Smaller Fin Spacing Research Articles

Structure optimization of U-tube solar collector integrated with phase change materials

Solar collectors are significantly influenced by weather conditions, leading to a mismatch between thermal energy production and demand. To mitigate this issue, U-tube solar collectors integrated with phase change material (PCM) were investigated to store excess solar energy and regulate the temperature of collectors. This study investigates the effects of fin spacing and fin length on the heat transfer performance of these collectors under various conditions. Additionally, the impact of different collector tube lengths was analyzed. The results show that adding fins in solar collectors enhances temperature distribution uniformity and accelerates the PCM melting process. And the addition of fins to the U-tube produces faster temperature increase and significant improvement of temperature uniformity. In configurations featuring with fin length 20 mm and fin spacing 30 mm, the average PCM temperature decreased by 9.4 % and the liquid fraction decreased by 10.2 %, compared with non-finned. Smaller fin spacing or longer fins can improve heat transfer efficiency, and reduce PCM temperatures and liquid fractions. The 2L configuration exhibited optimal performance with an average PCM temperature of 330 K and a liquid fraction of 0.60 and achieved a significant reduction in time to reach 318 K by 47.9 % when compared to the L configuration.

Theoretical Study on the Performance of Air Cooler in Cold Storage

Air cooler is the most common air cooling and conditioning equipment that used in frozen and cold storage. However, neither application-oriented or production-oriented enterprises have a sufficient understanding about the performance of air cooler, which will restrict its performance enhancement and technological innovation to some extent. Therefore, this paper conducts a theoretical study on the performance of air cooler to guide the optimal design of air cooler. The distributed parameter model of the air cooler is first established along with some sub-models calculating the structural parameters, the physical properties of the wet air, the heat transfer coefficient and the flow resistance on the refrigerant side and the air side. Then, the proposed models are integrated to calculate the performance of air cooler under the effect of different structural parameters, such as fin spacing, fin thickness, tube spacing, outer tube diameter and finned tube materials. Results show that choosing the relatively smaller fin spacing and outer tube diameter, the larger tube spacing and finned tube materials with high thermal conductivity would contribute to the performance improvement of the air cooler, while the effect of the fin thickness is very small. However, the occupied volume, cost and processing difficulty should also be considered for enterprises in the design stage.

Investigation of performance augmentation for natural convective heatsink with the help of chimney

The effect of adding a plastic chimney on the top of upward horizontal rectangular heatsink under natural convection was investigated experimentally and numerically. The effect of the chimney height, length, depth, inclination, view factor, and conductivity for different fins array dimensions were investigated as well. The presence of low thermal conductivity chimney induces airflow by creating effective pressure difference between the edge and the center of the chimney. Yet higher chimney height results in larger pressure difference. Yet the pressure difference is accentuated with a sharp edge chimney. A smooth edge chimney reduces the pressure gradient and entrained airflow. The chimney with low thermal conductivity is capable to entrain more airflow into the heatsink when comparing with high thermal conductivity chimney (aluminum). The entrained airflow can be as much as 25% higher than the metal chimney. A smaller fin spacing may block the airflow and reversed the heat transfer. For the present configuration, it is found that the chimney is only effective when the heatsink is placed horizontally upward. By employing a transparent chimney, the view factor of the heatsink can be appreciably improved when comparing with opaque chimney.

Augmentation of natural convection heat sink via using displacement design

Miniaturization of electronic devices demands an effective thermal management system for efficient cooling. Still, many electronic industries use natural convection cooling techniques like plate-fin heat sinks as far as no moving part (noise) and reliability is concerned. In this study, the widely-used plate fin heat sink is augmented by a novel fin displacement amid fin array. Yet the effect of fin displacement between alternate fins is experimentally and numerically investigated under natural convection condition. In the meantime, the effects of fin spacing, length, height, and heat flux on the heat sink performance subject to fin displacement is also studied. For the smaller fin pacing, introducing the fin displacement will delay the merging of boundary layers, and reduce the length of fully developed region accordingly. Smaller fin spacing can also entrain the outside air into the fin array at the upper portion of heat sink for offering additional enhancement. The fin displacement is especially effective for a smaller fin spacing. This is because fully developed flow prevails at a smaller fin spacing. On the other hand, the fin displacement may impair the performance when a very wide fin spacing is used. Similarly, the increase in the fin length also enhances the heat transfer performance under the fin displacement conditions. It is also found that the effect of fin height on the thermal performance is small and the effect of heat flux is negligible. The maximum reduction in the thermal resistance is 56% by adopting the displacement design. A drop in fin temperature at the upper portion with the displacement design may lead to a reduction in heat transfer coefficient. For the comparison containing the fixed volume, the heat sink with fin displacement offers a 30% heat transfer enhancement ratio, 28.7% reduction in total mass, and 27.4 % reduction in surface area when compared to the conventional heat sinks.

