Liquid Heat Transfer Research Articles

Thermoviscous liquid conjugate heat exchange simulation in cylindrical channel

The article is concerned with the flow of a thermoviscous fluid in a cylindrical channel for various types of viscosity functions in the joint solution of the problem of conjugate heat exchange between the channel and the surrounding material. A model of a cylindrical channel with a thermoviscous liquid flowing inside at a given velocity and viscosity is considered. The methodology of the process consists in applying a system of model equations that describes the dynamics of thermoviscous fluid flow processes based on the laws of phase energy conservation, the continuity equation, the Navier-Stokes momentum conservation equation taking into account conjugate heat transfer and the heat transfer equation for a solid. Numerical implementation of model representations was carried out using the Comsol Multiphysics digital package. Velocity and temperature profiles were obtained in the cross section of the channel. The influence of the viscosity function on the flow profile is shown, as well as the quantitative characteristics of the flow and heat transfer. An analysis was made of the dependence of the nature of the velocity and temperature profiles on the viscosity of the liquid and the type of dependence of viscosity on temperature. The result of the work done is the found features and regularities that arise in the process of conjugate heat transfer of a thermoviscous liquid in a cylindrical channel when comparing the linear and exponential dependences of viscosity on temperature. The analysis of the obtained dependences of viscosity and temperature in the flow profile, the value of the maximum flow rate was carried out. It is shown that viscous friction causes a local increase in temperature near the pipe walls, followed by an increase in fluid velocity due to a decrease in viscosity. The results obtained are basic for the further development of this topic and will be used to solve new problems in the field of modeling the thermoviscous fluid flow and conjugate heat transfer.

CFD investigation on heat transfer enhancement in shell and tube heat exchanger using copper oxide nano liquid

Traditional heat transfer liquids show very fewer thermal characteristics. Consequently, there is truly expanding request to foster liquids having excessive thermal characteristics. Thermo-liquid characteristics assume a crucial part in the refinement of such high heat transfer proficient gadgets. A nano liquid is an involvement of nano estimated particles be made of oxides, metals in a base liquid of oil, water, distilled water, or ethylene glycol of size up to 100 nm. As of late enormous quantities of analyses have been are done to assess the impact of nano liquid in rate of heat transfer improvement in different heat exchangers. The amplification of heat transfer utilizing nano liquid for the most part relies upon sort of nano molecules, state of nano molecules, kind of foundation liquid and concentration of nano molecules in the foundation liquid. In the current study, CFD assessment has been completed to decide the impact of different concentration of CuO nano molecules blended in distilled water on heat transfer attributes of shell and tube heat exchanger for counterflow positioning. CuO nano liquid of volume concentration 0.01% and 0.02% are prepared theoretically. The end inferred for the research is that coefficient of overall heat transfer and rate of overall heat transfer increments with expansion in CuO nano molecules volume concentration contrasted with distilled water.

Selection of refrigerants for refrigeration systems of fruit and vegetable stores

Due to the implementation of the Kigali Amendment to the Montreal Protocol, the paper explores the prospects for replacing HFC refrigerants R404a and R507 in refrigeration machines for fruit and vegetable storages. For the optimal choice of environmentally friendly synthetic and natural refrigerants, calculating the coefficient of performance for single-stage refrigeration machines with direct supply of refrigerant to air coolers was carried out. The calculations were made for the conditions of a sharply continental climate at an atmospheric air temperature of +20°C. It was found, that in the near future such refrigerants as R407a, R407c, and R407f can be used as a replacement for R404a and R507 refrigerants in the new energy efficient systems with reciprocating and scroll compressors in developing countries. In the long term, refrigerants such as R290 (propane), R450a, R455a, and R513a can be used after 2036. The use of refrigerants R450a, R455a, R513a will lead to an increase in capital costs for the creation of refrigeration machines due to the need to increase the volumetric performance of compressors. In addition, R450a and R513a refrigerants have a relatively high global warming potential GWP > 150, which may lead to restrictions on their use in large refrigeration systems. As refrigerants R290 and R455a are flammable, their safe use requires a reduction in their charge weight. Therefore, R290 and R455a can be used either in refrigeration systems for individual cold chambers, or in systems with an intermediate heat transfer liquid.

