Heat Exchanger Volume Research Articles

Numerical modeling and experimental validation of air-side forced convection on a Wire-on-tube condenser for a domestic refrigerator

In this study, the effects of various parameters on the air-side performance of a condenser used in a domestic refrigerator were investigated numerically and experimentally. A new condenser design with streamlined eye and kammtail tube shapes was studied to delay flow separation. The kammtail form was utilized in a wire-and-tube heat exchanger for the first time in this work instead of traditional round or elliptical geometry. Different design parameters were studied for the outer tube height (3, 3.5, 4, 4.5, and 5 mm), aspect ratio of the tube (1.5, 2, and 2.5), tube pitch (20 and 15 mm), tube arrangement (inline and staggered), and tube shapes (eye, kammtail, and ellipse forms) to improve the air-side performance. The model was validated using experimental data based on a performance test setup and wind tunnel measurements conducted at different air velocities. The impact of tube shape and tube dimensions on the convection coefficient and pressure drop were found to be dominant due to delayed flow separation and reduction in the recirculation area. The results showed that, for a similar heat-transfer rate, the total tube surface area was reduced by 7%, the convection coefficient was increased by 9.4%, and the static pressure drop was decreased by 27% with the new Kamm tail-form design of 3 × 6 mm compared to the respective values of the original condenser. In addition, for a similar air-side performance, decreasing the tube pitch from 20 to 15 mm resulted in subsequent decreases of up to 30% in the heat exchanger volume. When the tube arrangement was changed from inline to staggered, the convective coefficient increased by 23% and the pressure decreased by 14%. The numerical results were in good agreement with the experimental results, showing errors of less than 10% for air pressure drop and less than 9% for heat-transfer capacity.

Multi-Objective Finned-Tube Heat Exchanger Optimization Using a Genetic Algorithm

Heat exchangers are a significant component in many industries, particularly in energy conversion systems. The design of heat exchangers itself is a complex process because it involves experience-based decisions, numerous variables and parameters, and some of them are competing with each other. Genetic Algorithms (GAs) are one of the first evolutionary algorithms which remains one of the most extensively used non-linear optimization methods today. This study explores the implementation of Non-Dominated Sorting Genetic Algorithm II (NSGA-II) for thermal design and optimization of a finned-tube heat exchanger. The chosen objective functions were minimizing the heat exchanger volume and minimizing the air side pressure drop. The decision variables for the design were tube outer diameter, number of tube rows, fin pitch, unit height, and unit width. The calculated parameters and estimated cost of both preliminary design and optimized design were also compared. The optimized design offered a bigger alternative design while meeting all the constraints according to standards and industrial needs. The optimization reduced annualized operational and maintenance costs by 228% and lowered air pressure drop by 413% with bigger heat exchanger volume of 12% compared to the preliminary design.

High-purity CO2 recovery following two-stage temperature swing adsorption using an internally heated and cooled adsorber

The availability of relevant and efficient technologies to capture, store, and use carbon dioxide (CO2) is critical to reduce CO2 concentrations in the atmosphere and reach net-zero CO2 emissions. In this study, we captured CO2 by combining an adsorbent-packed heat exchanger with an internal heating and cooling process of thermal swing adsorption. A two-stage process was used to achieve CO2 purity greater than 90 % in the simulated flue gas because the single-stage process could only concentrate CO2 to ∼ 50 % purity. The results revealed that the volume of the second-stage adsorption heat exchanger is approximately-one-third of the first-stage adsorber because the CO2 concentration of the second-stage feed gas increases in the first stage, thereby leading to an increase in the adsorption capacity of the second stage. Maximum CO2 purity of 95 % was achieved using the rate of purge air flow and regeneration time in the second-stage regeneration process as operating parameters. The overall CO2 recovery ratio was ∼ 60 %. The results of the study indicate the need to enhance the recovery ratio for improved performance.

