Heat Exchange Mechanism Research Articles

Thermal Energy Production in an Electrochemical Cell and Heat Transfer to Its Dark Surroundings

The theoretical formulation presented in this abridged paper was developed to predict the transient cell average temperature of a lithium-based cell during its discharge in dark, extremely low material density surroundings where the predominant mechanism of heat exchange between its shroud surface and surroundings is the thermal radiation process for a given cell discharge current and its initial temperature. The average computed temperature of an ideal lithium-based button cell, such as Li(s)/electrolyte/CF(s), is presented as a function of time in the form of plots at two discharge currents as an example of the application of the derived formulation. The presented data are briefly discussed in light of the lithium-based cell component stability and its safe discharge operation.

Application of energy-saving control strategy in air conditioning terminal equipment based on constant temperature difference of chilled water

Effectively reducing the energy consumption of central air conditioning systems is an important aspect of building energy efficiency. The energy consumption of terminal equipment accounts for over 25% of that of air conditioning systems. Although the heat and moisture exchange mechanism of the terminal unit has been extensively studied, studies on control strategies for terminal unit operation are lacking. This study proposes an energy-saving optimization control strategy for terminal units based on the constant temperature difference of chilled water in an engineering application study. A fan coil unit (FCU) controller was designed and manufactured, and a Local Area Network (LAN) control system was constructed and compared to determine the optimal control strategy. When adopting the energy-saving optimization control strategy for the terminal unit based on a constant chilled water temperature difference, the energy consumption of the terminal equipment was significantly decreased by 7.2%. The flow rate of chilled water was reduced by 26.94% when the indoor air temperature requirements were met, effectively reducing the energy consumption of the central air-conditioning system. The adjustment time required to reach a stable indoor temperature was reduced and environmental comfort was improved. These results demonstrate the potential of this control strategy for use in engineering practices to replace traditional control modes.

Mathematical Modeling and numerical simulation for nanofluid flow with entropy optimization

Through their exciting features, hybrid nanofluids have found a key role in energy transport applications that can be managed according to requirements. The hybrid nanofluid has a spectacular role in improving the mechanism of heat exchange and is extensively used during the manufacture of industrial and engineering applications. In this work, considering the influences of Lorentz force and uniform heat flux, the hydrothermal nature of hybrid nanoparticle displacement from a wavy and perforated tank is examined. The non-Darcy model is exploited for the simulation of the porous domain. The functional hybrid nanofluid is a Newtonian fluid partially loaded by MWCNTs and Fe3O4 nanoparticles. Where an adiabatic condition is presumed just at the upper and lower walls of the tank but the lift and right walls of the tank are assumed to be heated and cooled respectively. In order to convert the fundamental set of PDEs into a non-dimensional shape, appropriate relationships are used. The converted expression is computed by using an innovative technique CVFEM and then evaluated by using entropy optimization. The effect on the virtual flow parameters of different parameters that occur in the fundamental flow regime is systematically studied and the results are graphically demonstrated in form of contours and 3D plots. Rising buoyancy as well as porosity is reported to increase convective flow but decline temperature. Quantitative relations are generated for heat fluxNuaveand Bejan numberBe, that illustrate its influence on the Reynolds numberRa, magnetic parameter Haand DarcyDanumbers.

Identification of radiative and advective populations in Canadian temperature time series using the Linear Pattern Discrimination algorithm

AbstractLong‐term high‐frequency air temperature time series, typically considered the most authoritative observed records for the detection of climate changes, appear physically heterogeneous by nature. We examine multiple Canadian air temperature records for the presence of physical heterogeneities, using the analysis of their diurnal temperature patterns as the main criterion for the separation of temperature series into ‘homogeneous’ populations. Based on the key differences observed in their diurnal air temperature patterns, two distinct populations of the air temperature sample are identified and assumed to be the result of different heat exchange mechanisms. The Linear Pattern Discrimination (LPD) algorithm, implemented in the R‐code, is introduced in this work and applied to 66‐year long hourly temperature records of 25 Canadian stations for the separation of the radiative temperature population from the advective temperature population and examination of incidences of specific, advective cases in air temperature data. The LPD analysis reveals a predominance of a remarkably warmer, radiatively driven air temperature regime. In contrast, the significantly colder and geographically controlled advective temperature regime plays a counterbalancing role on the overall magnitude of the midlatitude air temperature signal. Our findings suggest that a substantial temperature increase in annual averages of advective minima amplifies the effect of a positively shifted radiative temperature range, intensifying the overall heating observed in the Canadian North and northwestern regions.

