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Energy performance of a low-emissivity electrically heated oven
Abstract
A low-emissivity oven (LEO) provides an energy-efficient alternative to a conventional domestic electric oven. A prototype domestic LEO is described and its energy performance is assessed and compared with that of a current generation domestic electric oven and previous test-rig ovens. In standard tests, the prototype achieved energy-savings of 36–57% when compared with the commercially-available oven, providing thermal performances similar to those of ‘idealised’ test-rig ovens. It is, therefore, recommended that manufacturers implement low-emissivity oven designs for domestic users as a means of speeding thermal performance, reducing energy consumption, and thereby reducing the emissions and peak electrical demands associated with domestic cooking.
... In this instance, a reduction in energy consumption of about 33% is necessary to reach the highest category from A. This is a challenge for both manufacturers and researchers. Thermal efficiency, defined as the amount of energy transferred to the load divided by the total amount of energy supplied to the oven [5], determines the energy efficiency index. According to Bansal et al. [6], the reported thermal efficiency of conventional domestic electric ovens is around 12.7%. ...
... The analysis of radiative heat transfer in domestic ovens in recent literature has resulted in the "low-emissivity oven" concept [5,13,14]. Cavity walls of the conventional ovens which have high emissive surfaces, absorb most of the radiation energy emitted by the heaters that are placed inside the cavity causing a high rate of energy loss [13]. Low-emissive surfaces were used for the cavity walls to overcome this disadvantage, and resulted in energy savings up to 50% [6]. ...
... Low-emissive surfaces were used for the cavity walls to overcome this disadvantage, and resulted in energy savings up to 50% [6]. One subsequent attempt increased the thermal efficiency to 23% [5]. ...
In this study, the radiative properties of the surfaces of an electric oven were investigated. Using experimental data related to an oven-like enclosure, a novel combination of surface properties was developed. Three different surface emissivity combinations were analysed experimentally: low-emissivity, high emissivity (black-coated), and hybrid emissivity. The term “hybrid emissivity design” here corresponds to an enclosure with some high emissive and some low-emissive surfaces. The experiments were carried out according to the EN 50304 standard. When a brick (load) was placed in the enclosure, the view factors between its surfaces were calculated with the Monte Carlo method. These and the measured surface temperatures were then used to calculate the radiative heat fluxes on the surfaces of the load. The three different models were compared with respect to energy consumption and baking time. The hybrid model performed best, with the highest radiative heat transfer between the surfaces of the enclosure and the load and minimum heat loss from the cavity. Thus, it was the most efficient model with the lowest energy consumption and the shortest baking time. The recent European Union regulation regarding the energy labelling of domestic ovens was used.
... Domestic electric ovens are a convenient and versatile way to create high-quality baked goods. However, these ovens have low thermal efficiency because a considerable percentage of the energy input to an oven is absorbed by its construction (e.g., oven walls, doors) and released to the environment during baking (Shaughnessy & Newborough, 2000). In a conventional oven, the energy input is distributed as follows: 47% is absorbed by the oven construction, 25% is lost via walls, and 15% is lost out the exhaust as evaporated moisture (Bansal et al., 2011). ...
... Ovens with low-emissive surfaces were designed to alleviate this disadvantage, resulting in up to a 50% energy reduction (Bansal et al., 2011;Bignardi et al., 2013;Shaughnessy & Newborough, 2000). ...
In a baking oven, radiation heat transfer is the most prevalent mode of heat exchange. In the present investigation, a new baking oven was designed with two hemi cylindrical domes (called reflectors) attached to the heating coils at the top and bottom of the baking oven. Firstly, view factors were computed by finite element and analytical methods with different bread dimensions, as well as with and without the reflectors. The network representative method and S2S method were employed to analyze the radiation energy transfer in the oven at different baking temperatures using the same bread sizes. The results obtained from numerical and analytical methods were fairly similar. The radiative heat energy absorbed by bread surface was higher with the reflector than without the reflector in the oven. As the number of obstructions increased, the radiative heat flux was reduced. The inclusion of reflector shield in oven affect the heat lux on the bread. The radiative heat flux received by bread was found to have increased on increasing the oven temperatures. Moreover, quality parameter such as the color of the bread with and without the reflectors were also examined. The oven reflector had a noticeable effect on the color of the bread (p < 0.05).
