Heat Exchange Efficiency Research Articles

Reducing the specific energy use of seawater desalination with thermally enhanced reverse osmosis

This study investigates the concept of using heat to enhance reverse osmosis (RO) desalination. An analytical model is used to evaluate the effect of temperature on water permeate flux, specific energy, permeate quality, and applied operating pressures. When feed is heated from 20 to 50 °C, specific energy savings of up to 24 % are observed for high flux seawater desalination and up to 33 % for brackish water. Such improvements are consistent with the literature, but until now the thermal energy input required to heat feed has been mostly neglected from analysis. For the first time, the overall energy balance of thermally-enhanced RO is considered to evaluate the tradeoff between savings in mechanical pump work and thermal energy input. Results suggest that this tradeoff is favorable under the right conditions. In particular, there is a need for high thermal efficiencies including both a very high heat pump coefficient of performance and very high heat exchanger efficiency for recycling thermal energy. Under these conditions, overall energy savings of up to 12 % are observed for seawater desalination when feed is heated from 20 to 41 °C, and up to 18 % for brackish water with feed heated to 46 °C.

Validation and Application of a Finned Tube Heat Exchanger Model for Rack-Level Cooling

Abstract A thermosyphon-based modular cooling approach offers an energy efficient cooling solution with an increased potential for waste heat recovery. Central to the cooling system is an air-refrigerant finned tube heat exchanger (HX), where air is cooled by evaporating refrigerant. This work builds on a previously published two-dimensional (2D) model for the finned-tube HX by updating and validating the model using in-house experimental data collected from the proposed system using R1233zd(E) as the working fluid. The results show that key system variables such as refrigerant outlet quality, air and refrigerant outlet temperatures, and exchanger duty agree within 20% of their experimental counterparts. The validated model is then used to predict the mean heat transfer coefficient on the refrigerant side for each tube in the direction of airflow, indicating a maximum heat transfer coefficient of nearly 1200 W/(m2 K) for a HX duty of 5.3 kW among the tested cases. The validated model therefore enables accurate predictions of HX performance and provides insights into improving the heat exchange efficiency and the corresponding system performance.

The method of calculating the parameters of a heat exchanger with porous inserts based on the obtained criterion equation

The issues of improving the efficiency of heat exchange equipment are relevant. Heat exchange equipment is used in various industries. Porous metals have proven themselves well when used in heat exchange systems of gas turbine and rocket engines, laser mirror systems, nuclear reactors and other similar systems to increase the efficiency of heat exchange. The use of porous structures is effective due to a significant increase in the heat exchange area. The paper presents the results of experimental and theoretical studies of the efficiency of using porous aluminum inserts in the construction of a shell-and-tube heat exchanger. The efficiency of using porous aluminum inserts in the construction of a shell-and-tube heat exchanger has been experimentally shown. A similarity equation is obtained for calculating the Nusselt criterion, which makes it possible to find the heat transfer coefficient, and as a consequence, heat transfer for the coolant flowing through porous inserts in the inter-tube space of the heat exchanger. A cluster model was used to calculate the heat exchange area from the side of the coolant flowing through the pairs. The correspondence of the obtained calculation formula with the results of the experimental work is shown. A method of thermal calculation of a heat exchanger with porous aluminum inserts using a cluster model and the obtained criterion equation for calculating the heat transfer coefficient is proposed. The conclusion is made about the expediency of using porous metals in heat exchange structures.

