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The thermal performance of a Z shape enthalpy heat exchanger utilising 70 gsm Kraft paper as the heat and moisture transfer surface has been investigated. Effects of different inlet air humidity ratio conditions on the heat exchanger effectiveness and on the energy recovered by the heat exchanger have been the main focus of this investigation. A typical air conditioning cooling coil which incorporates an enthalpy heat exchanger has been modelled for tropical climate. Under test conditions, results have shown that latent effectiveness and the moisture resistance coefficient have strong dependency on the inlet air humidity ratio. Moreover, the latent effectiveness has been found to be strongly dependent on the moisture resistance coefficient rather than the convective mass transfer coefficient. Finally, annual energy analysis for Singapore weather conditions have also shown that energy recovered under variable inlet air conditions is 15% less than that recovered under constant inlet air conditions for the same heat exchanger. [ABSTRACT FROM AUTHOR]

This paper introduces three novel approaches to size geothermal energy piles in a MILP, offering fresh perspectives and potential solutions. The research overlooks MILP models that incorporate the sizing of a geothermal borefield. Therefore, this paper presents a new model utilizing a g-function model to regulate the power limits. Geothermal energy is an essential renewable source, particularly for heating and cooling. Complex energy systems, with their diverse sources of heating and cooling and intricate interactions, are crucial for a climate-neutral energy system. This work significantly contributes to the integration of geothermal energy as a vital energy source into the modelling of such complex systems. Borehole heat exchangers help generate heat in low-temperature energy systems. However, optimizing these exchangers using mixed-integer-linear programming (MILP), which only allows for linear equations, is complex. The current research only uses R-C, reservoir, or g-function models for pre-sized borefields. As a result, borehole heat exchangers are often represented by linear factors such as 50 W/m for extraction or injection limits. A breakthrough in the accuracy of borehole heat exchanger sizing has been achieved with the development of a new model, which has been rigorously compared to two simpler models. The geothermal system was configured for three energy systems with varying ground and bore field parameters. The results were then compared with existing geothermal system tools. The new model provides more accurate depth sizing with an error of less than 5 % compared to simpler models with an error higher than 50 %, although it requires more calculation time. The new model can lead to more accurate borefield sizing in MILP applications to optimize energy systems. This new model is especially beneficial for large-scale projects that are highly dependent on borefield size. [ABSTRACT FROM AUTHOR]

Pulsating Heat Pipe (PHP) is an emerging efficient heat transfer device, that transfers heat passively through oscillating motions of liquid slugs and vapor plugs within the device. PHP is of high effective thermal conductivity with great potential in heat transfer management for various applications. The objective of this review paper is to summarize and analyse the applications of PHP in various fields that have been reported in the open literature, emphasizing on studies reported in past half decade. The thermo-hydraulic behaviour of PHP is influenced by numerous geometric and operational parameters, which are discussed in detail in the first part of the paper. The thermal performance of the PHP under rotation condition, which is seldom discussed in previous review articles, is also discussed. These parameters act individually and in tandem to alter the performance of PHP, which makes its prediction extremely difficult. However, the benefit of numerous influencing parameters is that they can be altered to make PHP suitable for various applications. These highly variable configurations make PHP suitable for applications such as the transfer of absorbed solar energy to the location of interest, waste heat recovery, thermal management of electric vehicle batteries, fuel cells, cooling of electronic components etc. PHPs are recently being studied for applications in cryogenics and cooling of cutting tools in the machining process also. In addition, novel applications of PHP such as high-performance fins for heat exchangers, cooling of building roofs etc. are also being reported. All these applications of PHP reported in the open literature are reviewed and summarized in the present article. [ABSTRACT FROM AUTHOR]

Paper membranes have long been used in an enthalpy exchanger. However, there has been a continuous concern on the durability or the anti-bacterial performance. In this study, heat and moisture transfer characteristics of a recently-developed PE/PA (polyethylene/polyacetate) composite membrane was investigated as a possible substitute to the paper membrane. Results showed that the diffusion coefficients of the PE/PA membrane (7.7 × 10−10 m2/s to 1.8 × 10−9 m2/s) were higher than those of the paper membrane (1.8 × 10−11 m2/s to 6.0 × 10−11 m2/s). Furthermore, the diffusion coefficient increased as relative humidity increased, reached a maximum at 50 % to 60 % and then decreased. For PE/PA membrane, the sorption constant increased as temperature increased, which was the reversed trend to the paper membrane. Successful prediction of the moisture transfer effectivenesses of the separate pseudo-counter flow enthalpy exchangers further strengthened the validity of the obtained diffusion coefficients. [ABSTRACT FROM AUTHOR]

The use of passive heat transfer enhancement strategies to improve heat transfer performance in heat exchanger has received a lot of attention. In this paper, passive heat transfer enhancement methods utilizing vortex generation in the flow field have been discussed in detail. Three classic techniques for improving passive heat transfer in heat exchangers have been identified in the literature: boundary layer deformation, swirl formation, and flow destabilization. The longitudinal vortices generated by vortex generators have been found to reduce the wake region behind tubes, thus increasing turbulence strength and flow mixing. This review takes into account the effect of geometrical variations of vortex generators on thermo-fluid performance. Delta winglet vortex generators outperform rectangle-winglet vortex generators in terms of heat transfer performance. However, using hole-type rectangular winglets has shown promising results with more than 16% enhancement in thermo-fluid performance. Among several winglet angles examined by various researchers, the attack angle in the range of 30°–45° has resulted in optimum performance. Some variations of rectangular winglets such as wavy winglets have been reported to enhance the overall thermo-fluid performance by 8–16%. This paper provides insight into different experimental and numerical techniques for the enhancement of thermo-fluid performance of cross-flow heat exchangers. This review article can be very helpful to industrial and academic researchers working in the area of compact and efficient heat exchanger design with enhanced thermo-fluid performance. [ABSTRACT FROM AUTHOR]

In this paper, the heat transfer characteristics of multiple pairs of vortex generators (VG) mounted on vertical plate fins of plate fin heat sink (PFHS) are evaluated using computational fluid dynamic simulations. The delta winglet pairs are used as longitudinal VGs, and they are mounted one after the other in the axial direction. Critical design parameters for the double pair of VGs (DPVGs) are identified, and a design of experiment-based simulations is carried out to develop a response surface model for Nusselt number and thermal hydraulic performance parameter. Results show winglet length is a critical design parameter compared with winglet height, and the axial inter VG distance between VG pairs plays a crucial role in improving the heat transfer characteristics. The optimum inter VG distance for a double pair of VG is evaluated, and it is 2.2 to 3 times the length of the delta-winglet. Thermal hydraulic performance of PFHS with double pair of VG is 1.49 times higher than that of plain PFHS. Finally, the variation of heat transfer characteristics against velocity is also evaluated for the PFHS with a DPVG. [ABSTRACT FROM AUTHOR]

