Traditional Heat Exchanger Research Articles

Thermodynamics performance analysis of flue gas treatment process using ceramic membranes

Transport membrane condenser is a device for recovering water and heat from flue gas. Porous nature of ceramic membrane makes properties of water vapor condensation and fluid flow different from those in traditional heat exchangers. Therefore, irreversible losses caused by heat transfer and flow resistance of transport membrane condenser is also unique and worthy of studying. This paper uses entransy and entropy analysis methods to calculate irreversible losses of transport membrane condenser, and analyzes effects of fluid temperature on entransy dissipation and entropy generation rates. With the goal of reducing irreversible losses, operation mode and structure size of transport membrane condenser are optimized under designed conditions. Based on specific application cases, this paper finds that entropy analysis method has a certain limitations when studying irreversible losses of transport membrane condenser. The limitation is embodied in the analysis of heat transfer problems under the condition that fluid temperature changes significantly. Furthermore, an optimization method suitable for engineering design is proposed. According to theoretical results, flue gas inlet temperature is preferably in the temperature range of 52 °C–55 °C; under the condition that water balance of power plant is not destroyed, increasing flowrate of cooling water as much as possible.

A novel strategy utilizing local fracture networks to enhance CBHE heat extraction performance: A case study of the Songyuan geothermal field in China

To overcome the restrictions of the limited heat exchange area of the traditional coaxial borehole heat exchanger (CBHE), an enhanced CBHE is proposed. This strategy significantly improves the heat exchange area by constructing local hydraulic fractures for the low-temperature fluid to pass through. Herein, a thermo-hydraulic coupling model based on the Songyuan geothermal field was established to address the heat extraction performance of 15 fracture networks in the enhanced CBHE. The effects of engineering parameters on the thermal benefits are discussed. Results suggest that the proposed strategy improved the accumulated heat energy by more than 6.5 times. Although the lifetime and production temperature of the system declines with the fracture area growth, the net heat energy is improved due to significant reductions in pump energy consumption. A critical feature of this strategy is configuring the hydraulic fractures connecting the well section rather than simply expanding the stimulation volume. The enhanced CBHE is most sensitive to the injection flow, which controls the response process of the thermal benefits to other engineering parameters. Moreover, fracture permeability plays a dual role in regulating the positive and negative correlations of the net heat energy. This work provides substantial insight into CBHE technology upgrading.

A fast approximate method for simulating thermal pile heat exchangers

Ground source heat pump systems, operating in conjunction with vertical ground heat exchangers, will play a key role in decarbonising heating and cooling of buildings. Design of traditional borehole heat exchangers relies on tools which implement routine analytical relationships between heat transferred and the temperature change in the ground and circulating thermal fluid. However, for novel piled foundations used as ground heat exchangers, there are few such analytical solutions available that are practical for routine implementation. This paper examines the use of a radial approximation to simulate the dynamic thermal behaviour of pile heat-exchangers. Originally developed for small diameter and high aspect ratio borehole heat exchangers, the approach is more challenging for piles since unsteady heat transfer within the pile material is more significant over typical timescales. Nonetheless, we demonstrate that for pile diameters between 300 mm and 1200 mm, generally the error is <1 °C with centrally placed heat transfer pipes or four or more pipes placed near the edge with circumferential spacing less than 550 mm. The radial model is therefore practical for most pile configurations. The strong performance of the model is demonstrated for a year of hypothetical heating and cooling cycles, and also against a field-scale thermal response test.

