Specific Moisture Extraction Rate Research Articles

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.

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.

Performance Evaluation of Indirect Solar Dryer under Passive and Active Modes during Drying Beetroot Slices

In the present work, the drying characteristics of beetroot slabs, thermal and performance characteristics were estimated and analyzed in passive (mode-A) and active (mode-B) indirect solar dryers (ISD). The conventional mode-A dryer was updated with a diverging duct that comprises direct current fans run by photo-voltaic panels to make the mode-B dryer. In mode-B, the drying time of 16.67 and 42.31% is saved compared to mode-A and open sun drying (OSD), respectively, to achieve a final moisture content of 0.057 from 7.7535 kg/kg of dry basis. The Two-term exponential model was observed to be a perfect fit model for beetroot slices in both modes of ISD and OSD, respectively. The improvements in drying rate, dryer and collector efficiencies and specific moisture extraction rate in mode-B over mode-A are found to be 19.97, 19.18, 8.34 and 14.23%, respectively. It is found that mode-B has better thermal and performance properties than mode-A.

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.

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.

Energy, exergy and economic investigation of novel hybrid dryer, indirect solar dryer and traditional shade drying

By integrating a secondary energy source into solar dryers, more moisture can be removed from food products in the same time period. For this purpose, tomato slices of different thicknesses (7 mm, 15 mm and quarter size) were dried to see the drying, energy, exergy and economic performance of an innovative hybrid dryer consisting of an indirect solar dryer and geothermal heat exchanger unit. The hybrid dryer’s performance was compared simultaneously with indirect solar dryer and traditional shade drying. The analyzes were evaluated according to the feeding of drying air from the solar air collector and geothermal heat exchanger unit. Compared to the other two dryers, the hybrid dryer dried the 7 mm, 15 mm and quarter size samples in the earliest time, with an average of 1380, 2476.3 and 2397.3 min, respectively. The average highest specific moisture extraction rate (0.87 kg/kWh) and dryer efficiency (45.25 %) and the lowest specific energy consumption (4.75 kWh/kg) for hybrid dryer were obtained for the 15 mm. The highest exergy efficiency for the solar air collector and drying chamber of the hybrid dryer was determined at 7 mm with 3.08 % and 38.9 %, respectively. The lowest payback period for the hybrid dryer was found to be 0.37 years for 7 mm. The results showed that the hybrid dryer was superior to the other two dryers by drying continuously day and night. Hybrid dryer can create a successful commercial ecosystem as an important drying alternative for locations where geothermal energy is available.

Natural convective solar dryer powered by stepped fin plate integrated trough array solar air heater for agricultural produce preservations

In this work, heat energy analysis and economic feasibility of natural convection mixed mode solar dryer under three different methods viz., normal flat plate collector solar dryer (NFPSD), step fin plate integrated trough array collector solar dryer (SFPTSD) and SFPTSD with latent heat storage (LHS) are experimentally investigated. The drying time in SFPTSD – LHS (setup 3) to reach its safe moisture content for paddy, wheat, green chilli are 5.5 h, 6 h and 7 h respectively and it is significantly lowered to a maximum of 47 % as compared with NFPSD (setup 1). Also, the average maximum heat efficiency of 62.19 % for collector and 38.32 % for drying cabinet is obtained in setup 3. The specific heat energy consumption is lowered by 20.65 % and specific moisture extraction rate increases to 21.73 % for this proposed setup in comparison with setup 1. The improvement potential is reduced to a substantial margin of 136.5 W and yields an exergetic efficiency increase of 12.38 % than setup 1. An average annual saving increase of 193.08$ with its present value 94.33$ is achieved for setup 3 as compared with setup 1. We recommend this setup can dry edible produce at low cost and affordable to economically weak farming communities.

Thermal Performance and Technoeconomic Analysis of Solar-Assisted Heat Pump Dryer Integrated with Energy Storage Materials for Drying Cavendish Banana (Musa acuminata)

This study examines a novel solar-assisted heat pump dryer integrated with a thermal energy storage system using soapstone as storage material. The dryer is investigated through experimental analysis across three operating modes: mode 1 with thermal energy storage during daytime, mode 2 without thermal energy storage during nighttime, and mode 3 without thermal energy storage during daytime. Experiments were carried out to investigate the drying of 500 g of Cavendish banana. Thermal performance, as well as economic, and nutritional content were examined. Three replicates of the experiment yielded consistent results, showing a significant reduction in the moisture content of the initial sample from 74.4% to 9.6% after undergoing distinct drying durations. Mode 1 achieved this reduction in 270 minutes, mode 2 in 390 minutes, and mode 3 in 360 minutes. The average specific moisture extraction rates for modes 1, 2, and 3 were 0.13, 0.11, and 0.12 kg/kWh, respectively. Simultaneously, the drying rate ranged from 0.16 to 0.24% per minute. The drying efficiency varied among the tested modes, with mode 1 achieving the highest efficiency at 23.23%. In terms of coefficient of performance, mode 1, mode 2, and mode 3 exhibited values of 3.69, 2.57, and 2.54, respectively. The economic analysis conducted specifically for mode 1 revealed a payback period of 1.5 years, indicating the time required to recover the initial investment. Additionally, the results indicated that the dried Cavendish banana had significantly higher concentrations of proximate parameters and minerals compared to the fresh Cavendish banana, as evidenced by a p value less than 0.05.

