Heat Exchanger Research Articles

Effects of 24-h sleep deprivation on whole-body heat exchange in young men during exercise in the heat.

Sleep deprivation has been associated with impaired thermoregulatory function. However, whether these impairments translate to changes in whole-body heat exchange during exercise-heat stress remains unknown. Therefore, following either a night of normal sleep or 24 h of sleep deprivation, 10 young men (mean (SD): 23 (3) years) completed three 30-min bouts of semi-recumbent cycling at increasing fixed rates of metabolic heat production (150, 200, 250 W/m2), each separated by a 15-min rest in dry heat (40°C, ~ 13% relative humidity). Rates (W/m2) of whole-body total heat exchange (dry + evaporative) were measured continuously and expressed as peak responses [mean of the final 5-min of exercise at the highest metabolic heat production (250 W/m2)]. Body heat storage was quantified as the temporal summation of heat production and loss. Core temperature, indexed by rectal temperature, was measured continuously. Relative to normal sleep, sleep deprivation did not modify whole-body heat exchange (evaporative (-6 [-18, 5] W/m2; P = 0.245), or dry (7 [-5, 19] W/m2; P = 0.209; sleep deprivation-normal sleep mean difference [95%CIs]) and therefore total heat loss (1 [-14, 15] W/m2; P = 0.917). There were no differences in either the change in body heat storage (-9 [-67, 49] kJ; P = 0.732) or change in core temperature (0.1 [-0.1, 0.3] °C; P = 0.186) between conditions. Overall, we showed that 24-h sleep deprivation did not influence whole-body dry or evaporative heat exchange, resulting in no differences in total whole-body heat exchange or body heat storage in young adults during exercise under hot-dry conditions.

Effects of Combined Utilization of Active Cooler/Heater and Blade-Shaped Nanoparticles in Base Fluid for Performance Improvement of Thermoelectric Generator Mounted in Between Vented Cavities

Abstract A wide range of technical applications, including solar power, waste heat recovery, electronics thermal management, and heat exchangers, employ thermoelectric generators. They can be mounted in between channels / cavities where hot and cold fluid streams exist. In this study, two novel methods of enhancing the power generation from thermoelectric generator device mounted in between vented cavities are proposed by combined utilization of active heater/cooler rectangular blocks and blade-shaped nanoparticles in base fluid. Finite element method investigation is conducted numerically for a range of hot and cold stream Reynolds numbers (250–1000), non-dimensional hot and cold block sizes (0.01 $$-$$ - 0.4), and heating/cooling increments (0–10), with nanoparticle loading limited to 0.03. Higher values of Reynolds number results in a rise in thermoelectric generator power. When comparing the cases of lowest and highest Reynolds number combinations, a 219 $$\%$$ % increase in power is achieved. The thermoelectric generator power will rise by around 27.5 $$\%$$ % when the object size reaches its maximum. However, for moderate object sizes, up to 31.6 $$\%$$ % reduction in power generation can be realized. Greater temperature differences result in a linearly rising power generation, with an achievable power increase of up to 22 $$\%$$ % . When nanoparticle loading in the base fluid for both cavities is raised to its maximum value, the resultant power increases by around $$30\%$$ 30 % . Thermoelectric generator power rises by 67.8 $$\%$$ % when an active heater/cooler with nanofluid is used in vented cavities, as opposed to the reference scenario of employing no object and only water. The thermoelectric generator device’s hot and cold interface temperatures are accurately estimated using the artificial neural network based method. The estimated temperature can be used as boundary condition for the solution of the governing equations in the thermoelectric generator device domain which will decrease the computational cost when dealing with very complex channel configurations.

