Convection and radiation combined surface heat transfer coefficient in baking ovens (original) (raw)

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.

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.

Investigation of heat transfer and mass transfer parameters in a convection oven for model foods

2020

Forced air convection systems are the most preferred design of choice in many of the industrial-scale convection ovens. In this study, experimental investigation on convective heat transfer and mass transfer within a forced air convection oven was performed at different oven temperatures (100℃, 110℃ and 120℃) and at flow velocity (2m/s, 3m/s and 4m/s) using potato slices (10*10*60mm) as model food. The Yıldız et al., 2007 approach with slight modification was applied to estimate the effective convective heat transfer and mass transfer coefficient during convection frying. In addition to the experimental approach, the empirical correlation method was also used to calculate the convective heat transfer and mass transfer coefficient and compared with the coefficient values obtained from the experimental method. The effective heat transfer and mass transfer coefficient obtained from the Yıldız et al., 2007 method was found to be almost constant with increasing oven temperature. However, with increasing flow velocity the effective heat transfer coefficient increased but the influence of flow velocity on effective mass transfer coefficient was not significant. The comparison of the coefficient values obtained from the experimental method and the empirical correlations showed that the experimental method yields quite low values than the empirical method. This study was carried out as a degree project in food engineering at the Department of Food Technology, Engineering and Nutrition under the supervision of Associate Professor Andreas Håkansson. The examiner of the project is Professor Marilyn Rayner, Department of Food Technology, Engineering and Nutrition. Firstly, I would like to express my sincere gratitude to my supervisor Prof. Andreas Håkansson for giving me the opportunity to carry out this project and guiding me by providing his valuable suggestions and feedback throughout the project. Secondly, I would like to thank Grant Thamkaew Doctoral student at Department of Food Technology, Engineering and Nutrition for providing instructions required to operate the convection oven and cooperating during the entire project. Finally, I thank Almighty for being able to give my best and my special thanks go to my parents and friends for their constant moral support and encouragement which helped me to successfully completion this project.

A Computational Analysis of the Radiative and Convective Processes that Take Place in Preheated and Non-Preheated Ovens

Heat Transfer Engineering, 2003

This paper presents a computational method that implements an analytical approach to the determination of the thermal processes which take place in an electrically heated oven. The integral equations of radiative heat transfer were specialized to the threedimensional temperature field in the oven and numerically evaluated. The radiative fluxes at the surfaces of a thermal load situated in the oven were obtained in this way and combined with natural convection fluxes extracted from a well-established correlation.

Empirical Modeling Study in Predicting Temperature Profile within the Convective Oven

2015

Baking process is an important unit operation in the food industry. A good understanding on the dynamic behavior during baking process is important to ensure proper control. This study aims to develop the empirical model of the cake baking process using laboratory scale convection oven. Set point temperature was chosen as the manipulated variable and actual oven temperature was the controlled variable. No disturbance was considered in this process. Empirical model is developed by applying step change in the set point temperature. The model is represented using second order plus time delay (SOPTD). By increasing the operating temperature, there is a significantly decreases of process gain of the system and the damping coefficient, and a significantly increases of natural damping coefficient and time delay. The developed model fits well with the validated data, R2 > 0.9.

Heat Transfer Coefficients on Cakes Baked in a Tunnel Type Industrial Oven

Journal of Food Science, 1999

Using an h-monitor, surface heat flux and effective surface heat transfer coefficients were evaluated during baking of two cakes in a tunnel-type multi-zone industrial oven. An average 75–80% of total heat flux was counted as radiation heat. Air-mass temperature outside the boundary layer was determined from the experimental temperature profiles over the h-monitor top plate. In the range of baking temperatures (186–22 5°C), relative air velocities (0.02-0.437 m/s) and absolute humidities (0.0267–0.0428 kg H2O/kg dry air) heat transfer coefficients were 20 to 48.0 W/m2K. A simple regression model was developed based on experimental data.

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.

Convection Oven Frying: Heat and Mass Transfer Between Air and Product

Journal of Food Science, 1980

Heat and mass transfer between air and product, fried in a specially designed forced convection oven were analyzed. Minced meat loaves of an industrial recipe were fried for 1 hr at different temperatures, humidities, and velocities of the air. It was shown that the moisture loss rate was larger in the beginning of the frying than at the end. The heat transfer coefficients varied between 20 and 90 W/m2 "C. These values are low compared with other frying methods. The mass transfer coefficients varied between 0.04 and 0.115 m/s. The coefficients decreased markedly in going from the constant rate period to the falling rate period.

On the use of combined heat flux measurements and image analysis procedures for the change of scale between industrial and pilot ovens

Procedia Food Science, 2011

Searching for optimal baking conditions for cereal products in industrial ovens by trial and error is a very costly process. Therefore, a procedure involving a change of scale is often needed, where the baking cycle can be optimized in a much smaller sized pilot oven. The quality and sensory attributes of baked cereal products are linked to the heat flux received by the product during baking. However, the net flux seen by the product can involve complex combinations of heat and mass transfer, chemical reactions and changes in the product over time. A tractable change of scale between the industrial oven and the pilot is based on a simpler flux measurement, which basically takes the process conditions into account. In this article we define baking conditions in the industrial line by measuring the convective and radiative fluxes received by commercial sensors lying on the conveyor belt amongst the products. We show that reproducing these fluxes in a small-sized pilot leads to products with similar color and mass loss to those in the industrial oven. This change of scale (down-scaling) means that baking conditions in the pilot can be optimized with respect to the product properties and the optimized baking cycle can then be replicated in the industrial oven (up-scaling). In order to validate this approach suitable tools are required to quantify the product properties. We highlight the use of image analysis to quantify macroscopic properties (e.g. color) and microscopic properties such as the size distribution of 3D air cells in the bread upon which sensory and mechanical properties depend.

An instrumented oven for the monitoring of thermal reactions during the baking of sponge cake

Journal of Food Engineering, 2010

An electric convective oven was conceived and equipped to allow monitoring thermal reactions during the baking of sponge cake. High total heat fluxes of between 6000 and 9000 W m À2 were recorded under baking temperatures of 140-200°C. The mapping of thermal conditions indicated satisfactory thermal homogeneity, with average temperature variations of 5°C and maximum relative variations of the convective heat transfer coefficient of 15% on the thermal domain investigated. Internal heat and mass transfers, the extent of thermal reactions within the sponge cake and repeatability of the baking operation were all characterized by experimental measurements. Some of the main operating variables were monitored in the cake (core and surface temperatures, moisture content, levels of chemical reactants and products) and others in the baking atmosphere (temperature, humidity and concentrations of volatile compounds). Specific non-disruptive sampling devices were designed to extract data from cakes and the oven atmosphere in order to follow the kinetics of thermal reactions during the baking operation. Three phases could be identified during baking, corresponding to the relative importance of conductive and evaporative internal heat transfer regimes and to macroscopic changes in the cake structure with formation of a crust. The progress of thermal reactions was monitored with satisfactory precision in both the cake and the baking vapors: relative standard deviations of 2% and 8.7% were obtained respectively for the water content and hydroxymethylfurfural (HMF) content of three replicates during a baking operation.