Applications In Thermal Systems Research Articles

Effect of contact thermal resistance and skeleton thermodynamic properties on solid-liquid phase change heat transfer in porous media: A simulation study

Phase change materials (PCMs) have the potential for heat storage and release, but low thermal conductivity limits their wide application in thermal systems. This work proposes a mathematical model to simulate the freezing process of water in porous media. Unlike traditional methods that solve for two temperatures in different materials, the hybrid finite element method computes a single temperature satisfying the jump on the interface. The effect of contact thermal resistance and skeleton parameters on solid-liquid phase change heat transfer was investigated. This model was validated by experiments in reference. Results show that increased contact thermal resistance decreases temperature gradient, phase interface deflection and freezing rate. Specifically, with contact thermal resistance of 0.0001 K/W, 0.0005 K/W, and 0.001 K/W, freezing rates decrease by 36.4 %, 52.35 %, and 54.14 %, respectively, compared to the case without resistance. Although the contact thermal resistance reduced the temperature gradient, it stabilized the phase change process. Moreover, higher thermal conductivity of the skeleton enhances the freezing rate. However, after a certain value is reached, the rate increases only marginally. Skeletons with lower density and specific heat capacity are favorable to enhancing phase change heat transfer.

Performance enhancement of Photovoltaic-thermal system using hybrid tubes: An assessment of thermodynamic and thermohydraulic efficiencies

In this study, a novel hybrid tube configuration is proposed to develop an efficient photovoltaic thermal system. Subsequently, the impact of different working fluids is investigated, including ternary nanofluids and phase-change material slurries. The performance of the system is optimized by varying the geometrical parameters and working fluids. The combined impact of the hybrid tube and the working fluid is numerically investigated. Thermal, exergy, electrical, and hydraulic efficiencies of the PVT system are analyzed to ascertain the feasibility of the proposed configuration and working fluid. Compared to straight and wavy tubes, the proposed hybrid tube configuration achieves a more uniform and reduced temperature distribution. The optimised hybrid tube configuration performs significantly better than the straight tube configuration, with an improvement of 8.01%, 5.5%, and 32% in primary, exergy, and thermohydraulic efficiencies, respectively. However, compared to wavy tubes, marginally better performance is achieved coupled with a 30% reduction in pressure drop. Moreover, compared to water, the primary, exergy, and thermohydraulic efficiencies are improved by 6.3%, 1.1%, and 20%, respectively, when the optimized hybrid tube is used in conjunction with the proposed slurry. Thus, the hybrid tube design and novel slurry demonstrate high potential for photovoltaic thermal system applications.

Heating performance of a large-scale line heater by adding synthesized carbon- nanodots to the heater bath fluid: CFD simulation and experimental study

Numerous researchers have recently become interested in nanofluids because of their potential applications in thermal systems. Herein, various concentrations of nanofluid of synthesized carbon nanodots (C-dots) were used to survey the thermal performance of a line heater as a heater bath fluid, and a numerical model was proposed to simulate all of the line heater's components for the first time. C-dots nanoparticles were manufactured with the aid of the hydrothermal method and characterized using FTIR and XRD analysis. In addition, a two-stage approach was used to prepare the nanofluid with a varying concentration of C-dot nanoparticles, ranging from 0.5 to 5 wt%. Nanofluids were also measured and compared to the base fluid in terms of thermophysical properties. Additionally, a numerical model based on the finite element method (FEM) was proposed to simulate fluid flow and heat transfer in the line heater, and validation of the numerical results revealed good agreement with earlier studies. The mesh independence analysis shows that the results are much better and more consistent when mesh number 98,946 is used instead of the others. The results illustrate that temperatures were raised from roughly 300 K near the gas tubes to around 370 K near the fire tubes. In comparison to the situation of employing water as the bath fluid, the maximum heater power consumptions derived from the experiments and numerical findings were 9.7 % and 10.3 %, respectively.

