• Energy Research

AbstractNumerical study of the influence of Prandtl number on free convection flow phenomena in a solar collector having glass cover plate and sinusoidal absorber is done. The working fluid is water-Al2O3 nanofluid. The cover plate has initially constant temperature Th, while bottom absorber is at temperature Tc, with Th > Tc. The remaining walls are considered adiabatic. By Penalty Finite Element Method the governing differential equations with boundary conditions are solved. The effect of the Prandtl number on the flow pattern and heat transfer has been depicted. Comprehensive average Nusselt number, average temperature and mean velocity inside the collector are presented as a function of the governing parameter mentioned above. The highest Pr causes the greatest heat transfer. The enhancing performance of heat transfer rate is more effective for the water-Al2O3 nanofluid than the base fluid.

Microelectronic technologies are progressing rapidly. As devices shrink in size, they produce a substantial heat flux that can adversely affect performance and shorten their lifespan. Conventional cooling methods, such as forced-air heat transfer and essential heat sinks, are inadequate for managing the elevated heat flux generated by these devices. Consequently, microchannel heat sinks have been developed to address this challenge. The present research is intended to study forced flow convection and heat transfer in a cone–column combined microchannel heat sink (MCHS). This study examines a regularly shaped MCHS to evaluate its heat transfer rate. The heat transfer medium employed is a graphene–water nanofluid, and the heat sink’s base is assumed to maintain a constant heat flux. The Galerkin weighted finite element method solves the nanofluid’s governing partial differential equations. This thesis investigates the impact of varying intake velocities on the Reynolds number (100 ≤ Re ≤ 900), externally applied heat flux (104 ≤ q ≤ 106), and the volumetric ratio of nanoparticles (0.001 ≤ φ ≤ 0.04). The study conducts a mathematical analysis to explore how these parameters affect pressure drop, friction factor, average Nusselt number, average substrate temperature, and heat transfer enhancement. The findings are compared with those of a conventional MCHS as the Re increases. The results are analyzed and visually represented through isothermal lines for temperature contours and streamlines for velocity. An increase in the inlet velocity of the water–graphene nanofluid significantly enhances heat transfer and thermal efficiency, achieving improvements of approximately 27.00% and 21.21%, respectively. The research demonstrates that utilizing water–G as a smart coolant with the cone–column combined MCHS enhances thermal efficiency by 4.05% compared to standard water. A comparison of the hydraulic performance index at the substrate reveals that the cone–column combined MCHS is significantly more effective at dissipating heat than the traditional MCHS.

This article presents a numerical visualization of heat transport for forced convective heat transfer by a two-dimensional heat function formulation through a direct absorption solar collector (DASC) filled with water-copper nanofluid. The penalty finite element method is used to solve nonlinear partial differential equations, and the numerical results are presented for variations in the radiative heat flux, Prandtl number, particle diameter, and solid volume fraction of the nanoparticle. The rate of heat transfer, thermal efficiency, mean entropy generation, and Bejan number are strongly dependent on certain parameters. It is observed that the radiative heat flux variation decreases the mean heat transfer, but increases the collector efficiency and entropy generation for nanofluids more than that for pure water. According to the results obtained from this study, under similar operating conditions, DASC is found to have higher efficiency than a flat-plate solar collector (FPSC). Generally, a DASC performs...

This research aims to determine the impact of mass flow rate and inflow temperature on the utility and effectiveness of solar thermal systems using fins with air in various applications in Bangladesh. This study examines a three-dimensional (3D) photovoltaic thermal (PVT) system where we analyze the behavior of a hybrid system with six aluminum sheets (1 mm thick fin as a heat exchange material) inside the heat exchanger where the air takes the direction to pass in waveform through the channels (made of aluminum) using fins. The top side of the fins is bent and affixed to the bottom of the floor of the PV panel to allow heat transfer utilizing the conduction-based method. This study selects inlet fluid mass flow rate and inflow temperature between (0.015-0.535 kg/s), and (10-40 °C) respectively, while comparing the result with experimental/numerical published data based on Bangladesh's weather conditions and applies the finite element method (FEM) to solve heat transfer equations. A brief analysis of the association among Reynolds number with pressure drop and fanning friction factor is included in this paper. Our model can be mounted on building rooftops or open fields where air velocity will be controlled mechanically; thus, it has many applications. This model can be implemented within an agricultural photovoltaic (APV) system, domestic functions, dry agricultural products, and provide heat for greenhouses. The result indicates that 302-514 W thermal energy has been produced for 0.015-0.535 kg/s. For growing inflow temperature, despite the reduction in electrical efficiency, the value of adding electrical and thermal efficiency (overall efficiency) comes with elevation. A 5 °C increase in inflow temperature leads to an overall efficiency increase of 0.33%. This study's findings can help researchers better comprehend air's properties as a heat exchanger in a developed design, and they can be applied to government and commercial projects.

