Double Pass Solar Air Heater Research Articles

Thermal performance of a packed bed double pass solar air heater with a latent heat storage system: an experimental investigation

Purpose Solar energy applications are limited because of its intermittent and discontinuous availability with respect to time. Hence, solar energy thermal conversion systems need integration with thermal storage units (TSUs) to use solar energy in off sunshine hours. This paper aims to perform thermal analysis of a solar air heater (SAH) integrated with a phase change material (PCM)-based TSU to supply hot air during night period. Design/methodology/approach An experimental setup with TSU as main component was prepared with SAH at its upward side, food chamber at its downward side as subcomponents. In TSU, paraffin wax was used as thermal energy storage material. Mass flow rate of air considered as an input parameter in the experiment. Two different absorber plates, namely, plane and ribbed absorber plates were used for the experimentation. Each day for a fixed mass flow of air, observations were made during charging and discharging of PCM. Findings Nusselt number and convection heat transfer coefficients were analytically calculated by considering flow through TSU as external flow over bank of tubes in a rectangular duct. A temperature drop of around 7-8°C during charging of PCM and temperature rise of around 4-5°C during discharging of PCM was observed from the experimental results. The average practical efficiency of TSU with ribbed absorber plate SAH during charging and discharging of PCM was 22 and 6 per cent, respectively, higher than that of TSU with plane absorber plate SAH. Research limitations/implications There are no limitations for research on SAH integrated with TSU. Different PCM including paraffin wax, Glauber’s salt, salt hydrates and water are used for thermal storage. Only limitation is lower efficiency of SAH integrated with TSU because of lower heat transfer coefficients with air as working medium. If it can improve heat transfer coefficients of air then heat transfer rates with these units will be higher. Practical implications There are no practical limitations for research on SAH integrated with TSU. Sophisticated instrumentation is needed to measure flow rates, temperatures and pressure variations of air. Social implications In poultry farms during night, chicks cannot survive at cold climatic conditions. Hence, hot air should be supplied to poultry farms whenever the atmospheric temperature drops. It is proposed that, in combination with TSUs, heat produced by SAH is stored in day time in the form of either sensible or latent heat and is retrieved to provide hot air in the night times. This will reduce total operating costs in poultry farms. Originality/value Conventionally, people are producing hot air by combusting coal in poultry forms. This cost around Rs. 75,000 per month for a batch of 225 to 250 chicks in a poultry form. Hot air could be produced economically during off sunshine hours from SAH integrated with TSU compared to the conventional method of coal burning. Present experimental investigations conducted to fill the literature gap in this area of research and to design a SAH integrated with TSU to produce hot air for poultry forms.

Thermohydraulic performance of double pass solar thermal collector with inline, staggered and hybrid fin configurations

Abstract The present experimental and numerical investigations are aimed to increase the thermal performance of a finned absorber plate solar air heater. A commercial CFD tool is used to perform the numerical investigation and the obtained results are validated with the experimental data. The geometrical parameters such as fin angle (30o ≤ θ ≤ 90o), fin length (0.007 m ≤ L1 ≤ 0.028 m), fin height (0.007 m ≤ L2 ≤ 0.014 m), fin arrangements (inline, staggered, and hybrid), and hydraulic diameter (0.029 m ≤ Dh ≤ 0.057 m) of the heater duct are considered to obtain the optimum values using numerical simulation, while Reynolds number (3000 ≤ Re ≤ 20, 000) as a flow parameter is considered. The obtained CFD results revealed the best thermohydraulic performance for the hybrid staggered fins configuration and found to be about 3.5% and 3.8% in comparison to the staggered and inline fins configuration, respectively. Moreover, CFD investigation revealed the interesting results about the staggered fins configuration, which is the generation of the wavy motion inside the heater duct that confers the significant heat transfer enhancement. Whereas, the experimental thermohydraulic efficiency of the double pass solar air heater design is found to be 79% which is about 13% higher than that of similar design of single air pass.

Encapsulated PCM based double pass solar air heater: A comparative experimental study

An experimental investigation on thermal performance of a solar air heater with and without the usage of spherically encapsulated phase change medium (PCM) is presented in this paper. The PCM, paraffin wax, is filled in spherical balls mounted on the holes of the absorber plate so that heat transfer area is slightly extended. A comparative study of three different configurations of the absorber plate is made. Parameters that influence the collector efficiency are recorded and discussed. The results obtained are compared with a conventional absorber plate without PCM for similar conditions. The mean efficiency obtained for conventional absorber plate without PCM is 31%, for flat absorber plate with PCM is 39%, and for inclined absorber plate with PCM is 43%. The encapsulation efficiency is 40% for flat plate absorber with PCM and 42.2% for inclined plate absorber with PCM and the approximate cost of heating 1 kg of air is INR 0.95/$0.014.

