scholarly journals THE INFLUENCE OF THE CHANGES IN WIND VELOCITY ON THE OUTER HEAT EXCHANGE OF THE BUILDINGS

2021 ◽  
pp. 148-155
Author(s):  
D.V. Tarasevych ◽  
◽  
O.V. Bogdan ◽  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchange ◽  
Transfer Coefficient ◽  
Heat Loss ◽  
Wind Velocity ◽  
Air Temperature ◽  
Outer Surface ◽  
Climatic Parameters ◽  
The Heat Transfer Coefficient

When choosing architectural and planning solutions, such climatic factors as air temperature and humidity, having scalar quantities, as well as solar radiation, wind and precipitation having vector characteristics, must be taken into account. The calculated climatic parameters for the design of building enclosing structures, heat loss calculations and heat supply regulation are provided in the current documentation on norms and standards. The practical exploitation of various buildings demonstrates that in terms of initial climatic data, the choice of design parameters is not always efficiently justified; hence, the influence of the environment on the heating regime of the structures is insufficient in the estimations and sometimes erroneous. The wind is one of such climatic parameters. Its velocity and repeatability impact the heat exchange of the building structure with the environment as well as the alteration in temperature regime. The wind current towards the building creates additional pressure on the facade of the construction from the wind side direction. This leads, firstly, to air infiltration via the enclosing structures, and secondly, to the rise of heat exchange from the outer surface of the wall on the windward side. Based on estimated and analytical research, the values of the change in wind velocity depending on the altitude were analyzed, and its influence on the heat loss during heating of multi-storey buildings was assessed. The alterations in the wind velocity depending on the altitude were analyzed in the conditions of dense (urban) and broad construction. Besides, the authors presented the dependence of the convective component of the heat transfer coefficient of the outer surface of the structure on the values of the wind velocity. Based on the performed and presented calculations, it can be noticed that the heat transfer of the external structure will be much higher for multi-storey buildings than for mid-rise constructions. Thus, the convective component of the heat transfer coefficient of the outer surface rises by 36 % when the wind velocity increases from 5 m/s to 7 m/s. If not taking into consideration this dependence in the design, it can significantly influence the estimation of heat loss and energy efficiency of buildings, especially when it is about the increased percentage of facades glazing. The authors of the article assessed the heat loss for heating the windward and leeward facades at average values of the outside air temperature during the heating season in Ukraine. Hence, for constructions higher than 70 m with a calculated wind velocity of 5 m/s, heat losses increase from 10 % to 19 %. Such great difference in heat loss between the windward and leeward walls of the building requires increased thermal protection from the prevailing winter winds. Therefore, when designing multi-storey buildings, it is necessary to take into account changes in wind velocity according to the altitude. The obtained results can be useful both for choosing architectural and planning solutions, like the materials for external enclosing structures and for the objective assessment of the wind protection degree of individual buildings and territories.

scholarly journals 3D Numerical Simulation of Laminar Flow and Conjugate Heat Transfer through Fabric

2017 ◽  
Vol 17 (1) ◽  
pp. 53-60 ◽  
Author(s):  
Guocheng Zhu ◽  
Dana Kremenakova ◽  
Yan Wang ◽  
Jiri Militky ◽  
Rajesh Mishra ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Laminar Flow ◽  
Transfer Coefficient ◽  
Heat Loss ◽  
Human Skin ◽  
Human Body ◽  
Conjugate Heat Transfer ◽  
Air Flow ◽  
The Heat Transfer Coefficient

AbstractThe air flow and conjugate heat transfer through the fabric was investigated numerically. The objective of this paper is to study the thermal insulation of fabrics under heat convection or the heat loss of human body under different conditions (fabric structure and contact conditions between the human skin and the fabric). The numerical simulations were performed in laminar flow regime at constant skin temperature (310 K) and constant air flow temperature (273 K) at a speed of 5 m/s. Some important parameters such as heat flux through the fabrics, heat transfer coefficient, and Nusselt number were evaluated. The results showed that the heat loss from human body (the heat transfer coefficient) was smallest or the thermal insulation of fabric was highest when the fabric had no pores and no contact with the human skin, the heat loss from human body (the heat transfer coefficient) was highest when the fabric had pores and the air flow penetrated through the fabric.

scholarly journals Heat Exchange Modeling in Cooling Fins

2020 ◽  
pp. 669-676
Author(s):  
Evgeniy N. Vasil'ev
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchange ◽  
Transfer Coefficient ◽  
Heat Conduction Problem ◽  
Rectangular Cross Section ◽  
One Dimensional ◽  
Wide Range ◽  
Simulation Results ◽  
The Heat Transfer Coefficient