On the enhancement of the efficiency of concentrated solar power plants using nanofluids based on a linear silicone fluid and Pt nanoparticles

To reduce greenhouse emissions and producing electricity with the smallest environmental impact, developing solar power technology is one of the most important milestones to achieve. Thus, to improve the efficiency of the concentrated solar power (CSP) plants, with lower environmental impact, is of great interest. This work reports the development of nanofluids, a colloidal suspension of nanomaterials in a fluid, based on an environment-friendly base fluid for improving the performance of the heat transfer process in CSP plants. The nanofluids contain Pt nanoparticles in a linear silicone-based heat transfer fluid, and their stability is guaranteed for several weeks. Their properties of interest, density, surface tension, viscosity, isobaric specific heat and thermal conductivity were characterized to determine the performance of the nanofluids in solar thermal technology. Improvements of about 6% and 24% in specific heat and thermal conductivity were found, without significant increases in viscosity. In addition, their effect on the performance of collectors and heat exchangers in CSP using these nanofluids was analysed, and an enhancement of about 40% is found. Specific heat enhancements are also discussed in view of the strength of the interactions between methyl siloxane groups and low Miller index surfaces of Pt, with data from density functional theory simulations.

Numerical Studies on Phase Change Material–Operated Condenser and Preheater for Energy‐Efficient Refrigeration Cycle

ABSTRACTThe study investigates using solid–liquid phase change materials (PCMs) as heat exchangers in energy‐efficient refrigeration systems. A modified refrigeration cycle flow model was proposed and progressively refined for better performance. Initial simulations used simplified U‐tube flow models to reduce complexity, analyzing PCM charging and discharging separately before integrating them into the modified refrigeration system. Various parameters were examined, including the mass flow rate of refrigerant R134a, inlet temperatures of hot and cold refrigerants, and the heat transfer area. The refrigerant, termed HotR, flows through the condenser, while the cooler refrigerant, ColdR, flows through the preheater. PCM acts as the condenser during charging and as the preheater during discharging. Simulation techniques such as the enthalpy‐porosity model for the PCM mushy region, the Lee model for evaporation–condensation, and the volume‐of‐fluid (VOF) multiphase model were utilized to model the PCM‐operated condenser accurately. The study offers valuable insights for optimizing PCM utilization in refrigeration cycles. It emphasizes the importance of refining charging and discharging processes to enhance system efficiency and condensation performance. Simulations showed the need for flow rate adjustments to achieve optimal condensation. Using HotR (343 K) and ColdR (263 K) inlet temperatures and a flow rate of 0.000824 kg/s, the system achieved up to 47% condensation and 25.08 K preheating with the integrated setup.

Influence of Joule heating and slip on 3D MHD rotating nanoliquid flow with radiation, viscous dissipation, Soret and Dufour effects

Purpose The purpose of this study is to explore the impact of Joule heating, slip conditions, Dufour and Soret effects on three-dimensional magneto-convection of nanoliquid over a rotating surface in the existence of thermal radiation, viscous dissipation and internal heat generation/absorption. Design/methodology/approach The considered physical system is modelled by a set of partial differential equations (PDEs) with conditions at surface. Then, the nonlinear PDEs are altered into a system of ordinary differential equations and they are solved numerically by the Runge−Kutta−Fehlberg method. Plotting the collected velocity, temperature and solute concentration characteristics allows one to see how relevant parameters affect the results. Calculations are made for skin friction and the rate of heat and mass transfer. Findings The outcomes are portrayed in the form of tables and graphs with a wide range of parameter involved in the study. It is observed that the local thermal energy transfer rate enriches on increasing the value of both thermal and solute slips. The solutal slip parameter suppresses the solute transport rate and thermal slip supports the solute transport. Practical implications Combining the Dufour and Soret effects is used in oil reservoirs, binary alloy solidification and isotope separation in mixtures of gases. Heat exchangers, nuclear reactors and thermal engineering can all benefit from the usage of nanofluid with Joule heating. Social implications This study is mainly useful for thermal sciences and chemical engineering. Originality/value The investigation of the effects of slip circumstances and Joule heating on magnetohydrodynamic rotating nanoliquid stream with thermal radiation and cross-diffusion makes this work unique. The discoveries produced are valuable and distinctive, and they have applications in many areas of thermal science and technology.

