Heat Transfer Coefficient Of Flow Research Articles

Performance investigation of a concentric double tube heat exchanger using twisted tape inserts and nanofluid

A horizontal double-tube counter-flow heat exchanger with and without twisted tape inserts (twist ratio of 3.2, 4, and 6) has been investigated experimentally using TiO2-H2O nanofluid. In this study, the heat transfer coefficient and friction factor of turbulent flow of TiO2-H2O nanofluid have been determined for Reynolds’ number varying from 5,000 to 25,000. Convective heat transfer coefficient for TiO2-H2O nanofluid (0.05% by vol.) is found to be higher than base fluid (4–6%). Also, an increase in the heat transfer coefficients up to 6%, 10.9%, 17.4%, and 23.4% are observed numerically for the 0.05%, 1%, 2%, and 3% volume concertation of nanoparticles of TiO2. On the other hand, when TiO2-H2O nanofluid (0.05% by vol.) is investigated using twisted tape inserts of twist ratio 3.2, the heat transfer coefficient is found to be increasing by 45%. The variation of the heat transfer coefficient for different types of nanofluids such as; TiO2-H2O, Al2O3-H2O, and CuO-H2O with 1% concentration of nanoparticles (by vol.) has also been studied at different Reynolds’ numbers. The simulated results show no significant effect of the size (30 nm and 50 nm) of nanoparticles (TiO2) on the heat transfer coefficient values of TiO2-H2O nanofluid at 0.05% volume concentration.

Steady state modeling of steam condensate cooler

Mathematical models for steam condensate cooler were developed. The models were deduced by applying the principle of conservation of energy and yielded an ordinary differential equation, which were solved by using MatLab ODE45 solver and validated using industrial data of a fertilizer company. The result gives minimum percentage absolute error or deviation between model predictions and industrial plant of 0.09% and 0.10% respectively for hot and cold fluid outlet temperature. These shows that the developed model predicted the fluid outlet temperature of the steam condensate cooler closely and the models were used to study the effects of process parameters such as fluid inlet flow rate and heat transfer coefficient on the performance of the steam condensate cooler.

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.

An empirical investigation on flow pattern, heat transfer, and pressure drop during flow boiling of R1234yf in an inclined plain tube

In the present study, the flow pattern, boiling heat transfer, and pressure drop of R1234yf are experimentally studied inside a plain tube with an inner diameter of 8.3 mm, the outer diameter of 9.52 mm, and the length of 670 mm, in seven different inclination angles from −90° (downward vertical flow) to +90° (upward vertical flow). The experiments are conducted at four mass velocities of 80, 160, 240, and 320 kg m−2 s−1, mean vapor quality range of 0.1–0.77, saturation temperature of 31 °C, and four heat fluxes of 4.5, 9.0, 13.5, and 18.0 kW m−2. The effects of different parameters on the heat transfer coefficient and frictional pressure drop have been investigated. Based on the results, the tube inclination angle has a significant effect on the flow patterns and heat transfer coefficient, which is more prominent at low vapor qualities and low mass velocities. For all mass velocities, the highest and lowest heat transfer coefficients are attained in the tubes with inclination angles of +90° (vertical upward flow) and −90° (vertical downward flow), respectively. The frictional pressure drop is considerably affected by the tube inclination angle, and the effect is more noticeable at high vapor qualities. At low vapor quality regions, the heat flux strongly affects the heat transfer coefficient while it has a negligible effect on the frictional pressure drop. Finally, the experimental results are compared to the existing correlations, and modified correlations are proposed to predict the heat transfer coefficient and the frictional pressure gradient of R1234yf during flow boiling inside an inclined plain tube.

