Types Of Solar Air Collectors Research Articles

A Comprehensive Review of the Thermohydraulic Improvement Potentials in Solar Air Heaters through an Energy and Exergy Analysis

Supply disruptions, uncertainty, and unprecedented price rises of fossil fuels due to the recent pandemic and war have highlighted the importance of using renewable sources to meet energy demands. Solar air collectors (SACs) are major types of solar energy systems that can be utilized for space and water heating, drying, and thermal energy storage. Although there is sufficient documentation on the thermal analyses of SACs, no comprehensive reviews of the exergetic performance or qualitative insight on heat conversion are available. The primary objective of this article is to provide a comprehensive review on the optimum conditions at which the thermal performance of diverse types of solar air collectors is optimized. The effect of operating parameters such as temperature rise, flow rate, geometric parameters, solar radiation, and the Reynolds number on the thermal performance of SACs in terms of thermal hydraulic performance, energy, and exergy efficiencies has been reviewed adaptively. Beyond the operating parameters, a deep investigation is outlined to monitor fluid dynamics using analytical and computational fluid dynamics (CFDs) methodologies in the technology of SACs. In the third phase, thermodynamic irreversibility due to optical losses, thermal losses between absorber and environment, heat losses due to insulation, edge losses, and entropy generation are reported and discussed, which serve as the fundamental tools for optimization purposes.

Performance analysis of a textile based solar assisted air source heat pump with the energy and exergy methodology

Solar air collectors are integrated into the air source heat pump in order to increase the performance of the heat pump in cold climate regions. The evaporator air is heated by solar air collectors. In this study, two different types of solar air collectors which were textile based solar air collector and flat plate solar air collector were used. The thermal energy stored in the tank during the day was used to heat the room at day and night. The thermal storage tank was heated using three heating systems, textile based solar assisted air source heat pump (TSAHP), flat plate solar assisted air source heat pump (FSAHP) and air source heat pump (ASHP). In this study, energy, exergy and economic analysis of three different heating systems were performed. COP values increased by 32% in TSAHP and 21% in FSAHP compared to ASHP. Addition of solar air collectors to the ASHP heating system has been shown to improve thermal storage tank performance. Total exergy efficiency values were calculated as 14.4%, 13.4% and 11.3%, for TSAHP, FSAHP and ASHP heating systems, respectively. Levelized cost of heating of novel type system (TSAHP) ($/kWh) was 11.8% lower than conventional ASHP.

A comparative experimental investigation on thermal performance for two types of vacuum tube solar air collectors based on flat micro-heat pipe arrays (FMHPA)

Two types of solar air collectors (SACs), namely, a conventional-tube collector (C-TC) and a transparent-tube collector (T-TC), are designed on the basis of flat micro-heat pipe arrays (FMHPA) and are compared. FMHPA is used as the core heat transfer element for both collectors. Absorption coatings are located at different places. It is located at, namely, on the inner wall of vacuum tube and on the FMHPA evaporation section in the C-TC and the T-TC. A large volumetric flow rate of air contributes to high efficiency. Results of the comparative experiment show that even if the thermal efficiency of the C-TC (77.6%) is smaller than that of the T-TC (85.0%), the useful energy of the C-TC (641 W) is larger than that of the T-TC (497 W). Moreover, the COP values of the C-TC and T-TC are 11.4 and 8.9, respectively. The unit initial investments are 0.15 and 0.21 $/W. Hence, considering the heating capability and price advantage, the C-TC is a better collector form than the T-TC in the same collector gross area. The collector pressure drop does not exceed 19.1 Pa. These results can serve as a reference for the selection and design of SACs for heating applications and crop drying.

