Maximum Heat Transfer Rate Research Articles

A novel oval-shaped coaxial ground heat exchanger for augmenting the performance of ground-coupled heat pumps: Transient heat transfer performance and multi-parameter optimization

Ground-coupled heat pumps (GCHP) are highly impactful and promising systems for extracting geothermal energy. Nevertheless, the effectiveness of GCHP can be further improved by reshaping and optimizing the configuration of the coaxial ground heat exchanger (CGHE), which represents the core component of the GCHP and has a significant influence on the heat extraction performance of the system. This paper introduces a detailed comparative numerical study on a novel CGHE with an oval cross-section for enhancing the performance of the GCHP. The proposed design's simplicity stems from altering the outer tube to an oval shape, compared to the commercially used circular CGHE. The conjugate fluid flow and heat transfer are simulated utilizing a three-dimensional numerical model. Heat flux, GHE thermal resistance, and pressure drop within the tube are computed and analyzed. A comparison between circle and oval cross-sections is carried out. The adopted 3-D model shows a fit verification with their experimental pairs via a field experiment. Parametric study and sensitivity analysis are performed, and the effect of groundwater flow on heat transfer is also examined. An optimization approach is developed to explore the optimal inner tube position and incorporate multi-inner tubes that attain the maximum heat transfer efficiency of the oval-CGHE. The results reveal that oval-CGHE significantly surpasses the conventional circle-CGHE, improving the maximum and average heat transfer by 21.03% and 10.24%, corresponding to a reduction in thermal resistance by 28.83% and 9.06%, respectively. Additionally, optimizing the inner tube position and incorporating multi-inner tubes further enhances the performance of oval-CGHE by maximum and average heat transfer rates of 33.01% and 22.91% for inner tube position optimization and 39.08% and 28.84% for multi-inner tube optimization, respectively.

Numerical investigation of heat and mass transfer of the Sisko fluid in a wire-coating process with variable fluid properties

The fundamental and essential objective of the wire coating process is to reduce the shear stress and extraction force exerted on the wire from the die in order to achieve practical benefits. Therefore, the purpose of the present work is to develop a mathematical model for the wire coating process withdrawal of the wire from the die. The Sisko fluid model and the temperature-dependent thermophysical properties are taken into consideration for modelling the constitutive equation. The basic equations governing the flow are solved with the aid of the numerical method. The impact of key factors is scrutinized. The influence of shear stress on the surface of the wire and fluid flow rate are delineated. The linear regression model is formulated to explore the significance of the relationship between the amount of force required to pull the wire and flow control variables. Moreover, the heat transfer rate and shear stress rate of molten polymer are modeled using quadratic correlation models obtained through the Central Composite Design (CCD) technique. To simultaneously achieve maximum heat transfer rate and minimum shear stress rate for the melt, the ideal values of the variable viscosity parameter, Sisko fluid parameter, and Brinkman number are determined. The study reveals that the required result occurs for a low level of the variable viscosity parameter, Sisko fluid parameter, and the Brinkman number. Additionally, a sensitivity analysis has been performed. The result reveals that the shear stress rate and heat transfer rate exhibit the highest sensitivity to variations in the viscosity parameter.

Isı Kuyuları Kullanılarak Bir Termoelektrik Jeneratörün Sıcak ve Soğuk Yüzeyindeki Isı Transferinin Sayısal Olarak İncelenmesi

This study represents Computational Fluid Dynamics (CFD) analyses to improve the heat transfer on the two sides of a thermoelectric generator (TEG) by utilizing heat sinks to recover the waste heat of hot air. In this respect, the temperature difference between the hot and cold sides of the TEG, the heat transfer rate on the hot and cold sides and the pressure drop between the inlet and outlet of the hot and cold air are investigated for varying hot air inlet temperature and Re number in terms of improving the heat transfer and accordingly the output power of the TEG. According to the numerical results, the maximum temperature difference between the hot and cold sides of the TEG concerning hot air inlet temperature of 600 °C and Re number of 16800 is specified as 418.9 °C and 478.1 °C, respectively. In terms of heat transfer, maximum heat transfer rate on the hot side for hot air inlet temperature of 600 °C and Re number of 16800 is specified as 180.4 W and 205.1 W, respectively, while the maximum heat transfer rate on the cold side is specified as 168.0 W and 192.6 W. The maximum pressure drop occurs as 304.4 Pa for the Re number of 16800. As a result, increasing hot air inlet temperature and Re number yields an increase in the temperature difference, the heat transfer rate on the hot side, and the heat transfer rate on the cold side. Besides, pressure drop increases with increasing Re number.

