Use Of Artificial Roughness Research Articles

Experimental Investigation and Optimizing the Parameters of a Solar Air Heater Having Broken Arc-Shaped Ribs Using Hybrid Entropy-VIKOR Technique

Abstract In this article, thermal performance of a solar air heater (SAH) having broken arc-shaped ribs has been investigated experimentally, and then, performance parameters have been optimized. Study reveals that the use of artificial roughness enhances both heat transfer rate and pumping power requirement, and hence, the overall performance of solar air heater increases. Thus, it is imperative to optimize the performance-defining criteria viz. Nusselt number enhancement ratio, friction factor enhancement ratio, and thermohydraulic performance parameter, to propose an optimal set of flow and roughness parameters. The hybrid entropy-VIKOR technique has been employed to outline the optimal set of parameters using performance-defining criterions, to obtain maximum profit with the minimum incurred cost. The optimal set of parameters attained using entropy-VIKOR approach among all the alternatives is as follows: relative gap width = 4, relative roughness pitch = 10, and arc angle = 45 deg at Reynolds number = 9000.

Performance enhancement of solar air heater by attaching artificial rib roughness on the absorber Plate

Despite the limitations of conventional energy sources, the current energy scenario is still biased towards the use of these resources. Solar energy is regarded as a vital component of sustainable energy development due to its environmental friendliness and abundant resources. Solar air heaters (SAHs) are devices that convert solar energy into thermal energy by using air as a working fluid. SAHs are used in various applications due to their low cost and operation. The low thermal efficiency of SAHs can also limit their effectiveness due to the low temperature rise caused by the air. Due to the high thermal losses from the SAH, it is important to improve its performance in turbulent flow. Various efforts have been made to improve the heat transfer rate through the use of various components such as ribs, baffles, and fins in SAHs. This paper presents a detailed review on the thermal performance of a SAH with a ribbed absorbing plate. The use of artificial roughness has been found to improve the thermal performance of the SAH. The various configurations of the ribs have been presented in order to provide an optimized SAH design. This article aims to describe and conclude the studies on the influence of ribs on the SAH duct's pressure drop and heat transfer rate. It also explores the effects of varying the surface roughness on the performance of SAHs.

A Review on Heat Transfer Enhancement of Solar Air Heater Using Various Artificial Roughed Geometries

Solar air heater acts as one of the important components in utilization of solar energy. The air heater absorbs the irradiance and converts it into heat energy at the absorbing surface. The thermal energy is further use in heating flowing air through the duct. Solar air heaters are cost effective as well as simple in design. Solar air heater can be used in space heating, timber seasoning and agricultural drying. In spite of all these advantages the solar air heater has certain challenges such as the air has low heat transfer coefficient. The heat transfer rate from the heated absorber surface to the air is low. Hence in order to enhance the heat transfer coefficient the surface area either increases or the flow made to be turbulent. In order to do so the artificial roughened element must be incorporated on the heated surface. The use of artificial roughness is considered as an effective technique to enhance the heat transfer rate of fluid flowing through the duct of solar air heater. The heat transfer and friction characteristics of number of roughness geometries incorporated solar air heater have been investigated. In this paper an attempt has been made to review on element geometries used as artificial roughness in solar air heater in order to improve thermal and thermo hydraulic performance of solar air heater ducts.

