Single-phase Flow Heat Transfer Research Articles

Analysis of startup process of small modular reactor with OTSGs

The ACP100 adopts the design of Once-Through steam generators(OTSGs). During the startup process, it involves the complicated heat transfer phenomenon which changes from single phase flow heat transfer to two phase flow heat transfer on the secondary side of OTSGs. In order to avoid the OTSGs operating in the operating interval where flow instability will occur, the coolant temperature of primary side and the feedwater flow rate of secondary side are all strictly required in the two phase flow operating interval of OTSGs. Besides, the regulation and fluctuation of the reactor nuclear power during the startup process influenced the stability of OTSGs operation, which makes the development and the validation startup strategy more important. The OTSGs simulation model of Babcock & Wilcox company design has been developed with APROS, the simulation result shows that it has good accordance with the operation parameters in literature. This model can capture the two phase flow heat transfer phenomenon on the secondary side of OTSGs. On this basis, the ACP100 startup numerical model has been developed also with APROS. The key parameters influenced the OTSGs operation during the whole startup process has been acquired in simulation. The recommendation for improving OTSGs operation stability during ACP100 startup process has been given.

A novel convective heat transfer enhancement method based on precise control of Gyroid-type TPMS lattice structure

Innovative single-phase flow heat transfer enhancement technologies can improve heat dissipation efficiency and reduce the weight and volume of heat dissipation equipment. Triply Periodic Minimal Surfaces (TPMS) hold promise as a outstanding single-phase heat transfer enhancement structure. To further improve the convective heat transfer performance of TPMS, this study independently presents a novel lattice structure control method specifically designed for Gyroid-type TPMS, along with the corresponding mathematical equation. By adjusting the parameter “α” in the equation, the Gyroid lattice geometry can be controlled. This study named “α” as the “Lattice deformation control parameter of Gyroid”. Numerical simulations indicate that increasing α from 0 to 0.25 within the Reynolds number range of 282–2579 can lead to a 19.9–28.9% increase in the average convective heat transfer coefficient (h¯) of the Gyroid, a 0.3%-4.5% increase in the Nusselt number (Nu), and a 13.0%-20.3% decrease in the average friction factor (f¯). The research results suggest that optimizing α is a promising new technology for enhancing convective heat transfer of Gyroid-type TPMS, as it not only improves its heat transfer performance but also reduces its flow resistance. The main reason for the convective heat transfer enhancement of Gyroid-type TPMS with increasing α is the increase in the heat transfer area, while the reduction of flow resistance is mainly due to the formation of the “flow-guiding structure” inside the Gyroid.

Numerical investigation on two-phase oscillating flow and heat transfer enhancement for a cooling channel with ribs

Rib structures can enhance heat transfer in single-phase flows. In order to investigate the influence of semi-circular rib structures on the two-phase oscillating flow and heat transfer characteristics, two-dimensional computational fluid dynamics (CFD) models were established for the cooling channels with rib diameters of 2, 4, 6, and 8 mm. The shear stress transportation (SST) k-ω turbulence model and the Volume of Fluid (VOF) +Level-Set model were used to simulate the flow pattern and predict the two-phase flow interface. A visual experiment was performed to validate the CFD models. The results showed that during the reciprocating motion of the channel, both sides of the rib were impinged and flushed continuously by the cooling oil. Therefore, the heat transfer on the both sides of the rib was enhanced, and the peak value of the heat transfer coefficient (HTC) increased by 100.5% when the rib diameter was 2 mm compared to the channel without ribs. The rib diameter increase had little influence on the peak value of the cycle-average HTC near the rib and the left wall. However, the oil flow velocity on the flat wall and the impingement intensity on the top wall were weakened due to the rib structure, resulting in a reduction in the cycle-average HTCs of the flat wall and the top wall. Furthermore, the larger the rib diameter, the more reduction in the cycle-average HTCs of the flat wall and the top wall. When the rib diameter was 8 mm, the reductions in the cycle-average HTCs on the flat wall and the top wall were the most obvious, reaching 10.7% and 8.3%, respectively. The numerical results in this study can provide design guidance for heat transfer enhancement of cooling channels during reciprocating motions.

