Heat Exchange Efficiency Research Articles

Performance optimization of a mK dilution refrigerator based on the first law of thermodynamics

This paper analyzes and optimizes performance characteristics of the dilution refrigerator (DR) based on the first law of thermodynamics. The properties of the 3He-4He mixture below 0.7 K are analyzed and a simplified method to obtain the enthalpy of the working fluid in the whole dilution cycle is proposed. Then an enthalpy flow model is built, based on which the variations of the specific cooling capacity, specific still heating power and gross cooling capacity with the precooling temperature and upstream pressure are studied at the cooling temperature of 10 mK, and the effect of the first-stage heat exchanger efficiency on the gross cooling capacity is further analyzed. The results indicate that there exists an optimal upstream pressure which maximizes the gross cooling capacity for a given precooling temperature. The optimal upstream pressure and the maximum gross cooling capacity are investigated based on the fitting functions of precooling temperatures. Given a heat exchanger efficiency of 97 %, it is found that the optimal upstream pressure and precooling temperature should be 1.41 × 105 Pa and around 4 K, respectively, to achieve the maximum cooling capacity of 38.5 μW at 10 mK. This study provides a helpful theoretical guidance for the performance optimization of the DR.

Convective heat transfer enhancement by corona discharge in a wire–cylinder electrostatic precipitator with the water-cooling system

Aiming at the current wet plume problem, we present a novel technique to integrate electrostatic precipitator (ESP) and heat exchanger in order to simultaneously increase heat exchange efficiency, collect water and control particle emission from flue gases. Unlike the conventional ESP, a lab-scale wire–cylinder type ESP with the collection electrode cooling by water is used for investigations in this paper. Our research indicates that the heat transfer coefficient of the ESP rises with reducing gaseous velocity, increasing applied voltage, corona current or gas temperature. The maximum improvement of the total heat transfer coefficient of 271% was achieved at 0.15 m/s, 80 °C and 16 kV of the negative discharge. Moreover, the presence of Particle matters can enhance the heat transfer coefficient by 9%–16%. The ionic wind, which is quantitatively expressed by electro-hydrodynamic number, plays a key role in modifying the gas flow patterns and consequently improving the heat exchange coefficient. For lowering the overall energy consumption, it is suggested that the ESP should be operated at a specific mode of low voltage and high current.

A numerical analysis of ash fouling characteristics in elliptical tube bundles

Ash fouling in flue gas heat exchangers (FGHE) detrimentally affects waste heat recovery systems' performance and efficiency by impeding heat transfer, increasing operational resistance, and escalating maintenance costs. The main purpose of this study is to develop an improved particle deposition model for predicting ash fouling characteristics and to explore the fouling reduction performance of elliptical tube bundles (ETB) at various system parameters. The findings reveal that ETB can efficiently reduce operation resistance and ash fouling in FGHE with an insignificant loss in heat exchanger efficiency, especially at large eccentricities (E) and/or low flue gas velocity (vinlet). The most cost-effective E is 0.78, which decreases ash deposit and pressure drop by 66.4% and 48.4%, respectively, at the expense of a 14.2% Nusselt number reduction at vinlet = 10 m/s. Ash fouling reveals three distinctive hotspots: Hotspot 1 located approximately at ±30°, Hotspot 2 at the flow stagnation area, and Hotspot 3 roughly at ±150°. The deposit layer thickness at these hotspots varies between rows and with the E, vinlet and particle diameter (dp). The layer thickness at the flow stagnation regions increases with any of the E, vinlet, and dp. The study also found that medium-sized particles (dp = 5 μm) are the easiest to deposit on tube surfaces, followed by large particles (dp = 10 μm). Small particles (dp = 1 μm) are the least likely to deposit due to their small inertia. Medium-sized and large particles deposit primarily at the windward side of the tubes, while small particles tend to deposit more on the leeward side as they can be easily drawn into the recirculation zones behind those tubes. Increasing the E would significantly alleviate fouling by medium-sized and large particles but does not significantly change the ash fouling situation of small particles.

