Thermal Design Of Heat Exchangers Research Articles

Entropy generation analysis of turbulent flow in conical tubes with dimples: a numerical study

Minimizing the entropy generation rate is one of the key performance indicators for enhancing the thermal design of heat exchangers. This paper introduces a comprehensive numerical entropy generation analysis of turbulent water flow inside—newly proposed—conical tubes with dimples subjected to a constant heat flux. The effect of different tube diameter ratios (DR = 1, 1.5, 2, 3, and 5) and flow modes (convergent and divergent tube configurations) on the thermal, viscous, and total entropy generation rates is investigated within Reynolds number (Re) range of 3 × 103–40 × 103 using ANSYS-Fluent package. Realizable k-ε (RKE) turbulence model is adopted in this study. A well-validated 3D model was adopted to estimate the dimensionless indices: Bejan number (Be), enhanced entropy generation ratio (Ns,en), and the irreversibility distribution ratio ({phi }_{mathrm{s}}) to characterize the entropy generation performance and to compare conical dimpled tubes to smooth ones. The results showed that total entropy production rate values for dimpled tube geometries are lower than those for the corresponding smooth ones, especially for convergent dimpled tubes. Convergent dimpled tubes with DR in the range of 1.5–3 achieved the lowest total entropy production values over the whole Re range, with an average value of 0.20 W K−1, as compared to an average value of 0.34 W K−1 for the smooth configurations. The average Ns,en values for dimpled convergent tubes with DR = 1.5–3 are 0.46 and 0.80 at Re = 3000 and 40,000, with reductions of 50.54% and 3.61% at both Re values, respectively. The study also showed that the entropy generation analysis could provide an effective tool to highlight the optimal design of tube heat exchangers based on the minimum entropy generation and the enhanced entropy generation ratio.

ANALYSIS OF HOT WATER HEATERS FOR INDIVIDUAL HEATING STATION WHEN THE TEMPERATURE CHART OF THE DISTRIBUTION HEAT NETWORK IS CHANGED

The aspects of the functioning of centralized heating systems of residential urban districts after additional insulation of this district existing buildings were considered. The influence of the heat carrier temperature in the district distribution heating network on the heat transfer surface of the heat exchangers that are installed in the individual heat station schemes for hot water supplying was analyzed. Estimates were made for single-stage connection of the heat exchangers to the heating systems. When determining the heat transfer surface, known criterion equations for plate heat exchangers of heat supply systems were used. The range of changes in the heat transfer surface of hot water heaters and the consumption of network water is determined depending on the selected temperature chart of the distribution heat network. The proposed recommendations can be useful in developing a heat supply quality control schedule for a district buildings heating systems in a district when the building thermal insulation process is completed. Possible approaches to the thermal design of heat exchangers of the hot water supply system for insulated buildings individual heating stations are considered when changing the temperature chart of the district heating supply system of the residential urban districts. Estimates were made to understand the influence of the reduced temperature chart for heat supply of the districts on the network water consumption for hot water heating and the surface of heat exchangers of insulated buildings heaters. It was shown that the increase in network water consumption for building hot water supply can be 1.5 to 3 times higher. The analysis presented for the surface of the heat exchangers of heating installations for insulated buildings hot water supply shows that it can be even double increase of heaters heat transfer surface depending on the temperature chart. The results obtained should be taken into account when planning the temperature chart of the heat carrier for a distribution heating network. Keywords: district heating, heat supply systems reforming, individual heating station, hot water heaters, plate heat exchanger, heat exchanger thermal design.

Development and Application of a Multi-Objective Tool for Thermal Design of Heat Exchangers Using Neural Networks

This paper presents the design of a multi-objective tool for sizing shell and tube heat exchangers (STHX), developed under a University/Industry collaboration. This work aims to show the feasibility of implementing artificial intelligence tools during the design of Heat Exchangers in industry. The design of STHX optimisation tools using artificial intelligence algorithms is a visited topic in the literature, nevertheless, the degree of implementation of this concept is uncommon in industrial companies. Thus, the challenge of this research consists of the development of a tool for the design of STHX using artificial intelligence algorithms that can be used by industrial companies. The approach is implemented using a simulated dataset contrasted with ARA TT, the company taking part in the project. The given dataset to develop a theoretical STHX calculator was modeled using MATLAB. This dataset was used to train seven neural networks (NNs). Three of them were mono-objective, one per objective to predict, and four were multi-objective. The last multi-objective NN was used to develop an inverse neural network (INN), which is used to find the optimal configuration of the STHXs. In this specific case, three design parameters, the pressure drop on the shell side, the pressure drop on the tube side and heat transfer rate, were jointly and successfully optimised. As a conclusion, this work proves that the developed tool is valid in both terms of effectiveness and user-friendliness for companies like ARA TT to improve their business activity.

