5.4 Interphase heat transfer
7 min read•august 20, 2024
is crucial in multiphase systems, involving energy exchange between different phases. It plays a key role in industrial processes like and , impacting overall system efficiency and performance.
This topic covers three main modes: convective, conductive, and . Understanding these mechanisms, along with factors affecting them, is essential for designing and optimizing multiphase systems in various applications.
Modes of interphase heat transfer
- Interphase heat transfer refers to the exchange of thermal energy between different phases in a multiphase system
- Plays a crucial role in various industrial processes such as heat exchangers, boilers, and chemical reactors
- Three primary modes of interphase heat transfer include convective, conductive, and radiative heat transfer
Convective heat transfer
- involves the transport of thermal energy by the motion of fluids
- Occurs when there is a temperature difference between a fluid and a solid surface or between two immiscible fluids
- Convective heat transfer can be further classified into natural and
Convective heat transfer coefficients
Top images from around the web for Convective heat transfer coefficients
Frontiers | Numerical Analysis of FLiBe Laminar Convective Heat Transfer Characteristics in ... View original
Is this image relevant?
Enhancing the Convective Heat Transfer Coefficient Using a Single or Doubled Strainers View original
Is this image relevant?
Frontiers | Numerical Analysis of FLiBe Laminar Convective Heat Transfer Characteristics in ... View original
Is this image relevant?
Enhancing the Convective Heat Transfer Coefficient Using a Single or Doubled Strainers View original
Is this image relevant?
1 of 2
Top images from around the web for Convective heat transfer coefficients
Frontiers | Numerical Analysis of FLiBe Laminar Convective Heat Transfer Characteristics in ... View original
Is this image relevant?
Enhancing the Convective Heat Transfer Coefficient Using a Single or Doubled Strainers View original
Is this image relevant?
Frontiers | Numerical Analysis of FLiBe Laminar Convective Heat Transfer Characteristics in ... View original
Is this image relevant?
Enhancing the Convective Heat Transfer Coefficient Using a Single or Doubled Strainers View original
Is this image relevant?
1 of 2
- quantify the rate of heat transfer between a fluid and a solid surface
- Depend on fluid properties (density, viscosity, ), flow characteristics (velocity, turbulence), and surface geometry
- Commonly estimated using empirical correlations or computational fluid dynamics (CFD) simulations
Factors affecting convective transfer
- Fluid properties such as density, viscosity, and thermal conductivity influence convective heat transfer
- Flow regime (laminar or turbulent) significantly affects the rate of convective heat transfer
- Turbulent flow enhances mixing and increases convective heat transfer coefficients
- Surface roughness and geometry can impact the boundary layer development and convective heat transfer
Conductive heat transfer
- involves the transfer of thermal energy through a medium by molecular interactions
- Occurs in solid phases and across phase boundaries in multiphase systems
- Governed by , which relates the heat flux to the temperature gradient and thermal conductivity
Thermal conductivity in multiphase systems
- Thermal conductivity is a material property that quantifies the ability to conduct heat
- In multiphase systems, the effective thermal conductivity depends on the volume fractions and thermal conductivities of individual phases
- Effective thermal conductivity can be estimated using various models (series, parallel, Maxwell-Eucken)
Effective thermal conductivity models
- Series model assumes phases are arranged in layers perpendicular to the heat flow direction
- Parallel model assumes phases are arranged in layers parallel to the heat flow direction
- Maxwell-Eucken model considers dispersed phases as spherical inclusions in a continuous matrix
- Suitable for dilute dispersions with low volume fractions of the dispersed phase
- Other models (Bruggeman, Hashin-Shtrikman) account for higher volume fractions and phase interactions
Radiative heat transfer
- Radiative heat transfer involves the exchange of thermal energy through electromagnetic waves
- Significant in high-temperature applications and systems with participating media (gases, particles)
- Governed by the , which describes the propagation and attenuation of radiation
Radiative properties of phases
- quantifies the ability of a surface to emit radiation compared to an ideal black body
- , , and characterize the interaction of radiation with a medium
- describes the extent of radiation scattering by particles or droplets in a participating medium
Radiative transfer equations
- The radiative transfer equation (RTE) describes the spatial and directional variation of radiative intensity
