Heat Exchanger Module Research Articles

Aerothermal characterization of elementary structures of compact heat exchanger modules by additive manufacturing

Aerothermal characterization of elementary structures of compact heat exchanger modules by additive manufacturing

Aerothermal characterization of elementary structures of compact heat exchanger modules by additive manufacturing

Aerothermal characterization of elementary structures of compact heat exchanger modules by additive manufacturing

Air-to-Air Heat and Moisture Recovery in a Plate-Frame Exchanger Using Composite and Asymmetric Membranes.

The present work studied an air-to-air exchanger comprising a flat plate module with a diagonal channel and a counterflow configuration for the air streams. The objective of this study was to remove moisture and sensible heat from an exhaust air stream by indirect contact with another air stream. The temperature and flow rate of the exhaust air was in the range of 40–80 °C and 1–5 L·min−1, respectively, and the fresh ambient air to exhaust air flow ratio was 1–5. An asymmetric porous membrane (P-MEM), a thin film composite membrane (C-MEM), and a kraft paper were used as the core for the heat exchange module. The most influential parameter was the humid air temperature, with a direct positive effect (50–60%) due to the increase in the kinetic energy of the water molecules. The other effective parameter was the flow rate of the humid gas with a reverse effect on the enthalpy exchanger performance (25–37%). The ratio of “fresh” air to “exhaust” air had the lowest positive effect (8–10%) on the total effectiveness. The sensible effectiveness of different membranes under the studied conditions was relatively the same, showing their similar heat conductivity. However, the kraft paper showed the best performance compared to the synthetic membranes due to having a porous/hydrophile texture. P-MEM with an asymmetric porous texture showed the closest performance to kraft paper. Furthermore, it was found that under limited conditions, such as higher temperatures (70 and 80 °C) and flow rates (5 L·min−1) for the humid air, the performance of P-MEM was a little better than the kraft paper. However, C-MEM with the lowest total effectiveness and overall heat transfer coefficient (150–210 W·m−2·K−1) showed that the hydrophile PEBAX layer could not contribute to moisture recovery due to its high thickness.

A Process Intensification synthesis framework for the design of dividing wall column systems

In this work, we present a process intensification synthesis approach for the design of dividing wall columns based on the Generalized Modular Representation Framework. A superstructure-based representation is developed to represent chemical process alternatives leveraging modular phenomenological building blocks (i.e., pure heat exchange module, mass/heat exchange module). Novel process structures, including but not limited to dividing wall columns, can be systematically generated to enhance process cost and/or energy performance without pre-postulation of equipment design. To describe the possible liquid-vapor and liquid-liquid phase behaviors of the multi-component mixture, rigorous physical property calculations (e.g., UNIQUAC) are explicitly incorporated. The synthesis model is formulated as a single mixed-integer nonlinear optimization problem. The applicability and versatility of the proposed framework is showcased via an industrial case study on methyl methacrylate purification by Dow Global Technologies. Two new dividing wall column designs are obtained, both of which can achieve equipment size reduction and substantial energy savings compared to the original patent design.

3 kW Thermoelectric Generator for Natural Gas-Powered Heavy-Duty Vehicles—Holistic Development, Optimization and Validation

Emissions from heavy-duty vehicles need to be reduced to decrease their impact on the climate and to meet future regulatory requirements. The use of a cost-optimized thermoelectric generator based on total cost of ownership is proposed for this vehicle class with natural gas engines. A holistic model environment is presented that includes all vehicle interactions. Simultaneous optimization of the heat exchanger and thermoelectric modules is required to enable high system efficiency. A generator design combining high electrical power (peak power of about 3000 W) with low negative effects was selected as a result. Numerical CFD and segmented high-temperature thermoelectric modules are used. For the first time, the possibility of an economical use of the system in the amortization period of significantly less than 2 years is available, with a fuel reduction in a conventional vehicle topology of already up to 2.8%. A significant improvement in technology maturity was achieved, and the power density of the system was significantly improved to 298 W/kg and 568 W/dm3 compared to the state of the art. A functional model successfully validated the simulation results with an average deviation of less than 6%. An electrical output power of up to 2700 W was measured.