Issues of Development of Solar Collectors with High Efficiency

The article deals with the creation of energy-efficient solar water collectors. In order to develop energy-efficient solar water collectors (SWC), methods of rational enhancement of heat transfer in the channels of the collectors are proposed. It is noted that the methods used to increase heat transfer from the collector walls to the water should be tailored to a low-speed flow of the heat carrier. With such flow regimes, the most acceptable ways to enhance heat transfer are: flow swirling, the use of artificial roughness, renewal of the hydrodynamic boundary layer through the creation of an alternating pressure gradient in the flow. The analysis of the conducted research shows that the maximum effects of increasing heat transfer occur in the range of Re numbers from 2000 to 8000, i. e. in the laminar flow region and in the region of underdeveloped turbulence. An efficiency criterion is obtained for the conditions under which enhancers are installed inside the pipes. The criterion determines the ratio of the number of pipes with enhancers to the number of smooth pipes. The calculation is carried out for cases in which the heating capacity, flow rate, power for heat carrier circulation and the pipe diameter of the SWC with smooth pipes are equal to the heating capacity, flow rate, power for heat carrier circulation and pipe diameter of the SWC with the pipes with enhancers. In addition to the specified efficiency criterion of the SWC, a heat transfer comparison formula of the SWC having pipes with enhancers and SWC with smooth pipes is obtained

A detailed review on research, technology, configurations and application of wire ribs as artificial roughness in rectangular solar air heater duct

Use of artificial roughness in the duct of solar air heater (SAH) has been an interesting area of research during the last few decades. In present review article a holistic view about application of circular shape wire ribs as roughness element and its different geometry on the absorber plate of SAH duct for performance enhancement has been done. This article, reported in details numerous experimental as well as analytical studies for rib roughened SAHs which have been carried out by different researchers positively. Correlations for heat transfer and friction factor, developed by various investigators for different artificially roughened solar air heaters (SAHs) geometry have been reported in chronological order and in well tabulated form. The roughness and operating parameters into which investigators have obtained their maximum performances of SAHs have also been presented separately in the table. Effects of various rib roughness parameters on heat transfer and fluid flow process are also discussed in details.

Experimental Investigation on Thermal Performance in Three-Sided Solar Air Heaters Having an Alignment of Multi-v and Transverse Wire Roughness on the Absorber Plate

Abstract The use of artificial roughness is an efficient and commercial way to appreciate the thermal performance from the collector to the air in solar air heater ducts, for numerous applications such as space-heating, crop-drying, and seasoning of timber industrial purpose. In this paper, the tentative inquiry on thermal enactment using new-fangled of three-sided roughened quadrilateral duct solar air heater having an alignment of multiple-v and transverse wire is performed and compared the outcomes with smooth duct air heater under similar operational circumstances. The modification of an arrangement and operational constraints is inspected within the restrictions, the moral of four-sided duct aspect ratio (W/H) = 8, the Reynolds number occupied from 3000 to 12,000, fraction of pitch to roughness height, P/e in the range of 10–25; ratio of roughness height to hydraulic diameter, e/D in the range of 0.018–0.042; at flow attack angle, α = 60 deg for constant moral of relative roughness width, (W/w) = 6. The augmentation on thermal efficiency in three-sided rugged duct is found to be 23–86% when compared to smooth duct, and the maximum thermal efficiency can occur at P/e = 10 and e/D = 0.042. The enhancement in air temperature flowing under three-sided roughened duct is found to be 49.27% more than that of a smooth duct. The instant innovative form of three-sided roughened solar air warmer would be preferable to those of a smooth solar air heater with respect to heat assignment.

Calculation of Heat Exchange on the Surface of a Flexible Heat Exchanger for Use in Mobile Hospitals

Currently, the world is characterized by quite a large number of military conflicts, manmade disasters and natural disasters. Every year, about 50 thousand people die from various natural disasters in the world. The report of the UNISDR notes that natural disasters that occurred in the world between 1998 and 2017 led to the death of 1.3 million people (more than half of them – due to earthquakes). The analysis shows that human losses could be significantly less with rapid first aid. This requires the presence of a field hospital located as close as possible to the lesion. Currently, field hospitals for various purposes are produced. The heating system of the field hospital modules plays an important role in the operation. A heating system is proposed, which includes a vortex heat generator and heating devices made of polyvinyl chloride. The system is characterized by low weight and quick access to the operating mode. However, in the literature there is no method for calculating the heat exchange coefficient in a closed space, which is formed by flexible heater surface and an enclosing wall. Based on the analysis of criterion dependences and experimental data, new criterion equations for calculating the heat exchange coefficient for an arbitrary location of heaters in space are obtained. The following dependence is built lgNu = f(lg(Gr×Pr)), which allows to determine value of heat exchange coefficient for given range of temperature. A method of intensification of the heat exchange process by creating an artificial roughness is proposed. Graph is done to determine growth rate of heat exchange СK, which is included in criterion equation. The use of artificial roughness allowed increasing the heat transfer coefficient by 28 % and the thermal power of the heating device by about 26 %.

