Energy and exergy analyses of OMW solar drying process

The energy and exergy analyses of the drying process of olive mill wastewater (OMW) using an indirect type natural convection solar dryer are presented. Olive mill wastewater gets sufficiently dried at temperatures between 34 °C and 52 °C. During the experimental process, air relative humidity did not exceed 58%, and solar radiation ranged from 227 W/m² to 825 W/m². Drying air mass flow was maintained within the interval 0.036–0.042 kg/s. Under these experimental conditions, 2 days were needed to reduce the moisture content to approximately one-third of the original value, in particular from 3.153 g_water/g_{dry matter} down to 1.000 g_water/g_{dry matter}.Using the first law of thermodynamics, energy analysis was carried out to estimate the amounts of energy gained from solar air heater and the ratio of energy utilization of the drying chamber. Also, applying the second law, exergy analysis was developed to determine the type and magnitude of exergy losses during the solar drying process. It was found that exergy losses took place mainly during the second day, when the available energy was less used. The exergy losses varied from 0 kJ/kg to 0.125 kJ/kg for the first day, and between 0 kJ/kg and 0.168 kJ/kg for the second. The exergetic efficiencies of the drying chamber decreased as inlet temperature was increased, provided that exergy losses became more significant. In particular, they ranged from 53.24% to 100% during the first day, and from 34.40% to 100% during the second.     

Design of mixed-mode natural convection solar crop dryers: Application of principles and rules of thumb

A mixed-mode natural convection solar crop dryer (MNCSCD) designed and used for drying cassava and other crops in an enclosed structure is presented. A prototype of the dryer was constructed to specification and used in experimental drying tests. This paper outlines the systematic combination of the application of basic design concepts, and rules of thumb resulting from numerous and several years of experimental studies used and presents the results of calculations of the design parameters. A batch of cassava 160 kg by mass, having an initial moisture content of 67% wet basis from which 100 kg of water is required to be removed to have it dried to a desired moisture content of 17% wet basis, is used as the drying load in designing the dryer. A drying time of 30–36 h is assumed for the anticipated test location (Kumasi; 6.7°N,1.6°W) with an expected average solar irradiance of 400 W/m² and ambient conditions of 25 °C and 77.8% relative humidity. A minimum of 42.4 m² of solar collection area, according to the design, is required for an expected drying efficiency of 12.5%. Under average ambient conditions of 28.2 °C and 72.1% relative humidity with solar irradiance of 340.4 W/m², a drying time of 35.5 h was realised and the drying efficiency was evaluated as 12.3% when tested under full designed load signifying that the design procedure proposed is sufficiently reliable.     

Performance of indirect through pass natural convective solar crop dryer with phase change thermal energy storage

A state-of-the-art solar crop dryer was developed with thermal energy storage to maintain continuity of drying of herbs for their colour and flavour vulnerability. The dryer consists of flat plate solar collector, packed bed phase change energy storage, drying plenum with crop trays and natural ventilation system. Dryer is designed with a maximum collector area of 1.5 m², six crop trays with an effective area of 0.50 × 0.75 m², can hold 12 kg of fresh leafy herbs. The dryer is attached with a packed bed thermal energy storage having capacity of 50 kg phase change material (PCM). The drying system works in such a manner that phase change material stores the thermal energy during sun shine hours and releases the latent and sensible heat after sunset, thus dryer is effectively operative for next 5–6 h. The temperature in drying chamber was observed 6 °C higher than the ambient temperature after sunshine hours till the mid night during the month of June at Jodhpur. Economic performance of the dryer was analysed with return on capital and simple payback period as 0.65 and 1.57 year respectively on optimum cost of raw material and product sale price.     

