Performance Of Solar Air Heater Research Articles

Numerical Analysis of a Solar Air Heater With Jet Impingement—Comparison of Performance Between Jet Designs

Abstract One of the ways to improve the performance of solar air heaters (SAHs) is to use jet impingement on the absorber plate to cause turbulence mixing of air in contact with the plate and thereby augment the heat transfer coefficient. Although the jet impingement is a prospective way of improving the SAH performance, comparison of performance between jet designs is not performed so far. The objective of this work is to compare the thermo-hydraulic performance of a SAH with jet impingement through conical protruding jets and circular jets using finite element method based comsol multiphysics software. The simulation studies were conducted for solar radiation in the range 500–1000 W/m2 and mass flowrate in the range 0.01–0.028 kg/s. The flow physics of the jet impingement process is investigated to understand the heat transfer and fluid flow behavior of the SAH with the chosen jet designs thereby obtain their performance insights. The outlet hot air temperature from the heater and its thermal efficiency are compared for different mass flowrates and solar radiations. Also the temperature distributions in the jet plate with the jet configurations are captured and their heat transfer characteristics compared with understand the thermo-fluidic behavior of the SAH. The results demonstrate improved performance of the novel conical protruded jet design that enhances the thermal efficiency up to 78.52%, which is an increase of 13.53% compared with the circular jet design. More elongated streamlines and higher turbulent kinetic energy with increased mass flowrate leading to a wide jet affected area inside the duct are the main reasons of its improved performance.

Thermo-Hydraulic Performance Characteristics and Optimization of Protrusion Rib Roughness in Solar Air Heater

To enhance the thermal performance of solar air heaters (SAHs), protrusion ribs on the absorber are considered to be an attractive solution due to their several advantages. These ribs do not cause a significant pressure drop in the SAH duct and help to enhance the heat transfer to flowing air. On the other hand, a degree of roughness of the protrusion rib on the absorber can be produced by pressing the indenting device without adding additional mass. In this paper, the thermo-hydraulic performances of different roughnesses of the conical protrusion rib on the absorber plate have been evaluated by the mutual consideration of thermal as well as hydraulic performance in term of net effective efficiency. Therefore, an analytical technique has been exploited to predict the characteristics of the net effective efficiency under various operating conditions, such as the flow Reynolds number, temperature increase parameter and insolation. The effects of the conical protrusion rib roughness—namely the relative rib pitch (p/e) and relative rib height e/D) in the ranges of 6–12 and 0.200–0.044, respectively—have been evaluated. The highest value of net effective efficiency of 70.92% was achieved at a p/e of 10 and e/D of 0.0289. The optimization of the rib parameters has been carried out in different ranges of temperature increase parameters for the highest values of net effective efficiency. A unique combination of rib parameters—a p/e of 10 and e/D of 0.044—are observed to lead to the best performance when operating a solar air heater with a temperature increase parameter of more than 0.00789 K·m2/W.

Effect of extended geometry filled with and without phase change material on the thermal performance of solar air heater

The goal of this research is to conduct an experimental investigation of a solar air heater (SAH) on four different configurations of the two different absorber plates by using phase change material (PCM). Modified models of SAHs with PCM are tested under the climatic conditions of Moradabad city (latitude- 28o 50‘N and Longitude-78o 47‘E), India. Parameters affecting thermal performance of SAH are estimated and studied by conducting experiments on flat plate type absorber and absorber with small cylindrical tubes, with and without PCM. Thermal performance parameters of the modified systems are analyzed for varying mass flow rates such as; 0.01 kg/s, 0.02 kg/s and 0.03 kg/s and varying mass of the tested PCM. Experimental findings showed that the maximum temperature difference between the ambient air and the exhaust air temperature of SAH with PCM filled small cylindrical tubes is about 2 °C to 9 °C in comparison of SAH with flat plate absorber on forced convection. Configuration 4 is observed the optimum configuration among the all tested configurations which provided the exhaust temperature about 48 °C for a lengthy duration about 9.8 h/day minimum with 66% daily efficiency which is quite suitable for space heating and agricultural drying operations.

