Composite Heat Exchanger Research Articles

Experimental investigations for enhancing the performance of hemispherical cavity receivers using additively manufactured heat exchangers

ABSTRACT This research explores a pioneering approach in cavity-type solar parabolic dish collector technology (SPDCT) by introducing a novel, additive-manufactured thermally conductive polymer composite heat exchanger over a modified hemispherical cavity receiver for heat recovery applications. This manuscript investigates the performance of innovative configuration of SPDC for Wardha (442001), Maharashtra State (027), INDIA, 20.75° N, 78.65° E, modifying the traditional setup by employing copper coil with different arrangements. The unique aspect of this research lies in the implementation of a hemispherical cavity receiver with preheating water arrangement by installing a thermally conductive polymer composite (TCPC) heat exchanger developed with compositions TPU/MWCNT/GNP of 93/3.5/3.5 by wt.% using an additive manufacturing technique, a strategy not previously explored in the existing literature. A computational study (steady state thermal analysis) conducted using ANSYS Student Version R2023 revealed substantial heat availability over the receiver’s top exterior, forming the basis for the experimental tests. Under different test conditions, the highest thermal efficiency improvement reached to 10.91%. This paper contributes novel ideas to the field, emphasizing the potential of additive-manufactured thermally conductive polymer heat exchangers to increase the performance of solar parabolic dish collector systems.

Liquid-solid interface polymerization: A simple approach for efficient polyamide/polyethylene thin film composite total heat exchange membranes construction

A simple liquid-solid interface polymerization (LSIP) strategy was developed to prepare high performance polyamide (PA) based thin film composite (TFC) total heat exchange membranes (THEMs) to avoid the use of organic solvents and surfactant during the inverse phase interface polymerization processes between piperazine (PIP) and 1,3,5-benzenetricarbonyl trichloride (TMC) on porous polyethylene (PE) substrates. The non-polar organic solvent in the TMC organic phase coated on the surface of the PE surfaces was completely removed beforehand by evaporation to form polar TMC solid coating on the PE surfaces and facilitate the quick spreading of lately added aqueous PIP solutions, forming dense and highly cross-linked PA separation layers with superior total heat recovery efficiency and CO2 barrier property. The effects of TMC loading level, PIP concentration, and LSIP reaction time on the structure and performance of PA/PE-TFC THEMs were systematically investigated, leading to the formation of THEMs 0.20P-0.10T-6 with ultra-low CO2 permeance of 0.9 GPU, and high sensible heat exchange efficiency of 94.3 %, water vapor flux of 2128 g m−2·24 h−1, and enthalpy exchange efficiency of 76.8 %.

Quantification of the interactions between indoor environmental conditions and human thermal comfort and susceptibility in tropical coastal environments

The indoor environment in most of the tropical coastal regions is associated with the residents’ health and well-being. However, limited studies reported on quantifying the interrelation between indoor environmental quality, thermal comfort and residents’ health risks in such climatic regions. Here, we evaluate indoor thermal comfort in coastal eastern India that falls under the ‘ Tropical Savanna’ climatic region. The perception survey was conducted to collect primary data in summer, monsoon, post-monsoon and winter across the year and the perception of warmth appeared to have a similar trend to direct and rational human thermal indices derived from a composite body heat exchange. Results indicate that indoor thermal stress significantly differed ( p < .05) between seasons and across study locations. The maximum summer and monsoon days lay in a warm to very hot zone. Additionally, most of the heat-related stress or disorders significantly differed ( p < .01) amongst different age groups of people. Finally, a principal component analysis using the human thermal indices yielded three groups of heat-related symptoms (a) physical fatigue and responses, (b) neural stressors and (c) hyperhidrosis disorder. Overall, results suggested that physical fatigue and responses arose predominantly from climate-induced thermal stress. The study recommends an effective bioclimatic design strategy following human-environment friendliness that can improve indoor thermal comfort in coastal eastern India.

