High-efficiency Heat Exchangers Research Articles

Numerical Simulation Study of Geothermal Energy Extraction in Medium-deep Formation

Geothermal energy is a kind of renewable energy with rich content, relatively low cost and wide distribution. China is rich in geothermal reserves and urgently needs efficient heat extraction technology. Closed cycle heat extraction technology is a new geothermal development model that is suitable for medium-deep geothermal reservoir and has high heat exchange efficiency without taking water. In this system, the circulating working fluid is pumped into the annulus from the ground, and the heat is extracted from the formation through heat conduction, and then returned to the ground through the central pipe. In this paper, the heat recovery capacity of the heat extraction system is numerically simulated. The research results show that the coaxial borehole heat exchanger technology has a good heat recovery capacity, and the designed thermal insulation structure has a positive effect on heat extraction and heating, and the heat extraction 100 days can stably produce 360 Kw of heat.

Cost of Using Laser Powder Bed Fusion to Fabricate a Molten Salt-to-Supercritial Carbon Dioxide Heat Exchanger for Concentrating Solar Power.

Advances in manufacturing technologies and materials are crucial to the commercial deployment of energy technologies. We present the case of concentrating solar power (CSP) with molten salt (MS) thermal storage, where low-cost, high-efficiency heat exchangers (HXs) are needed to achieve cost competitiveness. The materials required to tolerate the extreme operating conditions in CSP systems make it difficult or infeasible to produce them using conventional manufacturing processes. Although it is technically possible to produce HXs with adequate performance using additive manufacturing, specifically laser powder bed fusion (LPBF), here we assess whether doing so is cost-effective. We describe a process-based cost model (PBCM) to estimate the cost of fabricating a MS-to-supercritical carbon dioxide HX using LPBF. The PBCM is designed to identify modifications to designs, process choices, and manufacturing innovations that have the greatest effect on manufacturing cost. Our PBCM identified HX design and LPBF process modifications that reduced projected HX cost from $750 per kilo-Watt thermal (kW-th) ($8/cm3) to $350/kW-th ($6/cm3) using currently available LPBF technology, and down to $220/kW-th ($4/cm3) with improvements in LPBF technology that are likely to be achieved in the near term. The PBCM also informed a redesign of the HX design that reduced projected costs to $140-160/kW-th ($3/cm3).

LNG 운반선 PCHE 열교환기 내 상변화에 대한 수치해석

In this study, we studied the ice accretion that occurs in the next-generation heat exchanger, the PCHE(Printed Circuit Heat Exchanger) channel. PCHE heat exchanger is called the next-generation heat exchanger, and it has the advantage of being able to reduce the heat exchange efficiency by less than 1/10 compared to the existing heat transfer tube type method along with high heat exchange efficiency of more than 90%. Three CFD(Computational Fluid Dynamics) analysis were conducted prior to modeling and analysing PCHE heat exchanger through Ansys Fluent and Fensap-Ice. Through the established interpretation methodology, simulated heat exchange and phase changes caused by temperature differences between fluids through Hot Water and LNG(Liquified Natural Gas) flowing into the PCHE channel. First, setting the temperature of Hot Water to 10℃ to 80℃, and identified the heat exchange according to each temperature through CFD simulation. Next setting the temperature of Hot Water to 10℃, 50℃ and 90℃ and identified the ice accretion in the channel according to each temperature through CFD simulation.

Deep convolutional surrogates and freedom in thermal design

A deep learning approach is presented for heat transfer and pressure drop prediction of complex fin geometries generated using composite Bézier curves. Thermal design process includes iterative high fidelity simulation which is complex, computationally expensive, and time-consuming. With the advancement in machine learning algorithms as well as Graphics Processing Units (GPUs), parallel processing architecture of GPUs can be used to accelerate thermo-fluid simulation. In this study, Convolutional Neural Networks (CNNs) are used to predict results of Computational Fluid Dynamics (CFD) directly from topologies saved as images. A design space with a single fin as well as multiple morphable fins are studied. A comparison of Xception network and regular CNN is presented for the case with a single fin design. Results show that high accuracy in prediction is observed for single fin design particularly using Xception network. Xception network provides 98 percent accuracy in heat transfer and pressure drop prediction of the single fin design. Increasing the design freedom to multiple fins increases the error in prediction. This error, however, remains within three percent of the ground truth values which is valuable for design purpose. The presented predictive model can be used for innovative BREP-based fin design optimization in compact and high efficiency heat exchangers.

