Heat Transfer最新文献

An autoclave is a medical device used to sterilize hospital surgical equipment and instruments. The electrical power shortages and pollution of fossil fuels in hospitals and rural health centers underline the need to consider various energy sources, with the use of which it is possible to operate autoclaves. This sort of situation necessitates that Solar autoclaves be applied as the means of operation. This study examines the extent to which solar-powered autoclaves perform in their functions of carrying out wet sterilization activities. The pressure vessel of the solar autoclave is composed of a Fresnel lens and a reflector of porous medium. Aluminum beads are a low-density porous material with special structural and thermal properties. Fluid-solid contact effects present in aluminum beads include both the porous matrix heat distribution capacity/ability combined with subsequent fluid heat transfer, thus resulting in an increased performance in heat transfer. The steam temperature within the vessel (porous material absorber model II) is highest at 128°C. The highest energy efficiency of 74 percent occurred at the mid-point of the day, 1 pm, when the solar radiation intensity was at its maximum of 913 W/m² in solar autoclave (porous material absorber model II), as compared to 25 percent by solar autoclave (flat plate absorber model I).

Minichannel heat sinks (MCHSs) are an effective solution for dissipating high heat flux due to their excellent convective heat transfer and low pressure drop. Improving the hydrothermal performance of these heat sinks is essential to meet the high heat flux requirements. This paper aims to study the behavior of fluid flow splitting on the hydrothermal performance of a multi-mini-channel heat sink using a numerical approach. Two models, Models A and B, are analyzed and their performances compared. Numerical results demonstrate that the flow splitting area through the MCHS is a critical factor in improving its thermal and hydraulic performance. All models were designed with a single inlet and outlet and simulated using ANSYS Fluent three-dimensional software. The findings show that applying the flow splitting strategy resulted in a significant increase in heat transfer efficiency, with a 40.96% increase in Nusselt number compared with the conventional design. Model A also demonstrates a superior overall performance factor of 1.43, confirming the effectiveness of the proposed design in improving the hydrothermal performance compared with the standard arrangement.

Temperature is a crucial factor influencing the quality of sleep, as it directly affects thermal comfort during sleep. The present work reports the investigation of the thermal performance of high-density and low-density (LDF) polyurethane foam mattresses impregnated with sodium-based phase-change materials (PCMs) and their efficacy in temperature buffering features. A controlled laboratory study comparing exposure to these mattresses was conducted by installing mattresses in an insulated wooden box and simulating body heat with incandescent light bulbs. Ten different mattress designs were tested, including variations such as the addition of PCM and perforations for maximum heat dissipation. A multichannel record system and a hygrometer were employed to constantly monitor the temperature and relative humidity, respectively. The results were both statistically significant and reliable, as confirmed by error and ANOVA tests (p < 0.0001). Among all the samples, it was found that PCM2/LDF possessed the most efficient thermal regulation capacity at a temperature difference of 6.98°C, which is most suitable for improving sleep comfort. These results provide a way to enhance user thermal comfort by providing informative data for better mattress design.

Improved thermal performance in solar air collectors (SACs) can be achieved by incorporating baffles under the absorber surface. This study presents a detailed numerical study of a helical SAC to investigate the effect of baffle length and operating conditions on thermal–hydraulic performance. Three baffle lengths d ranges from 375 to 699 mm are analyzed. The computational model is developed in ANSYS Fluent 2021, including thermal radiation via the Discrete Ordinates model. A mesh independence analysis is performed to ensure reliability. Moreover, the model is validated against experimental data and empirical correlations, showing mean deviations of 4.6% for outlet temperature, 5.8% for the Nusselt number, and 1.8% for the friction factor. The results showed that geometry with d = 669 mm enhances turbulence, increases air residence time, and maximizes heat transfer. Additionally, at a mass flow rate (MFR) of 0.0175 kg/s, the outlet temperature reaches 57.2°C, and the pressure drop is reduced to 1000 Pa compared with 1532.9 Pa for d = 375 mm. Furthermore, thermal efficiency rises with MFR, reaching 56.3% for the longest baffles. The thermohydraulic performance parameter of d = 669 mm ranges from 1.275 to 1.37 for Re between 8400 and 14,700, indicating superior thermal–hydraulic performance.