Practical applications
In recent years, reducing energy consumption has become more important in the design of ovens. Although domestic electric ovens are a convenient way to bake quality goods, they have a very significant energy loss. Prior research has focused on CFD modeling for commercial ovens to assess the thermal behavior of the system and overall energy efficiency of baking. Baking ovens operate at higher temperatures, hence, heat transfer by radiation is highly essential. In reality, one or more surfaces in oven are obstructing the surfaces. To calculate view factors and achieve accurate radiative heat transfer in such cases, the shadow effect must be taken into account. To solve them precisely in this situation, numerical techniques are highly beneficial.
... Oven manufacturers are increasingly forced to adjust their products to market requirements by developing ever more energy efficient ovens that fulfill Class A criteria [1][2][3]. Functionality, design and energy efficiency all need to be taken into account [4][5][6]. ...
... An example of using equation (6). Figure 6 shows a comparison between the measured and calculated temperature curves during heating of dry brick at natural convection. ...
For cookers with oven to be interesting for the market, they need to exhibit a high energy efficiency. On the basis of an analysis of individual influences on the energy efficiency of ovens, several solutions were proposed for improving oven operation. An analytical solution was made for describing the nonstationary temperature field within a test brick with convection at a constant heat transfer coefficient and a continuously variable temperature of the surrounding fluid using Green's functions. The influences of door sealing, vapor outlet slit, additional insulation, the oven regulation regime, door glazing and irradiation within the oven were experimentally analyzed. Because of the proposed improvements, the analyzed mass produced oven was moved to the A class of energy efficiency according to standard EN 50304:2001.
... walls, door and insulation), and is lost in the surrounding environment [8]. High-emissivity linings absorb the thermal radiation energy from the cavity and then it is lost through conductive bridges and convective leaks [9]. Furthermore, a lot of energy is lost through the venting of the evaporated moisture from the cavity. ...
... walls, door and insulation), and is lost in the surrounding environment [8]. High-emissivity linings absorb the thermal radiation energy from the cavity and then it is lost through conductive bridges and convective leaks [9].Furthermore, a lot of energy is lost through the venting of the evaporated moisture from the cavity. The analysis of the data from the test procedures show the need of a more comprehensive testing methodology for defining and calculating the balances of energy, which are required for a better characterization of the thermodynamic behaviour of the oven and to have an easier procedure for guiding the design phase. ...
The management optimization of energy fluxes applied in the professional cooking sector has an attractive potential, and represents a big step ahead, because it is characterized by a high energy demand and has a large diffusion all over the world. Furthermore, professional cooking sector still presents significant possibilities for energy efficiency enhancements, in both design solutions and operating strategies. The present study focuses on energy efficiency analyses on combined ovens for professional use. In the initial phase of the evaluation, energy efficiency standards EFCEM, ENAC and ASTM have been compared with experimental results. Discrepancies were shown by means of a systemic application of the mentioned standards to a specially instrumented prototype of professional oven. Different test conditions do not allow a meaningful comparison of test results, leading to the definition of a new methodology for the energy efficiency evaluation of a combined oven. structured on the experimental analysis of the balance of fluxes incoming and outcoming from the oven in different cooking modalities. It allows improving the knowledge of the machine and, afterwards, helps in the definition of different design choices, derived from the analysis.
... Shaughnessy ve Newborough [13] tarafından yapılan çalışmada ev tipi bir fırında enerji tüketimini düşürmek ve enerji test süresini kısaltmak için düşük emisiviteli bir fırın oluşturulmuş, çalışma sonucunda mevcut fırında test süresi 51 dakika ve enerji tüketimi değerleri 977 Wh olurken, oluşturulan düşük emisiviteli prototip fırında test süresi 34 dakika ve enerji tüketimi 624 Wh düşürülmüştür. Çalışma sadece deneysel bir çalışma olup sayısal analiz içermemektedir. ...