Heat extraction analyses and energy consumption characteristics of novel designs of geothermal borehole heat exchangers with elliptic and oval double U-tube structures

The borehole heat exchanger (BHE) is an efficient and economic tool for extracting geothermal energy within ground source heat pumps (GSHPs). The layout and cross-section tube configuration of the BHE is one of the crucial bottlenecks that strongly influenced the effectiveness of the BHEs, which recently attracted numerous attention.Hence, the interest in retrofitting cost-efficient configurations of BHEs is recently regarded as an improvement pathfor maximizing geothermal energy production. In this study, novel geothermal borehole heat exchangers with elliptic and oval double U-tube (2U) configurations are investigated and compared to a traditional circular 2U BHE.This paper explains the development of traditional circular 2U-tube BHEs that makes an optimally designed model for maximizing the heat extraction rates and minimizing the energy consumption characteristics and BHE number. A 3-D numerical model was developed and validated by relevant field experiments (Tianjin geothermal project). The numerical study was performed on four cases corresponding to different widths of elliptic and oval 2U BHEs configurations. Furthermore, a sensitivity analysis was performed to parametrically investigate the impacts of key design and operational parameters on heat extraction performance. Additionally, a 3-D numerical model coupled with a finite line heat source model was also developed to perform case studies for energy consumption analysis for two goals of optimization. The results show that the oval 2U BHE (type II) outperformed the other investigated 2U BHE configurations, which increased the maximal and mean heat transfer rate by up to 54.0% and 12.30%, respectively, compared to circular 2U BHE. While the elliptic 2U-tube BHE (type II) was minimal pressure drop and energy consumption rates, which showed a pressure drop of 36.20% lower than the circular 2U BHE. In the case study findings, the utilization of elliptic 2U-tube BHE (type II) can not only reduce the BHE number by 6.70% but also minimize the energy consumption of the water pump and the entire system by 36.9% and 8.2%, compared to that of traditional circular 2U-tube BHE, respectively.

Numerical and sensitivity study on the heat transfer due to bioconvection on unsteady radiative MHD blood flow over a permeable artery with chemical reaction effects

The primary goal of this research is to investigate the dynamics of nanoparticle-mediated blood flow in the presence of bioconvection effects caused by microorganisms. The boundary layer problem of unsteady magnetohydrodynamic blood flow in the porous medium of tissues in stretching motion is studied. The Casson fluid model of blood flow is mathematically represented by a system of partial differential equations (PDE). The resulting set of governing equations is numerically solved, and the physical interpretation is given for the outcomes that are presented as graphs and tables. The temperature and concentration distribution of blood, along with the organism density profile in the corresponding boundary layer, are plotted, and the effects of various physical parameters, including magnetic field, radiation, chemical reaction, and permeability of the porous medium, on the results are investigated. Additionally, physical effects on the heat and mass transfer coefficients of the flow are also discussed. It is observed that the rate of heat transfer and the temperature profile are improved by increasing the values of the thermophoresis and Brownian motion parameters. Furthermore, at the lowest value of the permeability parameter and the highest value of the Brownian motion factor, the maximum heat transfer rate is observed. The findings of the study bear the promise of significant application in targeted drug delivery, magnetic therapy, and therapeutic hyperthermia treatments.

