The increasing demand to enhance the efficiency of heat exchangers has sparked numerous investigations aimed at increasing heat transfer rates while simultaneously reducing the size and cost of industrial equipment. Among the various apparatus utilized in different industries, the double-pipe heat exchanger has garnered significant attention due to its simplicity and versatile applications. Over recent years, numerous meticulous and invaluable studies have delved into double-pipe heat exchangers. This review meticulously analyzes the developmental trajectory of this heat exchanger type while extensively discussing methods for enhancing heat transfer within these systems. In striving to present a comprehensive overview, the authors have meticulously gathered information on various enhancement methods, including active and passive. Recent studies exploring passive heat transfer augmentation methods in double-pipe heat exchangers have been summarized. These methods are summarized under surface modification (like dimples, vortex generators, and protrusion), inserts (like twisted tapes and helical coil), and extended surfaces (like fins and baffles). The prime objective of the current study is to organize the literature related to combining different heat transfer augmentation methods. An additional section on alternating cross-sectional tubes used in double-pipe heat exchangers has been summarized, exhibiting increased vorticity without vortex generator devices. Longitudinal vortices are created throughout the tube's length, leading to a notable improvement in its thermal efficiency. Furthermore, detailed discussions on using Nanofluids in these heat exchangers are provided. Additionally, correlations, primarily focusing on the Nusselt number and pressure drop coefficient, are presented within this review. This comprehensive review is anticipated to offer valuable insights for future investigations in this field.
The impact of a magnetic field on the convective heat transfer of ferrofluids from a heated sphere immersed in a porous medium is investigated. The dimensional governing boundary layer equations are initially transformed into a convenient non-dimensional form utilizing the non-dimensional variables. The resulting nonlinear systems of equations are then numerically solved inside the computing domain into a regular rectangle using the effective Finite Difference Method (FDM). Numerical outcomes are then represented in terms of local Nusselt number, velocity, temperature profile, and skin friction coefficient, respectively for a range of porosity parameters, ϵ = 0.4, 0.6, 0.8, magnetic effect parameter or Hartmann number, Ha = 0.0, 1.0, 3.0, 5.0 and the ferroparticle volume fraction coefficients, ϕ = 0%, 2%, 4%, 6%. It is thought that the base fluid’s Prandtl number, Pr=6.8733, is constant. In addition, the flow pattern inside the boundary layer region is shown using streamlines and isotherms, and the underlying physics of the flow behavior is then explored. There is a graphical presentation of the data. The findings show that velocity decreases with increasing value Ha, ϕ and ϵ. An increase in the Hartmann number Ha causes the temperature to rise. The local N_u and C_(f )are decreasing as Ha and ϕ values increase. With an increase in the porosity parameter ϵ and ϕ, the temperature profile rises and the C_f and local N_u decrease. For increasing Ha, the figure of streamlines seems to depict functions with more gradual changes, and for isotherms, it represents functions with sharper, exponential-like increases. While many works focus on ferrofluids or porous media individually, combining the study of heat transfer in ferrofluids within porous structures can represent a distinct focus. The problem is crucial for developing advanced heat transfer technologies for more efficient energy management in various engineering applications.
Fluidized bed apparatuses are widely used in chemical engineering. Description of the hydrodynamic state of the apparatus is the starting point for predicting most technological operations in gas-solid flows. The object of this study is the gas and solids distributions in a fluidized bed column. The key aim of the study is to develop a simple yet informative mathematical model of the migration of gas and particulate solids in a fluidized bed column. The model is developed to solve the problem in a two-dimensional formulation. The phase migrations of the fluidized bed along the height of the column are described on the basis of the mathematical apparatus of the theory of Markov chains, and an explicit difference scheme is used for the mathematical model of particle transfer in the radial direction. A cell of small but finite size acts as a representative volume of the simulated system. The representative volume of such geometry is apparently used for modeling the motion of fluidized bed phases for the first time. At the same time, it is precisely this model structure that corresponds to the tradition of identifying the radial and axial coefficients of particle macrodiffusion. Parametric identification of the model is carried out on the basis of the empirical relationships known from the literature. The numerical experiments performed in the study showed the qualitative consistency of the proposed model. A comparison of calculations with the results of a natural experiment also confirmed the presence of predictive capabilities in the model. Thus, the proposed model can be considered as a reliable scientific basis for computer methods for calculating fluidized bed devices.