Calculation and Analysis of Heat Transfer Characteristics of Internal Threaded Tube at High Reynolds Number

In the actual operation of a heat storage steam boiler heat exchanger, an internal threaded tube is used as a heat exchange element. Usually, the heat exchanger volume is large and there are many consumables because of the complex composition of flue gas in the pipe so the internal threaded tube in the actual long operation process will suffer from ash accumulation and serious wear phenomenon. In this paper, the heat transfer process of internally threaded tubes is taken as the main research object, and the convection-enhanced heat transfer of internally threaded tubes at a high Reynolds number is deeply studied. For gas under the condition of high Reynolds number, the strengthening of turbulent flow inside of inner grooved tubes convective heat transfer process of deduction and analysis is derived. A fluid calculation model which is more in line with the heat transfer mechanism of threaded pipe is proposed, which provides a reference for the subsequent theoretical studies of heat transfer enhancement of threaded pipe.

How Electrochemical Impedance Spectroscopy Helps Drive Innovation in Fully Hydrocarbon, Reinforced Polymer Electrolyte Membranes

The realm of hydrocarbon-based polymer electrolyte membranes (PEMs) has undergone substantial changes over the past decade. A new era has emerged, based upon strong, fundamental R&D emphasizing both improved performance across a wider range of operating conditions, and greater combined chemical-mechanical stability, when integrated into a state-of-the-art fuel cell. The groundwork has been laid for commercialization of highly promising, fluorine-free technologies which simultaneously outperform previous generation materials, and address weaknesses historically attributed to all hydrocarbon-based membranes. Hydrocarbons address critical issues with perfluorinated sulfonic acid (PFSA) materials. Reduced gas crossover allows longer component lifetimes, operational window for system pressures, and reduced hydrogen venting. Higher temperature tolerances allow system operation or excursions to ≥ 100 °C, which affords a myriad of potential benefits such as reduction in heat exchanger volume, improved system water management, and increased catalyst activity due to mitigated activation losses. Furthermore, higher operating temperatures go hand-in-hand with greater pollution tolerance, and hence reduced hydrogen purity requirements.The award-winning hydrocarbon-based PEM, Pemion®, produced by Ionomr Innovations, is nested at the center of these exciting developments. Mechanically reinforced composite membranes are produced at scale utilizing advanced roll-to-roll manufacturing techniques, affording a hydrocarbon-based PEM that, for the first time, exhibits performance parallel to or greater than incumbent perfluorinated sulfonic acid (PFSA)-based PEMs. These developments, however, would not be possible without powerful characterization methods such as electrochemical impedance spectroscopy (EIS). Assessments of a membrane’s in-plane and through-plane proton conductivity are used to derive valuable insight to its constituents, the ion-conducting ionomer and chemically-inert mechanical reinforcement, as well as their interrelation. The anisotropic nature of the composite membranes is probed via comparison of in-plane and through-plane conductivity. The sensitivity of through-plane conductivity measurements to experimental parameters such as cell pressure are probed, and a new cell design is realized to reduce measurement error. These data help identify favorable and unfavorable material processing and manufacturing techniques, and their implications to in-situ fuel cell performance. The net consequence of these findings is establishing EIS as a core component of an iterative material design and production process for output of consistent, high-performance PEMs.

Multiobjective geometry optimization of microchannel heat exchanger using real-coded genetic algorithm

• A weight-based, real-coded genetic algorithm optimization was performed. • Air-side Nusselt number, friction factor, and fin efficiency were modeled. • The fin pitch imposed the most significant effect on the volume and the fan power. • The microchannel heat exchanger became more compact at higher target heat duties. • The optimization approach provides optimal solutions at given design dimensions. In this paper, a multiobjective optimization of the structure of a flat-tubed microchannel heat exchanger is performed to reduce its volume and fan power at a specified capacity. Design variables include tube height, tube width, tube length, fin height, and fin pitch. A weight-based, real-coded genetic algorithm is implemented to optimize the design variables within their specified range of dimensions. To further improve the numerical simulations of the microchannel heat exchanger performance, correlations for the air-side Nusselt number, friction factor, and fin efficiency are developed and validated. In the optimization, the Pareto optimal fronts are obtained by varying weights of the two conflicting objectives. A reference microchannel heat exchanger operating at different capacities is optimized. Results show that the volume and fan power of the reference microchannel heat exchanger can be reduced by up to 45% and 51% respectively, depending on the weighting factor selected. The optimization approach of this study provides the optimal solutions at the given domain of geometric parameter dimensions.

