Flow Heat Exchanger Research Articles

Designing air handling unit in data center and estimating its performance

In this paper, the construction process of the enhanced plate, the heat transfer and fluid flow characteristics, and the domain decomposition method for AHU performance estimation are presented. The AHU heat exchanger 3D model is built from plate modeling to heat exchanger assembling. The heat transfer plate modeling starts from a basic flat plate, elliptic cylindrical dimples (ECDs) are firstly added to the fixed location, and then spherical crown dimples (SCDs) are applied to the flat surface among the ECDs. For the enhanced channels, the effect of channel height is weaker than SCD depth on the Nusselt number and friction factors. For all enhanced channels, the PECs are larger than 1.1 within Re from 5000 to 35,355. The performance of a deeper depth of SCD is superior to that of a shallow one when the channel height is the same. Among the nine channels studied, the highest enhanced effects are obtained for “H12-R10-h4” (PEC=1.45 at Re=5000). And all nine enhanced channels can enhance heat transfer at the same pressure drop among the Reynolds number of 5000 to 35,355. The energy saving performance decreases with Re, and the channels with smaller SCD depth can save more energy when channel height is identical at the higher Reynolds number region. A decomposition thermal design method is proposed for the cross-flow AHU heat exchanger design, and the typical AHU design result is picked based on the heat exchange rate and flow loss power. The recommended heat exchanger is “H7.5-R10-h3” whose heat exchange rate is 40.5 kW when flow loss power is 3.25 kW.

Investigation of phase change characteristics for refrigerant R-134a flow in a double pipe heat exchanger with the use of thermal non-equilibrium model

Investigation of phase change characteristics for refrigerant R-134a flow in a double pipe heat exchanger with the use of thermal non-equilibrium model

Improvement of Plate-Fin Heat Exchanger Performance with Assistance of Various Types of Vortex Generator

A 3-dimensional incompressible laminar flow and heat-transfer in a plate-fin heat exchanger (PFHE) where investigated numerically in this article. The influence of mounting a longitudinal vortex generator (LVG) on the offset rectangular-triangular fin (ORT) in the PFHE, on thermal and hydro-dynamic fields are presented. The novelty of this study is by attaching a LVG to an offset strip fin (OSF) surface. The cases of study for the PFHE are established, by using a built-in rectangular winglet pair type RWP longitudinal vortex generator carried out and fitted on this fin to improve the convective heat transfer of the (ORT) fin while minimizing pressure loss. The upper and lower plates are exposed to constant heat flux and the working fluid is air where chosen under a laminar range of RE (600 to 1400). The laminar flow and heat-transfer are governed by continuity, momentum and energy equations. ANSYS FLUENT (2021 R1) is used to get the numerical results, based on the finite volume method. The performance of the VG is assessed for an optimum winglet attack angle (45°), as well as by modifying the geometrical size parameters, namely the height and placement (L) of the RWP LVG. The result shows that the Nusselt number reaches its optimum enhancement values by using a common flow up CFU built-in rectangular winglet pair type RWP VG with a height and entrance length of (h=1.25mm, L=0.5mm), by 22.23% as compared with base case configuration (ORT). Finally, a two more LVG are tested with the optimum conditions of the RWP, which they are a delta winglet pair (DWP) and trapezoidal winglet pair (TWP). In addition, the temperature fields for the primary and secondary flows were shown in contour and streamline diagrams

Experimental and numerical analysis of heat transfer in a dimple pattern heat exchanger channel

In contrast to the predominant herringbone shape of heat plates, a microplate heat exchanger has an array of relatively small dimples. Its number and shape define the characteristics of such a plate heat exchanger. Literature, however, of the flow characteristics in such kinds of channels is scarce. Precise knowledge of the flow specifics in such a channel is of key importance to develop efficient new products. Single-phase water flow and heat transfer in microplate heat exchanger was investigated with the laboratory experiments and use of computational fluid dynamics simulations. A novel and innovative laboratory experiment was developed where flow characteristics and heat transfer in the microplate heat exchanger were measured. Experimental results were directly used as boundary conditions in numerical simulations. With this approach a direct validation of the results of numerical simulations were obtained. Heat transfer simulations were performed with three turbulence models: k- ε, k-ω SST and the Reynolds stress model. The most reliable results in heat transfer analysis were obtained using the Reynolds stress model where results are on average 7.05% lower compared to the results of the laboratory experiment. When all experimental uncertainty contributions were analysed, the simulation results were in the band between − 11% and 1.8% compared to the results of the laboratory experiment. Numerical simulations show that the heat transfer coefficient in the channel is proportional to Re0.64 in the analysed geometry of a microplate heat exchanger. The heat transfer coefficient was calculated and was between 9740 and 21990 W/m2K at Reynolds numbers 1170 and 4170 respectively.

