scholarly journals Natural convection heat transfer performance of additively manufactured tube bundle heat exchangers with novel fin design

2021 ◽  
Author(s):  
Sebastian Unger ◽  
Matthias Beyer ◽  
Heiko Pietruske ◽  
Lutz Szalinski ◽  
Uwe Hampel
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Nusselt Number ◽  
Heat Exchanger ◽  
Flux Density ◽  
Heat Flux Density ◽  
Tube Bundle ◽  
Convection Heat Transfer ◽  
Pin Fins ◽  
Fin Design

AbstractWe studied the heat transfer of finned heat exchanger configurations with a novel design. These novel fin designs use integrated pins to enhance the heat conduction from the fin base to the fin tip as well as the air-side heat transfer on the fin surface. Oval tubes with conventional circular plain fins (CPF) as well as novel circular integrated pin fins (CIPF) and serrated integrated pin fins (SIPF) were additively generated by a Selective Laser Melting (SLM) process and installed at the bottom of a 6.5 m long chimney. All heat exchanger designs were tested in a 2-row and 3-row configuration with Rayleigh numbers between 25,000 and 120,000. We found the average Nusselt number of SIPF to be higher and the Nusselt number of the CIPF to be lower than for the CPF. Moreover, the 2-row configuration achieved a higher Nusselt number compared to the 3-row configuration for all heat exchanger designs. The analysis of the individual tube rows showed the highest Nusselt numbers at the first tube row and the lowest one at the last tube row for both configurations. However, for the SIPF the difference between the first and second tube row is smaller compared to the CPF and CIPF. In order to evaluate the compactness of the heat exchanger, the volumetric heat flux density was considered. Similar to Nusselt number the volumetric heat flux density enhanced for the SIPF and reduced for the CIPF compared to the conventional design. Also the 2-row configuration reached greater thermal performance compared to the 3-row configuration. Additionally, the volume and the surface area of the heat exchanger are 6.9% and 30.7% lower for the SIPF compared to the CPF. The experimental data were used to develop an empirical heat transfer correlation between Nusselt number, Rayleigh number, fin design and tube row number.

Condensation of Flowing Vapor on a Horizontal Tube—Numerical Analysis as a Conjugate Heat Transfer Problem

1984 ◽  
Vol 106 (4) ◽  
pp. 841-848 ◽  
Author(s):  
H. Honda ◽  
T. Fujii
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Flux ◽  
Nusselt Number ◽  
Flux Density ◽  
Wall Temperature ◽  
Heat Flux Density ◽  
Tube Wall ◽  
Horizontal Tube ◽  
Uniform Wall

Condensation of flowing vapor on a horizontal tube is numerically analyzed under given conditions of vapor and coolant. Besides the usual boundary layer concept, some approximations are introduced for the determination of shear stress at the vapor-liquid interface. The conjugation of the two-phase boundary layer equations and the heat conduction equation within the tube wall is achieved by using an iterative scheme at the outer surface of the tube wall. The solution thus obtained reveals the effects of vapor velocity, tube material, heat transfer of coolant side, etc., upon circumferential distributions of temperature, heat flux density, and Nusselt number at the outer tube surface. Also the solution compared well with available experimental results for the wall temperature distribution and average Nusselt number. The heat transfer characteristics of steam and refrigerant vapors resemble those of the tubes with uniform wall heat flux density and uniform wall temperature, respectively.

Heat Removal and Thermal Stabilization of High-temperature Surfaces by a Dispersed Coolant Flow

Vestnik MEI ◽  
2021 ◽  
pp. 19-26
Author(s):  
Valentin S. Shteling ◽  
◽  
Vladimir V. Ilyin ◽  
Aleksandr T. Komov ◽  
Petr P. Shcherbakov ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flux Density ◽  
Flow Rate ◽  
Heat Flux Density ◽  
Coolant Flow ◽  
Transfer Coefficients ◽  
Stationary Heat ◽  
Heat Transfer Coefficients ◽  
Stationary Heat Transfer

