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Number of results: 9
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Abstract

Experimental investigation was conducted on the thermal performance and pressure drop of a convective cooling loop working with ZnO aqueous nanofluids. The loop was used to cool a flat heater connected to an AC autotransformer. Influence of different operating parameters, such as fluid flow rate and mass concentration of nanofluid on surface temperature of heater, pressure drop, friction factor and overall heat transfer coefficient was investigated and briefly discussed. Results of this study showed that, despite a penalty for pressure drop, ZnO/water nanofluid was a promising coolant for cooling the micro-electronic devices and chipsets. It was also found that there is an optimum for concentration of nanofluid so that the heat transfer coefficient is maximum, which was wt. %=0.3 for ZnO/water used in this research. In addition, presence of nanoparticles enhanced the friction factor and pressure drop as well; however, it is not very significant in comparison with those of registered for the base fluid.

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Authors and Affiliations

Amir Arya
Saeed Shahmiry
Vahid Nikkhah
Mohamad Mohsen Sarafraz
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Abstract

The paper presents the investigation of the optimum design parameters of a solar air heater (SAH) having wire ribs as artificial roughness by using the Taguchi method. The solar air heater has arc shape roughness geometry with apex upstream flow on the absorber plate. The objective of this paper is to obtain a set of parameters that deliver maximum thermo-hydraulic performance. For this objective, a new parameter the thermo-hydraulic improvement parameter ( ηTHIP), has been introduced. For the present analysis, the effects of Reynolds number (Re), relative roughness pitch ( P/e), angle of attack ( α), and relative roughness height ( e/Dh), denoted by A, B, C, and D, respectively, have been considered. An ( L 18 = 6 1 · 3 2) orthogonal array (OA) was chosen as an experimental plan for applying the Taguchi method. The set of control factors for the solar air heater SAH which delivers the maximum Nusselt number (Nu), and minimum friction factor ( fr) – are A 6B 2C 2, and A 1B 1C 3 respectively. To obtain the maximum THIP the experimental set-up requires only one single run using the parameter A 6B 2C 2, hence there is no need to run it all 54 times.
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Authors and Affiliations

Mukesh Kumar Sahu
1
Shivam Mishra
2
Avinash Kumar
1

  1. Cambridge Institute of Technology, Department of Mechanical Engineering, Tatisilwai, Ranchi, Jharkhand, Pin-835103, India
  2. G L Bajaj Institute of Technology and Management, Department of Mechanical Engineering, Greater Noida, Uttar Pradesh, Pin-201308, India
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Abstract

The paper presents a method for improving the lime production process by increasing the efficiency of the lime slurry transport that occurs in it. The aim of the study was to reduce the energy demand of the pump installed in the discharge line. The presented solution consists of applying an additive called deflocculant to the transported slurry in order to reduce its viscosity while increasing the concentration of solids content. The deflocculant applied to the slurry is composed of waste material from the lime slaking process and an environmentally neutral chemical substance in the form of sodium-water glass. The rheological studies conducted confirm the positive effect of the selected deflocculant on the properties of the slurry tested. As a result of the analysis, it has been shown that the proposed solution has a substantial effect on reducing the friction factor of the transported slurry, thus reducing the energy consumption in the investigated process.
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Authors and Affiliations

Beata Joanna JAWORSKA-JÓZWIAK
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Abstract

The paper presents a numerical study on the heat transfer and pressure drop, related to flow in pipes with helical micro-fins. For all tested geometries, one applied a constant wall heat flux and fully developed 3D turbulent flow conditions. The influence of the angle of micro fins (referred to the tube axis) on thermal-flow characteristics were tested. The value of this angle was varied – with a step of 10 degrees – from 0 to 90 degrees (representing grooves parallel and perpendicular to the axis, respectively). Before numerical investigation, the pipe with helical angle of 30 degree was tested on an experimental stand. The results obtained from experiment and numerical simulations were compared and presented on the charts. As an effect of the numerical simulations, the friction factor f and Nusselt number characteristics was determined for the range of Re=104/1.6x106. The analysis of the results showed high, irregular influence of the helical angle on thermal characteristics and pressure drops. Additionally, the ratios: f/fplain, Nu/Nuplainand efficiency indexes (Nu/Nuplain)/( f/fplain) as a function of the Reynolds number for every helical angle were shown on the charts.

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Authors and Affiliations

Piotr Jasiński
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Abstract

The study presents an attempt at increasing the effectiveness of the crushing process through the application of a new original crumbling system. In the process of crushing materials, friction is present in many crushers as extremely significant or even dominating factor. The proposed construction solution is characterized by the occurrence – always on one of the working surfaces – of the static friction factor, and thus a friction that is greater than the kinetic friction.

