Solar Water Heating Collectors Research Articles

Energetic and exergetic study of a flat plate collector based solar water heater - investigation of the absorber size

Small sized absorber in a flat plate solar collector is beneficial in terms of cost and minimum heat losses. However, its detailed thermal performance compared to standard size collector is still not fully understood. There is a paucity of research to appreciate thermal performance of solar water heating collector with consideration of a small absorber size (below 1m2) and a standard absorber size (2 m2). The present study attempts to investigate the energy and exergy efficiencies of flat plate solar water heating collector with two absorber plate areas (2 m2 and 0.74 m2) to enumerate size of the absorber required for improved first and second law thermal efficiencies of the collector. The efficiencies of these two collector designs are experimentally compared with the help of a test facility available in the site for given operating temperatures and rate of flow. The combined experimental uncertainty due to the measuring instruments and the measured parameters is also ascertained. The obtained results highlight the significance of the larger absorber size (2m2) for higher thermal efficiency, and lower absorber size (0.74m2) for higher exergetic efficiency. The highest thermal efficiency obtained is 77.38% for larger absorber size, and the highest exergy efficiency of 13.21% is obtained for lower absorber size collector. It is demonstrated that larger and lower absorber size of the collector have higher thermal efficiency and higher exergy efficiency, respectively, than some of the published works.

Enhanced Performance of Nickel–Cobalt Oxides as Selective Coatings for Flat-Plate Solar Thermal Collector Applications

Solar thermal collectors represent a practical option to capture energy from the sun, providing low-cost domestic and industrial heating and decreasing the dependency on fossil fuels. Spinel-type metal oxides show interesting physicochemical properties and so can be used as active materials for converting solar energy to electrical, chemical, and heat energy. We report the synthesis and characterization of nickel–cobalt mixed metal oxides used as an active phase in selective paints for solar absorber coatings applied to a domestic flat collector. The nickel–cobalt mixed oxides crystallized in the cubic phase related to the spinel structure, exhibiting good thermal stability and reproducibility. These mixed oxides presented oxidation states (2+ and 3+) for both nickel and cobalt. The coatings fabricated from the selective paints based on nickel–cobalt mixed oxides showed a solar absorptance value of 94%, while for the commercial paint Solkote®, the value was 93%. A representative coating based on the NiCo2O4 composition was evaluated for the first time in a domestic-type flat solar collector for water heating under real operating conditions, achieving an outstanding performance that competes with that of commercial collectors. The potential application of nickel–cobalt mixed oxides in solar collectors opens up new opportunities for future innovations and developments in functional absorber coatings.

Thermal Engineering and Technical-Economical Indicators of Seasonal Flat-Plate Capacitive Solar Water-Heating Collectors

Thermal Engineering and Technical-Economical Indicators of Seasonal Flat-Plate Capacitive Solar Water-Heating Collectors

An Experimental Comparison of the Performance of Various Evacuated Tube Solar Collector Designs
 
 
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An experimental study was carried out to assess the thermal performance of a few evacuated tube solar collectors (ETSCs) for water heating. The thermal performance of two kinds of ETSC (heat pipe ETSC and direct-flow ETSC) was investigated using an indoor experimental apparatus in lab testing conditions with a solar simulator. Several experimental tests were carried out for the heat pipe ETSC system under different operating conditions, such as the solar intensity (300, 500, and 1000 W/m2) and the tilt angle (0°, 30° and 90°) of the ETSC and the water flow rate (0.6, 1.2, and 2.4 LPM). Moreover, four configurations of direct-flow ETSC (U tube, double U tubes, coaxial tubes, and helical tube) were examined and compared to the conventional heat pipe ETSC. The results of the experiment proved that the ETSC system presents a great performance at higher solar irradiance and lower water flow rates, and the experiments indicated that with a 30° tilt angle, the ETSC reaches the maximum thermal efficiency of 36%. Furthermore, compared to the conventional heat pipe ETSC and the other proposed configurations of direct-flow ETSCs, the helical tube-based ETSC has a better thermal efficiency, 69%, and can be considered a greater potential heat exchanger that can be integrated in ETSCs. To the best of our knowledge, it is the first time this helical tube type been integrated into the ETSC and tested under these conditions.
 