Artificial neural network modeling and optimization of thermophysical behavior of MXene Ionanofluids for hybrid solar photovoltaic and thermal systems

• Thermophysical properties of MXene Ionanofluids are presented for PV/T system. • LMBPNN approach was used to predict the thermophysical behavior of MXene Ionanofluids. • LMBPNN model performance in predicting the thermophysical property behavior. • Optimization and Parametric analysis of thermophysical properties was performed using RSM. Newly developed MXene materials are excellent contender for improving thermal systems' high energy and power density. MXene Ionanofluids are novel materials; their optimum thermophysical behavior at various synthesis conditions has not been addressed yet. The aim of this study is to investigate the effect of synthesis conditions (temperature 303–343 K and nanofluids concentration 0.1–0.4 wt%) on the thermophysical properties (thermal conductivity, specific heat capacity, thermal stability, and viscosity) of MXene Ionanofluids. Levenberg Marquardt based Artificial Neural Network (ANN) model and Response Surface Methodology (RSM) based optimization techniques have been adopted for systematic parametric analysis of MXene Ionanofluids thermophysical properties using experimental data. ANN and RSM have predicted the thermophysical behavior of MXene ionanofluids at optimized conditions. The experimental data were used to train, test, and validate the ANN model. The neural network could correctly predict the outcomes for the four properties based on the numerical performance with R 2 values close to 1, and a prediction error is 2%. The performance of the proposed LM-based back-propagation algorithm demonstrates that the error involved has been minimal and acceptable. RSM has developed correction among input parameters and thermophysical properties of MXene Ionanofluids. The comparison between experimental results and the proposed correlations revealed excellent practical compatibility. Optimized thermophysical properties of MXene Ionanofluids thermal conductivity of 0.776 W/m.K, specific heat capacity of 2.5 J/g.K, thermal stability of 0.33931 wt loss %, and viscosity of 11.696 mPa.s were obtained at a temperature of 343 K and nanofluids concentration of 0.3 wt%. MXene Ionanofluids with optimal thermophysical properties could be used for the greatest performance of hybrid solar photovoltaic and thermal system applications.

Inclined surface slip flow of nanoparticles with subject to mixed convection phenomenon: Fractional calculus applications

The interest of researchers towards the nanofluids is noticed in recent years due to leading applications in thermal systems and industrial framework. Referring to such motivations, current study explores the role of velocity slip effects for the mixed convection flow of nanofluid endorsed due to inclined surface. The Casson base fluid model for which the thermal impact needs to be improved. The analysis is observed when the role of velocity slip is important. The modeling of unsteady free convective flow problem yields partial differential system. The Atangana-Baleanu (AB) and Caputo-Fabrizio (CF) fractional operators are implemented in order to simulates the computation of problem. The graphical presentations are prepared in order to check the physical dynamic of parameters.

Thermal conductivity, reliability, and stability assessment of phase change material (PCM) doped with functionalized multi-wall carbon nanotubes (FMWCNTs)

The thermal properties of Phase Change Material (PCM) can be altered by introducing nanoparticles, and composite formed from the addition of nanoparticles are termed Nano-Enhanced Phase Change Materials (NEPCM). In the present study, the enhancement of thermal conductivity and feasibility study of dispersing multi-walled carbon nano tubes (MWCNTs) and functionalized MWCNT (FMWCNTs) in various mass fractions (AFMW-0.1, AFMW-0.3, AFMW-0.5, AFMW-0.7, AFMW-1.0) into the Plusice A70 PCM were examined. Differential scanning calorimetry (DSC) and TEMPOS thermal analyzer measured the latent heat storage, melting temperature, and thermal conductivity of the nano PCM composite. The thermal conductivity measured for the prepared nanocomposite showed a 109.5% enhancement for 1.0 wt% of non-functionalized MWCNT and 150.7% enhancement for 1.0 wt% of functionalized MWCNT compared to pristine PCM's thermal conductivity. This statement concluded that 50% enhancement for a 1.0 wt% of functionalized MWCNT compared to non-functionalize MWCNT immersed in A70 PCM. The nano composite PCM was thermally stable up to 200 °C and no chemical reaction takes place between the base PCM and nanoparticles. The result shows that the microscopic structure remained stable for the nanocomposite while the optical transmittance reduced noticeably for the nanocomposite relative to pristine A70 PCM. It can be concluded, the prepared nano composite PCM may be useful for solar thermal, photovoltaic thermal system, and low concentrated photovoltaic thermal system applications.

