Sustainability of EHD drying technology: Energy and exergy analysis

Chapter 2 - Exergy and energy analyses

Chapter 2 - Exergy and energy analyses

Chapter 2 - Exergy and Energy Analyses

Electrohydrodynamic (EHD) drying is a promising technology to better preserve the nutritional content and sensory appeal of dried fruits and vegetables. To successfully scale up this technology, we need to rethink the current EHD dryer designs. There is also a significant potential to further enhance the nutritional content and sensory quality of the dried products by optimizing EHD process parameters. This study particularly highlights the current bottlenecks in scaling up the technology and improving nutrient retention and sensory appeal of the dried products. We discuss plausible future pathways to further develop the technology to produce highly nutritious dried products. Particular emphasis has been given to quantifying the residual nutritional and sensory properties of EHD dried products, and possible EHD dryer configurations for farmers and the industry. Concerning the nutritional content, EHD drying preserves vitamins, carotenes, and antioxidants significantly better than convective air drying. From the sensory perspective, EHD drying enhances the color of dried products, as well as their general appearance. With respect to scalability, placing the fruit on a grounded mesh electrode dries the fruit much faster and more uniformly than the grounded plate electrode. Future research should be directed toward simultaneous measurements of multiple food nutrients and sensory properties during EHD drying with a grounded mesh collector. Quantifying the impact of the food loading density on drying kinetics and energy consumption of the EHD drying process should also be a future research goal. Research comparing EHD drying with commercially available drying methods such as freeze-drying, microwave-drying, and infrared drying should also be carried out. This study gives promising insight toward developing a scalable novel thermal drying technology tailored to the requirements of the current and future society.

This paper presents energy and exergy analyses of solar drying of coconuts in a hemispherical solar tunnel drier. Coconuts were dried from an initial moisture content of about 55% (w.b.) to 7% (w.b.) in the solar tunnel drier in 60 hrs whereas the open sun drying process takes 153 hrs for reducing the moisture content to the same level. The drying experiments were conducted at a mass flow rate of 7.25 kg/s with an average air velocity of 0.1 m/s. Using the first law of thermodynamics, energy analysis was carried out to estimate the amount of energy received by the solar tunnel drier and the ratios of energy utilization. However, exergy analysis was accomplished to determine the exergy loss and exergy efficiency by applying the second law of thermodynamics. Energy utilization, energy utilization ratio, exergy inflow and exergy loss in the drier were studied and these values are found to be increased with increasing solar radiation. The exergy inflow and exergy loss in the drier varied between 0.194 kJ/s–8.18 kJ/s and 0.085 kJ/s–5.377 kJ/s respectively. The exergy efficiency of the drier varied between 23.6%–53%.

Kaynakları daha verimli kullanmanın en iyi yolu, enerji ve ekserji arasındaki ilişkiyi anlamaktır. Termodinamiğin birinci kanunu enerji analizi ile ilişkilidir. Bu kanun enerjinin niceliği ile alakalıdır. Enerji analizi sistemin enerji ve entalpi transferlerini açıklamaya yardımcı olur. Enerji yok edilemezken ekserji yok edilebilir. Ekserji bir sistemden elde edilebilecek maksimum teorik iş olarak tanımlanır. Diğer taraftan ekserji analizi termodinamiğin ikinci yasasına dayanır. Termodinamiğin ikinci kanunu enerjinin niteliği ile alakalıdır. Bir sistemin kullanılabilirliği ekserji analizi ile belirlenebilir. Bir sistemin termodinamik detaylarının belirlenmesi istenildiğinde hem enerji, hem de ekserji analizi yapılmalıdır. Ekserji ve enerji analizleri çeşitli alanlara uygulanabilir. Ekserji analizi, içten yanmalı motorlar konusunda önemli bir rol oynamaktadır. Bu çalışmada enerji ve ekserji analizi yapabilen bir programın tanıtımı ve yapısı gösterilmiştir. Program sayesinde hızlı ve güvenilir sonuçlar elde edilebilecektir.

