Heat Exchange Efficiency Research Articles

Design Optimization of Counter-Flow Double-Pipe Heat Exchanger Using Hybrid Optimization Algorithm

Double-pipe counter-flow heat exchangers are considered more suitable for heat recovery in the heat transfer industry. Numerous studies have been conducted to develop static tools for optimizing operating parameters of heat exchangers. Using this study, an improved heat exchanger system will be developed. This is frequently used to solve optimization problems and find optimal solutions. The Taguchi method determines the critical factor affecting a specific performance parameter of the heat exchanger by identifying the significant level of the factor affecting that parameter. Gray relational analysis was adopted to determine the gray relational grade to represent the multi-factor optimization model, and the heat exchanger gray relation coefficient target values that were predicted have been achieved using ANN with a back propagation model with the Levenberg–Marquardt drive algorithm. The genetic algorithm improved the accuracy of the gray relational grade by assigning gray relational coefficient values as input to the developed effective parameter. This study also demonstrated significant differences between experimental and estimated values. According to the results, selecting the parameters yielded optimal heat exchanger performance. Using a genetic algorithm to solve a double-pipe heat exchanger with counterflow can produce the most efficient heat exchanger.

Numerical simulation of condensation heat transfer characteristics of R134a at high vapor velocity under different angles

Heat pipe is widely used as an efficient built-in heat exchanger for thermal management of high pulse and heat flux power supplies. Enhanced heat dissipation at the condensing side is an important issue in heat pipe research, where vapor velocity is an essential factor affecting the condensing heat transfer characteristics. This study adopted the CFD method to numerically simulate the condensation heat transfer of R134a flowing in a smooth pipe. The flow condensation heat transfer characteristics, such as film thickness and heat transfer coefficient (HTC), were investigated under vapor velocities v = 20–100 m/s and tube inclinations β =-90–90° Geometric and numerical heat transfer modeling is established in high vapor velocity flow condensation. The error of numerical simulation results and model validation is 10%. The HTC increases rapidly with the change in vapor velocity under 60 m/s, increasing the rate to 0.4. When the vapor velocity exceeds 60 m/s, the growth trend slows to 0.15, 37.5% of the original increase. At high vapor velocities above 60 m/s, the effect of pipe inclination on condensation heat transfer coefficient can be almost negligible. A modified empirical correlation suitable for high vapor velocities is proposed, which has higher predictive accuracy when the vapor velocity exceeds 80 m/s.

Wind machines for frost damage mitigation: A quantitative 3D investigation based on observations

Wind machines have been increasingly used for frost damage mitigation in the agricultural community. During radiative frost nights, wind machines are used to erode near-surface thermal inversion by air mixing. The underlying mixing processes remain poorly understood. A full picture of warming effects caused by air mixing requires measurements with wide coverage and high resolution. Our study aimed to quantify the magnitude and area of warming by air mixing and identify the characteristic mixing processes downwind and upwind. We installed 9 km of fiber optic cables in a 6.75 ha orchard block, creating two horizontal planes and three vertical profiles. Quasi-3D temperature responses with spatial sampling and temporal resolution of 25 cm and 10 s, respectively, were obtained before and during machine operation. We found a 50% reduction of the local inversion strength (8 K) over 0.42 ha at 1 m and 0.46 ha at 2 m height. The warming area for a 30% reduction extends to 2.81 and 2.52 ha, respectively. As the propeller rotates 360°, the weak background wind substantially impacts the air mixing processes downwind and upwind. When jets blow along with background wind, the warming plumes arrive earlier than the jet due to horizontal advection from earlier warmed sections. The warming plumes consequently accumulate downwind and penetrate deep into the canopy. In contrast, in upwind direction, wind drag resistance causes warming plumes arrive later than the jet. Quadrant analysis reveals that flux transport during the machine operation is dominated by sweeping and ejection motions. Intermittent downdrafts of warm air and updrafts of cool air result in efficient vertical heat exchange. This feature makes wind machines highly effective in raising canopy airspace temperature to mitigate frost damage.