Heat Transfer and Flow Characteristics of Pseudoplastic Nanomaterial Liquid Flowing over the Slender Cylinder with Variable Characteristics

The present article investigates heat transfer and pseudoplastic nanomaterial liquid flow over a vertical thin cylinder. The Buongiorno model is used for this analysis. The problem gains more significance when temperature-dependent variable viscosity is taken into account. Using suitable similarity variables, nonlinear flow equations are first converted into ordinary differential equations. The generating structure is solved by the MATLAB BVP4C algorithm. Newly developed physical parameters are focused. It is observed that the heat transfer rate and the skin friction coefficient is increased remarkably because of mixing nano-particles in the base fluid by considering γb=1, 2, 3, 4 and λ=1, 1.5, 2, 2.5, 3. It is found that the temperature field increases by inclining the values of thermophoresis and Brownian motion parameters. It is also evaluated that the velocity field decreases by increasing the values of the curvature parameter, Weissenberg number and buoyancy ratio characteristics.

Experimentally validated pore-scale numerical analysis for high-temperature (>700°C), high-efficiency (>90%) volumetric solar receivers

• Proposes an innovative, high-temperature semi-transparent packed-bed solar receiver. • Hits SunShot target with one of the highest efficiencies, 92% for T outlet ≥ 700 °C. • Develops a 3-D pore-scale model which couples the optical and thermo-fluid analyses. • Minimises reflection loss via an optical baffle and the pore-scale arrangement. • Reports new experimental validation test data for heat transfer in packed bed. Concentrated solar thermal/power (CST/P) systems are evolving to operate at higher temperatures (i.e., above 700 °C) to drive advanced cycles and thermochemical processes. The development of high temperature, high efficiency solar receivers—as the highest temperature component in a CST/P system—represents a critical technical challenge in this evolution. Commercial solar receivers have been limited to operation below 600 °C due to (1) the historic trade-off between operation temperature and efficiency, and (2) the operating temperature limits of the liquid conventional heat transfer fluids. This paper investigates a gas-phase, packed-bed receiver, which is capable of addressing these limitations. To date, this novel design has shown promise for this application, but it has only been modelled on the macro-scale (i.e., a 1-D model). To obtain a more detailed understanding of this type of receiver, this paper presents the results of a novel 3-D pore-scale analysis of the proposed receiver to characterise the optical-thermo-fluid behaviour. To ensure the validity of this approach, experimental tests were conducted for a complex packed bed of spheres. The 3-D pore-scale analysis enables the development of innovative mechanisms to reduce radiosity losses. It also provides a deeper level of insight regarding the stagnation pressure loss caused by the inlet air-jet flows. The final results demonstrated that the pore-scale modifications of the design can yield an optimised packed-bed receiver with a maximum efficiency of ∼ 92 % (for a hot air outlet temperature well above 700 °C). This optimised receiver design represents a new pathway towards high-temperature solar receivers, which can operate at very high efficiency, to enable CST/P systems to utilise advanced power cycles.