Surface heat exchanger is extensively used for sustainable development in energy systems. In the surface heat exchanger, the heat transfers from hot flow to cold flow through separating solid surface. The heat transfer area of surface heat exchanger is usually constant when it is performing in energy system. Similarly, fixed plate heat exchanger is applied in electronic outdoor cabinet. In this paper, a novel approach to vary the heat transfer surface in heat exchanger is proposed. A blown plate heat exchanger is introduced for cabinet cooling system. The blown and fixed plate heat exchangers are compared. The heat transfer performances of the blown plate heat exchangers are the same with fixed plate heat exchanger for the same Reynolds numbers. For different Reynolds numbers, the blown plate heat exchanger with all mixed plates has the best performance and the temperature reduction of hot air is arrived 15.185 K, when the maximum temperature difference is 20 K. [ABSTRACT FROM AUTHOR]

The paper presents an analysis of tests carried out on a titanium plate of a heat exchanger in which the flowing medium was hot gases with a temperature of 110 °C and a pH of less than 1. Strong hydrogenation of the titanium plate caused by the corrosion of the adjacent steel frame plate was detected. As a result of the synergy of the hydrogenation and erosion, a relative reduction in the thickness of the plate was observed locally by up to 94% in relation to the thickness of the titanium plate in the area not affected by degradation. The results of this study are not only of key engineering importance with regard to equipment design and the prevention of mechanical failures in titanium heat exchangers, but also with regard to equipment in other industries. [ABSTRACT FROM AUTHOR]

One of the major problems of using nanofluids in heat exchange applications is the forming and deposition of nanoparticles on the inner surface of the heat exchanger. In this paper, Water-Cmc fluid is used as a surfactant for nanoparticles to prevent deposition and congregation. The pressure drops and heat transfer in U-bend double pipe heat exchanger based on water-MgO-Cmc fluid, are examined. Nanoparticles of Magnesium Oxide (MgO) and Carboxymethyl Cellulose (Cmc) are used with pure water as a base fluid. The experimental rig and procedures are designed to facilitate various operational conditions such as flow rate, volume concentration of MgO particles and weight concentration of Cmc particles. Furthermore, convective heat transfer coefficient, heat exchanger effectiveness, pressure drop, friction factor, under different conditions, are measured. The results demonstrate convective heat transfer coefficient of U-bend double pipe heat exchangers is enhanced by 35% for 1 MgO vol.% and 0.2 Cmc wt.% compared to base fluid (Water-Cmc). It is concluded that pressure drops are directly proportion to the increase of MgO nanoparticles at same Cmc concentration by 23% at 0.2 wt.%. Whilst, friction factor of the system is inversely proportion to the increase of volumetric flow rate of water-MgO-Cmc fluid. An increase in MgO nanoparticle concentration increases the friction factor, hence maximum friction factor enhancement by 38% for MgO concentration of 1 vol.%. The effectiveness of heat exchanger is slightly increased by 8% with increase of MgO concentration and flow rate. Finally, thermo-physical characteristics of water-MgO-Cmc fluid at various temperatures, are measured [ABSTRACT FROM AUTHOR]

This paper presents a study aimed at studying and evaluating the possibility of using machine learning in methods of predictive analysis of the operation of the cooling system of the IRT-T reactor. Machine learning is a subspecies of artificial intelligence used in large-volume data analytics. The currently existing methods of processing data on technological parameters are imperfect and do not allow predicting the development of operational events. The proposed approach will allow not only to centrally collect data on technological parameters, but also to output an analysis of possible outcomes and recommendations for changing operating modes. [ABSTRACT FROM AUTHOR]

In today's world, people have been facing different unpleasant phenomena like global warming, water shortage and thermal pollution. Power plants for electricity generation are one of the main sources of greenhouse gases and thermal pollution in aquatic ecosystem. On the other hand, these power plants consume high amount of freshwater for cooling purposes. Water scarcity is a detrimental crisis that the whole world is struggling with it. To combat the thermal pollution, various wet cooling and dry cooling technologies have been introduced and reviewed till today. While wet cooling systems use lots of water, dry cooling ones are not suitable options in warm weather and climates. Here, the need for an alternative element is felt more than ever. So far, water and air have been the main coolants in power generation units. According to specific heat capacities in different substances, hydrogen, by far has the highest amount. So, a novel heat exchanger containing hydrogen and water could be a promising solution for the mentioned issues. This paper focuses on advantages of this heat exchanger from different points of view, however, some assumptions, considerations and calculations should be carried out to have the best performance for this idea. Temperature control is such an important process that should be done in heat exchangers. Hence, a review on a control method has been carried out in this paper. The simulation results have been taken by MATLAB/SIMULINK software. [ABSTRACT FROM AUTHOR]

Background: District Heating (DH) is a technology that provides heating and domestic hot water to buildings and is an important technology for supporting the European energy transition. As such the heating systems increasingly resort to renewable heat sources and waste heat, it is even more important that they operate in the most efficient way possible. DH companies have access to the primary network of which they can impact system performance. To maximize the efficiency of the system, however, it is important that the system at the building level, known as the secondary system, is also efficient; otherwise, overall system efficiency is reduced. To increase system efficiency, return temperatures from the secondary system into the primary system have been targeted through motivational tariffs. There is limited information on how to establish a motivational tariff that motivates the customer to improve both the primary and secondary systems, which is a gap that this paper aims to fill. Results: In this paper, the impacts of retrofit actions in secondary systems are assessed through simulations. The identified relevant refurbishment measures to lower the return temperature to the primary system are variable flow pumps, low-temperature radiators, parallel heat exchangers, and a pass-through DHW system. Apart from simulated refurbishments, we also identify that the secondary system sometimes generates excess heat, which is valuable to recover, especially during peak load periods for the primary system. Hence, motivational tariffs targeting secondary system efficiency should also encompass an incentive for the customer to make use of waste heat in the secondary circuit to lower peak demand for the DH system. Conclusions: To date, the most commonly used parameters introduced to customers are linked to the flow of water through the customer's asset and the bonus malus principle. The results from simulations show that DH companies can introduce additional parameters to support customers in guiding their secondary system to perform more efficiently. Increased overall system efficiency has a positive impact on both costs and emissions. [ABSTRACT FROM AUTHOR]

Shell and tube heat exchanger failures during service have been a significant cause of petrochemical plant turnarounds and shutdowns. These failures not only cause an interruption in production operations and substantially impact financial losses but also necessitate immediate attention concerning different types of repairs and maintenance. Welding repair has recently become a significant concern because several process facilities have been in operation for more than 40 years, the world widely pioneering in the oil and gas refineries. Heat exchanger materials have lost strength and toughness due to degradation such as temper embrittlement, galvanic corrosion, and also other damages such as pitting corrosion, excessive wear, fatigue failure, and creep due to continuous long-term operation. This paper discusses the standardized welding procedures of heat exchanger failures during the turnaround period or due to aged conditions in various end-users worldwide. In other words, this paper summarizes the details of all the welding repairs of more than 100 heat exchangers during the study period. The frequent maintenance was refurbished successfully, and the standard procedure was prepared accordingly. Some critical tasks are explained, such as technical planning for welding repair, integrated challenges associated with working in the radiologically controlled zone, repair performance, organizational involvement, and fulfilling the standards such as ASME, NBIC, SAES, and SES codes. [ABSTRACT FROM AUTHOR]