- Includes terms for emission, absorption, and scattering of radiation
- Solving the RTE requires numerical methods such as or
- Simplified models (Rosseland approximation, P1 approximation) are often used for optically thick media
Interphase heat transfer coefficients
- Interphase heat transfer coefficients quantify the rate of heat transfer between phases in a multiphase system
- Important for predicting overall heat transfer rates and temperature distributions
- Depend on the specific multiphase flow regime (bubbly, slug, annular) and phase properties
Definition and significance
- Interphase heat transfer coefficients are defined as the ratio of the heat flux to the temperature difference between phases
- Crucial for designing and optimizing multiphase heat transfer equipment (heat exchangers, boilers)
- Accurate estimation of interphase heat transfer coefficients is essential for predicting system performance and efficiency
Correlations for estimating coefficients
- Empirical correlations are widely used to estimate interphase heat transfer coefficients
- Correlations are typically based on dimensionless numbers (Reynolds, Prandtl, Nusselt) and flow regime maps
- Examples include for turbulent flow in tubes and for boiling heat transfer
- Selection of appropriate correlation depends on the specific multiphase system and operating conditions
Interfacial area concentration
- quantifies the amount of interface between phases per unit volume
- Directly influences the rate of interphase heat transfer, as heat transfer occurs across phase interfaces
- Higher interfacial area concentration leads to enhanced interphase heat transfer
Definition and measurement techniques
- Interfacial area concentration is defined as the ratio of the interfacial area to the total volume of the multiphase system
- Can be measured experimentally using techniques such as photographic methods, light scattering, or tomography
- Computational methods (interface tracking, volume of fluid) can also be used to estimate interfacial area concentration
Influence on interphase heat transfer
- Interfacial area concentration directly affects the rate of interphase heat transfer
- Larger interfacial area provides more surface area for heat exchange between phases
- Enhancing interfacial area concentration through design modifications (internals, packing) can improve heat transfer performance
- Accurate prediction of interfacial area concentration is crucial for modeling and optimizing interphase heat transfer
Non-equilibrium heat transfer
- refers to situations where the phases in a multiphase system have different temperatures
- Occurs when the time scale of interphase heat transfer is slower than the time scale of fluid motion or phase change
- Requires separate energy equations for each phase to capture the temperature differences
Local thermal non-equilibrium
- assumes that the phases have different local temperatures
- Relevant in systems with large temperature gradients or rapid phase change (boiling, condensation)
- LTNE models use separate energy equations for each phase, coupled through interphase heat transfer terms
Heat transfer between phases
- Heat transfer between phases occurs through the phase interfaces
- Driven by the temperature difference between the phases and the interfacial heat transfer coefficient
- Modeling heat transfer between phases requires accurate estimation of interfacial area concentration and interphase heat transfer coefficients
- Non-equilibrium heat transfer models are essential for capturing the temperature variations between phases
Numerical modeling of interphase heat transfer
- Numerical modeling is widely used to simulate and predict interphase heat transfer in multiphase systems
- Involves solving the governing equations (conservation of mass, momentum, energy) for each phase
- Requires appropriate models for interphase heat transfer, interfacial area concentration, and phase interactions
Coupled vs segregated solution approaches
- solve the governing equations for all phases simultaneously
- Suitable for strongly coupled multiphase systems with significant interphase interactions
- solve the equations for each phase separately, with interphase coupling terms
- Suitable for weakly coupled systems or when the time scales of phase interactions are different
- Choice of solution approach depends on the complexity of the multiphase system and computational resources
Discretization schemes and solution algorithms
- Discretization schemes convert the governing equations into algebraic equations on a computational grid
- Finite difference, finite volume, and finite element methods are commonly used
- Solution algorithms solve the discretized equations to obtain the flow and temperature fields
- Examples include SIMPLE (Semi-Implicit Method for Pressure-Linked Equations) and PISO (Pressure Implicit with Splitting of Operators) algorithms