Investigation of noncircular orifice supporting baffle longitudinal flow heat exchangers

Owing to the disadvantages of the segmental baffle heat exchanger (SBHE–STHE), a novel type of supporting baffle longitudinal flow heat exchanger is proposed and numerically studied. This equipment includes hexagonal cinquefoil, regular quadrangular, trefoil fillet, and reticulated orifice baffle heat exchangers. The flow and heat transfer performance of the four noncircular orifice supporting baffle longitudinal flow heat exchangers are investigated. Combined sections were fabricated, and local performance characteristics of temperature, pressure, and flow field contours were examined. A composite dimensionless index based on SBHE–STHE is proposed to quickly estimate the comprehensive characteristics of the four supporting baffle longitudinal flow heat exchangers. Results show that the noncircular orifices within the supporting baffle induce jet flow and fluid disturbance. Consequently, periodic pulsating vortices among adjacent supporting baffles are generated, explaining the heat transfer enhancement mechanism. The heat transfer capability of the reticulated orifice baffle heat exchanger is higher than that of the other three orifice baffle schemes and similar to that of the SBHE–STHE. All the comprehensive performance indices of the four noncircular orifice schemes are higher than those of the SBHE–STHE.

Design of heat exchanger for producing nickel ferrite (NiFe2O4) nanoparticles using coprecipitation method

This study examines the design of a heat exchanger (HE) in the production process of nickel ferrite (NiFe2O4) nanoparticles using the coprecipitation method by determining the shell and tube heat exchanger. The Microsoft Excel application is used as a manual calculating machine to facilitate the analysis of heat exchanger (HE) data calculations. The research flowchart starts with a literature study, preparation of tools and materials for design, calculation of the main shell and tube components, and then fabrication. Based on the calculation results, the design specification data for a shell and tube heat exchanger has a shell diameter of 0.032 m, a shell length of 4.267 mm, a thickness of 0.002 m with an initial heat transfer rate (Q) of 460130 W resulting in a heat transfer efficiency of 95.706% and an NTU of 6.165. The high effectiveness value makes the design of the one shell and tube type turbulent flow heat exchanger (HE) considered to have met the standards of high effectiveness and good performance. The design and design process is complete if the device functions properly. This study can be used as a reference for researchers in designing heat exchangers during production to make them more effective, reliable, and economical.

Flow distribution and heat transfer performance of two-phase flow in parallel flow heat exchange system

Flow distribution and heat transfer performance of two-phase flow in parallel flow heat exchange system

Reduced order 1 + 3D numerical model for evaluating the performance of solar borehole thermal energy storage systems

This study presents a computationally efficient numerical model for solving the fluid flow and heat transfer phenomena in co-axial boreholes heat exchangers arranged on a rectangular grid (N × N) drill hole pattern. Such systems of boreholes are an integral component of a Solar-Borehole Thermal Energy Storage System for seasonal thermal storage application. The numerical model couples a one-dimensional fluid flow and convective heat transfer model in the heat exchanger with a three-dimensional model of conductive heat transfer in the strata. In addition to solving mass and heat transfer in borehole systems, it integrates a solar thermal collector system and building dynamic thermal load to design a Solar- Borehole Thermal Energy Storage system for a 182-unit residential apartment building. Simulation also considers and evaluates the conductive, convective, and radiative thermal losses of the system. The model is validated using experimental data from a coaxial borehole heat exchanger and compared to the results of a commercial finite volume solver for multiple co-axial boreholes. The computational cost of developed numerical model is reduced by a factor of 194 compared to a commercial finite volume solver. Solar- Borehole Thermal Energy Storage system simulation is performed for a period of five years considering hourly fluctuations in solar irradiance and building dynamic thermal energy demand. Parametric study is performed on depth and spacing of boreholes, and mass flowrate in the solar thermal collectors. It is found that a system of 100 boreholes, each 100 m deep, linked to 674 solar thermal collectors can provide the heating for the building with a total thermal demand of 5600 GJ per year.