High efficiency 3-D printed microchannel polymer heat exchangers for air conditioning applications

The design, fabrication, and experimental characterization of a counterflow Micro-pin array Polymer Heat eXchanger (MPHX) for HVAC applications is described. The design consists of water flow through microscale pin array plates, and airflow paths in a counterflow direction through adjacent rectangular channels. When compared to a Finned Tube Heat eXchanger (FTHX), the water plates take the place of fins and the crossflow tube bank is eliminated. The MPHX is fabricated by 3 D printing using a digital light synthesis method. A correlation-based model is developed and used to explore the parametric space to arrive at a baseline MPHX core geometry. Mechanical and fluidic simulations are performed on the baseline geometry to further develop the design. A sub-scale MPHX with a nominal cross duct area of 10.1 cm × 20.3 cm is designed and fabricated. Its thermal performance over a range of air and water flow rates corresponding to heat capacity rate ratios in the range of 0.25–1 is investigated. Results show that the effectiveness varies from 0.65 to 0.95 corresponding to a of 1 to 0.25. The experimental data are used to validate a correlation-based thermo-fluidic model of the MPHX. The validated model is further used to compare the performance advantages of the MPHX design over a FTHX. For a given heat exchanger volume and thermo-fluidic conditions, the MPHX transfers 55% more thermal energy when compared to a FTHX at comparable air-side pressure drops.

Numerical study on the naturally captured air volume of outside cabin heat exchanger for wind power generation

In this paper, the outside cabin heat exchanger based on the porous media approach was established. The effects of altitude, viscous resistance coefficient, inertial resistance coefficient, and core thickness on the naturally captured air volume of the heat exchanger were investigated by numerical simulation. Results showed that the naturally captured air volume of the heat exchanger tends to be larger on both sides and smaller in the middle, and there is a quasi-linear increase proportional to the incoming wind velocity. With the increment of altitude, viscous resistance coefficient, and inertial resistance coefficient, the average naturally captured air volume of the heat exchangers shows a downward trend. The trend would be clear with the increment of the incoming wind velocity, nevertheless, the effect of core thickness is weak. In addition, the design values of the viscous resistance coefficient and the inertial resistance coefficient should be restricted in the order of 106 and below 500, respectively. Based on the weak effect of the naturally captured air volume of the heat exchanger, the thickness of the core can be appropriately increased to ensure the heat transfer area of the heat exchanger.

Design and assessment of a molten chloride fast reactor

In recent years a resurgence of interest in flowing fuel Molten Chloride salt Fast Reactors (MCFRs) has been observed. However, no such reactors have been constructed. There are few core designs available in the open literature, and typical nuclear safety assessment tools are felt to be inadequate for MCFR concepts. Upon reviewing MCFR designs several issues are revealed. For instance, there is a lack of consistent thermophysical properties utilized in proposed core designs. Spherical cores are typically considered, which opens up the possibility of recirculation zones containing fuel salt. There has been minimal consideration for core component lifetimes and how to keep the reflector cool during operation. As part of an effort to consider transients in a MCFR, a preliminary reactor design is developed. In this newly developed design, the core has constrained inlet and outlet flow paths and a replaceable reflector. The design is developed using the fast reactor codes DIF3D, PERSENT, GAMSOR, and MC2-3. Additionally, a heat exchanger sizing study is conducted for this system. The design developed reveals significant engineering challenges such as a large core and heat exchanger volume, inner reflector lifetimes on the order of five years, a lack of verified thermophysical properties, and an operational temperature range above that of any nuclear qualified materials.

