Innovative Retrofit Solutions to Reduce Energy Use and Improve Drying Performance in Conventional Hot-Air Herb Dryers

Onion shreds of 2 mm thickness were dried in convective hot air dryer (HAD) at 60°C (28 ± 4% R.H.), heat pump dryer (HPD) at 50° C (15 ± 2% R.H.) and microwave assisted convective dryer (MWD) at 240 W power and 500 C individually and with combinations of drying methods. Drying times were observed to be 300, 360 and 75 min for lowering the moisture content of onion shreds from 675.8% to 6±1% (g/g dry matter) in HAD, HPD and MWD. In combination drying, application of MWD for completing drying after HAD or HPD reduced the drying time significantly, but there was higher discolouration of the products. Total drying time for HPD(50°C)-HAD(60°C) combination was lower with higher overall drying rate as compared to HAD(60°C)-HPD(50°C) drying. HAD(60°C)- HPD(50°C) combination drying yielded products of better colour, whereas the retention of pyruvic and ascorbic acids was higher in HPD(50°C)-HAD(60°C) drying method.

A randomized block design experiment was performed to investigate the influence of drying on the physical, chemical and nutritional quality attributes of five prominent cultivars of India under sun drying (SD) (mean temperature 35.5 °C, average daily radiation 5.26 kW h m-2 and mean relative humidity 73.66% RH), hot air drying (HD) at 65 °C, microwave vacuum drying (MVD) (800 W, 5 kPa) and freeze drying (FD) (-50 °C, 5 kPa). Water activity, pH, total phenolic content (TPC), ascorbic acid (AA), capsaicin, β-carotene, color and Scoville heat unit were studied. TPC, AA, capsaicin content, β-carotene, color and water activity were significantly affected by the drying method. FD was observed to be most efficient in minimizing the loss of color, capsaicin and β-carotene. The hotness of analyzed samples decreased in the order 'Bird's Eye' > 'Sannam S4' > 'CO-4' > 'PLR-1' > 'PKM-1' among the studied cultivars, and FD > MVD > HD > SD among the drying methods. The FD method was observed to be the most efficient drying method for retaining capsaicin content over other drying methods (SD, HD, MVD), whereas MVD was found to be most efficient in minimizing the loss to nutritional attributes for all five pepper cultivars. © 2018 Society of Chemical Industry.

The shell explosion by hot air drying is a critical step in the processing of Camellia oleifera fruit (COF), which directly affects the degree of the shell explosion, and the separation effect of Camellia oleifera seed and Camellia oleifera shell after the shell explosion of COF. To reveal the characteristics of the COF shell explosion, a hot air drying device was designed based on mass conservation and drying principles. The physical characteristics of COF and the evolution of drying parameters were thoroughly analyzed with a combination method of drying analysis and experimental. Moreover, under the conditions of air temperature 50–70 °C, relative humidity 20–50%, and air velocity 1.3–1.9 m/s, the internal relationship between COF shell explosion formation through hot air drying and the hot air drying medium was systematically investigated by response surface methodology, and a prediction model for the shell explosion rate of COF by hot air drying was constructed using statistical methods. Results demonstrated that decreasing the relative humidity and increasing the temperature and air velocity of the drying medium could reduce the dehydration time of COF. The moisture content of Camellia oleifera shell was found to be 177.45% d.b. (dry basis) at the initial cracking stage of COF. Furthermore, at temperatures ranging from 50 to 70 °C Deff values of COF were estimated to be within the range of 0.915 × 10−9 to 1.782 × 10−9 m2/s. Similarly, at relative humidity levels of 20 to 50%, Deff values ranged from 1.226 × 10−9 to 1.501 × 10−9 m2/s. At an air velocity of 1.3 to 1.9 m/s, Deff values ranged from 0.956 × 10−9 to 1.501 × 10−9 m2/s. The measured values of the shell explosion rate were in close agreement with that calculated using the fitted model, with a correlation coefficient of 0.997 and a root mean square error of 0.9743. This study will provide a theoretical basis for optimizing the shell explosion process and improving shell explosion rate of COF by hot air drying.