Experimental analysis of a CO2 closed heat pump drying system combined with rotary dehumidification for drying banana slices drying

A CO2 closed heat pump drying system combined with rotary dehumidification (HPRD) was investigated using both experimental and theoretical approaches. The advantages of HPRD over traditional CO2 closed heat pump drying systems (THPSs) for drying banana slices were analyzed. After drying, the drying kinetics and quality of banana slices were investigated. The results demonstrated that HPRD reduced the banana slice drying time during low-temperature processing while retaining more color and vitamin C content than THPS. In particular, HPRD increased the drying rate of banana slices dried at low temperatures by up to 41 % compared to the rate obtained by THPS. In addition, it increased the vitamin C content by an average of 12 % and reduced the total color difference by an average of 16 %. And the specific moisture extraction rate of HPRD increases by 26 % compared to THPS. The highest-quality banana slices, which were 3 mm thick and dried by HPRD at 43 °C, maintained a high drying rate and high drying quality. The optimal model of Henderson & Pabis predicted the drying behavior within the experimental range. The results indicated that the drying rate and quality of banana slices dried at low temperatures using HPRD were superior to those dried using THPS.

Experimental evaluation of performance, drying and thermal parameters of guava slabs dried in a forced convection indirect solar dryer without and with thermal energy storage

The forced convection indirect solar dryer (FISD) provides better quality food products for lower duration than open sun drying (OSD). The drying experiments on guava slices were executed on an FISD without a thermal energy storage (TES) (model-1) and with TES (model-2) to determine the impact of TES on drying. The guava slices attained a final moisture content in 14 and 9 sunshine hours in model-1 and model-2, respectively. The drying models appropriate to describe guava slices in model-1, model-2 and OSD were Page and modified Page models. The drying rate in model-1 and model-2 was found to be 0.3936 and 0.5728 kg/h, while the effective diffusivity was 7.98 × 10−9 and 8.63 × 10−9 m2/s (average), respectively. The average heat and mass transfer coefficients were 4.842 W/m2K and 4.20 × 10−3 m/s in model-1 & 5.394 W/m2K and 4.68 × 10−3 m/s in model-2. The average drying efficiency and specific moisture extraction rate were 6.84 % and 0.597 kg/kWh in model-1 & 9.77 % and 0.972 kg/kWh in model-2. The specific energy consumption and activation energy were decreased by 38.57 % and 5.25 % in model-2 compared to model-1. The performance, drying and thermal parameters were found to be better in model-2.

Comparative and comprehensive experimental analysis: Performance variation of a novel hybrid dryer

Conventional energy sources are integrated into solar dryers to allow them to operate day and night. Unlike previous applications, this work presents a novel hybrid dryer in which an external geothermal heat exchanger unit is integrated into an indirect solar dryer to overcome this problem. The tomato drying performance of the hybrid dryer was compared with a solar dryer and conventional shade drying in simple and ventilated modes. The proposed dryer's energy, exergy, and economic performance were evaluated using solar and geothermal energy. During the same period, the hybrid dryer reduced the samples to at least 3.64 times lower moisture content in simple mode than other dryers. In ventilated mode, this value was 2.97 times. Integration of ventilation into the hybrid dryer reduced average drying time from 64 to 56 h, specific moisture extraction rate from 0.63 to 0.60 kg/kWh, specific energy consumption from 3.94 to 2.78 kWh/kg, and payback time from 0.22 to 0.17 years. However, it increased the thermal and exergy efficiency of both dryers' solar air collectors by over 30 % and 27 %, respectively. As a result, the hybrid dryer continued the drying process even when there was no sun and achieved a significant advantage in drying tomatoes compared to the other two drying types. The proposed system will make locations where geothermal energy is available attractive for food drying.

