Average Thermal Efficiency Research Articles

DESIGN NEW PROTOTYPE OF AN INDIRECT SOLAR- ELECTRICAL DRYER TO DRY WHITE ONIONS SLICES

In the present research, a new specific model of an indirect solar–electrical dryer for onions slices was designed and constructed at a Zagazig City , Sharkia Governorate, Egypt. Solar dryer consists of solar flat plate air collector with V- corriugated absorption plate. The total area of the collector is 1.75 m2. The size of the drying cabinet is (1.5 × 0.50 × 1) m (height, width and depth). An experiment was conducted to study drying of onions slices 5 and 10 mm. The qualitative analysis for drying of onions slices of 5 mm under three air velocities (1.5,2.2 and 3) m/s, showed that moisture content was reduced from (669.23db to 6.95, 8.69 and 14.41db), (4.27,5.26 and 9.89db) and (2.04, 3.09 and7.52db) for( Tray1, Tray2, Tray3) while it were (19.33,26.90 and 33.51db), (14.41, 21.35 and 27.71db) and (9.89, 16.27 and 21.95db) for onions slices 10 mm respectiviely.The average moisture content of open sun dry were 20.60 and 50.95 db for onions slices of 5and10 mm. The average percentage thermal efficiency for the collector was found to be 33.03, 49.96 and 65.45 % while it were 21.37,15.43 and 10.29% of the dryer for air speed 1.5,2.2 and 3 m/s,, respectiviely.The average percentage value of the collector 34.07,37.59 and 42.69% while it were be24.82, 32.55and 41.85% for the dryer at air velocities were1.5,2.2 and 3 m/s, respectiviely. In order to estimate and select the suitable form of solar drying curves, five different mathematical models, were compared according to their coefficient of determination R2, MBE, RMSE, %E and chi square X2 to estimate experimental drying curves. The Modified page model in this condition proved to be the best for predicting drying behavior of onions slices of 5 and10 mm with (R2 = 0.9961and0.9899) and (X2 = 0.000148 and0.000591). The effective moisture diffusivity (Deff) was obtained using Fick’s diffusion equation and its value varied from 1.72958× 10-9 to 2.37261× 10-9 m2/s and 4.31037× 10-9 to 5.61732× 10-9 m2/s while the value of activation energy ranged from 23.49 to 29.82 kJ/mol k and 16.09 to 18.01 kJ/mol k for onions slices of 5and10 mm. Finally an economic evaluation was calculated using the criterion of payback period which is found very small 1.05 years compared to the life of the dryer 25 years.

Performance study of a solar chimney air heater

The thermal efficiency of conventional solar air heaters could be significantly improved by making some design configurations. In this study, a solar chimney air heater was employed and the effect of glazing, fins and convection (natural/forced) on the thermal efficiency of the heater was investigated. It was found that the incorporation of glazing and fins improved the performance of the heater. Further, the heater showed improved efficiency when operated under forced convection mode. Among the designs, the forced induced glazed solar chimney air heater with fins displayed the highest average thermal efficiency of 16.50%.

Performance improvement of solar photovoltaic/thermal heat pump system in winter by employing vapor injection cycle

Direct-expansion solar assisted heat pump (DX-SAHP) is a promising technology for saving energy. In this paper, vapor injection (VI) cycle system to DX-SAHP system is studied. Thermodynamic comparative analyses of ideal VI cycle and ideal conventional vapor compression cycle was carried out for verifying the advantages by applying VI cycle into DX-SAHP. Additionally, photovoltaic/thermal (PVT) modules were used in the system to harvest thermal energy and electric power. A PVT based solar heat pump system employing VI cycle (PVT-VISHP) was proposed, fabricated and investigated experimentally. Performance of the experimental prototype was subsequently evaluated for seven days in winter. The system’s performance was evaluated based on the average ambient temperature of −1.13 °C and solar irradiation of 164.03 W/m2. Results showed that the total generated electricity, heat, and consumed power of the system were 0.51 kWh, 23.68 kWh, and 7.24 kWh, respectively. Moreover, average heating coefficient of performance (COPth) and advanced coefficient of performance (COPPVT) of the PVT-VISHP system were 3.27 and 3.45, respectively. In the study, the ambient-evaporating temperature difference ranged from 9.2 °C to 17.1 °C. Furthermore, variations of injected vapor’s pressure, mass flow rate, mass flow rate ratio, and subcooling effects were analyzed in detail. Performance of the PVT modules during a sunny day was tested. It was found that the PVT modules’ average thermal collecting and PV efficiencies were 49.9% and 7.51%, respectively.

