Journal of Minerals and Materials Characterization and Engineering, 2012, 11, 800-806
Published Online August 2012 (
Finite Element Modeling of Low Heat Conducting
Building Bricks
Oluleke Oluwole*, Jacob Joshua, Henry Nwagwo
Department of Mechanical Engineering, University of Ibadan, Ibadan, Nigeria
Email: *
Received April 3, 2012; revised May 13, 2012; accepted June 9, 2012
Heat conduction through conventional and interlocking building bricks with cavities was studied in this work. Heat
transfer analysis was carried out using MATLAB® partial differential equation toolbox. Regular and staggered hole
arrangements were studied. Results showed that four staggered holed interlocking bricks were effective in thermal re-
sistance into the bricks and increasing the holes beyond four did not give any thermal resistance advantage. For the
conventional bricks staggered holes did not give any thermal resistance advantage but the four-holed bricks were also
adjudged to be effective in thermal resistance into the brick surface. Increasing the number of holes beyond four in
conventional bricks did give some thermal resistivity advantage but very minimal. Structural strengths of holed bricks
were not considered in this study.
Keywords: Building Bricks; Finite Element Modeling; Heat Conduction
1. Introduction
The conventional old form of building bricks in the trop-
ics with two rectangular cavities are known for their high
heat conduction property which causes so much discom-
fort in homes especially in hot and arid areas of the world.
From an economic and environmental conservation point
of view, it is more beneficial to design buildings with
high thermal insulation characteristics than the old prac-
tice currently followed in the construction of buildings.
This will result in long-term benefit of reducing the cost
of cooling as well as reducing the pollution of the envi-
ronment due to heavy use of fuel. Use of double skin
walls with insulating materials like chip boards contrib-
utes to some extent in reducing the high cost of air con-
ditioning in summer. These materials due to their high
cost are limited to government offices and commercial
complexes. However, in residential buildings, schools
and other constructions, the use of such systems is not
recognized and the traditional method of construction is
still dominant. It is well known that the thermal conduc-
tivity of concrete is much higher than the thermal con-
ductivity of air. By introducing holes or air-gaps in the
concrete block, the thermal conductivity of concrete
block can be greatly reduced.
Lacarrier et al. [1] analyzed numerically the vertically
perforated bricks. They reported that walls can be con-
structed without any other materials than clay and mortar.
They reported that heat transfer in these assemblies is not
totally understood. For perforated brick construction, it is
indicated that convection heat transfer is negligible in the
perforations. Therefore, the thermal resistance of the
brick increases. In a particular study of the ruptures it is
concluded that the convection present in these regions is
a local phenomenon since it breaks the thermal bridges
created by the mortar fill.
Bajorek and Lloyd [2] carried out an experimental
study to investigate the natural convection heat transfer
within a two dimensional partitioned enclosure of unit
aspect ratio using an interferometer. They reported that
dividing the cavity along its 5th European Thermal-Sci-
ences Conference, The Netherlands, 2008 vertical axis
results in a reduction in the heat transfer by approxi-
mately 15%.
Nishimura et al. [3] reported that Nusselt number is
inversely proportional to the number of partitions which
was also confirmed by experiments. They also observed
that effective heat leak reduction is attained using 2 - 5
Aviram et al. [4] investigated experimentally variable
aspect ratio cavity and reported that increasing aspect
ratio decreases flow magnitude, reduces circulation in-
tensity and increases the cavity thermal resistance. Nus-
selt number diminished with reduced cavity depth.
Recently, del Coz Diaz et al. [5] carried out an ex-
perimental and numerical study to investigate the thermal
transmittance coefficient, U, of a wall made of Arliblock
*Corresponding author.
Copyright © 2012 SciRes. JMMCE
bricks. They observed that wall insulation decreases with
the increase in the mortar and material conductivities.
They also noticed that changing the profiles of the holes
alters the rate of the heat transfer through the hollow
blocks. Then, they studied major variables influencing
the thermal conductivity of masonry materials and car-
ried out an optimization study for different brick geome-
tries based on both thermal resistance and weight [6].