A probabilistic model-based approach to assess and minimize scaling in geothermal plants

Geothermal installations often face operational challenges related to scaling which can lead to loss in production, downtime, and an increase in operational costs. To accurately assess and minimize the risks associated with scaling, it is crucial to understand the interplay between geothermal brine composition, operating conditions, and pipe materials. The accuracy of scaling predictive models can be impacted by uncertainties in the brine composition, stemming from sub-optimal sampling of geothermal fluid, inhibitor addition, or measurement imprecision. These uncertainties can be further increased for fluid at extreme conditions especially high salinity and temperature. This paper describes a comprehensive method to determine operational control strategies to minimize the scaling considering brine composition uncertainties. The proposed modelling framework to demonstrate the optimization under uncertainty workflow consists of a multiphase flow solver coupled with a geochemistry model and an uncertainty quantification workflow to locally estimate the probability of precipitation potential, including its impact on the hydraulic efficiency of the geothermal plant by increasing the roughness and/or decreasing the diameter of the casings and pipelines. For plant operation optimization, a robust control problem is formulated with scenarios which are generated based on uncertainties in brine composition using an exhaustive search method. The modelling and optimization workflow was demonstrated in a geothermal case study dealing with barite and celestite scaling in a heat exchanger. The results showed the additional insights in the potential impact of brine composition uncertainties (aleatoric uncertainties) in scaling potential and precipitation location. Comparing the outcome of optimization problem for the deterministic and fluid composition uncertainties, a change of up to 2.5% in the temperature control settings was observed to achieve the optimal coefficient of performance.

Influence of heat input and heat exchange coefficient on temperature and stress field of a X80 steel pipeline repair-weld root pass of a type-B sleeve

Abstract The formation of the type-B sleeve repaisring root pass seriously affects the quality of in-service repair of B-type sleeve. Therefore, it is necessary to systematically study the temperature field, stress field, and deformation field of type-B sleeve repairing root pass. In this paper, a double ellipsoid heat source model is developed to investigate the weld temperature, residual stress, and deformation field characteristics in the type-B sleeve repairing root pass. The results show that the heat exchange coefficient of the inner wall of the pipeline has a relatively small impact on the penetration depth, residual stress, and deformation of type-B sleeve repairing root pass, and the weld heat input has a significant impact on the penetration depth, residual stress, and deformation of type-B sleeve repairing root pass. In a whole, when the heat input of the repairing root pass is around 0.9 KJ mm−1, a well-formed repairing root pass with moderate residual stress and minimal deformation can be obtained.

Thermal inspection on MHD Prandtl fluid flow past a stretching sheet in the presence of heat generation/absorption and suction/injection

Abstract For the past several years, researchers have been investigating the thermal boundary layer behavior under various assumptions due to contemporary requirements. From the existing literature, it has been noticed that no investigation has been conducted to examine the thermal and mass transport of a magnetohydrodynamic (MHD) flow of a Prandtl fluid past a stretching sheet with heat generation/absorption and suction/injection. To address this gap, this study looks at how the changed thermal flux, heat generation/absorption, and suction/injection affect the convective flow of MHD Prandtl fluid over a stretching surface. The governing system of nonlinear partial differential equations (PDEs) has been reduced to a system of ordinary differential equations (ODEs) through appropriate transformations. The desired numerical solutions of the resulting ODEs have been obtained using the bvp5c MATLAB package. We have analyzed and presented the effects of the physical parameters on the velocity, temperature, and concentration fields using graphs and tables. Also, the drag coefficient, heat, and mass transport rates were examined. Additionally, an entropy analysis has been conducted to explore the reusability of heat production. It has been observed that intensifying the magnetic and porosity parameters reduces the flow velocity while increasing the Eckert number, heat generation parameter, and the Biot number significantly increases the temperature. The concentration drops with an increase in the Schmidt number and the chemical reaction parameter. This study holds significant implications for industries that rely on drug delivery, heat exchanger technology, polymerization, and refining processes.

