Heat Transfer In Pipe Research Articles

Experimental and numerical study of drag reduction and heat transfer enhancement in a vertical pipe using water/polyisobutylene/nano-SiO2 polynanofluids

Poly-nanofluids (PNFs) are a new type of material that is manufactured by dispersing nanoparticles in dilute polymer solutions. This study looked at heat transfer and drag reduction using a water/polyisobutylene/nano-SiO2 PNF through a vertical copper pipe under conditions of constant heat flux. The effects of ploy-isobutylene (PIB) polymer solution, water/nano-SiO2 nanofluid, and aqueous PNF on heat transfer and drag reduction in a vertical pipe have been studied, separately. All prepared solutions had Reynolds numbers ranging from 7000 to 22000. Nano-SiO2 particles with an average size 20 nm and concentration ranges of 0.1–1 wt.% have been dispersed in aqueous PIB solutions as base fluids with 10–50 ppm concentration of the polymer. The optimal nanoparticle and polymer concentrations for the prepared nanofluid, polymer solution, and PNFs were 0.75 wt.% and 50 ppm, respectively. The friction factor of PNFs at optimal concentrations was 75% less than pure water. Ansys Fluent software was employed to verify the findings of the experiment and simulate the heat transfer and drag reduction phenomena at optimal conditions. Based on the results, the experimental and numerical data were in reasonable agreement, with a deviation of less than 5%.

Mathematical Modelling of Heat Transfer in Pipes with Turbulators in the Laminar Region and in the Transition to Turbulent Flow

The article presents an analysis of mathematical modeling of heat transfer in pipes with turbulators at low Reynolds numbers characteristic of laminar and transient flow modes of heat carriers. The solution of the heat exchange problem for semicircular cross-section flow turbulators based on multi-block computing technologies based on the solution of Reynolds equations closed using the Menter shear stress transfer model and the energy equation (on multi-scale intersecting structured grids) by the factorized finite-volume method is considered. Both local and averaged characteristics of the flow and heat transfer to a pipe with a system of turbulators were obtained, which made it possible to determine the levels of heat exchange intensification for these regime ranges.

Experimental and CFD analysis of wire coil turbulators in biomass boilers

To achieve as complete fuel burnout with as little excess air as possible, small wood log boilers (< 50 kW) use stage combustion. The first stage is often a process similar to downdraft gasification that consequently produces a flue gas laden with particulates. To prevent the build-up of solids and promote heat transfer in pipes of the convective part of these boilers, wire coils are used. The paper presents their in-situ examination together with CFD analysis. The analysis is carried out in a 460 mm long pipe, with a diameter of 82.5 mm, equipped with different wire coils for flue gas temperatures in the range between 300?C and 150?C. The analyzed coils are with and without a conical spring at their free end. The addition of this conical top is economical and should influence the rotation of the core flow. Proper pipe surface cleaning limited the analyzed wire coil designs to the dimensionless pitch, p/d, in the range between 0.36-0.61, dimensionless wire diameter e/d = 0.04-0.1, and pitch to wire diameter ratios p/e = 3.75-14.3, and three different angles (60?, 90?, and 120?) of the conical top. The goals are to find the optimal flue gas velocity for the given operating conditions, pipe, and wire coil dimensions, and to investigate the addition of the conical top on heat transfer enhancement. Several evaluation criteria are used to achieve the goals.

A Computational Analysis Unsteady Incompressible Newtonian Fluid Flow and Heat Transfer in a Cylindrical Pipe Filled with Porous Media Via the Collocation Approach

In this study, the problem of unsteady incompressible flow was analyzed using collocation technique to find the most accurate solution for the velocity and energy distribution of the Newtonian fluid flow. The flow experienced a gradual decrease with a retarded flow and afterwards increases but not a steady increase. It is revealed that a little increase in the Darcy number leads to an increase in the velocity of the fluid flow, indicating that porosity increase enhances the fluid flow. Results further show that increase in the Hartman parameter decreases the fluid velocity which is due to the strength the Lorentz force. Temperature decreases with increase in the Prandtl number and the Brinkman parameter.