Experimental thermal performance analysis of finned tube-phase change material based double pass solar air heater

The present experimental study is performed to investigate the thermal performances of double pass solar air heater comprising of phase change materials (PCM) contained in metallic finned tubes to have increased energy storage and heat transfer rate. Experimental results were also helpful in the evaluation of the charging and the discharging characteristics of the PCMs. The air heater is studied for three different configurations. In the first configuration, is no PCM used. In the second configuration, RT44HC having higher melting point filled in semi-circular finned tubes (SFT) on the upper pass of double pass solar air heater (DPSAH) as a thermal storage medium (TSM) is used. While the third configuration is a combination of the second configuration and RT18HC having lower melting point, filled in circular finned tubes (FT) as TSM placed in the lower pass to enhance the thermal storage capacity of solar air heater (SAH). The heater's thermal performance is evaluated for all configurations separately. It was revealed that the third configuration containing RT44HC and RT18HC in upper and lower passes respectively is the best among others for optimum heater performance.

An experimental investigation of a double pass solar air heater performance: A comparison between natural and forced air circulation processes

This work involves an experimental study on a trapezoidal Double-Pass Solar Air Heater (DPSAH) to analyse its performance under natural and forced convection cases for the purpose of comparison. The experiments have been conducted in winter and compared for each case in same time and weather conditions. The collector has been carefully designed and constructed to prevent as possible the heat losses. A uniform fins have been fixed on both sides of the absorber plate to enhance the heat exchange rate. Effects of solar radiation and air mass flowrate on DPSAH performance have been investigated. The results show that DPSAH produces higher efficiency when the system is operated under natural convection case in comparison to forced convection case. The maximum efficiency has been found equal to 73.5% and 65% for natural and forced convection, respectively. A significant temperature difference has been obtained under natural convection case compared to forced convection. The results confirmed that DPSAH with adding fins leads to considerable performance improvement compared to conventional DPSAH due to enhance the absorbing solar energy caused by increasing surface area. The increasing in air mass flowrate has inverse influence on the performance of DPSAH. For natural circulation case, the outlet, plate and glass temperatures have been always observed higher than the forced convection case. It is evident that type of heat transfer has considerably affect the system performance and consequently, the selection of air circulation process are required to be satisfactorily chosen according to the application to achieve the desired objective.

Experimental study on double pass solar air heater with fins at lower and upper channel

Abstract Solar air heater with a double pass configuration and rectangular longitudinal fins on one side of the absorber plate was investigated experimentally. Performance parameters outlet temperature, absorber plate temperature, output power of the air heater with fins placed in lower channel and fins placed in upper channel were presented. The effect of mass flow rate of air on the efficiency of air heater with fins in lower and upper channel were also investigated. The result shows that air heater with fins placed in lower channel is more efficient than the air heater with fins placed in upper channel.

Experimental and numerical analysis of double-pass solar air heater utilizing multiple capsules PCM

This paper aims to investigate and analyze the thermal performance of a double-pass solar air heater using multiple rectangular capsules filled with paraffin wax-based on a phase change material PCM. An indoor projector simulator was used to test a new system during the charge/discharge process. In order to verify the accuracy of these readings, a mathematical model based on finite-volume scheme SIMPLE algorithm was applied to solve the three-dimensional forced convection turbulent flow in the double-pass solar heater. The computational results were in reasonable agreement with the experimental readings. The investigations were carried out at various airflow speed of (0.6, 0.9, 1.2, 1.5, and 1.8) kg/min and three solar irradiance intensities of 625, 725, and 825 W/m2. The results showed that the increased airflow rate leads to delay in the melting period and decrease melting temperature of the paraffin during the melting period. Furthermore, it can be detected that the optimal discharging period and the air temperature rise of the heater were reached of: 3hr with (17.95–3) °C, 2 h with (14–3) °C, and 1.25 h with (11–2.5) °C, for various solar intensity of 825, 725, and 625 W/m2 at the same airflow speed of 0.6 kg/min, respectively.