Considering the excellent properties of hybrid nanofluids, it is a good idea to use them to improve the performance of solar collectors. The performance of a parabolic trough solar collector equipped with an internally finned absorber tube (IFAT) has been numerically studied based on the environmental, economic, exergy, and energy perspectives. The working fluid of the collector is hybrid nanofluid (HNF), consisting of of MWCNT and Fe3O4 nanoparticles and Therminol VP-1 as base fluid (BF). The volume fraction of nanoparticles is 3%, the operating fluid temperature is 600 K, and the Reynolds number is in the range of 2×104-2×105. The fluid flow is simulated using Ansys-Fluent software. Environmental analysis was done using the life cycle method, and economic analysis was based on the levelized cost of energy. Investigation of the results showed that the energy and exergy efficiencies of the collector when using the IFAT is higher than the smooth absorber tube (SAT), and using HNF is higher than base fluid. The maximum energy efficiency enhancement of the PTC using IFAT-BF, SAT-HNF, and IFAT-HNF compared to SAT-BF is 4.93, 1.49, and 5.35%, respectively, and the maximum exergy efficiency enhancement is 6.09, 1.6 and 6.6%, respectively. Based on the economic approach, it was observed that for the Re lower than 5×104, the use of PTC with IFAT is more economical than the PTC with SAT. The environmental analysis showed that the use of the PTC with SAT compared to PTC with IFAT and also the use of HNF instead of the BF produces less CO2 in the life cycle of the collector.
Improving heat transfer in thermal systems has become a focus of many research studies due to the critical need for efficient waste of residual heat. The regulation of heat transfer between components in thermal systems has a direct impact on their efficiency and performance. As a result, effective heat management is critical to improving the efficiency of thermal systems and extending the life of their components. It should be noticed that baffles are important structural components widely used in various industrial applications like heat exchangers, solar collectors, electronic cooling, etc. In addition, baffles enhance fluid mixing and heat transfer behaviors. Most industrial systems do not operate in a steady state. In particular, transient phases occur during start-up and shut-down or during the control phase of controlled systems. Thus, in laminar flow, baffles induce flow unsteadiness or help the flow to bifurcate from a steady state to an unsteady flow. This paper treated the effects of different baffle shapes incorporated in channels on heat transfer rate, efficiency and friction factor in mixed and forced convection cases. Various experimental and numerical studies have been carried out on this topic to examine heat transfer enhancement compared to the flow energy. It was noticed that increasing the Reynolds number, blockage ratio and decreasing the Grashof number can achieve an increase in heat transfer. The maximum heat transfer enhancement was obtained for higher blockage ratio and higher Reynolds number in forced convective flow. The highest heat transfer improvement was obtained for the 45° angled baffles (between 150% and 850%). In mixed convective flow, the highest rate of heat transfer was obtained for transverse baffles (2.8 times compared to a similar channel with no baffles). Finally, This comprehensive review is beneficial for researchers focused on flow and heat transfer applications to use other baffle designs and fluids beyond air.
The thermal energy found in shower hot wastewater, which is usually dumped, can be recovered through heat exchangers and used to pre-heat shower cold-water, contributing to energy sustainability. The objective and novelty of this work are to present a computational fluid dynamics (CFD) model and a theoretical model based on literature correlations to evaluate the performance of a shower water horizontal heat exchanger with twisted tape inserts. CFD simulations are used to improve the shape of twisted tape in the setting of the turbulator. The findings suggest that the wastewater flow convection heat transfer coefficient is between the flow around a cylinder and the flow around a cylinder in a narrow channel. The results for the turbulator are consistent with theoretical data, except for twist ratios below 3. The most promising twisted tape design has a twist ratio of 4 and a thickness of 1 mm. A conclusion could be drawn that the efficacy of the twisted tape in the heat exchanger is greater at lower flow rates. The performance gain ranges from 18.1 % to 3.0 % for flow rates of 3–10 L/min. Future directions for this research should focus on the improvement of the external convection coefficient because it represents the highest thermal resistance in the shower wastewater horizontal heat exchanger.
