilaterally)
070002-10
20 December 2023 10:16:08
V. REFERENCES
1. Kirov, D. (2012). Heat holding. Technica, Sofia. ISBN-978-954-03-0701-5, №17992; (Kirov, 2012)
2. Kostov, P. (2004). Heat- and mass transfer. Sliven.
3. Krastev, Zh., Markov, V., & Chotorov, D. (1987). Technical thermodynamics and heat transfer. Technica,
Sofia. UC-536(075.8), №13737.
4. Stamov, S., Sendov, S., Nachev, N., Markov, A., Stoichkov, N., Kirii, A., Carlson, V., & Kirov, D. (1990).
Guidebook of Heating, ventilation and air conditioning. Part I. Fundamentals of heating and ventilation.
Technica, Sofia. UC 697:828.8, №16001.
5. Stamov, S., Aleksiev, N., Shushulov, K., Kirov, D., Zhechkov, N., Kadiiski, S., Kamburov, K., & Stankov, A.
(2010). Guidebook of Heating, ventilation and air conditioning. Part II. Heating, heat- and gas supply.
Technica, Sofia. ISBN-965-03-0601-9(part.2).
6. Skanavi, A. N., & Mahov, L. M. (2008). Heating educational book for universities. Moscow: ASB. ISBN-
978-5-93093-161-5.
7. Jauschowetz, R. (2004). Das HERZ der Warmwasserheizung die Hydraulik. Herz Armaturen Ges.m.b.H,
Wien.
8. Mižáková, J., & Piteľ, J. (2017). An analytical dynamic model of heat transfer from the heating body to the
heated room. MATEC Web of Conferences, 125, 02047. https://doi.org/10.1051/matecconf/201712502047
9. Petrik, M., Szepesi, G., & Jármai, K. (2019). CFD analysis and heat transfer characteristics of finned tube
heat exchangers, Pollack Periodica Pollack Periodica, 14(3), 165-176. doi:
https://doi.org/10.1556/606.2019.14.3.16
10. Maragkos, G., & Beji, T. (2021). Review of Convective Heat Transfer Modelling in CFD Simulations of Fire-
Driven Flows. Applied Sciences, 11(11), 5240. https://doi.org/10.3390/app11115240
11. Teskeredzic, A., & Blazevic, R. (2018). Transient Radiator Room HeatingMathematical Model and Solution
Algorithm. Buildings, 8(11), 163. https://doi.org/10.3390/buildings8110163
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20 December 2023 10:16:08
ResearchGate has not been able to resolve any citations for this publication.
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Guidebook of Heating, ventilation and air conditioning. Part I. Fundamentals of heating and ventilation
  • S Stamov
  • S Sendov
  • N Nachev
  • A Markov
  • N Stoichkov
  • A Kirii
  • V Carlson
  • D Kirov
Stamov, S., Sendov, S., Nachev, N., Markov, A., Stoichkov, N., Kirii, A., Carlson, V., & Kirov, D. (1990). Guidebook of Heating, ventilation and air conditioning. Part I. Fundamentals of heating and ventilation. Technica, Sofia. UC 697:828.8, №16001.
Technical thermodynamics and heat transfer
  • Zh Krastev
  • V Markov
  • D Chotorov
Krastev, Zh., Markov, V., & Chotorov, D. (1987). Technical thermodynamics and heat transfer. Technica, Sofia. UC-536(075.8), №13737.
Guidebook of Heating, ventilation and air conditioning. Part II. Heating, heat-and gas supply
  • S Stamov
  • N Aleksiev
  • K Shushulov
  • D Kirov
  • N Zhechkov
  • S Kadiiski
  • K Kamburov
  • A Stankov
Stamov, S., Aleksiev, N., Shushulov, K., Kirov, D., Zhechkov, N., Kadiiski, S., Kamburov, K., & Stankov, A. (2010). Guidebook of Heating, ventilation and air conditioning. Part II. Heating, heat-and gas supply. Technica, Sofia. ISBN-965-03-0601-9(part.2).
Heat holding. Technica, Sofia
  • D Kirov
Kirov, D. (2012). Heat holding. Technica, Sofia. ISBN-978-954-03-0701-5, №17992; (Kirov, 2012)
Heat-and mass transfer
  • P Kostov
Kostov, P. (2004). Heat-and mass transfer. Sliven.
Heating -educational book for universities
  • A N Skanavi
  • L M Mahov
Skanavi, A. N., & Mahov, L. M. (2008). Heating -educational book for universities. Moscow: ASB. ISBN-978-5-93093-161-5.