Heat Pump Dryer Research Articles

Design of New Heat Pump Dryer System: A Case Study in Drying Characteristics of Kitchen Waste

Existing kitchen waste treatment equipment primarily employs biological cultures for high-temperature fermentation of kitchen waste during the secondary decomposition stage. The temperature inside the fermentation chamber is mainly achieved by heating the air through electric heating tubes. However, this method of electric heating still possesses numerous shortcomings, such as high power consumption and significant energy loss. Given the aforementioned reasons, this article proposes a heat pump drying device specifically designed for the moisture removal process during the fermentation treatment of kitchen waste. This device effectively removes the moisture generated during the fermentation of kitchen waste and assists the electric heating unit in the biomass waste treatment equipment in heating the fermentation chamber, thereby reducing electricity consumption.The closed-loop heat pump drying system can continuously introduce hot, low-humidity air into the fermentation chamber through a circulating fan to remove moisture from kitchen waste.To investigate the dehumidification performance of this device, this article varies the airflow rate of the circulating fan in the heat pump drying system and the inlet water temperature of the plate heat exchanger, achieving changes in the airflow through the dehumidification evaporator and the condensation temperature of the system. Under experimental conditions, the range of the coefficient of performance (COP) achieved by the device is between 3.07 and 5.39; the specific moisture extraction rate (SMER) ranges from 0.62 to 1.81 Kg/(Kw·h), and the moisture removal rate (Mr) ranges from 1.9 Kg/h to 8.2 Kg/h.

Evaluation of Different Drying Methods and Leaf Age on the Retention of Phytochemical and Nutritional Attributes of Moringa Leaf Powder

Moringa (Moringa oleifera), indigenous to India and Africa, is esteemed for its dual utility as a minor timber source and, more importantly, as a vegetable crop. The leaves of the moringa tree are exceptionally nutrient-dense, containing essential elements such as iron, calcium, proteins, vitamins A, C, and E, dietary fiber, phosphorus, and potassium, all vital for human health. Furthermore, these leaves are rich in antioxidants, including flavonoids and phenolics, which endow them with significant medicinal properties. Despite its sporadic cultivation hindering global availability, the production of moringa leaf powder presents a viable strategy to bolster its international export potential. This study aims to assess the efficacy of various drying techniques in producing moringa leaf powder while preserving its nutritional integrity. Conducted at the Post-Harvest Technology Laboratory within the Department of Horticulture, Rajasthan College of Agriculture, and the Department of Processing and Food Engineering, College of Technology and Agricultural Engineering at Maharana Pratap University of Agriculture and Technology, Udaipur, Rajasthan, India, this research evaluates the nutritional quality of moringa leaf powder produced via different drying methods and from leaves of varying ages. Our findings indicate that the fluidized bed dryer excels in preserving the nutritional quality of the powder compared to tray and heat pump dryers. Additionally, the study concludes that heat pump dryers are unsuitable for producing high-quality moringa leaf powder.

Innovative hybrid strategy for quality improvement of Goji tea: ultrasonic-ethyl oleate pretreatment combined with heat pump drying.

Goji berries, renowned for their nutritional benefits, are traditionally dried to extend shelf life and preserve quality. However, conventional drying methods often result in uneven drying, color loss and reduced rehydration capacity. This study investigates an innovative hybrid strategy combining ultrasonic-ethyl oleate (US+AEEO) pretreatment with heat pump drying (HPD) to enhance the drying process of Goji berries. Fresh Goji berries underwent US+AEEO pretreatment, which significantly disrupted the waxy layer, enhancing drying efficiency and water infiltration during rehydration. Compared to freeze drying (FD), HPD combined with US+AEEO pretreatment resulted in higher retention of total polyphenol content (TPC) and total flavonoid content (TFC) in the Goji soaking soup. Specifically, the HPD-US+AEEO samples exhibited the highest TPC and TFC levels, significantly outperforming FD samples. Additionally, the DPPH and ABTS antioxidant assays demonstrated higher scavenging activities in HPD-US+AEEO samples. The rehydration kinetics revealed that HPD samples had a superior rehydration rate and final moisture content compared to FD samples. Low-field nuclear magnetic resonance and magnetic resonance imaging analyses confirmed enhanced water distribution and higher mobility in HPD-US+AEEO samples. Scanning electron microscopy indicated a more porous structure in US+AEEO-treated samples, facilitating better water absorption and functional component retention. The combination of US+AEEO pretreatment with HPD significantly improves the drying process of Goji berries, enhancing nutrient retention, color preservation and rehydration properties. This innovative drying method offers a promising solution for producing high-quality dried Goji berries, benefiting both the food industry and health-conscious consumers. © 2024 Society of Chemical Industry.