The experimental analysis on the influence of Non-closed droplet shape and location on Thermal/Flow performance of pin fin heat sinks

With the rapid development of electronic technology, high-performance chips and integrated circuits have been used more and more widely. Due to the extremely high heat transfer coefficient, the boiling heat transfer of working medium in micro pin fin channel have attracted more and more attention, and how to effectively meet the requirements of efficient heat dissipation in small space is an important issue. This paper focuses on the irregular structure of pin fin array with a non-closed pin shape, who retains the streamline structure as droplet shape and enhances the heat transfer performance. In this paper, a visualized experimental analysis on the influence of non-closed droplet pin shape and location on thermal/flow performance of pin fin heat sinks have been conducted. Through macroscopic performance and microscopic bubble dynamic behavior, the inner influence law of pin shape, stream orientation, location on thermal/flow performance have been studied. Results show that from macroscopic view, the non-closed pin shape of the micro pin fin array has a great influence on the flow and boiling characteristics. With the increase of Reynolds number, the pressure drop undergoes three stages: rapid rise, rapid decline and then rise again. Similarly, the variation tendency of convective heat transfer coefficient also get through such three stages. All of which corresponding to the flow pattern changes, indicating four heat transfer stages: film boiling, transition period, nucleate boiling, and single-phase flow heat transfer. Besides, for the scale as 40 < Re < 200 as well as 400 < Re < 800, the heat transfer appearance of non-closed droplet pin fin is better than that of droplet one. While for different stream orientations, the general performance of stream orientation with the opening part opposite the upstream direction is better. For the different locations of the front, middle and rear region, the bubble growth diameter in the front region is much larger than that in the middle region of the channel, and more growth time is required, with the bubble disappear - appear- reappearance interval as 0.536 s and 6.110 s respectively. While the growth time and waiting time of the front region with stream orientation B is 4.85 s as well as 0.86 s, which is much shorter than that of the front region with stream orientation A. Through the visual observation of the bubble dynamic behavior in the front section of the micro pin fin array, it could be concluded that with the increase of heat flux,the bubble diameter increases with time. Furthermore, the bubble growth/migration diameter increases first and then decreases with the increase of Re. Moreover, the bubble diameter in zone II is larger than that in zone III. Generally, the comprehensive performance of the non-closed droplet with stream orientation B is the best over the droplet as well as stream orientation A pin fin array, when it is at the range as 300 < Re < 800. Under comprehensive consideration, non-closed droplet with stream orientation B design is recommended, under operating conditions with Re > 300.

Multi-objective optimization of single-phase flow heat transfer characteristics in corrugated tubes

In this study, the use of corrugated surfaces as one of the passive heat transfer improvement methods on straight tubes is numerically investigated related to the determination of Nusselt number, friction factor, and performance evaluation criteria. With the same diameter of 5.75 mm and length of 390 mm, 9 corrugated tubes having corrugation pitches of 6, 12 and 18 mm, and depths of 0.6, 0.8 and 1.0 mm are considered for the parametric studies. Water is employed as a operating fluid with Reynolds number values from 480 to 6100 covering different flow regimes. Sensitivity analyses by Genetic Aggregation Response Surface Methodology and multi-objective optimization analyses by NSGA-II are performed in order to maximize heat transfer and minimize pressure drops. It is determined that the thermal-flow augmentation created by the use of corrugated surfaces in laminar flow conditions is quite higher than those in the turbulent region of the smooth tube. According to the obtained optimum parameters and flow conditions, the maximum value of the performance evaluation criteria is 2.48 in comparison to the use of equivalent smooth and corrugated tubes. In addition, Nusselt number and friction factor equations are suggested by using 220 data points within deviation bands of ±10% and ±15%, respectively.

