Design Of Solar Air Heater Research Articles

Numerical simulation of an innovative design of solar air heater using spiral duct inserts for enhancing thermal efficiency

ABSTRACT An innovative design of solar air heater (SAH) with spiral shape is numerically analyzed in this paper. The spiral-shaped SAH hydro-thermal performance is studied for different air mass flow rates using CFD COMSOL Multiphysics software. The outlet air temperature difference, thermal efficiency, flow structure, thermal field and pressure drop are the main parameters which are considered to estimate the fluid flow and heat transfer behaviors of the SAH. The simulation is realized for 1000 W/m2 of solar heat flux and 25°C of ambient temperature as typical climatic conditions in a middle day. The results show that the maximum outlet temperature difference of the SAH reached 93.08°C with 0.0083 kg/s of air mass flow rate. For the range of 0.0083–0.0332 kg/s, the thermal efficiency is varied from 91.41% to 99.01%. The ambitious percentage of the thermal efficiency of 99.01% was observed for 0.012 kg/s. The proposed design provides high thermal efficiency of SAH compared to other configurations of SAH.

Impact of collector aspect ratio on the energy and exergy efficiency of a louvered fin solar air heater

Solar air heaters have huge applications in renewable energy utilization segments concerning the issues of space heating, drying, and ventilation systems. Performance prediction of such systems largely depends upon the design of the collector itself. The present study has highlighted the influence of various aspect ratios of the collector on the thermal and exergy performance of louvered finned solar or air heaters. In this context, an experimental analysis has been carried out to compare the performance of LFSAH with conventional PSAH. These results show that an increase in aspect ratios enhances thermal efficiencies of heat transfer and the systems. An aspect ratio of 4:1 showed the maximum thermal efficiencies as 81.63 % for LFSAH and 68.13 % for PSAH. On the other hand, at larger mass flow rates, the exergetic efficiency of LFSAH becomes lower owing to the larger friction and exergy losses and sometimes even lower than that of PSAH. The novelties of the present study are in emphasizing the importance of aspect ratio in optimizing solar air heater design and providing relevant insight for better energy use.

Numerical analysis of a solar air heater with offset transverse ribs placed near the absorber plate

Solar air heater (SAH) is used to convert readily available solar energy into useful thermal energy. Several studies have been conducted with different roughness elements on the absorber plate. However, study with ribs which are placed slightly above the heated plate, termed as offset transverse ribs, are still scant in the literature. Such study would explain the effect of flow between the ribs and the absorber plate on heat transfer augmentation in a SAH. With this objective a 2-D numerical study is performed here by solving steady RANS equations with RNG k−ɛ turbulence model. The effect of offset transverse ribs on heat transfer, pressure drop and thermal enhancement factor (TEF) is investigated. The geometrical parameters, such as, relative gap (α), relative height (β) and relative pitch (λ) are varied in the range of 0.0–0.045, 0.015 to 0.09, and 0.0333 to 0.1, respectively. The performance of SAH is evaluated on the basis of highest enhancement in relative Nusselt number (NuR/Nu) and thermal enhancement factor (TEF). A slight gap between the ribs and the absorber plate (α = 0.0075) is observed to yield better thermal performance than that for the attached ribs (α = 0). The maximum enhancement in NuR/Nu is found to be 1.52 for α = 0.0075. However, increasing the gap (i.e., α) prevents the flow reattachment with the absorber plate. Increase in rib height, on the other hand, is found to be more effective in heat transfer enhancement, but with a price of a significant enhancement in pressure drop. This leads to a reduction in the overall performance of SAH. Increment in pitch distance, however, reduces the enhancement in both Nusselt number and friction factor. By considering these three parameters, the highest TEF is found to be 1.042 for α=0.0075, β=0.030, and λ=0.0333 at Re equal to 13000. Finally, correlations for NuR and fR are derived as a function of the parameters investigated for helping the design of SAHs.

