Design Of Compact Heat Exchangers Research Articles

Selection of phase change material for latent heat thermal energy storage using a hair-pin heat exchanger: Numerical Study

Abstract Phase change materials (PCMs) are promising for storing thermal energy as latent heat, addressing power shortages. Growing demand for concentrated solar power systems has spurred the development of latent thermal energy storage, offering steady temperature release and compact heat exchanger designs. This study explores melting and solidification in a hairpin-type heat exchanger (HEX) using three PCMs (RT 50, RT 27, and RT 35). A 3D model of the hairpin type heat exchanger (HEX) is drawn using Ansys-workbench. High-temperature fluid/Low-temperature fluid (HTF/LTF) with Stefan numbers (0.44, 0.35, and 0.23) flows through the inner pipe to charge the outer pipe's PCM. The Enthalpy-porosity model is used to study the melting and solidification of various PCMs, and the results were compared. Also, individual thermophysical properties that affect the heat transfer during the melting and solidification process have been discussed. It is observed that low thermal conductivity material with high latent heat is preferred for cold climates. In this study, RT 27 excels in cold climates due to extended solidification time, while RT 50 is effective in tropical regions due to its high melting points and lower latent heat.

Numerical simulation-based design of optimized surfaces for condensation heat transfer

Heat transfer enhancement is a well-established research topic due to its industrial relevance. The advent of 3D printing, also known as additive manufacturing, has opened up the pathway for the design of compact heat exchangers with innovative shapes, complex geometries and smaller size. In particular, additive manufacturing technologies speed up the transition from CAD models to physical prototypes and thus numerical simulation tools for two-phase heat transfer are expected in the future to play a key role for the design of heat exchangers. With regard to filmwise condensation, numerical methods capable to account for all the main forces involved (such as gravity, surface tension, vapor shear stress) must be considered for the optimization of the condensing surfaces. The present study is focused on the preliminary design of innovative shapes for enhancing the condensation heat transfer in a grooved wick heat pipe. Most of the condensation heat transfer studies available in the literature deal with vapor condensing inside tubes or over cylindrical/plain surfaces, while the condensation process occurring inside heat pipes has been less investigated. The grooved wick surfaces must be designed with the aim to promote the drainage of the condensate and minimize the thickness of the liquid film forming over the wick structures. In the present work, the behaviour of different surfaces is studied during condensation of refrigerants by performing Volume of Fluid (VOF) 2D numerical simulations with Ansys®Fluent. The numerical results allow to determine the liquid film thickness and the heat flux distribution along the grooves.

Experimental Analysis on Enhancement of Heat Transfer in Compact Heat Exchanger Using Nano Particles

This experimental study focuses on enhancing heat transfer in compact heat exchangers through innovative methods. Various augmentation techniques, including surface modifications, vortex generators, and advanced fluids, are systematically tested in a carefully designed experimental setup. The research aims to quantify the impact of these enhancements on heat transfer rates, pressure drop, and overall thermal performance. Controlled parameters such as fluid flow rates and temperatures are measured to assess heat transfer coefficients and effectiveness under different operating conditions. Results aim to provide valuable insights into the feasibility of implementing these techniques, offering practical guidelines for optimizing compact heat exchanger design. The study contributes to advancing thermal management technologies, promoting energy efficiency, and reducing environmental impact in industrial applications.

Thermal Energy Storage Heat Exchanger Design: Overcoming Low Thermal Conductivity Limitations of Phase-Change Materials

Abstract Recently, there has been a renewed interest in solid-to-liquid phase-change materials (PCMs) for thermal energy storage (TES) solutions in response to ambitious decarbonization goals. While PCMs have very high thermal storage capacities, their typically low thermal conductivities impose limitations on energy charging and discharging rates. Extensive research efforts have focused on improving PCM thermal conductivity through the incorporation of additives. However, this approach presents challenges such as achieving uniform mixtures, maintaining high latent heat, and cost. Alternatively, it has been demonstrated that, in this study, reducing the length scale of the PCM-encasement thickness can eliminate the low thermal conductivity effect of PCMs. To illustrate this concept, a one-dimensional PCM slab was numerically simulated. The thickness of the slab was varied to represent dimensions found in flow passages of compact heat exchangers, and the heat transfer coefficient of the heating fluid was varied to represent lower and upper bounds while also including nominal values encountered in air-to-air heat exchangers. The thermal conductivity was parametrically varied from the natural value of the PCM to simulated enhanced values (potentially achieved through additives) of up to 400 times larger. Results show that reducing the PCM-encasement thickness yields substantially better performance than by improving the thermal conductivity, thereby demonstrating the potential for compact heat exchanger design to overcome the PCM thermal conductivity limitations.

