•Drying performance of CO2 versus R-134a was compared via rationally based modeling.•Transient behavior of CO2 over R-134a was studied beyond environmental friendliness.•CO2 yielded air and clothes ...temperatures up to 15 °C and 6 °C higher over R-134a.•Increments of 13% and 8% in SMER and COP were achieved by CO2 compared to R-134a.•Parametric studies and optimization/control strategies have been provided.
A comparative study on the performance of CO2 and R-134a for heat pump clothes drying applications is conducted via a rationally based model. The model comprises unique features such as capability of handling transient behaviours of drying process, freedom from extra constraints normally imposed on heat pump drying modelling and accountability for detailed geometry of the major components. Simulations for both R-134a and CO2 system are performed, validated and further compared to experimental data available in literatures with good agreement. In comparison with R-134a, CO2 dryer yields higher drum outlet air and clothes temperatures, up to 15 °C and 6 °C, respectively. Yet, increments of 13% and 8% in specific moisture extraction rate (SMER) and coefficient of performance (COP) result on 15% reduction of drying time. Additionally, although subsequent parametric comparison studies on the transient performance of both systems revealed similar effect on system performance subject to same geometrical/operational parameter variation, the analyses also further confirm solid prevalence of the CO2 system over that of R-134a, in terms of COP, SMER and drying time. Finally, a brief discussion regarding pinch analysis is carried out, revealing further potential optimization for the CO2 system regarding heat exchangers.
•A novel heat pump drying prototype with relatively high air temperature is proposed.•The effects of compressor speed on the performance of the system is studied.•The maximum drying temperature that ...the system can achieve is greater than 70 °C.•The drying system has high energy efficiency and excellent drying effect.
In view of the current situation about environmental pollution and high energy consumption in industrial metal parts drying methods, a closed loop heat pump drying (CLHPD) system with a relatively high circulating air temperature was proposed and established. The compressor speed is a vital parameter that affects the performance of the CLHPD system. The effect of compressor speeds on circulating air temperature, coefficient of performance (COP), moisture extraction rate (MER·) and specific moisture extraction rate (SMER·) of the system were experimentally studied in this work. The results showed that, with the raise of compressor speed within 3000 to 4200 r/min, the drying air temperature and the MER· of the system increased, the COP and SMER· of the system decreased. The drying air temperature reached a maximum of 75 °C and the MER· obtained a maximum of 3.90 kg/h at the compressor speed of 4200 r/min. The COP reached a maximum of 6.4 and the SMER· obtained a maximum of 1.62 kg/(kW·h) at the compressor speed of 3000 r/min. In an actual industrial production, the compressor speed should be adjusted according to the specific demand to balance the relationship between MER· and SMER·. These can provide references for further research and application of heat pump drying technology in the metal parts drying and even other industrial drying fields.
In view of the present situation that the exhaust waste heat of the hot air hood in the paper drying section is too much and the environment is not friendly, a closed heat pump drying system model ...applied to the exhaust air hood is proposed and established. Effects of evaporation temperature and condensation temperature on supply air temperature, supply air moisture content, system performance coefficient (COP) and dehumidification energy consumption ratio (SMER) were studied. Results show that with the increase of condensation temperature, the supply air temperature is unchanged, and the moisture content of the supply air increase, while the COP and SMER of the system show a downward trend. The moisture content of supply air decrease with the increase of evaporation temperature, while the supply air temperature, COP and SMER all show an upward trend. Therefore, in order to improve the drying characteristics and improve the performance of the heat pump system, the condensation temperature can be reduced and the evaporation temperature can be increased.
In this study, an indirect forced convection solar drying system was tested for drying of palm oil fronds. The drying of 100 kg of palm oil fronds via solar drying system reduced the moisture content ...from 60% (w.b) to 10% (w.b) in 22 h (3 d of drying). During the drying process, the daily mean values of the drying chamber inlet temperature, drying chamber outlet temperature, drying chamber air temperature, and solar radiation ranged from 26 °C to 75 °C, 25 °C–65 °C, 26 °C–67 °C, and 96 W/m2 to 1042 W/m2 respectively, with corresponding average values of 53 °C, 46 °C, 48 °C, and 580 W/m2. At average solar radiation of about 600 W/m2 and air flow rate 0.13 kg/s, the collector, drying system and pick-up efficiencies were found about 31%, 19% and 67% respectively. The specific moisture extraction rate (SMER) was 0.29 kg/kWh. The exergy efficiency varied between 10% and 73%, with an average of 47%. In addition, the improvement potential of solar drying system for palm oil fronds ranged from 8 W to 455 W, with an average of 172 W.
•A solar drying system was tested for drying of palm oil fronds.•The collector, drying system and pick-up efficiencies were found about 31, 19 and 67% respectively.•The specific moisture extraction rate (SMER) was 0.29 kg/kWh.•The exergy efficiency varied between 10% and 73%, with an average of 47%.•The improvement potential was between 8 W and 455 W, with an average of 172 W.
•A mechanical vapor compression test platform driven by Roots compressor was set.•The mathematical model of evaluating mechanical vapor compression system was established.•Evaporation rate, Specific ...Moisture Extraction Rate and power consumption was measured in this paper.•The performance of mechanical vapor compression was analyzed by changing factors.
