Performance of a large-scale greenhouse solar dryer integrated with phase change material thermal storage system for drying of chili

ABSTRACT

Large-scale greenhouse solar dryers have been used for drying various products and this type of dryer is usually equipped with LPG burner as auxiliary heater, which creates more operating cost. To overcome this problem, phase change material (PCM) thermal storage was proposed to substitute for the LPG burner. In this work, the performance of a large-scale greenhouse solar dryer integrated with a PCM as a latent heat storage for drying of chili was investigated. Experimental studies were conducted to compare the performance of this dryer with that of another large-scale greenhouse solar dryer without the PCM thermal storage and open sun drying. Chili with an initial moisture content of 74.7% (w.b.) was dried to a final moisture content of 10.0% (w.b.) in 2.5 days, 3.5 days, and 11 days using the solar dryer integrated with the PCM thermal storage, the solar dryer without the PCM thermal storage and the open sun drying, respectively. The performance of the solar dryer integrated with the PCM thermal storage was also evaluated using exergy analysis. The exergy efficiency of the drying room of the solar dryer integrated with the PCM thermal storage and the solar dryer without the PCM thermal storage for drying of chili was found to be 13.1% and 11.4%, respectively and the thermal storage helps to dry chili during adverse weather conditions. The results of exergy analysis implied that the exergy losses from the dryer with the PCM should be reduced.     

Effect of PCM on temperature fluctuation during the door opening of a household refrigerator

Temperature fluctuation inside the cabinet of a household refrigerator significantly affects the quality of preserved food. Phase change material (PCM) is a latent heat storage system that can store and release the heat energy by changing its phase from liquid to solid and solid to liquid respectively. Therefore, use of PCM inside the refrigerator cabinet has the potential for minimizing the temperature fluctuation during the door opening and the power failure. However, very few studies in the literature were dedicated to investigating the role of PCM to reduce the temperature fluctuation. The aim of this work is to experimentally investigate the effects of PCM on temperature fluctuation inside the cabinet of a household refrigerator during the door opening and power failure. The results found that a significantly lower temperature fluctuation can be obtained using PCM. It was found that during the door opening condition the air temperature in the cabinet rose rapidly. However, when a PCM container was used, temperature variation was reduced to 3–5°C. During the power failure, the system with PCM maintained a lower temperature inside the storage chamber for a long period of time (about 2 hours). Moreover, the test results indicate that PCM maintains more stable temperature in the foodstuffs inside the refrigerator. This reduction of temperature fluctuation ultimately improves the quality of preserved food.     

Investigations on an evacuated tube solar water heater using hybrid-nano based organic phase change material

ABSTRACT

This work explores the opportunities to address the setback in thermal energy storage of solar-based water heaters by uniting it with a suitable hybrid-nano composite phase change material (HNCPCM) in a static mode of operation. The experiments were conducted on a natural circulation all-glass evacuated solar water heating system (AGSWH). The investigation was steered in five cases such that the first case without any phase change material (PCM), the second with pure paraffin as PCM, and remaining three cases with three different mass percentage of HNCPCMs (0.5%, 1.0%, and 2.0% mass fraction of hybrid nanoparticles within PCM) in real-time solar exposure. The system was analyzed based on the first and second law of thermodynamics to assess the performance in all the five cases. Erstwhile, the hybrid nanoparticles were prepared by blending equal mass of SiO₂ and CeO₂ nanoparticles and characterized to gauge its thermal storage properties. The achieved results substantiated that the thermal conductivity had boosted with the accumulation of hybrid nanoparticles within the paraffin matrix, and maximum enhancement of 65.56% was attained with 2.0% mass fraction. The first law and second law investigations revealed that the incorporation of hybrid-nano composites improved the energy and exergy content of the system, distinctly. Among the experimented cases, HNCPCM with 1.0 mass% of hybrid nanoparticles remarkably yielded a better result of 19.4% and 1.28% improvement in energy and exergy efficiencies, respectively. Besides, it evidenced the necessity of choosing the right quantity of nanoparticles for achieving better overall results.     

