Abstract
The effect of external-recycle operations on the thermal performance of double-pass cross-corrugated solar air heaters (SAH) under different operating conditions was investigated experimentally and theoretically. Additionally, the simultaneous ordinary equations were solved analytically for each proposed configuration. Four recycling types are introduced for improving the solar thermal performance with different external recycle processes, which are expected to enhance the heat transfer coefficient with a convective turbulent flow between the air and the absorber in the present study. Using recycling double-pass operations, two processes were conducted sequentially: air first flowed over the sinusoidal corrugated absorber plate and then flowed back later over the transverse sinusoidal corrugated bottom plate. Improved device performance was achieved due to the doubled heat transfer area over and under the corrugated absorber plate, from which both the sinusoidal cross-corrugated absorber plate and bottom plate enhanced turbulent intensity. Theoretical predictions and experimental results both indicated that the recycle ratio increased with the SAH thermal efficiency for all proposed designs. The results show a higher heat transfer efficiency for the proposed four configurations using wavelike corrugated plates compared to those conducted in single-pass and flat-plate absorber plates with up to a maximum 133% (from 0.301 to 0.703) increment. The optimal device performance was examined for all external-recycle configurations under the same working dimensions and operational conditions. The best configuration for optimal thermal performance was the device that lengthened the air flow pathway and increased the air velocity within the collector; thus, a higher heat transfer rate was accomplished. The evaluation of increments in the power consumption and of the heat-transfer efficiency enhancement together determined the optimal design based on an economic consideration across various configurations of cross-corrugated double-pass devices.
Highlights
Solar energy is becoming more available and favorable [1] among many new energy options used by human beings
The experimental setup was fabricated, and the experimental procedure is approved Energies 2021, 14, x FOR PEER REVIEfoWr experimental runs to establish the validity of the phenomena of the heat tra1n0sofef 2r5 problems, where the collector thermal performance was examined for various configurations of recycling double-pass sinusoidal cross-corrugated solar air collectors, as shown in Fuigreusre7s–71–01t0otroerperperseesnetnftofuorurexetxetrenrnala-lr-erecycyccleletytyppeess..TThheeeexxppeerriimmeennttaall mmeeaassuurreemmeennttss pprroo-vvidideeddaasesteotfoefxepxepriemriemnetanltraelsruelstus lttosvtaolivdaaltiedtahtee tthheeotrheetiocraeltpicraeldpicrteiodnicstoiofncsroosfs-ccroorsrsu-gcaotrerdusgoalaterdaisrocloarlleacirtocrosl.lectors
This study proposes an optimal design of the recycling double-pass cross-corrugated device which is expected to consider the compensation between collector efficiency improvement IC,i i = A, B, C, D. (i = A, B, C, D) due to external recycling and the power consumption increment IP,i, due to pumping the air circulation into the two divided subchannels by embedding both the wavelike absorber plate and bottom plate
Summary
Solar energy is becoming more available and favorable [1] among many new energy options used by human beings. Solar collectors may be the simplest type of the heat exchanger, which act as a blackbody for receiving worldwide sources of distant solar radiation to convert solar energy over an absorber plate into thermal energy; they have been used widely in many countries to warm water or air [2]. The simplest designs of the flatplate solar collector for transforming the form of energy are widely implemented in space heating [3], food dehydration and the drying of crops [4], and industrial technologies [5]. Das et al [8] and El-Sebaii and Al-Snani [9] investigated the effects of using absorber plates coated with various selective coating materials on the collector performance. Vaziri et al [10] presented the collector thermal performances of perforated glazed solar air heaters with different inner collector colors. Fudholi et al [11] and Gupta and Kaushik [12] developed the potential improvement of a solar collector based on energy and exergy analyses
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