Performance Assessment of Using Thermoelectric Generators for Waste Heat Recovery from Vapor Compression Refrigeration Systems

This article reports on an experimental analysis and performance assessment of using thermoelectric generators (TEGs) for waste heat recovery from residential vapor compression refrigeration systems. The analysis shows that there is a good opportunity for waste heat recovery using TEGs by de-superheating refrigerant after the compressor. Design and manufacturing of a de-superheater unit consisting of a tube and plate heat exchanger and thermoelectric generator modules (HE-TEGs) have been performed and integrated in an experimental test rig of R134a refrigeration cycle. Experimental assessment of the performance parameters, as compared to the basic refrigeration system, reveals that the overall coefficient of performance (COP) using HE-TEGs desuperheater unit increases by values ranging from 17% to 32% depending on the condenser and evaporator loads. Exergy analysis shows that the enhancement is attributed to reduction in the exergy destruction in the condenser and compressor due to lower values of condenser pressure and pressure ratio of the compressor. The output power of the HE-TEGs unit is found to be sufficient for driving the TEGs heat sinks air cooling fan, thus providing a passive de-superheating system without an additional external source of electricity. Further enhancement of the refrigeration cycle performance can be achieved by installation of additional HE-TEGs units.

Numerical and experimental investigation of multiple heat exchanger modules in cooling and desalination adsorption system using metal organic framework

The cooling and desalination adsorption system is a heat-activated system based on the solid sorption process. The main challenge in this system is concentrated to decrease the energy consumption of this system using a low desorption temperature (less than 90 °C) while maintaining a good performance. A scaled-up adsorption system using multiple heat exchanger modules packed with commercially available metal–organic framework material that operates at low desorption temperature, was numerically and experimentally investigated in the present paper. Three-dimensional and two-dimensional axisymmetric numerical models were developed to simulate heat and mass transfer phenomena considering the internal and external mass transfer in the adsorbent domains. Effects of the modules' connection options and vapor gap between modules on the system performance were examined. The highest coefficient of performance was achieved when connecting the modules in series, affected by the considerable reduction in the heating power. However, the increase in the effective amount of adsorbate resulted in the best specific cooling power when connecting the modules in parallel. Additionally, A scaled-up adsorption cooling/desalination system using 23.2 kg of Aluminium Fumarate packed in 16 modules was constructed and evaluated experimentally. The system produced desalinated water of 201 L/day and cooling capacity of 5.25 kW at the evaporator, condenser, and desorption water temperatures of 24 °C, 25 °C, and 85 °C, respectively. The specific daily water production decreased by 16.3% when the water salinity increased from 90 to 100,000 ppm, while the lowest specific electrical energy consumption of the proposed system is 1.87 kWh/m3. The theoretical and experimental results will enable further scaling up of an efficient MOF adsorption system for cooling and water desalination.

Simulation System for PeLUIt 150 MW Nuclear Reactor by using vPower

In developing the PeLUIt 150 MW nuclear power plant based on the High Temperature Gas-cooled Reactor (HTGR) technology, with the helium-coolant and output thermal power of 150 MW, the PeLUIt simulator is also developed for training the operators and educating other technical personnel. Referred to the balance of plant (BOP) design of the PeLUIt, the simulator utilized the vPower simulation platform to simulate the secondary loop for power generation with a water-steam Rankine cycle. The paper focuses on developing the secondary loop’s main components: steam generator, steam turbine, condenser, deaerator, and feedwater pump. The reactor module in the primary loop is simplified as a heat source with 150 MW output. The steam generator that connects the primary and secondary loops is modeled with the heat exchanger module by transferring heat from helium to water/steam. Meanwhile, pressure and flow parameters can also be simulated for both helium and water/steam flows in steady-state and transient operating conditions. The steady-state simulation results are almost the same as the design data. The differences in the main steam temperature, feedwater pressure, and feedwater temperature, are 0.03%, 0.53%, and 0.02%, respectively. Meanwhile, the transient condition carried out in the loss of coolant accident showed a decrease in flowrate of 43.31 kg/s and an increase in temperature of feedwater and main-steam of 52.32 and 15.38 °C, respectively. In addition, there was a pressure drop of around 10.37 (feedwater) and 10.16 MPa (main-steam).

