Gas Heat Exchanger Research Articles

A turnkey gaseous helium-cooled superconducting CORC® dc power cable with integrated current leads

High-temperature superconducting (HTS) direct current (dc) power cable systems, capable of delivering power exceeding 10 MW while being cooled with cryogenic helium gas, have been developed for applications on naval electric ships, electric aircraft and in data centers. Current injection from room temperature into the superconducting power cable causes by far the greatest heat load to the cryogenic system. Efficient current leads with integrated helium gas heat exchangers were developed to inject a current exceeding 1 kA from room temperature into a superconducting Conductor on Round Core (CORC®) power cable, without the need for liquid nitrogen pre-cooling. A 2 m long single-pole CORC® power cable system that included current leads was cooled using a Stirling cryocooler with a closed-loop helium gas circulation system. The turnkey power cable system allowed cool down from room temperature to its operating temperature of 60 K–70 K within 5 h, after which continuous operation at 1.2 kA was demonstrated. The successful development and demonstration of a CORC® power cable with current leads containing integrated helium gas heat exchangers enables widespread implementation of HTS MW-class, high current density superconducting dc power cables in many applications with constrained space that require a power dense solution.

Development of a near-5-Kelvin, cryogen-free, pulse-tube refrigerator-based scanning probe microscope.

We report the design and performance of a cryogen-free, pulse-tube refrigerator (PTR)-based scanning probe microscopy (SPM) system capable of operating at a base temperature of near 5 K. We achieve this by combining a home-made interface design between the PTR cold head and the SPM head, with an automatic gas-handling system. The interface design isolates the PTR vibrations by a combination of polytetrafluoroethylene and stainless-steel bellows and by placing the SPM head on a passive vibration isolation table via two cold stages that are connected to thermal radiation shields using copper heat links. The gas-handling system regulates the helium heat-exchange gas pressures, facilitating both the cooldown to and maintenance of the base temperature. We discuss the effects of each component using measured vibration, current-noise, temperature, and pressure data. We demonstrate that our SPM system performance is comparable to known liquid-helium-based systems with the measurements of the superconducting gap spectrum of Pb, atomic-resolution scanning tunneling microscopy image and quasiparticle interference pattern of Au(111) surface, and non-contact atomic force microscopy image of NaCl(100) surface. Without the need for cryogen refills, the present SPM system enables uninterrupted low-temperature measurements.

A Review of the Geothermal Potential Hot Spots in Iraq Using Geophysics Methods

This review introduces the concept of geothermal energy and the technologies used to harvest this sustainable and clean source. Geothermal systems were explained in details in the review. They were classified into two major types, steam cycle and binary cycle. The steam cycle is always used at higher enthalpy, and a binary cycle is used at low enthalpy. The power generation methods used to produce geothermal power from geothermal resources, typically, comprises of well production, injection and steam and gas separators, heat exchangers, preheaters, turbines and condenser. The steam cycle type allows the water to evaporate and the steam will be separated from brine solution and expanded in a turbine, generally the salty water will have discarded out of system, or it is flashed again at lower system part. Power generation methods were divided into single Flash Steam Plant, Double Flash Steam Plant, and Dry Steam Plant. The components of the geothermal power plant were elucidated, namely, feed pump, heat exchanger, preheater, evaporator, turbine, and condenser. After surveying the geothermal energy worldwide briefly, the Iraqi geothermal energy was introduced. Thermal gradient in Iraqi tectonic zone was analyzed. There is a very limited available literature on Iraq geothermal. However, we were able to analyze the geothermal temperature gradient in Iraq by dividing it into two regions; the northern Iraq, and the southern Iraq. Our analysis shows that Iraq is a poor zone for geothermal with no significant hot spots all over the country. However, low temperature applications can be invested using the exhausted petroleum wells.

A thermal conductivity sensor based on mixed carbon material modification for hydrogen detection.

In order to overcome the many shortcomings of traditional hot-wire thermal conductivity sensor design, a new design method was proposed in which a graphene-composite carbon nanotube mixed carbon material was used as a thermal conductivity sensor carrier instead of nano-alumina particles. Taking advantage of the large specific surface area and high thermal conductivity of graphene, as well as the characteristics of a large number of gas transport channels modified by carbon nanotubes, a high-efficiency gas heat exchange medium is made. In order to improve the consistency of the product, electrochemical preparation of an aluminum oxide film material is used to make the chip substrate of the thermal conductivity sensor by MEMS process technology, and the heating sensitive electrode of the sensor is made by a thick film process. Experiments show that the sensor prepared by this method has high sensitivity and zero point stability and has greatly improved the detection accuracy and response time. The sensitivity of the sensor to hydrogen detection increases to 3.287 mV/1%H2, and the response time is shorter than 5.4s. The research results have good application prospects.