The purpose of the present study is to examine the impact of Compression Ratio (CR) on energy and exergy efficiency of a Variable Compression Ratio (VCR) and Common Rail Direct Injection (CRDI) type diesel engine powered by a blend of diesel and biodiesel from Moringa oleifera. Experiments are performed at four distinct CRs of 15:1, 16:1, 17:1, and 18:1 at 100% loading condition with a fixed engine speed of 1500 rpm, Injection Timing (IT) of 23°before top dead center (bTDC), and Injection Pressure (IP) of 600 bar. Analysis was done on the energy and exergy potential of the fuel input, cooling water, exhaust gas, first and second law efficiency, entropy generation, and Sustainability Index (SI). The energy analysis results show that for all tested fuel blends, an increase in CR results in a decrease in fuel inlet energy, exhaust gas energy, and unaccounted losses, as well as an increase in cooling water energy and energy efficiency. The highest energy efficiency reported for the diesel and biodiesel blend MB30 was 27.20% and 28.13%, respectively, at a higher CR of 18:1. The maximum cooling water energy reported for diesel and biodiesel blend MB30 was 4.09 kW and 4.36 kW, respectively, at a higher CR of 18:1. The reported minimum energy of the exhaust gases for the diesel was 2.74 kW and for biodiesel blends MB10, and MB20 it was reported as 2.95 kW for both blends at a higher CR of 18:1. Across all tested fuel blends, the fuel exergy rate, exergy rate of exhaust gas, and destructed energy decrease as CR increases which results in improvements in entropy generation, SI, and exergy efficiency. The highest exergy efficiency reported for the diesel and biodiesel blend MB30 was 26.31% and 27.21%, respectively, at a higher CR of 18:1. The maximum SI reported for the diesel and biodiesel blend MB30 was 1.36 and 1.37respectively at a higher CR of 18:1. The minimum entropy generation reported for diesel and biodiesel blend MB30 was 0.019kW/K and 0.016 kW/K at higher CR of 18:1.An investigation of the thermodynamics of methyl esters of Moringa oleifera oil mixed with diesel in a VCR-CRDI type engine shows that the combination consists of CR 18:1 and fuel blend MB30 at full load condition offers better performance.
A propionic acid fermentation process not only provides a more sustainable approach but also opens the door to propionic acid production capacity in regions with limited petroleum supplies. With fermentation, low-cost substrates can be used, such as residual biomass; reducing their concentration in nature. This process becomes interesting because from it propionic acid is considered natural. Several models have already been developed to describe the dynamics of components such as: Microorganism (biomass), nutrients (substrate), metabolites (product). However, a challenge is how to define the model that best represents the kinetic term, and therefore, there are several models for this modeling. This article's novelty is the application of the Bayesian technique (Computational Bayesian Approximation) to estimate parameters and simultaneously select the best model. Model validation was carried out considering propionic fermentation regarding experimental data from the literature, which selected the Andrews model as the best to predict the dynamic of biomass, substrate and product by the following parameters estimated = 0.192, ms = 0.005, mp = 0.017.
The recovery of low-grade heat is crucial for energy conservation, particularly in manufacturing and process industries that discharge substantial waste energy into the atmosphere. This waste heat, varying from slightly above room temperature to several hundred degrees Celsius, can exist as liquids, gases, or a combination of both. Low-grade heat recovery, also known as waste heat recovery, involves capturing and transferring this energy using gas or liquid mediums, reintroducing it into the process as an additional energy source. This process is essential for improving energy efficiency and promoting sustainability, employing various techniques tailored to the waste heat temperature. Helical cone coils offer significantly enhanced heat transfer characteristics compared to straight tubes. These coils feature a secondary fluid flow running in planes parallel to the primary flow within their helical structure. This study focuses on designing and analyzing a shell and helical cone coil heat exchanger, highlighting its ability to reduce unit size compared to a standard shell-and-tube heat exchanger operating under the same thermal load. The experimental setup included a shell and helical cone coil configuration, utilizing diesel engine exhaust as the hot gas source and tap water as the cold fluid in a counterflow arrangement. The investigation revealed that helical cone coils extracted 15 to 20% more heat compared to conventional straight tubes, demonstrating improved effectiveness and compactness.