Heat Transfer of Nanomaterial over an Infinite Disk with Marangoni Convection: A Modified Fourier’s Heat Flux Model for Solar Thermal System Applications

The demand for energy due to the population boom, together with the harmful consequences of fossil fuels, makes it essential to explore renewable thermal energy. Solar Thermal Systems (STS’s) are important alternatives to conventional fossil fuels, owing to their ability to convert solar thermal energy into heat and electricity. However, improving the efficiency of solar thermal systems is the biggest challenge for researchers. Nanomaterial is an effective technique for improving the efficiency of STS’s by using nanomaterials as working fluids. Therefore, the present theoretical study aims to explore the thermal energy characteristics of the flow of nanomaterials generated by the surface gradient (Marangoni convection) on a disk surface subjected to two different thermal energy modulations. Instead of the conventional Fourier heat flux law to examine heat transfer characteristics, the Cattaneo–Christov heat flux (Fourier’s heat flux model) law is accounted for. The inhomogeneous nanomaterial model is used in mathematical modeling. The exponential form of thermal energy modulations is incorporated. The finite-difference technique along with Richardson extrapolation is used to treat the governing problem. The effects of the key parameters on flow distributions were analyzed in detail. Numerical calculations were performed to obtain correlations giving the reduced Nusselt number and the reduced Sherwood number in terms of relevant key parameters. The heat transfer rate of solar collectors increases due to the Marangoni convection. The thermophoresis phenomenon and chaotic movement of nanoparticles in a working fluid of solar collectors enhance the temperature distribution of the system. Furthermore, the thermal field is enhanced due to the thermal energy modulations. The results find applications in solar thermal exchanger manufacturing processes.

Review on application of phase change material for BIPV system

Solar energy storage technologies are an emerging technology that plays a vital role in photovoltaic and thermal system applications. In a photovoltaic system, thermal management is carried out by various approaches, such as the active and passive methods. The reduction in surface temperature of the PV system will improve the performance of the system. This work's passive approach with the phase change material for the building-integrated photovoltaic system and BIPV with thermal system (BIPV/T) is reviewed and presented.

A review of recent advances in green nanofluids and their application in thermal systems

An increase in energy demand is leading to the continuous rise in global temperature above pre-industrial levels with the discharges of toxic gases and radiations leading to severe climatical circumstances. Thus, it is mandatory to develop ever-lasting, highly efficient thermal systems to overcome this issue. Scientific works on different nanofluids for enhancing performance in thermal applications have gained attention significantly over the last few years owing to their superior qualities. However, it increases safety and health concerns as they are generally more reactive in solvents. Also, other undesired effects such as corrosion of the equipment, non-biodegradable byproducts occur due to the presence of strong chemicals. Therefore, developing cost-effective, and eco-friendly nanofluids has emerged as an alternate research area that is rapidly growing with a great deal of interest. The current review gives a comprehensive view of the different techniques utilized in the preparation of green nanofluids using several natural extracts. Unique morphology, optical properties, stability, high surface area, less toxicity, and enhanced thermo-physical properties of green nanoparticles makes them a favorable candidate in enhancing the performance of thermal systems. Further, various factors affecting the preparation of green nanofluids are highlighted in addition to the evaluation and enhancement techniques concerning the stability and thermophysical properties. Recent experimental and numerical works on the effect of green nanofluids in thermal systems are critically analyzed and provide an overview from economic and environmental perspectives. The challenges and future developments are highlighted to ensure safer health and environment using nanofluids.