A review of SPSAH and DPSAH characteristics by variation of fluid profile in the duct

The thermal performance of solar air heaters can be enhanced by increasing the rate of heat transfer. The thermal performance of DPSAH is higher than that of SPSAH based on the study of various researchers. Many researchers have studied the performance analysis of solar air heaters with various heat transfer enhancement techniques like using fins, corrugated absorber plate, packed bed, generating turbulence to the flow. By using ribs of different geometrical shapes and sizes attached to the absorber plate turbulence increases which in turn increases the thermal and thermo-hydraulic performances of the solar air heater. The paper presents the study of the research carried on various processes used to increase turbulence and so thermal performance of SPSAH and DPSAH.

A Review on Augmentation in Thermal Performance of Solar Air Heater

Low thermal efficiency is the remarkable drawback of solar air heaters. They have remarkable importance for low temperature applications. In a solar air heater due to formation of laminar sublayer between absorber plate and the flowing air convection coefficient of heat transfer is small. The laminar sublayer form on the absorber plate can be braked by applying the rib roughness of distinct shape and sizes due to which turbulence in the flowing air increases tremendously due to which friction factor increases between absorber plate and flowing air, resulting in increment in the convection coefficient of heat transfer and pressure drop. Design considerations of solar air heater, rib roughness geometries, fluid flow conditions and their effect on the turbulence, absorber plate temperature, convection coefficient of heat transfer and other thermo-hydraulic augmentation parameters have been minutely discussed. In this review, ongoing research and development on thermo-physical properties of solar air heater and effect of distinct roughness’s over absorber plate on heat transfer augmentation is summarized and to provide viewpoint for future research and development.

Review based on the absorber plate coating for solar air heater applications

The critical review presents the development of the solar selective coating on the absorber plate used for solar air heater. Absorber plate coatings directly convert the solar energy into heat. Different type of solar selective coating is therefore developed with high solar absorptance (α) and low emittance (ε).A critical investigation is done on the absorber plate metal multi-layers and nanomaterial based coating and resulting performance enhancement. This review reports the similarities in the result through in depth discussion on different type of parameters which can affect the solar air heater performance. Analysis was performed and reviewed here to rationalize and eventually explain the complex behaviors of spectrally selective coating. Based on a systematic review by many researches of published works, coating improves the heat absorbing characteristics for the absorber of SAH.

Unconventional solar air heater with triangular flow-passage: A CFD based comparative performance assessment of different cross-sectional rib-roughnesses

Roughness is one of the effective and promising method to improve heat transfer through the solar air heater. The cross-sectional shape of roughness provided on the absorber plate shows a strong influence on solar air heater performance. In this work, the influence of various roughness-elements (such as semi-circular, circular, triangular, square, rectangular) has been investigated on flow dynamics as well as thermal characteristics of solar air heater and these geometries were investigated in triangular passage solar air heater. Commercial software is used for simulating heat and flow dynamics of roughened solar air under steady-state conditions. At Reynolds number of 18.7 × 103, the best thermohydraulic performance parameter (TPP) obtained is 2.75 for forward-chamfered rectangular rib (with e/w = 2). The maximum value of TPP obtained for various roughness geometries decrease in the order of 2.68, 2.57, 2.45, 2.06, 1.79, and 1.60 for backward-chamfered rectangular rib (with e/w = 2), rectangular rib (with e/w = 2), rectangular rib (with e/w = 0.67), square rib, semi-circular rib, and circular ribs, respectively.

Performance analysis of different U-shaped heat exchangers in parabolic trough solar collector for air heating applications

In this article, the thermal performance of a parabolic trough solar air heater (PTSAH) with a U-shaped heat exchanger is evaluated. The solar air heater's performance is examined by using the copper and aluminum U-shaped heat exchangers (UHX) with and without fin alternately, inside the absorber tube placed at the focal length of the nickel-coated stainless steel parabolic trough. The system is examined in the form of temperature difference achieved at the outlet for both the heat exchangers and the solar air heater's efficiency. It is observed that the system performance with the copper heat exchanger is better than the aluminum heat exchanger. Further, it has been found that the efficiency of the solar air heater is increased by 9.29% at a high flow rate with the use of fin when using a copper heat exchanger in place of the aluminum heat exchanger. The temperature difference achieved by the system is also increased by 2.34% at a low flow rate. At elevated temperatures, the percentage increase in solar air heater performance for the aluminum heat exchanger is higher than the copper heat exchanger.

