Evacuated Tube Research Articles

Residential Solar Thermal Performance Considering Self-Shading Incidence between Tubes in Evacuated Tube and Flat Plate Collectors

The performance of solar thermal technology under high-altitude equatorial climatic and solar path conditions has not been determined. Evacuated tube solar collectors are more efficient than flat plate collectors in cold and cloudy regions; however, due to their dependence on orientation, the irradiation incidence between the tubes of these collectors can be blocked. In this study, the performance of these types of collectors was analyzed to determine the implications of their orientation under these specific climate conditions. Four solar thermal systems were installed: two of the systems used evacuated tube collectors, and two used flat plate collectors. Each collector was connected to storage and discharge points to simulate residential consumption when observing the real performance of the four systems in terms of irradiation availability. The evacuated tube collectors were more efficient and reduced the backup energy requirement by up to 20.6% more on average than the flat plate collectors. In addition, the performance of the evacuated tube collectors increased by up to 9.8% when the tubes were arranged parallel to the solar path, compared to when they were arranged perpendicular to the solar path, verifying that the blockage effect is an important parameter to consider for evacuated tube technology. The main novelty of this research is the comparison of these two technologies under different orientations, with perpendicular and parallel dispositions toward the solar path, in a high-altitude equatorial location where solar collectors are not typically oriented in any particular orientation. To the best of our knowledge, this is the first complete analysis of real systems deployed under these conditions.

Performance Evaluation of an Evacuated Tube Collector with a Low-Cost Diffuse Reflector

In order to increase the overall solar energy gain of evacuated tube collectors, rear-side reflectors are used. In this way, the otherwise unused incident radiation between the tubes can be reflected back to the absorber, and the performance of the collector can be improved. In this paper, the use of a low-cost, diffusely reflecting, trapezoidal roof covering made from a galvanized metal sheet is investigated and compared to a high-quality, specularly reflecting plane reflector made of aluminum. For this purpose, ray-tracing analysis and TRNSYS simulations were carried out. In the ray-tracing analysis, the experimentally determined zero-loss collector efficiency η0 as well as the incident angle modifiers for each reflector can be reproduced with an error lower than 7.5%. Thermal system simulations show that the performance of both reflectors is comparable. The use of the low-cost reflector leads to an increase in annual collector output of around 30% compared to an increase with the specular reflector of around 33%. Considering a typical domestic hot water system, both reflectors enable an increase in the solar annual yield of approx. 11%.

Analytical Model for the Prediction of Performance of a Solar Driven Diffusion Absorption Cooling System

In contrast to standard vapor compression cooling systems, diffusion absorption refrigeration (DAR) systems are heat-driven and contain no moving parts. Solar diffusion absorption cooling systems can extract heat from a cooling chamber without electricity, enabling food and medicine to be cooled in remote places where there is high solar radiation with unavailable or unreliable electricity. This work aims to model the performance of a solar-driven DAR system with an evacuated tubes collector. The model inputs were the local hourly ambient temperature and solar irradiance for the time of June to August in Ashdod, Israel. Also, collector data, ammonia concentration in the solution, evaporator temperature and the DAR system geometry were considered. The model results showed that as the generator heat input increased rapidly the evaporator cooling capacity was kept almost constant for a given concentration and collector area. This resulted in reduction in the COP values at peak hour. An increase in the collector area had more impact on the heat applied to the generator and not resulted in a significant growth of the cooling capacity, thus, the authors concluded that for optimal COP it is advised to operate the system with lower collector areas.