Numerical investigation on effects of rib shapes on oscillating flow and heat transfer in heat exchanger channels

Ribs are straightforward and cost-effective to improve the heat exchange efficiency, and the impact of cooling medium driven by the movement of the channel itself can also enhance the heat exchange capacity. This paper investigates the flow patterns of the gas–liquid two-phase flows in a smooth cubic and a cubic with semi-circular ribs by using a high-speed camera under different low-frequency oscillations. A numerical simulation method was used to study the impact of different ribs on each wall at various frequencies. The microscopic flow and heat transfer characteristics of the ribs were analyzed. Reflux occurred near ribs, and the fluid accumulated near the wall under the ribs with a liquid coverage ratio of approximately 79%. After the gas–liquid two-phase flow fully oscillated in the channel, the heat transfer contribution of the top wall to the entire channel reached the greatest value of approximately 40%, and the left and right walls contributed to the entire channel with 21% and 27%, respectively. An additional inertial force of the two-phase flow was sustained in the oscillating environment to form a periodic impingement flow on the rib and hence improve heat transfer. Due to the reflux near the rib, the local minimum values of the heat transfer coefficient appeared on the downwind of the rib. The difference in rib design affected the fluid motion and caused different heat transfer distributions on the top surface. These findings can support the application design of ribs in dynamic heat exchange channels for optimizing heat transfer.

A new optimization method of energy consumption for dynamic boil-off gas

Related research on refrigerant optimization based on the dynamic BOG has yet to be proposed. This study offers a new dynamic optimization method for boil-off gas (BOG) re-liquefaction system to improve the system's energy efficiency. The performance of C3MR (the propane precooling mixed refrigerant cycle) is analyzed based on the steady state model of leading liquefaction equipment in the process simulation in Aspen HYSYS software. And the principle of the energy consumption variation law of propane precooled compressor and mixed refrigerant compressor, based on the actual possible disturbance range obtained in the natural gas liquefaction process, is applied to construct the multi-objective optimization model with minimum energy consumption and maximum heat exchanger efficiency. Finally, the dynamic responses of disturbances were achieved and discussed with the aid of GA (Genetic Algorithm) and PSO (particle swarm optimization). The optimized performance of the dynamic liquefaction cycle is 34.8% better than the steady condition system in terms of energy efficiency, and the maximum energy consumption can be reduced by 50.60%. The advantage of the proposed optimization framework is its adaptability to other dynamic liquefaction processes. It has practical reference significance for the cost control of the BOG re-liquefaction recovery project.

Single-stage metal hydride-based heat storage system

The effective use of renewable energy sources (RES) becomes increasingly important, and energy storage systems are needed to ensure their stable operation. Metal hydrides (MH) can be used both for hydrogen storage and for thermal energy storage (TES). We present experimental results of heat, mass transfer and dynamic processes in a single-stage MH-based TES system based on a 5 kg La Ni4.8Mn0.3Fe0.1 metal hydride reactor. Stable cyclic operation in the temperature range 20–90 °C is demonstrated with volumetric energy storage density of 208 MJ/m3 and peak thermal power of 1.05 kW. The systems performance is analyzed regarding the energy and exergy efficiencies. The main bottlenecks include the connected thermal mass of the reactor and the necessity to use lightweight and efficient heat exchanger. In addition, a liquid flow rate in the heat exchanger should be kept low enough to decrease the difference between temperatures of the MH bed and coolant. Optimized low-temperature metal hydride TES systems can be used in climatic-oriented applications, such as MH starters for cold weather or “keep warm” systems.

Improvement potential detection of integrated biomethane liquefaction and liquid air energy storage system