The article discusses the process of heat exchange of a finned wall with a coolant. The temperature field in the wall volume was determined on the basis of a numerical solution of the two-dimensional heat conduction problem, and the analysis of the characteristics of temperature distributions was carried out according to the simulation results. The values of the heat transfer coefficient of cooling fins with rectangular cross section were calculated for two variants of heat transfer conditions at the end of the fins in a wide range of dimensionless parameters. The error in calculating the heat transfer coefficient in the approximation of a thin fin was determined by means of a one-dimensional computational model

scholarly journals TAKING INTO ACCOUNT DEPENDENCE OF VISCOSITY COEFFICIENT ON TEMPERATURE DURING VAPOR CONDENSATION ON A VERTICAL WALL

2020 ◽  
Vol 63 (5) ◽  
pp. 94-101
Author(s):  
Aleksandr I. Moshinskiy ◽  
Pavel G. Ganin ◽  
Alla V. Markova ◽  
Larisa N. Rubtsova ◽  
Vladislav V. Sorokin
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchange ◽  
Transfer Coefficient ◽  
Dynamic Viscosity ◽  
Viscosity Coefficient ◽  
Vapor Condensation ◽  
Condensation Temperature ◽  
Heat Exchange Equipment ◽  
The Heat Transfer Coefficient

In the present study, the problem of vapor condensation on a flat vertical surface is investigated in the case of an arbitrary dependence of the dynamic viscosity coefficient on temperature according to a fairly general law. At a constant value of this coefficient and other characteristics of a condensing liquid (heat conductivity coefficient, density) this task was considered by Nusselt in a constant gravitational field. The results obtained by Nusselt formed the basis (with certain modifications) for the computational practice of heat exchange equipment of chemical technology in the presence of steam condensation of any heat carrier. Formation of a condensate film occurs due to heat transfer through the liquid film, vapor condensation at the outer edge of the film and the flow of liquid along the surface. The article generalizes the Nusselt theory for the heat transfer coefficient under the indicated conditions, and as a result, convenient calculation formulas for the heat transfer coefficient, which are necessary to describe the operation of heat and mass exchange equipment. Approximate relations are proposed for calculating the dynamic viscosity coefficient, which are useful for calculating film flow on a flat surface. A comparison is made with the previously used ratios in an approximate manner taking into account the dependence of viscosity coefficient on temperature. When in technical applications one wants to determine the average value of two parameters, which are then used to calculate certain characteristics of a process, then, traditionally, the average of these parameters is considered. This article shows that by simplifying the dependence of the effective dynamic viscosity coefficient, more accurate results are obtained by dividing the interval of the width of the current film in the ratio of three to one, where three fourths refer to the wall temperature, and one fourth to the condensation temperature. The analytical dependencies presented in this paper can be used for practical calculations of the heat exchange equipment.

scholarly journals Development of an algorithm for determining the heat transfer coefficient of the body of an isothermal vehicle based on the results of analysis of the heat exchange processes occurring in it

2017 ◽  
Vol 76 (5) ◽  
pp. 306-311 ◽  
Author(s):  
A. A. Golubin ◽  
S. N. Naumenko
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchange ◽  
Transfer Coefficient ◽  
Thermal Imaging ◽  
The Body ◽  
Internal Heating ◽  
Heating Method ◽  
Exchange Processes ◽  
The Heat Transfer Coefficient

The article analyzes the heat exchange processes the thermal imaging method using a thermal imaging device. An occurring in the body of an isothermal vehicle when determining algorithm for determining the heat transfer coefficient is proposed, the heat transfer coefficient K by the internal heating method. which makes it possible to calculate its value with an accuracy not The differences are shown in the values of the heat transfer coef-exceeding 5 %, which is regulated by a number of international ficients obtained by the equilibrium internal heating method and normative documents, while reducing the duration of the experiment by at least 6 times. The study gives comparative experimental data and results of calculating the unknown values of K for bodies of isothermal vehicles obtained by the equilibrium method and an express method based on the algorithm described in the article. It is shown that the use of the algorithm for calculating the heat transfer coefficient of the body of an isothermal vehicle will not only increase the productivity of testing stations, but will also lead to the organization of an electronic passport for the thermotechnical state for each body of an isothermal vehicle, the control of which will enable timely diagnosing the thermo-technical condition of the bodies of isothermal vehicles, providing energy-optimal operating modes of energy equipment and, hence, increasing its resource.

scholarly journals DEVELOPMENT OF HIGH EFFICIENT SHELL-AND-TUBE HEAT EXCHANGERS BASED ON PROFILED TUBES

2020 ◽  
Author(s):  
Djamalutdin Chalaev ◽  
◽  
Nina Silnyagina ◽  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Heat Exchange ◽  
Transfer Coefficient ◽  
Hydraulic Resistance ◽  
Heat Exchangers ◽  
Experimental Studies ◽  
Corrugated Tube ◽  
The Heat Transfer Coefficient