Heat transfer coefficients were obtained for a range of non-wood kenaf bast pulp fiber suspensions flowing through a circular pipe heat exchanger test loop. The data were produced over a selected temperature and range of flow rates from the flow loop. It was found that the magnitude of the heat transfer coefficient of a fiber suspension is dependent on characteristics, concentration and pulping method of fiber. It was observed that at low concentration and high flow rates, the heat transfer coefficient values of suspensions were observed higher than that of the heat transfer coefficient values of water, on the other hand the heat transfer coefficient values of suspensions decreases at low flow rates and with the increase of their concentration. The heat transfer were affected by varying fiber characteristics, such as fiber length, fiber flexibility, fiber chemical and mechanical treatment as well as different pulping methods used to liberate the fibers. Heat transfer coefficient was decreased with the increase of fiber flexibility which was also observed by previous researchers. In the present work, the characteristics of fibers are correlated with the heat transfer coefficient of suspensions of the fibers. Deviations in fiber properties can be monitored from the flowing fiber suspensions by measuring heat transfer coefficient to adjust the degree of fiber refining treatment so that papers made from those fibers will be more uniform, consistent, within the product specification and retard the paper production loss. [ABSTRACT FROM AUTHOR]

The review paper presents the various passive methods used in the heat exchanger in detail with their advantages and disadvantages over the active methods. The paper studies the experimental and numerical studies of twist tape as an insert due to its retrofit capability and easy handling advantages. The experimental studies are categorized based on the geometrical parameter of the twist tape insert. The twisted tape with similar geometries is compiled in the same section. For example, twist tape with a clockwise twist, anticlockwise twist, alternate twist, or twist tape with a twist and no twist in the same section. It is a concise form that basically illustrates the studies based on similar geometrical parameters. The study covers both experimental and numerical studies and presents the advantages of experimental and numerical studies over one another. There is a section that shows statistical analysis of the Nusselt number and friction factor for various swirl flow inserts with comparison to the plain tube. The selection of twist tape inserts for the heat exchanger depends upon the cost and feasibility at the required point of application of the heat exchanger. This is done by comparing the thermal performance factor of the insert in the heat exchanger. The thermal performance factor of a particular insert in a tubular heat exchanger must be greater than 1, to justify its capability as a good insert. Finally, future recommendations are suggested to further carry out the work in this domain. [ABSTRACT FROM AUTHOR]

Air-cooled heat exchangers in various industries enjoy an increasingly wider use thanks to their environmental friendliness and absence of the need for cooling water. Air-cooled heat exchangers from annular finned tubes are widely used in chemical, petrochemical, oil-refining, gas, and food industries, and also at automobile compressed natural gas filling stations (NGV gas stations), in heat power engineering, electric power engineering, refrigeration technology, and at nuclear power plants. The thermal capacity of air-cooled heat exchangers is largely determined by the characteristics of the motion of a flow of cooling air through them that can be organized with consumption of electric power by means of a ventilator or in an energy-saving regime by free convection. Unfortunately, the region of ambient air temperatures at which it is possible to use air-cooled heat exchangers under the conditions of free convection is limited. Low heat transfer intensity compared to forced convection is the main drawback of the free-convection regime which is usually compensated by an increase in a heat-emitting area, namely, by finning the heat transfer surface. By equipping air-cooled heat exchangers with additional devices making it possible to intensify free convection, the thermal performance of heat exchangers can be improved significantly. The paper provides an overview of experimental and numerical investigations of free-convection heat transfer in annular finned tube bundles with an exhaust shaft installed above them. [ABSTRACT FROM AUTHOR]

This scientific paper investigates the flow and forced heat transfer characteristics of hybrid nanofluid in a channel with rotating circular cylinders. Two-dimensional simulations are used to analyze the effects of obstacle rotation, number, nanoparticle volume fraction, and Reynolds number on the Nusselt number and friction coefficient. The findings demonstrate that incorporating obstacles enhances heat transfer, while increasing the inlet flow frequency improves the system's performance coefficient. Interestingly, substituting hybrid nanoparticles with inlet frequency reduces the friction coefficient and further enhances the performance coefficient. The study underscores the potential of microscale heat exchangers with oscillating inlet velocity and rotating cylinders in optimizing heat transfer across various industries. Furthermore, it explores pulsating flow as a promising solution for high heat flux density challenges in single-phase cooling systems. Additionally, the investigation investigates the impact of inlet velocity frequency on heat transfer rate and friction coefficient, revealing that adjusting the cycle period and frequency improves the heat transfer rate. By modulating the flow frequency, the performance coefficient improves by mitigating the growth of the friction coefficient compared to a constant inlet velocity. By leveraging the advantages of nanofluids and manipulating the flow mode, we can optimize heat transfer performance without increasing the pump power. The investigation of different configurations of cylinders and oscillating flow conditions can provide valuable insights for engineering applications requiring efficient heat transfer and temperature regulation. The study concludes by highlighting the significance of investigating wake interactions in a three-cylinder system arranged in an intermediate triangular configuration under static and rotating conditions. These complex flow phenomena have substantial relevance to both fundamental fluid flow research and engineering applications. [ABSTRACT FROM AUTHOR]

In numerous industrial plants, controlling incorporated unit procedure is a difficult operation as a reason of the nonlinearity and intricacy linked with the dynamic designs. Moreover, sParallel flow HENs function as an essential and vital element in the energy recovery field and, with no efficient control stratagem, the utility demand reduction can't be attained in practice. As a consequence of the nonlinear behavior, intricacy, existence of disturbances, and noise, which causes incremented production costs, a Parallel flow heat exchanger's control is regarded as an intricate operation. There exists a necessity aimed at an optimum control stratagem for an HX, which can resolve all these problems. This paper has established an effective cascaded effect-based parallel-flow HX employing the NMPC-FO methodology. The NMPC-FO control stratagem developed evades the excessive energy utilization and raw materials, which results in lesser production costs. It boosts the energy efficacy and ensures the final product's quality via formulating the nonlinear transient designs. For enhancing the HEN's efficacy, this paper administers the HT system's diverse geometrical as well as operational parameters. Overall, the experimental result showed that the proposed work withstands better efficiency, reduced fouling rate, and low cost as compared with the existing state of art methods. [ABSTRACT FROM AUTHOR]

