PREFACE
Rationale
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Research aims and Objectives
This thesis utilizes ANSYS Fluent simulation software to model the SGHD, measuring 6m x 8m x 3.5m The drying house is situated in An Giang and Dong Thap provinces, encompassing two distinct categories.
The primary aim of this research was to simulate the effects of time on temperature and humidity distribution within the Solar Greenhouse Hybrid Dryer (SGHD), incorporating daily meteorological factors into the simulation The model was validated against experimental solar drying data, enhancing the accuracy of drying predictions and contributing to the design of a more efficient drying process Additionally, the study utilized ANSYS Fluent to analyze the impact of weather conditions on the temperature and humidity distribution inside the SGHD by employing various mesh types, including tetrahedral and hexahedral meshing, with cell sizes tailored to the specific requirements of the simulation.
Outline of thesis
This article is organized into five chapters: Chapters 1 and 2 cover the preface and literature review, focusing on the theoretical framework Chapter 3 presents the mathematical models utilized in the thesis Chapter 4 discusses the results, followed by the conclusions drawn in Chapter 5.
LITERATURE REVIEW
Solar drying process overview
The greenhouse effect is essential for solar drying equipment as it captures and retains heat from the sun This phenomenon occurs when radiant energy accumulates beneath glass or a specific gas layer, allowing for efficient drying processes By utilizing the principles of solar energy collection, these systems enhance the drying efficiency of various materials.
1 illustrates the solar dryer's heat recovery principle
Figure 1 Principle of heat collection of solar drying equipment [Héliantis: the principle]
2.1.2.Classification of drying methods using solar energy
Figure 2 Classification of solar drying methods [9, 10]
The structure of the forced convection solar drying equipment is shown in Figure
The structure of a solar greenhouse dryer (SGHD) allows a portion of solar radiation to be reflected into the atmosphere while the remainder enters the chamber, where it is absorbed by the material This absorption raises the product's temperature, causing it to emit long-wavelength radiation that is trapped by the dome, preventing heat loss and increasing the internal temperature of the drying chamber Although some heat loss occurs due to convection and evaporation, the dome acts as insulation, enhancing the drying process The primary objective of a solar dryer is to supply more heat than the ambient environment to elevate the vapor pressure of moisture in the material, thereby reducing the relative humidity of the drying air and improving its moisture-carrying capacity.
The indirect solar energy drying device consists of two main components: a heat collector and a drying chamber In this system, products are shielded from direct sunlight as they are housed within the drying chamber When hot air enters the chamber through natural convection, it is classified as a natural convection solar drying device Conversely, if a blower is used to introduce hot air, it is referred to as a forced convection solar dryer This forced convection system, equipped with a blower and ducting, can efficiently direct hot air to various locations, significantly enhancing water vapor diffusion and reducing drying time.
Figure 4 The structure of SGHD using the indirect method [9]
2.1.3.Various shapes of the SGHD
The structure and shape of solar drying houses significantly influence their ability to capture solar radiation, with irregular shapes generally receiving more sunlight compared to Quonset designs, which perform poorly in the east-west direction Research indicates that irregularly shaped drying houses achieve higher solar radiation levels from the east and west, while receiving less from the north and south Additionally, these unstructured designs require less energy and heating compared to traditional greenhouse shapes Studies have shown that a span-shaped dryer oriented east-west maximizes solar radiation absorption Furthermore, incorporating a brick wall on the sun-facing side can help minimize radiation loss Comparative analyses of various shapes and orientations, including even, uneven, vinery, semi-circular, and elliptical designs, highlight the importance of structure in optimizing solar greenhouse dryer performance.
(50 to 400 m 2 ), from which they observed that the elliptical shape performed better than other shapes [12] The varied shapes of the solar greenhouse dryer are shown in Figure
Figure 5 Various shapes of the SGHD [13]
Introduction to computational fluid dynamic (CFD) simulation
Computational Fluid Dynamics (CFD) is a vital branch of fluid mechanics that focuses on analyzing fluid flow, heat transfer, mass transfer, and chemical reactions By employing numerical methods and data structures, CFD solves governing mathematical equations related to momentum, mass, energy, and species conservation, as well as the effects of body forces This technology is widely applied across various industries, including aerodynamics in aviation and automotive sectors, hydrodynamics in shipping, power generation, turbomachinery, and chemical process engineering CFD significantly enhances optimization and process design, offering substantial time savings and cost reductions compared to traditional experimentation and data acquisition methods.