Investigation of effect of heat exchanger size on power output in low-temperature difference Stirling engines

The Stirling engine is capable of converting any source of thermal energy into kinetic energy, which makes it an attractive option for utilizing low-temperature sources such as geothermal or waste heat below 100 °C. However, at these low temperatures, the effects of losses are proportionally higher due to the lower thermal potential available. One such significant loss is excess dead volume, wherein a significant contributor is the heat exchangers. The heat exchangers must be selected to optimize power output by minimizing the dead volume loss while maximizing the heat transfer to and from the engine. To better understand what the optimal geometry of the heat exchanger components is, a Stirling engine is modelled using a third-order commercial modelling software (Sage) and trends of engine properties of power, temperature, and pressure for different heat exchanger geometries are observed. The results indicate that there is an optimum heat exchanger volume and geometry for low temperature Stirling engines. This optimum is also affected by other engine properties, such as regenerator size and engine speed. These results provide insight into the optimal geometry of these components for low-temperature Stirling engines, as well as providing design guidance for future engines to be built.

The Sizing of Plate-Fin Exchangers to Fixed Dimensions Within a Volume Design Region

This paper shows the development of a design approach for plate and fin heat exchangers to meet fixed dimensions. This approach adopts the concept of volume design region that establishes the limits within which the physical dimensions (length, width and height) of a specific design problem can be set. The design region is determined by minimum and maximum dimensions. The heat exchanger volume is dictated by the problem specifications and the type of secondary surface used on each of the fluids. High density surfaces tend to produce small volumes, while the opposite applies to low density surfaces. In principle, if the heat transfer and friction factor correlations for secondary surfaces are expressed as a function of the geometrical parameters that define the fin density, then it possible to fix the surface density boundaries that give the smallest and largest exchanger volume. The design methodology presented in this work enables to include exchanger dimensions as a design objective along with the heat load and the pressure drop. To achieve these objectives, surface design is a central strategy. In this work, triangular, louvered, rectangular and offset surfaces are used to demonstrate the methodology.

Differential mass evacuation sampling technique for measuring refrigerant charge and oil retention of round tube plate fin heat exchangers (ASHRAE RP-1785)

Equipment reliability, efficiency, charge migration, and refrigerant charge optimization of refrigeration systems has been widely emphasized as critical development focus. Numerous modeling tools are utilized to predict charge of oil and refrigerant in refrigeration systems during system design. However, there is a lack of experimental validation data to confirm the accuracy of these models. The sampling technique presented in this paper allows the separate measurement of refrigerant and oil charge. An accompanying heat exchanger volume measurement technique was utilized to estimate heat exchanger volume and required measurement accuracy. The high accuracy, simple, and comparatively fast measurement technique enables collection of high-fidelity experimental data efficiently, to be used to validate charge models. Key components which are crucial to implement the technique include a removable heat exchanger charge test module and a modular duct assembly. A test plan using a Box-Behnken design of experiments was developed that maximizes test effort effectiveness by minimizing the number of tests required for thorough model validation.

Enhanced cooling in compact helical tube cross-flow heat exchanger through higher area density and flow tortuosity

A novel configuration of compact cross-flow helical tube (CFHT) heat exchanger for cooling applications is proposed, in view of its inherent high surface area density and tortuous flow path. The cooling potential of such a configuration is assessed against that of its straight tube counterpart i.e., cross-flow straight tube (CFST) heat exchanger for similar volumetric air flow rates under laminar regime. Cross-flow experiments are conducted on CFST and CFHT unit systems for different helix angles ranging from 46∘ ≤ φ ≤ 72∘. CFHT exhibits superior cooling potential, with a manifold increase in heat extracted per unit volume of heat exchanger, as high as 1.5-3.3 times, and heat exchanger efficiency as high as 70% (for φ=72∘). The comparative assessment is extended to an array of (3 × 3) tubes in an inline arrangement, through CFD analysis, for a wider range of helix angles from 17∘ ≤ φ ≤ 72∘. Analysis reveals (i) flow intensification reflected in ~2.3 times increase in Re and (ii) 3D flow that eliminates dead zones otherwise observed behind the straight tubes. The flow features result in 1.4-2.5 times increase in Nu, 2-4 times increase in the rate of heat extracted and higher heat exchanger efficiency upto 90%. Thereby, the efficacy of CFHT heat exchanger in cooling applications is established.