Thermal energy storage and thermodynamic properties of (E)-3-m-tolylbut-2-enoic acid as a medium temperature phase change material

Phase change materials (PCMs) that can store and release heat energy over the temperature range from 363 to 393 K are crucial for solar absorption cooling, and it is worthy to seek new solid-liquid PCMs candidates that melt and crystallize in this temperature range. In this paper, (E)-3-m-tolylbut-2-enoic acid (mTBEA) was applied as a PCM candidate. Its thermal energy storage properties and thermal stability were systematically investigated. The results showed that mTBEA melted at 382.9 ± 0.5 K and crystallized at about 364 K, with a melting enthalpy (Δ_fusH) of 138.4 ± 6.9 J g^?1 and showed good long-term cyclic stability and thermal stability. The supercooling of mTBEA was stabilized at about 20 K, indicating that the conservation condition of melted mTBEA could be simple. In addition, the melted mTBEA could release all the absorbed thermal energy upon crystallizing. Besides, mTBEA exhibited good thermal stability for it to be applied as PCM. Hence, mTBEA is a promising PCM candidate for solar absorption cooling. Furthermore, the heat capacity of mTBEA was measured by modulated temperature differential scanning calorimetry (MTDSC) over the temperature range from 198.15 to 431.15 K, and the molar thermodynamic functions, [H_T-H_298.15]_m and [S_T-S_298.15]_m, were calculated based on the fitted molar heat capacity data.     

Experimental investigation on the phase change material-based modular heat exchanger for thermal management of a building

A phase change material (PCM)-based flat plate modular heat exchanger for free cooling application, suitable for the diurnal temperature variation that prevails during the summer months of Bangalore city, India is designed and experimentally investigated. The flow and other parameters selected in the present study are meant to suit the accelerated charging of the PCM in the modular heat exchanger during the early morning hours, and to provide cool energy to the room during the daytime, by circulating the ambient air through the heat exchanger at a lower velocity. It is observed from the charging experiments that the decrease in the inlet air temperature has more influence in reducing the solidification time than the increase in the inlet air velocity. The heat exchanger designed in the present investigation is capable of maintaining the room temperature around 30°C for a longer duration of 8 hr when the heat load is 0.5 kW. It is suggested to design the modular heat exchanger with a surface area proportionate to the present heat exchanger size when the room heat load increases beyond 0.5 kW, in order to maintain a minimum comfortable temperature of 30°C in the room.     

Energy and exergy analysis of a heat storage tank with a novel eutectic phase change material layer of a solar heater system

Solar energy is one of the most important renewable energy sources, but it is not available every time and every season. Thus, storing of solar energy is important. One of the popular methods of heat storage is use of phase change materials (PCMs) which have large thermal energy storage capacity. In this study, the heat storage tank in a domestic solar water heating system was chosen as control volume. The experiments were performed in the province of Elaz?g, Turkey, in November when solar radiation was weak due to cloudy sky. The heat storage tank of the system was modified to fill PCM between insulation and hot water part. A few PCMs which are Potassium Fluoride, Lithium Metaborate Dihydrate, Strontium Hydroxide Octahydrate, Barium Hydroxide Octahydrate, Aluminum Ammonium Sulfate, and Sodium Hydrogen Phosphate were analyzed to proper operating conditions using a Differential Scanning Calorimeter (DSC) and the best PCM was obtained with the Aluminum Ammonium Sulfate and Sodium Hydrogen Phosphate mixture. Thus, eutectic PCM was obtained and used in a heat storage tank of the solar water heating system. Energy and exergy analysis of heat storage tank was performed with and without the PCM. Energy and exergy analysis has shown that the heat storage tank with the PCM is more efficient than without the PCM and the maximum exergy efficiency was obtained as 22% with the heat storage tank with the PCM.     

Thermal Modeling and Performance Evaluation of Photovoltaic Thermal (PV/T) Systems: A Parametric Study

Conventional solar photovoltaic (PV) module converts the light component of solar radiation into electrical power, and heat part is absorbed by module increasing its operating temperature. Combined PV module and heat exchanger generating both electrical and thermal powers is called as hybrid photovoltaic/thermal (PV/T) solar system. The paper presents the design of a PV/T collector, made with thin film PV technology and a spiral flow absorber, and a simulation model, developed through the system of several mathematical equations, to evaluate the performance of PV/T water collectors. The effect of various parameters on the thermal and electrical efficiency has been investigated to obtain optimum combination of parameters. Finally, a numerical simulation has been carried out for the daily and annual yield of the proposed PV/T collector, and comparison with a standard PV module is discussed.     