Single-phase flow heat transfer characteristics in helically coiled tube heat exchangers

Abstract The aim of this review is to present a summary of the published papers of the heat transfer and pressure drop characteristics for single-phase flow in helically coiled tubes. The effect of geometrical parameters such as curvature ratio, coil pitch and working conditions such as Reynolds number, Dean number, flow rate and flow arrangement on heat transfer and pressure drop in helically coiled tubes are determined in the light of the experimental, numerical and analytical studies in the literature. Also, the effect of using nanofluids in comparison with conventional fluids, using enhanced surfaces such as corrugated, micro-finned, dimpled with regards to smooth surfaces and wire coil insert usage in helically coiled tubes are discussed. The correlations proposed for determination of Nusselt number and friction factor in helically coiled tubes are presented in detail separately under laminar and turbulent flow regimes. The studies show that usage of helically coiled tube merely gives higher heat transfer rate and pressure drop in comparison to straight one, additionally, the heat transfer performance increases with the inclusion of the combination of other passive heat transfer enhancement methods to helically coiled tube. Moreover, the subject of single-phase flow in helically coiled tubes is ascertained to be worth researching due to the fact that there are limited number of studies and is still no empirical or analytical model/correlation in the case of using enhanced surfaces and wire coil insert. Forthcoming researches on this issue in the near future will be considered as pioneer ones in literature.

INVESTIGATION OF SINGLE-PHASE FLOW CHARACTERISTICS IN A STAGGER PIN-FINS COMPLEX GEOMETRY

The cooling equipment project must use electrical and electronic equipment because of the need to remove the heat generated by this equipment. Investigation; R-113 single-phase flow heat transfer; (50 x 50 mm2) cross-section and (5 mm) height; used in a series of stagger-square micro-pin fins. Inlet temperature of (25 °C); (6) Mass flow rate at this temperature, the recommended range is (0. 0025 -0.01 kg/sec) the inlet and outlet pressures are approximately (1-1.10 bar), and through (25- 225 watts) applied heat. The iterative process is used to obtain the heat flow characteristics, for example; the single-phase heat transfer coefficient is completely laminar flow developing, in this flow, guesses the wall temperature, guess the fluid temperature. The possible mechanism of heat transfer has been discussed.&#x0D;

Experimental study on single-phase convective heat transfer of interlocking double-layer counterflow mini-channel heat sink

This study proposes an interlocking double-layer mini-channel heat sink that can realize counterflow in which the flow direction is opposite in the adjacent channel. The heat sink consists of two-channel layers and a header/plenum structure serving as a pre-flow path for counterflow into the channels. The novelty and significance of the current study are that the counterflow multi-channel heat sink was first experimentally implemented through the design of a new internal flow distribution structure. The test data are obtained from the experimental evaluation of the single-phase flow cooling performance of the heat sink. The heat transfer characteristics of the heat sink are analyzed by separating the change in the single channel heat transfer coefficient increased by the counterflow channel effect. The thermal resistance representing the overall cooling performance of the proposed heat sink shows a significantly small value of 10-4 K-m2/W order, which indicates the heat transfer performance advantage of the new heat sink. The beneficial effect of counterflow is verified by comparing the heat transfer coefficient obtained from the proposed heat sink and the prediction using the previous correlation for unidirectional single-phase flow heat transfer coefficient. The measured heat transfer coefficients are much larger than the predicted values by all kinds of past correlations. The difference between the measured value and the predicted value is much greater at low flow conditions where the temperature gradient increases more significantly with the flow direction. It can be concluded that this indirectly implies the fact that temperature gradient mitigation by counterflow results in an additional heat transfer improvement that is unpredictable in the previous unidirectional flow correlations. A new correlation is proposed to predict the heat transfer coefficient affected by the counterflow. This study is the first to experimentally implement a counterflow heat sink, confirming the distinct advantage of improved cooling performance over conventional heatsinks. In addition, this study is meaningful in that it presents a performance prediction model that can be used in design for the practical application of counterflow heat sinks.

Predictive correlations for heat transfer characteristics of oil-water horizontal pipe flow-an experimental study

