Flat Tube Research Articles

Experimental study on thermal–hydraulic performance of moist air inside flat tube of two kinds of plate-fin heat exchangers

The plate-fin heat exchanger is the core component of the condensing clothes dryer, which has a significant effect on the performance of the dryer. Two types of plate-fin heat exchangers with different fin structures are proposed to improve the performance of condensing dryers, offset-fin heat exchanger and slit-fin heat exchanger. Experimental investigations are conducted to study the thermal–hydraulic performance of moist air inside flat tube. The heat transfer coefficient and pressure drop of the moist air inside flat tube, the heat transfer rate per unit area, latent heat and sensible heat are compared and analyzed under different experimental conditions. The comparison shows that the offset-fin heat exchanger compared with the slit-fin heat exchanger can increase heat transfer rate per unit area by approximately 15%. Moreover, the comprehensive performance improves by 5%, respectively. Finally, correlations for predicting the Nusselt number and Darcy friction factor inside flat tube are proposed. The values deviate within20% and 10%, respectively. The results provide a design guide for applying plate-fin heat exchangers to condensing dryers.

Two-phase refrigerant distribution improvement by a new vertical multi-stream header in micro-channel heat exchangers

The Micro-channel heat exchangers (MCHXs) suffer from the non-uniform distribution of two-phase refrigerant due to the combined effects of inlet phase separation and differences in flow resistance, which becomes accentuated when faced with a large number of microchannel flat tubes. A multi-stream radial-tunnel header (MSRH) is presented to divide the refrigerant into several streams by radial-distributed tunnels and reduce the number of microchannels per stream, improving the distribution uniformity. The numerical models of conventional cylinder header (CCH) and MSRH are established and validated experimentally. Results show that the two-phase flow variation along the flow path is reduced by the radial tunnels with relatively equal flow resistance in MSRH. However, the two-phase separation and deflection will occur in the inlet bend due to the large gas–liquid density difference. Then, the MSRH with two rectifying structures is further proposed to mitigate the inlet phase separation. The average standard deviation of liquid refrigerant flow rate is reduced from 23.75 % to 9.4 % and 1.61 %, respectively. Furthermore, the design method of key parameters is also presented to provide guidance for various working conditions in actual application.

Numerical Simulation of Membrane Separation Characteristics of Supercritical Carbon Dioxide and Water.

To solve the problem of water carryover in the supercritical CO2 separation and mining process in the CO2 plume geothermal system, a three-dimensional shell-tube hollow fiber membrane absorption separator is designed in this study. A coupled species transport model, a porous medium model, and an absorption mathematical model are established, and the flow field and separation characteristics in the circular and flat tubes are analyzed using numerical simulation. The results show that the membrane separation efficiency increases with an increase in the flatness and membrane tube length. When the inlet velocity of the mixture is 0.1 m/s, the separation efficiency can reach 75.92%. Selecting a smaller flow Reynolds number and a more significant membrane tube flatness will reduce the water mass fraction at the outlet. When adding baffles of different shapes to the membrane tube, the mixture fluid in the membrane tube meanders forward and flows in the shape of "Z" under the blocking effect of the arcuate baffles. With an increase in the number of arcuate baffles in the membrane tube, the membrane separation efficiency of the separator increases continuously. The mixture fluid flows in the membrane tube with the built-in torsional baffles in a spiral manner, and the separation efficiency of the membrane separator increases with a torsion ratio reduction in the membrane tube.

Direct triboelectricity from friction of wheel tires on pavements

<p>Energy consumption in road and street traffic is significant and increasing. A partial recovery of this energy is the objective of the research briefly presented in the present paper. The proposed technique is totally innovative and has not been investigated, even through laboratory research, anywhere else. It aims to harvest triboelectric energy generated while wheel tires are directly rubbed against a pavement surface where oppositely charged electrodes are properly attached. The laboratory testing device consists of a rotating wheel bearing a vehicle tire, set up adequately to move down to a solid bench where flat bars, rods or tubes, susceptible to being oppositely charged by pairs, are attached. Metals, such as copper, bronze and aluminum, developing high electrical conductivity, were used in most experiments, as electrodes. Triboelectricity tests, under different placement of the electrodes regarding the wheel, were conducted in the laboratory and provided noticeable values of electric potential. Even more promising seem the results obtained following an intermittent application of the wheel load. Further experimentation introducing a much bigger wheel load, a different tire texture and other test improvements are ongoing, aiming at higher values of electric potential.<strong><em></em></strong></p>