Analysis of printed circuit heat exchanger (PCHE) potential in exhaust waste heat recovery

Exhaust waste heat recovery technology based on power cycles requires high efficiency, low flow resistance, and a compact structure for exhaust gas heat exchangers. It is a huge challenge for traditional heat exchangers, such as double tube or shell and tube heat exchangers. A printed circuit heat exchanger (PCHE), which is a compact heat exchanger, has not been used in the heat exchange process between the exhaust gas and supercritical CO2. Focusing on this application, a novel design concept of PCHE based on a comprehensive performance index is proposed, which fully considers the differences in physical properties and working conditions between the exhaust gas side and the CO2 side. A series of experiments were carried out in a CO2-based transcritical power cycle system. The experimental test results show that the PCHE with a novel structure is stable and feasible. To further optimise the PCHE, a numerical analysis of different structures was conducted. The calculation results show that the comprehensive performance of the PCHE with an optimised structure was improved by 11.92%. This research shows that PCHE has great potential for achieving a compact design with excellent performance, especially for use in engine waste heat recovery.

Industrial waste heat recovery: A helix-weaved convection-radiation converter for heat transfer enhancement in gas heat exchanger

Waste heat from industrial hot flue gas is worth to be recovered for energy conservation. While due to the poor heat transfer performance in gas side, heat recovery coefficient of conventional heat exchanger is restricted. Herein, a novel “Convection-radiation converter” (CRC) created with helix-weaved wire, possessing large specific area (1000∼10,000 m2/m3) and randomly wire-nested structure, is proposed. Helix-weaved CRC is placed in gas side, in which heat convection between flue gas and the Heat exchange wall (HEW) is converted to coupled convection-radiation among flue gas, CRC and the HEW. Comprehensive emissivity (εcomp) of the CRC is governed by heat transmitting thickness (H) rather than the CRC porosity (φ), helix wire diameter (d) and original surface emissivity (ε0). εcomp would approach to ∼1 with H getting large enough. The relation of εcomp and H, φ, d is proposed for helix-weaved CRC design. Numerical analysis of heat transfer process with & without CRC is carried out, which indicates that the apparent heat convective coefficient can be enhanced to 4∼5 times by the coupled heat convection and radiation of CRC. The helix-weaved CRC is further applied for industrial application, and its enhancing effect on heat transfer in gas side is verified.

Thermal and acoustic performance of silencing heat exchanger for engine waste heat recovery

The integrated design of gas heat exchanger and after-treatment unit can reduce the size and weight of the engine waste heat recovery system, releasing the back pressure of exhaust gas and enhancing net benefit of the waste heat recovery system. In this study, we propose a silencing heat exchanger that integrates an exhaust heat exchanger with an impedance composite muffler in the post-treatment system, using metal foam material instead of the sound absorbing material in the impedance composite muffler. By adapting ANSYS Fluent and LMS Virtual.Lab, thermal simulation and acoustic simulation of the silencing heat exchanger were realized, and comparative analysis of the modified structure and the basic structure was carried out. The modified silencing heat exchanger was then designed and fabricated, and the thermal and acoustic performance were tested. The results show that the modified silencing heat exchanger can achieve improved heat transfer and flow performance, and more uniform temperature distribution at the hot side, simultaneously resulting in an 8.4% reduction in exhaust pressure drop. Even more, the improvement of silence effect in the middle and high frequency band is fairly obvious, and the overall transmission loss is 44.4% higher than that of the basic structure.

Experimental investigation of the thermal performance in additively manufactured mini channels

With recent advances in robustness and design predictability of additive manufacturing (AM), this production method has taken its first steps towards implementation in heavy duty industrial applications such as gas turbines and heat exchangers. Among the benefits of using AM, the most important may be the significant higher degree of freedom in design than when using conventional manufacturing methods. In order to take advantage of these new possible solutions and to consider the surface roughness that arises from AM, it is necessary to have reliable correlations for pressure losses and heat transfer. In this study, the thermal performance for additively manufactured circular channels in Inconel 939 using the Selective Laser Melting (SLM) process are experimentally investigated.

