Performance of heat pump drying system integrated into a blood dryer

ABSTRACT

In general, most heat losses in industrial dryers arise due to the discharge of humid air. Using heat pump drying systems, heat from the exhaust humid air can be recovered, thus improving the energy efficiency substantially. In this study, the performance of heat pump integration in a blood dryer was examined. Computer simulation models of the original high-temperature (180°C) dryer and the proposed system with heat pump integration and auxiliary heating were developed. Different heat pump systems and working fluids were investigated to determine the best performing heat pump system. In this case, it was found that an R245fa heat pump system with a subcooler is the best solution. When using an absorption heat pump, the results showed that a type I absorption heat pump with H₂O–LiBr as working fluid pair performs the best. In addition, the economic benefit as well as the optimum operating conditions of the dryer with integrated heat pump were also determined.     

Influence of drum inlet air conditions on drying process in a domestic tumble dryer

This study examines how the inlet air temperature, relative humidity, and flow rate influence the textile drying process in an open cycle tumble dryer. An experimental setup was prepared by connecting a domestic tumble dryer to an external system for controlled heating, humidification, and transport of air. Experiments were conducted by drying cotton textiles (8?kg dry mass) at different air inlet conditions. On the basis of measured data, correlations for determination of the total drying time, the moisture evaporation rate during the constant drying rate, and the area-mass transfer coefficient were developed. The process in the drum was modeled by using an established moisture evaporation model, based on sorption isotherms. A commonly used and a recently reported sorption isotherm for cotton were used with the model. Agreement between calculated and measured drying curves was better in case of the commonly used sorption isotherm, but final moisture content was better predicted by the recently reported sorption isotherm.     

A rationally based model applicable for heat pump tumble dryer

The present study proposes a rationally based heat pump clothes dryer model which is capable of handling transient behaviors of both air-side and refrigerant side. The model can take into account the geometrical variation of the heat exchangers. Yet the proposed model is free from extra constraints that were normally imposed by previous studies. The simulation shows that there exist three stages in a typical drying process, including a preheat stage, followed by a constant evaporation stage, and finally a falling drying rate period. The calculation indicates that the variation of the clothes temperature and the system suction/discharge pressure show an appreciable rise in the first stage, remain nearly unchanged at the second stage, and increase again at the final stage of drying process. Also, the corresponding maximum specific moisture extraction rate (SMER) peaks at the end of the second stage while the corresponding coefficient of performance (COP) drops continuously. The simulation also indicates that increasing the air volumetric flowrate yields a lower discharge/suction pressure, a higher COP value, and a shorter drying time. The results also suggested that a good strategy to maximize COP is initiated by a low volumetric rate during the preheat stage, increasing it during the second stage and lowering it to an intermediate flowrate at the end of the drying period. Increasing heat exchanger size, either by increasing heat exchanger width or the number of tube row, results in a lower suction/discharge pressure and a shorter drying time. Although both approaches adopt larger surface area to promote overall performance, it is found that increasing the width of heat exchanger yields more effective results.     

Statistical analysis of clothing drying in a venting type dryer

An experimental study of the drying process using the prototype of a venting type dryer is presented. The machine has two motors: one for moving the drum and another for moving the turbine; electrical resistance is used as the heat source. The prototype operates under controlled test conditions in accordance with the Department of Energy (DOE) Standard 10 CFR 430. The aim of this study is to statistically determine the impact of the main factors and their interactions involved in the drying of clothing from a complete design of experiments. Statistical analyses for drying time and the energy consumption are determined from the studied factors. The factors studied are turbine motor frequency (to admit and expel air from the dryer); power supplied to the electric coil, amount and moisture of clothing and restriction of exhaust duct the gases. The results show that all of the studied factors and four of the interactions are statistically significant in the drying of clothes. The shortest drying time and the lowest energy consumption were obtained with the higher level of restriction and the lower initial moisture of clothing.     