Experimental investigation of a solar water distillation-cum-drying unit

In this communication, a new design of solar-energy-based water distillation cum drying unit with parabolic reflector has been designed, fabricated, and tested. Bitter gourd and potato slices are chosen as a drying commodity. Thermal performance of the developed system has been evaluated based on the experimental results and using linear regression analysis. Heat transfer coefficients (convective, evaporative, and radiative) for solar distillation system have been observed to be 2.48–4.09, 13.25–52.38, and 8.75–9.66 W/m²°C, respectively. Overall thermal efficiency and exergy efficiency for the distillation system has been found to be 18.77% and 1.2%, respectively. The convective heat transfer coefficient for potato slices are observed higher for initial hours and decreases as the day progresses. The average convective heat transfer coefficients for bitter gourd and potato slices have been observed as 2.18 and 5.04 W/m²°C, respectively. Experimental error in terms of percent uncertainty for bitter gourd and potato slices are found to be 42.93% and 37.06%, respectively. The present design of solar distillation and drying in a single unit could be beneficial for the development of remote, arid, and rural areas.     

The convective hot air drying of Lactuca sativa slices

The storage of fresh agricultural products is not easy because of its high moisture. Dehydration is an efficient preservation method. The investigation of drying modeling and transfer characteristics are important for selecting operating conditions and equipment design. The drying behavior of Lactuca sativa slices, with the thickness of 2 mm, was investigated at 60.0–80.0°C and 0.60–1.04 m sec^?1 velocity in a convective hot air drier. The mass transfer during the drying process was described using six thin drying models. The convective heat transfer coefficient α and mass transfer coefficient k_H were finally calculated. The results showed that the drying process could be separated into three stages including accelerating rate, constant rate, and falling rate period, which was influenced by hot air temperature and velocity, and the Modi?ed Page model agreed well with the experimental data. When the operating temperature was increased from 60.0°C to 80.0°C, α was found increased from 88.07 to 107.93 W·m^?2·K^?1, and k_H increased from 46.32 × 10^–3 to 68.04 × 10^–3 kg·m^?2·sec^?1·ΔH^?1. With the increase of air velocity from 0.60 to 1.04 m·sec^?1, α was increased from 78.85 to 101.35 W·m^?2·K^?1, and k_H was enhanced from 51.78 × 10^–3 to 65.85 × 10^–3 kg·m^?2·sec^?1·ΔH^?1.     

Global solar radiation and energy yield estimation from photovoltaic power plants for small loads

Daily global solar radiation on a horizontal surface and duration of sunshine hours have been determined experimentally for five meteorological stations in Saudi Arabia, namely, Abha, Al-Ahsa, Al-Jouf, Al-Qaisumah, and Wadi Al-Dawaser sites. Five-years of data covering 1998–2002 period have been used. Suitable Angstrom models have been developed for the global solar radiation estimation as a function of the sunshine duration for each respective sites. Daily averages of monthly solar PV power outputs have been determined using the Angstrom models developed. The effect of the PV cell temperature on the PV efficiency has been considered in calculating the PV power output. The annual average PV output energy has been discussed in all five sites for small loads. The minimum and maximum monthly average values of the daily global solar radiation are found to be 12.09 MJ/m²/d and 30.42 MJ/m²/d for Al-Qaisumah and Al-Jouf in the months of December June, respectively. Minimum monthly average sunshine hours of 5.89 hr were observed in Al-Qaisumah in December while a maximum of 12.92 hr in Al-Jouf in the month of June. Shortest range of sunshine hours of 7.33–10.12 hr was recorded at Abha station. Minimum monthly average Solar PV power of 1.59 MJ/m²/day was obtained at Al-Qaisumah in the month of December and a maximum of 3.39 MJ/m²/day at Al-Jouf in June. The annual PV energy output was found to be 276.04 kWh/m², 257.36 kWh/m², 256.75 kWh/m², 245.44 kWh/m², and 270.95 kWh/m² at Abha, Al-Ahsa, Al-Jouf, Al-Qaisumah, and Wadi Al-Dawaser stations, respectively. It is found that the Abha site yields the highest solar PV energy among the five sites considered.     