Coupling ε-NTU method for thermal design of heat exchanger in cabinet cooling system

In general, constant flow rates are assumed for thermal design of heat exchangers. However, the constant flow rates are not available in the heat exchangers used for fan-supplied systems. In this paper, a coupling ε-NTU method is presented to calculate the cooling efficiency of a fan-supplied cabinet cooling system, in which the pressure-flow rate characteristics of the fans and heat exchanger are considered simultaneously. The effects of heat exchanger parameters on the cooling efficiency of the cabinet cooling system are studied. It is found that the cooling efficiency of the system obtained by the coupling ε-NTU method is significantly different from that obtained by the traditional ε-NTU method. Therefore, it is necessary to using the coupling ε-NTU method for the heat exchanger thermal design in the cabinet cooling system.

A REVIEW OF LITERATURE ON THERMAL DESIGN OF FORCED DRAFT COUNTER TO CROSS FLOW AIR COOLED HEAT EXCHANGER

Heat exchangers are equipment that transfers heat from one medium to another. An air cooled heat exchanger, or ACHE, is simply a pressure vessel which cools a circulating fluid within finned tubes by forcing ambient air over the exterior of the tubes. In cross flow exchangers, the hot and cold fluids move perpendicular to each other. Some actual heat exchangers are a mixture of cross flow and counter flow (Known as Counter to Cross Flow Heat Exchangers) due to design features. The proper design, operation and maintenance of heat exchangers will make the process energy efficient and minimize energy losses. Heat exchanger performance can deteriorate with time, off design operations and other interferences such as fouling, scaling etc. It is necessary to assess periodically the heat exchanger performance in order to maintain them at a high efficiency level. This section comprises certain proven techniques of monitoring the performance of heat exchangers, coolers and condensers from observed operating data of the equipment. A major problem constantly faced by heat exchanger designers is to predict accurately the performance of a given heat exchanger or a system of heat exchangers for a given set of service conditions. The problem is complicated by the fact that uncertainties exist in most of the design parameters and in the design procedures themselves. The design parameters that are used in the basic thermal design calculations of a heat exchanger include process parameters, heat-transfer coefficients, tube dimensions (e.g., tube diameter, wall thickness), thermal conductivity of the tube material, and thermo physical properties of the fluids. Nominal or mean values of these parameters are used in the design calculations. However, uncertainties in these parameters prevent us from predicting the exact performance of the unit. The effect of the uncertainties is mostly in the performance degradation in service. Hence, there is an imperative need to consider all the uncertainties and to critically evaluate them and correctly predict the thermal performance of a heat exchanger. This is particularly true for critical applications. In thermal design of heat exchangers there are presently many stages in which assumptions in mathematical solution of the design problem are being made. Accumulation of these assumptions (e.g. use of mean values) may introduce variations in design as large as the uncertainties introduced in heat-transfer and flow friction correlations. The designer needs to understand where these inaccuracies may arise, and strive to eliminate as many sources of error as possible by choosing design configurations that avoid such problems at source. Heat Exchanger Thermal Design Problem referred to as the rating and sizing problems. KEYWORD:Thermal Design, Counter to cross flow heat exchanger, thermal design problems, uncertainties in design.

