Showing papers on "Concentric tube heat exchanger published in 2022"

Control of heat transfer in circular channels using oblique triangular ribs

Abstract: Enhancing heat transfer is crucial for improving the performance of heat transfer applications. Therefore, a novel method is proposed in this study for improving the heat transfer using a new rib geometry within a circular channel. The performance of the novel method was evaluated by comparing the results of the channel with ribs with that of an ordinary channel. In this study, numerical investigations were conducted on the temperature distribution and fluid flow properties of a 500 mm tube with an external diameter of 50 mm and an internal surface of 47 mm. To evaluate the effects of the ribs on the heat transfer via the tube wall, the tube was maintained at a steady temperature of 673 K, and the Reynolds number (Re) was set in the range of 1000–20000. Different cases were simulated using CFD-FLUENT (v. 16.1). For the three cases, three types of ribs (7 in total) with triangular transverse sections of 5 mm were set 62.5 mm apart in the tube. Subsequently, the turbulent parameters (k, ε) affecting the turbulent flow were evaluated. Moreover, the heat transfer coefficient and friction coefficient of the tube with ribs were calculated using the enhancement technique and compared with those of the plain tube. It was observed that the ribs inside the tube increased the temperature of the cooling air in the first, second, and third cases by 6.25%, 12.5%, and 17.5%, respectively. Furthermore, the difference in the velocity and temperature distribution across the centreline of the tube was observed for all three cases and a smooth tube. It was observed that the heat flow rate increased, particularly around Re = 14,000, in the ribbed tube. The tube with ribs exhibited a 90% increase in the flow rate compared to the flow rate in the tube with no ribs. The tube with ribs also exhibited better performance in terms of turbulent flow.

Numerical investigations of the impact of a novel turbulator configuration on the performances enhancement of heat exchangers

Abstract: This paper presents an numerical simulation of the thermo-fluid characteristics for a heat exchanger with smooth concentric double tube equipped by Turbulators operating in the turbulent regime with Reynolds numbers from 3000 to 17,000. This heat exchanger is designed to provide a tubular heat energy exchange from a primary fluid (hot air) to a secondary fluid (cold water) in order to ensure efficient heat transfer with less heat loss. The main focus of this work is the development of a novel configuration for the exchangers with the insertion of a small baffle turbulators on it. These tabulators act as a turbulence promoters for enhancing the thermal performance of the heat exchanger system. Besides, the optimization of these turbulators is assessed by evaluating different baffles configuration and the influence of the pitch distance between them on the thermos-hydrodynamic behavior of the coolant flow. To evaluate the performance of the proposed configuration we evaluated a bench of thermal parameters, mainly Nusselt number, the friction factor, the thermal performance factor, the turbulent viscosity, the temperature field and the velocity field among others. After that, correlations between the Reynolds and Nusselt numbers and Reynolds and the friction factor were conducted for the whole configurations. Results show that the structure of the flow is strongly influenced by the shape and dimensions of inserted baffles. The Nusselt number and the friction factor increase when the inter-Turbulator distance is reduced. Also, the separating of the tube by the insert of the turbulators induces a vortex flow which leads to the improvement of the forced convection. The improvements in heat transfer (ηTPF) is also evaluated using turbulators with different pitches (260; 108.57; 67.27 and 48 mm). These configurations leads to an increase of ηTPF with 2.36; 2.42; 2.53 and 2.71 in respect to the pitches mentioned above. Besides, the outlet temperatures are respectively equal to: 358.79, 340.15,337.39, 333.09 and 329.72 ° K. This reflects a difference in the overall inlet-outlet air temperature of: 14.21 ° K for the smooth case; 32.85 ° K (case (A1); 35.61 ° K case (A2); 39.91 ° ​​K case (A3) and 43.28 ° K case (A4).

