scholarly journals Modeling of temperature profiles and efficiency of heat transfer equipment with intensifiers

2020 ◽  
Vol 22 (2) ◽  
pp. 12-18
Author(s):  
T. M. Farakhov ◽  
A. G. Laptev
Keyword(s):  
Heat Transfer ◽  
Cell Model ◽  
Experimental Studies ◽  
High Viscosity ◽  
Hot Water ◽  
Temperature Fields ◽  
Turbulent Regime ◽  
Temperature Profiles ◽  
Heating And Cooling ◽  
Nominal Size

The problem of determination of temperature fields in the flow and efficiency of heat exchangers with intensification by metal chaotic packings is considered. Results of experimental studies of the heating of industrial oil with hot water in a "pipe-in-pipe" heat exchanger, where a chaotic packing of nominal size 6 mm is placed in the internal pipe, are presented. The packing, due to turbulence in the flow of oil, provides transition from the laminar to the turbulent regime and a significant increase in heat transfer coefficient (by 15-20 times). For calculating temperature profiles in channels, a cell model of the flow structure is written, where the main parameters are thermal number of transfer units and number of complete mixing cells. Expressions are given for calculating these parameters in pipes with chaotic packings. Results of calculating temperature profiles for various flowrates of the heated oil are presented and satisfactory agreement with experimental data is shown. The calculation of temperature fields makes it possible to take into account a change in thermophysical properties of flows along the length of the channels, which is especially important for hydrocarbon mixtures with high viscosity and large Prandtl numbers. The presented mathematical model allows to take into account the structure of heat carrier flows in apparatus with intensifiers and to calculate thermal efficiency of the processes of heating and cooling the media.

Direct numerical simulation of a turbulent jet impinging on a heated wall

2015 ◽  
Vol 764 ◽  
pp. 362-394 ◽  
Author(s):  
T. Dairay ◽  
V. Fortuné ◽  
E. Lamballais ◽  
L.-E. Brizzi
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Nusselt Number ◽  
Direct Numerical Simulation ◽  
Temperature Fields ◽  
Heated Wall ◽  
Small Scale ◽  
Turbulent Regime ◽  
High Heat Transfer ◽  
Radial Evolution

AbstractDirect numerical simulation (DNS) of an impinging jet flow with a nozzle-to-plate distance of two jet diameters and a Reynolds number of 10 000 is carried out at high spatial resolution using high-order numerical methods. The flow configuration is designed to enable the development of a fully turbulent regime with the appearance of a well-marked secondary maximum in the radial distribution of the mean heat transfer. The velocity and temperature statistics are validated with documented experiments. The DNS database is then analysed focusing on the role of unsteady processes to explain the spatial distribution of the heat transfer coefficient at the wall. A phenomenological scenario is proposed on the basis of instantaneous flow visualisations in order to explain the non-monotonic radial evolution of the Nusselt number in the stagnation region. This scenario is then assessed by analysing the wall temperature and the wall shear stress distributions and also through the use of conditional averaging of velocity and temperature fields. On one hand, the heat transfer is primarily driven by the large-scale toroidal primary and secondary vortices emitted periodically. On the other hand, these vortices are subjected to azimuthal distortions associated with the production of radially elongated structures at small scale. These distortions are responsible for the appearance of very high heat transfer zones organised as cold fluid spots on the heated wall. These cold spots are shaped by the radial structures through a filament propagation of the heat transfer. The analysis of probability density functions shows that these strong events are highly intermittent in time and space while contributing essentially to the secondary peak observed in the radial evolution of the Nusselt number.

Influence of Temperature Fields on the Quality of Dried Wood Products

2021 ◽  
Vol 1038 ◽  
pp. 336-344
Author(s):  
Olena Pinchevska ◽  
Andriy Spirochkin ◽  
Denys Zavialov ◽  
Rostislav Oliynyk
Keyword(s):  
Experimental Studies ◽  
Wood Products ◽  
Temperature Fields ◽  
Drying Process ◽  
Wood Moisture ◽  
Adequate Model ◽  
Heating And Cooling ◽  
White Spots ◽  
The Cost ◽  
Wood Heating

The reasons of white spots appearance in the middle of oak timber are determined. These white spots reduce the cost of the lamina made of oak timbers - the front covering of floorboards. It is proposed to intensify the drying process by using oscillating drying schedules to avoid this defect. A method for calculating the duration of such drying is proposed. This method includes the peculiarities of heating and cooling periods kinetics of oak timbers with 25 mm and 30 mm thickness. The inexpediency of using the oscillation of the drying agent parameters in the range of wood moisture content below 20% has been established. An adequate model for calculating wood temperature and air humidity during wood heating and cooling periods has been developed using heat and mass transfer criteria and experimentally determined oak wood moisture conductivity coefficient. Based on the results of theoretical and experimental studies oscillating drying schedules of different thickness oak timbers are offered. Tests of the proposed schedules in industrial conditions showed no discoloration of the central layers of European oak (Quercus robur) timbers. The drying process duration was reduced by 1.5–2.4 times and energy consumption were reduced by 1.53 times.

