Showing papers in "Thermal science and engineering in 2021"

Review on cold thermal energy storage applied to refrigeration systems using phase change materials

Abstract: This paper presents a thorough review on the recent developments and latest research studies on cold thermal energy storage (CTES) using phase change materials (PCM) applied to refrigeration systems. The presented study includes a classification of the different types of PCMs applied for air conditioning (AC) systems (20 °C) to low-temperature freezing of food (−60 °C). An overview of the influencing thermophysical properties of PCMs, as well as their respective characterisation methods, are presented. The current available PCMs on the market in the temperature range 10 °C to −65 °C are listed. Finally, research on CTES using PCMs in refrigeration systems are reviewed and grouped into applications for food transport and packaging, commercial refrigeration and various other refrigeration systems. The findings show that using ice/water as PCM for AC applications is the most commonly studied system, due to widespread use of these systems, expected growth in the future and low cost of using water as the PCM. Over the last ten years the published research integrating CTES in different parts of the food cold chain, using water-salt solutions and paraffin PCM in both active and passive methods, has increased. Suggestions for the integration of CTES in supermarkets and industrial applications are also emerging. The technology has received increased interest from the scientific community the last five years, due to the benefits of achieving peak shaving of the refrigeration demand, exploiting low-cost electricity hours and offering backup refrigeration in case of blackouts.

A review of geothermal energy-driven hydrogen production systems

Abstract: This paper presents a review of hydrogen production systems using geothermal energy, showing the importance and potential of this technology in addition to the main obstacles facing this domain. The effect of several parameters was taken into consideration, such as geothermal fluid temperature, water electrolysis temperature, working fluid, and type of power cycle. The different types of geothermal power plants were also compared, namely, flash, binary, flash-binary, recuperative, regenerative, and organic Rankine flash cycles. This study covers a wide range of investigations regarding hydrogen production rate, hydrogen production cost, energetic efficiency, exergetic efficiency, exergetic cost, and electricity generated. Hydrogen production rate is one of the most important mentioned parameters in which it was found to vary from 5.439 kg/h to 13958 kg/h. Multigeneration systems have shown great potential to enhance the overall system’s efficiency, leading to reduced production costs. The integration of another energy source was found to be interesting in geothermal-driven hydrogen production systems. This would promote the adoption of multigeneration system as well as increasing the geothermal fluid’s temperature before entering the power cycle.

Thermal transport of radiative Williamson fluid over stretchable curved surface

Abstract: The study of incompressible steady Williamson fluid flow is conducted in a curvilinear coordinate system. The flow is bounded below through curves stretchable sheet. Linear thermal radiation effects are considered to observe the heat flow in the system. The model was designed as an application to solar energy in thermal engineering processes. Employing suitable similarity transformations, a set of partial differential equations obtained from the flow situations are converted into a system of non-linear coupled ordinary differential equations. The subsequent equations are elucidated numerically via Runge-Kutta-4 along with the shooting algorithm. The outcomes for different flow properties are displayed and discussed both graphically and numerically. The observations shows that the curvature parameter reduces both velocity and temperature. Radiation parameter boosts the temperature of the fluid but reduces the local Nusselt number. Williamson fluid parameter has a reverse impact on velocity field but it works as a provoking agent for the case of thermal profile. The visual effects in the form of streamlines and isotherms are also presented for different Reynolds number.

Experimental investigation of thermo-physical properties, heat transfer, pumping power, entropy generation, and exergy efficiency of nanodiamond + Fe3O4/60:40% water-ethylene glycol hybrid nanofluid flow in a tube

Abstract: The synthesis method of in-situ/chemical co-precipitation was implemented for the addition of Fe3O4 nanoparticles on the surface of nanodiamond (ND) nanoparticles, and it is characterized by using x-ray diffraction, transmission electron microscopy and the magnetic property was estimated from the vibrating sample magnetometer. The 60:40% water-ethylene glycol mixture is used as a base fluid for the preparation of ND-Fe3O4 hybrid nanofluids. Experimental techniques are used to measure the thermophysical properties at various particle volume loadings, and temperatures and the obtained data is validated with literature data. The heat transfer, friction factor, and pumping power are evaluated at particle volume loadings from 0.05% to 0.2% and in the Reynolds number range from 2105 to 8126. The concepts of the second law of thermodynamics are used to evaluate the thermal entropy generation, frictional entropy generation and exergy efficiency of the hybrid nanofluids. The thermal conductivity enhancements are 5.03% and 12.79%, whereas, the viscosity enhancements are 108% and 50.84% at particle loading of 0.2% at temperatures of 20 °C and 60 °C in comparison with base fluid. The Nusselt number is augmented to 15.65%; thermal entropy generation is reduced to 20%, frictional entropy generation is augmented to 272.48% and exergy efficiency is increased to 38.24% with a maximum penalty in friction factor of 1.128-times at 0.2% particle loading and a Reynolds number of 7502 against base fluid data. New equations are modelled to evaluate the thermophysical properties, Nusselt number, and friction factor.