Moisture distribution change and quality characteristics of ultrasound enhanced heat pump drying on carrot

Abstract The study aims at investigating the impact of ultrasound enhancement on the water change and quality characteristics of dried carrots by heat pump drying (HPD). The results showed that ultrasound had obvious strengthening effect on the drying and dehydration process of HPD, but there was an attenuation effect of ultrasound in the propagation process of materials, and the magnetic resonance imaging results could visually demonstrate the change and migration of moisture inside carrot slices. Higher drying temperature and ultrasonic power could cause more micropores and higher content of polyphenols, flavonoids and niacin of carrot slices. Conversely, the elevated drying temperature reduced rehydration ratio. β-carotene content showed a trend of increasing first and then decreasing due to excessive temperature and ultrasonic power. Based on AHP-CRTITC method, the highest comprehensive score was attained at drying temperature of 60 °C and ultrasonic power of 80 W. Therefore, the reinforcement effect of ultrasound on HPD process could significantly enhance dehydration rate and improve product quality.

Experimental and simulation study on the performance of a solar assisted multi-source heat pump drying system in Zhengzhou area

Zhengzhou of Henan province is an important agricultural production base. To improve the performance of the combined drying system and promote the development of agricultural products in Zhengzhou area, a solar assisted multi-source heat pump (SMSHP) drying system was proposed based on a traditional solar assisted air source heat pump (SASHP) drying system. The simulation models were developed for the air source heat pump (ASHP), SASHP, and SMSHP drying system respectively. The coefficient of performance, energy consumption and specific moisture extraction rate of the drying systems under different seasons were analyzed. Moreover, to validate the simulation models, an experimental platform of the combined drying system was designed and set up, and the experimental tests were carried out on the ASHP, SASHP, and SMSHP drying system. The simulation results revealed that the SMSHP drying system had lower energy consumption, higher coefficient of performance and specific moisture extraction rate than that of the SASHP drying system. The most significant performance enhancement was observed in spring, where the SMSHP system demonstrated a 22.69 % increase in coefficient of performance, a 19.2 % increase in specific moisture extraction rate, and a 16.11 % decrease in energy consumption compared to the SASHP drying system. Comparing with the experimental data, the simulation model errors of the energy consumption, coefficient of performance, and specific moisture extraction rate of the SMSHP drying system were 3.19 %, 0.28 %, and 2.27 %, respectively. Therefore, the accuracy of the simulation results was confirmed. To better calculate the heat provided by the solar collection system, the concept of the tank heating guarantee rate was first introduced, and it was found to be more scientific than the solar energy guarantee rate. At last, The economic and environmental benefit of the drying systems were analyzed during the life cycle, and the SMSHP drying system exhibited better comprehensive performance than the SASHP drying system. This paper provides valuable insights into the comprehensive utilization of solar energy and the control logic of solar assisted air source heat pump combined drying system under different seasons.

Comparison of various drying methods on color, texture, nutritional components, and antioxidant activity of tumorous stem mustard