This paper reports the discovery that water can trigger a peculiar nuclear reaction and produce energy. Cavitation may induce unusual reactions through implosion of water vapor bubbles. Many of this research has been published formally or informally. We have conducted experiments using two reactor types made from multiple-pipe heat exchanger and found that the heat exchange process of water produces peculiar excess heat and abnormally high pressure leading to rupture of the reactor. Recently, we have tested another eight reactors. Interestingly, these reactors produce non-condensable gas. We suspected that they include 22Ne and CO2. We used a mass spectrometer (MS) to analyze 14 gas samples collected from 8 reactors, including ten samples showing a coefficient of performance COPx > 1.05 (with excess heat) and four having COPx < 1.05 (without excess heat). Several methods were adopted to identify the gas content. For CO2 identification, two methods are employed. For 22Ne identification, three methods are employed. All the results confirm that isotope 22Ne and regular CO2 really exist in the output gas from reactors determined to have excess heat. We conjecture a possible mechanism to produce 22Ne and CO2 and find out that 12C and isotope 17O are the intermediate. They finally form isotope gases containing 17O, including H2O-17 (heavy-oxygen water), isotope O2 (16O–17O), and isotope CO2 (12C–16O–17O). In the excess heat producing reactors, all these gasses were detected by MS in the absence of 20Ne and 21Ne. The observed isotope gases produced from reactors having excess heat verifies that water can trigger a peculiar nuclear reaction and produce energy. [ABSTRACT FROM AUTHOR]

The rising global temperatures, attributed to the high global warming potential (GWP) of conventional refrigerants, necessitate the adoption of low-GWP alternatives in HVAC systems. However, these low-GWP refrigerants often exhibit high toxicity and flammability, limiting their usage. To address these challenges, compact heat exchangers incorporating blended refrigerants have been introduced to enhance HVAC system performance. Researchers have also made significant strides in improving HVAC system efficiency by introducing the concept of suspending nanolubricants and nanorefrigerants within the system. This review paper seeks to comprehensively assess the potential of alternative refrigerants containing suspended nanoparticles, commonly referred to as nanorefrigerants. The paper reviews various mechanisms and potential combinations of different nanorefrigerants employed to enhance refrigeration system effectiveness and efficiency. A detailed examination of key heat transfer parameters and the performance predictions of low-GWP refrigerants, including those from the hydrofluoroolefin (HFO) and hydrocarbon (HC) classes, is conducted through energy and exergy analyses. Commercial refrigerants like R-134a, R-290, R-600, R-600a, R-123, R-125, R-22, R-141b, R-152, R-11, R-113, R-404a, R-407c, R-502, R-600a, R-507a, R-1234yf, R-1234ze, 1336mzz(Z), and R-410a are evaluated in conjunction with suspended nanoparticles, considering their specific properties. The findings indicate that the utilization of nanorefrigerants leads to notable improvements in overall system performance, characterized by reduced compressor workloads and increased heat transfer rates. Consequently, the integration of blended nanoparticles into refrigerants holds significant promise for advancing the HVAC field. [ABSTRACT FROM AUTHOR]

Energy, freshwater, and the environment are interrelated features that infuse all human activities. Addressing this nexus in an integrated energy conversion system is a big challenge for the research community. Adsorption desalination system, which is a good alternative to traditional desalination systems, could solve this problem because it uses eco-friendly working fluids and can be powered by renewable energy. Many experimental prototypes for the adsorption desalination cycle were built and tested in the last decades. Also, different adsorbent materials were developed and characterized. Therefore, this paper reviews adsorbent materials with water vapor utilized in experimental adsorption desalination studies, which is considered the first step in constructing an efficient system. After that, the paper comprehensively reviews all previous experimental adsorption desalination studies. It focuses on the design of the experimental test rig, the mass of adsorbent material, and system performance, such as the specific daily water production, coefficient of performance, and specific cooling power. This work also discusses the properties of heat exchangers (i.e., adsorbent beds) employed in adsorption desalination systems. [ABSTRACT FROM AUTHOR]

There are numerous reports and publications in reputable scientific and engineering journals that attribute substantial enhancement in heat transfer capabilities for heat exchangers once they employ nanofluids as working fluids. By definition, a nanofluid is a working fluid that has a small volume fraction (5% or less) of a solid particle with dimensions in the nanoscale. The addition of this solid material has a reported significant impact on convective heat transfer in heat exchangers. This work investigates the significance of the reported enhancements in many recent related publications. Observations on these publications' geographical origins, fundamental heat transfer calculations, experimental setups and lack of potential applications are critically made. Heat transfer calculations based on methodologies outlined in random selection of available papers were conducted along with a statistical analysis show paradoxically inconsistent conclusion as well as an apparent lack of complete comprehension of convective heat transfer mechanism. In some of the surveyed literature for example, heat transfer coefficient enhancements were reported to be up to 27% and 48%, whereas the recalculations presented in this work restrain proclaimed enactments to ~ 3.5% and − 4% (no enhancement), respectively. This work aims at allowing a healthy scientific debate on whether nanofluids are the sole answer to enhancing convective heat transfer in heat exchangers. The quantity of literature that confirms the latter statement have an undeniable critical mass, but this volition could be stemming from and heading to the wrong direction. Finally, the challenges imposed by the physical nature of nanoparticles, as well as economic limitations caused by the high price of conventional nanoparticles such as gold (80$/g), diamond (35$/g), and silver (6$/g) that hinder their commercialization, are presented. [ABSTRACT FROM AUTHOR]

This paper proposes an innovative method for time-series prediction in energy-intensive industrial systems characterized by highly dynamic non-linear operations. The proposed method can capture the true distributions of the inputs and outputs of such systems and map these distributions using polygon generation and video-to-video translation techniques. More specifically, the time-series data are represented as polygon streams (videos), then the video-to-video translation is used to transform the input polygon streams into the output ones. This transformation is tuned based on a model trustworthiness metric for optimal video synthesis. Finally, an image processing procedure is used for mapping the output polygon streams back to time-series outputs. The proposed method is based on cycle-consistent generative adversarial networks as an unsupervised approach. This does not need the heavy involvement of the human expert who devotes much effort to labeling the complex industrial data. The performance of the proposed method was validated successfully using a challenging industrial dataset collected from a complex heat exchanger network in a Canadian pulp mill. The results obtained using the proposed method demonstrate better performance than other comparable time-series prediction models. This allows process operators to accurately monitor process key performance indicators (KPIs) and to achieve a more energy-efficient operation. [ABSTRACT FROM AUTHOR]

For the outside cabin heat exchanger of wind power generation, the overall numerical simulation plays an important role in its design and optimization. The periodic iterative simulation method proposed in this paper makes up for the deficiency of analogy research using the local model in the previous research of plate-fin heat exchanger so that the research conclusions can be directly applied to practical engineering. The effectiveness of this method is verified by comparing 10 groups of simulation results with experimental results. It is concluded that the maximum relative error of the periodic iterative simulation method is 0.9%, which meets the requirements of engineering calculation. The number of iterations can be reduced to two when only the outlet average temperature is involved, which is more convenient than the dozens of iterations. Furthermore, the effects of altitude, air velocity, air temperature, wave fin structure parameters, and generator power on the performance of heat exchanger are comprehensively analyzed. The results show that larger naturally captured air volume, lower ambient temperature, and lower altitude can effectively reduce the outlet temperature of ethylene glycol solution. When the amplitude and wavelength of the corrugated fin on the airside of the heat exchanger are 0.6 mm and 20 mm respectively, the naturally captured air volume is effectively increased, the overall heat exchange performance of the heat exchanger is further improved. [ABSTRACT FROM AUTHOR]