Effect of polyvinylpyrrolidone and lithium chloride composite desiccant-coated heat exchangers on dehumidification studies

Cooling systems are necessities that remain energy intensive, particularly in tropical regions with elevated humidities and temperatures. Conventional vapor-compression air-conditioners are often inefficient because the sensible and latent heat loads are intrinsically coupled. To realize more energy-efficient cooling, solid desiccant-coated devices can be introduced to mitigate the latent heat load. Among such devices, desiccant-coated heat exchangers (DCHEs) are attractive for enabling nearly isothermal dehumidification. Hence, desiccants with high sorption capacity and rapid kinetics are essential. Solid polymeric desiccants are well-positioned to meet these requirements but comprehensive studies on the dehumidification performance of solid polymeric desiccant-coated heat exchangers are currently lacking. In this study, we investigated the potential of polyvinylpyrrolidone (PVP) and lithium chloride (LiCl) composites as desiccant materials at both material and system levels in terms of gravimetric water uptake. Specifically, LiCl is a hygroscopic salt bound by the moisture-sorbing PVP matrix. This work also demonstrates how the Elovich model accurately predicted the PVP-LiCl composite’s sorption kinetics. The results show that the optimum PVP-LiCl composite ratio is 66.7 wt%, with an equilibrium sorption capacity of 280 % at 75 % RH and 25 °C, compared to 29 % for silica gel under the same condition. With much superior sorption kinetics and capacity, the PVP-LiCl-coated prototype heat exchanger demonstrated a moisture removal capacity eight times higher than a silica gel-coated one under dynamic flow towards energy savings in air-conditioning systems.

Study on the Effects of Thermal Shaping for 316L Heat Exchange System of Submersible Vehicle on Fatigue Life

In this paper present the effects of 316L steel in the environment of repeated heat load, and the impact of the thermal load on fatigue life. Using thermal fatigue experiments and ABAQUS software, rain flow counting method is used to simplify the strain cycle spectrum of stress load. The Coffin-Manson nonlinear empirical equation was established based on thermal fatigue experiments, and the fatigue life estimation was completed in accordance with the Miner damage accumulation rule and FE-SAFE fatigue software. The test rods were respectively placed at room temperature and heated at 250°C for water cooling for tensile testing. Fatigue tests were performed with 5 strain parameters (0.8%, 0.7%, 0.6%, 0.5% and 0.4%). ABAQUS and FE-SAFE software used to study 316L testing rod fatigue life verification analysis. A composite heat exchange system model made of 316L was designed for the case study. It is found that the fatigue life after heating is reduced by 35% to 12% from the experimental results and numerical simulation calculation. Therefore, when the 316L steel is subjected to thermal fatigue, the fatigue life will be reduced. The research results can provide a reference for the design of heat exchangers using 316 steel in various fields.

Design and development of polymer composite heat exchanger tubes using an integrated thermal-hydraulic and material design framework

In the current study, thermal-hydraulic design of the heat exchanger and composite material design are integrated to develop polymer composite tube materials for heat exchanger applications. For preliminary analysis, the scheme utilizes basic thermal resistance equations, Kern and Bell-Delaware methods for the design of baffled shell and tube heat exchangers, and differential effective medium theory for the design of composite materials. The preliminary analysis clarifies that the thermal conductivity of tubes is a performance-limiting parameter in the case of liquid-liquid applications. The heat exchanger's design imposes that the tubes' thermal conductivity must be enhanced to ≥8.5 W/m.K for achieving heat transfer comparable to those of metal counterparts. To attain the threshold thermal conductivity, the design of polymer composites employing differential effective medium theory requires that high volume fractions (> 0.3) of high effective aspect ratio (> 10 or 0.1) thermally conductive fillers be incorporated in a polymer matrix. Finally, the samples are fabricated of polypropylene matrix and expandable graphite filler with variable volume fractions (0.1–0.4). The highest thermal conductivity of 8.3 W/m.K was achieved in a 40 vol% sample. The comparison of measured and computed thermal conductivity values shows an acceptable agreement supported by electron microscopy and thermal images.