Sustaining dropwise condensation on nickel-plated copper surfaces with As-grown graphene coatings

• Dropwise condensation on as-grown graphene on electroplated Ni has been achieved. • Dropwise condensation has been successfully promoted on Cu using Ni-Gr coatings. • Condensation rate has been enhanced up to 2.9 times higher than filmwise mode. • The electroplated Ni-Gr coatings on Cu are more robust than the Ni-Gr surface. Dropwise condensation (DWC) has been extensively investigated owing to its substantially higher efficiency compared with filmwise condensation (FWC). However, performing the highly efficient DWC has been hindered by the durability of existing hydrophobic surface coatings. Graphene grown on Nickel (Ni-Gr composite) has been demonstrated in our previous study to sustain the DWC in an aggressive condition for more than 36 months. Compared with traditional heat exchangers made of copper (Cu) and stainless steel, the high purity requirement of Ni substrate for graphene growth and high material cost greatly limit its practical applications. In this study, the cost-effective nickel-plating technique has been explored to apply the robust Ni-Gr coating on prevail metals such as Cu in industry. DWC can be sustained for more than 180 days without noticeable degradation in a steam/air mixture environment. After 180 days, the Ni-Gr coating electroplated on the copper surface (Cu-Ni-Gr) can still facilitate DWC with approximately 2.9 times higher condensation heat transfer rate than that of conventional metal surfaces. The consistently superior anticorrosion properties of Cu-Ni-Gr surfaces is further revealed by Tafel tests. An additional 46% lower corrosion rate than the Ni-Gr surface has been characterized. This study manifests a feasibility to implement the sustainable and highly efficient DWC on other popular heat exchanging metals using super-durable Ni-Gr coatings.

Design and modeling of a multiscale porous ceramic heat exchanger for high temperature applications with ultrahigh power density

The efficiency of a heat engine can be significantly improved by operating in a high-temperature and high-pressure environment, which is crucial for a wide range of applications such as hybrid and electric aviation as well as power generation. However, such extreme operating conditions pose severe challenges to the heat exchanger design. Although recently developed superalloys and ceramics can survive high-temperature and high-pressure loads, using these materials in a traditional heat exchanger design requires high cost and yields low power density. In this work, we propose an ultrahigh power density ceramic heat exchanger for high-temperature applications enabled by a multiscale porous design. By optimizing the design of centimeter-scale macrochannels and microchannels, significant improvement to both heat transfer and structural strength is predicted, with a negligible pressure drop penalty (< 1%). Based on finite element simulations, an optimized heat exchanger core design is expected to achieve power densities of 717 MW/m3 and 300 kW/kg, which indicates more than 2.5× enhancement in thermal performance compared to printed-circuit heat exchanger design. Furthermore, the heat exchanger design features low material costs and scalable fabrication, enabling highly customizable applications in aerospace and terrestrial power generation.

Experiments on the characteristics of a sewage water source heat pump system for heat recovery from bath waste

• This non-metallic heat exchanger has better corrosion resistance. • The thermal conductivity of this non-metallic material is higher than that of traditional non-metallic heat exchangers. • The heat transfer coefficient of the nonmetal heat exchanger is less than that of the metal heat exchanger. • The heat exchanger in the sewage tank at different depths affects the adhesion rate of stains on the surface of the device, which is mainly caused by the different water flow rates. • Sewage heat recovery system plays an important role in energy saving and environmental protection. Sewage water source heat pump (SWSHP) systems with energy saving and environmental protection advantages have been widely studied, and sewage heat exchangers are an important part of SWSHP systems. Problems such as scale formation, difficulty in cleaning, and rapid decrease of their heat transfer coefficient with time have long been associated with SWSHP systems. With these in mind, in this study, we build a SWSHP system for the recovery of heat from waste using a waste water bath experimental platform, and applied a new, rare earth element (REE) non-metallic immersion sewage heat exchanger, The heat exchanger has heat transfer ability in actual working condition, as well as the operational features of a SWSHP system. From test data, the attenuation of heat transfer and the heat transfer coefficient of the sewage heat exchanger with time were analyzed. An attenuation formula of the heat transfer coefficient was determined using a logistic function. The results show that during 90 days of continuous operation, the surface heat transfer capacity decreased by approximately 7.8%, and the rate of decline over time was much lower than that of traditional heat exchangers. The results show that the system can produce hot water at 40.4–60.6 ℃, and the highest system coefficient of performance (SCOP) of the system is 5.65. Our study shows that varying the depth of immersion of the heat exchanger in the water pool affects the heat transfer ability of the heat exchanger. Results show that when the heat exchanger is closer to the pool surface, water-flushing action is strong. With a long runtime, the heat exchanger’s heat transfer ability has a slower rate of decline over time. Based on the test results, the energy consumption of the system was analyzed, and the energy saved by the continuous operation of the system for one year was determined to be equivalent to that of burning 4.29 × 10 4 kg of standard coal.

