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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

Effect of aspect ratio of enclosure on free convection from horizontal cylinders in Bingham plastic fluids

Baranwal Ashok Kumar, Gupta Anoop Kumar, Tiwari Anurag Kumar, Melnik Roderick

Chemical and Process Engineering

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2022

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Vol. 43, nr 2

271--277

EN

Heat transfer in steady free convection from differentially heated cylinders enclosed in a rectangular duct filled with Bingham plastic fluids has been solved numerically for the ranges of the dimensionless groups as, Rayleigh number, 102 Ra 106; Prandtl number, 10 Pr 100 and, Bingham number, 0 Bn 50 for aspect ratios AR = 05, 0.6, 0.7, 0.8, 0.9 and 2. The streamlines, isotherm contours, yield surfaces, local and average Nusselt numbers were analysed and discussed. It is found that as the aspect ratio of the enclosure increases from 0.5 to 0.9, the average Nusselt number on the surface of the hot cylinder increases as a larger amount of fluid takes part in convection. Moreover, at sufficiently large Bingham numbers, yield stress forces dominate over buoyancy causing the flow to cease and thus the Nusselt number approaches its conduction limit. Finally, the Nusselt number approaches its conduction limit once the maximum Bingham number is reached.

3

Effect of aiding buoyancy on heat transfer from an isothermal square cylinder in power-law fluids

Mishra Pragya, Mishra Lubhani, Tiwari Anurag Kumar

Chemical and Process Engineering

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2022

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Vol. 43, nr 2

265–-270

EN

The aim of the present study was to explore the influence of aiding buoyancy on mixed convection heat transfer in power-law fluids from an isothermally heated unconfined square cylinder. Extensive numerical results on drag coefficient and surface averaged values of the Nusselt number are reported over a wide range of parameters i.e. Richardson number, 01 Ri 5, power-law index, 04 𝑛 18, Reynolds number, 01 Re 40, and Prandtl number, 1 Pr 100. Further, streamline profiles and isotherm contours are presented herein to provide an insight view of the detailed flow kinematics

4

Enhancement of turbulent airflow and heat transfer through a rectangular microchannel with different types of baffles

Saha Sandip, Raut Santanu, Das Apurba Narayan

Journal of Applied Mathematics and Computational Mechanics

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2021

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Vol. 20, nr 3

41--52

EN

The objective of this work is to discuss the turbulent air hydro-thermal phenomena over a rectangular microchannel with different types of baffle (rectangular, triangular, and trapezoidal) mounted on both the walls of the microchannel. The finite volume method with the second order upwind scheme has been utilized to discretize the governing equations and to study the turbulent airflow characteristics; the SST k-ꞷ turbulence model has been adopted. For nine different cases, the different characteristics of fluid flow phenomena and thermal behaviour with the variations in the Reynolds number ranging from [5,000-25,000] and for three different values of inter baffle spacing have been studied in this manuscript. Due to the presence of baffle, it is revealed that the vortex arises on the upper wall and the thermal phenomena enhances with the decrease in inter baffle spacing.

5

Flow features of thermophoretic MHD viscous fluid flow past a converging channel with heat source and chemical reaction

Kalita B. K., Choudhury R.

International Journal of Applied Mechanics and Engineering

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2021

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Vol. 26, no. 3

72--83

EN

A boundary layer flow of an electrically conducting viscous fluid past a converging channel in the presence of thermophoresis, heat source, chemical reaction, viscous dissipation and simultaneous heat and mass transfer characteristics is studied in the paper. An external magnetic field of uniform strength is applied transversely to the channel. The similarity solution has been used to transform the partial differential equations that represent the problem into a boundary value problem of coupled ordinary differential equations, which in turn are solved numerically using MATLAB’s built in solver bvp4c. Numerical computations are carried out to solve the problem and graphical illustrations are made to get the physical insight of the same. The convergent channel flow problem of an incompressible electrically conducting viscous fluid in the presence of a magnetic field has a wide range of applicability in different areas of engineering, specially in industrial metal casting and control of molten metal flow.

6

The complex Ginzburg Landau model for an oscillatory convection in a rotating fluid layer

Manjula S. H., Kiran P., Reddy P. Raj, Bhadauria B. S.