Heat transfer of thin flat heat pipes with gradually varied vapor–liquid channels

The heat flow density is constantly increasing due to the growing demand for the integration and compaction of electronic devices. A sintered thin flat heat pipe (TFHP) is a typical device for managing the heat flux of highly integrated electronic circuits. Four different structures of the vapor–liquid flow channel architecture are designed in this work. Heat transfer performance tests of different TFHPs are carried out for different thermal powers. The surface temperature distribution and thermal resistance of the TFHP under different operating conditions are investigated. The experimental results show that the design of the vapor–liquid flow channel significantly impacts the TFHP’s heat transfer performance and that the wedge-shaped wick is better suited to the flow channel. The wedge-shaped wick has the lowest thermal resistance of 0.28 °C/W and the most elevated maximum thermal power of 22 W. The heat dispatch performance of the sintered wick TFHP is improved.

Experimental investigation, CFD and theoretical modeling of two-phase heat transfer in a three-leg multi-channel heat pipe

Muti-channel flat heat pipe is an innovative technology recently used at the rear of photovoltaic cells to absorb and reuse the wasted heat. To better understand the fundamentals of two-phase heat transfer (boiling and condensation) taking place inside multi-channel heat pipes, a unique three-leg heat pipe has been built. This one-of-a-kind heat pipe was used to develop both computational fluid dynamic (CFD) and theoretical models of a multi-channel heat pipe. To simulate the heat pipe operation with ANSYS Fluent, the Volume of Fluid (VOF) approach and Lee model were investigated. Different types of Lee models using user defined function (UDF) were compared and the influence of the condenser's boundary condition, saturation temperature, and mass transfer coefficient on the simulations was studied. For the first time, major limits of the Lee model for the simulation of heat pipes are identified. It is concluded that the available Lee model cannot predict the heat pipe temperature as it shows low physical meaning and can easily be manipulated to adjust the simulation's results. Based on the three-leg heat pipe experimental data, a new multi-channel theoretical model was developed that uses the thermal-electrical resistance analogy to predict the three-leg heat pipe thermal resistance. By selecting the optimum correlations for pool boiling and filmwise condensation, the developed iterative theoretical model was able to predict the three-leg heat pipe thermal resistance with an error of 8.2%.

Study on the heat transfer enhancement of self-excited oscillating pulsating flow by the boundary vortex group

In this work, the self-excited oscillating pulsating circular pipe is the object of study. Based on the flow evolution characteristics of the boundary layer and vortex, the mechanism of enhanced heat transfer by self-excited oscillating pulsating flow is investigated. Moreover, a vital flow structure, the boundary vortex ring (BVR for short), is proposed. The study results show that the vortex evolution within the shear layer inside the self-excited oscillating pulsating chamber has an important influence on the formation of the downstream boundary vortex ring. Both have the same period but different phases. The boundary vortex group formed by the BVR is distributed at intervals in the pipe, and its role in promoting fluid flow increases first and then decreases. At the same time, the strength of the central mainstream area is gradually strengthened. The boundary vortex group's flow state determines the downstream pipe's heat transfer characteristics. The low-velocity zone on both sides determines the position of the heat transfer coefficient enhancement, and the central vorticity determines the amplitude of the enhancement. The boundary vortex group with a complete structure can effectively promote heat transfer, while the boundary vortex group with an incomplete structure can suppress heat transfer. The time-averaged boundary layer thickness increase ratio δ′ and the time-averaged equal diameter circular tube performance evaluation index ηT provide the fundamental indexes for designing and optimizing variable cross section heat transfer circular tubes. Furthermore, the heat transfer coefficient of the tube wall varies synchronously with the thickness of the boundary layer.

Analysis of Performance on Pump Test Equipment Series and Parallel

A boiler is one of the most significant components in a steam power plant system, as steam from the boiler is used to crank a steam turbine, which drives an electric generator. A sootblower is a piece of boiler equipment that cleans the ash and scale that has built up on the pipes. The heat-transfer pipes have been reduced. When soot builds up on the pipes or the riser on the boiler’s walls, heat transfer is impeded, resulting in less heat transfer. The amount of steam produced by the boiler will decrease if the heat transfer is lowered. Heat transfer is small in superheaters, reheaters, economizers, and air heaters, as well as in heat recovery regions like superheaters, reheaters, economizers, and air heaters. as well as the pipes for the superheater, reheater, economizer, and air heater As a result, the main objective of the sootblower is to analyze it so that lost energy in the boiler can be reduced. It also enhances the boiler’s efficiency once the sootblower has been employed.