This study investigates the effects of electrohydrodynamic (EHD) drying technology on the drying kinetics, microstructure, quality, and nutritional components of carrots, along with conducting experiments on EHD drying under different voltage gradients. The experimental results showed that EHD drying technology could significantly increase the drying rate and the effective moisture diffusion coefficient. Within a certain range, the drying rate was directly proportional to the voltage. When the range was exceeded, the increase in voltage had a minimal effect on the drying rate. In terms of quality, the EHD drying group's color, shrinkage rate, and rehydration performance were superior to the control group, and different voltages had no significant effect on the shrinkage rate and rehydration performance. The retention of carotenoids in the EHD drying group was 1.58 to 2 times that of the control group. EHD drying had a negative impact on the total phenolic content and vitamin A content of dried carrot slices. Based on the results of infrared spectroscopy and scanning electron microscopy (SEM), the dehydrated carrot slices showed wrinkling due to water loss, with numerous pores, a generally intact structure, and retained functional groups. EHD drying had a significant impact on the secondary structure of proteins, where an increase in voltage led to an increase in disordered structure, with a smaller proportion of disordered structure in the lower voltage group compared to the control group, and a similar proportion of disordered structure between the higher voltage group and the control group. Results from low-field nuclear magnetic resonance (NMR) showed that EHD drying could retain more bound water compared to the control group, with the best retention of cellular bound water at a voltage of 26 kV and the best retention of cellular immobilized water at a voltage of 38 kV, indicating the superiority of EHD drying in preserving cellular structure. This study provided a theoretical basis and experimental foundation for the application of electrohydrodynamic drying technology to carrot drying, and promoted the practical application of EHD drying technology.

Most of the electric energy which the world has utilized is generated from coal or gas based on thermal power plants. These power plants have increased the pollution to the maximum extent. In addition to this the population on the world has multiplied as well as their needs. Therefore, there is a scope for the enhancement of the power plants. All these factors have helped to write this research paper. It is based on the thermal power plant located in Ramagundam of Telangana state, India. Power plant performance evaluation is one of the important processes towards the optimization of its performance. Here in this research power plant performance is evaluated based on first law of thermodynamics (energy analysis) and second law of thermodynamics (exergy analysis) and after that organic rankine cycle based opcan power box is introduced in the power plant. By adopting it the performance of the plant is calculated, after that a comparison is made among the efficiencies with energy analysis, exergy analysis and plant efficiency after, before installation of the opcan power box. For all the components the exergy analysis based efficiency is less than efficiency based on energy analysis. The efficiencies of boiler, turbine using energy analysis are more compare with exergy analysis. In addition to this the efficiency of power plant before installation of opcan power box is calculated as 45% and after the installation of the opcan power box it is computed as 46.07%. It indicates that for a 500MW capacity power plant an extra electricity of 6.7MW power is produced without altering the input fuel quantity. The net increase of efficiency of 1.07% indicates that 2-3 % of reduced pollutants.

Thermal performance of gas turbine power plant based on exergy analysis

Electrohydrodynamic (EHD) drying is an energy-efficient drying method. This novel drying technology operates at room temperature, which makes it particularly suitable for drying biomaterials that contain heat-sensitive compounds. It has a higher drying rate than other low-temperature methods, such as solar and freeze-drying. However, its drying rate is not high enough to compete with other conventional thermal methods, such as hot-air drying. For industrial applications requiring high product throughput, the drying rate of EHD drying should be improved. One way to do this is to combine EHD with pre-treatment methods. Therefore, this study evaluated the impact of different pre-treatment methods on drying kinetics, energy consumption, and product quality attributes of apple slices dried using EHD drying. Pulsed electric fields (PEF), ultrasound, and blanching are the studied pre-treatment methods. Results show that only PEF pre-treatment could significantly decrease the EHD drying time by 39%. However, it resulted in a 26% higher browning index than the untreated EHD-dried apples, which is not appealing to consumers. The applied pre-treatment methods did not significantly affect other quality attributes, such as antioxidant activity, total phenolics, and rehydration ratio. In conclusion, using the studied pre-treatments for EHD drying increases the complexity of the process, whereas it is arguable whether the added values outweigh the energetic and quality downsides or not.

