Heat Loss Factor Research Articles

Heat recovery opportunities from electrical substation transformers

The transformation of voltages in electrical substations leads to energy losses in the form of waste heat; the quantity of which depends on transformer size and electrical loading. This paper investigates how a novel waste heat source, namely transformer waste heat could be harvested and distributed via district heating networks. Firstly, the investigation considered nameplate heat loss factors to quantify the theoretical waste heat potential from electrical substation transformers in England, Wales and Northern Ireland, which varied from 3.0 to 5.4 TWh a−1, equivalent to between 0.7 and 1.25% of annual heat demand for these countries, depending on loading assumptions. A number of heat recovery approaches which could be integrated with existing transformer cooling systems were then proposed. A spreadsheet model was then developed to simulate heat recovery from a transformer, together with the upgrade of the recovered heat using a heat pump prior to delivery via district heating. The model was used to evaluate the merits of capturing transformer waste heat losses, estimated using industry supplied electrical loading data, to meet different heat network demands based on an existing network, compared to conventional heating technologies. Findings suggest that the system proposed can achieve levelised costs that are up to 17% lower than the running costs of air-source heat pumps, whilst reducing emissions by almost 80% when displacing gas boilers. The methodology hereby described can also be used to evaluate the feasibility of recovering transformer waste heat in other countries.

Innovative mini-channel design for a compound parabolic solar thermal collector serving intermediate temperature applications

The heat flux in the focal region of a compound parabolic collector (CPC) and the receiver's surface is varying and ununiform, and its effective absorption is one of the challenging tasks. It opens new opportunities for suitable and appropriate designs for the receiver. Thus, a new design of the mini-channel receiver is proposed based on fluid flow optimization to address the issue. The pressure drop analysis enables the decision of the dimensions of the proposed mini-channel receiver. MATLAB programming enables flow optimization through a mini-channel receiver under variable solar flux falling its surface to attain the highest possible temperature. The performances of the optimized and parallel fluid flow mini-channel receivers are compared by integrating them with CPC.The results revealed that the thermal gain of CPC-optimized fluid flow mini-channel increases by 23% with minimum pressure drop and shows the variation in the outlet fluid temperature from 82 to 155 °C under the fluid flow rates 1.5–4 l/h. The results show a reduction in the heat loss factor, which ultimately contributed to increasing CPC's efficiency. Thus, the proposed new design of an optimized fluid flow mini-channel receiver will help researchers design and develop efficient solar thermal systems.

Experimental Investigation of Heat Transfer Coefficient in Parabolic Dish Solar Cooker with Thermal Energy Storage System

Abstract: The use of solar cooking can help cut back on the consumption of fossil fuels. Due to the rising expense of fossil fuels, there is a great demand for an energy efficient and affordable solar cooking technology, and it is currently the most popular study topic worldwide. This study examines how a thermal energy storage material (Erythritol) can improve the thermal performance of solar parabolic dish cookers. On the cooking vessel with and without thermal energy storage material, tests for stagnation temperature and water boiling and cooling are performed. In terms of thermal performance, heat loss factor, optical efficiency experimental results for the two instances are analysed. Heat loss factor was found to be 16.8 W/m2K and 28.21 W/m2K in with and without thermal energy storage system

Experimental study of phase change material performance as thermal insulation of a double-walled spherical tank under partial vacuum for storing solar energy

In solar systems, conservation of stored energy is even more important than energy storage. In this study, as an innovative idea, the thermal behavior of a phase change material (PCM) is investigated as thermal insulation of an energy storage tank based on the unique feature of phase change at a constant temperature. Condition for creating an ideal insulation is the existence of a heat source at the border. The PCM surrounding the tank stores the solar energy latently in the process of thermal charging, and as a heat source in the process of thermal discharge. By releasing energy at a constant temperature through the PCM, the heat loss factor that is the temperature difference between the hot water and the surface of the tank is controlled. The PCM shows three different behaviors as the thermal insulation. One, as long as the energy stored in the PCM is sensibly released, the heat loss coefficient is almost constant, in which the PCM acts as a super insulator. Two, by releasing the latent energy, the heat loss coefficient tends to zero, and the PCM acts as an ideal insulator. Three, by releasing all the stored energy, the PCM acts as a normal insulator. Creating the relative vacuum between the tank and the glass cover improves the thermal performance, thereby the hot water temperature decreases by 7.4 °C in the best case, and the thermal efficiency reaches 85%.

