A Computational Analysis of the Radiative and Convective Processes that Take Place in Preheated and Non-Preheated Ovens (original) (raw)
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Journal of Food Engineering, 2004
A fully predictive, algebraic method has been developed for the prediction of the timewise temperature variation of a thermal load situated in an electrically heated oven. The model which underlies the method takes into account both natural convection within the oven cavity and radiation between the thermal load and the oven walls. The model provides a complete description of heat transfer external to the thermal load. It can be used to provide boundary conditions for an analysis of thermal loads of various heatconducting characteristics. This method is able to accommodate loads of various shapes, sizes, materials, and radiation surface finishes, as well as oven heating conditions characterized by a wide range of oven setpoint temperatures. Extensive experiments were performed to validate the predictive method. These experiments encompassed thermal loads of different shapes, masses, and surface finishes. Measurements were made of the transient response of the thermal load. The results of these experiments, presented in , reveal overall agreement to within about 1% between the predictions and the data, thereby validating the veracity of the assumptions that underlie the predictive model. Encompassing temperature data were collected at 170 sites on the oven walls. These data have been brought together in the form of isotherms. Among the walls, the temperatures on the oven door were the lowest, whereas the highest temperatures were encountered on the oven floor and on the top wall. Thermal symmetry was found to prevail on most of the walls, with the greatest deviations from symmetry in evidence on the sidewalls.
Convection and radiation combined surface heat transfer coefficient in baking ovens
Journal of Food Engineering, 2009
The combined surface heat transfer coefficient is a determining parameter of convective baking process time and efficiency, as well as the resulting food product quality. By this study, the combined surface heat transfer coefficient term was determined at the convective oven temperature range of 70-220°C, with fan (turbo) and without fan (static oven) applications. The methods of ''Lumped Capacity" and ''Time-Temperature Matching" were used. Both methods utilize the time-temperature data at a fixed position of a definite material, during unsteady state heating up period inside the convective oven. The increase in oven temperature and the fan application in the oven derived higher calculated values of surface heat transfer coefficients. Good agreement was observed between both methods and the literature values. The given methods are applicable to other oven types and heating modes.
IJERT-Effect of Convection Mode on Radiation Heat Transfer Distribution in Domestic Baking Oven
International Journal of Engineering Research and Technology (IJERT), 2019
https://www.ijert.org/effect-of-convection-mode-on-radiation-heat-transfer-distribution-in-domestic-baking-oven https://www.ijert.org/research/effect-of-convection-mode-on-radiation-heat-transfer-distribution-in-domestic-baking-oven-IJERTCONV7IS12017.pdf The aim of this study is to analyze on the effect of radiation heat transfer inside an oven under natural and forced convection modes using network representative method. This analysis is important to understand the fundamental principle of heat transfer occur in an oven. Most previous work focused on conduction and convection process in an oven instead of radiation which leads to this research. The experiment was conducted using the baking oven with temperature ranges from 180°C, 200°C and 220°C. The oven was pre-heated 10 minutes prior taking the temperature reading for duration of maximum 20 minutes. The data collected were recorded in the data logger. Based on these data, analysis on the radiation exchanges that occurred inside the oven chamber were performed by the network representative method. The radiation rates of all surface involved were successfully determined. With the calculated radiation rate, analysis on the effects of radiation under natural convection and forced convection modes were performed. Based on the temperature profiles and radiation rate patterns, it was proven that the forced convection mode has more radiation effect compared to natural convection mode.
Modeling of transient natural convection heat transfer in electric ovens
Applied Thermal Engineering, 2006
Prediction of transient natural convection heat transfer in vented enclosures has multiple applications such as understanding of cooking environment in ovens and heat sink performance in electronic packaging industry. The thermal field within an oven has significant impact on quality of cooked food and reliable predictions are important for robust design and performance evaluation of an oven. The CFD modeling of electric oven involves three-dimensional, unsteady, natural convective flow-thermal field coupled with radiative heat transfer. However, numerical solution of natural convection in enclosures with openings at top and bottom (ovens) can often lead to non-physical solutions such as reverse flow at the top vent, partly a function of initialization and sometimes dependent on boundary conditions. In this paper, development of a physics based robust CFD methodology is discussed. This model has been developed with rigorous experimental support and transient validation of this model with experiments show less than 3% discrepancy for a bake cycle. There is greater challenge in simulating a broil cycle, where the fluid inside the cavity is stably stratified and is also highlighted. A comparative analyses of bake and broil cycle thermal fields inside the oven are also presented.
