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A new simplified method for the cost assessment analysis of shell-and-tube heat exchangers (STHE) is presented in this paper. A comparison was carried out between the values obtained by the proposed method with the FOB average real cost for a total of 410 heat exchangers, with heat transfer surfaces ranging between 5 to 1150 m2. It was found that the proposed method correlates well with an average error of 10.1% , for 84.15% of the available data. The method presents a lower adjustment in the range , with an average error of 12.9%, for 82.97 % of the available data. The best adjustments are located in the range, with an average error of only 8.0%, for 80.95 % of the available data. In all cases, the agreement of the proposed method is good enough to be considered satisfactory for practical design.

Dimensional analysis was utilized on this research to establish a shortcut model for predicting hydrogen sulphide gas discharge temperature in jacketed shell and tube heat exchangers. Since the equipment belongs to an online industrial facility, the passive experimental method was applied. Selection of the heat transfer process parameters was followed by application of the Buckingham Pi-theorem and the repeating-variables technique. After formulation of the dimensionless groups, approximation of the explicit model equation was carried out through a least-squares multivariate linear regression. The model predictive ability performance was appraised by comparing predictions versus measured discharge temperatures, hence attaining a Pearson correlation of 97.5 %, a mean absolute error of 2.1 K, and 1.7 % maximum deviations. The explicit equation that was obtained is pertinent to studied heat exchangers, when 0.55 ≤ ṁ1 ≤ 0.60, 1.06 ≤ ṁ2 ≤ 1.09, and 0.22 ≤ ṁ3 ≤ 0.24 (fluids flowrate, kg/s). It can be used as an alternative calculation method for quick anticipation of the equipment performance, which overcomes computation of the overall heat transfer coefficients., En esta investigación se utilizó el análisis dimensional para establecer un modelo abreviado de predicción de la temperatura de descarga de sulfuro de hidrógeno en intercambiadores de calor de tubos y coraza enchaquetados. Teniendo en cuenta que los equipos pertenecen a una instalación industrial en operaciones, se aplicó el método de experimentación pasiva. Después de seleccionar los parámetros del proceso de transferencia de calor, se procedió con la aplicación del teorema Pi-Buckingham y la técnica de repetición de variables. La aproximación de la ecuación explícita del modelo se llevó a cabo posterior a la formulación de los grupos adimensionales, mediante una regresión lineal múltiple basada en el método de mínimos cuadrados. La capacidad predictiva del modelo se evaluó comparando las predicciones con los valores medidos para la temperatura de descarga, obteniéndose una correlación de Pearson del 97.5 %, un error absoluto medio de 2.1 K, y desviaciones máximas de 1.7 %. La ecuación explícita obtenida es válida para los intercambiadores de calor estudiados, en los rangos 0.55 ≤ ṁ1 ≤ 0.60, 1.06 ≤ ṁ2 ≤ 1.09, y 0.22 ≤ ṁ3 ≤ 0.24 (flujo de los fluidos, kg/s). Puede utilizarse como método de cálculo alternativo para predecir con rapidez el rendimiento de los equipos, eludiendo la determinación de los coeficientes globales de transferencia de calor.

This paper presents the main results of the research developed by the author in his postdoctoral investigations on heat transfer calculations during film condensation inside tubes. The elements studied are combined in an analysis expression that provides a reasonable fit with the available experimental data, which includes a total of 22 fluids, including water, refrigerants and a wide range of organic substances, which condense inside horizontal, inclined and vertical tubes. These experimental data were obtained from the reports of 33 sources. Available data covers tube diameters from 2 to 50 mm, mass flow rates from 3 to 850 kg/(m2s), reduced pressures ranging from 0.0008 to 0.91, values for single-phase from 1 to , Reynolds number for two-phase from 900 to 594390, Reynolds number for single-phase from 65 to 84950 and vapor quality from 0.01 to 0.99. The mean deviation found for the analyzed data for horizontal tubes was 13.4%, while for the inclined and vertical tubes data the mean deviation was 14.9%. In all cases, the agreement of the proposed model is good enough to be considered satisfactory for practical design.

