Development of an improved heating system for industrial tunnel baking ovens

This objective of this work was to develop, test and optimise the design of a novel gas-fired radiant burner suitable for incorporation into industrial tunnel ovens. Computational fluid dynamics (CFD) simulations have been used to model the burner and baking chamber environment, and in particular to predict radiation heat fluxes incident on the top surface of the food, both across the width of the baking chamber and along its length. Data from thermocouple sensors attached to a full-scale 40 kW prototype burner have been used to validate the CFD model. Initial results presented here show that CFD model predictions agree with experimental data to within 10%. CFD simulations have indicated that the new burner is capable of delivering irradiation to a travelling conveyor more uniformly than existing radiant burner designs. The effects of oven chamber humidity and surface emissivity on radiation heat transfer have been quantified.     

Bakery product characteristics as influenced by convection heat flux

Energy consumption and product quality changes are often observed as the ratio of the convection to the conduction modes of heat transfer varies in industrial baking ovens. Air and oven-wall temperature profiles as well as air velocity can affect the convection/radiation heat transfer and hence the quality of the baked products. A programmable pilot-plant oven was used to establish five baking profiles by measuring the total heat flux and the convective component using a special heat flux meter called an h-monitor. The purpose was to keep the total heat flux delivered to the h-monitor constant while varying the convective component from 27% (for the standard profile) to 11%, 22%, 33% and 37% by modifying air characteristics and wall temperatures. Industrial cupcakes were baked using the five established baking profiles and then evaluated in terms of quality parameters. Compared to the standard profile, a 10% reduction in volume expansion and a 30% increase in texture properties were observed for extreme oven conditions; top colour was always darker but more uniform for the conditions with less convection. The moisture content of the middle part of the cake was always higher than that of the top, bottom and sides. Baking industries are interested in using the pilot-scale oven to modify baking profiles for the purposes of quality improvement, product development and energy savings, rather than having to engage in high-cost trial and error practices on the production site.     

Computational fluid dynamics (CFD) modeling of an electrical heating oven for bread-baking process

Radiation is the most dominant heat transfer mode in an electrical heating oven. A 3D CFD model for an electric heating baking oven was developed. Three different radiation models namely, discrete transfer radiation model (DTRM), surface to surface (S2S) and discrete ordinates (DO) were employed for the simulation of the electrical baking oven. All models predicted almost similar results, which tallied well with the experimental measurements. During the full heating cycle, the oven set-point temperature was reached after 360 s. Lower temperature zones occurred near oven wall due to lower air flow. Based on preliminary evaluation of applicability, the DO radiation model was selected for bread baking simulation and validated with the experimental measurement of bread temperature. Bread simulation was carried out to study the profiles of temperature and starch gelatinization of crust and crumb of the product. This study indicated the baking process to be complete at 1500 s when the temperature of bread-center reached 100 °C.     

An investigation of bread-baking process in a pilot-scale electrical heating oven using computational fluid dynamics

A computational fluid dynamics (CFD) model was developed for bread-baking process in a pilot-scale baking oven to find out the effect of hot air distribution and placement of bread on temperature and starch gelatinization index of bread. In this study, product (bread) simulation was carried out with different placements of bread. Simulation results were validated with experimental measurements of bread temperature. This study showed that nonuniform air flow pattern inside the oven cavity leads to uneven temperature distribution. The study with respect to placement of bread showed that baking of bread in upper trays required shorter baking time and gelatinization index compared to those in the bottom tray. The upper tray bread center reached 100 °C at 1200 s, whereas starch gelatinization completed within 900 s, which was the minimum baking index. Moreover, the heat penetration and starch gelatinization were higher along the sides of the bread as compared to the top and bottom portions of the bread.     

Apparent Heat Transfer in a Forced Convection Oven and Properties of Baked Food

Parameters for expressing the heating performance and baking results of sponge cakes dependent on heating performance in a forced convection oven were studied. The heating performance of a forced convection oven may be expressed by the apparent heat transfer coefficient which was measured at various air temperatures and velocities. Both the air velocity and temperature of the circulating air affected the apparent heat transfer coefficient in a forced convection oven and determined the final properties of the baked food. The effects of these parameters on sponge cakes baked in the forced convection oven were observed.     

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

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.     

Effect of oven temperature profile and different baking conditions on final cake quality

This study discusses the effect of airflow on oven temperature profiles, the internal cake temperature and the final cake quality. It was found that the presence of airflow reduced the oscillation in the oven temperature profile from 12.98–30.27% to 3.17–4.02%. The bottom of the oven chamber experienced the greatest reduction in temperature oscillation in the presence of airflow. During the second stage of baking with airflow, the heating rate was increased from 5.07 to 7.52 °C min^?1 and 8.35 °C min^?1 to the increase of the baking temperature from 160 to 170 °C and 180 °C, respectively. The cake volume expansion rate was also increased 5–10% during second stage when baking with airflow condition. The cakes baked in the presence of airflow had a more porous crumb texture and lower moisture content compared to the cakes baked without airflow.     

