Cross-flow Heat Exchanger Research Articles

New analytical-numerical method for modelling of tube cross-flow heat exchangers with complex flow systems

A new method for thermal calculations of cross-flow tube heat exchangers was proposed. The heat exchanger is divided into finite volumes, inside which the fluid temperatures are given by analytical formulas. The advantage of the semi-analytical method developed is that the temperature inside the finite volume can be determined at any point, unlike the finite difference method widely used in exchanger heat modelling. Even when dividing the entire tube in one heat exchanger pass into a few finite volumes, e.g. into three segments, satisfactory results are obtained. By dividing the whole heat exchanger into a small number of finite volumes, the computer calculation time of heat exchangers with complicated tube arrangement is very short. The proposed method can be used to calculate heat exchangers with a complicated flow system in which the physical properties of fluids depend on temperature. Analytical and numerical models were developed for one and two pass finned tube heat exchangers to assess the accuracy of the proposed method. A two-pass car radiator mathematical model with two rows of tubes using the proposed method was developed. The results of the car radiator and steam reheater calculations are in good agreement with the analytical or experimental results.

On-site experimental study on fouling and heat transfer characteristics of flue gas heat exchanger for waste heat recovery

A large number of fly ash particles in flue gas easily cause the fouling problem of heat exchangers, which seriously affects the efficient utilization of flue gas waste heat. In this study, experimental and numerical investigations on fouling and heat transfer characteristics in cross flow heat exchangers were carried out. The on-site experimental system was established, and the heat transfer coefficients for different heat-transfer surfaces at the fouling state were monitored in real time. The weakened degree of heat transfer coefficient and fouling thermal resistance are adopted to assess the effect of fouling on the heat transfer performance and compare the practicality of four different heat-transfer surfaces under dusty conditions. Numerical investigation was performed with the fouling model established in previous work to model the thermal-hydraulic and fouling processes. Numerical results are compared with experimental measurements and a good agreement is achieved. Results showed that compared with the aligned circular tube bundle, using H-type fins or honeycomb tube bundle both improve the anti-fouling performance, especially for the honeycomb H-type finned tube bundle, which has the lowest fouling thermal resistance. Therefore, due to the characteristics of easily soot-blowing and lower fouling thermal resistance, honeycomb heat exchangers are suitable for waste heat utilization of dusty flue gas.

Energy, exergy and economic (3E) evaluation of the photovoltaic/thermal collector-assisted heat pump domestic water heating system for different climatic regions in Turkey

In this study, the energy, exergy and economic (3E) analyses were performed for the photovoltaic/thermal collector-assisted heat pump domestic water heating system under two different climatic regions (Hakkari and Trabzon) in Turkey. Designed photovoltaic/thermal collector-assisted heat pump domestic water heating system with a storage tank having larger volume and cross-flow heat exchanger in Turkey can be considered as novelty of this study. The system modelled with the help of TRNSYS simulation code by using real weather data and energy analysis was performed based on year-round simulation results. And then, exergy and economic analyses were obtained based on monthly average temperatures. The system considered in this study was also compared economically with conventional natural gas and electricity water heating systems. According to the results, the maximum energy and annual average exergy efficiencies of the considered system were 68% and 22.3%, respectively, for Hakkari, and 67% and 21.4%, respectively, for Trabzon. Although Hakkari has cold climate conditions, the investigated system had lower energy consumption costs than conventional systems. The annual energy consumption costs of the system for Hakkari and Trabzon were calculated as 67.14$ and 135.75$, respectively. The results bring out that although the investment of the system is feasible for Hakkari, it is not feasible for Trabzon.

Annual Energy Performance of an Air Handling Unit with a Cross-Flow Heat Exchanger

Heat recovery from ventilation air is proven technology resulting in significant energy savings in modern buildings. The article presents an energy analysis of an air handling unit with a cross-flow heat exchanger in an office building in Poland. Measurements were taken during one year of operation, from 1 August 15 to 31 July 16, covering both heating and cooling periods. Calculated annual temperature efficiency of heat and cold recovery amounted to 65.2% and 64.6%, respectively, compared to the value of 59.5% quoted by the manufacturer. Monthly efficiency of heat recovery was from 37.6% in August to 68.7% in November, with 63.9% on average compared to 59.5% declared by the manufacturer. Cold recovery was from 63.3% in April to 72.8% in September, with 68.1% annually. Calculated recovered heat and cold amounted 25.6 MWh and 0.26 MWh, respectively. Net energy savings varied from −0.46 kWh/m2 in August, when consumption by fans exceeded savings, to 5.60 kWh/m2 in January.