Parametric investigation and correlation development for thermal-hydraulic characteristics of honeycomb 4H-type finned tube heat exchangers

The key to the design of dusty flue gas heat exchangers is to enhance heat transfer and solve the fouling problem. In this paper, a honeycomb 4H-type finned tube heat exchanger (FTHE) was proposed. A three-dimensional numerical investigation was conducted on heat transfer and flow friction characteristics of honeycomb 4H-type FTHEs. Firstly, the flow field and temperature of H-type FTHEs with inline and honeycomb arrangements were analyze. Then, the effect of different structural parameters (oblique tube pitch, fin height, slit width, fin pitch and fin thickness) and Re number were analyzed. Finally, the predicted correlations of Nu number and Eu number of honeycomb 4H-type FTHEs were obtained based on the multiple regression method and 105 sets of numerical data. The results show that the thermal-hydraulic performance of honeycomb 4H-type FTHEs is superior to that of aligned single H-type FTHEs. Through parametric analysis, it is found that Nu number is only negatively correlated with oblique tube pitch, and Eu number is negatively correlated only with fin pitch and slit width. Besides, the average error of correlations of Nu number and Eu number is less than 3%, which provides practical guidance for efficient recovery of industrial waste heat.

Optimization Design and Analysis of Single-Stage Mixed Refrigerant Liquefaction Process

Small-scale natural gas liquefaction processes have several clear advantages, particularly in the exploitation of ‘unconventional’ natural gas (NG) from sources such as difficult-to-access and offshore gas fields. Moreover, conventional liquefaction processes have a number of disadvantages such as high energy consumption, large cooling loads required in the refrigeration cycle, and non-uniform matching of cold and hot flows in liquified natural gas (LNG) heat exchanger (HE). The main objective of this study was to optimize the most commonly used mixed refrigerant process. The liquefaction performance of the optimized process was analyzed and the influence of gas parameters on the power consumption, exergy loss, freezing mixture circulation, and cooling water load were investigated. The results show that compressor power consumption can be reduced by 29.8%, the cooling water load can be reduced by 21.3%, and the system exergy efficiency can be increased by 41% with the optimized process. Furthermore, throttling and compression of the freezing mixture were increased during the refrigeration stage. It can be concluded that reducing the feed gas temperature and increasing the feed gas pressure can reduce the total power consumption, exergy loss, freezing mixture circulation, and cooling water load, which can significantly improve liquefaction performance.

A Parametric Examination of the Factors Affecting the Performance of a Diffusion Absorption Refrigeration System

Abstract Despite being identified nearly a century ago, the diffusion absorption refrigeration (DAR) cycle has received relatively little attention. One of the strongest attractions of the DAR cycle lies in the fact that it is thermally driven and does not require high value work. This makes it a prime candidate for harnessing low-grade heat from solar collectors, or the waste heat from stationary generators, to produce cooling. However, to realize the benefits of the DAR cycle, there is a need to develop an improved understanding of how design parameters influence its performance. In this vein, this work developed a new, validated, parametric model that can be used by designers and practitioners to examine the performance of the DAR cycle for a range of operating conditions. The results showed that the cycle’s performance was particularly sensitive to several factors: the rate of heat added and the temperature of the generator, the effectiveness of the gas and solution heat exchangers, the mass flowrate of the refrigerant and the type of the working fluid. It was shown that it can deliver good performance at low generator temperatures if the refrigerant mass fraction in the strong solution is made as high as possible. Moreover, it was shown that a H2O–LiBr working pair could be useful for achieving cooling at low generator temperatures.

The influence of the charge shape on heat exchange of a recessed nozzle

The paper deals with the numerical simulation of the flow of thermally conductive viscous gaseous combustion products in the flow paths of a power plant. The influence of the shape of the mass supply surface on the gas dynamics and heat exchange near the recessed nozzle of the power plant is investigated. The coupled problem of heat exchange is solved by the method of control volumes. It is shown that the compensator geometry determines the localization of both the topological features of the flow near the recessed nozzle and the position of local maximums of the heat transfer coefficient. It has been revealed that The use of a channel with a star-shaped cross section and a triangular form of compensator rays leads to an intensification of heat exchange processes near a recessed nozzle.