Experimental analysis of an innovative internally cooled dehumidifier

To address the absence of balance in existing heat and mass transfer structures and enhance their adaptability in high-temperature and humid environments, a new internally cooled dehumidifier has been developed. This innovative dehumidifier incorporates corrugated fins to increase disturbance and contact area, along with a multichannel flat tube to improve cooling efficiency and compatibility. Experimental research was conducted to investigate mass transfer characteristics under different air, solution, and cooling water conditions in a high-temperature and humidy climate, and the Sh number correlation was derived. The findings indicated that compared to previous designs, the new dehumidifier's performance is less influenced by air temperature due to the corrugated fins' disturbance and cooling efficiency of the multi-channel flat tube. Additionally, its dehumidification capacity is positively correlated with air humidity, making it well-suited for high-temperature, high-humidity regions; The presence of corrugated fins enhances the disturbance on the solution surface, leading to a non-linear improvement in dehumidification performance when increasing solution flow; Lowering solution and water temperatures is more effective in improving dehumidification performance than increasing the flow rate, resulting in maximum increases of 60 % and 18.3 %, respectively, in mass transfer coefficients. Therefore, temperature adjustments are recommended for operational optimization; The Sh number correlation demonstrates high accuracy, within ±25 %, ensuring reliability. This study provides technical support and a foundational dataset for the dehumidifier's application in buildings located in high-temperature and high-humidity areas.

Study on the influence characteristics of thermal effect of internally cooled dehumidifier

In order to investigate the dehumidification strengthening effect of multichannel flat tube thermal effect and analyze its strengthening mechanism, a corrugated fins-multichannel flat tube based internally cooled dehumidifier structure is designed. The optimum dehumidifier flow type was determined and the dehumidification strengthening characteristics and thermal mechanism of the multichannel flat tube under different air and cold source conditions were experimentally analyzed. The results showed that the flow type B2 (air–solution countercurrent and water–solution countercurrent) had the best dehumidification performance. High-temperature and high-humidity environments can worsen the dehumidification strengthening effect of the multichannel flat tube and the effective utilization of cooling power, although high humidity has a stronger inhibitory effect, its inhibition mechanism is different. When the inlet air humidity is 25.8 g/kg, the dehumidification performance increases by up to 16.6%; Decreasing the inlet water temperature and increasing the inlet water flow significantly improved the dehumidification strengthening effect of the multichannel flat tube. Furthermore, the multichannel flat tube can eliminate 100% of total heat when the inlet water temperature is below 20.7 °C.

Theoretical and experimental investigation of the glass tube solar collector with inclined N-S axis and relative E-W single-axis tracking flat absorber

This paper presents a new solar collector design that combines flat absorber plates and glass tubes with a compacted automatic time-controlled (E–W) single-axis tracking mechanism. The mentioned design incorporates the advantages of the single-axis tracking system with a relatively small increase in the solar collector dimensions. According to it, a mathematical model was formed, and the test sample was fabricated. Using a bespoke test rig, the experimental investigation was carried out by simultaneously measuring the thermal performances of the solar collector in question and the flat plate solar collector with the same inclined position and absorber material. The experimental results (from July 15 to October 15, 2021) showed that compared to a reference collector, the new solar collector’s average daily specific useful heat was higher in the range of 14–23%, and the overall thermal efficiency was higher in the range of 9.7–17.9%. Using the obtained experimental and simulation data, the mathematical model was verified within an average deviation of 5.67%. Despite the partial reduction of the useful heat due to the mutual shading of absorbers, the mentioned solar collector shows promising results along with a compact design. We propose that this device will present promising opportunities in future applications.

Development of an event-by-event based Li–ZnS(Ag) neutron imaging detector with selective neutron detection capability

High sensitivity and high resolution is desired in such technologies as neutron radiography. However, the contamination of gamma photons in neutron images decreases the accuracy of neutron radiography. To solve this problem, we developed an event-by-event based neutron imaging system that can selectively detect neutrons. The developed neutron imaging system consists of an Li–ZnS(Ag) scintillator plate optically coupled to a flat panel photomultiplier tube (FP-PMT) with a light guide. Scintillation light emitted from the Li–ZnS(Ag) by the interaction with neutron-induced particles is used to calculate the position based on the center of mass calculations. The spatial resolution of the neutron imaging detector is ∼2.3 mm FWHM, and the sensitivity for 252Cf at 2 cm from the source with 2-cm-thick polystyrene is 20 cps/MBq. Background count fraction from 60Co gamma photons was 0.2 %. For various types of neutron absorption phantoms, high-contrast and high-resolution neutron images are obtained with the developed neutron imaging detector using a252Cf neutron source.

