Pipe Evacuated Tube Solar Collector Research Articles

Heat transfer enhancement of a PCM-porous metal based heat pipe evacuated tube solar collector: An experimental study

Heat pipe evacuated tube solar collectors (HPETCs) are utilized in solar water heating systems, however, their thermal performance drops due to the intermittency of solar radiation. To overcome this issue, in this study phase change material (PCM) embedded with Copper (Cu) porous metal is directly integrated within the HPETC. For the purpose of comparison, the performance of the proposed system was evaluated in parallel with a conventional HPETC system under similar conditions. The thermal performance of each system is assessed based on the variation of fin temperature, outlet water temperature, exergy, energy efficiency and cost analysis. The results showed that when the value of solar radiation is at its peak, an increase of nearly 21 °C peak temperature was achieved for the evacuated tube filled with PCM + Cu porous metal. After sunset, the fin temperature difference of 36.1 °C was found between the conventional evacuated tube and evacuated tube filled with PCM + Cu porous metal. Moreover, the maximum water outlet temperature difference of 8 °C, 10 °C and 11 °C were found between two systems around at 10 PM on April 9–11, respectively. The proposed system reported maximum energy efficiency of 85.64% while the conventional system reported maximum of 36.91% daily energy efficiency. Lastly, combined system has showed 11.57% and 9.43% saving in hot water production cost for lifetime (Lt) of 5 and 10 years at 5% interest rate, respectively.

The performance response of a heat pipe evacuated tube solar collector using MgO/MWCNT hybrid nanofluid as a working fluid

Utilizing a hybrid nanofluid is a promising solution for enhancing the thermal performance of the solar collector in a sustainable manner. In the present work, the effect of using magnesium oxide/multi-walled carbon nanotubes (MgO/MWCNT) hybrid nanofluid on the thermal performance of the evacuated tube solar collector is experimentally investigated. Four different weight ratios of (80:20), (70:30), (60:40), and (50:50) are used for a hybrid of MgO with MWCNTs in a water base, respectively. The experiments are performed at a 0.02% particle concentration and at various volume flow rates ranging from 1 to 3 L/min. The results show an enhancement in the energy and exergy efficiencies with the increase in the weight ratios of MWCNTs nanoparticles and volume flow rate. The enhancement of the energy and exergy efficiencies of the collector is 55.83% and 77.14%, respectively, for MgO/MWCNT (50:50) hybrid nanofluid. It is found that increasing the weight ratio of MWCNTs nanoparticles from 20% to 30% achieves a significant increase in the collector efficiency enhancement compared to other hybrid nanofluids. The results conclude that MgO/MWCNT (50:50) performs better than all other hybrid nanofluids at all volume flow rates and is closer to MWCNT/water nanofluid.

Thermal performance investigation of energy storage based U-pipe evacuated tube solar collector: An experimental study

In this study thermal performance comparison of a custom made U-Pipe evacuated tube solar collector (ETC) vs commercially available heat pipe ETC (HPETC) was investigated experimentally. The performance comparison was performed over several days with and without thermal storage media. Results from testing without thermal storage media showed U-Pipe ETC achieved higher peak water temperatures than that of HPETC, maximum of 31 °C, resulting in 13% efficiency enhancement of U-Pipe ETC compared with HPETC. Results from testing with storage materials showed peak temperatures for fin and water tank of the U-Pipe ETC as 47 °C and 38.7 °C, respectively, whereas heat pipe showed values of 60 °C and 36.7 °C for max fin and water temperatures, respectively. Further performance enhancement to the U-Pipe ETC system was investigated through integration of phase change material (PCM)72 with added 1wt% multi-walled carbon nanotubes (MWCNT) nanoparticles. Peak temperatures recorded for this experiment were 63.9 °C and 43.3 °C for the U-Pipe fin and water tank, respectively. The results from this study show that the U-Pipe setup was able to achieve higher water temperatures than that of the HPETC setup. Incorporation of nano-PCM allowed for slower heat release in the water, extending useful duration of latent heat storage capability.