The effectiveness of stabilizing the surface temperature by a dispersed coolant flow is experimentally studied on a bench simulating energy intensive elements of thermonuclear installations A test section in which the maximum heat flux density can be obtained when being subjected to high-frequency heating was developed, manufactured, and assembled. The test section was heated using a VCh-60AV HF generator with a frequency of not lower than 30 kHz. A hydraulic nozzle with a conical insert was used as the dispersing device. Techniques for carrying out an experiment on studying a stationary heat transfer regime and for calculating thermophysical quantities were developed. The experimental data were obtained in the stationary heat transfer regime with the following range of coolant operating parameters: water pressure equal to 0.38 MPa, water mass flow rate equal to 5.35 ml/s, and induction heating power equal to 6--19 kW. Based on the data obtained, the removed heat flux density and the heat transfer coefficients were calculated for each stationary heat transfer regime. The dependences of the heat transfer coefficient on the removed heat flux density and of the removed heat flux density on the temperature difference have been obtained. High values of heat transfer coefficients and heat flux density at a relatively low coolant flow rate were achieved in the experiments.

Experimental and Numerical Investigation of Natural Convection Heat Transfer From Horizontal Rectangular Plate Fin Pin Fin Arrays

2020 ◽  
Author(s):  
Sunil V. Dingare ◽  
Narayan K. Sane ◽  
Ratnakar R. Kulkarni
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Numerical Model ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Pin Fin ◽  
Pin Fins ◽  
Fin Spacing

Abstract Fins are commonly employed for cooling of electronic equipment, compressors, Internal Combustion engines and for heat exchange in various heat exchangers. In short fin (length to height ratio, L/H = 5) arrays used for natural convection cooling, a stagnation zone forms at the central portion and that portion is not effective for carrying away heat. An attempt is made to modify plate fin heat sink geometry (PFHS) by inserting pin fins in the channels formed between plate fins and a plate fin pin fin heat sink (PFPFHS) is constructed to address this issue. An experimental setup is developed to validate numerical model of PFPFHS. The three-dimensional elliptic governing equations were solved using a finite volume based computational fluid dynamics (CFD) code. Fluent 6.3.26, a finite volume flow solver is used for solving the set of governing equations for the present geometry. Cell count based on grid independence and extended domain is used to obtain numerical results. Initially, the numerical model is validated for PFHS cases reported in the literature. After obtaining a good agreement with results from the literature, the numerical model for PFHS is modified for PFPFHS and used to carry out systematic parametric study of PFPFHS to analyze the effects of parameters like fin spacing, fin height, pin fin diameter, number of pin fins and temperature difference between fin array and surroundings on natural convection heat transfer from PFPFHS. It is observed that it is impossible to obtain optimum performance in terms of overall heat transfer by only concentrating on one or two parameters. The interactions among all the design parameters must be considered. This thesis presents Experimental and Numerical study of natural convection heat transfer from horizontal rectangular plate fin and plate fin pin fin arrays. The parameters of study are fin spacing, temperature difference between the fin surface and ambient air, fin height, pin fin diameter, number of pin fins and method of positioning pin fins in the fin channel. Experimental set up is validated with horizontal plate standard correlations. Results are generated in the form of variation in average heat transfer coefficient (ha), base heat transfer coefficient (hb), average Nusselt number (Nua) and base Nusselt number (Nub). Total 512 cases are studied numerically and finally an attempt is made to correlate the Nusselt Number (Nu), Rayleigh Number (Ra), increase in percentage by inserting pin fins (% Area), ratios like spacing to height (S/H) and L/H obtained in the present study.

Experimental Study on Natural Convection Heat Transfer Outside Tube Bundle in Space Under Low Temperature Difference

2020 ◽  
Author(s):  
Junxiu Xu ◽  
Ming Ding ◽  
Changqi Yan ◽  
Guangming Fan
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Low Temperature ◽  
Tube Bundle ◽  
Convection Heat Transfer ◽  
Heat Removal ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Reactor Pool ◽  
Residual Heat

