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1

Enhancement of heat transfer in helical coil heat exchangers using nano-fluids

Parveez Malik, Hanief Mohammad

Chemical and Process Engineering

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2022

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Vol. 43, nr 2

279--283

EN

Investigation for heat transfer behaviour of Al2O3 and CuO nano-fluid in helical coil heat exchangers was carried out in this study. The thermo-physical properties of the fluids have temperature dependent nature. The main emphasis was to depict the influence of nano-particle concentration by volume on the characteristics of temperature, rate of heat transfer and heat transfer coefficients (convective). In order to enhance efficiency, density and thermal conductivity are considered to be the most important variables. In comparison to water and for equal flow rate, the rate of heat transfer of nano-fluid increases conspicuously. Efficiency of the helical coil heat exchanger increased by 38.80%.

2

Simulations of Heat Transfer through Multilayer Protective Clothing Exposed to Flame

Puszkarz Adam K., Machnowski Waldemar

Autex Research Journal

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2022

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Vol. 22, no. 3

298--304

EN

In this paper, the safety and thermal comfort of protective clothing used by firefighters was analyzed. Three-dimensional geometry and morphology models of real multilayer assemblies used in thermal protective clothing were mapped by selected Computer-Aided Design (CAD) software. In the designed assembly models, different scales of the resolution were used for the particular layers – a homogenization for nonwoven fabrics model and designing the geometry of the individual yarns in the model of woven fabrics. Then, the finite volume method to simulate heat transfer through the assemblies caused by their exposure to the flame was applied. Finally, the simulation results with experimental measurements conducted according to the EN ISO 9151 were compared. Based on both the experimental and simulation results, parameters describing the tested clothing protective features directly affecting the firefighter’s safety were determined. As a result of the experiment and simulations, comparable values of these parameters were determined, which could show that used methods are an efficient tool in studying the thermal properties of multilayer protective clothing.

3

Numerical Investigation of Heat Transfer in Garment Air Gap

Zhang Yijie, Jia Juhong

Autex Research Journal

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2022

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Vol. 22, no. 1

89--95

EN

This article aimed to study the characteristics and mechanisms of 3D heat transfer through clothing involving the air gap. A three-dimensional finite volume method is used to obtain the coupled conductive, convective, and radiative heat transfer in a body-air-cloth microclimate system. The flow contours and characteristics of temperature, heat flux, and velocity have been obtained. The reason for the high flux and temperature regions was analyzed. Computational results show that the coupled effect of the air gap and the airflow between the skin and garment strongly influences the temperature and heat flux distribution. There are several high-temperature regions on the clothing and high heat flux regions on the body skin because the conductive heat flux can cross through the narrow air gap and reach the cloth surface easily. The high-speed cooling airflow brings about high forced convective heat flux, which will result in the temperature increase on the upper cloth surface. The radiative heat flux has a strong correlation with the temperature gradient between the body and clothing. But its proportion in the total heat flux is relatively small.

4

Investigation of Heat Transfer in Seersucker Woven Fabrics using Thermographic Method

Zgórniak P., Matusiak M., Frącczak L.

Autex Research Journal

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2022

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Vol. 22, no. 3

282--289

EN

Seersucker woven fabrics are characterized by unconventional structure and surface topography. Their crucial feature is a three-dimensional puckered effect created by puckered and flat strips occurring in the warp direction. Such a structure influences the basic mechanical and utility properties of the fabrics. The aim of the presented work is to analyze the heat transfer in seersucker woven fabrics. Measurement of the heat transfer was done using an infrared camera. Thermograms created for different seersucker woven fabrics, as well as for flat and puckered areas of the seersucker woven fabrics, were analyzed from the aspect of heat exchange between a hot plate and the environment through the fabric. The results showed that the linear density of the weft yarn influences the heat transfer through seersucker woven fabrics. The results allowed the comparison of the heat transfer through the seersucker woven fabrics in both flat and puckered areas. The investigations performed confirmed that the thermographic method can be applied to complex analyses of the heat transfer through seersucker woven fabrics.