Relationship Between Pressure Drop and Heat Transfer of Fully Developed Flow in Smooth Horizontal Circular Tubes and Spiral-Coiled Tubes in the Laminar Flow Regime

Abstract Studies on isothermal steady-state frictional pressure drop for flow of petroleum base oils SN70, SN150, diesel, and water are carried out in spiral coils with diameter to length ratio, 0.00042, 0.00047, 0.00073, 0.00164, 0.00189, 0.003, and 0.0037. An attempt is made to correlate friction factors with a better and more appropriate dimensionless group for flow of Newtonian fluids through spiral-coiled tubes. An innovative approach of correlating heat transfer data with the newly established dimensionless group is presented. Heat transfer experiments are performed for spiral coils with diameter to length ratio 0.000474, 0.00042, 0.001896, 0.00198, 0.000942, and 0.00164 in laminar flow regime. Suitable correlations for friction factors and Nusselt numbers are proposed. Relationship between pressure drop and heat transfer is studied. The incapability of the conventional analogy equations to estimate the heat and momentum transfer coefficients for laminar flow through straight or curved tubes is explained based on the viscous and form drag existing in straight and curved pipe flow. The limitations of the existing analogy equations are examined critically. A new general analogy equation is derived for laminar flow through spiral and straight tubes considering the influencing geometrical parameters of the tube.

The Effect of Mass Flow Rate and Heat Flux on Vertical Two-Phase Flow Regimes in a Small Diameter Tube

In recent years, there has been a rising concentration in investigating and researching the boiling of micro channel flow; since they afford high thermal effectiveness, small size, and low weight. In this paper, the boiling heat transfer was experimentally examined using water as the working fluid in small diameter tubes. Experiments for the flow model were performed using the same Pyrex glass tube test facility. The experiments of heat transfer were carried out using an internal diameter copper tube (10.922 mm). The range of other parameters was varied: mass flow rate (0.008–0.0214kg/s); heat flux (17351–80529W/m2); it has been found that the average coefficient of heat transfer depends on the form of flow pattern. The average heat transfer coefficient increases by about 37% when the flow pattern varied from slug flow to churn flow at a constant mass flow rate of 0.008kg/s. Besides, the heat transfer coefficient (h) in the two-phase flow, is 39%, which is more than that for single-phase flow, when the mass flow rate is 0.0214kg/s, and heat flux) increases from 17351W/m2 to 49105W/m2. Also, when mass flow rate rises from (0.008kg/s) to (0.0166kg/s), the pressure drop increases by about (15%) and increases by about (5%) when the mass flow rate rises from (0.0166kg/s) to (0.0214kg/s). The main regime of flow was a slug, churn, bubbly, dispersed bubbly, and confined bubbly flow.

Research on Flow and Condensation Heat Transfer Coefficient of multi-channel cylinder dryer in U-shaped Section

The cylinder dryer is the most energy-consuming part of the papermaking drying section. Whether the drying cylinder can effectively drain the drying cylinder affects the drying efficiency of the drying cylinder. The design of the multi-channel drying cylinder effectively improves the problem of the difficulty of the water accumulation discharge. In order to obtain a channel cross-sectional shape with better drainage and better heat transfer, two channels with different cross-sectional shapes are selected to study the flow and heat transfer of steam in this experiment. The changes of the channel heat transfer coefficient under different working conditions are studied and compared. The result show that the U-shaped channel heat transfer effect is better than that of other shape channels in the multi-channel dryer.

Computational Fluid Dynamics Analysis of Flow Patterns, Pressure Drop, and Heat Transfer Coefficient in Staggered and Inline Shell-Tube Heat Exchangers

In this numerical study, the heat transfer performance of shell-and-tube heat exchangers (STHXs) has been compared for two different tube arrangements. STHX having 21 and 24 tubes arranged in the inline and staggered grid has been considered for heat transfer analysis. Shell-and-tube heat exchanger with staggered grid arrangement has been observed to provide lesser thermal stratification as compared to the inline arrangement. Further, the study of variation in the mass flow rate of shell-side fluid having constant tube-side flow rate has been conducted for staggered grid structure STHX. The mass flow rate for the shell side has been varied from 0.1 kg/s to 0.5 kg/s, respectively, keeping the tube-side mass flow rate as constant at 0.25 kg/s. The influence of bulk mass-influx transfer rate on heat transfer efficiency, effectiveness, and pressure drop of shell-tube heat exchangers has been analyzed. CFD results were compared with analytical solutions, and it shows a good agreement between them. It has been observed that pressure drop is minimum for the flow rate of 0.1 kg/s, and outlet temperatures at the shell side and tube side have been predicted to be 40.94°C and 63.63°C, respectively.