Modeling and optimization of the parameters of the heat accumulator of the combined livestock-heliogreenhouse complex

In the article, the heat exchange process in the water tank battery, which acts as a wall between the livestock building and the solar greenhouse, is studied. The division consists of parallelepiped-shaped tanks, between which the coefficients of heat transfer in charge and discharge mode are determined, taking into account the different temperatures and speeds of the air in the livestock building through the air-moving corridors. A mathematical model of the temperature regime was developed based on the balance equation of the water tank accumulator. The geometric dimensions of the water tank accumulators are optimized based on the criterion equations. A computer model was created using the COMSOL Multiphysics software tool and thermal efficiencies were determined. Based on the results of the conducted research and numerical calculations, it is based on the high heat exchange and energy efficiency when the size of the water tank accumulator is 40x60x25 cm.

Computational fluid dynamics calculations of high efficiency heat exchangers operating in laminar motion consisting of extruded plastic profiles with inserts

Computational fluid dynamics calculations of high efficiency heat exchangers operating in laminar motion consisting of extruded plastic profiles with inserts

Investigations of protracted finned double pipe heat exchanger system for waste heat recovery from diesel engine exhaust

The need for energy and material savings, as well as environmental concerns, have helped to increase the demand for high efficiency heat exchangers in the modern era. In practice, a heat exchanger or the direct ejection of the hot working fluid is used to recover the waste heat from a heat engine or thermal power plant into the environment. Waste heat of a heat engine or power plant is recovered to the environment via a heat exchanger or by direct ejection from the hot working fluid. In many situations, waste heat recovery removes or greatly reduces the necessity for additional fuel energy input to achieve this goal. The double pipe heat exchanger equipment is taken in this research, heat from engine exhaust recovers due to its superior qualities. The design characteristics of the heat pipe will be changed in order to increase overall efficiency by studying the concepts of various authors. Different design parameters for a double pipe heat exchange system as well as different working fluid-flow rates are tested with the suggested device. Additionally, ANSYS performs CFD for the proposed heat exchanger system in order for the results to support the experimental findings.

Wetting characteristics of ethane droplet – A molecular dynamics study

The wettability significantly affects condensation heat transfer of alkanes on the surface. When designing high-efficiency heat exchangers, it is necessary to grasp the wetting patterns of alkanes. Therefore, the wetting characteristics of ethane droplets on the surface are investigated based on molecular dynamics simulation. The results show that the contact angle of pure ethane droplet reduces as the surface potential energy depth parameter ε increases. The contact angle of pure ethane is larger than that of pure methane under the same ε, and the difference augments with the increasing ε. The enhanced molecular thermal motion caused by the rise in temperature produces different orientation outcomes on different VDW-functioned surfaces. The cumulative effect of molecular movement leads to a macroscopic displacement of the droplet, which makes the contact angle of pure ethane augment on hydrophobic surface, remain constant on neutral surface, and decrease on hydrophilic surface, meaning that the rise in temperature will strengthen the wetting tendency of pure ethane droplet. The addition of methane to ethane droplet acts as a “lubricant”, resulting in local molecular activation and an increase in diffusion. The contact angles of mixed droplets on hydrophobic, neutral, and hydrophilic surfaces all decrease linearly with the increasing methane concentration. And the larger the contact angle gap between methane and ethane on the same surface, the larger the decrease in the contact angle of mixed droplets. This paper investigates the wetting characteristics and corresponding mechanisms of alkane droplets from a microscopic aspect, aiming to guide the design and development of high-efficiency heat exchangers.