International Journal of Applied Mechanics and Engineering

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2020

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Vol. 25, no. 1

75--91

EN

A weakly nonlinear thermal instability is investigated under rotation speed modulation. Using the perturbation analysis, a nonlinear physical model is simplified to determine the convective amplitude for oscillatory mode. A non-autonomous complex Ginzburg-Landau equation for the finite amplitude of convection is derived based on a small perturbed parameter. The effect of rotation is found either to stabilize or destabilize the system. The Nusselt number is obtained numerically to present the results of heat transfer. It is found that modulation has a significant effect on heat transport for lower values of ωf while no effect for higher values. It is also found that modulation can be used alternately to control the heat transfer in the system. Further, oscillatory mode enhances heat transfer rather than stationary mode.

7

Application of Nanoparticles in the Process of Phase Change Paraffin in a Chamber

Alizadeh As’ad

Advances in Science and Technology. Research Journal

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2019

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Vol. 13, no 3

113--119

EN

In this study, melting of a phase changing material enriched with nanoparticles in a circular ring-rectangular enclosure was investigated and the results were analyzed. At the beginning of the melting process in the absence of a natural displacement, the mechanism of conduction heat transfer around the hot cylinder is the dominant mechanism. Over time, natural displacement gradually appears and deforms the melting boundary above the cylinder. Over time, when the thickness of the liquid phase grows, the thermal resistance increases, this can be verified by reviewing the Nusselt chart. So this phenomenon reduces the rate of melting and temperature changes. The results show that increasing the nanoparticle volume fraction due to increased conductivity and decreasing latent heat causes an increase in the melting rate and the amount of energy absorbed. From the study of various volume fractions, it can be concluded that the use of a higher volume fraction of 3% is more appropriate both in terms of energy and in terms of the melting rate. However, it should be taken into account that if the melting rate exceeds this value, it may cause agglomeration and deposition of nanoparticles and reducing system efficiency.

8

Wpływ geometrii dysz stosowanych w strumieniowych układach chłodzenia na wymianę ciepła

Marzec K.

Modelowanie Inżynierskie

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2018

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T. 37, nr 68

75--84

PL

W ramach badań objętych niniejszą pracą analizowano wpływ zastosowania różnej geometrii dysz (cylindryczne, zbieżne oraz rozbieżne) na rozkład wartości liczby Nusselta podczas chłodzenia płaskiej płyty z wykorzystaniem strumieniowego układu chłodzenia składającego się z dziesięciu równomiernie rozmieszczonych dysz skierowanych prostopadle do powierzchni chłodzonej. Pierwszym krokiem prowadzonych badań było określenie najkorzystniejszej wartości parametru Y/D. Bezwymiarowa wartość Y/D określa odległość pomiędzy dyszą a powierzchnią chłodzącą Y w odniesieniu do średnicy dyszy D. Określenie tego bezwymiarowego współczynnika stanowiło podstawę do wykonania dalszych obliczeń cieplno-przepływowych układów chłodzenia o różnej geometrii dysz chłodzących. Równania opisujące przepływy oraz wymianę ciepła rozwiązano numerycznie metodą elementów skończonych za pomocą solvera Ansys CFX wykorzystując metodę RANS.

EN

This study analyzed the influence of application of various nozzle shape (cylindrical, convergent and divergent) on the Nusselt number distribution under impinged cooling of a flat surface. Cooling system composed of an inline array of ten uniformly arranged jets directed perpendicularly to the target surface. At the beginning of the calculations the most effective dimensionless factor Y/D was determined. This parameter described distance between nozzle and cooled surface Y in relation to the jet diameter D. Defining most effective Y/D parameter was a basis for further examinations of the impinging jets with various geometry of the cooling nozzles. The analyses of the flow and heat transfer characteristics were carried out using finite element method, software Ansys CFX and RANS approach.

9

Transient natural convection in partitioned enclosures

Zemani F., Sabeur-Bendehina A.