Combined effect of solar intensity and air mass flow rate on inline spherical dimple based solar air heater during summer season

Experimental investigation was done in this study to compare the effectiveness of flat and inline spherical dimple engraved absorber plates solar air heater (SAH). During the summer, a SAH with a single glass cover, one pass, and two different types of absorber plates was evaluated on alternating days by taking readings from 9.30 a.m to 2.00p.m at an interval of 30 min. In order to conduct the investigation, the air mass flow rate (Ma) was raised from 0.0098 kg/s to 0.0520 kg/s (corresponding Re: 1861–10218) while solar intensities varied throughout the days. By increasing the Ma, various parameters were measured and different thermal characteristics were examined, such as the convective heat transfer coefficient, the blower’s power consumption, extracted power, effective power, efficiency, the heat gain factor, the heat loss factor, the SAH-efficiency factor, the averaged Nusselt number (Nu), and the averaged friction factor (f). The investigation reveals that with an increase in Ma, both flat and dimpled roughened SAH exhibit an increase in convective heat transfer coefficient, extracted power, instantaneous efficiency, heat gain factor, heat loss factor, and SAH-efficiency factor. However, the enhancement rate of inline dimple plate-solar air heater (IDP-SAH) due to engraved dimples is always higher than the flat plate-solar air heater (FP-SAH). Up to a particular Ma, both types of SAH have higher effective efficiencies. Thereafter effective efficiency decreases due to a significant increase in required pumping power. Comparing IDP-SAH to FP-SAH, the averaged Nu and the averaged f of IDP-SAH is 83.42% and 176.51% greater, respectively. In addition, the effective efficiency of IDP-SAH is 31.24% higher than the FP-SAH. The friction factor (f) starts to decline as the Ma increases. Even though the IDP-SAH and FP-SAH performance analyses were conducted on different days during the summer, IDP-SAH outperformed FP-SAH. The indentation of dimple on absorber plate helps in increasing surface area as well as helps in changing flow structure which is responsible for augmentation of heat transfer rate.

Linear Stability of the Activation-Energy-Asymptotics Reactive-Layer Structure: I. Liñán’s Premixed-Flame Regime

ABSTRACT Overall linear instability characteristics of an asymptotically thin reactive layer in a flame are investigated, particularly for Liñán’s premixed-flame regime of activation-energy asymptotics. The reactive-layer instability analysis, formulated with the characteristic length and timescales of the inner reaction zone, is carried out not only by a numerical method but also by an asymptotic method, with the small expansion parameter obeying the distinguished limit of and , where , , and denote the downstream heat-loss factor, the Zel’dovich number, and the Lewis number, respectively. The asymptotic analysis yields an explicit dispersion relation, which is comprised of three distinct destabilizing or stabilizing contributions: (i) the reaction sensitivity associated with the downstream heat-loss effect, (ii) the reaction sensitivity associated with the preferential diffusion effect, and (iii) the diffusive relaxation. Three instability modes, namely cellular instability, planar instability, and pulsating instability, are found to be similar to the conventional diffusional-thermal instability. Consequently, the reactive-layer instability is seen to be good enough to serve as a general baseline for diffusional-thermal instability, despite lacking the detailed instability characterization in the proximity of , the corrections for which can be achieved by the conventional diffusional-thermal instability analysis within the NEF (nearly-equidiffusional flame) limit.

Investigating the Heat Release Rate of Large-scale Calorimeter using FDS Analysis

This study aims to identify the key design factors of a large-scale calorimeter and evaluate the accuracy of the simulation results using the Fire Dynamics Simulator (FDS) program. The design specifications of a domestic large-scale calorimeter were analyzed to determine the modeling and input conditions for the simulation. The simulation results of temperature, mass flow rate, and oxygen concentration reduction inside the duct were compared with the experimental results for heptane pool fires with diameters of 1.1 m, 1.24 m, and 1.44 m, respectively. To validate the accuracy of the simulation results, the deviations, calculated using FDS for the heat release rate as the experimental value, were found to be 19.12%, 11.86%, and 0.22% for temperature, mass flow rate, and oxygen concentration, respectively. Ultimately, the results of the heat release rate inside the duct obtained by the oxygen consumption method with FDS were found to be consistent with the experimental value, within 2.58%. However, the deviation of oxygen concentration is reduced as the deviation of mass flow rate increases for a constant heat release rate. This implies that for more accurate analysis, the heat loss and shape factors in the duct should be considered.