Energy-Exergy Analysis of A Novel Multi-Pass Solar Air Collector With Perforated Fins

This work presents performance analysis of a novel multi-pass solar air collector with perforated fins (MPSACF) in winter conditions, Ankara province, Turkey. The aim of this work is to experimentally test and compare the performance of the two different design of solar collectors in the same climatic conditions. In addition, a double-pass solar air collector without fins (DPSAC) at the same absorber area was manufactured and tested as a control group. The total absorber area of both solar collectors is 0.325 m2. Thermal effects for performance improvement of the collectors have been designated. Average thermal efficiency values of DPSAC and MPSACF were calculated as 47.85% and 51.86%, 67.10% and 72.86%, respectively in experiments performed at 0.0069 kg/s (0.7 m/s air velocity) and 0.0087 kg/s (0.9 m/s air velocity) mass flow rates. Exergy efficiency of DPSAC and MPSACF were 2.10-17.12% and 8.74-23.97%, respectively. Coefficient of performance(COP) values were ocomputed 4.63 and 4.94, 3.18 and 3.48 respectively in experiments performed at 0.0069 kg/s and 0.0087 kg/s mass flow rates. Although the MPSACF has high efficiency values, COP values are lower due to the presence of dual fans. Because of their high thermal efficiency, both collectors can be effectively practiced for applications such as preheating, space heating and ventilation, greenhouse heating and product drying©2019. CBIORE-IJRED. All rights reservedArticle History: Received May 16th 2018; Received in revised form October 16th 2018 ; Accepted January 6th 2019; Available onlineHow to Cite This Article: Aktaş, M., Sözen, A., Tuncer, A.D., Arslan, E., Koşan, M., Çürük, O. (2019) Energy-exergy analysis of a novel multi-pass solar air collector with perforated fins. International Journal of Renewable Energy Development, 8(1), 47-55.http://dx.doi.org/10.14710/ijred.8.1.47-55

Transient thermal analysis of a solar chimney for buildings with three different types of absorbing materials: Copper plate/PCM/concrete wall

A transient numerical simulation of a solar chimney system (SC), considering convective and radiative gains/losses to the exterior environment, in the warmest day of Madrid, Spain is presented. We performed a conjugate heat transfer analysis for SC with three types of absorbing materials: (1) SC with a lightweight plate (copper) – reference case, (2) SC with a phase change material (PCM 46-50) and (3) SC with a heavyweight wall (concrete). Numerical simulations for three orientations east (7:00–12 h), south (8:00–18 h), and west (12:30 to 18 h) were conducted to analyze the overall thermal performance of the SC throughout the day. The numerical in-house code was tested by solving two reference solutions reported in the literature, obtaining good agreement. Based on the numerical heat transfer analysis, the following is concluded: The SC with a copper plate shows the higher mass flow rates of 0.016, 0.019 and 0.016 kg/s for orientations east, west, and south, respectively. While the mass flow rate removed by the PCM configuration is higher than for the concrete wall configuration but is lower than for the copper plate (0.014, 0.017 and 0.0153 kg/s for orientations east, west, and south, respectively). The average thermal efficiencies of the SC with a copper plate are 34, 27 and 34% and with a PCM are 28, 19.8, and 27% for orientations east, west, and south, respectively. The SC with a concrete wall shows the lowest thermal efficiency values. Finally, it was observed that for orientations east and south, the PCM layer does not change its phase and it remains in the mushy zone. It reaches its melting point on approximately 30–45 min for the three orientations. Conversely, the PCM changed its phase to a liquid state in 135 min for orientation west.