Thermo-hydraulic performance analysis of a solar air heater roughened with reverse NACA profile ribs

The solar air heater is subjected to a low convective heat transfer coefficient on account of the formation of the laminar sub-layer between the absorber plate and flowing air. To increase the heat transfer coefficient, the laminar sub-layer can be interrupted with the use of artificial roughness (turbulator) on the absorber plate. In the present analysis, the effects of novel type of roughness element in the form of NACA 0040 profile ribs in the reverse position are studied on the performance of the solar air heater. The effects of relative roughness pitch (P/e) and relative roughness height (e/D) were studied for the Reynolds number (Re) ranging from 6000 to 18,000. Among the various roughness parameters, NACA 0040 profile ribs provided in the reverse direction with P/e as 5 and e/D as 0.065 was found to be the optimum. The thermo-hydraulic performance parameter for this case was found to be 2.53 at a Reynolds number of 6000. The experimental results validated the numerical results, and the maximum deviation was found to be 4.84%. An empirical correlation was developed for prediction of Nu and f in terms of Re and e/D and found to conform within ±3% of the corresponding experimental values.

A detailed review on various V-shaped ribs roughened solar air heater

Solar air heater (SAH) is a popular and economical device which collects the solar energy and is employed for space heating, drying of agricultural products, food items, and leather, seasoning of timber, etc. Attachment of artificial roughness on the absorber surface is an appropriate method to augment the heat transfer from the heated surface to the air flowing through SAH duct. Use of artificial roughness has been an area of great interest for researchers as far as the cooling of turbine blades, and combustion chambers are concerned. This technique is effective in enhancing the heat transfer in a micro-channel heating/cooling system. Present paper holistically furnishes concise information about various kinds of V-shaped roughness geometries used in SAHs for improving its performance covering experimental, analytical, numerical and computational fluid dynamics (CFD) approaches. In this paper, 124 research articles have been referred, which provide a detailed comprehensive and comparative study revealing the effect of various geometrical parameters and different V-shaped roughness patterns on the performance of SAH. This article also brings in the information about the correlation developed by researchers for heat transfer and friction factor. This comprehensive review will be quite useful for technical persons and researchers working in the area of SAH.

Heat Transfer and Friction Characteristics of Artificially Roughened Duct used for Solar Air Heaters—a Review

Solar air heater uses the energy coming from the sun to heat the air. The conversion rate of solar energy to heat depends upon the efficiency of the solar air heater and this efficiency can be increased by the use of artificial roughness on the surface of absorber plate. Various studies were carried out to analyse the effect of different roughness geometries on heat transfer and friction factor characteristics. The thermo-hydraulic performance of solar air heater can be evaluated in terms of effective efficiency, thermo-hydraulic performance parameter and exergetic efficiency. In this study various geometries used for artificial roughness and to improve the performance of solar air heaters were studied. Also correlations developed by various researchers are presented in this paper.

