Liquid Flat-plate Solar Collectors Research Articles

Numerical and Experimental Determination of Selected Performance Indicators of the Liquid Flat-Plate Solar Collector under Outdoor Conditions

The paper proposes applying an in-house mathematical model of a liquid flat-plate solar collector to calculate the collector time constant. The described model, proposed for the first time in an earlier study, is a one-dimensional distributed parameter model enabling simulations of the collector operation under arbitrarily variable boundary conditions. The model is based on the solution of energy balance equations for all collector components. The formulated differential equations are solved iteratively using an implicit difference scheme. To obtain a stable numerical solution, it is necessary to use appropriate steps of time and spatial division. These were found by comparing the results obtained from the model with the results of the analytical solution available in the literature for the transient state, which constitutes the novelty of the present study. The accuracy of the results obtained from the model was verified experimentally by comparing the measured and calculated history of the fluid temperature at the outlet of the collector. The calculation of the collector time constant is proposed in the paper as an example of the model’s practical application. The results of the time constant calculation were compared with the values obtained experimentally on the test stand. This is another novelty of the presented research. The analysed collector instantaneous efficiency was then calculated for selected outdoor conditions. The presented mathematical model can also be used to verify the correctness of the collector operation. By comparing, on an ongoing basis, the measured and calculated values of the fluid temperature at the collector outlet, conclusions can be drawn about the process of solar glass fouling or glycol gelling. The simplicity of the model and the low computational demands enable such comparisons in an online mode.

Energy, exergy and economic analysis of liquid flat-plate solar collector using green covalent functionalized graphene nanoplatelets

• Thermal efficiency of solar collector increased using eco-friendly nanofluids with maximum improvement up to 24%. • Exergy efficiency increased with weight concentration of eco-friendly nanoparticles. • Maximum increase in friction factor was around 7.9% for 0.1% nanofluid than base fluid. • Relative pumping power slightly increases with increment in nanofluid concentration but is quite close to that of the base fluid. • Pay back period was 5.615% lesser using nanofluids than water. The conventional method of synthesizing carbon-based nanofluids produces harmful products that are highly toxic and hazardous. The present investigation deals with the effects of using eco-friendly, non-corrosive, covalent functionalized Graphene Nanoplatelets with gallic acid (GGNPs) as heat transfer fluid on energetic and exergetic performance of a Liquid flat-plate solar collector (LFPSC). Long-term dispersible stable GGNP nanofluids with base fluid distilled water are prepared with different weight concentrations of 0.025%, 0.05% & 0.1%. For varying concentrations, fluid flow rates of 0.8, 1.2, and 1.5 L/min, heat flux intensities of 600, 800, and 1000 W/m 2 , and inlet temperature ranging from 303 to 323 K are considered for the conduction of experiments. Improvement in energy and exergetic efficiency was achieved using GGNP nanofluids. Thermal efficiency surges with increment in flow rate and heat flux intensities, meanwhile it decreases for increment in inlet temperature. The maximum enhancement in LFPSC efficiency is 24.09% for 0.1 wt% GGNPs and flow rate of 1.5 L/min than distilled water. Analysis of exergetic performance revealed that exergy efficiency reduces with a rise in mass flow rate meanwhile enhanced with an increase in nanofluid concentration. Exergy efficiency was maximum for 0.1% GGNP concentration and flow rate of 0.8 L/min. The maximum increase in friction factor values is approximately 1.5, 2.6 and 7.9% for 0.025, 0.05 and 0.1% GGNP nanofluids than distilled water. Relative pumping power slightly increases with the increment of GGNP concentration but is quite close to that of the base fluid. Performance index greater than one is obtained with higher values achieved at an increase in GGNP weight concentration. Economic consideration of GGNP nanofluids in LFPSC showcased a maximum reduction of 26.41% in the size of collector area using 0.1% GGNP nanofluid instead of distilled water. The payback period for LFPSC using GGNPs was 5.615% lesser than that of using water.

Experimental study on the effect of bio-functionalized graphene nanoplatelets on the thermal performance of liquid flat plate solar collector

Synthesis of carbon-based working fluid involves toxic acids that are hazardous to the human and surrounding environment. In the current experimental investigation, thermal analysis of liquid flat plate solar collector was carried out using distilled water and environmentally friendly, covalent functionalized graphene nanoplatelets. Gallic acid was grafted on GNPs using the green free radical technique. Chemical characterization was analyzed using EDX and FESEM. Colloidal stability of GGNP nanofluids was found to be stable for more than 60 days. GGNPs were dispersed in distilled water with varying mass concentrations from 0.025 to 0.1%, and analysis was carried out for flow rate ranging from 0.5 to 1.5 L min−1 for different heat flux intensities and inlet temperature. The thermal performance of LFP solar collector augments with the surge in GGNP concentration, flow rate and heat flux intensities, whereas declines with the increase in reduced temperature parameter. Maximum thermal efficiency enhancement of 21.48%, 16.06% and 12.36% is achieved using 0.1%, 0.05% and 0.025% GGNP nanofluid than distilled water. A penalty in the form of a slight surge in pressure drop and pumping power was observed with a subsequent increase in GGNP concentration. The maximum increase in pressure drop and pumping power was about 0.85% and 0.567% for 0.1% concentration and mass flow rate 1.5 L min−1. A maximum reduction of about 25% in the size of the LFP solar collector area is attained using 0.1% GGNPs than base fluid.

