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The pivotal role of Brownian and thermophoresis in investigating the flow characteristic of polar nanofluid is important nowadays due to various engineering applications. The enhanced thermal and transport properties in the field of biomedical nanomedicine for hyperthermia treatments, and for enhancing the efficiency of heat exchange processes in cooling electronic devices, heat exchangers, and automotive engines the use of Brownian and thermophoresis is important. Therefore, the present study reveals the importance of Darcy–Forchheimer inertial drag combined with the space‐ and temperature‐dependent heat generation/absorption on the flow of polar nanofluid over an elongating surface. The surface is considered to be permeable for which the hydromagnetic flow in the presence of thermal radiation specifically, Brownian and thermophoresis affects the flow phenomena significantly. The proposed flow model designed with the aforementioned physical properties is standardized into the set of nonlinear ordinary equations by the implementation of suitable similarity rules. Further, the characteristics of various physical quantities are deployed by solving the system by using traditional Rung–Kutta fourth‐order technique. Further, the analysis of several factors is deployed briefly via graphically, and simulation of rate coefficients is presented through tables. The important outcomes of the study are deployed as the inclusion of thermal and solutal buoyancy enhances the velocity distribution, whereas reverse impact is observed for the increasing inertial drag. Also, space‐ and temperature‐dependent heat source augments the temperature profile but Lewis number decelerates the fluid concentration significantly. [ABSTRACT FROM AUTHOR]

In this study, the primary objective was to enhance the hydrothermal performance of a dimpled tube by addressing areas with low heat transfer compared to other regions. To accomplish this, a comprehensive numerical investigation was conducted using ANSYS Fluent 2022 R1 software, focusing on different diameters of dimples along the pipe's length and the distribution of dimples in both in-line and staggered arrangements. The simulations utilized the finite element method to address turbulent flow within the tube by solving partial differential equations, encompassing Re numbers spanning from 3000 to 8000. The study specifically examined single-phase flow conditions, with water utilized as the cooling fluid. The results of the investigation indicated that increasing the Reynolds number resulted in higher average Nusselt numbers, pressure drops, the overall performance criterion, and a reduction in average thermal resistance across all models analyzed. Notably, both proposed models demonstrated improved heat transfer when compared to the conventional model. Out of all the models evaluated, the tube featuring staggered dimples (Model B) demonstrated the most notable improvement in the Nu number. It exhibited an enhancement of approximately twice the value compared to the conventional model. The mean thermal resistance for the tube with dimples in the staggered arrangement (Model B) is 0.0057 k/W, compared to 0.0118 k/W for the traditional model. The maximum overall performance criterion for Model -A- and Model -B- is 1.22 and 1.33, respectively. Graphic Abstract [ABSTRACT FROM AUTHOR]

Deep coaxial borehole heat exchanger (DCBHE) is a promising kind of ground heat exchanger for geothermal exploitation. In this study, effects of stratified ground thermophysical properties (GTP) are considered, and then an improved semi-analytical heat transfer model is developed and validated to analyze the DCBHE performance. Then, influences of stratified GTP on the DCBHE performance are investigated. Finally, thermal response test (TRT) of DCBHE with stratified GTP is simulated by a numerical model, and by using the simulated TRT data, the improved model is combined with a parameter estimation method to identify the effective values of GTP, which are compared with actual values. The results show that stratified ground thermal conductivities have an important influence on the DCBHE performance, and that stratified volumetric heat capacities of ground have a small influence on the DCBHE performance. The DCBHE performances based on the effective values and actual values of GTP match well with each other for different cases and geothermal gradients, indicating that for stratified thermal conductivities or volumetric heat capacities of ground, the effective GTP are reliable and can be used for accurately predicting the DCBHE performance. [ABSTRACT FROM AUTHOR]

This paper investigates the flow and thermal properties of a combined multiple shell pass (CMSP)‐shell and tube heat exchanger (STHE) with the provision of unilateral ladder‐type helical baffle (ULHB) and continuous helical baffle (HB) in the outer shell pass of the heat exchanger. Two CMSP‐STHEs with ULHB and HB, respectively, are compared with the traditional STHE having segmental baffles (SG‐STHE) using the computational fluid dynamics method. The computational outcomes are validated with the empirical correlations of the Kern and Esso method. The Reynolds‐averaged Navier–Stokes‐based standard k–ω turbulence model accurately predicts the heat transfer (HT) rate and pressure drop. The computed results of HT rate, pressure drop, and logarithmic mean temperature difference corresponding to various mass flow rates (m) for three STHEs are presented. The results show that the overall HT rate of CMSP (ULHB)‐STHE and the CMSP (HB)‐STHE at the same mass flow rate are nearly 28.3% and 14.8% larger than that of traditional SG‐STHE, respectively. Furthermore, the overall area‐weighted average pressure drop (ΔP) of CMSP (HB)‐STHE is smaller than that of SG‐STHE by 26.5% at the same mass flow rate (m) and for CMSP (ULHB)‐STHE it is larger by 2% than that of traditional STHE. Based on the above results, it is concluded that the CMSP (ULHB)‐STHE is a suitable replacement for the conventional SG‐STHEs. [ABSTRACT FROM AUTHOR]

The cross‐flow heat exchanger involves a tractor moving between two fluids that flow in a direction perpendicular to each other, and one of the fluids is often a liquid and the other is a gas. This type of heat exchanger has been studied in many previous studies for its importance in air conditioning applications and many industrial applications. In this type of heat exchanger, the surface area for heat transfer is very large. Therefore, many techniques have been used to improve the thermal and dynamic performance of this type of heat exchanger. In this study, previous studies that used metallic foam as one of the ways to improve the performance of heat exchangers were reviewed. The most important techniques that were used in previous studies during the process of evaluating the thermal performance of a cross‐flow heat exchanger in the presence of different types of metal foam were clarified. The use of metal foam depends on important factors, including (1) the type of material, where copper and aluminum were used in most of the previous studies, due to their availability and ease of foam formation using these materials, in addition to the good thermal properties, (2) porosity, where the porosity value of metal foam ranged between 0.85 and 0.98 in the previous studies, (3) the density of pores, most of the studies ranged between 10 and 40 PPI. [ABSTRACT FROM AUTHOR]