Experimental Investigation of Convective Heat Transfer Coefficient of Various Agricultural Products Under Open Sun Drying

Abstract

In this article, the convective heat transfer coefficients of various agricultural products were investigated under open sun drying conditions. Data obtained from open sun drying experiments for eight agricultural products, namely, mulberry, strawberry, apple, garlic, potato, pumpkin, eggplant, and onion were used to determine values of convective heat transfer coefficient. The value of convective heat transfer coefficient was determined as 1.861 W/m²°C for mulberry, 6.691 W/m²°C for strawberry, 11.323 W/m²°C for apple, 1.136 W/m²°C for garlic, 8.224 W/m²°C for potato, 8.613 W/m²°C for pumpkin, 6.981 W/m²°C for eggplant, and 6.767 W/m²°C for onion. The experimental error in terms of percent uncertainty was also calculated.     

Performance study on evacuated tubular collector coupled solar still in West Texas climate

Experimental study was performed on a single basin active solar distillation system augmented with a solar collector using evacuated solar tubes. Field tests were conducted over several days under the climatic conditions of West Texas to evaluate the effect evacuated solar tubes have on the daily distillate yield rate. To investigate the feasibility of the solar tubes, active and passive solar stills with and without exterior insulation were examined. The maximum daily production rate for the active distillation system using evacuated solar tubes and the passive distillation system was 3.6 and 1.4 kg/m²day, respectively. The results showed the augmentation of the still with evacuated solar tubes increased its production capacity by a factor of 2.63. It also increased the maximum temperature of the water in the still basin by at least 20 °C. Economic analysis shows that it is feasible to use evacuated tubular collector coupled solar still as an alternative means for reclaiming water in farmlands with a payback period of approximately 6 years.     

Investigation of activated carbon/ethanol for low temperature adsorption cooling

Commercially available adsorption cooling systems use water/silica gel, water/zeolite and ammonia/ chloride salts working pairs. The water-based pairs are limited to work above 0°C due to the water high freezing temperature, while ammonia has the disadvantage of being toxic. Ethanol is a promising refrigerant due to its low freezing point (161 K), nontoxicity, zero ozone depletion, and low global warming potential. Activated carbon (AC) is a porous material with high degree of porosity (500–3000 m²/g) that has been used in wide range of applications. Using Dynamic Vapour Sorption (DVS) test facility, this work characterizes the ethanol adsorption of eleven commercially available activated carbon materials for cooling at low temperature of ?15°C. DVS adsorption results show that Maxsorb has the best performance in terms of ethanol uptake and adsorption kinetics compared to the other tested materials. The Maxsorb/ethanol adsorption process has been numerically modeled using computational fluid dynamics (CFD) and simulation results are validated using the DVS experimental measurements. The validated CFD simulation of the adsorption process is used to predict the effects of adsorbent layer thickness and packing density on cycle uptake for evaporating temperature of ?15°C. Simulation results show that as the thickness of the Maxsorb adsorbent layer increases, its uptake decreases. As for the packing density, the amount of ethanol adsorbed per plate increases with the packing density reaching maximum at 750 kg/m³. This work shows the potential of using Maxsorb/ethanol in producing low temperature cooling down to ?15°C with specific cooling energy reaching 400 kJ/kg.     