A comparative study on the performance of liquid flat-plate solar collector with a new V-corrugated absorber

In this study, a new V-corrugated absorber with multi-channels is presented and applied in the liquid flat-plate solar collector. The absorber is extruded with aluminium and specific triangular channels are directly formed to improve the solar absorptance, reduce the heat conduction thermal resistance and decrease the pressure drop. Optical and heat transfer models for the new collector and a conventional sheet-and-tube collector are developed and experiments are carried out to validate the accuracy. Performance of the new and conventional collector are compared under different operational conditions and the results indicate that: (i) The daily average optical/thermal efficiency of the new and conventional collector are about 84.9%/69.4% and 69.1%/58.6%, respectively. (ii) The average exergy efficiency of the new and conventional collector are about 3.8% and 3.3% respectively under the mass flow rate of 10–90 g/s. (iii) The pressure drop and pump power consumption of the conventional collector are about 4.1 times higher than those of the new collector. The designing of V-corrugated absorber can improve the collector optical and thermal efficiency, and reduce the pressure drop and pump power consumption significantly, but exerts little effect on the exergy efficiency. Notwithstanding so, the performance improvement potential of the V-corrugated absorber is huge and the designing and manufacturing of the collector can be further developed.

Investigation and Development of Liquid Flat Plate Solar Collector using Concrete as Absorber Plate and its Performance Testing

In order to increase usage of solar water heater (SWH) for domestic purposes instead of conventional sources of heating water which contribute towards energy crisis& global warming an attempt is made to use non conventional cost effective method to produce hot water. Hence by keeping the objective of low cost liquid flat plate solar collector, we replace the costliest component of collector, which is the metal absorber plate with the concrete absorber plate. Here the feasibility of utilizing non metal (concrete) for making liquid flat plate solar collector, in Pune, has been investigated. Thus 2m X 1m concrete collector is designed, fabricated and tested for various months and for different mass flow rates. It was observed that, the average temperature of hot water collected in rainy season was in the range of 47 ˚C to 57 ˚C, in winter season was 48 ˚C to 59 ˚C and in summer season was 56 ˚C to 80 C˚. Therefore, concrete collector can be used to collect large quantity of hot water . This paper also paves way for possible integration of concrete collector with roof slab. Such integration will also provide comfort temperature zone within the building.

A Comparative Study on the Experimental and Computational Analysis of Solar Flat Plate Collector Using an Alternate Working Fluid

Solar liquid collectors are potential candidates for enhanced heat transfer. The enhancement techniques can be applied to thermal solar collectors to produce more compact and efficient energy collection/storage mechanism. Those collectors can be induced for simplest and most direct applications of energy conversion of solar radiation into heat. This work presents a comparative representation of computational simulation and experimental for the processes occurring in liquid flat-plate solar collectors. The working fluid used is propylene glycol and the concentration of propylene glycol (PG) is varied for various mass flow rates. The effect of this variation, on the efficiency of a flat plate solar collector was investigated computationally and experimentally. The experiments were carried out using 4 different mixture concentrations. The designed model is simulated under various flow conditions by varying the mass flow rate and varying the working fluid concentration. In order to verify the designed model and results, an experiment was designed and conducted for several days with variable ambient conditions, flow rates and concentrations. The comparison between the computed and measured results of the fluid temperature at the collector outlet showed a satisfactory convergence. The model is appropriate for the verification of overall efficiency of the system and can be used for any number of working fluids in order to find the outlet temperature.

Flat-Plate Solar Collector in Transient Operation: Modeling and Measurements

This paper describes a mathematical model for simulating the transient processes which occur in liquid flat-plate solar collectors. A discrete nodal model that represents the flat-plate solar collector's layers and the storage tank is employed. The model is based on solving a system of coupled differential equations which describe the energy conservation for the glass cover, air gap, absorber, fluid, insulation, and the storage tank. Inputs to the model include the time-varying liquid flow rate, incident solar radiation, and the ambient air temperature, as well as the volume of liquid in the storage tank and initial temperature of the system. The system of differential equations is solved iteratively using an implicit, finite-difference formulation executed with Matlab software. In order to verify the proposed method, an experiment was designed and conducted on different days with variable ambient conditions and flow rates. The comparison between the computed and measured results of the transient fluid temperature at the collector outlet shows good agreement. The proposed method is extremely general and flexible accounting for variable ambient conditions and flow rates and allowing for a geometrical and thermophysical description of all major components of the solar collector system, including the storage tank. The validated, general model is suitable to investigate the effectiveness of various components without the necessity of carrying out experimental work, and the flexible computational scheme is useful for transient simulations of energy systems.