- Appropriate discretization schemes and solution algorithms are crucial for accurate and efficient
Experimental techniques for measuring interphase heat transfer
- Experimental techniques provide valuable data for validating and improving interphase heat transfer models
- Enable the measurement of temperature distributions, heat fluxes, and interphase heat transfer coefficients
- Various techniques are available for different multiphase systems and operating conditions
Temperature measurement methods
- are widely used for point temperature measurements in multiphase systems
- Robust and suitable for high-temperature applications, but provide limited spatial resolution
- Infrared thermography allows non-intrusive temperature mapping of surfaces
- Useful for studying temperature distributions and identifying hot spots
- Laser-induced fluorescence (LIF) enables temperature measurements in fluids by using temperature-sensitive fluorescent dyes
Heat flux measurement techniques
- (calorimeters) measure the local heat flux through a surface
- Provide direct measurements of heat transfer rates, but may disturb the flow field
- Thermal capacitance methods estimate heat flux by measuring the temperature change of a known thermal mass
- Suitable for transient heat transfer measurements
- Optical techniques (laser interferometry, Raman spectroscopy) allow non-intrusive heat flux measurements based on temperature gradients
Industrial applications of interphase heat transfer
- Interphase heat transfer is encountered in various industrial processes and equipment
- Efficient design and optimization of these systems require a thorough understanding of interphase heat transfer mechanisms
- Two common industrial applications are heat exchangers and fluidized bed reactors
Heat exchangers and boilers
- Heat exchangers transfer heat between two or more fluids through a solid surface
- Widely used in chemical, petrochemical, and power generation industries
- Boilers generate steam by heating water using combustion gases or other heat sources
- Interphase heat transfer occurs between the water/steam and the heating medium
- Design of heat exchangers and boilers involves selecting appropriate geometries, materials, and operating conditions to maximize interphase heat transfer
Fluidized bed reactors and combustors
- Fluidized bed reactors and combustors involve the interaction of a gas phase with solid particles
- Used in chemical processing, combustion, and gasification applications
- Interphase heat transfer occurs between the gas and solid phases, influencing the overall reactor performance
- Heat transfer affects reaction rates, product yields, and energy efficiency
- Understanding and optimizing interphase heat transfer is crucial for the design and operation of fluidized bed systems
Key Terms to Review (38)
Absorptivity: Absorptivity is a measure of how much radiant energy is absorbed by a surface when exposed to incident radiation. It is an important property in heat transfer, particularly in the context of interphase heat transfer, as it influences how energy is transferred between phases, such as solid to fluid or gas to solid. Understanding absorptivity helps in analyzing thermal interactions and optimizing processes that involve energy exchange between different phases.
Annular Flow: Annular flow is a type of multiphase flow pattern where one fluid (usually gas) flows in the center of a pipe or conduit while another fluid (typically liquid) forms a ring or annular layer around it. This flow regime is crucial for understanding fluid dynamics, as it impacts various phenomena such as heat transfer, pressure drop, and phase interaction in pipelines and reactors.
Boilers: Boilers are closed vessels designed to heat water or other fluids to generate steam or hot water for various applications, including heating systems, power generation, and industrial processes. They operate by transferring heat from a fuel source, such as natural gas, oil, or coal, through the fluid inside the boiler, which can then be used for interphase heat transfer in multiphase systems.
Bubbly flow: Bubbly flow refers to a type of multiphase flow where discrete gas bubbles are dispersed within a liquid. This flow regime is significant as it influences various engineering processes, such as heat and mass transfer, momentum exchange, and the behavior of flow in confined spaces like pipelines or reactors.
Chen correlation: The Chen correlation is a mathematical model used to predict heat transfer coefficients during phase change processes in multiphase flow systems. This correlation helps in estimating the rate of heat transfer between different phases, such as liquid and vapor, which is critical in processes like boiling and condensation. Understanding this correlation is essential for optimizing thermal management in various engineering applications, particularly those involving pressurized systems.