Investigations on Acoustical and Thermal Properties of Ethylene Glycol Based Nickel Oxide Nanofluids: Concentration and Temperature

The acoustical and thermophysical properties of nanofluids is of great importance in heat exchange systems. Thus, these properties of nickel oxide (NiO) nanoparticles dispersed in ethylene glycol (EG) were studied after synthesizing and characterization of NiO nanoparticles. Speed of sound, acoustic impedance and free volume for NiO-EG nanofluids first increased upto 0.6 wt % and then decreased. However, viscosity, adiabatic compressibility and intermolecular free length first decreased upto 0.6 wt % and then increased. The density was observed to increase with increase in concentration and decrease with temperature. Speed of sound, viscosity and acoustic impedance decreases with increase in temperature, whereas, adiabatic compressibility, intermolecular free length and free volume increases. Thermal conductivity of NiO-EG nanofluids increased upto 0.6 wt % followed by its decrease, and it also decreased with the temperature at all concentrations. In conclusion, NiO-EG nanofluids upto 0.6 wt % concentration are very useful for nanofluids applications in thermal systems.

Assessment of the colloidal montmorillonite dispersion as a low-cost and eco-friendly nanofluid for improving thermal performance of plate heat exchanger

Synthetic nanofluids are produced by expensive and complex procedures which hinders their large-scale application in thermal systems. In this study the montmorillonite clay as a natural nanostructure material with a high dispersion ability has been introduced for achieving low cost and eco-friendly water-based green nanofluid. For this purpose, a set of montmorillonite nanofluids (MMTNFs) with different weight fractions of 0.2, 0.4, 0.6, 0.8, and 1% was mechanically prepared. The concentration-dependent properties of the samples including stability, thermal conductivity and viscosity were experimentally evaluated. The results indicated that MMTNFs were accompanied by a primary instability, but they gradually possessed excellent long-term stability. Adding montmorillonite to the water could enhance thermal conductivity up to 8.3%, which is worth with considering the naturalness, abundance and low-cost of this clay. MMTNFs exhibited excellent thermal performance when utilized as a working fluid instead of the pure water in a plate heat exchanger (PHE). The results showed that the best performance of PHE was obtained at an optimum MMT concentration (0.6 wt%). At optimal condition, the overall heat transfer coefficient, heat transfer rate, and thermal efficiency improved 27.25%, 17.65%, and 7.82%, respectively.

High-Temperature Heat Flux Sensor Based on Tungsten–Rhenium Thin-Film Thermocouple

Heat flux sensors (HFSs) are extensively used in combustion-related applications to collect important engineering data. However, most non-water cooling HFSs lack the durability to survive in the harsh, high-temperature environments where they are employed. A new type of thin-film HFS based on a W-5Re/W-26Re thermocouple has been developed for high-temperature heat flux measurement. The sensor consists of 136 pairs of micron-sized W-5Re/W-26Re thin-film thermocouples, an SiO2 thermal-resistance layer, and an AlN substrate. The SiO2 layer is sandwiched between the substrate and thermocouples, and allows the measurement of temperature differences arising from the difference in thermal conductivity between the substrate and the SiO2 layer. A protective layer with a sandwich structure prevents the tungsten-rhenium thin film from oxidizing at high temperatures in air. This small HFS with a protective layer can survive for 1 h in 1000°C air. Calibration data show that the HFS exhibits repeatable and fast thermal responses when a pulsed heat flux of 1000 kW/ $\text{m}^{2}$ is applied, and its sensitivity is 3.8* $10^{-6}$ V/(kW/ $\text{m}^{2}$ ). The experimental data agree with the simulated results. It can be concluded from the experimental results that the tungsten-rhenium thin film has a good thermoelectric response to high temperatures after the size is reduced to a micron. Thus the developed HFS can be a suitable alternative for applications in thermal systems, such as engines, turbines, and rockets.