ANSYS FLUENT, introduced by Ansys Inc in 2006, is a powerful computational fluid dynamics (CFD) software that offers essential tools for equipment design, optimization, and troubleshooting Its flexible technology allows engineers to gain insights into product performance in real-world scenarios before creating innovative prototypes The software features solvers that accurately model various flow behaviors, including Newtonian and non-Newtonian, single-phase and multi-phase, as well as subsonic and hypersonic flows Each solver is designed for rapid simulation, boasting high stability, thorough testing, validation, and optimization, ensuring both precision and speed in a unified environment.
2.2.2.Working principle of ANSYS CFD
The finite volume method serves as the core principle of this solver, enabling the numerical solution of partial differential equations By dividing the problem domain into a finite number of control volumes, this method applies the divergence theorem to numerically solve general conservation equations Additionally, it is designed to accommodate unstructured grids, enhancing its versatility in various applications.
Figure 6 The fluid region of the pipe flow is discretized into a finite set of control volumes
Fluid dynamics algorithms play a crucial role in understanding the kinematic properties of fluids To effectively tackle this issue, it's essential to utilize the physical characteristics of fluids alongside the descriptive tools of fluid mechanics This approach allows for the formulation of mathematical equations, specifically the Navier-Stokes equations, which serve as the fundamental governing equations in Computational Fluid Dynamics (CFD).
The Navier-Stokes equation, a set of differential equations, is typically solved using numerical methods on computers rather than analytically These methods, including finite difference, finite element, and finite volume, require the survey domain to be divided into smaller sections for iterative calculations Common programming languages for implementing these solutions are Fortran and C Once simulation results are obtained, they can be compared and analyzed against experimental or real-world data If the results lack reliability, the process must be repeated until a satisfactory solution is achieved, encapsulating the entire computational fluid dynamics (CFD) process.
Figure 7 The whole process of CFD simulation stages [19]
MATHEMATICAL MODELS
Conservation equations [20]
The mathematical terms are presented by the governing equations of fluid flow based on the following conservation law of physics:
The mass balance of the fluid elements is presented by:
Rate of increase of mass in fluid element = Net rate of flow of mass into the fluid element (1)
The rate of increase of mass in the fluid element is 擢
The equation states that the function of the variable is equal to the product of the first term and the second term of the equation.
峭貢憲 伐項岫貢憲岻
に絞捲嶌 絞検絞権 伐 峭貢憲 髪項岫貢憲岻
に絞捲嶌 絞検絞権
髪 磐貢懸 伐項岫貢懸岻
に絞検卑 絞捲絞権 伐 磐貢懸 髪項岫貢懸岻
に絞検卑 絞捲絞権
髪 磐貢拳 伐項岫貢拳岻
に絞権卑 絞捲絞検 髪 磐貢y-項岫貢拳岻
に絞権卑 絞捲絞検 The equation (1) is rearranged by divided by element volume 絞捲絞検絞権, then shown in the form of:
Pain can be associated with various conditions, including those related to the spine and joints Understanding the specific type of pain, whether it is acute or chronic, is crucial for effective treatment Identifying the underlying cause can help in developing a targeted approach to alleviate discomfort and improve overall well-being.
擢痛 髪 穴件懸岫貢憲岻"?"2 This equation is unsteady and used for a 3D continuity equation at an incompressible fluid point
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Rate of increase of momentum of fluid-particle = Sum of forces on the fluid particle (2)
The left-hand side source term for each dimension of a fluid particle's coordinate per unit volume is represented by the terms 貢 帖通 帖痛, 貢 帖塚 帖痛, and 貢 帖栂 帖痛 The forces acting on the fluid include surface forces, such as pressure, viscous, and gravity forces, as well as body forces like centrifugal, Coriolis, and electromagnetic forces Consequently, equation (2) is detailed through the equations for the x-, y-, and z-components, respectively.