Effects of different cross-sections of Body Centered Cubic cells on pressure drop and heat transfer of additively manufactured heat sinks

In many industrial applications, heat loads management requires the design and production of compact heat exchangers which are expected to handle high thermal loads with acceptable pressure losses, while assuring good mechanical performances. These challenging targets can be achieved by filling the cavities where the cool/hot fluid circulates with lattice structures promoting the heat exchange between the fluid and the cavity boundaries. Such lattice structures can be only produced through Additive Manufacturing due to their high geometric complexity. Recent experimental investigations proved the effectiveness of some kinds of lattice structures having a circular cross section. Here the aerothermal behaviour of Body-Centred Cubic (BCC) lattice stagger arrays in a rectangular channel was experimentally investigated by considerably extending the previous studies to higher Reynolds numbers (up to 30′000) and to new types of lattice structures. Specifically, three new BCC structures having a cam-like, drop-like and elliptical cross section were explored in this work and compared against those having circular cross section. All the samples were manufactured by means of Laser Powder Bed Fusion and made from AlSi10Mg. At first, the heat exchangers were comprehensively characterized by means of optical non-destructive methods. Successively they were tested in a dedicated rig by imposing constant heat flux boundary conditions. The characteristics of the transitional or fully turbulent approaching flow to the test section are also reported thanks to dedicated flow field measurements performed by Particle Image Velocimetry. According to the obtained results, the BCC structure with the circular cross section of larger diameter is the most effective in terms of heat transfer, although it is largely penalized by the pressure losses. Similar heat transfer performances were achieved by the tapered cross section of elliptical shape with the advantage of a considerably lower friction factor. Pressure losses resulted almost identical for all the tapered cross sections but lower than those of the circular one having an equal frontal dimension. When considering the thermal performance factor the circular shape becomes unfavourable for Re>20′000, while the elliptical cross section is the best choice to efficiently promote heat transfer up to Re=30′000.

AN INNOVATIVE METHODOLOGY TO DESIGN GYROID HEAT EXCHANGERS FOR METAL ADDITIVE MANUFACTURING

This study demonstrates an innovative approach to the automatic design of compact gyroid heat exchangers using the advanced engineering software nTopology, which is based on implicit modeling technology. The aim is to provide a modern enhancement to traditional 'Shell and Tube' type heat exchangers. Utilizing functions in implicit modeling and parametric design features, complex internal gyroid structures can be used as an alternative heat transfer interface in 'Shell and Tube' type heat exchangers. The most striking aspect of the methodology is its ability to fully automate the design process. By consolidating specific parameters into a single function block and entering scalar values, a fast and flexible workflow is activated, automatically generating the final geometry. Gyroid structures with high thermal performance and fluid dynamics are automatically adapted for various volumes and geometries. These structures can improve the overall efficiency of heat exchangers and offer significant advantages, especially in specialized application areas such as aerospace and space industries. In the design and sizing process of the gyroid heat exchanger, if manufacturing is planned, it is necessary to pay attention to the design principles for metal additive manufacturing. In conclusion, this study demonstrates that the advanced engineering software known as nTopology can create a synergistic effect in the rapid and easy design of gyroid heat exchangers and in establishing the automation of the design process.