Solar drying system for energy conservation

A low cost portable farm solar dryer was evaluated for drying goose berry candy in the conditions of Vidarbha region of Maharashtra state. Temperature profile at top, middle and bottom in its seven trays loaded with candy was studied with respect to ambient temperature during the course of drying and maximum solar radiation of 1120 W/m² was observed at 11.30 to 12 h. The solar radiation was varied from 720–500 W/m² at 9.00 h to 16.00 h. The minimum temperature of 27°C was observed at bottom tray of the dryer and maximum of 44°C in top tray at 9.00 h. The maximum temperature of 70°C was attained at 11.30 h. The conventional drying method took 8 days to dry the product. The moisture content was reduced from 36.38 to 8.33 per cent (wb) in three days in solar drying method. The product recovery was 71.55 per cent as compare to 35 per cent in conventional drying method. The drying period was reduced by 62 per cent and product recovery was doubled using portable farm solar dryer. The goose berry candy was also dried with and without shade drying methods. The temperature variation of dryer without shade was found, in the range of 23–36°C, 31–48°C and 38–55°C in bottom, middle and top trays respectively of dryer. The weight loss of 810, 870 and 820 g were observed in three days at bottom, middle and top trays of the dryer respectively. The thermal efficiency of the dryer onepy first day drying was found 15.55 and 15.23 per cent in shade and without shade drying methods respectively. Appearance, taste and flavour of goose berry candy dried in farm solar dryer with shade were superior to conventional drying. The cost of final product was Rs 114/kg. The profit from a single unit of farm solar dryer per year was Rs 57588/-.     

Experimental investigation of forced convection and desiccant integrated solar dryer

An indirect forced convection and desiccant integrated solar dryer is designed and fabricated to investigate its performance under the hot and humid climatic conditions of Chennai, India. The system consists of a flat plate solar air collector, drying chamber and a desiccant unit. The desiccant unit is designed to hold 75 kg of CaCl₂-based solid desiccant consisting of 60% bentonite, 10% calcium chloride, 20% vermiculite and 10% cement. Drying experiments have been performed for green peas at different air flow rate. The equilibrium moisture content M_e is reached in 14 h at an air flow rate of 0.03 kg/m² s. The system pickup efficiency, specific moisture extraction rate, dimensionless mass loss, mass shrinkage ratio and drying rate are discussed in this paper.     

Experimental analysis of evacuated tube solar air heater (ETSAH) with inbuilt sensible thermal energy storage

In the present work, an evacuated tube solar air heater (ETSAH) with inbuilt sensible heat storage material (SHSM) is experimentally evaluated. The system comprises two sets each having 50 evacuated tubes with an H-type arrangement and a total collector area of 16.92 m². For the purpose of hot air generation, ETSAH is simultaneously connected in series and in parallel with and without the use of reflectors. Three different mass flow rates of 122.90, 164.87, and 212.83 kg/h were fixed to get 12 diverse cases of ETSAH operation. The highest hot air temperature reported by the system is 121.7°C when it was connected in series with conventional reflectors at 212.83 kg/h of flow rate and 469 W/m² average solar intensity. The system reported an overall average energy efficiency of 49.76% and an exergy efficiency of 17.97% with the highest average hot air temperature difference of 56.12°C from 09:00 to 20:00 h. Without the incorporation of any additional SHSM, the average hot air temperature delivered by ETSAH (when under the neighbor building shadow) is 49.73°C logged from 17:00 to 20:00 h. The economic analysis is also carried out to ensure its practical application and feasibility. For the best system performance, the annual cost of hot air generation is 0.0194 Rs./kg (0.0002433 $/kg).     

Grape drying by using hybrid photovoltaic-thermal (PV/T) greenhouse dryer: An experimental study

A hybrid photovoltaic-thermal (PV/T) greenhouse dryer of 100 kg capacity has been designed and constructed at Solar Energy Park, Indian Institute of Technology, New Delhi (28°35′N, 77°12′E, 216 m above MSL), India. The developed dryer has been used to dry the Thompson seedless grapes (Mutant: Sonaka) when DC fan was in operation for forced mode convection. The drying of grapes was also performed in open as well as shade for comparison. Experiments were conducted for drying of grapes in the month of April, 2007. Various hourly experimental data namely moisture evaporated, grape surface temperatures, ambient air temperature and humidity, greenhouse air temperature and humidity, etc. were recorded to evaluate heat and mass transfer for the proposed system. It has been found that the value of the convective heat transfer coefficient for grapes (GR-I) lies between 0.26 and 0.31 W/m² K for greenhouse and 0.34–0.40 W/m² K for open conditions, respectively and that for grapes (GR-II) lies between 0.45–1.21 W/m² K for greenhouse and 0.46–0.97 W/m² K for open conditions, respectively.     

Experimental study on an adsorption icemaker driven by parabolic trough solar collector

An adsorption icemaker with energy storage system is proposed for the utilization of medium temperature solar energy. In this system, the solar energy collected by parabolic trough collector (PTC) was used to provide the heat source for the adsorption icemaker. The performance of the icemaker is tested and the experimental results showed that the highest COP reached 0.15 while the COP_sr could be 0.08 and the ice making capacity was 50 kg per day with 20 m² PTC and 30 kg compound adsorbent (calcium chloride + activated carbon) when the desorption temperature, condensing temperature and the direct normal solar radiation were 105 °C, 30 °C and 3 kWh/day·m², respectively.     