Abstract The Passive Residual Heat Removal System (PRHRS) is very important for the safety of the heating reactor after shutdown. PRHRS is a natural circulation system driven by density difference, therefore, the heat transfer performance of the Passive Residual Heat Removal Heat Exchanger (PRHR HX) has a great impact to the heat transfer efficiency of PRHRS. However, the most research object of PRHR HX is the C-shape heat exchanger at present, which located in In-containment Refueling Water Storage Tank (IRWST). This heat exchanger is mainly used for the PRHRS of nuclear power plants. In the swimming pool-type low-temperature heating reactor (SPLTHR), the PRHR HX is placed in the reactor pool, which the pressure and temperature of the reactor pool are relatively low, and the outside heat transfer mode of tube bundle is mainly natural convection heat transfer. In this study, a miniaturized single-phase pool water cooling system was built to investigate the natural convective heat transfer coefficient of the heat exchanger under the large space and low temperature conditions. The experimental data had been compared with several correlations. The results show that the predicted value of Yang correlation is the closest to the experimental data, which the maximum deviation is about 11%.

scholarly journals Graphing Behaviour of Heat Transfer In Terms of Nusselt and Reynolds

2021 ◽  
Vol 6 (2) ◽  
pp. 41-52
Author(s):  
Mohd Rahimie Md Noor ◽  
Nur Syafiqah Hidayah Mohd Fauzi ◽  
Siti Nur Fadhilah Masrom ◽  
Mohd Azry Abdul Malek ◽  
Muhammad Firdaus Mustapha ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Volume Flow Rate ◽  
Convection Heat Transfer ◽  
Heat Transfer Process ◽  
Two Fluids ◽  
The Relationship

Heat exchangers are tools used to transfer thermal energy between two fluids (liquid or gas) by convection and conduction at different level of temperatures. Heat exchangers are the common equipment and employed in many different applications because of ability to withstand high temperatures and compactness. There are no intermixing or leakage occurred between two fluids during the heat transfer process as fluids are separated by walls of heat exchanger. The main objective of this project is to determine the heat exchanger effectiveness in heat transfer performance. This will be done by investigating the performance of five different angles of heat exchanger which are 150,300, 450, 600 and 750. The effectiveness of heat exchanger depends on the convection heat transfer coefficient of the fluid. Besides that, this project also aims to develop some parameters such as Nusselt number, Reynolds number and Prandtl number for evaluating the heat transfer. It is found that the Nusselt Number at angle of 150 is lower compared to angle of 750. Meanwhile, Reynolds number for angle 150 is higher than angle 750 which means that the type of flow produced by angle 150 is turbulent flow while for 750 angle is laminar flow. Hence, the overall result of this project proved that 150 is the best angle for heat exchanger in chimney because of higher velocity, higher volume flow rate, higher density of gas and higher LMTD. The relationship between Nusselt number and Reynolds number between different angles can be observed by plotting the graph using Maple Software.

scholarly journals The Process Characteristics of Rapid Freezing: Continuous and Discrete Heat Removal Method

2019 ◽  
Vol 49 (1) ◽  
pp. 104-112
Author(s):  
Евгений Неверов ◽  
Evgeniy Neverov ◽  
Людмила Лифенцева ◽  
Lyudmila Lifenceva ◽  
Андрей Усов ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flux Density ◽  
Heat Sink ◽  
Heat Flux Density ◽  
Meat Products ◽  
Freezing Process ◽  
Rapid Freezing ◽  
Process Characteristics ◽  
Continuous Heat

The research features the rational conditions of the process of rapid freezing for unpackaged small-sized foods by the method of continuous and discrete heat sink. The paper presents a graphical interpretation of the calculations of the average volume temperature for various temperature regimes that are used to freeze semi-finished products. The method makes it possible to determine the temperature at any time. The experiment defined the most rational range of air circulation speeds with a continuous heat sink in the range from 4 m/s to 6 m/s. The article features curves of changes in temperature and heat flux density during the rapid freezing of small-sized semi-finished meat products. They show the nature of the changes in the air coefficient of the meat sample heat transfer curves and the medium velocity of the object air. An increase in the heat flux density and a reduction in the duration of freezing by about 1.4 times occurred when the temperature of the cooling medium decreased from –20°C to – 40°C at an air speed of 6 m/s. The research determined the process characteristics of rapid freezing in continuous mode using a discrete heat sink. The authors describe the comparative characteristics of the change in the duration of the freezing process and the speed of the process with continuous and discrete heat sinks. The study presents the curves of changes in temperature and heat flux density during rapid freezing of small-sized semi-finished meat products, depending on the conditions of heat transfer. When a discrete heat sink was used, the duration of the freezing process was fpund to be 20 min, while with a continuous heat sink it lasted 26 min. The paper also includes a thermogram and the kinetics of heat sink during freezing in discrete conditions, as well as a software program for quick freezing of semi-finished minced meat products. The indicators of the meat quality are considered depending on the conditions of the heat sink, as well as the change in the physicochemical properties of the product after freezing and during storage. Studies of quality indicators of small-sized semi-finished meat products were carried out in the laboratory of the scientific-innovative enterprise “Sibagropererabotka” (Novosibirsk, Russia).