Numerical simulations of heat exchange and vapor flow in ice fractures on Enceladus

Cassini spacecraft observed plume of water vapor and ice particles above the south polar terrain (SPT) of Saturn's moon Enceladus in 2005. The area of the SPT is marked by four prominent linear depressions in the ice dubbed “tigers stripes” (TS) that appear to be the source of the plume. The area around TS is also the source of anomalously high heat flux. The current consensus based on analysis of Cassini observations and modeling suggests that TS are fractures in the ice that penetrate to warm sub-ice ocean. Escaping vapor laden with ice particles forms the visible plume and latent heat of condensing vapor serves as the source of the surface thermal anomaly. In the present work previously developed numerical model of vapor flow and heat exchange inside TS fractures is refined and used to explain Cassini observations. Model improvements include consideration of a possible snow layer on the surface and inclusion of surface ice sublimation into energy balance model. Results of the simulations with improved model suggest that Cassini observations of vapor mass flow and endogenic heat flux can be explained if the width of the ice fractures is in the range 0.05–0.1 m, similar to previously published results. Wider fractures are possible if only a small portion of TS total length produces vapor plume, but the whole ~500 km length of TS fractures still contributes to the surface thermal anomaly. Alternatively, wider fractures are also possible in fractures with high effective friction due to wall roughness or channel tortuosity. Simulated heat output of fractures with different widths and depths in the range of 1.5–3 km is ~2.5–3.0 GW and is only weakly dependent on fracture width. A 2-m-thick surface snow layer covering the fracture can significantly lower outgoing heat flux to 0.9–1.9 GW and reduce surface temperatures by 20–40 K. The total heat flow from different fractures (including conduction from the water-filled portion) is remarkably similar - it is ~3.3 GW and 2.3 GW for fractures without and with a surface snow layer, respectively. The simulated heat flow is lower than the observed heat flow, suggesting that each TS depression may host 2 to 6 narrow ice fractures. The long-standing puzzle of the large difference between the observed heat flow from near TS (~4.2 GW) and from the whole SPT (~15.8 GW) is explained by conduction of ~11 GW of heat from the ocean through the ~5 km-thick ice shell underlying the SPT. Predicted high surface temperatures near fracture exit result in high rates of ice sublimation, which may produce a secondary source of water vapor feeding the observed plume. Fracture outlet likely evolves into a cone-like cross-section widening towards the surface on timescales from 1 to 100 years.

Energy, exergy and economic (3E) study on waste heat utilization of gas turbine by improved recompression cycle and partial cooling cycle

ABSTRACT As the bottom cycle of gas turbine waste heat utilization, the S-CO2 cycle can enhance the power output capacity of the system. Based on the energy analysis of the recompression cycle and the partial cooling cycle for gas turbine waste heat utilization, the two cycles are improved from the matching of heat exchange flow of regenerator and heater in this paper. Under the same parameters, compared with the cycle before improvement, increase in heat source utilization rate and net power output of improved cycles is 45.69% and 39.31%, 43.54 MW and 35.43 MW, and the power consumption cost is decreased by 0.6106 $/kWh and 0.6289 $/kWh. However, as part of heat recovery inside the system is replaced by the heat of the heat source, the thermal efficiency is decreased by 10.43% and 8.7%, respectively. Variable parameter study is conducted on the two improved cycles to analyze the cycle characteristics from the perspective of energy, exergy, and economy (3E). The results showed that the improved recompression cycle has a high thermal power conversion capacity, higher system thermal efficiency and exergy efficiency and lower power generation cost, while the improved partial cooling cycle has higher waste heat utilization potential. However, the area of heat exchangers in both cycles tends to increase, which is not conducive to the compactness of the system.

Experimental/Numerical Investigation and Prediction of Fouling in Multiphase Flow Heat Exchangers: A Review

Fouling build-up is one of the most challenging problems for heat exchangers in industry. The presence of fouling leads to a degradation of system efficiency, an increase in operating cost, and possibly, a harmful environmental impact. For this reason, fouling analysis has become an extremely important research subject in order to have a safe and efficient operation. The analysis is more difficult where phase change of fluids is involved during the heat transfer process, as in the case of boilers and condensers, which are critical units in industrial facilities. Due to the lack of a comprehensive review of fouling analysis for the case of multiphase heat exchangers, this paper examines available approaches and techniques used for fouling characterization, modeling, monitoring, and prediction in heat exchangers for both single-phase and multiphase heat exchangers with a focus on fouling in thermal desalination systems. It also gives an overview of heat exchanger condition monitoring solutions available in the market.