A complete analysis of the effects of transfer phenomenons and reaction heats on sono-hydrogen production from reacting bubbles: Impact of ambient bubble size

Several experimental and computational works have been focused on the production of hydrogen by using ultrasonic irradiation. However, the effects of the different ultrasonic conditions have been analyzed by considering a single value for the ambient bubble radius R0 (mean value), which is not the true case as the size of active bubbles in sonicating medium is an interval rather than a sole value. In the present paper, the impacts of mass transport, heat exchange and chemical reactions heat on the sono-production of hydrogen are examined over a range of ambient bubble radii. These effects are shown for various ultrasonic frequencies of 355, 500 and 1000 kHz and under a range of acoustic amplitudes, from 1.5 to 3 atm. The numerical simulations results demonstrated that the increase of the production rate of hydrogen (around R0 of the maximal production rate) is amortized (for all models) for the wave frequencies of 355 and 500 kHz at higher amplitude (i.e. 3 atm). On the other hand, the total production rate (around R0 of the maximal response) is increased proportionally with the reduction of ultrasonic frequency or if the acoustic amplitude is increased. The effect of heat exchange mechanism (on H2 and the total production rate) was found to be dominant whatever the acoustic amplitude or the wave frequency (on all the range of R0). It has been demonstrated that at the acoustic amplitudes >1.5 atm (for f = 355 and 500 kHz) and >2 atm (for f = 1000 kHz), the impacts of chemical reactions heat and mass transport are clear compared to the normal model throughout a range of bubble sizes. The ambient bubble size (R0) of the maximal response (maximal production rate) is shifted toward lower values when the ultrasound frequency or the acoustic amplitude is raised. In addition, it is observed that the increase in the wave frequency or the decrease in acoustic amplitude cause a narrowing in the range of active bubbles.

Modeling of an air-to-air exchanger with dual-core in cascade connection

With the current leaning towards finding effective solutions to maintain a good indoor air quality (IAQ) inside houses and buildings and to simultaneously reduce the energy consumption, air-to-air exchangers with heat/energy recovery have emerged as one of the promising technologies to provide a healthy and comfortable indoor environment. To deeply evaluate these systems performances, the present investigation focuses on modeling a combined ERV-HRV exchanger using the effectiveness-NTU (ε−NTU) method. To this end, a detailed mathematical model introducing heat and mass exchange mechanisms was developed and applied to predict the system energy recovery efficiency. To assess its suitability, the developed model was validated and compared to real measurements which carried out under the Atlantic Canada weather. The comparison findings disclosed that the developed model can predict the system performance with a maximum relative discrepancy less than 10%.• The detailed mathematical model including heat and mass exchange mechanisms was clearly developed using the ε−NTU approach in order to carefully predict the dual-core system performance in terms of sensible and latent recovery potential.• The developed model was validated against real data to evaluate its suitability and accuracy. Obtained results show that it could be satisfactory for predicting the dual-core system performances.• The ε−NTU approach adopted in this study could be a convenient method for modeling single or/and dual-core air-to-air heat/energy recovery systems.

Recognition of two-phase flow pattern inside evaporator tubes

The convective heat exchange mechanism in two-phase regime, can allow high exchange coefficients, as long as particular conditions are respected, in terms of vapor quality. In evaporator tubes this problem is particularly important as a deviation from the optimal flow conditions can drastically drop the efficiency of the heat exchange. This work describes an innovative methodology for identifying the different two-phase flow regimes in evaporator pipes, through the processing of the vibrational data acquired on the pipe itself. An experimental apparatus with transparent pipes has been built up to recognize flow patterns by a fast image acquisition camera. Images have been associated to vibration data acquired on pipes by accelerometer. The analysis of frequency spectrum, led to first interesting results thus it is possible to distinguish between “no bubbles” regimes and different “bubbles” regimes. A wide test campaign has been realized on vertical and horizontal pipes, simulating steam bubbles with nitrogen bubbles, reproducing the main flow patterns. The paper demonstrates the possibility to design smart and non-intrusive sensor to be applied on evaporated tubes for the recognizing of anomalous thermal flow condition and sets the stage for future engineering work.

