Solar Air Heating Collector Research Articles

Fabrication and characterization of nano structured honeycomb absorbers and thermal analyses on solar air heating collector

Fabrication of nano structured absorber is mandatory for reaping the enhanced thermal performance of solar collectors. In this connection, the nano carbon and aluminium composite was coated on aluminium substrate, which was similar to the hexagon shaped honey comb, and the solar absorber was developed. It was characterized through X-ray Diffractometer (XRD), Fourier Transform Infrared (FTIR) spectrometer and UV–Visible spectrophotometer (UV). It was also thermally analyzed not only in outdoor conditions but also in stagnant conditions in solar air heating collector. The research results pertaining to characterization of solar absorber showed that the crystallite size was in nano ranges and the nano particles had face-centre cubic structure. The research results pertaining to characterization of solar absorber also showed that the nano composite had excellent absorption in UV and visible region. The research result related to thermal analysis in outdoor environment revealed that the enhancements of temperature on solar absorbers coated with carbon and aluminium nano composite in the mass ratio of 60:40, 70:30 and 80:20 were 23.5oC, 25.1oC and 24.4oC respectively. The research result related to thermal analysis in stagnation environment also revealed that the enhancements of temperature on glass cover, carbon and aluminium nano composite coated absorber and working fluid were 69.4oC, 110.6oC and 99.0oC respectively. On the basis of research outcomes, it could be concluded that nano carbon and aluminium composite coated solar absorber would be used for photo thermal applications due to their desirable optical and thermal properties. It could also be concluded that nano carbon and aluminium composite coated solar absorbers would be used in photo thermal appliances due to their positive impact on thermal performances.

Increasing Performance Efficiency by Investigating the Surface of the Solar Air Heater Collector

This article discusses the issues of increasing the working surface of the device by giving a geometrically concave shape to the air ducts of the proposed solar air heater, designed to save energy and increase the possibility of efficient use of renewable energy sources, which is becoming increasingly important topical issue today. The influence of the concave shape on the air movement relative to the outer surface of the concave air duct is investigated.

Performance of Cylindrical Plastic Solar Collectors for Air Heating (Dept.M)

Performance of Cylindrical Plastic Solar Collectors for Air Heating (Dept.M)

Flat solar air heater collector with phase change materials for domestic purposes in Iraqi climate

In this study, a solar air heater was built and flat in shape, one with a black plate to gain heat and the other was placed by a tank under this plate containing paraffin wax to increase thermal storage. Energy and exergy for air heater were also analyzed. The performance of heat air heaters was analyzed by measuring various variables such as the intensity of solar radiation, the ambient temperature, the temperature of the air inside and out of the heater, and thermal efficiency. The maximum thermal efficiency of solar heater with PCM is 16.3% compared to normal heater which was 12.4%. The addition of paraffin wax to the air heater caused an increase in the duration of air heating. The maximum exergy effectiveness of a flat solar air heater collector with heat storage materials (PCM) is 0.7%.

Thermal Efficiency of a Solar Air-Heating Collector with a Metal Chip Absorber

It is known that one of the main issues of heat transfer in complex designs of solar air-heating collectors is the problem of determining the coefficient of convective heat transfer in some parts of absorbers. The article studies the processes of heat transfer occurring in a solar air-heating collector with an absorber, which is a system of metal flow chips and a V-shaped surface. A description of the design of a solar air-heating collector with a metal chip absorber is given. The absorber allows us to increase the contact surface between the coolant and the absorber. The experimental procedure and the results are presented. The experiments have shown that within the range of 850 – 950 W / m2 of direct incident solar radiation density, the average heating of coolant is 17.5 °C; within the range of 650 – 750 W / m2, it is 14.1 °C; within the range of 450 – 550 W / m2, it measures 10.1 °C. The maximum coolant heating is 27 °C which is equal to the output collector temperature 60 °C. The average heating of the coolant is 14 °C, which corresponds to the average output temperature of 45 °C. According to the data obtained in the experiment, empirical formulas are concluded. They are presented in the form of the dependence Nu = f (Re), it is aimed at determining the heat transfer coefficient of flow metal chips and V-shaped absorbers of a solar air-heating collector. The dependence of the absorbers heat transfer from metal flow chips and the V-shaped surface of the solar air-heating collector on the Re numbers within the range of 103÷104 is shown. A formula is derived that allows us to compare the effectiveness of absorbers of various types with a flat absorber of a solar air-heating collector