Double-Pass Solar air Heater (DP-SAH) utilizing Latent Thermal Energy Storage (LTES)

The solar air heater is a device rises air flowing temperature in numerous engineering applications as; heating of buildings, and agricultural crops drying. An indoor investigation was experimentally established using the solar simulator to test the flat plate double-pass solar air heater performance with and without paraffin wax-based on phase change material PCM. Although the temperature inside this collector is higher than the required temperature. Therefore, being a paraffin wax may be used as a heat storing material will enable the collector to work during the night. The tests were applied to evaluate the charge and discharge process of the new system and was performed under various air MFRs of (0.6, 0.9, 1.2, 1.5, and 1.8) kg/min and constant solar irradiation of 625 W/m2. The results showed that the maximum thermal efficiencies obtained for the double-pass with and without PCM were 63.53% and 68.23%, respectively, for airflow rate of 1.8 kg/min and also the efficiencies is a strongly dependence on the air MFR. Also, the maximum air temperature rise was about 10.9°C, and 12.25 °C with and without PCM, respectively, above the inlet temperature at air MAF of 0.6 kg/min and solar irradiation of 625 W/m2 during charging period and this leads to energy saving. The experimental tests showing reasonable agreement with the previous study with a maximum error of thermal efficiency was about (4.5%) at the same indoor conditions.

An experimental investigation of performance of a double pass solar air heater with foam aluminum thermal storage medium

The enactment of a double pass solar air heater was experimentally probed using four different formations. The scope of present study encompasses the use of Thermal Storage Medium (paraffin wax) integrated with porous/foam metal (aluminum) during the winter season. In the first phase of experimentation, first formation consisted of flat plate whereas foam aluminum embedded with paraffin wax was placed inside two copper ducts in the second configuration. In the third configuration, four copper ducts were used. During the second phase of experiment, similar configurations were used as in the first phase but with pre-heat. No melting of wax was accomplished when the outside air temperature ranged between 12 and 24 °C, however increased thermal conductivity was attained for configuration two and three. Melting of wax was achieved when the outside air temperature ranged between 15 and 29 °C, using pre-heat. The increase in thermal conductivity was achieved using foam aluminum but at the expense of slight decrease in storage capacity of the paraffin wax. In the last configuration no fan was used during the day time, and melting of wax achieved under similar conditions. Fourth configuration provided beneficial heat for 2.5 h after the sunset while the second and third configurations provided expedient heat for 1.5 h after the sunset.

Experimental Study on Double-Pass Solar Air Heater with and without using Phase Change Material

In this paper, an experimental study was conducted to enhance the thermal performance of a double-pass solar air heater (SAH) using phase change material (PCM) for thermal storage at climatic conditions of Baghdad city - Iraq. The double-pass solar air heater integrated with thermal storage system was manufactured and tested to ensure that the air heating reserved after the absence of the sun. The rectangular cavity filled with paraffin wax was used as a latent heat storage and incorporated into the lower channel of solar air heater. Experiments were carried out to evaluate the charging and discharging characteristics of two similar designed solar air collectors with and without using phase change material at a constant air mass flow rate of (0.0375 kg/sec). The parameters that affect the thermal performance of the SAH with and without the PCMs presented by solar radiation, the difference in air temperature, outlet air temperature, instantaneous thermal efficiency, and daily efficiency are evaluated. The experimental results show that when using the PCM, the temperature of the outlet air was enhanced and increased over the ambient temperature by (1.5 - 6.5 C) after sunset for 5 hours period. It was found that the instantaneous thermal efficiency of the heater using thermal storage exceeds 100% after sunset, this is due to a large amount of heat stored in the paraffin wax that has been released during the discharge process. Also, it was found that the daily efficiency of the double pass SAH integrated with and without thermal energy storage unit was (56, 47%) respectively.

Theoretical prediction of performance of Single and Double pass solar air heaters with artificial roughened absorber plates

Investigations are carried out on artificial roughened absorber plates on Solar air heater. The roughness parameters are identified in to five basic profiles A, B, C, D and E. The profiles A, B and C are basic cubical and cylindrical profiles and the profiles D and E are categorized as rod arrangement of inline and staggered nature. Both frictional and heat transfer characteristics have been studied. Optimum results of frictional and heat transfer characteristics have been arrived out. Results show a higher value of frictional factor for the profile E. All reasons of variations have been justified and discussed. The deviation of friction factor from modified Balsius equation is within the limit of 4.32 %. Results also show higher value of Nusselt number for the inline rod arrangement of SAH than the other profiles.

