scholarly journals Numerical study on heat transfer performance of vacuum tube solar collector integrated with metal foams

2019 ◽  
Vol 14 (3) ◽  
pp. 344-350
Author(s):  
Yalin Lu ◽  
Zhenqian Chen
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Solar Collector ◽  
Heat Transfer Performance ◽  
Metal Foam ◽  
Metal Foams ◽  
Local Thermal Equilibrium ◽  
Transfer Performance ◽  
Vacuum Tube ◽  
The Impact

Abstract Applying vacuum tube solar collector is one effective way to reduce heat loss in solar collection. However, low conductivity of pure water leads to poor heat transfer performance in vacuum tube. In order to enhance heat transfer in tube, a novel vacuum tube solar collector using water as medium and metal foams as filler is presented, which consists of outer glass tube, inner metal tube and metal foam filler. The heating process of vacuum tube with metal foam filler of different structural parameters (porosity in range of 0.8991–0.9546 and PPI of 5, 10 and 20) is numerically studied and local thermal equilibrium model is applied.The temperature distribution of vacuum tube collectors with and without metal foam filler are compared. The impact of porosity and PPI on heat transfer performance is obtained. The results show that metal foams plays a great role in heat transfer enhancement for vacuum tube solar collector. Thermal performance of the novel vacuum tube solar collector is influenced by porosity and PPI of metal foams. Compared with traditional vacuum tube solar collector, the proposed vacuum tube solar collector has better thermal performance and greater potential in solar building integration.

scholarly journals Numerical Analysis on Thermohydraulic Performance of the Tube Inserted with Rectangular Winglet Vortex Generators

Energies ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 179
Author(s):  
Yicong Li ◽  
Zuoqin Qian ◽  
Qiang Wang
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Heat Transfer Performance ◽  
Circular Tube ◽  
Vortex Generators ◽  
Transfer Performance ◽  
Empirical Formulas ◽  
Influence Mechanism ◽  
Simulation Results ◽  
The Impact

The aim of this design was to improve the heat transfer performance significantly due to larger turbulent region and much vortices formed by tube inserted. In this article, the BSL k-ω model was chosen as turbulence model to simulate the thermohydraulic performance of the proposed tubes inserted with rectangular winglet vortex generators (RWVGs) when the Re was set as 5000 to 15,000. The reliability of the simulation results was obtained by comparing with the empirical formulas and experimental results. By means of numerical simulation, the influence mechanism of geometric parameters of RWVGs on thermal-hydraulic performance in tubes was analyzed. And the impact of three configurational parameters on the thermal performance was studied, namely the angle α, the height H and the number N of the RWVGs, respectively. The results revealed that the capacity of heat transfer in tubes with RWVG inserts was obviously larger than that in ordinary circular tube. In addition, it could be seen from the results that both Nu and f increased with the increase of H and N. At the same time, the case of α = 135° showed the greatest enhancement of thermal performance than the case of α = 45° and α = 90°.The PEC achieved the highest value of 1.23 when the height H of RWVG was 0.7 mm, the number N was 20, and angle α was 135°.

scholarly journals Numerical Assessment of an Innovative Design of an Evacuated Tube Solar Collector Incorporated with PCM Embedded Metal Foam/Plate Fins

2021 ◽  
Vol 13 (19) ◽  
pp. 10632
Author(s):  
Mohamed Houcine Dhaou ◽  
Sofiene Mellouli ◽  
Faisal Alresheedi ◽  
Yassine El-Ghoul
Keyword(s):  
Heat Transfer ◽  
Pore Size ◽  
Thermal Performance ◽  
Solar Collector ◽  
Metal Foam ◽  
Metal Foams ◽  
Heat Transfer Fluid ◽  
Evaluation Procedure ◽  
Evacuated Tube Solar Collector ◽  
Evacuated Tube