scholarly journals Research on the Heating of Deicing Fluid in a New Reshaped Coiled Tube

2017 ◽  
Vol 2017 ◽  
pp. 1-9 ◽  
Author(s):  
Mengli Wu ◽  
Chiyu Wang ◽  
Yunpeng Li ◽  
Qi Nie
Keyword(s):  
Heat Transfer ◽  
Ethylene Glycol ◽  
Heating System ◽  
High Viscosity ◽  
Negative Influence ◽  
Heating Time ◽  
Temperature Fields ◽  
Outlet Temperature ◽  
Coiled Tube ◽  
Deicing Fluid

Aircraft ground deicing operation is significant to ensure civil flight safety in winter. Helically coiled tube is the important heat exchanger in Chinese deicing fluid heating system. In order to improve the deicing efficiency, the research focuses on heat transfer enhancement of deicing fluid in the tube. Based on the field synergy principle, a new reshaped tube (TCHC) is designed by ring-rib convex on the inner wall. Deicing fluid is high viscosity ethylene-glycol-based mixture. Because of the power function relation between high viscosity and temperature, viscosity has a negative influence on heat transfer. The number of ring-ribs and inlet velocity are two key parameters to the heat transfer performance. For both water and ethylene glycol, the outlet temperature rises when the number of ring-ribs increases to a certain limit. However, the increasing of velocity reduces heating time, which results in lower outlet temperature. The heating experiment of the original tube is conducted. The error between experiment and simulation is less than 5%. The outlet temperature of TCHC increases by 3.76%. As a result, TCHC efficiently promotes the coordination of velocity and temperature fields by changing the velocity field. TCHC has enhanced heat transfer of high viscosity deicing fluid.

Convection in a long box driven by heating and cooling on the horizontal boundaries

1996 ◽  
Vol 310 ◽  
pp. 61-87 ◽  
Author(s):  
J. J. Sturman ◽  
G. N. Ivey ◽  
J. R. Taylor
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Turbulent Flow ◽  
Flow Visualization ◽  
Turbulent Flows ◽  
Heat Fluxes ◽  
Temperature Fields ◽  
Glycerol Water ◽  
Heating And Cooling ◽  
Scaling Arguments

Convection driven by spatially variable heat transfer across the water surface is an important transport mechanism in many geophysical applications. This flow is modelled in a rectangular tank with an aspect ratio, H/L, of 0.1 (where H and L are the tank height and length, respectively). Heat fluxes are applied through horizontal copper plates of length 0.1 L located at the top of one end of the tank and at the bottom of the other end. Experimental flows have been forced with heating at the bottom of the tank and cooling at the top, which gives rise to unstable convection in the end regions. Using water and a glycerol/water mix as the experimental fluids, flow visualization studies and measurements of temperature, velocity and heat flux have been made. Flow visualization studies revealed that complex unsteady turbulent flows occupied the end regions, while cubic velocity profiles characterized the horizontal laminar flow in the interior of the tank. Simple scaling arguments were developed for steady-state velocity and temperature fields, which are in good agreement with the experimental data. In the current experiments the portion of the plates closest to the tank interior (and to the tank endwall in the case of the glycerol/water experiments) were occupied by laminar boundary layers, while the remainder of the plates were occupied by turbulent flow. An effective Rayleigh number Ra* was defined, based upon the portion of the plate occupied by turbulent flow, as was a corresponding modified Nusselt number Nu*. The heat transfer was well predicted by classical Rayleigh-Bénard scaling with the Nusselt number Nu* ∼ Ra*1/3. The range of Ra* was 4.3 × 105 ≤ Ra* ≤ 1.7 × 108. Scaling arguments predicted the triple occupancy of the plates by differing boundary layer regimes within the range of 105 ≤ Ra* ≤ 1014.

scholarly journals Flow and Heat Transfer in a Liquid Film over a Permeable Stretching Sheet

2013 ◽  
Vol 2013 ◽  
pp. 1-9 ◽  
Author(s):  
R. C. Aziz ◽  
I. Hashim ◽  
A. K. Alomari
Keyword(s):  
Heat Transfer ◽  
Liquid Film ◽  
Stretching Sheet ◽  
Temperature Fields ◽  
Temperature Profiles ◽  
Suction Parameter ◽  
Boundary Layer Equations ◽  
Similarity Transformations ◽  
Flow And Heat Transfer ◽  
Homotopy Analysis