Analysis of H2O/EMISE absorption chiller driven by stationary solar collectors in hot-humid climate

The performance of H2O/EMISE (1-ethyl-3-methylimidazolium ethyl sulfate) absorption chiller driven by stationary solar collectors including the flat plate collector (FPC), evacuated tube collector (ETC), compound parabolic collector (CPC) in hot-humid climate is the focus of this study. As a case study, the cooling capacity of the absorption chiller is constant at 100 kW and used for air conditioning in Guangzhou, China with the inlet/outlet temperature of cooling water fixed at 32/37 °C and the inlet/outlet temperature of chilled water set at 17/12 °C. The effects of heat source temperature between 78 and 100 °C on the thermodynamic as well as economic performance of the solar absorption chiller system have been analyzed and meanwhile the application potentials of the three candidate solar collectors are compared also. The results show that there is an optimum heat source temperature makes the coefficient of performance (COP) and exergetic efficiency (ECOP) of solar absorption chiller system maximum, which is featured with a shifting to lower values compared to the optimum one that leads to the COP of absorption chiller machine maximum. Besides, while the CPC absorption chiller system has the best thermodynamic performance with the overall COP and ECOP about 0.351 and 0.027, respectively, the ETC system becomes the most economic one with the specific investment cost about 1194 USD/kW. Recommendations are given based on the findings as resources to help the design of solar driven H2O/EMISE absorption chiller systems in the hot-humid region.

Design and Simulation of a New Solar Paraboloid Dish Collector

Solar energy utilization is vital for our society which faces the global warming problem and the increase in the prize of fossil fuels. Concentrating solar collectors are a promising technology for producing useful energy from the sun. In this study, an innovative concentrating collector with a paraboloid dish reflector is presented and simulated. The main idea of this collector is the use of a dish reflector for continuous heat production with a high concentration ratio. For this reason, a spherical receiver absorber with two linear insulated ducts is used. The cost of this system is relative low because there is not a glass cover but a tracking system is required. The final results show better performance than the typical collectors such as the flat plate collectors and the evacuated tube collectors, fact that makes this collector a promising solution. The design and the simulation are carried out with the commercial software Solidworks, in the flow simulation studio.

Techno-economic assessment of solar water heating systems for sustainable tourism in northern Pakistan

This study is designed to examine the feasibility of the solar water heating (SWH) system for sustainable tourism in Gilgit-Baltistan (GB) of Pakistan and a tourist resort is taken as a base case. Hot water demand, solar irradiance and economic feasibility are the key parameters considered to investigate the potential of SWH systems using simulation tool T*SOL. Three different types of solar collectors were investigated, based on solar fraction, maximum collector temperature and overall system efficiency. Among these collectors, the evacuated tube collectors (ETC) show high solar fraction, efficiency and CO2 emissions saved as compared to flat plate collectors (FPC) and unglazed collectors (UnGC), for both locations. The ETC shows 75 % solar fraction, 40 % efficiency, and 676 kg CO2 emission saved and payback period of is recorded 6.6 years for Gilgit. While for Skardu, 84 % solar fraction, 36 % efficiency, 756 kg CO2 emissions avoided and payback period of 4.6 years is analysed. Sensitivity analysis based on design parameters such as collector area, tilt angle and tank volume is performed to highlight the important design considerations. Based on the techno-economic analysis, it is concluded that ETC is the most feasible SWH system for the northern regions of Pakistan.

Performance evaluation of evacuated solar collector assisted hybrid greenhouse solar dryer under active and passive mode

The novel hybrid greenhouse solar dryer (HGSD) attached with evacuated tube collector (ETC) is developed for faster drying of high moisture content crops. The slow drying rate of high moisture crops lead to microbial attack on crop surface and have more chance of deterioration. Hence the HGSD is designed and tested for faster drying of crops. The experiments are performed to evaluate the performance of HGSD under active and passive mode. Ginger has been taken as a high moisture crops for the experimentation on two cases. In both the cases the ginger is dried from 79.8% to 9.82% moisture level (wb). In active mode, dryer takes 43.47% less time than the passive mode. The overall efficiency of the dryer in active and passive mode is 4.81% and 3.39% respectively. The lower drying time makes this dryer suitable for rural as well as commercial applications for drying agricultural or non-agro based products.