Biomethane (BM) is highly competitive bio-energy alternatives for lowering the dependency on fossil fuels globally. The form of BM that is most suitable for storage as well as shipping to far-flung areas of the world is liquefied biomethane (LBM). However, due to the significant power consumption by compressors used in BM liquefaction process (like natural gas), it is a cost- and energy-intensive operation. Additionally, because biomethane is created at atmospheric pressure, unlike ordinary natural gas, liquefaction requires more power consumption because the pressure at which BM is produced is much less than corresponding critical pressure. Therefore, an integrated system of liquid air energy storage (LAES) system discharging end and a biomethane liquefaction process is introduced that is both economical and efficient in terms of energy use. The sub-cooling and liquefaction processes of biomethane are aided by the cold-exergy of liquid air at the time of regasification mode of LAES, which eventually lowers the refrigeration cycle duty of LBM process. On the other hand, gaining the additional advantage, the expansion stage of liquid air is aided by the thermal exergy of a compressed mixed refrigerant (MR). On the basis of conventional exergy analysis, composite curves analysis, advanced exergy analysis, and sustainability index, the impacts of novel integration of LBM and LAES are estimated in this study. Conventional exergy analysis determines that 15.9 % of exergy destruction is decreased in the proposed LBM-LAES system having additional power production of 4529 kW using gas turbine. Results based on advanced exergy analysis conclude that avoidable, endogenous and exogenous portions of exergy destructions are decreased by 28.9 %, 39.9 % and 43 %, respectively; which implies the significant improvement potential. Composite curves analysis depicts that the efficiency of primary cryogenic heat exchanger is improved in the proposed integrated scheme. Additionally, the overall sustainability index is increased from 1.55 to 2.13 for LBM-LAES process.

Cu/oriented-carbon nanotubes composite with ultralow thermal contact resistance

In this paper, a simple material preparation method is proposed to meet the requirements of efficient heat exchange interface materials for spacecraft on-orbit modular assembly. First, carbon nanotubes (CNTs) were uniformly dispersed on the surface of spherical copper (Cu) powder, and then the bulk was obtained by hot-pressing sintering. Finally, the Cu on the surface was removed by electrolysis, so that the CNTs can protrude from the surface to a certain height. After contacting with the matching materials, the exposed CNTs can fill the inevitable pores at the interface, increase the heat transfer channel, and effectively reduce the interface thermal contact resistance (TCR). By adjusting the type of CNT, contact pressure, the height of CNT protruding from the surface of Cu powder, the minimum TCR of the interface between the obtained Cu/oriented carbon nanotube (Cu/OCNT) composite and pure Cu was 25.4 mm2 K W−1 under 2.26 MPa, which is superior to most existing commercial thermal interface materials. Moreover, the heat exchange interface designed based on the prepared materials can be repeatedly contacted and separated, which is expected to provide a solution for the heat exchange of on-orbit modular assembly spacecraft.

Experimental and numerical investigation of flow and thermal characteristics of aluminum block exchanger using surface-modified and recycled nanofluids

PurposeThe purpose of this study is to numerically and experimentally survey the thermal efficiency of a block-type heat exchanger operated in different working conditions by using pure water and two nanofluids as heat transfer fluids.Design/methodology/approachAn aluminum block-type heat exchanger integrated with Peltier thermoelectric element was designed and installed to operate in a cycle, and the thermal performance of the heat exchanger, heat transfer rate, Nusselt and heat transfer coefficient variations were examined at different bath water temperatures by using recycled nanofluids. New generation surface-modified Fe3O4@SiO2-mix-(CH2)3Cl@Imidazol/water nanofluid was used as heat transfer fluid in the cycle. In addition, CFD simulation was performed using ANSYS/Fluent to investigate the temperature distribution and fluid flow structure in the used heat exchanger.FindingsExperiments were carried out by using numerical and experimental methods. In the experiments, the operating conditions such as flow rate, volume fraction of the nanofluid and water bath temperature were changed to find the effect of each parameter on the thermal efficiency. The Reynolds number varied depending on the test conditions, which was calculated in the range of approximately 100 < Re < 350. In addition, Nusselt number and heat transfer coefficient of test fluids were very close to each other. For 0.4% nanofluid, the maximum h value was obtained as 3837.1, when the Reynolds number was measured as 314.4.Originality/valueIn the scientific articles published in the field of heat exchangers operated by nanofluids, little attention has been paid to the stability of the nanofluids and sedimentation of particles in the base fluids. In addition, in most cases, experiments were implemented using an electrical resistance as a heat source. In this research, stable surface-modified nanofluids were used as heat transfer fluids, and it was found that the Peltier thermoelectric can be used as heat sources with acceptable efficiency in flat-type heat exchangers and even non-circular channels.

