Liquid Heat Transfer Research Articles

Experimental study of liquid metal heat transfer in a vertical duct affected by coplanar magnetic field: Upward flow

Liquid metal cooling is of interest in high heat load applications. Convection of liquid metals in mass force fields, i.e., buoyancy, inertia, magnetic fields, is a problem which is still difficult to predict due to lack of experimental data. There is a special interest in the heat removal systems of a tokamak reactor, where high heat and magnetic fields form unprecedented conditions. Continuing the study of heat transfer in channels with a liquid metal coolant, we consider the upward flow of mercury in a vertical heated rectangular duct located in a strong magnetic field. Specifically, we study experimentally the mercury flow under a coplanar magnetic field (directed transverse to the main flow and along the long side of the duct) for symmetrical (two-sided) and asymmetrical (one-sided) duct heating.The upward flow configuration has enabled us to explore experimentally flow development along the duct using a 3D probe temperature measurement scanning technique. As in the downward flow configuration, the joint action of buoyancy and magnetic forces result in a drastic peculiarity of heat transfer regimes, where buoyancy and magnetic influence can not be neglected. We show that, in contrast to the downward flow, buoyancy effects play a primary role in flow and heat transfer.

Liquid Impingement Flow and Heat Transfer of a Cone Heat Sink With Filet Profiles

Abstract Jet impingement is a technique for removing heat efficiently. A liquid jet impingement on a cone heat sink was investigated numerically to explore the effect of filet profiles at the top and bottom edge of conical protuberances on fluid flow and heat transfer. An adopted turbulence model was validated through an experiment as described in the literature. Numerical results of pressure coefficient and Nusselt number were obtained for cases with and without filet profiles for variable jet Reynolds numbers and conical angles. Results showed that the flow and heat transfer of conical protuberances with small tip filet profiles are similar to that of the original cone. Pressure coefficient curves are similar to that of convex surfaces, and the average heat transfer slightly increases when the radius of the tip filet profiles exceeds 1 mm. A small filet profile of a conical bottom edge can improve the average Nusselt number. A secondary jet that enhanced the overall heat transfer was demonstrated, and the heat transfers of convex surfaces, as the comparison, with small angles were enhanced in most cases.

Liquid metal mixed convection in an annulus with twisted tape

Liquid metals are promising coolants and working environments for high-energy technologies such as nuclear power plants, liquid metal batteries, solar collectors, and high temperature chemical reactors. Liquid metal heat transfer in these applications is crucial for the effective and reliable work of the technology as a whole. In this work we study the problem of local heat transfer in a swirled flow in an annulus. The problem model is idealized for ease of comparison between a numerical solution and an experiment. Experimental data was obtained using scanning probe measurements in a swirl flow at certain conditions suitable for the measurement technique, while extensive numerical modeling was executed in a number of possible scenarios, using the RANS equations solution enclosed by an SST model of turbulence. Velocity, temperature, temperature fluctuations, and heat transfer irregularity at the heated pipe perimeter are presented for several base situations that highlight key features of liquid metal flow in an annulus with twisted tape. The paper presents novel results on the influence of thermogravitational convection, helical pitch, tape gap, and inner pipe heating eccentricity on local characteristics of heat transfer in liquid metals. A parametric analysis provides key insights in the prediction of local overheating in a geometrically similar system and discusses differences of problem formulation and the consequent results in both a numerical and an experimental approach. The study reveals a strong influence on the scheme of flow and heat transfer, which is dependent upon the size of the width of the gap between the tape and the external pipe, as well as upon conditions at the entrance of the test section.