An experimental study of a built-middle Photovoltaic Trombe wall system

This paper proposed a PV-integrated Trombe wall system (PVTW) with the photovoltaic panel installed in the middle of air channel, named as built-middle photovoltaic Trombe wall system (PVMTW). The system has multiple functions: such as photovoltaic power generation, passive space heating, heat preservation and heat insulation. A series of tests were carried out in winter between the comparable hot- boxes to investigate the thermal and electrical performance of the PVMTW system. The results showed that the average electrical efficiency and thermal efficiency were 0.12 and 0.40, respectively, under the natural convection mode. The total efficiency of the PVMTW system was calculated to be 0.587, which is 11.4 % higher than that of traditional PVTW system with the solar cells laminated on the glass cover.

Detaljno matematičko modeliranje i eksperimentalna evaluacija solarnog PV modula hlađenog površinskim slojem vode

In this research article, an analytical model has been developed to examine the electrical and thermal behaviour of a solar photovoltaic module with top water cooling. Mathematical calculations have been performed under India, Chennai (latitude: 13.06° N and longitude: 80.11° E) prevailing weather conditions. Three modes of heat transfer mechanisms are considered in the thermal model and computed using improved correlations. The model validation against the experimental data exhibited a good agreement. Daily average electrical and overall thermal efficiency of a PV module with top water flow have been found to be 14.29% and 45.44% respectively. Water flows on top side of the PV module decreases the average module temperature of a day from 56.67°C to 39.44°C, and the average daily module electrical efficiency is increased up to 14.29%, compared to 12.74% efficiency of PV module without cooling.

A diesel engine performance measurement with diesel fuel and biodiesel

Rapid growth in the energy consumption has conditioned the need for discovering the alternative energy resources which would be adapted to the existing engine constructions and which would satisfy the additional criteria related to the renewability, ecology, and reliability of use. The experimental research are conducted according to the (European Stationary Cycle - Directive 1999/96/EC) 13-mode. Using biodiesel fuel average thermal efficiency is kept at the level of the application of conventional diesel fuel, average emission of CO is reduced by 13.6%, average emission of NO is increased by x 27.6%, average emission of hydrocarbon is increased by 59.4%, and average particles emission is reduced by 43.2%.

Mathematical Modelling and Techno-economic Evaluation of Hybrid Photovoltaic-thermal Forced Convection Solar Drying of Indian Jujube (Zizyphus mauritiana)

Two identical units of a hybrid photovoltaic-thermal (PV/T) solar dryer designed and constructed at ICAR-Central Arid Zone Research Institute, Jodhpur, were used to dry Indian jujube (Zizyphus mauritiana) fruit, one operated under natural and the other under forced convection modes. The fruits were dried to safe moisture content (24 %) in a period of 192 h in forced convection mode, and in 240 h in natural convection mode with drying load of 18 kg. There was a significant difference in performance of the dryer under forced and natural convection mode. The average thermal efficiency of solar energy utilization under forced convection mode was higher (16.7 %) than that of natural convection solar dryer (15.6 %). Logarithmic drying model was suitable for describing the thin layer drying behaviour of the fruit. Effective moisture diffusivity of forced convection dryer was 3.34 × 10-7 m2 .s-1 . Economic evaluation of the solar dryer indicated high value of IRR (54.5 %), and low value of payback period (2.26 years), suggesting the dryer to be cost efficient.

Design and Implementation of an Automatic Control for Two Axis Tracking System for Applications of Concentrated Solar Thermal Power

The present work presents design and implementation of an automated two-axis solar tracking system using local materials with minimum cost, light weight and reliable structure. The tracking system consists of two parts, mechanical units (fixed and moving parts) and control units (four LDR sensors and Arduino UNO microcontroller to control two DC servomotors). The tracking system was fitted and assembled together with a parabolic trough solar concentrator (PTSC) system to move it according to information come from the sensors so as to keep the PTSC always perpendicular to sun rays. The experimental tests have been done on the PTSC system to investigate its thermal performance in two cases, with tracking system (case 1) and without tracking system (case 2). The experimental results showed that the average solar radiation falling on the PTSC prototype in the two cases during the same time was 854 and 701 watt/m2, respectively, which means an increase in the solar radiation about 21.8 % when using tracking system. It was found that the average useful heat gain output of solar collector was equal to (376.2, 252.6 watt) for the two cases, respectively, so there was an increase of about 48.9 % when using the tracking system. Also, the average thermal efficiency of the PTSC was found to be (20.7, 26.5 %) for the two cases, respectively, which means an increase in the average efficiency by 28% with use of tracking system compared to the fixed case.