CFD modeling of a tubular three-pass solar air heater with phase change material: Investigating heat transfer enhancement and energy efficiency

The present study introduces a novel solar air heater design featuring a tubular surface with three passes arranged in a counter-flow configuration, aimed at improving compactness and enhancing heat transfer characteristics. The research involved the development and validation of a computational fluid dynamics (CFD) model, which was utilized to accurately depict the distribution of solar flux through the system components by comparing the model results with experimental data. The study involved conducting a comparative analysis between the tubular three-pass solar air heater with phase change material (TTPSAH_PCM) and conventional flat plate solar air heaters (FPSAH) to ascertain the superior design characteristics. A thorough investigation was carried out, encompassing evaluations of energy, exergy, outlet temperature, convection heat transfer coefficient, and useful heat gain. The findings indicate that the TTPSAH_PCM outperforms alternative geometries. For instance, when operating at a mass flow rate of 0.006 kg/s, the TTPSAH_PCM demonstrates substantial enhancements in several key metrics, including an 11.4 % increase in the system's daily thermal efficiency, a 17 % improvement in exergy efficiency, and a 4 % rise in outlet air temperature. The convection heat transfer coefficient of TTPSAH_PCM exhibited a 155.6 % increase compared to the FPSAH type. Moreover, the system being investigated demonstrates an 8.5 % rise in useful heat gain. The results underscore the enhanced efficacy of the TTPSAH_PCM system in contrast to alternative solar air heater arrangements, and its applicability for both drying operations and indoor heating applications.

Thermal Performance Improvement of a Spiral Channel Solar Air Heater: Numerical and Experimental Investigation in the Desert Climate of Gabes Region

Abstract This study focuses on improving the thermal performance of a solar air heater (SAH) using a single-pass spiral-shaped ducts. The SAH is designed and tested under prevailing weather conditions of Gabes, Tunisia (33°52.8876′ N,10°5.892′ E). The experimental measurements are carried out over 4 days. Similarly, a computational fluid dynamics (CFD) model was developed to study the fluid flow and the heat transfer inside the SAH using the commercial software ansys fluent 2021 R1”. The discrete ordinate (DO) radiation model and the k-ω shear stress transport (SST) turbulence model are used to study the radiative heat transfer and the turbulent flow in the SAH, respectively. The numerical model is validated against experimental data, and the average error does not exceed 3.6%. To improve the heat transfer phenomena, the ratio of horizontal baffle spacing “d” to vertical baffle spacing “p” (d/p) is numerically investigated. Moreover, the highest air outlet temperature during the test days reached 81.1 °C under a mass flowrate of 0.0077 kg/s. The maximum efficiencies are 57%, 54%, 49%, and 46% for the configurations d/p = 1.5, d/p = 2, d/p = 1, and d/p = 0.5 under a mass flowrate of 0.02 kg/s, respectively. The SAH design with d/p = 1.5 is about 4–10% more efficient than the standard design with d/p = 1 under a mass flowrate ranging from 0.0077 kg/s to 0.025 kg/s.

Numerical investigation of thermal performance factor in dimpled-solar air heater (SAH)

ABSTRACT A novel solar air heater design with dimples in a rectangular channel with a 7:1 aspect ratio was examined mathematically by ANSYS FLUENT 14.0. Four different cases of dimples configuration namely A (a spherical dimple), B (hemispherical symmetric protrusion is made in the center), C (secondary protrusion is present at an angle of 26.5o) and D (secondary protrusion is made tangent to the upstream) were simulated over the Reynolds number range of 10,000 to 30,000. CFD simultaions were performed for the inlet mass flow rate corresponding to the Reynolds number value of 10,000 and constant wall temperature of 320K. After turbulnec model selection and grid independence study, the numerical results are validated with the experimental data within the error band of ±15%. Secondary protrusion inside the dimple, an improvement in heat transfer and reduced flow recirculation was observed. The maximum thermal performance factor for the B, C, and D cases was found at Reynolds numbers of 10,000, 15,000, and between 20,000 and 30,000, respectively. Over the spectrum of Reynolds numbers, case D exhibits the most promising design overall with an increase of 37.5% in thermal performance factor. These design scenarios demonstrate an encouraging improvement in thermal performance factor.