Isothermal piston gas compression for compressed air energy storage

Currently, Compressed Air Energy Storage systems mainly use adiabatic compression. Compared with isothermal compression, approximately twice the electricity is transformed into heat. Twice the heat passed into heat exchange mediums leads to twice the heat transfer losses. Enhancement of the heat transfer between air and environment to achieve isothermal compression is an effective approach to improve the turnaround efficiency of CAES systems. An isothermal piston structure is proposed to do isothermal compression. One end of the isothermal piston is connected to a traditional piston, and the other end dips into a liquid medium in the bottom of a cylinder. This forms a gas–solid–liquid three-layer heat transfer structure. A porous medium is used to enhance the heat transfer from the air to the liquid. As the heat capacity of the liquid is much greater than that of the air, the temperature of the liquid remains unchanged as well as the compressed air. A new method is proposed to look at the thermodynamics of the compressor with two dimensionless parameters Ka and Xu. Ka describes the extent of the compressor approaching isothermal. When Ka is over 80, the temperature of the air is reduced by 80% compared with adiabatic condition. In the case of using an aluminum porous medium, the compression efficiency increases by 11% at the compression ratio of 7 and the speed of 1200 r/min.

Liquid metal MHD effect and heat transfer research in a rectangular duct with micro-channels under a magnetic field

The liquid metal blanket of a fusion reactor acts the role of tritium multiplication and energy transportation in a strong magnetic field environment. Liquid metal in fusion blanket is different from traditional flow and heat transfer due to magneto hydrodynamics (MHD) effects. A numerical simulation is employed to investigate the convection heat transfer between liquid metal and micro-channels heated surface under an external magnetic field. It can be found that under the influence of magnetic field, liquid metal can produce strong jet near the wall which drives the liquid metal flow together inside the channel. The MHD Hunt flow effect is intensified with the enhancement of the magnetic field and the results indicate that the magnetic field is beneficial to the energy transport and conversion of liquid metal blanket due to the jet flow on the wall that caused by the magnetic field. From the point of view of enhanced heat transfer, 32% of the heat transfer enhancement under the influence of strong magnetic field provides a new way to solve the heat transfer with high heat flux density. The expression is fitted between Nu number with Re number, the magnetic interaction number and flow distance, which can be used to predict the change of heat transfer intensity between the liquid metal and the micro-channels heated plate with the magnetic field intensity.

Influence of nanofluid properties on turbulent forced convection heat transfer in different base liquids

This paper analyses the influence of nanofluid properties on turbulent convective heat transfer characteristics for various base fluids. The turbulent characteristics of heat transfer and flow have been determined by applying the Van Driest model of the eddy diffusivity for water and ethylene glycol‐based nanofluids. The properties of CuO, Al2O3 and SiO2 nanofluids in two base liquids (water and EG‐water mixture with the ratio of 60:40) have been considered for various concentrations, as well as large temperature ranges. Based on the observations, it is concluded that numerical outcomes are validated with experimental measurements for heat transfer properties. It is also established that SiO2 reaches a higher temperature gradient in comparison with CuO at a similar temperature and concentration in EG‐water, with the mixture of 60:40. The gradients are greater for the EGW mixture compared to water‐based nanofluids. However, the water‐based nanofluids have higher heat transfer coefficients compared to EG‐water nanofluid at identical flow velocities. It is also notable that the key findings demonstrate that for the heat transfer coefficient, especially in practical situations, the use of nanoparticles and the base fluids tends to enhance the parameter of the coefficient of heat transfer. Also, this study is deemed contributory to the literature and extends the works of some of the previous scholarly contributors by affirming that the factor or parameter concerning the coefficient of heat transfer has its values or behavior dependent on the ratio between the water base liquid and the EG. Overall, it is shown that for higher values of the coefficient of heat transfer to be obtained, there is a need for the introduction of base liquids and nanoparticles, especially because these materials come with or exhibit superior thermal conductivity.

Darcy-Forchheimer MHD Hybrid Nanofluid Flow and Heat Transfer Analysis over a Porous Stretching Cylinder

This research work deals with investigation of the thermal characteristics of the Darcy–Forchheimer hydromagnetic hybrid nanofluid (Al2O3-Cu/H2O) flow through a permeable stretching cylinder. The model equations, which consist of continuity, momentum, and energy equations, are converted to a set of coupled ordinary differential equations through similarity variables transformations and appropriate boundary conditions. Brownian motion and Thermophoresis effects are mainly focused in this work. The impacts of some interesting parameters over velocity, temperature, and concentrations profiles are graphically studied. The present study will be helpful in understanding the thermal characteristics of heat transfer liquids.