An analysis has been carried out to study the flow and heat transfer in a liquid film over a permeable stretching sheet. Using similarity transformations, the time-dependent boundary layer equations are reduced to a set of nonlinear ordinary differential equations. The resulting parameter problem and velocity as well as temperature fields are solved using the homotopy analysis method (HAM). Analytic series solutions are given, and numerical results for velocity and the temperature profiles are presented through graphs of different values for pertinent parameter. The effects of unsteadiness parameter and permeability parameter on the velocity and temperature profiles are explored for different values of blowing or suction parameter.

scholarly journals Experimental studies and mathematical modeling on the effects of rapid airflow and baking temperature during baking

2020 ◽  
pp. 469
Author(s):  
Mazidah Mior Zakuan Azmi ◽  
Anvarjon Ahmedov ◽  
Farah Saleena Taip
Keyword(s):  
Heat Transfer ◽  
Volume Expansion ◽  
Numerical Models ◽  
Experimental Studies ◽  
Operating Conditions ◽  
Transfer Model ◽  
Temperature Profiles ◽  
Convection Oven ◽  
Baking Process ◽  
Cake Baking

Rapid airflow in oven will influence the heat transfer in baking process therefore the purpose of this study is to experimentally and numerically investigate the effects of operating conditions on the heat transfer mechanism and volume expansion during baking. Cakes are baked in an air fryer and convection oven with constant speed 5.11 m/s and 0.88 m/s respectively at 150, 160, 170 °C in different baking times. A heat transfer model was defined to describe the influence of baking temperature on internal cake temperature by Fourier’s law. It was observed that the presence of rapid airflow (air fryer) and increment in oven temperature yielded an increase in volume expansion but produced a less moist product. Cakes baked in the presence of rapid airflow at 150 °C were moister but with little volume expansion in the cakes compared to convection oven-baked cakes. Significant correlation between the numerical models with experimental temperature profiles were recorded during complete cake baking process.

Numerical Investigation of Flow and Heat Transfer in Microchannels

2008 ◽  
Author(s):  
Emrah Deniz ◽  
I. Yalcin Uralcan
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Factor ◽  
Experimental Studies ◽  
Numerical Results ◽  
Turbulent Regime ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Micro Channels

Mini and microchannel applications have become an important and attractive research area during the past decades. For micro systems design purposes, numerical and experimental studies have been conducted on flow and heat transfer characteristics of mini and microchannels and various friction factor and Nusselt number correlations have been proposed. Some researchers have tried to apply conventional tube correlations to mini and micro channels, rather than deriving new correlations. In this study, using commercial CFD software, flow and heat transfer characteristics in laminar and turbulent flow through circular channels are analyzed numerically. The applicability of conventional correlations in calculating the friction factor and Nusselt number is investigated. It is concluded that, in laminar regime conventional correlations can be used to calculate the friction factor for the channel sizes considered. In turbulent regime, however, numerical results for friction factor yielded greater values than those calculated by the conventional correlations. Numerical Nusselt numbers are found to be closer to the conventional values in laminar and turbulent regimes. In turbulent regime, on the other hand, Nusselt number values calculated with the microchannel correlations are determined to be greater than the numerical results and the values calculated with the conventional correlations.

scholarly journals Experimental Studies of the Heat Exchange Between the Water Film and the Casting Roller in the Thermal Preconditioning Chamber

2021 ◽  
pp. 42-46
Author(s):  
Alexander Pereselkov ◽  
Olga Kruglyakova
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Flow Rate ◽  
Large Diameter ◽  
Experimental Studies ◽  
Water Film ◽  
Scientific Paper ◽  
Operating Conditions ◽  
Hot Water ◽  
Thermal Preparation

When the casting roller is cooled or heated in the preconditioning chamber the water is supplied to its surface by flat-jet nozzles. The visual inspection of the model of the casting roller showed that a considerable part of it can be covered with the water film spreading from sprinkling zones. It was established that the heat conductivity in the roller body is considered to be a crucial thermal preparation factor in the conjugate heat-exchange problem for the roller of a large diameter at Bio criterion values exceeding 20. Hence, it is sufficient to provide an essential level of the heat transfer that corresponds to the heat transfer coefficient of 2000 W/(m2∙K) to provide appropriate operating conditions for the thermal preparation of the roller. The conditions are also met in sprinkling zones. Due to this fact this scientific paper studies the heat exchange conditions under the water film that spreads between the adjacent sprinkling zones. A range of changes in the flow rate of the spreading water film was determined experimentally. The conditions of heat exchange between the surface of alpha-calorimeter and the water film were analyzed depending on its flow rate and the heat meter surface temperature. A generalized correlation equation was derived. It was established that the heat exchange intensity in sprinkling zones and under the spreading water film meets technological roller treatment conditions in the preconditioning chambers. The obtained research data can be used for the rational arrangement of the collectors and flat-jet nozzles in casting roller preconditioning chambers to reduce the cold and hot water consumption and cut down operating costs.