A Newly Proposed Method for Hydrogen Storage in a Metal Hydride Storage Tank Intended for Maritime and Inland Shipping

The utilisation of hydrogen in ships has important potential in terms of achieving the decarbonisation of waterway transport, which produces approximately 3% of the world’s total emissions. However, the utilisation of hydrogen drives in maritime and inland shipping is conditioned by the efficient and safe storage of hydrogen as an energy carrier on ship decks. Regardless of the type, the constructional design and the purpose of the aforesaid vessels, the preferred method for hydrogen storage on ships is currently high-pressure storage, with an operating pressure of the fuel storage tanks amounting to tens of MPa. Alternative methods for hydrogen storage include storing the hydrogen in its liquid form, or in hydrides as adsorbed hydrogen and reformed fuels. In the present article, a method for hydrogen storage in metal hydrides is discussed, particularly in a certified low-pressure metal hydride storage tank—the MNTZV-159. The article also analyses the 2D heat conduction in a transversal cross-section of the MNTZV-159 storage tank, for the purpose of creating a final design of the shape of a heat exchanger (intensifier) that will help to shorten the total time of hydrogen absorption into the alloy, i.e., the filling process. Based on the performed 3D calculations for heat conduction, the optimisation and implementation of the intensifier into the internal volume of a metal hydride alloy will increase the performance efficiency of the shell heat exchanger of the MNTZV-159 storage tank. The optimised design increased the cooling power by 46.1%, which shortened the refuelling time by 41% to 2351 s. During that time, the cooling system, which comprised the newly designed internal heat transfer intensifier, was capable of eliminating the total heat from the surface of the storage tank, thus preventing a pressure increase above the allowable value of 30 bar.

Theoretical and experimental studies for a transcritical CO2 heat pump with spirally fluted tube gas cooler

Transcritical CO2 system has been widely used in many fields to provide heating and cooling capabilities, and optimizing the structure of the gas cooler is an effective way to improve its performance. This paper presents a theoretical and experimental study of a spirally fluted tube-in-tube heat exchanger used as a gas cooler in a transcritical CO2 heat pump. The theoretical research uses numerical simulations to investigate the flow and heat transfer characteristics. The effect of the different CO2 mass flow rates, inlet pressure, and temperature on the performance of the spirally fluted gas cooler is evaluated and analyzed. The simulation results show that the spirally fluted structure can significantly improve the heat transfer performance of the CO2 side compared to the flat tube, which indicates that the spirally fluted gas cooler could be an effective way to enhance the operating performance of the transcritical CO2 system. Then experimental research is conducted in a transcritical CO2 heat pump prototype to validate the functional performance of the spirally fluted gas cooler. The effect of the different CO2 mass flow rates, inlet pressure and temperature, and the different water inlet and outlet temperatures on the performance of the spirally fluted gas cooler in the prototype are tested. The heat exchanger efficiency - number of transfer units (ε-NTU) method is employed to analyze the operating performance based on the experimental data. In addition, the exergy loss method is used to quantitatively evaluate the side-effect of the large pressure drop by the spirally fluted structure. Both the theoretical and experimental results show that the spirally fluted tube gas cooler can significantly improve the performance of the transcritical CO2 system. Besides, a heat transfer and friction coefficient correlation are established based on the experimental data for future research guidance.

Effects evaluation of Fin layouts and configurations on discharging performance of double-pipe thermochemical energy storage reactor

Thermochemical energy storage (TCES) based on hydrated salts is gaining popularity because it can provide high storage capacity at low costs. It is critical to improving heat storage efficiency and capacity due to technical challenges such as low thermal conductivity of thermochemical materials (TCMs) and poor mass transfer. The reversible reaction of strontium bromide monohydrate (SrBr2·H2O) and water vapor forming strontium bromide hexahydrate (SrBr2·6H2O) for TCES is used in numerical simulation, aiming to investigate the discharging performance of a double-pipe closed TCES reactor considering the influences of fin layouts (radial and longitudinal fins) by evaluating several indicators such as the reaction time and outlet temperature. The results show that the use of fins can improve the exothermic process. The discharging time of the reactor with upward L-shaped fins is reduced by 8.6% for radial fins and by 8.9% for the reactor with four longitudinal fins. The addition of fins expands the heat transfer area and makes the hydration rate of TCM around fins significantly higher than other parts. The Taguchi method is adopted to optimize the structure parameters of case 7 as it has the highest heat transfer amount of heat transfer fluid (HTF), and the optimal combination (A (fin number) = 4, B (fin extension length) = 20 mm, C (fin thickness) = 2 mm) increases the peak value of average outlet temperature by 1.47% and the heat exchange efficiency by 4.7% compared with case 7.