5

Conductive Heat Transfer Prediction of Plain Socks in Wet State

Mansoor Tariq, Hes Lubos, Khalil Amany, Militky Jiri, Tunak Maros, Bajzik Vladimir, Kyosev Yordan

Autex Research Journal

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2022

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Vol. 22, no. 4

391--403

EN

In this study, an algebraic model and its experimental verification was carried out to investigate the effect of moisture content on the heat loss that takes place due to conduction of sock fabrics. The results show that increasing moisture content in the studied socks caused a significant increase in their conductive heat loss. Plain knitted socks with different fiber composition were wetted to a saturated level, and then their moisture content was reduced stepwise. When achieving the required moisture content, the socks samples were characterized by the Alambeta testing instrument for heat transfer. Three different existing modified mathematical models for the thermal conductivity of wet fabrics were used for predicting thermal resistance of socks under wet conditions. The results from both ways are in very good agreement for all the socks at a 95% confidence level. In the above-mentioned models, the prediction of thermal resistance presents newly a combined effect of the real filling coefficient and thermal conductivity of the so-called “wet” polymers instead of dry polymers. With these modifications, the used models predicted the thermal resistance at different moisture levels. Predicted thermal resistance is converted into heat transfer (due to conduction) with a significantly high coefficient of correlation.

6

Dimethicone-assisted laser cutting of CFRP hole

Chen Xinghua, Li Wenyuan, Rong Youmin, Zhang Guojun, Chen Long, Huang Yu

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 4

art. no. e182, 2022

EN

When cutting carbon fiber reinforced polymer (CFRP) plate with UV nanosecond laser, the surface heat-affected zone (HAZ) such as fiber exposure and carbonization will occur, which affects the surface morphology and properties of CFRP. In this paper, dimethicone-assisted laser cutting technology is proposed. Compared with laser direct cutting, we found that dimethicone-assisted cutting has obvious advantages in cutting CFRP. Due to the heat transfer inhibition of dimethicone, there is almost no burning phenomenon of matrix materials. The orthogonal test method was used to study the three key process parameters (laser scanning speed, repetition frequency and concentric circle spacing) of dimethicone-assisted laser cutting CFRP. It is concluded that the HAZ width can be controlled at 38.70–54.77 μm with dimethicone, compared with the traditional direct machining (HAZ width: 109.64–439.13 μm). Under the optimal cutting parameters of laser scanning speed of 500 mm/s, repetition rate of 50 kHz and concentric circle spacing of 0.04 mm, the minimum HAZ is 38.70 μm, which is reduced by 85.89% (the HAZ width of laser direct machining is 274.37 μm).

7

Influence of the position of the electrical contact on the size of the temperature distribution

Medveď Dušan, Zbojovský Ján

Przegląd Elektrotechniczny

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2021

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R. 97, nr 12

230--233

EN

This paper deals with the investigation of temperature field distribution around the high-current electric contact. The analyses of temperature field were realised in simulation environment ANSYS and provide better understanding why the electrical contact position influences the heat dissipation. Material of electrical contact was copper, aluminium, brass and non-standard material for power devices, silver. Results were compared and the conclusion with the recommendation were stated in the end of this paper.

PL

Artykuł dotyczy badania rozkładu pola temperatury wokół wysokoprądowego styku elektrycznego. Analizy pola temperatury zostały przeprowadzone w środowisku symulacyjnym ANSYS i pozwalają lepiej zrozumieć, dlaczego położenie styku elektrycznego wpływa na rozpraszanie ciepła. Materiałem styku elektrycznego była miedź, aluminium, mosiądz oraz niestandardowy materiał do urządzeń zasilających, srebro.

8

Effects of pressure gradient on convective heat transfer in a boundary layer flow of a Maxwell fluid past a stretching sheet

Kashif A. N., Salah F., Sankar D. S., Izyan M. D. N., Viswanathan K. K.