scholarly journals Analysis of the possibility of applications for a two-phase reverse thermosyphon in passive heat transport systems

2018 ◽  
Vol 49 ◽  
pp. 00020 ◽  
Author(s):  
Michal Duda ◽  
Jurij Dobrianski ◽  
Daniel Chludzinski
Keyword(s):  
Heat Transfer ◽  
Heat Source ◽  
Heat Transport ◽  
Heat Load ◽  
Experimental Studies ◽  
Hot Water ◽  
Transport Systems ◽  
Working Fluid ◽  
Two Phase

Devices called reverse thermosyphon enable passive heat transfer when the heat source is above the place of its receipt. This is often the case in solar installations for the preparation of hot water. The article concerns the determination of the possibility of using a two-phase inverted thermosyphon with two working factors in a passive downwards heat transport installation. The analysis was carried out on the basis of previous experimental studies. The height of the tested installation in one case was 1.5 m, in the second 18 m, at a heat load of 300, 600 and 900 W. Water and pentane was used as a working fluid inside the loop. Initial conclusions from the analysis confirm the possibility of using reverse thermosyphon with two working factors in the construction of a passive heat transport system.

Experimental Study of the Characteristics of Heat Transfer and HLMC Cross-Flow Around Tubes

2014 ◽  
Author(s):  
Aleksei Chernysh ◽  
Mikhail Iarmonov ◽  
Kirill Makhov ◽  
A. V. Beznosov
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Liquid Metal ◽  
Experimental Studies ◽  
Cross Flow ◽  
Velocity Fields ◽  
Temperature Fields ◽  
Experimental Site ◽  
Lead Coolant ◽  
Velocity And Temperature Fields

The process of heat transfer in a heavy liquid-metal coolant (HLMC) cross-flow around heat-transfer tubes is not yet thoroughly studied. Therefore, it is of great interest to carry out experimental studies for determining the heat transfer characteristics in a lead coolant cross-flow around tubes. It is also interesting to explore the velocity and temperature fields in a HLMC flow. To achieve this goal, experts of the R.E. Alekseev Nizhny Novgorod State Technical University performed the work aimed at the experimental determination of the temperature and velocity fields in high-temperature lead coolant cross-flows around a tube bundle. The experimental studies were carried out in a specially designed high-temperature liquid-metal facility. The experimental facility is a combination of two high-temperature liquid-metal setups, i.e., FT-2 with a lead coolant and FT-1 with a lead-bismuth coolant, united by an experimental site. The experimental site is a model of the steam generator of the BREST reactor facility. The heat-transfer surface is an in-line tube bank of a diameter of 17×3.5 mm, which is made of 10H9NSMFB ferritic-martensitic steel. The temperature of the heat-transfer surface is measured with thermocouples of a diameter of 1 mm being installed in the walls of heat-transfer tubes. The velocity and temperature fields in a high-temperature HLMC flow are measured with special sensors installed in the flow cross section between the rows of heat-transfer tubes. The characteristics of heat transfer and velocity fields in a lead coolant flow were studied in different directions of the coolant flow: the vertical (“top-down” and “bottom-up” [1]) and the horizontal ones. The studies were conducted under the following operating conditions: the temperature of lead was t=450–500°C, the thermodynamic activity of oxygen was a=10−5−100, and the lead flow through the experimental site was Q = 3–6 m3/h, which corresponds to coolant velocities of V = 0.4–0.8 m/s. Comprehensive experimental studies of the characteristics of heat transfer in a lead coolant cross-flow around tubes have been carried out for the first time and the dependences NU = f(Pe) for a controlled and regulated content of the thermodynamically active oxygen impurity and sediments of impurities have been obtained. The effect of the oxygen impurity content in the coolant and characteristics of protective oxide coatings on the temperature and velocity fields in a lead coolant flow is revealed. This is because the presence of oxygen in the coolant and oxide coatings on the surface, which restrict the liquid-metal flow, leads to a change in the characteristics of the wall-adjacent region. The obtained experimental data on the distribution of the velocity and temperature fields in a HLMC flow permit studying the heat-transfer processes and, on this basis, creating program codes for engineering calculations of HLMC flows around heat-transfer surfaces.

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