The objective of this manuscript is to study the possibility of improving the thermal performance of an Evacuated Tube Solar Collector (ETSC) with the integration of a Phase Change Material (PCM) incorporated into metallic foam and fitted with plate fins. A 2D mathematical model has been proposed. Two types of metal foams (copper and nickel) were inserted. In addition, the effect of metal foam pore size of on heat transfer was studied. The results were acquired through numerical simulations of four different cases; namely, Case 1: pure PCM, Case 2: with metal foam, Case 3: with fins and Case 4: with metal foam and fins. The evaluation procedure involved observing the total change in Heat Transfer Fluid (HTF) temperature and melted PCM fraction during a single day. The results proved that the thermal performance of ETSC is improved considerably by inserting metal foam and fins simultaneously. The time required for the whole process is improved by almost 9% compared to the case of pure PCM, and 2% compared to the case of inserting only plate fins. Results revealed that the pore size of the metal foams slightly affects the dynamic process of heat storage/release in the ETSC/PCM system.

scholarly journals Numerical Study of a New Solar Vacuum Tube Integrating with Phase Change Material

2019 ◽  
Vol 11 (24) ◽  
pp. 6960
Author(s):  
Juan Shi ◽  
Hua Xue ◽  
Zhenqian Chen ◽  
Li Sun
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Heat Transfer Performance ◽  
Melting Time ◽  
Transfer Performance ◽  
Vacuum Tube ◽  
Fin Thickness ◽  
Phase Change Heat Transfer ◽  
Fin Spacing ◽  
Change Material

In this work, a new solar vacuum tube (SVT) integrating with phase change material is introduced and numerically investigated. The mathematical model and the numerical solution of phase change heat transfer is introduced. The heat transfer of the solar energy collection system during the energy storage process is simulated. Solid-liquid phase change characteristics of the SVT with paraffin inside is analyzed. Optimization analysis of fin structure parameters (fin thickness and fin spacing) in the vacuum tube is conducted. The results showed that the metal fin has a great effect on the phase change heat transfer of paraffin in SVTs. The closer the paraffin is to the fins, the more uniform the paraffin temperature is and the sooner the paraffin melts. As the fin thickness increases and the spacing between the fins decreases, the melting time of the paraffin decreases. Meanwhile, the effect of fin spacing on the overall heat transfer performance of the phase change energy storage tube is larger than the effect of the fin thickness. When the fin thickness is 2 mm, the melting time of paraffin with a fin spacing of 80 mm is 21,000 s, which is almost three times of that with a fin spacing of 10 mm (7400 s). Therefore, decreasing fin spacing is an effective way of enhancing phase change heat transfer. When the total fin volume is constant, a SVT with small fin space and small fin thickness performs better in heat transfer performance.

Optimization of a U-Bend for Minimal Pressure Loss in Internal Cooling Channels—Part II: Experimental Validation

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
Filippo Coletti ◽  
Tom Verstraete ◽  
Jérémy Bulle ◽  
Timothée Van der Wielen ◽  
Nicolas Van den Berge ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Loss ◽  
Heat Transfer Performance ◽  
Internal Cooling ◽  
Transfer Performance ◽  
Cooling Channel ◽  
Piv Measurements ◽  
Cooling Channels ◽  
Numerical Predictions ◽  
The Impact

This two-part paper addresses the design of a U-bend for serpentine internal cooling channels optimized for minimal pressure loss. The total pressure loss for the flow in a U-bend is a critical design parameter, as it augments the pressure required at the inlet of the cooling system, resulting in a lower global efficiency. In the first part of the paper, the design methodology of the cooling channel was presented. In this second part, the optimized design is validated. The results obtained with the numerical methodology described in Part I are checked against pressure measurements and particle image velocimetry (PIV) measurements. The experimental campaign is carried out on a magnified model of a two-legged cooling channel that reproduces the geometrical and aerodynamical features of its numerical counterpart. Both the original profile and the optimized profile are tested. The latter proves to outperform the original geometry by about 36%, in good agreement with the numerical predictions. Two-dimensional PIV measurements performed in planes parallel to the plane of the bend highlight merits and limits of the computational model. Despite the well-known limits of the employed eddy viscosity model, the overall trends are captured. To assess the impact of the aerodynamic optimization on the heat transfer performance, detailed heat transfer measurements are carried out by means of liquid crystals thermography. The optimized geometry presents overall Nusselt number levels only 6% lower with respect to the standard U-bend. The study demonstrates that the proposed optimization method based on an evolutionary algorithm, a Navier–Stokes solver, and a metamodel of it is a valid design tool to minimize the pressure loss across a U-bend in internal cooling channels without leading to a substantial loss in heat transfer performance.