Experimental Evaluation of the Heat Output/Input and Coefficient of Performance Characteristics of a Chemical Heat Pump in the Periodic Operation of CaCl<sub>2</sub> Hydration

We herein evaluate the use of a chemical heat pump (CHP) for upgrading waste heat. CaCl2 was used in the system of CHP. We evaluated the heat storage and heat releasing of CHP, and confirmed the practicality from the experimental results. The reactor module employed was an aluminum plate-tube heat exchanger with corrugated fins, and the CaCl2 powder was in the form of a packed bed. Heat storage operation and heat dissipation operation are performed at the same time and supplied to the heat demand destination. At this time, an environmental heat source can be used during the heat radiation operation, and the heat output can release more heat than the heat input during heat storage. The heat discharging and charging characteristics of the reactor module were evaluated experimentally. The coefficient of performance (COP) was calculated for the heat upgrading cycle, and the heat output in the system was determined. A COP of 1.42 and output of 650 W/L, based on the heat exchanger volume, were obtained using a 600 s change time for the heat pump.

Thermal Conductivity of Superfluid ^3He-B in a Tubular Channel Down to 0.1T_mathrm{c} at the ^{4}He Crystallization Pressure

We studied the thermal conductivity of superfluid ^{3}He in a 2.5-mm effective diameter and 0.15-m-long channel connecting the two volumes of our experimental assembly. The main volume contained pure solid ^{4}He, pure liquid ^{3}He and saturated liquid ^{3}He–^{4}He mixture at varying proportions, while the separate heat-exchanger volume housed sinter and was filled by liquid ^{3}He. The system was cooled externally by a copper nuclear demagnetization stage, and, as an option, internally by the adiabatic melting of solid ^{4}He in the main volume. The counterflow effect of superfluid just below the transition temperature T_mathrm{c} resulted in the highest observed conductivity about five times larger than that of the normal fluid at the T_mathrm{c}. Once the hydrodynamic contribution had practically vanished below 0.5T_mathrm{c}, we first observed almost constant conductivity nearly equal to the normal fluid value at the T_mathrm{c}. Finally, below about 0.3T_mathrm{c}, the conductivity rapidly falls off toward lower temperatures.

Combined neural networks and predictive control for heat exchanger networks operation

Optimal operation of integrated heat exchangers is a challenging task in the field of process control due to system nonlinearities, disturbances and adequate model identification. This paper describes the design of an advanced neural network predictive control (NNPC) applied to a heat exchanger network. A case study with two hot and one cold streams, through three counter-current heat exchangers is used to test the proposed strategy. A lumped dynamic model is built based on the concept of multi-cells topology (mixed tanks), where the hot and cold cells are connected by a wall element throughout the heat exchanger length. Each cell is assumed perfectly mixed and all physical properties are constant. A distributed behavior is achieved by increasing the number of cells. The main assumptions of the lumped model are constant temperature in each cell, heat exchanger volume and area equally distributed between cells and negligible heat loss to the environment. The predictive controller relies on a neural-based model of the plant that is used to identify the system and to predict future performance over a predefined horizon. Results were compared to a traditional controller, and the control performance was improved when compared to the Ziegler-Nichols tuning method.

Multi-objective optimization of plate fin heat exchanger using constructal theory

In this paper a plate fin heat exchanger (PFHE) with constructal configuration is modeled and optimized and the results are compared with a conventional configuration. Effectiveness as well as the total annual cost (TAC) are considered as two objective functions and 12 design parameters related to the fin and size of PFHE are selected in constructal case (it is 6 in conventional case). Multi objective optimization is performed in each case using Particle Swarm Optimization algorithm. Constructal PFHE is a thermo-economically optimum for the effectiveness higher than 0.747 while conventional PFHE is thermo-economically optimum for the effectiveness lower than 0.747. In addition, the higher values of fin parameters and lower values of PFHE size are required in the constructal compared with conventional PFHE for a specific effectiveness. Moreover, the higher values of the fin sizing parameters are selected in the second part compared with first part of constructal PFHE. Furthermore, the higher values of PFHE sizing parameters are selected in the second part compared with first part of constructal PFHE. Finally, optimum results show that the higher heat exchanger volume is required in the second part than the first part of the constructal PFHE.