Experimental and computational investigation of flow boiling in microgravity

This study explores use of Computational Fluid Dynamics (CFD) to predict near-saturated flow boiling of FC-72 in microgravity. The computational method employs transient analysis to predict detailed interfacial behavior and heat transfer characteristics along a rectangular channel heated along two opposite walls. Predicted results are validated against experimental temperature measurements and high-speed video images captured during a series of parabolic aircraft maneuvers for three sets of operating conditions which include variations of both mass velocity and wall heat flux. The computational method is based on the multi-phase volume of fluid (VOF) model, which is combined with appropriate phase change and turbulence models, and accounts for both shear-lift force on bubbles and conjugate heat transfer along the heating walls. A key advantage of the CFD method is ability to capture details that are very difficult to measure experimentally, including detailed spatial variations of bubble shape, void fraction, mixture fluid temperature, liquid velocity, and vapor velocity, results for which are presented for each of the three test cases. Different flow regimes predicted along the heated length exhibit a number of dominant mechanisms including bubble nucleation, bubble growth, coalescence, vapor blankets, interfacial waviness, and residual liquid sub-layer, all of which agree well with experiment. Vapor velocity is shown to increase appreciably along the heated length because of increased void fraction, while liquid velocity experiences large fluctuations. Non-equilibrium effects are accentuated with increasing mass velocity, contributing minor deviations of fluid temperature from simulations compared to those predicted by the analytical method. Predicted wall temperature is fairly uniform in the middle of the heated length but increases in the entrance region, due to sensible heat transfer in the subcooled liquid, and decreases toward the exit, mostly because of flow acceleration resulting from increased void fraction.

Motion of Liquid Convective Flow and Heat Transfer Analysis of Flame Spread over butanol fuel within narrow channels

In actual fire, a solid wall is commonly established using nearby noncombustible solid materials to resist flame propagation. However, there are always some narrow channels owing to uneven surface of solid materials. There are inherent differences between liquid flame spread in narrow channels and infinite width fuel, including dynamic shear and heat dissipation. The experiments of flame spread over n-butanol fuel in narrow channels with lengths of 30, 50, 100, 200 and 300 mm and widths of 3, 4, 5, 6, 7, 8, 9 and 10 mm are carried out. The flame spread is divided into initial stage, restriction stage and jet flow stage. The velocity of subsurface flow decreases strongly once the convective flow enters narrow channel. Based on the assumption that surface tension is balanced with sum of viscous force and shear force, the velocity of subsurface flow at restriction stage is calculated which overestimates ∼10% of measurement. The flame cannot pass through the channel when heat loss accounts for more than 43% of total heat flux of subsurface flow. The heat absorption by sidewalls always accounts for more than 80% of total heat loss. The current finding provides a theoretical guidance for actual liquid firefighting.

Thermoelectric precession in turbulent magnetoconvection

We present laboratory measurements of the interaction between thermoelectric currents and turbulent magnetoconvection. In a cylindrical volume of liquid gallium heated from below and cooled from above and subject to a vertical magnetic field, it is found that the large-scale circulation (LSC) can undergo a slow axial precession. Our experiments demonstrate that this LSC precession occurs only when electrically conducting boundary conditions are employed, and that the precession direction reverses when the axial magnetic field direction is flipped. A thermoelectric magnetoconvection (TEMC) model is developed that successfully predicts the zeroth-order magnetoprecession dynamics. Our TEMC magnetoprecession model hinges on thermoelectric current loops at the top and bottom boundaries, which create Lorentz forces that generate horizontal torques on the overturning large-scale circulatory flow. The thermoelectric torques in our model act to drive a precessional motion of the LSC. This model yields precession frequency predictions that are in good agreement with the experimental observations. We postulate that thermoelectric effects in convective flows, long argued to be relevant in liquid metal heat transfer and mixing processes, may also have applications in planetary interior magnetohydrodynamics.

Flow and heat transfer evaluation of lead-bismuth eutectic coolant for nuclear power application

The understanding of flow and heat transfer characteristics of liquid lead–bismuth eutectic (LBE) is essential for nuclear applications. In this paper, a corresponding experimental facility was established and a set of experiments of heat transfer of lead–bismuth eutectic flow in a circular tube was carried out, and a new heat transfer correlation was obtained through the experimental data to study the flow and heat transfer characteristics and evaluate a suitable computational fluid dynamics (CFD) model for LBE flow. The correlation fits well to the experimental data and the deviation of the correlation is smaller than 15%. At the same time, a CFD program was employed to evaluated the applicability of various turbulent models (standard k-∊, standard k-ω, SST k-ω) and turbulent Prandtl number models for LBE flows in the circular tube. Among the turbulence models, SST k-ω model shows the best agreements, the relative deviation of the simulation result from the experimental data is −3.0%∼34.7%. Among the turbulent Prandtl number models, Cheng-Tak model shows the best agreement, the relative deviation is 0.18%∼24.7%. This work provides valuable experimental data and CFD simulation method for liquid metal flow and heat transfer analysis.