Effect of ambient conditions on drying of herbs in solar greenhouse dryer with integrated heat pump

An even span solar greenhouse dryer was built and applied to dry Java tea (Orthosiphon aristatus) and Sabah snake grass (Clinacanthus nutans Lindau). Findings showed that the solar greenhouse dryer performs satisfactorily during clear weather except at nighttime and rainy day due to product rehydration which is heavily influenced by high relative humidity from ambient air. Integrating of heat pump into the solar greenhouse dryer has successfully reduced the room relative humidity by 10–15%. Also, heat pump has mitigated the product rehydration issue by maintaining room relative humidity at maximum of 65% throughout the drying period. The drying rate of Java tea was improved three to fourfold, i.e., from 0.004–0.008 to 0.018–0.025?g H₂O/g DM min, whereas 10% of drying time was saved for both Java tea leaf and Sabah snake grass leaf with the assistance of heat pump system. Meanwhile, the supply of dry air from the heat pump system with a magnitude of 0.25–0.50?m/s helps in enhancing the drying rate of the herbs as well as minimizing the nonuniformity of drying temperature and relative humidity inside the solar greenhouse dryer.     

Heat pump drying of grape pomace: Performance and product quality analysis

Abstract

Grape is one of the most popular fruits and various types of grape have been cultivated by more than 100 countries around the World. The wine and juice industry produces large quantities of by-product, called grape pomace (GP) as an industrial waste and it consists of skins, seeds, and stems. Various processes such as separation, pressing, drying, and milling are applied to benefit from its health effects. In this study, the seeded black GP Kalecik karas? (Vitis vinifera) was dried in an assisted closed cycle heat pump dryer (HPD) designed for high-moisture products to investigate the drying behaviors of GP. The effects of drying air temperature on bioactive properties and the drying characteristics of GP, and performance of system have discussed. Experiments were carried out at two different temperatures (45 and 50°C) and air velocity of 1.0 m/s. It was seen that increasing temperature decreased the drying time, coefficient of performance of whole system (COP_ws), and specific energy consumption (SEC). The average values of COP_ws for temperatures 45°C and 50°C were calculated as 3.28 and 3.10, respectively. The drying efficiencies (DE) at drying air temperature of 45°C and 50°C ranged from 2 to 12% and from 2 to 15%, respectively. Additionally, result of analysis has indicated that using a HPD at lower temperatures increases performance of system despite of higher energy input. Bioactive properties of dried samples at drying air temperature of 45°C are better than 50°C. The results show that drying the GP at low temperature is more suitable for product quality. For this reason, heat pump may be preferred. It shows that this drying system with higher capacities in the future can be recommended as an alternative technique in terms of energy usage, drying time, and performance of system.     

喷雾干燥器节能降耗的措施

论述了喷雾干燥器的工作原理及特点，并探讨了其节能的途径。     

Energetic and financial assessment of the implementation of an absorption heat pump in an industrial drying system

Abstract

Absorption heat pump (AHP) cycles provide opportunities to reduce the energy use of drying systems. However, different configurations can be conceived and the results vary. In this work, data from an existing industrial convective dryer are used as an input to simulate different heat pump cycles. Energy that is lost in the dryer exhaust can be partly recovered to reduce the total energy demand. Energetic analyses are done for three AHP cycles: type I, type II and double-lift cycle. The maximal relative energy saving compared to the original dryer is for the respective cycles equal to 20%, 11% and 15%. With quotes gathered from manufactures, a financial analysis is carried out on the implementation of a type I AHP in the system. This unique approach of an extensive energetic and financial study results in a calculated internal rate of return over ten years equal to 18%, which make the system feasible for the implementation in industrial dryers.     

Parallel plate heat exchanger for heat energy recovery in a farm grain dryer

One of the methods with the most potential to reduce energy consumption in grain drying is heat recovery from the dryer exhaust air. A parallel plate heat exchanger to recover heat energy from the exhaust air of a recirculating batch grain dryer was examined by theoretical assessments as well as by measurements in a scaled-down research dryer and experimental heat exchanger. In addition to the heat transfer performance, the operability in dusty conditions was investigated. Finally, the optimization of the heat exchanger was introduced by the aid of the calculation models and practical measurement. The heat exchanger performed satisfactorily, providing an average energy saving of approximately 18%. A significant improvement in the performance could be achieved by increasing the air velocity. No severe dust accumulation was observed, and a heat exchanger of this type could provide remarkable energy saving possibilities in grain drying. Further tests are necessary to ensure the operability in long-term use.     