Modeling of simultaneous heat and mass transfer during convective oven ring cake baking

The convective oven ring cake baking process was investigated experimentally and numerically as a simultaneous heat and mass transfer process. The mathematical model described previously by the authors for cup cake baking was modified to simulate ring cake baking. The heat and mass transfer mechanisms were defined by Fourier’s and Fick’s second laws, respectively. The implicit alternating direction finite difference technique was used for the numerical solution of the representative model. Prior to the utilization of the developed model in predicting the temperature and moisture profiles for ring cake baking, the results of the numerical model were compared with analytical results involving only heat or mass transfer with constant thermo-physical properties. Excellent agreement was observed. The numerical temperature and moisture contents predicted by the model were compared with the experimental profiles. They agreed generally reasonably well with the experimental temperature and moisture profiles.     

Two-dimensional CFD modeling and simulation of crustless bread baking process

A special type of baking oven was developed where crustless bread was made by gently baking the dough at controlled temperature by spraying water at prefixed intervals on the surface of the dough. In this study, a two-dimensional (2D) CFD model for crustless bread during baking has been developed to facilitate a better understanding of the baking process. Simultaneous heat and mass transfer from the bread during baking was successfully simulated. It was found that core temperature of the bread reached at 95 °C at the end of baking where as moisture of the bread satisfies the normal bread quality. The model can be successively applied to study the unsteady heat and mass transfer from the crustless bread during baking.     

Humidity change and its effects on baking in an electrically heated air jet impingement oven

A high temperature humidity sensor was used to monitor the absolute humidity inside an electrically heated conveyorized, food service-scale, two-zone, air-jet impingement tunnel oven as commonly used by pizza chain restaurants. The oven was first operated empty, then loaded with dummy loads consisting of pans of water in perlite while baking layer cakes, and finally when baking cakes with added dummy loads. Temperature and loading affected humidity, and humidity affected final product quality. High humidity lightened cake crust color, increased volume, and raised the final moisture content of the cake. There was no significant effect of humidity on the heat transfer coefficient as determined by a standardized metal target plate. In this study, one pan of perlite approximated three pans of cake. Adding perlite dummy loads was shown to be a useful technique to quantitatively measure and to demonstrate the effect of humidity during baking. It is also a convenient way to accelerate oven load-testing without producing and discarding a large number of samples.     

网带式热风循环电热比萨炉的设计和研制

重点阐述了网带式热风循环电热比萨炉的工作原理和烘烤过程、结构设计和控制系统设计,以及对差异性结构设计的可行性分析;并通过研发试产后,提出功能扩展的设想,探讨遂道式万能蒸烤炉的初步设计方案,可以通过增加蒸气加湿功能来扩大比萨炉的适用范围。     

Cake Baking in Conventional, Impingement and Hybrid Ovens

White layer cakes were baked in three types of air impingement ovens, a hybrid (microwave/air impingement) oven, and a reel oven. Cakes were evaluated based on volume, crust color, and texture. Oven heat transfer rates were measured directly, and ranged from 22.8 to 84.8 J/s m²C° for top and from 17.4 to 110.9 for bottom surfaces, exposed in the different ovens, with the conventional reel oven having the lowest values. An RSM design was used to establish optimum baking conditions for each oven. For air impingement ovens, baking time was reduced by almost half but produced cakes very similar to those from the control (reel) oven. Incorporating microwaves enabled a further reduction in baking time, to one fourth. Cakes baked with microwaves had similar color, but had 15% less volumes and firmer textures than control cakes.     

Baking kinetics of muffins in convection and steam assisted hybrid ovens (baking kinetics of muffin…)

Effects of oven type and baking temperature on acrylamide concentration, surface browning, temperature profiles and drying rates of muffins were investigated. Muffins were baked in convection and steam assisted hybrid ovens at 145, 160 and 175 °C for different baking times. For all oven types, the acrylamide concentration of muffins increased with increasing baking time and temperature (p < 0.05). The formation was considered as the first order reaction kinetics except for the lowest baking temperature at natural convection and steam assisted hybrid ovens. The reaction rate constant, k was found to be in the range of 0.027–0.078 (min⁻¹). For the forced convection oven, the effect of baking temperature on acrylamide concentration followed the Arrhenius type of equation; with activation energy of 36.35 kJ/mol. The minimum drying rate was observed by the steam assisted hybrid oven, at all conditions. Steam assisted baking resulted in lower acrylamide concentration at all baking temperatures, while providing the average moisture content not significantly different.     

Heat transfer properties of the numerical human body simulated from the thermal manikin

This paper seeks to predict the heat transfer properties of the numerical manikin. It also aims to establish a simplified clothing model based on computational fluid dynamics (CFD) to predict the temperature in air layers between thermal manikin and clothing under different environments. The field experiments of naked or clothed thermal manikin were conducted in a climatic chamber. The CFD method was employed to build a naked or clothed numerical manikin to simulate the field experiment. The distribution of temperature and the velocity field around the naked human body and heat transfer coefficients was simulated in the optimized numerical climate chamber with a temperature of 20°C and velocity of 0.05?m/s. The temperature in air layers entrapped in clothing on the torso of manikin was also predicted under the same environmental condition. The CFD results showed good agreement with that of the naked or the dressed thermal manikin experiment. It demonstrated that CFD could properly predict the heat transfer properties of indoor human and temperature distribution in the air layer between human body and clothing.     