Performance analysis of parabolic dish solar cooking system with improved receiver designs

Lack of access to clean energy for cooking and heating applications is one of the challenges faced by households in developing countries. Solar cooking is one of the solutions, but suffers low adoption and utilization due to various challenges including technical limitation. This study investigated initiatives on improving the technical viability of parabolic dish solar system used for direct cooking by focusing on the receiver. Three receiver prototypes namely; Insulated, Oil-filled and Air-filled, all incorporated with a base circular ring, were constructed and their performance was compared experimentally with the conventional receiver. The maximum temperature inside cooking vessels were 154 °C, 99 °C, 141 °C and 128 °C while standardized stagnation temperature and first figure of merit (F1) were found to be 159 °C, 100 °C, 154 °C and 109 °C; and 0.26, 0.15, 0.54 and 0.17, for systems with insulated receiver, oil-filled receiver, air-filled receiver, and conventional receiver, respectively. The second figure of merit (F2), overall heat loss factor, heat exchange factor and optical efficiency were determined as 0.36, 0.15, 0.14 and 0.33; 59.7 W/m2 K, 28.6 W/m2 K, 20.49 W/m2 K and 73.4 W/m2 K; 0.18, 0.75, 0.69 and 0.23; 25%, 4%, 4% and 17%. The study found that the cooking system with Insulated Receiver gave more merits and was established as the best.

Investigation of a High-Pressure Turbine Stage in a High-Speed Rotating Transient Test Facility for Rotor Tip Study and a Parametric Study for Improved Heat Transfer Calculation

Abstract The first part of the paper presents commissioning of a single-stage high-pressure (HP) turbine employed in a series of extensive experiments to study the aerodynamics and heat transfer on the rotor surface and casing liner. The Oxford Turbine Research Facility (OTRF), a high-speed rotating transient test facility has the capability to take unsteady aerodynamic and heat transfer measurements at engine representative conditions with a variety of inlet temperature profiles including radial distortion and swirl. A temperature profile survey was conducted at the inlet of the HP nozzle guide vane (NGV). Static and total pressure and temperature measurements have been taken at various locations on the rig including NGV surface, inlet and exit, and rotor exit to establish rig operating conditions. Detailed description of mass flow rate measurements along with calculation of heat loss factor in the rig is presented. The second part of the paper presents a parametric study performed to improve heat transfer measurement calculations from high-frequency response thin-film gauges. The effect of parameters like material properties and thickness of substrate on heat flux has been studied. A detailed uncertainty analysis for heat flux is also presented. A thermal model calibrated with analytical solutions has been developed to optimize thin-film gauge configurations and to study side-conduction effects.

Exergetic performance, combustion and emissions studies in a CI engine fueled with Al2O3 nano additive in a mixture of two different biodiesel and diesel blends

ABSTRACT This study uses an equal proportion of two different biodiesels obtained from waste cooking, neem oil and blended with diesel fuel to investigate the diesel engine’s combustion, emission, and exergetic performance. Al2O3 nano additive of 50ppm and 100ppm is used in diesel-biodiesel blends of B10 and B20 to improve the overall performance of the engine. The experimentations are conducted on a single-cylinder, four-stroke diesel engine at a fixed speed. The results reveal that 50ppm in the B10 blend improves the combustion with high exergetic efficiency and low exergy destruction. The various heat loss factors like exhaust, cooling, and radiation from the engine are determined using the second law of thermodynamics and the loss factor results reveal that the blend B10 with 50ppm shows high useful work of 32.84% with low radiation losses of 32.05% at 75% load. At 100% load, the blend B20 with 50ppm dominate the other blends. Finally, the addition of Al2O3 in biodiesel blends refines the combustion as a result, low exhaust emissions of NOx, CO, UHC, and smoke are reported.