Investigation of Thermal Engineering Processes in a Plate Heat Exchanger

Purpose of research. The aim of the study is to identify vortex formation zones in the modified corrugated channel of a plate heat exchanger using computer modeling to increase the intensification of the heat exchange process.Methods. Plate heat exchangers have a compact design, which significantly saves space on production areas and facilitates the installation and dismantling of equipment. In accordance with the purpose of this work, we solved the problem of creating artificial turbulence of the flow to increase the thermal characteristics.To implement this task, plates have been developed that have a special geometry that creates a turbulent fluid flow in the channels between the plates and increases the heat transfer coefficient. This makes it possible to achieve higher heat exchange efficiency with the same exchange area, which reduces equipment and operating costs.Results. The result of this work is the implementation of a computer model of a modified corrugated channel for visual assessment of the impact of artificially created turbulators on the degree of vortex formation.Conclusion. The introduction of plates, the main heat exchange part of which contains spherical technological wells, makes it possible to increase the efficiency of the heat exchange process by increasing the heat transfer coefficient. In addition, an increase in the heat transfer coefficient will help reduce the metal consumption and the cost of heat exchange equipment.

A double-glazed solar air-phase change material collector for nocturnal heating: Model development and sensitivity analysis

Solar air collector with latent heat thermal energy storage (LHTES) is widely used in space heating. However, the thermal efficiency of the solar air collector with LHTES is low when the heat is stored during the day and released at night. The method of optimizing thermal efficiency by studying the influence of design parameters on thermal performance is yet to be explored. In this study, a numerical model is developed and validated to investigate the thermal performance of the double-glazed solar air- phase change material (PCM) collector. The heat storage (in daytime) and release (at night) process of the solar collector under different design parameters are studied by orthogonal test. The results show that the heat storage process is mainly affected by the type of PCM, while the heat release process is affected by the air velocity of air channel, length-width ratio of the collector, height of the air channel and the type of PCM. Then, range and variance analysis are applied to analyze the degree of influence of air velocity of air channel, length-width ratio of model, height of air channel, and type of PCM on the outlet parameters and efficiencies of the double-glazed solar air-PCM collector. Finally, according to the degree of influence of each factor on the indexes, the optimization scheme of the collector performance is obtained. When the airflow rate is 64.80 m3/h, the average temperature rise at night is 9.54℃, and the heat exchange efficiency is 66.41%, and solar thermal efficiency is 34.10%.

Heat Recovery Using PCM in Decentralised Façade Ventilation

A study of heat recovery in a façade ventilation unit was carried out under laboratory conditions using a climate chamber that allowed stable outdoor and indoor conditions to be simulated. The unit, equipped with a reversible fan and a chamber for the heat exchanger, controlled by an automation control system, was designed to exchange air in the room by alternating supply and exhaust cycles of specific durations. Three types of heat exchangers were tested, which were filled with different phase change materials, in order to estimate the efficiency of the façade ventilation unit in terms of its heat recovery capability. The efficiency of the unit was determined based on the temperature efficiency of heat recovery for 144 setting combinations. The best efficiency results between 73.56% and 76.29% were obtained with a solution using a heat exchanger consisting of cylinders with an external diameter of 10 mm and a wall thickness of 1 mm filled with jojoba oil in a one minute cycle. The tests confirmed that the heat exchangers, which are part of the façade ventilation unit, fulfil their function and allow heat recovery from the exhaust air to pre-heat the supplied air. The study complements the existing scientific knowledge on the efficiency of heat exchangers filled with phase change material, operating in winter conditions with work cycles up to 5 min.

Research and Improvement of Heat Transfer Performance of Plate and Shell Evaporator

Evaporator plays a key role in indirect refrigeration system, so improving the efficiency of evaporator is of great significance to improve the overall performance of refrigeration system. For the plate and shell evaporator, the reliability of the model is proved by numerical simulation of the existing evaporator and comparison with the experiment. An improved scheme is proposed for the existing evaporator, and the improved model is simulated and analyzed. The result shows that compared with the previous model, the improved model improves the heat exchange efficiency, reduces the pressure drop, and improves the overall efficiency of the evaporator.

