Absorber Pipes Research Articles

Simultaneous energy storage enhancement and pressure drop reduction in flat plate solar collectors using rotary pipes with nanofluid

Flat plate solar collectors waste a massive part of the heat accumulated near the contact region, mainly due to poor thermal characteristics of working fluid. The demanding power for pumping the flow through the pipes seems a permanent concern in solar collectors. Also, active methods seem not to be applicable in such systems due to the external energy requirement and cost associated with it. An innovative and simple technique is considered here to eliminate such deficiencies all at once by equipping the flat plate collector with rotary absorber pipes and Fe3O4/water nanofluid. Results indicate that the applied method improves the convection mechanism in each pipe by mixing the accumulated heat in the whole flow regions and saves more available solar energy. It also reduces the pressure drop by preparing a slip flow condition inside the pipes, thereby reducing the consuming pumping power. Results also reveal that by dispersing 2% Fe3O4 in water and utilizing rotary pipes one can restore around 1.65% and 10.44% of the energy loss of the collector, respectively. In other words, additional energy of 120.16 W can be stored by equipping a flat plate solar collector with rotary tubes and Fe3O4/water nanofluid. Also, equipping the collector by both rotary pipes and nanofluid causes 5.83% and 3.21% enhancement in energy and exergy efficiencies, respectively. The reported results substantiate that the required power for operating the employed method can be provided by the collector itself, which makes the proposed technique more cost-effective.

INVESTIGATIVE STUDY OF THERMAL PERFORMANCE OF THERMOSYPHON SOLAR COLLECTOR

Experimental and Numerical investigation has been performed to improve the thermosyphon thermal performance. Optimization process concentrated on both the water and the operating liquid temperature inside the tank and the thermosyphon. For this purpose, three different models of improvement methods have been studied that depend on increasing the surface area with no changing in the volume of operating liquid. The first one (case-A-) is by add ten ring fins about the absorber pipe. The second method (Case-B-) is by add twenty ring fins about the absorber pipe. While, the third way (Case-C-) is by add ten ring fins with ten grooves about the absorber pipe. The thermosyphon thermal performance was compared between the traditional model and experimental model. Moreover, numerical simulate for all cases were done with computational fluid dynamic (CFD), ANSYS 19.R3. It was observed through the results that a good convergence between the numerical and, experimental results. Furthermore, the thermal performance for case-A- is found greater than all other cases under study.

Energy, exergy, enviroeconomic & exergoeconomic (4E) assessment of thermal energy storage assisted solar water heating system: Experimental & theoretical approach

In this study, exergy, energy, enviroeconomic & exergoeconomic analysis of evacuated tube collector with/without latent heat storage material has been done for different flow rates i.e. 0.13, 0.26, 0.40 & 0.46 LPM. In this manuscript, palmitic acid has been used as a latent heat storage material. The storage material was filled in the annuls between the absorber pipe and heat pipe termed as palmitic acid integrated evacuated tube collector system while another heat pipe based evacuated tube collector system was tested without latent heat storage material termed as evacuated tube collector without storage system. The results of the experimental investigation revealed that daily thermal & exergy efficiencies of palmitic acid integrated evacuated tube collector increased in the range of 36-44% and 28-35% respectively in comparison to evacuated tube collector without storage.Furthermore, storage based evacuated tube collector system mitigated 21-28 tCO2/lifetime and 6-8 tCO2/lifetime based on environmental and exergoenvironmental approaches respectively. Whereas, evacuated tube collector without storage mitigated 14-19 tCO2/lifetime and 4-6 tCO2/lifetime based on environmental and exergoenvironmental approach respectively. In comparison to collector without storage, the revenue generated by collector with storage was found to be 95-112 $/lifetime and 22-25 $/lifetime higher based on energy and exergy approach respectively.Overall, palmitic acid integrated evacuated tube collector based continuous flow solar water heating system found to be the most promising system comparison to the collector without storage for different selected flow rates of water.

Assessing the thermal efficiency of energy tunnels using numerical methods and Taguchi statistical approach

The use of ground source heat pump systems (GSHPs) with tunnels (so-called energy tunnels) to provide space heating and cooling is one of the latest concepts that has recently raised research interest but has not yet been commercially established. This study represents the first attempt to investigate the influence of design parameters on the energy efficiency of a GSHP using an underground tunnel as the energy geostructure. Seven important design parameters, namely absorber fluid diffusivity, concrete diffusivity, pipe thermal conductivity, pipe diameter, length of pipe, pipe spacing and absorber pipe location were considered. The influence of these design parameters on the tunnel thermal efficiency was studied by using an experimentally validated 3-D numerical model and then deploying the Taguchi method to efficiently explore parameters space. The results show that concrete diffusivity and pipe total length are the most influential parameters, followed by the pipe location and diameter, while spacing was found to be the least influential factor. Hence the overall thermal output of an energy tunnel depends largely on the available area for heat exchange and the thermal properties of the tunnel lining. Results also show that within the range of pipe diameter considered, using a larger pipe diameter in energy tunnels is more efficient from the thermal output and pump power requirements. These results can be used as thermal efficiency optimisation guidance for both researchers and practitioners.