A comparative investigation of the effect of honeycomb core on the latent heat storage with PCM in solar air heater

The aims of this study were to comparatively investigate the effect of using PCM and honeycomb as the internal fin structure in the PCM panel on the thermal performance of solar air heater. The tests performed at six air mass flow rates from 0.008 to 0.048 kg/s. The heat storage material was tested in two forms, PCM with honeycomb core in the first heater (Type I) and only PCM in the second heater (Type II). The third heater (Type III) with a flat absorber plate (without PCM) was used for comparison. The average day-time thermal efficiency of the Type I-II heaters with PCM increased from 8.4% to 9.0% for the mass flow rates of 0.032, 0.04, and 0.048 kg/s, while from 0.8% to 8.0% decreased for the mass flow rates of 0.008, 0.016 and 0.024 kg/s. The use of honeycomb as the internal fin structure significantly reduces the charge-discharge time, while slightly reducing the instantaneous-daily thermal efficiency, and provides a temperature increase of up to 8.8 °C at the PCM-temperature. The daily thermal efficiency comparison between heaters with PCM was in favor of the heater without honeycomb at values ranging from 0.1% to 4.4%. Taking into consideration the daily thermal efficiency, the Type I-II heaters with PCM are more efficient between from 2.6 to 22.3%, especially at high mass flow rates. It took approximately one hour to equal the outlet air temperature of the Type-III with the inlet air temperature. In PCM heaters, the inlet-outlet temperatures are approximately equal to 6 to 10 h.

Modeling and matching performance of a hybrid-power gas engine heat pump system with continuously variable transmission

Based on the steady-state efficiency of the engine and the motor and characteristic curve of Lithium iron phosphate (LiFePO4) battery, an energy management strategy is proposed for a coaxial parallel hybrid-power gas engine heat pump (HPGHP) with V-belt continuously variable transmission (CVT) by using logic threshold approach to control the dynamical transitions between the various operation modes. The torque distribution between engine and motor, and CVT ratio are regulated through predetermined optimal operation lines of hybrid powertrain system in different operations. The results demonstrate that the energy management strategy can satisfy heat pump demand performance and reduce gas consumption effectively, as well as keep battery state of charge (SOC) in reasonable range. The average thermal efficiency of driving system in three main operating modes is 3.8%, 1.9% and 2.5% higher than that of multi-stage transmission system respectively, indicating that the system has better energy saving performance.

Experimental investigation of a novel low concentrating photovoltaic/thermal–thermoelectric generator hybrid system

This paper presents and explores a novel low concentrating photovoltaic/thermal–thermoelectric generator (LCPV/T-TEG) hybrid system. Unlike the conventional hybrid photovoltaic-thermoelectric generator (PV/TEG), the system mainly consists of a compound parabolic concentrator, a double-glazing PV panel, a micro-channel heat pipe array, the TEG and the data acquisition and control system. The TEG is designed to be associated with the cold side of heat pipe array which acts as the cooling method of the LCPV/T system to improve PV efficiency instead of directly adhering to the backplane of the PV panel for practical applications. The outdoor experiment of the LCPV/T-TEG system was accomplished on the rooftop of a building in Beijing on a sunny day and the environmental conditions, the inlet and the outlet temperature, and output power of the LCPV/T and TEG were tested and analyzed. The daily average thermal efficiency is 45.0%, add to the daily average PV electrical efficiency 11.8% and daily average TEG electrical efficiency 0.23%, the daily average overall efficiency reaches 57.03%.Furthermore, the effects of the cooling flow on the system performance are also considered and the results show that the PV and TEG efficiencies both increase with the increasing of the flow.