High power and energy density of a wavy PCM unit embedded in a solar air heater utilizing fractional porous media

This experimental and numerical investigation presents the optimization of a wavy PCM unit to obtain high power and energy density with and without porous media for solar air heater applications at low ambient temperature (12oC≤Ta≤24oC). Hence, paraffin wax as a thermal energy storage material and wire mesh as a porous media are selected in this investigation. The effect of the fractional porous region (25%≤ψ≤100%) and porosity (94%≤ϕ≤100%) of the PCM unit is investigated to obtain desired power and energy density. The obtained numerical results revealed that the porous fraction region (ψ) of 50% and porosity (ϕ) of 96% are the optimum value in wavy PCM unit to obtain high power and energy density. As an extension of this work, the optimized thermal energy storage unit is further utilized in an impinging jet solar air heater design to obtain instant and long thermal backups and, consequently, outlet air at high temperature. The wavy PCM unit embedded impinging jet solar air heater is experimentally investigated under outdoor conditions for two cases; viz, to obtain instant and long thermal backups. To obtain instant and long thermal backups, a full day and alternative operations are conducted. Whereas, in case of alternative operation, charging of the PCM unit is only done up to the maximum sunshine hour of the day and solar air heater is operated during the night to utilize stored thermal energy at high power and energy density to deliver outlet air at high temperature for the long duration. Moreover, the experimental results revealed a maximum outlet air temperature of 59°C at 0.01 kg/s and a significant thermal energy backup up to 5 h at an outlet air temperature gain of ≥ 5°C. The economic analysis is also conducted for the solar air heater design and the operating cost is obtained as 0.02 INR/kWh at the optimum condition.

Machine learning-based modelling using ANN for performance prediction of a solar air heater design with jet impingement

The prediction of heat transfer performance for solar air heater (SAH) designs is important to assess its potential without relying on extensive experimental studies. This work aimed to predict the heat transfer characteristics of a SAH design with jet impingement using an extensive artificial neural network (ANN) study and covering a complete year-long ambient and various operating parameters (commensurate and non-commensurate). Total 84 ANN models were developed using different network types, transfer functions, and training functions. They were tested on 174 representative datasets collected throughout a year. The best ANN model was found to be the feed forward backpropagation model with tangent-sigmoid transfer function and LM training algorithm, which produced accurate predictions for thermal efficiency, exergy efficiency, and thermo-hydraulic efficiency, with sample errors within ±5 %. The numerical values of R2, MAE, RMSE, and COV from the ANN model results were respectively 0.9972, 0.9053, 1.1884, and 2.0618 for thermal efficiency, 0.9947, 0.2631, 0.3363, and 1.7157 for exergy efficiency, and 0.996, 0.0139, 0.0193, and 0.8076 for thermo-hydraulic efficiency. The study concluded that ANN models can accurately predict the heat transfer characteristics of an SAH design, requiring less time and less computational resources compared to conventional experimental or computational methods.

Analytical investigation of solar parabolic trough receiver with multiple twisted tapes using exergy and energy analysis

Exergy analysis is an important thermodynamic approach to studying the system's actual output, considering all losses. The present study is an analytical approach to calculating the thermal and exergetic efficiencies of the parabolic trough receiver using MATLAB R2018a simulation software. These efficiencies are evaluated considering temperature rise characteristics and parametric design factors. The influence of the solar air heater's thermal and exergy analysis-based mathematical model on all design parameters is examined. The receiver tube has multiple twisted tape inserts with three varying parameters, i.e., twist ratio (y/w) = 3 to 5, perforation ratio (dp/w) = 0.05 to 0.25, and winglet ratio (d/w) = 0.1 to 0.3. The twisted tape with y/w, dp/w, and d/w having values 3, 0.1, and 0.05 perform better regarding energy and exergy with values 84.27% and 4.28%, respectively. This thorough examination can prove to be highly effective and advantageous in generating the design model for the specified twisted tape parameter value without requiring extensive investment in actual experimentation while also furnishing an evaluation of the performance of the solar air heater design.