 
 
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A Review on Experimental Validation of Heat Pipe Solar Collector for Water Heating

Now a day’s climate of growing energy needs and increasing environmental concern, alternatives to the use of non -renewable and polluting fossil fuels have to be investigated. One such alternative is solar energy; solar water heating is the prime application of solar energy. The problem faced by the existing solar water heating system is periodic inspections, maintenance, time to time component may need repair or replacement and also sufficient quantity of hot water is not available during cloudy/rainy days. Hence to overcome these problem , the use of heat pipe concept which utilizes the low boiling temperature fluid to increase the heating efficiency, the objective of present work is to increase the heating efficiency solar water heater using low boiling temperature fluid. Key Words: Solar water heater, concept of heat pipe, low boiling temperature fluid (working fluid), thermosiphon.

Experimental study on heat storage integrated flat plate solar collector for combined water and air heating in buildings

• The effect of dual fluids in a solar collector is investigated experimentally. • The effect of different mass flow rates is investigated with short-term heat storage. • The dual function of the short-term heat storage with the FPSC is studied. • The average overall heat loss coefficient for the hybrid FPSC is 4.61 W/m 2 K. • The peak energy and exergy efficiency of FPSC with PCM is 88.8% and 3.5%. Combined water and air heating flat plate solar collectors can reduce water and space heating-associated energy costs at minimal installation. This study uses the serpentine copper tubes for water to have a more surface area and flow duration. Baffles are provided to increase air flow residence duration. In addition, multifunctional heat storage tubes are fixed on the absorber. The results reveal that the energetic and energetic performances of the collector are significantly affected by the solar radiation and mass flow rates of water and air. The heat storage integrated collector's peak energy and exergy efficiencies are 88.8 % and 3.5 %, respectively, higher than the collector without heat storage at the water flow rate of 0.025 kg/s and air mass flow rate of 0.0132 kg/s. The overall heat loss coefficient of heat storage integrated collector is 4.2 % lower at a higher flow rate than without heat storage. The heat storage tubes reduce heat loss, increase the absorber area, and compensate for the fluctuation of available solar energy. The presented hybrid solar collector has more economical and environmental benefits than the conventional collector with shorter payback periods.

A Comparative Thermal Performance Assessment of Various Solar Collectors for Domestic Water Heating

Growing population, depleting fossil fuels, economic expansions, and energy intensive life style demand are resulting in higher energy prices. We use energy as of heat and electricity, which can directly be obtained from sun using thermal collectors and solar cells. Solar thermal systems are gaining attention for water and space heating applications due to green aspects of solar energy. A solar thermal collector is a vital part of solar thermal energy system to absorb radiant energy from the sun. In this study, a solar water heating (SWH) system has been designed and simulated in the TRNSYS ® software using thermal and chemical properties of heat transfer fluids using REFPROP for dwellings located on ±31° latitudes (+31 Lahore in Pakistan and -31° Perth in Australia). We present an efficiency parametric optimization-based model for water and space heating. Simulation results for four types of solar thermal collectors are presented, and performance is analyzed on the basis of output temperature ( T out ), solar fraction ( f ), and collector efficiency ( η ). This study evaluates the comparative performance of evacuated tube collector (ETC), flat-plate collector (FPC), compound parabolic concentrator (CPC), and thermosiphon-driven systems. Our findings conclude the evacuated glass tube collector achieves the highest solar fraction, i.e., 50% of demand coverage during August in Pakistan and February in Australia, with an overall average of 43% annually.

Determination Of Thermal Parameters Of Solar Water Heating Collectors Using The “Dark” Testing Method

In the production of flat solar water heating collectors, thermal testing occupies a special place, the purpose of which is to determine their thermal characteristics experimentally. The corresponding approximation expressions are proposed for determining the coefficient of heat loss, inclined to the horizon at an angle of 300 for the average conditions of their operation in the hot water supply system

Daily Variations of Water Temperature and Useful Heat Accumulation in Flat-Plate Solar Water-Heating Collectors with Capacitive Solar Radiation Absorbers with Bottom Absorption of Radiation

This study presents the results of numerical experiments conducted for determining the daily variations of water temperature and useful heat in flat-plate solar water-heating collectors (FSWHCs), with capacitive solar radiation absorbers (SRAs) with bottom absorption of radiation. These absorbers are made as rectangular containers 5–7 cm in thickness from translucent plastics.

Experimental investigation on the performance of spherical solar collector for water heating

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Increasing the Convective Heat Transfer Coefficient Inside Heat Removal Channels of Sheet-Piped Light-Absorbing Panels of Flat-Plate Solar Collectors in the Laminar Flow Regime of Heat Transfer Fluid

The study presents ways to improve convective heat transfer inside heat removal channels of light-absorbing heat-exchange panels of flat-plate solar water heating collectors in laminar viscous and viscous gravity modes of the heat transfer fluid flow by affecting the thermal boundary layer formed on the inner surfaces of their walls.