Thermo-mechanical behaviour of energy pile considering non-uniform initial ground temperatures

Ground temperature varies along the vertical direction at shallow depths, whose influences on the thermo-mechanical response of energy piles during heating and cooling processes remain unclear so far. This paper aims to fill this gap by performing finite element numerical analysis based on Comsol Multiphysics software, taking energy piles in the Yellow River flooded area as an example. A three-dimensional numerical model is established and is then validated by comparing with published experimental results. Parametric analyses are conducted with a focus on the heat exchange efficiency, temperature distribution, displacement and axial stress of energy piles caused by heating in summer and cooling in winter. It is found that the ignorance of ground temperature variation could lead to: (i) overestimation of the heat exchange efficiency in both winter and summer; (ii) underestimation of pile head displacement in summer and overestimation in winter; (iii) overestimation of the axial stress in summer and underestimation in winter.

Determining of the thermophysical properties of materials with indirect control of the temperature of the medium bordering the wall

Temperature control of a medium bounded by walls without direct placement of sensors in it is important to ensure efficient operation of many devices and process units (heat treatment devices, engines, reactors, etc.). However, development of a monitoring method with a wide scope of application requires automation of determination of thermophysical properties of wall and medium materials without specialized tests, which is difficult due to the individual specifics of each object. The paper presents the results of determining the thermophysical properties of materials during indirect monitoring of the temperature of the medium bordering the wall. We investigated the difficulties arising in the automation of determining the properties of materials during adaptation of models of complex heat exchange between the medium and the wall with partially uncertain properties. We used simplified heat exchange models making it possible to present the model signals as increments relative to the initial moment for the time period and to reduce the effect of the mismatch between the functional form of the model and the object on the indirect monitoring results. The parameters unknown during model adaptation were determined based on retrospective data of a limited time domain. It is shown that the model can be used to monitor a generalized estimate of the temperature of the medium near the point of temperature monitoring in the wall with subsequent prediction of the consequences of varying the temperature of the isolated medium. The efficiency of the proposed approach is demonstrated using a case study of heating fireclay bricks. The results obtained can be used in developing universal temperature control methods applicable to various objects.

Impacts of Fins on The Heat Transfer Characteristics in A Shell and Cone-Shaped Coil Heat Exchanger

Due to the high cost of solar air heating systems, performed a parametric analysis to find ways to improve their efficiency. Solar air heating systems with ribs, a novel design, are the subject of the research. Carry out a numerical investigation of a "solar air heater" in "ANSYS Fluent" using "computational fluid dynamics" (CFD) for this work. Enhanced the absorber plate by modifying the pitch and adding more ribs. In order to get the best possible outcome, it was necessary to evaluate the outlet temperature, air temperature inside the duct, friction factor, and heat transfer rate. Case 4, having a maximum outlet temperature, air temperature inside the duct, friction factor, and heat transfer rate with increment of 4.75 %, 1.11%, 35.5%, and 5.52% from case 1 respectively.

Enhancing Thermal Performance of Vertical Ground Heat Exchangers Through a Central Borehole Removal Design

The high initial cost of ground heat exchanger (GHE) systems, particularly in applications with significant annual building thermal load imbalances, remains a major barrier to their adoption. In traditional rectangular grid patterns of boreholes, thermal saturation in cooling-dominated buildings mainly affects the central zone, rendering central boreholes less effective. This study investigates an innovative approach to enhance the thermal performance of vertical GHEs by removing these central boreholes using the pygfunction Python package. The central borehole removal design (CBRD) was implemented across various building thermal loads and ground conditions, resulting in reduced borehole interaction and a substantial decrease in total GHE length. Specifically, the CBRD approach achieved up to 51% savings in total GHE length compared to traditional rectangular grid patterns, significantly lowering the initial cost without additional expenses. Although energy consumption savings over a 30-year period were modest (up to 2.2%), the initial cost savings were substantial. Further optimizations indicated that additional reductions in borehole length could be achieved by removing boreholes beyond the central ones, while still maintaining the maximum entering fluid temperature (EFT). Yet, additional optimizations are needed as achieving optimal configurations requires detailed information on factors such as available land area and drilling depth limits, which are site-specific.