Effect of PCM material and vibration on the performance of evacuated tube solar collector

Abstract It can be considered that the solar collector is an essential thermal device, and it can be used to utilize solar energy via collecting and concentrating solar radiation. This system has many applications, such as water heating, building heating and other industrial applications. In this work, two new systems of heat pipe evacuated tube solar collector (HP-ETSC) were built. The first one was integrated with phase change material (PCM) and the second one without PCM. The first part investigated the effect of integrating PCM on the behavior and performance of HP-ETSC. While in the second part, the influence of applying vibration with different frequencies on the system to enhance the system’s overall performance and efficiency was studied. All executed tests were done in Iraq and during the winter season. It selected four cases, (1) system without integrated PCM, without applying vibration; (2) system without integrated PCM, with applying vibration; (3) system with integrated PCM, without applying vibration; (4) a system with integrated PCM, with applying vibration, to find the optimal system of them. The results proved that the system’s performance was enhanced.

Design optimization and heat transfer enhancement of energy storage based solar thermal collector

The application of solar collectors in water heating systems has attracted attentions in recent years, however, due to the inconsistency of solar radiation, performance of such systems will diminish over time. In this study, performance optimization of a heat pipe evacuated tube solar collector integrated with phase change materials (PCMs), is investigated under normal and on-demand operations. In phase-I, the effect of heat pipe position and in phase-II, the effect of various PCMs are investigated. The results from phase-I show phase change process of PCM was expedited by 48 min under on-demand operation compared with conventional system, where in normal operation, thermal storage enhancement is achieved by 24% increase in PCM’s melting fraction. In phase-II, the selected PCMs are tritriacontane paraffin, xylitol, and erythritol. In normal mode, the paraffin tube exhibited total energy storage of 295.39 kJ/kg, however, the fin temperature of xylitol tube was around 10 °C higher compared with the other tubes throughout the day. In on-demand operation, erythritol tube shows energy storage of 413.15 kJ/kg, however, the paraffin tube shows fin temperature difference of 14 °C compared with other tubes. Consequently, utilization of paraffin/xylitol in normal and paraffin/erythritol in on-demand operation is recommended to enhance system’s thermal performance.

Performance Evaluation of Dual Purposes Solar Heating System Using Heat Pipe Evacuated Tube Solar Collector

The aim of this work is to develop dual purposes solar heating system using a heat pipe evacuated tube solar collector. The heat transfer fluid between the thermal loads and the solar collector loop was heating oil. The study provided two thermal loads; a solar water heating system and a solar baking/cooking system that had experimentally investigated under various weather conditions. The experimental pilot unit was installed in the Solar Energy Department, National Research Centre, Giza, Egypt. Several test runs were performed to measure all assigned parameters that affect the system performance. The system is designed to provide hot oil surrounding the inner vessel of the baker with a temperature up to 250o C while the raw food can be baked/cooked and the outlet thermal energy can be used for heating water via an immersed coil in the hot water storage tank; then the relatively cooled oil is returned to the solar collector via hot oil circulating pump. The tested system can be positively contributed to baking and cooking purposes and providing hot water as well. It is considered an environmentally friendly system and can significantly enhance sustainable communities. The system is capable to produce hot water temperature up to 85 oC and an average temperature of about 60 oC during the day which is suitable for residential purposes and industrial process as well The auxiliary heating system can be an electric source in case of using in urban areas and can be renewable energy source like biogas or hydrogen fuels in rural and isolated areas.