Comparison of metal foam heat exchangers to a finned heat exchanger for low Reynolds number applications

Due to its high porosity and large specific surface area, open-cell metal foam is an attractive material for heat transfer applications. In this article the performance of metal foam heat exchangers is compared to the performance of a bare tube bundle and the performance of an existing conventional louvered fin heat exchanger. A macroscopic model consisting of the Darcy–Forchheimer–Brinkman flow model and the thermal non-equilibrium energy model is used to perform two-dimensional simulations on metal foam heat exchangers. Because thermal design of heat exchangers is always a trade-off between heat transfer and pressure drop, both are considered together when evaluating the heat exchangers’ performance. The foamed heat exchangers show up to 6 times higher heat transfer rate than the bare tube bundle at the same fan power. If the fins are replaced by metal foam while keeping the overall dimensions the same, the finned heat exchanger shows in all cases the best performance. However, a metal foam heat exchanger can outperform the finned heat exchanger if the frontal area is changed. Optimization is required to select the best foam parameters, material and dimensions. This clearly shows the potential of open-cell metal foam for high performance heat exchanger designs.

On heat transfer in tubes

Heat transfer coefficients for thermal design of heat exchangers are taken from equations in laminar or turbulent flow. The equations used to calculate the Nusselt numbers in tubes do not agree in the transition region between laminar and turbulent flow. There is a gap at Re=2300.A linear interpolation between the Nusselt numbers at Re=2300 and Re=4000, each resulting from well-known equations is presented. The linear interpolation is based on the results of a paper published recently.New experimental findings about the Nusselt numbers in tubes at turbulent flow again confirm the respective equation.

A technique for thermal design of a heat exchanger with porous inserts

A technique of designing a heat exchanger with porous inserts that is the development of the classical method for thermal design of recuperative finned heat exchangers is presented. A criterion equation was suggested to calculate the effective length of a rib, which is equivalent to a porous insert; the given equation takes into account the influence of the heat carriers flow regime, their thermo-physical properties, geometrical and thermo-physical parameters of porous inserts. Using a hot water calorifer as an example, we compared the thermal design techniques as well as the mass-dimensional indicators and heat and power effectiveness of the heat exchanger with porous inserts with similar characteristics of a standard plate-type one.

Unity Mach number axial dispersion model for heat exchanger design

Recently a new axial dispersion model for the thermal design of heat exchangers with deviations from plug flow has been developed by considering the limiting case of unity dispersive Mach number of the hyperbolic dispersion model. The main advantage of the new dispersion model is that known and proved design charts and formulae for plug flow can further be applied. Only the numbers of transfer units have to be corrected. The corrections are simple functions of the dispersive Peclet numbers of the hot and the cold flow stream. In this paper a method for the determination of the dispersive Peclet numbers by transient tracer experiments is presented. The experimental inlet signals and outlet responses are evaluated in the frequency domain using Laplace transforms. Together with the analytical solution of the model equations the dispersive Peclet numbers are obtained. For comparison the evaluation procedure in the frequency domain is also applied to the parabolic dispersion model and the model of stirred tanks in series.

Determining parameters of heat exchangers for heat recovery in a Cu–Cl thermochemical hydrogen production cycle

A heat exchanger is a device built for efficient heat transfer from one medium to another. Shell and tube heat exchangers are separated wall heat exchangers and are commonly used in the nuclear and process industry. The CuCl cycle is used to thermally crack water in to H2 and O2. The present study presents the heat exchanger thermal design using analysis of variance for heat recovery from oxygen at 500 °C, coming from the molten salt reactor. Polynomial regressions in terms of the amount of chlorine in the oxygen, the mass flow rate on the tube side, and the shell's outlet temperature are estimated for various exchanger parameters and the results are compared with the bell Delaware method. Based on energy and exergy analysis, this study also discusses the best possible path for the recovered heat from oxygen. Optimal heat exchanger parameters are estimated by Design-Expert® Stat-Ease for most effective heat recovery.

Thermal modeling of a shell and tube type evaporator with R404A

In this study, the two-phase heat-transfer coefficient of R404A inside horizontal tubes is analyzed through the evaporator's overall heat-transfer coefficient, obtained using the effectiveness—Number of Transfer Units thermal design approach. This method constitutes an approximation that can be used in the evaporator's thermal design with an attempt to break some of the initial assumptions established in the heat exchanger thermal design method development. For the analysis, an experimental refrigeration system that is commercially available is built up with a shell and tube evaporator. All the experiments are performed at different evaporator pressures (270, 570 kPa), evaporator temperatures (−20, 0°C) and cooling water temperatures (20, 40°C). For these parameters, overall heat-transfer coefficient of the heat exchanger is found in the range of 0.05–0.35 kW °C−1. Copyright © 2010 John Wiley & Sons, Ltd.