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項捲 髪項酵掴槻
項検 髪項酵 佃掴
項権 髪 鯨 暢掴
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項検 髪項酵佃槻
項権 髪 鯨 暢槻
経建 噺項酵 掴佃
項捲 髪項酵 槻佃
項検 髪項岫伐貢 髪 酵 佃佃 岻
項権 髪 鯨暢佃
衿緊 擢岫貸諦袋邸 擢掴 猫猫 岻 髪 擢邸 擢槻 猫熱 髪 擢邸 擢佃 年猫
擢掴 髪 擢岫貸諦袋邸 擢槻 熱熱 岻 髪 擢邸 擢佃 年熱
擢掴 髪 擢邸 擢槻 熱年 髪 擢岫貸諦袋邸 擢佃 年年 岻
- 鯨 暢掴 , 鯨 暢槻 , 鯨 暢佃 : body forces
- p is pressure or normal stress, cpf"k"ku"vjg"xkueqwu"uvtguu
The energy conservation equation is modeled based on the first law of the thermodynamic, which is presented by:
Rate of increase of energy of fluid-particle = Net rate of heat added to fluid-particle + Net rate of work done on the fluid particle (3)
- The rate of heat addition to the fluid particle due to heat conduction:
伐 穴件懸 圏"?"穴件懸岫 倦 訣堅欠穴 劇岻
- The total rate of work done on the fluid particle by surface stresses:
岷伐 穴件懸岫喧憲岻峅 髪
欣項岫憲酵 掴掴 岻
項捲 髪項盤憲酵 槻掴 匪
項検 髪項岫憲酵佃掴岻
項捲 髪項岫懸酵掴掴岻
項捲 髪 項盤懸酵 槻掴 匪
項検 髪項岫懸酵佃掴岻
項捲 髪項岫拳酵掴掴岻
項捲 髪項盤拳酵 槻掴 匪
項検 髪項岫拳酵佃掴岻
項捲 筋禽禽禽禁
- The total energy equation with SE is the source of energy
経建 噺 伐喧 穴件懸 憲 髪
欣項岫憲酵 掴掴 岻
項捲 髪項盤憲酵 槻掴 匪
項検 髪項岫憲酵佃掴岻
項捲 髪項岫懸酵掴掴岻
項捲 髪 項盤懸酵 槻掴 匪
項検 髪項岫懸酵佃掴岻
項捲 髪項岫拳酵掴掴岻
項捲 髪項盤拳酵 槻掴 匪
項検 髪項岫拳酵佃掴岻
項捲 筋禽禽禽禁
髪 穴件懸岫 倦 訣堅欠穴 劇岻 髪 鯨帳
- For the total enthalpy equation
項岫貢月待岻
項建 髪 穴件懸岫 貢月待憲岻
噺 伐喧 穴件懸 憲"-"穴件懸岫 倦 訣堅欠穴 劇岻 髪 酵掴掴項憲
項捲 髪 酵槻掴項憲
項検髪 酵佃掴項憲
酵 掴槻 項懸
項捲髪 酵 槻槻 項懸
項検髪 酵 佃槻 項懸
項権 髪 酵 掴佃 項拳
項捲 髪 酵 槻佃 項拳
項検 髪 酵 佃佃 項拳
項権 髪 鯨 朕 Where:
The equations 月 噺 件 髪 椎 諦 and 月待 噺 月 髪 怠 態 岫憲 態 髪 懸 態 髪 拳 態 岻 represent the relationships between specific enthalpies and total enthalpy in thermodynamic systems, where h and h0 denote specific enthalpy and specific total enthalpy, respectively.
3.1.4.Heat and mass balances in SGHD:
The assumptions in building a mathematical model for a solar dryer are:
- Do not stratify the air inside the drying house
- Calculation of drying based on thin plate drying model
The specific heat capacity of air, the coating, and the product remains constant in the solar drying house Figure 8 illustrates the energy transfer diagram utilizing the greenhouse effect, which is essential for understanding the heat and mass balances within the system.
