Numerical and Experimental Analysis of Convection Heat Transfer in a Lean-To Type Greenhouse

Solar Energy ◽  
2004 ◽  
Author(s):  
Wei Chen ◽  
Wei Liu
Keyword(s):  
Heat Transfer ◽  
Mathematical Model ◽  
Moisture Content ◽  
Gas Flow ◽  
Solar Irradiation ◽  
Wall Material ◽  
Insulation Material ◽  
Remarkable Effect ◽  
The North ◽  
North Wall

In this paper, heat transfer and flow in a lean-to passive solar greenhouse has been studied. A mathematical model based on energy equilibrium and a one-dimensional mathematical model for the unsaturated porous medium have been founded and developed to predict the temperature and moisture content in soil and the enclosed air temperature in the greenhouse. On the condition that plant and massive wall is neglected, the air is mainly heated by the soil surface in the greenhouse, which absorbs the incident solar radiation. With increase in depth, the variation of the temperature and moisture content in soil decreases on account of ambient, and the appearance of the peak temperature in soil postpones. Solar irradiation absorber, heat storage and insulation are the main effects of the north massive wall on greenhouse, which is influenced by the structure and the material. The specific heat capacity and thermal conductivity of wall material have a remarkable effect on the north wall temperature. The build-up north wall with thermal insulation material may be chosen for greenhouse. The temperature distribution and gas flow in greenhouse is influenced by the cover material of the inside surface of the north wall. All results should be taken into account for a better design and run of a greenhouse.

Evaporation of Gravity- and Gas Flow-Driven Thin Liquid Films in Micro- and Minigrooves

2004 ◽  
Author(s):  
T. Gambaryan-Roisman ◽  
P. Stephan
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Gas Flow ◽  
Thin Liquid Film ◽  
Flow Region ◽  
Wave Theory ◽  
Liquid Films ◽  
Wall Material ◽  
Wall Structure ◽  
Ultra Thin Film

Using microstructured wall surfaces may improve the heat transfer performance of falling film or shear-driven film cooling devices enormously. The advantages of the structured surface include the prevention of the formation of dry patches on hot surfaces, the promotion of ultra-thin film evaporation, and a wavy motion of the film that enhances mixing of the liquid. We develop a model describing the hydrodynamics and heat transfer by evaporation of gravity- and gas flow-driven liquid films on grooved surfaces. For low Reynolds numbers or low liquid mass fluxes the heat transfer is governed by the evaporation of the ultra-thin film at a micro region, in the vicinity of the three-phase contact line. We investigate the hydrodynamic stability of the film flow using the long-wave theory. In addition to the films completely covering the wall structure, we study the stability characteristics of a thin liquid film partly covering the grooved wall, so that the flow region is bounded by contact lines. Two cases are analyzed: fully wetting liquids and liquids which form a small but finite contact angle with the wall material.

scholarly journals Determining the thermal mode of bio-based raw materials composting process in a rotary-type chamber

2021 ◽  
Vol 2 (8 (110)) ◽  
pp. 41-52
Author(s):  
Gennadii Golub ◽  
Ivan Grabar ◽  
Dmytro Derevyanko ◽  
Anna Нolubenko ◽  
Oleksandr Medvedskyi ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Moisture Content ◽  
Heat Generation ◽  
Temperature Regime ◽  
Raw Materials ◽  
Wall Material ◽  
Thermal Mode ◽  
Organic Substrates ◽  
Surface Cooling ◽  
Composting Process

One of the promising methods to dispose of agricultural bio-based raw materials is to produce compost by aerobic fermentation in rotary chambers. High efficiency of the composting process is achieved when a proper temperature mode is maintained at each phase of the process. Changes in temperature are directly related to the effective transformation of organic substrates by microorganisms and are the reason for the low quality of produced compost in terms of its agrochemical and microbiological parameters. It was established that a high-temperature regime is achieved on the condition that the amount of heat released during the biodegradation of raw materials by microorganisms is greater than the heat loss associated with the substrate aeration and surface cooling. Therefore, the time during which the fermented mass remains warm depends entirely on the substrate's physical-chemical characteristics, the parameters of the equipment, and the modes of its operation. To describe the established conditions, based on the equation of thermal balance, a mathematical model has been built. The model relates the thermal costs necessary to maintain the optimal temperature regime of the process to the substrate's moisture content and specific active heat generation, as well as to such an important thermal physical parameter of the chamber as the coefficient of heat transfer of the wall material. A rotary chamber was manufactured to investigate the thermal mode of the bio-based raw materials composting process. It has been experimentally established that the chamber walls' heat transfer coefficient of 1.6 W/(m2·°C), a value of the substrate's specific active heat generation of 9.2 W/kg, and a moisture content of 58 % provide for the thermal needs for the process with the release of 140 MJ of excess heat. The reported study could be the basis for the modernized methodology of thermal calculations of the bio-based raw materials composting process in closed fermentation chambers

scholarly journals Mathematical study of transport phenomena along a tuyere of the Teniente converter

2006 ◽  
Vol 2006 ◽  
pp. 1-12
Author(s):  
J. San Martín ◽  
R. Gormaz ◽  
C. Conca ◽  
F.-Z. Saouri ◽  
A. Benaddi ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Mathematical Model ◽  
Gas Flow ◽  
Refractory Lining ◽  
Transport Phenomena ◽  
Gas Velocity ◽  
Mathematical Study ◽  
Air Inlet ◽  
Solid Part ◽  
Velocity Pressure

This paper presents a comprehensive mathematical model of transport phenomena which occur along a tuyere of the Teniente converter during injection of oxygen-enriched air. Inlet pressure, gas velocity and temperature, the dimensions of the tuyere, and the properties of gas are the basic data. From these inputs, temperature distribution of the refractory walls of the converter around the tuyere as well as the velocity, pressure, and the Mach number along the pipe can be calculated. In this model, the heat transfer through the metal jacket of the tuyere and the refractory lining are duly taken into account. More precisely, a mathematical model is developed where the equations of momentum and energy of the gas are coupled with the equations of heat transfer inside the solid part. This new model couples a partial differential equation in the solid part with four ordinary differential equations in the gas flow.