Applying CFD for designing a new fruit cabinet dryer

Cabinet dryers are the most popular equipment for fruit drying. One of the drawback of this dryer can be non-uniformity in the desired moisture content of end product. A new cabinet dryer with a side mounted plenum chamber was designed, constructed and evaluated. To obtain a uniform distribution of drying air flow and temperature taking into account the overall operating conditions, seven different geometries of cabinet dryer were envisaged theoretically (computational fluid dynamics (CFD) by using fluent software) and experimentally. Experiments were conducted on the most appropriate sketch with acceptable uniform air flow and temperature distribution. The experimental results showed that the new cabinet dryer illustrated an even distribution of air velocity and temperature throughout the dryer. Comparing the experimental and predicted (extracted for the CFD analysis) data revealed a very good correlation coefficient of 99.9% and 86.5% for drying air temperature and air velocity in the drying chamber, respectively.     

Baking of Sponge Cake: Experimental Characterization and Mathematical Modelling

Sponge cake is a sweet bakery product that begins as a fluid batter and, during baking, transforms into a porous solid, presenting an important volume expansion. The aim of this work was, first of all, to study experimentally the influence of operative conditions (natural and forced convection; oven temperature, from 140 to 180 °C; steam addition) on volume expansion and the heat transfer dynamics during baking of sponge cake. It was observed that an increase in oven temperature, airflow and steam injection produces an increase in volume expansion. Secondly, a mathematical model was developed to simulate heat transfer coupled with volume expansion. Both experimental and simulated temperature profiles verified that the last region to achieve a correct degree of baking is the one near the crust around the axial axis. In consequence, the minimal baking time was defined as the average time at which this region reaches 95–98 °C. The baking time was strongly affected by the effective oven temperature, with a slight influence of the convection mode.     

隧道式干燥机风速与温度分布及协调性

隧道式干燥机隧道内部风速和温度的分布不均匀是导致干燥效率低、干燥不均匀的主要原因。通过对隧道内风速分布规律的研究,为对设备进行进一步优化改造和对物料进行干燥参数实验研究提供理论依据。由于风速原因,致使设定温度与实际得到的介质温度并不相符,这就需要对温度进行校正。利用自行研制的隧道式热风干燥机对隧道内部的风速进行了研究,并研究了风速对实际介质温度的影响及其协调性。     

Improved 3-D temperature uniformity in a laboratory drying oven based on experimentally validated CFD computations

The present paper discusses a experimentally validated 3-D CFD analysis of the flow and thermal processes in a laboratory drying oven with a forced air circulation. The device is mainly used in the food and chemical industry to store products at a constant, spatially uniform temperature. The existing device has been assessed according to a certification procedure and then numerically simulated on the basis of the mathematical model developed, including all heat transfer modes, temperature-dependent air properties and local heat transfer coefficients on the external walls, etc. Furthermore, parameters such as the rotational speed of the device fan, the effectiveness of the distribution gaps and the rate of heat generated in the electrical heaters have been tested to improve the temperature uniformity within the chamber. Finally, several changes of the device configurations, such as the location of the heaters, the fan and the fan baffle, have been considered. As a result, the temperature uniformity has been significantly improved, which was also confirmed in the experimental test of the modified prototype.     

CFD modeling of heat transfer and flow field in a bakery pilot oven

A bakery pilot oven is modeled using computational fluid dynamics software. This approach relies on integration of an instrument into modeled geometry. The instrument is a heat flux measuring device that can be used in the industrial baking process. All three heat transfer mechanisms are considered and coupled with turbulent flow. Turbulence is taken into account via the k–ε realizable model whereas the surface-to-surface model simulates the radiation. Additionally, buoyancy forces are introduced by means of a weakly compressible formulation. The model predictions show a good qualitative agreement with the experimental measurements. A quantitative agreement was obtained to some extent. Limitations came from the difficulty to measure the temperature of the radiant surfaces of the oven. Operating conditions used are typical of bakery products and, as expected, radiation was the dominant mode of heat transfer. The integration of the instrument was useful for assessing the model. Since it is designed for industrial use, it may be a valuable tool for future challenges in the field, such as simulation of an industrial scale oven.     

Computational Fluid Dynamics (CFD) Modeling for Bread Baking Process—A Review

Computational fluid dynamics (CFD) modeling of entire bread baking process is very complicated due to involvement of simultaneous physiochemical and biological transformations. Bread baking is a fickle process where composition, structure, and physical properties of bread change during the process. CFD finds its application in modeling of such complex processes. This paper provides the basics of CFD modeling, different radiation models used for modeling of heating in electrical heating ovens, modeling of bread baking process along with the predictions of bread temperature, starch gelatinization, and browning index. In addition, some recent approaches in numerical modeling of bread baking process are highlighted. Moreover, current limitations, recent developments, and future applications in CFD modeling of bread baking process are discussed in detail.