In the present times, the use of air cooled condenser (ACC) has become generalized where the installation of power plants is required and access to condensation water is difficult. At present it is known that performing the thermal evaluation of an ACC is a complex task, since the existing methods do not consider all the elements that directly influence the performance of the ACC. A very widespread method is that attributed to Kröger, however its use does not provide adequate results for high values of environmental temperature, which is a limitation to be applied in tropical countries like Cuba. This document provides an analysis method that includes the effect of environmental variables and that allows reasonable results to be obtained for high values of ambient temperature. The new proposal follows the logical sequence of the Kröger method, but considering a new procedure for the determination of the mean heat transfer coefficients and pressure drops, required for the thermal evaluation of ACC.

Introducción: El proyecto actual de centrales eléctricas (CE) de biomasa en la industria azucarera de Cuba, tiene como limitante el acceso al agua requerida por las instalaciones de condensación. En la actualidad, el uso de condensadores secos es la solución más difundida a nivel mundial reducir los altos índices de consumo de agua en los sistemas de condensación y flexibilizar la ubicación de la CE, siendo más difundidos los aerocondensadores (ACC). Objetivo: Realizar un estudio simplificado que demuestre la efectividad de la implementación de la condensación seca en el proyecto de CE de Biomasa en la industria azucarera cubana. Materiales y Métodos: Se muestra el estado actual del uso de la condensación seca a nivel mundial en las industrias de generación eléctrica y azucarera, posteriormente se detalla los elementos vinculados al proyecto de CE de biomasa, requeridos para el análisis. Resultados y Discusión: Se realiza un análisis sobre el consumo, generación de potencia y área de transferencia de calor requerida por cada variante, además se efectúa un estudio de caso aplicando criterios de selección, VAN, TIR, período de recuperación de la inversión y costo nivelado de la energía, a partir del uso de los métodos de Conradie y col. y CamarazaMedina y col. Conclusiones: El estudio realizado muestra que el uso del ACC en Cuba es una alternativa ventajosa para los proyectos previstos de CE, al cumplir con los requerimientos de la ley 124/2017 y mostrar indicadores técnico-económicos de operación que resultan adecuados.

Introduction: The current biomass power plant (CE) project in Cuban sugar industry is limited by water access required by condensation facilities. At present, the use of dry condensers is the most widespread solution worldwide to reduce high rates of water consumption in condensing systems and to make the location of the CE more flexible, with aero condensers (ACC) being more widespread. Objective: To carry out a simplified study that demonstrates the implementation of dry condensation in EC Biomass project in Cuban sugar industry effectiveness. Materials and methods: Dry condensation worldwide use in electricity and sugar generation industries current state is shown, subsequently the elements related to biomass CE project, required for the analysis, are detailed. Results and Discussion: An analysis is carried out on the consumption, power generation and heat transfer area required by each variant. In addition a case study is carried out applying selection criteria, NPV, IRR, investment recovery period and leveled energy cost using Conradie, et al and Camaraza-Medina, et al methods. Conclusions: The study carried out shows that ACC use in Cuba is an advantageous alternative for planned CE projects, as it complies with Law 124/2017 requirements. It and demonstrates adequate technical-economic operation indicators.

Efficient utilities usage and enhanced heat transfer are imperative in todays’ industrial and technological processes. However, there are several facilities in the nickel industry not upgraded yet. This research studied a hydrogen sulphide production plant with limited heat exchange capacity. Within this context, a neuro-genetic procedure was proposed for optimization of the water flowrates distribution on a hydrogen sulphide gas coolers system. It relied on Genetic Algorithms, combined with an improved ɛ-NTU model for simulation of jacketed shell-and-tube heat exchangers. Artificial Neural Networks were furtherly applied to correlate the optimum water flowrates to predictive variables. The heat transfer incremental was estimated from 3695 to 10514 W, while reduction of the gas exit temperature was projected between 2.9 and 9.8 K. Calculated heat recovery averaged 12.44 %. The optimized water distribution scheme have improved the system energy performance. Applied concept of fixed network and unvaried overall feed water flowrate avoided the additional costs related to topology modifications. A technological solution was provided, consisting on installation of automatic valves and programmable flow control-loops linked to a PLC.

