Heat Pipe Solar Collector Research Articles

Experimental studies of thermal performance of an evacuated tube heat pipe solar collector in Polish climatic conditions

This work presents the results of experimental studies on the energy performance of an evacuated solar collector, heat pipe type, consisting of 24 tubes, over the period of 2 months. The solar collector with a gross area of 3.9 m2 is part the solar hot water test system located in Lublin (Poland). The effect of the weather conditions and operating parameters on the thermal and exergy efficiencies of the evacuated tube solar collector has been defined. The solar irradiation per month for July amounted to 80 kWh/m2, and for August, it equalled 112.8 kWh/m2. The average thermal gain was found to be in July 163 W/m2 and in August 145 W/m2, respectively. For the considered study period, the average value of energy yield in the solar collector was obtained at the level of 4.28 MJ/(m2·d). The average monthly energy efficiencies of the solar collector in July and August were 45.3% and 32.9%, respectively, while the average monthly exergy efficiencies reached 2.62% and 2.15%, respectively. Increasing the wind speed to 0.86 m/s decreases the thermal efficiency and the exergy efficiency by 67% and 41%, respectively.

Comparative and performative investigation of various data-based and conventional theoretical methods for modelling heat pipe solar collectors

Solar collector, as the key component of any solar system, has always been the focal point of research in the field of solar energy. Based on the literature, data-based methods, which have been proven to be promising in accurate modelling of solar collectors, have not been used for modelling heat pipe solar collectors (HPSCs). At the same time, accurate equations relating the thermal efficiency of solar collectors to the operational and climatic conditions have not been obtained for HPSCs. Therefore, in this study, various data-based and energy balance-based modelling methods were proposed, and based on different accuracy criteria, their precisions were compared in predicting the performance of HPSCs. First, an experimental rig was manufactured and the operational data of the system was recorded throughout a year. The recorded experimental data was used to train and validate various modelling approaches. Then, the accuracies of the proposed models were analysed and assessed. The evaluated models included Artificial Neural Network (ANN), Thermal Resistance Network (TRN), Artificial Neuro Fuzzy Inference System (ANFIS), and Fuzzy methods. Among different modelling approaches, ANN had the best performance which was followed by the ANFIS and TRN methods. The Fuzzy method was not recommended due to its poor accuracy. In addition, the optimum equations relating the outlet temperature of HPSCs to the operational conditions of the solar water heating systems as well as the climatic conditions were obtained and verified.

On-demand dynamic performance of a thermal battery in tankless domestic solar water heating in the tropical region

This paper reports an experimental investigation of a new design of solar water heater (SWH) employing evacuated tube heat pipe solar collectors (HPSCs) and latent heat storage (LHS) as a thermal battery. In this design, the solar energy incident on the HPSC is collected and stored in the LHS tank via a heat pipe with fins attached to the condenser ends. The stored solar heat is then transferred to the domestic hot water supply via another set of finned-tube heat exchangers located inside the LHS tank. The experimental results of the on-demand performance of the latent heat thermal storage were reported under three different modes, which are weather condition, the daily volume of hot water production, and draw-off starting situation. Results indicated that this design of the thermal battery is able to provide the demanded hot water for households in any weather condition in a tropical climatic region like Malaysia. For a domestic application with solar collector size of about 2 m2, this design can provide at least 112–170 L per day in the worst weather condition. In a fully/partially sunny day, the thermal battery is able to provide much more hot water for domestic demands. It was also found that low thermal conductivity of the Paraffin is useful here, by preventing heat loss of the tank to ambient for long-term heat storage. Therefore, the system is able to provide hot water for the next morning normal usage.