Analysis of Temperature and Stress Fields in the Process of Hot-Rolled Strip Coiling

During the coiling process of a hot-rolled strip, with the increasing layers the temperature and stress distribution inside the coil constantly change and interact with each other. Due to the contact with the sleeve and the transition of the heat exchange state, it is inaccurate to consider the temperature of the whole coil as the coiling temperature set by the process requirement. Meanwhile, due to the periodic interlayer contact in the radial direction, the relation between stress and deformation is nonlinear. For the coiling process, it is difficult to consider the above factors using conventional methods. Therefore, an incremental model has been established to couple the temperature and stress of the coil. In order to obtain the mechanical properties of the strip and radial elastic modulus of the coil, tensile tests and laminated compression experiments are conducted at different temperatures. The effects of changes in strip thickness, coiling tension, and initial temperature of the sleeve on the stress and the temperature inside the coil are studied. Finally, by comparing the model results with measurements and analytical solutions, the effectiveness of the incremental coupled model is verified and the errors caused by the analytical method are analyzed.

Insight into the corrosion in non-ferrous alloy heat exchangers

Insight into the corrosion in non-ferrous alloy heat exchangers

Design and Operation of a Novel Cross Fin in Hot-Water Production System for Buildings

The importance of phase change heat storage (PCHS) in solar thermal applications is limited by the low thermal conductivity of phase change materials (PCMs) and the uneven temperature distribution during heat transfer. This study proposes to use composite fins for heat exchange in the PCHS module and integrate them into a hot-water production system (HWPS) for building heating. The effectiveness of the novel fin structure is assessed through thorough numerical simulations and experimental validation. An examination of melting fractions, temperature distribution, and flow characteristics of the molten PCMs across various fin structures indicates that increasing the lengths and quantities of the cross fins can alleviate the challenge of incomplete melting at the end of the charging process. Notably, expanding the surface area of the cross fins results in a 7.37-fold increase in the average thermal storage rate and a 781.25% enhancement in the average temperature response compared to the original design. These findings show that the new composite fin design greatly improves the heat storage performance of an HWPS, which is of great significance for building energy conservation.

Particle Vertical Mixing and Horizontal Conveyance Within an Ambient Temperature Fluidized Bed

Previous studies have shown the advantages of particle-to-sCO2 fluidized bed (FB) heat exchangers, which include high heat transfer coefficients, low material cost, and the ability to horizontally convey solid particles. This paper outlines the design and testing of a compact cold flow FB test apparatus to characterize horizontal conveyance through convolutions within a 100 kWth FB heat exchanger design. Horizontal conveyance is an advantage in FBs because it enables more compact designs for heat exchangers. Two mass flow rates, 0.5 & 1 kg/s, at the inlet & outlet of the FB. To determine consistency of the flow rates, Student’s t-tests were used to assess whether the inlet & outlet values were statistically similar. The mass flow rate exiting the bed was statistically similar to the flow rate entering the bed for both cases, but each case featured a wider range and standard deviation. The range and standard deviation of the 1 kg/s flow rate was 0.69-1.23 kg/s and 0.12 kg/s respectively, and the 0.5 kg/s test featured a range and standard deviation of 0.37-0.73 kg/s and 0.09 kg/s, respectively. These measurements provide confidence that large-scale designs can successfully horizontally convey particles at ````~1.5x minimum fluidization velocity (U­mf) without significant variation in flow rate. A method to characterize the degree of particle vertical mixing and bubble frequency within the FB is also introduced. By using a high-resolution camera together with particle velocimetry, particle motion in the X and Y directions can be estimated to assess bed mixing and bubble frequency.