Investigation of nano composite heat exchanger annular pipeline flow using CFD analysis for crude oil and water characteristics

This study focuses on the dual-core annular process of crude oil and water. The crude oil exhibits non-Newtonian behavior with high viscosity. The heat transmission flow in pipeline locations is complex. In this process, the cooled water passes through the annular core, experiencing turbulence effects, while the crude oil flows in a laminar manner. The influence of the non-Newtonian behavior is investigated in terms of pipe angles and deformations. In the valve, the inlet velocity flow is set at 1.75 m/s. The flow is executed in downhill orientations in high-velocity locations. The simulation results show CFD variations with a velocity of 3.5 m/s, pressure of 2.33 MPa, pressure gradients of 1.33 MPa, and Reynolds numbers of 1.38 MPa. This study is being conducted for a horizontal pipeline. The CFD solution solvers investigate the volumetric flow characteristics of the fluid as well as the temperature effects. The maximum heat energy has been reduced, resulting in unique flow directions.

Experimental study on the performance of a novel superabsorbent polymer and activated carbon composite coated heat exchangers

Desiccant coated heat exchangers have attracted great attention for their ability to handle both sensible and latent heat loads. However, widely used salt-embedded composite silica gels risk salt solution leakage. To alleviate this problem, a novel superabsorbent polymer (sodium polyacrylate) and activated carbon composite coated heat exchanger (C-DCHE) was developed and tested. Effects of air-side and water-side parameters on the performance of C-DCHE in terms of average dehumidification capacity (Davg) and thermal coefficient of performance (COPth) were investigated and compared to an activated carbon coated heat exchanger (A-DCHE). With the outdoor air of 38 °C&60% RH, Davg and COPth of C-DCHE can be up to 6.1 g kg−1 and 3.6, an improvement of 43% and 26% over A-DCHE, respectively. Besides, the performance of C-DCHE was compared with conventional and salt-embedded silica gels coated heat exchangers in recent publications. C-DCHE showed superior air supply comfort owing to a lower average outlet air humidity ratio and larger COPth under most conditions. Especially, at low regeneration temperatures of 40∼50 °C, its COPth can be 50%–220% higher. This paper provides a promising direction for salt-free composites in DCHE-based systems.

Polyethyleneimine (PEI) based thin film nanocomposite (TFN) total heat exchange membranes (THEMs) composed of shaped ZIF-8 crystalline Micro-leaves (ZIF-L)

A novel strategy was developed to build high-performance thin film composite (TFC) total heat exchange membranes (THEMs) by in situ growing ZIF-8 crystalline micro-leaves (ZIF-L) from Polyethyleneimine (PEI) coated on polysulfone (PSF) ultra-filtration substrates. It was found that flexible PEI polymeric chains could tightly cross-link and seal large masses of ZIF-L micro-leaves (ZIF/PEI wt. ratio up to 18.5) to thwart CO2 permeation, on top of PSF substrate. Such PEI cross-linking could also effectively open up the internal channels of ZIF-L micro-leaves to enhance moisture permeance and latent heat recovery without trading off CO2 gas barring property. ZIF-L in varied shapes protruded into the air stream could provide ultra-rough surfaces with increased surface area for improved total energy recovery efficiency. Optimized PEI/ZIF-L TFC THEMs showed ultra-low CO2 permeance of 0.5–8 GPU and ultra-high total heat recovery rates of 68–74%.

Measuring the maximum capacity and thermal resistances in phase-change thermal storage devices

Thermal energy storage can increase the efficiency of the electric grid by adding flexibility to thermal systems. The value of thermal storage is a function of its energy and power density, which are driven by the capacity and thermal resistances in the storage device. Measuring these properties in-situ at the device level is an important step to understanding the performance and improving the design of thermal storage systems. In this paper, we present methods to measure the total capacity and thermal resistances in heat exchangers with integrated phase change materials. These methods are demonstrated on two thermal storage devices—a 570-kWh ice-based storage tank and a 0.35-kWh graphite-tetradecane composite device. The results show how thermal resistances evolve with the state of charge and discharge rate in these devices and quantify the impact of applied pressure on the contact resistance in composite phase change material heat exchangers. The proposed method allows for easy comparison between different systems and provides information on the thermal bottlenecks limiting performance. Ultimately, these measurements will allow designers to make robust, high-performance thermal storage devices for next-generation thermal systems.

