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Research article
Development of an enhanced electrical injera baking pan
(Ethiopian Traditional mitad) using steel powder additives and
gypsum insulation
Altaseb Kegne Sisay
a,*
, Melese Shiferaw Kebede
a
, Abayenew Muluye Chanie
b
a
Department of Mechanical Engineering, Institute of Technology, University of Gondar, Gondar, Po.Box: 196, Ethiopia
b
Department of Automotive Engineering, Arba Minch University Sawla campus, po box: 21, Ethiopia
ARTICLE INFO
Keywords:
Baking energy
Thermal efciency
Uniform heat distribution
Baking time
ABSTRACT
Electric Injera baking Pan are prevalent in Ethiopia but are highly inefcient, resulting in sig-
nicant heat loss, high energy consumption, and increased energy bills. This research investigates
improving these devices using steel powder as an additive and gypsum as an insulator. The study
examines thermal conductivity, baking time, energy consumption, heat loss, and insulation
effectiveness. The objectives of this research are to improve the thermal conductivity of the
baking surface while ensuring even heat distribution, enhance the insulation properties of the pan
to reduce heat loss, improve the safety of the user by reducing the risk of excessive heat exposure
to the outer surfaces, and reduce the overall energy consumption of the Injera baking process.
Temperatures were measured using an infrared thermometer, digital thermometer, and thermo-
couple. Four samples (A0, A1, A2, & A3) with different steel powder compositions (0 %, 15 %, 25
%, and 35 %) and a constant 75 % clay soil composition were tested. The analysis showed an
average baking energy of 0.45 kWh per kg of injera (0.198 kWh per injera) and a thermal ef-
ciency of 86.4 % when baking 4.395 kg of injera. The total heat energy loss was 1402.78 KJ
(14.08 % of 10300 KJ input energy). The losses were distributed among the retained (92.17 %),
the baking plate (3.95 %), the bottom enclosure (2.08 %), the side enclosure (1.04 %), and the
cover lid (0.76 %).
1. Introduction
Injera, a fundamental food in Ethiopian cuisine, is crafted from a blend of cereals like teff, maize, wheat, rice, or a mix thereof. Its
production entails fermentation and meticulous baking. This atbread is a dietary mainstay in Ethiopia, traditionally enjoyed
frequently throughout the day and often served two to four times per day [1]. Injera is usually cooked on a clay plate known as a pan
positioned over a three-stone re or a specialized electric stove, necessitating temperatures ranging from 180 ◦C to 220 ◦C [1–3]. In the
standard electric Injera baking system, heat is produced using high-resistance heating elements through which electric current ows.
This resistance within the elements generates heat in the coil, which is then transferred to the baking pan via conduction. Depending on
the clay construction, single- and double-plate pans are available in the market. In a double plate system, the bottom plate is designed
to house the heating element, while the top plate functions as the surface where the baking takes place, heated and ready for cooking
* Corresponding author.
E-mail addresses: 2112altu@gmail.com, altasebkegne5@gmail.com (A.K. Sisay).
Contents lists available at ScienceDirect
Heliyon
journal homepage: www.cell.com/heliyon
https://doi.org/10.1016/j.heliyon.2024.e38952
Received 9 July 2024; Received in revised form 1 October 2024; Accepted 3 October 2024
Heliyon 10 (2024) e38952
Available online 5 October 2024
2405-8440/© 2024 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC license
( http://creativecommons.org/licenses/by-nc/4.0/ ).
[4]. Electric stoves are recognized for their signicant energy use and comparatively low efciency. This is largely due to factors such
as the thickness of the heating elements, the thermal properties of the materials used in the cookware, and insufcient insulation
systems. In traditional electric baking pans, there is a risk of uneven heat distribution due to inherent manufacturing inaccuracies.
These issues include variations in the depth of the groove where the electrical resistor is embedded, inconsistencies in resistor density
along its length, and slight differences in the thickness of the baking plate. Moreover, these pans typically require a considerable
amount of time (approximately 24 min) to initially heat up and for the baking process [1,3,5]. Energy is vital for fundamental
household tasks like cooking, baking, lighting, and heating water. Ethiopia has one of the lowest access levels to modern energy
services, relying primarily on biomass for its energy supply. Although different studies show some variation in the data, researchers
generally agree that around 90 % of the country’s total energy consumption is from the household sector. Within this sector,
approximately 95 % of energy comes from biomass, 1.5 % from petroleum, 3.3 % from electricity, and 0.2 % from other [1,6–9].
Electric Injera baking is primarily seen in urban areas of Ethiopia and plays a signicant impact on the country’s electricity con-
sumption. These pans consume between 50 % and 75 % of total household energy and account for 60 %–70 % of the hydroelectric
power generated in Ethiopia [5,7,10]. However, each existing electric Injera baking pan consumes a substantial amount of electricity,
approximately 3.5 kW–3.9 kW per baking session, resulting in signicant energy waste during the process [11,12]. The current
electrical pan is often criticized for its inefciency, stemming from its outdated design and manufacturing aws dating back to the
1960s, with no design improvements made since then [3,13]. The average thermal efciency of an electric Injera baking pan is found to
be 50 % for those with a clay plate and 60 % for those with a ceramic plate [8,10]. Most researchers have found that the efciency of a
better-controlled electric Injera baking pan ranges from 43 % to 55 % [6,14,15]. In almost all research done on electric Injera baking
stoves, the amount of energy dissipated (loss) during the baking process is roughly predicted to vary from 50 to 60 percent [3,16,17]. In
a solar-powered Injera baking system, heat is not supplied directly to the baking pan; Instead, the system uses energy storage methods,
Table 1
Devices utilized for measuring experimental parameters.