Compact Diesel Engine Waste-Heat-Driven Ammonia–Water Absorption Heat Pump Modeling and Performance Maximization Strategies

Abstract An investigation of the best ways to achieve optimal performance from a waste-heat-driven ammonia–water absorption heat pump over a wide range of operating conditions is presented. Waste heat from an 8-kWe diesel engine generator is recovered using an exhaust gas heat exchanger and delivered to the desorber by a heat transfer fluid loop. The absorber and condenser are hydronically coupled in parallel to an ambient heat exchanger for heat rejection. The evaporator provides chilled water for space-conditioning with a baseline cooling capacity of 2 kW. All heat and mass exchangers employ novel microscale geometries. A detailed thermodynamics model is developed to simulate performance and develop strategies to achieve the best performance in both cooling and heating modes over a range of operating conditions. These parametric studies show that improved coefficients of performance can be achieved by adjusting the coupling fluid temperatures in the evaporator and the condenser/absorber as the ambient temperature varies. With the varying return temperatures, the system is able to provide the 2-kW design cooling capacity for a wide range of ambient temperatures.

Temperature-Modulated Pyroelectricity Measurements of a Thin Ferroelectric Crystal with In-Plane Polarization and the Thermal Analysis Based on One-Dimensional Layer Models

A temperature-modulated pyroelectricity measurement system for a small single crystal is developed and applied to standard sample measurements performed on a thin single crystal of lithium niobate. The modulation measurement is based on the AC technique, in which the temperature of the sample is periodically oscillated, and the synchronized pyroelectric signal is extracted using a lock-in amplifier. Temperature modulation is applied by irradiating periodic light on the sample placed in the heat exchange gas. To apply this technique to the transparent reference sample, a commercially available black resin is coated on the sample’s surface to absorb the light energy and transmits it to the specimen. The experimental results are analyzed using a two-layer heat transfer model to verify the effect of the light-absorbing layer as well as the radiative temperature modulation system.

Thermal and mechanical improvement of the air supply system of a turbocharged piston engine

A method of thermomechanical improvement of pulsating air flows in the intake system of a turbocharged piston engine is described. The main objective of this study is to develop a method for suppressing the rate of heat transfer to improve the reliability of a piston turbocharged engine. A brief review of the literature on improving the reliability of piston engines is given. Scientific and technical results were obtained on the basis of experimental studies on a full-scale model of a piston engine. The hot-wire anemometer method was used to obtain gas-dynamic and heatexchange characteristics of gas flows. Laboratory stands and instrumentation facilities are described in the article. The data on gas dynamics and heat exchange of stationary and pulsating air flows in gas-dynamic systems of various configurations as applied to the air supply system of a turbocharged piston engine are presented. A method of thermomechanical improvement of flows in the intake system of an engine based on a honeycomb is proposed in order to stabilize the pulsating flow and suppress the intensity of heat transfer. Data were obtained on the air flow rate and the local heat transfer coefficient both in the exhaust duct of the turbocharger compressor (i.e., without a piston engine) and in the intake system of a supercharged engine. A comparative analysis of the data has been carried out. It was found that the installation of a leveling grid in the exhaust channel of a turbocharger leads to an intensification of heat transfer by an average of 9%. It was found that the presence of a leveling grid in the intake system of a piston engine causes the suppression of heat transfer within 15% in comparison with the baseline values. It is shown that the use of a modernized intake system in a diesel engine increases its probability of failure-free operation by 0.8%. The data obtained can be extended to other types and designs of air supply systems for heat engines.

석탄화력 배연탈황설비 가스재열기용 열소자 성능 전산 평가

Gas Gas Heater (GGH) is a facility that cools the hot gas generated after combustion to the temperature appropriate to react in the absorption tower and improves the corrosion and ventilation of the duct through heat exchange of the low-temperature gas discharged again through the desulfurization process with the hot gas. The hot-temperature gas passing through the GGH causes scale build-up, such as scattered gypsum inside the thermal element, including various air pollutants, which increases the differential pressure, causing losses of fan load and power plant shutdown. Computational fluid dynamics (CFD) was used to analyze how much the MU_Profile was developed to effectively reduce the differential pressure compared to the LS_Profile currently installed in the power plant. An optimized k-e model was found by performing comparative verification with actual power plant operation data, and this model was applied to MU_Profile for analysis. In addition, as the unit was expanded, the analysis grid and analysis time were reduced by using the porous medium method. As a result, MU_Profile decreased by -28.49% (based on Sector Unit 100% NR) in the differential pressure portion than LS_Profile. In the heat exchange performance, it was confirmed that MU_Profile was -15.61% (based on Sector Unit 100% NR) than LS_Profile. In terms of heat exchange LS is better, but heat exchange in GGH is performed to eliminate the white smoke effect of the gas escaping to the stack, and it was confirmed that there was no white smoke effect in both the LS_Profile and MU_Prfile. Therefore, the newly developed MU_Profile improves GGH performance than LS_Profile.