Magnetic nanofluids have gained significant attention in recent years due to their unique properties and potential applications in various fields. This review paper provides an in-depth analysis of the utilization of magnetic nanofluids in thermal applications. Article presents a comprehensive overview of the various synthesis methods of magnetic nanofluids and key properties of magnetic nanofluids. The thermal stability of magnetic nanofluids is also highlighted in this review. Additionally, various thermal applications of magnetic nanofluids, such as cooling systems, heat exchangers, and thermal energy storage, solar systems are explored along with their potential benefits and challenges. Finally, future research directions and prospects for magnetic nanofluids in thermal applications are highlighted. [ABSTRACT FROM AUTHOR]

Geothermal energy is one type of renewable source of energy that can be used as shallow geothermal system for the use of cooling and heating of residential and commercial buildings. In this paper, an intense review is carried out on geothermal heating and cooling for air conditioning with a focus on Earth-Air Heat Exchanger (EAHE) and Ground Source Heat Pump (GSHP) systems. The study is carried out to understand the factors which have a significant effect on the performance of the EAHE and GSHP systems. This paper also focuses on the hybrid work of geothermal heating and cooling system with other forms of energy and provides benefits for designing efficient GSHP and EAHE systems. This study indicates that the important parameters for EAHE and GSHP systems are the thermal conductivity of soil, the water content present in the ground will significantly improve the performance of the systems, and further benefits are discussed in this study. [ABSTRACT FROM AUTHOR]

Demand for renewable energy sources has increased significantly during the past 15–20 years. Due to this demand, one positive scenario has occurred as there has been a decrease in the use of fossil fuels. Among various usages of the fuels, a significant amount of energy is being used in heating and cooling for commercial, domestic houses, etc. Traditional air conditioning systems use a lot of energy and are particularly inefficient in tropical countries. Earth-air heat exchanger (EAHE) systems can help to reduce the air conditioning demand while also promoting the development of renewable energy. This paper focuses on a review of previous research on this notion for system installation done by earlier researchers. Researchers working on efficient heating and cooling for human comfort will benefit from this review article. The researchers working on EAHE for heating and cooling will benefit from this review paper because it will give them the basic knowledge they need to begin their experimental work. [ABSTRACT FROM AUTHOR]

In this paper, numerical simulation of wire on tube condenser and louver fin micro-channel heat exchanger is discussed. Simulation data of both heat exchangers were compared with the experimental data, and they show good agreement. In case of louver fin micro-channel heat exchanger, prediction error of heat capacity was within ± 5%. In addition, from the result of simulation, it was found that, for same thermal performance, micro-channel heat exchanger occupies less space as well as requires less refrigerant charge than wire on tube condenser. Therefore, in this paper, two louver fin micro-channel condensers are proposed to replace wire on tube condenser of household refrigerator. Response surface methodology was used to find out the optimal condition of the louver fin micro-channel condenser. [ABSTRACT FROM AUTHOR]

This study investigates thermal performance enhancement by utilizing vortex generators (VGs). VGs come in many designs, and this paper proposes optimizations for the sinusoidal vortex generator (SVG) when used in an annular conduit to improve heat transfer with minimal pressure drop. Two vital parameters of the SVG are analyzed, namely, blockage ratios (BRs) (0.1 and 0.2) and attack angles (α) (0–90°). The investigated fluid regime is turbulent, with the Reynolds number (Re) ranging from 5973 to 11,947. Three rows of SVGs are fitted on the surface of the inner pipe, where constant heat flux is applied, while the outer pipe wall is entirely insulated. The results indicate that the highest Nusselt number is enhanced by 20.4% over the smooth pipe when the case with BR = 0.2 and α = 90° is used at Re = 5973. However, the friction factor increases by 56.5% for the same case. Two types of transverse vortices are identified, where one type has its rotational axis normal to the inner pipe surface, and the other has its rotational axis parallel to the inner pipe surface. Those vortices with the axis perpendicular to the pipe surface merge with the fluid above the SVG to develop longitudinal vortices in different BRs and α. The case with BR = 0.2 and α = 15° yields the greatest average performance evaluation criterion (PEC) compared to other tested cases with a value of 1.054. This study finds that SVGs can contribute to a more efficient annular pipe-based heat transfer system. [ABSTRACT FROM AUTHOR]

Hybrid nanofluids have better thermal conductivity and heat transfer properties than common fluids and currently have good prospects for applications in enhanced geothermal development. In this paper, a convective heat transfer experimental platform was built independently to study the convective heat transfer capability of Al2O3–SiO2/water hybrid nanofluid. The effect of different parameters on the enhanced heat transfer capability of the hybrid nanofluid was investigated, and the stability of the hybrid nanofluid under flow heat transfer conditions was evaluated. The following research results were obtained. Compared to water and single nanofluid, Al2O3–SiO2/water hybrid nanofluid has better enhanced heat transfer capability. The coaxial casing with "outside in and inside out" is more energy-efficient compared with the U-shaped heat exchanger tube. For Al2O3–SiO2/water hybrid nanofluid, there was an optimal particle concentration and ratio to optimize the convective heat transfer capability: a particle concentration of 0.10 wt % and a particle ratio of 5:5. The heat extraction of the fluid was negatively correlated with the inlet temperature and positively correlated with the flow rate. However, after the flow rate was higher than a certain extent, the heat exchange energy efficiency dropped significantly. The stability of Al2O3–SiO2/water hybrid nanofluid was well maintained in the flow heat exchange process. And the higher the flow rate, the more stable the particles are. However, the enhancement effect of macroscopic flow on the particle suspension stability would be weakened by too high fluid temperature. [ABSTRACT FROM AUTHOR]

Heat transfer enhancement using nanofluids has been an established technique for the past few decades. However, the practical usage of the nanofluids is limited due to their various colloidal issues viz fouling and colloidal stability. This paper presents an experimental analysis of the fouling factor of carbon-dot nanofluid synthesized using a one-pot synthesis technique. In addition, the thermal performance of this heat transfer fluid/ nanofluid on a double-pipe heat exchanger was studied. Design of experiment concept was adopted to analyse the influence of various parameters like flow rate of hot and cold fluid and the inlet temperature of hot fluid on heat transfer coefficient. The resultant fouling factor observed during the study was 0.000682 m2 K W−1. In addition, the experimentation on heat transfer performance of double pipe heat exchanger revealed that at optimum flowrates of 85 L h−1 (Cold and hot fluid) and inlet hot fluid temperature of 48 °C a maximum heat transfer coefficient of 369.5 W m−2 K−1 was observed. As it is well know that the operation conditions of the heat exchanger highly influence the heat transfer performance. This was studied using the response surface methodology, a statistical technique, which reveals that the flow rate of hot fluid highly influence the heat transfer coefficient of the heat exchanger. Whereas the temperature of the hot fluid exhibits less significance on the performance. A regression model has been developed to predict the heat transfer coefficient, which was further validated with the experimental data. [ABSTRACT FROM AUTHOR]