Name of thermometer Picture of device Device Features and Accuracy Uses of device
Digital thermometer
⁃ Temperature measurement:
−50
◦C–300 ◦C
⁃ Temperature accuracy: ±1 ◦C/℉
⁃ On/off keys switching
⁃ Measure the temperature at the bottom of a baking
pan.
Infrared
Thermometer
⁃ Temperature measurement:
−50
◦C–380 ◦C
⁃ Temperature accuracy: ±1.5 ◦C/℉
⁃ Response time 500 ms.
⁃ Non-contact thermometer
⁃Measure the surface temperature of stove
enclosures and baking
pan surfaces.
Digital mass balance
⁃ Mass measurement: 0.01g–610g
⁃ Measurement accuracy: 0.1 mg
⁃ Measure the weight of the dough and injera.
Multimeter ⁃ Voltage measurement: 200
mV–1000V
⁃ Measurement accuracy: ±3 %
⁃ Measure the current and voltage owing to the stove.
A.K. Sisay et al.
Heliyon 10 (2024) e38952
2
such as phase change materials and pressurized water vessels with auxiliary heating components. The solar system collects heat from
solar radiation, transfers it to a working uid or storage medium, and then delivers the heat to the pan for baking Injera [1,12,14]. The
main issue is that the solar-powered Injera baking system is efcient only during sunlight hours. It takes over 100 min to heat initially
the baking pan and has a higher idle time of over 3 min between baking sessions compared to the electrical Injera baking system [11,
16]. In contrast, biomass Injera baking stoves use rewood as the primary energy source, but they have signicant drawbacks, such as
indoor air pollution, rampant deforestation, low efciency, and high wood consumption. Researchers have estimated that traditional
biomass Injera baking stoves have an efciency ranging from 5 % to 35 % [3,9]. The importance of this study lies in developing a new,
improved electric mitad by incorporating steel powder as an additive and gypsum as an insulator and evaluating its energy con-
sumption and heat loss across various parts of the baking system. From the literature review above, the current electric mitad suffers
from low efciency due to inadequate thermal properties of the pan plate, signicant heat loss, long initial heating times, extended
baking durations, and high energy consumption for heating and baking. Steel powder can improve the thermal conductivity of the
baking surface, promoting more even heat distribution, which helps achieve a consistent cooking temperature and reduces hot spots,
thereby enhancing the quality of Injera. Gypsum, known for its thermal insulation properties, can help to prevent excessive heat from
reaching the pan’s outer surfaces, improving user safety, protecting the baking environment, reducing burn risks., lowering energy
usage, and boosting baking efciency. This research may also shed light on how various materials and additives impact cooking
appliance performance, potentially leading to further innovations and improvements in traditional cooking tools and household
appliances.
2. Materials and methods
2.1. Materials used for experimental test
The devices employed for measuring various parameters during the experimental tests are detailed in Table 1. This table includes
essential information such as the names and images of each device, along with their specic characteristics and accuracy. Additionally,
it highlights the particular applications of these devices, primarily focusing on how they are used to measure different temperature
parameters of various components of the baking pan.
2.2. Methods
Composite materials for baking pans are prepared using clay soil and steel powder. The clay soil is sourced from Kolay, near Deber
Tabor in the Amhara region of Ethiopia. Clay soil is dried and powdered to increase its contact surface area for better mixing with the
steel powder. The steel powder is made by grinding steel bars with a grinding machine. Fig. 1a, b below shows the steel powder and
clay soil used for pan preparation.
2.3. Sample preparation
The samples were created by mixing a consistent amount of clay soil with varying amounts of steel powder, as specied in Table 2.
To the mixture, 45 g of water were added and stirred at 200 RPM for 15 min. The resulting mixtures were then poured into standard
molds with a diameter of 40 mm, as shown Fig. 2a, b below.
Fig. 1. a) Clay soil and b) Steel powder.
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2.4. Thermal conductivity test
A thermal conductivity meter (WL 374) was employed to measure the thermal conductivity of the samples, as illustrated in Fig. 3.
The thermal conductivity values obtained for each sample are presented in Table 3.
A composition of 25 % steel powder and 75 % clay soil was chosen for baking pan preparation. This blend increases the thermal
conductivity of clay soil by 42 %. Consequently, sample A2 was selected to prepare the new electric pan. As the thermal conductivity of
a composite material increases, its specic heat capacity typically decreases. Materials with high thermal conductivity indicate how
heat moves through a material; heat capacity measures how much heat the material can store. Both properties impact the material’s
overall thermal performance in different ways. Achieving an optimal heat capacity is essential to effectively store thermal energy and
minimize idle time between consecutive injera baking sessions. Further, increasing thermal conductivity value can complicate the
baking process, similar to baking on metal, and reduce the signicance of heat capacity in the process.