ANSYS Simulation of Enhanced Heat Transfer in Compact Pipes Using Al2O3-Water Nanofluids

Al2O3-Water nanofluids have become popular for their significantly higher heat transfer rates, which are related to their increased thermal conductivity. These fluids are particularly useful in tiny pipelines, especially in situations where effective thermal control is required. Because of this, they are particularly beneficial to sectors like aerospace and automotive, where the need for lightweight and compact heat exchanger designs is crucial. This research investigates several input factors, such as temperature and velocity, using ANSYS Fluent. The investigation's initial temperature was 290 K, and the pipe's entry velocity was 3.78×10-1 m/s. At 2.98×102 K, the exit temperature stabilized. However, a clear inverse link between the temperature at the pipe's output side and the velocity at its entrance side was found. This unique development served as the main focus of our investigation on how to optimize heat flow and thermal conductivity inside the pipe. We used a two-phase approach, incorporating the nanofluid phases phi-0 and phi-4, to increase our comprehension. This methodological decision departs from traditional research, which frequently uses simulations in a single phase. Our new method was inspired by the necessity for a more thorough investigation. The results of this study demonstrate the effectiveness of the two-phase method, showing a significant rise in heat flow and thermal conductivity when compared to traditional one-phase simulations used in earlier research. This emphasizes how our approach was original and significant, bringing fresh perspectives to the field of nanofluid heat transfer research.

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 performance of a novel compact high-effectiveness transparent-wall counter-flow heat exchanger fabricated using additive manufacturing

Compact high-effectiveness counter-flow heat exchangers (CFHEX) are an essential building block of remote cooling systems and Reverse Turbo-Brayton coolers. This technology enables a wide variety of on-ground and space applications, including the cooling of infrared detectors, cryogenic chains of quantum computers and ultra-sensitive superconducting SQUID sensors. A mesh-based CFHEX design was previously proposed for such applications and demonstrated a great potential to meet the high effectiveness and compactness needs [1]. This paper presents a novel improved mesh-based CFHEX concept with a “transparent” inner wall and outlines the methods used for its manufacturing. Two of such CFHEXs are constructed and integrated in a technology demonstrator of a remote cooling system. Their performance is tested in the ▪ temperature, 1bar–5bar pressure and 50mg/s–250mg/s helium mass flow rate ranges. An effectiveness of ▪ (NTU=39–124) has been experimentally achieved with a pressure drop of less than 10mbar per stream at the nominal operating conditions of the system. The experimental effectiveness and pressure drop results are analysed and compared to numerical predictions. The implications of the achieved high effectiveness on the final performance of the designed remote cooling system are also discussed.

Functional morphology change of TPMS structures for design and additive manufacturing of compact heat exchangers

Functional morphology change of TPMS structures for design and additive manufacturing of compact heat exchangers

Prediction and Validation of Flow Properties in Porous Lattice Structures

Abstract High-porosity metal foams have been extensively studied as an attractive candidate for efficient and compact heat exchanger design. With the advancements in additive manufacturing, such foams can be manufactured with controlled topology to yield highly tailorable mechanical and transport properties. In this study, a lattice Boltzmann method (LBM)-based pore-scale model is implemented to simulate the fluid flow in additively manufactured (AM) metal foams with unit cell topologies of Cube, Face Diagonal (FD)-Cube, Tetrakaidecahedron (TKD), and Octet lattices. The pressure gradient versus average velocity profiles predicted by the LBM model were validated against in-house measurements on the AM lattice samples with the same unit cell topologies. Based on the simulation results, a novel hybrid model is proposed to accurately predict the volume averaged flow properties (permeability and inertial coefficients) of the four structures. Specifically, the linear LBM (neglecting inertial forces) is first implemented to obtain the intrinsic permeability, and then the standard LBM is applied to obtain the inertial coefficient. Convenient correlations for those flow properties as a function of porosity and fiber diameter are constructed. The effects of the AM print qualities on the flow properties are also discussed. The advantages of the hybrid model compared to the polynomial fitting approach for determining flow properties are discussed and compared quantitatively. The hybrid model and presented results are valuable for flow and thermal transport evaluation when designing new metal foams for specific applications and with different materials and topologies. The presented correlations based on pore-scale simulations can also be conveniently used in volume-averaged models to predict the macroscale flow behavior in such complex structures.