The effects of ultrasound pretreatment (US) before hot air drying (HAD) and microwave drying (MWD) of garlic slices were investigated. For this aim ultrasonic bath at 30°C for 30min (35kHz), microwave oven at 540W power and tray dryer at 60°C and with 1.0m/s air flow rate were used to reach the final moisture content of 5%. Drying rate increased in the US + HAD and the US + MWD groups by 19.30% and 13.82% respectively in comparison with control groups. The effective moisture diffusivity (Deff) of garlic slices were calculated from Fick's diffusion model for the HAD, US + HAD, MWD and the US + MWD groups as 1.420 × 10-10, 1.826 × 10-10, 1.177 × 10-8, 1.363 × 10-8 m2/s respectively. The rehydration rates increased, and bulk densities were decreased in the US + HAD and the US + MWD compared to the control groups. The color values were significantly affected after ultrasound pretreatment. Redness, and yellowness increased most in the US + HAD group.

In the agricultural processing industry, drying technology plays a crucial role in ensuring product quality, extending shelf life, and reducing transportation costs. Given the rising energy prices and increasingly strict environmental regulations, enhancing the energy efficiency of drying technologies has become an urgent priority. This study systematically reviews widely used drying technologies in grain and fruit and vegetable processing, including hot air, heat pump, infrared, convection, vacuum, solar energy, fluidized bed, microwave, refraction window, and freeze drying. It also covers various combined drying techniques, such as solar heat pump, infrared hot air, and microwave vacuum drying. Detailed analyses were conducted on the specific energy consumption, specific heat consumption, and specific moisture extraction rate of different drying systems. The results demonstrate that Solar hybrid drying system offers the highest energy efficiency, followed by the hybrid drying system combining microwave and infrared drying. Solar hybrid drying technology has the shortest payback period, at just 0.33 years, followed by hot air drying at 0.43 years. These insights provide valuable recommendations for optimizing future equipment development and improving energy management and operational practices in the industry.

Convective hot air drying technology is widely used for fruits and vegetables drying process due to its simplicity in usage, small investment, and convenience in operation. However, it is generally considered energy-intensive process with lower drying efficiency and quality because of unprecise control of drying process. In order to solve these problems, step-down relative humidity (RH) hot air drying technology was applied for papaya drying to improve drying efficiency and quality and reduce energy consumption. The effect of constant RH (20%, 30%, 40%, and 50%) and step-down RH of 50% with different holding times (10, 30, 60, and 90 min) and then decrease to 20% on heat and mass transfer process, drying quality, and energy consumption was examined. Results showed that decreasing RH contributed to improvement in the drying rate (DR). Compared to constant RH of 20%, the drying time under initial RH of 50% for 30 min followed by 20% RH shortened by 21.4%. Additionally, under this RH control strategy, the rehydration ratio (RR) and energy consumption achieved their maximum (7.71 ± 0.06) and minimum value (0.015 ± 0.001 kJ/g), respectively. During initial drying stage, high RH improved convective heat transfer coefficient (ht ) values and material temperature increased quickly. Furthermore, high RH contributed to maintaining pore structure formation, which benefited moisture diffusion. When RH was reduced, low RH enhanced convective mass transfer coefficient (hm ) significantly, resulting in rapid diffusion of internal moisture at high temperature, as well as rapid moisture evaporation from the surface. Therefore, step-down RH hot air drying was verified to improve drying of papaya slices, making it energy efficient process. The findings in current work indicate step-down relative humidity strategy is a promising technique to enhance hot air drying process, quality, and energy efficiency of papaya slices.

This study investigated the kinetics of drying and polyphenol degradation during hot air and sun drying of cocoa beans. Hot air drying was carried out using a constant humidity‐controlled (50% relative humidity) oven at temperature range of 60–80C, and sun drying was carried out by exposing the beans under direct sunlight. Several semi‐theoretical models were used to model the kinetics of moisture diffusion and it was found that the Page and Logarithmic models were able to provide good prediction. A first‐order reaction kinetics was used to predict the polyphenol degradation process with rate constants ranging from 0.011/h to 0.052/h. Activation energy for polyphenol degradation was determined at 8.97 kJ/mol using the Arrhenius equation. Effective diffusivity during drying was found within the order of magnitude (10−12–10−10 m2/s) reported in most drying literatures.Practical ApplicationsThe understanding of moisture diffusion is important in dryer design especially in the determination of effective diffusivities during drying. Polyphenols are important antioxidants that are beneficial to human health. By investigating the polyphenol degradation kinetics, this helps to link the reactions with moisture diffusion kinetics.