A 1D Reduced-Order Model (ROM) for a Novel Latent Thermal Energy Storage System

Phase change material (PCM)-based thermal energy storage (TES) systems are widely used for repeated intermittent heating and cooling applications. However, such systems typically face some challenges due to the low thermal conductivity and expensive encapsulation process of PCMs. The present study overcomes these challenges by proposing a lightweight, low-cost, and low thermal resistance TES system that realizes a fluid-to-PCM additively manufactured metal-polymer composite heat exchanger (HX), based on our previously developed cross-media approach. A robust and simplified, analytical-based, 1D reduced-order model (ROM) was developed to compute the TES system performance, saving computational time compared to modeling the entire TES system using PCM-related transient CFD modeling. The TES model was reduced to a segment-level model comprising a single PCM-wire cylindrical domain based on the tube-bank geometry formed by the metal fin-wires. A detailed study on the geometric behavior of the cylindrical domain and the effect of overlapped areas, where the overlapped areas represent a deviation from 1D assumption on the TES performance, was conducted. An optimum geometric range of wire-spacings and size was identified. The 1D ROM assumes 1D radial conduction inside the PCM and analytically computes latent energy stored in the single PCM-wire cylindrical domain using thermal resistance and energy conservation principles. The latent energy is then time-integrated for the entire TES, making the 1D ROM computationally efficient. The 1D ROM neglects sensible thermal capacity and is thus applicable for the low Stefan number applications in the present study. The performance parameters of the 1D ROM were then validated with a 2D axisymmetric model, typically used in the literature, using commercially available CFD tools. For validation, a parametric study of a wide range of non-dimensionalized parameters, depending on applications ranging from pulsed-power cooling to peak-load shifting for building cooling application, is included in this paper. The 1D ROM appears to correlate well with the 2D axisymmetric model to within 10%, except at some extreme ranges of a few of the non-dimensional parameters, which lead to the condition of axial conduction inside the PCM, deviating from the 1D ROM.

Compact latent heat exchanger for the fast supply of hot water with serpentine tubes in shape-stabilized composite phase change material and auxiliary electric heating

• A composite phase change material-based heat exchanger is designed. • The composite phase change material owns a large enthalpy of 252 J/g. • An electric heating film is introduced to improve the heating efficiency. To realise a fast supply of hot water, this study proposes a compact latent heat exchanger. This heat exchanger consists of a certain number of heat-exchange plates. In each plate, serpentine tubes are wrapped with an inorganic composite phase change material (CPCM), Ba(OH) 2 ·8H 2 O/modified expanded graphite (MEG). An auxiliary electric heating film is attached to the face of the entire heat exchanger to improve the heating efficiency. The parameters of the plate, such as thickness, tube pass number, thermo-physical properties of the CPCM, flow rate, auxiliary heating power size, and position are numerically evaluated to achieve the best performance of this heat exchanger. The reliability of the simulation method is verified by comparing the simulated results with the experimental data in previous study. The simulation results indicate that a plate with a thickness of 15 mm, plate tube pass number of 10, and CPCM with a Ba(OH) 2 ·8H 2 O mass fraction of 85.8 wt% is the optimal choice. Based on the optimal conditions, 196.48 kg of hot water over 40 ℃ can be produced in 875 s and the average power reaches 23 kW. Furthermore, with the addition of a heating film (3600 W), the mass of heated water can be increased by nearly 50 kg.