Thermal Response of Three Strains of Hens Housed in a Cage-Free Aviary at the Amazon Rainforest

ABSTRACT This study aimed to evaluate the thermal response of three strains of hens housed in a cage-free system at the Amazon rainforest in order to evaluate how feather coverage influences thermal exchange with the environment. The experimental method was completely randomized and treatments comprised three strains of hens (Rhode Island Red (red feathers with feathers on the neck), alternative strain FCI (red feathers without feathers on the neck), and alternative strain FCIII (white feathers without feathers on the neck)), with 20 hens (replicates) analyzed per strain. Thermal images of each bird were captured in order to record the birds’ surface temperatures on five points in five targets. All data collected in this study were subjected to ANOVA and subsequently to the Tukey test at p≤0.01 and p≤0.05. The aviary’s left wall presented a lower average temperature, indicating lower heat accumulation, while the floor presented higher heat accumulation. FCIII hens (white feathers) presented higher (p<0.05) heat accumulation on the head and legs, and lower (p<0.05) heat accumulation on the neck and back in relation to other analyzed hens, indicating increased heat exchange efficiency and high concentration of this process in specific body areas. FCI and FCIII hens (without feathers on the neck) presented lower (p<0.05) heat accumulation on the neck and higher (p<0.05) heat accumulation on the head and legs, indicating that the feather coverage directly influenced heat exchange mechanisms, and an increased area without feathers provided great heat exchange zones for birds in a tropical climate.

English

Unlike mammals, birds have a unique respiratory tract that conditioning of inspired air takes place only within the nasal cavity alone. Nasal conchae are scroll-like structures situated on either side of the nasal cavity and lined by mucous membrane. Nasal conchae perform this function by counter-current heat exchange mechanism. The study was performed to document the gross and histoarchitectural details of rostral, middle and caudal conchae in Nandanam Chicken. The framework of the conchae is made of hyaline cartilage. The mucosa is lined by stratified squamous keratinized epithelium, pseudostratified ciliated columnar and olfactory epithelium in rostral, middle and caudal conchae respectively. Intraepithelial glands are made of mucus type in rostral and middle conchae serous variety located in propria-submucosa in caudal concha. Nasal cavity associated lymphoid tissue is made of CD3+ T lymphocytes

Transient heat exchanges under fast Reactivity-Initiated Accident

Heat exchanges during fast transient are very complex phenomena. Many studies have been led in this field, trying to quantify the heat exchanges between a heating wall, under fast increasing power, and a coolant. This kind of situation is encountered for instance during RIA (Reactivity-Initiated Accidents) in nuclear reactors, whose characteristics times of wall heat flux excursion can be as low as orders of 1 ms. The CABRI reactor, an experimental pulse reactor funded by the french Institute for Radiological protection and Nuclear Safety (IRSN) and operated by CEA at the Cadarache nuclear center (France), was build in order to study and thus to better understand RIA effects on nuclear fuels. Heat exchanges characterization is definitely one of major points to tackle in the understanding and modeling of such transients, involving single and two phase flows.This paper broaches the question of single phase heat exchanges coefficients during fast transient power excursions in the CABRI reactor.The single phase pure convection is the overlap of two main mechanisms: the advection (wall axial supply in upstream cold water) and the turbulent mixing inside the boundary layer. This latter phenomenon is due to vortices in boundary layers inducing radial mixing through the velocity boundary layer. In most cases involving turbulent flows, the turbulent mixing phenomenon is preponderant. To these mechanisms is added a pure conduction heat exchange mechanism through the thermal boundary layer. Convection and conduction overlap defining a conducto-convective heat transfer coefficient, improperly only called “convection” coefficient. This paper suggests a way to model this coefficient during a CABRI-RIA transient by a non-linear superposition of transient pure conduction and convection mechanisms. Two distinct transient phases are considered; the first one presenting a wall heat flux of exponential shape followed by the second one during which the wall heat flux remains constant. The potency of this analytical model, which is implementable into computational system tools, is demonstrated.

ANALYSIS OF HEAT TRANSFER IN BUILDING PARTITIONS WITH THE USE OF COMPUTATIONAL FLUID DYNAMICS TOOLS

The article presents the mechanisms of heat exchange in building partitions along with a description of the phenomena occurring there. The methods of heat transport on selected examples of the construction of sandwich building walls were presented and discussed. A review of the methods allowing to determine the heat flux value by means of analytical methods and simulations based on numerical analyzes was carried out. The methodology of solving thermal problems has been presented, indicating the complexity of the phenomena occurring at the contact points of surfaces, for which the correct characteristics should be selected in more than one selected form of determining temperature distributions. Heat transport simulation was performed in ANSYS Fluent 2020 R2 software. The value of the heat flux density flowing through the outer wall of a single-family house located in Lublin, Poland was analytically determined. Three different structural wall solutions were adopted: one, two and three-layer. The obtained results were presented in a tabular manner, allowing for a clear verification of the correctness of the calculations performed with both selected methods.

