Experimental Study on Heat Transfer and Pressure Drop Characteristics of Four Types of Plate Fin－and－TUbe Heat Exchanger Surfaces

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The Thermal Behavior of Coal—Ash Deposits on Heat Exchangers

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Efficient Equipment with Special Heat Exchanger for Thermal Treatment of Polluted Air—Experiments,Computations, Applications

A quite new and unique piece of equipment for the thermal treatment of gas wastes (i.e., the incineration of volatile organic compounds contained in polluted air) has been developed. This compact equipment is characterized by a cylindrical combustion chamber placed inside a heat exchanger—a polluted air preheater. This cylindrical preheater consists of several concentric stainless sheets. Both flue gas from the combustion chamber and polluted air heated by flue gas flow in the spaces between the cylindrical sheets. Narrow distance strips placed between the sheets form helical rectangular ducts, through which we can achieve a counter-current flow of process fluids. A mathematical model for the calculation and/or simulation of the equipment consists of submodels of a heat exchanger and combustion chamber and the annular space between them. Based on the results of measurements on an industrial scale experimental facility, new correlations for the thermal and hydraulic calculations of the heat exchanger were developed. Some industrial applications are briefly mentioned.     

Experimental and Numerical Simulations of Flow and Heat Transfer in Heat Exchanger Elements Using Liquid Crystal Thermography

Experimental and numerical investigation of heat transfer and fluid flow were conducted for classic heat exchanger elements (flat plate with fin-tubes in-line, staggered and with vortex generators) and corrugated-undulated ducts under transitional and weakly turbulent conditions.The dependence of average heat transfer and pressure drop on Reynolds number and geometrical parameters was investigated. Distributions of local heat transfer coefficient were obtained by using liquid crystal thermography and surface-averaged values were computed. Three-dimensional numerical simulations were conducted by a finite-volume method using a low-Reynolds number k-e model under the assumption of fully developed flow. Computed flow fields provided otherwise inaccessible information on the flow patterns and the mechanisms of heat transfer enhancement.     

Strategies against Particle Fouling in the Channels of a Micro Heat Exchanger When Performing μPIV Flow Pattern Measurements

The measurements of flow patterns in the channels of micro devices such as mixers and heat exchangers are usually performed with the well-established μ PIV (micro Particle Imaging Velocimetry) technique. Yet, the micro particles in this technique introduce particle fouling (PF), which is observed by the inherent active imaging system. This phenomenon is enhanced during the active measurement, leading to erroneous signals long before the flow is blocked. Investigating the roots of PF in micro devices and selecting appropriate means to mitigate or delay it is essential in order to achieve sufficient experimental running time. The history of development on the fouling effect is discussed, thereby emphasizing the influence of pumps, flow guidance, surface roughness and chemistry, fluid chemistry, supersonic disintegration, and particle aging by agglomeration on PF. The cleaning procedures are also discussed. Furthermore, the capability of μ PIV to detect early deposits and their impact on the flow is demonstrated.     

Transient Performances of a Two—Pass Gas—to—Gas Crossflow Heat Exchanger

INTaoDUCTIoNThecrossllowgas-trtasheatexchngehasbeenwidelyusedinmanengineeringfields,suchastheenvironmDtalcontrosystemofaeroplanes.Itstransientbehaviourshavebecomemoreandmorebopor-ta-nttothedesignandtheperformanceofthewholesystem.Theinvestigationofthetransielltbehavioursisthefocusoftoday'sresearches.Bothnumericalll]andanalyticalmethodsl2]havebeenusedforthispurpose.Thenumericalmethodismoregenerala-ndcanbeusedfordifferentkindsofheatexchangersandworkingconditions,butitiscomplicatedandmoredriei…     

The Feasibility Study of the Waste Heat Air—Conditioning System for Automobile

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Numerical Simulations of Fluid Flow and Heat Transfer through Aluminum and Copper Metal Foam Heat Exchanger – A Comparative Study

Abstract

This article discusses about a numerical simulation of a metal foam heat exchanger system carried out by a commercial software. A metal foam layer is attached to the bottom of the heat exchanger to absorb heat from the exhaust hot gas leaving the system. Two types of metal foams with two different pores per inch (PPI) values are considered for heat transfer enhancement. Similarly, two different materials Aluminum and copper, that poses high thermal conductivity, metal foams are considered for the present numerical simulations. The heat exchanger system is simulated over a range of 6–30?m/s fluid velocity. The proposed simulations are compared with theoretical and experimental data available in the literature. The goal is to improve the thermal performance of the heat exchanger by decreasing the pressure drop and maximizing the heat transfer rate. Finally, it has been noticed that the velocity of the fluid decreases as PPI increases at the expense of its pressure drop. The copper metal foam gives a maximum increase of 4–10% heat transfer rate compared to aluminum metal foams for a fluid velocity of 30?m/s.     