CONTACT THERMAL RESISTANCE BETWEEN THE FIN AND PIPE-BASE FOR COMPOSITE HEAT TRANSFER SURFACES

Experimental setup for investigation of contact thermal resistance (CTR) of composite heat-exchange tube, made of flat-oval steel tube – base and aluminum fins, which are connected to the base by means of contact welding, has been developed. By direct measurement, the СTR values for a composite heat exchanger tube are compared to the CTR values for three types of bimetallic tubes with rolled aluminium fins: carbon steel 20 base tube, stainless steel 1X18H10 base tube and brass base tube. It is established that for a composite heat-exchange tube the mean thermal resistance of contacting surfaces doesn't depend on the density of supplied heat flow and makes constant value Rk = 2,75×10–6 Km2/W, that is practically equal to zero for engineering calculations and it is possible to neglect it. For composite heat-exchange tube the application of contact welding technology makes it impossible to deteriorate thermal contact between monorail and tube due to temperature fluctuations in the process of operation of heat-exchange apparatuses. The results obtained show that the composite surface with welded aluminium monofin has two orders of magnitude lower CTR than the heat exchange surfaces made of widely used bimetallic tubes of all known types. This provides the highest heat transfer coefficient.

Numerical and Experimental Study of a Novel Additively Manufactured Metal-Polymer Composite Heat-Exchanger for Liquid Cooling Electronics

In order to meet increasing power-dissipation requirements of the electronics industry, compact, low-cost, and lightweight heat exchangers (HXs) are desired. With proper design, materials, and manufacture, polymer composite heat exchangers could meet these requirements. This paper presents a novel crossflow air-to-water, low-cost, and lightweight metal-polymer composite HX. This HX, which is entirely additively manufactured, utilizes a novel cross-media approach that provides direct heat exchange between air and liquid sides by using connecting fins. A robust numerical model was developed, which includes the dimensional effects of additive manufacturing. The study consists of a simplified 3D CFD model based on ellipsoidal-shaped staggered tube banks for the laminar range. It then uses an analytical approach to compute entire HX performance. The model is validated experimentally within 8% for thermal performance, 12% for air-side impedance, and 18% for water-side impedance. Finally, HX is compared with a conventional CPU radiator and performs within 10% of the conventional unit for reasonable flow rates and pressure-drop ranges. Moreover, HX also provides added design and cost advantages over the conventional unit, which makes the HX a potential candidate for electronic cooling applications.

A New Composite Phase Change Material for Cold and Heat Storage and Its Application

In today's society, energy consumption is growing at an alarming rate. Because of the huge economic benefits brought by traditional industries such as non renewable energy and fossil fuel power generation, people have to study them. The phase-change heat storage materials are widely used in the condensation heat storage due to their high temperature, low density and environmental protection. This paper considers the advantages, disadvantages and application scope of the new energy storage equipment based on the phase-change storage characteristics, and proves through experiments that under certain conditions, the appropriate solid-liquid ratio and the degree of substitution of different components are conducive to improving the performance of the composite storage heat exchanger. In this paper, a new composite phase change material for cold storage and heat storage is tested. The test results show that, because the carbon nanotubes added in the composite phase change material have no latent heat contribution in the whole phase change process, the phase change enthalpy of the composite phase change material will inevitably decrease with the increase of the carbon nanotube mass fraction.

Preliminary study on air-to-air latent heat exchanger fabricated using hollow fiber composite membrane for air-conditioning applications

In this study, an air-to-air type hollow fiber composite membrane latent heat exchanger was built and its latent heat exchange characteristics were experimentally investigated under various test conditions. Based on experiments conducted on four prototypes, polyethersulfone with 9 wt% of polyvinyl-pyrrolidone was selected as the membrane material suitable for the latent heat exchanger. Using the selected material, shell-and-tube structured hollow fiber membrane modules were fabricated and tested under various operating conditions. The experimental data showed that the proposed membrane modules exhibited 35.3%–82.7% latent effectiveness and moisture removal rates of 0.027–0.124 g/s under various operating conditions; furthermore, the modules could provide latent cooling with few temperature changes. In addition, the results of the parametric analysis indicated that the inlet primary air humidity ratio was a critical factor affecting the latent cooling performance of the proposed system and the optimal ratio of the secondary to primary air flow was 1.0. The number of mass transfer units (NTUm) in the membrane module design should be higher than 1.7 to attain satisfactory latent cooling performance, that is, higher than 70% latent effectiveness.