A study of unidirectional spiral tube for air evacuation in a solar heater with phase-change material

Solar air heaters combined with a phase-change material (SAH-PCM) have become a focus of research on the use of solar thermal energy. However, the specific heat of the air is small and the heat exchange efficiency is slow. In this study, we carried out three designs to improve the thermal efficiency of evacuated tube solar air heater including unidirectional flow, PCM-rod, and spiral tube. An experimental test platform was built to evaluate the thermal performance of the SAH-PCM, the temperature field and flow field in the vacuum tube were analyzed using ANSYS software, and the environmental assessment was also carried out. The numerical analysis obtained the optimal size of the PCM-rod, and also calculated the heat enhancement coefficient of the spiral tube to be 1.1. The experimental tests found that the outlet temperature fluctuation of the SAH-PCM could be effectively avoided, but the average outlet temperature is reduced by 31.5 °C; the heat loss rate was reduced by 58.5%; the thermal efficiency of PCM can reach up to 844.9%; the operating hours at night have been extended by more than 3 h. In addition, the correlation equation between the outlet temperature and the air flow rate is also established. Concerning the environmental aspect, the 8 m2 SAH-PCM can reduce CO2 emissions by more than 226.4 kg per hour. The results show that the structural design of unidirectional flow and spiral tube and the use of phase-change materials can improve the thermal performance of the air heater.

Decoupling the Monitoring of Solar Water Heaters and their Usage Profiles

South Africa is the most technologically advanced nation in Africa. However, the country is plagued with constant load shedding. The country receives about 2500 sunshine hours annually, with daily average irradiation levels of 4.5–6.5 kWh/m2. Despite these potentials, the use of electricity for domestic water heating is still prevalent in the country. The mass rollout of solar water heating (SWH) technologies in the low-cost housing sector across the country were met with massive failures. This study aims to assess the energy yield of a passive flat plate and an evacuated tube solar water heating system by evaluating the performance of these systems to address the energy crisis in South Africa. The flat plate (FP) and evacuated tube (ET) solar water heating systems were monitored for four days, characterised by varying sky conditions through instantaneous data measurement at 5 s. The parameters measured were water temperature, ambient temperature, irradiance at the plane of array, relative humidity, wind speed and direction. The results obtained show that a maximum irradiance of 1050 W/m2 was obtained on a clear day and corresponded to a hot water temperature of about 58 °C and 65 °C for the FP and ET, respectively. However, a cloudy day with a maximum irradiance of 400 W/m2 produced about 22 °C and 29 °C of hot water for the FP and ET, respectively. The results obtained in this study will guide stakeholders in the renewable energy sector towards employing SWH systems to replace or augment the electric geyser. Solar water heaters (SWH) can be used in the low-cost housing sector to provide hot water. Hence, the assessments in this study offer essential information for the deployment of these systems to reduce demand on the ailing South African electricity utility, Eskom, and mitigate climate change.

Transient simulation of a solar-based hydrogen production plant with evacuated tube collector and ejector refrigeration system

This article is a careful examination of an energy poly-generation unit integrated with an evacuated solar thermal tube collector. A proton exchange membrane (PEM) electrolysis unit is used for hydrogen production, an ejector refrigeration system (ERS) is utilized for cooling demand, and a heater unit is used for heating demand. All sub-systems are validated by considering recent articles. Cooling and heating demand, as well as the net output power are calculated. The modeled poly-generation system's exergy and energy efficiency are maximized by considering the inlet temperature of the heat exchanger and primary pressure of the ejector with the parametric evaluation of the system. The proposed poly-generation set-up can produce cooling load, heating load, and hydrogen with amounts of 5.34 kW, 5.152 kW, and 63 kg/year, respectively. Based on these values, the energy efficiency, and exergy efficiency are computed to be 64.14%, and 49.62%, respectively. Higher energy and exergy efficiencies are obtained by reducing high pressure of the refrigeration cycle or decreasing the temperature outlet of an auxiliary heater. The heat exchanger and thermal energy storage unit have the highest cost rate among all system components with 73,463 $ and 46,357, respectively. Parametric study indicates that the main determinative elements in the total cost rate of the system are the heater, and the solar collector.