Assessment of the Impact of Temperature on Biofilm Composition with a Laboratory Heat Exchanger Module.

Temperature change over the length of heat exchangers might be an important factor affecting biofouling. This research aimed at assessing the impact of temperature on biofilm accumulation and composition with respect to bacterial community and extracellular polymeric substances. Two identical laboratory-scale plate heat exchanger modules were developed and tested. Tap water supplemented with nutrients was fed to the two modules to enhance biofilm formation. One “reference” module was kept at 20.0 ± 1.4 °C and one “heated” module was operated with a counter-flow hot water stream resulting in a bulk water gradient from 20 to 27 °C. Biofilms were grown during 40 days, sampled, and characterized using 16S rRNA gene amplicon sequencing, EPS extraction, FTIR, protein and polysaccharide quantifications. The experiments were performed in consecutive triplicate. Monitoring of heat transfer resistance in the heated module displayed a replicable biofilm growth profile. The module was shown suitable to study the impact of temperature on biofouling formation. Biofilm analyses revealed: (i) comparable amounts of biofilms and EPS yield in the reference and heated modules, (ii) a significantly different protein to polysaccharide ratio in the EPS of the reference (5.4 ± 1.0%) and heated modules (7.8 ± 2.1%), caused by a relatively lower extracellular sugar production at elevated temperatures, and (iii) a strong shift in bacterial community composition with increasing temperature. The outcomes of the study, therefore, suggest that heat induces a change in biofilm bacterial community members and EPS composition, which should be taken into consideration when investigating heat exchanger biofouling and cleaning strategies. Research potential and optimization of the heat exchanger modules are discussed.

Design and Performance Evaluation of a Heat Pump System Utilizing a Permanent Dewatering System

The earth provides a vast resource of groundwater from aquifers a few meters beneath the surface. Thus, buildings that use underground space must be equipped with dewatering wells to drain the permeated groundwater to the sewage pipelines to ensure the structural stability of the building. Although the inflowing groundwater temperatures and flow rates are stable enough for groundwater to be used as an energy source, 79% of the permeated groundwater is discarded through the sewers, generating significant sewerage expenses. This study introduced a novel heat exchanger module to utilize the permeated groundwater as an unused energy source using heat pumps, and the performance of the system was evaluated by TRNSYS simulations. First, the sizing of the unit heat exchanger module was proposed according to the mean inflow rate of the permeated groundwater. Second, the heat pump system was configured using multiple modules in the source-side loop. Finally, the performance of the proposed heat pump system was compared with that of a conventional air source heat pump using realistic load and temperature profiles. This preliminary study demonstrated interesting performance results, with a coefficient of performance for heating that was higher than that of a conventional heat pump system by 0.79. The results show the potential utilization of the systems for a construction project requiring large-scale underground spaces, where abundant groundwater is available.

A New Type of Enhanced Heat Transfer Technology for Mobile Heat Storage Medium

Mobile heat storage technology is to alleviate the energy supply and demand both sides on the time, intensity and location does not match the effective way, is the rational utilization of energy and the effective ways to reduce environmental pollution, but the current mobile heat storage technology is not used widely in domestic, the main factor of restricting its development is exothermic filling time is too long, cause heat loss and power consumption is too large. After analyzing the heat transfer module of the mobile heat storage system and searching a lot of literature, it is found that Hydrogen fluoride ether (HFE) has excellent heat transfer characteristics. Through the principle exploration and experimental verification, the following conclusions are finally drawn: Adding HFE7000 with a concentration of 1.2% into the heat exchange module can improve the heat exchange effect by about 58%, which has good energy-saving and emission reduction.