Optimization of Converging and Diverging Microchannel Heat Sink for Electronic Chip Cooling

This article presents a steady-state 3-D conjugate heat transfer and single-phase liquid flow simulation in the microchannel heat sink (MCHs). The 3-D governing equations with boundary conditions are solved for a constant heat flux of 200 W/cm2, applied at the bottom surface of MCHs. An array of microchannels with three different cross-sections—uniform, converging, and diverging—are investigated for a fixed chip dimension of 20-mm length, 4-mm width, and 0.15-mm substrate thickness. This article aims to present a comparative analysis of the hydraulic and thermal performance of MCHs with three different cross-sections. Simulations are performed for volume flow rate and microchannel depth range of 20–140 mL/min and 0.25–1.25 mm, respectively, with silicon microchannel using water as the working fluid. Numerical simulations are performed using COMSOL Multiphysics 5.3. Comparative analysis shows that for a wide range of volume flow rate, diverging channels MCHs shows superior thermohydraulic performance. Furthermore, it is observed that with an increase in depth or aspect ratio of the channel, there is a significant reduction in pumping power requirement with some marginal reduction in thermal performance. Furthermore, to calculate the optimized channel dimensions for minimum thermal resistance and pressure drop, a MATLAB code was written. Based on the results, the optimized channel dimensions are identified. The work presented and discussed in this article is relevant and beneficial for designing compact MCHs for electronic cooling applications.

Optimising graphite composites and plate heat exchangers for latent thermal energy storage using measurements and simulation

Low thermal conductivity is a significant issue for the deployment of phase change based thermal energy stores. A structured methodology is required to find the best overall design, in order to assess its techno-economic feasibility. In this study the optimised structural configuration of graphite composites for this purpose are first considered from three different perspectives using both experimental measurements and numerical simulations. Both steady state and dynamic performance are taken into account, with the latter being considered both with and without phase change. In all three cases it is demonstrated that thin, parallel graphite sheets offer the most optimal results compared to other options. Resulting in the highest composite thermal conductivity measured to date at a loading of 3.5 mass%. The next step in achieving the best overall performance is the optimisation of this composite in the context of a plate and frame heat exchanger. For this purpose a simplified analytical model of this configuration was developed and validated. This was used in conjunction with the log mean temperature difference approach to optimise the exchanger for two typical applications: low temperature, low duty and high temperature, high duty. The results indicate that, even under an idealised configuration, the system will only be suitable for high temperature applications with gas heat transfer fluids and short discharge times (~1 h). For low temperature applications it may be possible to use liquid heat transfer fluids but also only for short discharge times. From an economic perspective, the range of graphite sheets currently available on the market will have to be reduced in cost by two or more orders of magnitude in order to be cost-effective.

Natural convection of a hybrid nanofluid affected by an inclined periodic magnetic field within a porous medium

Heat transfer enhancement for various engineering systems can be achieved by the inclusion of metal nanoparticles inside the heat transfer liquid. Such an effect can be improved by considering the hybrid nanofluid when nanoparticles of different materials are added to the base fluid. The present study is devoted to computational analysis of thermal gravitational convection within a porous chamber under the impact of tilted periodic magnetic force. Governing equations formulated employing the single-phase nanoliquid approach, Brinkman-extended Darcy model for transport processes within the porous layer with the local thermal non-equilibrium approach, Boussinesq approximation for the description of the buoyancy force and magnetic field, have been resolved using the Galerkin finite element method. Impacts of the Darcy number, Hartmann number, Rayleigh number, periodicity of the magnetic field, magnetic field inclination angle, thermal conductivity ratio, and medium porosity on flow and thermal patterns have been examined. It has been found that parameters of the periodic magnetic field have the non-monotonic influence of the heat transfer performance.