Investigation of Heat Transfer Performance of Nanofluids on Conical Solar Collector under Dynamic Condition

2014 ◽  
Vol 984-985 ◽  
pp. 1125-1131
Author(s):  
G. Vijayan ◽  
S. Giridharan ◽  
R. Karunakaran
Keyword(s):  
Heat Transfer ◽  
Solar Collector ◽  
Heat Transfer Performance ◽  
Dynamic Condition ◽  
Sheet Steel ◽  
Transfer Characteristic ◽  
Transfer Performance ◽  
Heat Transfer Behavior ◽  
Transfer Behavior ◽  
Key Issues

Heat transfer improvement in solar operated devices is one of the key issues of energy saving and compact designs. Researches in heat transfer have been carried out over the past several decades, culminating in the development of the heat transfer techniques used at present. The use of additives is a technique employed to enhance the heat transfer performance of base fluids. Recently, an innovative material, nanosized particle has been used in suspension in conventional heat transfer fluids that changes the heat transfer characteristic. In this project, an attempt has been made to verify change in heat transfer behavior while using nanofluids. For this purpose, a conical solar collector has been designed, constructed using locally available sheet steel. Polyurethane foam material is used as a insulating liner inside the cone. Thin reflective aluminum sheet is used to focus the solar radiation onto the absorbing surface. The main objective of this paper is to study the heat transfer behavior of Al2O3, Cu2O and ZnO nanofluid and especially Al2O3nanofluid of various concentrations in absorber space of conical solar collector. Experimental study was conducted on different days and the data were recorded. The results obtained show that addition of nanoparticles in the base fluid, improve the heat transfer rate.

Heat Transfer Enhancement of Phase Change Materials (PCMs) in Low and High Temperature Thermal Storage by Using Porous Materials

2010 ◽  
Author(s):  
C. Y. Zhao ◽  
D. Zhou ◽  
Z. G. Wu
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Phase Change ◽  
Porous Materials ◽  
Phase Change Materials ◽  
Heat Transfer Performance ◽  
Expanded Graphite ◽  
Metal Foams ◽  
Transfer Performance ◽  
Solid Liquid

In this paper the solid/liquid phase change heat transfer in porous materials (metal foams and expanded graphite) at low and high temperatures is experimentally investigated, in an attempt to examine the feasibility of using metal foams to enhance the heat transfer capability of phase change materials for use with both the low and high temperature thermal energy storage systems. In this research, the organic commercial paraffin wax and inorganic hydrate calcium chloride hydrate salts were employed as the low-temperature materials, while the sodium nitrate is used as the high-temperature PCM in the experiment. The heat transfer characteristics of these PCMs embedded with open-cell metal foams were studied experimentally. The composites of paraffin and expanded graphite with different graphite mass ratios, namely, 3%, 6% and 9%, were also made and the heat transfer performances of these composites were tested and compared with metal foams. Overall metal foams can provide better heat transfer performance than expanded graphite due to their continuous inter-connected structures. But the porous materials can suppress the natural convection effect in liquid zone, particularly for the PCMs with low viscosities, thereby leading to the different heat transfer performance at different regimes (solid, solid/liquid and liquid regions). This implies that the porous materials don’t necessarily mean they can always enhance heat transfer in every regime.

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