Modelling of liquid flat-plate solar collector operation in transient states

The article presents a one-dimensional mathematical model for simulating the transient processes which occur in liquid flat-plate solar collectors. The proposed method considers a collector model with distributed parameters. In the model, the boundary conditions can be time dependent. The proposed model is based on solving equations which describe the energy conservation for the glass cover, air gap between cover and absorber, absorber, working fluid, and insulation. The differential equations derived were solved using the implicit finite-difference method in an iterative scheme. All thermo-physical properties of the fluid, absorber and air gap are computed in real time. The time-spatial distributions of heat transfer coefficients are also computed in the on-line mode. In order to experimentally verify the proposed method, a test bench was built and measurements were carried out. Comparing the measurement results of the transient fluid temperature at the collector outlet with computational results, satisfactory convergence is found. The proposed method is appropriate for the verification of the effectiveness of various absorbers and their surface coatings, without the need to carry out research on existing collectors. It allows the influence of fluid mass flowrate on the collector performance to be analysed and collector time constant to be determined. The presented model is suitable for collectors working in a parallel or in a serpentine tube arrangement with single or double covers.

Mathematical modelling of heat transfer in liquid flat-plate solar collector tubes

Mathematical modelling of heat transfer in liquid flat-plate solar collector tubesThe paper presents a one-dimensional mathematical model for simulating the transient processes which occur in the liquid flat-plate solar collector tubes. The proposed method considers the model of collector tube as one with distributed parameters. In the suggested method one tube of the collector is taken into consideration. In this model the boundary conditions can be time-dependent. The proposed model is based on solving the equation describing the energy conservation on the fluid side. The temperature of the collector tube wall is determined from the equation of transient heat conduction. The derived differential equations are solved using the implicit finite difference method of iterative character. All thermo-physical properties of the operating fluid and the material of the tube wall can be computed in real time. The time-spatial heat transfer coefficient at the working fluid side can be also computed on-line. The proposed model is suitable for collectors working in a parallel or serpentine tube arrangement. As an illustration of accuracy and effectiveness of the suggested method the computational verification was carried out. It consists in comparing the results found using the presented method with results of available analytic solutions for transient operating conditions. Two numerical analyses were performed: for the tube with temperature step function of the fluid at the inlet and for the tube with heat flux step function on the outer surface. In both cases the conformity of results was very good. It should be noted, that in real conditions such rapid changes of the fluid temperature and the heat flux of solar radiation, as it was assumed in the presented computational verification, do not occur. The paper presents the first part of the study, which aim is to develop a mathematical model for simulating the transient processes which occur in liquid flat-plate solar collectors. The experimental verification of the method is a second part of the study and is not presented in this paper. In order to perform this verification, the mathematical model would be completed with additional energy conservation equations. The experimental verification will be carry out in the close future.

Numerical analysis of two dimensional parallel flow flat-plate solar collector

Temperature distribution over the absorber plate of a parallel flow flat-plate solar collector is analyzed with one- and two-dimensional steady-state conduction equations with heat generations. The governing differential equations with boundary conditions are solved numerically using a control volume-based finite difference scheme. Comparisons of one- and two-dimensional results showed that the isotherms and performance curve, stated in terms of an effectiveness/number-of-transfer-unit relationship, for one-dimensional analysis slightly deviate from that of two-dimensional analysis, particularly under low mass flow rate conditions. In addition, collector efficiency as a function of operating point is computed and presented graphically for different collector configuration and various operating conditions. For general engineering purposes, these performance curves may be used for efficient and optimum design of liquid flat-plate solar collectors.

Modeling and Analysis of an All-Plastic Flat-Plate Solar Collector

The concept of an all-plastic liquid flat-plate solar collector was studied. Such a collector eliminates the need for coatings, metals, and all other materials except plastics. The concept appears to offer possibilities for the mass production of a low-cost, lightweight solar collector which is reasonably efficient. Material considerations for the concept are discussed, and thermal analysis is presented. Mathematical models were developed for study of this concept. Convection and nonlinear radiation between the covers was computed in all of the models. In addition absorptance and conduction in the cover(s) and the fluid cover plate were studied in order to determine their effects on the panel performance. A model panel was fabricated, and computer results were compared with test data for the efficiency of the panel.