Optimizing heat transfer characteristics in dry centrifugal Granulation: Impact of particle population trajectory and cooling strategies

Efficient recovery of heat and utilize blast furnace slag resources are crucial for achieving energy savings and reducing consumption in the steel industry. This study focuses on applying dry centrifugal pelletizing technology for recovering waste heat from slag. A comprehensive two-dimensional model was developed to investigate heat transfer dynamics within particle clusters, considering the variable physical parameters of the slag, latent heat of the phase change, and slag particle characteristics. Through an extensive analysis of the heat exchange within the granulation bin, we examined the temperature variations of slag particles and the distribution of absorbed heat by the water-cooled and air. Findings underscore the significant influence of flight trajectory, residence time, air-inlet flow rate, and temperature on heat exchange efficiency. Additionally, we explored the impact of auxiliary cooling measures and investigated how slag particle characteristics affect the bin wall, highlighting their importance for safe operations. Our results provide valuable insights for enhancing waste heat recovery efficiency from blast furnace slag and optimizing the implementation of dry centrifugal granulation technology. It serves as a vital reference for promoting energy-saving initiatives and reducing consumption in the steel industry.

An investigation on structural parameters optimization and coupled heat transfer of LNG submerged combustion vaporizer

Submerged combustion vaporizer (SCV) owns an extremely efficient multiphase heat exchanger adopted in the coastal liquefied natural gas (LNG) receiving terminal. Overall vaporization efficiency of SCV mostly depends on the matching relationship of structural parameters and coupled heat transfer characteristics, which has been rarely addressed in previous studies. In the present work, an integrated SCV experimental platform with handling capacity of 50 kg/h was set up to validate the reliability of numerical model and method. Additionally, on account of multi-parameter orthogonal combination optimization method, the effects and sensitivity orders of structural parameters (transverse tube pitch, longitudinal tube pitch, orifice size and number of distributor branch) on dynamics performance of SCV were investigated. Finally, the coupled heat transfer between gas–liquid two-phase flow and supercritical LNG gasification was revealed in view of optimized parameters. Results indicated that the transient numerical tube-side outlet temperature could be consistent with experimental data. For the shell-side heat transfer coefficient, the sensitivity order was transverse tube pitch > orifice size > longitudinal tube pitch > number of distributor branch. Nevertheless, for the shell-side pressure drop, the sensitivity order was longitudinal tube pitch > transverse tube pitch > orifice size > number of distributor branch. Under the condition of optimization scheme, the heat provided by gas–liquid two-phase flow could meet the requirements of supercritical LNG gasification, the NG outlet temperature might achieve approximately 272 K. The present outcomes could lay a foundation for the optimization design and deep understanding for actual SCV facility.

Assisted heat transfer enhancement in non-Newtonian dielectric fluids based on ion conduction phenomena

Electric field-assisted technologies show prospects for heat removal in electronic cooling scenarios with electro-thermo-convection phenomena. The coupled multiphysics field model is built using the finite volume method, and two configurations (depending upon the orientation of the electric field and gravity) are investigated for different shear-thinning properties and polymer elasticities. The results demonstrate a remarkable impact on the heat exchange efficiency, energy budget, plume morphology, and force distribution features. Two key partitions (buoyancy or Coulomb force-dominated regions) can be divided by Rayleigh number Ra ≤ 103 and electric Reynolds number ReE ≤ 1.57. A heat transfer boost of 13.9 times and 5.0 times was obtained in the two arrangements vs no electric reinforcement. The shear-thinning shows a noticeable positive contribution, and the heat transfer efficiency can be modulated by polymer elasticity within a wide parameter range. A detailed evaluation of the interfacial forces reveals the nonmonotonic curves of fluid convection and energy inputs.

Design and numerical assessment of an additively manufactured Schwarz diamond triply periodic minimal surface fluid-fluid heat exchanger