Numerical study of heat transfer across in-line circular cylinders for low to moderate Reynolds numbers

A computational fluid dynamics (CFD) model is generated to study the fluid flow and heat transfer from a series of six cylinders arranged in a horizontal row. The momentum and energy equations were solved using the finite volume method, with convective terms discretized using a second-order upwind method and diffusion terms discretized using central differencing. A second-order implicit technique was used for time integration. Simulations were run with four different values of the free stream Reynolds numbers 100, 200, 300, 400 and three different values of the longitudinal pitch (SL ) 1.5D, 2D, 2.5D to analyze the heat transfer behavior with fluid flow over a series of horizontal cylinders. First the grid independence test and CFD model validation are performed with the exact relation available in the literature. Next, the numerical results obtained from the developed CFD model for the row of cylinders were compared with the previously published analytical model, and correlation available in the literature, and were found to be in good agreement. The average Nusselt number calculated from the analytical and numerical models falls in the range of 8 to 10 for free stream Reynolds number equal to 100 for all values of dimensionless longitudinal pitches. Moreover, for the free stream Reynolds number equal to 400 with longitudinal pitch of 2.5D, the values of the average Nusselt number reach up to double the above-mentioned range. The maximum percentage error between the average Nusselt number obtained from the numerical and analytical solutions was less than 20% for larger free stream Reynolds number. The study found that the average Nusselt number for the array of cylinders increases with both the free stream Reynolds number and the dimensionless longitudinal pitch ratio increments. This information can be used to design more efficient heat exchangers or other fluid systems involving arrays of cylinders.

Theoretical analysis using thermal efficiency concept in straight micro channel printed circuit heat exchanger

The objective is to analyze the thermal and hydraulic performance in a Micro Channel Straight Printed Circuit Heat Exchanger. Counterflow and parallel flow configurations were analyzed for water cooling using ethylene glycol-based fluid and platelet-shaped non-spherical Boehmite alumina nanoparticles. The work presents results from applying a dimensionless theory that uses the concepts of thermal efficiency of heat exchangers and quantities associated with the second law of thermodynamics. Thermal efficiency, thermal effectiveness, thermal and viscous irreversibilities, thermodynamic Bejan number, and outlet water temperatures are presented in graph form. The data obtained allow us to conclude that the heat exchanger can work in a range of water and refrigerant flow rates below the design parameters. With the inclusion of nanoparticles with a volume fraction equal to 5.0%, the flow rates of the refrigerant fluid can be significantly reduced. The analysis performed shows that the use of nanoparticles improves the operational cost-benefit of the heat exchanger with a significant reduction in the hot water outlet temperature.

Assessment of flow and heat transfer of triply periodic minimal surface based heat exchangers

An efficient intermediate heat exchanger is crucial for ensuring the safe operation, lifespan and energy efficiency of the advanced nuclear systems. Benefiting from the development of additive manufacturing technology, it is possible to design and optimize heat exchangers by introducing triply periodic minimal surface (TPMS) structures. With the excellent mechanical and thermal performance of TPMS, further improvements in the energy efficiency of advanced nuclear systems are achievable. In this study, I-WP surface, Primitive surface based heat exchangers and a printed circuit heat exchanger for accelerator driven subcritical systems are constructed in three dimensions. In order to obtain the potential enhancement of thermal performance of TPMS-based heat exchangers, the fluid flow and conjugate heat transfer characteristics in TPMS heat exchangers, especially for the specific working medium of lead-bismuth eutectic (LBE) are investigated. A parametric analysis is conducted on the key design variables including the solid volume fraction and hydraulic diameter. The results indicate that TPMS-based heat exchangers could achieve about 2–3 times the total heat transfer rate with half the volume of a printed circuit heat exchanger. The TPMS topologies contribute greater heat transfer enhancement on the Helium side than the LBE side, which helps to optimize the thermal resistance allocation in Helium-LBE heat exchangers. An increase of solid volume fraction enhances the convective heat transfer of Helium in I-WP heat exchanger, while homogenizing the local thermal performance. This study provides a database for the design and optimization of TPMS-based heat exchangers, which contributes to the sustainable future target.