The minimum web thickness for safe construction was
reported by Kumar [7]. Ciofalo and Karayiannis [8] re-
ported that the mechanism responsible for the large re-
duction in heat transfer in partitioned enclosures was
because of the breaking down of the unicellular circula-
tion near the regions.
Manz [9] studied natural convection heat transfer in
rectangular, gas-filled tall cavities in building elements
such as insulating glazing units, double-skin facades and
others. He reported that flow regimes depend on Ra and
the aspect ratio. A linear temperature profile exists as a
function of the x-position within the so-called conduction
Al-Hazmy [10] investigated the heat transfer through a
common hollow building brick. Insulation assessment of
the building blocks was examined based upon the heat
transfer rate. Three different configurations for building
bricks were studied including a gas-filled and insulation-
filled cavity. Results show that the cellular air motion
inside blocks’ cavities contributes significantly to the
heat loads. The insertion of polystyrene bars reduced the
heat rate by a maximum of 36%.
Lee and Pessiki [11] carried out a study to investigate
the performance characteristics of precast concrete sand-
wich wall panels with two or three wythes separated by
air layers. It was found that, in general, the thermal per-
formance of three-wythe panels is better than that of two-
wythe panels due to the increased thermal path length.
Ho and Yih [12] analyzed conjugate natural convec-
tion and conduction in a multi-layer wall. They consid-
ered isothermal left and right sides of the wall and adia-
batic boundary condition in both top and bottom sur-
Tong and Gerner [13] analyzed natural convection in
partitioned air-filled rectangular enclosures and reported
that placing a partition midway between the vertical
walls results in the greatest reduction in heat transfer.
Kangni et al. [14] investigated natural convection in
partitioned walls for various aspect ratios and for a wide
range of Ra and wall thicknesses. Turkoglu and Yucel
[15] investigated numerically natural convection heat
transfer in enclosures with conducting multiple partitions
and side walls. However, in their analysis the sidewalls
were assumed to be isothermal, thus eliminating the
temperature gradient in the y-direction within the solid.
They also kept the top and bottom surfaces perfectly in-
sulated. They reported that Nusselt decreases as the
number of partitions is increased up to 4. They also re-
ported that the cavity aspect ratio had an insignificant
effect on their calculations.
Lorente [16] published a review article to illustrate the
heat flow through walls with relatively complicated in-
ternal structure. He reported the effect of Rayleigh num-
ber and aspect ratio showing that for Re = 3550, no fluc-
tuations were observed and a unicellular flow was ob-
served. As the Rayleigh number increases, the flow be-
comes multi-cellular.
Antar and Thomas [17] addressed the heat transfer
across a hollow building block and estimated two dimen-
sional effects of the heat transfer across the block. In
another study [18] they developed a numerical finite-dif-
ference analysis for steady-state heat transfer in a com-
posite wall with a two-dimensional rectangular gray body
radiating cavity with and without natural convection cir-
culation of air. The purpose of their analysis was to pro-
vide a basis for evaluating the accuracy of the first-order
two-dimensional model. Recently, Antar [19] investiga-
ted the significance of multi-dimensional effects in esti-
mating the rate of heat loss and identified the cases
where simple one-dimensional convection/radiation ana-
lysis may be considered a good approximation for heat
transfer rate calculations.
It was reported by Antar and Thomas [17,18] and
Antar [19] that the approximate simple one dimensional
analysis for the problem under investigation had two
alternative thermal circuits, an upper bound thermal cir-
cuit and a lower bound one. Calculations showed that the
percentage difference in estimating the upper bound and
lower bound heat transfer rate reaches 39%. This indi-
cated significant two dimensional effects. Neither the
upper bound nor the lower bound solution provided reli-
able value for the heat leak, and a two dimensional model
was seen to be needed to estimate the heat transfer rate
accurately. Therefore, another work at developing and
using a two-dimensional model for investigating the ef-
fect of cavities layout on the thermal resistance of the
block was done using a block of 5 cavities. The study
showed that the shape and distribution of the cavity
played an equally important role in thermal resistance.