Numerical analysis of a novel solar air heater design with V-ribs and jet cooling

The application of solar air heaters (SAHs) is an effective method of utilizing abundant solar energy for heating purposes and reducing the consumption of fossil fuels. However, the performance of SAHs is characteristically low owing to a sublayer formation over the heated surface. To address this low performance, numerical examinations on a novel configuration of SAH have been performed in this study. The proposed design encompasses a combined arrangement of both impinging air jets and rectangular sectioned V-ribs on the absorber surface. The effect of varying roughness height, pitch, and angle of attack from 0.016 to 0.024, 0.264 to 0.792, and 30° to 75° respectively is investigated while keeping impingement parameters fixed and varying Re from 3000 to 18000. Nusselt number (Nu) and friction factor (ff) characteristics as functions of roughness parameters are evaluated. The results exhibit a considerable enhancement of 3.36 and 5.31 in Nu and ff respectively in contrast to conventional SAHs under similar boundary conditions. Moreover, the proposed model performs best at Re = 18000 with the highest thermohydraulic performance (ηcombined) of 1.92. The study concludes that the proposed arrangement of jet cooling with rectangular sectioned V-ribs is an efficacious way for improving the performance of SAHs.

The optimal geometric design of a v-corrugated absorber solar air heater integrated with twisted tape insert

The proper design of a solar air heater depends on the highest thermal performance of the solar collector. In the present paper, proposed a method to find an optimal dimension of V-corrugated absorber solar air heater (VSAH) combined with a twisted tape insert (TTI). The design variables of the VSAH-TTI are length, width, number of channels, and twisted tape ratio. The effect of each design variable is examined and studied under various ranges of Reynolds number (Re). Given the complexity in changing design variables of solar collector having a V-corrugated absorbing plate with twisted tape insert (VSAH -TTI) to find the highest thermal performances, the multi-objective function genetic algorithm is used to find the optimal dimensions of VSAH-TTI based on maximizing the heat gain, thermal and effective efficiency as well as minimizing the pressure drop on solar collector. The range of each design variable of the VSAH-TTI by means of length (1 – 2.5 m), width (0.5 – 1.5 m), number of channels (4 – 14), and twisted tape ratio (1 – 8) are specified in paper based on the most common practical values of the solar collector. The results showed for the case under study that each design variable of VSAH-TTI affect the thermal performance and the optimized geometry by using a genetic algorithm (Ga) can find the optimal geometric dimensions of VSAH-TTI. The optimal dimension by using Ga can increase the heat gain by more than 8% and increase the effective and thermal efficiency of more than 7% for the original geometry. Furthermore, the optimized geometry can reduce more than 29% for the original geometry. These improvements in optimized geometry for VSAH- TTI without introducing any additional items.

Design of a recyclic solar air heater for low temperature regions utilizing integrated wavy corrugated thermal energy storage systems

This work presents thermal performance prediction of a design of solar air heater for low temperature regions utilizing integrated thermal energy storage systems (PCM unit). Recyclic double air pass is considered for a range of recycle ratio, G = 0–1 at a mass flow rate of 0.01 kg/s. Paraffin wax as a PCM for thermal energy storage is used in two different designs of wavy corrugated PCM unit. Geometrical parameters related to PCM units are considered such as wavelength 0.05≤λ≤0.1m, amplitude 0≤α≤0.015m, length 1≤L≤2m, width 0.5≤W≤1.414m, and height 0.02≤h≤0.04m. Energy-enthalpy method is used to predict the temperatures and phase change of PCM employing finite volume method. Explicit time marching scheme is applied to present transient thermal performance of solar air heater designs. In addition, employed non-orthogonal structured mesh in the complex wavy corrugated PCM units, ensured the numerical accuracy in the prediction. Ambient temperature, Ta and heat flux of the range 5o≤Ta≤20oC and 1000 W/m2 is considered to present realistic situation of low temperature regions, respectively. Thermal backup of 24 h at a significant high outlet air temperature than ambient is aimed to provide in order to support wide thermal applications of solar air heater. The obtained results reported the significantly higher outlet air temperature for the heater design i.e. 9 °C than ambient corresponding to 24 h. Optimum value of different geometrical and flow parameters is obtained as ṁ=0.01kg/s,G=1,λ=0.1m,α=0.005m,L=1.414m,W=1.414mandh=0.04. In addition, presented contours results revealed the associated physics and important guidelines upon the use and size of the thermal energy storage systems in solar air heaters.