Thin layer convective solar drying and mathematical modeling of prickly pear peel (Opuntia ficus indica)

This paper presents the thin layer convective solar drying and mathematical modeling of prickly pear peel. For these purposes, an indirect forced convection solar dryer consisting of a solar air collector, an auxiliary heater, a circulation fan and a drying cabinet is used for drying experiments. Moreover, the prickly pear peel is sufficiently dried in the ranges of 32 to 36 °C of ambient air temperature, 50 to 60 °C of drying air temperature, 23 to 34% of relative humidity, 0.0277 to 0.0833 m³/s of drying air flow rate and 200 to 950 W/m² of daily solar radiation. The experimental drying curves show only a falling drying rate period. The main factor in controlling the drying rate was found to be the drying air temperature. The drying rate equation is determined empirically from the characteristic drying curve.Also, the experimental drying curves obtained were fitted to a number of mathematical models. The Midilli–Kucuk drying model was found to satisfactorily describe the solar drying curves of prickly pear peel with a correlation coefficient (r) of 0.9998 and chi-square (χ²) of 4.6572 10⁻⁵.     

Experimental study of impingement spray cooling for high power devices

An experimental study of a closed-loop impingement spray cooling system to cool a 1 kW 6U electronic test card has been conducted. The system uses R134a as working fluid in a modified refrigeration cycle. The spray from four vapor assisted nozzles is arranged to cover a large ratio of the heated area of the card. Investigations are currently focused on effects of mass flow rate, nozzle inlet pressure and spray chamber pressure. Experimental results are promising with a stable average temperature of around 23 °C being maintained at the heated surface, and maximum temperature variation of about 2 °C under suitable operating conditions. Heat transfer coefficients up to 5596 W/m² K can be achieved with heat flux input around 50,000 W/m² in this study. It is found that cooling performance improved with increasing mass flow rate, nozzle inlet pressure and spray chamber pressure, whereas uniformity of the heated surface temperature can only be improved with higher mass flow rate and nozzle inlet pressure. The mechanisms for the enhanced performance are also presented.     

Induced flow for ventilation and cooling by a solar chimney

An experimental and numerical model of a solar chimney was proposed in order to predict its performance under varying geometrical features in Iraqi environmental conditions. Steady, two dimensional, turbulent flow was developed by natural convection inside an inclined solar chimney. This flow was investigated numerically at inclination angles 15° to 60°, solar heat flux 150–750 W/m² and chimney thickness (50, 100 and 150) mm. The experimental study was conducted using a single solar chimney installed on the roof of a single room with a volume of 12 m³. The chimney was 2 m long; 2 m wide has three gap thicknesses namely: 50, 100 and 150 mm. The performance of the solar chimney was evaluated by measuring the temperature of its glass cover, the absorbing wall and the temperature and velocity of induced air. The results of numerical model showed that; the optimum chimney inclination angle was 60° to obtain the maximum rate of ventilation. At this inclination angle, the rate of ventilation was about 20% higher than 45°. Highest rate of ventilation induced with the help of solar energy was found to be 30 air changes per hour in a room of 12 m³ volumes, at a solar radiation of 750 W/m², inclined surface angle of 60°, aspect ratio of 13.3 and chimney length of 2 m. The maximum air velocity was 0.8 m/s for a radiation intensity of 750 W/m² at an air gap of 50 mm thickness. No reverse air flow circulation was observed even at the largest gap of 150 mm. The induced air stream by solar chimney can be used for ventilation and cooling in a natural way (passive), without any mechanical assistance.     

Automotive fuel cell stack and system efficiency and fuel consumption based on vehicle testing on a chassis dynamometer at minus 18 °C to positive 35 °C temperatures

This paper presents an in-depth laboratory technology assessment of a 2016 Toyota Mirai Fuel Cell (FC) vehicle based on chassis dynamometer testing. The 114.6 kW FC stack has a high dynamic response, which makes this powertrain a FC-dominant hybrid electric vehicle. The measured peak efficiency is 66.0% FC stack and 63.7% FC system with an idle hydrogen flow rate of 4.39 g/hr. The high FC system efficiencies at low loads match typical vehicle power spectrums, resulting in a high average vehicle efficiency of 62% compared to 45% and 23% for a hybrid electric vehicle and a conventional vehicle, respectively. An energy breakdown accounts for the FC stack losses, FC system losses, air compressor loads, and heater loads for different drive cycles and different thermal conditions. The cold-start North American city drive cycle (UDDS) energy consumption values are, respectively, 758, 581, 226, and 321 Wh/km at ambient conditions of −18 °C, −7 °C, 25 °C and 35 °C with 850 W/m² of solar loading. The FC system shutdown and startup processes at temperatures below the freezing point contribute to the increased hydrogen consumption. The raw test data files are available for download, thus providing the research community with a public reference data on a modern production automotive FC system.     