Thermodynamic performance analysis of air-to-air hybrid heat recovery unit driven by pump combined with booster

The air conditioning energy consumption for fresh air handling in buildings increases yearly, especially in low energy buildings. This energy consumption can be greatly reduced when exhaust air is recovered for preheating or precooling fresh air. Then, significant savings in the total energy consumption in buildings will be achieved, which in turn helps achieve the carbon peak in the building field. In this paper, a booster/pump coupled energy recovery ventilator is proposed for energy recovery in buildings. The system performance, which depends on the loop number and combination strategies were analyzed and compared through model simulations. Results indicate that the heat transfer rate of different coupling systems increases with the temperature difference. In summer, the pump/booster driven dual-loop system has the highest average temperature effectiveness of 47.3% and average heat transfer rate of 4.97 kW. The booster/booster-driven dual-loop system has the highest average heat transfer rate of 5.07 kW and average temperature effectiveness of 47.1%. The average temperature effectiveness of the pump/booster/booster driven triple-loop system reaches up to 45% and average heat transfer rate of 4.73 kW. The booster/booster/booster-driven triple-loop system has the highest average heat transfer rate of 4.82 kW and average temperature effectiveness of 44.7%. In winter, the maximum average heat transfer rate and temperature effectiveness of the pump/booster driven dual-loop system are 8.54 kW and 44.44%, respectively. The maximum average heat transfer rate and temperature effectiveness of the pump/booster/booster driven triple-loop system are 7.90 kW and 41.5%, respectively. Throughout the year, the best coupling scheme of the dual-loop system is the pump/booster driven dual-loop system, and its average heat transfer rate and temperature effectiveness are 6.755 kW and 45.85%, respectively. The best coupling scheme of the triple-loop system is the pump/booster/booster-driven triple-loop system, and its average heat transfer rate and temperature effectiveness are 6.315 kW and 43.25%, respectively.

Performance improvement of a double tube heat exchanger using novel electromagnetic vibration (EMV) method in the presence of Al2O3-water and CuO-water nanofluid; An experimental study

In this research, the novel approach of the electromagnetic vibration (EMV) method was utilized for the first time to increase heat transfer in a double-tube heat exchanger (DTHEX). In this method, a magnetic turbulator (comprising a magnet and an oscillator) was installed inside a central tube that vibrated using an AC magnetic field. The influences of various parameters such as the geometry of the oscillator, magnet position, employing nanofluids, and fluid flow were assessed on the thermal-frictional behavior. The thermal enhancement factor (TEF) was assessed to select the optimal option. The studied options were economically evaluated based on energy efficiency. According to the results, the maximum heat transfer rate could be achieved when the magnet is positioned at 0.374. L from the tube inlet. The highest value observed for overall heat transfer was related to CuO-water 1% nanofluid, which was 277.5% more than simple heat exchanger. Also, the findings showed that heat transfer can be increased up to 13.3 times the energy used and reached to TEF = 3.92, which is a very significant number. Regarding the high potential of the EMV in reaching high thermal performance, it can be utilized as a game changer to save materials, energy, and compaction of the heat exchangers and solar systems.

Experimental study of non-condensable gas effects on sonic limit of sodium heat pipe

Due to unexpected gas leakage and long-term operation, the non-condensable gas (NCG) inevitably exists in high-temperature alkali metal heat pipe. Previous studies have mainly focused on its influences on startup and steady state operation characteristics of heat pipes. However, few of them conducted experiments to study the effects of NCG on sonic limit, which usually occurs during heat pipe startup or during steady state operation when the heat transfer coefficient at condenser section is high. In present work, experimental and analytical studies are conducted to the explore the effects of NCG on sonic limit of sodium heat pipes. With the heating power ranging from 500 to 1400 W, the sonic limit of 1 m-long sodium heat pipes with artery wick and axial groove wick are obtained based on oil-cooling system, which can widely adjust the cooling capacity at condenser section. The amount of NCG in heat pipe is estimated by Heat Pipe Transient Analysis Code (HPTRAN) and verified by experimental data. It is found that the existence of NCG in heat pipe leads to the decrease of maximum heat transfer rate under sonic limit. The mechanism of NCG effects on sonic limit is discussed based on phenomenological analysis. By introducing the added back pressure, a modified model to predict sonic limit considering NCG effect is proposed and the comparison with experimental data shows good agreements.