A Critical Review on Geometric Improvements for Heat Transfer Augmentation of Microchannels

With the application of microdevices in the building engineering, aerospace industry, electronic devices, nuclear energy, and so on, the dissipation of high heat flux has become an urgent problem to be solved. Microchannel heat sinks have become an effective means of thermal management for microdevices and enhancements for equipment due to their higher heat transfer and small scale. However, because of the increasing requirements of microdevices for thermal load and temperature control and energy savings, high efficiency heat exchangers, especially microchannels are receiving more and more attention. To further improve the performance of microchannels, optimizing the channel geometry has become a very important passive technology to effectively enhance the heat transfer of the microchannel heat sink. Therefore, in this paper, the microchannel geometry characteristics of previous studies are reviewed, classified and summarized. The review is mainly focused on microchannel geometry features and structural design to strengthen the effect of heat transfer and pressure drop. In addition, the correlation between boiling heat transfer and geometric characteristics of microchannel flow is also presented, and the future research direction of microchannel geometry design is discussed.

An analytical heat transfer model for the mid-deep U-shaped borehole heat exchanger considering groundwater seepage

Ground source heat pump systems consisting of deep boreholes and heat pumps can be used for heating buildings. It is known as an effective way to utilize geothermal resources, however, there is a problem with high development costs. Therefore, it is important to establish a precise heat transfer model to develop a high-efficiency geothermal heat exchanger to reduce the development cost of mid-deep geothermal energy. Most of the existing heat transfer models for deeply buried pipes only consider thermal conductivity and treat the geotechnical soil as a homogeneous medium, or do not consider the stratification and groundwater seepage phenomena, which make the models inaccurate. This study established an analytical heat transfer model considering geotechnical stratification and seepage developed for the U-shaped deep borehole heat exchanger (U-DBHE), and the analytical solution for temperature response is obtained. Using the developed analytical model, we plotted the trends that reveal the relationship between the thermal performance of U-DBHE and various parameters and explored the influence of seepage phenomena on heat extraction performance. The model can also serve as a reference for the development of heat transfer models for buried pipe heat exchangers with groundwater seepage. Given that the proposed analytical model is time-consuming and stable, and can be an efficient tool for U-DBHE design and optimization.

EMT2-ITA Regione Piemonte Greening Initiatives for Building Climate Resilient Field Hospital

Background/Introduction:The World Health Organization (WHO) declared climate change a defining issue in the 21st century with more intense heatwaves, higher risks of flooding and damaging storms, and a changing pattern of emerging infectious diseases. In this scenario, the response of Emergency Medical Teams (EMTs) to disasters represents a fundamental resource.Objectives:To expand EMT2-ITA-Regione Piemonte operational independence and to minimize its environmental footprint.Method/Description:A multiphasic and prospective project is planned in order to:(1) Reduce water consumption: use of a sterilizer designed with a set of high-efficiency heat exchangers enabling a substantial saving in water consumption by the vacuum pump and a significant reduction of total water usage through a recirculation system.(2) Reduce demand for diesel: photovoltaic (PV) system to integrate the current energy production system based on diesel generators.(3) Reduce paper consumption: use of sterilization management and traceability system and computerized medical record in order to be paperless.(4) Improve staff awareness and education on greening practices: educational program for the staff focused on waste segregation/management and energy and water saving both in the hospital and in the Base of Operation (BoO).Results/Outcomes:EMT2-ITA-Regione Piemonte aims to reduce energy and water consumption by 30% and to become paperless.Conclusion:Advances in greening initiatives offer to EMT2-ITA-Regione Piemonte the potential to improve its disaster medical response capabilities and to reduce its ecological footprint.

Study on the thermal storage performance of a new electric heating device with phase change materials

The heating method for reducing the viscosity of crude oil is mainly electric heating currently. In order to meet the needs of environmental protection and industrial production, a new electric heating device with phase change thermal storage is designed by combining the crude oil viscosity reduction heating method, off-peak electricity, and phase change materials. Numerical simulation research is carried out for the phase change thermal storage and release performance of the device, and the structure is optimized according to the research results. Also, the influences of different inlet flow rates and metal foams porosity on the heat release process are analyzed. The results show that the outlet temperature decreases continuously with the increase of the working medium inlet flow rate. With the addition of nickel foam, the internal temperature of PCMs becomes more uniform as the porosity of the added metal foam decreases in the range of 0.7–1.0. Using this device to reduce the viscosity of crude oil cannot only maintain high heat exchange efficiency but also reduce production costs, which provides a reference for the design and operation of crude oil viscosity reduction methods.