Pyrolysis of commingled waste textile fibers in a batch reactor: Analysis of the pyrolysis gases and solid product

The main object of this study was the investigation of the thermal recycling of commingled waste textile fibers, with the aim of the production of useful end products. Differential scanning calorimetry/Thermo gravimetric analysis (DSC/TGA) was applied to determine the thermal degradation characteristics of the commingled waste textile fibers and there are two peaks located at the temperature ranges of 299–360°C and 399–500°C. Commingled waste fiber was pyrolyzed in a nitrogen atmosphere in relation to three different temperatures (500, 600, and 700°C), heating rates (25 and 50°C min^?1), and retention times (15 and 30 min). The effect of the experimental conditions such as pyrolysis temperature, heating rates, and retention time on the formation of char and gas--liquid products was investigated and the product yields were determined from the rate of the weight loss. The highest conversion rate 82.9 wt.% liquid--gas product and 17.1 wt.% char product was achieved at 700°C. Pyrolysis gases were taken for every 7, 15, and 25 min and were analyzed for major components such as CO, CO₂, CH₄, and H₂ by gas chromatography. The pyrolysis char called as carbon black derived from the pyrolysis of commingled waste textile fibers was analyzed for a range of properties, including the elemental analysis, moisture content, ash content, calorific value, and trace metal analysis.     

Performance of a small-scale solar-powered adsorption cooling system

In this study, an experimental investigation on the performance of a small-scale residential-size solar-driven adsorption (silica gel-water) cooling system that was constructed at Assiut University campus, Egypt is carried out. As Assiut area is considered as hot, arid climate, field tests for performance assessment of the system operation during the summer season are performed under different environmental operating conditions. The system consists of an evacuated tube with a reflective concentration parabolic surface solar-collector field with a total area of 36 m², a silica gel-water adsorption chiller of 8 kW nominal cooling capacity, and hot and cold water thermal storage tanks of 1.8 and 1.2 m³ in volume, respectively. The results of summer season field test show that under daily solar insolation varying from 21 to 27 MJ/m², the solar collectors employed in the system had high and almost constant thermal efficiency. The daily solar-collector efficiency during the period of system operation ranged from about 50% to 78%. The adsorption chiller performance shows that the chiller average daily coefficient of performance (COP) was 0.41 with the average cooling capacity of 4.4 kW when the cooling-water and chilled-water temperatures were about 31°C and 19°C, respectively. As the chiller cooling water is cooled by the cooling tower in the hot arid area, the cooling water is at a higher temperature than the design point of the chiller. Therefore, an experiment was carried out using the city water for cooling. The results show that an enhancement in the chiller COP by 40% and the chilling power by 17% has been achieved when the city water was 27.7°C.     

Thermal analysis of tilted wick solar distillation-cum-drying system

The performance of the designed tilted wick solar water distillation-cum-drying unit has been tested at water flow rates of 50 and 65 ml/min in the distillation unit. Effect of water flow rates on the heat transfer coefficients of distillation and drying unit for drying ginger has been evaluated. The energy and exergy efficiency of the distillation system have also been evaluated. Average distillates of 2.36 and 2.2 l/m² were collected from the tilted wick solar still at flow rates of 50 and 65 ml/min, respectively. Large variation in convective and evaporative heat transfer coefficients of distillation unit has been observed at given water flow rates. Water flow rate in the distillation unit significantly affects the performance of the drying unit. Average convective heat transfer coefficients of 6.56 and 3.75 W/m^{2 o}C have been observed for drying ginger at flow rates of 50 and 65 ml/min, respectively. Energy and exergy efficiency of the distillation unit have been found to be nearly 19% and 0.9%, respectively. Experimental uncertainty has also been evaluated for distillation and drying units. The distillate cost for the developed distillation-cum-drying unit is calculated as $0.03729/l along with dried ginger of about 2.5 kg/m²/day.     

Photovoltaic-thermal (PV/t) panel to minimize electrical and air conditioning energy consumption of a typical office in Beirut

A combined photovoltaic–thermal (PV/t) panel is proposed to produce simultaneously electricity and heat from one integrated unit. The unit utilizes effectively the solar energy through achieving higher PV electrical efficiency and using the thermal energy for heating applications. To predict the performance of the PV/t at a given environmental conditions, a transient mathematical model was developed. The model was integrated in a heating application for a typical office space in the city of Beirut to provide the office needs for electricity, heating during winter season, and dehumidification and evaporative cooling during the summer season. To minimize the yearly office energy (electrical and heat) needs, the PV/t panel cooling air flow rate and the dehumidification regeneration temperature were determined for opimal unit operation. Thermal energy savings of up to 85% in winter and 71% in summer were achived compared to conventional systems at a payback period of 8 years for the panels.     