This paper presents convective heat transfer characteristics of liquid-liquid horizontal pipe flow. Experiments are carried out in a stainless-steel pipe of diameter 1.59 cm with L/D ratio of 377. Three different oils with varying properties (viscosity: 630 mPa-s, 202 mPa-s and 1.95 mPa-s and density: 919 kg/m3, 901 kg/m3 and 790 kg/m3 respectively) are employed as oil phase and the other fluid phase being water. The experiments are conducted for four oil-water flow patterns-stratified flow, stratified flow with droplets at the interface, dispersed oil-in-water and dispersed water-in-oil with fluid fractions ranging 0 to 1 at different fluid velocities. A constant temperature heat supply, using jacketed hot water flowing over the test pipe, is maintained. The analysis of heat transfer experiments indicates that the heat transfer process in liquid-liquid flow depends on the same dimensionless terms, the Reynolds number and the Prandtl number, that signifies single-phase flow heat transfer. Accordingly, it is found that the established and existing single-phase heat transfer correlations, modified according to flow regime, flow pattern and fluid flow and thermal properties, are also applicable for liquid-liquid flow. The heat transfer in liquid-liquid flow found to be influenced by the fluid fraction. Effectively, for stratified flow, the heat transfer in the liquid-liquid flow is the sum of heat transfer of the individual fluid phases. However, for dispersed flow, the presence of additional fluid phase is incorporated by employing the effective Reynolds number and effective Prandtl number. Using this methodology, more than 85% of stratified flow and 92% of dispersed flow heat transfer characteristics are predicted within ±20% of experimental data.

Single phase flow heat transfer characteristics of quad-channel twisted tape inserts in tubes

Heat transfer and pressure drop of turbulent fluid flow were studied numerically and experimentally in a quad-channel with twisted tapes placed in a circular tube under uniform heat flux boundary condition. All the tests were conducted with water as the working fluid where the turbulent flow range of Reynolds numbers were maintained at 4250 to 11000. Quad-channel twisted tapes (QCTT) were manufactured by 3D printer with the material PLA, the lengths of 50 mm, 100 mm, 200 mm with the twist ratio of 4.48. The tapes were identified with their tape/pipe length ratios (TPR) of 0.025, 0.05 and 0.1. Validation of the experimental data was performed by the comparison of the experimental results with the data from the well-known empirical correlations. Alteration of the friction factors and Nusselt numbers with the Reynolds numbers are presented in this paper. The results showed that the Nusselt number and the friction factor increased with the increasing of the length of QCTTs. On the other hand, the performance evaluation criteria (PEC) should be declining with the increase of the lengths of the tapes. The evaluated temperature distributions inside the tested tubes with the inserts were plotted in order to investigate the observed data. Based on the obtained experimental data, the empirical correlations for the Nusselt number within the deviation of ±2% and the friction factor within the deviation of ±5% were developed for the practical usage.

Numerical Simulation of Circumferential Non-Uniform Heat Transfer of Single-Phase Flow in Helical Pipes

Numerical Simulation of Circumferential Non-Uniform Heat Transfer of Single-Phase Flow in Helical Pipes

An experimental investigation on forced convection heat transfer of single-phase flow in a channel with different arrangements of porous media

Nowadays, heat transfer in porous zone plays an important role in many industrial and modern applications. For this reason, issues related to porous media are important in the design and analysis of heat exchangers. In this study, a single-phase flow of air in channel having circle cross-section with different arrangements of porous media is experimentally studied. Changes in hydrodynamic parameters, improvement of heat transfer by porous media in the channel as well as pressure drop resulted from porous media are considered. Results from these experiments show that presence of porous media leads that the thermal flux applied to walls of channel be transferred into fluid due to creating a uniform space and high conductivity of porous media. Also, the mean temperature of the fluid increases and this leads to decrease temperature difference between channel wall and the mean temperature of the fluid. Because of the heat transfer coefficient has an inverse relationship with the temperature difference between the walls of the channel and the mean temperature of the fluid, the heat transfer coefficient increases. For investigation the heat transfers with pressure drop simultaneously, heat transfer performance ratio and heat transfer enhancement ratio are defined. The results of this study show that fully filled channel of porous media has the best heat transfer enhancement (in both laminar and turbulent flows). In turbulent flow, channel with annulus shape porous zones (the porous zone inserted adjacent to wall) has the best thermal performance that means has the large value of heat transfer with low pressure drop.

Experimental and numerical study about local heat transfer in a microchannel with a pin fin

Local single-phase flow heat transfer downstream a single pin fin in a microchannel was experimentally and numerically studied. Three distinct flow regimes, depending on the Reynolds number, were characterized, namely: laminar flow with steady wake, laminar flow with unsteady wake, and turbulent flow. Local temperature measurements with high spatial resolution were obtained by incorporating an array of micro resistance temperature detectors (RTDs) (∼55 µm × 55 µm) on the internal microchannel surface. Local surface temperatures were related to the flow structures under different flow regimes. An enhanced local heat transfer coefficient at the trailing edge of the wake region downstream the pillar was observed. It is believed to be a result of vortex shedding and large-scale flow mixing triggered by flow instability at high Reynolds number. The numerical model enabled a full conduction/convection conjugate analysis of the entire system including heat conduction within the solid substrates and heat losses to the surrounding environment. Local heat transfer coefficient downstream the pin fin at each Reynolds number was obtained.