Numerical Study of Turbulent Nanofluid Flow in Double-Tube Heat Exchanger: The Role of Second Law Analysis

Numerical Study of Turbulent Nanofluid Flow in Double-Tube Heat Exchanger: The Role of Second Law Analysis

Leading Edge Bumps for Flow Control in Air-Cooled Condensers

Air-cooled condensers (ACCs) are commonly found in power plants working with concentrated solar power or in steam power plants operated in regions with limited water availability. In ACCs, the flow of air is driven toward the heat exchangers by axial fans that are characterized by large diameters and operate at very high mass flow rates with a near-zero static pressure rise. Given the overall requirements in steam plants, these fans are subjected to inflow distortions, unstable operations, and are characterized by high noise emissions. Previous studies show that leading edge bumps in the tip region of axial fans can effectively reduce the sound pressure levels without affecting the static efficiency. Nevertheless, the effects of this treatment in terms of flow patterns and heat exchange in the whole ACC system were not investigated. In this work, the effect of leading edge bumps on the flow patterns is analyzed. Two RANS simulations were carried out using OpenFOAM on a simplified model of the air-cooled condenser. The fans are simulated using a frozen rotor approach. Turbulence modeling relies on the RNG k-epsilon model. The fan is characterized by a diameter of 7.3 m and a 333 m3/s volumetric flow rate at the design point. The presence of the heat exchanger is modeled using a porous medium. The comparison between the flow fields clearly exerts that the modified blade is responsible for the redistribution of radial velocities in the rotor region. This drastically reduces the losses related to the installation of the fan in a real configuration.

Optimal designs for flow uniformity at inlet of microchannel flat tube heat exchanger

Microchannel flat tube heat exchangers and circular tubes commonly used in thermal engineering applications vary in size and shape. Uniform flow distribution is an essential factor affecting the performance of heat exchangers. This paper proposes three types of inlet distributors to achieve connection and reduce the non-uniformity of the working fluid flow: Column-type, Diffuser-type, and Drainage-type. The flow uniformity, pressure drop, and heat transfer efficiency of R410A refrigerant two-phase flow in a microchannel flat tube heat exchanger with various mass fluxes are investigated by numerical simulation. Verification is done by experiment and empirical correlation. The concept of heat transfer offset rate is proposed to characterize the impact of flow uniformity on heat transfer. The eddy current at the distributors is a significant factor in the uneven distribution of the flow field. Different distributors will affect the distribution of gas and liquid phases. The standard deviation of the mass flow rate in Column-type is less than 9.10%, and uniformity is best when the mass flux is low. The heat transfer coefficient is 5800 W/m2K, and the heat transfer offset rate is less than 5.77%. When the mass flux exceeds 300 kg/(m2s), the flow distribution performance of the diversion flow is the best, and the flow standard deviation can be reduced by up to 36.56% at high flow.

On the Hydrothermal Behavior of Fluid Flow and Heat Transfer in a Helical Double-Tube Heat Exchanger with Curved Swirl Generator; Impacts of Length and Position

The hydrothermal behavior in a helical double-tube heat exchanger is numerically estimated. A new type of swirl generator with two sections, including; outer curved blades and a semi-conical section with two holes in the inner section, is employed. Two geometrical factors, containing the length (L1) and the position of the swirl generator (S), are used for investigation. The calculations were performed by a commercial FVM code, ANSYS FLUENT 18.2. The numerical outcomes show that a shorter length of the swirl generator leads to a better hydrothermal behavior. Accordingly, the model with L1 = 100 mm at m˙ = 0.008 kg/s achieves the maximum thermal performance by about 17.65, 53.85, and 100% enhancement compared to the models L1 = 200, 300 mm, and without swirl generator. Among the different studied positions of the swirl generator, the maximum heat transfer coefficient and average Nusselt number in entire mass flow rates belong to the case with position S = 0.3π mm. Moreover, the thermal performance of the case with S = 0.3π mm is higher than cases with S = 0.1π mm, S = 0.5π mm, and without swirl generator by about 11.11, 53.84, and 100%, respectively.

Performance Analysis and Structural Optimization of Torsional Flow Heat Exchangers with Sinusoidal Corrugated Baffle

Performance Analysis and Structural Optimization of Torsional Flow Heat Exchangers with Sinusoidal Corrugated Baffle

Obstacle's effects and their location inside the square cavity on the thermal performance of Cu–Al2O3/H2O hybrid nanofluid

