A novel method to improve the efficiency of a cooking device via thermal insulation

We propose a method of finding the transient temperature variation in an insulated cooking device. We also report a means of optimising the thickness of insulation. The cooking device is a double walled cylindrical vessel with spacing of 5–20 mm between the vertical walls (width) and spacing of 560 or 870 mm between top and bottom surfaces (height). The height to width ratio (H/L) is between 28 and 174 and Rayleigh number (Ra) is between 907 and 2.61 × 105. First, an energy balance for the cooking device is established. A correlation is developed to predict the heat transfer coefficient (HTC) as a function of Ra and H/L. The method developed for finding the transient variation in temperature has been tested on two cooking device volumes: 120 and 700 lit. Using the optimised parameters, a reduction in heat loss of 22% and 30%, respectively, is observed

Development of efficient designs of cooking systems. I. Experimental

In the conventional cooking practice, where a pot or a pan is directly placed on a flame, the thermal energy efficiency is in the range of 10-25%. It was thought desirable to increase this efficiency up to 60% or more. The cooking systems can be of various sizes. In the developing world (85% of the worlds population), open pan cooking is largely still practiced at the family level (4-10 people) or at the community level (50-2000 people or more). The latter requirement is encountered in schools, homes for senior citizens, jails, social and/or religious centers (temples, mosques, churches), social and/or educational functions (conferences, marriages, celebrations, etc.), remand homes, etc. For these different types of final application, in the present work, cooking systems have been developed. A systematic work has has been reported regarding the effect of several parameters on thermal efficiency. The parameters include the cooker size, number of pots, size and aspect ratio of the pots, heat flux, flame size, flux-time relationship, insulating alternatives, etc. Local and global optima of the parameters have been obtained, resulting in thermal efficiency of about 70%. © 2011 American Chemical Society

Development of efficient designs of cooking systems. II. Computational fluid dynamics and optimization

Sections 2-6 of Part I were devoted to the analysis of heat transfer characteristics of cookers. In all the experiments, only water was employed as a working medium. Now, we extend such an analysis to the actual cooking process in order to arrive at an improved cooking device. The major strategies for the optimization of energy utilization is to design appropriate insulation that has been obtained by two cover vessels. In order to select an air gap, the flow and temperature patterns in the air gap have been extensively analyzed using computational fluid dynamics (CFD). The flow pattern and heat transfer in cooking pots have also been analyzed by CFD. This has enabled us to design suitable internals for minimizing the stratification of temperature. The understanding of fluid mechanics has also given basis for selection of heat flux, gap between burner tip and cooker bottom, and temperature of flue gases leaving the cooker. Chemical engineering principles have been used for modeling and optimization. Kinetics have been obtained in batch cookers. The knowledge of kinetics, thermal mixing, axial mixing, and optimum selection of insulation have been employed for the development of continuous cookers. The continuous mode of operation also helps in saving of energy. Systematic data have been collected for the design and scale up of continuous cookers. © 2011 American Chemical Society

Development of efficient designs of cooking systems. III. Kinetics of cooking and quality of cooked food, including nutrients, anti-nutrients, taste, and flavor

Part III of the series on cooking systems presents a qualitative description of cooking methods such as open pan cooking, pressure cooking, steam cooking, solar energy-based cooking, microwave cooking, etc. A large number of chemical and physical changes occur during the process of cooking. These changes have been comprehensively covered in published literature including some textbooks. An attempt has been made to discuss a brief coherent description regarding the changes occurring in starches, proteins, fats, etc. The kinetics of the cooking reaction has also been investigated. This information can be advantageously employed for developing a protocol for an optimum temperature-time program. Because the cooking process is practically thermally neutral, a good scope is available for the optimization of energy supply. It was also thought desirable to understand the kinetics of degradation of proteins, vitamins, anti-nutrients, and flavors in different cooking practices, including microwave ovens and pressure cookers. The mechanism of cooking of rice and lentils has been described. The cooking process involves first the transfer of water from bulk to the particle surface, where the resistance for transfer is provided by a thin film in the vicinity of grain (rice and lentils) surfaces. Second, water has to transfer from the external surface to swollen cooked mass to uncooked core. Finally, on the surface of the uncooked core, the cooking reaction occurs. All published literature regarding this mechanism has been systematically analyzed, and the procedure has been given regarding the rate controlling step(s) and the estimation of the overall rate of cooking. For this purpose, the mathematical models have been given and methods have been described for the quantitative evaluation of the model parameters. A substantial amount of additional work is needed on the mechanism of cooking and suggestions have been made for future research. © 2011 American Chemical Society