Room temperature Magneto-Caloric Refrigerator: system level analysis

A system consisting of magneto-caloric fluid, which releases (absorbs) heat in the presence (absence) of a magnetic field, is used to achieve refrigeration. Gadolinium is used as a magneto-caloric material. The influence of using water and galinstan as heat transfer liquid, on the refrigerator performance is numerically analysed by varying the mass flow rate of the magneto-caloric fluid, and MCM volume fraction (0.4 to 0.6). A cooling load upto 20 W at room temperature is obtained over a temperature difference of 0.5 K.

Basic analysis on heat transfer phenomena in natural circulation for liquid sodium

Natural convention, the heat transfer on fluid due to density differences that can be caused by differences in fluid temperature. One example application of natural convection is cooling system, such as nuclear reactor cooling system. The purpose of this study is to analysis the basic characteristic heat transfer of sodium liquid in the natural circulation system for steady state analysis and transient characteristic with Finite Element Method. The selected module is the Non-Isothermal FLow (NITF) module. This module is a combination of three basic equations, namely the continuity equation, the Navier-Stokes equation, and the dynamic equation of heat transfer in fluid. The simulation model measures 1.5 x 2 (m) with sodium liquid (Na) as a fluid.

Heat flux during boiling of superfluid helium inside a porous body based on a two-fluid model

The calculation of the recovery heat flux density is considered for superfluid helium boiling on the cylindrical heater inside porous structure. System of equations is based on the methods of continuum mechanics and molecular kinetic theory. The new type of boundary condition on the vapor-liquid interface based on the two-fluid model is formulated. Heat transfer in a free liquid is described by the Gorter-Mellink semi-empirical theory. Inside the porous structure the processes is discussed by the two-fluid model and filtration equation. Experimental data on the boiling of superfluid helium inside the porous structure are interpreted based on the formulated mathematical model. The qualitative and in some cases quantitative agreement between the calculated and experimental values of the recovery heat flux were obtained in the considered range of parameters

Interfacial waviness during condensation heat transfer

Heat transfer coefficients and liquid film thickness have been measured during convective condensation inside a 3.4 mm internal diameter channel. Condensation tests have been run with refrigerant R245fa during vertical downflow at mass velocity equal to 50 kg m-2 s-1 and 100 kg m-2 s-1. The test section is composed of two heat exchangers for the measurement of the heat transfer coefficient connected by means of a glass tube designed for the visualization of the two-phase flow patterns and for the measurement of the liquid film thickness. The liquid film thickness is determined by coupling a shadowgraph technique and chromatic confocal measurements. The measured values of heat transfer coefficient and liquid film thickness are reported and analysed together to investigate the effect of waves on the condensation heat transfer mechanisms.

Decreasing the Weight-Size Parameters of Gas-Steam Turbine Plant by Increasing the Efficiency of Thermodynamic Processes in the Condenser

The aim of this work is decreasing the weight-size parameters of the contact gas-steam turbine plant and contact condenser elements by increasing the efficiency of thermal-gas dynamic processes of condensation through rational irrigation of countercurrent gas-steam flow. To achieve the goal the total efficiency of water-return drops ranging from 0.1 to 1 mm at different initial velocities from 5 to 35 m/s emitted by the multi-nozzle sprinkler was determined by mathematical modeling of the liquid droplet movement processes, heat and mass transfer between the liquid droplet and gas-vapor mixture, and gas-vapor mixture pressure loss. The effect of increasing the gas-steam mixture velocity from 3.3 to 6 m/s on the overall efficiency of water return was determined. The novelty of the obtained results was defined by an increase in the water return into cycle from 12 to 13% with a droplet diameter of 0.3 -- 0.4 mm and the initial velocity from the sprinkler of 5--10 m/s. The velocity of the mixture was to 6 m/s at rational correlations of the initial velocity of the droplets’ escape, which increased the total amount of heat withdrawn to 11%. The positive effect conditions of irrigation processes on thermogasdynamic and weight-size parameters of the condenser elements for the contact gas and steam turbine plant at full pressure recovery coefficients of over 0.967 were substantiated. The most significant result was the reduction of the weight-size parameters of the marine infrastructure object power plant from 8 to 19%.