Table 2
Sample dimensions and weight composition.
Sample labeling Diameter (mm) Length (mm) Clay (g) Steel powder (g) Water (g)
A0 40 52 75 0 45
A1 40 52 75 15 45
A2 40 52 75 25 45
A3 40 52 75 35 45
Fig. 2. a) Instrument used for sample preparation; b) Samples created using the materials.
Fig. 3. Thermal conductivity testing machine, and procedures.
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2.5. Fabrication of pan (Ethiopian Traditional mitad)
Traditionally, at and circular clay pans with diameters ranging from 500 mm to 600 mm and a thickness of 20 mm are commonly
used as baking pans. However, for this research, the pan plate was designed with a thickness of 12 mm and a diameter of 580 mm,
which closely matches the dimensions of existing baking pans; with other physical dimensions of the various components of the pan
shown in Table 4. This decision ensures social acceptance among users accustomed to the typical size of injera, as signicant changes
could affect their willingness to adopt the new system. The manufacturing process of the pan plate begins with creating the composite
material by mixing clay soil (75 %) and low-carbon steel (25 %) in appropriate proportions. The composite material is then mixed with
water until it attains a plaster-like consistency using a mixer operating at 200 RPM. Subsequently, the moit pan is allowed to dry
slowly, during which it loses excess water while retaining moisture bound in crystal lattices. The surface nishing of the new pan
involves smoothing the baking side and bottom surfaces using emery paper and shaping the effective baking diameter using a metal
le. Finally, the pan plate is red at high temperatures to reduce pores, increase density, and strengthen the structure. Fig. 4a–d below,
illustrates the manufactured pan plate.
3. Experimental tests and procedures
During the experimental setup, temperature readings were collected from various points across the pan surface, as illustrated in
Fig. 5a. Specically, temperatures were measured at the following locations.
⁃ At the center of the baking plate, both on the top and bottom surfaces.
⁃ At a distance of 13.75 cm from the center of the baking plate, at both above and below positions.
⁃ At a distance of 27.5 cm from the center of the baking plate, on both the top and bottom surfaces.
⁃ Immediately after removing the injera, the surface temperature of the baking plate was recorded.
⁃ Intermittent baking surface temperature measurements were taken just before the baker placed the dough.
⁃ Temperatures were recorded on the side enclosure at different points.
⁃ Temperature measurements were taken at the center tip, middle, and bottom of the lid cover.
⁃ Room temperature and dough temperature were also monitored.
⁃ The temperature of the injera was measured immediately after removal from the pan.
3.1. Input and useful energy
The heat generated by the heating element serves as the input energy for the baking process. This energy depends on the voltage (V)
and current (I) passing through the heating element.
Ein =V*I*tT(1)
Table 3
Thermal conductivity reading for each sample.
Sample Thermal conductivity W
/mK
A0 0.85
A1 1.18
A2 1.46
A3 1.59
Table 4
The physical dimensions of the various components of the pan.
Parameters Dimensions Unit
Baking pan plate thickness 12 Mm
Mass of the baking mitad 6 Kg
Mitad plat diameter 580 Mm
Effective pan diameter 560 Mm
Gypsum insulation thickness (bottom) 20 Mm
Side Gypsum insulation thickness 10 Mm
Groove depth 6.5 Mm
Distance b/n grooves or pitch 14.5 Mm
Resistance wire diameter 0.9 Mm
Resistor coil diameter 6 Mm
Resistance coil length before stretching 680 Mm
Resistance coil length after stretching 8500 Mm
A.K. Sisay et al.
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Where: Ein =input energy (W), V =voltage (volt), I =current ow (A), tT=Total time required for baking 10 injera.
The useful baking energy is estimated as the sum of sensible heat, which heats the dough from room temperature to the boiling
point of water, and latent heat, which evaporates some of the water content in the dough.
Eu=miCPi(Tb−Ta) + hfg (md−mi) + (md−mi)Cw(Tb−Ta)(2)
Fig. 4. Part manufacturing of the Pan: a) Modeling and manufacturing of the pan; b) Modeling and manufacturing of the cover lid; c) Pan plate
casing; d) Manufactured leg of the electric pan plate.
A.K. Sisay et al.
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Where: Eu=useful energy, md=mass of dough, mi=mass of injera, CPi =specic heat capacity of injera, Cw=specic heat capacity
of water, Tb=boiling temperature of water, Ta=room temperature, hfg =latent heat of evaporation for water based on water boiling
point temperatures at atmospheric pressure.
Fig. 5. Experiment setup of a pan stove: a) Digital and infrared thermometer positions; b) Thermometer positions strategically across the setup; c)
Different viewpoints on experimental studies; d) The experimental setup and equipment arranged for the research project.
A.K. Sisay et al.