Integration of standing column wells in urban context: A numerical investigation-case in the City of Montreal

While the use of new technologies with low greenhouse gas emissions is growing quickly, ground source heat pump systems offer net advantages for urban environments. Standing column well, which exploits groundwater as a heat transfer fluid, requires less space and is less expensive than traditional closed-loop ground heat exchangers. However, a lack of information regarding standing column well is observed, especially in terms of interference with neighboring systems. A semi-regional finite element model was thus developed to emulate the thermal and hydraulic behavior of several standing column wells operated in an area of the City of Montreal. Five municipal and residential buildings were considered, with a total of 14 standing column wells and 5 injection wells. Numerical simulations indicate that infrastructure, such as buildings and roads, have a greater effect on increasing ground temperature than standing column wells. Results show the viability of each system over 10 years of operation without noticeable performance degradation and environmental impacts. Results also indicate that thermal modifications in the ground have a wider and greater extent than hydraulic modifications and decreases rapidly with depth. The study demonstrates that the operation of those systems in an urban context is viable in short and mid-term. • A semi-regional model emulated the impact of standing column wells in an urban area. • Operation of standing column wells in dense urban area is possible. • Results indicated no performance degradation or noticeable environmental impacts.

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.

Simulation study on the effect of fins on the heat transfer performance of horizontal dual-inner-tube latent thermal energy storage heat exchangers

Compared with the traditional horizontal double-tube heat exchangers, the horizontal dual-inner-tube latent thermal energy storage (LTES) heat exchangers can effectively shorten the melting time of the phase change materials (PCMs). This paper analyzed the liquid phase distribution, temperature field, melting rate and heat storage about finless horizontal dual-inner-tube latent thermal energy storage heat exchangers during the melting, and researched the effects of the fin position and number on melting progress and heat storage performance. The results showed that compared with the variation of fin number, the reasonable fin arrangement is better to improve heat transfer performance, and the heat transfer performance reaches to the optimal value when the single fin is placed at the bottom of the lower tube, which can shorten the melting time by 23.91% compared with the finless condition, but the increase of fin number on the basis of the optimal single fin arrangement only shortens the melting time by 1,2%. Additionally, it also obtained that the time of the high melting rate reduces by 9.14% when the fin is installed in the middle of the exchangers body, which weakens the effect of strengthening heat transfer. These results indicate that the less fins, if the arrangement is designed properly, can be as efficient as more fins in horizontal dual-inner-tube LTES heat exchangers.

Numerical study of nano-particle composite paraffin phase change heat storage capsule

The heat exchange characteristics of traditional heat exchange fluids such as water and oil in phase change heat storage can no longer meet the ever-increasing heat exchange requirements. The researchers found that by adding nano-scale particles to the basic phase change material (pure PCM) in a certain proportion to form a composite phase change material, the heat transfer characteristics of the material can be improved. In this paper, a model study of the phase change heat storage characteristics of the nano-particle composite paraffin wax phase change capsule with holes is carried out, and the effects of thermal disturbance, natural convection heat transfer and external convection heat transfer on the phase change heat storage are mainly studied. It is found that when nanoparticles are added to the phase change heat storage capsule, the composite phase change heat storage capsule formed by the phase change heat storage, the internal natural convection intensity increases, and with the increase of the particle share, the heat storage rate increases, and the heat exchange intensity increases.