Preserving fruits and vegetables by drying is a traditional yet effective way of reducing food waste. Existing drying methods are either energy-intensive or lead to a significant reduction in product quality. Electrohydrodynamic (EHD) drying is an energy-efficient low-temperature drying method that presents an opportunity to comply with the current challenges of existing drying methods. However, despite its promising characteristics, EHD drying is yet to be accepted by industry and farmers. The adoption of EHD drying is hindered due to different reasons, such as uncertainties surrounding its scalability, quality of dried product, cost of operation, and sustainability compared to conventional drying methods. To address these concerns, this study quantifies and benchmarks the Key Performance Indicators (KPIs) of EHD drying compared to the standard conventional drying methods based on lab-scale experiments. These drying methods include hot-air, freeze, microwave, and solar drying. The results show that drying food using EHD is at least 1.6, 20, and 70 times more energy-efficient than the microwave, freeze, and hot-air, respectively. Similar results could be observed for exergy efficiency. EHD drying has superior product quality compared to other drying methods. For instance, it could retain 62% higher total phenolic content with 21% less color degradation than freeze-drying. Although microwave drying resulted in significantly higher drying kinetics than other techniques, EHD performed better than solar and freeze-drying but was comparable with hot-air drying. EHD drying also shows promising results in economic performance assessment. It is the cheapest drying method after solar drying and has the highest estimated net present value (NPV) after hot-air drying. Overall, compared to the currently used drying methods for small to medium-scale drying, EHD was found to be a more exergy and energy-efficient, cost-effective, and sustainable alternative that can provide higher-quality dried products. However, its drying kinetics should be improved for industrial applications.

Drying is one of the most energy-intensive processes in the multiple industries, due to the high latent heat required to evaporate the water, which is often done by employing hot-air drying. Electrohydrodynamic (EHD) drying is an alternative, innovative drying technology with large potential for industrial application and lower energy consumption. EHD drying is non-thermal, which makes this technology particularly suitable for drying of heat-sensitive biomaterials. A key bottleneck for EHD drying is the process scalability in order to uniformly dry large amounts of product, which is limited by the geometrical design of the collector electrode. To overcome this challenge, a recently introduced electrode configuration – a mesh collector – is further optimized in order to significantly reduce the energy consumption of the process. Exergy analysis was used to identify the energy conversion losses in ion production, ionic flow generation, and convective dehydration stages of fruit. As a result, a much more energy-efficient mesh configuration was designed. This improved design resulted in a similar drying rate as a normal mesh collector but showed a seven times smaller energy consumption. This upscalable, cleaner, and also much more energy-efficient EHD dryer design paves the way for industrial prototypes and pilot plants.

Recently, to reach zero emission levels, some new energy systems based on fuel cells have been developed. This paper presents a review of investigations of these systems by thermodynamics performance, mainly, energy and exergy analysis. With energy analysis, the performance of an energy conversion system cannot be effectively and accurately evaluated. But exergy analysis complements and reinforces energy analysis. Using exergy analysis in relation to the degree of irreversibility in each section is a quality method and can be useful in fuel cell analysis. Analysis based on the first and second laws of thermodynamics seems useful in most cases and here reviews for low-temperature and high-temperature fuel cells are given. As a result, regardless of the type of the FC-system and its application, there is always a need of thermo-economic analysis to investigate the effect of various parameters on the system performance, such as different fuel sources, different operating conditions, different subsystems and energy sources to combine with the fuel cell.

Nowadays, drying process has taken an important role in food and agricultural production fields. Drying process is necessary to prepare the products for consumption and storage. There are various drying process techniques, point from the technological and process technique. Fluidized bed drying is usually preferred, because of high heat and mass transfer coefficient. In this work, fluidized bed was used in the experiments. The scope of this work is the exergy and energy analysis of fluidized bed drying of bean and chickpea. Drying process was employed at different temperatures and velocities for both products. Exergy analysis was accomplished to determine the type and magnitude of exergy losses during the drying process by applying the second law of thermodynamics. As a result, the parameters that affected the exergy efficiency were determined. As the exergy efficiency is evaluated, it can be seen that it is proportional to drying air temperature and velocity. Also, it was found that the efficiency for the same drying air temperature (47.1°C), is between 56 to 65% for bean and it is between 45 to 62% for chickpea. Key words: Exergy and energy analysis, fluidized bed drying, drying.

Electrohydrodynamic (EHD) drying is an emerging drying technology that is based primarily on the phenomenon of ionic discharge between two electrodes. The aim of this study was to experimentally investigate the energy efficiency of the EHD drying based on the corona discharge current. Moreover, we aimed to compare the energy efficiency of the EHD drying with that of other available drying technology options under the condition of high humidity, which mimics Indonesia’s environment as a potential target for implementation, given that it is of interest to investigate the feasibility of the EHD drying in a real environment. The results show that the dominant parameters of the EHD drying rate are the corona discharge current and the moisture content zones of the target objects. Findings from this study show that the EHD drying technology could be effectively used to replace the conventional drying process in developing countries having high humidity environments and facing energy consumption challenges.