Exploring new dehydration technology can help to deal with the challenge of quality preservation and high salt waste brine problem in pickled mustard industry. In the current study, effects of vacuum freeze-drying (FD), heat pump drying (HPD), air-impingement jet drying (AIJD), and hot air drying (HD), on color, texture, nutritional component, and antioxidant capacity of tumorous stem mustard were determined. All drying methods significantly affected color and texture. The ascorbic acid (Vc), reducing sugar, protein, total phenolic content (TPC), ABTS, DPPH, and FRAP level of tumorous stem mustard were 123.20–768.74 mg/100 g, 2.49–17.90 g/100 g, 30.74–53.03 g/100 g, 1.98–4.13 mg gallic acid equivalent (GAE)/g, 1.42–8.28 mg Vc/g, 1.04–9.73 mg Vc/g, and 2.11–6.83 mg Vc/g, respectively. The content of individual phenolics were influenced by drying methods, and ferulic acid was determined as a major phenolic compound for all samples (8.15–65.43 μg/g). The content of total phenolic and monomeric polyphenols except for ferulic acid, positively correlated to their antioxidant activity. Furthermore, HD, FD, and AIJD were beneficial to promote the production of umami amino acids and reduce bitter amino acids, thus improving the flavor of tumorous stem mustard. The quality of tumorous stem mustard of FD was closest to that of fresh tumorous stem mustard. Overall, the drying technology is promising to replace the salt infiltration process to realize the dehydration of tumorous stem mustard in the manufacturing of pickled mustard.

Viability of an Open-Loop Heat Pump Drying System in South African Climatic Conditions

Drying agricultural produce consumes a considerable amount of energy. As an energy-efficient system, a heat pump can improve the energy efficiency of the drying process and hence reduce the energy consumption, especially in South Africa, where both sub-tropical and temperate weather conditions dominate. The objective of this research is to experimentally investigate the impacts of weather conditions on the operational conditions and thermal performance of an open-loop air-source heat pump drying system. The experimental investigation was conducted in a climate chamber where the climate conditions were simulated from −10 °C to 20 °C with an interval of 10 °C for the typical temperature range of the harvesting season in South Africa. The findings indicate that ambient temperatures have a significant impact on both the operating conditions and thermal performance of an open-loop heat pump system; the change in ambient temperatures from −10 °C to 20 °C leads to a 141.6% improvement in the suction pressure, a 214.2% increase in the discharge pressure, and 30.1% increase in the compression ratio, as well as a consequent increase of 130.6% in the refrigerant mass flow rate (from 0.0067 to 0.0155 kg/s), resulting in a corresponding increase in the coefficient of performance (COP) of the heat pump drying system by about 42.1%. Therefore, this study suggests that, while using an open-loop air-source heat pump drying system utilising R134a refrigerant is feasible in South Africa, it may be practically limited to regions with warm climates or during warmer seasons.

Correlation of Viscoelastic Properties with Water Status of Scallop Adductors During Heat Pump Drying: Effects of Ultrasound Pretreatment and Drying Conditions

Correlation of Viscoelastic Properties with Water Status of Scallop Adductors During Heat Pump Drying: Effects of Ultrasound Pretreatment and Drying Conditions

Experimental study on effects of compressor speed on a heat pump dryer system with auxiliary solar source

A novel heat pump drying system with auxiliary solar source and ejector using a variable speed compressor has been experimentally investigated. The influences of compressor speed on the performances of novel system were comprehensively evaluated and compared to the basic heat pump drying system. Moreover, the relationship between the compressor speed and the drying temperature under different solar radiation intensity was clarified. The experimental results indicated that the novel system achieved the higher heating capacity and drying temperature because of the input solar energy. However, the excessive heat input to the drying system also would increase the electrical consumption. To solve this problem, the novel system using a variable speed compressor could obtain the same drying temperature as the basic system at the lower compressor speed. When drying at the same temperature of 70 °C, compared to basic system, the novel system using a variable speed compressor improved the moisture extraction rate by 6.8 %–22.4 %, the specific moisture extraction rate by 23.7 %–31.4 %, and the COP by 26.5 %–42.3 %. The results could provide the guidance for combining the variable speed compressor and the heat pump drying system with auxiliary solar source.

GC-IMS-Based Volatile Characteristic Analysis of Hypsizygus marmoreus Dried by Different Methods.