Effect of Volume Fraction of γ‐Al2O3 Nanofluid on Heat Transfer Enhancement in a Concentric Tube Heat Exchanger

In this work, γ-Al₂O₃ nanoparticles with mean diameter of 10 nm are dispersed in deionized water with four nanoparticle volume concentrations of 0.25, 0.5, 0.75, and 1%. The effect of γ-Al₂O₃/water nanofluids on the heat transfer enhancement of heat exchangers is investigated under turbulent regime for four different volumetric flow rates of 150, 200, 250, and 300 L/h. The experimental results showed that the convective heat transfer is increased by increasing particles volume fraction as well as flow rate. The maximum enhancement obtained in Nusselt number and heat transfer coefficient was 20 and 22.8%, respectively, at Reynolds number of 6026 and particle volume fraction of 1%. The experimental Nusselt numbers of nanofluids showed good agreement with the available empirical correlation at particle volume fractions of 0.25 and 0.5%. An empirical correlation is obtained to estimate the Nusselt number of nanofluid under the conditions of this work.     

Study of the Thermal Behavior of Multi Tube Tank in Heat Recovery from Chimney—Analysis and Optimization

This work discusses the utilization of multi tube tank heat exchanger for waste heat recovery. The thermal behavior of the system is studied in order to understand the contribution of the different heat transfer modes governing the system. As application, heating water in residential application from chimney heat recovery is considered. A prototype illustrating the suggested system is implemented and tested. Different waste heat scenarios by varying the quantity of burned firewood (heat input) are experimented. The temperature at different parts of the system and the gas flow rates of the exhaust pipes are measured. Measurements showed that the temperature of 95 L tank of water can be increased by 68°C within one hour. Obtained results show that the convection and radiation exchanges at the bottom surface of the tank have a considerable impact on the total heat transfer rate of the water (as high as 70%). Moreover, the proposed system allows saving 9.8 L of gasoline, 10.6 L of diesel or 15 kg of wood for 12 hours of chimney operation.     

Thermal Design of Multistream Plate Fin Heat Exchangers—A State-of-the-Art Review

Multistream plate fin heat exchangers have replaced two-stream heat exchangers in diverse applications due to their compactness, capacity of handling multiple fluid streams in a single unit, and possibilities of having intermediate entry and exit of the streams. Unique features of such heat exchangers like direct/indirect crossover in temperatures due to several thermal communications among the fluid streams and the dependence of the thermal performance on “stacking pattern” have no equivalent in two-stream modules. As a consequence, an extension of the commonly used design/simulation techniques like ?-NTU or the LMTD method, applicable for two-stream exchangers, fails miserably in the case of multistream units. Though several techniques have been suggested over the years, in reality, no universally accepted methodology exists for the “thermal design” of multistream plate fin heat exchangers to date. In this communication, a state-of-the-art review of the thermal design of multistream plate fin heat exchanger is provided. Reported techniques based on heuristics, extension of the analysis applicable for two-stream heat exchangers, differential analysis, network analysis, and rigorous numerical solutions are briefly reviewed. Advantages and limitations of such techniques are also critically judged. The method of “area splitting” and “successive partitioning” proposed by the present research group is also elaborated. Apart from the basic design methodology, the techniques adopted for accounting for variable fluid properties, axial heat conduction in the solid matrix, and thermal communication with the environment have been discussed. Further, the suggested methodologies for optimizing the thermal design are reviewed. Finally, comments have been made indicating the future need of research in this topic.     