Analysis of Enhanced Heat Transfer Characteristics of Coaxial Borehole Heat Exchanger

Coaxial borehole heat exchangers provide a practical method for geothermal energy extraction, but heat transfer efficiency is low. In order to address this problem, three coaxial borehole heat exchangers with vortex generators, based on the enhanced heat transfer theory, are proposed in this paper. The author compared and analyzed the heat transfer performance of three coaxial borehole heat exchangers with vortex generators and those of traditional structures, which explains why the new heat exchanger’s heat transfer mechanism is enhanced. The results demonstrated that the vortex generator can enhance the fluid flow’s turbulent kinetic energy in the coaxial heat exchanger. This generator can also improve the mixing characteristics of the fluid flow and heat transfer. The resultant increase in the inlet flow velocity can decrease the friction coefficient f, increase the Nusselt number and strengthen the coaxial sleeve. As a result, the heat exchange performance of the tubular heat exchanger will also be improved. The thread vortex generator (TVG) heat exchanger outperforms the other three heat exchangers in terms of heat exchange performance, extraction temperature and heat extraction power. The results evidenced that the TVG heat exchanger is better than the smooth tube heat exchanger. The thermal performance coefficient PEC was improved by 1.1 times, and the extraction temperature and heating power were increased by 24.06% and 11.93%, respectively. A solid theoretical foundation is provided by the extracted outcomes for designing and selecting high-efficiency coaxial borehole heat exchangers suitable for geothermal energy extraction.

A Numerical Study on Heat Transfer Characteristics of a Novel Rectangular Grooved Microchannel with Al2O3/Water Nanofluids

The microchannel heat exchanger is one of the most compact and effective heat exchangers used for cooling devices in building air conditioning system, while application of nanofluids in microchannel further enhance its thermal performance due to its much higher thermal conductivity. Considering the continuous rapid increase in energy consumption in the building sector, especially in air conditioning systems, the heat transfer performance of a microchannel with nanofluids should be further enhanced to realize energy savings. This study analyzes the influence of combining nanofluid and flow disturbance structure on the heat transfer enhancement of a microchannel, which is also the noted novelty. A rectangular grooved microchannel (RGMC) is proposed, and its thermal performance using Al2O3/water nanofluids is investigated using the CFD method, with the mixture model to simulate the Al2O3/water nanofluids considering the slip velocity between the base fluid and nanoparticles. The results show that at 1.5 m/s, Nu of RGMC with 2 vol% nanofluids is 38.5% larger than that of smooth microchannel (SMC) with the same nanofluids, and 36.7% larger than that of RGMC with pure water, indicating the much better heat transfer performance of the novel designed RGMC structure. The maximum temperature for RGMC is 5 K lower than SMC with 2 vol% Al2O3/water nanofluid at inlet velocity of 1.5 m/s. Further analysis on the integrated effect between fluid flow and heat transfer shows that the synergy angle β near the center line of RGMC is much lower than that of SMC, representing that the better thermal performance is caused by the flow structured induced by the grooves. Moreover, at 1.5 m/s, βα of SMC with 2 vol% nanofluid is 89.4 Deg, which is 1.66 Deg higher than the βα value of RGMC, while at 0.25 m/s, the βα of two types of microchannel are close to each other. This indicates that the groove structure shows greater enhancement at higher inlet velocity. It is concluded that combining nanofluid and groove structure can significantly enhance heat transfer of the microchannel. The nanofluid enhances heat transfer at lower inlet velocity, while the groove structure enhances it at higher inlet velocity. This study will be helpful for the design of a high-efficiency microchannel heat exchanger that promotes building energy savings.