The CFD analysis of the effect of internal peak angle and mass-flow rates on the thermal performance of solar air heater with triangle cross-section

A new design of solar air heater with triangle cross-section is numerically studied. The thermal performance of solar air heater is studied at various mass-flow rates, inlet air temperatures, and solar irradiation intensities. The CFD model is developed using the software ANSYS FLUENT to study the fluid-flow and heat transfer in the solar air heater. The 3-D discretization is applied to study the thermal performance of solar collector with triangle cross-section. Mesh independence is performed in order to choose the adequate mesh. The discrete ordinate radiation model and the RNG k-? turbulence model are used to study the radiative heat transfer and the turbulent flow inside the solar air heater. Particularly, effects of different internal peak angles (145?,126?, 100?, 80?, and 67.5?) under different solar irradiation intensities (from 620-1081 W/m2) are studied to improve the thermal performance of the solar air heater. The results show a good agreement between the numerical model and the experimental data with an average error of 6%. The maximum outlet air temperature of the solar air heater reached 72 ?C for the geometries with 12 and 16 channels (internal peak angles of 80? and 67.5?, respectively) under mass-flow rate of 0.0264 kg/s. The thermal performances of the solar air heater with 16 and 12 channels are 24.2% higher than standard geometry, respectively for solar irradiation intensity of 1081 W/m2. The configuration with internal peak angle of 80? and 12 channels is selected as the optimal with a thermal efficiency of 79%, a low pressure drops compared to geometry with 16 channels and lower costs.

THERMOHYDRAULIC PERFORMANCE ANALYSIS OF A SOLAR AIR HEATER DESIGN EMPLOYING WAVY CORRUGATED PLATES AND IMPINGING AIR JET ARRAY

This work presents numerical investigation of the thermohydraulic performance of a wavy corrugated solar air heater design employing impinging circular air jet array. Geometrical parameters such as streamwise pitch to hydraulic diameter ratio (0.45 ≤ X/Dh ≤ 1.80), spanwise pitch to hydraulic diameter ratio (0.45 ≤ Y/Dh ≤ 1.80), jet diameter to hydraulic diameter ratio (0.06 ≤ D/Dh ≤ 0.18), duct height (0.021 m ≤ h ≤ 0.046 m), length of the duct (0.75 m ≤ L ≤ 2.25 m), and flow parameter, i.e., Reynolds number, (2000 ≤ Re ≤ 26,000) are considered for investigation. Output parameters, i.e., net power and least required outlet air temperature (≥ 40°C), are introduced. Numerical investigation presents the best thermohydraulic performance at X/Dh = 0.45, Y/Dh = 0.90, D/Dh = 0.06, and h = 0.021 m due to significant jet strength and interaction. Higher value of the Reynolds number, i.e., 18,000, is recommended to obtain effective air jet strength and high thermohydraulic performance for the present design. Moreover, the exiting air causes bending of the impinging air jets that lowers thermohydraulic performance. The maximum angle of jet deflection, 0 = 66°, is obtained at Re = 2000 and L = 2.25 m. Hence, the use of shorter collector length with impinging air jet array is strongly recommended.