Design Optimization and Simulation of an Ice Plant Working by Solar Adsorption Technology

This research presents a design optimization of a solar adsorption ice plant using activated carbon and methanol as working pairs in the climate of Makkah to produce a ton of ice per day. The plant consists of six adsorption refrigeration units. Each unit has 72 separate cylindrical adsorbent beds connected with its own condenser, valve, and evaporator. The unit is heated by seven evacuated-tube collectors connected in parallel. Then the total number of collectors are 42 collectors. The beds are filled by estimated amount of 540 kg of activated carbon with 178 kg of methanol. Selection and dimensioning of each component were carried out based on previous recommended values. A mathematical model and simulation were developed to validate the system performance along the year. The results showed that plant could produce up to ton of ice daily along the year. The coefficient of performance can reach 0.9 with condenser and evaporator temperatures of 35°C and -5°C respectively. The performance of the system is greatly affected by ambient temperature than solar radiation. Therefore, the best performance and largest amount of ice was found in the winter season.

CFD analysis of rib roughened solar evacuated tube collector for air heating

Using Computational Fluid Dynamics analysis, thermo-hydraulic performance of a rib roughened solar evacuated tube collector has been evaluated for different relative roughness pitch and mass flow rate values. Half portion of absorber tube is roughened and heated uniformly with a heat input of 1000 W/m2. The investigated roughness geometry parameters include relative roughness pitch (P/e) of the order 6–12 whereas relative roughness height is having a fixed value of 0.071. Reynolds number was varied from 2500 to 8000. In contrast to a smooth solar evacuated tube collector, Nusselt number and frictional resistance of a roughened solar evacuated tube collector increased by 1.88 and 2.89 times respectively. Thermo-hydraulic performance parameter of roughened solar evacuated tube collector was found to be 1.36 corresponding to Reynolds number and P/e values of 8000 and 10 respectively which indicates considerable benefit of applying rib roughness in a solar evacuated tube collector.

Performance Analysis of Solar Thermal Powered Supercritical Organic Rankine Cycle-Assisted Low-Temperature Multi-Effect Desalination Coupled With Mechanical Vapor Compression

Abstract Power and freshwater demand are increasing as populations around the world keep growing. Due to the environmental impact of using fossil fuels and limited resources, using solar thermal in desalination application is a valuable option. In this paper, an innovative new design of low-temperature multi-effect desalination coupled with mechanical vapor compression (LT-MED-MVC) powered by supercritical organic Rankine cycle (SORC) utilizing a low-grade solar heat source using evacuated tube collectors is analyzed. The proposed design has the potential to desalinate water of high salt concentrations or brine with high salinity more than 100,000 ppm or effluent streams from a power plant with low energy consumption and high efficiency when compared to other systems. The performance of the LT-MED-MVC was found to be better than similar systems found in the literature. The specific power consumption for the system is lower than 4 kW h/m3 for seawater feed salinity of 100,000 ppm, 14 forward feed effects, and a recovery rate of 50%. The overall system efficiency is about 14%. The impact of increasing the number of effects, motive steam temperature, pressure of SORC, and salt concentration on the specific power consumption, solar collector area, and the system efficiency are also analyzed.