To deploy a lunar habitable base, a new elemental composition of the system for providing a thermal regime is being developed. To reduce the mass and increase the reliability of the operation of a radiation heat exchanger of the system of providing thermal regime under the conditions of the lunar surface, it is proposed to replace the radiant duralumin panel of the radiation heat exchanger with heat pipes by a highly conductive radiant panel of hybrid structure based on pyrolytic graphite. This paper is devoted to determining the thermophysical properties of an anisotropic hybrid structure based on graphite. The thermal diffusivity and thermal conductivity of samples were determined by the laser flash method. Approximations of the dependences of the in-plane and out-of-plane thermal diffusivities and thermal conductivity of the hybrid structure from pyrolytic graphite on temperature for the temperature range 256–372 K have been obtained. [ABSTRACT FROM AUTHOR]

In this paper, earth–air heat exchanger is examined to achieve better system operation to cool a building in the arid climate of Ouargla city (Algeria). A higher cooling power requires a big pipe size which increases the pressure losses. Based on fluid dynamics, a new approach is carried out to evaluate the air flow pressure losses that contribute to the determination of the required blower power. The mathematical model of governing equations set is presented, and its numerical solution is calculated using a Matlab program. The multi-objectives optimization between two opposite targets is adopted for achieving the compromise solutions between maximal efficiency and minimal system size. For a given cooling power, the resolution of the earth–air heat exchanger model is carried out using the weighting method to perform the bi-objective optimization. At each cooling power, Pareto curves are generated for plotting the optimal points of efficiency and lateral pipe area. Obtained results show that for a chosen cooling power range, the system operation must reach at least an efficiency of 35% but less than 90% to cover all the size-efficiency compromises. Also, the lateral pipe area must be at least 6.025 m2/kW to start with acceptable efficiency. On the hottest summer day, for 3.5 kW as cooling power, the pipe outlet temperature reaches about 26 °C at a relatively high pipe length of about 95 m. [ABSTRACT FROM AUTHOR]

In this paper flow features and heat transfer characteristics of finned and finless double-tube counter flow heat exchanger at wide range of Reynolds numbers were numerically analyzed. Various fins configurations combined with use of water-based TiO2 nanofluid at different nanoparticles volume concentrations were employed in this study to show their effects on nanofluid Nusselt number, friction factor and thermal performance index. Furthermore, the thermal perfection and the overall assessment of heat exchanger were also taken into account in the light of thermodynamics second law efficiency which is defined as a ratio of recovered to expended exergy. The results showed that thermo-hydrodynamical performance of heat exchanger was intensively dependent to the thickness of embedded fins. Employed sensitivity analysis revealed that fins with large thicknesses equal or larger than 10 mm provide better thermal performance than fins with small thicknesses (i.e. t = 1 mm). Furthermore, the use of circular fin with thickness as large as 10 mm at the highest Reynolds number up to about 87,500 led to pronounce both Nusselt number and flow resistance up to 15% and 4.64 folds, respectively. On the other hand, using smooth heat exchanger operating at the lowest Reynolds number (i.e. Re = 3400) filled with 1% TiO2 water-based nanofluid led to obtain the highest recovered exergy and thermodynamic second law efficiency up to 0.46 W and 10.33%, respectively. [ABSTRACT FROM AUTHOR]

Common phase change materials (PCMs) have serious shortages, and the most important one is the low thermal conductivity. This issue makes the phase change process a time-consuming period that decreases the performance of thermal storage units. This paper concentrated on improving energy and exergy performance with the aid of an air–PCM heat exchanger, which could be employed for free cooling of buildings. For the heat exchanger, the PCM of Rubitherm 22 °C high capacity (RT22HC) and the nanoparticles of multi-wall carbon nanotube were employed. The initial charging and discharging experiments showed that due to thermal conductivity enhancement, melting and solidification periods decreased using nano-PCM with three concentrations of 0.1, 0.2, and 0.5 mass% compared to the PCM without nanoparticles. Moreover, the highest exergy and energy efficiencies were obtained for the case of nano-PCM 0.5 mass% during the charging process and the values were 11.03 and 21.33%, respectively. Experiments with nano-PCM 0.5 mass% were accomplished during three continuous days. The results demonstrated that the heat obtained from nano-PCM 0.5 mass% encapsulations varied with weather conditions. In addition, the output energy and exergy rose with sunrise and fell with sunset. Finally, an economic analysis was carried out for cold climate conditions. The results indicated that the whole invested capital expenditures will return in the ninth year of exploitation. [ABSTRACT FROM AUTHOR]

In this paper, the simultaneous impacts of using nanofluid and ultrasonic vibrations in a double-pipe heat exchanger are experimentally investigated. The vibrating heat exchanger is designed so that the ultrasonic waves with the power of 60 watts and frequency of 40 kHz are applied to its body at equal length distances in a uniform and effective manner. Water-based Al2O3 nanofluid is used in this research. The available empirical correlation has been used to confirm the accuracy of the measurements and validate the results. The effective thermal parameters have been tested in three cases using water, nanofluids, and ultrasonic-excited nanofluids as the working flow of the double-pipe heat exchanger. These tests have been performed in a relatively wide range of flow rate (113–257 lh−1), Reynolds number (3230–7431), inlet hot fluid temperature (40–60 °C), and nanoparticle volume fraction (0.4–0.8%). The results indicate the positive effect of adding nanoparticles and applying ultrasonic vibrations, especially at higher inlet hot fluid temperatures and higher nanofluids concentrations. The nanoparticles are more effective at high-flow rates, whereas the ultrasonic vibration is highlighted at low-flow rates. Also, the effectiveness-NTU analysis carried out for the current heat exchanger shows that using nanofluid and ultrasonic-excited nanofluid instead of water can increase the efficiency of the thermal system up to 18.3% and 42.3%, respectively. [ABSTRACT FROM AUTHOR]

A wide range of studies was conducted to increase the heat transfer rate and reduce the size and cost of shell and tube heat exchangers (STHE). The paper's contributions lie in its ability to provide a comprehensive, up-to-date, and systematic overview of the various methods available for heat transfer enhancement in STHEs, making it an essential resource for researchers, engineers, and practitioners in the field of heat transfer. The studies that researched the overall heat transfer coefficient (U), number of transfer units, exergy efficiency, pressure drop, and thermal–hydraulic performance were reviewed. There are some advantages of the passive method such as no external needed power and lower operating cost compared to the active methods. The studies broadly support the view that heat transfer enhancement in STHE is heading toward considerable progress. A total of 47.8% of studies have focused on the passive approach, the air injection method, enhancing heat transfer utilizing nanofluids, and compound methods have percentages of studies 20.2, 22.3, and 9.7%, respectively. The air bubble injection causes the rise of the U ratio where the maximum value was indicated at 452% compared to only water flow. Swirl vane, corrugated tube, and wire coil insert have U ratio values of 130, 161, and 264%, respectively. Nanofluid results in a growth in the heat transfer where the TiO2 has the maximum U ratio (175.9%) compared to traditional fluid. The combination of air injection and passive heat augmentation methods, which was shown to be a substantial solution to several issues, needs to be the focus of more work in the future. Geometrical changes in tube surfaces in STHE are too required in the future with the use of materials coating to enhance heat transfer. The theoretical analysis of heat transfer techniques still needs to be improved, especially for pertinent empirical formulations. Also, since there aren't many relevant numerical simulations, more attention is required. [ABSTRACT FROM AUTHOR]