The contribution of a solar air heater collector to the cooling load in a building

Over the last few decades, there is a clear target for reducingenergy needs in the building sector. The above objective can be achieved both by renovating the existing building stock and/or by constructing new buildings that will meet the characteristics of zero or nearly zero energy buildings. In order to construct or renovate a building into a zero or almost zero energy building, different passive, active and hybrid systems can be used. One such system is a solar air heater collector. The above system was installed in the south facade of the outdoor test cell (ZED-KIM (Zero Energy Demand – Kimmeria)), located at the Campus of the Environmental Engineering School, DUTH at Xanthi (Greece). In the present study, the monitoring results of the solar air heater collector and its contribution to cover the cooling load of a building will be presented. The system was monitored under real weather conditions for the period June 2017 to August 2017. This period was separated in two sub-periods. In the first one, the system operated as a solar air heater and with the appropriate modifications air from inside the test cell was passed through solar collector and hot air was rejected out. In the second sub-period, a ventilation inlet was added in the north facade of the test cell, and the system operated as a solar chimney. The heating load that rejected out in the first sub-period was 12 KWh and in the second sub-period was 58.5 KWh. In other terms the cooling load of the test cell was reduced by 70.5 KWh for the whole period of measurements. In addition the cooling load for the specific climate zone of Greece and for 20 m2 cooling space was 488 KWh so there was a reduction of 15 percent. Furthermore, it was noticed that the thermal efficiency of the system increased above 50 percent between 1st and 2nd sub period, with values being 16% and 34% respectively. Based on the above results, it is concluded that even in hot weather conditions prevailing in northern Greece, the use of a solar air heater collector with the appropriate modifications can cover, in a significant degree, the cooling load of a building and in conjunction with other passive and active systems it can lead at a nearly zero energy building.

Steady state simulation on combination of glazed and unglazed flat plate solar collectors for air heating

Unglazed flat plate solar collectors usually have lower costs and can have an advantage in situations where heat loss is low. In this study a steady state simulation of the combination of glazed and unglazed flat plate solar collectors for air heating was performed for various conditions of heat transfer coefficient (3, 12 and 21 W/m2-°C), inlet temperature (30, 45, 60 and 75°C) and solar irradiation (350, 600 and 850 W/m2). The efficiency of combined system of the glazed and unglazed solar collector area was better compared to the system which consists entirely of glazed at a low coefficient of heat transfer (3 W/m2-°C), except for high inlet temperature (more than 60°C) and low solar irradiation (350 W/m2-°C). For the combination of 6m2 unglazed and 9m2 glazed solar collector, the higher percentage of flow rate through unglazed collector slightly increases efficiency except at high inlet temperatures (> 60°C) for high heat transfer coefficient (12 and 21 W/m2-°C) and at low solar irradiation (350 W/m2). For air heating operations which are maintained in equilibrium conditions the temperatures of the air produced were slightly higher than that of the collector inlet.

Building façade integrated solar thermal collectors for air heating: experimentation, modelling and applications

In this paper the design and the energy performance investigation of a new flat-plate solar thermal air collector prototype is presented. The adoption of cost-effective materials and simple design solutions represent the main novelties of the proposed device when compared to existing commercial collectors. In addition, the prototype is suitably designed to be integrated into the building envelope (façade), which is a key feature for the market uptake of building integrated solar thermal systems. The paper includes the description of the dynamic simulation model, developed for the energy and economic performance analyses of the whole building-prototype system. The simulation model, implemented with a computer code written in MatLab, is able to predict both active (hot air production for building space heating) and passive (winter free heating and summer overheating) effects due to the building integration of the proposed solar collector. By such tool, indoor comfort investigations can also be carried out. The dynamic simulation models of both the building and the collector prototype were successfully validated.In order to show the features of the developed simulation code, a suitable case study was carried out. It refers to an office space, part of a high-rise multi-use building, simulated as located in three different weather zones (Freiburg, Naples and Almeria). The examined solar collector is modelled as vertically integrated into the building façade, and three different orientations (East, South-East and South) were taken into account. Interesting results for the energetic, economic and occupants comfort points of view are obtained. By taking into account an initial cost of the system of about 5 k€, the primary energy savings achieved by the proposed system against the traditional buildings range between 1.9 and 8.0 MWh/y (depending on the selected weather zone and backup system). The shortest payback for all the investigated weather zones is obtained for Naples, which is equal to 6.2 years.

