Heat Transfer最新文献

The fouling behavior of whey protein concentrate (WPC) in food-grade polyether ether ketone (PEEK) heat exchangers was compared to benchmark stainless steel (SS) to evaluate if fouling can be better mitigated by using PEEK. No research has been conducted on WPC fouling behavior of PEEK at WPC concentrations of 2–6 g/L and heat flux densities of 45–55 kW/m². It was found that PEEK materials led to a reduction in heat resistance of up to 40%. At WPC concentrations of 6 g/L, a fouling factor of 0.9 m² K/kW was measured for PEEK compared to 1.6 m² K/kW for SS. Despite a constant heat flux, fouling curves for PEEK showed an asymptotic behavior, whereas linear fouling was observed for SS. To achieve a comparable heat resistance between PEEK and SS heat exchangers, the operating time could be extended by 9 h when using PEEK materials. Investigations of the deposit mass showed that even though the heat transfer resistance is limited on PEEK, fouling continued to grow at a decreased rate. It was found that the fluid started to evaporate underneath the fouling layer, which led to a partial detachment of the fouling layer and therefore mitigated the heat resistance effects of fouling. To test whether these results are transferable to larger setups, experiments on a scale-up apparatus were conducted. A very similar behavior was qualitatively observed; however, measured deposition deviated on average by 18%. PEEK surfaces also showed great promise regarding cleanability, with fouling layers detaching completely after drying for 10 min and restarting the process. This restored the heat transfer coefficient to its clean state. A cleaning in place therefore seems feasible. In contrast, fouling layers on SS did not detach through drying and had to be chemically cleaned to restore its heat transfer capacity.

The Jeffery–Hamel flow phenomenon appears in a variety of real-world applications involving the flow of two nonparallel plates. BY using a similarity transformation derived from the equation of continuity, partial differential equations determining flow characteristics are translated into nonlinear ordinary differential equations. The problem involves the flow of a specific type of fluid, namely, an incompressible and electrically conducting fluid, between two nonparallel plates. The flow is assumed to be steady, two-dimensional, and subject to certain boundary conditions. Specifically, the plates are impermeable, and the fluid adheres to a no-slip condition, resulting in zero fluid velocity at the plates' surfaces. Moreover, the problem incorporates the effects of magnetic fields and pressure fluctuations, making it highly applicable to scenarios, such as blood flow through arteries in the human body, which can be modeled as a special case of the magnetohydrodynamic (MHD) Jeffery–Hamel problem referred to as the (MHD) blood pressure equation. This work compares two numerical approaches for solving the MHDs Jeffery–Hamel problem: B-spline and Bernstein polynomial collocation. The given approaches are used to discretize and transform the equation into a system of algebraic equations. Matrix algebra techniques are then used to solve the resultant system. A complete error analysis and convergence rates for different grid sizes are derived for both methods and are used to compare the accuracy and efficiency of the two approaches. Both approaches produce correct solutions, according to the numerical findings, although the Bernstein polynomial collocation method is more efficient and accurate than the B-spline collocation.

The current small passenger car vapor compression refrigeration systems use high global warming potential (GWP) refrigerants causing the greenhouse gas effect. In the present work, the low GWP of two pure refrigerants, R1234yf and R1234ze (E), and 16 blends of R134a, R1234yf, and R1234ze (E) are analyzed numerically. The experiments were conducted with R134a refrigerant to validate the numerical results. The experiments were conducted at the compressor speed of 600–1500 rpm and the condensing air at 30–40°C, relative humidity of 85%, and velocity of 1–3 m/s. The simulation and experimental results for R134a are deviated by a minimum of 10% and a maximum of 15%. It is found that the latent heat of vaporization of the two refrigerant mixtures with 80% R134a–20% R1234yf and the three refrigerant blends of 50% R134a–10% R1234yf–40% R1234ze (E) are the highest among 16 combinations. The other blends show a moderate difference of latent heat with R134a, but for maximum cooling capacity, the blends with 80% R134a–20% R1234yf and 50% R134a–10% R1234yf–40% R1234ze (E) are found to be more suitable for practical applications.