Gas chromatography-ion mobility spectroscopy (GC-IMS) was used to analyze the volatile components in dried Hypsizygus marmoreus of different drying methods, including hot air drying (HAD), heat pump drying (HPD), heated freeze-drying (HFD), and unheated freeze-drying (UFD). A total of 116 signal peaks corresponding to 96 volatile compounds were identified, including 25 esters, 24 aldehydes, 23 alcohols, 13 ketones, 10 heterocyclic compounds, 8 carboxylic acids, 7 terpenes, 3 sulfur-containing compounds, 2 nitrogen-containing compounds, and 1 aromatic hydrocarbon. The total content of volatile compounds in H. marmoreus dried by the four methods, from highest to lowest, was as follows: HAD, HPD, HFD, and UFD. The main volatile compounds included carboxylic acids, alcohols, esters, and aldehydes. Comparing the peak intensities of volatile compounds in dried H. marmoreus using different drying methods, it was found that the synthesis of esters, aldehydes, and terpenes increased under hot drying methods such as HAD and HPD, while the synthesis of compounds containing sulfur and nitrogen increased under freeze-drying methods such as HFD and UFD. Nine common key characteristic flavor compounds of dried H. marmoreus were screened using relative odor activity values (ROAV > 1), including ethyl 3-methylbutanoate, acetic acid, 2-methylbutanal, propanal, methyl 2-propenyl sulfate, trimethylamine, 3-octanone, acetaldehide, and thiophene. In the odor description of volatile compounds with ROAV > 0.1, it was found that important flavor components such as trimethylamine, 3-octanone, (E)-2-octenal, and dimethyl disulfide are related to the aroma of seafood. Their ROAV order is HFD > UFD > HPD > HAD, indicating that H. marmoreus using the HFD method have the strongest seafood flavor. The research findings provide theoretical guidance for selecting drying methods and refining the processing of H. marmoreus.

Recent trends on energy-efficient solar dryers for food and agricultural products drying: a review

AbstractThe energy efficiency enhancement of solar dryers has attracted the attention of researchers worldwide because of the need for energy storage in solar drying applications, which arises primarily from the irregular nature of solar energy that leads to improper drying which will reduce the quality of the products being dried. This work comprehensively reviews the state-of-the-art research carried out on solar dryers for energy efficiency enhancement using various alternative strategies, including hybrid solar dryers that use auxiliary heating sources, such as electric heaters or biomass heaters, solar-assisted heat pump dryer, use of desiccant materials, and heat storage systems that use both sensible and latent heat storage. The advent of phase change materials (PCM), such as thermally and chemically stable PCMs, for long-term storage, bio-degradable and bio-compatible PCM materials to alleviate the negative environmental impact of conventional PCMs is also presented. The performance parameters considered for evaluating dryers include the maximum temperature attained inside the drying chamber, drying time and efficiency, specific moisture extraction rate (SMER), energy and exergy efficiency and CO2 mitigation effect. The factors considered to analyze the PCMs application in solar dryers include cost and sustainability of PCMs, and both energy and exergy analyses of dryers using PCMs. The gaps in current knowledge and future scope for further improvement of solar dryers are also elucidated. Graphical abstract

Study on drying characteristics of sludge under different conditions based on the low-temperature sludge heat pump drying model

The study established a model for a closed low-temperature heat pump drying (HPD) system and structured a sludge drying experimental platform to validate it. The effects of incoming air temperatures of the drying cabinet, circulating air volume, and ambient temperature on both drying rate and system performance were investigated. The findings revealed that the drying rate and specific moisture extraction rate (SMER) rise with higher incoming air temperatures of the drying cabinet and circulating air volume, while the coefficient of performance (COP) exhibited a contrasting trend. The sludge dried the fastest with a drying rate of 6.01 kg/h when the incoming air temperatures of the drying cabinet and circulating air volume were set to 65 °C and 900m³/h, respectively. At the incoming air temperature of the drying cabinet was 65 °C and the circulating air volume was set to 850 m3/h, the SMER reached the maximum value, 2.782kg/(kW·h). In addition, the COP increased as the ambient temperature rose, while the drying rate and SMER both decreased gradually. The drying rate demonstrated an average decline of 0.29 kg/h for every 2 °C rise in ambient temperature, while the SMER exhibited an average decrease of 0.148kg/(kW·h). These works offer guidance for the practical implementation of the sludge HPD system.