Experimental performance analysis of sensible heat storage in solar air collector with cherry pits/powder under the natural convection

It is important to enhance the availability of SACs either in cloudy weather or after sunset for space heating and agricultural drying process. In this context, this study aims to determine experimentally thermal performance of cherry pits as sensible heat storage material under natural convection conditions. In the first collector (Type I), powdered cherry pits (32 kg) were used as heat storage material and cherry pits (24 kg) were used in the second (Type II). The third collector (Type III) with a flat absorber plate is for comparison. Although the maximum thermal efficiencies were found 26.54% and 27.03% for Type I and Type II respectively, average thermal efficiency of Type I is higher than Type II. According to the test results, the inlet-outlet temperatures were equalized 46 min for the Type III, 200 min for Type II, and 270 min for Type I collector after sunset. As a result, it can be said that the use of cherry pits and powder as sensible heat storage material is promising.

Parametric analysis and annual performance evaluation of an air-based integrated solar heating and radiative cooling collector

Given the disadvantaged seasonal adaptability of solar air heaters and radiative air coolers, this study proposed an air-based integrated solar heating (SH) and radiative cooling (RC) collector (SH–RC collector). Such dual-function collector is capable of obtaining heat in SH mode and gaining cooling energy in RC mode. Accordingly, an air-based SH–RC collector can offer hot air during cold and harvest seasons and provide cool air during hot seasons. A spectrally selective plate termed as TPET collecting plate was trial-manufactured, serving as the panel of the air-based SH–RC collector. Also, this study developed a mathematical model and investigated the SH and RC performances of the proposed collector on a fine summer day. As the results suggest, the average thermal efficiency of the collector in SH mode reaches 45.88%, and the average cooling power of the collector is 36.61 W/m2. Parametric studies on the effect of various ambient temperatures, inlet air temperatures, air flow rates, relative humidity values, and wind velocities on the SH and RC performances of the collector have been conducted. In addition, the monthly energy gains of the air-based SH–RC collector were calculated. The annual heat and cooling gains of the SH–RC collector reached 2328.45 and 980.43 MJ, respectively.

Performance analysis of double-pass oscillating bed solar dryer for drying of non-parboiled paddy grains

ABSTRACT Drying of agricultural produce like paddy grains is necessary for reducing moisture content in them to the required level towards diminishing the deterioration and enhancing the storage time. Conventionally, open-space sun drying is widely used to reduce the moisture content of the most of the agricultural produce.. Now-a-day, so many solar dryers are used for drying agricultural produce. In the present work, a double-pass oscillating bed with a double-pass flat plate collector has been used for drying of non-parboiled paddy grains. The bed oscillated at a frequency of 2.75 Hz. The oscillating bed solar dryer can dry 45 kg of non-parboiled paddy grains in just a single day to the required level of moisture content, and the average moisture present in the dried grains was 13.55%. The average dryer thermal efficiency and pick-up efficiency in non-parboiled paddy were 28.79% and 52.17%, respectively.

Numerical investigation of a solar air heater comprising longitudinally finned absorber plate and thermal energy storage system

In the present work, the thermal performance of a double glazed single pass solar air heater consisting of a longitudinally finned absorber plate on its top surface and attached to a phase change material (PCM) with its bottom surface is investigated, theoretically. Paraffin wax (Rubitherm RT42) is used as a PCM. The main idea of this solar air heater design is to use it during nocturnal hours or off sunshine hours. A computational heat transfer and fluid dynamics solution using an implicit scheme has been developed and employed to study the effects of the mass flow rate and number of fins on its thermal performance under transient conditions. The maximum outlet air temperature of the finned type solar air heater with latent heat storage is achieved as 40 °C, 37 °C, and 35 °C for mass flow rates of 0.01, 0.015, and 0.02 kg/s, respectively, and it is predicted that the system can be used for 14, 12, and 10 h after sunset at respective mass flow rates. The maximum daily average thermal efficiency is predicted to be 62.4% at a mass flow rate of 0.02 kg/s which is higher than the other designs considered in the present investigation.