Compact heat exchanger designs for difluoromethane-activated carbon composites based adsorption cooling systems

Compact heat exchanger designs for difluoromethane-activated carbon composites based adsorption cooling systems

Evolutionary design of compact counterflow heat exchanger

Abstract This investigation includes a geometric optimization for a compact heat exchanger built from hexagonal channels with the rely of Constructal design. A three-dimensional numerical analysis based on the finite volume method (FVM) are conducted to identify hydrodynamic and thermal behaviors of the counterflow arrays. We considered several configurations for the inactive channel emerged from packing the hexagonal channels within the compact heat exchanger, considering the easier access for the heat from the hot fluid to the cold fluid. The hexagonal arrays considered for the CFD study is first assumed to be well insulated. The hot and cold fluids (water) flow with variable Reynolds numbers; 10, 100, 200 and 300. The results are presented in term of heat transfer effectiveness, thermal conductance, and the thermal-to-flow performances ratio. The CFD code was verified with an experiment work to assess the accuracy of the current numerical analysis. Triangular channels (β = 1) employed in the inactive region showed better performance for the counterflow hexagonal bundle. High pressure drop is associated with the trapezoidal shape especially with smaller hydraulic diameter (small cross-sectional area).

Adsorption of difluoromethane onto activated carbon based composites: Adsorption kinetics, heat of adsorption, cooling performance and irreversibility evaluation

To further the research on R32 refrigerant-based adsorption cooling applications, Maxsorb-III activated carbon composites synthesized with the additives of H25 Graphene nanoplatelets (GNP), 1-Hexyl-3-methylimidazolium bis(trifluormethylsulfonyl)imide ([HMIM][Tf2N]) ionic liquid with polyvinyl alcohol (PVA) are studied for cooling performance evaluation. Their respective kinetic characteristics and heat of adsorption assessments are carried out for this purpose in the present study. The adsorption kinetics characteristics are studied using gravimetrically for the composite samples. A first-order kinetics model is seen to fit their kinetic uptakes with regression coefficients ≥ 0.97. The heat of adsorption estimates of the composites for varying uptakes and temperatures are numerically evaluated, incorporating the non-ideal behavior of the refrigerant. An approach for a holistic comparison of the cooling performances of the composites containing their respective heat and mass transfer characteristics for compact heat exchanger designs is further proposed. While the composite with the highest Maxsorb-III mass fraction yields the highest specific and volumetric cooling powers, the composite with the highest thermal conductivity requires the lowest heat exchanger area with a slightly larger adsorbent volume of around 12.1% over the former. A second law thermodynamic analysis is further carried out to evaluate the composite performances for cooling applications.

A comprehensive design and optimization of an offset strip-fin compact heat exchanger for energy recovery systems

• Parametric, sensitivity, and optimization of compact heat exchanger is presented. • A normalized sensitivity analysis is used to identify the critical parameters. • Geometric parameters and fluid velocity appeared as the most influential parameters. • The optimization reduced the operational cost by 78%, and the total cost by 77%. Energy recovery in conventional thermal systems like power plants, refrigeration systems, and air conditioning systems has enhanced their thermodynamic and economic performance. In this regard, compact heat exchangers are the most employed for gas to gas energy recovery because of their better thermal performance. This paper presents an economic optimization of a crossflow plate-fin heat exchanger with offset strip fins. A detailed software-based numerical code for thermal, hydraulic, economic, and exergy analysis is developed for three fin geometries. Genetic Algorithm, parametric, and normalized sensitivity analyses are used to discover the most influential parameters to optimize the total cost. The parametric study showed that with the increase of mass flow rates and plate spacing, outlet stream cost and operating cost increased due to the rise in pressure drops. Finally, the optimization reduced the operational cost by ∼78.5%, stream cost by ∼64.5%, and total cost by ∼76.8%.