Nanofluid migration within an absorber pipe of solar unit considering radiation mechanism

To intensify the efficiency, T-shaped fins were utilized inside the tube in current LFR unit. Various configurations of fins with same volume were employed. The carrier fluid is Al2O3-water and turbulent regime was considered. Incorporating DO model and solving pure radiation results in distribution of radiation flux around the tube which is employed as source term in energy equation. Convective transportation with ambient was considered in outer wall. Various inlet temperature and velocity for four cases were examined and outputs were shown in term of plots and contours. Thermal and energy efficiency, irreversibility component and Bejan number were main outputs of this paper. Outputs indicate that selecting Case A leads to obtain the maximum turbulent fluctuation and lowest temperature of outer wall. Replacing Case C instead of A makes temperature of surface to augment about 0.19% while pressure drop decreases about 23.72%. Rise of Re for Case A leads to decrease of Darcy factor about 26%. Highest Nu belongs to Case A and it increases about 79.82% with rise of Re. Lowest values of total irreversibility belongs to case A and growth of Re lead to reduce Sgen,h about 41.88%. Also, this case has minimum value of Be. The highest exergy and thermal efficiency belong to case A. Augment of Tin makes $$\eta_{th}$$ to decline about 23.46% while $$\eta_{ex}$$ augments.

Coupled optical and thermal analyses of a new type of solar water heaters using parabolic trough reflectors

A new type of solar water heating system using an array of parabolic trough collectors (PTCs) was investigated. A coupled simulation technique was used to solve the complex radiation, convection, and conduction heat transfer problem inside the system. The realistic non-uniform heat flux at the walls of the receiver pipe was obtained by optical analysis and was used simultaneously in thermal modeling. A comprehensive model by considering thermal losses under the non-uniformity of heat flux was proposed and verified with experimental data. In the experiments, the water with different inlet temperatures and flow rates was tested. The obtained results demonstrate that the location of the receiver pipe relative to the PTCs significantly affects the system's thermal efficiency. For the system under study, the best position of the absorber pipe was found at the d/f ratio of 0.8. At the optimal position of absorber pipe, the average daily system's thermal efficiency is about 70%, and for an absorber pipe located at the focal line of the collectors, it is less than 60%. It can be concluded that the thermal efficiency of the current system is higher than that of conventional systems under the same conditions.

UNJUK KERJA KOLEKTOR TABUNG PEMANAS AIR PADA SAAT CHARGING MENGGUNAKAN PHASE CHANGE MATERIAL (PCM) DENGAN DAN TANPA REFLEKTOR

In solar powered water heaters, solar radiation falls into and then absorbed by tube collectors which are then used as a source of water heaters for household and industrial needs. One effort to improve efficiency in solar-powered water heater systems is by adding a reflector under the collector. The main purpose of this study is to find out the effect of the reflector on the collector's efficiency during the charging period. The tube collector consists of absorber pipes, water pipes, and reflector. While the parabolic reflector is made of stainless to maximize reflection to the collector. In these experiments, the water flow was varied at 0.48 l/min, 0.59 l/min, and 1.82 l/min. Temperature measurements were carried out at several points: (i) inlet, (ii) outlet and (iii) phase change material (PCM). While radiation intensity was measured using a pyranometer. The data were compared between heater with and without the reflector. The highest collector efficiency was achieved when applying 1.82 l/minute with the maximum collector performance with reflector and without a reflector is 76.8% and 69.7% respectively. It is be concluded that the use of reflectors can increase the efficiency of tube collectors for water heaters. The outlet temperature was higher by 1.7% than the previous result when using water flow rate of 0.59 l/min.