In this research, a combined cooling system of heating and electricity is proposed and a complete thermodynamic analysis is presented. The system includes a gas turbine, a heat cooling system, a cogeneration system and a hot water heat exchanger. The basis of the work is that by using the recovery of waste gases in the gas turbine can be generated by a steam turbine and, with the help of an absorption chiller, can recover the waste heat in the steam turbine and provide the required cooling. The cogeneration system saves energy consumption, and reduces environmental pollution. In this study, we have tried to increase the economic justification of using the cogeneration system under study by using up-to-date cost functions. The energy efficiency and exergy efficiency of the studied system are 20 and 21%, respectively, which is a reasonable amount. The results of the economic analysis show that with a total cost of $ 93.56 per second and a total investment and maintenance cost of $ 1732 per second, the proposed system is highly economical and profitable in practice. This may provide a new way to increase the efficiency and effectiveness of thermodynamic performance of cogeneration systems.
Numerous industrial and biological processes like water filtering, air filtering, blood flow through arteries, and absorption of digested foods are a few examples of flow with suction/injection at the walls. Studies related to the injection/suction of Newtonian fluids have been reported by several researchers in the past, but studies related to the flow of non-Newtonian fluids with injection/suction are scarce in the open literature. Rivlin-Eriksen fluid (also known as third-grade fluids) is an important class of non-Newtonian fluids that is applied for modeling crude and slurry material in a liquid state, molten lava, blood flow, petroleum etc. Considering this, the flow of a Rivlin-Ericksen fluid of grade three through large porous parallel plates with bottom injection and top suction (same velocity of suction and injection) is analyzed in the present study. The governing equations of fluid flow are solved by using the least square method, which is an important part of the present study. Choosing the trial function for the least square method in this particular case is a difficult task since the velocity profile turns out to be asymmetric for higher velocity of suction and injection. In this study, proper implementation of the least square method is demonstrated for such types of asymmetric velocity distribution, which is a novelty. In the present study a solution for non-dimensional velocity distribution is obtained, and the results are validated with the solution obtained by perturbation method. The results reveal that with an increase in the non-Newtonian parameter (when the cross-flow Reynolds number is low), velocity decreases at the same rate, both near the bottom and top walls. However, when the cross-flow Reynolds number is higher, velocity near the bottom plate is nearly unaffected by a decrease in the non-Newtonian parameter, whereas, near the top plate, velocity decreases with an increase in the non-Newtonian parameter.
Fuel saving and emission control in transportation is a global critical issue, so research is required to concentrate on the energy conservation of diesel engines. Generally, in an internal combustion Engine, around 66 % of the total heat is lost and, around 33% is used for Brake Power. It is very important to improve the energy level of the engine in the field of automobiles, and this will be shown in the heat balance sheet of diesel engines. An attempt has been made to fulfill the above requirement by adding CuO and ZnO nano-additives to pure diesel fuel and Al2O3 and ZnO nano-lubricant additives to SAE 15W-40 engine lubricant oil by sonication process. Experimental work on a vertical twin-cylinder four-stroke, water-cooled, advanced computerized diesel engine was carried out with no load to full load condition using a computerised eddy current dynamometer attachment. The performance of the engine is evaluated by considering specific fuel consumption, brake thermal, mechanical, and volumetric efficiency, and exhaust emission. Results show that Specific fuel consumption is reduced by about 14.98%, Brake thermal efficiency is increased by about 17.62%, and Mechanical efficiency is increased by about 3.94%, respectively, using both nano fuel additives and nano lubricant additives. For exhaust, the emission is reduced by 20.04%, 10.25% for CO and NOx, and increased in CO2 by 29.16%. With the application of nano additives in fuel as well as in lubricating oil, the overall thermal performance can be appreciably improved, and the exhaust gas pollutant from the engine can be significantly reduced.