Mathematical model of natural gas flow in pipelines in the presence of hydrate formation

2008 ◽  
Vol 6 ◽  
pp. 205-209
Author(s):  
V.Sh. Shagapov ◽  
R.R. Urazov
Keyword(s):  
Heat Transfer ◽  
Mathematical Model ◽  
Mass Transfer ◽  
Natural Gas ◽  
Phase Transformations ◽  
Gas Hydrates ◽  
Heat Conductivity ◽  
Gas Flow ◽  
Hydrate Formation ◽  
Natural Gas Flow

The flow of wet natural gas in the pipeline is considered in the presence of the formation of gas hydrates on the internal walls of the channel. In the description of the phenomenon, such interrelated processes as phase transformations and mass transfer of water into the composition of gas hydrates, heat transfer between the gas stream and the environment, heat conductivity in the ground are taken into account.

scholarly journals Problem of conjugate heat transfer between main gas pipeline and frozen ground

2019 ◽  
Vol 102 ◽  
pp. 01001
Author(s):  
Edward Bondarev ◽  
Igor Rozhin ◽  
Kira Argunova
Keyword(s):  
Heat Transfer ◽  
Mathematical Model ◽  
Gas Flow ◽  
Hydrate Formation ◽  
Conjugate Problem ◽  
Gas Pipeline ◽  
Frozen Ground ◽  
Flow Area ◽  
Tube Cross Section ◽  
Main Gas Pipeline

Mathematical model of non-isothermal gas flow within the framework of tube hydraulics including change of tube cross-section due to hydrate formation and the dependence of coefficient of heat transfer between gas and hydrate layer on varying flow area is proposed. The corresponding conjugate problem of heat exchange between imperfect gas in the pipeline and the environment is reduced to the solution of differential equations describing non-isothermal flow of gas in pipes and heat transfer equations in ground with the corresponding conjugation conditions. In the quasi-stationary mathematical model of hydrate formation (dissociation), the dependence of gas-hydrate transition temperature on gas pressure is taken into account. Some decisions taken in the design of the first section of the main gas pipeline «Power of Siberia» have been analyzed. It has been shown that if gas is not sufficiently dried, outlet pressure may drop below the technological limit in about 6-7 hours. At the same time, for completely dry gas ,it is possible to reduce the cost of thermal insulation of the pipeline at least two fold.

Mathematical Model of Powder Material Particles Heating in Thermal Spraying

2018 ◽  
Vol 769 ◽  
pp. 336-345 ◽  
Author(s):  
Valery I. Bogdanovich ◽  
Mikhail G. Giorbelidze
Keyword(s):  
Heat Transfer ◽  
Mathematical Model ◽  
Powder Material ◽  
Gas Flow ◽  
Radiative Heat ◽  
Thermal Spraying ◽  
Correct Selection ◽  
Coated Surface ◽  
The Mathematical Model ◽  
Selection Of

This paper discusses the mathematical model of powder material particles heating in the gas flow when applying plasma gas and thermal coatings. It has been assumed that while moving in the plasma, the particle is heated by convective heat transfer and radiative heat transfer. To ensure accuracy and validity of calculation, two characteristic regions have been outlined: Core, where the temperature, density, and viscosity of plasma, as well as the other parameters are assumed as constant; and the region from the core to the coated surface (substrate), where these parameters are the functions of the plasma flow coordinates. One of the assumptions is that the shape of the particles is near-spherical, and the thermal flow’s action to the particles’ surface is uniform. Special attention has been paid to correct selection of criteria , which allowed to simplify the solution and reduce it to the ordinary first-order differential equation derived from the particle heat balance equation.

scholarly journals Numerical investigation of the north wall passive thermal performance for Chinese solar greenhouse

2020 ◽  
Vol 24 (6 Part A) ◽  
pp. 3465-3476
Author(s):  
Yiming Li ◽  
Xingan Liu ◽  
Fengsheng Qi ◽  
Li Wang ◽  
Tianlai Li
Keyword(s):  
Solar Energy ◽  
Wall Thickness ◽  
Thermal Performance ◽  
Thermal Environment ◽  
Energy Utilization ◽  
Wall Material ◽  
The North ◽  
Solar Energy Utilization ◽  
Solar Greenhouse ◽  
North Wall

The fully passive solar energy utilization system of Chinese solar greenhouse is efficient for ensuring year-round cultivation of vegetables, owing to the high amount of heat charge and discharge characteristic of the north wall enclosure. In the present research, the thermal performance is investigated using CFD. A 3-D mathematical model has been established to evaluate the wall thickness, layered configuration and material property. The predicted thermal environments are in good agreement with the experimental measurements, indicating the reliability of the established numerical model. The results showed that the increase of north wall thickness could cause the waste of resources due to the thermal masses mainly concentrate in the superficial layer. Constructing layered configuration is rec-ommended for the north wall which uses Styrofoam in the outer layer to reduce heat loss. Nevertheless, the property of north wall material has little effect on the thermal environment. The research results, thus obtained, will give good guidance for completing the Chinese solar greenhouse engineering database and optimizing the solar energy utilization.

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