Analysis and assessment of a nanoparticle seeded small scale absorption refrigeration system driven by a low‐grade waste heat source

AbstractThe thermoeconomic behaviour of a nanoparticle seeded single effect LiBr‐H2O absorption refrigeration system (ARS) is investigated for a small scale application. In the proposed method, alumina nanoparticles with volume concentrations of 3%, 5%, and 7% are dispersed into an aqua lithium bromide solution. The multiobjective heat transfer search algorithm is employed to examine the design trade‐off between the coefficient of performance (COP) and total annualized cost (TAC). To analyze the overall performance of the system, the influence of five design parameters, namely the temperatures of the generator, absorber, evaporator, condenser and heat exchanger pipe diameter, are studied. It is found that with an increase in the COP, the TAC of the system is initially raised marginally, and after that, raised rigorously with further increment. The comparative results indicate that the COP and TAC of the nanofluid based ARS system are increased by about 7% and decreased by about 3.2%, respectively, corresponding to the Pareto points of the base ARS system. A lower break‐even point of about 2.6 years is achieved for the ARS system containing nanoparticles compared to the base ARS system. Overall, the ARS system containing 5% nanoparticles is the best solution from a thermodynamic and economic point of view.

Investigations into thermal resistance of tunnel lining heat exchangers

Geothermal energy is a promising and sustainable source that can reduce current dependence on conventional fuels for thermal energy production. To exploit this source of energy thermo-active geostructures such as tunnel lining heat exchangers are being investigated theoretically as well as experimentally. These geostructures are composed of concrete panels embedded with reinforcement cages fitted with absorber pipes. Several engineering projects in China, Finland and Italy have deployed such heat exchangers in tunnels. To achieve efficient energy production, characterisation of these systems require realistic models of the substructure heat exchanger. Therefore investigations into thermal resistance of the heat exchanger is vital. The present study is concerned with quantifying the thermal resistance of tunnel lining heat exchangers where the thermal boundary surfaces are applied at surfaces representing the adjacent ground and the exposed concrete, in addition to the pipe surface. Steady state temperature distribution in a two dimensional cross section of a tunnel lining heat exchanger is investigated using the boundary collocation least squares method. Design parameters including pipe and tunnel lining specifications are used as model inputs.

Experimental and simulated performance of hot mirror coatings in a parabolic trough receiver

Thermal radiation is the dominant heat loss mechanism for receiver units on a parabolic solar collector plant at high temperatures. Reduction of these losses is traditionally achieved through the use of an optically selective coating on the absorber pipe, which absorbs visible light well but emits poorly in the IR region. Another possibility is the use of a hot mirror coating on the glass cover of the receiver, which reflects thermal radiation back onto the absorber pipe for reabsorption. In this paper, novel experimental results of a receiver unit operating with a hot mirror coating are presented, and the results between a developed model and a simulation are compared. It is seen that the correspondence is encouragingly close (Chi-squared test p-values between 0.995 and 0.80), where the simulation underestimates the experimental performance. Further, simulations to investigate the performance of various candidates for hot mirror coating (ITO, Gold, and Silver) in a Solar trough receiver are presented, where it is seen that the hot mirror coating has access to higher temperature regions (above 700 K). Lastly, optical parameter variation effects were simulated, related to overall plant efficiency and compared to existing selective coatings.

Controllable and flexible energy production in a water-based photovoltaic/thermal system

A combined solar photovoltaic and thermal (PV/T) system is not just a product that makes our life easier, nor is it a luxury. In the future economics will make the use of the PV/T system essential. The purpose of this to improve the energy balance in a PV/T system, by control-ling the thermal energy (useful heat) production for the domestic hot water as well as the electrical production. Simulation and analysis of a simplified model of the PV/T system for cooling the PV cell and heating the working fluid inside of the absorber pipe attached at the back of the PV cell were implemented in MATLAB /Simulink software. The optimal electrical and thermal power were obtained by selecting a par-ticular value of Rse that partially converts the output of the PV cell into useful thermal energy. It was discovered that increasing the chosen value of Rse results in higher heat dissipation in the PV/T cell, an increase in thermal efficiency, and also a decrease in electrical efficiency.

3D thermal-hydraulic analysis of a symmetric wavy parabolic trough absorber pipe

We analyzed a symmetric wavy parabolic trough absorber pipe using an experimentally validated 3D FEM coupled to a semi-analytical optical model. The proposed absorber design was assessed based on the first and second law efficiency as well as the performance evaluation criteria (PEC), which accounted for both heat transfer enhancement and pressure drop relative to a conventional design, as we varied the wave amplitude, periodicity length, and fluid mass flow rate. Significant improvement in the first law efficiency was observed with the proposed design, especially at high mass flow rates due to the accelerated flow across the pipe throat which in turn enhanced the mixing. The second law efficiency variation shifted from an increasing to a decreasing trend with respect to the wave amplitude as the mass flow rate increased, and the exergy destruction due to pressure drop became evident accordingly. The PEC verified the superior performance of the proposed absorber design over the traditional straight pipe as its peak value was approximately 1.25. We also determined critical wave amplitude, periodicity length, and mass flow rate below which the PEC was less than unity due to an escalated pressure drop that offset the heat transfer enhancement.