Günümüzde tüketicilerin çevre bilinci arttıkça, enerji tasarruflu ev aletlerine olan talep de artmaktadır. Dolayısıyla yenilikçi tasarımlar ve üretim teknolojilerinin gelişmesi ile birlikte çevre dostu ev aletlerinin üretimi gündemde olmaktadır. Çalışma kapsamında fanlı pişirici cihazlarda fan-motor grubunun farklı dönüş devirlerinde ve yönlerinde kavite içi sirkülasyon debisi, hız dağılımı ve sıcaklık dağılımı sayısal ve deneysel olarak incelenmiştir. Çalışmada kavite içinde 600 rpm’ den 2400 rpm’ e kadar motor dönüş devri taraması yapılmıştır. Kavite içerisinde belirlenen üç düzlem üzerindeki lokal noktalardan hız verileri deneysel olarak sıcak tel probu ile alınmıştır. Çalışmaya paralel olarak sayısal çözüm aşamasında Ansys Fluent programı kullanılarak farklı türbülans modelleri incelenmiş ve en kararlı, en doğru sonucu veren model olarak k-w SST modeli uygun bulunmuştur. Çalışma sonucunda deneysel ve sayısal sonuçların birbirlerine uyumlu olduğu görülmüştür. Fan-motor grubunun dönüş devri arttıkça düzlemler üzerindeki kavite içi ortalama hız ve standart sapma değerlerinin de arttığı görülmüştür. Homojen pişirme için düzlemler üzerindeki standart sapma değerleri minimum ve düzlemler üzerindeki ortalama sıcaklığın hedeflenen sıcaklığa en yakın olduğu koşulun ~2272 rpm motor dönüş devri ve saat yönü motor dönüş yönü olduğu belirlenmiştir. Yapılan sayısal ısıl analizlerin çıktıları deneysel veriler ile karşılaştırıldığında en yüksek %3’ lük bir sapma olduğu tespit edilmiştir.
... Regarding oven interior walls, there has been debate over the years around emissivity and energy consumption. Certain studies point out that low-emissivity ovens use around 35% less energy than standard ovens (Shaughnessy, 2000), whereas others indicate that wall emissivity should be high, as dark surfaces adsorb energy but are also efficient energy radiators. The project named Highly Efficient Oven (Santacatterina et al., 2016) is a demonstration project involving four European partners, co-financed by the LIFE Environmental Programme. ...
Ecodesign and Energy Labelling Regulation of domestic cooking appliances entered into force in 2015. Since then, the market has evolved and new technologies are available. The implementing measures contain review clauses that are already due. Energy classes also need rescaling. Therefore, the Commission launched the revision of this Regulation. The study has been led by DG ENER and conducted by the Joint Research Centre.
Some areas where revised regulation could provide added value in this product group have been identified. Some oven manufacturers may be exploiting the characteristics of current measurement methods to declare energy consumption values that are lower than real-life use. The current approach for energy declaration allows the use of heating modes that are not consumer representative. Similarly, current energy efficiency measurement methods in cooking fume extractors may be pushing the market towards high airflow appliances, rather than to energy efficient ones. Other aspects that required further research were the ambition level of material efficiency requirements, the feasibility of energy sources such as hydrogen or the harmonization with other horizontal regulation such as low power modes.
Based on these aspects, a set of policy options have been evaluated and presented as potential aspects to review in a hypothetical new version of the ecodesign and energy labelling regulation for cooking appliances.
... Overall, studies showed %17 -%20 thermal efficiency increment. B.M. Shaughnessy et al. studied low emissivity ovens and compared them with the conventional ovens [4]. Low-emissivity components (oven compartment, removable panels, and door-inner) emissivity were 0,07. ...
There is a big demand from the customer and regulatory side for higher efficiency products to save electricity consumption and decrease the carbon footprint. Manufacturers and designers must check new improvements to afford such an important request. New improvements related with the energy efficiency cause the new competitive between manufacturers about fast cooking, multi cooking, well designed esthetics etc. During the studies, it needs to high number test to ensure the international regulatory standards. In this study, different heater functions are examined to decrease energy consumption of the oven during standard energy test as an experimentally. 3 versions of the heater working cycles are studied and it shows what is the effect of these function on energy consumption.