Mechanics and Mechanical Engineering

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2018

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Vol. 22, nr 4

1015--1030

EN

In this paper, the natural convection flow in a cavity heated differentially with a partition placed in the middle of the hot wall is numerically simulated. The aspect ratio of the geometry, Prandtl number are fixed at 0.24, 6.64, respectively, for different partitions lengths; however the Rayleigh number values were ranging from 106 to 3:77 x 109 in order to observe the transition regime. The fluid flow and the heat transfer described in terms of continuity, linear momentum and energy equations were predicted by using the finite volume method. To approach the physical reality experience, calculations were performed in a cavity with the same size and same priority of the fluid with an average temperature Tm imposed on the cooled wall, also another simulation with an average temperature Tm imposed on the horizontal wall. Time evolution, isotherms and mean Nusselt number are presented for all investigated values. Representative results illustrating the effects of the partition length for the heat transfer and the thermal boundary layer are also reported and discussed. The results indicate that the flow and heat transfer properties are altered by the presence of the partition, especially in the initial stage. In a certain sense, the partition blocks the flow and forces it to come off the hot wall. Since the partition parameters are critical for the transient natural convection ow in the cavity, different partition lengths on the warm wall have been studied.

10

Numerical study of natural convection in a vertical cylindrical partially annular

Medebber M. A., Retiel N.

Mechanics and Mechanical Engineering

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2018

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Vol. 22, nr 1

77--92

EN

A study of free convection in a vertical cylinder partially annulus is conducted numerically. Uniform temperature is imposed cross a vertical wall, while the top and bottom walls are adiabatic. The governing equations are solved numerically by using a finite volume method. The coupling between the continuity and momentum equations is effected using the SIMPLER algorithm. Solutions have been obtained for Prandtl numbers equal to 7.0, Rayleigh numbers of 103 to 106 and height ratios of 0 to 1. The influence of physical and geometrical parameters on the streamlines, isotherms, average Nusselt has been numerically investigated.

11

Jednomianowy model liczby Nusselta w pomiarze zmiennej temperatury metodą "w ciemno" przy niestacjonarnych przepływach

Nabielec J., Jamróz P.

Zeszyty Naukowe Wydziału Elektrotechniki i Automatyki Politechniki Gdańskiej

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2016

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Nr 49

79--84

PL

Pomiar zmiennej w czasie temperatury medium poruszającego się ze zmienną prędkością obarczony jest istotnym błędem dynamicznym. Jego źródłem są zależne od tej prędkości właściwości dynamiczne toru pomiarowego określone przez współczynnik dynamiki. Metoda "w ciemno" umożliwia zidentyfikowanie jego chwilowych wartości i skorygowanie błędu dynamicznego na drodze numerycznej. Zadanie to jest dobrze postawione przy wykorzystaniu jednomianowej reprezentacji liczby Nusselta, od której zależy chwilowa wartość tego współczynnika. W artykule zaprezentowano podstawy teoretyczne metody pomiarowej, wyniki badań symulacyjnych oraz eksperymentalnej jej weryfikacji.

EN

Measurement result of time-varying temperature of the medium moving at a variable velocity is encumbered with a significant dynamic error. The main reason of that error are the dynamic properties of the measurement channel described by the dynamic coefficient. The “blind” correction method gives a possibility of identifying the instantaneous values of this factor and numerically correcting the dynamic error. This task is well defined when the monomial Nusselt number is used in a dynamic coefficient model. The article presents the theoretical basis of the measurement method, the simulation results and experimental verification.

12

Experimental investigation of heat transfer characteristics of nanofluid using parallel flow, counter flow and shell and tube heat exhanger

Dharmalingam R., Sivagnanaprabhu K. K., Yogaraja J., Gunasekaran S., Mohan R.