The thermal performance of a mechanical vapor compression (MVC) system was investigated. This work presented describes the mathematical and experimental study of the MVC system, focusing on mathematical models that were established based on the energy and mass balance equations as well as correlations of the thermophysical properties and heat-transfer coefficients. As a result, a MVC experimental platform, which can handle 100 kg/h evaporation rate was designed, with a falling film evaporator heater area of 10 m2. A Root compressor was selected as a vapor compressor, utilizing a power of 18 kw. This paper has studied the feed temperature, evaporation pressure, compressor speed and vapor pressure increment effect on evaporation rate, Specific Moisture Extraction Rate (SMER) and power consumption, as to evaluate the MVC system performance. It was found that feed temperature reach the optimal conditions for saturated liquids. Evaporation pressure should be controlled in low level to ensure that SMER can reach high values and it was furthermore observed that the compressor speed determines the evaporation rate whilst SMER variations showed very subtle effects.
The article provides an overview of the economic prospects and political risks that emerged in Slovakia after the first wave of Coronavirus restrictions. Despite a significant GDP decline, ...unemployment and a worsening socio-economic situation, pandemic consequences is not catastrophic. First of all, economic recovery is associated with significant assistance of EU, which plans to invest substantial funds in Slovakia. However, the implementation of the plan runs up against internal political obstacles – the lack of cohesion within the ruling cabinet of Igor Matovič. Due to the nature of his political power, and due to the changes that have taken place in him as a politician over the six months. The author shows several conflict lines that influence on the stability of the current government. In these circumstances, successful implementation of the modernization plan for Slovakia directly depends on the stability of the cabinet. However, the author believes that conflicts are inevitable.
•A MVR system with single screw compressor was developed.•Distilled water was atomized and injected to eliminate the compressor superheat.•Compression ratio and evaporation capacity increased with ...the frequency rising.•Without water injection the temperature difference increased sharply.•By water injection more water could be removed with the same power consumption.
The mechanical vapor recompression (MVR) is a highly energy-efficient process, in which the compressor is the core unit. In order to improve the compressor efficiency the distilled water is atomized and injected into the compressor to cool down the overheated vapor during compression. The performances of the system with water injection compressor were tested and compared with a common compressor without water injection. Four groups of tests with different water spray rate were analyzed experimentally. The tests show that without water injection, the temperature difference increases sharply with frequency rising. It also shows that the values of compression ratio and evaporation capacity increase with the frequency increasing, and the values vary with the spray flow rate: the higher the flow rate, the larger the values. The values for the situations with water injection are closer to each other with the increas of the water spray rate while the situation without water injection is much lower. Specific moisture extraction rate, abbreviated as SMER is a parameter which reflects the removal water from the feed per kilowatt hour. With spray flow rate of 300kg/h the SMER is 34kg/kWh at frequency of 20Hz while the value is 25kg/kWh without water injection.
The performance of an enhanced vapor-injection heat-pump drying system was designed and theoretically studied in cold areas. According to the simulation findings, the ideal vapor-injection charge of ...the system ranges from 12.3 to 13.9%, and its ideal intermediate pressure is between 1.278 and 1.498 MPa when the evaporation temperature is above 0 °C. The ideal vapor-injection charge of the system ranges from 13 to 20%, and its optimal intermediate pressure ranges from 1.078 to 1.278 MPa when the evaporation temperature is −15–0 °C. The ideal vapor-injection charge of the system ranges from 20 to 24%, and the intermediate pressure ranges from 0.898 to 1.078 MPa when the evaporation temperature is below −15 °C. The heat and humidity exhausted air source heat-pump drying (HHE–ASHPD) system has higher dehumidification efficiency than the closed heat-pump drying (CHPD) system under the same air temperature, humidity, and volume parameters.
The performance of a domestic hybrid dehumidifier combined with a solid desiccant rotor and a vapor compression (VC) system is superior to that of the conventional VC and adsorption dehumidifier. In ...this study, the performance of a domestic hybrid dehumidifier was measured and analyzed by varying the room temperature, the rotating speed of the desiccant rotor, the bypass air-flow rate, and the power consumption of the heater. The specific moisture extraction rate (SMER) of the hybrid dehumidifier was 6.1–9.6% higher than that of the VC dehumidifier at the room temperatures ranging from 10 to 26.7 °C. In addition, the performance of the hybrid dehumidifier was optimized by varying the control parameters. The optimum rotating speeds of the desiccant rotor were 40 rph and 50 rph at room temperatures of 26.7 °C and 10 °C, respectively, for maximizing the SMER. The optimum bypass air-flow rate was 0.6 m3 min−1, which corresponded to a 6.2% improvement in the SMER at a temperature of 26.7 °C. The optimum power consumption of the heater under low room-temperature conditions was 0.15 kW.
•A hybrid dehumidifier combined with desiccant rotor and VC system is investigated.•The performances of VC and hybrid dehumidifier are compared with room temperature.•The rotating speed and bypass flow rate are optimized to obtain the maximum SMER.•The performance is improved by using heater at low room temperature condition.
This work presents a new extension to the artificial CPGs (Central Pattern Generators) based on Scheduling by Multiple Edge Reversal (SMER) proposed by Yang and França. The insertion of a total ...support phase between each particular swing and support legs phase was produced for all different hexapod gait patterns. Thus, pseudo-synchronous gait pattern transitions are easily allowed and walking stability is potentially improved. Moreover, the insertion of such new phases facilitates to work with two distinct time periods: (i) when legs are in the typical swing–support phases, i.e., carrying the body of the robot to its future position, and (ii) during total support phases. All new extended SMER-based gait patterns are presented by means of a kinematic analysis made through simulations of a hexapod walking robot.
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