Hydrodynamics and heat transfer in single-phase fluid flows in artificially rough pipes

Studies on hydraulic resistance and heat transfer in pipes with artificial roughness of different profiles are reviewed; artificially rough surfaces, flow regimes, boundaries of flow regimes, and equations for calculation of the coefficients of hydraulic resistance and heat transfer during single-phase flow in rough pipes are classified. It has been ascertained that many available equations for calculation of hydraulic resistance and heat transfer for single-phase flows in artificially rough channels, however, do not allow these data to be always used, because of the many types and forms of artificial roughness. The generalized equations presented in this review mainly relate to flows in channels with sand-grain roughness. The absence of studies of the hydraulic resistance and heat transfer in single-phase flows in rough channels with flow swirling is noted, which is an effective way for intensification of heat transfer in practical applications.

Single phase flow heat transfer and pressure drop measurements in doubly enhanced tubes

Global in-tube flow heat transfer and pressure drop measurements were conducted with Water (Pr = 4.42) and Ethylene Glycol (Pr = 80.5–135.7), in the laminar-transition-turbulent flow regime (Re = 400–39,750) in double pipe heat exchangers fabricated from doubly enhanced tubes. The internal fin height to effective diameter ratio ef,i/deff varied between 0.0289 and 0.0314. The internal groove helix angles varied between 35 and 40°, while the internal fin pitch to height p/ef,i ratios varied between 3.4 and 5.36. The external fin density was 40 fins per inch (25.4 mm). In comparison to a smooth tube, tube-side (internal) heat transfer enhancements (hdeff,enhanced/hdeff,smooth) of up to 6% were measured with Ethylene Glycol in the laminar regime, while tube-side enhancement of up to 34% was measured with water in the turbulent flow regime. The overall heat transfer enhancement (UAeff)enhanced/(UAeff)smooth based on the overall heat transfer coefficients was measured as 116% with water in the turbulent flow regime. Transition to fully developed rough pipe flow was detected in the enhanced tubes after a critical Reynolds number and the corresponding Prandtl number exponent was estimated to be 0.47. At constant pumping power, the maximum tube-side heat transfer enhancement was 6% with Ethylene Glycol in the laminar regime, and 18% with water in the turbulent regime. On a constant heat duty basis, the maximum reduction in pumping power was 23% with Ethylene Glycol in the laminar regime and 54% with water in the turbulent regime. Although the inner (tube-side) heat transfer enhancement is lower than that measured in conventional micro-fin tubes (inner grooves only), the overall heat transfer enhancement suggests that these tubes will be useful for designing heat exchangers deploying fluids of similar thermal conductivity in the tube and annulus. Typical applications include, but are not limited to, design of marine oil coolers, lubricating oil coolers, and sub-cooled sections of condensers.

Convective heat transfer of MWCNT / HT-B Oil nanofluid inside micro-fin helical tubes under uniform wall temperature condition

Experiments are performed to investigate the single-phase flow heat transfer augmentation of MWCNT/HT-B Oil in both smooth and micro-fin helical tubes with constant wall temperature. The tests in laminar regime were carried out in helical tubes with three curvature ratios of 2R/d=22.1, 26.3 and 30.4. Flow Reynolds number varied from 170 to 1800 resulting in laminar flow regime. The effect of some parameters such as the nanoparticles concentration, the dimensionless curvature radius (2R/d) and the Reynolds number on heat transfer was investigated for the laminar flow regime. The weight fraction of nanoparticles in base fluid was less than 0.4%. Within the applied range of Reynolds number, results indicated that for smooth helical tube the addition of nanoparticles to the base fluid enhanced heat transfer remarkably. However, compared to the smooth helical tube, the average heat transfer augmentation ratio for finned tube was small and about 17%. Also, by increasing the weight fraction of nanoparticles in micro-fin helical tubes, no substantial changes were observed in the rate of heat transfer enhancement.