scholarly journals ON THE CALCULATION OF CONVECTIVE HEAT TRANSFER UNDER MUTUAL-ACTION OF A JET WITH LIMITING SURFACE

2019 ◽  
Vol 62 (3) ◽  
pp. 208-214
Author(s):  
I. A. Pribytkov ◽  
S. I. Kondrashenko
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Convective Heat Transfer ◽  
Flux Density ◽  
Convective Heat ◽  
Heat Flux Density ◽  
Flat Surface ◽  
Dynamic Potential ◽  
Velocity Coefficient ◽  
Limiting Surface

The paper proposes a method for calculating convective heat transfer in the interaction of a single circular jet with a flat surface. The differences of the proposed method from the existing ones are given. The concepts “energodynamic potential of the flow” and “energodynamic power of the flow” are introduced, allowing to determine the intensity of convective heat transfer at “gas-solid” boundary. Differences of the proposed definitions from the existing ones are given: heat flux and heat flux density. The principal difference between the heat flux density q and the energy dynamic potential qэ is as follows: the heat flux density q for convective heat transfer problems means the amount of heat that is transferred from a liquid to a solid surface (or vice versa) per unit of time through a unit of heat exchange surface area. Thus, quantity q characterizes the intensity of convective heat transfer process at the interface. The energy dynamic potential qэ characterizes the flow property as a source or carrier of heat. Value of qэ characterizes the specific energy power of the fluid flow. When calculating the heat transfer, it was proposed to divide the jet when interacting with the flat surface into two parts: before the interaction – the jet part, after – the fan flow. The method for calculating convective heat transfer under jet heating, in which the Reynolds criterion calculated by characteristics of the gas at the nozzle exit is decisive, is not entirely correct. It is proposed to use criteria specific to the fan flow. Characteristic values for the fan flow are its initial average velocity Uвп, distance from the critical point of the jet (point of intersection of vertical axis of the jet with the surface) to the current coordinate of radius downstream. To assess the changes in basic characteristics of a free jet at different distances from the nozzle exit to limiting surface, dependences of the following criteria are presented: jet expansion coefficient; jet injection coefficient; velocity coefficient for any jet section; velocity coefficient for any jet section, except h/d0 = 0; relation of the Reynolds criteria, confirming the need to carry out calculations of heat transfer on the values characteristic separately for the fan flow.

scholarly journals Numerical study of combined convection heat transfer for thermally developing upward flow in a vertical cylinder

2008 ◽  
Vol 12 (2) ◽  
pp. 89-102 ◽  
Author(s):  
Hussein Mohammed ◽  
Yasin Salman
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Nusselt Number ◽  
Temperature Profile ◽  
Local Nusselt Number ◽  
Convection Heat Transfer ◽  
Convection Heat ◽  
Flux Boundary Condition ◽  
Number Range ◽  
Dimensionless Velocity

The problem of the laminar upward mixed convection heat transfer for thermally developing air flow in the entrance region of a vertical circular cylinder under buoyancy effect and wall heat flux boundary condition has been numerically investigated. An implicit finite difference method and the Gauss elimination technique have been used to solve the governing partial differential equations of motion (Navier Stocks equations) for two-dimensional model. This investigation covers Reynolds number range from 400 to 1600, heat flux is varied from 70 W/m2 to 400 W/m2. The results present the dimensionless temperature profile, dimensionless velocity profile, dimensionless surface temperature along the cylinder, and the local Nusselt number variation with the dimensionless axial distance Z+. The dimensionless velocity and temperature profile results have revealed that the secondary flow created by natural convection have a significant effect on the heat transfer process. The results have also shown an increase in the Nusselt number values as the heat flux increases. The results have been compared with the available experimental study and with the available analytical solution for pure forced convection in terms of the local Nusselt number. The comparison has shown satisfactory agreement. .

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