Influence of the Nozzle-to-Surface Distance on Spray Cooling Efficiency

Spray cooling is a highly effective method of heat removal that has broad practical applications, including use in modern cooling systems designed for microelectronics and microchips. It is known that spray cooling performance is influenced by a huge number of factors. This experimental research is devoted to the study of the influence of a liquid flow rate in the range of 15.1–24.2 cm3/s, heat flux up to 6.4 MW/m2, and nozzle-to-surface distance on the heat transfer rate in non-boiling mode and the distribution of the local temperature of the heat exchange surface during spray cooling. It is shown that the heat transfer coefficient weakly depends on the heat flux for all studied nozzle-to-surface distances. It is demonstrated that the nozzle-to-surface distance has a significant influence on the heat transfer and the temperature distributionon the heating surface during spray cooling in non-boiling mode. At the same time, there is an optimal distance at which the maximum heat transfer rate and uniformity of the temperature are achieved. Criteria and a ratio for determining the optimal distance from the spray nozzle to the heated surface are proposed.

Thermal performance of a thin flat vapor chamber with a multiscale wick fabricated by SAC305/Sn58Bi micro-sized particles

In this study, we theoretically and experimentally investigated the thermal performance of a thin flat vapor chamber (TFVC) with a multiscale wick to understand the effect of the additional capillary microstructures on the cooling performance. To fabricate the multiscale wick with the additional capillary microstructures, micro-sized particles of SAC305 (Sn3.0%Ag0.5%Cu) and Sn58Bi were mixed in ethanol, including indium flux. The suspensions were sequentially sprayed onto a conventional screen mesh wick and spontaneously sintered at 150 ℃. The rate-of-rise method was used to measure the capillary performance of the multiscale wick experimentally. When the results were compared with that of the conventional screen mesh wick, the effective pore radius and permeability of the multiscale wick were 45.4 and 29.5% lower than those of the conventional screen mesh wick, respectively. The capillary performance of the multiscale wick enhanced up to 30% higher than that of the conventional screen mesh wick. With the measurement data of the multiscale wick, the thermal performance of TFVCs with multiscale wicks was theoretically obtained. Based on the theoretical results, it is shown that the maximum heat transfer rate of the TFVC using the multiscale wick increased by up to 82.8% compared with the conventional screen mesh wick.

Experimental Study For a Laminar Natural Convection Heat Transfer From an Isothermal Heated Square Plate With and Without Circular Hole

An experimental investigation of natural convection heat transfer from an isothermal horizontal,vertical and inclined heated square flat plates with and without circular hole, were carried out in two cases, perforated plates without an impermeable adiabatic hole "open core" and perforated plates with an impermeable adiabatic hole "closed core" by adiabatic plug. The experiments covered the laminar region with a range of Rayleih number of (1.11x106 ≤RaLo≤4.39x106 ), at Prandtle number (Pr=0.7). Practical experiments have been done with variable inclination angles from horizon (Ф=0o ,45o,90o,135oand 180o),facing upward (0o≤Ф<90o), and downward (90o≤Ф<180o). The results showed that the temperature gradient increases while the thermal boundary layer thickness decreases when Grashof number and perforation ratio (m) increase . The temperature gradient for inclined position facing upward is less than facing downward,while the thermal boundary layer thickness is greater. The temperature gradient decreases while the thermal boundary layer thickness increases for perforated plates with an adiabatic core as compared with perforated plates without an adiabatic core. The value of average Nusselt number increases with increasing perforation ratio, and Grashof number for all specimens with and without an adiabatic core, also increases by increase in inclination of plates approaching the higher value at vertical position (Ф=90o), then decreases with increasing inclination of plates till horizontal position (Ф=180o). The average Nusselt number values for perforated plates with an adiabatic core are lower than for perforated plates without an adiabatic core for all perforation ratios. Maximum heat transfer rate occurs at perforated plate with perforation ratio of (m=0.1) without adiabatic core for vertical position (Ф=90o), at a range of Grashof number (1.576x106≤GrLo≤6.292x106 ), while the rate of heat transfer decreases with increasing perforation ratio for plates with and without adiabatic core for decrease in heat transfer rate area. The rate of heat transfer forperforated plates with circular hole is more than for perforated plates with square hole at the same perforation ratios (m=0.1,0.16,0.24 and 0.36). It found that the lack of core flow decreases the overall heat transfer rate by (6.477%) . There was a good agreement for the experimental present work results compared with other pervious results .