Design and Performance Evaluation of a Novel Solar Dryer for Drying Potatoes in the Eastern Algerian Sahara

Abstract In this paper, experimental work has been presented to study the novel design of a solar crop dryer that includes an inverted absorber perforate type collector with forced airflow. A novel design configuration was constructed and tested in the eastern Algeria climate (El-Oued city) for drying of potatoes. Aim to present a test of the thermal performance of the novel dryer and use only clean energy sources for evaluated of the drying efficiency. Under real climatic conditions, the experimental test indicates that the average air temperature of the drying chamber of 50°C, and the time required for drying potato starting at the initial moisture contents (MC) of 84.17% until final MC of 12.5% was 6h. Highest specific moisture extraction rate value was obtained as 1.074 g water/kWh. The Drying efficiencies ranged from 20.37 to 34.01%, whereas the exergy efficiency ranged from 58.48 to 93.22%. Payback period was estimated as 1.39 years. The proposed novel dryer will dry potatoes free of cost for almost its entire life period and about $13.92 can be saved. Compared with electric oven drying, the advantage of the novel one, the cost of electricity saving and avoiding penalty tax for CO2 emission, were $11.69 and $2.235, respectively.

Effect of drying air supply temperature and internal heat exchanger on performance of a novel closed-loop transcritical CO2 air source heat pump drying system

A novel closed-loop transcritical CO2 air-source heat pump drying (HPD) system with a relatively simple structure, higher drying temperature, and internal heat exchanger (IHX) for the drying of medical equipment was proposed and built. With or without the IHX in the system, the effects of different drying air supply temperatures on the performance of transcritical CO2 HPD system were studied experimentally. The results showed that the maximum drying air supply temperature (DAST) in the designed system could reach 72.9 °C. As the DAST raised, whether with or without the IHX in the system, the coefficient of heating performance (COPh), coefficient of system performance (COPsys), and specific moisture extraction rate (SMER) decreased gradually and moisture extraction rate (MER) increased continuously. When the DAST was 70 °C, COPh, COPsys, MER and SMER were respectively 3.68, 6.07, 3.27 kg/h and 1.68 kg/(kW·h) in the HPD system without the IHX, and were respectively 4.00, 6.89, 3.67 kg/h and 1.97 kg/(kW·h) in the HPD system with the IHX. In contrast, the compressor discharge pressure decreased 4.26 %–5.99 %, COPh increased 1.39 %–8.65 %, COPsys increased 1.89 %–13.57 %, MER increased 4.68 %–14.01 %, SMER increased 6.93 %–17.18 % in the HPD system with the IHX.

Heating performance, exergy, and economic analysis of a heat pump drying system with an independent operating ability for drying shiitake mushrooms

In response to the problems of untimely drying in place of agricultural products after harvesting, low drying temperature of open heat pump drying system and low energy utilization of closed heat pump drying system. A novel heat pump drying system is proposed, which uses a gasoline generator as the power source and an open-closed combined heat pump system equipped with a box-type drying chamber. A prototype was constructed to investigate the feasibility and heating performance of this system, and experimental studies were carried out with wet towels and shiitake mushrooms as drying objects, and the system heating performance and specific moisture extraction rate (SMER) were analyzed. The results from the wet towels experiment revealed that the drying temperature decreased by 30%–74% when the system operation mode was the dehumidifying mode (open cycle) compared with the switching of the heating/dehumidifying mode. When the air speed was increased from 2.2 m/s to 4.3 m/s, the mass of water removed increased by 39.4%. The results of the shiitake mushrooms experiment showed that the SMER were 1.19 kg/kWh, 1.18 kg/kWh and 1.05 kg/kWh for gasoline generator drive and electric drive, respectively, which is an improvement of 42%∼61% comparing with the data of other researchers. This study provides guidance for heating performance and structural optimization of a new type of heat pump drying system driven by gasoline generator.

Feasibility of Air Conditioning (AC) Utilization as Heat Pump System for Fish Cracker Drying Machine

Fish crackers are one of the most popular snacks in Southeast Asian countries, including Malaysia. Traditionally, the process of fish crackers drying usually uses sun drying method. The problem of this method is uncontrollable weather conditions. Drying of fish crackers requires an alternative in the drying process. The heat pump is the most effective and controllable alternative dryer in reducing the moisture content of the material. Air Conditioning (AC) is one type of heat pump. The heat produced by the AC condenser can be used to dry fish crackers. In this study, the AC utilization as a heat pump system to dry fish crackers has an Evaporate Capacity (EC) of 1,838kg/h, a Specific Moisture Extraction Rate (SMER) of 1,998kg/kWh, and a Specific Energy Consumption (SEC) of 0.425kWh/kg of dry crackers. This drying machine is also economically feasible because it has an NPV> 0 which is RM28201.58 with an investment period of 1 year.