Thermal Performance of Four-Lobe Swirl Generator and its Transition Parts Under a Different Type of Nanofluids

Due to the importance of promoting the thermal performance of heat exchangers, innovating a new technique is the main goal of many researchers. In swirl flow techniques, keeping the pressure drop at the practical level still requires more and more attention. In the current paper, a numerical study is conducted to explore the impact of a novel lobe swirl generator and its transition parts on forced convective heat transfer and friction factor in a circular pipe subjected to constant heat flux.The swirl mechanism is investigated at the pitch to a diameter of P/D = 8 as the optimum design. The transition part under several parameters of variable beta (β), transition multiplier (n= 0.5) and variable helix (t = 1) have been adopted. The effect of SiO2, Al2O3, and CuO volume concentrations (1 to 5%) in water under various Reynolds numbers (Re) from 15,000 to 35,000 have been carried out. The turbulent swirling flow was modelled using the applicable shear-stress transport (SST) k-ω. The outcome demonstrated an enhancement in heat transfer value ranging from 1.35 to 1.87 with an increased pressure drop value from 1.23 to 1.67. It was also found that using SiO2/water at 5% volume concentration and Re 15000 created the highest thermal performance, with a significant factor of 1.67.

Effect of passive commutation on heat transfer and flow characteristics of non-circular pipes

Based on the need for energy-saving and consumption reduction in industrial applications, the effect of an internal concave structure on a heat exchanger tube with a right-angle trapezoidal cross-section and changing the flow direction on the heat transfer and flow characteristics in the tube was investigated. CFD techniques were used to study the effect of the inner concave structure with 15mm and 30mm center spacing and 1.88mm and 3.75mm radius of curvature on the heat transfer and flow characteristics of air under turbulent flow conditions in the range of Re13349 to 57847, and the heat transfer law was explored in terms of the combined heat transfer performance PEC and the coefficient of variation of the convective heat transfer coefficient and verified to be consistent with the field The effect of the variation of the synergy angle was confirmed. The results show that the PEC of the pipe is enhanced with the increase of the inner concave radius and the decrease of the inner concave center spacing.

Relation between triple phase contact line and vapor groove width for enhancing thermal performance of a loop heat pipe evaporator

• The effects of changing vapor groove width of a porous wick and improving wettability of a LHP evaporator on heat transfer performances were evaluated experimentally and theoretically. • The micro-grooves processed on the heating plate improved heat transfer performances regardless of the vapor grooves width. • The micro-grooves increased heat transfer performances more greatly as the vapor grooves width increased. • Numerical model explained that the length of triple phase contact line has a great influence on the evaporative heat transfer coefficient. In this study, the effects of an increased evaporation area known as the triple-phase contact line (TPCL), of the porous wick and improved evaporator wettability on the loop heat pipe (LHP) heat transfer performance were evaluated experimentally and theoretically. An infrared camera and a microscope were used to observe the thermo-fluid behavior of porous wicks with different vapor grooves widths and evaporator heating plates with different inner wall structures in the experiment. The porous wick's vapor groove widths were 1.0 mm, 0.5 mm, and 0.2 mm. A normal heating plate and a micro-grooved heating plate were used as the evaporator case. As a result, it was clarified that processing the micro-grooves on the heating plate improved the evaporative heat transfer coefficient and maximum heat flux, regardless of the vapor grooves width of the porous wick. Furthermore, it was proposed that both of them increased significantly as the vapor grooves width increased. The thermal-hydraulic numerical model that predicted the heat transfer coefficients for each case was developed. The calculation results showed a significant increase in the heat transfer coefficient as the TPCL appearance rate, which expresses how much the TPCL appears in the micro-grooves, increased, and this increasing tendency was in good agreement with the experimental results. Furthermore, it was proposed that the TPCL appearance rate at a high heat flux was reduced as the vapor grooves width decreased. The results indicate a new promising approach for improving the heat transfer performance of LHP evaporators.

Experimental and numerical study of forced convictive heat transfer in a horizontal circular pipe with varying angles ribs

Experimental and numerical study of forced convictive heat transfer in a horizontal circular pipe with varying angles ribs