In aerospace, thermal applications demand compact, lightweight, and efficient heat exchangers. Additive manufacturing processes offer the potential to create highly complex structures that are not achievable through traditional manufacturing methods. This work presents the development of an additively manufactured fluid-fluid heat exchanger that shows the potential to enhance the performance, reduce weight, and increase compactness compared to a conventional plate heat exchanger. A numerical model of the conventional plate heat exchanger was created, and fluid dynamics simulations with heat transfer were performed. Validation of the simulations was done by experiments. Then, a novel heat exchanger was designed using a bottom-up approach and investigated at different levels of complexity using computational fluid dynamics. The internal structure of the final heat exchanger consists of a repeating triply periodic Schwarz diamond minimum surface elongated in the direction of flow. The heat exchanger was manufactured with laser powder bed fusion process using AlSi10Mg. It had a 108% higher compactness and 54% lower weight compared to the plate heat exchanger. Numerical analysis yielded the pressure loss in pascal was reduced by 50%–59% while heat transfer in watts was improved by 3%–5%. Future researches should experimentally investigate the thermal and fluid mechanical characteristics of the novel additively manufactured heat exchanger and increase compactness and heat transfer further by analyzing the minimum partition wall thickness and the impact of wall roughness and deposit formation.

Simulation of borehole thermal energy storage (BTES) systems using simplified methods

This paper presents two complementary approaches for simulating the thermal performance of borehole thermal energy storage (BTES) systems. The first approach uses the concepts of heat exchange and storage efficiencies as a function of the state-of-charge of the BTES. The second method employs a technique similar to thermal response factors used to model bore fields in ground-source heat pump systems. It utilizes non-dimensional average storage temperatures and bore field thermal resistances of the BTES over time. The two methods rely on numerical experiments to obtain the required performance curves. As shown through examples, the two approaches are relatively simple to use, and it is shown that they are in good agreement with the well-known duct ground storage model. In one of the examples, it is suggested that the design of a BTES could be performed using three successive thermal pulses, similar to the approach used to determine the length of vertical ground heat exchangers in a ground-source heat pump systems.

Experimental and numerical study of an innovative twined tube HX design

An innovative twined tube heat exchanger (HX) design is proposed, which is simple, robust, and efficient for use in advanced nuclear reactors. The heat exchanger is designed with two tubes twined around each other. Multiple modules can be assembled within a shell to meet the necessary heat load. Thermal-hydraulic investigations of the novel design are performed through experiments and numerical simulation. The experimental investigations of the twined tube HX are carried out on a laboratory-scale thermal–hydraulic rig commissioned at the Pakistan Institute of Engineering & Applied Sciences (PIEAS). The primary loop contains water at a high temperature and a pressure of 4.0 bar pressure, while the secondary loop operates at atmospheric pressure. Single-phase forced convection heat transfer characteristics of the twined tube HX are investigated experimentally. Pressure drop is measured for mass fluxes ranging from 350 kg/m2s to 1376 kg/m2s. A correlation for the estimation of friction factor is developed based on the experimental studies. Heat transfer measurements are carried out for mass fluxes ranging from 244 kg/m2s to 419 kg/m2s. Based on these experiments, the Nusselt number is evaluated for the mass flux range mentioned above. The numerical simulations of a twined tube HX are performed on a full-scale STAR-CCM + model. The model is validated against the experimental results. The performance factor of the twined tube HX is higher than that of straight tube HX, with a maximum performance enhancement of 60%. The thermal–hydraulic performance of the twined tube HX is comparable with helical coil HX designs. However, the proposed HX design is easier to fabricate and maintain than the helical coiled HX. Overall, the study provides valuable insights into the thermal–hydraulic performance of the twined tube HX, which could be useful in the design of compact and efficient heat exchangers for small modular reactors.

Design and mechanical performances of stress adaptive porous structures based on triply period minimal surface

In this study, a design method is proposed for the stress adaptive porous structures with triply period minimal surface (TPMS). The method depends upon the modeling method of solving porous structures with complex contour and the mapping method achieved by mapping functions of mechanical properties for TPMS based porous structures. Additionally, the implementation framework is provided, and the proposed modeling method is evaluated by an example. The results show that the stress adaptive structures possess higher stiffness and peak stress, compared with uniform or graded type, which proved the promising potential in engineer applications, bone implants and efficient heat exchanger.