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Authors and Affiliations

Feliks Chwarścianek
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Abstract

Providing roughness is an effective method to heat fluids to high temperature. Present paper make use of concave dimple roughness on one and three sides of roughened ducts aimed at determining rise in heat transfer and friction of three sides over one side roughened duct. Three sides roughened duct produces high heat transfer compared to one side roughened. Results are shown as a rise in Nusselt number and friction factor of three sides over one side roughened duct. Experimental investigation was conducted under actual outdoor condition at National Institute of Technology Jamshedpur, India to test various sets of roughened collectors. Roughness parameter varied as relative roughness pitch 8–15, relative roughness height 0.018–0.045, dimple depth to diameter ratio 1–2, Reynolds number 2500–13500 at fixed aspect ratio (width/hight) 8. Highest enhancement in Nusselt number for varying relative roughness pitch, height, and diameter ratio was respectively found as 2.6 to 3.55 times, 1.91 to 3.42 times and 3.09 to 3.94 times compared to one side dimple roughened duct. Highest rise in friction for three sides over one side roughened duct for these varying parameters was respectively found as 1.62 to 2.79 times, 1.52 to 2.34 times and 2.21 to 2.56 times. To visualize the effect of roughness parameter on heat transfer and friction factor, variation in Nusselt number and friction factor for varying roughness parameters with Reynolds number is shown.

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Authors and Affiliations

Vikash Kumar
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Abstract

Limiting energy resources has led researchers to find new innovative ways to enhance heat exchanging devices thermal performance in power generating systems. Thus, the present paper analyzes passive techniques of enhancing the thermal performance of a single tube heat exchanger. Experimental and numerical investigation on heat transfer enhancement using aserrated circular ring with twisted tape is carried out. The work incorporates the determination of Nusselt number, friction factor, thermal performance factor for serrated circular ring with twisted tape with variation in diameter ratio (0.8 and 0.85) and pitch ratio (2 and 3). Air is used as a working fluid with Reynolds number 6000–24000. The experiment is conducted by providing a constant wall heat flux of 1000 W/m2 to the system and thereby taking results at a steady state. The experimental and computational findings obtained for the smooth tube case are compared with the standard correlations of Dittus–Boelter and Blasius. Based on experimental and numerical investigation, there is 5.16 times augmentation in heat transfer and 3.05 times improvement in thermal performance factor over the smooth tube heat exchanger. In addition, the study of entropy generation rate for every geometrical parameter has been conducted, and their influence on the system’s thermal behaviour is presented. The results obtained in the present study may help the researchers of the same research area to find similar inserts and new ways of enhancing the thermal performance of heat exchangers.
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Bibliography

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Authors and Affiliations

Himanshi Kharkwal
1
Satyendra Singh
1

  1. Department of Mechanical Engineering, B.T. Kumaon Institute of Technology, Dwarahat-263653 (Almora), Uttarakhand, India
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Abstract

Solar air heater is regarded as the most common and popular solar thermal system and has a wide range of applications, from residential to industrial. Solar air heater is not viable because of the low convective heat transfer coefficient at the absorber plate which contributes to decreasing the thermal efficiency. Artificial coarseness on the plain surface is the most effective method to enhance heat transfer with a moderate rate of friction factor of flowing air in the design of solar air heater duct. The different parameters and different artificial coarseness are responsible to alter the flow structure and heat transfer rate. Over the years different artificial roughness and how its geometry affects the performance of solar air heater have been thoroughly studied. Various investigators report the correlations between heat transfer and friction factors. In the present study, a comparison of several artificial coarseness geometries and methods with a view to enhancing the performance of solar air heater has been made. A brief outline has also been presented for future research.
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Authors and Affiliations

Manoj Kumar Dubey
1
Om Prakash
1

  1. National Institute of Technology Patna, Patna, Bihar 800005, India
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Abstract

Flow mechanism under roughened solar air heater is quite complex. This paper is an effort towards determining the governing equations for heat transfer and friction factor for inclined spherical balls roughened ducts. With the availability of these equations, it is easier to predict the thermal and thermohydraulic performance of such roughened solar air heaters. The governing equations are derived based on the experimental data generated under actual outdoor condition at the test rig designed and fabricated at the terrace of the Mechanical Engineering Department, the National Institute of Technology Jamshedpur in India, in terms of roughness and flow parameters. Maximum augmentation in Nusselt number and friction factor for varying relative roughness pitch, relative roughness height, spherical ball height to diameter ratio, and angle of attack was respectively found to be of the order of 2.1 to 3.54 times, 1.87 to 3.21 times, 2.89 to 3.27 times and 1.74 to 3.56 times for Nusselt number and 0.84 to 1.79 times, 1.46 to 1.91 times, 1.67 to 2.34 times and 1.21 to 2.67 times for friction factor in comparison to non-roughened duct. The optimum roughness parameters under present investigation have been found.

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Authors and Affiliations

Ramesh Murmu
Parmanand Kumar
Hari N. Singh

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