Investigation of Crystallization Fouling on Novel Polymer Composite Heat Exchanger Tubes

Metals are common construction materials for heat exchangers. However, metals may suffer from failure due to corrosion, especially in harsh environments. Innovative thermally conductive polymer composite tubes based on polypropylene or polyphenylene sulfide filled with graphite have been developed. Crystallization fouling on metal surfaces has been extensively studied. However, fouling data for polymer surfaces are very limited. In the current study, a stirred vessel test rig and a horizontal tube falling film test rig were used to compare the fouling propensity of the polymer composite tubes and common stainless steel tubes. Experiments were performed with calcium sulfate solutions and mixed salt solutions containing calcium carbonate and calcium sulfate. The induction periods and the fouling resistances over time were measured. The novel polymer composite tubes showed a lower crystallization fouling propensity compared to the stainless steel tubes. The induction period was longer and the reduction of the overall heat transfer coefficient over time was notably lower compared to the metal tubes.

Multi-factor analysis on thermal conductive property of metal-polymer composite microstructure heat exchanger

Multi-factor analysis on thermal conductive property of metal-polymer composite microstructure heat exchanger

Dehumidification Effect of Polymeric Superabsorbent SAP-LiCl Composite Desiccant-Coated Heat Exchanger with Different Cyclic Switching Time

This study investigated a composite polymer desiccant material’s performance, which is prepared by impregnating solid desiccant such as sodium polyacrylate (SAP) on to hygroscopic salts such as lithium chloride (LiCl). Dehumidification performance of the proposed composite polymer desiccant (SAP-LiCl) was analyzed by coating the suitable weight percentage (wt %) of the desiccant onto a single fin-tube heat exchanger (FTHE) system and testing the desiccant-coated heat exchanger (DCHE) in a testing tunnel under various operating conditions. Net dehumidification efficacy of DCHE in terms of sorption and desorption amount and thermal performance (COPth) were analyzed. For instance, with processed air inflow temperature, relative humidity and regeneration temperature setting of 30 °C, 80% RH and 70 °C, DCHE’s sorption, desorption amount and COPth were recorded as high as 945.1 g, 1115.1 g, and 0.39, respectively. It was further realized that the performance of the DCHE could be enhanced by modulating the cyclic switching time for dehumidification and regeneration processes. For instance, with the aforementioned processed airflow conditions, when the cyclic switching time tuned as 60 min instead of 10 min for a total time period of 120 min, there is a net 58% improvement to the COPth of the system. It was further observed that, under the same time period corresponding to the increase in cyclic switching time, the overall COPth can be enhanced; however, the water vapor sorption and desorption amounts of desiccant were decreased.

“Desigrated”-Desiccant Integrated Façade for the Hot-Humid Climate of Bangkok, Thailand

“Desigrated” presented an attempt to integrate heat prevention strategies with low-ex cooling technologies, namely the desiccant and M-cycle evaporative cooling technology, in the form of a façade system for high-rise office buildings. The project targets to provide an alternative cooling solution for the hot and humid climate context of Bangkok. The results from experiments by various researchers are used as assumptions in developing the system, which was then evaluated through numerical methods and dynamic simulations. Being one of the prominent dehumidification technologies, a composite silica gel heat exchanger (CCHE) was implemented as the primary part of the façade system, while the M-cycle technology would also be implemented as a secondary cooling technique to cool down the supply air. The evaluation shows a promising result with up to 36% energy consumption reduction in comparison with the conventional cooling system, presenting itself as a transitioning tool in order to replace refrigerant cooling.