Thermal-mechanical characteristics of stationary and pulsating gas-flows in a gas-dynamic system: In relation the exhaust system of an engine

It is a relevant objective in thermal physics and in building reciprocating internal combustion engines (RICE) to obtain new information about the thermal-mechanical characteristics of both stationary and pulsating gas-flows in a complex gas-dynamic system. The article discusses the physical features of the gas dynamics and heat transfer of flows along the length of a gas-dynamic system typical for RICE exhaust systems. Both an experimental set-up and experimental techniques are described. An indirect method for determining the local heat transfer coefficient of gas-flows in pipe-lines with a constant temperature hot-wire anemometer is proposed. The regularities of changes in the instantaneous values of the flow rate and the local heat transfer coefficient in time for stationary and pulsating gas-flows in different elements of the gas-dynamic system are obtained. The regularities of the change in the turbulence number of stationary and pulsating gas-flows along the length of reciprocating internal combustion engines gas-dynamic systems are established (it is shown that the turbulence number for a pulsating gas-flow is 1.3-2.1 times higher than for a stationary flow). The regularities of changes in the heat transfer coefficient along the length of the engine?s gas-dynamic system for stationary and pulsating gas-flows were identified (it was established that the heat transfer coefficient for a stationary flow is 1.05-1.4 times higher than for a pulsating flow). Empirical equations are obtained to determine the turbulence number and heat transfer coefficient along the length of the gas-dynamic system.

Determining design criteria to reduce power and cost in filling high-pressure oxygen cylinders directly from cryogenic air separation plants

Cryogenic air separation plants produce pressurized oxygen gas at 150 bar and 99.8% purity to fill oxygen cylinders directly. It is either produced by compression in oxygen compressor (external compression) or pumping and vaporizing liquid oxygen in main heat exchanger by incoming air (internal compression). Small and medium-scale plants differ in the types of main heat exchanger, compression and expansion devices owing to limitations of market availability. Levelized cost of production of oxygen gas is about 9% less in external compression, though internal compression process is far more fire-safe. Design and operating parameters applicable for internal compression plants supplying oxygen at 40 bar cannot be extended to 150 bar plants due to the differences of fluid properties between super-critical and sub-critical oxygen. UA (surface area times overall heat transfer coefficient) of main heat exchangers, flow and pressure of incoming air are optimized for minimum capital and operating costs. If the chosen flow and pressures deviate substantially from the optimum points, size of main heat exchanger may even increase five-fold. Ideally, 27–29% of total air intake should be compressed between 110 and 100 bar in a medium-scale internal compression plant to keep levelized cost of production at the minimum.

Influence of porous inserts on flow boiling heat transfer in horizontal tubes

In this paper we want to assess the mechanisms by which metal porous inserts influence flow boiling heat transfer in horizontal tubes. For this purpose, measurement data of the local and circumferentially averaged heat transfer coefficient of CO2 flow boiling in horizontal tubes with two different porous inserts are presented. As inserts, different sponges (open-cell network structures) and a wire matrix element are chosen and compared with each other. Different operating conditions were investigated. The mass flux was varied in a range from 25 kg m−2 s−1 to 190 kg m−2 s−1 and the vapor quality from 10% to 100%. Saturation pressures of 12 bar, 19 bar and 26.5 bar and average heat fluxes up to 65 kW m−2 were realized. By comparing the local heat transfer coefficient with empty tube data, wetting and convective heat transfer can be identified as the main influencing factors. Thus, we can obtain guidelines for the development of a model to describe the heat transfer coefficient of two-phase flow in porous inserts. A model derived in this way describes the measurement data of flow boiling of CO2 in horizontal tubes with inserts with a high degree of accuracy. The model is based on established sub-models without any additional fitting parameter. More than 90% of all measured data are predicted with less than 30% deviation

Heat transfer, pressure drop and flow patterns of flow boiling on heterogeneous wetting surface in a vertical narrow microchannel