The antioxidant activity (AA) and color degradation were monitored in tomato quarters (Rio Grande) during hot air drying in a cabinet drier at five temperatures (60, 70, 80, 90 and 100°C) at an airflow rate of 0.2 m/s and 20% relative humidity. AA values of fresh tomatoes determined by total phenolic content (TPC), FRAP and DPPH assays were 85.3 mg GAE, 26.2 µmol TE and 31.3 µmol TE/100g dm, respectively. Increasing drying temperature resulted in a reduction in Hunter Lab and a/b color values of tomatoes as well as their AA values. During hot air drying, the degradation of AA and color values of tomatoes followed a first-order reaction. Activation energy values for AA degradation determined by TPC, FRAP and DPPH assays were 24.36, 22.91 and 23.67 kJ/mol, respectively. High correlations were found among the TPC, DPPH and FRAP values and lycopene and β-carotene contents of tomatoes during hot air drying. Degradation kinetic data revealed that color values and tomatoes AA are susceptible to drying temperature.

SummaryThis study investigated the changes in colour, volatile compounds, fatty acids, total phenolic content (TPC), total flavonoid content (TFC) and antioxidant activity of kaffir lime leaves (makrud in Thai) Citrus hystrix D.C. after three drying treatments, namely hot‐air (HA) drying, low relative humidity (LRH) air drying and far‐infrared radiation (FIR) drying. Overall, when compared with fresh leaves, a slight decrease in L* values of the three dried samples was observed. TPC, TFC and ferric‐reducing/antioxidant power (FRAP) values were increased by LRH and FIR drying (LRH: 39%, 43% and 28%; FIR: 62%, 39% and 39%), while HA drying decreased TPC, TFC and FRAP values (28%, 21% and 1%), compared with fresh leaves. The main volatile compounds in fresh leaves were citronellal, followed by linalool and viridiflorol. Drying brought about an increase in the concentrations of volatile components, such as citronellal with HA, LRH and FIR drying (79%, 83% and 64%, respectively), compared with the results for fresh leaves (56%). LRH and HA drying increased essential fatty acid alpha‐linolenic acid (ALA, 18:3n‐3), while linoleic acid (LA, 18:2n‐6) was increased by FIR drying. The present study has provided useful information for the industrial use of dried kaffir lime production.

<div class="section abstract"><div class="htmlview paragraph">Increased market penetration of electric drive vehicles (EDVs) requires overcoming a number of hurdles, including limited vehicle range and the elevated cost in comparison to conventional vehicles. Climate control loads have a significant impact on range, cutting it by over 50% in both cooling and heating conditions. To minimize the impact of climate control on EDV range, the National Renewable Energy Laboratory has partnered with Hyundai America and key industry partners to quantify the performance of thermal load reduction technologies on a Hyundai Sonata plug-in hybrid electric vehicle. Technologies that impact vehicle cabin heating in cold weather conditions and cabin cooling in warm weather conditions were evaluated. Tests included thermal transient and steady-state periods for all technologies, including the development of a new test methodology to evaluate the performance of occupant thermal conditioning. Heated surfaces demonstrated significant reductions in energy use from steady-state heating, including a 29%–59% reduction from heated surfaces. Solar control glass packages demonstrated significant reductions in energy use for both transient and steady-state cooling, with up to a 42% reduction in transient and 12.8% reduction in steady-state energy use for the packages evaluated. Technologies that demonstrated significant climate control load reduction were selected for incorporation into a complete thermal load reduction package. The complete package is set to be evaluated in the second phase of the ongoing project.</div></div>