Three-effect tubular solar desalination system with vacuum operation under actual weather conditions

Solar still is an environmentally friendly technology to mitigate water scarcity in remote area. However, the high cost and low efficiency limits its application. To this end, this study presents a novel three effects tubular solar still (TSS) with greatly improved productivity. This still features a cascade feed design and vacuum operation system, and consists of three enveloped distillation chambers, where each chamber comprises a water trough and a tubular shell. A prototype was fabricated and tested in an experiment conducted over four sunny days in Chengdu, China. The prototype TSS was powered by an evacuated heat pipe solar collector. The freshwater yield of the still was measured at four operating pressures: 95 (local atmospheric), 60, 40, and 20 kPa. Both the operating temperature and the temperature difference between the three chambers decreased when the operating pressure was reduced. The freshwater yields were 3.27, 6.323, 7.056, and 4.287 kg/d, respectively, with energy utilisation efficiencies of 0.77, 1.28, 1.39, and 0.88, respectively. The best overall performance was seen at an operating pressure of 40 kPa. At 20 kPa, freshwater yield and energy utilisation efficiencies were relatively low because of heat transfer deterioration on the outer shell at such low pressure. Based on the experimental results, the optimum operating pressure for the small-scale solar still was determined to be 40–60 kPa.

Heating the air in buildings by evacuated tube solar collector used AL2O3/ water nanofluid at Cairo-Egypt climates

The present paper investigates experimentally the performance of the evacuated tube heat pipe solar collector in Cairo-Egypt climate conditions. The experimental work conducts by using an evacuated solar collector with nanofluid in indirect building heating. The investigation parameters are tilt angle, AL2O3 nanoparticles concentrations, mass flow rates, water temperature difference, useful heat gain, collector thermal efficiency, air temperature difference, thermal optical efficiency and energy loss coefficients. The results show that the tilt angle 45o gives best performance characteristics of the collector. At tilt angle of 45o, 90 kg/h flow rate, 0.2% of nanofluid concentration and at 1:30 PM the air temperature difference increases by 16.4% than the reference fluid. The collector thermal efficiency increases by high concentrations of nanofluid, which reaches to 49%, 44.8%, 42.9% and 39% at a nanofluid concentration of 0.2%, 0.15%, 0.1% and 0% at 1:30 PM and 90kg/h, respectively. Also at low mass flow rate the air temperature difference increases by 9oC at 0.2% of nanofluid concentration.

Research on Impact of Nanofluids in Heat Pipes

The basic aim of this study is to study the impact of nanofluids such as (Al2O3+Distilled water) in complete liquid form by dispensing aluminium oxide (fluid form) in base fluidand also to investigate the thermal performance of heat pipe solar collector using nanofluids under real operating conditions by theoretically and experimentally.The experimental setup is made with heat pipes and real time temperatures are measured for experimental efficiency. The theoretical investigation is to be done by using Computational Fluid Dynamics (CFD).The main innovation done in this experiment is the nanofluid prepared in complete fluid form without particles suspension to avoid the settling of nanoparticles in thermo syphon setup.For long term applications, we opted this method of preparing the fluid. The operating parameters to be considered are solar intensity, effect of tilt angle and effect of working fluid. Finally, the experimental output is to be compared with the theoretical one (CFD). The efficiency of theoretical was higher than experimental because ofassumptions considered in CFD. The nanofluid filled with 25% of total capacity of heat pipe i.e. 25ml/pipe.Heat pipes are best energy conserving technology for solar energy conversion.

Experimental study of a large-area ultra-thin flat heat pipe for solar collectors under different cooling conditions

Due to the demands of thermal performance enhancement of heat pipe solar collector, the fabrication of large-area flat heat pipes with the advantages of low cost and outstanding thermal performance has become more urgent. In this paper, a large-area ultra-thin flat heat pipe (LUFHP) with multiple parallel microchannels was fabricated by the aluminum extrusion process. Its total thickness is only 1.5 mm while the effective width is 170 mm. The effect of different filling ratios on the thermal performance was investigated under natural air convection and forced water cooling, respectively, including heat transport capability and thermal resistance. The experimental results indicate that the maximum heat transport capabilities for natural air convection and forced water cooling are 40 W with an optimal filling ratio of 25% and 25 W with an optimal filling ratio of 30%, respectively. The minimum total thermal resistances of the LUFHP are about 0.22 °C/W (natural air convection) and 0.73 °C/W (forced water cooling), which decrease by 74% and 57% compared with these of aluminum plate, respectively. That is, the proposed LUFHP shows better thermal performance under NAC for the replacement of aluminum plate in a wider range of heat load.