Numerical assessment of mixed convection flow of Walters-B nanofluid over a stretching surface with Newtonian heating and mass transfer

Abstract: The existing research investigates the numerical solution of a mixed convection flow of Walters-B nanofluid over a stretching sheet with Newtonian heating and mass transfer subject to the availability of magnetic field and mass suction. The impact of thermal radiation and chemical reaction with the Newtonian heat and mass transfer is conducted in detail. Also, the effects of nanoparticles are analyzed via considering the Brownian and thermophoresis motion. By utilizing similarity transformations, the relevant nonlinear governing equations with corresponding boundary conditions are modified to coupled nonlinear ordinary differential equations. These transformed coupled nonlinear ordinary differential equations are then solved numerically by providing the numerical approach bvp4c in MATLAB. The influence of multiple values of emerging parameters is studied by providing some graphs and tables with the consideration of both assisting and opposing flow regions. It is observed that the buoyancy parameter decays the velocity boundary layer thickness for assisting flow and the reverse trend is observed for opposing flow, as well as the viscoelasticity of nanofluid and Hartman number gradually reduces the boundary layer thickness. Further, the viscoelasticity parameter results in boosting the skin friction coefficient for both assisting and opposing flows whereas the Brownian and the thermophoresis motion have a reducing effect on the Nusselt number and Sherwood number enhances with the improvement of radiation parameter.

Recent progress in solar water heaters and solar collectors: A comprehensive review

Abstract: Solar water heating (SWH) is a clean, reliable, and cost-effective method of harnessing solar energy effectively to satisfy 50–80% of hot water needs. SWH technology is currently employed in many countries to reduce utility bills in both commercial sectors and houses. With the advancement of technology, SWH systems can be operated efficiently in any geographical area and climatic region in the world. However, the installation and overall performance of the system are still questionable. This review aims to provide an overview of the most commonly used solar water heating technologies. This paper seeks to critically analyze and summarise recent advancements in the technology, including storage tank/integrated collector storage solar water heater, solar water heaters (active and passive), solar thermal collectors, including concentrated and non-concentrated collectors and different policies. Substantial experimental studies and research works, including optimal designs, geometric modifications, and simulation works, were carried with respective technologies to enhance the system performance. Besides, the effect of solar collectors, radiation, region, water tank temperature, experimental modelling/simulation and studies conducted in Asia, America and Europe on SWHS improvements are also included. Policy developments of renewable energy heat consumption in different countries by technology from 2012 to 2024 were also included for better understanding. A detailed status on current and ongoing solar power projects based on solar technologies for electricity generation has been provided. The final section introduces the technical advancements of SWH technologies, policies, and future research SWHS.

Energy, exergy and economic analysis of an indirect type solar dryer using green chilli: A comparative assessment of forced and natural convection

Abstract: The energy, exergy and economic analysis of indirect type solar dryer (ITSD) was performed while drying green chilli under forced and natural convection. Fans powered by PV panels were used for forced convection setup. The collector and drying efficiencies of the forced convection dryer were found to be 63.3% and 10.4% and the same was 53.84% and 8.90% in natural convection ITSD, respectively. The specific moisture extraction rate (SMER) of green chilli in ITSD was found to be 0.6526 and 0.5603 kg/kW-h under forced and natural convection, respectively. The exergy output of the solar air collector was 3.61 to 677.84 J/kg and 6.50 to 1447.96 J/kg under forced and natural convection, respectively. The exergy loss of the drying cabinet was in the range of 0.2 to 327.76 J/kg and 0.84 to 664.63 J/kg in forced and natural ITSD, respectively. The exergy efficiencies of collector and drying cabinet were in the range of 1.91%, 56.12% and 2.26%, 51.85% for forced and natural convection setups, respectively. The exergy sustainability indicators were estimated. The exergetic performance of ITSD was improved with forced convection compared to natural convection ITSD. Economic analysis was performed and the payback period was found to be less in forced convection due to decreased drying time. Uncertainty analysis was carried out.