The objectives of this research were to investigate model for describing equilibrium moisture content of fresh rubber sheet and drying kinetics of Air Dried Sheet (ADS) rubber using hot air (HA) drying, green house (GH) drying and conventional open-air (OA) drying. The experimental results were mathematical simulated by non-linear regression analysis. Equilibrium moisture content (EMC) of natural rubber (NR) were evaluated using the gravimetric-static method among surrounding temperature of 40–60°C provided to relative humidity surrounding of 10–90%. The results showed that The Modified Halsey model was found to be the most suitable for describing the relationship among equilibrium moisture content, relative humidity and temperature. The appropriate thin-layer drying equation model for predicting the drying kinetic of rubber sheet. The experiments were carried out under the conditions of constant drying temperature 30–55°C, the initial moisture contents of sample rubber were operated in range of 15–40 % dry-basis. The final moisture content for each drying strategies was fixed at 1±0.05 % dry-basis. The effects of drying conditions on evolution of moisture content, drying rate and quality of rubber were determined. The experimental results showed that for both forced and natural convection the drying rate of rubber sheet was relatively related to drying temperature. The fresh rubber sheets were dried by OA drying took longer drying period than those of HA drying. Twelve thin layer drying equation models were used for evaluating experimental data and the results showed that the simulated data using Weibull Distribution model had a good relation to the experimental values of sample drying with HA, experiment results using Modified Henderson and Pabis model was the best fitting model for GH and conventional OA drying. According to the quality and energy analysis, the results showed that quality of the rubber sheet was acceptable in market level for all drying heat sources. However, ADS rubber drying with HA and OA were slightly better than GH drying.

The effects of combined humid-convective drying (CHCD) on quality attributes of shiitake mushrooms regarding surface color, microstructure, texture, volatile compounds, and polysaccharides were investigated. Initially, mushrooms were subjected to various hot air drying (HAD) procedures, and the influential parameters (initial temperature, relative humidity [RH], and time) were optimized based on highest yield of polysaccharides. Among them, nonuniform drying was selected to design CHCD, with final parameters—initial temperature: 40 °C, maximum temperature: 60 °C, RH: 30%, and time: 28 h. CHCD produced shiitake mushrooms with less surface color changes (p < 0.05), softer texture, and less shrinkage (47.1 ± 1%) than conventional HAD. Scanning electron microscopy results showed a honeycomb-like pore-network in CHCD samples. The yield of polysaccharides, predominantly β-glucans as detected by MALDI-TOF and CP-MAS NMR, was 12.3 ± 0.5 g/100g in CHCD samples, significantly higher than conventional HAD (p < 0.05). A total of 51 significant volatile compounds were detected with higher concentration in CHCD compared with HAD samples using GC × GC-QTOF. Along with increasing shelf-life, CHCD process produces dry mushrooms with lower surface color changes, good preservation of internal structure, softer texture, lesser shrinkage, increased rehydration, increased content of polysaccharides, and volatile compounds compared with conventional HAD.

Thermal characteristics of a novel enclosed cascade-like heat pump dryer used in a tunnel type drying system

More effective stewardship of our resources contributes to the security, environmental sustainability, and economic well-being of the nation. Buildings present one of the best opportunities to economically reduce energy consumption and limit greenhouse gas emissions. Geothermal heat pumps (GHPs), sometimes called ground-source heat pumps, have been proven capable of producing large reductions in energy use and peak demand in buildings. However, GHPs have received little attention at the policy level as an important component of a national strategy. Have policymakers mistakenly overlooked GHPs, or are GHPs simply unable to make a major contribution to the national goals for various reasons? This brief study was undertaken at DOE's request to address this conundrum. The scope of the study includes determining the status of global GHP markets and the status of the GHP industry and technology in the United States, assembling previous estimates of GHP energy savings potential, identifying key barriers to application of GHPs, and identifying actions that could accelerate market adoption of GHPs. The findings are documented in this report along with conclusions and recommendations.

Gac fruit (Momordica cochinchinensis Spreng.) is a rich source of carotenoids for the manufacture of powder, oil and capsules for food, cosmetic and pharmaceutical uses. Currently, only the aril of the Gac fruit is processed and the peel, similar to the other components, is discarded, although it contains high level of carotenoids, which could be extracted for commercial use. In the present study, four different drying methods (hot-air, vacuum, heat pump and freeze drying), different temperatures and drying times were investigated for producing dried Gac peel suitable for carotenoid extraction. The drying methods and drying temperatures significantly affected the drying time, carotenoid content and antioxidant capacity of the dried Gac peel. Among the investigated drying methods, hot-air drying at 80 o C and vacuum drying at 50 o C produced dried Gac peel that exhibited the highest retention of carotenoids and the strongest antioxidant capacity. Hot-air drying at 80 o C and vacuum drying at 50 o C are recommended for the drying of Gac peel. © 2016 Society of Chemical Industry.