Thermal conductivity and pore structure analysis of alkali-activated foam cement with supercritical CO2 modified slag: Feasibility evaluation for geothermal applications

• Foam cement with AAMs modified by CO 2 can be used as energy pile filling materials. • CO 2 modified AAMs decrease dry density and increase water adsorption of foam cement. • CO 2 modified AAMs increase the thermal conductivity of foam cement. Geothermal energy is a clean and renewable energy that can be extracted by energy piles. Low density filling materials with relatively high thermal conductivity are ideal for energy pile construction, due to the low cost and high heat exchange efficiency of filling materials. In this study, three types of low density filling materials (Class G foam cement, alkali-activated foam cement, and supercritical CO 2 (ScCO 2 ) modified alkali-activated foam cement) were tested to evaluate their performances to serve as candidate filling materials for energy piles. The thermal conductivities of the three materials were measured and showed that the minimum thermal conductivity was 0.22 W·mK −1 (foam cement without slag), and the maximum thermal conductivity was 0.32 W·mK −1 (foam cement with 5 % CO 2 modified slag). By analyzing the cement hydration products and distribution of pores, adding slag improved the hydration of cement, which caused a longer foaming time and increased the porosity of samples. ScCO 2 modification of slag increased the porosity and the thermal conductivities of the samples. In summary, slag with ScCO 2 modification can promote the thermal conductivity of foam cement, which is beneficial to the application of shallow energy piles.

A Novel Step-by-Step Automated Heat Exchanger Network Retrofit Methodology Considering Different Heat Transfer Equipment

Improving the energy efficiency in heat exchanger networks (HENs) remains a significant industrial problem, specifically in energy-intensive operations. A particular method for such an objective is the modification of HENs at the equipment-use level, where structural changes take place and units within the network are moved, replaced and/or removed. This practice is usually known as retrofit. The objective of a retrofit is to maximize the heat recovery using the minimum modifications possible and minimum retrofit cost. Traditional retrofit techniques would normally consider one type of heat exchanger (based on the original network) with no additional design features (i.e., heat transfer enhancement technologies). The expansion of such alternatives is limited by practical use and availability of theoretical methods. In this context, the inclusion of high-performance heat exchangers such as plate heat exchangers (PHEs) has not been widely explored, even when their design and operational advantages are known. In this work, a new step-by-step automated HENs retrofit approach based on Pinch Analysis is proposed. The approach is possible to identify the best modification, its location within the network, and its cost simultaneously. Moreover, to increase energy savings, this work presents a strategy that seeks to utilize high efficiency heat exchangers such as plate heat exchangers for retrofit. A distinctive feature of this new method is the ability to handle different minimum approach temperatures, given the different types of exchangers, within the optimization of HENs. Three cases are studied using this methodology to quantify the potential benefits of including PHEs in HEN retrofits, via the analysis of the retrofit cost. Results are compared with a baseline consisting in the same network, where only Shell-and-Tube-Heat-Exchangers (STHXs) are used. In addition, the results demonstrate that this methodology is flexible enough to be applied in a wide range of retrofit problems.

Thermal–hydraulic characteristics and structure optimization of Z-channel printed circuit heat exchanger

Printed circuit heat exchanger (PCHE) is a compact equipment, which has the characteristic of high heat exchange efficiency. In practical application, the Z-type microchannel PCHE has shown unique advantage, and its structural parameters, such as pitch angle, pitch length, and channel diameter, have significant impact on its thermal–hydraulic characteristics. In this study, a series of PCHE models with a pitch angle of 5° to 45°, a pitch length of 12.3 mm to 24.6 mm, and a channel diameter of 1.25 mm to 2.25 mm are built by numerical method. Using a working medium of helium, we in detail analyze effects of these structural parameters of the PCHE on the related thermal–hydraulic characteristics. More importantly, to obtain the optimized structure of the PCHE, the response surface analysis of the simulation data is present. It shows that both the pitch angle and the inlet Reynolds number have greater effects on the flow and heat transfer performance of the PCHE. The quadratic polynomials of Nu and f are fitted by DesignExpert and the genetic algorithm is used for the multiobjective optimization. Three sets of optimized structures are given and also verified by the numerical simulations. The study could provide a guidance for the design and application of the PCHE in related engineering.