Investigation on optimal thermohydraulic performance of a solar air heater having arc shaped wire rib roughness on absorber plate

This paper presents an investigation on optimal thermohydraulic performance of a solar air heater having arc-shaped wire rib roughness on underside of the absorber plate. The use of artificial roughness on the absorber plate of a solar air heater causes enhancement in rate of the heat transfer between absorber plate and flowing air, by creating turbulence, however, there is substantial increase in the frictional resistance which leads to more pumping power consumption. The effective efficiency is evaluated on the basis of useful thermal energy gain minus equivalent thermal energy to the power required to propel the air through solar air heaters. A mathematical model and procedure for prediction of effective efficiency of an arc shaped wire rib roughened absorber plate solar air heater has been presented and the effects of roughness and various geometrical and operating parameters on effective efficiency have been worked out. The effective efficiency of the roughened absorber plate solar air heater has also been compared with smooth absorber plate solar air heater operating under similar conditions. It is observed that effective efficiency of a roughened solar air heater has an optimum value corresponding to a certain Reynolds number and specific values of operating and geometrical conditions. A correlation between system and operating parameters that delivers optimum effective efficiency has been developed and presented, which can be used for optimal design of such systems.

Numerical simulation of effective efficiency of a discrete multi V-pattern rib solar air channel

The use of artificial roughness in the form of repeated ribs has been found to be an efficient method of improving the heat transfer to fluid flowing in the channel. In this study, performance of solar air channel as a function of discrete multi V-pattern rib shapes has been investigated. The e/D was varied from 0.022 to 0.043, Gd/Lv was varied from 0.24 to 0.80, g/e was varied from 0.5 to 1.5, α was varied from 30° to 75°, P/e was varied from 6.0 to 12.0 and W/w was varied from 1.0 to 10.0. A methodology has been developed for the prediction of effective efficiency. Based on the values of effective efficiency, an optimization has been carried out to determine the set of data of roughness shapes parameters that correspond to better effective efficiency for given values of operating parameters of the air channel. Design plots have been represent to depict the data of individual roughness shapes parameters that characterize the optimum condition as a function of performance parameter and intensity of radiation. It was observed that the maximum values of effective efficiency for e/D of 0.043, Gd/Lv of 0.69, g/e of 1.0, α of 60°, P/e of 8.0 and W/w of 6.0. Discrete multi v-rib shape has been found to be better thermohydraulic performance (effective efficiency) as comparison to other rib shapes solar air channels.

Artificially roughened solar air heater: Experimental investigations

Abstract Solar air heater is the cheapest and extensively used solar energy collection device for drying of agricultural products, space heating, seasoning of timber and curing of industrial products. The use of an artificial roughness on a surface is an effective technique to enhance the rate of heat transfer to fluid flow in the duct of a solar air heater. Use of artificial roughness in solar air heater has been topic in research for the last thirty years. In the present article an attempt has been made to present holistic view of different kinds of roughness geometry used for creating artificial roughness in solar air heater for performance enhancement by experimental approaches. In this article thirty eight experimental studies have been reported on solar air heater, roughened with different kinds of roughness geometry. However, no comprehensive comparative study has been carried out or found in the literature so far, in order to investigate the relative performance of different types of artificially roughened solar air heater. The objective of this article is to perform such a study. In this article twenty known different shapes and orientations of roughness elements are considered for comparative analysis. In order to obtain the results numerically, codes are developed in MATLAB-7. Correlations for heat transfer and friction factor, developed by various investigators for artificially roughened solar air heaters have been reported in this article. The effects of various rib parameters on heat transfer and fluid flow processes are also discussed.

A numerical investigation of square sectioned transverse rib roughened solar air heater