Study of hybrid dryer prototype and its application in pregerminated rough rice drying

In this study, a hybrid dyer, combining heat pump drying (HPD) with fluidized bed drying (FBD) concepts were designed and fabricated. The pregerminated rough rice (pre-GRR) was dried in multistage using this hybrid dryer to compare with the single-stage drying by hot air dryer. The objectives were to test the application of this hybrid dryer and determine the suitable drying condition for pre-GRR. The result indicated that the punched plate distributor was the most suitable distributor. The pre-GRR should be dried by the three-stage drying method using either FBD or HPD at 45°C in the last stage to obtain higher head rice yield, lower fissure grain, and better color values than their counterparts. The scanning electron micrographs proved that starch gelatinization occurred when applying FBD at temperatures between 100 and 140°C causing the adhesive connections inside the kernels and subsequent decrease in fissures.     

Effect of two stage, tray and heat pump assisted-dehumidified drying on drying characteristics and qualities of dried ginger

Desorption isotherms for sliced gingers have been measured. A non-linear regression programme was used to fit four moisture sorption isotherm models to the experimental data. The Modified Halsey and Modified Oswin models gave the best fit for X_e = f(RH_e, T) and RH_e = f(X_e, T), respectively. Tray and heat pump dehumidified drying incorporated by single and two stage drying were conducted. It was found that the modified Page model was the most effective. The drying constant was fitted to drying air temperature using the Arrhenius model. Effective moisture diffusivities were determined using the drying data. The heat pump dehumidified drying incorporated by the two stage drying could reduce the drying time at 40 °C by 59.32% and increase 6-gingerol content by 6%. Quality evaluation by 6-gingerol content, rehydration ratio and ΔE* showed the best quality for dried sliced gingers in the heat pump dehumidified drying incorporated by the two stage drying at 40 °C.     

Wrinkling mechanism of woven cotton fabrics during domestic tumble drying

Cotton wrinkling after home laundry has become an unfavorable phenomenon for consumers for a long time. Research has indicated that the wrinkles during tumble drying result from complicated changes of fabric physical properties as well as drying parameters such as temperature of drying air and drying duration. However, most of the research that has been done in this field has showed certain limitations, such as not simulating the real drying process or not understanding the cotton wrinkling mechanism accurately. This research, through an experimental design of 21 cotton fabrics in tumble drying, has explained the wrinkling behavior of woven cotton fabric in different drying stages and has investigated the wrinkling forming stage during tumble drying. Results showed that fabric characterization (such as thickness, density, and weight) does not significantly influence the smoothness appearance of the cotton fabrics in the tumble dryer. Moreover, heater power in the falling-rate period (heater power 2) and relative humidity dividing point between falling-rate period and unheated air blowing stage (air RH dividing point 2) were the most important factors that influenced the smoothness appearance of cotton fabrics. Therefore, it is indicated that wrinkles are formed in the latter part of the drying cycle. The results can provide a reference for dryer design and drying performance optimization.     

热泵干燥装置的调控分析

热泵干燥具有节能、低温干燥及环境友好等特点，控制热泵干燥装置运行在较佳的状态，是保证热泵干燥装置效率和可靠性的基础。以带循环空气旁通的封闭式热泵,干燥装置为例，对热泵干燥装置的调控方法进行了分析，给出了装置的被控参数和一组较佳的控制参数，并建立了各控制参数的计算公式。     

On-farm heat pump - assisted fluidized bed dryer and its kinetics calculation

Abstract

The expediency of using the heat pump (HP) as a part of the farm drying plant is considered taking drying corn grain in a batch fluidized bed (FB) as an example. Using the HP, it is possible to heat the air supplied to the dryer to a temperature about 60?°C. The refrigerant R600a (isobutаne) is selected as the working medium. According to analysis of a thermodynamic cycle of the HP, it was found that the energy conversion coefficient is equal to 2.98. The use of the HP allows saving 66% of the energy needed for corn drying. A mathematical model has been developed for the kinetic calculation of a drying plant with a batch FB for granular materials, based on the use of an analytical solution to the problem of mass conductivity and taking into account the changes in drying agent parameters over time and the bed height. The adequacy of model to the real process is shown.     