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3.2. Heat energy loss analysis during baking process
During the electric injera baking process, heat energy was lost from the top, bottom, and sides of the pan plate During the electric
injera baking process, heat energy was lost from the top, bottom, and sides of the pan plate, which can be quantied using Equations
(7), (9) and (13). This heat transfer occurs through conduction, convection, and radiation. Fig. 6 below depicts a thermal circuit that
represents the different pathways through which heat is transferred from the electric injera baking stove to the surrounding envi-
ronment. This thermal circuit effectively illustrates the intricate nature of heat loss in various directions and through multiple
mechanisms.
a. Heat loss on the cover lid to the surrounding
Heat energy is lost from the cover lid to the surroundings by natural convection and radiation heat transfer modes. The cover lid,
when heated by the electric mitad, emits infrared radiation. This radiation transfers heat directly from the lid to the surrounding
environment. The intensity of radiation loss depends on the temperature of the lid and its surface characteristics. Warm air rises from
the stove cover lid as it heats up. This creates convection currents around the stove. Heat is lost to the air, which then spreads this heat
throughout the room.The natural convective heat transfer coefcient can be calculated by Heat energy lost from the cover lid to the
surroundings through natural convection and radiation. The natural convective heat transfer coefcient can be calculated using
empirical correlations that depend on the properties of the uid (air in this case), the temperature difference between the cover lid and
the surrounding air, and the physical dimensions of the lid. Typically, the natural convective heat transfer coefcient (hcov) can be
calculated using equation (3).
hcov =Nu*K
L(3)
Where: hcov =natural convection Nu=Nusselt number, K thermal conductivity (w/mk) and L =characteristic length of circular plate
=0.3 Dm.
The fundamental parameters for natural convection include the Grashof number (Gr), Rayleigh number (Ra) can be determined by
equation (4), Nusselt number (Nu), and Prandtl number (Pr).
Ra=Gr*Pr=gβΔTL3
v2*Pr(4)
Where: g =gravitational acceleration (m /s2, β=Coefcient of volume expansion (1/K), ΔT=Temperature change of the surface
(◦C), L characteristic length of the geometry (m)&
ν
Kinematic viscosity of the air (m2/s.
Fig. 6. Thermal circuit diagram and heat loss for Injera baking stove.
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Qloss,cl−s=˙
Qc−c−a+˙
Qr−c−a=Ucl−sA(Tcl −Ta)*tT(5)
Where: ˙
Qloss,cl−s=heat energy loss from cover lid to the surrounding (KJ), A =area of conic cover lid heat loss surface (m2), tT=Total
time required for baking 10 injera, Tcl =average temperature of the cover lid (◦C), Ta=ambient temperature of the experimental room
(◦C), ˙
Qc−c−a, ˙
Qr−c−a=heat energy lost by convection & radiation heat transfer from cover lid to surrounding (KJ), Ucl−s =overall heat
transfer coefcient for convective and radiative heat transfer modes from cover lid to surrounding, W/m2K) and it can be calculated
by equation (6).
Ucl−s=1
hc,cl−s
+1
hr,cl−s−1
(6)
hc,cl−s=Convective heat transfer coefcient from cover lid to surrounding =Nu*K
L,(W/m2.k) hr,cl−s=Radiative heat transfer coef-
cient from cover lid to surrounding =ϵδTcl 2+Ta2(Tcl +Ta),(W/m2.k).
b. Heat Losses on Baking Mitad to Cover Lid
Heat loss from the baking pan plate to the cover lid can happen through natural convection and radiation heat transfer mechanisms.
The baking plate radiates heat upwards towards the cover lid. The cover lid, once heated, absorbs this radiation and may then emit heat
to the ambient environment. The amount of heat lost through radiation depends on the temperature difference between the plate and
the lid, as well as the surface emissivity of the materials. Heat from the baking plate warms the air directly above it, which then
transfers heat to the cover lid through convective currents. The warmed air between the plate and the lid circulates, carrying heat away
from the plate. This heat is then conducted and convected through the lid to the ambient environment. Condensation was considered
negligible in this heat transfer scenario.
Qloss,b−cl =˙
Qc−p−c+˙
Qr−p−c=Ub−clA(Tb−Tcl )*tT(7)
Where: Qloss,b−cl =heat energy loss from baking pan plat to the cover lid, (KJ), A =area of baking pan, m2, tT=Total time required
for baking 10 injera, Tb=Average temperatures of baking pan surface, Tcl =Average Temperatures of cover lid, Ub−cl =overall heat
transfer coefcient for convective and radiative heat transfer modes from baking surface to cover lid, W/m2Kand calculated by
equation (8).
Ub−cl =1
hc,b−cl
+1
hr,b−cl−1
(8)
c. Heat Loss from the Bottom Enclosure To Surroundings
Gypsum, chosen for its low thermal conductivity, serves as thermal insulation to minimize heat loss from the bottom of the electric
injera baking pan. A 20 mm thick layer of gypsum reduces the amount of heat lost through the bottom surface of the pan. The heat
energy lost during the baking of injera can be expressed in terms of the surface temperatures at the top (TT) and bottom (TB) of the
insulation.:
Qloss,bo−s=Ubo−sA(Tbo −Ta)*tT(9)
Where: Qloss,bo−s =heat lost from the bottom enclosure to surrounding with an insulator, (KJ) Tbo =Average temperatures of the
bottom enclosure, tT=Total time required for baking 10 injera, Ta =Temperatures of ambient, Ubo−s=allover heat transfer coef-
cient from the bottom enclosure to surroundings evaluated as follow equation (10).