One—Dimensional Analysis of Thermal Choking in Case of Heat Addition in Ducts

IntroductionThe s up ersonic- combus t ion ram j et (s cramj et ) engine is one of the most prollilsing air breathing prOPulsion systems for hypersonic transports. It is essentialto the design of scramjet engines that the fueLair miX-ture remains supersonic throughout the combustor.The subsonic combustion is better than the supersonic combustion from a standpoint of efficiency, bescause total pressure losses in heated supersonic flowsare higher than those in heated subsonic flows withsame st…     

Effect of Radiative Heat Transfer on Indoor—Fire

The importance of radiative heat transfer in the simulation of indoor-fire has been studied.Computer codeshave been developed based on four-flux model and discrete transfer model,respectively.Evaluation of the codesagainst exact analytic solution and experimental data shows that the discrete transfer model gives numericalresults with acceptable accuracy while the four-flux model underpredicts the heat fluxes although the gen-eral trend is reasonable.Numerical studies have been performed of two-dimensional,axisymmetric turbulent,buoyancy-controlled indoor fire.The computational results show that neglecting radiation in the simulationcan cause overprediction of 500K in the maximum temperature and less uniform velocity field compared to theprediction by discrete transfer model.The four-flux method has been found to produce less uniform velocityand temperature values than discrete transfer model,but is more economic in computation.     

Numerical–Theoretical Analysis of Heat Transfer,Pressure Drop,and Fouling in Internal Helically Ribbed Tubes of Different Geometries

A numerical analysis of heat transfer and pressure drop for turbulent flow in a series of 15.54-mm inside diameter helically ribbed tubes has been performed. The ranges of geometric parameters were number of rib starts (10 to 40), helix angle (25 to 55 degrees), and rib height (0.3 to 0.6 mm). The effect of grid independence was extensively examined. The computational results match well with the experimental data to validate the accuracy of the numerical model. The effect of each main parameter, rib starts, helix angle, and rib height, on heat transfer and pressure drop is investigated. Considering fouling in practical situations, the ratio of pitch over rib height is an important parameter to select the tubes. It is advisable to select tubes with pitch over rib height ratio greater than 3.5, which have better heat transfer and lower fouling potential.     

Studies on Fanning Friction (f) and Colburn (j) Factors of Offset and Wavy Fins Compact Plate Fin Heat Exchanger–A CFD Approach

The objective of this work is to address the uncertainties in the estimation of the Fanning friction (f) and Colburn (j) factors in a compact offset plate fin heat exchanger, and the generation of flow friction and heat transfer correlations in the form of f and j for compact wavy plate fin heat exchangers. A typical offset fin has been analyzed using FLUENT software (a general purpose computational fluid dynamics (CFD) simulation tool) for estimation of f and j data. These results are compared with the results of the available correlations in the literature and in-house experimental results. Uncertainties in estimation of f and j data are reviewed and the variations in the results are highlighted. In the case of wavy fin configuration, very limited correlations are available in the literature. Hence, with the objective of developing correlations, 18 different types of wavy fins geometries have been analyzed using a CFD tool to find out the f and j data in the laminar and turbulent regions. Multiple regression analysis has been carried out on the set of data to generate the correlations for f and j. These correlations have been compared with the experimental results of wavy fin reported in the literature.     

Numerical Modeling of Biomass Pyrolysis—Heat and Mass Transport Models

We consider the pyrolysis of robinia pseudoacacia, which is a common material for biomass gasifiers. We formulate three models of the process, with increasingly detailed physics, best suited for different spatial scales from large to small. For each model, we perform numerical simulations of adaptable complexity and compare the results with the thermogravimetric analysis (TGA) experiments.     

Experimental Research on Heat Transfer and Pressure Drop of Two Configurations of Pin Finned—Tubes in an In—line Array

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On the C^r-Closing Lemma and the Koebe–Morse Coding of Geodesics on Surfaces

We consider the -closing lemma for vector fields with finitely many singularities on an orientable closed surface M of genus g2. Given a nontrivially recurrent trajectory, there is the corresponding geodesic having the same asymptotic directions (both negative and positive). Using the Koebe–Morse coding for the corresponding geodesic, we introduce the notion of p-expansions in the form of two sequences of nonnegative integers. The main result is the following. Suppose a vector field , r, has a nontrivially recurrent trajectory l through a point m; then there exists arbitrarily close to X (in the -topology) having a periodic trajectory through m provided that the Koebe–Morse coding of the corresponding geodesic g(l) has p-expansions of unrestricted type.