Experimental parametric passive solar desalination prototype analysis

Passive solar desalination is a simple system that is convenient for use in arid areas. In this paper, an experimental investigation with a theoretical parametric analysis was performed for a passive solar desalination system composed of an evacuated tube collector integrated with a steel condenser. The impacts of the porosity of the stainless-steel wool in the evaporation section and the radiation shading for the condenser were examined. It was found that the less porosity of the stainless-steel wool achieves an overall efficiency enhancement of 5% compared to the maximum porosity. The condenser's shading achieved an overall efficiency enhancement of 12.4%, compared to the unshaded condenser's case. The theoretical analysis showed that the condensate increases with the increase of both ambient temperature and global solar irradiance, while decreases with the increase of wind speed. The theoretical model was validated with the experimental shading case with maximum error of 8.6% in the overall efficiency. The cost of the produced desalinated water reached 0.01287 $/kg/m2 in the proposed system.

An Experimental Study on Micro-Enhanced TESM Incorporated Inside Evacuated Tube Solar Collector Equipped with Heat Pipe

The incorporation of thermal energy storage materials (TESMs) into solar energy systems is a factor that boosts the performance of these systems. In this paper, an experimental study was addressed for enhancing the heat pipe’s thermal performance that works with an Evacuated Solar Tube Collector with Heat Pipe (ETCHP) as a solar water heater system. This is done by adding micro-zinc oxide (ZnO-MP) to the paraffin wax integrated as TESM into the evacuated tube (ET) of the system, where the evaporator section of the heat pipe is completely submerged within the micro-enhanced paraffin wax. Three experimental prototype rigs with one evacuated tube were designed, built, and tested to do the investigation. The most important parameters that have been studied in this study are the thermal resistance and the temperature distribution pattern along the heat pipe. The results show a clear indication of the decrease in the thermal resistance of the heat pipe of the proposed system compared to the system in which pure paraffin wax was incorporated. Also, it was noticed that there is a significant improvement in the temperature distribution along the heat pipe due to the improvement in the conductivity of the micro-enhanced wax compared to the pure wax.

Performance Analysis of Shell and Tube Type Heat Exchanger Using Aluminium Oxide (Al2O3) Nano-Particle

Abstract: Research in convective heat transfer using suspensions of nanometer sized solid particles in a base fluid started only over the past decade. Recent investigations on nanofluids, as such suspensions are often called, indicate that the suspended nanoparticles markedly change the transport properties and heat transfer characteristics of the suspension. The very first part of the research work summarizes about the various thermo physical properties of Al2O3 Nanofluid. In evacuated tube solar water heating system nanofluids are used as primary fluid and DM water as secondary fluid in Shell and Tube Heat Exchanger. The experimental analysis of Shell and Tube heat exchanger integrated with Evacuated tube solar collector have been carried out with two types of primary fluids. Research study of shell and tube heat exchanger is focused on heat transfer enhancement by usage of nano fluids. Conventional heat transfer fluids have inherently low thermal conductivity that greatly limits the heat exchange efficiency. The result of analysis shows that average relative variation in LMTD and overall heat transfer coefficient is 24.56% and 52.0% respectively. The payback period of system is reduced by 0.4 years due to saving is in replacement cost of Evacuated Tube Collector. Keywords: ETC; Nanofluid; LMTD; Thermal Conductivity; Overall heat transfer coefficient

Experimental investigation of a solar energy based cooking system for the steam method of cooking using evacuated tube collector

ABSTRACT The present manuscript includes the experimental performance investigation of a solar cooking system for the cooking of Indian articles using steam. The system incorporates a novel SCP (steam cooking pot), evacuated tube collector, and thermal oil as working fluid to generate steam. The Indian food items like idli, dhokla, and momos were prepared using the investigated solar cooking system with SCP. The preparation of these items has been carried out by loading the pre-requisite material in the SCP during different times of the day. The maximum and minimum time for the carried out cooking was observed as 95 min and 65 min for dhokla and momos respectively. The energy of the thermal oil flowing through the SCP was utilized for the cooking and its value was calculated. The maximum of the averaged values of thermal oil energy in SCP was observed 300 kJ during the cooking performed at 13:55 h. The study concludes that the proposed SCP incorporated solar cooking system can be useful over conventional solar cooker regarding the cooking of food items with steam and three times a day.