Finite element analysis on transient MHD 3D rotating flow of Maxwell and tangent hyperbolic nanofluid past a bidirectional stretching sheet with Cattaneo Christov heat flux model

Abstract: The finite element analysis on the transient magnetohydrodynamic three-dimensional rotating flow of Maxwell and tangent hyperbolic nanofluid flow past a bidirectional stretching sheet with Cattaneo Christov heat flux model has been explored numerically. The thermophoresis and Brownian motion effects are taken into account in the flow governing boundary layer equations. Appropriate similarity transformations are applied for the principal PDEs to transform into nonlinear ODEs. A widely recognized Numerical scheme known as the Finite Element Method is employed to solve the resultant convective boundary layer balances. The portrayal of certain physical parameters on the flow model is portrayed via figures and numerical tables. The temperature and concentration distribution for tangent hyperbolic nanofluid is prominently than that of Maxwell nanofluid, but inverse trend is observed for velocities profiles. An outstanding comparison with existing literature ensures a remarkable accuracy and concludes the rate of convergence is extraordinary for nonlinear differential systems. These examinations are relevant to the field of plastic films, crystal growing, paper production, and cooling of metal sheets.

Thermal management of single and multiple PCMs based heat sinks for electronics cooling

Abstract: The present study focuses on passive thermal management of electronic devices using heat sinks embedded with single or multiple phase change materials (PCMs) RT58, RT44 and n-Eicosane are used as PCMs, while aluminium fins are used as thermal conductivity enhancer (TCE) Single PCM cases are investigated independently while multiple PCMs pairs are studied through their filling in alternate enclosures separately Three constant heat fluxes of 15, 25 and 35 kW/m2 are applied to the heat sinks to investigate PCMs’ thermal performance The numerical model is validated against available experimental results where an acceptable 29% difference in the transient temperature is achieved High values of Nusselt number were discovered at the beginning of melting and the end of solidification stages The RT44 shows the lowest peak temperature and longest melting duration among single PCM cases, due to its high latent heat of fusion When n-Eicosane and RT44 are paired in a heat sink, the best overall thermal performance is achieved where its operational time is increased by 33–12% comparing to single n-Eicosane or RT44 The results show that the multiple PCMs pair of n-Eicosane/RT44 is feasible for high critical temperature devices due to its longer operating time and also lowest average transient temperature

Swimming of microbes in blood flow of nano-bioconvective Williamson fluid

Abstract: As blood flow patterns are employed in the diagnosis of circulatory disorders such as arteriosclerotic disease, bioengineers and medical scientists are interested in blood flow identification via the circulatory system. Researchers used non-Newtonian fluid models to measure blood flow cardiovascular system (e.g., hyperbolic tangent fluid, Powell Erying fluid, Casson fluid, Williamson fluid, etc.) as these fluids provide a rheological representation of blood with a more detailed thinning component. In this study, blood is taken as Williamson's fluid, and flow velocity is unsteady towards the stretching/shrinking surface in consonance with exothermic/endothermic function. The theology of gyrotactic microorganisms (GM) is addressed to nanofluid to stabilise nanoparticles due to bioconvection. A finite-difference computational approach evaluates the mathematical model followed by a stability and convergence analysis. The nanofluid blood velocity characteristics, temperature, concentration, and microorganisms are discussed following the diagrams. The skin friction, Nusselt number, Sherwood number and the microorganisms density are evaluated and clarified in detail. Besides, iso-concentrations and iso-microorganisms are configured for various factors to assess the nanofluid blood flows' boundary line thickness. The present analysis may be useful for many hyperthermia therapies, such as cancer treatment, tumour therapy and cardiac surgery, and applications in microbial fuel cells, microfluidic systems, and heat transfer contrivances.

Recent advances of composite adsorbents for heat transformation applications

Abstract: Low-temperature waste heat-powered adsorption heat transformation (AHT) is an energy-efficient and green technology, which is considered a promising alternative to the conventional vapor compression systems. The performance of an AHT system generally depends on the properties of adsorbents and adsorbates. The poor heat transfer and low packing density of adsorbent materials are the main limiting factors of an AHT system. Several researchers are working on composite adsorbents to overcome these drawbacks, and they observed enhanced thermal conductivity, packing density and volumetric adsorption capacity, which are very favorable to develop an efficient and compact system. There is hardly found any complete review on the composite adsorbents for heat transformation applications. This manuscript presents a comprehensive review on the thermophysical and adsorption properties of composite adsorbents developed so far for the AHT applications. This review also provides future research directions towards attaining adsorption-based efficient heat transformation systems. This review would greatly assist in selecting an optimum composite adsorbent or developing a new composite for a specific AHT application.