Thermo-hydraulic performance evaluation of a NACA 63-015 heat exchanger with shark denticles as surface textures

In this study, the effect of using bio-inspired surface texturing as a technique to further enhance the efficiency of a single Plate Fin Heat Exchanger (PFHX) was investigated experimentally. By using biomimicry across disciplines, the denticle, which is a body adaptation from shark skin for enhanced hydrodynamics, was identified as a surface texture to be used on the fin of a PFHX. A smooth NACA 63-015 PFHX (HX0) was used as baseline for thermo-hydraulic performance comparisons. Initially, three PFHXs (HX1, HX2 and HX3), consisting of arrays of denticles upscaled to different scale factors, were designed and printed in ABS plastic to evaluate Additive Manufacturing (AM) limits. By analysing optical images and pressure drop results, HX2 was found to be the best performing array in terms of printing quality and pressure drop performance. Both HX0 and HX2 were then printed in stainless steel 17-4PH by using a Markforged Metal X printer, and then experimentally compared to evaluate their flow and heat transfer behaviours. Results demonstrate that the addition of shark denticles as surface textures on HX2 shifted the onset of turbulence from a fully turbulent to a transitional regime compared to HX0. For Re < 5.7×104, the friction factor for HX2 was less than that of HX0, while at higher Re values the trend was reversed due to increases in skin friction drag. At Re = 3.9×104, the friction factor for HX2 was 56% lower than that of HX0. Overall, a mean improvement of 14% in Nusselt number was noted for HX2 compared to HX0. Further, a mean thermo-hydraulic performance of 1.11 was noted for HX2 for the range of tested Re values, which demonstrated that the addition surface textures in the form of shark denticles to a NACA 63-015 profile yielded a more efficient PFHX compared to a smooth one.

Experimental Study on the Effect of TiO2–Water Nanofluid on Heat Transfer and Pressure Drop in Heat Exchanger with Varying Helical Coil Diameter

The growing demand for efficient heat exchangers has promoted extensive research in exploring advanced heat transfer fluids and novel geometries. This paper investigates the heat transfer and pressure drop characteristics in helical coil heat exchanger employing water-based TiO2 as nanofluid. The utilization of nanofluids offers promising enhancements in thermal conductivity and convective heat transfer in heat exchanger applications. The effect of nanofluid concentration and flow rate on heat transfer and pressure drop with varying helical coil diameter performance is investigated. Experimental tests were conducted using a heat exchanger with different helical coil pipe diameters of 9.53mm, 12.7mm and 15.88mm with constant pitch of 30mm and varying concentrations of TiO2 nanoparticles in water (ranging from 0.1% to 0.5% by volume). The heat transfer coefficient and pressure drop were measured at different operating conditions. The results shows that the addition of TiO2 nanoparticles to water significantly enhanced the heat transfer performance in the helical coil heat exchanger. There is an enhancement in heat transfer coefficient with increasing nanofluid concentration and with increase in pipe diameter. The maximum enhancement in heat transfer coefficient is observed at nanofluid concentration of 0.5% and for pipe diameter of 15.88 mm. However, there is increase in pressure drop with increase in nanofluid concentration and with decreasing pipe diameter. The pressure drop found to be higher for nanofluids compared to pure water. The maximum pressure drop is observed at a concentration of 0.5% and for pipe diameter 9.53mm. In conclusion, the use of a water-based TiO2 nanofluid in a helical coil heat exchanger offers improved heat transfer performance compared to pure water. However, the pressure drop also increases with nanofluid concentration and decreasing pipe diameter. Therefore, a trade-off between heat transfer enhancement and pressure drop should be considered in the design and operation of such heat exchangers.