... Gerçekte, alt ve üst ısı akısı arasında %50 fark oluşması fırınlarda pişirme kalitesi açısından olumlu değildir. Kontrol stratejisi olarak sıcaklık ölçümlerine dayanan geleneksel kontrol stratejilerinin yerine ısı akısına dayanan yaklaşım kullanılmalıdır [12,13]. ...
... To evaluate the performance of oven-baking appliances used in domestic cooking, their characterisation in terms of oscillations in the amplitude and frequency above the set-point temperature (i.e., compliance with and oscillations above the set-point temperature) appears to be more informative than standard air-temperature measurements [1,4,5,16]. ...
The effects of thermal treatment conditions on the 2-amino-1-methyl-6- phenylimidazo[4,5-b]pyridine (PhIP) and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) levels formed in pork samples of different matrices (pork steak vs. pork mince) were studied. Oven air temperature oscillations above the set-point temperature of 200 °C were produced using an on-off controller. Oscillations that reached 1.2 °C amplitude showed formation of one-fifth to one-tenth the PhIP levels in the pork steak and mince compared to the maximum air temperature oscillations that produced temperatures of up to 211.5 °C. The MeIQx levels in pork steaks were not significantly affected by the temperature oscillations, while they were doubled in pork mince. To reduce the levels of these heterocyclic aromatic amines, an oven with precise temperature control is significantly more important than other options during the cooking of pork.
... De nombreuses études traitent de l'optimisation ou de l'amélioration des fours industriels continus (Carvalho and Nogueira, 1997;Gupta, 2001;Ma et al., 2015;Niamsuwan et al., 2015) mais aussi des fours "traditionnels" (type four de cuisine) (Kokolj et al., 2017;Pinelli and Suman, 2017;Ploteau et al., 2012;Purlis, 2012;Scarisbrick et al., 1991;Shaughnessy and Newborough, 2000;Sparrow and Abraham, 2002). ...
La cuisson par contact direct est un mode de préparation des aliments très courant à travers le monde, cependant peu d’études s’intéressent à cette problématique à l’échelle domestique. Ces travaux tentent d’apporter une contribution à l’étude des phénomènes mis en jeu durant cette opération. Ce manuscrit débute par une revue de différents facteurs impliqués lors de la cuisson : les consommations d’énergie, les types d’appareils utilisés, les phénomènes physico-chimiques intervenant dans le produit ou les problématiques de modélisation y sont abordés. Il s’en dégage qu’une donnée essentielle est la connaissance du flux de chaleur transmis au produit. Une méthode d’estimation de ce flux basée sur les techniques inverses est développée. Celle-ci a contribué à concevoir un prototype instrumenté permettant de suivre les cinétiques des températures dans la plaque chauffante et dans un élastomère simulant un produit alimentaire. Les résultats obtenus montrent que la méthode permet d’estimer le flux de chaleur transmis avec une bonne précision. Dans un second temps, une étude expérimentale de la cuisson d’une pâte céréalière d’environ 8mm d’épaisseur est présentée. Après avoir caractérisé les propriétés thermophysiques et hydriques, le prototype est utilisé pour suivre les évolutions de différents paramètres comme les températures, le flux de chaleur, la masse en dynamique, et les teneurs en eau. La répétabilité et la variabilité des résultats suivant la température initiale de la plaque sont menés. Ensuite, un modèle 1D simulant les transferts de matière et d’énergie, est utilisé pour étudier les différents facteurs intervenant lors de la cuisson. Un second modèle 2D est réalisé permettant de tester les consommations d’énergie lors d’une opération de cuisson en cadence suivant différents scénarios de conception du prototype.
... The authors showed how the geometry of the heating elements and the load together with their relative positions influence the uniformity in heating. In [15], the same authors compared the energy performance of a LEO with a traditional high-emissivity oven, demonstrating a significant reduction in energy consumption and cooking time both in natural and forced convection modes. ...