Heat transfer in pipes with twisted tapes: CFD simulations and validation

Inserts are placed inside heat exchangers to promote turbulence and maximize the heat transferred. Twisted tapes enhance heat transfer with minimal pressure drop increase for double pipe heat exchangers. Their design typically relied on experimental correlations, but nowadays CFD software is gaining interest. The choice of the turbulent model is of paramount importance and not addressed in the literature. This research aims to compare the combinations of k-ε, k-ω and RSM as well as their different wall treatments available in Ansys Fluent® and literature experimental data. Different twist ratios and Reynolds numbers are tested. Currently, no research is found in literature comparing different CFD methods for this type of units. The main objective of this research is to find the combination of RANS turbulent model and wall treatment that will most accurately reproduce the global values needed (Nusselt number and friction factor) when designing a heat exchanger with twisted tape inserts. Results show that the selection of the wall treatment is far more relevant than the turbulence model. Simulations have less discrepancy between themselves than the empirical correlations. Best performing models were k-ε Standard with ML wall treatment, which provided an average deviation from correlations ranging between 15 and 18%. K-ω SST models also provided accurate performance when estimating friction factor values with 17 to 20% deviation. Results provide clues for choosing a suitable turbulent model and are useful to minimize the error provided by the models.

Research on the Manufacturing Process and Heat Transfer Performance of Ultra-Thin Heat Pipes: A Review.

This paper reviews the manufacturing process of ultra-thin heat pipes and the latest process technologies in detail, focusing on the progress of the shape, structure, and heat transfer mechanism of the wick. The effects of the filling rate and tilt angle on the heat transfer performance of the ultra-thin heat pipe, as well as the material selection of ultra-thin heat pipes, is sorted out, and the surface modification technology is analyzed. Besides, the optimal design based on heat pipes is discussed. Spiral woven mesh wick and multi-size composite wick have significant advantages in the field of ultra-thin heat pipe heat transfer, and comprehensive surface modification technology has huge potential. Finally, an outlook on future scientific research in the field of ultra-thin heat pipes is proposed.

A three-dimensional full-scale model for predicting the performance of deep-buried ground heat exchanger considering groundwater flow

It is critical to precisely determine the performance of deep-buried ground heat exchangers involving different geological layers in engineering projects of the geothermal energy utilization. Compared to the existing approaches solving only conduction between the ground heat exchanger and the surrounding ground based on the two-dimensional model, this paper established a three-dimensional full-scale coaxial ground heat exchanger model containing both aquifer and aquifuge layers involving groundwater effect. The convective heat transfer in pipes was calculated using the empirical correlation of Nusselt number to improve the computation efficiency. The groundwater velocity in the energy governing equation was assumed to be constant and along with the horizontal direction to further simplify the computation. The developed method was applied to a 2800 m and 2600 m depth ground heat exchangers with different geological conditions, and was validated by the field test and published data. The relative errors are less than 6.9%. The thermal influence ranges of the aquifer layer and the aquifuge layer close to aquifer are asymmetric about the circumferential direction. The results demonstrated that the three-dimensional full-scale model is necessary for accurately evaluating the performance of ground heat exchangers when there is groundwater migration.

Thermo-hydraulic performance investigation of heat pipe used annular heat exchanger with densely longitudinal fins

To enhance the heat transfer capacity of the condenser end in the heat pipe heat exchanger, heat transfer and flow characteristics investigations of three densely longitudinal fin-equipped annular heat exchangers have been carried out by using a combined method of experimental testing and numerical simulation. One of the heat exchangers as a baseline is featured by the long straight fins. The other featured folded fins and arc-shaped fins, in which 40 rows of short fins were arranged just like the blade-lattice. The attained results showed that the short fold fins and arc-shaped fins had Nusselt numbers that were 27% and 35% higher than the long straight fins, and had friction factors that were 1088% and 2209% higher than the long straight fins. It indicates that the dense fin arrangement has a relatively limited influence on the wall temperature and overall heat transfer capacity. However, the friction loss is significantly sensitive to the fin arrangement because of the severe flow drag and flow separation induced by the blade-lattice like fins. The thermo-hydraulic performance evaluation suggests that the three densely longitudinal fins are suitable for different application scenarios with different heat transfer and pressure loss requirements. This work serves as a reference for the heat exchanger design in the heat pipe-based thermal power conversion system.

Effect of core configuration on natural convection and heat transfer in heat pipe cooled micro-MSRs

Heat pipes are used to remove the nuclear heat of liquid fuel salt in heat pipe cooled micro molten salt reactors (micro-MSRs). The natural convection and heat transfer of fuel salt are influenced by the core configuration. This paper used the ANSYS to simulate the natural convection in a horizontal reactor core with heat pipes arranged in triangular and concentric circular layouts of 0° and ±30°, which can obtain the temperature distribution and heat transfer characteristics of the reactor core and optimize the core design. Also, the influence of the number and diameter of heat pipes were analyzed in this paper. It shows that the temperature distribution under tilt conditions in heat pipes with a concentric circular layout is more uniform and stable than that with a triangular layout. Moreover, stronger heat transfer capacity and more uniform temperature distribution were obtained with denser heat pipes under the same cross-sectional area. Therefore, a concentric circular layout of heat pipes should be adopted in designing the heat pipe cooled micro-MSRs.