Effect of intermittent operation on the thermal efficiency of energy tunnels under varying tunnel air temperature

This paper focusses on hot underground tunnels and studies the effect of ground source heat pump (GSHP) intermittent operation and changing tunnel air temperature profile on energy tunnel thermal efficiency. The effects of heat pump operation on the tunnel surrounding soil and the soil recovery rate when the heat pump is not in operation were also studied. A 3D numerical model was developed to simulate the transient heat transfer intermittent operation of an energy tunnel. The intermittent operation was reproduced by controlling the convective heat flux at the boundary between the absorber pipe and the tunnel lining. Variation in the tunnel air temperature was defined in the model as a periodic sink amplitude. Results show that in energy tunnels, strategic intermittent operation increases thermal efficiency and allows the surrounding soil to thermally recover and prevent any adverse effect on the system. A high daily intermittent operation ratio increases the average thermal output but might lead to higher operating costs. Therefore for a given site, it is important to determine the optimum intermittent ratio. The paper also shows how the variation in tunnel air temperature affects the thermal performance of the energy tunnel. The importance of including this variation (rather than assuming a constant average value) when estimating the geothermal potential of underground tunnels was also highlighted. Insights are also provided on the soil temperature recovery rates after prolonged operation. These would serve as a basis for working out a seasonal intermittent operation strategy to optimise the use of ground source heat pumps in underground tunnels.

The experimental performance of the semi-cylindrical type of solar concentrator collector on the addition of heat storage material

The heat absorbability and the efficiency of water heaters are increased by adding phase change material as heat storage in solar water heaters known as cylindrical through collectors type. It used to absorb heat from solar energy and will concentrate towards an absorber pipe containing water, so it can increase the water temperature that flows through the tube. In this study, two absorber copper pipes used with Ø 2.54 and Ø 1.91 cm, respectively. The copper pipes arranged parallel and placed the heat storage materials with different conditions. A drum with a diameter of 55.5 cm and a length of 10 cm is split vertically into two parts which will be used as a cylindrical type of solar collector — the solar intensity measured during the experiment. Results show the highest water out temperature is 65 °C at 13:00 WIB that the position of paraffin inside pipe 2 with a solar intensity is 1195 W/m2 and the efficiency is 13.5%. The water inside of pipe 2 found the water out temperature is 62 °C and the efficiency is 12.31%. The position of air inside of pipe 2 recorded the water out temperature is 60 °C, and the efficiency is 10.21%. It can be concluded that the effect of adding paraffin inside of pipe 2 is better than water and air.

A numerical simulation of a linear Fresnel solar reflector directed to produce steam for the power plant

The concentrating solar systems of linear Fresnel reflectors offer the ability to generate electricity from solar energy. The main objective of this paper is to perform a transient numerical simulation on a linear Fresnel solar reflector directed to produce superheated water steam for the power plants, in order to determine its efficiencies (optical and thermal), where the heat transfer fluid mass flow inside the copper absorber tube is 0.045 kg/s. The dimensions of the studied linear Fresnel solar collector are the same dimension as the modular system Nova-1 of NOVATEC SOLAR Company. The dimension of the studied model is 1D. For this purpose, El-Oued region has been designated as a study field. The twelve recommended average days for months have been selected for the study. This paper was based on a numerical solution using the finite differences method. MATLAB has been used as a software language. The optical efficiency of the LFR solar receiver has reached 53.7% where the thermal efficiency has reached 37.5%, while the pressure drop within the absorber pipe has reached 02 bars. As for superheated steam temperatures variations, it ranged between 233.35 °C and 263.75 °C, knowing that the water steam inlet temperature when entering the absorber tube is equal to 140 °C. As for the overall coefficient of heat loss, its mean value is 5.84 W/m2.°C. The results obtained are very encouraging to invest in this steam power plant, especially in the desert areas, which are rich in solar energy.

Parabolic trough collector’s heat transfer analysis with changes of variation on the pipe absorber system

Solar energy is one of the most important sources of renewable energy. One of the technologies used for converting solar energy is Parabolic Trough Collector (PTC). The PTC is used to focus the heat of solar radiation. This study discusses the analysis of the PTC heat transfer with an alteration of the pipe absorber system. The goal of the research is to know the design of efficiency absorber pipe system for PTC. The research method used is an experimental research by testing the system in sunny weather conditions. The pipe absorber system is designed with two variations: PTC1 and PTC2. PTC1 uses an open loop system while PTC2 uses a closed loop system. When the experiment was conducted, the pool water temperature, the intensity of the sun, and the temperature of the fluid in the pipe absorber were measured. The results obtained showed that the highest pool water’s temperature fro m PTC1 is 39.3°C at an intensity of 806.59W/m2. Meanwhile, at PTC2 the highest pool water’s temperature is 36.2°C at an intensity of 828.71W/m2. Based on the findings, PTC1 with an open loop pipe system has a better efficiency than the PTC2 with a closed loop pipe system.