Sound reduction in heat exchanger modules by integrating plate absorbers with sub-millimeter openings

In air conditioning systems heat exchangers are frequently installed upstream of ventilators. These modules are part of the daily life of humans and should therefore create an environment that is as quiet as possible. The heat exchanger generates increased turbulence, which leads to increased sound emissions of the ventilator. Due to installation space limitations, it is not possible to connect silencers to the heat exchanger module. A novel concept is presented, which allows to reduce the sound emissions of heat exchanger due to plate absorbers without the need of additional installation room. The plates contain sub-millimeter openings. They are integrated into the heat exchanger housing together with back volumes. This arrangement guarantees compactness and generates no additional flow resistance. The emitted sound could be reduced by up to 2.9 dB in the partial load range. The main advantages of the concept presented are individual adjustment, cost-effective design and simple installation.

Evaluation of the efficiency of a heat recovery steam generator via computational simulations of off-design operation

This work investigates the flow and heat transfer on the gas side of a heat recovery steam generator. During the operation of a power plant, off-design conditions that significantly impact the steam generator efficiency, caused by variations in the gas flow, corrosion and fouling of tube walls, may be encountered. In addition, passages around the heat exchanger modules develop along the equipment lifetime, allowing the bypass of flowing gas into zones of the boiler of low heat transfer effectiveness. These issues are here addressed via computational simulations, using a commercial software application for solving the mass, momentum, and energy conservation equations. The boiler geometry and the boundary conditions for the simulations are taken from a real, typical industrial heat recovery steam generator fed by gas turbines exhaust gases. Flow turbulence is modeled using the k- $${\epsilon}$$ model, and heat exchanger modules are considered as porous media, through which the exhaust gases flow while supplying heat to the water. The water flow properties are specified from process data. Numerical results for thirteen realistic off-design conditions are compared to those for the boiler normal operation point. It is found that the cases considering deviation of gas to the trapdoors and lateral passages have the greatest impact on the boiler efficiency. Results indicate an efficiency drop from 86% for the base case to 48% for the case with gas deviations. In addition, a reduction in the gas flow or the plugging of the low-pressure economizer tubes may decrease the boiler efficiency by more than 10% points.

One piece ceramic heat exchanger for concentrating solar power electric plants

Abstract Using additive manufacturing techniques, a ceramic heat exchanger was optimized for a concentrating solar power (CSP) electric power plant with a corrosive molten salt at atmospheric pressure as the solar field heat transfer fluid and supercritical carbon dioxide at 200 bar as the power block fluid. Temperatures ranged from 750 °C to 540 °C. The plant heat exchanger was optimized for heat transfer and stress using 1 m3 modules arranged in parallel. Heat transfer was optimized using COMSOL Multiphysics software resulting in a unique semi-elliptical cross section for the fluid flow channels in a counter-flow configuration. Counter-flow was made possible through additive manufacturing of the fluid headers as part of each modular heat exchanger thus producing the entire module as a single piece and minimizing cost. Using reasonable parametric values, a heat exchanger module was optimized to 0.5 MW/m3, and a section of it was manufactured including the fluid headers. Parametric studies showed the potential for a module to reach 3.5 MW/m3.

Exergy analysis of a vacuum membrane distillation system integrated with mechanical vapor recompression for sulfuric acid waste treatment

A vacuum membrane distillation (VMD) system integrated with mechanical vapor recompression (MVR) concentrating sulfuric acid solution was proposed. Mathematical models were established based on the first and second laws of thermodynamics. The effects of operating parameters on exergy efficiency of the system were investigated by Matlab simulation. Besides, further experiment using pure water as feed was implemented to validate the feasibility of the integration of VMD in MVR process, and then the energy and exergy analysis were performed comprehensively. The obtained results showed that the total input power increased but exergy efficiency decreased at higher feed concentration and heat transfer temperature difference of heat exchanger, lower feed temperature and velocity. The energy efficiency was improved through recovering the latent heat of vaporization in the VMD process. But the current coupled system was still inefficient and far from perfect with lower exergy efficiency of 3.72% and higher exergy destruction of 3.563 kW, the compressor was identified as the most exergy destruction of 36.99% followed by VMD module, heat exchanger and circulating pump with 18.16%, 11.98% and 11.34%, respectively. Therefore, the incorporation of enhancingheat-insulatingproperty and using more efficient compressor, heat exchanger and VMD module is expected to improve the exergy performance.