This study aims to fully evaluate the radiation effect in existing cooling systems. The research, a combination of experimental analysis and numerical simulations using ANSYS Fluent, examines the complexity of radiative cooling processes and their impact on thermal management in various engineering applications. The experiments began by carefully placing a 112.5 W heater into the thermal channel. Next, temperature measurements were made under various conditions. In particular, the use of black cotton fabric as the inner duct lining applied in the thermal channel stands out as an innovation that aims to optimize heat absorption by increasing radiative properties. The findings highlight the significant impact of radiation on cooling performance. A temperature drop of 2–3°C was observed in cooling under the effect of radiation. Additionally, numerical simulations reveal the feasibility of radiative cooling systems by providing valuable information about the flow dynamics and heat transfer mechanisms within the channel. The novelty of this work is its detailed examination of radiative cooling effects and its focus on its potential to optimize thermal management strategies in various engineering applications. Explaining the role of radiation in heat transfer and providing practical information to improve cooling efficiency demonstrates that this research brings important insight and lays the foundation for future advances in the field. Considering the urgent need for energy-efficient cooling solutions and the increasing demand for sustainable engineering practices, the findings of this study will provide important insights for researchers and practitioners. This study provides innovative perspectives and solutions to address the increasing challenges of heat transfer and energy conservation in engineering systems. It makes a significant contribution to the field of thermal management by offering methodologies.

This paper reports on a novel hybrid thermal management strategy. It uses secondary coolants (air and liquid) to withdraw heat simultaneously from the composite phase change material, resulting in increased heat extraction capability of the composite phase change material and improved thermal environment of the battery module. The significance of this strategy is that the fluid used in the liquid cooling stays stationary. Comprehensive experimental and numerical studies are performed, and parametric studies are conducted to reduce the volume of the phase change material, size of the air duct, and airflow Reynolds number. The numerical results showed that the maximum temperature was limited to 27.8°C, and a high-temperature uniformity of 0.4°C was obtained. Furthermore, the required volume of the composite phase change material is reduced by ~50%. Additionally, beyond a 6 mm height of the air duct, the reduction in maximum pressure drop is not significant enough, and it is considered the optimal height, and a Reynolds number of 1950 is considered the optimal airflow Reynolds number. Therefore, the proposed thermal management concept for the battery module can sustain the thermal environment needed for the effective operation of Lithium-ion batteries.

The investigation is about the effect of heat and mass transportation over a dragging out cylinder for Cross fluid flow in addition to free stream. This research is a notable effort to measure heat and mass transportation of the flow over an expanding cylinder with the imposition of the external flow. The system of complex partial differential equations is converted into highly nonlinear ordinary differential equations. The solution of the nonlinear system of equations is made with the numerical technique Runge-Kutta fifth order just after the implementation of the shooting technique with suitable conditions. MATLAB solver bvp4c has solved the problem of the flow over stretching cylinder very efficiently and presents the facts in the form of the graphs and numerical values. The results claim that for the values of gamma parameter from 0.1 to 0.5 the rate of heat transfer increases by 14% on the other lambda with values from 0.1 to 0.3 the heat transfer rate declines 11%. For the growing values of Schmidt number from 1.0 to 5.0 the rate of mass transfer decreases by 85%. The rate of heat transfer has fallen by 86% for the improving values of the Prandtl number from 1, 2, and 3.

The present investigation aims to study the comparative analysis of CNT, GO, and CNT + GO nanoparticle coatings on copper surfaces under a pool boiling situation. Coating on copper surfaces is performed using the dip coating method. Pool boiling experiments are conducted for all the coated surfaces at atmospheric pressure. Water is used as a working fluid. A comparison was made based on the coated surface characteristics and pool boiling behavior of the samples. The results show that CNT + GO coating on copper surfaces is better in terms of critical heat flux (CHF) and boiling heat transfer coefficient (BHTC). It is also observed that CHF and BHTC of the CNT + GO-coated surface are 129.19% and 194.75% higher, respectively, compared to the bare copper surface. Bubble dynamics studies were also performed for all the samples.