The use of artificial roughness in the form of repeated ribs on a surface is an effective technique to enhance the rate of heat transfer. A numerical investigation on the heat transfer and fluid flow characteristics of fully developed turbulent flow in a rectangular duct having repeated transverse square sectioned rib roughness on the absorber plate has been carried out. The commercial finite-volume CFD code ANSYS FLUENT (ver. 12.1) is used to simulate turbulent airflow through artificially roughened solar air heater. The Navier–Stokes equations and the energy equation are solved in conjunction with a low Reynolds number RNG k–ɛ turbulence model. Twelve different configurations of square sectioned rib (P/e = 7.14–35.71 and e/D = 0.021–0.042) have been considered. The flow Reynolds number of the duct varied in the range of 3800–18,000, most suitable for solar air heater. The effects of relative roughness pitch and relative roughness height on Nusselt number and friction factor have been discussed and the results are compared with the square sectioned rib roughened duct and smooth duct under similar flow conditions to investigate the enhancement in Nusselt number and friction factor. Roughness and flow parameters for artificially roughened solar air heater have been optimized by considering the thermo-hydraulic performance parameter based on constant pumping power requirement. It has been found that the square sectioned transverse rib roughened duct with P/e = 10.71 and e/D = 0.042 offers the best thermo-hydraulic performance parameter for the investigated range of parameters.

평판형 태양열 집열기의 압력강하 및 열전달 성능 향상에 관한 수치해석적 연구

Abstract : The use of artificial roughness in various forms of shapes and sizes is the most common and effec-tive way to improve the performance of a flat-plate solar collector. In the present study, numerical analysis on heat transfer and pressure drop was performed in a rectangular channel with various rib arrays. The uni-form heat flux is applied to the channel from the upper side. The forms of ribs considered in this study were rib 90°, groove 90°, groove 60°, baffle 90°, baffle 60°, wave 90° and wave 60°. Air is the working fluid, and the Reynolds number ranges from 3200 to 17800. Nusselt number and friction factor were investigated to predict the performance of the system with various type of ribs. The average Nusselt number and pressure drop were increased with the increase of velocity in all types of ribs. The highest heat transfer and pressure drop occurred for the baffle 90°, but highest performance factor considering heat transfer and pressure drop together occurred for the groove 60°. Therefore, heat transfer and pressure drop should be considered together when a flat plate solar collector is designed.

A CFD (computational fluid dynamics) based heat transfer and fluid flow analysis of a solar air heater provided with circular transverse wire rib roughness on the absorber plate

This article presents the study of heat transfer and fluid flow processes in an artificially roughened solar air heater by using computational fluid dynamics (CFD). The effects of small diameter of transverse wire rib roughness on heat transfer and fluid flow have been investigated. The Reynolds number, relative roughness pitch (P/e) and relative roughness height (e/D) are chosen as design variables. A two-dimensional CFD simulation is performed using the ANSYS FLUENT 12.1 code. The Renormalization-group (RNG) k–ε model is selected as the most appropriate one. Results are validated by comparing with available experimental results. It is apparent that the turbulence created by small diameter of transverse wire ribs result in greater increase in heat transfer over the duct. However, the use of artificial roughness results in higher friction losses. The present CFD investigation clearly demonstrates that the average Nusselt number and average friction factor increase with increase in the relative roughness height while giving opposite trend with increase in relative roughness pitch. The condition for optimum performance has been determined in term of thermal enhancement factor. A maximum value of thermal enhancement factor has been found to be 1.65 for the range of parameters investigated.

Modeling and Simulation of Turbulent Flows through a Solar Air Heater Having Square‐Sectioned Transverse Rib Roughness on the Absorber Plate

Solar air heater is a type of heat exchanger which transforms solar radiation into heat energy. The thermal performance of conventional solar air heater has been found to be poor because of the low convective heat transfer coefficient from the absorber plate to the air. Use of artificial roughness on a surface is an effective technique to enhance the rate of heat transfer. A CFD-based investigation of turbulent flow through a solar air heater roughened with square-sectioned transverse rib roughness has been performed. Three different values of rib-pitch (P) and rib-height (e) have been taken such that the relative roughness pitch (P/e = 14.29) remains constant. The relative roughness height, e/D, varies from 0.021 to 0.06, and the Reynolds number, Re, varies from 3800 to 18,000. The results predicted by CFD show that the average heat transfer, average flow friction, and thermohydraulic performance parameter are strongly dependent on the relative roughness height. A maximum value of thermohydraulic performance parameter has been found to be 1.8 for the range of parameters investigated. Comparisons with previously published work have been performed and found to be in excellent agreement.