Archive of Mechanical Engineering

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2015

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Vol. LXII, nr 4

509--522

EN

Cooling is indispensable for maintaining the desired performance and reliability over a very huge variety of products like electronic devices, computer, automobiles, high power laser system etc. Apart from the heat load amplification and heat fluxes caused by many industrial products, cooling is one of the major technical challenges encountered by the industries like manufacturing sectors, transportation, microelectronics, etc. Normally water, ethylene glycol and oil are being used as the fluid to carry away the heat in these devices. The development of nanofluid generally shows a better heat transfer characteristics than the water. This research work summarizes the experimental study of the forced convective heat transfer and flow characteristics of a nanofluid consisting of water and 1% Al2O3 (volume concentration) nanoparticle flowing in a parallel flow, counter flow and shell and tube heat exchanger under laminar flow conditions. The Al2O3 nanoparticles of about 50 nm diameter are used in this work. Three different mass flow rates have been selected and the experiments have been conducted and their results are reported. This result portrays that the overall heat transfer coefficient and dimensionless Nusselt number of nanofluid is slightly higher than that of the base liquid at same mass flow rate at same inlet temperature. From the experimental result it is clear that the overall heat transfer coefficient of the nanofluid increases with an increase in the mass flow rate. It shows that whenever mass flow rate increases, the overall heat transfer coefficient along with Nusselt number eventually increases irrespective of flow direction. It was also found that during the increase in mass flow rate LMTD value ultimately decreases irrespective of flow direction. However, shell and tube heat exchanger provides better heat transfer characteristics than parallel and counter flow heat exchanger due to multi pass flow of nanofluid. The overall heat transfer coefficient, Nusselt number and logarithmic mean temperature difference of the water and Al2O3 /water nanofluid are also studied and the results are plotted graphically.

PL

Chłodzenie jest niezbędne dla właściwego funkcjonowania i niezawodności różnorodnych produktów, jak urządzenia elektroniczne, komputery, samochody, systemy laserowe wielkiej mocy, itp. W sytuacji wzrostu obciążenia cieplnego i strumieni ciepła wytwarzanych przez urządzenia przemysłowe, chłodzenie jest jednym z najważniejszych wyzwań występujących w różnych gałęziach przemysłu, transporcie, mikroelektronice, itp. Płynami, które zwykle są używane do odprowadzania ciepła z tych urządzeń są woda, glikol etylenowy i oleje. Nanopłyny, opracowane w ostatnim czasie, wykazują generalnie lepsze charakterystyki przewodnictwa cieplnego niż woda. Przedstawiona praca stanowi podsumowanie badań doświadczalnych nad wymuszonym, konwekcyjnym odprowadzaniem ciepła i charakterystykami przepływu nanopłynu składającego się z wody i cząsteczek Al2O3 (w 1% stężeniu objętościowym) w warunkach laminarnego przepływu współprądowego i przeciwprądowego w płaszczowych i rurowych wymiennikach ciepła. W przedstawionych badaniach użyto cząstek Al2O3 o średnicy ok. 50 nm. Wybrano trzy różne prędkości przepływu masy, opisano wyniki eksperymentów. Wyniki te wskazują, że całkowity współczynnik odprowadzania ciepła i bezwymiarowa liczba Nusselta nanopłynu są, przy tej samej prędkości przepływu masy i temperaturze na wlocie, nieznacznie wyższe, niż dla samego płynu bazowego. Z wyników doświadczalnych wynika, że całkowity współczynnik odprowadzania ciepła wzrasta wraz z prędkością przepływu masy. Pokazano, że gdy wzrasta prędkość przepływu masy, całkowity współczynnik odprowadzania ciepła wraz z bezwymiarową liczbą Nusselta ostatecznie wzrastają, niezależnie od kierunku przepływu. Stwierdzono także, że ze wzrostem prędkości przepływu masy wartość LMTD (średniej logarytmicznej różnicy temperatur) ostatecznie maleje, niezależnie od kierunku przepływu. Niemniej, płaszczowe i rurowe wymienniki ciepła zapewniają lepsze charakterystyki odprowadzania ciepła niż wymienniki z przepływem współprądowym i przeciwprądowym, co wynika z wielostrumieniowego przepływu nanopłynu. Badano także całkowity współczynnik odprowadzania ciepła, bezwymiarową liczbę Nusselta i średnią logarytmiczną różnicę temperatur dla wody i nanopłynu złożonego z wody i Al2O3, a wyniki przedstawiono w formie graficznej.

13

Symulacja konwekcji wymuszonej w przewodach prostoosiowych przy przepływie laminarnym metodą elementów brzegowych

Teleszewski T.

Zeszyty Naukowe. Inżynieria Środowiska / Uniwersytet Zielonogórski

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2014

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nr 153 (33)

117--127

PL

W pracy przedstawiono algorytm symulacji konwekcji wymuszonej MEB przy przepływie laminarnym w przewodach prostoosiowych niezależnie od kształtu poprzecznego przewodu. Weryfikacja algorytmu została wykonana poprzez porównanie rezultatów MEB z rozwiązaniem analitycznym. W publikacji wyznaczono zależność liczby Nusselta od liczby boków w przewodach o przekroju wielokąta foremnego.