潜油电泵系统能耗研究

针对潜油电泵的系统能耗问题,结合我国潜油电泵的应用现状,首先对潜油电泵的系统效率进行深入分析,在此基础上,对影响潜油电泵系统能耗的相关因素进行深入研究,分析这些因素出现的原因,并提出降低能耗的相关措施,为推动潜油电泵技术的进一步发展奠定基础。研究表明:参数设计、库存以及结垢等因素都会影响潜油电泵的系统能耗,各因素影响系统能耗的途径各不相同,但是都会给油田单位带来一定的经济损失,因此相关单位必须从这些影响因素出发,采取必要的措施,降低系统能耗。     

常规乙烯塔系与热泵乙烯塔系的能耗比较

通过适当手段，在同一基准之上比较常规乙烯塔系和热泵乙烯塔系的能耗差距。     

旋转闪蒸干燥器在碳酸钡干燥中的应用

介绍了河北诺达化工设备有限公司开发生产的旋转闪蒸干燥器代替回转圆筒干燥器在碳酸钡干燥过程中的应用.通过对投资、能耗、产品质量、环保效益的详细分析得出结论:用旋转闪蒸干燥器代替回转圆筒干燥器,具有节省投资,节约能耗,提高产品质量,减小环境污染等优势,为碳酸钡的干燥提供了一种新方法.该设备也适用于碳酸锶、硫酸钡、碳酸钙等滤饼类物料的干燥,同样对于冶金、化工、医药、食品等行业的滤饼类物料的干燥也具有极高的应用价值.     

热泵干燥机三元控制的初步研究

以更有效提高热泵干燥性能为出发点，结合湿空气的性质和压缩机的性能，提出了热泵干燥机三元控制理论。并定性分析了它的特点。     

Experimental analysis and CFD simulation of infrared apricot dryer with heat recovery

Drying is one of the easily accessible and the most widespread processing technologies that have been used since ancient times for preserving fruits. Drying is an energy-intensive and time-consuming process, so reducing energy demand is important. The main aim of this paper is to analyze the heat and mass transfer characteristics of product in the drying chamber and in addition to this, three-dimensional (3-D) computational fluid dynamic (CFD) simulation was performed. The analyses of heat and mass transfer were investigated theoretically and experimentally in infrared dryer (IRD). The dryer consists of air to air heat recovery unit and proportional temperature controller. Experiments were performed at 0.5 and 0.25?m/s air velocities and at 60 and 65°C apricot surface temperatures which were controlled by three thermocouples contacted on top side of the product. In order to use energy more effectively and improve the drying characteristics of apricot, analyses were performed under different drying conditions. Since the heat recovery unit has a key role in this system, the performance of this unit was investigated and recovered energy ratio was between 58 and 62%. The calculated moisture diffusivity values varied from 1.7?×?10^?10 to 1.15?×?10^?9 for apricot, and the highest value of average energy efficiency was obtained as 16.43% at 65°C temperature and 0.25?m/s air velocity. Theoretical and experimental results are in line with each other.     

Measurement and simulation of the contact drying of sewage sludge in a Nara-type paddle dryer

Contact drying experiments were carried out in a Nara-type paddle dryer to study the drying kinetics of sewage sludge in the presence of air. In order to have a better understanding of the sewage sludge drying mechanism, a penetration model developed by Tsotsas and Schlünder is used to simulate the drying kinetics of the pasty, lumpy and granular phase which the sludge experiences during the drying process. The pasty phase is assumed to be a saturated particulate phase, and the granular phase is considered as a mono-dispersed particulate phase whose diameter was experimentally determined. In the lumpy phase, a sludge wall sticking still to the paddle-shaft surface was formed, and the heat transfer resistance from the sludge wall is considered during the model calculation. The influence of the drying parameters (temperature, stirrer speed and air flowrate) on the drying process is investigated experimentally and theoretically. The result indicates that the penetration theory is able to describe the sludge drying kinetics of the three distinct phases. Experimental and calculated drying kinetics are in satisfactory agreement for different drying parameters.