This paper presents a mathematical deduction of a new improved model for heat transfer during condensation inside tubes. This new model has been developed with the aid of the Gaussian Equation for an infinite straight line, considering this relation with the differential equations that govern the heat transfer process. The proposed model was verified by comparison with available experimental data of 22 different fluids, including various refrigerants, water, and organic substances, which condense inside vertical, inclined and horizontal tubes. The proposed model is valid for an reduced pressure values ranging from 0.0008 to 0.91, values of Reynolds number for single-phase between 68 and 84,827 and for Reynolds number for two-phase between 900 and 59,4373, a range of internal diameters ranging from 2 to 50 mm, vapor quality from 0.01 to 0.99, P r values for single-phase from 1 to 18 and mass flux rates in the ranges of 3 to 850 kg/(m 2 s). The mean deviation found for the analyzed data for horizontal tubes was 11.8%, while for the vertical and inclined tubes data the mean deviation was 13.0%. In all cases, the agreement of the proposed model is good enough to be considered satisfactory for practical design.

In this short technical note is presented a new improved model for heat transfer calculations during fluid flow in single-phase inside tubes. The proposal model was verified by comparison with available experimental data of 35 different fluids, including water, air, gases and organic substances. The proposal model is valid for a range of Reynolds number for single-phase from 2.4 · 10 3 to 8.2 · 10 6 , Prandtl number for single-phase from 0.65 to 4.71 · 10 4 , dimensionless length in the interval 2 ⩽ l / d ⩽ 450 and values of Petukhov’s correction in the interval 0.006 ⩽ μ F / μ P ⩽ 177 . In 3096 data analyzed, for Re 1 · 10 4 , the mean deviation found was 13.91% in the 80.32% of the experimental data, while for 1 · 10 4 ⩽ R e , the mean deviation found was 13.96% in 80.94% of experimental data.

The investment project of 25 thermoelectric plants (CTE) of biomass in Cuba with powers of 20 and 50 MW, as well as the proven lack of water for their cooling systems, point to the possible use of dry capacitor systems (ACC) in these plants. However, the increase in the initial project cost and the reduction in useful power associated with its use is a limitation to consider. To define the feasibility of ACC use in these projects, a case study is carried out in which several selection criteria for investment alternatives are considered. Also three other types of condensation technologies are evaluated in order to establish the investment and operation cost comparison, as well as the profits generated. In all cases, these analyzes were carried out for a 20-year horizon. The results obtained confirm the feasibility of using ACC systems, with a composed investment recovery period from 7.6 to 8.4 years, the IRR computes values between 18.2 to 23.8 percent. The NPV with an update rate of 15% reaches values between 10682.4 and 3 024 MUSD, Life cycle cost is between 10 682.4 and 24 406.1 MUSD. Level cost of energy fluctuates between 0.062 to 0.071 USD / kWh, with a cost-benefit ratio between 0.1 to 0.13.

An improved method for heat transfer calculations inside rough tubes is provided. The model has been obtained from a second assessment developed early by the authors on fluid flow in single-phase inside rough tubes. The proposed correlation has been verified by comparison with a total of 1666 experimental available data of 34 different Newtonian fluids, including air, gases, water and organic liquids. The proposed model covers a validity range for Prandtl number ranging from 0.65 to 4.52×104, values of Reynolds number from 2.4×103 to 8.32×106, a range of relative roughness ranging from 5×10−2 to 2×10−6 , and viscosity ratio from 0.0048 to 181.5. The proposed model provides a good correlation for 2.4×103≤Re

This research proposed an optimized water distribution scheme in order to increase the heat transfer on a hydrogen sulphide gas coolers system. The system is comprised by two jacketed shell and tube heat exchangers, installed in a series-parallel arrangement. Each equipment operates with three streams, hence two major thermal communications are present. The water flowrates optimization was performed through genetic algorithms, using a model based on the ɛ-NTU method for simulation of the heat exchangers. The heat transfer incremental was estimated within the range 3695 to 10514 W, while the gas temperature reduction at the system outlet was projected between 2,9 and 9,8 K. Calculated heat recovery varied from 3,90 to 22,16%, averaging 12,44%. Multivariate linear regression was implemented for determination of the functions that solves the studied problem from a technological point of view., En esta investigación se propuso un esquema optimizado de distribución de agua para incrementar la termotransferencia, en un sistema de enfriadores de sulfuro de hidrógeno. La instalación está compuesta por dos intercambiadores de calor de tubos y coraza enchaquetados, instalados en un arreglo serie-paralelo. Cada equipo opera con tres fluidos y posee dos vías principales de intercambio térmico. La optimización de los flujos de agua se realizó mediante algoritmos genéticos, utilizando un modelo con base en el método ɛ-NUT para la simulación de los intercambiadores de calor. Se estimó un incremento del calor transferido entre 3695 y 10514 W, así como una disminución de la temperatura del gas a la salida del sistema entre 2.9 y 9.8 K. La recuperación termoenergética calculada osciló entre 3.90 y 22.16 %, con 12.44 % como promedio. Mediante regresión lineal múltiple se determinaron las funciones para solución tecnológica del problema investigado.