The use of advanced heat transfer surfaces (corrugated tubes of various modifications) is an effective way to intensify the heat transfer and improve the hydraulic characteristics of tubular heat exchangers. The methods for evaluating the use of such surfaces as working elements in tubular heat exchangers have not been developed so far. The thermal and hydrodynamic processes occurring in the tubes with the developed surfaces were studied to evaluate the efficiency of heat exchange therein. Thin-walled corrugated flexible stainless steel tubes of various modifications were used in experimental studies. The researches were carried out on a laboratory stand, which was designed as a heat exchanger type "tube in tube" with a corrugated inner tube. The stand was equipped with sensors to measure the thermal hydraulic flow conditions. The comparative analysis of operation modes of the heat exchanger with a corrugated inner tube of various modifications and the heat exchanger with a smooth inner tube was performed according to the obtained data. Materials and methods. A convective component of the heat transfer coefficient of corrugated tube increased significantly at identical flow conditions comparing with a smooth tube. Increasing the heat transfer coefficient was in the range of 2.0 to 2.6, and increased with increasing Reynolds number. The increase in heat transfer of specified range outstripped the gain of hydraulic resistance caused by increase of the flow. Results and discussion. CFD model in the software ANSYS CFX 14.5 was adapted to estimate the effect of the tube geometry on the intensity of the heat transfer process. A two-dimensional axially symmetric computer model was used for the calculation. The model is based on Reynolds equation (Navier-Stokes equations for turbulent flow), the continuity equation and the energy equation supplemented by the conditions of uniqueness. SST-turbulence model was used for the solution of the equations. The problem was solved in the conjugate formulation, which allowed assessing the efficiency of heat exchange, depending on various parameters (coolant temperature, coolant velocity, pressure). The criteria dependences were obtained Nu = f (Re, Pr). Conclusions. The use a corrugated tube as a working element in tubular heat exchangers can improve the heat transfer coefficient of 2.0 - 2.6 times, with an increase in hydraulic resistance in the heat exchanger of 2 times (compared with the use of smooth tubes). The criteria dependences obtained on the basis of experimental studies and mathematical modeling allow developing a methodology for engineering calculations for the design of new efficient heat exchangers with corrugated tubes.

scholarly journals THE STUDY OF HEAT TRANSFER IN INTENSIFIED SHELL AND TUBE DEVICE

2019 ◽  
Vol 4 (4) ◽  
pp. 77-82
Author(s):  
Н. Никулин ◽  
Nikolay Nikulin
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchange ◽  
Transfer Coefficient ◽  
Heat Exchange Surface ◽  
Shell And Tube ◽  
Heated Fluid ◽  
Supply Systems ◽  
The Heat Transfer Coefficient ◽  
Exchange Surface

The use and prevalence of heat exchangers in Russian heat supply systems are considered. Attention is paid to the improvement of serial heat exchangers with smooth tubes – the increasing of heat transfer coefficient. One of the ways to increase the heat transfer coefficient is considered: it is the turbuliza-tion of the fluid flow on the heat exchange surface. The original design of the heat exchange surface for shell and tube devices of heat supply systems is presented. The dynamics of the heated fluid in the annular space of a shell and tube heat exchanger when flowing around the heat exchange surface with a modified geometry is studied (RF Patent 149737). A feature of the dynamics is a circular edge (element of the surface of heat exchange), which contributes to the creation of turbulence in the flow of the heated liquid on the plate and on the surface of the next edge. Emphasis is placed on heat ex-change processes between the solid surface of the edges and the heated fluid. For a circular cross sec-tion, the equation of thermal conductivity in cylindrical coordinates is compiled, taking into account the stationary heat exchange process, with an internal source of thermal energy. Solution of equation makes possible to determine the change in temperature on the surface and the average temperature of the edge. This value allows determining the Prandtl number to calculate the heat transfer coefficient.

scholarly journals Improving the heat transfer efficiency of a direct-flow recycling boiler using organic fluid

2021 ◽  
Vol 266 ◽  
pp. 04009
Author(s):  
M.A. Peretyatko ◽  
P.V. Yakovlev ◽  
S.A. Peretyatko
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchange ◽  
Transfer Coefficient ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Direct Flow ◽  
Heat Exchange Surface ◽  
The Heat Transfer Coefficient ◽  
Exchange Surface