Extensive experimental validation of a model for pneumatic drying of cassava starch

A pneumatic drying model, developed in a previous work, was tested and validated based on a series of 56 experiments of cassava starch drying conducted on a pilot-scale pneumatic dryer. After fitting two parameters, the average diameter of starch particles and a heat loss factor, the model predicted the effects of main operating conditions with a level of accuracy comparable to that of the experimental measurements. Transient phases with sudden variations of product feed rate were also successfully simulated. The model is therefore suitable for equipment design purposes. The experimental results showed that the size of starch particles considerably decreases with increasing air velocity. As a result, at high air velocity, despite the shorter residence time in the drying pipe, the overall drying performance is improved due to the smaller particle size. It is therefore possible to increase air velocity, and hence product feed rate and production capacity, without detrimental effect on the drying efficiency.

Experimental studies on in-cylinder combustion, exergy performance, and exhaust emission in a Compression Ignition engine fuelled with neat biodiesels

In the last decade, the search for cleaner fuels like biodiesels is gaining wide popularity, and exergy analysis are widely used in design and performance evaluation to identify the various losses. In this study, three neat biodiesels are tested for energy and exergetic performance in a single-cylinder, four-stroke IDI diesel engine. The experiments are conducted for waste poultry fat biodiesel (WPFBD), palm oil biodiesel (POBD), and waste cooking oil biodiesel (WCOBD) at various loads by maintaining a fixed rpm of 1500. Parameters like exergetic efficiency, exergy destruction, and various heat loss factors are computed from the thermodynamic models. The in-cylinder combustion pressures, heat release rate, and fuel consumption are also measured. Results show that WCOBD dominates the other two biodiesels by achieving high exergetic efficiency (52.74%) and low exergetic destruction (3.74 kJ). The in-cylinder combustion pressures and net heat release for WCOBD show smoother combustion with better torque conversion. In contrast, POBD shows high fuel consumption and more unaccounted heat losses. Better utilization of heat input by converting it into useful work was achieved for WCOBD at 75 and 100% loads. Similarly, the exhaust emissions from WCOBD compared with diesel fuel at all the loads reveal that except for NOx, there is a drastic reduction of CO, UHC, and exhaust smoke.

Performance investigation of a new designed vacuum flat plate solar water collector: A comparative theoretical study

This paper presents a new design of vacuum flat plate solar collector (VFPSC). This inspired design is based on a combination of two conventional systems; the flat plate solar collector (FPSC) and the evacuated tube solar collector (ETSC). The new configuration, which is characterised by a curved evacuated cover and rear Rockwool insulation is compared with FPSC and ETSC. Collectors’ performance is predicted through a theoretical approach that includes heat transfer and energy balance equations, where thermo-physical and geometrical properties of each collector are considered. The developed computational program is validated against experimental results carried out on FPSC. The optimal number of tubes is identified to perform a comparative study under the best efficiency point for different values of absorber emissivity including collectors’ cost. The new VFPSC proves that the combination of front vacuum insulation and back opaque thermal insulation can result in significant heat loss reduction, and thus performance enhancement for the whole emissivity range. As a result, the proposed VFPSC provides more thermal efficiency than FPSC and ETSC by 7.13% and 28.32%, respectively, for an emissivity of 0.95, while for an emissivity of 0.05, it reaches ratios of 22.77% compared to FPSC and almost the same ETSC efficiency levels, with a much lower cost. Moreover, it shows lower heat loss factor compared to other similar VFPSCs. Overall, VFPSC offers a promising solution that has the required ability for producing hot water with a low cost and may take place as heating device in buildings and industrial sectors.

Experimental study of downward flame spread and extinction over inclined electrical wire under horizontal wind

Flame spread and extinction behavior are significantly influenced by both fuel inclination and wind velocity, however, the coupling effect of two has not been well quantified yet. In this paper, downward flame spread and extinction over inclined electrical wire under horizontal wind is investigated. Polyethylene(PE)-insulated wires (0.5 mm/0.15 mm in core diameter/insulation thickness) of two representative core materials (Copper/Nickel-Chrome: high/low conductivity) are used as samples. Flame geometrical characteristics (flame length Lf, pyrolysis length Lp, gas-phase thermal length Lg), as well as the flame spread rate (FSR) are quantified. Results show that as the horizontal wind velocity increases, FSR demonstrates a non-monotonic trend before extinction, where four regimes are identified based on different heat transfer controlling mechanisms. On the other hand, FSR of Cu-core wire and NiCr-core wire show different dependence on inclination angle. FSR reaches the maximum when the flame is pushed by the horizontal wind to be parallel to wire, which can be explained by a balance of horizontal wind and buoyancy-induced flow (i.e. inclination). A quantified model based on the three characteristic lengths (Lf,Lp,Lg) and a proposed mixed-convective coefficient hmix combining the effect of inclination angle and wind velocity is established. The proposed model well represents the experimental FSR and interprets the controlling heat transfer mechanism. Moreover, the extinction limit is represented by a heat loss factor Rloss as a function of strain rate a, showing an enhanced quenching effect and a weakened blow-off effect with increased inclination angle. The flame with Cu-core is more difficult to extinguish at small inclination but becomes easier at large inclination than that with NiCr-core, indicating a transition of inner core role from “heat source” to “heat sink”. This work provides essential knowledge on flame spread and extinction mechanism over inclined fuel under wind.