Pressure Drop and Heat Transfer Characteristics of MWCNT/Heat Transfer Oil Nanofluid Flow inside Microfinned Helical Tubes with Constant Wall Temperature

Experiments are performed to investigate the single-phase flow heat transfer augmentation of MWCNT/HT-B oil in both smooth and microfinned helical tubes with constant wall temperature. The tests in laminar regime were carried out in helical tubes with three curvature ratios of 2R/d=25, 30 and 35. Flow Reynolds number varied from 170 to 1800 resulting in laminar flow regime. The effect of some parameters such as the nanoparticles concentration, the dimensionless curvature radius (2R/d) and the Reynolds number on heat transfer was investigated for the laminar flow regime. The weight fraction of nanoparticles in base fluid was less than 0.4%. within the applied range of Reynolds number; results indicated that for smooth helical tube the addition of nanoparticles to the base fluid enhanced heat transfer remarkably. However, compared to the smooth helical tube, the average heat transfer augmentation ratio due to nanoparticle addition for finned tube was small, about 17%. Also, by increasing the weight fraction of nanoparticles in microfinned helical tubes, no substantial changes were observed in the rate of heat transfer enhancement. For the pressure drop, the results show that the pressure drop of nanofluids was slightly higher than the base fluid and increase as the volume concentrations go up.

Applicability of Minichannel Cooling Fins to the Next Generation Power Devices as a Single-Phase-Flow Heat Transfer Device

The heat transfer characteristics of copper minichannel-finned heat sinks are experimentally investigated in order to clarify their applicability as a single-phase flow cooling device for next generation power devices. The influence of the channel width and the fin thickness are evaluated in detail. In particular, the minichannel-finned heat sink having a channel width of 0.3 mm and a fin thickness of 1.0 mm achieves a heat transfer performance of approximately 70,000~9,5000 W/m2K at 300 W/cm2 even in a single-phase flow heat transfer regime. Simple estimation proves that single-phase-flow heat transfer with the minichannel-fins heat sink is able to sufficiently cool future power devices under the allowable pumping power conditions.

0608 偏平ミニチャンネル内流動沸騰熱伝達と二相流に関する研究(第2報)(S45-2 原子炉システムおよびその要素技術(2),S45 原子炉システムおよびその要素技術)

Flow and Heat transfer characteristics of the boiling two-phase flow of water in flat mini-rectangular-channels were examined. The cross-sections were in a range of 0.22mm×10mm〜0.65mm×10mm The length of the flow channel was 240mm including 50mm heating region. When the flow channel gap was relatively large; 0.65mm-0.37mm, the pressure drop of the single-phase water flow was well expressed with the correlations for the usual size over the laminar flow and the turbulent flow region. However, when the flow channel gap was narrow; 0.22mm, the measured pressure drop results showed the laminar flow trend in the experimental range until the Reynolds number=4,000. The single phase flow heat transfer was well expressed with the correlations for the usual size over the laminar flow and the turbulent flow region. However, when the flow channel gap was narrow; 0.22mm, the measured heat transfer coefficients followed the trend of the turbulent flow in the present experimental range. The nucleate boiling was dominant in the boiling heat transfer region. The critical heat flux was much lower than that of the pool nucleate boiling.

Friction losses and heat transfer of single-phase flow in a mini-channel

Experimental frictional pressure drop and heat transfer during single phase flow in a vertical mini-channel have been studied with the aim of determining the validity of classical correlations available for conventional size channels. A 1 mm square channel etched in a 420 mm long test section of aluminum has been investigated. The Reynolds number has been varied from 310 to 7780 in order to cover the laminar regime as well as the beginning of the turbulent regime. The heat flux supplied to the fluid varies from 1 kW/m 2 to 8 kW/m 2. Experimental frictional pressure drop measurements show that classical correlations accurately apply. Temperature measurements along the channel show that the temperature profile is drastically different from the expected linear behaviour owing to an important longitudinal heat flux in the channel wall. This heat flux mal-distribution which has been recently discussed in the literature is clearly shown and studied in more details by a numerical simulation of the experiment. This numerical work has allowed to make a correction on temperature measurements. Once corrected, the heat transfer measurements are in fair agreement with the classical literature results.