Conjugate Mixed Convection Heat Transfer From a Shrouded Vertical Nonisothermal Heat Sink

A computational analysis of conjugate mixed convection heat transfer from shrouded vertical nonisothermal heat sink on a horizontal base is performed. The overall Nusselt number and the product of friction factor (f) and Reynolds number (Re) are found to vary significantly with the spacing of heat sink as well as with the clearance between shroud and heat sink. By increasing the fin conductance by 200%, an enhancement of Nusselt number is noted to be around 58%, while the same Nusselt number enhancement is 134% for isothermal fin, within the range of parametric studies. The fRe value for smaller fin spacing shows a maximum with clearances, while the same for higher fin spacing remains the same or increases with clearances. Finally, overall Nusselt number and friction factor are well correlated with the governing parameters of the problem.

Analytical analysis and experimental verification of interleaved parallelogram heat sink

In this study, a novel air-cooled heat sink profile is proposed to compete with the conventional design. The new design is termed as IPFM (Interleaved Parallelogram Fin Module) which features two different geometrical perimeter shapes of fins. This new design not only gains the advantage of lower pressure drop for power saving; but also gains a material saving for less fin surface area. An assessment of flow impedance and performance between the conventional and IPFM heat sink is analytically investigated and experimentally verified. A new modified dimensionless friction factor for triangular region is proposed. The analytical predictions agree with experimental measurements for both conventional and IPFM design. In electronic cooling design, especially for cloud server air-cooled heat sink design, the flow pattern is usually laminar with Reynolds number being operated less than 2000. In this regime, the IPFM design shows 8–12% less of surface than conventional design when the flow rate is less than 10 CFM; yet the thermal performance is slightly inferior to the conventional design when the flowrate is raised towards 25 CFM. Yet in the test range of 5–25 CFM, a 10–15% lower flow impedance is observed. The smaller fin spacing, the more conspicuous reduction of flow impedance is observed. The optimization of cutting angle is around 35° for 10 CFM, and it is reduced to 15° at a larger flowrate of 20 CFM.

Impact of fin spacing on temperature distribution in adsorption cooling system for vehicle A/C applications

Effects of fin spacing on the temperature distribution in a finned tube adsorber bed are studied to decrease the temperature gradient inside the adsorber bed and minimize the adsorber bed to adsorbent mass ratio (AAMR) for vehicle air conditioning applications. Finned tube adsorber beds have shown higher specific cooling power and coefficient of performance, and low AAMR among the existing adsorber beds. A single-adsorber bed ACS with interchangeable heat exchangers is built and equipped with hermetic type T thermocouples. Two copper heat exchangers with 6.35 mm (1/4″) and 9.5 mm (3/8″) fin spacing are custom-built and packed with 2–4 mm silica gel beads. The experimental results show that by decreasing the fin spacing from 9.5 mm to 6.35 mm, the temperature difference between the fin and adsorbent reduces by 4.6 °C under the cycle time of 600 s and an adsorption to desorption time ratio (ADTR) of one. A greater reduction in the temperature gradient inside the adsorber bed with smaller fin spacing is observed for short cycle time operation, e.g. 600 s, compared to long cycle time operation, e.g. 1400 s. Finally, simultaneous comparison of the temperature gradient between the fins and AAMR against fin spacing indicates that the optimum fin spacing for a finned tube heat exchanger packed with 2–4 mm silica gel beads is about 6 mm.

Finite circular fin method for wavy fin-and-tube heat exchangers under fully and partially wet surface conditions

The present study proposes the finite circular fin method for analyzing the heat and mass transfer characteristics of wavy fin-and-tube heat exchangers under fully and partially wet surface conditions. The analysis is carried out by dividing the wavy fin-and-tube heat exchanger into many tiny segments. The tiny segments can be analyzed based on surface conditions, i.e. fully wet, fully dry or partially wet surface condition. From the experimental results, it is found that the heat and mass transfer characteristics are insensitive to the inlet relative humidity but the effect of relative humidity on mass transfer characteristic become more pronounced when the partially wet surface condition takes place. The heat transfer characteristic is independent of the fin spacing. Effect of fin spacing on mass transfer characteristic is small when fin spacing is larger than 2.5mm. However, at smaller fin spacing, the mass transfer characteristic slightly decreases when the relative humidity increases. The ratios of hc,o/hd,oCp,a are in the range of 0.6–1.2. Correlations are proposed to describe the heat and mass transfer characteristics. These correlations can describe 95.63% of the heat transfer characteristic within 15% and 95.14% of the mass transfer characteristic within 20%. Correspondingly, 94.68% of the ratios of hc,o/hd,oCp,a are predicted by the proposed correlation within 20%.