The impact of using twisted double tube of innovative turbulator on the efficiency of a flat panel solar collector with geometric optimization

BackgroundFluids as water, ethylene glycol, etc. employed to enhance heat transfer, have a lower thermal conductivity (TC) coefficient compared to metals and even metal oxides. This paper presents computational fluid dynamics (CFD) simulation of the twisted double tube heat exchanger (HE) filled with two-phase MWCNT-TiO2/water hybrid nanofluid (Hnf). MethodsThe FLUENT 16 software is employed for numerical simulations of the HE with novel turbulator. The hybrid nanofluid is simulated using the two-phase mixture model and turbulent flow is modeled utilizing Realizable k-ε turbulence model. The Reynolds number (Re) alters from 7000 to 28000, the volume fraction of nanoparticles (φ) varies from 1.0 to 4.0%, and the pitch ratio of the innovative turbulator is 1.0, 2.0, 3.0, and 4.0. Outcomes proved average Nusselt number (Nuave) and pressure drop are strongly influenced by Re and φ. ResultsThe maximum thermal efficiency and HE pressure drop correspond to φ = 4%, Re = 28000, and a pitch ratio of 4. When φ = 4% and Re = 28000, adding turbulator with a pitch ratio of 4 inside the heat exchanger enhances Nuave by 106.92% in comparison with heat exchanger without turbulators. When φ = 4% and Re = 28000, adding turbulator with a pitch ratio of 4 inside the heat exchanger increases the pressure drop by 296.19% compared to HE without turbulators. Finally, exergy efficiency of HE with a turbulator with a pitch ratio of 4 is improved by 21.83% as Re increases from 7000 to 28000 when φ = 4%.

Effects of fuel injection and energy efficiency on the production and environmental parameters of electric arc furnace -heat recovery systems

A stoichiometric model of an electric arc furnace (EAF)-heat recovery system was constructed to display material, energy, and exergy behaviors, as well as production and environmental parameters, in order to study the effects of different fuel injection indexes. The injection of high-calorific value fuel (rather than hydrogen and biomass) reduces power consumption more effectively, but hydrogen utilization reduces the amount of off-gas and improves heat recovery slightly (0.06 MJ/Nm3) in the case of 30% energy efficiency. It is more efficient to directly use the energy released from fuel combustion in the furnace than to recover the heat in the off-gas, showing the importance to increase energy efficiency. In the scenario of improved equipment and technology using large amounts of hydrogen (20 m3/t) and biomass (40 kg/t), power consumption will reach 322 kWh/t. Near-zero carbon emissions (41.20 kg CO2/t) can be achieved in an EAF by using green power, green hydrogen, and advanced equipment and processes. However, realizing this process requires long-term transformation, including the use of coke oven gas rather than gray hydrogen, which has high upstream emissions. Moreover, there is a significant exergy loss in the off-gas heat recovery system (>70%), which requires the adoption of stoichiometric combustion and an increase in the efficiency of heat exchange.

Simplified calculation method for hydrodynamic noise of multi-tube heat exchanger based on acoustic cavity model

Because of the complex structure of the heat exchanger, its hydrodynamic noise simulation is difficult and the problem of low computational efficiency can not be solved well. An acoustically simplified calculation method for a large shell and tube heat exchanger with 2000 heat transfer tubes is proposed for a multi-tube number heat exchanger. The heat exchanger tubes are equated to different numbers of heat exchanger tubes according to their through-flow areas of 2000 heat exchanger tubes. Based on the LMS Virtual.Lab acoustic finite element module, acoustic cavity model calculations and analysis are performed for heat exchangers with different numbers of heat transfer tubes. From the acoustic cavity model laws of heat exchangers with 20, 100, 500 and 1000 tubes, it can be found that the distribution of vibration patterns and the intrinsic frequencies of heat exchangers with different tube numbers are similar. Therefore, the calculation model of 20 heat exchanger tubes is selected for noise calculation based on the fluid calculation software ANSYS-CFX and the acoustic calculation software ACTRAN. Based on the results of the noise calculation and the comparison verification of the experimental data, it is concluded that the heat exchanger models with similar acoustic cavity model have similar sound pressure levels. In addition, the sound transmission loss law and the contribution of the acoustic cavity model of the shell and tube heat exchanger are analyzed. Therefore, the effectiveness of the simplified calculation method of multi-tube number heat exchanger proposed is verified. The proposed simplified calculation method can be used to reduce the calculation difficulty and improve the calculation efficiency of complex heat exchangers.