Natural convection of power-law fluid in a horizontal annulus between outer cylinder and inner flat tube

Natural convection of power-law fluid in a horizontal annulus between outer cylinder and inner flat tube

Experimental behavior of concrete-filled double-skin tubular columns with outer galvanized corrugated steel tubes under axial compression

Twelve lightweight and corrosion-resistant concrete-filled double-skin tubular (CFDST) columns with outer galvanized corrugated steel tubes (CSTs) and inner flat carbon steel tubes were subjected to monotonic axial compression tests. Compared to a traditional CFDST column, a CFDST column with a CST as the outer tube can reduce the longitudinal stress transmitted by the steel and better provide hoop confinement for the sandwiched concrete. The key parameters were the hollow ratio (χ) and inner tube thickness (ti). The failure mode, axial load capacity, strain and ductility of specimens with different parameters were analysed. There was noticeable slippage at the lock seam of the CST under axial loading, which releases the CST and results in the relatively low strength and ductility of the specimens. Keeping other parameters constant, an increase in χ and a decrease in ti led to a reduction in the peak load (Nu), strength index (SI) and ultimate strain (εcc). On the other hand, the ductility index (DI) increased as χ and ti increased. The strain development of the outer CST in one corrugation period was nonuniform. The hoop strain (εho) dominated at the crest of the CST, while the vertical strain (εvo) dominated at the trough. εvo gradually decreased from the trough to the crest, whereas εho increased from the trough to the crest. The applicability of the current standard design code formulae and axial load capacity equations for circular CFDST columns was evaluated using a newly expanded database, and a satisfactory axial load capacity model for circular CFDST columns with outer CSTs was proposed.

Braiding Polythene Lay‐Flat Tube into Cotton Threads for Artificial Muscle Actuation

In wearable robotics, soft actuation principles have been increasingly explored and tested due to their safety and comfort in human–robot interactions. Herein, a braided flat‐tube artificial muscle (BFAM) is presented. BFAMs are fabricated by braiding cotton threads together with an inexpensive lay‐flat tube (LFT) in a specific conform‐to‐LFT weaving method. They generate uniaxial contractions when powered by compressed fluids. The basic structure and working mechanism of the proposed BFAM are explained, and a quasistatic model is also developed. A comparison with other fluidic driven soft actuators is made and tabulated. Based on experimental studies, the proposed BFAM can contract close to 30% and yield force outputs more than 150 times their weight at an air pressure of 0.12 MPa. BFAM can be braided with multiple layers of flat tube without large increase of size. Experimental studies have shown that more layers of flat tube give a larger strain and output force up to four layers, beyond which layer increase does not yield visible improvement in strain and output force. Finally, potential applications of BFAM to arm joint actuations are illustrated to show its easy fitting to wearable robotics.

Degradation Evaluation of LaCrO3-Based Interconnect on the Basis of Oxygen Permeation Measurements

Degradation of LaCrO3-based Interconnect was evaluated by comparing the oxygen permeation flux for flat tube SOFC cell before and after long term operation (20,000 hours). Oxygen permeation flux was estimated based on the amount of water vapor, which was generated as a result of oxygen permeation from the hydrogen side to the air side. The estimated oxygen permeation flux for the SOFC cell before long term operation was found to be in the range of 0.02~0.06 mL cm−2 min−1 at 750 °C. For the cell after long term operation, the oxygen permeation flux was determined to be 0.049 mL cm−2 min−1, which was almost similar with that for the cell before long term operation. This suggested that degradation of LaCrO3-based Interconnect, i.e., increase in oxygen permeation, is quite small.