A critical review of parameters governing the boiling characteristics of tube bundle on shell side of two-phase shell and tube heat exchangers

Abstract: Heat transfer by the process of boiling is advantageous due to the high heat transfer coefficient associated with the process. In many heat transfer applications, boiling on tubes and tube bundles are encountered. Tube bundle studies are important as these are an integral part of shell and tube heat exchangers, reboilers, evaporators used commercially both in industrial and non-industrial applications. Similarly, tube bundles with vertical configuration are integral part of nuclear reactors. In this review, the effects of different parameters affecting heat transfer in tube bundles on the shell side of two-phase shell and tube heat exchangers are analysed based on available literature. The studies included are subdivided into effect of performance parameters for flow boiling and for pool boiling. The pool boiling heat transfer devices do not require any active flow equipment, whereas in case of flow boiling active flow equipment is essential for continuously supplying the working fluid. In order to design an effective heat exchanging device having tube bundles the combined effect of parameters such as heat flux, mass flux, quality, tube geometry, spacing etc. need to be considered. This article highlights various critical parameters, considered by studies available in the open literature, which affect the heat transfer in two-phase flow heat exchanging devices.

3D Numerical Modeling to Evaluate the Thermal Performance of Single and Double U-tube Ground-coupled Heat Pump

Abstract: The heat transfer rate and borehole design represent great challenges to the thermal equipment designer of the ground-coupled heat pump. The present model represents a mathematical and numerical technique implemented to tackle such a problem. A thermal assessment was established to estimate the total energy dissipated to the ground zone for a heat pump utilized for cooling purposes in the summer season. Comsol Multiphysics 5.4 software was used to build a 3-dimensional model to assess the thermal performance of single and double U-tube boreholes that circulate water as a thermal transfer medium. The (Heat Transfer) module has been implemented for this investigation under the (Stationary) study option. The model couples both heat conduction in solids, including tube metal, grout, and soil regions, and thermal medium fluid flow inside the U-tubes. The numerical solutions were compared for both heat exchangers at fixed borehole geometry, diameter, and depth and constant operating conditions in a steady-state mode. The double U-tube heat exchanger was tested in the parallel circuiting orientation of the U-tubes. The total mean resistance of the single U-tube borehole was higher than the half-loading double U-tube heat exchangers by 14.6%. The results also revealed that the heat transfer rate enhancement for the double U-tube was in the range of 10–14% when operating at the same fluid mass flow rate and inlet temperature for a given borehole design. Doi: 10.28991/HIJ-2022-03-02-01 Full Text: PDF

Investigation of Heat Transfer Characteristics in Double Tube Heat Exchanger with Helical Turbulator Using CFD

Abstract: The mechanism to increase thermal heat transfer will directly influences the performance increment in the heat transfer system. In the heat transfer applications, the improvement of heat exchange also would substantially increase heat transfer efficiency and part of its economical operation. The double tube heat exchangers are primarily ideal for high temperature and high-pressure applications due to their limited diameters. Turbulent enhancer used in heat exchanger pipes is an important way to increase efficiency. Several techniques have been developed to achieve required heat transfer speeds within the specified design and length of the heat exchanger with economic pumping capacity. Helical inserts are the most common and efficient methods for heat transfer enhancement in heat exchangers. This article attempts to explore the performance of an exchanger for double tube with a helical insert using ANSYS CFX fluid dynamics software. The pitch of the inserts is varied in three levels and heat transfer characteristics were studied and compared.

Numerical analysis of thermal performance of heat exchanger: Different plate structures and fluids