Experiments on thermal performance of heat pipes using nanoparticle layer as the wick

To enhance the usability of heat pipes and vapor chambers as the cooling device for portable electronic systems, necessity of thin wick is rapidly increasing. In the present work, the layer of silica nanoparticles of about 10 μm in thickness was formed on the copper tube inner wall to explore experimentally if it works as the thin wick. It was demonstrated that in comparison with the ordinary heat pipe using a wire mesh as the wick, the thermal resistance was even improved (0.62 to 0.23 K/W) and the deterioration of the maximum heat transfer rate was not significant (120 to 78 W). This indicated that the present nanoparticle layer can be used as a very thin wick of the heat pipes and vapor chambers. If the mass of nanoparticles deposited on the heat pipe inner wall was sufficient, the thermal performance was not deteriorated even after the maximum heat transfer rate condition was experienced. It was also demonstrated that the maximum heat transfer rate can be enhanced up to 100 W when the nanoparticles were suspended in the working fluid enclosed in the container.

Experimental investigation of indirect heat transfer through a novel designed lab-scale setup using functionalized MWCNTs nanofluids (MWCNTs-COOH/water and MWCNTs- OH/water)

This study aims to investigate the influence of functionalized multi-walled carbon nanotubes (MWCNTs-COOH and MWCNTs-OH) on the performance of a novel indirect laboratory heater redesigned with a helical tube. Experiments were performed using a bath of water and the two nanofluids mentioned above. The nanofluids were prepared at concentrations of (0.025, 0.05, 0.075, and 0.1) wt%. To ensure the stability of the utilized nanofluids and the structure of the nanoparticles, characterization studies such as dynamic light scattering (DLS), FT-IR, and XRD were carried out. The results indicated that when concentration levels rose, the system's performance rose as well. For instance, the MWCNTs-COOH nanofluid bath had a maximum heat transfer rate of 1709 W, which was 19.04% better than pure water, and a maximum Nusselt number of 15.61, which was an increase of 36.33% over pure water. In summary, heat loss increased with an increment in flow rate, and by increasing the concentration of nanofluids, the lowest heat loss, the highest heat transfer rate, and the best efficiency of the system were achieved. This study can establish the foundation for redesigning indirect heaters to reduce thermal energy consumption and for further research on the use of nanofluids in indirect bath heating.

Modeling and simulation of a helical falling film evaporator to improve its performance and design

This work presents a computational model of a helical falling film evaporator of 13 tubes based on physical principles. The momentum and energy transfer of the system are modeled. The work aims to understand the behavior of a horizontal falling film evaporator and to improve the evaporator design by analyzing the heat transfer. In the evaporator, the wetting efficiency varies in each tube because the evaporation of the falling film is performed gradually. Therefore, the behavior of the evaporator variables, such as the wetting efficiency in each tube, is studied. Furthermore, the model granularity based on the analysis of the subcooling and saturation zones is investigated. The effect of the film breakdown onset Reynolds number and the mass flow rate on the evaporator performance is studied. This analysis shows that the maximum heat transfer rate of the simulation is reached when the falling film Reynolds numbers of the tubes are as close as possible and pass by the film breakdown onset Reynolds number value. Additionally, the results indicate that at a low mass flow rate, the heat transfer is carried out almost completely in the first five tubes, and at a higher mass flow rate, the heat transfer is more significant in the last tubes. Finally, a comparison between the evaporator of 13 tubes and an arrangement of two evaporators of five tubes each one is performed. From this analysis, the results show that the heat transfer rate of the arrangement of two evaporators is 21.16 % and 18.69 % higher than the evaporator of 13 tubes at 0.00529 and 0.00793 kg/s⋅m, respectively.