Numerical Investigation for Strengthening Heat Transfer Mechanism of the Tube-Row Heat Exchanger in a Compact Thermoelectric Generator

According to the basic principle of heat transfer enhancement, a 1-kW compact thermoelectric generator (TEG) is proposed that is suitable for use at high temperatures and high flow speeds. The associated heat exchanger has a tube-row structure with a guide-plate to control the thermal current. The heat exchanger has a volume of 7 L, and the TEG has a mass of 8 kg (excluding the thermoelectric modules (TEMs)). In this paper, the heat transfer process of the tube-row exchanger is modeled and analyzed numerically; and the influences of its structure on the heat transfer and temperature status of the TEMs are investigated. The results show that use of the thin - wall pipes and increase of surface roughness inside the pipes are effective ways to improve the heat transfer efficiency, obtain the rated surface temperature, and make the TEG compact and lightweight. Furthermore, under the same conditions, the calculated results are compared with the data of a fin heat exchanger. The comparison results show that the volume and mass of the tube-row heat exchanger are 19% and 33% lower than those of the fin type unit, and that the pressure drop is reduced by 16%. In addition, the average temperature in the tube-row heat exchanger is increased by 15°C and the average temperature difference is increased by 19°C; the tube-row TEG has a more compact volume and better temperature characteristics.

Accelerated melting of PCM in energy storage systems via novel configuration of fins in the triplex-tube heat exchanger

Thermal energy storage with Phase Change Materials (PCMs) can be used to fill the gap between energy supply and demand. The main reason preventing their widespread application is the low thermal conductivity of PCMs which makes the systems to have slow energy storage and recovery rates. This study achieved better PCM melting rate with novel fin configuration in triplex-tube storage compared to the use of nanoparticles. This will eliminate problems such as associated viscosity increases and sedimentation. Since heat transfer at different parts of the unit is not the same, a variety of fin arrangements were investigated with numerical analyses of the PCM melting in the triplex-tube. Significant increases in the rate of PCM melting were achieved using special arrangements of fins. Results show that using long fins at the lower half of the storage unit where conduction dominates resulted in accelerated melting. It was further found that using fewer and relatively shorter fins at the upper half of the unit results in better performance. Using this arrangement in the storage unit containing pure PCM achieved significantly faster melting rate compared to the use of fin-nanoparticles combination or nano-enhanced PCM in the same volume of the triplex-tube heat exchanger.

Optimal design of microtube recuperators for an indirect supercritical carbon dioxide recompression closed Brayton cycle

This paper presents a baseline design and optimization approach developed in Aspen Custom Modeler (ACM) for microtube shell-and-tube exchangers (MSTEs) used for high- and low-temperature recuperation in a 10 MWe indirect supercritical carbon dioxide (sCO2) recompression closed Brayton cycle (RCBC). The MSTE-type recuperators are designed using one-dimensional models with thermal-hydraulic correlations appropriate for sCO2 and properties models that capture considerable nonlinear changes in CO2 properties near the critical and pseudo-critical points. Using the successive quadratic programming (SQP) algorithm in ACM, optimal recuperator designs are obtained for either custom or industry-standard microtubes considering constraints based on current advanced manufacturing techniques. The three decision variables are the number of tubes, tube pitch-to-diameter ratio, and tube diameter. Five different objective functions based on different key design measures are considered: minimization of total heat transfer area, heat exchanger volume, metal weight, thermal residence time, and maximization of compactness. Sensitivities studies indicate the constraint on the maximum number of tubes per shell does affect the number of parallel heat exchanger trains but not the tube selection, total number of tubes, tube length and other key design measures in the final optimal design when considering industry-standard tubes. In this study, the optimally designed high- and low-temperature recuperators have 47,000 3/32 in. tubes and 63,000 1/16 in. tubes, respectively. In addition, sensitivities to the design temperature approach and maximum allowable pressure drop are studied, since these specifications significantly impact the optimal design of the recuperators as well as the thermal efficiency and the economic performance of the entire sCO2 Brayton cycle.