International Journal of Applied Mechanics and Engineering

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2021

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Vol. 26, no. 3

104--118

EN

The pressure gradient term plays a vital role in convective heat transfer in the boundary layer flow of a Maxwell fluid over a stretching sheet. The importance of the effects of the term can be monitored by developing Maxwell’s equation of momentum and energy with the pressure gradient term. To achieve this goal, an approximation technique, i.e. Homotopy Perturbation Method (HPM) is employed with an application of algorithms of Adams Method (AM) and Gear Method (GM). With this approximation method we can study the effects of the pressure gradient [...], Deborah number [...], the ratio of the free stream velocity parameter to the stretching sheet parameter [...] and Prandtl number [...] on both the momentum and thermal boundary layer thicknesses. The results have been compared in the absence and presence of the pressure gradient term m. It has an impact of thinning of the momentum and boundary layer thickness for non-zero values of the pressure gradient. The convergence of the system has been taken into account for the stretching sheet parameter. The result of the system indicates the significant thinning of the momentum and thermal boundary layer thickness in velocity and temperature profiles.

9

Projektowanie drzwi przeciwpożarowych - propozycja metody

Kreft Dominik

Izolacje

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2020

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R. 25, nr 7/8

44--46, 48

PL

W artykule opisano propozycję projektowania jednoskrzydłowych drzwi przeciwpożarowych w oparciu o normy PN-EN 1363 oraz PN-EN 1634. Wykorzystano podstawowe równania przenikania ciepła, wynikające z prawa Pecleta, dotyczącego tego rodzaju przenoszenia ciepła. Zaprezentowano wyniki badań statystycznych zebranych na podstawie przeprowadzonych badań ogniowych w certyfikowanych laboratoriach.

EN

The paper presents the method of design of single leaf fire resistant doors according to PN-EN 1363 and PN-EN 1634 standards. Basic heat transfer equations derived from the Peclet formula have been used. Statistical data resulting from fire resistance tests conducted by certified laboratories have been presented.

10

Outcome of nanofluid flow containing arbitrary shape nanoparticles induced by a permeable stretching sheet

Sarkar A., Kundu P. K.

International Journal of Applied Mechanics and Engineering

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2020

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Vol. 25, no. 2

142--156

EN

In this work we have discussed the impact of thermal radiation on heat transfer to nanofluid flow over an unsteady permeable stretching sheet using various types of arbitrary shape nanoparticles of Copper (Cu), Silver (Ag), Alumina [...], and Titania Oxide [...] in the base fluid. Suitable transformations have been employed to build ODEs from the partial differential equations. Numerical results are therefore obtained particularly for cylindrical shape and spherical shape nanoparticles. Our analysis substantiates that the velocity and temperature profiles increases with enhanced thermal radiation parameter. Further, Nusselt number is more advanced for the nanofluid that contains cylindrical shape nanoparticles as compared to spherical shape nanoparticles.

11

Unsteady MHD thermal diffusive and radiative fluid flow past a vertical porous plate with chemical reaction in slip flow regime

Ravi Kumar D., Jayarami Reddy K., Raju M. C.

International Journal of Applied Mechanics and Engineering

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2019

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Vol. 24, no. 1

117--129

EN

An analytical solution of an MHD free convective thermal diffusive flow of a viscous, incompressible, electrically conducting and heat-absorbing fluid past a infinite vertical permeable porous plate in the presence of radiation and chemical reaction is presented. The flow is considered under the influence of a magnetic field applied normal to the flow. The plate is assumed to move with a constant velocity in the direction of fluid flow in slip flow regime, while free stream velocity is assumed to follow the exponentially increasing small perturbation law. The velocity, temperature, concentration, skin friction, Nusselt number and Sherwood number distributions are derived and have shown through graphs and tables by using the simple perturbation technique.

12

Reconstruction of selected operating parametersof a thermoelectric device

Nowak Iwona, Buchalik Ryszard, Nowak Grzegorz

Computer Assisted Methods in Engineering and Science

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2019

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Vol. 26, no. 1

36--46

EN

This paper presents preliminary research aimed at recognizing some selected operating parameters of a thermoelectric device. The inverse problem was formulated, for the solution of which a population heuristics (Ant Colony Optimization) was used. In the inverse task, selected parameters important for the cell operation were reconstructed based on relatively easy to obtain temperature measurements within heat exchangers and appropriate measurements of electrical quantities. The heuristics used, reconstructs the estimated variables, minimizing the differences between data from the measurements and data calculated in the model for their determined values. Since inverse tasks, as ill-conditioned problems, are characterized by high sensitivity to measurement errors, the tests began with calculations based on numerically generated data in order to fully maintain control of their disturbances.