Thermal Performance Analysis of Parabolic Trough Solar Concentrator with Helical Tube Receiver

In this paper, the experimental thermal performance for a parabolic trough solar concentrator (PTSC) combined with helical tube receiver and directed by two axes solar tracking system at different amount of water flow rates has been analyzed. The experimental test results of thermal performance with regard to temperature rise of water, useful heat gain and collector thermal efficiency for the PTSC prototype at controlled water flow rates (2.3, 22.5 and 29.4 L/h) are collected. The results show that the increase of water mass flow rates causes decrease in the average water output temperature as (120.8, 63.82 and 46.08oC), respectively, the maximum outlet temperature becomes (160.5, 76, 47) oC, respectively, and thus, the average useful heat gain will be (1249.4, 732, 732.5W), respectively and the average thermal efficiency decreases as (73.021, 49.51 and 44.31 %), respectively. The experimental results show that decrease the water mass flow rate by 74.4%, causes an increase in the thermal efficiency of the PTSC by 64.7%.

Comparative Study for Two Types of Solar Dryers (Modified-Quonset and Lean-to) for Drying Stevia Plants (Rebaudiana bertoni)

The main objectives of this research work were to design, construct, and operate two different active solar dryers (Modified-Quonset and Lean-to structural forms). Thermal performance analysis of the two solar dryers, drying characteristics of thin layer of Stevia plants, and comparing experimentally between them were also tested, examined and evaluated. Moreover, the effect of drying process on the three different physical and chemical components (pigments, primary components, and anti-oxidant) had measured before and after the drying process using the two different solar dryers. The experimental work carried out on the completed plants (comprehended stems, branches, and leaves) from 25st to 28th of September 2016. The obtained results revealed that, the completed Stevia plants dried from the initial moisture content of 73.56% w.b. to 7.55% w.b. within 36 hours with drying rate of 30.03 g/hr using the Modified-Quonset solar drier. While, using Lean-to solar drier, the initial moisture content reduced from 73.56% w.b. into 5.35% w.b. within 12 hour achieving drying rate of 90.9 g/hr. For the duration of the experimental work, the hourly average thermal efficiencies for the Modified-Quonset and Lean-to solar driers, respectively, were 59.57% and 61.91%. The diurnal average solar drying efficiencies for the two solar driers during this research work were 20.45% and 25.51%, respectively. Therefore, the drying efficiency of the Lean-to solar drier was greater than that of the Modified-Quonset solar drier by 24.74%. Results also revealed that, the quality of dried product using Lean-to solar drier is better than Modified-Quonset solar drier. The very important content in the Stevia plants as a glycoside species, is the total sugar, which on an average slightly reduced (23.35%) due to drying process using Lean-to solar driers as compared with the Modified-Quonset solar drier when the total sugar reduced by 29.44%.

Heat transfer investigations on impinging flame jets of a multi-port convex burner

Multi-port curved surface burners are used in industrial boilers, preheating of large diameter pipes, textile industries, preheating of cylindrical metal billets and other industrial applications. The present work reports the heat transfer characteristics of convex shaped burner with 49 inline ports arranged in an array of 7 each. The methane-air premixed flame jets are impinged on the concave surface of a curved plate placed with radial spacing of 12 mm. Two different burners with port diameters of 2 mm and 3 mm with pitch to diameter ratio of 2.33 are used. The flame jet is studied for Reynolds number (Re) ranging from 75 to 200 and equivalence ratio of 0.9–1.5. The characterisation is done by impinging the pre-characterised air jets of various flow rates on the rear surface and capturing the wall temperature. The wall temperature is analysed to get the distributions of Nusselt number and effectiveness. The variation of coefficient of variance of Nusselt number, average Nusselt number and thermal efficiency is reported in the present work. The Nusselt number and effectiveness distributions increase with the increase in mixture Reynolds number. For a fixed mixture Reynolds number, the optimum heat transfer is obtained for stoichiometric flame. The thermal efficiency and average heat transfer of 2 mm port diameter is observed to be 18–25% higher as compared with burner with port diameter of 3 mm. Correlations are developed to predict the average Nusselt number, average effectiveness, coefficient of variance (COV) of Nusselt number distribution and thermal efficiency.