Energy and Exergy Analysis of Dual Channel Solar Air Collector with Different Absorber Plates Geometry

Flat-plate collector considers most common types of collectors, for ease of manufacturing and low price compared with other collectors. The main aim of the present work is to increase the efficiency of the collector, which can be achieved by improving the heat transfer and minimize heat loss experimentally. Five types of solar air collectors have been tested, which conventional channel with a smooth absorber plate (model I), dual channel with a smooth absorber plate (model II), dual channel with perforating “V” corrugated absorber plate (model III), dual channel with internal attached wire mesh (model Ⅳ), and dual channel with absorber sheet of transparent honeycomb, (model Ⅴ). The dual channel collector used for increasing heat transfer area and heat removal factor to improve thermal performance. The outdoor test was conducted during the period December (2016) to February (2017) at different mass flow rates 0.0217 kg/s, 0.0271 kg/s and 0.0325 kg/s. The experiments were carried out from 8:30 AM to 3:00 PM for clear days. Experimental results show that the average thermal efficiency was (72.2 %) for model (III), (40.2 %) for model (I), (51.6 %) for model (II), (65.1 %) for model (Ⅳ) and (59.7 %) for model (Ⅴ). At the last part of the study, the exergy analyses were derived for both collectors. The results of this part showed that the conventional channel model (I) is having largest irreversibility, and the dual channel collector model (III) is having a greatest exergetic efficiency.

Dynamic thermal performance analysis of two solar air collectors with and without porous media

The paper presents the thermal performance comparison between two types of solar air collectors, with and without porous absorber material. In order to simulate the transient processes which occur in the collectors two mathematical models were developed. Each model consists of a set of time dependent equations which describe the energy balance for the main components of the collector considering time-dependent thermo-physical properties and heat transfer coefficients. The theoretical models were validated by experimental data obtained from measurements performed in different meteorological conditions characteristic to the city of Bucharest – Romania (latitude 44°26′ N, longitude 26°6′ E). Good agreement between the simulation results and experimental data was achieved.

Validation of the Simulation of Solar Air Collector Prototypes.

The solar air systems can be appropriated into constructions due to the easy integration of air collectors in building facades, either into walls and roofs or by replacing one of them. There are several types of solar air collectors, which differ from each other on how the cover, absorber and airflow pattern are laid out in the collector. It is important to know the collector performance in order to design other system elements. Designsof solar air collectors and their respective models can be found in some solar engineering books. The model equations allow measuring the collector performance at a particular time. However, it is necessary to know some state variables of the collector such as the collector element temperatures, and heat transfer coefficients. It is important to emphasize that the collector state variables are changing with time due to the environmental effects.This study deals with the mathematical models, the implementations and the validations of numerical simulation for three experimental prototypes of solar air collector. The Solar-Institute Jülich of Germany developed the prototypes.In a general form the mathematical one-dimensional transient model of heat flux of each solar air collector is presented. Besides, the implementation of the collector models in the MATLAB-Simulink software is described.As a result of the validation of experimental data, the mathematical models and numerical implementations are able to estimate the air temperature inside of the collector. Average absolute error between integrals of simulated and measured temperatures reached hardly 1.2°C. In general, the three solar air collector models had a very good performance.