AbstractThe current study focuses on the effect of obstacles and their positioning within the square cavity (L = H) on heat exchange. This work considers heating the cavity's bottom wall to a steady, high temperature. The top wall of the cavity is adiabatic, while the two vertical side walls are cooled. Four cases are explored under these conditions: the first case is a square‐shaped cavity holding a square‐shaped obstacle h = l = 0,15 L, while the other three cases, respectively, each include two, three, and four square obstacles. The cavity was filled with Cu–Al2O3/H2O hybrid nanofluid with a volume fraction φ = 0.03. Numerical results for laminar and stationary flow regimes with Rayleigh numbers 104 ≤ Ra ≤ 106. The finite volume approach solves the governing equations numerically. The findings show that the number of square obstacles within the square‐shaped cavity significantly impacts heat exchange and hybrid nanofluid flow. The second example, with two square obstacles, improves heat exchange more than other cases with one to four barriers. In the second example, the obstacle location at the plane Y = 0.25H is suitable and helps boost heat transmission of the hybrid nanofluid. The ideal obstacle position in the fourth scenario, which has four square barriers, is at the plane Y = 0.75H.

A Vertical Fountain Dryer Adjusted for Sawdust and Wood Chips Drying

This article presents the preliminary results on the drying process in a fountain dryer designed and adapted to drying waist sawdust and/or chips of various morphology and moisture content. In terms of drying technology, it is important to reduce the demand for heat and electricity. The phenomena occurring during the drying of sawdust in a fountain dryer were analyzed. Modifications of a typical fountain dryer were proposed in order to dry the chips, to obtain appropriate moisture and quality suitable for the process of their further granulation for the production of pellets. The test stand and the most important properties of the fountain dryer were described and discussed. Such characteristic aims of the device, i.e., efficiency, combustion, air and exhaust gas flow measurements, among others, were presented. The characteristics of the sawdust drying curves as a function of temperature were also determined. Computer simulations of heat exchange, air, and exhaust gas flow velocities were also performed and compared with the results obtained directly from the modified test stand. The maximum combustion of sawdust measured during startup of the furnace was 0.14 m3/h, which is 0.46 m3 of the fuel consumption for the production of 1000 kg. Drying times of wet sawdust is relatively short and takes ~50 s for (weight of wet sawdust 4.75 kg, with moisture of 35%) the relatively low air temperature of 175 °C.

Numerical study on application of orthogonal elliptic tube in torsional flow heat exchanger

Orthogonal elliptical tube are highly applied in torsional flow heat exchanger to optimize the heat transfer performance and reduce the flow resistance. A full-section periodic model of the torsional flow heat exchanger with orthogonal elliptical tube with four axial ratios is established. The heat and flow transfer on the tube and shell sides are numerically simulated with the computational fluid dynamics(CFD) method. Besides, the transfer performance on the shell side is evaluated based on the field synergy principle. The results show that compared with the round tube, for the tube side, the convective heat transfer coefficient of the orthogonal elliptical tube is increased by 26.7–73.2 %, and the comprehensive performance is increased by 6.4–25.6 %.On the shell side, the heat transfer coefficient of the torsional flow heat exchanger with orthogonal elliptical tube is increased by 4.5–16.8 %, the pressure drop is reduced by 17.1–21.3 %, and the comprehensive performance is improved by 14.8–34.7 %. The comprehensive performance of the orthogonal elliptical tube with an axial ratio of 1.7 on the shell side is the best. This research provides ideas and theoretical references for the development of special-shaped tube torsional flow heat exchanger.

Active Turbulence Grid-Controlled Inflow Turbulence and Replication of Heat Exchanger Flow Fields in Fan Applications

A novel active turbulence grid of the Institute of Fluid Mechanics at FAU Erlangen-Nuremberg is introduced. The focus of this grid is not on basic investigations of fluid mechanics, as is usually the case with active turbulence grids, but the generation of defined inflow conditions for axial fans. Thus, by means of the active turbulence grid, individual turbulence characteristics in the flow to the fan can be changed; therefore, fundamental interactions between the flow mechanics at the axial fan and the sound radiation can be analyzed. In addition, the replication of the flow fields of heat exchangers by the active turbulence grid is the focus of the investigations. The investigations showed that it is possible to use the active turbulence grid to generate defined inflow conditions for axial fans. It was also possible to reproduce the heat exchanger flow fields both for the mean turbulence values and for the spatial distributions. It was found that the grid induces tonal components due to the drive motors, but also that the inherent noise has no significant influence on the spectrum of the fans under investigation. Based on selected turbulence characteristics, direct correlations were found between the spatial distribution of the turbulence level and sound radiation at the first blade passing frequency of the axial fan. As the variance of the turbulence level increases, the sound radiation of the tonal components becomes more pronounced. The total sound pressure level, however, is mainly determined by the low-frequency broadband sound. A linear relationship between the spatial mean value of the turbulence level and the total sound pressure level was found for the investigated axial fan.