Figure 8 Distribution of some parameters in SGHD [21]
The heat energy accumulation rate on the cover is determined by several factors: the convection heat transfer rate between the indoor air and the polycarbonate cover, the thermal radiation heat transfer rate from the outdoor air to the cover, the convection heat transfer rate between the roofing sheet and the surrounding air, the thermal radiation heat transfer rate from the roofing sheet to the product, and the solar radiation energy absorbed by the cladding This comprehensive energy balance equation encapsulates the various heat transfer mechanisms at play.
兼 頂 系 椎頂 穴劇頂
The equation describes a relationship involving various parameters, where the values are derived from specific functions and their differences It highlights the interaction between multiple variables, indicating how they contribute to the overall outcome By analyzing these components, one can better understand the dynamics at play in the system.
髪 畦 椎 月 追 椎貸頂 盤劇 椎 伐 劇 頂 匪 髪 畦 頂 苅 頂 荊 痛
3.1.4.2 Energy balance for the air inside the SGHD
The heat energy accumulation rate in a drying house is determined by several factors: the convection heat transfer between the product and the air, the convection heat transfer between the floor and the air, the heat energy increase in the air from the product, the heat gain from air circulation within the chamber, the heat loss to the surrounding air, and the energy absorbed from solar radiation This comprehensive energy balance equation highlights the complex interactions affecting the thermal dynamics within the drying environment.
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The article discusses the intense pain associated with certain conditions, particularly focusing on the impact of various factors on pain levels It highlights the significance of understanding the underlying causes of pain to develop effective treatment strategies Additionally, the text emphasizes the importance of proper diagnosis and the role of healthcare professionals in managing pain effectively By addressing these key elements, the article aims to provide readers with valuable insights into pain management and the complexities of pain-related disorders.
糠庁岻 髪 盤な 伐 糠椎匪 繋椎飯 畦頂酵頂荊痛"
3.1.4.3 Energy balance for the product
The accumulation of heat energy in a product is determined by several factors: the heat energy transfer from air to the product through convection, the radiation heat transfer between the coating and the product, the heat energy lost due to latent heat loss from the product, and the solar energy absorbed by the product.
The energy balance equation for the product:
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3.1.4.4 Energy balance for the concrete
The accumulation of heat energy in the floor is determined by three key factors: the convection heat transfer rate between the air in the dryer and the floor, the heat transfer rate from the floor to the ground, and the rate of solar radiation absorption by the floor This relationship can be expressed through the energy balance equation.
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Viscous Model [20]
The viscous model in ANSYS FLUENT is essential for defining flow parameters, including inviscid, laminar, and turbulent conditions Various models are available, such as inviscid, laminar, Spalart-Allmaras, k-epsilon, k-omega, and LES This study specifically focuses on k-epsilon models, as the spray dryer operates without turbulent flow.
The turbulent k-epsilon and k-omega standard models, including RNG and realizable k-omega, exhibit three key differences Firstly, they differ in their methods for calculating turbulent viscosity Secondly, there is a variation in the turbulent Prandtl number Lastly, the equations governing these models have distinct terms related to generation and destruction processes.
The investigation of turbulent length and time scales utilizes two distinct transport equations, which are widely employed in industrial flow and heat transfer due to their robustness, cost-effectiveness, and high accuracy across various turbulent flows The standard k-ε model, based on empirical transport equations, is derived from the exact equation for turbulent kinetic energy (k), while the transport equation for the dissipation rate (ε) closely resembles its mathematically precise counterpart.
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項捲 沈 岫貢倦憲 沈 岻 噺 項
項捲 珍 峪磐航 髪航痛
購 賃 卑項倦
項捲 珍 崋 髪 罫 賃 髪 罫 長 伐 貢綱 伐 桁 暢 髪 鯨 賃
項建岫貢綱岻 髪 項
項捲沈岫貢綱憲沈岻 噺 項
項捲珍峪磐航 髪航痛
購悌卑 項綱
項捲珍崋 髪 系 怠悌 綱
倦岫罫賃 髪 系戴悌罫長岻 伐 系態悌貢綱 態
+ Gk: the generation of turbulence kinetic energy due to the mean velocity gradients
+ Gb: the generation of turbulence kinetic energy due to buoyancy
+ YM: the contribution of the fluctuating dilatation in compressible turbulence to the overall dissipation rate
+ j k cpf"ji