Comprehensive thermal-hydraulic performance and thermoelectric conversion efficiency of bionic battery waste heat recovery system

To recover battery waste heat, the influence of different groove arrangement (symmetrical and staggered), groove depths (H = 1, 2 and 3 mm) and nanofluids mass fractions (ω = 0.0–0.5%) on the heat transfer performance and power generation characteristics of the battery waste heat recovery device were studied by experiments. The innovation of this paper is: replacing the traditional heat exchange working fluid with a new type of heat exchange working fluid; designing grooves of different shapes based on a sinusoidal curve, and studying the influence of different structural parameters on the thermal-hydraulic performance and power generation characteristics of the battery waste heat recovery device. The experimental results showed that when the mass fraction is 0.5%, the groove depth is 2 mm and the groove arrangement is staggered, the thermal-hydraulic performance and power generation characteristics of the waste heat recovery device are the best. Compared with symmetrical arrangement, the Nusselt number and power generation efficiency of staggered grooves are increased by 1.24 and 5.98% at most.

Study on Behavior of the Heat Exchanger with Conically-Corrugated Tubes and HDD Baffles

Baffles with holes in different diameters (or HDD baffles) and conically-corrugated tubes are respectively longitudinal flow baffle and high-efficiency heat exchange tubes proposed by the author. In this paper, vibrations of tube bundles with HDD baffles and fluid flow as well as heat transfer inside conically-corrugated tubes were numerically simulated, and the heat exchanger with conically-corrugated tubes and HDD baffles was tested for the heat transfer efficiency. It is found that compared with the traditional segmental baffles, tube bundle vibrations in heat exchangers, if using the HDD baffles, can be significantly reduced. Regarding heat transfer efficiency, conically-corrugated tubes are much better than smooth tubes and even better than other high-efficiency heat transfer tubes. Compared with the traditional heat exchangers, heat exchangers constructed with conically-corrugated tubes and the HDD baffles can provide better heat transfer efficiency and less tube bundle vibration.

Experiment and simulation research on heat exchange of different types of underground heat exchangers

Compared with traditional bored pipe heat exchanger geothermal collection technology, the continuously optimized energy pile technology is more efficient and economical in the application of building energy-saving projects. According to the structural characteristics of three different underground heat exchangers of deep buried pipe energy pile, inside buried pipe energy pile and traditional bored and buried pipe heat exchanger, we analyze the heat transfer characteristics through field test and numerical simulation. The results show that at the same depth, the heat exchange and heat exchange efficiency of single deep buried pipe energy pile are higher than those of traditional bored buried heat exchanger. Under the same pile length, the heat exchange rate of single deep buried pipe energy pile is higher than that of the inside buried pipe energy pile. The high thermal conductivity of the pile foundation can significantly improve the heat exchange effect of the heat exchanger. The well-pile section heat exchange ratio of the deep buried pipe energy pile reaches 1.95. The installation of the deep well can not only reduce the thermal interference caused by the pile foundation thermal accumulation, but also compensate for the adverse effect of the small heat exchange tube spacing on the heat exchange. By optimizing the construction process of the heat exchanger and reducing the thermal interference effect between the heat exchange tubes, the overall heat exchange effect of the heat exchanger will be effectively improved. <fig fig-type="abstract-image" id="F1" orientation="portrait" position="float"><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="SP.J.1249-2022-39-1-20/48BEB0D3-18F9-4a9d-93C3-E7253C6DB4C2-F001.jpg"/></fig>

Experimental and numerical study on the cooling performance of a new earth-air heat exchanger(EAHE) system with a supply air static pressure chamber

Earth-air heat exchanger (EAHE) is a low-carbon device that use renewable energy to improve the thermal environment of buildings by heating/cooling the air with the help of the thermal inertia of the soil. However, the traditional earth-air heat exchanger has the problem of large fluctuations in air temperature with the outdoor air temperature fluctuations. A system that combines an air supply chamber with an EAHE is proposed to address this problem. The outdoor air first enters the underground air supply static pressure chamber for initial cooling, and then enters the EAHE treatment. To investigate the effect of this air supply static pressure chamber on the cooling performance of EAHE, a three-dimensional numerical model was developed in ANSYS Fluent and validated with field measurement data. Then comparative studies of the EAHE system with a supply air static pressure chamber and the traditionnal EAHE system were conducted under summer conditions in Chongqing (China). The results show that the air supply static pressure chamber can reduce the EAHE outlet air temperature fluctuation by 31.98% at the maximum under the continuous operation of different air volume systems for 7 days. At the same time, the cooling capacity can be increased by 19.89% at maximum compared with the conventional EAHE cooling capacity.