Liquid metal thermal hydraulics: State-of-the-art and future perspectives

The energy consumption worldwide will increase for the coming decades. In order to address global warming, international experts agree that no low CO2 emitting energy production routes should be omitted. In fact, nuclear energy production is appointed an important role in the transition towards a low CO2 emitting world. Taking into account the identified reserves of uranium and assuming a stable consumption of uranium in light water reactors, the uranium reserves will surely fit for one or two centuries. However, by switching to another fuel cycle using uranium in fast reactors, the uranium reserves may serve the world for a multi-fold of centuries. Nowadays, the most mature fast reactor designs are liquid metal cooled fast reactors.Design support and safety analysis of liquid metal reactors strongly relies on thermal hydraulic simulations and experiments. This paper will discuss the current state-of-the-art in liquid metal thermal hydraulics and also its future perspectives. In particular, the following topics will be discussed: liquid metal heat transfer, fluid-structure interaction, fuel assembly thermal hydraulics, coolant solidification, efficient 3-d system modelling, and validation at large. For each topic, the state-of-the-art, challenges and the future perspectives will be described from the author’s point of view.

Magnetohydrodynamic flow of Carreau liquid over a stretchable sheet with a variable thickness

PurposeThe magnetohydrodynamic (MHD) flow problems are important in the field of biomedical applications such as magnetic resonance imaging, inductive heat treatment of tumours, MHD-derived biomedical sensors, micropumps for drug delivery, MHD micromixers, magnetorelaxometry and actuators. Therefore, there is the impact of the magnetic field on the transport of non-Newtonian Carreau fluid in the presence of binary chemical reaction and activation energy over an extendable surface having a variable thickness. The significance of irregular heat source/sink and cross-diffusion effects is also explored.Design/methodology/approachThe leading governing equations are constructed by retaining the effects of binary chemical reaction and activation energy. Suitable similarity transformations are used to transform the governing partial differential equations into ordinary differential equations. Subsequent nonlinear two-point boundary value problem is treated numerically by using the shooting method based on Runge–Kutta–Fehlberg. Graphical results are presented to analyze the behaviour of effective parameters involved in the problem. The numerical values of the mass transfer rate (Sherwood number) and heat transfer rate (Nusselt number) are also calculated. Furthermore, the slope of the linear regression line through the data points is determined in order to quantify the outcome.FindingsIt is established that the external magnetic field restricts the flow strongly and serves as a potential control mechanism. It can be concluded that an applied magnetic field will play a major role in applications like micropumps, actuators and biomedical sensors. The heat transfer rate is enhanced due to Arrhenius activation energy mechanism. The boundary layer thickness is suppressed by strengthening the thickness of the sheet, resulting in higher values of Nusselt and Sherwood numbers.Originality/valueThe effects of magnetic field, binary chemical reaction and activation energy on heat and mass transfer of non-Newtonian Carreau liquid over an extendable surface with variable thickness are investigated for the first time.

Numerical Investigation of Enhanced Heat Transfer in a Rectangular Channel with Winglets

The liquid flow and heat transfer performance in rectangular channels with winglets are determined numerically in the Reynolds number range of 100 to 300. Water with constant thermophysical properties is used as the working fluid and modeled to be Newtonian. Three-dimensional numerical simulations have been performed on a rectangular plain channel and a rectangular channel with five pairs of winglets heated by a constant wall temperature of 320 K, and the channel has a hydraulic diameter of 6.4 mm. The winglets are mounted at different locations and attack angles inside the rectangular channel. It was found that using winglets can remarkably enhance the heat transfer rates inside the rectangular channel as compared to plain channel. The friction factor increases with increasing the attack angle, while friction factor decreases with increasing Reynolds number. The numerical simulations show an enhancement of 59% in heat transfer performance by using proposed channel with winglets in contrast to a plain channel.