Feasibility study on the geothermal utility tunnel system

Based on the analysis of several cases applying a ground source heat pump (GSHP) system and geothermal tunnel system, this paper proposes the idea of a geothermal underground utility tunnel (GUUT) system. By installing a GSHP system into a tunnel structure, the resultant GUUT system is designed to collect heat from the soil around the underground utility tunnel and absorb the waste heat inside the tunnel space, which will reduce the general temperature of the tunnel space and the energy consumption by optimizing a ventilation strategy. In this study, an analysis model that describes the heat transfer characteristics of the GUUT system is established. The heat-transfer process is simulated by analyzing the difference in temperature between inlet and outlet water of the heat absorber pipes. Various conditions are considered in evaluating the heat exchange efficiency, such as the distance of heat absorber pipes, flow velocity, ventilation condition, heat exchange load, and operation mode. Finally, the economic benefits of using the GUUT system are analyzed in this study.

A CFD-supported dynamic system-level model of a sodium-cooled billboard-type receiver for central tower CSP applications

This work focusses on the dynamic modeling of a sodium-cooled billboard-type receiver, as adopted in the reference plant of this study, the Jemalong Solar Thermal Station, in Australia. A detailed system-level thermal-fluid-dynamic model is developed in the OpenModelica framework, with the aim to predict the receiver behavior during transients, as well as its performance upon reaching steady-state conditions. The model solves the conjugate heat transfer problem relating conduction in the receiver pipes to the internal flow of sodium. The convective losses from the irradiated face of the receiver, due to the external flow of air, are calculated using empirical correlation available in literature for flat-plates and then carefully evaluated using 3D Computational Fluid Dynamics (CFD), which allows taking into account the actual geometry of the receiver. The CFD results, considering different wind speeds and highlighting the cavity-like effects of the receiver geometry under consideration, are first compared with those obtained from empirical correlations available in the literature for vertical plates in the case of uniform temperature distribution on the absorber pipes, showing significant differences. Then an iterative coupling procedure with the system-level model of the same receiver is proposed, which facilitates handling of the more realistic case of a non-uniform temperature distribution. Finally, we present and discuss the successful benchmark in a simple case of the system-level model against another model from the literature, its preliminary validation against experimental data, and first applications to a fast start-up/passing cloud/shut-down transient and to a whole-day simulation with controls.

Theoretical performance analysis of new class of Fresnel concentrated solar thermal collector based on parabolic reflectors

The main advantage of Fresnel systems is their capability to use flexible reflectors which are cheaper in comparison to glass reflectors. In this study, the effects of using parabolic reflectors instead of flat reflectors on Fresnel solar concentrator have been studied for the first time. For this new system by ray trace statistical method, local concentration ratio distribution has been determined. The new system is compared with linear Fresnel reflector (LFR). The effect of geometrical parameters, such as absorber height and reflectors width, on the concentration ratio is studied. The results have shown that using the parabolic reflectors with low curvature has a pronounced effect on the absorber pipe diameter. Comparison of the performance of linear and parabolic systems with identical parameters such as reflectors width, reflectors number and absorber pipe height showed that the absorber tube diameter in a parabolic system is smaller than the absorber tube diameter in a linear system, thus decreased rate of heat loss from the pipe surface. Comparison of the two systems under equal solar energy radiation and absorber pipe diameter showed that in parabolic system wider reflectors can be used, thus reduced number of reflectors and simpler control system.

Apparent delay analysis for a flat-plate solar field model designed for control purposes

This study presents an analysis of the effect of the transport delay which occurs in solar flat-plate collector fields and how to include its behavior in dynamic models suitable for control purposes. This investigation has been carried out using simplified models based on dynamic energy balances and models based on step response methods and experimental tests. The solar flat-plate collector field encompasses parallel absorber pipes intertwined with pipelines which act as several first-order plus dead time systems in parallel. The effect is an apparent delay observed at the outlet temperature that must be included in the dynamic model in order to reduce the error between the real measurement and the model prediction. The main contribution of this paper is the procedure to evaluate the apparent delay to obtain adequate dynamic models aimed to be used for control purposes.