Ubo−s=tinsu
kinsu
+1
hc,bo−s
+1
hr,bo−s−1
(10)
If an electric pan lacks insulation, the bottom surface of the pan is directly exposed to the aluminum enclosure, which has a thin
thickness. This setup results in increased wastage of energy.
Qloss,bm−s=Ubm−sA(Tbm −Ta)*tT(11)
Where: Qloss,bm−s=Heat energy lost from the bottom enclosure of the pan to surroundings, without insulator (KJ), tT=Total time
required for baking 10 injera, Tbm,Ta=Temperature of the bottom surface of the electric pan and ambient respectively, Ubm−s=
Allover heat transfer coefcient from the bottom surface of the baking pan to the surroundings evaluated by equation (12).
Ubm−s=1
hc,bm−s
+1
hr,bm−s−1
(12)
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9
d. Heat loss on the side enclosure to the surroundings
Heat loss by convection and radiation from the side enclosure to the surroundings and by conduction through the thickness of side
insulation. The side enclosure, which is in contact with or close to the baking plate and cover lid, also radiates heat to the surrounding
environment. The effectiveness of this radiation loss is inuenced by the temperature of the enclosure and its radiative properties.The
side enclosure transfers heat to the surrounding air via convection. The air in contact with the hot surface of the enclosure heats up,
rises, and is replaced by cooler air, creating convection currents. This process transfers heat from the enclosure to the ambient air.
Qloss,s−s=˙
Qc−s−a+˙
Qr−s−a=Us−sA(Ts−Ta)*tT(13)
Where: Qloss,s−s=heat energy lost from the side enclosure, (KJ), Us−s=overall heat transfer coefcient from the side surface of the
baking pan to the surroundings and tT=Total time required for baking 10 injera. The overall heat transfer coefcient With and
without side insulator could be simply calculated by using equations (14) and (15) respectively:
Us−s=tS,insu
k+1
hcs−s
+1
hrs−s−1
;(With side insulation)(14)
Us−s=1
hc,s−s
+1
hr,s−s−1
;(Without side insulation)(15)
e. Retained heat loss at baking pan at the end of the baking process
After the baking process ends, heat energy retained within the pan plate contributes signicantly to overall heat loss. During
experiments, injera can continue to bake even after the power is turned off, till a pan surface temperature of 140 ◦C and prolonged
baking times and may result in poorer quality. The gradual cooling from this elevated temperature (Te=140◦C) back to ambient
temperature (Ta=17.4◦C) takes approximately 14 and a half minutes. This heat exchange between the surroundings and the pan due
to temperature differences is referred to as retained energy loss:
Qr=Um*A(Te−Ta)*te(16)
Where: Qr=Retained heat energy at the end of the baking process, (KJ), Te=Temperature at the end of baking, te=Time required to
cold the pan plat to ambient temperature,
tm=Thickness of pan, Km=Thermal conductivity of improved pan, (W/m.k), Um=Overall heat transfer coefcient of the baking
pan, W/m2.kit can be Computed by equation (17).
Um=tm
Km−1
(17)
f. Total Heat Energy Loss
Qtotal,loss =Qr+Qloss,b−cl +Qloss,bo−s+Qloss,s−s+Qloss,cl−s(18)
g. Thermal Efciency of the System
The thermal efciency of the enhanced electric pan is determined by dividing the net useful energy by the gross energy supply.
η
thermal =Eu
Ein
*100 (19)
Where values of Ein and Eu a are determined by equations (1) and (2), respectively.
4. Results and discussion
The temperature prole during the baking process is crucial for understanding how energy is used in the electric pan. This prole is
analyzed under two conditions: without any load and with a load placed inside the pan.
4.1. No load Temperature prole
As shown Fig. 5b in the experimental investigation, temperatures at various parts of the mitad; specically the bottom of the mitad
plate, the top of the mitad plate, the side enclosure, the cover lid, and the bottom enclosure, were recorded every 2 min during the
injera baking process. The results showed that the temperature increased over time at all measured locations. The temperature
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10
increasing rate is largest through the mitad plate, second, from the bottom enclosure, the third largest temperature increase rate from
the side enclosure surface and least is from cover lid as depicted in Fig. 7. For analytical purposes, average temperatures for each
component were used. The average temperatures recorded were 211.58 ◦C for the mitad plate, 105.5 ◦C for the bottom enclosure, 65.2
◦C for the side enclosure, 45.8 ◦C for the cover lid, and 17.4 ◦C for the surrounding environment.
Fig. 8 depicts temperature changes recorded at different points: the center, 13.75 cm away from the center, and 27.5 cm away from
the center of the baking pan. The temperature proles begin from the ambient temperature of 17.4 ◦C and reach a maximum of 269.8
◦C. Under no load conditions, the surface of the baking pan heats up almost uniformly, with temperature variations of less than 6 ◦C
across the three measured points. This uniform heating is attributed to precise groove proles and the homogeneous blending of low-
carbon steel powder with clay soil.