Enhanced Heat Transfer in Moderately Ionized Liquid Due to Hybrid MoS2/SiO2 Nanofluids Exposed by Nonlinear Radiation: Stability Analysis

This study considers ethylene-glycol as a moderate ionized regular liquid whose rheological behavior can be analyzed through the relations of the Carreau stress–strain tensor. Hybrid nanoliquids are potent liquids that give better performance for heat transfer and the properties of thermo physical than regular heat transfer liquids (water, ethylene glycol, and oil) and nanoliquids by single nanomaterials. Here, a type of hybrid nanoliquid involving silicon oxide (SiO2) and Molybdenum disulfide (MoS2) nanoparticles with ethylene glycol as a base liquid are considered. In addition, the impact of nonlinear radiation along with Lorentz force is invoked. Similarity variables are utilized to acquire the numerical findings and their solutions for transmuting ordinary differential equations (ODEs). Using bvp4c from MATLAB, we can obtain these quantitative and numerical results of the converted nonlinear equations. The impacts of the pertinent constraints on the temperature distribution, velocity, Nusselt number, and skin friction are estimated. The outcomes indicate that the double-edged methods for the results originate from the precise values of the permeable parameters. Further, the critical values (Sc = 1.9699, 2.0700 and 2.2370) are enhanced due to the influence of the local Weissenberg number. This implies that the increasing value of the local Weissenberg number accelerate the boundary layer separation. Furthermore, a stability investigation is performed and confirms that the first solution is a physically reliable solution.

Experimental Investigation of Thermophysical Properties and Combustion Characteristics of Thickened Jet Fuel

ABSTRACT The thermophysical properties and combustion characteristics of PIB thickened jet fuel are investigated based upon both aims of expanding basic combustion theory (i.e., the coupled gas phase and liquid phase flows and heat transfer involving flame spread over liquid fuel) and potential practical applications (i.e., the oil additive in two-stroke gasoline engine and in-situ burning of leaked oils). The effects of PIB on the thermophysical parameters of jet fuel including density, flashpoint, viscosity and surface tension are experimentally measured. The logarithm of the dynamic viscosity varies linearly with the proportion of PIB, which is in good agreement with predictions. Then, the impact of PIB on fire safety of jet fuel is examined through flame spread and ignition experiments. The temperature evolution, flame spread rate, length and velocity of subsurface flow are quantitated and analyzed. The addition of PIB into jet fuel reduces the flame spread rate, but promotes the ignitability. The viscosity augment plays the principal role in hindering flame spreading over thickened jet fuel.

Numerical modeling of vapor condensation over a wide range of non-condensable gas concentrations

This paper presents a numerical model to study the process of vapor condensation on surfaces characterized by film-wise condensation with the presence of Non-condensable gases (NCG). State variables in both the condensate film and the diffusion layer were solved separately and the condensation interface was used to couple the two solutions. The solution of the condensate film was obtained using well-established solutions of laminar film condensation of pure vapor. In contrast to other models surveyed, this work provides a inexpensive and accurate predictions of heat and mass transfer characteristics. We validated the work against two classical condensation problems. The model was first validated against empirical correlations and experimental work, resulting in a very good agreement. We then assessed the applicability of ignoring the condensate film effect, as performed in previous models, on the condensation processes by observing the thermal resistances of both the condensate film and diffusion layer. Results indicated that for the studied cases of NCG mass fractions above 20%, the condensate thermal resistance was at least an order of magnitude lower than that of the diffusion layer. However, the two thermal resistances seem to approach each other as NCG mass fraction becomes smaller. On another front, we observed that models that ignore the condensate film thermal resistance underestimate the interfacial temperature albeit accurately predicting the overall heat transfer rate. To simulate even lower NCG mass fractions, we validated our model to the classical analytical work of Sparrow and co-workers. Results showed a striking agreement between the two solutions at different NCG mass fractions (0.5%–10%) and subcooling degrees (5∘F–40∘F). Finally, we found a good agreement between results of our model and the heat/mass transfer analogy. The heat/mass transfer analogy is a semi-empirical method therefore, is limited to the existing correlations and their uncertainties. On the other hand, our model does not use any empiricism and relies on the available solutions of laminar condensate film of pure vapor in predicting the liquid side heat transfer coefficient.