Double Pass Solar Air Heater with Transvers Fins and without Absorber Plate

The single pass solar air heater, with transverse fins and wire mesh used as an absorber plate, is constructed and tested for thermal efficiency at a geographic location of Cyprus in the city of Famagusta. The absorber plate was replaced by sixteen steel wire mesh layers, 0.18 x 0.18cm in cross section opening and a 0.02cm in diameter. The fins were painted with black color and positioned transversely along the bed such that four equally spaced sections were created. The transversely fins are arranged in a way to force the air to flow through the bed like eight letter path. The obtained results show that for air mass flow rate rang between 0.011-0.032 kg/s, the thermal efficiency increases with increasing the air mass flow. The maximum efficiency obtained is 58% for the mass flow rate of 0.037 kg/s. Moreover, the temperature difference between the outlet flow and the ambient, ΔT, reduces as the air mass flow rate increases. The maximum difference between the outlet and ambient temperature obtained was 40.6 o C for mass flow rate of 0.011kg/s. Comparison with a conventional single pass collector shows a substantially enhancement in the thermal efficiency. INTRODUCTION: Heating air with solar energy is much cleaner than heating with fossil fuel, the delivered heat from air solar device can be used for drying agricultural products such as crop, grains, seeds, fruits, and vegetables. Solar air heaters are also used as pre heaters in industries and as auxiliary heaters in building to save energy during winter times [1]. Conventional solar air heaters mainly consist of panels, insulated hot air ducts and air blowers in active systems. The panel consists of an absorber plate and a transparent cover. There are many different parameters affecting on the solar air heater efficiency, e.g. collector length, collector depth, type of absorber plate, glass cover plate, wind speed, etc. [2]. The absorber plate area and heat transfer coefficient between the air and the absorber plate are two important parameters affecting the efficiency of the collector. When increased these parameters will increase the collector efficiency. On the other hand it will increase the pressure drops inside the solar air heater and increases the pumping power required [2]. The convective heat transfer rate between air flow and absorber plate could be augmented by increasing the absorber surface area and by increasing turbulence inside the bed [3]. The use of Vgroove absorber was found to be more efficient by 12% than the flat plate collector of similar design [4] [5]. Using corrugated plates is a suitable method to increase the thermal performance and provides higher compactness [6]. A mathematical model that allows the determination of the thermal performances of the single-pass solar air collector with offset rectangular plate fin absorber plate is developed by [7]. Experimental and theoretical investigations are carried out on sheet metal absorber in the form of a chevron pattern [8]. The effect of using absorber plates coated with various selective coating materials on the heater performance was also investigated by [9]. Comparisons were made among four types of solar air collectors by Suleyman [10]. It has been found that the performance of a solar air heating system can be improved by operating several sub collectors in series in place of a single large collector with the same total area [11] [12]. The study concludes that the performance of solar air heater with single plastic glazing and flat plate absorber were approximately 9% more than the collector with double plastic glazing. Another study was carried out to determine the comparative performance of one-pass for fixed and free fins,

Case study of a two-stage rotary desiccant cooling/heating system driven by evacuated glass tube solar air collectors

A solar driven two-wheel two-stage desiccant cooling/heating system has been installed and operated for an Electronics Plant at Himin Solar Company in China. First, two different configurations and connection types of solar air collectors are analyzed. It is found that the thermodynamic and economic properties of 25mm alumina are superior to 19mm stainless steel and two-stage connection type is more suitable for desiccant cooling. This system is designed to satisfy space cooling demand and heating demand. In cooling cycle, the outlet temperature of the solar air collectors is about 60–100°C and their thermal efficiency can reach 50%. For the solar driven two-stage desiccant cooling system the moisture removal can reach 9–12g/kg and supply air condition is approximately 18°C and 60% RH. Experimental results indicated that the average thermal COP in cooling cycle is 0.97 and the cooling capacity in the range of 16.3–25.6kW under hot and humidity ambient conditions. The solar COP of system in heating cycle is about 0.45 when thermal efficiency of collector is 50%. Compared to direct heating, heating with humidification can reach a higher state of comfort.

Investigation on thermal performance calculation of two type solar air collectors using artificial neural network

In this study, two types of solar air collectors are constructed and examined experimentally. The types are called as zigzagged absorber surface type and flat absorber surface type called Model I and Model II respectively. Experiments are carried out between 10.00 and 17.00 h in August and September under the prevailing weather conditions of Karabuk (city of the Turkey) for 5 days. Then, thermal performances belongs to experimental systems are calculated by using data obtained from experiments. To estimate thermal performances of solar air collectors an artificial neural network (ANN) model is designed. The measured data and calculated performance values are used at the design of Levenberg–Marquardt (LM) based multi-layer perceptron (MLP) in Matlab nftool module. Calculated values of thermal performances are compared to predicted values. Statistical error analysis is used to evaluate results. Comparing and statistical results demonstrate effectiveness of the proposed ANN. Also reliability of ANN and meaningfulness of input variables are tested via applying stepwise regression method to the data used in designing ANN.