13

Boiling, steaming or rinsing? (the physics of chinese cuisine)

Varlamov A., Zhou Z., Chen Y.

Physics for Economy

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2018

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Vol. 2, No.1

55-68

EN

Some physical aspects of Chinese cuisine are discussed. We start from the cultural and historical particularities of Chinese cuisine and their food production technologies. What is the difference between raw and boiled meat? What is the difference in the physical processes of heat transfer during either the steaming of dumplings or during cooking them in boiling water? Why is it possible to cook meat stripes in a "hot pot" in ten seconds, whilst baking a turkey requires several hours? This article is devoted to a discussion of these questions.

PL

W artykule zostały przedyskutowane niektóre aspekty kuchni chińskiej. Autorzy zaczynają od omówienia szczegółów kuchni chińskiej i technologii produkcji żywności. Autorzy zadają następujące pytania: jaka jest różnica pomiędzy mięsem surowym a gotowanym? Jaka jest różnica w fizyce procesu przenoszenia ciepła podczas przyrządzania klusków na parze wodnej a w gotującej się wodzie? Dla czego jest możliwe przyrządzanie kawałków mięsa w "gorącym garnku" w ciągu kilku sekund, podczas gdy po to, aby upiec indyka potrzebujemy kilku godzin? Artykuł ten udziela odpowiedzi na te i inne pytania.

14

Role of slip velocity in a magneto-micropolar fluid flow from a radiative surface with variable permeability: a numerical study

Sharma B. K., Tailor V., Goyal M.

International Journal of Applied Mechanics and Engineering

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2017

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Vol. 22, no. 3

637--651

EN

An analysis is presented to describe the hydromagnetic mixed convection flow of an electrically conducting micropolar fluid past a vertical plate through a porous medium with radiation and slip flow regime. A uniform magnetic field has been considered in the study which absorbs the micropolar fluid with a varying suction velocity and acts perpendicular to the porous surface of the above plate. The governing non-linear partial differential equations have been transformed into linear partial differential equations, which are solved numerically by applying the explicit finite difference method. The numerical results are presented graphically in the form of velocity, micro-rotation, concentration and temperature profiles, the skin-friction coefficient, the couple stress coefficient, the rate of heat and mass transfers at the wall for different material parameters.

15

Initial unsteady free convective flow past an infinite vertical plate with radiation and mass transfer effects

Khan A., Solanki R.

International Journal of Applied Mechanics and Engineering

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2017

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Vol. 22, no. 4

931--943

EN

An exact solution and analysis of an initial unsteady two dimensional free convection flow, heat and mass transfer in the presence of thermal radiation along an infinite fixed vertical plate when the plate temperature is instantaneously raised, is presented. The fluid considered is a gray, absorbing emitting radiation but a nonscattering medium. Three cases have been discussed, in particular, namely, (i) when, the plate temperature is instantaneously raised to a higher constant value, (ii) when, the plate temperature varies linearly with time and (iii) when, the plate temperature varies non-linearly with time. A close form general solution for all the cases has been obtained in terms of repeated integrals of error functions. In two particular cases, the solutions in terms of the repeated integrals of error functions have been further simplified to forms containing only error functions. It is observed that for an increase in the radiation parameter N or a decrease in the Grashof number Gr or Gm, there is a fall in the velocity or temperature, but compared to the no radiation case or no diffusing species, there is a rise in the velocity and temperature of the fluid.

16

Hydromagnetic rarefied fluid flow over a wedge in the presence of surface slip and thermal radiation

Das K., Sharma R. P., Duari P. R.