Comparing exergy losses and evaluating the potential of catalyst-filled plate-fin and spiral-wound heat exchangers in a large-scale Claude hydrogen liquefaction process

Detailed heat exchanger designs are determined by matching intermediate temperatures in a large-scale Claude refrigeration process for liquefaction of hydrogen with a capacity of 125 tons/day. A comparison is made of catalyst filled plate-fin and spiral-wound heat exchangers by use of a flexible and robust modeling framework for multi-stream heat exchangers that incorporates conversion of ortho-to para-hydrogen in the hydrogen feed stream, accurate thermophysical models and a distributed resolution of all streams and wall temperatures. Maps of the local exergy destruction in the heat exchangers are presented, which enable the identification of several avenues to improve their performances.The heat exchanger duties vary between 1 and 31 MW and their second law energy efficiencies vary between 72.3% and 96.6%. Due to geometrical constraints imposed by the heat exchanger manufacturers, it is necessary to employ between one to four parallel plate-fin heat exchanger modules, while it is possible to use single modules in series for the spiral-wound heat exchangers. Due to the lower surface density and heat transfer coefficients in the spiral-wound heat exchangers, their weights are 2–14 times higher than those of the plate-fin heat exchangers.In the first heat exchanger, hydrogen feed gas is cooled from ambient temperature to about 120 K by use of a single mixed refrigerant cycle. Here, most of the exergy destruction occurs when the high-pressure mixed refrigerant enters the single-phase regime. A dual mixed refrigerant or a cascade process holds the potential to remove a large part of this exergy destruction and improve the efficiency. In many of the heat exchangers, uneven local exergy destruction reveals a potential for further optimization of geometrical parameters, in combination with process parameters and constraints.The framework presented makes it possible to compare different sources of exergy destruction on equal terms and enables a qualified specification on the maximum allowed pressure drops in the streams. The mole fraction of para-hydrogen is significantly closer to the equilibrium composition through the entire process for the spiral-wound heat exchangers due to the longer residence time. This reduces the exergy destruction from the conversion of ortho-hydrogen and results in a higher outlet mole fraction of para-hydrogen from the process.Because of the higher surface densities of the plate-fin heat exchangers, they are the preferred technology for hydrogen liquefaction, unless a higher conversion to heat exchange ratio is desired.

Analysis of natural circulation behaviors and flow instabilities of passive containment cooling system design for advanced PWR using MARS-KS code

Several design basis accidents such as loss of coolant accident (LOCA) and main steam line break (MSLB) of pressurized light water reactor could threaten the integrity of containment building by increasing containment temperature and pressure. Although containment spray systems (CSS) have been installed for the depressurization of containment against the accidents, iPower nuclear power plant requires additional passive safety system design to provide for malfunction of CSS. Therefore, passive containment cooling system (PCCS), which consists of passive containment cooling tank (PCCT), heat exchanger modules, and connection pipelines, is under development. The natural circulation behavior of the PCCS is an important hydraulic phenomenon for the guarantee of decay heat removal capacity, required to satisfy the safety acceptance criteria. Especially, flow instabilities, which could threaten the structural integrity and enlarge the performance uncertainty of the system, have been reported for multi-channel heat exchangers operating with natural circulation like present PCCS design of iPower reactor. In this study, the natural circulation behaviors of iPower PCCS according to various operating conditions and design parameters (elevation of returning pipeline) were analyzed by MARS-KS code to observe the flow instability phenomenon inside the system. Two types of flow instabilities, flashing-induced instability and density wave oscillation were observed in the PCCS with different heights of returning pipeline. Through additional analysis on flow stability map of PCCS design, effects of mitigation strategies (system pressure and flow resistance) on natural circulation behavior of the system were quantified. The analysis results provide physical insight on possible flow instability and its mitigation strategies, that would be crucial information on designing natural circulation-driven multi-channel heat exchanging system consisting of more than two heat exchanger modules.