Borehole heat exchanger (BHE) array is a key element in the ground source heat pump system (GSHPS). The BHE array is traditionally simplified by assuming the same heat exchange rate for each BHE, which normally is not correspondent to the real applications. In this investigation, a TRT was firstly conducted for a site located in Shanxi Province (China) to get the local ground thermal properties. A numerical simulation framework was next verified by the TRT results. Subsequently, the ground thermal properties obtained by the TRT were used in the numerical simulation model to investigate the influence of two operation strategies on the ground temperature development of the surrounding soil and the BHE performance. The results showed that both ground temperature and BHE array performance decreased during the 8-year operation period of the BHE array in the heating mode. The ground temperature around the center BHE was lower in the same heat load (SHL) scenario (same heat load for the BHEs in the array) than in the same inlet temperature (SIT) scenario (same carrying fluid inlet temperature for the BHEs in the array), and this difference can be 2 °C in the 7th year. The annual average outlet temperature in the SHL scenario was also lower than that in the SIT scenario, especially in the long term. The investigation shows that SIT working strategy superiors the SHL strategy, providing a reference for the upcoming investigation on the design aspect of the GSHPS. [ABSTRACT FROM AUTHOR]

The present experimental investigation incorporates the winglet twisted tapes as an insert to determine the thermal and hydraulic performance of a heat exchanger tube. The purpose of connecting the winglet to the twisted tape is to improve the heat transmission while minimizing the pressure loss by not disrupting the flow at the core portion. The thermal performance of a heat exchanger with turbulent promoters is assessed by varying geometric factors, such as the size of the promoters, Twist ratio ( y / W), Winglet pitch ratio ( P w / L T ), and Winglet height ratio ( h w / b w ). Experiments were carried out for Reynolds numbers (Re) ranging from 3,000 to 21,000. For a set of geometric parameters, the greatest thermohydraulic performance achieved was 1.58. Regression analysis is used to build a statistical association for Nusselt number N u and friction factor f , and the anticipated data obtained is of acceptable accuracy. The entropy generation is expressed in the form of entropy generation number and the Bejan number to fetch the dominance of thermal or friction entropy using winglet twisted tape. [ABSTRACT FROM AUTHOR]

Deep coaxial borehole heat exchangers (CBHEs) are being widely used in clean space heating of buildings in winter. Here we report a new field test on a 1800m deep CBHE in the southern Daxing uplift, Beijing, a representative geological region in North China. Under the economic flow rate of 20–25 m3/h, the steady heat extraction power is 237.24–256.54 kW. Further, numerical modelling and simulation calculations are performed to compare the applicability of the Eskilson-Claesson model and Al-Khoury model for different operation patterns and then analyze the operation performance of deep CBHE during the whole heating season. For typical flow rates, compared with the continuous pattern, the intermittent pattern can increase the heat extraction power per unit depth by 25.4–31.0% and reduce the thermal influence radius by 1.46–1.89 m due to a better ground temperature recovery around the borehole. In addition, a new contribution factor (CF) is introduced to evaluate the temperature contribution of different ground layers during the heat extraction, which can reveal the influences of flow conditions, geothermal gradient, thermal properties, and even groundwater flow. The present results support that deep CBHEs have more obvious advantages for space heating of buildings with intermittent heating requirements. [ABSTRACT FROM AUTHOR]

• Development of a novel procedure for optimal distribution of heating/cooling demand among individual borehole heat exchangers (BHEs) in a field. • A methodology that sequentially updates the operation strategy of BHEs to deal with spatiotemporal uncertainties in subsurface thermal properties. • The procedure accounts for estimation errors and fluctuations in the transient energy demand. Unmanaged heat extraction, as well as the adjacency of multiple borehole heat exchangers (BHEs) in a field, can lead to undesirable thermal conditions in the ground. The failure to properly control induced thermal anomalies is perceived as a severe risk to closed-loop geothermal systems, as the detrimental effects on the ground can substantially deteriorate performance or nullify the compatibility of an operating system with regulatory mandates. This paper presents a flexible framework for the combined simulation-optimization of BHE fields during the entire lifespan. The proposed method accounts for the uncertainties in subsurface characteristics and energy consumption in order to minimize the temperature change caused by the heat extraction during the operation. The descriptive uncertainty is introduced as a deviation of the monitored temperature from the simulated temperature change, whereas the variation of the energy demand appears as over- or under-consumption against the scheduled demand. The presented new sequential procedure, by updating the thermal conditions of the ground with temperature measurements, continuously executes the optimization during the operation period and enables the generation of revised load distributions. In this study, two fields with five and 26 BHEs are considered to demonstrate the performance of the proposed method. Sequential optimization outperforms single-step optimization by providing the basis for more strategic load-balancing patterns and yielding lower temperature anomalies of about 2.9 K and 8.9 K in each BHE configuration, respectively, over 15 operational years. [Display omitted] [ABSTRACT FROM AUTHOR]

Printed Circuit Heat Exchangers (PCHEs) are considered an excellent alternative for the main cryogenic heat exchanger of Floating Liquefied Natural Gas (FLNG) facilities due to their compact structure and strong heat transfer performance. However, it is unclear how to configure the geometry of the PCHE channels to achieve its optimal performance in the trans-critical liquefaction process of natural gas (NG), which is critical for the main heat exchanger. In this paper, we numerically studied the thermal-hydraulic characteristics of PCHEs with different channel types under the specified condition. The results elucidate that all channels have an enhancement of heat transfer near the pseudo-critical point of NG. All the wavy channels could improve the heat transfer performance of PCHEs, where the trapezoidal channel achieves the largest promotion. Compared with the straight channel, the local heat transfer coefficient could be increased by up to 53% in the trapezoidal channel. Additionally, vortex appeared at the bends of the wavy channels, which greatly increase the local friction loss. Among several channels, the total pressure drop of zigzag, fillet and the sinusoidal channel was almost the same, while that of the trapezoidal channel was the largest. Furthermore, we compared the comprehensive performance of different types of channels and found that the benefit of heat transfer enhancement could not offset the penalty of flow deterioration. Our work provides important guidance for the design of PCHEs employed in FLNG. [ABSTRACT FROM AUTHOR]