The star fruit (Averrhoa carambola) samples are collected randomly from the market of Rangiya, a major city of the Lower Assam division in the Kamrup region of Assam, India. The rheometer ARES-G2 is used to collect experimental data on the juice's rheological flow characteristics at different temperatures. The curve tracing tool is then used to fit the data to the Power-law fluid model. A mathematical analysis is conducted to interpret the influence of slip on the flow and heat transfer of star fruit juice past a moving permeable sheet. The resulting governing equations, along with relevant boundary conditions, are obtained utilizing appropriate similarity variables. The MATLAB programming code “bvp4c” is employed to compute the governing equations. With the aid of relevant flow parameters, the momentum and thermal profiles are plotted for discussion. Using graphical analysis, the impacts of the slip parameter, flow index, Eckert number, and heat generation or absorption parameter are investigated, and conclusions are made based on physical insights. To examine the impacts of the relevant flow parameters, the Nusselt number and local skin friction values are also tabulated. The study examines how rheological parameters influence the flow characteristics, which is helpful in designing and evaluating juice transportation systems.

This study investigates the mixed convection heat transfer of non-Newtonian power-law fluids in a rotating cylindrical enclosure containing a stationary triangular block, considering various fin configurations. The outer cylinder rotates at a constant angular velocity and is maintained at a lower temperature, while the inner block remains fixed and heated. Key parameters, such as rotational speed (Re), thermal buoyancy (Ri), number of fins, and the power-law index (n), were varied to evaluate their effects on flow dynamics and thermal performance. Numerical simulations were performed using the finite volume method, and the fluid's rheology was modeled using Ostwald's law. The results show that fins do not always enhance performance in rotating mixed convection systems. The finless triangular block yields up to 50% higher Nusselt numbers compared with finned cases, due to reduced obstruction and stronger recirculation. Entropy generation analysis reveals a trade-off: shear-thinning fluids (n = 0.6) and finned blocks enhance heat transfer but increase irreversibility, whereas shear-thickening fluids (n = 1.6) minimize entropy generation at the expense of weaker convection.

This paper presents a comprehensive computational fluid dynamics (CFD) analysis of butterfly valve performance to reduce pressure drop and improve flow characteristics through geometric modifications. Three designs were considered: a Base-Model and two modified configurations (Model-1 and Model-2) with streamlined disc profiles. ANSYS Fluent was used to simulate water flow at various disc angles. Results indicate that the optimized models exhibit significantly lower pressure-drop and higher flow coefficients compared with the original design. Results derived from the idealized computations and CFD analysis show a very close agreement. Model-1 (rectangular strip with chamfers) reduced pressure drop by up to 50% at small openings, while Model-2 (aerodynamic front profile) further minimized wake size and improved flow uniformity. The study demonstrates that CFD can effectively guide geometric design in butterfly valve discs and can significantly enhancing flow efficiency, minimizing energy losses, and improving operating performance, making it suitable for industrial flow control applications.

This study tests how using three kinds of wavy-edge tapes, wavy-edge tape (WET), perforated wavy-edge twisted tape (PWETT), and perforated wavy-edge twisted tape with semicircular cut shape (PWETTc), with a semicircular cut, affects how well a dual-pipe heat exchanger (DPHE) works and compares it with the smooth one. The HE was selected as a heat renewal apparatus in the brick plant to reclaim heat from exhaust gases for the preheating of the heavy fuel oil (HFO). Air was used as a hot gas as a replacement for furnace exhaust gases because it possesses analogous thermal characteristics, flowing through the inner pipe at different speeds (13, 20, and 27 m/s) and temperatures (200°C and 250°C). In contrast, HFO enters the shell side in the opposite direction at mass flow rates (0.06, 0.08, and 0.1 kg/s) with a steady temperature of 40°C. Both the pipes and tapes are composed of stainless steel. The trial outcomes show that when the Reynolds number increased from 90,440 to 187,837, the heat transfer rate, oil outlet temperature, and effectiveness of the HE improved, with the PWETTc having a semicircular-cut shape showing increases of 45%, 21%, and 23%, respectively. Conversely, an augmentation in the oil flow rate from 0.06 to 0.1 kg/s led to a reduction in the oil outlet temperature by 8.5% for the WET pipe at 250°C, and by 8.6%, 12.6%, and 17% for the smooth pipe at 200°C, 225°C, and 250°C, respectively. The outcomes indicate that the DPHE with PWETTc form boosts the Nusselt number and the enhancement in heat transport by about 26%–28% and 50%, respectively, compared with a smooth dual pipe. The results show that using a twin pipe with PWETTc inserts to preheat HFO at an exhaust air temperature of 250°C and a speed of 27 m/s can lower viscosity, diminish the needed electric power, and save 2.3 MW of energy for one factory each year.