Performance analysis of arc rib fin embedded in a solar air heater

A thermal model is developed for analysing the influences of arc rib fin arrangement and length of absorber plate on the heat transfer characteristics of a solar air heater. The arc rib fin arrangement is designed by varying the fin relative roughness height ratio (e/De) in the absorber plate. Solar air heater with fixed arc rib fin configuration with e/De (0.0422) and variable arc rib fin configuration with two different relative roughness height ratios of e/De (0.0422 and 0.0541) are modelled. The influence of absorber plate length (1 and 2 m) on the solar air heater performance is compared with the configurations mentioned above at various mass flow rates of air (0.02 kgs−1 to 0.06 kgs−1). The outlet air temperature of solar air heater, mean absorber plate temperature, heat transfer characteristics (Nusselt number and frictional factor), pressure drop, thermo-hydraulic performance parameter, efficiencies (thermal, effective, and exergy), collector efficiency factor, and collector heat removal factor are predicted at different air flow rates. The variable arc rib fin arrangement in the solar air heater leads to maximum utilization of available solar energy from the absorber plate, and reported maximum outlet air temperature and lower mean absorber plate temperature when compared to fixed arc rib fin arrangement and smooth duct. Further, the variable arc rib fin arrangement has better heat transfer and thermo-hydraulic characteristics than the fixed arc rib fin arrangement and smooth duct. Thus implementation of the variable arc rib fin arrangement will significantly enhance the overall performance of the solar air heater.

Carbon nanotubes/paraffin wax nanocomposite for improving the performance of a solar air heating system

The study aims to demonstrate the possibility of taking advantage of the high solar radiation in Iraq effectively in heating the air for worming rooms and buildings in winter. The optimal diffusion of solar air heating applications depends mainly on the amount of heat stored and how quickly this heat is transferred to the air. The use of phase change materials to increase thermal storage is one of the best alternatives to date. The disadvantage of these materials is a clear reduction in their thermal conductivity, which impedes the rapid transfer of heat from them to the air. In this study, single wall carbon nanotubes (SWCNT) was added to a local Iraqi made paraffin wax, and the nanocomposite was used in a solar air heater. The SWCNT/paraffin nanocomposite thermophysical properties were examined to show its effect on the solar air heater performance. From the thermophysical properties of the carbon nanotubes added to paraffin in variable mass fractions, 3 wt% was selected. The addition of nanoparticles caused a slight increase in product density and viscosity. The percolation threshold of 3 wt% CNTs increased its thermal conductivity by 12%, reducing the melting and solidification points by 4.5 °C and 9 °C, respectively. The SWCNT/paraffin nanocomposite has improved the stored thermal energy by 20.7% for natural convection, and by 21.2% for forced convection compared to pure paraffin. Results of practical tests confirmed the possibility of using the proposed air heater to work in Iraqi weather conditions.

Performance Augmentation of Solar Air Heater for Space Heating Using a Flexible Flapping Guide Winglet

A new idea is presented in this paper for improving the performance of solar air heater (SAH) designed for space heating by employing a thin flexible guide winglet. In addition to the role of winglet in pushing the convective airflow toward the heated surface, it behaves as a vortex generator (VG) due to its vibration by fluid-solid interaction (FSI) that causes flow mixing and breaking thermal boundary layer. In flow simulation, the finite element method (FEM) is employed with considering a two-way strongly-coupled FSI approach at transient condition. Numerical solution of the governing equations, including the continuity, momentum and energy for convective flow and the equation of motion for VG are obtained by COMSOL multi-physics. The well-known model is employed for computation of turbulent stress and heat flux. The present numerical results are validated against the most recent relevant literature. To provide a clear and deep understanding of the proposed concept, extensive comparisons are made between different test cases. Results reveal considerable performance enhancement of SAH with elastic guide winglet compared with clean solar air heater (CSAH), such that 56% increase in the natural airflow rate and 9% decrease in the average absorber temperature is seen because of the flapping winglet. But, the air outlet temperature decreases about 14% due to flapping VG. This study aims to make the proposed SAH as an essential renewable thermal-solar system more efficient and attractive so that this improvement pushes the industrial society toward more sustainable infrastructure.