Experimental investigation on the thermal performance of heat pipe solar collector (HPSC)

In this work an experimental study is made to find out the thermal performance of heat pipe solar collector (HPSC) using distilled water and R134a as working fluid. The HPSC is fabricated from the copper tube with the outer diameter of 58 mm and length of 1800 mm. The experimental work is carried out under different operating conditions. The input parameters such as temperature distribution and time on the thermal efficiency of the HPSC were investigated, compared and discussed. From the results, it is observed that the efficiency of the HPSC increases when R134a was used instead of distilled water.

An analytical and comparative study of the charging and discharging processes in a latent heat thermal storage tank for solar water heater system

Over the last decades, the science of solar cells has been substantially soared; however, the existence philosophy needs to follow almost the same mechanism due to the known limitations. Building upon this fact, until now, several generations of solar collectors have been introduced to the field of renewable energies. This current study reports an analytical investigation of the new compact design of evacuated heat pipe solar water heater integrated with latent heat storage tank. This device has a set of evacuated heat pipe solar collector (ETHPSC) arrays directly connected to a tank, which is filled by paraffin wax as the phase change materials (PCM). This work is carried out in two steps. Firstly, the system is modeled theoretically by applying the mathematical equations by using MATLAB in order to study the thermal performance of the thermal battery. Afterwards, a parametric and comparative investigation is conducted to study the performance of the system with different PCMs, different climate condition and different flowrates. This study is also carried out to compare the model with the conventional system. In the baseline system, and for the best chosen PCM, the system efficiency is between 32 and 42% in low solar radiation days, while it is in the range of around 40 ± 3% in the high radiation intensity days, whereas these magnitudes are ∼57% and higher than 50% in the new design, respectively. The efficiency of the new design, for all three types of PCMs, in a typical sunny day is in the range of the 36–54%, while, interestingly and positively, this efficiency increases to the range of 47–58% in a typical cloudy/rainy day. On the other hand, this trend happens reversely for the conventional system. Overall, the average efficiencies of the proposed system are increased from approximately 10% to 58% for three different PCMs in compared to the baseline.

Experimental study of water-based CuO nanofluid flow in heat pipe solar collector

The main goal of this study is the experimental evaluation of the thermal performance of heat pipe solar collector (HPSC) at different high flow rates of water and CuO–water nanofluid with various volume fractions. In this regard, a test bench of the HPSC was manufactured and tested in the laboratory of Vali-e-Asr University, while the co-precipitation method was used to prepare CuO nanoparticles. The structural and optical properties of the nanostructure were characterized by means of X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and UV–visible analysis. The collector efficiency and pumping power were calculated for nanofluids, and the results were compared with ones of water working fluid; based on the experimental results, copper oxide nanofluid and deionized water at a volume fraction of 0.017 and a flow rate of 14 L min−1 yields the greatest improvement in the efficiency of the solar collector. The results also showed that the efficiency of solar collector increases with the flow rate and the volume fraction of the nanofluid.

A Study of a Hybrid Heat Pipe Solar Collector with an Absorber Plate

Solar collectors have always been radical tools in the theoretical field of mechanical engineering as well as for any relevant establishment. Owing to uplifting demand for renewable energy sources, the investment for solar collector use is augmenting. Apart from flat plate or regular types, hybrid heat pipe solar collector could be taken for a neoteric type of solar collector. This research work aimed at designing and setting up a hybrid heat pipe solar collector and to evaluate the efficiency. A hollow copper pipe was used as heat pipe whose bottom end was closed by brazing a tiny solid copper block. Later the copper pipe was filled with acetone as the working fluid of heat pipe and by a burner, the bottom end of the pipe was heating until the pipe was filled with the vapor of acetone and then top of the pipe was closed by soldering. All other heat pipes, made of the same approach, were assembled then to an absorber plate touching the heat pipes forming the entire layout of heat pipe solar collector. The structure was then examined in the month of November and December and provided peak efficiency of about 27.44%. The efficiency could be properly enhanced by further research and examination of the methodology of fabricating the heat pipes.