Evaporation heat transfer enhancement by a laser-textured heterogeneous surface

Numerous studies have explored the influence of surface wettability on liquid vapor heat transfer through surface modification; especially when the surface can be modified with heterogeneous wettability. Herein the heterogeneous wettability surfaces with the designated patterns can be created on surfaces only in a few seconds after laser irradiation. LSCM images indicated the surfaces with laser irradiation became rougher and provided more nucleation sites. In this study, experiments for evaporation behaviors of water droplet were performed on picosecond laser-textured heterogeneous copper surfaces. The CCD images revealed that bubble dynamics play an important role in droplet evaporation on heated surfaces. Based on the behavior of bubble coalescence and departure, the heterogeneous laser-textured surface exhibited superior evaporation efficiency.

Study of Heat Transfer Rate in Electric Evaporators of Liquefied Petroleum Gas Using Electrothermal Modeling

In modern domestic and foreign experience of gas power supply to houses and industrial facilities located remotely from the main power station, decentralized gas power supply systems fed with propane-butane mixtures of liquefied petroleum gases from tanks are increasingly used. When using liquefied petroleum gases as the main energy carrier in gas tank systems, they are evaporated artificially in evaporators with an intermediate solid-state or liquid heat transfer agent, under conditions of its natural convection. The main operational characteristic of industrial tube evaporators of propane-butane mixtures of liquefied petroleum gases used for gas power supply from tank installations of housing and communal, industrial and industrial facilities that are remote from the main power supply stations is evaporation capacity. The evaporation capacity of industrial tube evaporators of propane-butane mixtures with a solid-state intermediate heat transfer medium is determined by the heat input from the tubular electric heaters through the aluminum casting layer. Therefore, the study of heat transfer in the solid–state intermediate heat transfer medium-evaporation coil system is the most important prerequisite for the effective operation of industrial tube evaporators of propane-butane mixtures and requires detailed research. To solve the problem of determining the heat transfer resistance between the layers of aluminum casting in contact with the surface of the tubular electric heaters group and the outer evaporation coil surface studies were performed on an electrical model. The average value of the total error of the results of experimental studies on electrothermal modeling is 3.7 %, with a confidence probability of 95 %. Recommendations are given for reducing the thickness of the layers in clear from the lower coil of the evaporative tube coil to the lower generatrix of the solid-state aluminum mass and the upper coil of the evaporative tube coil to the upper generatrix of the solid-state aluminum mass.

Impact of hybrid nanofluids on MHD flow and heat transfer near a vertical plate with ramped wall temperature

Heat transfer augmentation is a modern challenge in various engineering fields including heat exchangers, electronics, chemical and bio reactors, and others. Nanofluids as a new heat transfer liquids can be considered as effective media for increment of energy transport. Such gain is getting due to an increase in the effective thermal conductivity and change in the fluid flow dynamics. In the case of hybrid nanofluids when we can include two or several nanoadditives to the host liquid one can obtain more essential enhancement of transport processes. Therefore, this paper deals with the energy augmentation using hybrid nanofluids. The objective is to find exact analytical solutions to the unsteady hybrid nanofluid flow with heat transfer past an infinite flat vertical plate with a ramped temperature profile concerning time. The effects of various hybrid nanofluids on the unsteady flow and heat transfer features in the presence of the magnetic field, thermal radiation and a temperature-dependent heat source are explored. Results of radiation parameter, heat source parameter, magnetic parameter and nanoparticle volume fraction obtained by employing the Laplace transform technique for engineering variables such as skin friction coefficient and Nusselt number along with velocity and temperature profiles are analyzed using graphs. It has been found that a growth of the average Nusselt number occurs with the nanoparticle volume fraction, while this augmentation can be improved with use of hybrid nanofluid.