Brownian motion and thermophoresis effects on bioconvection of rotating Maxwell nanofluid over a Riga plate with Arrhenius activation energy and Cattaneo-Christov heat flux theory

Abstract: The heat and mass transportation for the bioconvection transient rotating flow of Maxwell nanofluid over Riga plate is inspected in the present investigation The bioconvection is utilized alongside nanofluids to provide stability to improved thermal transportation Further, Cattano-Christov theory, Buongiorno model, binary chemical reaction, and activation energy are incorporated The unsteady three dimensional partially differentiate formulation is simplified in the form of two independent coordinates ( ζ , η ) For steady-state solution ( ζ = 1 ) , Glerikin discretization in used to employ finite element simulation in MATLAB environment The buoyancy ratio parameters, unsteady parameter, rotating parameter, thermophoresis, and Brownian motion parameter escalated the nanofluid temperature field Modified electromagnetic parameter M H accelerated the primary flow velocity and activation energy augmented the volume fraction of nanoparticles in the boundary layer region The larger modified Hartmaan number M H reduces the coefficient of skin friction in primary direction but the magnitude of coefficient of skin friction in secondary direction is augmented The local Nusselt number Re x 1 / 2 Nu x is directly proportional to M H and β 2 but it is inversely related to β 1 and α T

Carbon nanotubes/Paraffin wax nanocomposite for improving the performance of a solar air heating system

Abstract: The study aims to demonstrate the possibility of taking advantage of the high solar radiation in Iraq effectively in heating the air for worming rooms and buildings in winter. The optimal diffusion of solar air heating applications depends mainly on the amount of heat stored and how quickly this heat is transferred to the air. The use of phase change materials to increase thermal storage is one of the best alternatives to date. The disadvantage of these materials is a clear reduction in their thermal conductivity, which impedes the rapid transfer of heat from them to the air. In this study, single wall carbon nanotubes (SWCNT) was added to a local Iraqi made paraffin wax, and the nanocomposite was used in a solar air heater. The SWCNT/paraffin nanocomposite thermophysical properties were examined to show its effect on the solar air heater performance. From the thermophysical properties of the carbon nanotubes added to paraffin in variable mass fractions, 3 wt% was selected. The addition of nanoparticles caused a slight increase in product density and viscosity. The percolation threshold of 3 wt% CNTs increased its thermal conductivity by 12%, reducing the melting and solidification points by 4.5 °C and 9 °C, respectively. The SWCNT/paraffin nanocomposite has improved the stored thermal energy by 20.7% for natural convection, and by 21.2% for forced convection compared to pure paraffin. Results of practical tests confirmed the possibility of using the proposed air heater to work in Iraqi weather conditions.

Energy, exergy, and exergoeconomic evaluation of a novel CCP system based on a solid oxide fuel cell integrated with absorption and ejector refrigeration cycles

Abstract: An innovative cogeneration power and cooling system is presented in which a solid oxide fuel cell (SOFC) is integrated with absorption and ejector refrigeration cycles. To assess the practicality of the suggested system, it is evaluated from energy, exergy, and exergoeconomic vantage points. The effects of key design parameters including SOFC input temperature, ammonia concentration, evaporation temperature, and hot temperature difference of the generator on the system’s technical and economic performance are determined. The results revealed that the suggested system can generate overall electricity, and cooling load of 398.4 kW, 51.31 kW, respectively. Further, the energy and exergy efficiencies, and product cost rate of the system are 55.46%, 47.29%, and 106.7$/GJ, respectively. Heat exchanger 3 is indicated as the major source of inefficiency by an exergy destruction rate of 106.2 kW. Furthermore, the results demonstrated that higher energy productivity is achievable by increasing the ammonia concentration, SOFC input temperature, and evaporation temperature. Moreover, results revealed that the higher the input temperature of the fuel cell, and the hot temperature difference of the generator are, the higher the exergy efficiency is obtainable. Considering the exergoeconomic assessment, it is observed that the product cost rate of the suggested CCP system can be decreased by the augmentation of the fuel cell input temperature, ammonia concentration, and evaporation temperature.

A critical review of power generation using geothermal-driven organic Rankine cycle

Abstract: Organic Rankine Cycle (ORC) is a promising electricity production technology that exploits low and medium heat sources. Usually, renewable and alternative heat sources can be used in order to feed an ORC with heat. The exploitation of geothermal energy is a usual and sustainable way to feed an ORC because it is a sustainable, abundant, economical and environmentally friendly choice. The main objective of this study is to review and to discuss the geothermal-driven ORC systems for power generation in a detailed way. Moreover, the special novelty is the emphasis that is given in the use of geothermal ORC systems inside cogeneration, trigeneration and polygeneration units. Both experimental and numerical investigations are included in the present work, while they are discussed in energy, exergy and economic terms. It is found that the geothermal-driven ORC systems are viable investments with relatively low payback periods, as well as these systems lead to high energy efficiency. Moreover, it is concluded that a 20% to 30% increase in the performance of geothermal-fed ORC systems is possible by optimization. Lastly, it is useful to state that the polygeneration systems that include geothermal-driven ORCs are promising units that present high exergy efficiency values.