The Method of Hydraulic Calculation of a Heat Exchange Panel of a Solar Water-Heating Collector of a Tube–Tube Type with a Given Nonuniform Distribution of Fluid Flow Along Lifting Pipes

The purpose of this work is to develop a method for the hydraulic calculation of a heat exchange panel of a solar tube collector of a tube type with a given nonuniform distribution of fluid flow under conditions of forced circulation. On the basis of previously obtained design dependencies, a method of hydraulic calculation of a heat exchange panel of a solar thermal collector of a flat-plate type with a given uneven distribution of fluid flow under conditions of forced circulation has been developed. An example of calculation using the developed method is given.

Optimization Of The Flow Distribution In V-Groove Flat Plate Solar Collector using Cfd Simulation

Flat plate solar collector is the major component of a solar heating system that converts solar radiation to thermal energy. It provides clean energy at no operating cost, however, its poor performance constitutes a serious drawback to adopt it for small application. This inefficiency is the result of involved thermal losses and the lack of full exploitation of the available energy. To exploit the maximum potential, the working fluid flow should be uniformly distributed through the collector to extract the heat from the hot absorbing surface. This study addresses the uniformity of the flow distribution for v-groove flat plate solar collector for water heating to optimize the performance of the collector. The study investigated the effect of the manifold geometry and the number of the side riser channels on the flow distribution by using numerical computational fluid dynamics simulation on Ansys Fluent Software. The mass flow rate was optimized for maximum thermal performance and then the optimum point was used for investigating the flow distribution. The simulation was validated against experimental data from literature with 99% confidence. The study found that the circular manifold gives uniform flow distribution with a standard deviation of 5% at the optimum mass flow rate of 11.5g/s. the study concluded that the tapered circular manifold is the optimum geometry for uniform flow distribution as it provides the least pressure difference inside the manifold.

Features of Convective Heat-Exchange in Flat-Plate Solar Water-Heating Collectors

Low-potential solar plants, including flat-plate water-heating collectors (FSWHC), are complex systems in terms of heat engineering. A problem in the development of both stationary and non-stationary heat engineering FSWHC models is to specify convective heat exchange in SWHC channels. This paper considers the features and conditions of convective heat transfer in SWHC channels to water. It is shown that the water flow hydrodynamic and thermal stabilization sections in FSWHCs and at potential speeds of their heat carriers reach only 10 to 13 cm in length and the convective heat exchange in SWHCs can be calculated at a constant value of Nu. It is found that the differences in temperature between the walls of a SWHC channel and between the wall and the liquid will not exceed 10 and 5°C, respectively. These conditions make mixed free and forced convection in SWHC channels possible. Since the heat mainly comes from the upper walls of the channel, this determines the need for pilot studies to determine the distribution of temperature on the walls and in the liquid along the channel length and the difference in temperature between them. The heat exchange in SWHC channels can be heavily affected by free convection. An important issue when elaborating design models of heat exchange in SWHCs is the possibility of applying the convective heat exchange formulas used for plates to the walls of SWHC channels.

Development and validation of a new TRNSYS Type for thermosiphon flat-plate solar thermal collectors: energy and economic optimization for hot water production in different climates

This paper presents a new TRNSYS Type (called Type 99) which can be used for the energy assessment of thermosiphon Flat-Plate solar thermal Collectors (FPCs) for water heating. The accuracy of this new type is higher than the standard type (Type 45a) available in TRNSYS library, since the density and specific heat of water are estimated according to the operating fluid temperature. The results of a suitable experimental campaign are also presented for different commercial FPCs system layouts. The developed Type 99 is successfully validated, proven by the very good agreement achieved between the simulation and experimental results. By the new Type 99 a suitable Design of Experiment (DoE) analysis is carried out with the aim to assess the design and operating parameters mostly affecting the energy and economic performance of two types of FPCs. Specifically, collector pipe diameters, slope, storage tank volume, and thermal insulation thickness are investigated. The analysis is carried out for three case studies which refer to residential Domestic Hot Water (DHW) production applications and to three different European weather zones (Freiburg, Naples and Larnaca). For these case studies an optimization procedure is also carried out by varying the same design and operating parameters for two different objective functions: best energy behaviour [maximum Primary Energy Saving (PES)] and best economic performance [minimum Simple Pay Back (SPB)]. Interesting novel design criteria and encouraging economic results are obtained.