Almost 25% of the overall environmental impact of buildings can be attributed to appliances, among which electric domestic ovens represent a low-efficiency category when considering apartments. In order to improve their low efficiency, usually lying between 10% and 12%, the oven industry is often stimulated to develop more efficient technologies, among which there is the design of suitable strategies for the control of the oven center temperature, as required by the EN 60350-1 European standard, which regulates the energy consumption test. This work describes the simulation of the transient thermal behaviour of a domestic electric oven in natural convection heating mode by means of dynamic models suitable for control design purposes. A lumped-parameter approach based on the thermoelectric analogy was chosen, in order to obtain a low-order dynamic model with a proper level of discretization which allowed to reproduce the main temperatures within the cavity, in particular at the oven's centre and the temperature sensed by the probe used for oven control during normal operating conditions. Eight lumped parameters were introduced to represent walls, glass door, cavity air and temperature probe, and three parameters to simulate the thermal behaviour of the heaters were considered, resulting in an 11-th order model. Moreover, the influence of non-linearized radiative terms on model accuracy was investigated, leading to two different lumped-parameter, semi-physical models. Two sets of capacities and conductances were identified for both the models through an optimization procedure based on experimental data, giving a grey-box nature to the models; subsequently the prediction potential of the models was verified at different temperature set-points.
... Για να βελτιωθεί η αποδοτικότητα των ηλεκτρικών φούρνων ενδεχόμενες λύσεις είναι η βελτίωση της μόνωσης, η χρήση πόρτας χωρίς τζάμι ή η βελτιστοποίηση των ήδη υπαρχόντων σχεδίων, η βελτιστοποίηση της ροής του αέρα, η χρήση υλικών χαμηλής εκπομπής, η μείωση της κατανάλωσης ενέργειας βοηθητικών λειτουργιών καθώς και η τοποθέτηση ανακλαστήρα πίσω από τα στοιχεία θέρμανσης [14]. ...
... Other papers present interesting ideas for the improvement of the energy performance of the ovens, such as the employment of low-emissivity internal walls [3], or the use of oxygen enriched air by using permselective membranes for reducing fuel consumption [4]. The latter is a simple and attractive option, especially in case a syngas is wished to be adopted as fuel. ...
Kiln burners for industrial tile production are usually fuelled by methane gas. However, the interest towards the use of coal or synthesis gases is rapidly increasing, mainly due to the opening of important markets in developing countries. The widely variable chemical composition of these fuels demands the gas burner to be adapted on case-by-case basis, since the firing parameters are strictly fixed, to guarantee the required temperature distribution within the kiln. In this context, computational fluid dynamics analysis represents a very convenient alternative to the traditional design based on experi- ments. In this article three-dimensional numerical predictions are presented for a syngas-fired burner. Three different fuels, two burner layouts and two burner nominal power are considered. Temperature, velocity and oxygen mass fraction distributions are discussed, and general design lines for low lower heating value gas burners are extracted.
... Tests for a comparison of the heating performance and energy consumption between a conventional domestic oven and a lowemissivity one have been undertaken only on bricks and not directly on food products (Shaughnessy & Newborough, 2000). Few experiments have been carried out on bakery products and pizza showing that for most of the recipes tested the low-emissivity oven is a suitable alternative to a conventional type (Steinbrück et al., 2005). ...
... In these last years increasing is the availability in the market of oven arrangements with a high versatility in their performances due to the introduction of innovative heating systems and/or the combination of different heating systems (forced air convection, steam, microwave, etc.) and finalised mainly to improve sensorial properties of food preparations and to decrease process time and costs (Murphy et al., 2004;Shaughnessy & Newborough, 2000;Vittadini, Rinaldi, Chiavaro, Barbanti, & Massini, 2004). Meanwhile, the high interest in developing easy-to-use and friendly cooking systems, in which the optimisation of the heating conditions have been achieved and/or their manual control has been reduced, has leaded to simple and automatic setting of the equipments. ...