Experimental investigation and ANN modelling on thermo-hydraulic efficacy of cross-flow three-fluid plate-fin heat exchanger

Compact cross-flow three-fluid heat exchanger with plain rectangular fins is experimentally investigated for both thermal and hydraulic efficacy under steady-state condition. The elaborative investigation is conducted for all the four viable flow arrangements of cross-flow configuration which comprises the effect of Colburn factor and effectiveness ratio of central and adjacent fluids, and friction factor with Reynolds number. It is learnt that thermal efficacy is sentient to the operating conditions, type of flow arrangement and variation in flow rate. The comparison of the efficacy between the plain duct (without fin core) and with fin heat exchanger core is presented to analyse the impact of fins in enthalpy exchange. The regression correlation is developed to estimate the thermal and hydraulic performance which are accurate within ±16% and ±5.8% respectively. The investigation is further assisted with the ANN modelling for the prediction of the thermo-hydraulic efficacy with two input (Reynolds number and flow arrangement type) and four output performance parameters (Colburn factor, friction factor and effectiveness ratios). The fraction of 77% and 23% of data is considered for training and testing the neural network respectively. It is learnt that ANN predictions are more promising and accurate than regression predictions and the magnitude of the value of an absolute fraction of variance equals unity.

Nano-Fluids as a Coolant for Automotive Engine Radiators: Review Study

Low-efficiency crossflow heat exchangers which are used as radiators in the automotive sector may cause engine damage. Nano-fluids are ideal coolants due to their high heat diffusion coefficient and can be added to almost any process that requires a fast reaction to thermal performance, such as the automobile. The nanofluid's thermal conductivity is greater than that of the base fluid such as water and ethylene glycol and can achieve more than 40% and enhance the heat transfer coefficient by more than 50%. The best results for heat transfer were to use carbon nanoparticles with base fluid. This article reviews previous research investigating the effect of nano-fluid in automotive radiators in which nanoparticles such as Al2O3, CuO, TiO2, and MWCNT are used. The preparation and application of nano-fluid and measurement of thermal properties and the effect of volume fraction on efficiency are discussed. The review also is focused on the numerical and experimental studies of previous work related to nano-fluid performance in automobile radiators

Analysis of Heat Transfer Performance in a Brayton Cycle Recuperator

Thermodynamic cycles are currently the most wanted means of converting nuclear power into available work due to the higher conversion efficiencies provided. Rankine cycles have been greatly applied for terrestrial reactors and nuclear submarines, while a lot of space projects have been using Brayton cycles for power conversion mainly due to mitigation in power-to-radiator area ratio. Regenerative Brayton cycles can present a considerable power conversion efficiency improvement when compared to the regular ones because of a reduction on the power demand from the hot heat exchanger of a cycle to achieve the same net output power. In this work, a cross-flow heat exchanger with He-Xe (40 g/mol) working fluid and Inconel 617 structural material used as the recuperator for the closed Brayton cycle of a nuclear reactor applicable for space systems is assessed in terms of heat transfer performance. The recuperator tubes are arranged in a staggered distribution around the exchanger axis. The matrix of tubes has a fixed count of 4 rows along the exchanger axis, while the number of tubes around the axis is variable, where the samples of 5, 7, 9, 12 and 16 are tested. The characteristic curves of heat transfer rate, effectiveness, convection coefficient and Colburn factor are built for each of the studied geometries in function of the Reynolds number. The obtained values for each of these parameters range between 1892.49 and 8493.21W (heat transfer rate), 0.165 and 0.325 (effectiveness), 60.3822 and 176.9682 W/m2K (cold side convection coefficient), 30.3276 and 104.3263 W/m2K (hot side convection coefficient), 0.0071 and 0.0109 (cold side Colburn factor), 0.0523 and 0.1370 (hot side Colburn factor).