Buoyancy Driven Flow, Heat Transfer, and Entropy Generation Characteristics for Different Heater Geometries Placed in Cryogenic Liquid: A Computational Fluid Dynamics Study

Abstract The present work reports a 3D computational study of buoyancy-driven flow and heat transfer characteristics for a localized heater (analogous to superconductor) submerged in cryogenic liquid nitrogen in an enclosure. Seven different heater geometries are considered and the effect of heater geometry on flow and heat transfer characteristics is illustrated. The heater is generating heat at a constant rate (W/m3). Continuity, momentum, and energy equations are solved using the finite volume method. Liquid flow and heat transfer features are demonstrated with the help of velocity vector and temperature contours. Rayleigh number, average Nusselt number, the maximum vertical velocity of fluid flow, and the average velocity of fluid flow are the parameters that are considered for comparing seven different geometries of the heater. Additionally, an analysis of the entropy generation owing to the transfer of heat and friction due to fluid flow is reported. Furthermore, the dependency of average Nusselt number, maximum velocity of the fluid, entropy generation owing to transfer of heat, and fluid friction as a function of heat generation rate is illustrated graphically. The results of this study indicate that heater geometry can considerably affect the transfer of heat, fluid flow features, and entropy generation under the same heat generation rate in the heater. The highest average Nusselt number on the heater surface is obtained when heater geometry is circular, whereas the lowest value of total entropy generation in the domain is obtained when heater geometry is an equilateral triangle.

Thermogravitational convection of power‐law nanofluid in a cavity with a heat‐generated section on the bottom wall

Optimization of cooling systems for electronic devices is one of the crucial challenges in the modern engineering world. Inclusion of nanosized particles to working heat transfer liquids can enhance the heat removal from the heated elements in electronics. Taking into account these data, the present research is devoted to numerical analysis of natural convection in a cavity filled with a non‐Newtonian nanosuspension under an influence of a heat‐generating wall section. The paper contains the simulation outcomes for two different cases, namely, a heat‐generating wall section with constant heat flux and a heat‐generating wall section with constant temperature. The considered phenomenon has been described using the single‐phase nanofluid model where the base liquid is a pseudoplastic fluid. The rheological parameters of the host liquid including the coefficient of flow density and an indicator of fluid behavior are the empirical data of MWCNT nanofluids. The non‐Newtonian nature of the nanoliquid has been described by the Ostwald‐de‐Waele power law. Detailed analysis has been carried out for different governing parameters including the Rayleigh number, the volume fraction of nanoparticles, and the size of the heater using the non‐primitive dimensionless variables and the finite difference method. Obtained results illustrate different temperature patterns for various boundary conditions. Moreover, in the case of heat‐generating element, the average Nusselt number is greater than for the isothermal heater. It should be noted that the considered nanofluid model reflects the energy transference degradation with a growth of the nanoparticles concentration.

Experimental investigation on melting heat transfer of an organic material under electric field

In this paper the melting heat transfer process of n-octadecane when confined in a cylinder-cubic cavity under the influence of an electric field is experimentally investigated. n-octadecane is a typical organic phase change material (PCM) and possesses a well-defined melting point. The cylinder is subject to the simultaneous actions of electric potential and heating, while the bottom wall or the four sidewalls of cavity are grounded. The effects of the voltage's magnitude and polarity on the solid–liquid phase change heat transfer performance are studied. The dynamic evolutions of the melting front and liquid fractions, the measurement of velocity field and electric current–voltage characteristics, and the distribution of electric field are presented to understand the physical mechanism. It is observed that when the applied voltage is higher than a certain threshold charge injection at the cylinder takes places, and the resulting strong Coulomb force promotes melting. In addition, heat transfer enhancement is more significant when the charge injection takes place at a negative voltage. The strong electric field that surrounds the whole cylinder with the four grounded sidewalls would facilitate injection and accelerate phase change. In this case, the melting time can be reduced by up to 68.0% when the −25.0 kV is applied.