Shakedown and ratcheting analysis of Printed Circuit Heat Exchangers under multiple cyclic mechanical and thermal loads

Printed Circuit Heat Exchangers (PCHEs) is a kind of compact plate heat exchanger with a lot of fine channels in a solid block, called PCHE core. It can withstand high temperature and high pressure. And beyond that, it has many advantages, such as high heat exchange efficiency, low pressure drop, high compactness, good corrosion resistance, long service life and many other advantages. However, PCHEs will endure complex mechanical and thermal loads in service. Meanwhile, shakedown and ratcheting assessment, especially how to determine shakedown and ratcheting boundary for PCHEs in an efficient and accurate way, is still an intractable problem so far. This article makes deep research and analysis to shakedown and ratcheting boundary for PCHEs subjected to complex cyclic load combinations as well as the effect of channel shape and size effects based on the linear matching method (LMM). The influences of load parameters, e.g. temperature difference and pressure difference between hot and cold channels, and geometric parameters, e.g. channel radii, channel shapes, arrangement of channels, and transition radius of the local corner of the semicircular channel, were all discussed in detail. Based on these different types of influence parameters, two-dimensional shakedown and ratcheting boundaries for different kinds of PCHEs models under complex mechanical-thermal load combinations are presented in this paper. It is demonstrated that pressure differences between the hot and cold channel have significant effect, but different channel radii are not so significant. Core size and channel shape are observed to influence the shakedown and ratcheting responses significantly, however, the corner radius shows more significant effect on the shakedown boundary than the ratcheting limit boundary. The PCHE core arrangement, i.e. total number and position, is also found to influence the shakedown and ratcheting responses significantly, especially for the constant pressure loading case. Based on a series of LMM analysis results, it can be concluded that accumulative incremental plastic strain will occur at the region between the cold and the hot channel when the combination of mechanical and thermal loads exceeds the ratcheting limit, which should be under strict control. The results from current parametric studies can be an effective reference for design and optimization of the diffusion bonded PCHE channels in high temperature nuclear applications.

Analyses of True-Triaxial Hydraulic Fracturing of Granite Samples for an Enhanced Geothermal System

Abstract The fracturing behavior of enhanced geothermal system (EGS) reservoirs merits investigation under field-relevant temperature and stress conditions, in order to understand the creation of an extensive fracture network that helps achieve a high heat exchange efficiency. In this work, hydraulic fracturing tests were conducted on two 300 mm sized cubic granite samples at room (32°C) and field-relevant (250°C) temperatures under true triaxial compression conditions. The failure behavior and fracturing plane were studied using acoustic emission (AE) testing, μm-scale computed tomography (μm-CT), and scanning electronic microscopy (SEM), in addition to the monitoring and analyses of pressure-flow curve during fracturing. The results show that (1) at the macroscale, the strength of the granite sample was weakened at high (field-relevant) temperature, as shown by a decrease in the breakdown pressure and increase in closure pressure from the pressure-flow curve; (2) at the microscale, the failure pattern of grains during fracturing did not differ much at high and room temperatures for both intergranular and transgranular fractures; and (3) due to upscaling issues from the laboratory to field, however, the laboratory experiment will not directly provide some critical parameters (e.g., mud window pressure needed for fracture initiation and borehole failure avoidance) needed for an EGS field exploration.

Comprehensive Numerical Analysis on Flow and Heat Transfer Characteristics of Printed Circuit Heat Exchanger With Fins

Abstract Printed circuit heat exchanger (PCHE), as a high-efficiency and compact heat exchanger, shows a high potential in high temperature, high pressure, and some extreme environments, thus, it is widely used in nuclear power generation, refrigeration, aerospace, etc. In this paper, the flow and heat transfer characteristics of heat transfer channels with different fins were numerically analyzed, by changing helium inlet temperature and mass flowrate. The results indicate that, with the increase of helium mass flowrate, Nusselt number and pressure loss grow, while Colburn factor and Fanning friction factor drop. As helium inlet temperature rises, Nusselt number, Colburn factor, and pressure loss grow, whereas Fanning friction factor decreases. In addition, the heat transfer characteristics of the channels with different fins are higher than that of the finless channel, among which the circular finned channel has the best heat transfer performance. In spite of a slightly degraded flow performance, the comprehensive performance of the finned channels is superior to that of the finless channel, and the elliptical finned channel has the best performance, followed by airfoil finned channel and circular finned channel.