Design and optimization of intermediate heat exchanger for lead-bismuth cooled fast reactor coupled with supercritical carbon dioxide Brayton cycle

Printed circuit heat exchanger has become a new choice for the intermediate heat exchanger of the lead/lead–bismuth cooled fast reactor coupled with supercritical carbon dioxide nuclear power system because of its large heat transfer area density, high power density and ability to work at high temperature and high pressure. In this study, the channel dimensions of the intermediate heat exchanger were optimized to improve its thermal–hydraulic performance. An in-house code for the thermal–hydraulic design of printed circuit heat exchanger with lead–bismuth and supercritical carbon dioxide as working fluid was built. The relationship between the cold side pressure drop of intermediate heat exchanger and cycle efficiency of the nuclear power system is revealed. The power density and pressure drop of the cold side are selected as two optimization objectives, and the multi-objective optimization process is conducted with the non-dominated sorting genetic algorithms II. The optimal design results of the intermediate heat exchanger are obtained with Pareto-front method. The Pareto-front shows that when the heat exchange density increases, the pressure loss of the cold side also increases, but more quickly than the former. Finally, considering the design limitations, the intermediate heat exchanger core design scheme is selected by the auxiliary function which considering both capital cost and operating cost.

Experimental Study on the Influence of Wind Speed on the Start-Up Characteristics and Thermoelectric Generation Characteristics of Gravity Heat Pipe in Gangue Dump

As an efficient heat exchange component, the gravity heat pipe can effectively control the accumulated temperature inside gangue dumps and enable reuse of transferred heat. This study establishes a similar simulation experimental platform for gravity heat pipes to control gangue dumps and thermoelectric generation. The influence of wind speed on the start-up performance and isothermal performance of gravity heat pipes is analyzed, along with the impact of wind speed on their thermoelectric generation performance. Initially, the optimal working fluid height and heating height are determined, followed by a comparison and analysis of the isothermal performance, start-up performance, and thermoelectric generation performance of the gravity heat pipe under different wind speeds. The results indicate that at a wind speed of 1.0 m/s, the gravity heat pipe exhibits better start-up and isothermal performance. At a wind speed of 2.0 m/s, the thermoelectric power generation reaches its peak. In the range of 1.0~2.0 m/s wind speeds, the curve of thermoelectric generation exhibits the most fluctuations.

The Numerical Investigations of Heat Transfer and Bubble Behaviors of R22 in Subcooled Flow Boiling in Casing Tubes

Amidst the background of “double carbon”, energy saving and emission reduction is a popular direction in the current refrigeration industry. Therefore, the research on the boiling heat transfer of gas–liquid two-phase flow is helpful to strengthen the heat transfer and design a more efficient heat exchanger. In this paper, a research method combining numerical simulation and experimental verification is adopted. Firstly, an experimental platform used for the subcooled flow boiling of refrigerant in casing tubes is introduced and experiments are carried out to obtain experimental data, which provides a theoretical basis for the development of numerical simulation and verifies the feasibility of numerical simulation. A numerical model of subcooled flow boiling in R22 was established and the grid independence test was carried out. Based on the simulation results, three factors affecting the boiling heat transfer of R22 are analyzed: First, the boiling heat transfer coefficient of R22 increases with the increase of the mass flow rate of R22, but the increase decreases when the mass flow rate increases from 0.018 kg/s to 0.020 kg/s. Second, the boiling heat transfer coefficient of R22 increases significantly with the increase of hot water flow rate. Third, the influence of R22 subcooling on boiling heat transfer is more complex. When the subcooling is 5 °C and 1 °C, heat transfer can be enhanced; high subcooling at 5 °C can enhance convective heat transfer and low subcooling at 1 °C can accelerate the arrival of saturated boiling. In this paper, three kinds of bubble behaviors affecting heat transfer in supercooled flow boiling, including sliding, polymerization, and bounce are also studied, which provides a basis for further research on heat transfer mechanism of supercooled flow boiling.