CFD Analysis for Different Types of Fins to Enhancement the Heat Transfer Rate Through A Cross Flow Heat Exchanger

The main target of this study is to find and compare the effect of fins design, surface area and air distribution on the heat transfer of the Cross-flow heat exchanger. This study includes Six different models designed using Solid work 2017 program and numerically analyzed using ANSYS 16.1. All finned tubes share similar dimensions with (24, 19 and 21) mm of outer, inner and root diameters respectively. The study clarified non-linear relationship between the increase in surface area, the rate of the heat transfer, the coefficient of the heat transfer and enhancement ratio, taking into consideration the effect of the external shape of the fin and the method of air distribution on the surface of the tubes. Circular fins with a rectangular section showed the best heat transfer rate among all others models, although the increase in surface area of circular fins was not optimal among the other fins.

Study the flow direction and number of tubes in cross-flow heat exchanger to improve the heat transfer coefficient.

This study deals with the effects the number of tubes and flow direction on the heat transfer coefficient. This investigation complete by study different lengths of smooth copper tubes (50,100, 150, 200 and 250) mm with different passes (2, 4, 6, 8 and 10) for cross flow heat exchanger to attain the best length to heat transfer numerically, by Solid work 2017 and ANSYS 16.1 program. The diameters of outer and inner tubes are (24 and 19 mm), air velocity (3 m/s), volumetric flow rate (5 L/min) and the inlet temperature of cold and hot fluid (25 °C and 80°C) respectively. Also been studying the effect of a smooth and triangle finned tube (4 passes) to enhance the heat transfer. Moreover, studying the effect of up and horizontal direction of the flow on heat transfer, by designing smooth tube 8 passes heat exchanger with the same dimension, air velocity inlet (1 m/s), volumetric flow rate (6 L/min), the temperature of the cold fluid inlet (22 °C) and the temperature of the hot fluid (50 °C). It can be noted that whenever the number of passes of tubes increases, the amount of heat transfer increase at the expense of the increase in pressure drop. The finned tube gives better heat improvement than a smooth tube and the direction of flow does not effect on the heat transfer.

Estudio Numérico Mediante CFD del Proceso de Enfriamiento con Intercambiadores de Calor en Sistemas Computacionales

El presente artículo científico trata el estudio y simulación de un radiador que se basa en un intercambiador de calor tubular de flujo cruzado, el cual tiene un propósito de refrigerar el procesador, tarjeta gráfica de una CPU o diversos hardware en los sistemas de computación. Se realizan diversas simulaciones en el programa ANSYS teniendo varias temperaturas de ingreso que van en rangos desde 75 °C hasta 90 °C y con flujos másicos diferentes. Los resultados muestran que, al aumentar la temperatura de ingreso del fluido a refrigerar, la salida de este fluido tambien aumenta. Sin embargo, cuando se aumenta el flujo másico existe una merma en el rechazo de calor en los dispositivos computacionales.

Experimental Investigation of The Performance of A Cross Flow Heat Exchanger with Bundle of Semi – Circular Tubes.(Dept.M)

Experimental Investigation of The Performance of A Cross Flow Heat Exchanger with Bundle of Semi – Circular Tubes.(Dept.M)

Plate-fin heat exchanger network modeling, design and optimization – a novel and comprehensive algorithm

PurposeThe purpose of this paper is to present a novel and applied method for optimum designing of plate-finned heat exchanger network. Considering the total annual cost as the objective function, a network of plate-finned heat exchanger is designed and optimized.Design/methodology/approachAccurate evaluation of plate-finned heat exchanger networks depends on different fin types with 10 different geometrical parameters of heat exchangers. In this study, fin numbers are considered as the main decision variables and geometrical parameters of fins are considered as the secondary decision variables. The algorithm applies heat transfer and pressure drop coefficients correction method and differential evolution (DE) algorithm to obtain the optimum results. In this paper, optimization and minimization of the total annual cost of heat exchanger network is considered as the objective function.FindingsIn this study, a novel and applied method for optimum designing of plate-finned heat exchanger network is presented. The comprehensive algorithm is applied into a case study and the results are obtained for both counter-flow and cross-flow plate-finned heat exchangers. The total annual cost and total area of the network with counter-flow heat exchangers were 12.5% and 23.27%, respectively, smaller than the corresponding values of the network with cross-flow heat exchanger.Originality/valueIn this paper, a reliable method is used to design, optimize parameters and the economic optimization of heat exchanger network. Taking into account the importance of plate-finned heat exchangers in industrial applications and the complexity in their geometry, the DE methodology is adopted to obtain an optimal geometric configuration. The total annual cost is chosen as the objective function. Applying this technique to a case study illustrates its capability to accurate design plate-finned heat exchangers to improve the objective function of the heat exchanger network from the economic viewpoint with the design of details.