Numerical Investigation of Charging and Discharging Processes of a Shell and Tube Nano-Enhanced Latent Thermal Storage Unit

Abstract Phase change materials (PCMs) generally suffer from low thermal conductivity which limits their application in thermal systems. The effective thermal conductivity may be improved by including fins, metallic powders, fine wires, and nanoparticles. The objective of this study is to investigate the thermal performance of graphene nanoplatelets (GNPs) dispersed in small quantities in 1-tetradecanol (C14H30O) PCM. This nano-enhanced PCM (NPCM) is placed in the annular space of a shell and tube in a solar thermal storage unit. The numerical simulations have been carried out using a numerical model based on the enthalpy-porosity and the control volume methods. The numerical model has been successfully validated by comparison with experimental data available in the literature. The numerical results showed that the higher the GNPs concentration, the lower the stored energy. The higher the GNPs concentration the shorter the discharging time. But, during the charging process, though the reduction in the melting time by 9.5% for GNPs concentration increase from 0 to 1 wt%, the melting time increased in contrast by 10.5% for GNPs content increasing from 1 to 3 wt%. For the GNPs concentration of 3 wt%, the heat transfer rate enhancement was limited by an undesirable increase in viscosity which led to weak natural convection and hence a longer charging time. Thus, the GNPs concentration of 1 wt% showed better thermal performance than that of 3 wt% concentration. These results may guide the improvement of solar thermal storage by dispersing GNPs in PCM.

Fabrication of a novel nano phase change material emulsion with low supercooling and enhanced thermal conductivity

A novel nano phase change material emulsion (NPCE) with low supercooling and high thermal conductivity was prepared by sonication method. N-octadecane was employed as phase change material, multi-walled carbon nanotubes (MWCNTs) were utilised as high thermal conductivity material, and octadecanol was utilised as nucleating agent. The characterization and thermal properties of the nanoemulsions prepared with various concentrations of MWCNTs and octadecanol were measured and analysed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), particle size analyser, differential scanning calorimeter (DSC) and thermal conductivity meter. The results indicated that the nanoemulsions prepared had great stability, low supercooling and enhanced thermal conductivity. The thermal conductivity was enhanced by 4.32% for 10 wt% nanoemulsion with addition of 1 wt% MWCNTs. The supercooling degree of 20 wt% nanoemulsion was decreased by 36.4% from 17.3 °C to 11.0 °C with addition of 1 wt% octadecanol. It can be concluded that the nanoemulsions prepared were able to be utilised as heat transfer and energy storage fluids, with great potential in thermal system applications.

An optimal control strategy for a heat pump in an integrated solar thermal system

In this paper, an optimal control strategy is developed for managing a heat pump in an integrated solar thermal system. Solar thermal systems usually operate with both feedback and feedforward controllers. The focus of many existing studies in solar thermal system applications has been on the feedback part, while less effort has been made to improve the performance of the feedforward part. This paper introduces a novel robust feedforward controller as a sub-controller of an optimal controller for operating a heat pump integrated with the solar thermal system. In a simulation environment, the optimal control structure is implemented, and the performance of the robust feedforward controller is compared with a simple feedforward controller. Regarding the electrical power consumption, the simulation results demonstrate that the optimal control structure with the proposed robust feedforward controller outperforms the control structure with the simple feedforward controller.

Experimental analysis of water-based nanofluids using boron nitride nanotubes with improved thermal properties

Nowadays, the use of nanofluids as alternative to commonly-used industrial heat transfer fluids is a topic of increasing interest. Analysing the improved efficiency of heat transfer processes according to advanced nanomaterials and obtaining stable nanofluids is one of the most interesting challenges. This paper presents a study of nanofluids based on boron nitride nanotubes and using an aqueous solution of Triton X-100 (which acts as a surfactant) as the base fluid. UV-vis spectroscopy, particle size measurements (size between 150 and 170 nm) and ζ potential (at about −25 mV) showed that stable nanofluids were obtained. Surface tension measurements were also performed. The surface tension of water was weakly affected by the presence of any amount of nanoparticles and was mainly governed by the presence of surfactant. The rheological properties of the fluids were also analysed, as were their isobaric specific heat and thermal conductivity values. A Newtonian behaviour was observed for the base fluid and the nanofluids, with no significant increase in viscosity. The isobaric specific heat increased by 8% and thermal conductivity by 10% compared with the base fluid. Thus, the results obtained are interesting because while thermal properties improved with nanoparticle content, rheological behaviour did not change. Consequently, the nanofluids studied in the current paper do not raise the pressure drop and pumping power significantly and may therefore be a good option for thermal system applications.