Experimental characterisation of a Fresnel lens photovoltaic concentrating system

An extensive indoor experimental characterisation program to investigate the heat loss from a point focus Fresnel lens PV Concentrator (FPVC) with a concentration ratio of 100× was performed for a range of simulated solar radiation intensities between 200 and 1000 W/m², different ambient air temperatures, and natural and forced convection. From the experimental program it was found that the solar cell temperature increased proportionally with the increase in simulated solar radiation for all experimental tests, indicating that conductive and convective heat transfer were significantly larger than the long wave radiative heat transfer within and from the FPVC system. For the simulated worst case scenario, in which the FPVC system was tested under a simulated solar radiation intensity of 1000 W/m² and ambient air temperature of 50 °C with no forced convection, the predicted silicon solar cell efficiency in the FPVC system was reduced to approximately half that at standard test conditions.     

Energy and exergy analysis of timber dryer assisted heat pump

In this research, poplar and pine timbers have been dried from the moisture contents of 1.28 kg water/kg dry matter and 0.60 kg water/kg dry matter to 0.15 kg water/kg dry matter in heat pump dryer functioning on the basis of 24 h operation. The change in weight in all of the timbers was followed in the drying chamber and drying stopped when the desired weight was achieved. At 40 °C dry bulb temperature, 0.8 m/s air velocity, and initial moisture content of the poplar timbers 1.28 kg water/kg dry matter, the moisture content was reduced to 0.15 kg water/kg dry matter moisture content in 70 h, and the moisture content of the pine timbers which was 0.60 kg water/kg dry matter was reduced to the same amount in 50 h. All data collected while drying were saved on computer and analysed afterwards. For this system, energy analysis was made to determine the energy utilization. Exergy analysis was accomplished to determine of exergy losses during the drying process.     

Single layer solar drying behaviour of Citrus aurantium leaves under forced convection

Convective solar drying experiments in thin layers of Citrus aurantium leaves grown in Marrakech, morocco, were conducted. An indirect forced convection solar dryer consisting of a solar air collector, an auxiliary heater, a circulation fan and a drying cabinet is used for the experiments. The air temperature was varied from 50 to 60 °C; the relative humidity from 41% to 53%; and the drying air flow rate from 0.0277 to 0.0833 m³/s. Thirteen statistical models, which are semi-theoretical and/or empirical, were tested for fitting the experimental data. A nonlinear regression analysis using a statistical computer program was used to evaluate the constants of the models. The Midilli–Kucuk drying model was found to be the most suitable for describing the solar drying curves of Citrus aurantium leaves with a correlation coefficient (r) of 0.99998, chi-square (χ²) of 4.664 × 10⁻⁶ and MBE of 4.8381 × 10⁻⁴.     

Development of a new type of solar dryer: Its mathematical modelling and experimental evaluation

A solar dryer fitted with a novel design of absorber having inbuilt thermal storage capabilities was designed, fabricated, simulated and also tested at Rajiv Gandhi College of Engineering Research & Technology, Chandrapur (MS) India. Thermic oil was used as a storage material. The main objective of the study was to reduce the drying period and enhance the quality of dried product mainly chillies and fenugreek leaves. The products were laid in a single layer. The dimensions of the dryer were arrived at using the well-defined procedure available in literature. The mass of thermic oil needed in the absorber and mass of product to be dried in trays were optimized using simulation techniques. The maximum drying air temperature required for drying agricultural products was around 65°C. The ambient conditions at the location were 25–40°C, 16–43% RH and solar radiation 105–1024 W m⁻². Experimental studies based on temperature and humidity measurements were performed on the dryer. The research concluded that the desired drying air temperature was achieved and maintained for a longer period. The length of operation of the solar air heater and the efficiency of the dryer were increased, and better quality of agricultural products in terms of colour value were obtained compared with open sun drying. Copyright © 2007 John Wiley & Sons, Ltd.     