Experimental studies and 3D simulations for the investigation of thermal performances of a solar air heater with different spiral-shaped baffles heights

A new design of Solar Air Heater (SAH) with spiral flow path is studied experimentally and numerically. The spiral-shaped SAH performance is studied at various mass flow rates, inlet temperatures, radiation intensity and baffle heights. Similarly, a CFD model is developed using “ANSYS Fluent” software to study the fluid flow and heat transfer in the SAH. Mesh independence is performed in order to choose the appropriate mesh. The discrete ordinate (DO) radiation model and the k-ω Shear Stress Transport (SST) turbulence model are used to study the radiative heat transfer and the turbulent flow, respectively in the SAH. Effects of different baffle heights (42 mm,50 mm,70 mm,90 mm, 110 mm and 130 mm) for different mass flow rates (input velocities:5 m/s,10 m/s,15 m/s, 20 m/s and 25 m/s) are numerically investigated. Local flow characteristics are presented and discussed. The results show a good agreement between the numerical model and the experimental data with an average error of 3.6%. The maximum outlet air temperature of the SAH during the test days reached 77.7 °C with input velocity of 5 m/s. The maximum thermal efficiency is founded for geometries having 110 mm and 130 mm baffle-heights ranges between 40% and 59% for an airflow of 0.0075 kg/s and 0.038 kg/s, respectively. The geometry having a 110 mm baffle-heights shows the optimum thermal performance of 13% higher than standard geometry (50 mm baffle height).

Closed collector –storage solar air heating system thermal performance: an experimental study

ABSTRACT A novel solar air heater design is proposed in the present study. The new design is a closed collector – storage solar air heater system (CCSSAHS) integrated with an internal finned heat exchanger filled with PCM. Two identical solar air heaters were manufactured for the sake of comparison. The first one was filled with RT42, and the second one was filled with RT50. The thermal performance of the solar air heaters was studied for RT42 and RT50, utilizing reflecting mirror; air mass flow rate, that is, 0.25, 0.045, and 0.065 kg/s; series and separation arrangements. For RT42, the experiments showed at 0.025 kg, with mirror, and series arrangement that the stored power, charging efficiency, discharged power, and discharging efficiency were 1255 W, 90.7%, 420 W, and 93.9%, respectively, while for RT50 were 1203 W, 87%, 332 W, and 88.1%, respectively. The highest air temperature difference between the exit and entrance of the solar air heater was found for RT42 at 0.025 kg/s with mirror for the separation arrangement, that is, 16.8°C. In addition, an economic evaluation was presented. CCSSAHS can satisfy tremendous industrial and domestic needs. The internal finned heat exchanger, the core component of the solar air heater, can be recycled from damaged air condition devices. The present proposed design combines the principle of recycling and clean energy to preserve the environment.

Parametric investigation on the thermo-hydraulic performance of a novel solar air heater design with conical protruded nozzle jet impingement

A numerical investigation is carried out on heat transfer behaviour of a novel solar air heater (SAH) design with impinging jets through conical protruded nozzles using CFD simulations. The impact of non-dimensional parameters is analyzed by varying the nozzle length ratio (Ln/Dh) from 0.0434 to 0.434, nozzle throat diameter ratio (Dnt/Dh) from 0.0217 to 0.1086 and nozzle base diameter ratio (Dnb/Dh) from 0.0434 to 0.1086 for Reynolds number (Re) variations from 2900 to 14300. The present results with jet impingement design have been compared with a conventional parallel flow SAH under similar conditions and also with some existing designs. Results show that for a combination of Ln/Dh = 0.2608, Dnt/Dh = 0.0217, and Dnb/Dh = 0.0652, the highest thermal efficiency of 91.25 % and exergy efficiency of 3.55 % are obtained at Re value of 14,300 and 2900, respectively. Also, the highest Nusselt number (Nu) of 223.18 is observed for the same combinations at Re = 14300, whereas the highest thermo-hydraulic performance parameter (THPP) of 3.65 is observed for Re = 5740 owing to minimum pressure drop across the collector. With much improved thermal efficiency and THPP, the proposed design and the developed CFD model can be used for further development of impinging jet SAH design.