Improving Efficiency of Heat Pump Dryer Using R32 Refrigerant by Nanofluid

Drying process are important in many areas in the agriculture and food sectors, including increasing shelf life, improving transportability by reducing product weight or adding value to products. However, the main problem in the drying process is the relatively high energy consumption. Therefore, the development of energy-saving dryers is necessary. Based on the above reasons, this research aims to study the performance enhancement of heat pump dryers using R32 refrigerant by using heat recovery and nanofluid. The heat that is exhausted from the refrigerant by a heat exchanger. In this work, a Nano titanium dioxide (Ti2O3) was selected. Pork was dried under the conditions of drying temperature of 45, 50 and 55 °C and water flow rate in the heat exchanger at the front of the drying chamber of 2, 3 and 4 L/min. Criteria for evaluating heat pump dryer performance include drying rate, specific moisture extraction rate, specific energy consumption, heat pump dryer performance coefficient compared to heat pump dryers without nanofluid. The results showed that increasing the drying temperature and water flow rate in heat exchanger increased the drying rate, power and specific moisture extraction rate in the heat pump dryer using nanofluid. Whereas, the specific energy consumption was lower than the case without nanofluid. Increasing the drying temperature and the water flow rate in the heat exchanger had relatively little effect on the coefficient of performance (COP) of the heat pump dryer. Moreover, the study found that the coefficient of performance of heat pump dryer with nanofluid was in the range of 4.33 - 4.42.

Drying characteristics of eggplant drying in a heat pump dryer

Drying characteristics of eggplant drying in a heat pump dryer

Drying characteristics of sewage sludge pre-conditioned by CaO and sawdust under low-temperature drying conditions

ABSTRACT Heat pump drying is a low-carbon method of sludge drying. The operating temperature of a heat pump is generally not more than 70℃. To improve the drying efficiency of heat pump dryers, the effects of air parameters and additives on sludge drying characteristics at low temperatures were studied. The sludge drying experiments were conducted at an air temperature 50-70℃ and an air velocity of 0.5-1.7 m/s. The experimental results showed that the increase of air temperature, velocity and the addition ratio of additives can accelerate the sludge drying process. The average and maximum drying rates of sludge pre-conditioned by CaO and sawdust increased by 14.23% and 25.71%, respectively, compared with those of pure sludge. The two-way analysis of variance (ANOVA) revealed that the influence of air temperature on the sludge drying was higher than that of air velocity. Five reference models were fitted by the drying experiment data. The Page model has the highest R2, so it is the most suitable model to predict the drying time of sludge at low temperatures.

Performance analysis of a two-stage evaporation heat pump drying system for graded cooling/dehumidification

Single-stage evaporation heat pumps are widely used in drying fields, but they suffer from relatively low efficiency. To enhance the performance of conventional heat pump drying systems with single-stage evaporating, a two-stage evaporation heat pump drying (TSE-HPD) system is proposed in this paper for graded cooling/dehumidification. In this innovative system, the quasi dual-stage compression, matching a double temperature level evaporation process, achieves graded cooling and dehumidification of air. Its performance is investigated using energy and exergy analysis methods and compared with that of a single-stage compression heat pump drying (SSC-PHD) system. The results indicate that the TSE-HPD system exhibits 15.5 %–19.3 % improvement in the coefficient of performance (COP) and 16.3 %–18.9 % enhancement in the specific moisture extraction rate (SMER) compared to those of the SSC-PHD system when the condensing temperature varies between 50 °C and 70 °C. The parametric analysis reveals that the highest COP, SMER, and exergy efficiency (ηex) occur when the optimum first-stage evaporating temperatures are 16 °C, 25 °C, and 34 °C, respectively, under three standard operating conditions. At this time, the first-stage evaporator handles 36 %–40 % of the cooling/dehumidification tasks, the refrigerant mass flow ratio at the intermediate-pressure suction port of the compressor ranges from 47 %–58 %, and the optimum first-stage and second-stage compression ratios are 1.49–1.52 and 2.45–2.61, respectively. The research results provide guidance and reference for the determination of matching design parameters and efficient operation control parameters of drying systems.