Effect of Roughness Parameters on Performance of Solar Air Heater Having Artificial Wavy Roughness Using CFD

Effect of Roughness Parameters on Performance of Solar Air Heater Having Artificial Wavy Roughness Using CFD

Experimental investigation for thermal performance of inclined spherical ball roughened solar air duct

This work deals with determination of thermal efficiency of spherical ball roughened collector aligned inclined to flow direction. Roughened collector produces more heat transfer compared to smooth ones but heat transfer augmentation comes at the cost of increased frictional losses. Lesser thermal efficiency of solar air heater has necessitated researchers to focus on its improvement by providing artificial flow modification techniques in the flow field. Laminar sublayer beneath the absorber plate will get disturbed and this helps to increase turbulence level of air. Present work discusses the influence of inclined spherical ball shaped roughness element and improving its thermal performance. Design considerations, geometries used viz. relative roughness pitch 9–18, relative roughness height 0.024–0.040, height-diameter ratio 0.5–2, angle of attack 35°-75°, flow conditions and their influence on turbulence viz. Reynolds no 2500–18500, heat transfer rate, absorber temperature and thermal performance enhancement factor have been thoroughly discussed. Finally concluding remarks and future scope for additional enhancement in performance of solar air heater is proposed. Maximum thermal efficiency for roughened ducts was found as 81% compared to 38% for smooth duct at parameters viz. ‘relative roughness pitch = 12, ‘relative roughness height’ = 0.036, ‘height-diameter ratio’ = 1 and ‘angle of attack’ = 55֠ at mass flow rate = 0.0319 kg/s.

Incorporation of a solar tracking system for enhancing the performance of solar air heaters in drying apple slices

The main aim of this study was to develop an integrated solar-tracking system to maximize the efficiency of solar heaters manufactured from recyclable aluminum cans (RAC) for optimum drying of apple slices. The results revealed that the thermal efficiency of the solar air heater incorporated with a tracking unit was significantly improved by about 45% compared with the conventional fixed heaters at all tested air flow rates. The highest thermal efficiency of 87.1% of the solar air heater equipped with a tracking unit was achieved at the highest air flow rate of 44 m3 h-1. The effective moisture diffusivity (Deff) increased at the high levels of drying air temperature and flow rate and the highest value of Deff (5.43 × 10−10 m2s−1) was obtained in the dryer with a tracking system at the highest air flow rate of 44 m3 h-1. The drying rate of apple slices under such a tracking module was considerably higher than that of either the traditional fixed system or the ambient sun drying.

Energy, exergy, and enviroeconomic assessment of double and single pass solar air heaters having a new design absorber

This paper experimentally examines the performance of solar air heater (SAH) having a newly designed tubular absorber comprising adjacent parallel tubes called tubular SAH (T_SAH) via energy, exergy, and enviroeconomic standpoints. A comparative performance assessment between T_SAH and flat plate solar air heater (F_SAH) at diverse air mass flow rates (MFRs) of 0.075, 0.05, and 0.025 kg/s is performed. Experiments for both heaters are tested using two flow pass arrangements of single-pass (SP) and double-pass (DP). The results reveal that maximum enhancement in thermal and exergy efficiencies of 133 % and 330 %, respectively is obtained when using SP T_SAH against SP F_SAH at air MFR of 0.025 kg/s. It is found that when there is an increase in air MFR, there is a significant increment in thermal efficiency, whereas there is a reduction in exergy efficiency. Despite the performance in the case of T_SAH is more effective than F_SAH, the enhancement in the case of DP F_SAH due to using DP flow configuration is greater than that of DP T_SAH. Finally, the results indicate that the carbon credit earned regarding the amount CO2 mitigated for SP F_SAH and SP T_SAH at MFR of 0.075 kg/s is estimated at 391.6 $/year and 561.9 $/year, respectively.

Evaluation of the performance analysis of an improved solar air heater with Winglet shaped ribs

ABSTRACT The present article is focused to improve the thermal performance of solar air heater using Liquid crystal thermography (LCT) approach, an improved type solar air heater comprises of winglet type rib roughened surface. In the present case, an experimental analysis and its effects on heat transfer and collector efficiency are examined using non-dimensional roughness parameters taken as relative roughness pitch (P/e) ranges between 5–12, attack angle (α) values of 30 degree-75 degree and relative roughness width (W/w) ranges between 3–7.These experimental results when compared with the smooth channel was improved by 17 % to 46 % under the given conditions.