Theoretical and experimental studies for a transcritical CO2 heat pump with spirally fluted tube gas cooler

Transcritical CO2 system has been widely used in many fields to provide heating and cooling capabilities, and optimizing the structure of the gas cooler is an effective way to improve its performance. This paper presents a theoretical and experimental study of a spirally fluted tube-in-tube heat exchanger used as a gas cooler in a transcritical CO2 heat pump. The theoretical research uses numerical simulations to investigate the flow and heat transfer characteristics. The effect of the different CO2 mass flow rates, inlet pressure, and temperature on the performance of the spirally fluted gas cooler is evaluated and analyzed. The simulation results show that the spirally fluted structure can significantly improve the heat transfer performance of the CO2 side compared to the flat tube, which indicates that the spirally fluted gas cooler could be an effective way to enhance the operating performance of the transcritical CO2 system. Then experimental research is conducted in a transcritical CO2 heat pump prototype to validate the functional performance of the spirally fluted gas cooler. The effect of the different CO2 mass flow rates, inlet pressure and temperature, and the different water inlet and outlet temperatures on the performance of the spirally fluted gas cooler in the prototype are tested. The heat exchanger efficiency - number of transfer units (ε-NTU) method is employed to analyze the operating performance based on the experimental data. In addition, the exergy loss method is used to quantitatively evaluate the side-effect of the large pressure drop by the spirally fluted structure. Both the theoretical and experimental results show that the spirally fluted tube gas cooler can significantly improve the performance of the transcritical CO2 system. Besides, a heat transfer and friction coefficient correlation are established based on the experimental data for future research guidance.

Dynamic modelling and performance prediction of a novel direct-expansion ice thermal storage system based multichannel flat tube evaporator plus micro heat pipe arrays storage module

Direct-expansion ice thermal storage (DX-ITS) system can improve the energy efficiency ratio (EER) by integrating the evaporator and the storage module. In this paper, a dynamic model for a DX-ITS system is developed to predict system behavior. This system consists of multichannel flat tube evaporator plus micro heat pipe arrays storage module, a 4-HP compressor using R134a, an air-cooled condenser with 40 m2 area and an electronic expansion valve. On this basis, the influences of the condenser's cooled-air temperature, cooled-air flow rate, and compressor speed on the system energy and thermodynamics performance are studied. Results show that the EER and the charging power could reach 2.24 and 5.41 kW, respectively, under cooled-air temperature, cooled-air flow rate, and compressor speed of 28.5 °C, 4660 m3/h, and 1450 rpm. The exergy efficiency is more sensitive to cooled-air temperature, which decreases by 22.48% from 11.52% to 8.93% as the cooled-air temperature increases from 18 °C to 35.5 °C. Moreover, the compressor has the highest exergy destruction ratio of 40%–55% in the exergy analysis of the system component, while the condenser has the lowest exergy destruction ratio of 7%–15%, indicating that optimizing the compressor is the key to improving the system's performance.

Effect of rhombus mesh on 3D falling film flow characteristics over microchannel flat tube for LiBr (Lithium bromide) absorber

Effect of rhombus mesh on 3D falling film flow characteristics over microchannel flat tube for LiBr (Lithium bromide) absorber

Optimal design of wall temperature measurement for microchannel flat tube based on resistance temperature detector

Optimal design of wall temperature measurement for microchannel flat tube based on resistance temperature detector

Analysis of factors affecting the performance of a novel micro-channel heat pipe PV-Trombe wall system for space heating

Building energy consumption accounts for about 1/3 of the world's total energy consumption. Photovoltaic Trombe wall (PV-TW) is an effective way to reduce a building's energy consumption, but it still has disadvantages such as low energy efficiency and uneven indoor temperature distribution. To address these issues, a novel system with a PV-TW and a micro-channel heat pipe (MCHP) was initially presented in this research. By cooling the PV cell with both air and refrigerant, the system can reduce its surface temperature and improve its electrical performance. To promote thermal performance and user comfort, an air-cooled condenser is also employed to regulate the room's heat transfer. This paper establishes the system's dynamic mathematical model for winter and theoretically evaluates its performance. Besides, the key factors influencing the system’s performance were examined. In winter, the total power generation and average daily electrical efficiency are 3.12 MJ and 13.52%, respectively, with a maximum indoor temperature of 21.46 °C and a daily average thermal efficiency of 56.76%. The system’s performance is all improved with the incremental change of the factors besides the size of the micro-channel flat tube (MAFT), and the performance is not sensitive to the change of the air channel width. The optimal number and width of the MAFT in the evaporator section are 11 and 45 mm. The indoor air-cooled condenser should have about 10 rows of tubes and an ideal air volume of 540 m3/h. The recommended airflow channel thickness is between 5 cm and 10 cm.