Energy and quality analysis of forced convection air-energy assisted solar timber drying

Discontinuities due to weather conditions and daylight affect solar drying, so to address that, a working mechanism of air energy-assisted solar drying was developed in this study. An air-energy assisted solar dryer was used to dry timber, from a green average moisture content of 183%–11.3% in 161.5 h, where the moisture diffusion coefficient ranged from 1.28 ×10-10 m2/s to 6.41 ×10-9 m2/s. The effective solar radiation intensity during drying ranged from 221.3 to 750.3 W/m2. The overall drying efficiency was 30.7%, and the effective solar heat supply ratio was 58.5%. The specific moisture extraction rate and specific energy consumption were measured within a range of 0.32–3.0 kg/kWh and 924 - 11390 kJ/kg, respectively. The average power consumption per m3 of wood volume was 254.2 kW h/m3. The results showed that the energy-assisted solar dryer was suitable for a condition with low radiation and various weather conditions.

Experimental study of a novel photovoltaic-thermal-thermoelectric generator-based solar dryer for grapes drying

ABSTRACT  In the present work, a novel photovoltaic-thermal-thermoelectric generator (PVT-TEG) based solar dryer has been developed, and its drying performance is experimentally investigated and compared with open sun drying (OSD). The reason for incorporating the PVT-TEG system in the solar dryer is to improve the system’s utility in practical drying applications by augmenting electrical power generation with the combination of PV and TEG along with extracting thermal energy for drying, thereby improving the overall system efficiency. Grapes drying has been performed to analyze the drying process and thermal and electrical performance of the system. The moisture content level after the experiment is evaluated as 1.71 (d.b.) from an initial value of 4.00 (d.b.) in PVT-TEG solar drying compared with 2.51 (d.b.) in OSD. The findings of the drying performance are determined as 17.81% for drying efficiency, 1.10 kWh/kg for specific energy consumption, and 0.68 kg/kWh for specific moisture extraction rate. The energy efficiencies obtained for the experiment are PV panel efficiency of 14.07%, TEG efficiency of 11.64%, PVT efficiency of 72.36%, and thermal efficiency of 48.50%. When compared to the open literature, the utility of the present novel dryer is found in terms of its enhanced drying and energy performances.

Evaluating the environ-economic and exergy-energy impacts of drying carrots in passive and active mode solar dryers

On the basis of exergy-energy and economic-environmental (4E) parameters, passive and active indirect solar dryers (PISD and AISD) were analysed and compared by drying carrot slabs. The PISD dryer was upgraded using fans run by photovoltaic panels those were placed at the gate of a divergent duct to make an AISD setup. Experimentally measured primary parameters were used to evaluate the 4E parameters. Accordingly, AISD had enhancement in collector and drying efficiencies of 19.27 and 11.86% than PISD, respectively. Specific energy consumption (32.2%) and moisture extraction rate (47.17%) were better for AISD than PISD. Both setups were examined for their exergy parameters (mean efficiency, outflow, loss, and inflow). Exergy and environmental stability indicators such as sustainability index, environmental factor, waste exergy and improvement potential were calculated and distinguished for both dryers. AISD dryer gave better CO2 mitigation and carbon credit than PISD. The payback period of energy over 30 years lifespan was 1.33 and 1.78 years, and the economic payback period was 1.02 and 0.622 years, for PISD and AISD respectively. In comparison with PISD, the AISD achieved better in all the evaluated parameters. An uncertainty study was carried out for all the measured and estimated criteria. Results were compared with existing studies.

Enhancing the performance of a greenhouse dryer with natural dolomite powder-embedded latent heat thermal energy storage unit and air-to-air heat recovery system

Greenhouse drying systems (GDSs) are grouped in direct-type solar dryers and are widely utilised because of their easy applicability, high product drying capacity and cost-effectiveness. In the present work, it is aimed to improve the drying performance of a GDS by using natural dolomite powder-embedded latent heat thermal energy storage unit (LHTESU) and air-to-air heat recovery system (HRS). In this context, three different types of GDSs have been designed and manufactured including a GDS with paraffin-based LHTESU, a GDS with natural dolomite powder-embedded LHTESU and a HRS-assisted GDS with natural dolomite powder-embedded LHTESU. Designed and manufactured GDSs have been experimentally analysed under the same environmental conditions. According to the experimentally achieved findings, combined utilisation of HRS and dolomite powder in the LHTESU reduced the drying time approximately as 36.36%. Moreover, highest instantaneous outlet air temperature was achieved as 51.4 °C in the system that used natural dolomite-embedded LHTESU and HRS. The exergetic efficiency of the GDS was upgraded as 46.21% by using the mentioned modifications in comparison to the base case (the system contains only paraffin-based LHTESU). In addition, specific moisture extraction rate for the analysed GDSs was attained between 0.96 and 1.52 kg.kWh−1.