The aim of this study is to analyze and calculate the thermosolutal mixed convection in a porous cylindrical cavity containing a Casson nanofluid (aluminum nanoparticle). This research was conducted under Darcy regime conditions with . Analysis is carried out for a range of model factors, including Richardson’s number (0.1 to 1), Reynolds number (1 to 9), porosity (0.1 to 1), Soret and Dufour numbers (0.1 to 1), Casson fluid parameter (0.1 to 0.5), Buoyancy ratio (1 to 10), Prandtl number (1 to 10), and Geometric aspect ratio (2 to 3). The volume fraction of nanoparticles was set at % for the flow of Casson nanofluid through porous layers, as explained by the extended Brinkman-Forchheimer DARCY law. As we note in this research that the thermosolutal transfer decreases with the increase in Richardson number in the case of >10, and the thermosolutal transfer increases with the increase in casson fluid parameter; on the contrary we notice that the transfer of heat decreases with the increase in the Soret and Dufour numbers, and at the end we find that thetmosolutal transfer increases with the increase in Reynolds number in the Dacian regime. Numerical simulations were conducted using numerical methods rooted in the finite volume method (FVM). Fortran numerical codes using FVM were implemented in the experiments to achieve the results. Therefore, we examined how various factors impact both heat transfer and concentration rates.
The advancement and commercialization of electric vehicles due to their advantages have increased research in this field. Lithium-ion batteries are among the most important components of electric vehicles, and their performance is affected by temperature. In this study, fluid dynamics and heat transfer in a cooling system for battery cells were investigated using three-dimensional solid-fluid simulations. The thermophysical properties of the cooling fluid were considered variable with temperature and implemented using a user-defined function (UDF). Numerical simulation can effectively predict the thermal behavior of battery cells during discharge and match experimental data. This study examined the impact of different flow patterns and solid block contact surfaces on the maximum surface temperature and temperature distribution uniformity. The results show that the structure of incremental blocks can affect the temperature distribution of battery cells, such that in parallel flow, the maximum temperature of cells near the inlet increases by 0.65°C, and cells near the outlet decreases by 0.2°C. In contrast, in counter-flow, the maximum temperature of side cells is higher by 0.25°C. Additionally, the study shows the impact of increased contact surface on system weight, indicating a significant weight reduction of about 28.5% in solid blocks with increased contact surface. This research demonstrates the potential of using numerical simulations to improve the design of thermal management systems in battery cells.
Activation energy is of considerable significance in diverse applications such as chemical kinetics, catalyst development, enzymes, semiconductors, and systems sensitive to temperature, such as chemical reactors and engines. The objective of this research is to investigate the influence of activation energy on a magnetized couple stress fluid over an inclined stretching permeable cylinder in a non-Darcy porous medium. The effects of cross-diffusion and stratified mixed convection are also considered in fluid model. The boundary layer equations, which describe the flow, have been converted into dimensionless form through suitable transformable variables. Subsequently, these transformed equations are solved using fourth order Runge-Kutta mechanism along with the shooting technique. The outcomes comprise visual depictions and comprehensive explanations demonstrating the influence of relevant variables on thermal, concentration, and velocity fields. Observations reveal that the concentration profile is directly influenced by the Forchheimer number and activation energy parameter, whereas both temperature and concentration fields decrease with elevated thermal and solutal stratification parameters. Additionally, numerical outcomes for the skin-friction coefficient, Nusselt number, and Sherwood number are presented in tabular form.
In this study, a floating photovoltaic power plant (FPVPP) on the Amir Kabir dam in Karaj, Iran is designed and optimized in terms of energy, economic, and environmental analysis. The FPVPP is designed to supply the power needs of Varian village, which is located near the Amir Kabir dam. The results showed that under the same climatic conditions, the operating temperature of the panels of the ground-mounted PVPP is 4.7℃ higher than that of the floating PVPP, and the output voltage and power of the floating PVPP are 5.7 V and 2.05 kW higher than that of the ground-mounted one, respectively. The floating PVPP provides approximately 69.4% of the annual power needs of the Varian village. The average daily output of the floating PVPP is 280 kWh/day, which meets the daily needs of the village. The payback time is 9.88 years, 3.59 years, and 7.47 years by considering the electricity cost in Iran with subsidy and without subsidy and the electricity cost in the United States, respectively. The designed floating PVPP saves 488 m2 of land and a total of about 260,000 m3 of water is directly and indirectly saved. This floating PVPP can prevent the emission of 22768 kg/year of carbon dioxide, 99 kg/year of sulfur dioxide, and 48 kg/year of nitrogen oxide.