Numerical and experimental analysis of a tube-and-fin cross-flow heat exchanger with a controlled non-uniform inflow of gas

The paper presents results of numerical and experimental analyses of a fin-and-tube air-water heat exchanger. The analysed device is a one-row heat exchanger with finned elliptical tubes. The aim of the analyses is to investigate the impact of a controlled non-uniform inflow of air on the heat exchanger performance. The heat exchanger was modelled numerically using the ANSYS Fluent program. The developed model was applied to simulate the heat exchanger operation in the conditions of the uniform inflow of air. Cases of an uncontrolled non-uniform inflow of gas were investigated experimentally, using a purpose-designed test station. On the experimental test station the effect of a controlled non-uniform air inflow was also achieved by placing appropriately shaped inserts in the air inlet duct, directing the air partially to the region of the water inlet header. By controlling the gas inflow, it was possible to significantly enhance the heat exchanger performance. The results of the multivariate numerical analyses conducted for the adopted parameters of the mediums (air and water volumetric flow rates and water temperature) show that the heat exchanger performance can be improved by up to almost 5% compared to a variant with a natural non-uniform air inflow taking place in the exchanger under consideration.

New calculation method for tube cross-flow heat exchangers

A new method for thermal calculations of the cross-flow tube heat exchangers was proposed. The temperature of both fluids and the wall temperature are determined. The heat exchanger is divided into control volumes, in which outlet fluid temperatures are calculated by closed analytical formulas. Two examples of the application of the method for the calculation of two-pass cross-co-current and cross-countercurrent superheaters were presented. An exact analytical model was also developed for both superheaters to estimate the accuracy of the proposed method. The results of the superheater calculations using the developed method are in good agreement with the results obtained by the exact analytical models. The proposed method can be used to calculate heat exchangers with a complicated flow system in which the physical properties of fluids are temperature-dependent.

Comparison of Fluid Flow and Thermal Characteristics of Sequential and Simultaneous Crossflow Heat Exchangers

Comparison of Fluid Flow and Thermal Characteristics of Sequential and Simultaneous Crossflow Heat Exchangers

Fast and stable approximation of laminar and turbulent flows in channels by Darcy’s Law

In the design of flow geometries consisting of channels such as high-temperature gas heat exchangers, a great number of design parameters can be chosen, why solving the turbulent Reynolds Averaged Navier-Stokes (RANS) equations by CFD coupled with other physics can become computational demanding. Therefore, we here propose a method for a significant reduction of computational resources and consequent high speed. This is done by using the less computational demanding Darcy’s Law (DL) to approximate the laminar and turbulent flows in channels with circular and arbitrary cross-sections. To obtain the right velocity profile, an artificial permeability variation across the cross-section of the channel is determined. This is obtained based on the analogy of the DL and Darcy–Weisbach equation (DW). Results demonstrate that the DL approximations predict velocities and pressures distributions from the laminar and turbulent flows in the channels with circular and arbitrary cross-sections very well. At the same time, the models with DL approximations reduce the runtime up to ~40 times as compared to RANS, and improve the stability and convergence of the model. Lastly, a cross-flow heat exchanger is studied as an application of the DL approximations.