Influence of Ambient Temperature, Wind Speed, Emissivity, and Average Working Temperature of Light-Absorbing Heat-Exchange Panels of Flat-Plate Solar Water-Heating Collectors on Their Thermal Losses Through Translucent Coatings

This article presents the results of computational experiments aimed at determining the influence of the ambient temperature ( $${{t}_{a}}$$ ), wind speed (v), average working temperature ( $${{\bar {t}}_{{avw}}}$$ ), and emissivity of light-absorbing heat-exchange panels (LAHPs) $$\left( {{{\varepsilon }_{p}}} \right)$$ on their thermal losses through the translucent coating (TC) of the case of flat-plate solar water heating collectors (FSWHC) with a single-layer TC.

Influence of Meteorological Factors on the Thermal Loss Coefficient of Light-Absorbing Heat Exchange Panels of Flat-Plate Solar Water Heating Collectors through Transparent Coatings of Their Casings

The results of computational studies aimed at determining the coefficient of thermal losses of light-absorbing heat-exchange panels (LAHP) of flat-plate solar water-heating collectors (FPSWHC) through their translucent coatings (TC) are presented. The calculations take into account the effect of free and forced convection on the external surface of the TC, as well as on the convective heat transfer coefficient and the FPSWHC tilt, the atmospheric transparency, and the air humidity on the total heat transfer coefficient from the external surface of the TC to the environment. An example is given to test the proposed approach for practical use to determine the values of $$~\alpha _{{{\text{i}}{{{\text{n}}}_{{{\text{w}} - {{c}_{1}}}}}}}^{\Sigma }$$ , $$\alpha _{{{\text{ex}}{{{\text{t}}}_{{{{c}_{2}} - {\text{amb}}}}}}}^{\Sigma }$$ , and their convective and the radiant components, and also the degree of their influence on the value of $${K}_{{{{c}_{{{\text{w}} - {\text{amb}}}}}}}^{~}$$ .

Dependence of Techno-Economic and Ecological Indicators of Flat-Plate Solar Water Heating Collectors in Hot Water Supply Systems from the Temperature of Heating Water

The main ways of improving the performance efficiency of solar energy (SE) use in hot water supply systems (HWSSs) are discussed. It is established that the environmental characteristics of flat-plate solar water heating collectors (FPSWHCs) for heating water in HWSSs depend on the water heating temperature in these systems.

Heat Transfer Coefficient from the Sheet-Piped Light-Absorbing Panels of the Flat-Plate Solar Water-Heating Collectors to the Heat Transfer Fluid in Their Heat-Removing Channels

It has been proposed to introduce a new parameter into the practice of the heat calculation and testing of the flat-plate solar water-heating collectors (FSWHCs)—the coefficient of heat transfer from the light-absorbing panel (LAP) to the heat transfer fluid in its internal heat-exchange channels (HECs) reduced to the unit area of the frontal surface of their cases. The mechanism of the formation of this parameter is studied, the design expression is derived, and a practical example of the calculation to define its value is performed. The structures of the flowing LAPs of a sheet-piped thin parallelepiped form are selected as the objects of the investigation. The reliability of the results of the investigations is proved by comparing the values of the specific (relative to the area unit of the frontal surface of the case) heating efficiency of the collector obtained based on the various formulas.

EVALUATE THERMAL PERFORMANCE OF SOLAR AIR COLLECTORS

Solar energy has an important place in sustainable and clean energy sources. Solar collectors can play a vital role among applications of solar energy system. Solar collectors are divided into solar air heating collector (SAHC) and solar water heating collector (SWHC) according to the fluid used. Although its efficiency is low because of air’s worse thermodynamic properties in terms of heat exchange compared to liquid, SAHC is still widely used in the world for the advantages of simple structure, convenient installation and easy maintenance. The absorber surface material is the most important parameter in the design for solar air collectors. The present study aimed to evaluate the thermal performance of solar air collectors. The treatments under this study were three types of solar panels absorbent. Stainless steel, aluminum and iron) and three different air velocities of 1.7, 2.4 and 3.6 m/s represented. Stainless steel solar panels absorbent give the highest value of absorption efficiency, useful heat gain to storage and overall thermal efficiency and they were 86.4, 71.42 and 59.87 %, respectively at midday air flow inlet temperature (Tai =31.7 C°), air flow outlet temperature (Tao =49.9 C°) and Average plate temperature (Tpm =70 C°) at 2.4 m/s fan velocity.