Thermal performance of heat pipe evacuated tube solar collector integrated with different types of phase change materials at various location

This paper presents an experimental investigation of a new method of phase change materials (PCMs) integration in one or both the evacuated tube (ET) and two separated tanks adjacent to the water tank of heat pipe evacuated tube solar water heater collector (HP/ETC). In this method, the evacuated tube was filled with medical paraffin wax as thermal heat storage, while the two separated tanks were filled with paraffin wax (grade-A). Therefore, owing to the thermal isolation of the evacuated tube and PCM storage tanks, heat is efficiently accumulated and stored for a longer time. The advantage of this new method is that improved overall solar water heater performance by delayed heat release, thereby supplying hot water for a long time at high demand or when low solar intensity. Four HP/ETSCs with gravity assist heat pipe (GAHP) rigs were used for a comparative study. The first HP/ETC was equipped with PCM in its ET and two PCM storage tanks. The second and third HP/ETCs were integrated with PCM in an ET and two PCM storage tanks, respectively. While the fourth HP/ETC was considered a reference as it was left without PCM. Each heat pipe was filled with a 0.7 filling ratio of pure acetone. The tests are carried out with two different rates of water flow (i.e. 1 and 2L/h). The results demonstrate that the integration of PCM in both the ET and the separated tanks gives an efficiency improvement of 55.7%, While the integration of PCM in the ET led to an increase in the efficiency of 49.9%. Whereas the efficiency has been improved with the integration of PCM in the separated tanks by about 36.5%, compared with PCM-free reference collector.

The Influence of Exciting Vibrational Force on the Performance of Evacuated Tube Heat Pipe Solar Collector

In this research paper, it examined the effect of excitation vibration force on the thermal performance of the heat pipe evacuated tube solar collector (HPET-SC). The main target of this work is to predict the temperatures of the water when applied different values of excitation vibration force (frequency). In order to achieve these tasks, it was designed and implemented a new test rig (HPET-SC) from scratch, that containing the vibration unit to generate the excitation vibration force. We added a control board to regulate the magnitude of frequency of the excitation vibration force. The range of the vibration frequency is from 6 to 14 V. All results were compared with the reference case study (static case). All tests were done in Iraq during the winter season. It was found based on the obtained results, that the vibration has a influence on the performance of the heat pipe evacuated tube solar collector, especially when applied the vibration force with high frequency.

Study the Effect of Phase Change Material on the Performance of Evacuated Tube Heat Pipe Solar Collector under Iraqi Climatic Conditions

This work presents an experimental study to investigate the effect of integration phase change material (PCM) on thermal performance and efficiency of heat pipe-evacuated tube solar collector (HP-ETSC). The experiments were conducted under the Iraqi weather condition during the winter season (January, February, and March). To thoroughly investigate the thermal performance of HP-ETSC, a new experimental test rig was designed and manufactured based on standard criteria. The results showed that when integrating PCM with the system, it can significantly enhance the thermal capacity of the HP-ETSC system. The efficiency is increased by 3-5% and maintains the high temperature of water for a longer time at night. Moreover, the coefficients of evaporator heat transfer (EHTC) and condenser heat transfer (CHTC) of the heat pipe are also increased. The results from the developed HP-ETEC system are promising, and this experimental model can be applied using different types of phase change materials that are suitable to be used in Iraq.

Energetic and exergetic analysis of a heat pipe evacuated tube solar collector using MWCNT/water nanofluid

Increasing the energy demand and the limited availability of conventional energy sources are the main challenges to secure the human future. Solar energy is an attractive source of energy to ensure the sustainability of energy in this world for now and for the future. Evacuated tube solar collector is a solar thermal collector mostly used for domestic applications. The replacement of the working fluid with nanofluid can enhance the heat transfer even for low temperature applications. The effect of multi-walled carbon nanotubes and water nanofluid as working fluid in evacuated tube solar collector is used to experimentally investigate the energy and exergy efficiencies of the collector. Weight fractions of 0.005%, 0.01% and 0.05% were used in the investigation at flow rates from 1 to 3.5 L/min. The efficiency analysis of the collector was made as ASHRAE Standard 93–2010 stated. The results showed increase in energy and exergy efficiencies with the increase of volume flow rate and the concentration. The highest average energy and exergy efficiency achieved with 0.05 wt% MWCNT/water nanofluid were 55% and 10% respectively. The overall heat loss coefficient decreased with the increase of the concentration. It was found that 2 L/min were a critical flow rate and the behaviour of the system changed afterwards.