A study on heat transfer enhancement of Copper [formula omitted]-Ethylene glycol based nanoparticle on radial stretching sheet

Copper nanoparticles are getting attention because of their outstanding physical characteristics and wide range of uses. The motivation of this research is to investigate axisymmetric flow and heat transfer for various shapes (Cylinder, Platelets and Sphere) of Copper (Cu) nanoparticles on a radial stretching sheet. Energy and momentum partial differential equations are transformed into nonlinear ordinary differential equations (ODE). The dimensionless equations are solved using the BVP4C method to yield numerical solutions for the represented problem. The impacts of multi-shape Copper (Cu) nanoparticles are thoroughly examined, as are other parameters such as solid volume fraction (ϕ), Prandtl number Pr, unsteadiness parameter S, magnetic parameter M, slip parameter k, and Eckert number EC. According to the findings, Platelet shape Copper (Cu) nanoparticles have the highest flow and Sphere shape particles contain maximum heat transfer rate.

Experimental approach to bio-waste nanoparticles suitable for radiator coolant

ABSTRACT The purpose of this research is to experimentally test the thermo physical properties of the corn cob ash nanofluid as a heat transfer fluid. The experimental procedure involve in preparation of extraction of silica nanoparticles from corn cob ash agro-waste and its performance evaluations. The results obtained from the EDS test shows the dominant constituents of corn cob to be Silica, Oxygen, Aluminium, and Calcium with the highest concentrations of 40.20%, 20.20%, 15.65%, and 10.40% respectively. However, with the use of the chemical synthesis method, silica nanoparticle powder made from corn cob ash was produced (CCA). The generated silica particles ranged in size from 10 to 28 nm, with an average diameter well inside the nanometre range at 18.585 nm. The combination of ‘Water, Coolant and Nanofluid (0.0015% Concentration)’ gives the maximum heat transfer rate, demonstrating that it is the greatest cooling fluid out of the all the coolants that were experimented. Conclusively, this cooling fluid with the highest rate of heat transfer, ‘Water + Coolant + Nanofluid (0.0015% Concentration)’, would increase the performance of the car engine cooling system, thereby resulting in less fuel consumption and making it more economically efficient for general uses.

Numerical simulation of heat transfer and melting process in a NEPCM: Using new fin shape

Nowadays, phase change materials (PCMs) have gained further importance as they are the main substance in thermal energy storage systems. The observations indicated that the rate of thermal storage is related to the rate of melting and thermal distribution within these materials, where it has been concluded in almost works that convection is an effective contributor to boosting heat transfer, mainly in the upper layers of PCM capsules unlike in the lower layers. This article aims to accelerate heat distribution and fusion rates of NEPCM inside rectangular capsules by using novel fins in the shape of dendrites planted in the lower region of the capsule. Three different cases are considered and analyzed; in the first case without fins, in the second case fin branches length is decreasing downward (type 1), and in the third case, fin branches length is increasing downward (type 2). The porosity enthalpy method is used in modeling heat transfer during phase change. The impact of nanoparticles volume fraction is investigated by three different concentrations (ϕ = 0, 3%, and 6%). The findings indicated that enriching the weight of the nano-elements and using fins yield improving the thermal conductivity characteristic of the base PCM, besides, integrating the fin in the lower region of the PCM, i.e. under the heat source extends the heat transfer area, particularly where the dominated heat transfer in the low region is conduction, thereupon, as a result, both the thermal resistance and fusion time diminish. The maximum heat transfer rate and shorter fusion time were achieved by case 3 (fin type 2) with ϕ = 6%, where, fin-type 2 increased the melting rate by 33% compared to no fin case due to the largest branch of the fin is located in the bottom area, whereas the conduction is more dominated as approaching the lower wall. Finally, it is recommended to further investigate the dimension characteristic of this new kind of fins, for instance, the number of branches, spacing between the fin branches, and the branches' angle.

Shape-Factor Impact on a Mass-Based Hybrid Nanofluid Model for Homann Stagnation-Point Flow in Porous Media