Enhancing the Convective heat transfer in the carrier fluids, by augmenting the thermal conductivity in fluids, with nano particles is one of the passive techniques. Enhancement in the thermal conductivity in the carrier fluids can be achieved by suspending particles of nano-size into the base fluids, such colloidal suspensions are called as nanofluids. Nanofluids are proven fluids which improve the convective transfer of heat in the base fluids in the heat exchangers. But still, there are lot of challenges that are existing in understanding the mechanisms of enhancement of convective heat transfer for large scale applications. In this work, an attempt is made to summarize recent advancements on augmentation of convective heat transfer in heat exchangers in turbulent flows using various nanofluids and present various setbacks for the development of nanofluids for critical applications. [ABSTRACT FROM AUTHOR]

Undisturbed ground temperature (UGT), thermal conductivity (TC) and heat capacity (HC) are essential parameters to design geothermal heat pumps and underground thermal energy storage systems, particularly borehole heat exchangers (BHE). However, field methods to assess the thermal state and properties of the subsurface are costly and time consuming. Moreover, HC is often not evaluated in situ but arbitrarily selected from literature considering the geological materials intercepted by boreholes. This work proposes an original empirical approach to reproduce a UGT profile and estimate in situ thermal diffusivity (TD) and HC in the scope of conventional thermal response tests (TRTs). Empirical equations were developed to reproduce a UGT profile measured along a BHE. Experimental coefficients are found with a non-linear least square solver optimization and used to calculate the damping depth, TD and HC. The suggested heat tracing method was verified and validated against other field methods demonstrating to be fast and reliable. The novelty of this new empirical approach relies on the use of a single temperature profile providing a simple way to better assess subsurface thermal properties. [ABSTRACT FROM AUTHOR]

The high initial investment of borehole heat exchanger (BHE) prevents the popularization and application of ground-coupled heat pump system (GCHPs). As the premise of designing BHE, ground thermal properties are usually obtained using thermal response test (TRT), and parameter estimation method are applied based on homogeneous BHE model independent of geological stratification. In this paper, a multi-parameter estimation method using Bat algorithm (BA) is firstly proposed to obtain the layered rock-soil thermal properties based on the numerical layered BHE model, considering the characteristics of geological stratification. Then, a TRT experimental platform of three-layer BHE is developed to measure thermal responses of different stratified subsurface. Finally, the six thermal properties are obtained by the proposed multi-parameter estimation method based on BA, and their accuracy is validated using the experimental data in TRT. The five temperatures obtained from the numerical layered BHE model using the estimated results are compared with the corresponding experimental data, the results show that the maximum error of the inlet and outlet water temperatures of the BHE is respectively 3.32 % and 3.59 %, and it is 3.31 %, 2.38 % and 2.7 % for the coarse sand, fine sand and brown soil, respectively. [ABSTRACT FROM AUTHOR]

The ground thermal properties are the basic parameters for the design of borehole heat exchanger (BHE) in ground–coupled heat pump system (GCHPs), and their accuracy directly affects the economy and reliability of the heat pump system. In traditional design, ground is usually regarded as an isotropic homogeneous medium, and its thermal properties are obtained by solving the inverse heat transfer problem in BHE through in-situ thermal response test (TRT). In fact, different geological layers can be observed along the depth of BHE, and thermal physical properties of each layer are different based on the ground geological conditions. In order to investigate the effect of geological stratification on estimated accuracy of ground thermal parameters in TRT, a validated numerical layered BHE model (NLBM) is presented to simulated TRT, and the fluid temperature response is used to estimate effective ground thermal conductivity and borehole thermal resistance based on line source model (LSM). Secondly, the distributions of fluid temperature in U-pipe and heat flux of BHE along the depth are compared and analyzed based on the NLBM and the numerical homogeneous BHE model (NHBM). At last, borehole thermal resistance from the NLBM and estimated borehole thermal resistance from LSM are compared. The results show the maximum heat flux in the 3rd layer of the NLBM is 21.1% higher than that of NHBM, and the minimum heat flux in the 1st layer is reduced by 46.9% in the 100 h duration. The estimated λ LSM using the fluid temperature responses in the NLBM is 1.3% higher than the thickness-weighted thermal conductivity in the NLBM. The minimum relative error between R LSM and R b is still up to 10.45% in the duration of 100 h even though extending the duration is helpful to improve the estimated accuracy of R LSM. • A numerical layered BHE model is proposed and validated by the experiment. • The distributions of fluid temperatures are compared from the two models. • The differences of heat flux are illustrated in the two models. • Effect of geological stratification on estimated accuracy is investigated in TRT. [ABSTRACT FROM AUTHOR]

To assess the performance of triple tube heat exchangers, it is not possible to apply the traditional methods (e.g., Wilson plot method) because they can be only applied to the classical shell-in-tube configuration that can be easily modelled by the logarithmic mean temperature difference approach. Therefore, to overcome this limitation, some new methodologies have been proposed in the literature and, among them, a promising tool is represented by the parameter estimation procedure. Parameter estimation procedure is a powerful technique already adopted in many engineering applications. However, this procedure requires, for the application investigated in the present study, a detailed numerical model of the triple tube heat exchanger and the measurement of the temperature of the fluids in each tube at inlet and outlet sections. These elements make its application feasible only in well-equipped research labs, limiting its massive employment in industrial facilities. In this paper, a novel parameter estimation procedure to characterize the thermal behavior of the triple concentric-tube heat exchanger is proposed. This approach is based on a simple model of the exchanger and it requires to measure the fluid temperature only in four sections. The simplified proposed procedure is numerically validated and compared to the full one. [ABSTRACT FROM AUTHOR]

This study was mainly conducted to enhance the thermal properties of paraffin wax, as a promising thermal storage material, by adding nanoparticles of CuO with different mass fraction concentrations. Moreover, the effect of using a helical finned tube in the heat exchanger unit on the charging and discharging processes of the paraffin wax/CuO nanocomposite was also studied. The experimental results showed that the optimal concentration of paraffin wax/CuO nanocomposite is 1%, where it achieves the highest improvement in melting time of 22.22% compared to pure paraffin. An additional improvement in melting time of 42.85% was achieved when a helical finned tube was used. In addition, a reduction of 66.66% of the solidification time of paraffin wax/CuO nanocomposite was achieved when the helical finned tube was used. [ABSTRACT FROM AUTHOR]