A printed-circuit heat exchanger consideration by exploiting an Al2O3-water nanofluid: Effect of the nanoparticles interfacial layer on heat transfer

Abstract: Supercritical carbon dioxide (S-CO2) Brayton cycle is an encouraging power conversion technology pertaining to waste heat recovery applications, because of the high compactness and efficiency it presents. A key technological challenge for the commercialization of this technology is the improvement of the cooling process of these cycles. In this study, an analytical investigation of a printed-circuit heat exchanger (PCHE) used as precooler for S-CO2 Brayton cycles and employing an Al2O3-water nanofluid is presented. In particular, the heat exchanger is modeled as segments in series to investigate the nanofluid impact on the PCHE’s thermal-hydraulic performance. Regarding the nanoparticles consideration, the selected theoretical model for the estimation of the thermal conductivity takes into account the radius of the nanoparticles and the nanolayer thickness which is formed around it. In brief, the maximum used nanoparticle volume fraction of 5% results in an improvement of 75% for the heat transfer coefficient leading, in turn, to a reduction of 1% for the heat exchanger length and a pressure drop increase of 8%. Finally, the increase of nanoparticle radius results in a reduced effective thermal conductivity, while the nanolayer thickness of 2 nm showed an improved heat transfer coefficient by 43% compared to the minimum nanolayer thickness of 0.5 nm.

A comprehensive numerical investigation of unsteady-state two-phase flow in gravity assisted heat pipe enclosure

Abstract: In this study, thermal performance analysis of glass and copper two-phase closed thermosyphons (TPCTs) were investigated as 3D using comprehensive experimental methods and a new combined numerical model containing two stages. For this purpose, Volume of Fluid model has been used for the first 60 s, and Eulerian model has been employed after 60 s until 180 s for the first time in the literature. For the verification of this numerical analysis, the surface temperatures of TPCTs were measured at twenty different points by K-type thermocouples. The pressure change inside the pipes was measured by a vacuum manometer. A video camera was utilized to observe the change of steam and water volumes in the glass TPCT. The experimental and numerical results were also compared with each other in real-time for the first time in the literature. According to results, the numerical temperature distributions and steam volumes in TPCTs have shown a similar trend with the studies in the literature. It was observed that the maximum absolute temperature difference values in the evaporation, middle and condenser regions for TPCTs ranged from 6.81 K to 18.63 K. These values are similar to the values in the other studies. The maximum absolute temperature difference values were calculated between 12.09 K and 26.07 K for different turbulence models.

Thermal energy storage performance of PCM/graphite matrix composite in a tube-in-shell geometry

Abstract: Melting heat transfer performance and measuring energy storage efficiency via total melting time of PCM/graphite matrix in a tube-in-shell for solar thermal energy storage and recovering waste heat applications is studied experimentally. The phase change material (PCM)-organic/paraffin (P56-58), is impregnated into the graphite matrix, with the bulk density of 50 g/L. The effect of inlet temperature (Tinlet = 75 °C and 85 °C) of heat transfer fluid (HTF) on total melting time is obtained. The time-history of temperature measurements, thermal camera imaging, and liquid fraction are obtained to reveal the thermal performance of PCM/graphite matrix in a tube-in-shell latent heat thermal energy storage (LHTES) system in detail. The results show that the PCM/graphite matrix has a remarkable effect on the phase change heat transfer and total melting time. The thermal performance of the PCM/graphite matrix is presented comparatively with the conventional tube-in-shell storage unit. Effective thermal conductivity which enhances the heat transfer rate is shown to increase 35 times compared to that of pure paraffin. The total melting time decreases by about 92% compared to the conventional tube-in-shell unit. Uniform melting behaviour is observed based on highly conductive abundant thermal paths for PCM/graphite matrix. Heat transfer takes place by dominant conduction for the PCM/graphite matrix. Leakage issue is prevented using graphite matrix encapsulation. Total melting time is decreased by about 31% with the increase in HTF inlet temperature for the PCM/graphite matrix.

Influence of the geometrical parameters and particle concentration levels of hybrid nanofluid on the thermal performance of axial grooved heat pipe

Abstract: In the present study, a numerical model is developed to maximize the thermal performance of axial grooved heat pipe (AGHP) working on CeO2 + MWCNT / water based hybrid nanofluid (HNF). The effects of a wide range of volume concentration (0.25%−1.50%) at different operating temperatures (55 ℃−75 ℃) are analyzed to maximize the thermal performance of AGHP. The current numerical work aims at finding the heat transport capacity, Qmax, and total thermal resistance, Rtotal, of AGHP with acceptable accuracy by validating it with the past experimental studies. It has been observed that the highest Qmax is achieved at 1.25% of the volume concentration of HNF for each operating temperature. The novel HNF based AGHP shows an enhancement of 61.27% in the heat transport capacity and a reduction of 30% in the total thermal resistance compared to the water-based AGHP. The study is further extended by incorporating the effects of geometrical parameters on AGHP’s thermal performance. Three geometrical parameters are considered in this study, namely groove height (hg), number of axial grooves (N), and their inclination angle (α). A total of 128 combinations of N, hg, and α have been analyzed to optimize Qmax and Rtotal. The maximum thermal performance of AGHP is achieved at N = 28, hg = 1.3 mm, and α = 76°, where the Qmax = 78.5 W and Rtotal = 0.054 °C/W.