A CFD investigation of the design variables affecting the performance of finned-tube heat exchangers

A wide variety of heating and cooling applications use heat exchangers. The increase in energy prices, the requirement for size reduction, and restriction on greenhouse gas emissions has led to the need for finding ways to develop efficient heat exchangers. A cost-efficient way to enhance the model of a heat exchanger by visualizing the effects of the design parameters is using Computational Fluid Dynamics (CFD). The reason for this exploration was to lead an examination of the varieties/changes in the general intensity move process for a Finned-Tube Heat Exchanger (FTHE), also known as Air Coil Heat Exchanger (ACHE) with a variety of plan boundaries like the quantity of tubes, course of action of tubes, and the material utilized for the intensity exchanger. The widely used heat exchanger that uses refrigerant R314a and air as the working fluids was simulated with different design modifications. The simulated results exhibited as to how the number of tubes, arrangement of coils/tubes, material of tubes, and density / spacing of fins, effects the pressure drop, temperature and velocities profiles, and heat exchangers’ transfer of a heat. The use of copper coils improved the heat transfer by approximately 61% as compared to aluminium coils.

Experimental investigation of the micro-power generation system based on porous burning

This study presents a micro-power generation system based on porous combustion and gasification of biomass energy. The efficient heat exchange between porous combustion-based technology and a free-piston Stirling engine generator (FPSEG) was investigated to convert biomass energy into electric energy. Alumina ceramic particles were used to build a porous medium area within a heat transfer power generation experimental platform to explore the influence of the porous medium bed height and particle diameter, as well as the effect of inlet gas conditions on the system power generation performance. Specifically, the speed of power generation of the system increased and then decreased with an increase in the height of the bed, with maximal power generation speed observed when the height of the bed was 45 mm. The change in the alumina ceramic particle diameter was not significantly related to the rising speed of the system; however, when the diameter of the alumina ceramic particles was less than 15 mm, the flame front could not be stabilized in the porous medium, indicating that a critical particle size existed in the porous medium. Increased gas intake resulted in the power generation rate of the system to first increase and then decrease. When the gas intake was 9.3 m3/h, the power generation rate of change reached 1.2 W/s.

Augmenting the double pipe heat exchanger efficiency using varied molar Ag ornamented graphene oxide (GO) nanoparticles aqueous hybrid nanofluids

The optimization of heat transfer in heat exchanging equipment is paramount for the efficient management of energy resources in both industrial and residential settings. In pursuit of this goal, this empirical study embarked on enhancing the heat transfer performance of a double pipe heat exchanger (DPHX) by introducing silver (Ag)-graphene oxide (GO) hybrid nanofluids into the annulus of the heat exchanger. To achieve this, three distinct molar concentrations of Ag ornamented GO hybrid nanoparticles were synthesized by blending GO nanoparticles with silver nitrate at molarities of 0.03 M, 0.06 M, and 0.09 M. These Ag-GO hybrid nanoparticles were then dispersed in the base fluid, resulting in the formation of three distinct hybrid nanofluids, each with a consistent weight percentage of 0.05 wt%. Thorough characterization and evaluation of thermophysical properties were performed on the resulting hybrid nanomaterials and nanofluids, respectively. Remarkably, the most significant enhancement in heat transfer coefficient, Nusselt number, and thermal performance index (62.9%, 33.55%, and 1.29, respectively) was observed with the 0.09 M Ag-GO hybrid nanofluid, operating at a Reynolds number of 1,451 and a flow rate of 47 g/s. These findings highlight the substantial improvement in thermophysical properties of the base fluid and the intensification of heat transfer in the DPHX with increasing Ag molarity over GO. In summary, this study emphasizes the vital importance of optimizing the molarity of the material, which also plays a significant role in nanoparticle synthesis to achieve the optimal amplification of heat transfer.