International Journal of Applied Mechanics and Engineering

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2017

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Vol. 22, no. 4

827--837

EN

An analysis is presented to investigate the effects of thermal radiation on a convective slip flow of an electrically conducting slightly rarefied fluid, having temperature dependent fluid properties, over a wedge with a thermal jump at the surface of the boundary in the presence of a transverse magnetic field. The reduced equations are solved numerically using the finite difference code that implements the 3-stage Lobatto IIIa formula for the partitioned Runge-Kutta method. Numerical results for the dimensionless velocity and temperature as well as for the skin friction coefficient and the Nusselt number are presented through graphs and tables for pertinent parameters to show interesting aspects of the solution.

17

A numerical study of coupled non-linear equations of thermo-viscous fluid flow in cylindrical geometry

Pothanna N., Aparna P., Gorla R. S. R.

International Journal of Applied Mechanics and Engineering

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2017

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Vol. 22, no. 4

965--979

EN

In this paper we present numerical solutions to coupled non-linear governing equations of thermo-viscous fluid flow in cylindrical geometry using MATHEMATICA software solver. The numerical results are presented in terms of velocity, temperature and pressure distribution for various values of the material parameters such as the thermo-mechanical stress coefficient, thermal conductivity coefficient, Reiner Rivlin cross viscosity coefficient and the Prandtl number in the form of tables and graphs. Also, the solutions to governing equations for slow steady motion of a fluid have been obtained numerically and compared with the existing analytical results and are found to be in excellent agreement. The results of the present study will hopefully enable a better understanding applications of the flow under consideration.

18

Zastosowanie schłodzonego azotu do likwidacji termicznych skutków działania georeaktora podziemnego zgazowania węgla

Cygankiewicz J.

Przegląd Górniczy

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2016

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T. 72, nr 2

3--9

PL

Wyznaczono pole temperatury skal wokół czynnego georeaktora podziemnego zgazowania węgla. Dla ograniczenia skutków działania tego georeaktora zaproponowano podanie w miejsce jego działania azotu schłodzonego do temperatury -100°C. Korzystając z metody modelowania numerycznego, badano jaki jest wpływ czasu podawania schłodzonego azotu na zmiany pola temperatury skał. Zmiany tego pola badano również dla przypadku, gdy zimny azot nie jest podawany.

EN

The temperature field of rocks surrounding the active georeactor for underground coal gasification was determined. A proposal for the reduction of adverse effects of the georeactor operation was submitted, consisting in feeding nitrogen gas cooled down to 100°C into the place of operation. By the use of the numerical modeling method, it was examined how the duration of feeding cooled nitrogen affects the variations in the temperature field of rocks. Variations of this field were also examined for the case in which the cooled nitrogen was not used.

19

Three-dimensional MHD boundary layer flow due to an axisymmetric shrinking sheet with radiation, viscous dissipation and heat source/sink

Madhu M., Balaswamy B., Kishan N.

International Journal of Applied Mechanics and Engineering

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2016

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Vol. 21, no. 2

393--406

EN

An analysis is made to study a three dimensional MHD boundary layer flow and heat transfer due to a porous axisymmetric shrinking sheet. The governing partial differential equations of momentum and energy are transformed into self similar non-linear ordinary differential equations by using the suitable similarity transformations. These equations are, then solved by using the variational finite element method. The flow phenomena is characterised by the magnetic parameter M, suction parameter S, porosity parameter Kp, heat source/sink parameter Q, Prandtl number Pr, Eckert number Ec and radiation parameter Rd. The numerical results of the velocity and temperature profiles are obtained and displayed graphically.

20

Closed form solutions of heat and mass transfer in the flow of a MHD visco-elastic fluid over a porous stretching sheet

Ashokkunar K., Veena P. H., Pravin V. K.

International Journal of Applied Mechanics and Engineering

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2013

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Vol. 18, no. 4

989--1002

EN

The problem of heat and mass transfer in a visco-elastic fluid flow over a stretching sheet in the presence of a uniform magnetic field is examined. The important physical quantities such as the skin friction coefficient, heat transfer co-efficient and the mass transfer co-efficient are determined. It is found that the heat and mass transfer distribution decreases with the increasing values of the visco-elastic parameter k1.