The impingement of liquid boiling droplet onto a molten phase change material as a direct-contact solidification method

Abstract: The boiling of a fluid dripping on the surface of molten phase-change materials provides an efficient means for heat exchange or cooling of the melt. For the first time, in this study, the impact of acetone drops onto molten paraffin as a direct-contact solidification method is experimentally investigated to get a better insight into the interaction between the drop boiling and the heat extraction process from the phase change materials during impact. As the acetone drop impacts the molten paraffin surface, acetone starts to boil, and a portion of molten paraffin is solidified. Four impact Weber numbers (corresponding to heights of 10, 20, 30, and 40 cm) for the acetone drop and six surface temperatures for the molten paraffin (66, 68, 70, 75, 80, and 90 °C) are considered. Given the range of these two parameters, four distinct regimes of impact were observed using a high-speed camera and categorized, including the formation of the crater, crown, returned liquid paraffin column (jet), and the drop pinching off from the jet tip. Moreover, as We increased or the paraffin surface temperature decreased, the solidified paraffin’s on the molten surface grew. A correlation was obtained based on the impact Weber number and surface temperature of molten paraffin to determine the spread of solidified paraffin area on the melt free surface after drop impact. Results also showed that both the maximum crater depth and width increase with the increment of both the molten paraffin temperature and the impact Weber number.

Statistical analysis of MHD convective ferro-nanofluid flow through an inclined channel with hall current, heat source and soret effect

Abstract: The role of Hall current, heat source and Soret effects on MHD convective ferro-nanofluid (Fe3O4-water) flow through an inclined channel with porous medium has been theoretically and statistically examined. Velocity, thermal and concentration boundary layer in nanofluids are considered to be oscillatory. Heat due to radiation is induced by the huge disparity in temperature between the plates. Hall current is generated by the uniform application of a strong magnetic field perpendicular to the flow of fluid. Boundary layer equations are changed to non-dimensional type and it is resolved by perturbation approximation. The outcomes are displayed in the form of tables and figures using MATLAB software. The outcome of pertinent parameters on concentration, temperature and velocity profiles are evaluated through graphs. Besides, wall heat, mass transfer rates and surface drag are investigated through statistical tools like regression and probable error. Results explain that heat source and hall current have a negative impact on skin friction whereas heat source has a positive impact on Nusselt number. Also, Soret number has a negative impact on Sherwood number.

A comparative heat transfer study between monotype and hybrid nanofluid in a duct with various shapes of ribs

Abstract: In this study, the flow of water-based monotype nanofluid (Al2O3/water) and hybrid nanofluid (Al2O3-Cu (60:40%)/water) having constant 1.0% nanoparticle volume fraction (npvf) in a duct with rib is analyzed under turbulent flow regime concerning heat transfer and flow behavior. The Nusselt number (Nu), friction factor (f), PEC number, temperature contour, and turbulence intensity are examined in the study. Furthermore, the significance of the shape of rib (ellipse, square, and triangular), Reynolds number (20000, 30000, 40000, 50000, and 60000), and types of nanofluids (monotype and hybrid) are studied. The outcomes of the study are justified with the previous studies in the literature and an acceptable consistency is obtained. The results show that the Nusselt number increases with the rising of the Reynolds number (Re) and in the case of using monotype nanofluid and hybrid nanofluid in the duct with the rib and no rib condition. At the highest Reynolds number and the use of the triangular rib, while the increase in Nusselt number with monotype nanofluid is 18.0%, the increase in Nusselt number with hybrid nanofluid is approximately 32.0%. The shape of the rib is substantial on heat transfer and flow characteristics. Moreover, the triangular rib has the best heat transfer rate in comparison with the other shape of the rib. Eventually, the results in the duct placed the triangular rib and forced the hybrid nanofluid indicate a bright conclusion in terms of the future of hybrid nanofluid for cooling and heating practices in the industry.