The Role of WISHE in the Rapid Intensification of Tropical Cyclones

Abstract This study examines the role of surface heat fluxes, particularly in relation to the wind-induced surface heat exchange (WISHE) mechanism, in the rapid intensification (RI) of tropical cyclones (TCs). Sensitivity experiments with capped surface fluxes and thus reduced WISHE exhibit delayed RI and weaker peak intensity, while WISHE could affect the evolutions of TCs both before and after the onset of RI. Before RI, more WISHE leads to faster increase of equivalent potential temperature in the lower levels, resulting in more active and stronger convection. In addition, TCs in experiments with more WISHE reach a certain strength earlier, before the onset of RI. During the RI period, more surface heat fluxes could provide convective instability in the lower levels, and cause a consequent development in the convective activity. More efficient intensification in a TC is found with higher surface heat fluxes and larger inertial stability, leading to a stronger peak intensity, more significant and deeper warm core in TC center, and the axisymmetrization of convection in the higher levels. In both stages, different levels of WISHE alter the thermodynamic environment and convective-scale processes. In all, this study supports the crucial role of WISHE in affecting TC intensification rate for TCs with RI.

Mechanisms of thermal dysregulation in primary hyperhidrosis and hypohidrosis.

Mechanisms of thermal dysregulation in primary hyperhidrosis and hypohidrosis.

Computationally Efficient Stochastic Model Predictive Controller for Battery Thermal Management of Electric Vehicle

The performance and safety of batteries of electric vehicles deteriorate when the battery temperature is too low or too high. The thermal management system regulating the battery temperature consumes considerable electric energy, particularly, for cooling the battery. To maximize the vehicle driving range, the means of controlling the battery temperature should minimize the energy consumption. In this paper, stochastic model predictive control is applied to the battery-cooling controller. Effective model predictive control requires a good but simple system model with proper estimation of near-future disturbances. The components of the battery cooling system are modeled to represent the energy-consumption and heat exchange mechanism with some assumptions for simplicity. The future information is estimated using historical driving data in a stochastic sense. For real-time implementation, an unequally spaced probability distribution is introduced when designing a stochastic model of future heat generation. The proposed control method shows significantly lower energy consumption while maintaining an acceptable temperature regulation performance compared to other temperature controllers, such as a thermostat-type controller and a model predictive controller with simply assumed future information. The proposed predictive controller shows robust performance compared to typical controllers by utilizing the stochastic estimation of future information.

Caring for the horse in a cold climate—Reviewing principles for thermoregulation and horse preferences

In the Nordic countries, permanent outdoor housing of horses in winter is gaining popularity. This practice will expose the horses to harsh weather conditions. However, horses that are kept indoors at night and turned out in the cold during daytime also experience thermoregulatory challenges. With emphasis on the special challenges in a Nordic climate, this paper aims to increase the understanding of thermoregulation in horses, and ultimately to improve management practices. First, factors related to the environment and the mechanisms of heat exchange are summarised, thereafter the factors related to the horse, such as anatomy and physiological mechanisms which are important for balancing heat gain and heat loss. Human utility of horses and management practices such as clipping, the use of rugs, and provision of shelter are discussed in the light of thermoregulation in horses. The management and care for horses should take into account the principles of thermoregulation and mechanisms of heat loss and gain, and horses should be given a freedom of choice to cope with changing weather conditions. This should include space for movement, protection from sunshine, precipitation and wind, dry bedding, and appropriate feeding. Several studies indicate that the combination of cold rain and wind is a very demanding weather type, not just very low ambient temperatures. A shelter offers the horse protection from wind, precipitation and radiation which it can use when needed, and is therefore a more flexible management solution than a rug, especially when weather conditions change rapidly. In inclement weather, a rug may be a useful supplement. Too many horse owners clip their horse, which often necessitates the use of rugs on a regular basis. More knowledge is needed on how to best manage sport horses, especially when being sweaty after exercise in winter, to ensure good welfare.