A Long-Term Analysis of the Possibility of Water Recovery for Hydroponic Lettuce Irrigation in an Indoor Vertical Farm. Part 2: Rainwater Harvesting

The aim of this study was to determine the suitability of a rainwater harvesting system to cover the water demand for indoor hydroponic lettuce cultivation located in Wrocław (Poland). The analysis was performed on the basis of the recorded rainfall in Wrocław in 2000–2019. The analyzed cultivation is located in a hall with an area of 300 m2, where the lettuce is grown vertically by the hydroponic method. The calculations of the rainwater harvesting (RWH) system were carried out considering the selection of the tank capacity for the collected water. The operation of the water storage is simulated using a yield after spillage (YAS) algorithm. It was evident that the proposed system might be an auxiliary system that relieves the water supply network or supports other water recovery systems (e.g., the water vapor condensation in a cross-flow heat exchanger operating as an element of the air conditioning system, proposed in Part 1 of this study). The harvesting system for the selected vertical farming indoor hall covers an average of 35.9% of water needs and allows a saving of 146,510 L of water annually for the cultivation. An average water demand coverage increases up to 90.4%, which allows a saving of 340,300 L per year when the RWH system is combined with water recovery from exhaust air from the hall.

Thermoeconomic assessment of integrated solar flat plat collector with cross flow heat exchanger as solar air heater using numerical analysis

A new configuration including liquid solar thermal collector integrated with fin and tube heat exchanger is proposed as solar air heater. Proposed system is modelled and optimized considering rate of heat transfer and total annual cost (TAC) as objective functions. 16 design parameters for both collectors and heat exchanger including water and mass flow rates are considered and optimized. It was found that, the maximum efficiency for the optimum rate of heat transfer could reach to 0.6359. Moreover, the higher value of air mass flow rate is required than the water mass flow rate. In addition, air to water mass flow rate ratio increases for the rate of heat transfer in the range of 0–60 kW while decreases for the higher values of 60 kW. In the optimum collector design parameters, the higher values of both collector length and width are selected to improve the rate of heat transfer and the effect of collector length is found stronger.

Влияние угла атаки на теплообменные и гидродинамические характеристики шахматного пучка труб каплевидной формы в поперечном обтекании

Tube bundles can be used as a separation heat exchanger in the organic Rankine cycle power plants (ORC), while the hot gas passes over the outer surface, and the working substance ORC flows inside the tubes. A numerical study has been conducted to clarify heat transfer and hydrodynamics of a cross-flow heat exchanger with staggered drop-shaped tubes at different flow angles of attack in comparison with circular tubes of the same equivalent diameter. The study was performed for the Reynolds number Re= 1.8  103 ~ 9.4  103, the longitudinal and transverse spacing of the tubes in the bundle are the same and are equal to 37 mm. Four cases of the tube’s arrangement with different angles of attack were investigated: 0, 45, 135, and 180 angles. The article presents a literature review related to the subject of the study. A mathematical and numerical model has been developed to calculate the heat transfer coefficient of the studied staggered drop-shaped tubes bundle using the ANSYS package, taking into account the stress-strain state of the tubes. Correlations of the average Nusselt numbers and the friction coefficient for the considered bundles in terms of the Reynolds number and angle of attack were presented. The results reveal that the thermal–hydraulic performance of the drop-shaped tubes bundle with zero-angle of attack is about 1.6 ~ 1.7 times greater than the circular one.

A Long-Term Analysis of the Possibility of Water Recovery for Hydroponic Lettuce Irrigation in Indoor Vertical Farm. Part 1: Water Recovery from Exhaust Air

This paper presents the characteristics of the operation of the system for recovery of water from exhaust air in moderate climates in the years 2012–2019. The proposed system for water recovery uses the phenomenon of condensation in a cross-flow heat exchanger operating as an element of the air conditioning system. The parameters of exhaust air behind the heat exchanger have been determined using a mathematical model of the so-called black box. The mathematical model considers the risk of the cross-freezing of the heat exchanger. The calculations carried out for variable parameters of external air during the analyzed period confirm that the system allows to cover the demand for water for lettuce irrigation during the cold and transitional period, which is a major part of the year. It has been noted that the effectiveness of the system is very high (av. 67.12% per year) due to the specific parameters of the internal air in which the lettuce must be grown and the need for continuous air exchange in such facilities. This means that air is a stable source of water recovery, where the recovery rate depends on the parameters of external air.