Yearly investigation of a solar-driven absorption refrigeration system with ammonia-water absorption pair

Abstract: The objective of the present investigation work is the analysis of a solar-driven refrigeration unit with parabolic trough solar collectors. The refrigerator is a single-stage absorption machine with NH3/water working pair for producing refrigeration in the temperature range from −35 °C up to 5 °C. The system is studied energetically, exergetically and financially. The yearly analysis is performed for the weather data of Athens, Greece. The thermodynamic model was created in Engineering Equation Solver and it is validated with literature data, while the dynamic model was programmed in language Matlab. More specifically, the thermodynamic analysis is conducted by applying the energy rate balances and the mass flow rates balances in the system devices, while the dynamic analysis is performed by applying the energy balance in the storage tank of the solar field. According to the final results, there is an optimum generator temperature that maximizes the system performance and it is depended on the operating conditions. For refrigeration product at −20 °C and heat rejection at 40 °C, the yearly system coefficient of performance is 0.255, the yearly exergy efficiency 4.86% and the simple payback period is close to10 years.

Performance analysis of arc rib fin embedded in a solar air heater

Abstract: A thermal model is developed for analysing the influences of arc rib fin arrangement and length of absorber plate on the heat transfer characteristics of a solar air heater. The arc rib fin arrangement is designed by varying the fin relative roughness height ratio (e/De) in the absorber plate. Solar air heater with fixed arc rib fin configuration with e/De (0.0422) and variable arc rib fin configuration with two different relative roughness height ratios of e/De (0.0422 and 0.0541) are modelled. The influence of absorber plate length (1 and 2 m) on the solar air heater performance is compared with the configurations mentioned above at various mass flow rates of air (0.02 kgs−1 to 0.06 kgs−1). The outlet air temperature of solar air heater, mean absorber plate temperature, heat transfer characteristics (Nusselt number and frictional factor), pressure drop, thermo-hydraulic performance parameter, efficiencies (thermal, effective, and exergy), collector efficiency factor, and collector heat removal factor are predicted at different air flow rates. The variable arc rib fin arrangement in the solar air heater leads to maximum utilization of available solar energy from the absorber plate, and reported maximum outlet air temperature and lower mean absorber plate temperature when compared to fixed arc rib fin arrangement and smooth duct. Further, the variable arc rib fin arrangement has better heat transfer and thermo-hydraulic characteristics than the fixed arc rib fin arrangement and smooth duct. Thus implementation of the variable arc rib fin arrangement will significantly enhance the overall performance of the solar air heater.

Pool Boiling Review: Part I- Fundamentals of Boiling and Relation to Surface Design

Abstract: The pool boiling process is one of the most effective heat transfer modes capable of transferring large amounts of heat with small temperature difference between the heated surface and the fluid. In addition, fundamental knowledge of pool boiling processes is the starting point of flow boiling research and applications. It is therefore no surprise that it has been, and still is, the subject of extensive research globally for quite some time and a critical analysis is now required in order to move forward with enhanced surface designs. The current on-going research focuses on the understanding of boiling fundamentals including bubble generation, growth and bubble dynamics. In this context, fluid-surface interaction is critical. In the first part of this two-part paper we present the factors and parameters affecting the above, starting with the criteria for gas/vapour entrapment, nucleation site stability and the superheat required for heterogeneous nucleation. The models predicting the incipience superheat are critically described, classified into phase instability and superheated boundary-layer based models. This first part includes bubble growth and departure models, elucidating the effect of surface topology and wettability that can inform and facilitate the design of enhanced surfaces that are presented in Part II [10] . Three fluids of industrial interest, i.e. FC-72, HFE7100 and water were used through the discussion, as examples, to represent low and high surface tension fluids and help the understanding of surface-fluid interactions and relation to possible heat transfer enhancements.

Experimental investigation of fill pack impact on thermal-hydraulic performance of evaporative cooling tower

Abstract: The present work deals with an experimental study of the performance of an evaporative cooling tower (ECT) with a developed fill pack. The fill pack consists of inclined-corrugated contact elements (ICCE) made of the metal plates with perforations, providing a uniform distribution of interacting phases over the ECT cross-sectional area. This study investigates the effect of fill pack design on hydraulic and thermal characteristics of the ECT. Four empirical equations were found for the pressure drop through four types of dry fill packs. The detailed analysis includes two fill packs consisting of ICCE with 6 mm holes with and without a metal grid. Hydraulic operating regimes of the ECT and empirical equations for the wetting pressure drop through the fill packs had been defined. Based on experimental data and the method of transfer units, empirical relationships of the volumetric mass transfer coefficients were determined. The comparison between the obtained results and those found in the literature for other types of proves the high performance of the developed fill packs. Besides, using the Lewis relation, the dependencies of the volumetric heat transfer coefficient on the average air velocity were analyzed. The results indicate that maximum cooling efficiency of the studied fill packs was observed at the low wetting rates according to the Merkel number. The fill pack from ICCE with 6 mm holes and without the metal grid seems to be more efficient, as it provides relatively higher values of the heat and mass transfer coefficient and lower pressure drop.