A methodology to model flow-thermals inside a domestic gas oven
Applied Thermal Engineering, 2011
In this paper, the authors describe development of a CFD based methodology to evaluate performance of a domestic gas oven. This involves modeling three-dimensional, unsteady, forced convective flow field coupled with radiative participating media. Various strategies for capturing transient heat transfer coupled with mixed convection flow field are evaluated considering the trade-off between computational time and accuracy of predictions. A new technique of modeling gas oven that does not require detailed modeling of flow-thermals through the burner is highlighted. Experiments carried out to support this modeling development shows that heat transfer from burners can be represented as nondimensional false bottom temperature profiles. Transient validation of this model with experiments show less than 6% discrepancy in thermal field during preheating of bake cycle of gas oven.
Heat transfer and heating rate of food stuffs in commercial shop ovens
Sadhana, 2007
The CFD analysis of flow and temperature distribution in heating ovens used in bakery shop, to keep the foodstuffs warm, is attempted using finite element technique. The oven is modelled as a two-dimensional steady state natural convection heat transfer problem. Effects of heater location and total heat input on temperature uniformity of foodstuffs are studied. Placing the heater at the bottom of the oven improves the air circulation rate by 17 times and 10 times than that at the top and side of the oven. But the top location provides better uniformity in foodstuff temperature than the other cases. Side location is not preferable. In the present ovens, the heating elements are located at the top. The analysis shows that if heaters are located at the bottom along with additional flow guidance arrangements, energy efficient oven configuration can be obtained.
International Journal of Heat and Mass Transfer, 2002
An in-depth experimental study of heat transfer in ovens has provided basic data that is directly applicable to design. Heat transfer coefficients were measured for thermal loads having either black or highly reflective surface finishes. Approximately 100 different data runs were carried out. These heat transfer coefficients enabled the separation of the heat transfer into convective and radiative components, with radiation being the dominant transfer mechanism for blackened loads. The thermal response of the load to the presence of blockages situated either below or above the load was quantified. This response was only slightly affected by the blockages when they were empty of water, but major effects were observed when the blockages were water filled. Major effects were also encountered when the load was supported from below by cookie sheets. On the other hand, extensive investigation of various positions throughout the oven indicated a very weak effect of load position on the thermal response. Ó
One temperature model for effective ovens
Most of the thermodynamic analysis of ovens are focused on efficiency, but they need to behaves under real-life conditions, then the effectiveness of the ovens plays a crucial role in their design. In this paper we present a thermodynamical model able to describe the temperature evolution in ovens, furnaces or kilns to harden, burn or dry different products and which provides a methodology to design these heating devices. We use the required temperature evolution for each product and process as main ingredient in the methodology and procedure to design ovens and we place in the right role the efficiency criteria. We use global energy balance equation for the oven under transient situation as the thermodynamic starting point for developing the model. Our approach is able to consider different configurations for these heating devices, or recirculating or open situations, etc.
ANALYSIS OF BAKERY HEATING OVENS
wseas.us
CFD analysis of flow and temperature distribution in heating ovens used in bakery shop, to keep the foodstuffs warm, is attempted using finite element technique. The oven is modeled as a twodimensional steady state natural convection heat transfer problem. Effects of number of heaters and total input power on temperature uniformity of foodstuffs are studied. The heaters are located at bottom with different number of coils (One, Two and Three) and different input power (10 W, 15 W, 25 W and 50 W) are analyzed. Placing the two heaters with input power 15 W at the bottom of the oven improves the uniform heating of foodstuffs than the one and three coils. The analysis shows that if heaters are located at the bottom along with additional flow guidance arrangements, energy efficient oven configuration can be obtained.
Performance Modeling and Parametric Analysis of a Double Glazed Solar Oven
Journal of Clean Energy Technologies, 2015
This paper investigates the thermal performance of a unique box type solar oven whose five sides are exposed to ambient and provisions are also provided to install the reflectors to enhance the intensity of incident solar radiation on the oven. Experiments were performed where temperatures attained inside the box cavity are recorded on different days and times of the day corresponding to various intensities of available solar radiation. A steady sate heat transfer numerical model of the solar oven without reflectors is also developed based on six individual thermal resistance networks which account for the heat losses through each flat-side of the oven box and a good agreement with the experimental data is achieved. A parametric study based on numerical calculations and experiments is then carried out to study the effects of various parameters on oven's thermal performance, e.g. number of glazings, distance between glazings and box, type of absorber coating, etc. Higher box temperature is attained using double glazing than single glazing. As compared to black paint, selective surface coating results in significantly higher oven temperatures (up to 40 o C). Plate spacing of 20-30 mm is found to be optimum distance between oven box and glass covers. Index Terms-Solar oven, oven box temperature, reflectors, overall heat transfer coefficient.