Research on shell-side heat and mass transfer with multi-component in LNG spiral-wound heat exchanger under sloshing conditions

The spiral-wound heat exchanger (SWHE) is the primary low-temperature heat exchanger for large-scale LNG plants due to its high-pressure resistance, compact structure, and high heat exchange efficiency. This paper studied the shell-side heat and mass transfer characteristics of vapor-liquid two-phase mixed refrigerants in an SWHE by combining a multi-component model in FLUENT software with a customized multicomponent mass transfer model. Besides, the mathematical model under the sloshing condition was obtained through mathematical derivation, and the corresponding UDF code was loaded into FLUENT as the momentum source term. The results under the sloshing conditions were compared with the relevant parameters under the steady-state condition. The shell-side heat and mass transfer characteristics of the SWHE were investigated by adjusting the component ratio and other working conditions. It was found that the sloshing conditions enhance the heat transfer performance and sometimes have insignificant effects. The sloshing condition is beneficial to reduce the flow resistance. The comprehensive performance of multi-component refrigerants has been improved and the improvement is more significant under sloshing conditions, considering both the heat transfer and pressure drop. These results will provide theoretical support for the research and design of multi-component heat and mass transfer enhancement of LNG SWHE under ocean sloshing conditions.

Theoretical thermal performance of cross-flow finned heat pipe heat exchanger used for air conditioning in surgery rooms

The thermal efficiency of heat exchangers was applied for theoretical analysis of the thermal performance of a finned heat pipe heat exchanger (FHPHE) used as an auxiliary device to control the temperature and quality of the air conditioning in operating rooms. The theoretical analysis performed is punctual and distributed. It is divided into three aspects: analysis of the evaporator section, analysis of the condenser section, and analysis of the heat exchanger in terms of overall performance. The distributed procedure contrasts with the theoretical-experimental study, which uses the concept of thermal effectiveness (ε-NTU) for global heat exchanger analysis. The developed approach considers the number of heat pipes, the number of fins, and the flow rate variation at the inlet of the heat exchanger as fundamental parameters for determining the thermophysical quantities of interest. Theoretical values were determined for the average velocities, Nusselt numbers, thermal effectiveness, heat transfer rates, and exit temperatures. The localized theoretical-experimental comparisons are consistent, and the absolute relative error for the global heat transfer rate ranges from 0.5% to 35%.

The novel designs for increasing heat transfer in ground heat exchangers to improve geothermal heat pump efficiency

Heat transfer between ground heat exchangers (GHE) and the soil is highly important for the overall efficiency of geothermal heat pump systems. Therefore, the present study investigates how adding materials with high thermal conductivity influences the efficiency and outlet temperature of horizontal heat exchangers. To this end, novel methods were developed and evaluated. Initially, metal sheets were used under pipes as fins or blades to enhance the heat transfer rate (HTR) between GHE and the ground and involve a larger portion of the soil. Due to soil moisture effects on thermal conductivity, the boxes used in this study were filled using two distinct methods. Given its higher moisture content, the soil (backfill material) within the box demonstrated a higher thermal conductivity than the soil surrounding the box. In the first method, the box was connected to the ground so that water could enter it when irrigating the green space, thereby increasing the soil's moisture content and the thermal conductivity of the backfill material. In the second method, the boxes were equipped with aluminum and steel blades to enhance heat transfer through pipes. The simulation was performed using the 1D-3D method and COMSOL software was used. After confirming the efficiency of the proposed methods, their dimensions and thermal properties were altered to produce optimal modes. The temperature of the outlet fluid was reduced by 3.8% in cooling mode using only one aluminum sheet, and the overall efficiency of the GHE increased by 37%. Moreover, the reduction in the outlet temperature of the GHE when the blade was connected to the box filled with the proposed backfill materials was reduced by 10%, which is a very significant result.