Experimental investigation on the condensation of R32 flowing inside alternating cross-section flattened tubes with different aspect ratios

In this experiment, we investigated the condensation of R32 flowing inside alternating cross-section flattened (ACF) tubes with various aspect ratios. ACF tubes were made from a copper circular tube with a 4.31-mm inner diameter. Three ACF tubes with aspect ratios of 5.82 (ACF1), 4.11 (ACF2), and 3.23 (ACF3) were used as test tubes. The experimental conditions covered a mass flux of 280–580 kg/m2s, a heat flux of 10–20 kW/m2, a saturation temperature of 40 °C, and a vapor quality of 0.1–0.8. The results revealed that most experimental data fell into the annular flow regime when using existing flow patterns. In comparison, the ACF1 tube obtained the highest heat transfer coefficient (HTC) and pressure drop (ΔP). The HTC of ACF tubes outperformed those of the circular tube by about 1.7–6.9 (for ACF1), 1.1–2.8 (for ACF2), and 1.2–2.1 (for ACF3) times. In addition, ACF tubes provided a greater frictional pressure drop than circular tubes, around 1.0–2.3 (for ACF1), 1.2–1.9 (for ACF2), and 1.0–1.4 (for ACF3) times. However, the ACF1 achieved the best overall performance by approximately 2.1 times, superior to the circular tube. Since the existing correlations failed to predict the Nusselt number and two-phase friction factor, we propose new correlations for the ACF tube with mean deviations of 14.9% and 7.3%, respectively.

THE STUDY OF HEAT TRANSFER INTENSITY AND AERODYNAMIC DRAG INSIDE A FLAT PIPE

It is know that a heat exchange tube with a flat-oval profile has excellent thermal and aerodynamic characteristics in contrast to a round tube. Thus, with the same planes, a flat tube has a significant increase in thermal and aerodynamic efficiency compared to a round tube, which is widely used in industry. However, at present, there are a limited number of publications on the study of heat transfer and aerodynamics inside a flat pipe.
 In this paper, we present the methodology and results of the study of heat transfer and aerodynamic drag in a pipe, and describe the experimental stand for such studies.
 The experiments performed in a flowing wind tunnel with an internal diameter of 36 mm, operating in an open-loop circuit. The working medium is air drawn from the laboratory room. The prototype was a steel pipe with a flat-oval profile, 320 mm long, 30x15 mm cross section, and 2 mm wall thickness.
 The created experimental stand allows us to study the heat transfer and aerodynamic drag of a flat pipe under the boundary condition q=const. An electric heater ensured this condition, which is a nichrome wire with a diameter of 0.6 mm wound along the entire length of the pipe and insulated from the external environment.
 The experiments were carried out in the range of Reynolds numbers (10.5 - 55.0) 103 and dissipated powers (50 - 150) W. The average air temperature in the pipe was set in the range (20 - 55) 0C, and the average temperature of the pipe wall was set in the range (24 - 140) 0C in accordance with the electric power supplied to the heater.
 Empirical correlations proposed for determining the intensity of heat transfer and aerodynamic drag inside a flat pipe. The data had compared with a round tube. The results had analyzed, and it had shown for the first time that the intensity of heat transfer and aerodynamic drag in a flat-oval pipe is 1.1 to 1.2 times and 1.4 to 1.7 times higher, respectively.

Deployable tubular bar structures with laterally confined flattened ends

The article proposes a simple and efficient system for connecting the bars and the linkages in deployable structures. These structures must allow precise movements for unfolding and folding, which requires specific linkages that have been the subject of numerous studies. In contrast, the linkage-bar connection has hardly been studied. This article analyses this connection using a system based on crushing the ends of the bars, but introducing a modification that considerably improves its efficiency. It consists of flattening the end of the tube in a press with lateral confinement, which concentrates the entire section of the tube, but which limits the transversal expansion. The response of flattened tubes without accessory elements is studied, as well as other variants of the system by inserting at the ends of the bar either intermediate plates or a section of tube. The different types of bars with flattened ends have been tested to failure and the resistance capacities of the proposed solutions have been analysed. The results obtained demonstrate the structural efficiency of the proposed system, with a clear improvement over unflattened tubes.