Numerical Analysis and Optimization of Area Contribution of The PV Cells in the PV/T Flat-Plate Solar Air Heating Collector

This paper presents a practical design of combination solar photovoltaic panel (PV) and an ordinary flat-plate air heating solar collector (FPSC. (The offered collector generated both electrical and thermal power for many applications such as (drying, heating, cooling, etc...). The PV cells are placed in the entrance of the (FPSC), the design avoids the temperature increasing of the PV. In this paper the photovoltaic thermal (PV/T) collector energy analysis were carried out. A mathematical model has been built in order to determine the optimum contribution ratio of the PV cells in the offered collector. The model takes into account the variation of the electrical characteristics with solar radiation and the PV cell's temperature. The obtained results have shown that for a (PV/T) collector of 3m long, the maximum energy extracted from the collector, when the length of the PV panel is 2.4 m and the rest of the collector is ordinary FPSC. Furthermore, the electrical efficiency and the thermal efficiency of the PV/T system was found to be higher than that of the conventional separated systems.

Developing of a ventilation system for residential houses with solar air heater

Ventilation of buildings in winter period, especially in cold climatic conditions, requires rather big quantity of heat for preheating the ventilation fresh air. Consequently, an average low-income family pays a tangible cost for ventilation of apartments. To provide low cost ventilation of houses it is becoming attractive the use of solar energy for preheating the outside fresh air, before its supplying into the house. For this purpose, cheap solar air heaters are needed. To solve this problem a simple and cheap construction of solar air heater was developed, which is the main part of the ventilation system. The system consists of air heating solar collectors, installed on the roof of the house, warm air distribution ductwork, internal air circulation ducts and air-circulating fan. In summer period, the system is used only during nighttime period for circulating outside colder air through the internal space of the house. Such operation allows cooling internal air and as well the constructions of the house. As a result, the house accumulates nighttime natural cold for using it at daytime cooling purposes. Presentation includes the scheme, explanation of operation and method for design of suggested ventilation system. Analysis proved the energy efficiency and cost effectiveness of the new system.

Transient numerical study of thermo-energetic performance of solar air heating collectors with metallic porous matrix

This paper presents the numerical modeling of the thermo-energetic behavior of solar air heaters with a porous matrix to enhance the heat transfer from the absorber plate to the circulating air. The porous matrix was modeled by defining an average strand at which the porosity, the effective cross-sectional area for conduction heat transfer, and the effective lateral area for convection and radiation heat transfer were determined. The pressure drop along the collector was small because the porosity of the matrix was high (97%). For this collector, the thermohydraulic efficiency reaches a maximum value of 63% for an air mass flow of 0.06 kg/s and thereafter decreases as the power consumed by the fan increases. Using data measured during the winter of 2015 in a prototype solar collector, the numerical model was validated. The fit relative error between measured and modeling values was 3% for the air output temperature and 5%, on average, for the useful energy gain of the collector. The dependence of the collector heat removal factor, FR, on the porosity was studied through numerical simulation. The results of this study revealed that, as the porosity of the matrix decreases, the FR factor increases. Therefore, in order to maximize the thermal efficiency of the collector, it is recommended to use matrices with a porosity close to 90%. The thermal efficiency of solar air heaters of double-pass counterflow with a metallic porous matrix with a porosity of 90% is 20% higher than that of the same collector without a porous matrix for the same operating parameters. The results of this study are of technological importance for the efficient design of solar air heaters of double-pass with a porous matrix.

Performance prediction of extended surface absorber solar air collector with twisted tape inserts

The present work predicts the thermal and thermohydraulic performance of the extended surface absorber solar air heating collector equipped with twisted tape inserts of twist ratio Y = 2, 4, 6 and 8. A mathematical model has been formulated based on energy conservation equations of the various elements of the collector under consideration. The model is numerically solved using the MATLAB codes. Effects of mass flow rate, twist ratios and the solar intensity of the performance of the heater have been investigated. The results obtained are compared with the results of conventional and finned absorber solar air collector. Results conveyed that at mass flow rate of 0.025 kg/s, with increase in solar intensity from 500 W/m2 to 1000 W/m2, the thermal efficiency of the collector with twist ratio Y = 2 increases by 8.3%. Furthermore, integrating fins and twisted tape (FTTs) with the absorber plate, a maximum enhancement of 22.56% in the thermal efficiency has been achieved as compared to 11.49%, when only fins are attached. This maximum enhancement is observed with the tape with minimum twist ratio. Hence, the collector having absorber plate attached with fins and twisted tapes of twist ratio Y = 2 is the most efficient.