CFD modeling of a thermal energy storage based heat pipe evacuated tube solar collector

Abstract The increase in greenhouse gases makes it necessary to utilize renewable energy sources such as solar energy. The most important component of any solar system is solar collector. Among various types of solar collectors, evacuated tube solar collector (ETC) has attracted many attentions especially for the application in solar water heating systems (SWHs). However, due to the intermittency in solar intensity, the ETCs may not work at their maximum functionality. In this study, the computational fluid dynamics (CFD) modeling of a heat pipe ETC (HPETC) with and without the integration of phase change materials (PCMs) is performed. In order to cross-validate the obtained results from CFD and recent experimental analysis, the boundary conditions are set as the field-testing data. In phase-I, the 3D model of commercially available HPETC is simulated, while in phase-II, the HPETC integrated with the PCM is developed. The selected type of PCM is Tritriacontane paraffin (C33H68) with melting point of 72∘C. The simulation results show an acceptable agreement with the experimental data with an average deviation of 4.80% and 2.04% for phase-I and phase-II, respectively. The result from this study can be a benchmark for further optimization of HPETCs in thermal energy storage systems.

Thermal performance of phase change material integrated heat pipe evacuated tube solar collector system: An experimental assessment

This manuscript presents an experimental investigation of heat pipe evacuated tube solar collector with and without phase change material for water heating application under the same weather conditions. In this study, a comparative analysis of two systems has been done in the same weather condition. Where evacuated tubes of the first system (evacuated tube collector-A) were left without phase change material and second system (evacuated tube collector-B) was integrated with SA-67 as phase change material. In order to ensure the thermal and chemical stability of the selected phase change material, thermal cycling treatment was carried out. The results showed that SA-67 has excellent chemical and thermal stability even after 1500 thermal cycling treatment.In order to analyze the thermal performance of the designed systems, the experiment was conducted with five different water flow rates (8, 12, 16, 20 and 24 L per hour). The daily thermal efficiency of evacuated tube solar collector with and without phase change material was varied in the range of 42–55% and 79–87% respectively. Although, the daily energy efficiency of evacuated tube collector integrated with phase change material was 37.56%, 35.31%, 36.69%, 32.34%, and 32.73% higher than evacuated tube collector without phase change material for water flow rates of 8, 12, 16, 20 and 24 L per hour respectively. The daily thermal efficiency for both systems was maximum at the flow rate of 20 L per hour. The heat transfer parameters for the designed systems have also been evaluated and compared.

Experimental performance evaluation of a novel designed phase change material integrated manifold heat pipe evacuated tube solar collector system

In this study, the thermal performance of a novel solar collector integrated with stearic acid as phase change material has been investigated. In this design, the solar radiation was collected by heat pipe equipped evacuated tubes and then stored in manifold integrated with phase change material. The stored thermal energy of phase change material then transferred to water flowing through bundle of finned copper pipes placed inside the manifold. In present study, the design, the operating principle and the experimental investigation of the developed system have been presented. The developed system was investigated with different mass flow rates and also discussed the influence of varying mass flow rate on the thermal performance of system. The experimental investigation of designed and developed system has been carried out for two modes i.e. mid-day charging mode and full-day charging mode. It has been observed that for considered mass flow rates, thermal efficiency of the system was varied in the range of approximately 52–62% for full-day charging mode while for mid-day charging mode, it was varied between 55 and 72%. The maximum value of thermal efficiency was approximately 72.52% at mass flow rate of 24 LPH for mid-day charging mode. The efficiency of phase change material for both modes was varied in the range of approximately 61–64%. The annual cost and annual fuel cost of the developed system are much lower than conventional system. Also, the initial capital cost for the developed system can be recovered after 6 years of operation. However, there is no recovery of initial investment for electricity based water heating system.The proposed system overcomes two problems associated with conventional heat pipe evacuated tube solar collector: elimination of heat pipe overheating problem and low thermal conductivity of phase change materials. By this novel design of manifold, the influence of thermal stratification on the thermal performance of solar collectors can be completely eradicated.