What Matters Most: Are Future Stream Temperatures More Sensitive to Changing Air Temperatures,Discharge, or Riparian Vegetation?

Simulations of stream temperatures showed a wide range of future thermal regimes under a warming climate — from 2.9°C warmer to 7.6°C cooler than current conditions — depending primarily on shade from riparian vegetation. We used the stream temperature model, Heat Source, to analyze a 37‐km study segment of the upper Middle Fork John Day River, located in northeast Oregon, USA. We developed alternative future scenarios based on downscaled projections from climate change models and the composition and structure of native riparian forests. We examined 36 scenarios combining future changes in air temperature (ΔT_air = 0°C, +2°C, and +4°C), stream discharge (ΔQ = ?30%, 0%, and +30%), and riparian vegetation (post‐wildfire with 7% shade, current vegetation with 19% shade, a young‐open forest with 34% shade, and a mature riparian forest with 79% effective shade). Shade from riparian vegetation had the largest influence on stream temperatures, changing the seven‐day average daily maximum temperature (7DADM) from +1°C to ?7°C. In comparison, the 7DADM increased by 1.4°C with a 4°C increase in air temperature and by 0.7°C with a 30% change in discharge. Many streams throughout the interior western United States have been altered in ways that have substantially reduced shade. The effect of restoring shade could result in future stream temperatures that are colder than today, even under a warmer climate with substantially lower late‐summer streamflow.     

Heat transfer of vapor chamber with different types of microchannels

Two 40-mm × 35-mm × 1.525-mm micro vapor chambers were fabricated by inductively coupled plasma etching on silicon substrates and tested in this study. One vapor chamber exhibited convergent microchannels, whose widest and narrowest width were 0.3 mm and 0.1 mm, respectively, and the other exhibited discontinuous microchannels having width of 0.3 mm. Those micro vapor chambers that were filled with deionized water in a filling ratio of approximately 48% were tested with various titled angles and input powers. The results showed that the thermal performance of the vapor chamber having discontinuous microchannels was inferior because the spacing between microchannelend and the micropostin both condensing and evaporating sections was too far to return the condensed fluid from condensing section to the evaporating section of the vapor chamber. On the contrary, the convergent microchannel in the other vapor chamber enhanced capillary force, so that the condensed liquid could be successfully forced from the condensing section to the evaporating section even with top heating mode (–90°). The thermal resistance of the vapor chamber having convergent micro channels with top heating mode was 2.08°C/W at 22 W, while the thermal resistance of the vapor chamber with horizontal heating mode was 1.46°C/W at 28 W.     

Fabrication and characterization of electrospun porous cellulose acetate nanofibrous mats incorporated with capric acid as form-stable phase change materials for storing/retrieving thermal energy

Electrospun cellulose acetate (CA) nanofibrous mats incorporated with capric acid was studied to fabricate form-stable phase change materials (PCMs) for storing/retrieving thermal energy. Electrospun CA nanofibrous mats with different porous structures and specific surface areas were firstly prepared through regulating the volume ratio of mixture solvent of acetone/dichloromethane (DCM). Effects of different volume ratio of mixture solvent and mat thickness on the morphological structure, specific surface area, and absorption capacity of CA nanofibrous mats were systematically investigated. The results indicated that CA nanofibrous mats were highly porous on the surface; hence, they were capable of absorbing a large amount of capric acid. The maximum absorption capacity of CA mats via electrospinning with volume ratio of acetone/DCM being 5/5 was ~95.8 wt%, due to its higher specific surface area of ~17.1 m²/g. The specific surface area and capric acid absorption capacity of CA nanofibrous mats increased with the increases of mat thickness. As the thickness of nanofibrous mats increased from 10 to 85 μm, the corresponding specific surface area and capric acid absorption capacity of mats increased respectively from 7.2 to 29.0 m²/g and 92.1 to 98.5%. Morphological structures, as well as the properties of thermal energy storage and thermal insulation of the fabricated form-stable PCMs, were studied by scanning electron microscopy, differential scanning calorimetry, and measurement of freezing times, respectively. The results indicated that the resulting form-stable PCMs could well maintain their phase transition characteristics and demonstrated great thermal energy storage capability and temperature regulation ability.