In the work carries out a comprehensive thermo-energetic analysis of the steam generation system of a 49 MW thermal power plant, which has not been rigorously studied from an energy point of view. In a algorithm synthesizes the methodology for calculating the gross thermal and exergetic performances of the boilers that comprise it, aspects that have not been interrelated in previous studies. The results show a high degree the harnessing of thermal energy and a low capacity for using the exergy available in the facilities, caused by the deterioration of some of its operationals parameters and by irreversibilities inherent in the process of transforming water into steam. The thermal and exergetic yields of the system amounted to 90.106 and 45.491%, respectively. The proposed algorithm foresees the calculation and the comparison of the real thermo-energetic parameters of the boilers with the nominal ones and the scientific and technical-organizational actions to develop out to achieve superior thermo-exergetic performances. Its future implementation will take into account the analysis of the net thermal yields, the economic-environmental indicators and the energy-operational optimization of the boilers., En el trabajo se realiza un análisis termoenergético integral del sistema de generación de vapor de una termoeléctrica de 49 MW, lo cual no ha sido estudiado con rigor desde el punto de vista energético. En un algoritmo se sintetiza la metodología para el cálculo de los rendimientos térmicos brutos y exergéticos de las calderas que lo integran, aspectos que no se han interrelacionado en estudios precedentes. Los resultados evidencian un elevado grado de aprovechamiento de la energía térmica y una baja capacidad de utilización de la exergía disponible en las instalaciones, provocados por el deterioro de algunos de sus parámetros de operación y por irreversibilidades inherentes al proceso de transformación del agua en vapor. Los rendimientos, térmico y exergético del sistema, ascendieron a 90.106 y 45.491 %, respectivamente. El algoritmo propuesto prevé el cálculo y la comparación de los parámetros termoenergéticos reales de las calderas con los nominales y las acciones científicas, y técnico-organizativas, a desarrollar para lograr rendimientos termoexergéticos superiores. Su implementación futura tendrá en cuenta el análisis de los rendimientos térmicos netos, los indicadores económico-ambientales y la optimización energético-operacional de las calderas.

In this paper a new model is presented for heat transfer calculation during film condensation inside pipes. This new model has been verified by comparison with available experimental data of a total of 22 different fluids, including water, various refrigerants and organic substances, which condense inside horizontal, vertical and inclined tubes. The model is valid for a range of internal diameters ranging from 2 mm to 50 mm, reduced pressure values ranging from 0.0008 to 0.91, Pr values for the liquid portion of the condensate from 1 to 18, values of Reynolds number for the liquid portion between 68 and 84827, and for the portion of the steam between 900 and 594373, steam quality from 0.01 to 0.99 and mass flux rates in the ranges of 3–850 kg/(m2 s). The mean deviation found for the data analyzed for vertical and inclined tubes was 13.0%, while for the horizontal tube data the mean deviation was 11.8%. In all cases, the agreement of the proposed model for horizontal, vertical and inclined tubes is good enough to be considered satisfactory for practical design.

A current trend for electrical power generation in areas with water difficult access is the use of air-cooled steam condensers (ACC). Currently in the literature available there is no single method that brings together all factors that are considered in the evaluation of a power plant operating with dry condensation system. In present work a unique method of analysis is developed that considers the action of the environmental variables that act on the ACC installation, allowing therefore to determine its final effect on the power installation. The new proposal follows the logical order of the Kröger method because this is the most widely accepted and disseminated among researchers and specialists working in this field. In a total of 127 tests carried out, there is an average uncertainty in the results obtained with this method of 8.2%, which they are considered sufficiently precise for their use in thermal engineering.