Improved heat transfer efficiency with considering economic analysis in heating systems is an interesting topic for researchers and scientists in recent years. This research investigates the heat transfer rate (HTR) and flow of non-Newtonian water-Carboxyl methyl cellulose (CMC) based Al2O3 nanofluid in a helical heat exchanger equipped with common and novel turbulators using two-phase model. The requirements for dimensions and cost reduction and also energy saving in thermal systems are the main goal of this study. According to gained results usage of corrugated channel in helical heat exchanger has a considerable influence on thermal and hydraulic performance evaluation criteria (THPEC) index of helical heat exchanger and can improve the THPEC index. Thus, Re = 5000 is obtained as an optimum value, in which the maximum THPEC value is achieved. As it is found in this paper, in case of using novel heat exchanger instead of the basic smooth system, the thermal properties (by considering Nusselt number) increases about 210%, the hydraulic performance (friction factor) reduces about 28%, performance evaluation criteria index increases about 57% and the material consumption (in case of similar THPEC) decreases about 31%. In another word, with considering economic analysis for the basic and novel system which has same efficiencies, the novel one has lower length and consequently 31% lower material. [ABSTRACT FROM AUTHOR]

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This paper models the thermal transport properties and performance of a water-based CuO nanofluid (with varying volume fractions of CuO) in a laboratory-sized double pipe heat exchanger (DPHE). Copper oxide (CuO) nanoparticles were used and their quantity was varied from a volume fraction of 0% to 0.1% with an incremental step size of 0.025%. The mass flow rates of the hot and cold fluids were maintained at 0.87 kg/s and 0.9 kg/s, respectively. Simulation results revealed that temperatures of 410 and 306.75 K, respectively, were attained at the hot and cold fluid outlets. Analysis of the DPHE showed that for cold fluids, thermophysical properties such as viscosity, thermal conductivity, specific heat capacity (SHC) and density were enhanced by the addition of nanoparticles. The temperature distribution, effectiveness and the heat transfer in the DPHE were observed to linearly increase with increment increases of the nanoparticle volume fraction. [ABSTRACT FROM AUTHOR]

U-bend deep borehole heat exchanger (DBHE) is a new promising kind of ground heat exchanger, but nowadays there are lack of accurate efficient models to simulate U-bend DBHE. This paper has developed a semi-analytical model of U-bend DBHE, which considers the unsteady heat transfer of borehole, heterogenous soil thermal properties and geothermal gradient. A 2D numerical model and an analytical model based on infinite line-source theory are also developed, and the three models are compared with experimental data for different boundary conditions. Based on the soil thermal properties estimated by logging data and rock identification, the three models have large errors when compared with experimental data. Based on a soil thermal conductivity λ s estimated by matching experimental data, the three models match better with experimental data, and it is inferred that λ s should be measured by thermal response test instead of rock identification. The semi-analytical model and 2D numerical model match very well for all the time, but the analytical model has large differences with 2D numerical model, which is because the analytical model ignores borehole heat capacity and time-varying heat flows at the borehole wall. This paper could provide a cost-effective semi-analytical model and some advices for U-bend DBHE. [ABSTRACT FROM AUTHOR]

Thermal Response Tests (TRT) have been extensively studied in the past decades and is an important area of research belonging to ground heat exchanger design. The most important thermal property inferred in a TRT is the equivalent subsurface thermal conductivity. Previous studies were presented where the thermal diffusivity was estimated but with limited success. In this paper, a TRT with an oscillatory excitation (OTRT) is used to obtain a better uncoupling between thermal conductivity found from constant heat injection and thermal diffusivity. The method was already used in the past with a simplified ground model. It is presented here with a better model that takes into account the ground and the borehole thermal response. The method is based on the concept of concentric composite cylinder where the equivalent radius is used for the U-tube arrangement. Results obtained with this method were successfully correlated to those obtained with numerical simulations and the method was then used to analyze an experimental field test. • New Thermal Response Test with Oscillatory heat injection. • Estimation of soil diffusivity or volumetric capacity. • Numerical and Experimental Verification. [ABSTRACT FROM AUTHOR]

The experimental study, thermal performance, and pressure drop of single-walled carbon nanotube (SWCNT) and graphene quantum dot (GQD) nanofluids in shell and tube heat exchanger with fin blade tubes are evaluated. The effects of the working fluid (water) volume flow rates (VÌ= 2.5-10 L/min), volume concentration of nanoparticles (Ï= 0.0%, 1%, 3%, and 5%), Reynolds number of working fluid (Re = 850-3300), and tube building (heat exchanger with fin blade tubes and without fin blade tube) have been analyzed. Results represent that with augmentation of volume concentration of SWCNT nanoparticle up to 1%, heat transfer rate increases by â5% and then up to 5% volume concentration of SWCNT nanoparticle decreased about 17%, also this calculation for GQD nanoparticle conducted and results represented decreasing 6% and approximately unchanged heat transfer rate, respectively. With regard to obtained results, heat transfer rate of heat exchanger can be improved by using the fin blades by 188%, compered without fin blade heat exchanger also most related increase for pressure drop of heat exchanger was recorded about 80% for 5% SWCNT of nanofluid. At the end, the mean enhancement in effectiveness of heat exchanger with various concentrations of SWCNT and GQD nanofluids and using the fin blades is about over 100% and 85%, respectively. In fact, the present study shows that applying the new finned tubes in the heat exchanger has more impact, related to the mentioned nanoparticles on the thermal properties of heat exchanger. [ABSTRACT FROM AUTHOR]

In this study, a commercial grade of talc is used as filler in a bimodal high‐density polyethylene (HDPE) used for the pressure pipe application. The composites are characterized by thermogravimetric analysis (TGA), differential scanning calorimetry, dynamic mechanical thermal analysis, and tensile testing. The results illustrate that the presence of talc has a considerable effect on the material properties and the pipe life‐length. It is presented that the thermal stability measured by TGA is enhanced, while the oxidation induction time decreases in cooperation of the talc. The nucleation behavior of talc particles during crystallization has no obvious effect on melting temperature; however, an increase in crystallization temperature is evidenced. Storage modulus as recorded from the dynamic mechanical analysis is also increased in all composites, furthermore, the temperature of the α relaxation is shifted toward higher temperature and finally the strain hardening modulus for the HDPE/talc composites is assessed and compared to the neat HDPE as a measure of environmental stress crack resistance. [ABSTRACT FROM AUTHOR]