Numerical study on enhanced melting heat transfer of PCM by the combined fractal fins

The melting heat transfer characteristics of PCM were studied in different combined types of heat exchangers. The effect of combining two different bifurcation level fractal fins was considered for PCM melting heat transfer in a phase change heat exchanger. Based on fractal theory and enthalpy-porosity method, a PCM melting model of two-dimensional unsteady heat transfer was established in a combined fractal fin heat exchanger. The influences of some factors, such as combined types of fractal fins, bifurcation level, heat transfer area of the fins and the spacing of the fins, were discussed for the melting heat transfer process. The results show that the complete melting time of PCM in a combined fractal fin heat exchanger is reduced by 68% compared with the traditional fractal fin heat exchanger. The melting time shows decreasing first and then gradually stabilizing as the bifurcation level number and heat transfer area of the combined fractal fins increase. The melting rate of PCM is the fastest in the Case 4 heat exchanger, and the complete melting time of PCM is the shortest in the Case 3 heat exchanger. Fin spacing and heat transfer area have a significant impact on the complete melting time. On this basis, the thermal performance coefficients between the fins zone and PCM zone are defined. The complete melting time of PCM is found to be exponentially negatively correlated with the thermal performance coefficient by curve fitting. The temperature distribution uniformity coefficient is proposed to evaluate the temperature distribution uniformity during the melting process of PCM. It is found that the temperature distribution uniformity of Case 2 has the best at the end of melting. The above results provide a theoretical basis for structural design of the heat exchanger with combined fractal fins to enhance PCM melting heat transfer.

Experimental and Numerical Study of Thermal Performance of an Innovative Waste Heat Recovery System

One of the biggest challenges the world is facing these days is to reduce the greenhouse gases emissions in order to prevent the global warming. Since a significant quantity of CO2 emissions is the result of the energy producing process required in industry or buildings, the waste heat recovery is an important aspect in the fight for preserving the planet. In this study, an innovative waste heat recovery system which can recover waste heat energy from cooling liquids used in industry or in different processes, was designed and subjected to experimental investigations. The equipment uses heat pipes to capture thermal energy from the residual fluids transiting the evaporator zone and transfer it to the cold water transiting the condenser zone. The efficiency of the heat exchanger was tested in 9 scenarios, by varying the temperature of the primary agent to 60, 65 and 70 °C and the volume flow rate of the secondary agent to 1, 2 and 3 L/min. The temperature of the secondary agent and the volume flow rate of the primary agent were kept constant at 10 °C, respectively 24 L/min. The results were later validated through numerical simulations, and confirmed that the equipment can easily recover waste thermal energy from used water with low and medium temperatures at very low costs compared to the traditional heat exchangers. The results were promising, revealing an efficiency of the equipment up to 76.7%.

Impacts of common faults on an air conditioner with a microtube condenser and analysis of fault characteristic features

Split system air conditioners are widely used to cool residential buildings, because of their low cost and simplicity. However, their efficiency is impacted by installation faults, which include: improper refrigerant charge (undercharge or overcharge), improper evaporator airflow, liquid line restrictions (LL), and the presence of non-condensable gas (NC) in the refrigerant. No known previously published research has studied the effect of these four faults on a system equipped with a microtube condenser, which has smaller tube size than a traditional condenser and therefore holds less refrigerant charge, but has a different configuration than a microchannel. Furthermore, very few have studied the impacts of LL and NC. This paper describes laboratory fault tests of a microtube-equipped system, compares the fault impacts with those of a traditional system, and considers the characteristic fault features. The tested system uses R-410A refrigerant and has a scroll compressor, a fixed orifice expansion device, and two fin-tube heat exchangers. The tests were carried out under steady operation with a range of fault intensities and operating conditions. The microtube system’s performance degradation from faults is similar to systems with traditional heat exchangers, despite the reduced capacity to hold refrigerant charge.