Preliminary Analysis of Compression System Integrated Heat Management Concepts Using LH2-Based Parametric Gas Turbine Model

The investigation of the various heat management concepts using LH2 requires the development of a modeling environment coupling the cryogenic hydrogen fuel system with turbofan performance. This paper presents a numerical framework to model hydrogen-fueled gas turbine engines with a dedicated heat-management system, complemented by an introductory analysis of the impact of using LH2 to precool and intercool in the compression system. The propulsion installations comprise Brayton cycle-based turbofans and first assessments are made on how to use the hydrogen as a heat sink integrated into the compression system. Conceptual tubular compact heat exchanger designs are explored to either precool or intercool the compression system and preheat the fuel to improve the installed performance of the propulsion cycles. The precooler and the intercooler show up to 0.3% improved specific fuel consumption for heat exchanger effectiveness in the range 0.5–0.6, but higher effectiveness designs incur disproportionately higher pressure losses that cancel-out the benefits.

Evolutionary Design of Compact Counterflow Heat Exchanger

Evolutionary Design of Compact Counterflow Heat Exchanger

Numerical analysis of thermal performance of heat exchanger: Different plate structures and fluids

Due to compact size, high power density, low cost and short construction time, the small modular reactors are considered as one of the candidate reactors, in which the power generation system is important with a compact heat exchanger for modular construction. Therefore, the effect of plate structure and nature of the working fluid on the thermal performance of plate heat exchanger are analyzed for the design of compact and efficient heat exchanger. The heat transfer rate, temperature counters, velocity vectors, and pressure drop have been optimized and investigated using FLUENT. The Nusselt number has been calculated for the corrugated and flat plate heat exchanger to validate the convective heat transfer. The numerical results are agreed well with correlation within deviation of ~5-7%. The performance of heat exchanger can be improved by controlling the mass-flow rate, and temperature of working fluid. The corrugation plate heat ex-changer increases the heat transfer rate 20% and effectiveness 23%, respectively, as compare to flat plate heat exchanger when the working fluid is water. In the case of air, heat transfer rate, and effectiveness are about 10% and 9%, respectively. The results show that the corrugated plate heat exchanger is more effective than the flat plate heat exchanger because corrugation pattern enhances the turbulence of fluids, which further increase heat transfer rate and coefficient. The selection of the working fluid and structure of the plate must be considered carefully for efficient and compact design of heat exchanger.

Towards the Development of Generalized Correlations for the Design of Compact Heat Exchangers

This work looks at the design of finned surfaces, explores existing generalised correlations and further shows the development of new ones. The aim is to develop correlations with the following features: a) the range of validity of the Reynolds number is extended from laminar to turbulent regimes, and b) the correlations are a function of the fin geometry. In this work new generalised correlations for finned surfaces of the plain triangular type are developed and validated against experimental data and other existing generalised correlations. The new correlations are implemented in a design methodology. The results indicate that compared with experimental data, the average absolute error is 5 % for the friction and 7 % for Colburn factor. In design, the exchanger size results in smaller volumes down to 41 % compared with the use of published correlations.

Numerical analysis on heat transfer performance of oscillating flow in wavy channel

This study focuses on the unsteady characteristics of heat transfer process and its augmentation in wavy channels working in an acoustic resonator with a standing wave imposing the oscillating flow. A two-dimensional numerical model is developed after a careful verification with the published experimental results. Forty cases, involving fifteen wavy channel structures along with a comparative parallel channel working in different driving ratios, were established considering the heating and cooling process in different heat exchangers. The dynamic characteristics of temperature and velocity field, redevelopment of boundary layer, spatial and time-spatial averaged Nusselt number are presented to depict the heat transfer performance in oscillating flow. The results show that the viscous boundary layer follows a procedure of generating, expanding, separating and merging in each acoustic cycle. Thermal boundary layer keeps a longer stability after experiencing the redevelopment, during which heat transfer augmentation occurs. However, heat transportation will be inhibited when thermal boundary layer separation happens. Besides, the heat transfer enhancement capacity of wavy channel compared with parallel channel can reach to 1.10 in both hot and cold side under driving ratio of 0.83 %. The optimal dimensional height of the wavy channel normalized by thermal penetration depth is also found to be located between 2–3. At last, the heat transfer performance is correlated with the change of amplitude height of wave, Reynolds and Prandtl number considering the heating and cooling processes. This study will provide numerical heat transfer data of oscillating flow using wavy channel and help the design of compact heat exchanger in thermoacoustic system.