Numerical study on effects of nozzle hole spacing distance on steam submerged jet condensation from triangular holes spray nozzle

Steam-water direct contact condensation (DCC) is a phenomenon which is frequently found in the industrial sector due to its rapid and efficient heat and mass exchange rates. In this work, three dimensional numerical study of steam injection from triangular hole nozzles (with different holes pitch circle diameter, PCD = 6, 8,10 and 12 mm) into subcooled water tank has been carried out using Eulerian multiphase flow model along with realizable k-epsilon turbulence model. The thermal phase change model as User Defined Function (UDF) was employed in Fluent software for capturing submerged steam jet condensation. The simulation results were validated using experimental results as well as previously published numerical study and a fairly good agreement was observed. The effects of nozzle hole spacing distance on distributions of various thermal hydraulics parameters including velocity, pressure, temperature, heat and transfer characteristics have been studied. The axial distribution of the velocity, temperature, heat transfer coefficient and mass transfer computed at the centerline of the nozzle was found weaker than observed at the centerline of the nozzle holes. However, these distributions were not weak at nozzle centerline for nozzle with PCD 6 mm. The heat transfer coefficient has been found in the ranges of 1.75–2.3 MW/m2 K. The results reveal that the heat transfer coefficient for nozzle PCD 8 mm is higher than rate obtained for other nozzles. The rate of mass transfer at the holes centerlines has been found increasing with the holes PCD. The axial distribution of the mass transfer curve shifts downstream for nozzle with smaller PCD. Additionally, the mutual shielding effect of the jets weakens as holes PCD increases.

Numerical modeling of bioconvection and heat transfer analysis of Prandtl nanofluid in an inclined stretching sheet: A finite difference scheme

The addition of nanoparticles in the base fluid increases the thermal conductivity of the fluid but the stability of the fluid gets affected due to the presence of nanoparticles in the base fluid. The addition of motile microorganisms in the nanofluid increases the stability of the nanofluid by enhancing thermal conductivity as well as mass transport. In this perspective, the current investigation deals with the study of the behavior of microorganisms in bioconvection over the fluid variables in the non-Darcy background. A two-dimensional Prandtl-nanofluid moving along an inclined stretching flat surface subject to inlet and outlet rate of flow to the surface under the action magnetic drag force normal to the surface. The non-linear partial differential equations are transmuted to ODEs through appropriate similarity transformations. The MATLAB inbuilt bvp4c solver has been employed to generate the solution of the transformed ODEs. The stability of the finite difference scheme is demonstrated by a stability test, and the influence of various parameters on the nanofluid velocity, thermal as well as concentration, and density of motile microorganisms is depicted using graphs for each of them. Additionally, interested physical quantities, shearing stresses, rate of thermal diffusion, rate of mass diffusion, and rate of motile microorganism at the surface, have been plotted by varying the controlling parameters. Growth in the shear stress as well as the rate of thermal diffusion has been detected for the increasing values of and However, the Sherwood number decays for augmented values of The findings could be utilized to increase the thermal efficiency of heat exchangers in order to maintain thermal balance management in small heat-density equipment and gadgets, as well as the thermal efficiency of microbial fuel cells, enzyme biosensors, and microfluidics devices.

Maximizing Efficiency of Earth-Air Heat Exchangers with Galvanized Blocks

Earth-air heat exchangers (EAHE) consist of buried ducts and a ventilation system, which require minimal electricity, making them a cost-effective and sustainable solution for improving the thermal conditions of built environments. To enhance the efficiency of the EAHE system and optimize its use of the soil's thermal potential, we employed a galvanized block with a cross-sectional area of 1.5 m2 around the duct. The simulations conducted in this study used climatic data from Viamão, a city in southern Brazil, and demonstrated the effectiveness of this strategy. The galvanized block increased the thermal conductivity of the soil region and enabled the EAHE system to utilize higher quantities of thermal energy. The first part of the work highlights the importance of block coupling in improving thermal efficiency and the two potentials of EAHE systems. We also introduce a new method for calculating EAHE efficiency throughout the year. We name it maximum efficiency because it measures how much thermal potential an EAHE installation can extract from the highest amount available in the soil during the year. Subsequently, we conducted simulations of ducts at different depths to evaluate their performance. Our results showed that annual efficiencies increased significantly with the addition of the galvanized block. We also found how the installation depth impacts the thermal potentials. Specifically, we obtained almost 4.0°C and 3.8°C for the (annual RMS) soil and EAHE thermal potentials, respectively, at 3.5m.