Effect of the heat transfer liquid fin on critical heat flux enhancement under ERVC condition

Several critical heat flux (CHF) enhancement methods for in-vessel retention through external reactor vessel cooling (IVR-ERVC) have been researched. However, they have some limitations for practical applications. In the present study, heat transfer liquid fin concept was suggested to address the issue of CHF by spreading focusing effect of the heat flux. The liquid fin was located outside of the reactor pressure vessel; it is activated by filling under the accident situations. Liquid metal and oil were selected as the fin materials as they are characterized by significantly different Prandtl numbers; this property helps to clearly distinguish the heat transfer mechanisms involved. Analysis were conducted based on both experimental and numerical methods. As expected, conduction and natural circulation were the dominant heat transfer mechanisms in the case of liquid metal fin and the oil fin, respectively. Regardless of the Prandtl number of the fin, safety margin for the CHF was significantly increased in both fin cases. The heat flux profile of the conduction dominant liquid metal fin showed a moderately flattened shaped. However, for the oil fin, heat flux was mitigated and upwardly shifted (natural circulation as the primary heat transfer mechanism). Although both materials exhibited good performance in terms of securing a margin for CHF, temperature increment by the liquid fin was much higher in the oil case because of the relative lower thermal conductivity of the latter. Thus, the use of low thermal conductivity fins requires the temperature limit to be taken into consideration.

Heat transfer and residence time distribution of liquid flow in direct contact evaporation heat exchanger

To enhance the heat transfer of liquids, a new gas-liquid-liquid three-phase exchanger based on the SK elements was proposed for utilization in energy recovery. Visual experimental investigation of the particle transport characteristics was carried out. The effects of the flow velocity, pipe diameter, arrangement, number and length-to-diameter ratio of elements on the mean residence time (MRT) were studied. An analysis of the velocity distribution of the particles of the operated cell through the SK element was performed. A pentane-water direct contact evaporation heat transfer experiment was carried out to investigate the effect of the SK elements on the heat transfer performance. The results indicated that the SK elements reduced the evaporation height, and the volumetric heat transfer coefficient was more than two times greater than that in the heat exchanger without the SK elements.

Drying of Oblate Spheroidal Solids via Model Based on the Non-Equilibrium Thermodynamics

Food drying is one of the most used methods of preservation. To accurately describe moisture migration within biological products (grains, fruits, vegetables, etc.) during drying and explain the effects of this process on the quality of the material, have been proposed several mathematical models, but few incorporate the phenomena of simultaneous heat and mass transport applied to complex geometry. In this sense, this paper aims to present a mathematical model, based on the thermodynamics of irreversible processes to describe the heat and mass transfer (liquid and vapor) during the drying of bodies with oblate spheroidal geometry. This model was applied to describe drying of lentil, considering the variables transport coefficients and equilibrium conditions at the surface of the solid. Results of the average moisture content, average temperature, liquid flux, vapor flux, and moisture content and temperature distributions inside a lentil kernel during drying process, at different temperatures (40 and 60 oC) were presented and analyzed.

Experimental Characterization of a Compact Milli-Channel Heat Exchanger for Liquid–Liquid Heat Transfer

The use of Milli-Channel Heat Exchangers (MCHE) presents numerous assets: efficient heat transfer, huge compactness, and limited pressure drop. For an engineer, the Fanning friction factor and the convective heat transfer coefficient are two main parameters to describe the performance of a heat exchanger. A brazed MCHE with rectangular channels in stainless steel made by the Institut für Mikrotechnik Mainz (IMM, Mainz, Germany) has been characterized experimentally and theoretically in a counter-current configuration. The selected working fluids are deionized water and oil without any phase change during experiments. The pilot unit ensures measurements of pressure drops, temperatures, and volumetric flow rate of each fluid flowing in laminar regime. A one-dimensional model has been developed. The temperature and pressure profiles of each fluid are represented by differential equations associated with boundary conditions. The system of coupled equations consists in a two-point boundary value problem solved numerically by the Matlab software. The parameters of a Nusselt number correlation are identified together with those of a Fanning friction factor one by minimizing a sum of squared differences between experimental and predicted data. The calculated temperature and pressure profiles present a good agreement with measurements. A statistical analysis shows that each optimized parameter is significant.