An experimental investigation on the influence of hybrid nanofluids (HNFs) on heat transfer and flow performance of a heat exchanger tube is presented in this paper. A custom-made thermo-hydraulic loop containing a 1200 mm long copper tube with 12 mm internal diameter is used for the present purpose. The tube was exposed to a constant heat flux of 4530 W m−2. Water-based novel HNFs of SiO2-MgO, SiO2-ZnO, SiO2-TiO2 and SiO2-ZrO2 at 0.05 mass % and pure Deionized (DI) water are used as working fluids. The test-fluids are fed into the loop at a varying mass flow rate from 0.03 to 0.27 kg s−1. Significant enhancement in heat transfer of the tube is obtained with the HNFs when compared to DI-water. The heat transfer performance is enhanced up to 94% with the application of HNFs. The SiO2–MgO exhibits the best heat transfer performance as compared to the other HNFs. The SiO2-ZrO2 HNF shows the worst performance, even worse than DI-water. The rise in friction factor caused by HNFs is identical and very limited as compared to DI-water. Finally, thermo-hydraulic performance of HNFs is analyzed by drawing Figure of Merit (FOM). Based on the FOM analysis, an optimum flow rate of 0.13 kgs−1 and SiO2–MgO HNF are recommended for future heat transfer applications. [ABSTRACT FROM AUTHOR]

A solar pond is a simple system that collects and stores heat for thermal and electrical applications. Heat storage and heat extraction are the key factors in the solar pond. Salt is added to the pond with fresh water to form a salinity gradient solar pond (SGSP). The solar pond comprises of three zones, namely, the upper convective zone (UCZ), the non-convective zone (NCZ) and the lower convective zone (LCZ). The LCZ is also called the storage zone. Generally, the LCZ stores the heat energy of the incoming solar radiation, and this heat may be used for various applications. In this paper, a review is done on the study of solar ponds with various designs and modifications, heating methods, use of floating devices, use of baffle plates, use of heat exchangers, use of flat plate collectors, use of different types of insulation, etc. [ABSTRACT FROM AUTHOR]

The performance of the heat exchanger has a huge impact on the cycle efficiency and levelised cost of electricity in solar thermal power generation. This paper proposes a novel scaled structure for the cold-side channel of the printed circuit heat exchanger (PCHE) that combines good heat transfer performance with lower pressure drop. A numerical simulation is employed to investigate and compare the performance of PCHEs with scaled, zigzag, and straight channels. When using the comprehensive performance evaluation criteria (PEC) as evaluation indicator, the scaled channel demonstrate the best overall performance, with an increase in comprehensive performance by 6 % and 12 % compared to zigzag and straight channels, respectively. The above conclusions indicate that the adoption of scaled channel structures could enhance the heat transfer performance of PCHE, providing valuable insights for the development and improvement of novel PCHE and other heat exchanger's heat transfer efficiency. [ABSTRACT FROM AUTHOR]

The performance of the heat exchanger has a huge impact on the cycle efficiency and levelised cost of electricity in solar thermal power generation. This paper proposes a novel scaled structure for the cold-side channel of the printed circuit heat exchanger (PCHE) that combines good heat transfer performance with lower pressure drop. A numerical simulation is employed to investigate and compare the performance of PCHEs with scaled, zigzag, and straight channels. When using the comprehensive performance evaluation criteria (PEC) as evaluation indicator, the scaled channel demonstrate the best overall performance, with an increase in comprehensive performance by 6 % and 12 % compared to zigzag and straight channels, respectively. The above conclusions indicate that the adoption of scaled channel structures could enhance the heat transfer performance of PCHE, providing valuable insights for the development and improvement of novel PCHE and other heat exchanger's heat transfer efficiency. [ABSTRACT FROM AUTHOR]

Pulsating heat pipes are widely used in cooling electronic devices, automotive radiators, refrigeration, and air conditioning systems. The addition of nanoparticles is one of the effective ways to improve the heat transfer characteristics of fluids. This paper, based on large eddy simulation (LES) numerical method and field synergy theory, investigates the heat transfer characteristics of Al2O3/Cu mixed nanofluid in a self-excited oscillating heat exchanger tube. Through multi-objective optimization of field synergy angles, field synergy factors, and structural parameters, the enhanced heat transfer mechanism of mixed nanofluids in a self-excited oscillating heat pipe is investigated. It is found that there is a significant negative correlation between the heat transfer coefficient h at the wall surface of the heat exchanger tube and the synergistic angle β. The incorporation of nanoparticles improves the synergistic properties between the velocity and temperature fields. The optimum structural parameters are L/D = 0.469931, α = 128.9904° and d2/d1 = 2.047937, and the optimization increases Nu by 1.92%, decreases f by 10.46%, and decreases the temperature synergy angle β by 2.24°. At the same time, the orthogonality or lack of orthogonality between isotherms and streamlines determines the extent of synergistic performance in the countercurrent vortex. [ABSTRACT FROM AUTHOR]

In this paper, we address the morphology of nanoparticles in a base fluid as a variable to see how different shapes can be used to control thermal conductivity along with the types of nanoparticles. Hybrid and mono particle suspensions, including TiO2, Al2O3, and hybrid TiO2–Al2O3, have been used. Water and ethylene glycol are used as base fluids, and nanoparticles range from 0 to 4% in a volume fraction. The Nusselt number, average heat transfer, thermal resistance, pressure drop, and pumping power as a function of Reynolds number are studied for different nanofluids in microchannels. Overall performance is characterized by the analysis of pressure drop, pumping power, thermal resistance, and maximum power. Simulation results show that the thermal conductivity increases linearly with particle morphology. By adding 4% of HyNF (50% Al2O3-50% TiO2) with a morphology of n1 = 7 and n2 = 3, respectively, it results in a substantial 18.6% enhancement in thermal conductivity, compared to 12% and 10.04% enhancement for mono-nanofluids with Al2O3 and TiO2 nanoparticles, respectively. The type of base liquid has a negligible effect on the thermal conductivity of the same kind of nanoparticles. Nevertheless, the findings of this study provide valuable guidance for cooling microelectronic cooling components via nanofluid-based thermal management. [ABSTRACT FROM AUTHOR]