This paper considers the problem of studying the heat transfer exchange during boiling in a direct-flow recycling boiler using an organic coolant. The study was conducted using numerical modelling in the ANSYS software package. Asaresultofthestudyavisual picture eofvaporphasedistributionwasobtained. This picture shows that the studied heat-exchange surface can be conditionally divided into two areas: the area of intense vaporization and the area in which the degree of dry vapor varies insignificantly. Analysis of changes in the heat transfer coefficient along the length of the heat-exchange surface led to the conclusion that heat transfer in the second area is inefficient. Based on the results of the study, it was concluded that intensification of heat transfer is necessary, for which it is proposed to install a separator at the boundary between the selected areas. The subject of the study is the dependence of the variationin the heat transfer coefficient along the length of the pipe and the determination of the boundary between the selected areas at various values of the defining parameters. Numerical simulation for therange of variationofthe defining parameters corresponding to the actual temperature regimeof power steam boilers and the conditions for the implementation of heat recovery in organic Rankine cycle unitswas performed.

scholarly journals Optimization of the built-in recuperator surface of recuperative burner according to the criterion of energy coefficient maximum

Vestnik IGEU ◽  
2020 ◽  
pp. 5-11
Author(s):  
A.B. Biryukov ◽  
A.N. Lebedev ◽  
P.A. Gnitiev ◽  
Ya.S. Vlasov
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchange ◽  
Transfer Coefficient ◽  
Fuel Consumption ◽  
Thermal Power ◽  
Aerodynamic Resistance ◽  
Combustion Products ◽  
Energy Coefficient ◽  
The Heat Transfer Coefficient

The recuperative burners is a modern direction of reducing fuel consumption during the heat treatment of metals in furnaces. Their use can significantly reduce fuel consumption. Despite the evident advantages, the spread of such equipment is constrained due to its high cost. The research is conducted for determining ribs rational profile and optimizing mass and size characteristics of a built-in recuperator. There are results that make it possible to reduce either the recuperator mass or its aerodynamic resistance. However, such changes contradict each other, so a compromise solution must be found. Currently, there are no generally accepted methods of thermotechnical calculations for recuperative burners. This work aims to develop a methodology to optimize the built-in recuperator surface according to the criterion of maximizing the energy coefficient. To conduct the study, the elements of recuperative heat exchange theory for counter-flow media were used. The proven methodology for determining the temperature of heated air and cooled combustion products after recuperator was applied. Also, the known concept of energy coefficient was used for the research. A technique has been developed to optimize the surface of the incorporated heat exchanger according to the criterion of maximizing the energy coefficient. The technique includes composing an expression for determining the energy coefficient, taking its derivative and equating it to zero with further solving the obtained equation with respect to heat exchange surface. The developed method was used in the recuperative burner with the thermal power of 500 kW. For the range of heat transfer coefficient 75–200 W/(m2·K) associated to the smoothtube part, a fifth-degree polynomial has been determined which describes the dependence of the smoothtube part optimal value of a built-in recuperator surface on the heat transfer coefficient. The developed technique is important for recuperative burners design, for increasing their efficiency and reducing their production cost. The methodology error associated with the assumption that the heat transfer coefficient is constant when the length of the built-in recuperator changes does not exceed 5 %.

scholarly journals Experimental Investigation and Mathematical Modelling of Heat Transfer Coefficient in Double Slope Solar Still

2021 ◽  
Vol 67 (7-8) ◽  
pp. 369-379
Author(s):  
Raj Vardhan Patel ◽  
Anshul Yadav ◽  
Jerzy Adam Winczek
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Wind Velocity ◽  
Water Depth ◽  
Glass Surface ◽  
Solar Still ◽  
Basin Water ◽  
The Impact ◽  
The Heat Transfer Coefficient

In this study, a double slope solar still has been designed and fabricated with the help of locally available materials for the climatic condition of Sultanpur, India. The experimental study was performed to investigate the effect of basin water, wind velocity on the heat transfer coefficient (convective, evaporative, and radiative) and yield of solar still. A mathematical model is developed to understand the impact of wind velocity and basin water depth in the double slope solar still on the heat transfer coefficient. It was found that the convective heat transfer coefficient depends upon the water mass and the temperature of basin mass, and glass cover temperature. The maximum value of hew (55.05 W/(m²K) and 31.80 W/(m²K)) and hcw , (2.48 W/(m²K) and 2.38 W/(m²K)) found for depths of 2 cm and 5 cm, respectively. The radiative heat transfer coefficient found to be a maximum of 8.31 W/(m²K) for 2 cm depth, and it increases as the condensation increases, because the glass surface temperature increases as vapour transfers its energy to the surface. On increasing the depth from 2 cm to 5 cm, the yield from the solar still decreases by 25.45 %. The maximum yield of 2.5 l/m²/day was found for a 2 cm water depth. The theoretical and experimental yield agreed with an error of 7.5 %, 3.25 %, 7.4 %, and 8.4 % for water depths of 2 cm, 3 cm, 4 cm, and 5 cm, respectively. It was also found that the yield from the solar still increases as the wind speed increase because this leads the faster condensation at the glass surface.

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