A cost-effective method to improve the performance of solar air heaters using discrete macro-encapsulated PCM capsules for drying applications

The present experimental work attempts to sustain the thermal response of the double-pass solar air heater system (DPSAHS) by the thermal lag of phase change material (PCM). At the same time, this analysis investigates the role of metallic macro-encapsulation on the heat storage and recovery from PCM integrated inside the DPASHS. The objectives are to investigate the influence of the geometry of encapsulation used for storage and to examine whether the discrete units allow faster charging and discharging of organic paraffin wax (PCM). In this work, an average encapsulate efficiency of 47.2% and 67% was obtained respectively for rectangular and cylindrical macro-encapsulates equipped DPSAHS. A performance comparison of DPSAHS with and without storage was presented. An overall cost analysis shows that with a small margin in constructional cost, operational time of DPSAHS was improved. The cost of heating 1 kg of hot air was 0.0074$. The overall work aims to support marginal and subsistent farmers to deal with improper drying during winter on which the potential sunshine hours are limited to 7 h/day at Calicut (11o32'N, 75o93'E) located in peninsular India.

Performance analysis of a double-pass solar air heater system with asymmetric channel flow passages

The present work seeks to address the forced convection heat transfer behaviour of a double-pass solar air heater system (DPSAHS) provided with asymmetric channel flow configuration used for solar drying of agro-products. Outdoor experiments were performed on a DPSAHS having a constant channel depth ratio of 1.5. Thermal response of the DPSAHS under different influencing parameters such as flow rate, channel depth, and thermophysical properties of the working fluid was experimentally determined. The influence of ambient parameters such as solar intensity, ambient temperature, wind speed, and relative humidity on the thermodynamic behaviour of the DPSAHS was also investigated. Among which, solar intensity and ambient temperature were found to be the major parameters influencing the energy and exergy efficiency followed by wind speed. Relative humidity was found to have the least percentage contribution towards the thermal characteristics of the system. Overall thermal efficiency and exergy efficiency were found to vary in the range of 20–41% and 5.6–18% at two different mass flow rates of 0.02 kg s−1 and 0.03 kg s−1, respectively. The results also inferred that the influence of thermophysical property variation on the thermodynamic performance depends upon the operating temperature range and on the nature of working fluid. Air temperature in the lower channel was found to be an average 3 °C higher than that of upper channel passage corresponding to two different mass flow rates. Hence, the thermodynamic behaviour of DPSAHS was found to be strongly influenced by the variation in channel depth, ambient parameters, and mass flow rate. The obtained experimental results were also compared with the available literatures.

Numerical investigation of a solar air heater comprising longitudinally finned absorber plate and thermal energy storage system

In the present work, the thermal performance of a double glazed single pass solar air heater consisting of a longitudinally finned absorber plate on its top surface and attached to a phase change material (PCM) with its bottom surface is investigated, theoretically. Paraffin wax (Rubitherm RT42) is used as a PCM. The main idea of this solar air heater design is to use it during nocturnal hours or off sunshine hours. A computational heat transfer and fluid dynamics solution using an implicit scheme has been developed and employed to study the effects of the mass flow rate and number of fins on its thermal performance under transient conditions. The maximum outlet air temperature of the finned type solar air heater with latent heat storage is achieved as 40 °C, 37 °C, and 35 °C for mass flow rates of 0.01, 0.015, and 0.02 kg/s, respectively, and it is predicted that the system can be used for 14, 12, and 10 h after sunset at respective mass flow rates. The maximum daily average thermal efficiency is predicted to be 62.4% at a mass flow rate of 0.02 kg/s which is higher than the other designs considered in the present investigation.

Performance evaluation of a new counter flow double pass solar air heater with turbulators

Performances of the new Double Pass Solar Air Heater (DPSAH) with and without turbulators has been studied experimentally in the present investigation. Aluminum cans are attached to the upper and lower surface of the absorber plate and used as turbulators to enhance the heater efficiency. Effects of aluminum cans on Nusselt number and pressure drop of SAHs have been investigated. In addition, guide blades are attached to DPSAH entrance for ensuring adequate air distribution over the surface of the absorber which in turns enhancing the performance. Each case is compared with another Single Pass Solar Air Heater (SPSAH) at the same time. The air mass flow rate range is from 0.02 kg/s to 0.05 kg/s. Three variously designed absorber plates for DPSAH are tested: (a) flat plate absorber without cans, (b) absorber with cans in aligned configuration, (c) and the third one contains cans arranged in a staggered configuration. The purpose of the aluminum cans is to create turbulence intensity in the flow field and enlarge the heat transfer area of DPSAHs; hence, and consequently enhance heat transfer rate. Results showed that the maximum daily efficiency was 68% at 0.05 kg/s for the staggered DPSAH.