Thermal performance of an evacuated tube heat pipe solar water heating system in cold season

This study evaluates the performance of a heat pipe solar water heating system to meet a real residential hot water consumption pattern theoretically and experimentally under non-ideal climatic conditions during a cold day in Perth, Western Australia. A mathematical model was developed and used to calculate the optimum number of glass tubes of the heat pipe solar collector. Based on the obtained data, an experimental rig with 25 glass tubes was designed, built, and tested as the temperature changes after 25 tubes reached the insignificant value of 0.6%. The results showed that hot water extraction had significant impact on the thermal performance of solar water heating system by increasing the amount of the absorbed energy and overall efficiency and decreasing exergy destruction. This indicates the importance of considering hot water consumption pattern in design and analysis of these systems. Auxiliary heating element was a necessary component of the system and played an important role mainly at the beginning of the operation in early morning (operation time of 19 min) and partly during the cloudy and overcast periods (operation time of 8 min). Two empirical equations relating the thermal and exergetic efficiencies of the heat pipe solar collector to the operational and environmental parameters were proposed. Comparison of the theoretical and experimental outlet temperature of the collector showed very good agreement with the maximum absolute and standard errors being 5.6% and 1.77%, respectively.

Improving the performance of heat pipe embedded evacuated tube collector with nanofluids and auxiliary gas system

An attempt was made to design an evacuated tube heat pipe solar collector (ETHPSC) with a gas package for a four-member family to supply the required energy and to evaluate the effect of different nanofluids on its performance. CuO, TiO2 and MWCNT nanofluids were used, whose performance was compared with water as the working fluid. The given system was tested in the weather conditions of Sanandaj city, Iran. The results showed the maximum temperature of output working fluid from collector was recorded in second half of august 2016 between 13:00 and 15:00 p.m. and in second half of October 2016 between 12:00 and 14:30, at which time solar radiation intensity and air temperature were at their maximum level. MWCNT, CuO and TiO2 nanofluids, owing to high thermophysical properties, had a better performance than water. The fuel consumption saving of the designed solar system, compared to the common package system, during the testing period was found to be 67.7% in August and 42.2% in October. With nanoparticles MWCNT, CuO and TiO2, compared to water, the efficiency of collector increased by 25%, 12% and 5%, respectively in August and by 25%, 15% and 7%, respectively in October.

Experimental investigation of heat pipe solar collector using MgO nanofluids

This paper investigates an evacuated heat pipe solar collector (HPSC) experimentally. The main aim was to study the efficiency of the HPSC. An experimental apparatus for testing solar heat pipe collectors was designed and built at Vali-e-Asr University. By using the two-step method, copper oxide and deionized water was prepared. The structural and optical properties of the nanostructure were characterized by means of X-ray diffraction (XRD), Fourier transform-infrared (FT-IR), scanning electron microscopy (SEM), and UV–visible analysis. Water or MgO-water nanofluid with varying concentrations was used as working fluids. The effect of the working fluid flow rates was also investigated and discussed. The effect of concentration of nanofluid was studied experimentally on the performance of solar heat pipe collector. The thermal performance of HPDC is determined through the experimental results by using this apparatus. The results reveal that the efficiency of the collector increases as the coolant flow rate increases. The efficiency of the heat pipe solar collector with MgO nanofluid is higher than ones with pure water. Also, performance enhances with the increase in the concentration of the nanofluid.

Alpha-tACS effects in working memory performance depend on both the number of relevant and non relevant items

In this work an experimental study is made to find out the thermal performance of heat pipe solar collector (HPSC) using distilled water and R134a as working fluid. The HPSC is fabricated from the copper tube with the outer diameter of 58 mm and length of 1800 mm. The experimental work is carried out under different operating conditions. The input parameters such as temperature distribution and time on the thermal efficiency of the HPSC were investigated, compared and discussed. From the results, it is observed that the efficiency of the HPSC increases when R134a was used instead of distilled water.