4.2. With load Temperature prole
Fig. 9 illustrates the temperature prole observed during the baking process with a load. Initially, the temperature rises from the
ambient temperature of 17.4 ◦C to the minimum required baking temperature of 170.1 ◦C for 0–13 min. This phase represents the
heating-up period. Beyond 13 min, the temperature variation on the baking surface uctuates: it decreases when the dough is poured
onto the surface and increases after Injera removal during idle periods, oscillating within these intervals with some variation. The
baking time for the rst two Injera was longer, approximately 240 s because the baking process started at a lower temperature (170.1
◦C–190 ◦C). Baking at lower temperatures reduces the quality of Injera, characterized by fewer "eyes" that contribute to its desired
texture. Beyond 190 ◦C, the average baking time required is consistently 120 s, with 60 s of idle time between successive Injera baking
cycles. Experimental ndings indicate that the cover lid was open for 33.3 % of the baking process time (60 s) to remove baked Injera
and pour dough. While previous studies suggest a temperature range of 180–220 ◦C for baking Injera, this investigation challenges that
assertion by demonstrating that temperatures below 190 ◦C result in longer baking times. Therefore, the recommended acceptable
temperature range is 190 ◦C–220 ◦C. Temperatures exceeding 220 ◦C lead to burnt Injera and lower-quality products.
Fig. 10 demonstrates that the temperature of the dough started at 17.4 ◦C and rose to an average temperature of 101.5 ◦C upon
being poured onto the hot pan surface. The average surface temperature of the baking pan, initially at 211.58 ◦C, decreased to 101.5 ◦C
immediately upon contact with the dough. During idle periods, the surface temperature of the pan remains at the baking temperature
due to the continuous supply of electrical energy.
Fig. 11illustrates the temperature proles of various parts of the enhanced pan stove under load conditions. The temperature of the
bottom enclosure steadily increased over time without signicant oscillation. In contrast, the temperature of the cover lid uctuated
over time: it was lower when the dough was poured onto the baking surface and higher just before removing freshly baked Injera from
the pan and just before pouring new dough. The temperature of the side enclosure increased gradually over time, positioned between
the temperatures of the bottom enclosure and the cover lid.
4.3. Energy consumption analysis
Despite reaching the required baking temperature early in the heating-up process, the temperature of the heating element con-
tinues to rise, indicating that the system is consuming additional power unnecessarily. Consequently, this excess energy is dissipated as
various losses, including retained heat loss, side enclosure heat loss, bottom enclosure heat loss, and cover lid heat losses. Based on
analytical calculations, the total heat loss in the Injera baking pan (for baking 10 Injera) is estimated to be 1402.78 kJ, as determined
by Equation (18). Specically, the heat energy losses due to retained heat at the end of the baking process were evaluated to be 1300
kJ, according to Equation (16). Additionally, the losses from the baking plate, bottom enclosure, side enclosure, and cover lid were
calculated using Equations (((5), (7), (9), (11), (13) and (16), and resulting values of 55.7 kJ, 29.08 kJ, 7.3 kJ, and 10.7 kJ,
Fig. 7. Surface temperature of electrical pan parts.
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respectively, as illustrated in Fig. 12.
Insulation plays a crucial role in improving the efciency of the electric pan. For example, heat losses without insulation were
measured at 69.2 kJ for the bottom enclosure and 14.541 kJ for the side enclosure evaluated by equations (11) and (13). With
insulation, these losses reduced signicantly to 29.08 kJ and 7.3 kJ respectively. Minimizing losses due to plate heat retention can be
achieved by prolonging cooking sessions and using a single pan rather than multiple pans simultaneously, a practice less common in
Ethiopia where families often share electric pans to reduce retained heat losses. This strategy is particularly benecial for larger pans
like clay pans, which have a higher heat capacity. The retained heat within the plate can also be repurposed, such as for baking bread
on the pan plate after the Injera baking process, as bread requires a lower temperature than Injera dough. Experimental ndings
indicate that the total heat energy lost from the electric pan was 1402.78 kJ, accounting for 14.08 % of the 10300 kJ input energy used
for baking 10 Injera over 43 min. The efciency of the electric injera baking mitad is measured at 86.4 % computed by equation (19).
This indicates a high level of energy utilization during the baking process.Retained heat loss constituted the majority at 92.17 % of the
total heat loss in the baking system, with the baking plate contributing 3.95 %. The losses from the bottom enclosure, side enclosure,
and cover lid accounted for 2.08 %, 1.04 %, and 0.76 % respectively, as depicted in Fig. 13.
4.4. Performance Comparisons with previous researchers work
Tables 5 and 6 present some parameters of recent research on electrical injera baking stove efciency. After baking, a stove needs
time to cool down to a safe handling or cleaning temperature. During this cooling period, any residual heat not used in baking results in
retained energy loss. Stoves with effective insulation and thermal management can reduce this loss by managing the excess heat
Fig. 8. Temperature variations over the surface of the baking pan.