Heat transfer and friction factor correlations for a solar air heater duct roughened artificially with multiple v-ribs

The use of artificial roughness on the underside of the absorber plate is an effective and economic way to improve the thermal performance of a solar air heater. Several experimental investigations, involving different types of roughness elements, have been carried out to improve the heat transfer from the absorber plate to air flowing in solar air heaters. This paper presents an experimental investigation carried out to study the effect of multiple v-rib roughness on heat transfer coefficient and friction factor in an artificially roughened solar air heater duct. The experiment encompassed Reynolds number (Re) from 2000 to 20000, relative roughness height ( e/ D) values of 0.019–0.043, relative roughness pitch ( P/ e) range of 6–12, angle of attack ( α) range of 30–75° and relative roughness width ( W/ w) range of 1–10. Extensive experimentation has been conducted to collect data on heat transfer and fluid flow characteristics of a rectangular duct roughened with multiple v-ribs. Using these experimental data, correlations for Nusselt number and friction factor in terms of roughness geometry and flow parameters have been developed.

Use of artificial roughness to enhance heat transfer in solar air heaters – a review

Improvement in the thermo hydraulic performance of a solar air heater can be done by enhancing the heat transfer. In general, heat transfer enhancement techniques are divided into two groups: active and passive techniques. Providing an artificial roughness on a heat transferring surface is an effective passive heat transfer technique to enhance the rate of heat transfer to fluid flow. In this paper, reviews of various artificial roughness elements used as passive heat transfer techniques, in order to improve thermo hydraulic performance of a solar air heater, is done. The objective of this paper is to review various studies, in which different artificial roughness elements are used to enhance the heat transfer rate with little penalty of friction. Correlations developed by various researchers with the help of experimental results for heat transfer and friction factor for solar air heater ducts by taking different roughened surfaces geometries are given in tabular form. These correlations are used to predict the thermo hydraulic performance of solar air heaters having roughened ducts. The objective is to provide a detailed review on heat transfer enhancement by using an artificial roughness technique. This paper will be very helpful for the researchers who are researching new artificial roughness for solar air heater ducts to enhance the heat transfer rate and comparing with artificial roughness already studied by various researchers.

Heat transfer and friction characteristics of solar air heater ducts having integral inclined discrete ribs on absorber plate

The use of artificial roughness in a solar air heater duct has been proposed to be an excellent option to enhance the heat transfer from absorber plate to the air. This paper presents an experimental investigation on heat transfer and friction characteristics of solar air heater ducts with integral repeated discrete square ribs on the absorber plate. The effect of geometrical parameters, especially, the gap width and gap position has been investigated. The roughened duct has a width to height ratio ( W/ H) of 5.83. The relative gap position ( d/ W) and relative gap width ( g/ e) has been varied from 0.16 to 0.5 and 0.5–2.0, respectively. Experiments have been carried out for the range of Reynolds number from 3000 to 18,000 with the relative roughness pitch ( P/ e) range of 4–10; relative roughness height ( e/ D) range of 0.018–0.037; and angle of attack ( α) range of 30–90°. The optimum values of parameters for rib arrangement have been obtained and discussed. For Nusselt number, the maximum enhancement of the order of 2.83 times of the corresponding value of the smooth duct has been obtained, however, the friction factor has also been seen to increase by 3.60 times of that of the smooth duct. The maximum enhancement is observed at a relative gap position of 0.25 for relative gap width of 1.0, relative roughness pitch of 8.0, angle of attack of 60° and relative roughness height of 0.037. Based on the experimental data, correlations for Nusselt number and friction factor have been developed as function of roughness parameters of inclined discrete square ribs and flow Reynolds number.