Cooking represents an important step in food processing for both sensorial and safety aspects. Aim of this study was to optimise the cooking cycles of a semi-automatic oven by definition and settling of minimum thermal conditions to guarantee safety while keeping sensorial quality of cooked foods. To this purpose, the heat penetration curves and the correspondent thermal lethality effect (FT) of cooking cycles conventionally adopted to prepare some foods and dishes characterised by different microbial risk (high: lasagne pie, meat minced roll, meat filled peppers; standard: spinach and salmon), were determined. On the basis of the microbial quality and the desired safety level, minimum thermal conditions (F71.1 = 5 min and T = 75 °C at the slowest heating point of the food) were defined and settled in the electronics of the oven. These conditions were found to determine a sufficient number of log reduction of both total microbial count and coliforms able to guarantee safety as well as sensory quality at consumption. The oven with modified electronics during the heating step of cooking cycles records in real time the temperature in the product by a multipoint thermocouple, detects the slowest heat penetration curve and computes, by an internal computer the correspondent F71.1. After initial setting of the food category, this semi-automatic oven is able to find automatically the proper process conditions during cooking to obtain the correspondent FT, to let the cooking stop at the end of the recipe or to conduct the thermal treatment till the reaching of the set FT according to the risk category chosen before cooking start.
In this study, the heater usage algorithm has been studied for cooking process in a domestic oven. For the analysis, numerical simulation and experimental study have been performed, focusing on heat distribution and heat loss mechanism. Better fidelity of baking process model was achieved by incorporating enthalpy jump at the phase change and evaporation-condensation mechanism into the thermal properties of cupcake. The result of heat flux calculation over enclosed walls shows that the back surface has the highest heat flux due to high temperature of convection heating during preheating process. During baking process, the heat flux on the top surface of cupcake on a upper tray was found to be about 1.8 times as that on the lower tray due to radioactive heat flux from grill heater. For an energy saving purpose, the more balanced use of heating units, for instance, more use of grill heater than convection heater, was recommended. The thermal conductivity of insulation material was a more important factor than specific heat on the power consumption during preheating. © 2018, The Korean Society of Mechanical Engineers and Springer-Verlag GmbH Germany, part of Springer Nature.
The aim of this study is to investigate the design parameter effects of an aspirating cooling system on the outer surface temperature of a household pyrolytic oven glass. Pyrolytic ovens include complicated components, such as an oven door, a cross-flow fan and an aspirating cooling system, and their complex interactions should be investigated in detail. In this study, the oven door and cross flow fan and aspirating cooling systems were modeled as a three dimensional system using a computational fluid dynamics and heat transfer method to investigate the fluid flow and temperature distribution of outer surface of the oven door. The simulation model predicted the temperature distribution based on the cross flow fan speed, cross flow fan position and channel design of the aspirating cooling system. The numerical results were validated against results obtained from an experimental study. The computational results show that the rotational speed of the cross flow fan, the cross flow fan position and the channel design of the aspirating cooling system play important roles in affecting the outer surface temperature distribution of the oven glass of a pyrolytic oven.
By comparison with those in industry, domestic cooking processes are rarely studied with respect to heat transfer although they can drastically modify the quality of heated products. In order to compensate for this lack of information in the literature, the aim of this work was to propose test procedures to evaluate the variability of domestic appliance heating performances in the case of oven-baking and pan-frying. The measurements included the continuous recording of pan temperature during pan-frying using different types of hobs (electric, halogen, gas, induction) and pans; the continuous recording of air temperature and measurement of the convective heat transfer coefficient and equivalent radiative temperature during oven-baking using different types of ovens. The results revealed broad variations in heating conditions depending on the type of appliance used and on consumer behaviour. For pan-frying, it was shown that pan temperature varied constantly during heating. From an initial value of 200 °C and a given product load, it could fall to 150 °C or rise to 330 °C at medium or high heat, respectively. For oven-baking, heating was sometimes performed at an actual air temperature that differed considerably from the air temperature set on the oven. These measurements also showed relatively low convective heat transfer coefficient values, ranging from 6 W/m2 K under free convection to 16 W/m2 K under forced convection.