As the number of holes or air-gaps is increased, the
thermal conductivity is reduced. Therefore, this paper
focuses on the development of blocks with different ar-
rangements of holes, which are characterized by good
thermal resistance.
2. Methodology
The basic geometries under consideration are presented
in Figures 1 and 2. This problem was solved by heat
transfer by conduction whereas the cavities were as-
Copyright © 2012 SciRes. JMMCE
sumed to be vacuum. That is, there was no heat transfer
by convection in the cavities. Ordered and scattered hole
layouts were considered. The geometry modeling and
meshing are shown in Figures 3 and 4 respectively.
right © 2012 SciRes.
2.1. Regular Bricks
w1 = 0.05 m w2 = 0.06 m
L1 = 0.05 m L2 = 0.15 m
Boundry Co nditions:
Heat flux (g) = h*T = 375 (W/m2).
Heat transfer coefficient (q) = h = 15 (W/m2·˚C).
where, h is the conduction heat transfer coefficient, T is
the ambient temperature of the
Brick, Density (
) = 1922 kg/m3, Heat capacity C =
0.79 KJ/kg·˚C.
Coefficient of heat conduction () = 0.72 W/m·˚C.
Temperature at the entrance of heat is assumed to be
Temperature at other sides had Neumann condition of
No heat transfer by convection. Therefore, convective
heat transfer coefficient (h) is zero.
Transient state conditions.
Constant properties.
No heat generation within the brick.
2.2. Interlocking Bricks
w1 = 0.05 m, w2 = 0.1, L1 = 0.05 m, L2 = 0.2 m
Boundry Co nditions:
Heat flux (g) = h*T = 375 (W/m2).
Heat transfer coefficient (q) = h = 15 (W/m2·˚C)
where; h is the convection heat transfer coefficient or
film conductance.
T is the ambient temperature of the brick, Density (
= 2300 kg/m3,
Heat capacity C = 0.960 KJ/kg·˚C, Coefficient of heat
conduction () = 0.3 W/m·˚C.
(b) (c)
Figure 1. (a) Regular Hollow brick geometry; (b) Monolithic brick; (c) Geometry of regular hollow bricks.
Figure 2. Hollow interloc king bric k ge ometry.
Figure 3. Geometry modeling of interlocking bricks with
Figure 4. Meshing the interlocking bric k domain.
2.3. Governing Equation
One-dimensional conduction heat transfer in the block
solid material is governed by the following equation:
Let the density of the brick be
, Specific heat c, and
area of the brick normal to the direction of heat transfer
is A.
An energy balance on the brick during a small time
interval t can be expressed as
Rate of heat conduction through
= Rate of change of the energy the brick in y-direction
content of the element (brick) (1)
tt t
tt t
y TT
tt t
EE Emc
 (3)
Substituting Equation (3) into Equation (2):
tt t
Dividing Equation (4) by Ay
tt t
Taking the limit as y 0 and t 0 yields
kA c
yy t
 (6)
But since the area A is constant, the one-dimensional
transient heat conduction equation for the brick becomes
yy t
 (7)
Or, where k is constant
3. Results and Discussion
Figures 5-10 show the results of the models of different
cases of transient heat transfer in building bricks with
cavities, subjected to the same ambient temperature to
study the temperature variation across the brick from the
outside to the inside of the building. These results show
the effect of the cavities in building bricks.
Figure 5. (a) Model of a Solid conventional building brick;
(b) Model of a Solid interlocking building brick.