A Review-Experimental Investigations on Performance Enhancement of Double Pass Solar Air Heater having Inverted V-type Perforated Baffles on Absorber Plate

A Review-Experimental Investigations on Performance Enhancement of Double Pass Solar Air Heater having Inverted V-type Perforated Baffles on Absorber Plate

Experimental analysis and numerical modeling of solar air heater with helical flow path

In the present research, effect of helical channeling on the performance of a solar heater is investigated both experimentally and numerically. The innovation of this research is designing a triangular cross-section channel, in such a way to establish a helical air flow through the air heater, in which the flow exchanges heat with the bottom and the top of the absorber plate. Once finished with measuring various thermal parameters of the system experimentally at two different flowrates, overall heat transfer coefficient and thermal efficiency of the system are calculated. It is followed by numerical modeling of the flow inside the air heater which has 3% maximum error compared to experimental data. The results indicate that, the average thermal efficiency of a double pass solar air heater with helical channeling is estimated 14.7% higher than simple duct and 8.6% higher than double pass-finned solar air heaters with the same mass flow rate. For the mass flow rate of 0.026 kg/s the day average of overall heat transfer coefficient and thermal efficiency of the system are obtained 65.14 W/m2 K and 55.4% respectively. Numerical aspect shows that Vortexes are formed at turning points inside the air heater, increasing heat exchange and pressure drop locally. Furthermore, as far as the application of the air heater in dryers is concerned, one can use nitrogen rather than air to maintain quality of the product while achieving the same heat exchange performance.

Device Performance Improvement of Recycling Double-Pass Cross-Corrugated Solar Air Collectors

The device performance of cross-corrugated double-pass solar air heaters under external recycle conditions was investigated experimentally and theoretically, and solved numerically using the Newton method. Comparisons were made and represented graphically among three different configurations of the single-pass, flat-plate double-pass and cross-corrugated double-pass devices. Air flowing simultaneously over the wavelike corrugated absorbing plate and in-between both wavelike cross-corrugated absorbing and transverse bottom plates was conducted under double-pass operations. A considerable heat-transfer efficiency enhancement is obtained employing such a recycling double pass device with welding cross-corrugated absorbing plates, instead of using the flat-plate device. An effective thermal performance was achieved because the heat transfer area is doubled and the turbulent intensity is enhanced as well. The power consumption increment owing to the reduction in the cross-sectional area was taken into account associated with the heat-transfer efficiency enhancement for comparisons in determining the optimal design on an economic consideration for the recycling cross-corrugated double-pass device.

Nusselt number and friction factor correlations for forced convective type counter flow solar air heater having discrete multi V shaped and staggered rib roughness on both sides of the absorber plate

In this work, the results of an experimental study on heat transfer and friction factor in a counter flow double pass solar air heater (DPSAH) duct with discrete multi V-shaped and staggered rib roughness on two broad surfaces of the heated plate have been investigated. The investigation covers a wide range of Reynolds number (Re) from 2000 to 20,000, relative staggered rib pitch (p′/p) from 0.2 to 0.8, relative staggered rib size (r/e) from 1 to 4 and relative roughness width (W/w) from 5 to 8. The optimum values of flow and geometrical parameters of roughness have been attained and explained in detail. For the Nusselt number (Nu), the maximum increase of 4.52 times to the corresponding value of smooth double pass duct has been achieved, however it has also been seen that the friction factor (f) enhanced by 3.13 folds as compared to smooth one. The rib parameters corresponding to maximum increase in Nu and f are r/e=3.5, p′/p=0.6 and W/w=7. Further, correlations for Nu and f have also been developed on the basis of experimental data.

The influences of recycle effect on double-pass V-corrugated solar air heaters

ABSTRACTThe study of the heat transfer enhancement for the recycling double-pass V-corrugated solar air heaters, which implement the external recycle of flowing air, was investigated experimentally and theoretically. The comparison among different designs of V-corrugated, baffled and fins attached, and flat-plate collectors was made to show the device performance improvement with various operating parameters under the same working dimensions. The recycling double-pass V-corrugated device developed here was proposed in aiming to strengthen the convective heat-transfer coefficient and enlarge the heat transfer area. The error analysis of experimental results deviate by 0.85–2.46% from the theoretical predictions with the fairly good agreement, and both results show that the device performance of the recycling double-pass V-corrugated operation is better than those of the other configurations under various recycle ratios and mass flow rates. The suitable selections were obtained for operating recycling double-pass V-corrugated devices while considering with an economic viewpoint by both the collector efficiency enhancement and the power consumption increment.