Study on turbulent flow in wave wall tube heat exchanger

The traditional straight wall tube heat exchanger has low heat exchange efficiency, in order to solve this problem, the turbulent flow in wave wall tube heat exchanger was studied by numerical simulation. It is found that the unique corrugated structure of the heat exchange tube in the wave wall tube heat exchanger can improve the flow state of the fluid in the heat exchanger. The average pressure drop of heat exchanger gradually increases with the increase of Reynolds number Re. Under the same conditions, the average pressure drop of wave wall tube heat exchanger is lower than that of straight wall tube heat exchanger. The improvement of heat exchange performance of heat exchanger can not be realized only by increasing the inlet flow of heat exchanger. The wave wall tube heat exchanger can strengthen the heat exchange of the fluid in the heat exchanger.

Smart microchannel heat exchanger based on the adaptive deformation effect of shape memory alloys

Microchannel heat exchangers that are compact and have high efficiency have significant application value in the cooling of high-power electronic components. In this study, a smart microchannel heat exchanger with a shape memory alloy vortex generator (SMA-VG) was proposed to address the challenges associated with complex working conditions and random hotspots of electronic components. Owing to the shape memory effect, the structure of the SMA-VG can automatically adjust to change the flow characteristics of the microchannel, such that the cooling capacity and heat dissipation demand can be matched intelligently without external control. Herein, the principle underlying smart microchannel heat exchangers is analyzed, and a relationship between coil deformation and the Nusselt number (Nu) is proposed. Subsequently, the responses of the SMA-VG to different heat fluxes and Reynolds numbers are revealed, and a SMA-VG of three unequal lengths is proposed. The performance of microchannel heat exchangers with SMA-VG was investigated by combining experimental and numerical methods. The results showed that the SMA-VG adaptively adjusted its pitch configuration with changes in heat flux, improving the overall heat transfer performance of the channel in comparison to the non-deformed vortex generator (NDF-VG). The channel with the SMA-VG exhibited a stronger localized disturbance performance. When the heat flow density was 100 000 W/m2, Nu increased by 112% relative to that of the channel without a vortex generator, which was 9% higher than that of the channel with NDF-VG. Therefore, this novel heat exchanger resolves the challenges of poor automatability that are associated with traditional microchannel heat exchangers, in addition to removing random hotspots. Moreover, it facilitates the achievement of different levels of heat dissipation demands without external control, and it has potential for application in fields involving the usage of high-heat-flux chips.

Study on thermal-hydraulic characteristics of hybrid heat exchangers with interpolated etched plates

The Supercritical carbon dioxide (S-CO2) Brayton cycle can be used to recover the exhaust heat energy of marine diesel engines. The hybrid heat exchanger is one of the potential solutions for heat exchange between flue gas and S-CO2, but there is no good design theory and design method at present. The traditional hybrid heat exchanger has an one-to-one correspondence between the fin and the etched plate. However, under special requirements, it is necessary to insert etched plates in the hybrid heat exchanger to improve the thermalhydraulic characteristics. In this study, four CFD models of the hybrid heat exchangers with interpolated etched plates were established. When the total mass flow rate and the total mass velocity are constant, the thermalhydraulic characteristics of the hybrid heat exchanger are analyzed by Fluent. The results show that regardless of the constant mass flow rate or the constant mass velocity, inserting etched channels into the hybrid heat exchanger will increase the total heat transfer coefficient. When the total mass flow rate of the cold and hot fluids is unchanged, the heat transfer coefficient and pressure drop of the etched channel decrease with the increase of the inserted etched channel. When the total mass velocity of the hybrid heat exchanger is unchanged, the insertion of the etched channel causes the pressure drop and the convective heat transfer coefficient of the fin channel to increase. Meanwhile, the pressure drop and convective heat transfer coefficient of the etched channels are reduced, but the total heat transfer coefficient is increased. The study can provide guidance for the design of the hybrid heat exchangers.