Experimental investigation of a Scheffler reflector for the medium temperature applications

This research problem reveals the experimental investigation at a pressure of 1.5 bar and temperature of 120°C for the medium thermal applications utilizing the four Scheffler reflectors with 16 m2 surface area each. The Scheffler collector associated with absorber plate of mild steel of size, 0.45 m diameter, and 0.025 m thick was assessed in June 2018. The variation in solar beam radiation over the entire day was observed from 840 W/m2 to 1278 W/m2, while, the absorber plate temperature was recorded within the extent of 116–195°C, however, the maximum heating temperature was measured 129°C at the end-use. The Scheffler collectors performed appropriately in the morning and evening time with substantial heat loss factor and lower optical efficiency factor. The energy efficiency of 59.28% has been achieved which is higher as compared to the parabolic solar concentrator. The higher concentration ratio of the Scheffler collector indicates it as an efficient substitute to replace fossil fuels. The system is viable for more than 1600 kWh/m2 yearly solar potential while the cost of heating is greater than 0.05 $/kWh for them. This paper concludes that the Scheffler reflector is the most promising solar technology for the medium-temperature applications.

The efficiency of thermosyphon solar water heating system and traditional solar water heating system

Loop thermosyphon (LT) is typically used for solar water heaters (SHW) to solve the freezing and corrosion issues. The LT – SWH system has a less night time heat loss compared to conventional SWH due to its thermal diode property but a greater heat loss due to the secondary heat exchange. However, the above interactions have rarely had an effect on system performance based on long-term operation [6]. In this paper, the annual results of above two processes, including productive supply day numbers and efficient heat gains and night power losses, was evaluated in this analysis in two separate operating modes on the basis of standard meteorological year data from the City of Fuzhou. Variations of the above variables are addressed with the change in the stated temperature. The results show that the effective delivery days of the LT – SWH system are 139 and 153, respectively, in irregular heating method. The number of days is 168 to 173 in ongoing heating method. The SWH system is predictable to have a higher ratio at nighttime with an annual average of 15.07%, which equates to 6.15% for the LT – SWH system. In fact the LT – SWH method results in a lesser decrease in temperature at night and therefore a smaller raise in the temperature on the following day because of multiple relative heat loss factors running at various hours. The results produced are unpredictable, and lead to an approximately successful heat gain for the same month between November and April. The fixed temperature influences substantially the relative quantities of effective annual supply days and effective annual heat gain, slowly reducing the overall dominance of the LT – SWH method and even changing it as the set temperature increases [12]. This shift is triggered by the biggest daily heat loss leading the domination. In combination with a long static reimbursement time, a conventional SWH system must be substituted by an LT - SWHsystem, particularly when water temperatures are high on demand.

Energetic and exergetic performance comparison of three solar cookers for developing countries

Three different domestic solar cookers are compared experimentally during water heating experiments using different loads. The solar cookers experimentally tested using energy and exergy thermal performance parameters are: a solar box cooker without a reflector, a solar box cooker with a reflector and a parabolic dish solar cooker. The rate of heat losses is more detrimental to the performance of the parabolic solar cooker since the cooking vessel is exposed more to the ambient weather conditions. Heat losses seem to have little effect on the performance of the solar box cookers. The solar box cooker with the reflector shows the highest average energy efficiencies, which increase with the water heating load. The parabolic solar cooker shows the lowest average energy efficiencies with the lower loads, which increase to be higher than those of the solar box cooker without the reflector at the higher loads. The solar box cooker with the reflector shows the highest average energy and exergy efficiency values, which are not dependent on the water load. The parabolic dish solar cooker shows average exergy efficiencies, which increase with the water heating load. The greatest cooking potential in terms of the speed of cooking is shown by parabolic dish solar cooker. The best overall thermal performance is shown with the solar box cooker with a reflector, but its cooking speed is rather slow when compared to the parabolic dish solar cooker. The solar box cooker without the reflector shows the worst thermal performance in most of the tested parameters except for the heat losses where it shows the lowest heat loss factors for all the experimental tests.