Thermal uniformity performance of a hybrid battery thermal management system using phase change material and cooling plates arrayed in the manner of honeycomb

Abstract: A hybrid battery thermal management system (BTMS) with phase change material (PCM) coupled cooling plate arrayed in the manner of honeycomb is proposed for the cylindrical lithium battery pack in this paper. Paraffin wax and glycol are used as PCM and cooling liquid, respectively. 3D numerical simulations are carried out to analyze temperature characteristics of the system, coupling characteristics of PCM and cooling plate, mass flow rate of cooling liquid and channel number of cooling plate on the heat dissipation of battery pack. Results show that the temperature distribution of the battery pack has good uniformity, which is the most prominent advantage of the proposed system. The coupling of PCM and cooling plate greatly improve heat dissipation effect. Increasing mass flow rate of cooling liquid can significantly improve heat dissipation efficiency, but the maximum temperature difference (Δ T max ) of battery cell also increases. However, the influence of channel number of cooling plate on heat dissipation efficiency is lower than that of mass flow rate. Adding one channel can reduce the battery temperature by 2 K, but it has little effect on Δ T max . This study may provide effective guidance for the design of the PCM coupled liquid cooling BTMS.

Numerical investigation of PCM melting using different tube configurations in a shell and tube latent heat thermal storage unit

Abstract: Thermal energy storage plays an essential role in energy systems to reduce the mismatch between the energy supply and demand. Phase change materials are widely used in different technologies but suffer from low heat transfer performance. This numerical study aims to investigate the enhancement in the melting thermal characteristics of lauric acid as a phase change material by using Ansys-Fluent. Three inner tubes of heat transfer fluid were employed with four different arrangements: inline-central array (normal case, Case A), downward and upward triangle arrays (Case B and C) and an arc array at the shell bottom (Case D). Results revealed that the arc array and downward triangle configurations reduced the melting time by about 76% and 72%, respectively. However, the upward triangle tube arrangements increased the melting time by about 10% compared with the normal case.

Augmenting performance of fuel cells using nanofluids

Abstract: Fuel cells (FCs) have gained increasing attention over the past few years as sustainable energy conversion devices. This is mainly due to their high efficiency which related to the direct conversion of chemical energy into electrical energy (the most desirable energy form). Despite the high-energy conversion efficiency of FC, still substantial part of the produced energy is lost as waste heat, hence, proper cooling is necessary to maintain the optimum operating temperature and integrity of the FC. Different heat transfer fluids (HTFs), with water as the most common, are typically used as coolants for FC. In recent years, nanofluids (NFs) have emerged as high-efficiency HTF with remarkably enhanced thermophysical properties. In this work, the application of NFs for the heat management and waste heat recovery (WHR) in the FCs has been reviewed and discussed. NFs have been proved to be effective coolants for the FCs. The presence of NFs almost doubles the thermal performance of the FCs while decreasing the size of the cooling system. Additionally, NFs found various applications in the different WHR technologies that can be used for FC devices, like absorption chillers, thermoelectricity generator (TEG), and organic Rankine cycle (ORC) enhancing the performance of the FC-based poly-generation systems. For instance, the use of 0.1 vol% Al2O3/water-ethylene glycol NF has reduced the heat exchanger size of 2.13 kW proton-exchange membrane FC by about 30%. Moreover, carbon-based NF demonstrated a significant role in improving the performance of microbial FC through the enhancement of the electron transfer between the bulk microorganisms and the anode surface resulting in about a 50% increase in current and power densities.

Synthesis and thermal characterization of paraffin-based nanocomposites for thermal energy storage applications

Abstract: Nowadays, phase change materials (PCMs) have gained considerable attention for thermal energy storage applications. However, commonly used PCM, such as paraffin wax, suffers from low thermal conductivity. Therefore, the main objective of this study is to develop relatively higher thermally conductive PCM composites employing different mass fractions of paraffin wax and two thermally conductive nanomaterials, namely silicon carbide (SiC) and silver (Ag). After the synthesis, the thermal characterizations have been performed. Results showed a significant enhancement in thermal conductivity. It has been found that 15 wt% SiC contained nanocomposite exhibits almost 58.2% improvement of thermal conductivity over the parent paraffin, whereas 15 wt% Ag contained nanocomposite reveals 31.2% improvement. However, a slight reduction in the latent heat of fusion, melting point, and specific heat capacity is observed at the lower concentration of nanoparticles in the composites, and it becomes more significant at the higher concentration (>5 wt%). Thus, all the presented results would carry vital importance for the selection of an optimal PCM nanocomposite for designing a nano-PCM based thermal energy storage system.