Coupled simulation of a thermoelectric generator applied in diesel engine exhaust waste heat recovery

This work develops a heat transfer model of a thermoelectric generator to explore the coupled relationship between high temperature exhaust flows, structure, and the external cooling air. The coupled heat transfer results showed that the fins reached a uniform high temperature, for the rated speed, the average temperature is 474 K. The coupled design scheme of the thermoelectric generator tested by installing it in a 4-cylinder turbocharged Diesel engine exhaust system. Comparison of the test and simulation results showed that as engine speed in-creased, the inlet and outlet exhaust temperatures of the thermoelectric generator exhibited a parabolic trend increase. The cooling water outlet temperature and the top, middle, and bottom fin temperatures increased linearly, and the coupled model was verified. From idle speed to rated speed, the top, middle, and bottom fin temperatures increased from 458 K to 476 K, 417 K to 463 K, and 406 K to 449 K, respectively; the cooling water outlet temperature increased from 293.6 K to approximately 303 K. Hence, the thermoelectric components installed in fins can experience temperature differences of over 100 K, the heat transfer efficiency can increase which ensures consistent output performance of the thermoelectric generator based on coupled design between the heat exchanger and thermoelectric modules array column.

Optimum Design, Heat Transfer and Performance Analysis for Thermoelectric Energy Recovery from the Engine Exhaust System

Thermoelectric waste heat recovery can improve the thermal efficiency of internal combustion engines and reduce CO2 emissions. In this study, a mathematical optimization using a genetic algorithm method is applied to obtain the optimal fin parameters of a rectangular offset-strip fin heat exchanger, used with an automotive thermoelectric generator (TEG) system. Three fin parameters are considered (fin spacing, fin thickness and fin height). Their effect on the exhaust pumping power, the exhaust heat transfer coefficient and the system performance is explored. The main goal is to maximize the net power output of the system. Results show that fin spacing has the most significant effect on the system performance. Moreover, when fin spacing is reduced below 0.5 mm, a negative net power output is obtained. By comparing the performance of stainless-steel (SS) and copper heat exchangers, it was found that the SS heat exchanger requires smaller fin spacing and fin height, which induces a higher pressure drop. TEGs with higher maximum operating temperature will allow further utilization of the exhaust heat, without a decline in performance due to overheating. Finally, a maximum net power output of 553.3 W is achieved using the copper heat exchanger and commercial bismuth-telluride (Bi2Te3) thermoelectric modules.

Dynamic Simulation and Operating Characteristics of Ground-Coupled Heat Pump with Solar Seasonal Heat Storage System

A hybrid ground-coupled heat pump (GCHP) is an efficient and sustainable technology for space heating and cooling. A demonstration house equipped with GCHP with a solar seasonal heat storage (SSHS) system had been built in Harbin, a severe cold zone of China. A dynamic simulation model was built for the house and GCHP with the SSHS system using TRNSYS. The model used a newly developed vertical ground heat exchanger (VGHE) module which considered coupled heat and moisture transfer (CHMT) in ground with variable soil properties (VSPs) and phase change of soil moisture (PCSM). In the simulation, a large amount of computing is consumed for VSP and PCSM, while the computing amount for moisture transfer is small. The model with the new VGHE module produced better simulated results, compared with the field data. So, CHMT-VSP-PCSM affects the performance of VGHE and system to some extent, especially CHMT. Hourly variation laws of temperatures and energy parameters were analyzed, and different characteristics were showed up at different operating stages in heating and cooling seasons for both long and short terms. The GCHP with the SSHS system can meet the heating and cooling demands of the house in general. In cooling season, adjusting the ratio of the two groups of VGHE for heat storage and cooling will increase the utilization efficiency of VGHE and make the soil temperature more balanced.