Convective heat and mass transfer are common phenomena in the field of engineering. In recent years, the research on convective heat and mass transfer is getting deeper and deeper. People are constantly seeking new methods to improve the efficiency of heat and mass transfer, but the research on the mechanism of heat and mass transfer is not yet systematic and mature. The theory of the field synergy has made up for this research gap, but the research progress and application of its heat and mass transfer theory lack systematic summary and evaluation. This paper summarizes the theory of enhanced heat and mass transfer based on field synergy theory, analyzes the field synergy equation of heat transfer, mass transfer, and heat-mass cooperation under laminar and turbulent conditions, and gives the evaluation standard of field synergy equation. Field synergy theory shows that improving the synergy between the velocity field and temperature gradient field, that is, reducing the angle between them, can effectively improve the heat transfer efficiency, and improving the synergy between the velocity field and concentration gradient field can effectively improve the mass transfer efficiency. Subsequently, the research progress of field synergy theory in different engineering fields is summarized. It is shown that field synergy theory can be used to analyze the cooperation between fields in heat exchangers, micro-components, nanofluids, reactors and other fields to guide the optimal design of equipment, which proves the universality of field cooperation theory. Finally, in view of the universality of the damp-heat exchange in the cooling exchangers and the research object of field synergy theory, a new idea of using the field synergy theory to guide the research on the structural design of cooling exchangers is put forward, which provides new ideas and methods for effectively improving the underground humid and thermal environment. [ABSTRACT FROM AUTHOR]

The use of air-cooled heat exchangers in various industries has increasingly become wide-spread due to their environmental friendliness and the absence of the need for cooling water. Air-cooled heat exchangers made of annular-finned tubes are widely used in chemical, petrochemical, oil-refining, gas, and food industries, and also at automobile CNG filling stations, in heat power and electric power engineering, refrigeration technology, and at nuclear power plants. The heat power of air-cooled heat exchangers is largely determined by the characteristics of the motion of the flow of cooling air through it, which can be organized with consumption of electric power by means of a ventilator or in an energy-saving regime, i.e., by free convection. Unfortunately, the region of ambient air temperatures, at which it is possible to use air-cooled heat exchangers under the conditions of free convection, is limited. Low intensity of heat transfer compared to forced convection is the main disadvantage of a free convective regime, which is usually compensated by an increase in the heat-transfer area, namely, by finning the heat-transfer area. In the case of equipping air-cooled heat exchangers with additional devices that make it possible to intensify free convection the heating capacity of a heat exchanger can be significantly increased. The paper presents a review of experimental and numerical investigations of free convection heat transfer on air-cooled annular-finned tubes and bundles thereof. [ABSTRACT FROM AUTHOR]

Minimizing the entropy generation rate is one of the key performance indicators for enhancing the thermal design of heat exchangers. This paper introduces a comprehensive numerical entropy generation analysis of turbulent water flow inside—newly proposed—conical tubes with dimples subjected to a constant heat flux. The effect of different tube diameter ratios (DR = 1, 1.5, 2, 3, and 5) and flow modes (convergent and divergent tube configurations) on the thermal, viscous, and total entropy generation rates is investigated within Reynolds number (Re) range of 3 × 103–40 × 103 using ANSYS-Fluent package. Realizable k-ε (RKE) turbulence model is adopted in this study. A well-validated 3D model was adopted to estimate the dimensionless indices: Bejan number (Be), enhanced entropy generation ratio (Ns,en), and the irreversibility distribution ratio ( ϕ s ) to characterize the entropy generation performance and to compare conical dimpled tubes to smooth ones. The results showed that total entropy production rate values for dimpled tube geometries are lower than those for the corresponding smooth ones, especially for convergent dimpled tubes. Convergent dimpled tubes with DR in the range of 1.5–3 achieved the lowest total entropy production values over the whole Re range, with an average value of 0.20 W K−1, as compared to an average value of 0.34 W K−1 for the smooth configurations. The average Ns,en values for dimpled convergent tubes with DR = 1.5–3 are 0.46 and 0.80 at Re = 3000 and 40,000, with reductions of 50.54% and 3.61% at both Re values, respectively. The study also showed that the entropy generation analysis could provide an effective tool to highlight the optimal design of tube heat exchangers based on the minimum entropy generation and the enhanced entropy generation ratio. [ABSTRACT FROM AUTHOR]

In the present research paper, the thermal performance of helical ground air heat exchanger (HGAHE) has been experimentally analyzed under Saharan climate conditions during summer season. A flexible PVC pipe with a diameter of 0.06 m and a length of 30 m has been arranged as a helical-coil layout to design the HGAHE, and it is inserted into a borehole of 5 m depth. The study acknowledges that a drop as high as 11.0 °C in air temperature can be achieved with an air velocity of 10 m s−1 and an inlet air temperature of 38 °C. The study also revealed that, by incrementing the air velocity from 10 to 20 m s−1, the heat exchange rate of the HGAHE system increases by 158% after 3 h of operation time; however, the efficiency of the HGAHE decreases by 21.51%. Moreover, thermal performance derating factor (TPDF) increments with increasing the operation time and air velocity. After 3 h of operation time, the highest TPDF is attained as 0.27 with a velocity of 20 m s−1, whereas the lowest TPDF is observed as 0.14 for a velocity of 10 m s−1. [ABSTRACT FROM AUTHOR]

The heat exchanger has been widely used in the energy and chemical industry and plays an irreplaceable role in the featured applications. The design of heat exchanger is a mixed integer complex optimization problem, where the efficient design significantly improves the efficiency and reduces the cost. Many intelligent methods have been developed for heat exchanger optimal design. In this paper, a novel variant of sine and cosine algorithm named EDOLSCA is proposed, enhanced by dynamic opposite learning algorithm and the elite strategy. The proposed method is tested in CEC2014 benchmark and proved to be of significant advantages over the original algorithm. The new algorithm is then validated in the plate-fin heat exchanger (PFHE) optimal design problem. The comparison results of the proposed algorithm and other algorithms prove that EDOLSCA also has demonstrated superiority in heat exchanger optimal design. [ABSTRACT FROM AUTHOR]

In this paper, a heating process control law with steam supply is designed for a fluid in a heat exchanger. The process is described by a linear hyperbolic equation of the first order with a nonlocal boundary condition with a time-delayed argument. The temperature of the supplied steam is found as a linear dependence on fluid temperature values at measurement points in the heat exchanger. Explicit formulas are obtained for the gradient of the objective functional of the control problem in the space of the feedback coefficients (parameters) of this dependence. A numerical scheme is developed for determining the feedback parameters based on these formulas. Finally, an algorithm is proposed for determining the rational (optimal) number of measurement points. [ABSTRACT FROM AUTHOR]

Dehumidification is one of the key challenges facing the air conditioning (AC) industry in the treatment of moist air. Over many decades, the dual role of heat exchangers of AC chillers for the sensible and latent cooling of space has hindered the thermal-lift reduction in the refrigeration cycle due to the requirements of water vapor removal at dew-point and heat rejection to the ambient air. These practical constraints of AC chillers have resulted in the leveling of energy efficiency of mechanical vapor compressors (MVC) for many decades. One promising approach to energy efficiency improvement is the decoupling of dehumidification from sensible processes so that innovative but separate processes can be applied. In this paper, an advanced microwave dehumidification method is investigated in the laboratory, where the microwave (2.45 GHz) energy can be irradiated onto the dipole structure of water vapor molecules, desorbing rapidly from the pores of adsorbent. Results show a significant improvement in performance for microwave dehumidification, up to fourfold, as compared to data available in the literature. [ABSTRACT FROM AUTHOR]