Sneak analysis and its applications in thermal systems

The traditional method of sneak analysis of a thermal system is based on mass flow and cannot reflect system functionality and overall characteristics. Therefore, this study presents a network tree topology model based on energy flow. The heat transfer process in the thermal system is described by introducing the concept of energy flow. According to the design function of the thermal system, hot and cold source of the system are defined as the beginning and end of path search, respectively. All possible paths of heat transfer for the thermal system are obtained. The method is applied in the central cooling system of a ship and compared with sneak analysis based on mass flow. Results of the comparison show that sneak analysis based on energy flow can find new sneak problems on the basis of sneak analysis based on mass flow. Thus, the new method is feasible and effective.

An experimental investigation of forced convection heat transfer with novel microencapsulated phase change material slurries in a circular tube under constant heat flux

This paper proposes novel microencapsulated phase change material slurries (MPCSs) as both the energy storage media and heat transfer fluids. The flow and heat transfer characteristics of MPCSs have been experimentally investigated. A series of experiments were conducted in laminar, transition and turbulent flow conditions for MPCSs in a circular tube under constant heat flux, respectively. The results of pressure drop measurements showed that transportation costs of slurries were close to pure water. The heat transfer experiments demonstrated that proposed MPCSs could enhance the heat transfer performance as the heat transfer fluids for thermal system applications in comparison with pure water. The average enhancement percentages of the Nusselt number were 23.9%, 20.5% and 9.1% for MPCS of 5 wt%, and enhancement of the Nusselt number was achieved when phase change material in the microcapsules were in solid, solid/liquid and liquid states, respectively. However, heat transfer enhancement of MPCS depends on the following combination factors: the slurry concentration, the flow rate, the pumping power and the heating rate. Importantly, the phase change process must be carefully controlled in the heat transfer test section with above combination factors in order to take advantages of MPCS over pure water.

Enhancement of Heat Transfer over a Double Forward Facing Step with Square Obstacle through Taguchi’s Optimization Technique

In this paper, the heat transfer to the fluid, passing through the double forward facing step (FFS) channel with square obstacle is enhanced by Taguchi’s S/N ratio analysis. Flow through the forward facing step channel has a wide range of applications in thermal systems due to its flow separation and subsequent reattachment, which in turn enhances the heat transfer. Flow separation and reattachment mainly depends on the channel geometry, obstacle and flow parameters. Hence, in this study, step height in the channel, obstacle size, Reynold’s number and gap between the obstacle and step are included as control paramters in the S/N ratio analysis for maximizing the heat transfer. These parameters are varied through three levels of values and L9 orthogonal array is employed. Numerical simulation technique is applied to analyze the L9 cases through computational fluid dynamics code. From the simulation, the rise in temperature at the channel exit with reference to the inlet is predicted. The best values for the identified control parameters conclude to a temperature raise of about 2.86°C. The optimum result obtained from the S/N ratio analysis is also compared with response surface methodology technique. Finally, analysis of variance (ANOVA) is conducted and identified that step height and flow Reynold’s number affect the heat transfer by about 79 and 19%, respectively.

Parameters affecting forced convection enhancement in ferrofluid cooling systems

Over the last decade, lots of research works showed that ferrofluids could have great interests in thermal systems. However, convective heat transfer coefficient and pressure drop in such systems are very sensitive to many physico-chemical and geometrical parameters which must be well adjusted. In this paper, several key parameters are studied in the range of 100<Re<2500 such as magnetic field density, length of the magnetic source, mass flow rate and particle concentration. The thermal-hydraulic behaviors of a ferrofluid and its carrier fluid are also compared regarding the hydraulic power which is required to cool the system. This study shows that the ferrofluids application in thermal systems is the best when the Reynolds number is low. Furthermore, it seems that the best thermal-hydraulic behaviors are obtained when the ferrofluid is magnetically saturated, the magnetic field is perpendicular to the heat flux and the magnetic source is short and located in the thermally developed region of the fluid flow.