Melt pond CO2 dynamics and fluxes with the atmosphere in the central Arctic Ocean during the summer-to-autumn transition

Melt ponds are a common feature of the Arctic sea-ice environment during summer, and they play an important role in the exchange of heat and water vapor between the ocean and the atmosphere. We report the results of a time-series study of the CO2 dynamics within melt ponds (and nearby lead) and related fluxes with the atmosphere during the summer-to-autumn transition in the central Arctic Ocean during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. In late summer 2020, low-salinity meltwater was distributed throughout the melt ponds, and undersaturation of pCO2 in the meltwater drove a net influx of CO2 from the atmosphere. The meltwater layer subsequently thinned due to seawater influx, and a strong gradient in salinity and low-pCO2 water was observed at the interface between meltwater and seawater at the beginning of September. Mixing between meltwater and underlying seawater drives a significant drawdown of pCO2 as a result of the non-linearities in carbonate chemistry. By the middle of September, the strong stratification within the meltwater had dissipated. Subsequent freezing then began, and cooling and wind-induced drifting of ice floes caused mixing and an influx of seawater through the bottom of the melt pond. The pCO2 in the melt pond reached 300 µatm as a result of exchanging melt pond water with the underlying seawater. However, gas exchange was impeded by the formation of impermeable freshwater ice on the surface of the melt pond, and the net flux of CO2 was nearly zero into the pond, which was no longer a sink for atmospheric CO2. Overall, the melt ponds in this Arctic sea-ice area (both melt ponds and lead water) act as moderate sinks for atmospheric CO2.

Dynamic Heat Transfer Modeling and Validation of Super-Long Flexible Thermosyphons for Shallow Geothermal Applications

In comparison to borehole heat exchangers that rely on forced convection, super-long thermosyphons offer a more efficient approach to extracting shallow geothermal energy. This work conducted field tests on a super-long flexible thermosyphon (SFTS) to evaluate its heat transfer characteristics. The tests investigated the effects of cooling water temperature and the inclination angle of the condenser on the start-up characteristics and steady-state heat transfer performance. Based on the field test results, the study proposed a dynamic heat transfer modeling method for SFTSs using the equivalent thermal conductivity (ETC) model. Furthermore, a full-scale 3D CFD model for geothermal extraction via SFTS was developed, taking into account weather conditions and groundwater advection. The modeling validation showed that the simulation results aligned well with the temperature and heat transfer power variations observed in the field tests when the empirical coefficient in the ETC model was specified as 2. This work offers a semi-empirical dynamic heat transfer modeling method for geothermal thermosyphons, which can be readily incorporated into the overall simulation of a geothermal system that integrates thermosyphons.

Predicting the Performance of a Helically Coiled Heat Exchanger for Heat Recovery from a Waste Biomass Incineration System

Predicting the Performance of a Helically Coiled Heat Exchanger for Heat Recovery from a Waste Biomass Incineration System

Numerical Investigation of Heat Transfer and Flow Dynamics in Tubes with DNA-Inspired Slotted Inserts

Within the realm of industrial energy conservation, the optimization of heat exchanger performance is paramount for the augmentation of energy utilization efficiency. This investigation employs computational fluid dynamics (CFD) simulations to elucidate the effects of an innovative DNA-Inspired Slotted Insert (DSI) on the convective heat transfer and pressure drop characteristics within heat exchange tubes. The study provides a thorough analysis of fully turbulent flow (Re = 6600−17,200), examining the effects of various DSI pitches, key lengths, and geometries. The findings reveal that the DSI instigates a three-dimensional spiral flow pattern, which is accompanied by an escalation in the Nusselt number (Nu) and friction factor (f) with increasing Reynolds numbers. An inverse relationship between Nu and both pitch and key length is observed; conversely, f exhibits a direct correlation with these parameters. The study identifies an optimal configuration characterized by a pitch of 10 mm and a key length of 1.5 mm, with square keys demonstrating superior heat transfer performance relative to other geometrical configurations. This research contributes significant design and application insights for double-helical inserts, which are pivotal for the enhancement of heat exchanger efficiency.