The micro-structured surfaces have a significant impact on the flow patterns and heat transfer mechanisms during the flow boiling process. As illustrated by previous studies, there is a trade-off between a hydrophobic and a hydrophilic surface. To examine the effect of heterogeneous wetting surfaces on the flow boiling process, an experimental investigation of flow boiling in a rectangular vertical narrow microchannel with the heterogeneous wetting surfaces and original silicon surface was conducted with deionized water as the working fluid. Hydrophobic patterns perpendicular (HC) and parallel (HP) to the flow direction are compared. The subcooled boiling curves, heat transfer coefficient, and pressure drop were discussed with the variation of heat flux and mass flux, the trends of which were analyzed along with the flow patterns. The heat transfer coefficient of flow boiling on heterogeneous wetting surface HC was enhanced for up to 39.55% compared to a silicon surface with less pressure drop. During the boiling process, the dominant heat transfer mechanism was nucleate boiling, with numerous nucleate sites between the hydrophilic/hydrophobic stripes. The easily formed bubble can be easily detached due to the supply of liquid from the hydrophilic regions nearby. With the increasing wall heat flux, the boiling heat transfer coefficient of the heterogeneous wetting surface HP is gradually lower than HC due to hydrophobic stripes parallel to the flow direction cannot restrict the bubbles from expanding in the axial direction.

Modeling, multi-objective optimization and comparison of fire and water tube heat recovery steam generators for gas engine cogeneration plants

An innovative modeling and optimizing of fire and water tube heat recovery steam generators (HRSG) for gas engine cogeneration plant are performed here. In modeling section, the equations of ɛ-NTU, LMTD and heat transfer coefficients for one-phase flow and two-phase flow are organized to form a nonlinear system of equations. Furthermore, in the next step, two pairs of objective functions (annual expenses—exergy destruction rate and annual expenses—thermal effectiveness) are selected for multi-objective optimization of HRSG by the use of genetic algorithm for one, two and three MW gas engine cogeneration plants. Results for a 2 MW gas engine (as an example) show that the fire tube HRSG total expenses are 50% lower than that for water tube HRSG. In this situation, for water and fire tube boilers, the effectiveness and cost are 0.9, 40,000 ($/year) and 0.9, 20,000 ($/year), respectively. Furthermore, the exergy destruction rates are close and equal to 1373.45 kW and 1366.2 kW for water tube and fire tube boilers, respectively. Moreover, for each gas engine, six equations with thirty constant coefficients are obtained to explain the behavior of HRSG outlet exhaust gas temperature, pinch temperature difference, steam generation mass flow rate, working pressure, thermal effectiveness and exergy destruction rate at partial load.

Experimental study of supercritical CO2 in a vertical adaptive flow path heat exchanger

The density variation of supercritical carbon dioxide exerts significant effects on heat transfer and the adaptive flow path is verified to be effective in reducing pressure loss. Meanwhile, the effects differ from flow directions of supercritical carbon dioxide. Previous studies focused on heat transfer in vertical tubes rather than vertical heat transfer exchangers. In this paper, an experimental study of supercritical carbon dioxide in a vertical adaptive flow path heat exchanger is conducted to investigate the heat transfer and flow characteristics. The pressure of cold side varies from 14.2 MPa to 16.7 MPa and that of hot side varies from 8 MPa to 10 MPa. The inlet temperature of cold side is 328 K and that of hot side varies from 398 K to 418 K. When mass flow rate ratio increases, the minimum heat transfer effectiveness occurs at 0.6 and maximum overall heat transfer coefficient occurs at 0.65. Due to the effect of flow direction, the overall heat transfer coefficient of horizontal flow is approximately 9% higher than that of upward flow for cold side and 6% lower than that of downward flow for cold side. Hence, the downward flow (cold side) is suggested for installation of heat exchanger in Brayton cycle.

Experimental and Numerical Investigation on Flow Boiling in a Small Semi-circular Channel of Plate Once-Through Steam Generator

The heat transfer coefficients of flow boiling in a small semi-circular channel of plate once-through steam generator were tested by experimental method in this paper. Based on the experimental data, the numerical simulation of flow boiling in the semi-circular channel was carried out using STAR-CCM + software. The numerical models are the homogenous flow model, the Rohsenow model and the two-fluid model. The heat transfer coefficients of homogenous flow model are lower than the experimental results. The heat transfer coefficients of Rohsenow model and experiment are in good agreement.

Испытание компоновки коррекционного контура с пластинчатым теплообменником

Pulse enhanced heat transfer technology is introduced, and a plate heat exchanger is designed. A pulsating valve is installed at the outlet of the heat exchanger to pulsate the heat medium. Pulsating and non-pulsating heat transfer tests are carried out on the same heat exchanger. On the basis of experiments, the effective temperature difference, heat flow and convective heat transfer coefficient of the heat exchanger at different pulse frequencies are analyzed by combining the theory of pulse enhanced heat transfer technology, heat transfer capacity, heat flow and convective heat transfer coefficient. Find the relationship between pulsation frequency of heat transfer effect of heat exchanger. The experimental results show that the heat exchanger has high heat transfer efficiency under the experimental conditions when there is pulsation.