For an air-cooled vapor condenser (ACC), environmental wind can cause a large reduction of the flow in the axial fans mainly near the windward side of the air-cooled platform due to cross-flow effects, resulting in a reduction of heat transfer. This leads to an increase in the turbine’s counter-pressure. This paper proposes a new method to evaluate the effect of wind on the output pressure of the turbine, as well as the effect of the combination of ambient temperature with the direct action of the wind. Finally, the results obtained are given in graph forms and a group of equations are proposed that allow attaining the output pressure of the turbine once ambient temperatures and wind speed are known. These expressions correlate in all cases with a mean error of 11.27% in 89.12% of the experimental data available, and they are considered, therefore, sufficiently precise for their use in thermal engineering.

This paper provides a second evaluation, with the intention of formulating an improved model that is capable of predicting the mean coefficients of heat transfer during condensation inside tubes with any orientation. This model has been developed through the application of transportable borders for the propagation of heat inside an elementary volume, up to the macro system considered. The theoretical model obtained leads to two basic dimensionless groups, which establish the study intervals that should be considered in the correlation of experimental quantities available, for the development of future experimental models.

In this paper new improved models for heat transfer calculation in inclined and vertical tubes with viscous-gravitational effects are presented. Three models, two for vertical tubes with upward and downward flow and one for inclined tubes were developed. For the validation of the models, available data of 14 different fluids, including water and organic liquids were used. The first model is valid when forced and natural convection have the same direction, obtaining a correlation adjustment with an average error of 11.6% for 77.8% of the data. The second model is valid when forced and natural convection are in opposite directions and provides a good correlation with an average error of 12.8% for 74.4% of the available experimental data. The third model is valid for inclined tubes with an angle of inclination with respect to the horizontal line between 1∘ ≤ θ ≤ 88∘, and provides a good correlation adjustment with an average error of 15.9% for 75.0% of the available experimental data. A new procedure of analysis to consider the influence of the viscous-gravitational effect on the non-isothermal laminar flow was developed, with the purpose of obtaining a better adjustment index from the experimental available data and to increase the validity range.

This work presents the results of the continuity of the research process carried out in the Energy Studies Center belonging to the Faculty of Technical Sciences of the University of Matanzas, which involves the establishment of a dimensionless model to determine the average condensation heat transfer coefficient of Air Coleed Condenser (ACC) systems in straight and inclined tubes. The research consists in obtaining in an analytical way the solution of the differential equation of the velocity profile, considering that condensation is of pellicular type, finally the empirical condition of Roshenow is combined with the theoretical solution to generate a numerical expression that allows obtaining with a 15.2% of deviation in 2,192 tests, a value of the average coefficient of heat transfer by condensation very similar to the one obtained with the use of the most referenced model in the consulted literature, the empirical model of Chato.

El proyecto inversionista de 25 centrales termoeléctricas (CTE) de biomasa en Cuba con potencias de 20 y 50 MW, así como la carencia probada de agua para sus sistemas de enfriamiento, apuntan al posible empleo de sistemas de condensadores secos (ACC) en dichas plantas, sin embargo el encarecimiento del proyecto inicial y la reducción de potencia útil asociada su empleo es una limitante a considerar. Para definir la factibilidad del empleo de ACC en estos proyectos se realiza un estudio de caso en el cual son considerados varios criterios de selección para alternativas de inversión, siendo evaluados adicionalmente otros tres tipos de tecnologías de condensación con el objetivo de establecer comparación de costos de inversión y operación, así como de las utilidades generadas. En todos los casos los análisis fueron efectuados para un horizonte de 20 años. Los resultados obtenidos confirman la factibilidad del empleo de sistemas ACC, con un período de recuperación compuesto de la inversión de 7,6 a los 8,4 años, la Tasa de Interés de Retorno (TIR) computa valores entre el 18,2 a 23,8 por ciento, el Valor Actual Neto (VAN) con una tasa de actualización del 15% alcanza valores entre los 1 126,9 a 3 024,0 MUSD, el costo del ciclo de vida se ubica entre los 10 682,4 a 24 406,1 MUSD, mientras que el costo nivelado de la energía fluctúa entre los 0,062 a 0,071 USD/kWh, con una relación costo beneficio entre 0,1 a 0,13.