Computational Fluid Dynamics Study of Roughened Solar Air Heater

A 2-dimensional numerical investigation has been conducted to examine the effect of three distinct turbulators (namely M shaped, Wedge shaped and Reverse wedge shaped) on the performance of solar air heater (SAH) for relevant Reynolds number ranges from 4000 to 18000. CFD code ANSYS FLUENT is used for simulation of turbulent airflow. For all three geometries constant ratio of e/Dh = 0.021 (where e = 0.7 and Dh = 33.33) and ratio P/e = 14.285 (where p = 10) is used. Turbulence Kinetic energy and velocity contours for all turbulators have also been studied in this analysis. M-Shaped turbulators outperformed the other two turbulators with maximum value of THPP.

Experimental investigation for pitch and angle of arc effect of discrete artificial roughness on Nusselt number and fluid flow characteristics of a solar air heater

Artificial roughness element with gap used to enhance the performance of solar air heater. Compared to the traditional smooth absorber plate and absorber plate with artificial roughness element without gap, the thermo-hydraulic performance (THP) of discrete artificial roughened solar air heater was found more. An experimental study of the heat transfer and fluid flow properties of the solar air heater was carried out using artificial roughness with an area in the absorbent plate. At present, discrete rib roughness in a double reverse arc manner has been used with variations in mass flow from 3000 to 14000 in the form of Reynolds number. The range of roughness parameters, such as the first used for the constant value of α of 600 and p/e from 6.67, 8.33, 10, 11.67 and the second used for the fixed value p/e of 8.33 along with the arc angle change, α of 300, 450, 600, 750 in the properties of heat transfer and fluid flow to achieve. These experimental results are important for applying an improved solar air heater.

Thermoelectric Generator–Integrated Solar Air Heater: A Compact Passive System

Abstract Solar air heater is a promising, economically viable, and matured technology for space heating and drying applications. One of the primary reasons for the limited usage of a solar air heater in developing countries is the unavailability of continuous electricity supply. Although the solar air heater is theoretically passive, practically electrical energy is required to achieve a steady airflow. Therefore, the unreliability of electricity forces people to rely on firewood for heat during the cold weather, which has severe effects on health and climate change. In the present work, the potential of thermoelectric generators (TEGs) to meet the electrical energy requirement of a solar air heater is studied. Two configurations, each with three different numbers of stages of TEGs, are analyzed. The effect of the integration of TEGs on the thermal performance of solar air heater is analyzed alongside the comparison between the electrical energy required by solar air heaters and electrical energy generated upon the integration of TEGs. A numerical model is developed in matlab and validated using the experimental results. One of the designs meets the electrical energy requirement of the fan in a wide operational range but lowers the process heat generation by approximately 1–6.25%. The electrical energy generated by the other design falls short of demand posed by the system in most operating range. However, the thermal energy generation is marginally higher compared to that of the conventional solar air heater.

Numerical investigation on the performance of a solar air heater using jet impingement with absorber plate

Solar air heater is the simplest heating device for utilizing solar thermal energy. Jet impingement technique can be used to amplify the performance of a solar air heater by increasing the heat transfer between fluid and heated surface. Under the present study, an attempt has been made to carry out a numerical investigation on heat transfer behaviour of a solar air heater having absorber plate with impinging jet. 3D-Computational fluid dynamics (CFD) simulation using ANSYS-18.1 has been carried out with RNG k–ɛ turbulence model, and the upwind scheme is applied for the discretization of governing equations. Jet diameter ratio and jet height ratio are the considered system parameters, and their considered ranges are 0.065 to 0.195 and 0 to 0.433, respectively. The performance of solar air heater with jet impingement is investigated under different flow conditions taking Reynolds number ranging from 3500 to 17,500. It has been found that a significant increase in heat transfer for jet impinging solar air heaters is achieved in comparison to smooth solar air heater under similar operating conditions. The maximum heat transfer enhancement of 7.58 with a friction factor penalty of 9.01 times is obtained at jet diameter ratio of 0.0650 and jet height ratio of 0.216 for Reynolds number of 17,500. Maximum thermal-hydraulic performance parameter value of 3.66 is obtained correspond to jet height ratio of 0.216 and jet diameter ratio of 0.065 for Reynolds number of 15,500.