Thermodynamic Analysis of Various Heat Loss Factors from a Diesel Engine Fueled with Neat Biodiesels

In this study, three neat biodiesels are tested for the energy and exergetic performance in a single-cylinder, four-stroke diesel engine. The experiments are conducted for waste poultry fat biodiesel (WPFBD), palm oil biodiesel (POBD) and waste cooking oil biodiesel (WCOBD) at various loads by maintaining a fixed rpm of 1500. Parameters like exergetic efficiency, exergy destruction and various heat loss factors are computed from the thermodynamic models. The in-cylinder combustion pressures, heat release rate and fuel consumptions are also measured. Results show that WCOBD dominates the other two biodiesels by achieving high exergetic efficiency (32.62%) and low exergetic destruction (1.158 kJ). The in-cylinder combustion pressures and net heat release for WCOBD shows smoother combustion with better torque conversion. Whereas POBD shows high fuel consumption and more heat losses. Better utilization of heat input by converting into useful work was achieved for WCOBD at 75% and 100% loads. Similarly, the exhaust emissions from WCOBD compared with diesel fuel at all the loads reveal that except NOx, there is a drastic reduction of CO, UHC and exhaust smoke are observed.

Experimental study of flame extinction with fuel diffusion combustion inside a wall-opening compartment under reduced ventilation conditions

The present study investigates experimentally the transient flame extinction behavior with fuel diffusion combustion inside a wall-opening compartments at reduced ventilation condition. The characteristic parameters to quantify the flame extinction mechanism include the Global Equivalence Ratio (GER) extinction time and critical gas temperature right before extinction. Their coupling effect on the dynamic process of flame extinction with fuel diffusion combustion inside compartments of various scales and opening sizes is quantified and formulated. It is found that: (1) flame extinction is easier to occur for smaller opening size or relatively larger compartment scale which could be well represented by two non-dimensional quantities i.e. the GER and non-dimensional heat loss; (2) the time to reach flame extinction is shorter as the fuel supply flow rate is higher while it is longer as the opening size is larger; (3) the gas temperature inside the compartment when flame extinction is reached first increases with fuel supply rate until a plateau is reached. A formula is established to describe the critical gas temperature right before extinction as a function of a newly defined non-dimensional integrated parameter including both fuel combustion heat release and heat loss factors in which the fuel supply rate opening ventilation compartment scale and transient extinction time scale are involved in general to reflect physically their interplay in controlling the flame extinction inside the compartment. The present study provides new observation quantification and formulation of the mechanism of flame extinction with fuel diffusion combustion inside a wall-opening compartment under reduced ventilation condition.

Solar cooking in Ethiopia: Experimental testing and performance evaluation of SK14 solar cooker

Fuel-wood shortage is a rising issue that has so far been frequently addressed. Solar cooking is a promising solution to firewood dependency, and the prettiest method to exploit solar energy. The objective of this paper is to manufacture and testing of the performance of SK14 solar cooker under the Ethiopian climate. The cooker was contrived from market available flat iron and reflective aluminum sheets having a reflective index of 0.9. Experimental tests without and with load were carried out. The performance tests were conducted on March 1st and March 13th, 2020 in Bahir Dar, Ethiopia. The no-load test results revealed that the maximum temperature, stagnation temperature inside the midpoint of the cooking pot and first figure of merit were 212 °C, 188 °C, and 0.22 °C/W/m2 respectively. The load tests have shown that the cooking power, standard cooking power, thermal efficiency, and second figure of merit are 635 W, 375.8 W, 46.4%, and 0.625 respectively. The cooling test also showed an optical efficiency of 51.59 and heat loss factors of 0.328. In conclusion, cooking power and achieved temperature acquired by SK14 confirms cooking of common Ethiopian dishes with great flexibility.