Design and evaluation of a municipal solid waste incineration power plant integrating with absorption heat pump

The absorption heat pump can consume a small amount of high temperature heat source instead of electricity to realize the waste heat recovery. It has a potential to be applied in the energy efficiency improvement of municipal solid waste incineration power plant. In this study, a proposed integrated system has been designed, where the sludge heat pump drying system and dump pit heating system are coupled with the absorption heat pumps. The power generation improvement is evaluated through simulation calculation by EBSILON Professional and Aspen Plus. The results show that the power generation of proposed integrated system is 1.21 MW higher than that of reference power plant in winter operating condition. This is mainly due to the reductions of energy loss and exergy loss in incinerator and boiler system according to the energy flow and exergy flow analysis. The extracted steam from turbine is more suitable than the flue gas out of bag filter as the high temperature heat source of heat pump. In addition, the variable operating condition analysis is carried out for the proposed integrated system.

Multi-objective optimization and benefit evaluation of heat pump system for tobacco drying using waste heat from data center

Tobacco drying is a highly energy-consuming process that requires a large amount of thermal energy. In this study, the waste heat from a data center is utilized to reduce fossil energy consumption in the tobacco drying process. A heat pump system is designed to address the issue of the waste heat temperature from the data center not meeting the required temperature for tobacco drying. Multi-objective optimization is performed with the goal of maximizing the specific moisture extraction rate and minimizing the specific investment cost, and seven hydrofluoroolefins are selected as the circulating working fluids. Coal-fired tobacco drying and Air Source Heat Pump Tobacco Drying (ASHPTD) are selected as comparison benchmarks to evaluate the energy efficiency and environmental benefits of the Data Center Waste Heat Tobacco Drying (DCWHTD) method in this study. The results indicate that R1234ze(Z) is the best working fluid. The specific moisture extraction rate of DCWHTD is improved by 36.69% and 20.21% compared to the coal-fired tobacco drying and ASHPTD, respectively, demonstrating enhanced energy efficiency. Although the specific investment cost of DCWHTD is higher compared with the coal-fired tobacco drying, it is 21.00% lower than that of ASHPTD. DCWHTD produces fewer emissions, the life-cycle carbon emissions are 26.93% and 16.80% lower than that of the coal-fired tobacco drying and ASHPTD, respectively. Furthermore, waste heat recovery improves the energy reuse efficiency of the data center by 64.92%. The tobacco drying method proposed in this study has better comprehensive performance and greater application potential.

Comparative assessment of solar dryer with thermal energy storage system and heat pump dryer in terms of performance parameters and food analysis

Comparative assessment of solar dryer with thermal energy storage system and heat pump dryer in terms of performance parameters and food analysis

Application of heat pump drying technology to produce dried mango products from Tu Quy mango (Mangifera india L.), Vietnam, on a pilot scale

In this study, the heat pump drying technique was applied to develop the production process of dried mango from Tu Quy mango sources, Ben Tre province, Vietnam. The experiment was performed in three steps. First, mango slices were treated through the blanching process. Samples were pretreated with sizes from 6 to 12 mm at 80–95°C for 3–6 min, and then the mango slices were soaked in a syrup solution concentration range of 25–40°Bx, citric acid of 0.5–2%, and glycerol of 0.1–0.4% at 35–65°C for 90–180 min. Finally, the samples were dried using a pilot-scale heat pump dryer until the moisture content reached 14–16%. The results showed that the blanching and osmosis processes were carried out under optimal conditions to inactivate the Polyphenol oxidase (PPO) enzyme, obtain maximum polyphenol compounds, and conform to the product appearance. Additionally, the drying process was carried out at 30°C for 1,080 min with the polyphenol content retaining 11.71 mgGAE/gDW—This signifies a successful endeavor in developing production methodologies and expanding the range of mango-derived products. Employing innovative technological processes enhances both the quantity and quality of the products. Moreover, the manufacturing procedure was executed on a pilot device, streamlining the synchronization of large-scale production processes effortlessly. This advancement not only enhances economic value but also addresses the issue of congestion prevalent in the current state of the mango industry in Vietnam.