Drying saturated zeolite pellets to assess fluidised bed performance

This work studies the drying rates of zeolite pellets (Type 1 [D.M. Ruthven, Principles of Adsorption and Adsorption Processes, John Wiley & Sons, New York, 1984]) in spouted beds and in conventional fan assisted ovens. Three temperatures were studied: 48, 85 and 133 °C for drying times up to 1 h. Heat transfer is deduced from measured mass transfer rates and literature correlations. Maximum heat transfer coefficients were found to be 115.6 W/m² K for the fluidised bed and 31.8 W/m² K for the oven using correlations from literature. Higher figures were found by experimentation and calculation, typically about 200 W/m² K. A finite element model was used to estimate the temperature profile within pellets, the predictions agree well with experimental temperature measurements.     

A large-scale solar greenhouse dryer using polycarbonate cover: Modeling and testing in a tropical environment of Lao People’s Democratic Republic

A large-scale solar greenhouse dryer with a loading capacity of 1000 kg of fruits or vegetables has been developed and tested at field levels. The dryer has a parabolic shape and the dryer is covered with polycarbonate sheets. The base of the dryer is a black concrete floor with an area of 7.5 × 20.0 m². Nine DC fans powered by three 50-W solar cell modules are used to ventilate the dryer. The dryer was installed at Champasak (15.13 °N, 105.79 °E) in Lao People’s Democratic Republic (Lao PDR). It is routinely used to dry chilli, banana and coffee. To assess the experimental performances of the dryer, air temperature, air relative humidity and product moisture contents were measured. One thousand kilograms of banana with the initial moisture content of 68% (wb) was dried within 5 days, compared to 7 days required for natural sun drying with the same weather conditions. Also three hundred kilograms of chilli with the initial moisture content of 75% (wb) was dried within 3 days while the natural sun drying needed 5 days. Two hundred kilograms of coffee with the initial moisture content of 52% (wb) was dried within 2 days as compared to 4 days required for natural sun drying. The chilli, coffee and banana dried in this dryer were completely protected from insects, animals and rain. Furthermore, good quality of dried products was obtained. The payback period of the dryer is estimated to be 2.5 years. A system of partial differential equations describing heat and moisture transfer during drying of chilli, coffee and banana in the greenhouse dryer was developed. These equations were solved by using the finite different method. The simulated results agree well with the experimental data. This model can be used to provide the design data for this type of dryer in other locations.     

Energy and exergy analyses and optimization study of an integrated solar heliostat field system for hydrogen production

In this paper, we propose an integrated system, consisting of a heliostat field, a steam cycle, an organic Rankine cycle (ORC) and an electrolyzer for hydrogen production. Some parameters, such as the heliostat field area and the solar flux are varied to investigate their effect on the power output, the rate of hydrogen produced, and energy and exergy efficiencies of the individual systems and the overall system. An optimization study using direct search method is also carried out to obtain the highest energy and exergy efficiencies and rate of hydrogen produced by choosing several independent variables. The results show that the power and rate of hydrogen produced increase with increase in the heliostat field area and the solar flux. The rate of hydrogen produced increases from 0.006 kg/s to 0.063 kg/s with increase in the heliostat field area from 8000 m² to 50,000 m². Moreover, when the solar flux is increased from 400 W/m² to 1200 W/m², the rate of hydrogen produced increases from 0.005 kg/s to 0.018 kg/s. The optimization study yields maximum energy and exergy efficiencies and the rate of hydrogen produced of 18.74%, 39.55% and 1571 L/s, respectively.     

Energy and Exergy Analysis on Drying of Banana Using Indirect Type Natural Convection Solar Dryer

Abstract

Energy and exergy analysis, in the thermodynamics, is an important tool used to predict the performance of drying system. In this work, energy and exergy analyses are made during the drying process of banana using an indirect type passive solar dryer. Solar flat plate air collector is used to heat the air. Banana gets sufficiently dried at temperatures between 28 and 82?°C. Solar radiation is measured and it is ranged from 335 to 1210?W/m². Using the first law of thermodynamics, energy analysis was carried out to estimate the amounts of energy gained from solar air heater. Also, applying the second law of thermodynamics, exergy analysis was carried out to determine exergy losses during the drying process. The exergy losses varied from 3.36 to 25.21?kJ/kg. In particular, the exergy efficiency values vary from 7.4 to 45.32%.