Thermo-hydraulic efficiency of lung-inspired compact plate heat exchangers made using additive manufacturing techniques with steel, aluminum and titanium powders

The selection of material for compact plate heat exchangers (CPHEs) is of increasing importance due to global economic and supply constraints. Additionally, the influence of material selection on the thermo-hydraulic characteristics of CPHEs is an area of ongoing research. This study aims to address these issues by analyzing the thermo-hydraulic performance of CPHEs made from steel, aluminum, and titanium materials with small, complex channels. Using an additive manufacturing method (specifically Direct Metal Laser Sintering), lung-inspired CPHEs of identical geometry and roughness were manufactured from steel, aluminum and titanium powders. The thermo-hydraulic characteristics of CPHEs as well as that of a traditional one with Chevron-type, were investigated using both experimental and numerical techniques under specific operating conditions to determine the optimum between maximum heat transfer and minimum pressure drop. The findings of this study reveal that as the temperature difference between the inlet on the hot and cold sides, as well as the flow rate, were increased, there was a corresponding increase in both amount of heat transferred and loss of pressure across all investigated CPHEs. Compared to the chevron type brazed plate heat exchanger, the CPHE made from aluminum showed a 75.2 % and 11.2 % increase in heat transfer and a 31.8 % and 10.9 % reduction in pressure drop at 3 and 6 L/min, respectively, for a temperature difference of 90–40 °C. This study suggests that the use of materials with different thermal conductivities in CPHEs may offer a promising solution to achieve elevated heat transfer rates while minimizing pressure drop.

Numerical Analysis of the Thermal-hydraulic Performance of Supercritical LNG in Airfoil Fin PCHEs

Abstract As a novel, compact, and efficient plate-fin heat exchanger, the Printed Circuit Heat Exchanger (PCHE) is a prospective candidate for liquefied natural gas (LNG) vaporization at low-temperature and high pressure. Generally, the airfoil fin PCHE has better thermal-hydraulic performance than the zigzag channel PCHE. In this study, the thermal-hydraulic performance of supercritical LNG in PCHEs with different airfoil fin types and arrangements is investigated by numerical simulations. First, the effects of six different airfoil fin types, NACA0010, NACA0020, NACA0025, NACA0030, NACA 0040, and NACA 0050, on the thermal-hydraulic performances were studied. The results show that NACA0025 has the best comprehensive heat transfer performance. Then, the effects of staggered, vertical, and horizontal pitch of the airfoil fin arrangement on thermal-hydraulic performance were investigated. The results show that the optimal values of the dimensionless number for staggered and vertical arrangements are 1 and 4, respectively. The comprehensive performance does not change much when the dimensionless horizontal pitch number exceeds 3.0. Finally, the thermal-hydraulic performance of uniformly distributed, three front sparse and rear dense, and three front dense and rear sparse distributed airfoil fins was investigated. The results show that the front dense and rear sparse airfoil fins enhance and the front sparse and rear dense airfoil fins reduce the comprehensive performance compared to the uniform arrangement. The results show that a denser arrangement of airfoil fins near the quasi-critical point can improve the comprehensive performance while keeping the number of airfoil fins constant.

Novel thermal conductivity and anti-corrosion coating with hydrophobic properties for heat exchanger applications

Industrial heat exchangers commonly encounter the issue of metal corrosion. Conventional anti-corrosion coatings typically exhibit poor heat conduction, leading to diminished heat exchange efficiency. This study presents a novel coating that combines high thermal conductivity with enduring anti-corrosion performance. The interfacial compatibility between the boron nitride (BN) / silicon carbide (SiC) and fluorosilicone resin (FSR) is effectively enhanced through fluorosilane modification. This improvement, in conjunction with the superior thermal conductivity of the BN/SiC composite filler and the multi-barrier effects of the two-dimensional BN material, results in the composite coating with a high thermal conductivity of 1.65 W/(m·K). After 60 days of immersion in 3.5 wt% NaCl solution, the coating maintains a low-frequency impedance exceeding 1011 Ω·cm2. Good hydrophobicity can promote the long-term anti-corrosion performance of the coating. Thanks to the inherent hydrophobicity of FSR and the reduced surface energy of the filler due to fluorosilane modification, the coating also exhibits hydrophobic characteristics, evidenced by a water contact angle of 109.69°. The development of this novel multifunctional coating holds significant implications for heat exchangers and other applications requiring a balance between thermal conductivity and anti-corrosion performance.