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.

Thermo-environomical and drying kinetics of bitter gourd flakes drying under north wall insulated greenhouse dryer

The greenhouse dryers consist opaque and insulated north wall with solar air heating collector at the bottom. It has been used for bitter gourd flakes drying under natural and forced modes. Thermal models were developed for the both modes of drying. Experiments were performed concurrently for open sun, natural and forced modes to compare their thermal modeling and drying kinetics results. Energy analysis includes; embodied energy, CO2 emission, CO2 mitigation and economic evaluation were done for both modes of drying. The predicted values of bitter gourd flakes and room air temperature, and moisture evaporation rate showed the fair agreement with the experimental observations within the root mean square of percentage deviation ranged from 3.25% to 5.82% and 2.83% to 5.26%, and the coefficient of correlation ranged from 0.98 to 0.99 and 0.99 to 1 under natural and forced modes, respectively. The final moisture ratio was achieved 0.12 after 15 h, 0.14 after 16 h and 0.25 after 21 h under forced, natural and open sun modes respectively. Crop drying under forced mode is found significantly faster than other modes of drying. The Logarithmic model was selected as best curve fitting technique for non-linear regression analysis for forced mode. The energy payback time of developed dryers under natural and forced modes is 1.68 and 2.35 years, respectively. The net CO2 mitigation of bitter gourd flakes drying is 33.04 and 36.34 t under natural and forced modes, respectively.

Agronomic and Physiological Performances of Tomato (Lycopersicum esculentum L.) Under Latent Storage Solar Air Heating Conditions

Greenhouse heating during cold seasons is costly as it is high energy-consuming. The use of latent heat stored during sunny periods for greenhouse heating could be an interesting alternative in several regions worldwide as in Tunisia. Thus, new agronomic/climatic approaches were developed to produce several crops such as tomato (Lycopersicum esculentum L.) in a sustainable way. In this context, the growth, photosynthesis, yield and quality of tomatoes cultivated inside a greenhouse equipped with a new solar air heater with latent storage (IGLHS) were studied in comparison to an unheated greenhouse (IG). Using the solar air heater, the night recovered heat reached 30% of total heating requirements. Consequently, IGLHS microclimatic conditions positively affected plant growth and physiology and led to an early fructification and an increased yield as compared to the unheated greenhouse. Besides, fruit quality evaluation allowed observing significant increases in the lycopene, phenolics, flavonoids and tannins contents (61%, 57%, 63% and 54%, respectively) under IGLHS conditions. The solar air heater collector revealed to be an efficient competitive system enhancing early maturity, leading to increased tomato yields and reducing considerably greenhouse heating costs as it utilizes a highly solicited natural renewable energy.

Thermal modeling and drying kinetics of bitter gourd flakes drying in modified greenhouse dryer

Abstract A modified greenhouse dryers with solar air heating collector were used for bitter gourd flakes drying under natural and forced convection modes till stagnation in their moisture evaporation. Experiments were performed simultaneously for open sun, natural and forced convection modes to validate the thermal modeling and compare drying kinetic results. The predicted temperatures of bitter gourd flakes, room air temperature and moisture evaporation rate show the fair agreement with the experimental observations within the root mean square of percentage deviation ranges from 6.10 to 10.41% and coefficient of correlation ranges from 0.96 to 0.99 under natural convection mode. Similarly, for the forced convection mode, coefficient of correlation ranges from 0.96 to 1 and root mean square of percentage deviation ranges from 3.74 to 7.55%. Logarithmic and Midilli-Kucuk models are selected as best curve fitting techniques for non-linear regression analysis for bitter gourd flakes drying under natural and forced convection modes respectively based on SSE, R-square, adjusted R-square and RMSE values. Proposed thermal models will be helpful in designing energy efficient greenhouse drying system for given crop mass and greenhouse dryer location.