CFD modeling and evaluation the performance of a solar cabinet dryer equipped with evacuated tube solar collector and thermal storage system

This paper investigates the performance of a solar cabinet drying system equipped with a heat pipe evacuated tube solar collector (ETSC) and thermal storage system with application of PCM. The thermal analysis of the solar collector, drying efficiency, CFD modeling of the system and quality evaluation of dried apple slices was considered. The performance of the dryer was simulated and validated by experimental data. The experiments was conducted at three air flow rates (0.025, 0.05 and 0.09 kg/s) for the drying system with and without using PCM for drying apple slices with the thickness of 5 mm. The result of thermal analysis showed that using PCM increases the input thermal energy about 1.72% and 5.12% for the air flow rates of 0.025 and 0.05 kg/s respectively, but excessive increase in air flow rate (up to 0.05 kg/s) decreases input thermal energy. The maximum overall drying efficiency was related to the system with PCM at the air flow rate of 0.025 kg/s and it was 39.9%. CFD simulation of the storage system and the dryer showed that there is a good agreement between the simulated and experimental. Using PCM has no adverse effect on the quality of the dried product.

Theoretical and experimental studies of impacts of heat shields on heat pipe evacuated tube solar collector

The heat pipe evacuated tube solar collectors, which is non-concentration, no-tracking and working at medium temperatures, suffer from low efficiency and thus rare application. The heat loss exerts serious negative influence on its performance at high operation temperatures. Thus, heat shields were introduced between the absorber plate and the glass tube to decrease the heat loss. Experimental and theoretical work were conducted to evaluate the thermal performance of the novel and traditional heat pipe evacuated tube solar collectors. According to the experimental results, the heat shields improved thermal efficiency at inlet water temperature of approximately 20 °C–150 °C, and the solar collector performed better at higher inlet water temperatures. The thermal efficiency of the novel one was enhanced by 11.8% at the inlet temperature and solar radiation of approximately 150 °C and 820 W/m2, respectively. Moreover, the novel one’s efficiency coefficients in the instantaneous efficiency curves, which can reflect the decrease rate of instantaneous thermal efficiency, resulted in decrease of 28.4% and 29.9%, respectively. Meanwhile, simulated results showed that, the thermal efficiency increments of novel collector over traditional one increased at weaker solar radiation and lower ambient temperature at each inlet water temperature.

Improving the performance of heat pipe-evacuated tube solar collector experimentally by using Al2O3 and CuO/acetone nanofluids

Research has been undertaken on heat pipe evacuated tube solar collector (HP-ETSC) for hot water applications, which is common in most Middle East regions. The enhancement in thermal performance by using various types of acetone based nanofluids has been explored. This work includes two experimental parts of the gravity-assisted heat pipe (GAHP) installed in evacuated tube solar collector system. The first part is designed to reach the optimal performance conditions for HP-ETSC which is charged with acetone as a working fluid inside the GAHP. Various values of filling ratios (40, 50, 60, 70 and 80%) and tilt angles (30°, 45° and 60°) are considered. The results show that there is an optimal performance at filling ratio equal to 70% and inclination angle equal to 45° when compared with other values during the course of study. This indicates that the importance of fully integrating design process right from the outset of the system design if GAHP is to be installed into an ETSC system to give the maximum possible solar energy benefits of efficient hot water solar collector designs. The main objective of the second experimental investigation is analyzing the impact of the two types of nanofluid (Al2O3 and CuO/acetone-based) on the thermal performance of the HP-ETSC. These two nanofluids are used as working fluid inside the GAHP and two concentration values (0.25% and 0.5% vol.) at the optimal conditions from the first experimental part. On the basis of the present study, it is recommended that HP-ETSC systems should be charged with nanofluids for thermal performance enhancement (20–54%) and efficiency (15–38%).