Conductive heat transfer: Conductive heat transfer is the process of thermal energy moving through a material without any movement of the material itself, occurring due to temperature differences. This mode of heat transfer is crucial in understanding how heat is exchanged between different phases in multiphase flow systems, impacting overall energy efficiency and system design.
Convective heat transfer: Convective heat transfer is the process of heat energy being transferred between a solid surface and a fluid (liquid or gas) that is in motion. This process occurs due to the combined effects of conduction, where heat is transferred through direct contact, and fluid motion, which enhances the transfer by moving the heated or cooled fluid away from the surface. Understanding convective heat transfer is crucial for analyzing energy exchange in multiphase systems, particularly when considering the interactions between phases during processes like boiling or condensation.
Convective Heat Transfer Coefficients: Convective heat transfer coefficients are values that quantify the rate of heat transfer between a solid surface and a fluid in motion over that surface. They play a crucial role in determining the efficiency of heat exchange processes, particularly during interphase heat transfer, where energy is transferred between different phases, such as liquid to gas or solid to liquid. Understanding these coefficients is essential for optimizing thermal systems and enhancing energy efficiency in various applications.
Coupled solution approaches: Coupled solution approaches refer to methods used in multiphase flow modeling that simultaneously solve the governing equations of different phases, accounting for their interactions. This method is essential in accurately predicting the behavior of complex systems where multiple phases coexist, such as liquid and gas or solid and fluid interactions, particularly in heat transfer scenarios where energy exchange between phases significantly influences overall system performance.
Discrete Ordinates Method (DOM): The Discrete Ordinates Method (DOM) is a numerical technique used for solving the radiative transfer equation in participating media, which describes how radiation interacts with matter. This method involves discretizing the angular domain into a finite number of directions, allowing for an analysis of the energy transfer processes occurring during interphase heat transfer. By capturing the angular distribution of radiation, DOM helps in understanding how heat is transferred between different phases, enhancing the accuracy of thermal modeling in multiphase flows.
Dittus-Boelter correlation: The Dittus-Boelter correlation is an empirical relationship used to estimate the heat transfer coefficient for turbulent flow in a pipe. This correlation is crucial in calculating convective heat transfer during interphase heat transfer processes and plays a vital role in understanding thermal dynamics in pressurized water reactors, where effective heat exchange is essential for safety and efficiency.
Effective thermal conductivity models: Effective thermal conductivity models are mathematical frameworks used to estimate the overall thermal conductivity of a multiphase system, taking into account the contributions from different phases and their interactions. These models help in understanding how heat transfers between phases, which is essential for predicting thermal behavior in processes involving multiple materials, such as in interphase heat transfer scenarios where different phases, like solid, liquid, and gas, interact.
Emissivity: Emissivity is a measure of a material's ability to emit thermal radiation compared to that of a perfect black body. It ranges from 0 to 1, where 1 signifies that the material is a perfect emitter of thermal radiation. The emissivity of a surface can affect heat transfer processes, particularly in interphase heat transfer, where energy exchange occurs between different phases, such as solid, liquid, and gas.
Finite difference method: The finite difference method is a numerical technique used to approximate solutions to differential equations by discretizing them into a grid of points. This approach transforms continuous equations into algebraic equations, allowing for the simulation of various physical phenomena, including heat transfer between phases. By using differences in values at adjacent points, the method provides a way to model complex systems where analytical solutions may be difficult or impossible to obtain.
Finite Element Method: The finite element method (FEM) is a numerical technique used to find approximate solutions to complex engineering and physical problems by breaking down a large system into smaller, simpler parts called finite elements. This method allows for the analysis of interphase momentum and heat transfer by providing a framework for modeling interactions between different phases in a multiphase system. It is crucial in multiscale modeling as it enables the understanding of phenomena at different scales, facilitating accurate predictions and optimizations in various applications.
Finite Volume Method: The finite volume method is a numerical technique used for solving partial differential equations, particularly in fluid dynamics, by dividing the domain into small control volumes. This approach helps in conserving mass, momentum, and energy by integrating these quantities over each control volume and applying the principles of flux across the boundaries. It connects well with various models and transfer processes involved in multiphase flows, as it efficiently handles complex geometries and varying flow conditions.
