Double-pass Flow Research Articles

Optimization of single and double pass solar air heater-phase change material (SAH-PCM) system based on thickness to length ratio

This paper presents a two-dimensional transient model for a solar air heater with phase change material (SAH-PCM), focusing on the thickness-to-length ratio (t/L) of the PCM container. Verified through experiments, the model considers single (SP) and double pass (DP) flow configurations, assessing liquid fraction, dead length, outlet temperature, energy, exergy, and system efficiency during PCM charging and discharging. Increasing the t/L ratio improves peak liquid fraction, reduces dead length, and delays PCM discharge in both configurations, enhancing system energy and exergy efficiencies. In a SP flow system, optimizing t/L at 0.042 yields a peak liquid fraction of 0.928, a 92.28% dead length reduction, and a 2 h and 22 min delay for PCM discharge (base-case t/L ratio: 0.0182), achieving a highest discharging efficiency of 39.1%. For a DP flow system, the optimized t/L ratio of 0.058 results in a peak liquid fraction of 0.976 and a 1 hour and 34 min delay for PCM discharge, attaining the highest discharging efficiency of 63.34%. Moreover, an improvement in the energy payback time (EPBT) is observed for both SP and DP flow as the t/L is increased. For the DP flow, a minimum EPBT of 0.68 years (energy basis) and 6.55 years (exergy basis) is observed at a t/L ratio of 0.058. In terms of energy cost, SP flow reaches a minimum of Rs. 20.824 Rs/kWh at a t/L ratio of 0.042. For DP flow, the minimum energy cost is 13.033 Rs/kWh at a t/L ratio of 0.058, representing a noTable 37.42% improvement compared to SP flow. These findings underscore the critical role of optimizing system parameters, specifically the t/L ratio, for enhanced energy and exergy performance, and economic viability of SAH-PCM.

Experimental evaluation of the performance of newly designed tubular SAH with infinity (∞) shaped inner tubes

A new design of tubular solar air heater (SAH) is examined experimentally in this work. The SAH absorber consists of one row of adjacent equal tubes forming flat pack. Each tube contains two adjacent inner tubes, the diameter of each of which equals the radius of the outer tube. The two inner tubes form the shape of infinity (∞), therefore, the new design is expressed as infinity shaped tubular SAH (∞TSAH). The performance of the ∞TSAH is examined against ordinary tubular SAH (OTSAH)) having tubular absorber consists of one row of only adjacent equal tubes. The comparison is performed at different mass flow rates of the air (MFRs) and under single pass flow (SPF) and double pass flow (DPF) of the air. The findings show clearly that the output air temperature, energy efficiency and thermohydraulic efficiency, of ∞TSAH are better than that of OTSAH. The maximum output air temperature rise is about 47.1 °C and 37.1 °C for ∞TSAH and OTSAH, respectively at MFR of 0.017 kg/s and DPF condition. In addition, the ∞TSAH achieves maximum energy efficiency of 84.5% at MFR of 0.079 kg/s and DPF condition with percentage increment of 8.4% relative to OTSAH which achieves energy efficiency of 77.3% at the same condition. Moreover, the ∞TSAH achieves maximum thermohydraulic efficiency of 79% at MFR of 0.052 kg/s and DPF condition, while OTSAH achieves a value of 72.6% at MFR of 0.079 kg/s and DPF condition.

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.

Assessment of double-pass pin finned solar air heater at different air mass ratios via energy, exergy, economic, and environmental (4E) approaches.

In this study, an assessment based on energy, exergy, economic, and environmental approaches on a double-pass (DP) solar air heater (SAH) having pin finned absorber at different air mass ratios up and down the absorber is investigated experimentally. Four air mass ratios are considered: (i) all the air mass flow passes up the absorber and returns to pass down the absorber (DP), (ii) 2/3 of the airflow passes up the absorber and returns to mix with the remainder of air to pass down the absorber (2/3 DP), (iii) the same as (ii) but 1/3 of the air passes up the absorber (1/3 DP), and (iv) all the air mass passes only down the absorber (single pass, SP). For all mass ratios, the performance of pin finned SAH (P_SAH) is compared with that of flat SAH (F_SAH). The results indicated that the air temperature rise and energy and exergy efficiencies of P_SAH are highly greater than those of F_SAH. The highest average thermal efficiency of F_SAH is 56.7% obtained at DP flow condition, whereas the highest value of P_SAH is 65.21% obtained at 2/3 DP with an increase of 17.6% compared with F_SAH. Also, P_SAH has higher average exergy efficiency of about 34.7% compared to F_SAH. Furthermore, P_SAH achieves energy payback time (EPBT) lower than that of F_SAH, while P_SAH has higher embodied energy. The findings indicated that F_SAH at SP airflow pattern has the maximum energy cost (0.0427$/kWh), whereas P_SAH at 2/3 DP airflow pattern achieves the minimum energy cost (0.037$/kWh). Finally, the proposed P_SAH system appears to be more viable from exergoeconomic and enviroeconomic approaches compared to F_SAH.

An Analytical Study of Concentric Circular Heat Exchangers with an Impermeable Sheet Inserted for Double-Pass Operations

A design of inserting a concentric tube with negligible thickness to divide a circular conduit into two subchannels for double-pass flow and recyclic operations, resulting in substantially improved the heat transfer, has been designed and investigated. The results are represented graphically and compared with those in a single-pass device (without an inserting concentric tube and recycle). Heat transfer improvement IS considerably obtainable by employing such a double-pass recyclic device, instead of using the single-pass one. The effect of concentric tube location on the heat transfer efficiency enhancement as well as on the power consumption increment, has been also discussed.