Influence of heat exchange on the motion characteristics and mechanical behavior of fine particles in an electrostatic precipitator

An experimental platform was established in order to study the motion characteristics and mechanical behavior of fine particles in an electrostatic precipitator utilizing a heat exchange mechanism. The concentration of fine particles in different states was tested. The force behavior model of particles was established in order to analyze their motion characteristics. The results show that the thermophoretic effect led to a reduction in the size range of the entrained particles and the size range of particles settling efficiently expanded. As compared to the dry state, the removal efficiency of particles in the heat exchange state, smaller than 0.3 μm, greatly improved and that of 0.01 μm particles improved by 30%. The re-entrainment depended on the magnitude of Fm + Fi and Fv + FJ, the heat exchange effect led to an increase in the in-layer force due to an electric field, Fm, van der Waals force, Fv, the electrostatic attraction force, FJ, and the repulsion forces, Fi. It was observed that the size of Fm + Fi and Fv + FJ was not much different.

Experimental Study on the Heat Exchange Mechanism in a Simulated Self-Circulation Wellbore

Self-circulation wellbore is a new technique for geothermal development in hot dry rocks (HDR), which uses a U-shape channel composed of tubing and casing as the heat exchanger. In this study, a self-circulation wellbore in HDR on a laboratory scale was built, and a serial of experiments were conducted to investigate the heat exchange law and the influencing factors on the heat mining rate of the wellbore. A similarity analysis was also made to estimate the heat-mining capacity of the wellbore on a field scale. The experimental results show that the large thermal conductivity and heat capacity of granite with high temperature can contribute to a large heat-mining rate. A high injection rate can cause a high convective heat transfer coefficient in wellbore, while a balance is needed between the heat mining rate and the outlet temperature. An inner tubing with low thermal conductivity can significantly reduce the heat loss to the casing annulus. The similarity analysis indicates that a heat mining rate of 1.25 MW can be reached when using a 2000 m long horizontal well section in a 150 °C HDR reservoir with a circulation rate of 602.8 m3/day. This result is well corresponding to the published data.

Thermal Simulation of Rolled Concrete Dams: Influence of the Hydration Model and the Environmental Actions on the Thermal Field

Mathematical models for the simulation of the thermal evolution of roller-compacted concrete (RCC) dams during construction constitute an important tool for preventing excessive temperature rise, which may lead to cracking and losses of functionality. Here, we present a framework for the simulation of the thermal process. We define the boundary conditions of the problem using a careful description that incorporates the main heat exchange mechanisms. We adopt both a non-adiabatic and an adiabatic heat generation model for the simulation of the cement hydration. Our numerical framework lets us study the effect of the adopted heat generation model on the thermal field. Moreover, we study the influence of the weather conditions on the evolution of the hydration, and on the starting date of construction. Our simulations have shown that the hydration model has an important influence over the temperature field during the construction and the heat generation rate. Moreover, the hydration process and the temperature evolution are driven by the weather conditions. Once the next lift is cast, its thermal insulation effect makes the hydration take place under quasi-adiabatic conditions. As expected, dams built in cold months are prone to dissipate more heat than those built in warm seasons.

Modelling and Exergetic Analysis of a Parabolic Trough Solar Collector

A parabolic trough collector was subject of a thermal study considering heat exchange mechanisms involved in the conversion process of solar energy into heat. The physical model presented was developed with assumptions related to steady state conditions. A code, developed under Matlab, allowed to estimate, by an iterative calculation, all temperatures encountered in the studied system and to calculate, consequently, various efficiencies: optical, energetic and exergetic. After validation of the model, a parametric analysis was carried out in order to consider the influence of the main model parameters on the exergetic behavior of the solar system.

Numerical Study of Transient Bio-Heat Transfer Model With Heat Transfer Coefficient and Conduction Effect in Cylindrical Living Tissue

The human thermal comfort is affected by the body’s heat exchange mechanism conduction, convection, radiation, and evaporation. The mode of heat transfer between the body and environment depends upon the human internal physiological phenomena, together with the boundary conditions. The present paper provides the comprehensive overview of the thermoregulatory system of human body and studies the numerical solution of unsteady-state one dimensional Pennes bio-heat equation with appropriate boundary conditions. The solution is used to observe the temperature profiles at different thermal conductivities, and different heat transfer coefficients in the living tissue at the various time steps. Various physical and physiological factors across the cylindrical living tissue have been incorporated in the model.