Design a low-cost, medium-scale, flat plate solar air heater: An experimental and simulation study

The most efficient solar air heater is expensive, and attempts to reduce costs lead to reduced efficiency. The current study presents a low-cost, medium-scale, flat plate solar air heater's design, simulation, and experimental thermal analysis. Carbon steel, thermocol, window glass, and aerosol spray paint were utilized for fabrication to decrease manufacturing costs. Initially, a mathematical model was developed, and experimental tests on this system were carried out with different absorber plates and glass covers in various weather conditions. The air mass flow rate of the collector is set at 0.073 kg/s. According to the experimental results, the solar air collector with a finned steel absorption plate, black paint, and double-glazing exhibit optimal performance. Under average solar radiation and ambient temperature of 910 W/m2 and 29.44 °C, respectively, the maximum thermal efficiency is 60.81 %, the average thermal efficiency is 56.01 %, and the average air temperature difference between the inlet and outlet is 40 °C. Whereas, for the solar air collector with plain steel absorber plate and single glazing, the least desirable performance was observed with a maximum collector efficiency of 45.76 %, an average thermal efficiency of 39.22 %, and an average air temperature difference of 20.14 °C between inlet and outlet under average solar radiation and ambient temperature of 810 W/m2 and 29.98 °C, respectively. Compared to the results, the thermal performance of solar air collectors with a finned steel absorption plate, black paint, and double-glazing was improved by 14 % to 20 % under different conditions. In addition, the solar air heater was designed, and a simulation study was performed in COMSOL Multiphysics software to find the temperature distribution of the glass cover and absorber plate. The experimental findings demonstrated that this convenient and cost-effective solar air collector was designed successfully and can be utilized in heating applications.

Utilising fractional porous interface for high thermal performance of serpentine wavy channel solar air heater

This work investigates the thermohydraulic performance of a porous serpentine wavy channel solar air heater. Comprehensive illustration on the effect of fractional porous interface (25%≤ξ≤100%), channel porosity (90%≤φ≤100%) and Reynolds number 2000≤Re≤11000 on the thermohydraulic performance of solar air heater design is presented. Experiments are performed and numerical results are validated to conduct further investigations for the optimization of the input variables. This study is a unique idea that broadly presents the scope of thermal performance improvement by utilizing the porous media in fraction and varying porosity in solar air heater channel and highly useful for the researchers of this field. Finite volume method based computational fluid dynamics tool is used to conduct numerical investigations, Forchheimer equation is used to account the effect of porous media and surface to surface (S2S) radiation model to capture the effect of shape factor and emitted radiation in collector channel. It is obtained that ξ of 25% and φ of 93% delineated the best thermohydraulic performance (THPP) of 4.52 for the present solar air heater design. While, the obtained thermohydraulic performance is 186% times higher compared to the smooth design. The excellent results that come into the light from numerical investigation are the secondary flow formation in the porous and flow zones at higher Reynolds number and lower fraction of porous region (ξ), and for all configurations of ξ at large channel porosity (φ). Hence, results of this investigation not only present the best operational configuration to obtain higher thermal performance, but also present the measures to reduce the material cost of porous media and consequently pumping power.

Eco-Friendly and Economical Solar Heater Design Using Internal Structure and Phase Change Materials

Indoor heating systems currently used are highly dependent on fossil fuels; hence, it is urgent to develop a new heating system to achieve carbon zero-emission. A solar air heater is eco-friendly because it generates nearly zero greenhouse gases. In this study, a parametric study was conducted for optimizing solar air heater design applicable to indoor heating. Installing the internal structure in the solar heater changes the interior flow characteristic, resulting in the air temperature increased by about 14.2 K on average compared to the heater without the internal structure. An additional case study was carried out to optimize the ideal quantity of phase change materials (PCM) in terms of mass fraction and heat capacity for various operating conditions. An excessive amount of PCM (e.g., 66% of the storage space filled with PCM) deteriorates the performance of the air heater unless the entire PCM could be melted during the daytime. After heating, the air temperature was maintained the longest when only 33% of the internal space was filled with PCM. The solar air heater can fully replace or partly assist a conventional heater for indoor heating, and it could reduce approximately 0.6 tCO2 per year.