A Parametric Study on the Thermal Performance of a Solar Air Collector with a V-Groove Absorber

In this paper, a parametric study on the thermal performance of a solar air collector with a v-groove absorber has been investigated. In this single-cover collector, the air flowing in the channel formed by the v-groove absorber and the bottom plate—which is flat and insulated—is along the groove, aiming at enhanced heat transfer rate between the air and the absorber by increasing the heat transfer surface area, which is crucial to the improvement of thermal performance of a solar air collector. To quantify the achievable improvements with the v-groove absorber, a flat-plate solar air collector where both the absorbing plate and the bottom plate are flat, is also considered. The thermal performance of these two types of solar air collectors is analyzed and compared under various configurations and operating conditions. The results show that the v-groove collector has considerably superior thermal performance to the flat-plate collector. It is also found that to achieve better thermal performance, it is essential to; use a small size of the v-groove absorber for the v-groove absorber collector and to maintain a small gap between the absorber and the bottom plate for the flat-plate collector; to use selected coatings that have a very high absorptivity of solar radiation but a very small emissivity of thermal radiation on the absorber and glass cover; to maintain an air mass flow rate above 0.1kg/m2s; and to operate the collectors with the inlet fluid temperature close to that of the ambient fluid.

Sensitivity analysis of thermal performances of flat plate solar air heaters

Sensitivity analysis is a mathematical tool, first developed for optimization methods, which aim is to characterize a system response through the variations of its output parameters following modifications imposed on the input parameters of the system. Such an analysis may quickly become laborious when the thermal model under consideration is complex or the number of input parameters is high. In this paper, we develop a mathematical model to analyse the heat exchanges in four different types of solar air collectors. When building this thermal model we show that for each collector, at quasi-steady state, the energy balance equations of the components of the collector cascade into a single first-order non-linear differential equation that is able to predict the thermal behaviour of the collector. Our heat transfer model clearly demonstrates the existence of an important dimensionless parameter, referred to as the thermal performance factor of the collector, that compares the useful thermal energy which can be extracted from the heater to the overall thermal losses of that collector for a given set of input parameters. A sensitivity analysis of our thermal model has been performed for the most significant input parameters such as the incident solar irradiation, the inlet fluid temperature, the air mass flow rate, the depth of the fluid channel, the number and nature of the transparent covers in order to measure the impact of each of these parameters on our model. An important result which can be drawn from this study is that the heat transfer model developed is robust enough to be used for thermal design studies of most known flat plate solar air heaters, but also of flat plate solar water collectors and linear solar concentrators.

Development of solar air collectors for drying applications

In the present work, an experimental study of three types of solar air collectors, namely flat plate, finned and v-corrugated, has been performed towards achieving an efficient design of air collector suitable for a solar dryer. A series of experiments were conducted, based on the ASHRAE standard, under Singapore climatic conditions. The performance of all three collectors is examined over a wide range of operating and design conditions. The v-corrugated collector is found to be the most efficient collector and the flat plate collector the least efficient. The collectors are also studied in double pass mode to investigate the extent of improvement in efficiency that can be achieved without increasing the collector size or cost. Double pass operation of the collector leads to further improvement of the efficiency compared to the single pass of operation. The improvement in efficiency for the double pass mode is most significant in the flat plate collector and least in the v-groove collector.

Thermal performance of three types of solar air collectors for the jordanian climate

The application of solar energy for air heating in Jordan has been explored by using numerical computations. Three flat-plate (bare-covered- and finned-plate) collectors are evaluated for use in air heating. Based on efficiency and cost per square metre, the covered-plate collector is found to be most suitable for air heating. A set of design curves is developed for the covered-plate collectors, which can be used to predict temperature rises for different flow rates and collector areas.

Agricultural solar air collectors: Design and performances

Several types of solar air collectors made from plastic film can be used for drying operations on the farm (fodder, fruit, grain, etc.). Four types of collector are discussed as well as a ventilated horticultural greenhouse. The purpose of this article is to give detailed thermal models for these collectors and to compare their respective performance. The solution of these models gives the values of the parameters used in Duffie-Beckman flat-plate collector theory.