The influence of serrated circular rings with rectangular winglets (SCRWRW) on the thermal performance of circular tube heat exchanger has been studied experimentally and computationally. The geometrical parameters considered are diameter ratio (DR = 0.8, 0.85), pitch ratio (PR = 3, 4), attack angle (ϴ = 15°, 30°, 45°), and blockage ratio (0.05). The test section is a circular tube of length 1.5 m and diameter 68.1 mm, in which uniform heat flux of 1000 W/m2 has been applied. Air is the working fluid flowing in the range of Reynolds number between 6000 and 24000. The results obtained showed that SCRWRW enhances heat transfer rate 5.54 times of smooth tube while the maximum thermal performance obtained is 3.2 at DR = 0.85, PR = 3, and ϴ = 15°. The computational investigation has also been carried out using Ansys fluent and presented the effect of SCRWRW on temperature distribution and fluid flow. SCR: Serrated Circular Ring; SCRWRW: Serrated Circular Ring with Rectangular Winglets; DR: Diameter Ratio (d/D); PR: Pitch Ratio (l/D); BR: Blockage Ratio (H/D) [ABSTRACT FROM AUTHOR]

Fouling of heat exchangers in energy and power plant industry, oil and gas industry, pharmaceutical and food process industry, industrial waste heat recovery is a major problem which needs to be solved urgently. In the United Arab Emirates, a majority of oil & gas processing plants are located in the desert where water accessibility is limited, thus fin-fan type of heat exchangers are used for cooling and/or heating applications. Such harsh environments cause external fouling which becomes an unavoidable problem in these heat exchangers. With increased humidity and high process temperatures, the dust particulates start to stick on the outer surface of heat exchangers which drastically reduces the thermal performance and increases power consumption. In order to identify possible methods to control and/or eliminate such kinds of external fouling, it is important to identify the composition and morphology of such foulants. This study presents the characterization of selected fouling samples collected from several fin-fan type air cooled heat exchangers taken from a gas processing plant. Scanning electron microscope (SEM) tests were carried out to determine the physical characteristics of sample foulant. Variability in sizes and shapes was found between samples due, perhaps, to different working temperature ranges of the selected heat exchangers. X-ray diffraction (XRD) analyses revealed presence of quartz, calcite, and alumina with traces of halite and hematite. Laser flash analysis (LFA) was conducted to quantify the specific heat capacity, thermal diffusivity and thermal conductivity of the fouling samples. The diversity of these fouling samples reflects complexity with respect to their potential removal and effects on heat transfer characteristics. Though, this research work is a case study for a specific petrochemical plant, however, findings in this study can be adopted by other industries involved in similar chemical processing in the Middle East as well as other countries having similar weather and geological conditions. [ABSTRACT FROM AUTHOR]

The paper considers the application of metal - fibrous microstructures in the development of highly efficient heat exchangers. Such structures can be successfully used in air conditioning systems of modern planes or in heat pipes located in planes and spacecraft. Copper fibers of 50 mm diameter have been used to produce coatings of different volumetric porosity. The sintering process was used to produce the samples. Pool boiling heat transfer tests have been performed on the non - isothermal surfaces of the fin with distilled water and ethyl alcohol (99.8% purity) as boiling agents. A significant enhancement of heat transfer has been recorded with the use of the metal - fibrous microstructures in comparison to the smooth surface without any coating. The enhancement proved to vary considerably depending on the superheat value. [ABSTRACT FROM AUTHOR]

Applying lumped thermal model networks to interconnected electrical systems and fluids, in analogy with the electrical circuit methods, the system temperatures can be advantageously calculated in every node of the thermal networks with a complete system of equations, which considers the geometry, heating sources, fluid properties and material characteristics. In this paper, the lumped model parametrization for steady-state calculation is explained, and comparisons of the calculated results with the lumped model and with the computational fluid dynamic tools are presented. For example, the heat transfer is calculated here in the case of a) - heating of cooled hollow conductors and b) - heat exchangers of a water heating system. [ABSTRACT FROM AUTHOR]

Cardiac surgeries that involve cardiopulmonary bypass technique require a stable temperature maintenance for oxygenated blood or the cardioplegia solution. For this purpose, the heat exchangers are used. Nowadays, these exchangers consist of stainless steel tubes or bellows in a plastic shell. The blood is then warmed or cooled by water flowing in the shell around these structures. In the paper, the thermal specifications of two commercially used cardioplegia heat exchangers Capiox Cardioplegia and MYOtherm XP were evaluated and compared. For this purpose, a water was used as a substitution for blood. Both components were tested for varying flow rates in the pipes in the range 20-150 l/h and fixed flow rate 700 l/h in the shell. The thermal performances of both devices resulted similarly (up to 2.4 kW) at maximal flow rate. The performance factors for low flow rates approached values close to 0.98 and with increasing flow rate decreased down to 0.50. MYOtherm XP shows lower pressure drop than Capiox Cardioplegia due to more optimal construction. The major difference between the heat exchangers was observed in overall heat transfer coefficients at maximal flow rate and resulted in 2191.3 W/m²K or 1760.2 W/m²K for MYOtherm XP or Capiox Cardioplegia, respectively. [ABSTRACT FROM AUTHOR]

Ground thermal properties (thermal conductivity and heat capacity) are the key parameters for design of borehole heat exchanger (BHE) in ground source heat pump (GSHP). This study presented a novel sequential estimation for ground thermal properties of coaxial BHE by using distributed thermal response test (DTRT) data. Firstly, a comprehensive heat transfer model for coaxial BHE was built to obtain the vertical temperature files. Then a new sensitivity analysis using Spearman correlation method was performed to obtain the correlation between the thermal properties and fluid vertical temperature, determining the estimation sequence. Lastly, according to the sequence, Monte Carlo stochastic method was used to estimate the thermal properties by applying the DTRT data. In addition, the effect of borehole depth and random samples on estimations was investigated. The simulations revealed that the heat input into BHE was mainly used to heat the circulating fluid during the earlier time. It was found that the estimation steps following the thermal conductivity first, then heat capacity got higher precision than other estimation steps with 0.6% and 4% respectively for the two parameters. In addition, the effect of borehole depth on estimation error could be eliminated by using the DTRT data. • DTRT data was interpreted for ground thermal properties estimation. • Sequential parameters estimation was presented for DTRT analysis. • The estimation precision for ground heat capacity was improved to 4%. • Effect of borehole depth on estimate error was eliminated by using DTRT data. [ABSTRACT FROM AUTHOR]