In the present technical note a new method is provided for determining the heat transfer in the fluid flow in single-phase inside rough pipes. The model was tested by adjusting it with existing experimental quantities of a total of 33 different fluids, including gases, organic substances, water and air. The method presented is valid for a range of Prandtl number for single-phase from 0.65 to 4.5 × 10 4 , Reynolds number for single-phase from 2.4 × 10 3 to 8.2 × 10 6 , relative roughness in the interval 0.05 ≤ e / d ≤ 0.00005 and correction values of the viscosity factor between 0.006 ≤ μ F / μ P ≤ 177 . In 868 data analyzed, for Re 1 × 10 4 , the average error found was 18.51% in the 81.06% of the disposable experimental samples, while for 1 × 10 4 ≤ R e , the average error found was 19.06% in 80.54% of the disposable samples.

Una tendencia en la actualidad para la generación de potencia eléctrica en las zonas con difícil acceso al agua es el empleo de condensadores de vapor refrigerado por aire (ACC). Actualmente en la literatura disponible y conocida no existe un método único que aglutine la totalidad de factores que son considerados en la evaluación de una planta de potencia que opere con sistema de condensación secos. En el presente trabajo se desarrolla un método único de análisis que considera la acción de las variables ambientales que actúan sobre la instalación ACC, permitiendo por lo tanto determinar su efecto final sobre la instalación de potencia. La nueva propuesta sigue el orden lógico del método de Kröger, por ser este el de mayor aceptación y difusión entre los investigadores y especialistas que se desenvuelven en esta esfera. En un total de 127 pruebas efectuadas se encuentra una incertidumbre media en los resultados obtenidos con el método del orden del 8,2%, por lo que se consideran suficientemente precisas para su empleo en la ingeniería térmica.

Para un condensador de vapor refrigerado por aire (ACC), el viento ambiental puede causar una gran reducción del caudal en los ventiladores axiales principalmente cerca del lado de barlovento de la plataforma enfriada por aire debido a los efectos de flujo cruzado, lo que resulta en una reducción de transferencia de calor. Esto conduce a un aumento de la contrapresión de la turbina. En este documento se propone un nuevo método para evaluar el efecto del viento en la presión de salida de la turbina, así como el efecto de la combinación de la temperatura ambiental con la acción directa del viento. Finalmente los resultados obtenidos son dados en formas de gráficas y son propuestas un grupo de ecuaciones que permiten obtener la presión de salida de turbina, siendo conocidas las temperaturas ambientales y la velocidad del viento. Estas expresiones correlacionan en todos los casos con un error medio igual al 11,27 % en el 89,12 % de los datos experimentales disponibles, por lo que se consideran suficientemente precisas para su empleo en la ingeniería térmica.

En el trabajo se realiza un análisis termoenergético integral del sistema de generación de vapor de una termoeléctrica de 49 MW, lo cual no ha sido estudiado con rigor desde el punto de vista energético. En un algoritmo se sintetiza la metodología para el cálculo de los rendimientos térmicos brutos y exergéticos de las calderas que lo integran, aspectos que no se han interrelacionado en estudios precedentes. Los resultados evidencian un elevado grado de aprovechamiento de la energía térmica y una baja capacidad de utilización de la exergía disponible en las instalaciones, provocados por el deterioro de algunos de sus parámetros de operación y por irreversibilidades inherentes al proceso de transformación del agua en vapor. Los rendimientos, térmico y exergético del sistema, ascendieron a 90.106 y 45.491 %, respectivamente. El algoritmo propuesto prevé el cálculo y la comparación de los parámetros termoenergéticos reales de las calderas con los nominales y las acciones científicas, y técnico-organizativas, a desarrollar para lograr rendimientos termoexergéticos superiores. Su implementación futura tendrá en cuenta el análisis de los rendimientos térmicos netos, los indicadores económico-ambientales y la optimización energético-operacional de las calderas.

In this paper is compared a proposal model for heat transfer calculations during fluid flow in single-phase inside tubes with others existing in the literature. This comparison used 3096 available experimental data of 36 different fluids. The proposal model is valid for a range from to and 0.65 to for Reynolds and Prandtl number respectively, dimensionless length values and viscosity correction in the interval . The comparison proves that the suggested model presents the better index of correlation, being found an average error of 13.8% in the 80.6% of the experimental data and a maximum error of 24.6%.