Analyzing the Performance of Double Spiral Tube Ground Heat Exchangers in a Zero-Energy Building Using Measurement Data

A ground-source heat pump (GSHP) system is a renewable energy technology that effectively reduces greenhouse gas emissions and consequently mitigates the progression of global warming. The thermal efficiency of ground heat exchangers (GHEs) is a critical component in the GSHP system that must be accurately estimated for its long-term operationality. Therefore, in this study, the thermal performance of double-spiral GHEs incorporated within the thermal piles of a zero-energy building in Sapporo, Japan, was investigated using the actual measured data obtained from the site and a novel metric, namely, the coefficient of heat extraction/injection, for a more precise evaluation. Moreover, this study assessed the coefficient of performance (COP) of the GSHP units during various periods of cooling or heating. The temperature of the circulating fluid remained within an ideal operational range over an operational period of 2 years, and the COP calculations indicated a high operational efficiency. The results derived in this study substantially exceeded those of traditional U-tube GHEs, indicating the enhanced efficiency and superior performance of large-diameter thermal piles with augmented thermal capacity. Our findings suggest that GSHP systems with double-spiral-tube GHEs have superior efficiency than conventional GHEs.

Effect of Hole Geometry Shape in Vortex Generators on Fluid Output Temperature: Computational Fluids Dynamics Validation

<p>Several methods to enhance heat transfer can be classified into three categories: active, passive, or hybrid. Among these methods, Vortex Generators (VGs) are one passive heat transfer enhancement device widely used in heat exchangers. This study aims to explore the geometric shapes of VGs equipped with longitudinal holes and examine their influence on the outlet temperature of the fluid. For the analysis in this research, a three-dimensional Computational Fluid Dynamics (CFD) simulation using ANSYS Fluent software was employed. The increased heat transfer and flow resistance in the VG geometry were evaluated based on previous research for validation. The study results demonstrate that the simulation produces fluid outlet temperature values and velocity contours that closely resemble the results obtained from the reference study. The validation error of this research was found to be only 0.02%, indicating high-quality and accurate simulation results. Furthermore, the study compared various geometries of the VG holes in the system. Among these geometries, hexagonal-shaped VG holes exhibited high-velocity contours on the VG side while achieving the lowest fluid outlet temperature at approximately 303.53 K. The findings of this study serve as a basis for further developments in enhancing the efficiency and performance of heat exchangers using VGs.</p>

Feasibility study and dimensionless theoretical analysis of cylindrical lithium-ion battery module cooled by dynamic circulating transformer oil

Direct contact liquid cooling has demonstrated superior cooling capacity and heat exchange efficiency in battery thermal management when compared to alternative methods. This article presents the design of a battery thermal management system (BTMS) utilizing dynamic circulating transformer oil as an immersion cooling medium. This oil-immersed BTMS is examined for its cooling performance across different flow rates, ranging from 30 to 600 ml/min, with an analysis of heat transfer characteristics during dynamic cycles. The findings reveal that transformer oil can significantly reduce the temperature of the battery module under circulating flow conditions. Even at the lowest flow rate of 30 ml/min, the maximum temperature of the battery module remains below 45 °C. However, beyond a flow rate of 200 ml/min, specifically in the range of 300–600 ml/min, the temperature drop in the battery module becomes less noticeable. Theoretical analysis indicates that at 200 ml/min (Re = 44.1), the dynamic circulation cooling system achieves its best cooling efficiency. These results underscore the effectiveness of the oil-immersed BTMS as an efficient thermal management solution for cylindrical battery modules, supported by both experimental and theoretical perspectives.

Coupld thermo-hydraulic modelling of heat storage in an embankment

Coupld thermo-hydraulic modelling of heat storage in an embankment