Thermal performance of a thermosyphon heat pipe evacuated tube solar collector using silver-water nanofluid for commercial applications

Abstract An experimental study was performed to determine the thermal efficiency of thermosyphon heat pipe (THP) evacuated tube solar collector using silver-water nanofluid for commercial applications. Firstly, the synthesis of silver-water nanofluid was carried out which can maintain its long-term stability. The identification of nanofluid was determined by X-ray diffraction, scanning electron microscopy, UV–visible spectroscopy and thermophysical analysis. Secondly, the heat transfer properties of cylindrical copper THPs charged with silver-water nanofluid and pure water was investigated experimentally. Experiments of THP charged with silver-water nanofluid were repeated four times at intervals of two weeks in order to observe changes in the performance of THP. It was observed that the THP charged with silver-water nanofluid maintained its improved heat transfer characteristic in the THP experiments. Nanofluid working fluid increased the efficiency of solar collector between 20.7% and 40% compared with the pure water. In conclusion, the experimental results show the use of silver-water nanofluid provides a significant improvement in the THP evacuated tube solar collector.

Design of Evacuated Tube Solar Collector with Heat Pipe

The Renewable source of energy is the future energy source that meets out our demand for energy. In this solar energy is one of the prime sources. The harnessing of the solar energy can be done in both ways Solar (PV), Solar Thermal. Solar thermal finds more suitable for domestic needs such as Space Heating, Cooling, Hot water systems, drying. Hence the need for producing thermal energy from the collectors is important. Out of all the thermal collectors the evacuated tube solar collector (ETSC) is found to have the best efficiency with low solar insolation. In this paper the evacuated tube is modelled with heat pipe for the enhancement of the heat generated from the collector. The objective of this research is to design and investigate the heat transfer analysis of Heat Pipe Evacuated Tube solar collector is made of Borosilicate glass with length 1.8m and 0.058m and 0.049m diameter of outside and inside tubes for the Coimbatore location.

Energy and exergy evaluation of an integrated solar heat pipe wall system for space heating

In this paper, an integrated solar heat pipe wall space heating system, employing double glazed heat pipe evacuated tube solar collector and forced convective heat transfer condenser, is introduced. Thermal performance of the heat pipe solar collector is studied and a numerical model is developed to investigate the thermal efficiency of the system, the inlet and outlet air temperatures and heat pipe temperature. Furthermore, the system performance is evaluated based on exergy efficiency. In order to verify the precision of the developed model, the numerical results are compared with experimental data. Parametric sensitivity for design features and material associated with the heat pipe, collector cover and insulation is evaluated to provide a combination with higher thermal performance. Simulation results show that applying a solar collector with more than 30 heat pipes is not efficient. The rate of increasing in temperature of air becomes negligible after 30 heat pipes and the trend of the thermal efficiency is descending with increasing heat pipes. The results also indicate that at a cold winter day of January, the proposed system with a 20 heat pipe collector shows maximum energy and exergy efficiency of 56.8% and 7.2%, which can afford warm air up to 30°C. At the end, the capability of the proposed system to meet the heating demand of a building is investigated. It is concluded that the best method to reach a higher thermal covered area is to apply parallel collectors.

Exergy Analysis of a Solar-Driven Dual Parallel-Connected Ejector Refrigeration System

Nowadays, developing solar cooling technologies, especially ejector refrigeration system, has become preferable to scientific researchers. Exergy analysis is a technique in which the basis of evaluation of thermodynamic losses follows the second law rather than the first law of thermodynamics. An experimental exergy analysis of a solar-driven dual parallel-connected ejector (DPE) refrigeration system was conducted using water as working fluid. Saturated steam with 2 bar and 120oC was provided by heat–pipe evacuated tube solar collector with an assistant of an electric heater. The saturated stream was used as a motive flow for the ejectors. The exergy destruction and exergetic efficiency of the main components of the DPE refrigeration system were determined and compared with those when using a single ejector (SE) under same operating conditions. It was found that the most irreversibilities of both systems occurred at the solar collector, electric boiler and ejectors, respectively. Also, the total irreversibility (Exergy destruction) of the system when using DPE was lower than using a SE. In additions, the exergetic efficiency of the ejector, evaporator, and overall system when using DPE were increased by 21%, 10%, and 27%, respectively. The system thermal ratio (STR) and coefficient of performance (COP) of the system using DPE compared with SE were increased by 20% and 23%, respectively.