Forced Convection: Forced convection is a heat transfer process where fluid motion is generated by an external force, such as a pump or a fan, rather than by natural buoyancy effects. This method significantly enhances heat transfer rates by promoting a more uniform temperature distribution and increasing the overall energy exchange between the fluid and solid surfaces. In contexts involving interphase heat transfer, forced convection plays a crucial role in managing temperature differences between phases, improving efficiency in multiphase systems.
Fourier's Law: Fourier's Law describes the heat conduction process, stating that the rate of heat transfer through a material is proportional to the negative gradient of temperature and the area through which the heat flows. This principle is crucial in understanding how heat energy moves between different phases, influencing interphase heat transfer and overall thermal management in multiphase systems.
Heat exchangers: Heat exchangers are devices designed to efficiently transfer heat between two or more fluids at different temperatures without mixing them. They are crucial in many industrial processes, allowing for energy recovery and temperature regulation in systems such as HVAC, refrigeration, and power generation. By maximizing surface area and optimizing flow patterns, heat exchangers enhance heat transfer rates and overall system efficiency.
Heat flux sensors: Heat flux sensors are devices that measure the rate of heat transfer per unit area, typically used to monitor heat flow in various materials and systems. These sensors are essential for understanding interphase heat transfer, as they provide real-time data on thermal interactions between different phases, such as solid-liquid or gas-liquid interfaces. By accurately gauging heat flux, these sensors aid in optimizing thermal management in multiphase flow systems.
Interfacial area concentration: Interfacial area concentration refers to the surface area of the interface between different phases in a multiphase flow system per unit volume of the mixture. It plays a crucial role in understanding how different phases interact, particularly in processes involving heat and mass transfer. This concept is essential for predicting the efficiency of various engineering processes, such as reactors and heat exchangers, where energy exchange across interfaces significantly impacts performance.
Interphase heat transfer: Interphase heat transfer refers to the exchange of thermal energy between different phases of matter, such as solid, liquid, and gas. This process is critical in multiphase flow systems, as it influences the overall energy balance and phase interactions, impacting phenomena like boiling, condensation, and the efficiency of heat exchangers.
Local thermal non-equilibrium (LTNE): Local thermal non-equilibrium (LTNE) refers to a condition in multiphase flow systems where the temperatures of the different phases do not equilibrate at a local level, leading to variations in temperature between the phases. This phenomenon is particularly important in understanding interphase heat transfer, as it can significantly affect the heat transfer rates and overall thermal behavior of a system. LTNE can occur due to various factors, such as differing heat capacities, phase-specific thermal properties, and different velocities of the interacting phases.
Monte Carlo Simulations: Monte Carlo simulations are a statistical technique that utilizes random sampling and statistical modeling to estimate complex mathematical outcomes. They are particularly useful in scenarios involving uncertainty and variability, allowing for the assessment of risk and prediction of future events by running numerous simulations based on different input parameters. This technique can be applied to understand interphase heat transfer by simulating the interactions between different phases, such as solid, liquid, and gas, under varying conditions.
Natural convection: Natural convection is the process of heat transfer in a fluid due to the movement of the fluid itself, which occurs when temperature differences create density variations that lead to fluid motion. This mechanism is essential in various systems where heat needs to be distributed without external forces like pumps or fans, relying instead on the natural movement induced by buoyancy effects. It plays a crucial role in interphase heat transfer as it enhances the exchange of thermal energy between different phases, such as liquid and gas.
Non-equilibrium heat transfer: Non-equilibrium heat transfer refers to the process of heat exchange between phases in a multiphase system where thermal equilibrium is not established. This type of heat transfer occurs when temperature differences exist between phases and involves transient thermal effects that can significantly influence the efficiency and behavior of the system. Understanding non-equilibrium heat transfer is essential in analyzing interphase interactions, as it accounts for the complex dynamics involved when different phases exchange thermal energy without reaching uniform temperature conditions.