Study on Boil-off Gas (BOG) Minimization and Recovery Strategies from Actual Baseload LNG Export Terminal: Towards Sustainable LNG Chains

Boil-off Gas (BOG) generated at the liquefied natural gas (LNG) export terminal causes negative economic and environmental impacts. Thus, the objective of this study is to develop and evaluate various handling schemes to minimize and/or recover the generated BOG from an actual baseload LNG export terminal with a capacity of 554 million standard cubic feet per day (MMSCFD) of natural gas feed. The following three main scenarios were assessed: JBOG re-liquefaction, LNG sub-cooling, and lean fuel gas (LFG) reflux. For the LNG subcooling, two sub-cases were considered; standalone subcooling before LNG storage and subcooling in the prevailing liquefaction cycle. Steady-state models for these scenarios were simulated using Aspen Plus® based on a shortcut approach to quickly evaluate the proposed scenarios and determine the promising options that should be considered for further rigorous analysis. Results indicated that the flow of attainable excess LNG is 0.07, 0.03, and 0.022 million metric tons per annum (MTA) for the standalone LNG sub-cooling, LNG sub-cooling in the main cryogenic heat exchanger (MCHE), and both LFG-refluxing and jetty boil-off gas (JBOG) liquefaction, respectively. This in turn results in a profit of 24.58, 12.24, 8.14, and 7.63 million $/year for the LNG price of 7$ per Metric Million British Thermal Unit (MMBtu) of LNG.

Mechanisms and strategies for ash deposition reduction in flue gas heat exchanger

Mechanisms and strategies for ash deposition reduction in flue gas heat exchanger

Heat Exchanger Assisted Exhaust Heat Recovery with Thermoelectric Generator in Heavy Vehicles

The automobile industry is in a constant pursuit to improve the fuel economy of vehicles. The internal combustion engine is inefficient due to its inherent irreversibility. Around 30% of the combustion energy is lost in the form of heat with the exhaust gasses. If this lost energy is recovered and utilized, then it will improve the overall fuel economy of the vehicle. Herein, a waste heat recovery concept is presented to recover heat from exhaust gasses in a heavy commercial vehicle. Two exhaust gas heat exchangers are conceptualized and their performances are compared. A novel idea of immersing thermoelectric modules in coolant is proposed instead of using a separate cooling block or channel. The thermal performance is evaluated considering transformer oil as coolant instead of commonly used engine coolant. The performance of two heat exchangers one having a parallel flat plate fin core and the other having a pin fin core configuration is investigated. The effect of coolant volume flow rate and exhaust gas mass flow rate also is analyzed.

On-site experimental study on fouling and heat transfer characteristics of flue gas heat exchanger for waste heat recovery

A large number of fly ash particles in flue gas easily cause the fouling problem of heat exchangers, which seriously affects the efficient utilization of flue gas waste heat. In this study, experimental and numerical investigations on fouling and heat transfer characteristics in cross flow heat exchangers were carried out. The on-site experimental system was established, and the heat transfer coefficients for different heat-transfer surfaces at the fouling state were monitored in real time. The weakened degree of heat transfer coefficient and fouling thermal resistance are adopted to assess the effect of fouling on the heat transfer performance and compare the practicality of four different heat-transfer surfaces under dusty conditions. Numerical investigation was performed with the fouling model established in previous work to model the thermal-hydraulic and fouling processes. Numerical results are compared with experimental measurements and a good agreement is achieved. Results showed that compared with the aligned circular tube bundle, using H-type fins or honeycomb tube bundle both improve the anti-fouling performance, especially for the honeycomb H-type finned tube bundle, which has the lowest fouling thermal resistance. Therefore, due to the characteristics of easily soot-blowing and lower fouling thermal resistance, honeycomb heat exchangers are suitable for waste heat utilization of dusty flue gas.