Numerical and experimental study on a tube-in-tube heat exchanger working at liquid-hydrogen temperature with a large temperature span

With the advantages of no moving parts at low temperature and a flexible and simple structure, the precooled Joule–Thomson cryocooler working at liquid-hydrogen temperature has the potential to be used in the liquid-hydrogen zero-boil-off storage system. The recuperative heat exchanger is one of the key components of Joule–Thomson cryocoolers, and it is usually a tube-in-tube heat exchanger (T-THX). In this study, a numerical model of a T-THX working from room temperature to liquid-hydrogen temperature was developed. Based on the requirement that the heat-exchanger efficiency should be at least 97%, a T-THX was designed and tested. The performance of the T-THX with a temperature span of 280 K was obtained at pressure of 0.539–0.982 MPa and mass flow rate of 4.57–25.81 mg/s. The heat-exchanger efficiency varied from 95.83% to 97.50%, by which the feasibility of the numerical model was preliminarily verified. To improve the calculation accuracy, the T-THX model was modified. Compared with further experimental results, using the modified T-THX model, the relative deviation of the outlet temperature was within 0.3% and the deviation of the heat-exchanger efficiency was less than 0.05%.

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.

Numerical Simulation on Heat Transfer Augmentation by Using Innovative Hybrid Ribs in a Forward-Facing Contracting Channel

This study aims to investigate the thermal behavior and aerodynamic phenomena in a heated channel with varied rib configurations using computational fluid dynamics (CFD) simulations. Incorporating ribs in such systems enhances heat transfer and increases flow resistance and manufacturing costs. Understanding heat exchanger theory, measurement methods, and numerical calculations are crucial for creating efficient heat exchangers. The current research employs numerical analysis to assess the impact of hybrid ribs on heat transfer enhancement in forward-facing contracting channels (FFS). A two-dimensional forced convection heat transfer simulation under turbulent flow conditions was performed, considering the presence and absence of ribs with dimensions of 1 cm by 1 cm and spaced 11 cm apart. The arrangement of the ribs causes symmetrical temperature and flow distribution after and before each rib. The results demonstrate that the use of hybrid ribs outperforms the use of individual rib configurations in terms of thermal performance. This is due to the distinct flow patterns generated as the fluid passes through each rib. The triangle ribs had a more significant impact on the pressure drop than other rib configurations, while the cross ribs showed a lesser effect. The ribs improve the heat transfer coefficient while increasing the pressure drop, and the values of the Reynolds number were found to be directly proportional to the heat transfer coefficient and the pressure drop. The study concludes with a qualitative and quantitative analysis demonstrating the accuracy and coherence of the obtained computational results.

Development of a high capacity single stage GM cryocooler at 30 K range

Recently, there has been a demand for high-performance cryocoolers at the 30 K range to support emerging developments in high-temperature superconductors, green hydrogen power systems and circulating cooling system applications. The Low Pressure Cooler (LPC), a mobile circulating cooling system used to cool down superconducting magnets, mainly MRI’s, is currently a four cold head system running with four compressors. There is a strong demand to develop a more compact system to replace the LPC to cool down legacy and helium-free MRI magnets, which addresses ease of use, faster cool down, low power consumption, and simplifies handling and logistics. A more efficient large capacity cold head can replace multiple smaller cold heads and achieve these demands. Sumitomo (SHI) Cryogenics of America, Inc. has developed a high-capacity single-stage GM cryocooler, CH-160D2LT, for low temperature, circulating cooling and HTS applications. It has a capacity of 200 W around 30 K at 60 Hz, which is described in this paper. This cryocooler is part of the high-performance, low-noise, high capacity single-stage CH-160D2 Cryocooler family. This paper will discuss developments such as the cryocooler’s performance, heat exchanger efficiencies and regenerator designs.