This paper studies the impact of shape factor on a mass-based hybrid nanofluid model for Homann stagnation-point flow in porous media. The HAM-based Mathematica package BVPh 2.0 is suitable for determining approximate solutions of coupled nonlinear ordinary differential equations with boundary conditions. This analysis involves discussions of the impact of the many physical parameters generated in the proposed model. The results show that skin friction coefficients of Cfx and Cfy increase with the mass of the first and second nanoparticles of the hybrid nanofluids w1 and w2 and with the coefficient of permeability in porous media. For the axisymmetric case of γ = 0, when w1 = w2 = 10 gr, wf = 100 gr and Cfx = Cfy = 2.03443, 2.27994, 2.50681, and 3.10222 for σ = 0, 1, 2, and 5. Compared with w1 = w2 = 10 gr, wf = 100 gr, and σ = 0, it can be found that the wall shear stress values increase by 12.06%, 23.21%, and 52.48%, respectively. As the mass of the first and second nanoparticles of the mass-based hybrid nanofluid model increases, the local Nusselt number Nux increases. Values of Nux obviously decrease and change with an increase in the coefficient of permeability in the range of γ < 0; otherwise, Nux is less affected in the range of γ > 0. According to the calculation results, the platelet-shaped nanoparticles in the mass-based hybrid nanofluid model can achieve maximum heat transfer rates and minimum surface friction.

Modeling and techno-economic comparison of two types of coaxial with double U-tube ground heat exchangers

Among different types of ground heat exchangers (GHEs), multi-external chamber coaxial GHE is recently a promising design due to its geometrical characteristics of concentric tube-in-tube configuration and maximal heat exchange performance. Nevertheless, the characterization and commercialization of multi-external chamber coaxial GHEs need a deep understanding of the effect of different opt-geometrical and operational parameters on their thermo-economic performance. Therefore, accurate numerical modeling of the transient heat transfer proficiencies and the techno-economic feasibility of the multi-external chamber coaxial GHE and coaxial GHE compared to conventional double U-tube GHE is crucial to promise an optimal design of ground-coupled heat pump systems. This study introduces a comprehensive systematic and techno-economic analysis of the transient heat transfer characteristics of coaxial and multi-external-chamber coaxial GHEs compared to conventional double U-tube GHE. A three-dimensional numerical model was adopted and validated by field experiments. Moreover, a sensitivity analysis was conducted to investigate the impacts of several key operating and design parameters on heat transfer performance under heating and cooling modes conditions. Furthermore, various case studies, along with a comprehensive analysis of multi-objective optimization for minimization of the GHE number and energy consumption, were also carried out. In addition, a techno-economic analysis was also carried out using the total annual cost method to assess the economic viability of the proposed GHE designs. The results reveal that, compared to double U-tube GHE, coaxial GHE has the best thermal performance with maximum and average heat transfer rates of 127.54% and 17.67%, while the multi-external-chamber coaxial GHE is estimated to be 62.38% and 11.72%, respectively. Also, the corresponding total thermal resistance of coaxial GHE is the lowest by 14.86%, and for multi-external-chamber coaxial, it is 10.30%; also coaxial GHE has the lowest pressure drop by 76.45%, followed by multi-external-chamber coaxial GHE with 57.18%. In the case studies, replacing double U-tube GHE with coaxial or multi-external-chamber coaxial GHEs, the GHE number can be decreased by 13.3% for both the designs, or the energy consumption of the water pump by 33.91% and 30.97%, and the energy consumption of the entire system by 17.21% and 10.54%, respectively. The techno-economic analysis results indicate that replacing double U-tube GHE with coaxial GHE is the most feasible alternative, which can decrease the total annual cost by 13.58%, followed by multi-external-chamber coaxial GHE by 6.77%. Further discussion for the deep applications was performed, which concluded the optimal GHE design. The findings of this paper can be used as a guide for future research on GHEs for potential applications of ground-coupled heat pump systems.

Analysis of heat transfer and thin film flow of Au−Np over an unsteady radial stretching sheet

The analysis of heat transfer and thin film flow over an unsteady radial stretching surface is the primary focus of this work. For the two-dimensional motion of the pair stress nanofluid made of gold nanoparticles, a mathematical model is put forth. Nonlinear governing partial differential equations for momentum and energy are converted into a set of ordinary differential equations via similarity transformations. By using the BVP4c method, the resulting nonlinear differential equations were calculated. The relationship between the Nusselt number, temperature, skin friction, and fluid motion velocity is examined and graphically analyzed. This study suggests that thin film thickness increases for rising values of volume fraction whereas it dropped for increasing values of the magnetic parameter and unsteadiness parameters Maximum heat transfer rate and skin friction coefficient has been observed for blade and cylinder shaped nanoparticles and minimum for brick shape.