Fig. 9. Temperature prole of baking pan with load.
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release. Retained energy loss affects the overall efciency of the stove, indicating that not all electrical energy used for heating was
transferred effectively to the food. This inefciency can lead to increased energy consumption if the stove continues to draw power for
subsequent cooking or baking tasks. There is currently no research on the amount of retained energy loss. This study reveals that 92.87
% of the total heat energy loss during baking is due to retained heat energy, alongside an investigation using steel powder as an
additive for injera baking pans. Efciency can be slightly improved by adjusting cooking methods and dough water content. To
enhance the efciency of electric baking pans, consider the following recommendations.
➢ Injera Thickness: To the greatest extent possible reducing the dough’s water content can decrease energy consumption during
baking, as more energy is required to evaporate higher moisture levels.
➢ Baking Session Duration: Shorter baking sessions result in a higher fraction of heat being stored in the baking plate, increasing
overall energy use. Baking more injera at once and reducing the number of baking sessions can lower retained and heat-up energy
loss.
Fig. 10. Temperatures of pan surface and dough during each baking cycle.
Fig. 11. Temperature proles of pan stove parts.
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➢ Shared Baking stove: Instead of using multiple baking stoves, neighboring families could share a single pan. In Ethiopia, it’s
common for different households within a compound to use separate stoves, which increases retained and heating-up energy.
➢ Utilizing Retained Heat: The heat retained in the baking plate can be used for other purposes, such as baking bread, which requires
a lower temperature than injera.
➢ Power Management: If the power exceeds what is needed for baking injera, bakers could turn off the stove briey. Additionally,
turning off the power a few minutes before the end of the baking session can also reduce retained energy loss.
4.4.1. Economic Feasibility of improved mitad
The average specic baking energy consumption was found to be 0.198 kWh and 0.250 kWh per Injera for the improved and
conventional electric Injera baking pans respectively, as detailed in Table 4. This indicates a difference of 0.052 kWh per Injera,
Fig. 12. Energy ow (Sankey) diagram of electric injera baking pan heat energy loss.
Fig. 13. Percentage contribution of heat loss from each part.
Table 5
Summary of analysis on the energy consumption of improved & convectional (reviewed) electric stove [6] [8] [18] [19] [20] [21].
Parameters Improved mitad Convectional
Mitad
Difference
Input voltage (V) 214 214 0
Input current (A) 18.5 17 1.5
Mitad power requirement (kW) 3.96 3.64 0.32
Mass of dough (kg) 5.234 7.07 1.836
Total injera baked (kg) 4.395 5.25 0.855
Total mass of water evaporated (kg) 0.839 1.82 0.981
The energy required for heat up (KJ) 3089 5364 2275
Energy consumption for baking only(KJ) 7126 10836 3710
Gross energy consumption (kJ) 10215 16200 5985
Time for heat up (min) 13 24 11
Time for only baking process (min) 30 56 26
The energy required for baking only (kJ/injera) 712.6 1083.6 371
The energy required for baking only (KWh/injera) 0.198 0.250 0.053
Energy required for baking only (KWh/kg, injera) 0.45 0.573 0.123
Latent heat of water (KJ) 4883 4111 771.4
Sensible heat present in injera (kJ) 3969 1568 2401
Total useful energy (kJ) 8852 5679 3173
Specic useful energy (KJ/injera) 885.2 603.92 281.28
Total heat lost(KJ) 1400.02 10520.2 9120.28
Thermal efciency of mita 86.4 38 49.3
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equivalent to 187.2 kJ per Injera. If an individual consumes an average of 2 Injera per day, this translates to 730 Injera per year per
person. Therefore, switching to the improved pan could save 37.96 kWh per year per person, amounting to 91.104 ETB per year per
person in electricity cost savings (calculated at a rate of 2.4 ETB/kWh). This potential energy savings would increase with more
households adopting the improved pan. Choosing the improved pan over the conventional one not only benets individual households
but also has signicant implications for the national grid. However, there remains a widespread lack of awareness about energy-saving
practices among both Mitad pan manufacturers and end-users alike.
5. Limitations of this research
The addition of steel powder and gypsum insulation might increase the manufacturing costs of the pan. Higher production costs
could lead to higher retail prices, potentially limiting the affordability and market acceptance of the enhanced pan. The process of
incorporating steel powder and gypsum insulation might complicate the manufacturing process. This includes issues related to uniform
distribution of additives, maintaining structural integrity, and ensuring consistency across production batches. Increased
manufacturing complexity could affect production efciency and consistency. Comprehensive testing is required to validate the
performance of the enhanced pan under various conditions and ensure it meets the desired specications for heat distribution,
insulation, and safety. Inadequate testing could lead to unanticipated issues in real-world use, affecting the reliability and user
satisfaction.
6. Conclusions
The comprehensive experimental investigations lead to the following conclusions.
➢ The thermal conductivity of the pan plate improved signicantly from 0.85 W/(m⋅K) to 1.46 W/(m⋅K), marking a 42 %
enhancement in thermal performance compared to conventional pan plates. This improvement was achieved by incorporating 25 %
steel powder into 75 % normal clay soil.