Calculation of temperature and thermoelastic stresses in backups with collars of the unit of combined continuous casting and deformation in steel billets production. Report 1

The article describes the main loads affecting shaped backups of the unit of combined process of continuous casting and deformation in billets production. Importance of determining the temperature fields and thermoelastic stresses in shaped backups with collars is provided at formation of several billets, at slab compression and at idle during water cooling of backups. The authors describe strength and thermophysical properties of steel from which the backups are made. Geometry of backups with collars used for obtaining billets of three different shapes in one pass is shown. Initial data of the temperature field calculation are given for backups with collars of the combined unit. Temperature boundary conditions are considered for calculation of temperature fields of backups with collars. Boundary conditions determining temperature of such backups are described and values of the heat flow and effective heat transfer coefficient are given. The results of calculation of temperature fields are performed in four sections and are given for typical lines and points located on contact surface of backups with collars and in contact layer at depth of 5 mm from the working surface. The sizes of finite elements grid which is used at calculation of temperature field of backups with collars are provided. Temperature field of backups with collars is determined on the basis of solution of unsteady thermal conductivity equation corresponding initial and boundary conditions. Values and regularities of temperature distribution in bases and in tops of the middle and extreme edges of the shaped backups are presented during slab compression and at idle when obtaining billets of three shapes in one pass at the unit of combined continuous casting and deformation.

Estimation of Heat Transfer Coefficient of Surface Flow Induced by DBD Plasma Actuator

Estimation of Heat Transfer Coefficient of Surface Flow Induced by DBD Plasma Actuator

Experimental investigation on heat transfer characteristics of two-phase flow boiling in offset strip fin channels of plate-fin heat exchangers

To optimize the plate-fin heat exchangers in the cryogenic processing system, the heat transfer characteristics of two-phase flow boiling for high-efficiency and pressure-resistant offset strip fins in plate-fin heat exchangers were investigated experimentally. The experimental conditions cover heat fluxes of 0.7–5.5 kW/m2, mass fluxes of 64–128 kg/(m2·s) and vapor qualities of 0.1–1.0. The research results show that, as the vapor quality increases, the heat transfer coefficient initially increases and then decreases, representing a maximum at vapor quality of 0.75–0.85; the criticalconditions of the bubbly-annular transformation and the annular-mist transformation are corresponding to the void fractions of 0.92 and 0.985, respectively. A new correlation of two-phase heat transfer coefficient for flow boiling in offset strip fin channels was developed based on the experimental data in the present study and in the literature, and the prediction deviation is within ±25%.

Calculation of Temperature and Thermoelastic Stresses in the Backups with Unit Collars of Combined Continuous Casting and Deformation during Steel Billet Production. Report 1

The article describes the main loads affecting shaped backups of the combined process unit of continuous casting and deformation during billet production. The importance of determining the temperature fields and thermoelastic stresses in shaped backups with collars is provided during the formation of several billets, at slab compression, as well as during idling water cooling of backups. The authors describe strength and thermophysical properties of steel from which the backups are made. Geometry of backups with collars used for obtaining billets of three different shapes in one pass is shown. Initial data of the temperature field calculation are given for backups with collars of the combined unit. Temperature boundary conditions are considered for the temperature field calculation of backups with collars. Boundary conditions determining temperature of such backups are described and the values of the heat flow and effective heat transfer coefficient are given. The calculation results of temperature fields are performed in four sections and are given for typical lines and points located on the contact surface of backups with collars and in contact layer at 5-mm depth from the working surface. The sizes of the finite element grid, which is used for the temperature field calculation of backups with collars, are provided. The temperature field of backups with collars is determined based on the solution regarding the unsteady thermal conductivity equation corresponding to initial and boundary conditions. When obtaining billets of three shapes in one pass at the unit of combined continuous casting and deformation, values and regularities of temperature distribution in the bases and tops of the middle and extreme edges of the shaped backups are presented during slab compression and at idle.