This paper proposes an innovative algorithm using the idea of step-wise to estimate of multiple parameters of the shallow ground and U-shaped geothermal heat exchangers. This procedure uses an infinite composite-medium line-source solution. The short-term solution not only enables testing data collected during short times (< 10 h) to be used in parameter estimation but also provides a feasible approach to estimating geometric parameters and thermal properties inside a borehole. The step-wise estimation consists of four stages: 1) determine soil thermal conductivity k s , 2) estimate the thermal conductivity of grout k b , 3) estimate the distance between centers of U-tube pipe D , the thermal diffusivities of soil and grout, a s and a b , and 4) an iteration process if necessary. The outstanding feature of this step-wise algorithm is that the TRT data used in each step can be controlled separately, which can increase the accuracy of estimation because it alleviates the linear dependence among the sensitivities of parameters. It is shown that the accuracy of the estimates is ranked in descending order as follows: k b (± 1.0%), k s (± 2.0%), D (± 16.0%), a s (± 20.0%) and a b (± 70.0%). • New step-wise parameter estimation method is created and validated by TRTs data. • The new algorithm uses a compositemedium line-source solution. • Multi-parameter of the ground and GHE are determined in a set of procedures. • Early-time (<10 h) data is effectively and sufficiently used for estimations. [ABSTRACT FROM AUTHOR]

The soil moisture contents affect significantly the soil thermal properties and consequently the thermal efficiency of shallow geothermal systems. This effect becomes more complex to be evaluated for an Earth-Air Heat Exchanger (EAHE) because of its non-stable energy performance due to a large fluctuation of the temperature of air. In this study, the impact of soil moisture content and soil thermal properties has been investigated on the long-term energy performance of an instrumented EAHE site. First, a full-scale experimental EAHE site in University of Strasbourg as well as its measured data are presented. The thermal properties of different soil layers present in the site were experimentally and theoretically characterized with different soil moisture contents. Based on these results, an analytical solution was proposed to simulate the soil temperature of the field and the output air temperature of the EAHE. A computer program based on this analytical solution was developed to assess the performance of the system for a period of three years. The numerical calculation was validated for an average saturation condition by comparing simulation results with measured data. Different soil saturation conditions were also used in the numerical simulation to consider the effect of soil moisture on the system performance. The results show that if the turbulent flow of the circulating air is fully developed, the difference of the exchanged energy could reach more than 40%. • The long-term performance of a full-scale earth-air heat exchanger was assessed. • The soil thermal properties were characterized at different moisture contents. • An analytical solution was used to simulate the system for a period of 3 years. • Different soil moisture conditions were used in numerical simulations. • The difference of exchanged energies reached more than 40%. [ABSTRACT FROM AUTHOR]

Nowadays, a bio-inspired heat exchanger incorporating a triply periodic minimal surface (TPMS) structure has demonstrated great potential in the fields of new energy research and aerospace, which necessitates achieving a balance between low volume and high heat transfer efficiency while maintaining low pressure drop. In this paper, the adjustable heat efficiency of the heat exchanger with TPMS in gradient thicknesses is specially designed. A steady-state conjugate heat transfer (CHT) model is coupled with computational fluid dynamics (CFD) analysis. In addition, the temperature profile and velocity streamline are also checked to analyze the fluid flow behavior of the radiator. The results show that the convective heat transfer coefficient of the Gyroid with gradient level set values is 26.02–60.10% higher than that of the uniform Gyroid model, and the pressure drop is decreased by 9.66–18.05%. Both high heat transfer efficiency and low pressure drop can be achieved when the thickness is 0.2–0.3 mm and Re is 100–125. The heat exchangers with a TPMS thickness gradient in the ratio of 2:4:6 demonstrate a remarkable enhancement in overall heat transfer efficiency, achieving a 30.22% improvement compared to those with a TPMS thickness gradient in 6:4:2. [ABSTRACT FROM AUTHOR]

Although the enhanced thermal response test (ETRT) method has been used to determine the distribution of ground temperatures and effective thermal conductivities, there are a number of obstacles which limit the wide application of this technology in the discipline of geoengineering. In this literature, four aspects of ETRT technology were investigated: (a) acquisition of ground temperature, (b) installation of the heat exchange tubes, (c) optimization of the monitoring positions, and (d) the difference in thermal conductivity obtained by the ETRT and numerical simulation. To investigate these issues, a field trial was carried out in Heze, Shandong Province, China, and the corresponding numerical models were built. The results demonstrate that: (i) the conventional methods that infer undisturbed ground temperature using water in tubes have large errors, whereas the distributed temperature sensing (DTS) technique enables the measurement of precise temperature profiles; (ii) the thermal conductivity measured using double U-tubes reflects the soil thermal property more accurately than that for a single U-tube; (iii) it is more reasonable to install optical fibers outside the U-tube sidewall than inside the observation tube; and (iv) it is essential to quantitatively consider various interface thermal impedance when estimating ground thermal conductivities using numerical simulation. [ABSTRACT FROM AUTHOR]

A g-function links heat extraction rates to the mean borehole wall temperatures in geothermal heat exchangers. New computation methods are proposed continuously, becoming more accurate as they rise in complexity. In this work, it is shown how artificial neural networks can be assembled and trained to approximate g-functions rapidly and accurately for varying numbers of boreholes placed on a regular or irregular layout. This article focuses on geothermal heat exchangers made up of one to ten boreholes in a field of 30 by 30 m with various borehole geometries and soil thermal properties. After a training phase that used a database of 500,000 g-functions obtained with a block matrix formulation, a mean computation time of 11.18 ms was reached. This is 37% faster than using the block matrix formulation and represents a small fraction of the time required to simulate the fluid temperature over a 5-year period. The accuracy of the network against regular and irregular configurations of boreholes was evaluated and median errors of 0.18% and 0.39% were noted. The methodology introduced in this work is general and can be used together with any method allowing construction of g-functions. [ABSTRACT FROM AUTHOR]