Copyright © 2012 SciRes. JMMCE
Figures 5(a) and (b) show the solid bricks heated at y
= 0 mm to 40˚C, and held at that temperature for 8 hours
on the side representing the outside of a room wall which
was initially at ambient temperature of 25˚C. After 8
hours of application of heat at a temperature of 40 deg·C,
the inside of the bricks had risen to a temperature of 40
deg·C. This equality in the temperatures outside and in-
side the wall shows the scenario in a building; since all
the heat are conducted from outside the brick to the in-
side of the brick showing the level of discomfort that can
be experienced in the inside of a building with solid
Figures 6(a) and (b) show results for two-cavitied
bricks. The temperature at the inner part of the bricks had
reduced to 26.22˚C and 26.88˚C for conventional and
interlocking bricks respectively.
Taking the analysis further to four-cavity bricks (Fig-
ures 7(a) and (b)), the temperature dropped further on
the inside to 25.43˚C and 25.3˚C for conventional and
interlocking bricks respectively. This showed the in-
creasing resistance to heat flow with increasing cavities
in the bricks. The reduction in heat transfer with increas-
ing cavities was more pronounced in the interlocking
Figure 6. (a) Heat transfer in conventional building brick
with 2 cavities in 8 hours; (b) Heat transfer in interlocking
brick with 2 cavities in 8 hours.
Figure 7. (a) Heat conduc tion in c onve ntional building br ic k
with 4 cavities in 8 hours; (b) He at conduction in interlock-
ing brick with 4 cavities in 8 hours.
Increasing the cavities further still to eight holes in the
conventional brick (Figures 8(a)) did not show any ap-
preciable increase in resistance to heat transfer over the
four-cavity conventional brick as the temperature at the
inside wall decreased minimally to 25.3˚C. However, for
the interlocking brick (Figure 8(b)) there was an appre-
ciable increase in thermal resistance to the extent that
over an 8 hour period, the inside wall temperature did not
increase and was kept at the ambient temperature of 25
Case of Staggered Hole Arrangements
Figures 9(a) and (b) show the results of heat conduction
in interlocking and conventional bricks with four stag-
gered cavities. There was appreciable effect of the hole
staggering on thermal resistance for interlocking brick
(Figure 9(a)). There was enough thermal resistance over
an 8 hour period to keep the inside of the brick at the
ambient temperature of 25 deg·C. However, for the con-
ventional brick there was no advantage as the tempera-
ture was 25.45 deg·C showing a rise in temeperature of
0.02 deg·C over the ordered hole arrangement.
Increasing further the number of holes in the staggered
arrangement (Figures 10(b)), showed significant effect
on thermal conductivity in the conventional brick. Inside
Copyright © 2012 SciRes. JMMCE
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wall temperature reduced to 25.03 deg·C. Increasing the
cavities to 8 in interlocking bricks (Figure 10(a)) was
not necessary as the ambient temperature was maintained
as in the four-cavitied staggered arrangement. However,
it was observed that the heat within the brick was kept
almost within the first third of the brick.
(a) (b)
Figure 8. (a) Heat transfer in conventional building brick with 8 cavities in 8 hours; (b) Heat transfer in interlocking brick
with 8 cavities in 8 hours.
(a) (b)
Figure 9. (a) Heat conduction in interlocking brick with 4 cavities in 8 hours; (b) Heat conduction in conventional building
brick with 4 cavities in 8 hours.
(a) (b)
Figure 10. (a) Heat conduction in interlocking brick with 8 cavities in 8 hours; (b) Heat conduction in conventional building
brick with 8 cavities in 8 hours.
4. Conclusions
Conduction heat transfer within ordinary (conventional)
and interlocking bricks with hollow cavities was investi-
In conventional bricks, increasing the number of cavi-
ties played a substantial role in decreasing heat flow into
the building and hence enhanced thermal insulation. Af-
ter the four-hole arrangement, increasing the number of
holes only gave marginal thermal resistance over the
four-hole arrangement.
In the case of interlocking bricks, it was observed that
staggered hole arrangement helped in decreasing heat
flow into the brick wall. Four-staggered-hole arrange-
ment gave the same thermal resistance as an ordered
eight-hole arrangement. The 8-hole brick arrangement
may also tend to compromise the strength of the brick.
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