The Variation Effect of Collector Tilt Angle on the Heat Pipe Solar Collector Performance

The thermal performance of FPHPSC has been studied experimentally and theoretically. The collector consists of copper absorber plate, single glass cover, glass wool insulation and aluminum case, ten wickless heat pipes of 12.7 mm inner diameter. The experimental studies of collector performance have been performed on four different CTA (22°, 32°, 45° and 60°). The relation between the solar intensity and the collector energy losses are also discussed. The collector are tested under the climate condition of Kut city (32.602 latitude and 45.752 longitude). It is investigated that the increasing of CTA increase the efficiency of collector up to certain limit after that the efficiency decreases with the increasing of tilt angle of collector. A computer program which is based on VISUAL BASICE language (version 6) is made for the theoretical analysis. The experimental results agree reasonably with the theoretical predictions.

Experimental investigation of evacuated heat pipe solar collector efficiency using phase-change fluid

Performance of a microencapsulated phase-change material (PCM) as a heat-transport medium in an evacuated heat pipe solar collector was evaluated and the results compared with those using water. Collector efficiency was experimentally determined according to the method based on European Standard EN 12975–2:2006. This method proved unsuitable when using an encapsulated PCM suspension. A modified test method was proposed, which was appropriate for predicting solar collector efficiency when using a phase-change fluid. Average solar collection efficiency when using a PCM suspension was higher than that using water.

The Effect of Cooling Water Mass Flow Rate Variations on the Heat Pipe Solar Collector Performance

The thermal performance of FPHPSC has been studied experimentally and theoretically. The collector consists of copper absorber plate, single glass cover, glass wool insulation and aluminum case. Ten wickless heat pipes of 12.7 mm inner diameter. The experimental studies of collector performance have been performed on four different CWMFR (0.03, 0.04, 0.05 and 0.06) kg/s. The relation between the amount of useful heat, instantaneous collector efficiency and solar intensity is discussed. The collector are tested under the climate condition of Kut city (32.6 latitude and 45.7 longitude). It is investigated that the increasing of CWMFR increase the efficiency of the collector. The percentage increase in the efficiency of the solar collector is in order of (13%), when the cooling water mas flow rate changes from 0.03 kg/sec to 0.06 kg/sec at (45o) collector tilt angle. A computer program based on VISUAL BASIC language (version 6) used for the theoretical analysis. The experimental results are in agreement reasonably with the theoretical predictions.

Review of Thermal Performance and Efficiency in Evacuated Tube Solar Collector with Various Nanofluids

With the development of nanotechnology, building a new technology area in a variety of fields and achieving the best performance has become possible. Several studies on the performance of a solar heating system have been conducted using various nanofluids because the efficiency of heat transfer of nanofluids is high. Various previous studies, including theoretical, numerical, and experimental methods, were conducted using nanofluids for flat-plate, evacuated tube, direct solar absorption, parabolic trough, and heat pipe solar collectors. The present work provides an overview of the recent research on the performance of evacuated tube solar collectors using various nanofluids. The experimental and numerical results reported by several researchers, such as the thermal conductivity, heat capacity, and heat transfer coefficient of nanofluids, are first reported. The studies on the evacuated tube solar collectors with nanofluids were then investigated and summarized.

Thermal performance of a compact design heat pipe solar collector with latent heat storage in charging/discharging modes

This paper reports an experimental investigation on a design of solar water heater system (SWH) employing evacuated tube heat pipe solar collectors (HPSCs) and a latent heat storage (LHS) tank. In this design, solar energy incident on the HPSC is collected and stored in the LHS tank via a heat pipe with fins attached to the condenser ends inside the LHS tank. The stored heat is then transferred to the supply water via a set of finned pipes located inside the LHS tank. In this paper, the design, the working principles and the experimental thermal operations of the charging only and discharging only modes are presented. The effects of weather conditions in a tropical region and supply water flowrates and hot water draw off time are also reported. The thermal efficiency of the system in sunny days is in the range of the 38%–42%, while in cloudy-rainy days this efficiency drop to the range of 34%–36%, which indicates a range of about 8% fluctuation in different conditions. It was illustrated that the flowrate has direct proportion on the overall efficiency of the system in the tested range. Advantages of the heat pipe and phase change material together cover their disadvantages like overheating of the heat pipe and low thermal conductivity of the phase change material. By this design for energy storage tank, the thermal stratification effect is completely removed. This system could be a stand-alone system for night hot-water demands or part of a SWH configuration.