An overview of options and potential barriers and risks for reducing the energy consumption, peak demand, and emissions for seven key energy consuming residential products (refrigerator-freezers, dishwashers, clothes washers, clothes dryers, electric ovens, gas ovens and microwave ovens) is presented. The paper primarily concentrates on the potential energy savings from the use of advanced technologies in appliances for the U.S. market. The significance and usefulness of each technology was evaluated in order to prioritize the R&D needs to improve energy efficiency of appliances in view of energy savings, cost, and complexity. The paper provides a snapshot of the future R&D needs for each of the technologies along with the associated barriers. Although significant energy savings may be achieved, one of the major barriers in most cases is high first cost. One way of addressing this issue and promoting the introduction of new technologies is to “level” the playing field for all manufacturers by establishing Minimum Energy Performance Standards (MEPS) which are not cost prohibitive and promoting energy efficient products through incentives to both manufacturers and consumers.
A self-cleaning oven was tested to evaluate the energy efficiency of a representative oven unit and to develop a data base for validation of an oven thermal model. Efficiency testing of the oven was accomplished using a black anodized aluminum block. The oven was instrumented with 21 chromel-constantan thermocouples in order to develop a data base of temperature as a function of time to use to validate the dynamic thermal model. Design parameters were varied for the purpose of improving theoretical energy efficiency. It was concluded that the greatest improvement in efficiency for the gas oven was attainable pilot light and introduction of a forced convective mode. For the electric oven, the improvement in energy efficiency is most sensitive to changes in oven thermal mass and oven vent flow rate. If standard ovens had the same insulation and door seals as the self-cleaning ovens, and if the interior size of the oven cavity could be size of the oven cavity could be reduced by two inches in each dimension, an increase in oven efficiency of 15 percent may be possible.
A theoretical model was developed to predict the heat and mass transfer phenomena in porous materials. A water-filled sandstone was heated in a convective oven and its water loss rates and temperature profiles were compared with theoretical results. In addition to local temperatures, moisture content, gas densities and pressure, this model also predicts the fluid flow pattern in the heated sample.
The social-psychological aspects of energy use in UK households have been reviewed. A major survey, which focused on identifying environmental attitudes and beliefs, energy-use behaviour, ownership levels for certain appliances and their utilisation patterns, was undertaken among householders resident in the south-east of England. The results indicate that members of the general public are (i) interested in receiving information concerning household energy use and the associated environmental impact, and (ii) willing to modify their behaviour in order to reduce household energy consumption and environmental damage. Therefore, there is an urgent need to provide end-users with accurate energy-consumption and environmental-impact information, persuasively presented, to stimulate energy-rational and environmentally sustainable behaviour. For each major domestic electrical appliance, the survey data permit estimates of the variations in energy consumption per household and of the aggregate annual consumption nationally.
Experimental analyses of the thermal performances of (i) various heating-element configurations, (ii) a low-emissivity internal oven-lining, (iii) control systems for regulating internal air temperatures, and (iv) various thermal-insulation systems for an oven have been undertaken. Overall, a substantial increase in the thermal efficiency was achieved, i.e. from 17 to 26%. This compares favourably with the value of 13%, as measured for a typical commercially available domestic oven.
Low-emissivity ovens have linings of εe<0.1 that enhance the thermal radiation exchange between sheathed electrical heating elements (that are exposed within the cavity) and the thermal load(s). These ovens are a quick and energy-efficient alternative to conventional ovens; however, due to the high levels of thermal radiation, they must be carefully designed and controlled so that uneven radiation distributions over loads are minimised. In this paper, a Monte Carlo ray-tracing model was employed to undertake a parametric analysis of low-emissivity ovens. The factors that influence the magnitudes and uniformities of radiation distributions occurring over loads are identified, and recommendations for optimal heating configurations and control algorithms are presented.
The paper gives an overview picture of the role of water in heat processing of solid foodstuffs. Special attention is given to sorption isotherms and water diffusivity and recent work in this field is referred to. Thawing of foodstuffs is given as an example to illustrate the influence of water on the transfer of heat.
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- Fig
Fig. 6. In¯uence of temperature rise setting when heating the CENELEC-1998 test brick upon energy consumption, test time, and brick weight loss following heating. The ovens were operated in natural convection mode. Linear best ®t lines added.
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