Multi-Objective Optimization of Heat Exchanger Design by Entropy Generation Minimization

In the present work, a multi-objective optimization of heat exchanger thermal design in the framework of the entropy generation minimization is presented. The objectives are to minimize the dimensionless entropy generation rates related to the heat conduction under finite temperature difference and fluid friction under finite pressure drop. Constraints are specified by the admissible pressure drop and design standards. The genetic algorithm is employed to search the Pareto optimal set of the multi-objective optimization problem. It is found that the solutions in the Pareto optimal set are trade-off between the pumping power and heat exchanger effectiveness. In some sense, the optimal solution in the Pareto optimal set achieves the largest exchanger effectiveness by consuming the least pumping power under the design requirements and standards. In comparison with the single-objective optimization design, the multi-objective optimization design leads to the significant decrease in the pumping power for achieving the same heat exchanger effectiveness and presents more flexibility in the design process.

A generalised mean temperature difference method for thermal design of heat exchangers

A Generalised Mean Temperature Difference (GMTD) method instead of the Logarithmic Mean Temperature Difference (LMTD) method for heat exchangers is proposed. Unlike the LMTD method, the GMTD method allows the performance analysis of heat exchangers with distributed physical properties. GMTD is calculated by a new method to take fluid temperature profiles as a function of heat load. Mathematical proof is made that the formula of the LMTD can be derived from that of the GMTD, in the case of constant physical property. The GMTD method is applied to experiments of a hot water supplier with supercritical carbon dioxide as a heating media that works through its pseudo-critical point where specific heat behaves anomalously. The empirical correlations of the local Nusselt number and pressure loss coefficient based on the GMTD gives an accurate prediction of the overall heat transfer coefficient, with a 5% error rating, whilst an error two times larger appears in the case of the LMTD.

Linear Matrix Operator Formalism for Basic Heat Exchanger Thermal Design

The matrix formalism used for the thermal description of heat exchangers is extended to include streams with variable temperature distributions. In this approach, a heat exchanger is described by a temperature-independent matrix operator, which, acting on the inlet temperature distributions, generates the outlet ones. This formalism is particularly useful for the evaluation of the thermal effectiveness of complex heat exchanger configurations that can be broken into simple constitutive parts, linked to each other by unmixed streams. Applications to crossflow configurations of practical interest are shown.

Flow reversal symmetry in a convective heat exchange model

Under some simplifying assumptions often used in the thermal design of heat exchangers, a system of two coupled linear homogeneous first-order partial differential equations with variable coefficients is used to describe a steady-state convective heat exchange process. Using an integral representation for the outlet temperatures as functions of the inlet ones, a symmetry property is proved for the transformation that inverts the velocity fields of both fluids. In particular, the average thermal effectiveness is shown to coincide for the direct and reversed processes.

Thermal design of a heat exchanger for heating or cooling blood

Experimental data, and their correlation with predictions from theory, are presented for the thermal design of a countercurrent heat exchanger for heating or cooling blood. The thermal design considers the influence on the Nusselt number of blood and the heat exchanger effectiveness of variables such as the blood flow rate, tube diameter and length, and the thermal properties of blood. The data presented are compared with data from the literature and with predictions from theory. Insofar as the design of a blood heat exchanger is concerned, flowing blood can be considered a single-phase fluid. Some applications of the thermal design analysis, the production and control of blood hyperthermia or hypothermia are discussed.

Generalization of test data pertaining to the mean heat transfer coefficient for tube bundles in a turbulent longitudinal stream of air and superheated steam

A method has been developed for the generalization of test data on heat transfer which takes into account the effects of the temperature factor and of the bundle geometry. From a compilation and an analysis of the test data have come out new and reliable recommendations for the thermal design of heat exchangers.

Thermal Design of Heat Exchangers

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThermal Design of Heat ExchangersDonald MortonCite this: Ind. Eng. Chem. 1960, 52, 6, 474–478Publication Date (Print):June 1, 1960Publication History Published online1 May 2002Published inissue 1 June 1960https://doi.org/10.1021/ie50606a018RIGHTS & PERMISSIONSArticle Views442Altmetric-Citations4LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (585 KB) Get e-Alerts