Numerical modeling of interphase heat transfer: Numerical modeling of interphase heat transfer involves using computational methods to simulate the transfer of thermal energy between different phases in a multiphase system, such as solid-liquid, liquid-gas, or solid-gas interactions. This modeling is crucial for understanding how heat moves across phase boundaries, influencing processes like evaporation, condensation, and melting. Accurate simulations can provide insights into thermal efficiency and performance in various engineering applications.
PISO Algorithm: The PISO algorithm (Pressure Implicit with Splitting of Operators) is a numerical method used to solve incompressible fluid flow problems by decoupling the pressure and velocity fields. This approach enhances stability and accuracy, making it especially effective for simulating complex flows, including multiphase systems where heat transfer between phases is critical. It combines aspects of both the SIMPLE and fractional step methods, allowing for efficient handling of pressure-velocity coupling.
Radiative heat transfer: Radiative heat transfer is the process of energy transfer through electromagnetic radiation, primarily occurring in the form of infrared radiation, between surfaces or substances at different temperatures. This mode of heat transfer does not require a medium, allowing energy to be transferred through a vacuum or transparent media, which makes it distinct from conduction and convection. Understanding radiative heat transfer is crucial when analyzing interphase heat transfer as it can significantly impact the thermal behavior in multiphase systems, particularly where gas and solid interfaces are involved.
Radiative Transfer Equation (RTE): The Radiative Transfer Equation (RTE) describes the transport of radiation through a medium, accounting for absorption, emission, and scattering processes. This equation is crucial for understanding heat transfer in multiphase systems where different phases interact, impacting the overall energy balance and temperature distribution.
Reflectivity: Reflectivity is the measure of a material's ability to reflect radiation, such as light or heat, that strikes its surface. It plays a crucial role in interphase heat transfer as it directly influences how energy is exchanged between phases, affecting thermal efficiency and temperature gradients. Understanding reflectivity helps in predicting how different materials interact with energy under various conditions, impacting processes like heat absorption and emission.
Scattering coefficient: The scattering coefficient is a measure of how much light or radiation is scattered by particles within a medium. It quantifies the extent to which photons are redirected in various directions after interacting with particles, and plays a critical role in understanding interphase heat transfer, particularly in multiphase systems where different phases interact thermally.
Segregated solution approaches: Segregated solution approaches are numerical methods used in computational fluid dynamics to solve multiphase flow problems by treating different phases separately during the simulation process. This technique allows for the independent calculation of variables associated with each phase, which can improve computational efficiency and simplify the complexity involved in modeling interphase interactions.
Simple algorithm: A simple algorithm is a straightforward, step-by-step procedure or formula for solving a problem or performing a task. These algorithms are characterized by their ease of understanding and execution, often involving basic operations and clear logical structures. In complex fields like interphase heat transfer and numerical methods, simple algorithms serve as foundational tools that can be built upon for more intricate simulations and calculations.
Slug Flow: Slug flow is a flow regime characterized by the intermittent movement of large, discrete bubbles or slugs of gas within a liquid, creating a distinct interface between the gas and liquid phases. This type of flow can significantly impact the dynamics of multiphase systems, influencing factors such as volume fraction and interphase interactions.
Thermal conductivity: Thermal conductivity is a measure of a material's ability to conduct heat. It quantifies how easily heat flows through a substance when there is a temperature difference. This property plays a crucial role in determining heat transfer rates in various applications, affecting efficiency and performance in systems involving heat exchange, such as reactors and condensers.
Thermocouples: Thermocouples are temperature sensing devices made of two different metals joined at one end, producing a voltage that correlates to temperature differences. They are widely used in industrial and scientific applications to measure temperature due to their reliability, wide temperature range, and quick response time. The voltage generated is based on the thermoelectric effect, which is crucial for interphase heat transfer measurements where accurate temperature readings are essential.
Transmissivity: Transmissivity is a measure of how easily heat is transferred through a material, defined as the product of the thermal conductivity and the thickness of the material. This concept is crucial for understanding how heat flows between different phases in multiphase systems, influencing efficiency and performance in applications such as heat exchangers and insulation materials.