The current study investigates mixed convective flow of an unsteady MHD tangent hyperbolic nanofluid due to a stretching surface with motile microorganisms via convective heat transfer and slip conditions. The flow analysis's governing equations were converted into a nondimensional relation by using the proper alteration. The pertinent similarity transformations are utilized in the main equations, and the solutions are obtained using the integrated bvp4c software. A good agreement with previously published data indicates the efficacy of the numerical technique. The following are the main findings: increasing the magnitude of the radiation and mixed convection parameters improves the velocity profile, whereas the Weissenberg number and magnetic field demonstrate the opposite influence; improvements in heat transfer occur due to the thermal radiation parameter, Brownian movement, and thermophoretic effects; activation energy improves concentration profile, whereas Lewis number shows opposite effect; bioconvection Lewis number and Peclet number declines the Motile microorganism density. Additionally, a tabular analysis of the skin friction, motile microorganism density, Nusselt number, and Sherwood number is also provided.
In the present study, mixed convective heat transfer inside a square enclosure in the presence of a rotating cylinder with various numbers of grooves is presented. Effects of counterclockwise and clockwise rotations with non-dimensional rotating speeds (RS) in the range from -1000 to 1000 are studied for different radius ratios (R) of 0.1, 0.2, and 0.3. Computations are carried out for Rayleigh numbers 103, 104, and 105 using the finite volume approach. The obtained results are validated against the available data for an empty enclosure (in the absence of a cylinder) as the reference case and also for an enclosure with a rotating smooth cylinder. It is demonstrated that for a specific value of the Rayleigh number, increasing the radius ratio enhances the thermal performance inside the enclosure regardless of the groove number and rotating speed. Increasing the Rayleigh number attenuates the roles of rotating speed and radius ratio, gradually. It is concluded that among all cases, the case with counterclockwise rotating smooth cylinder and among the grooved cases, Case 5 with three grooves provide the maximum heat transfer enhancements.
According to the severe global warming and increasing demand for freshwater worldwide, different sustainable solutions for supplying water have been considered. Solar desalination is a promising method to convert saline and brackish water resources to distilled water. Solar stills are one of the simple solar desalination methods and have low costs compared to similar solar-powered methods. However, the low distillation capacity and vast distillation area requirements present a challenge for further development of this technique. The application of novel materials that enhance the heat and mass transfer rate in solar stills can be a suitable approach for performance enhancement. In the current review, the most recent advancements according to the novel materials that enhance the distillation rate of the solar stills will be discussed and reviewed concisely. The investigated novel materials in the current review includes different types of natural materials that have been proposed by researchers. Finally, concluding points and future study suggestions will be presented to the researchers. The current review provides the researchers with the most recent advances in the integration of novel materials with conventional solar stills for heat and mass transfer enhancement.
Mixed convection within a ventilated square cavity with a baffle at the bottom wall and heating elements at the side walls has been analyzed. The inlet opening has been set at the bottom of the left wall, while the exit opening is put at the bottom of the right wall. Considering air (Pr = 0.71), dimensionless and steady form of mass, momentum and energy equations are solved by implementing proper boundary conditions with the help of the Galerkin method-based finite element scheme. Maintaining pure mixed convection (Ri = 1), baffle length is changed from 0 to 0.95L, and heater location is varied from 0.1L to 0.7L across Re = 10 to 1000. Qualitative changes of the domain are observed with the help of streamlining and isothermal plots. For quantitative comparison, average temperature, Nusselt number, pressure drop and performance index have been considered. The counteracting effects of the increase in Nusselt number and pressure drop are accounted for together with the help of the performance index, which yielded the most economical and optimum baffle height and heater location. The final evaluation shows that the optimum length of the baffle and the position of the heaters can perform most effectively in the range of Re = 20 – 400.