Modelling of solar thermal energy for household use in equatorial latitude by using the F-Chart model

The Andean Equatorial Region, due to its geographic location, shows great potential for using solar energy. Solar thermal energy is of interest in the residential sector in Ecuador and other Andean countries as a method to avoid fossilderived fuels consumption. However, previous learnings of the operation of solar water heating systems in other latitudes cannot be used in the conditions of Ecuador. Thus, the performance of the solar thermal energy systems in this geographic region deserves further study that consider typical high levels of cloudiness and fast climate oscillations. The objective of this work was to investigate the effect of the orientation of solar thermal plates on their energy efficiency and model the behaviour of these systems to predict their operation under Equatorial Andean climate conditions. For the F-Chart calibration different slopes angles were used, according to the typical roofs slopes in Cuenca, Ecuador. Results showed a monthly solar fraction, contributed by an evacuated tube collector is 26% higher than the flat plate collectors. The results also depict that, in the conditions of Cuenca, the greater solar water heating occurs when the collector is inclined 14° and facing towards the south. These findings can be used to predict the best operational conditions for using solar thermal energy collectors to produce hot water in the residential sector under equatorial highland altitude conditions.

Thermodynamic analysis and comparison of different absorption cycles driven by evacuated tube solar collector utilizing hybrid nanofluids

The utilization of hybrid nanofluids is the most attractive way to improve the heat transfer rate of solar thermal applications. Evacuated tube solar collector is one of the most important solar collector that is being utilized in thermal applications. The objective of the present study is to thermodynamically investigate and compare four different absorption cycles (namely, single, double, triple and quadruple effect absorption cycles) driven by evacuated tube collector and hybrid nanofluids are used as a heat transfer fluid. The operating parameters for instance, inlet temperature, direct normal irradiation, evaporator and generator temperatures are varied to assess the performance of different systems. Results showed that the efficiency of collector is higher for hybrid nanofluids as compared to the other heat transfer fluids. In addition, the coefficient of performance of quadruple effect absorption cycle is found to be 2.287, while it is 1.752 for triple effect system. The coefficient of performance of single and double effect cycles is found to be 169% and 88% less than the quadruple effect absorption cycle. The coefficient of performance of all systems increase with rise in the weak solution percentage due to the more vapor generated, while reduce as the generator temperature increases. Furthermore, hybrid nanofluid has the highest percentage of exergy destruction of 114.93 kW and quadruple effect absorption cycle is found to have the lowest exergy destruction rate, approximately 82.2 kW.

Real-Time Experimental Performance Assessment of a Photovoltaic Thermal System Cascaded With Flat Plate and Heat Pipe Evacuated Tube Collector

Abstract In response to the global quest for a sustainable and environmentally friendly source of energy, most scientists’ discretion is solar energy, especially solar thermal. However, successful deployment of solar thermal technologies such as solar-assisted process heating (SAPH) systems in medium- to large-scale industries is still in quandary due to their inefficacy in raising ample temperatures. Cascaded SAPH system, which is essentially a series combination of two same or different types of thermal collectors, may provide a worthwhile solution to this problem. In this article, performance assessment and comparison of two cascaded SAPH systems have been presented: photovoltaic thermal (PVT) cascaded with flat-plate collector (PVT-FPC) and PVT coupled with heat pipe evacuated tube collector (PVT-HPETC). Simulation models have been presented for individual FPC, HPETC, and PVT as well as PVT cascaded with FPC and HPETC systems in TRNSYS and validated through outdoor experimentation. Both the first and the second laws of thermodynamics have been employed to reveal veritable performance of the systems. Results show that PVT-HPETC delivers better performance with 1625 W thermal energy, 81.59% energy efficiency, and 13.22% exergy efficiency. It cuts 1.37 kg of CO2 on an hourly basis. Cascaded systems can be effective in sustaining industrial process heat requirements.