ABSTRACT: 

Additive alignment in polymer composites can enhance the physical properties of the constitutive material. Researchers have attempted to understand and predict the additive orientation during the fabrication process, such as injection molding. In this study, the rotation of carbon fibers embedded in uncured polydimethylsiloxane flowing in an orifice channel is analyzed via a flow visualization experiment and image processing of obtained images. The angular velocity of additives is correlated with the shear rates in the flow field calculated from the computational fluid dynamics simulation with the assumption of a single-phase and a non-Newtonian flow. The effective shear rate is found to have a larger effect on the rotation of fiber compared with the aspect ratio of the fiber and the initial alignment angle to the flow direction. A correlation between the effective shear rate and angular velocity of the fibers is developed and verified experimentally. This correlation can be used to predict the fiber rotation during polymer composite fabrication within an orifice channel and hence provide useful information regarding the anisotropic physical properties of the final product.

ABSTRACT:

This study aims to design a novel modified hot mixing chamber (HMC) with high performance and light weight by improving the existing basic model with high surface temperature, heavy weight, and nonuniform flow and temperature distribution at the outlet. The basic and modified HMC models were simulated and compared, and an experiment was performed on the modified model for validation. Results showed that the HMC surface temperature of the modified model was reduced by 289 °C compared with that of the basic model. Numerical simulations for the centerline and surface temperatures of the modified HMC model exhibited good agreement with the experimental results. The highest combustion temperature was achieved with a stoichiometric reaction within a range of equivalent ratios of 0.8–1.2. The modified HMC model that adopted the aforementioned design and configurations reduced surface temperature, extended operating life, and significantly decreased HMC weight.

ABSTRACT:

The present study was to investigate the effect of the conic constants of rough geometries and the associated Reynolds numbers on the heat transfer and pressure drop of a solar air heater. An absorber plate attached to multiple conic-curve profile ribs was comprehensively analyzed. The results showed that decreasing the conic constant induced an increase in the Nusselt number and a decrease in the friction factor; therefore, the thermohydraulic performance parameter increased. The friction factor was notably invariable when the conic constant changed in the range of - 0.5 to 0. The maximum thermohydraulic performance parameter occurred at a Reynolds number of 8000, whereas the largest thermogeometric performance parameter occurred at a Reynolds number of 12,000. A regression analysis was performed for the correlations of both the Nusselt number and the friction factor as functions of the Reynolds number and the conic constant. The correlation coefficients of the Nusselt number and friction factor equations were 0.9978 and 0.9351, respectively. 

ABSTRACT:

The objective of this study is to improve the exit flow uniformity of a gas torch with multiple exit holes for effective heating of a steel plate. The torch was simulated, and combustion experiments were performed for validation. Based on a basic model, three different revised models were designed and analyzed with the software ANSYS FLUENT 18.2. The flow uniformity (γ) of the velocity distribution at the multiple exit holes was investigated with the pressure drop ranging from 100 to 500 Pa. The basic model had flow uniformity ranging from 0.849 to 0.852, but the three new models had γ₁ = 0.901–0.912, γ₂ = 0.902–0.911, and γ₃ = 0.901–0.914, respectively. The maximum percentage difference of the flow uniformity index between the three new models and the basic model was 7.3%. The basic model with nonuniform flow distribution made a temperature difference of the back side of the steel plate from the center to the edge of around 229 °C, while the modified model with uniform flow distribution had a smaller temperature difference of 90 °C. The simulation results showed good agreement with our experimental results for both the basic model and the modified model. The modified gas torch made a wider and more uniform temperature distribution on a preheated steel plate than the basic one. The results revealed that a trade-off between cost and flow uniformity, as well as the new gas torch, could be applied to a steel-plate preheating process before welding.

ABSTRACT:
본 연구의 목적은 소둔로의 입구 구조를 변경하여 내부에 배열된 강관 군 사이의 온도차를 최소화 하는 것이다. 기본 및 수정된 소둔로 내부의 유동장 및 강관의 온도 분포를 ANSYS FLUENT 18.2 소프트웨어를 사용하여 조사하였다. 3개의 수정된 입구 모델은, 스월 유동을 생성하기 위해 엘보우 입구를 채택하고, 하향 제트유동 생성 후 상향 부력 흐름이 발생되도록 엘보우의 수평방향에 대한 하향 제트각은 0도에서 45도 범위에서 설계되었다. 기본 모델에 대한 강관 군의 온도 차는 37℃이었다. 반면, 하향 제트각 0도, 30도 및 45도 엘보우들을 사용한 강관 군의 온도 차는 각각 10℃, 8℃ 및 15℃이었다. 하향 제트각 30도 부근의 엘보우는 강관 군 사이의 온도 차를 줄이기 위해 본 연구 범위 내에서 최적화된 각도이었다. 본 연구로부터, 소둔로에서 강관 군 간의 온도 차의 최소화는, 적정각의 하향 분사 엘보우 입구를 사용한 입구형상을 통해서도 달성될 수 있음을 알 수 있었다.