Thermal response tests (TRTs) are performed on borehole heat exchangers in order to evaluate ground and borehole thermal properties, which are needed in the design of ground-source heat-pump systems. When parameter estimation techniques are applied to evaluate the ground thermal conductivity and borehole thermal resistance, the map of the root mean square error (RMSE) sometimes shows a shallow descent to the global minimum. This study obtains a steeper descent by estimating the component of borehole resistance without heat capacity as a separate parameter. A temperature derivative curve is introduced to identify the boundaries between three distinct periods of a TRT, which are borehole-dominated, transition, and steady heat-flux periods. The effective borehole resistance and ground thermal conductivity can be evaluated independently from each other during the borehole-dominated and steady heat-flux periods, respectively. Meaningful estimates of the ground volumetric heat capacity can be obtained from the TRTs in this study in only limited cases. The best chance is when the grout and ground thermal conductivities are nearly equal and the borehole thermal resistance is small. [ABSTRACT FROM AUTHOR]

• Pure fine silver powder sinter heat exchanger materials were studied. • Bond strength between particles in a sinter was assessed using thermal diffusivity. • A 0.13 μm sinter had surface area 1.4 m2/g and pore volume 5.99 × 10−3 cm3/g. • A 0.13 μm sinter showed bond strength equal to that of a common 0.07 μm material. • The 0.13 μm sinter is suitable for use in ultra-low-temperature cooling. This work investigated sinters made of pure fine silver powders having nominal particle sizes of 0.07, 0.13 and 10.6 μm, using nitrogen gas adsorption, laser flash analysis and field emission-scanning electron microscopy. The goal was to improve the efficiency of heat exchangers used in ultra-low-temperature cooling. This study also examined the bond strength between particles in the sinters, which is associated with the thermal conductivity of the materials, based on thermal diffusivity data. The 0.13 μm sinter had a specific surface area greater than 1.4 m2/g, while the 0.07 μm material, which is most widely used for ultra-low-temperature cooling, had a value of approximately 0.4 m2/g. The latter surface area was less than 25% of previously reported values. The 0.13 μm sinter with a 55% packing fraction exhibited a large total pore volume of 5.99 × 10−3 cm3/g, a high specific surface area of 1.6 m2/g, and the largest room temperature intrinsic thermal diffusivity of 9.12 × 10−5 m2/s in air. Therefore, the 0.13 μm material represents the optimal heat exchange sinter for ultra-low-temperature applications. [ABSTRACT FROM AUTHOR]

The thermal response test (TRT) is the standard method for characterizing the thermal properties of the ground and those of a borehole heat exchanger (BHE). During the TRT, the inlet and outlet temperatures of the BHE are monitored. However, this test typically considers the ground as a homogeneous, isotropic, and infinite media, and therefore, it only determines the bulk and effective parameters, such as effective thermal conductivity and thermal borehole resistance. Hence, the enhanced TRT protocols are necessary where the depth-dependent temperatures are measured to estimate depth-specific thermal properties. Thus, a novel instrument with a data logger to automatically obtain the temperature measurements along the BHE is introduced. This device is based on a Zynq-7000 all programmable system on a chip. It has a dual-core central processing unit and a field-programmable gate array on one chip, thus providing a versatile architecture that reduces cost and improves efficiency in comparison with other systems of similar characteristics. This paper describes the implemented hardware and software developments that range from user interface application to a free-distribution operating system based on an embedded Linux. The proposed instrument can be easily incorporated throughout a TRT, and the nonspecialized staff can remotely manage or visualize the results through a menu-driven interface. The device is tested in a specific BHE installation and validated with standard Pt100-temperature-sensors. The results are comparable and, therefore, demonstrate the applicability of this novel instrument called Geowire. [ABSTRACT FROM AUTHOR]

In this article, an experimental comparison between open sun and solar drying is done. The thermal performance of evacuated tube based solar dryer is investigated with drying characteristics of Phyllanthus Emblica (Anvla), Aloe Vera, Aegle Marmelos (Bel) and leaves of Azadirachta Indica (Neem), Aegle Marmelos (Bel) and Psidium Guajava (Guava). In this setup, an evacuated tube collector, shell and tube heat exchanger and drying chamber are used. It was found that the maximum temperature difference between hot air and ambient air is 35.4°C and maximum efficiency of the setup is calculated as 55%. The average drying rate of Phyllanthus Emblica (Anvla), Aloe Vera and Aegle Marmelos (Bel) is measured as 0.46 g/min, 0.44 g/min, and 0.39 g/min respectively which are higher than that of Open Sun Drying. The leaves of Azadirachta Indica (Neem), Aegle Marmelos (Bel) and Psidium Guajava (Guava) also get dried with faster rates of 0.18 g/min, 0.17 g/min, and 0.14 g/min respectively. [ABSTRACT FROM AUTHOR]

Highlights • Single phase flow heat transfer measurement in a vertical channel filled with metal-foams. • Characteristics of fluid flow and heat transfer of R245fa in a hot-water-driven test facility. • Foams made of copper and nickel were compared. • Correlations developed for average heat transfer coefficient and pressure drop. Abstract High-porosity open-cell metal foams made of copper and nickel were inserted into a rectangular channel containing R245fa refrigerant with mass flux ranging from 76 to 391 kg/m2 s. The single-phase heat transfer from the surrounding channels is driven by hot water in a closed cycle and ranges from 0.53 to 1.37 kW. The heat transfer and pressure drop across the embedded metal-foam samples were measured while maintaining constant conditions of the refrigerant inlet pressure and hot water supply. The heat transfer coefficient was calculated based on a modified Wilson-plot method. The results were compared with published correlations, and new correlations are proposed to take into account the characteristics of the foam geometry and material. In addition, three parameters are introduced to compare different types of metal foam samples. The results of the experiment show that the metal-foam-filled channel increases the Colburn j -factor by up to 6.3 times compared to an empty channel. As a result, the metal foams with higher pore density and higher thermal conductivity perform better than other samples in single-phase flow. [ABSTRACT FROM AUTHOR]

The hot-wall heat exchanger (HWHE) has been widely used in thermal engineering fields such as ceiling radiant heating/cooling, refrigerator condenser, solar heat collection, and high-temperature heat recovery. However, the numerical simulation normally used for heat transfer prediction in HWHE is usually not as convenient as the analytic solutions in engineering applications. In this paper, a new heat transfer mathematical model of HWHE-based on analytic solutions was developed, which could be much faster to obtain the heat transfer properties of HWHE. The proposed model was validated under four conditions with literature values, which showed that the deviations of heat flux are 2.53%, 0.99%, 2.12%, and 1.96%, indicating its accuracy is satisfied. The model was then used to analyze the thermal property of HWHE. The results show the thermal resistance caused by panel with heat convection and conduction accounts for 96.54% of HWHE thermal resistance, and the thermal resistance caused by heat convection on the surface of panel is 74.43%. The analyzation results also show that adding aluminum foil around pipes could decrease HWHE thermal resistance by 5.11%. Besides, the influence of pipe diameters, pipe distance, pipe heat conductivity, side wall heat conductivity, and convective heat transfer coefficient on the heat transfer performance of HWHE was analyzed. The research in this paper can be used for fast prediction and optimization of heat transfer in HWHE. [ABSTRACT FROM AUTHOR]