Abstract: Due to compact size, high power density, low cost and short construction time, the small modular reactors are considered as one of the candidate reactors, in which the power generation system is important with a compact heat exchanger for modular construction. Therefore, the effect of plate structure and nature of the working fluid on the thermal performance of plate heat exchanger are analyzed for the design of compact and efficient heat exchanger. The heat transfer rate, temperature counters, velocity vectors, and pressure drop have been optimized and investigated using FLUENT. The Nusselt number has been calculated for the corrugated and flat plate heat exchanger to validate the convective heat transfer. The numerical results are agreed well with correlation within deviation of ~5-7%. The performance of heat exchanger can be improved by controlling the mass-flow rate, and temperature of working fluid. The corrugation plate heat ex-changer increases the heat transfer rate 20% and effectiveness 23%, respectively, as compare to flat plate heat exchanger when the working fluid is water. In the case of air, heat transfer rate, and effectiveness are about 10% and 9%, respectively. The results show that the corrugated plate heat exchanger is more effective than the flat plate heat exchanger because corrugation pattern enhances the turbulence of fluids, which further increase heat transfer rate and coefficient. The selection of the working fluid and structure of the plate must be considered carefully for efficient and compact design of heat exchanger.

Heat transfer analysis in counter flow shell and tube heat exchanger using of design of experiments

Abstract: In this research aimed to estimate the overall heat transfer coefficient of counter flow shell and tube heat exchanger. Heat transfer is the phenomenon to analysis of heat transfer from one medium of fluid to another medium of fluid, it is considered as a major role in industrial applications. Numerous heat exchangers are available, in this research considered as shell and tube heat exchanger. Overall heat transfer coefficient informed that three major factors are influenced as passing of fluid (film) media coefficient inside the tubes, circulating of fluid (film) media coefficient over in the shell, and the resistance of wall made on metal. In this study Taguchi L9 orthogonal array is executed to found the overall heat transfer coefficient with effective process parameters. Three major parameters are considered for this work are coil diameter (25 mm, 30 mm, and 35 mm), baffle thickness (15 mm, 20 mm, and 25 mm) and baffle gap (200 mm, 300 mm, and 400 mm. Baffle plate thickness is highly significant factor for this experiment.

Thermo-hydraulic performance investigation of a heat exchanger tube inserted with twisted tapes modified with various twist ratio and alternate axis

Abstract: This paper presents a numerical investigation on a heat transfer enhancement by using a computational fluid dynamics software. The heat transfer enhancement is implemented by inserting twisted tape into a heat exchanger tube. The twisted tapes with twist ratios of 4, 6 and 8 were modified with alternate axis. The pitch of the twisted tape having the rotation direction such as clockwise and counterclockwise are connected with 90º connection angle. Water is selected as working fluid and turbulent flow condition corresponding to Reynolds number ranging from 5000 to 29000 are considered in the study. The heat exchanger tube is under constant heat flux of 50 kW/m2. Numerical analysis results prove that the use of twisted tape improves thermal performance compared to smooth tube. As the twist ratio increased, the heat transfer performance and the friction loss penalty decreased. Overall results are determined with thermohydraulic performance criteria (THP). The highest THP value is obtained as 1.21 for the tube inserted with the twisted tape which has the twist ratio of 4 and alternate axis between the twist pitches at Reynolds number of 5913

Performance assessment of annular fins and cellulose cooling pad on heat transfer enhancement of evaporative heat exchangers using volumetric heat and mass transfer coefficients

Abstract: Abstract In the present work, a test facility has been built to assess the performance of evaporative heat exchangers. The experimental set-up consists of Fan-Cooling pad-Water spray-Heat exchanger (FCWHX) unit with four different configurations namely a) plain tube heat exchanger and b) finned tube heat exchanger with water spray arrangement on their top and without cooling pad, c) plain tube heat exchanger and d) finned tube heat exchanger with cooling pad and water spray arrangement on the top of cooling pad. Experiments are conducted during various durations with climatic conditions in the range of 27 °C–31 °C DBT and 45%–65% RH. While testing the FCWHX unit with and without cellulose pad, exit temperature and humidity of air, exit temperature of spray water and exit temperature of hot water from heat exchanger were continuously monitored. The performance parameters namely heat exchanger duty, evaporative cooling rate and evaporation rate of spray water, volumetric heat and mass transfer coefficients have been determined. Correlations for Nusselt and Sherwood number for all four configurations of FCWHX unit have been presented from these studies, with a maximum of ±10% error band.