➢ As shown Fig. 5c, d the development of the Enhanced Electrical Injera Baking Pan (Mitad) has signicantly improved the quality of
injera production. By incorporating steel powder additives and gypsum insulation, this innovative design enhances heat retention
and distribution, ensuring uniform cooking. As a result, the injera produced exhibits improved texture, avor, and consistency,
meeting the high standards of traditional Ethiopian cuisine.
➢ The enhanced thermal performance of the pan plate results in improved heating-up time, baking time, and idle time during the
cooking process.
➢ Specic baking energy consumption was measured at 0.198 kWh per Injera for the improved pan and 0.250 kWh per Injera for the
conventional pan.
➢ The total heat energy lost from the electric pan amounted to 1402.78 kJ out of 10300 kJ input energy. Specically, retained heat at
the end of the baking process accounted for 1300 kJ, while losses from the baking plate, bottom enclosure, side enclosure, and cover
lid were 55.7 kJ, 29.08 kJ, 7.3 kJ, and 10.7 kJ respectively.
➢ Insulation signicantly enhances pan efciency. For instance, heat losses without and with insulation on the bottom enclosure of
the electric pan were reduced from 69.2 kJ to 29.08 kJ, and on the side enclosure from 14.541 kJ to 7.3 kJ. This represents a savings
of 58 % and 49.89 % respectively in heat energy by using bottom and side insulation.
These ndings underscore the potential for improving energy efciency in cooking appliances, highlighting the benets of material
enhancements and insulation strategies in reducing energy consumption and heat losses.
Table 6
Compares various parameters, drawing on both present work with recent research ndings.
Name of
authors
Materials for
pan
Power
source
Heating up
Time (min)
Baking
Time
(min)
Idle
Time
(min)
Thermal
Efciency
(%)
Energy
consumption
Kwh/Kg, injera
Retained heat loss
after baking (KJ)
Present work
(2024)
Low carbon steel
(additive)
Electrical 13 2 1 86.4 0.45 1300
R. Jones et.al
2017
Glass pan Electrical 8 1
2
3–Increased by
30 %
Non-evaluative
Mesele H et. Al
(2017)
Aluminum sheet solar 30–45 5 –65 Non-evaluative
Hiwot B et al
(2022)
Copper (additive) Electrical 11 1.67 0.83 88.55 0.272 Non-evaluative
Garedew A.
2015
Ceramic Electrical 12 2 2 82 0.554 Non-evaluative
A.K. Sisay et al.
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Funding
The author(s) received no nancial support for the research, authorship, and/or publication of this article.
Data availability statement
All data generated or analyzed during this study are included in this published article.
Nomenclature
TmMain lm temperature, ◦C
Tcl Average cover lid surface temperature, ◦C
TaAmbient cover lid surface temperature, ◦C
TbAverage baking mitad surface temperature, ◦C
TTAverage top surface temperature of insulator, ◦C
TBAverage bottom surface temperature of insulator, ◦C
Tbo Average bottom enclosure surface temperature of, ◦C
Tbm Average surface temperature of bottom baking mitad, ◦C
TsAverage side surface temperature, ◦C
ΔTChange in temperature, ◦C
ASurface area, m2
RLRayleigh number
GrGrashof number
PrPrandtl number
gGravitational constant, m/s2
βVolumetric expansion coefcient, k−1
DmDiameter of mitad, m
L Characteristic length, m
vKinematic viscosity, m/s2
NuNusselt number
hc−p−cConvective heat transfer coefcient from baking plat to cover lid, W/m2.k
hr−p−cRadiative heat transfer coefcient from baking plat to cover lid, W/m2.k
hc−c−aConvective heat transfer coefcient from the cover lid to surrounding, W/m2.k
hr−c−aRadiative heat transfer coefcient from the cover lid to surrounding, W/m2.k
hc−s−aConvective heat transfer coefcient from side of mitad to surrounding, W/m2.k
hr−s−aRadiative heat transfer coefcient from the side enclosure to surrounding, W/m2.k
Ub−cl Over heat transfer coefcient from baking mitad to cover lid, W/m2.k
Ucl−sOver heat transfer coefcient from cover lid to surrounding, W/m2.k
Us−sAll over heat transfer coefcient from the side enclosure to surrounding, W/m2.k
Qloss,b−cl Heat loss from baking surface to cover lid, KJ
Qloss,cl−sheat energy loss from cover lid to the surrounding, KJ
Qloss,s−sHeat loss from side enclosure to surrounding, kJ
tinsu Thickness of bottom insulators, m
tS,insu Thickness of side insulators, m
tTTotal time required for baking session, min
ϵEmissivity of the material
δStefan Boltzmann constant, W
m2.K4
CRediT authorship contribution statement
Altaseb Kegne Sisay: Writing – original draft, Methodology, Investigation, Formal analysis, Data curation, Conceptualization.
Melese Shiferaw Kebede: Visualization, Supervision, Conceptualization. Abayenew Muluye Chanie: Writing – review & editing,
Supervision.
Declaration of competing interest
The authors declare that they have no known competing nancial interests or personal relationships that could have appeared to
inuence the work reported in this paper.
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