The aim of this paper is to present a new model for the prediction of scaling formation in tubular heat exchangers. In design, the effect of fouling upon the heat transfer performance is accounted for by using fixed values of the fouling factor. In real operation, however, fouling strongly depends upon the prevailing operating conditions and they change over time. Under some conditions, the growth of fouling with time can be linear or it can show an asymptotic behaviour. Fouling factors reported in the open literature are not accompanied with specific information regarding the conditions at which they were obtained such as velocity, temperature, concentration and pH. Therefore, the designer must exercise caution when choosing fouling factors since this choice has an impact upon the size of the unit and upon capital expenditure. In view of the above, the purpose of this paper is to present a new fouling model for the prediction of scaling to assist in the design of heat exchangers and in the assessment of their thermal-hydraulic performance. The new model is validated against experimental data published in the open literature and its performance compared to other published theoretical models. The new model shows improved results. [ABSTRACT FROM AUTHOR]

Highlights • Research using subcooling as way to improve CO 2 refrigeration is analysed. • COP improvements up to 37.8% of CO 2 base systems have been reported. • State-of-the art subcooling systems are presented and discussed. • New opportunities for research are highlighted in the review. Abstract CO 2 subcooling has resulted a method to upgrade the performance of CO 2 refrigeration plants in the recent years, with overall improvements up to 12% with internal heat exchangers, 22% with economizers, 25.6% with thermoelectric systems and 30.3% with dedicated subcooling methods. This paper comprehensively reviews the recent studies that consider subcooling as a way to upgrade the performance of CO 2 refrigeration cycles. The review is limited to CO 2 refrigeration cycles with accumulation receiver for commercial purposes and does not consider air conditioning or MAC systems. It is organized as follows: first, the thermodynamic aspects of subcooling in CO 2 refrigeration cycles are described and discussed; second, the main results and conclusions of the recent investigations are analysed inside two big groups: subcooling internal methods and subcooling external methods. Finally, the review synthesizes the current state of the art and points out the lines of research that deserve future developments. [ABSTRACT FROM AUTHOR]

Grout plays an important role in the heat-transfer performance of borehole heat exchangers. The current study developed a numerical model to investigate the effect of grout thermal conductivity and heat capacity on the heat-transfer performance of borehole heat exchangers. The “relative thermal conductivity” was defined to obtain the best matching relationship of thermal conductivity between grout and soil. The numerical model was validated through sandbox experiments. The results showed that, when the grout thermal conductivity and heat capacity were both varied by 47.00%, the effect of the grout thermal conductivity on the pipe wall temperature was 26.44% stronger than that of the grout heat capacity; whereas the effect of the grout heat capacity on the heat-transfer radius was 5.21% stronger than that of the thermal conductivity. As the same variation of the grout thermal conductivity, when the soil thermal conductivity change from 1.30 to 1.90 W/(m·K) (1.60 kcal/[m2 · h · °C]), the effect of the changing grout thermal conductivity on the heat-transfer performance decreased by 8.04%. The results also showed that the optimal relative thermal conductivity was 1.20-1.30. These results can serve as guidelines for selecting appropriate grouts for different geological conditions. [ABSTRACT FROM AUTHOR]

Experiments are described to investigate the thermal performance of a discharging heat exchanger for a small storage tank filled with oil. Experimental results are presented in terms of the discharging energy rates (power) and the discharging exergy rates for low (~4 ml/s) and high discharging flow rates (~8 ml/s). Water heating energy rates, which are respectively maximized at approximately 600 W and 1200 W at low and high flow-rate discharging, are found to be higher than the discharging energy rates, which are respectively maximized at 450 W and 900 W. These results indicate that the energy rates do not accurately evaluate the thermal performance of the discharging heat exchanger since the energy heating rate of the water is greater than that for the oil that heats it, which is thermodynamically inconsistent. The energy rates should thus be used with caution when the thermal performance of the heat exchanger is evaluated. Water heating exergy rates, which are respectively maximized at approximately 45 W and 130 W at low and high flow-rate discharging, are generally smaller than the discharging exergy rates, which are respectively maximized at 65 W and 170 W. Exergy rate results are thus more consistent in the physical process of water heating, and an exergy factor is suggested as a proper measure for evaluating the performance of the discharging heat exchanger. The maximum value of the exergy factor is found to increase from 0.15 at low flow rates to a maximum value of approximately 0.19 at high flow rates. This implies that to extract more energy from a storage tank to a discharging heat exchanger, the flow rate has to be high, which is consistent with the physical process of heating water faster to higher temperatures. The exergy factor can thus be used as a design parameter for discharging heat exchangers. [ABSTRACT FROM AUTHOR]

The thermal properties of soil are vital in designing the length of buried heat exchangers. Based on a matured experimental technique commonly used for thermal response test in situ, a simulation model was built in this paper to determine the thermal properties of soil. Several sets of thermal response tests were carried out using the simulation model under different experimental conditions. The line heat source model (LHSM) and the column heat source model (CHSM) were applied to identify the thermal properties of soil. In order to analyze the variation of the identification error of the thermal properties under different experimental conditions, the identification results were then compared with the original setting values. The results showed that both identification methods could produce some errors in the identification of soil thermal and physical parameters under different experimental parameters. However, the accuracy of identification could be improved by selecting an appropriate test time. The best test time was duration to determine the thermal properties of soil was defined as an optimum length of time when the identification error was minimized. The best test time duration varied with different experimental parameters and different identification models. It is found that the best test time duration of the column heat source model was shorter than the one of the line source model. Giving longer lead time before counting the test time duration, increasing the thermal conductivity of the backfill material and heat injection, or reducing the circulating fluid flow rate, could effectively shorten the best test time duration. [ABSTRACT FROM AUTHOR]