Development and applicability of heat transfer analytical model for coaxial-type deep-buried pipes

Based on the infinite line source model and logarithmic mean temperature difference, an analytical model for solving the heat transfer of coaxial-type deep-buried pipe has been proposed in this investigation. The actual assignment of vertical lithology and temperature values of the ground around the buried pipes could be realized by layered modeling. To validate the analytical model in terms of reliably calculating the real-time and on-way water temperature of buried pipes, the field experiment of buried-pipe heat transfer (at a depth of 2539 m in Xi'an) was carried out, and the numerical model developed based on the experiment was employed for corroboration. Further, by setting combined conditions of multiple factors affecting the heat transfer of buried pipes, the applicability of the analytical model under different model parameter combinations was substantiated, and the main factors affecting the calculation accuracy of the analytical model were analyzed. The results showed that the relative error between the analytical solution and experimental value was less than 5.92% for the buried-pipe heat transfer intensity under the experimental condition. The relative error between the analytical and numerical solutions was less than 6.20% under the combined conditions of multiple factors.

A fast approximate method for simulating thermal pile heat exchangers

Ground source heat pump systems, operating in conjunction with vertical ground heat exchangers, will play a key role in decarbonising heating and cooling of buildings. Design of traditional borehole heat exchangers relies on tools which implement routine analytical relationships between heat transferred and the temperature change in the ground and circulating thermal fluid. However, for novel piled foundations used as ground heat exchangers, there are few such analytical solutions available that are practical for routine implementation. This paper examines the use of a radial approximation to simulate the dynamic thermal behaviour of pile heat-exchangers. Originally developed for small diameter and high aspect ratio borehole heat exchangers, the approach is more challenging for piles since unsteady heat transfer within the pile material is more significant over typical timescales. Nonetheless, we demonstrate that for pile diameters between 300 mm and 1200 mm, generally the error is <1 °C with centrally placed heat transfer pipes or four or more pipes placed near the edge with circumferential spacing less than 550 mm. The radial model is therefore practical for most pile configurations. The strong performance of the model is demonstrated for a year of hypothetical heating and cooling cycles, and also against a field-scale thermal response test.

Modeling of heat transfer and hydraulic resistance in short and long straight round pipes with semicircular turbulators depending on geometric and operating parameters

Objective. The aim of the study was to determine the dependence of the distributions of average integral hydraulic resistances and convective heat transfer in turbulent flow in pipes with small (short channel) and large (long channel) sequences of semicircular periodic protrusions based on numerical solutions of the Reynolds equation systems, closed using Menter's shear stress transfer models, and energy equations on a multi-scale intersecting structured grid.Method. The calculation technique based on finite volume solutions of the Reynolds equation, closed using the Menter shear stress transfer model and the energy equation on a multi-scale intersecting structured grid, made it possible, with acceptable errors, to calculate the average coefficients of hydraulic resistance and heat transfer in a pipe with different quantities annular semicircular ledges.Result. Analytical comparisons were made of the calculated ratios for relative heat transfer and hydraulic resistance on the number of protrusions in channels with different values of relative heights of turbulators h/D, relative steps between turbulators t/D, different values of the Reynolds criteria Re, with other equivalent parameters, which showed that in in which case the qualitative deviations of the above characteristics are carried out monotonously, and in which case they are accompanied by extrema or inflections, and also showed cases of qualitative changes in the calculated characteristics. With the transition from 30 protrusions to 50, as a rule, only quantitative differences occur for the relative parameters of hydraulic resistance and heat transfer, and their qualitative changes are insignificant; with a further transition from 50 protrusions to 100, their quantitative changes also become insignificant.Conclusion. The nature of the patterns of distributions of the mean integral characteristics of flows and heat transfer for a channel with protrusions of various numbers must be taken into account for a short channel. An analysis of the calculated information obtained showed that when moving from a short channel with turbulators to a long one, most often, there is an increase in relative heat transfer and a decrease in relative hydraulic resistance, which justifies the advantage, from the point of view of intensification, of heat transfer by turbulence of the flow of the last channels in relation to the first channels.