Abstract Photovoltaic power generation is a suitable option to counter depleting and environmentally hazardous fossil fuels. However, increased cell temperature of the photovoltaic module reduces the electrical performance. Therefore, for enhancing the electrical performance as well as to obtain the useful thermal, a combined photovoltaic thermal system is suitable technology. Furthermore, the addition of phase change materials into photovoltaic thermal systems adds more dual benefits in terms of cooling of PV cell as well as heat storage. Hence, there are still issues to transfer heat from the system efficiently, which cause lower performance of PVT and PVT-PCM systems. In this paper, the aluminium material of thermal collector is used by introducing a novel design to enhance heat transfer performance, which is assembled in PVT and PVT-PCM systems. Experimental validation is carried out for the 3D FEM-based numerical analysis with COMSOL Multiphysics® at 200 W/m2 to 1000 W/m2 varying irradiation levels while keeping mass flow rate fixed at 0.5LPM and inlet water temperature at 32 °C. The experiment is carried out at outdoor free weather conditions with passive cooling of the module by an overhead water tank scheme. A good agreement in numerical and experimental results is achieved through experimental validation. Cell temperature reduction of 12.6 °C and 10.3 °C is achieved from the PV module in case of the PVT-PCM system. The highest value of the electrical efficiency achieved is 13.72 13.56% for PV and 13.85 and 13.74% for PVT numerically and experimentally respectively. Similarly, for PVT-PCM, electrical efficiency is achieved as 13.98 and 13.87% numerically and experimentally respectively. In the case of the PVT system, electrical performance is improved as 6.2 and 4.8% and for PVT-PCM, it is improved as 7.2 and 7.6% for numerically and experimentally respectively.

Electrical power as well as thermal energy are converted from solar radiation in a photovoltaic thermal (PVT) system. At a fixed temperature, thermal energy is absorbed by phase change materials (PCM) in terms of latent heat. PCM has storage ability of latent heat. The heat is stored in PVT/PCM system and used latterly as an ultimate application. For PVT/PCM system heat removal procedure is concurrent due to the dependence of its charging and discharging on ambient. In this research, a 3D mathematical model of PVT/PCM system has been solved numerically using finite element method. Results have been shown in terms of surface temperature and streamline pattern of PVT/PCM system with time variation. The values of average temperature of solar cell, electrical power, heat energy, electrical-thermal efficiency and overall efficiency have been found. It is observed that using PCM in the PVT module the temperature of solar cell reduces and consequently the output power and efficiency enhance.

The buoyancy flow and heat transfer characteristics inside a solar collector having the flat‐plate cover and sinusoidal corrugated absorber are analyzed numerically. The water‐based nanofluid with alumina and copper nanoparticles is used as the working fluid inside the solar collector. The governing partial differential equations with proper boundary conditions are solved by the finite element method using Galerkin's weighted residual scheme. The behavior of both nanoparticles related to performance such as temperature and velocity distributions, radiative and convective heat transfers, mean temperature, and velocity of the nanofluid is investigated systematically. This performance includes the solid volume fraction, namely ϕ1 and ϕ2, with respect to Al 2 O 3 and Cu nanoparticles. The results show that the better performance of heat transfer inside the collector is found by using the highest ϕ2 than ϕ1. The result of this study expresses a good agreement with the theoretical result available in the literature. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 43(1): 61–79, 2014; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21061

Abstract Irradiations incident on the photovoltaic module are converted only 15–20% into electrical energy and remaining are transformed into heat and drop electrical efficiency. Therefore, to harness both the thermal and electrical energy, hybrid photovoltaic thermal system is an optimum option. Moreover, phase change materials add more advantages of PV cell cooling and heat storage. A novel thermal collector has been designed as PVT and PVT-PCM systems to improve the heat transfer and performance. The 3D numerical analysis is done with COMSOL Multiphysics® software, and is validated at different volume flow rates of 0.5LPM to 3LPM, by experimental investigation at conditions of keeping the inlet water and ambient temperature at 27 °C and solar irradiation at 1000 W/m2. The experiment is carried out in indoor weather under controlled operating parameters and conditions with passive cooling of the module. Maximum 12.4% and 12.28% electrical efficiency of PVT is achieved numerically and experimentally respectively. Similarly, 12.75 and 12.59% electrical efficiency for PVT-PCM is obtained for experimental and numerical cases respectively. For PVT system, 10.13 and 9.2% electrical performance is improved. For PVT-PCM the electrical performance improvement is obtained as 12.91 & 12.75% numerically and experimentally respectively.

Abstract This work is focused on the numerical modeling of steady laminar natural convection flow in an annulus filled with water–alumina nanofluid. The inner surface of the annulus is heated uniformly by a uniform heat flux q and the outer boundary is kept at a constant temperature T c . Two thermal conductivity models namely, the Chon et al. model and the Maxwell Garnett model, are used to evaluate the heat transfer enhancement in the annulus. The governing equations are solved numerically subject to appropriate boundary conditions by a penalty finite-element method. A parametric study is conducted and a selective set of graphical results is presented and discussed to illustrate the effects of the presence of nanoparticles, the Prandtl number and the Grashof number on the flow and heat transfer characteristics for both nanofluid models. It is found that significant heat transfer enhancement can be obtained due to the presence of nanoparticles and that this is accentuated by increasing the nanoparticles volume fraction and Prandtl number at moderate and large Grashof number using both models. However, for the Chon et al. model the greatest heat transfer rate is obtained.