Thermal modeling and drying kinetics of gooseberry drying inside north wall insulated greenhouse dryer

The north wall insulated greenhouse dryers with solar air heating collector are used for gooseberry drying under passive and active modes till stagnation in their moisture evaporation. Experiments are performed simultaneously for open sun, passive and active modes to validate thermal models and compare their drying kinetics. The predicted moisture evaporation rate, gooseberry surface and greenhouse room air temperatures show the fair agreement with the experimental observations within the root mean square of percentage deviation ranges from 4.58 to 16.39% and coefficient of correlation ranges from 0.96 to 1 under passive and active mode. For active mode, coefficient of correlation ranges from 0.94 to 0.99 and root mean square of percentage deviation ranges from 3.49 to 12.24%. The passive mode greenhouse dryer was found more effective than other dryers. Based on SSE, R-square, adjusted R-square and RMSE, Prakash and Kumar model was selected as best curve fitting technique for non-linear regression analysis for gooseberry drying under passive mode. The proposed thermal model will be useful tool for designing energy efficient greenhouse drying system for given mass and location.

Performance analysis of a multi-pass solar thermal collector system under transient state assisted by porous media

An enhanced forced convective multi-pass solar air heating collector (MPSAHC) system aided with granite pebble bed has been investigated in this present article. The air heating collector system was tested in the outdoor solar research site of Universiti Teknologi PETRONAS, Malaysia (4.385693° N and 100.979203° E). Transport pipe for movement of heated air around the system was eliminated in the design of the MPSAHC facility to minimise the thermal losses, pressure drop and the pumping cost of the hot air in the control volume. The daily ambient temperature and relative humidity range recorded during the repeated tests are 21.09–36.64 °C and 48.04–87.9%, respectively. The collector unit achieved a peak temperature of 80.29 °C while the optimum system air mass flow rate of 0.016 kgs−1 was applied. Despite high relative humidity of the environment, the stream of ambient air was heated to 48.53 °C, 57.75 °C and 71.19 °C at different positions in the MPSAHC which correspond to single pass, double pass and multi-pass effects, respectively. The porous matrix exhibited slow energy discharge at night time with air temperature difference of 14.27 °C at 18:00 h to 4.54 °C at 24:00 h over environmental air temperature. MPSAHC system delivered specific energy demand (SED) of 11.51 kWh kg−1 while the maximum thermal collector and daily average transient collector efficiencies of 72.59% and 36.38% were achieved, respectively. A good agreement has been established between reported studies and the present investigation. Although continuity of system operation at night was achieved using porous matrix but improvement is still needed to optimise the system performance.

Experimental validation of an analytical model for performance estimation of natural convection solar air heating collectors

In this paper, the experimental validation of an analytical model that describes the thermal behaviour of double parallel flow air heating collectors working by natural convection is presented. This model was validated with data measured on a collector of these characteristics at the National University of Salta, in the northwest of Argentina. Comparisons between measured and simulated values show an excellent agreement for both the air output temperature and the useful energy produced by the collector, with RMSE values smaller than 6%. The instantaneous thermal efficiency curve of the collector was determined experimentally in winter of 2015. Daily values of efficiency ranged between 0.48 and 0.5 during sunny days, and between 0.41 and 0.46 during semi-cloudy days. A novel correlation between the velocity of the air movement by natural convection and the temperature difference between the building and the collector's interior was obtained by means of linear regression with a correlation coefficient R2 = 0.94. A new correlation Nu = f(Ra) to estimate the average convective coefficients by natural convection was obtained, based on an effective convective heat transfer coefficient calculated with the temperature values measured inside the collector and the absorbed solar irradiance.

A highly efficient solution of off-sunshine solar air heating using two packed beds of latent storage energy

Abstract In order to increase the efficiency of the solar air collector and to improve their thermal efficiency in terms of operating time, hot outlet air temperature and starting operation time, the performance of a compact phase change material solar air heater collector based on latent heat storage energy was investigated. In this solar collector, the two-packed bed absorber unit performs two functions: absorbing the solar energy and storing the thermal heat onto PCM. The solar energy was stored as sensible heat and latent heat in the encapsulated PCM as spherical capsules forms. The experimental apparatus designed and realized in the Research and Technology Center of Energy (CRTEn) in Tunisia. Moreover, the solar air heater with PCM is used only at night on natural convection mode. To assess the performances of the collector, outdoor experiments was carried out to validate the availability of using this solar collector for air heating application. During the experimental test, the inlet and outlet air temperature, the relative humidity, external wind speed, the global solar radiation and the PCM temperature distribution in different bed of the solar collector were recorded. The experimentally obtained measurements are used to analyze the performance of the PCM system, the thermal instantaneous stored, absorbed and useful energy during the charging and discharge process was calculated. The experimental results showed that in the charging process, the stored heat increasing with the absorbed solar radiation. The daily energy efficiency is around 47%.