ABSTRACT:

The main objective in the present research is to reduce temperature difference of the steel pipes in furnace and arranging pertinently a bundle of the inside steel pipes. Moreover, transient numerical simulation was conducted by using ANSYS FLUENT commercial software to study temperature distribution of steel pipes inside the original and new designed annealing furnaces. The new model was designed by adopting the elbow inlet for generating the swirl flow. The temperature difference of steel pipes for the original furnace was 55.4 °C. However, the temperature differences of a bundle of steel pipes for the new model by using downward inlet angle of 30° was 13 °C. Moreover, temperature difference by modified model had more uniform than those of by Prieler et al. of 50 °C. Effect of Reynolds number, the horizontal and the vertical steel spacing on the temperature difference among the steel pipes was also examined. The transient simulation were performed to investigate steel pipe temperature during annealing process. In short, the results revealed that a new designed inlet configuration with this kind of geometry of an annealing furnace could be applied to minimize the temperature difference among steel pipes in steel annealing process.

ABSTRACT:

The paper presents the effect of the Reynolds number, relative roughness height and relative roughness pitch on the heat transfer and pressure loss in a solar air heater. A novel absorber plate with metal shavings from the turning of a steel shaft is employed to reduce the cost of production and to be available for the manufacturing industry. The parameters studied ranged from 5000 to 25000 for the Reynolds number, from 4.7 to 9.4 for the relative roughness pitch (P/e) and from 0.26 to 0.43 for the relative roughness height (e/D_h). The results show that there are some characteristics that differ from the published studies. The optimum e/D_h is 0.35 to obtain the highest thermo-hydraulic performance parameter, and the parameter increases with a decrease in P/e. Within the scope of the study, the maximum thermo-hydraulic performance parameter is approximately 1.5. The correlations between the Nusselt number and the friction factor are developed based on the experimental data. The results from the correlations and from the experimental data are fairly in agreement.

ABSTRACT:

The current study is the authors’ next work from the perspectives of the second law and economics of an air collector having artificial roughness of metal waste. In a previous study, heat and fluid flow characteristics and thermo-hydraulic performance were experimentally investigated. In the present paper, thermal efficiency, effective efficiency, exergetic efficiency and economic-based optimization are analytically appraised. The influences of the relative roughness pitch, relative roughness height, collector area and Reynolds number on the above parameters are examined. The optimal roughness parameters to achieve the best exergetic performance are formulated as design plots for the design and operation of a solar air heater. The weighted sum method is used to optimize the objectives of exergetic performance and total annual cost. The results reveal that too high Reynolds numbers result in low effective performance and unexpected exergetic performance. In that case, a lower roughness should be used, i.e. a smaller relative roughness height and larger relative roughness pitch. This is because the pressure loss penalty and irreversibility are quite large at high Reynolds numbers. An absorber plate area of 1.3 m² was found to achieve the maximum exergetic performance and minimum total annual cost.

ABSTRACT:

In this study, an experimental apparatus was used to produce dried shrimp. From experiments with various air velocities and temperatures, the drying constant, moisture transfer coefficient and moisture diffusivity were obtained by using a Bi-Di correlation. An equation for determining the drying constant was established to determine the drying parameters for different drying conditions. To obtain the targeted moisture, i.e., a moisture content of 0.25 (dry basis, d.b.), drying with the highest temperature and air velocity (60 °C, 2 m/s) took 3.6 h, while the lowest temperature and air velocity (50 °C, 1 m/s) required up to 5.8 h. The transport parameters were then used to simulate the temperature and moisture content distribution inside the shrimp using ANSYS software for a certain drying condition. The results showed that the shrimp temperature increased rapidly, reaching the dry air temperature after approximately 15 min. The moisture content in the tail was markedly lower than that at the centre, which is the thickest part of the shrimp. The data from this study can be used to optimize the energy consumption in shrimp convective drying technologies.

ABSTRACT: 

The basement parking lot, which provides a certain number of car spaces for users, is an effective solution for parking in crowded cities. The required ventilation system design is generally based on the number of air changes per hour, provided by local authority standards. An appropriately designed ventilation system plays an important role in ensuring a safe environment for people in case of a fire. This study aims to establish the smoke spread behavior and tenability criteria for a car fire in a basement parking lot with a small area of 2,700 m2, by using Autodesk computational fluid dynamics 2019 software. The car-fire growth rate was assumed to be a low t-squared curve. For numerical analysis, a steady-state fire was adopted at the sixth minute of the curve. The completely developed heat release rate of the car fire was 4 MW. Two common ventilation systems–a ductwork system and a combined impulse and ductwork system–were used for the simulation. The ventilation system was designed to extract 10 air changes per hour. The re-sults suggested that the two ventilation systems guarantee a safe route for evacuation through the ramp. Besides, the ductwork venti-lation system performs better at preventing the smoke from spreading, as compared to the combined ventilation system, during 6 min after ignition.

ABSTRACT:

The parabolic trough solar collector has a very high absorber tube temperature due to the concentration of solar radiation. The high temperature leads to large heat loss to the environment which reduces efficiency of the parabolic trough collector. The heat loss reduction can be obtained by adopting a multi-pass fluid flow arrangement. In this chapter, airflow travels in three passes of the receiver to absorb heat from the glass covers and absorber tube to decrease surface temperatures. 1D mathematical model is developed to evaluate effective efficiency and the temperature distribution of surfaces and fluid. The mathematical modeling is based on air temperature gradients and solved by a numerical integration. Diameter ratios of outer glass to inner glass (r23) and inner glass to absorber tube (r12), Reynolds number (Re), and tube length (L) are varied to examine the efficiency and the temperature distribution. Results showed that the highest efficiency is archived at r23 = 1.55 and r12 in the range of 1.45 to 1.5. The efficiency increases with Re and decreases with L due to dominant heat transfer in terms of thermohydraulic behavior of a concentrating solar collector. With the optimum ratios, absorber tube temperature can reduce 15 K compared with another case.