EN

The paper presents the numerical algorithm Boundary Element Method to simulation modelling forced convection in a duct. The efficiency and the credibility of proposed algorithm were verified by numerical tests in theoretical solution. A numerical examples are presented fully developed forced convection through pentagon duct. In this study is proposed for determining the Nusselt number in regular polygonal channels.

14

Nusselt Number Correlation of SAH

Chabane F., Moummi N., Benramache S., Bensahal D., Belahssan O.

Journal of Power Technologies

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2013

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Vol. 93, nr 2

100--110

EN

This paper presents the experimentally investigated thermal performance of a single pass solar air heater. The effects of mass flow rate of air on the outlet temperature, Nusselt Number, Reynolds Number, Prandtl Number, heat transfer in the thickness of the solar collector and thermal efficiency were studied. Experiments were performed for the mass flow rates of 0.0108, 0.0145 and 0.0184 kg/s. For this effect was have created a new correlation correspondent of solar air collector with using fins it was written Nu=K1Re^0.939 Pr^0.523 exp(1.2 m) h^(0.0505Pr).The maximum efficiency levels obtained for the 0.0108, 0.0145 and 0.0184 kg/s were 28.63, 39.69 and 55.69% respectively. A comparison of the results of the solar collector without fins shows a substantial enhancement in thermal efficiency.

15

Effects of heat transfer on dusty gas flow past a semi-infinite vertical plate

Kulandaivel T.

International Journal of Applied Mechanics and Engineering

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2012

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Vol. 17, no. 4

1339-1346

EN

Effects of heat transfer on dusty gas flow past a semi-infinite vertical plate with variable temperature is considered. The governing boundary layer equations for this problem are set up and non-dimensional governing equations are solved by an implicit finite difference scheme of Crank-Nicolson method, which is fast convergent and unconditionally stable. Gas velocity, dust particle velocity, temperature, skin-friction and Nusselt numbers are calculated numerically for various parameters and are shown graphically. It is observed that an increase in the mass concentration of dust causes a fall in the dusty gas velocity but an increase in the skin-friction.

16

Numerical study of non-Darcy forced convective heat transfer in a power law fluid over a stretching sheet

Prasad K. V., Datti P. S.

International Journal of Applied Mechanics and Engineering

|

2009

|

Vol. 14, no 2

473-488

EN

An analysis has been carried out to study the non-Darcy flow behavior and heat transfer characteristics of a non-Newtonian power law fluid over a non-isothermal stretching sheet with variable thermal conductivity and internal heat generation/absorption. Thermal conductivity is assumed to vary as a linear function of temperature. The partial differential equations governing the flow and heat transfer are converted into ordinary differential equations by a similarity transformation. The presence of non-Darcy forced convection and power law index leads to coupling and non-linearity in the boundary value problem. Because of the coupling and non-linearity, the problem has been solved numerically by the Keller box method. The computed values of horizontal velocity and temperature, boundary layer thickness are shown graphically in tables and figures. Several reported works on the problem are obtained as limiting cases of the present study. The results of the study have implications in extrusion processes and in other applications with porous media.

17

Unsteady free convection flow of a dusty gas past a semi-infinite inclined plate with constant heat flux

Ganesan P., Palani G.

International Journal of Applied Mechanics and Engineering

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2004

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Vol. 9, no 3

483-492

EN

A numerical solution for the flow of fluid with dusty particles past a semi-infinite inclined plate with a constant heat flux is obtained by an implicit finite difference method, which is unconditionally stable. Gas-velocity, dust-velocity, temperature, skin friction and Nusselt number are shown graphically. It is observed that the velocity of the dusty-gas decreases with decreasing the inclination angle 'phi' to the horizontal. An increase in the mass concentration of dust also causes a fall in the gas-velocity.

18

Transient free convection flow of dissipative fluid past an infinite vertical porous plate

Soundalgekar V. M., Uplekar A. G., Jaiswal B. S.

Archives of Mechanics

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2004

|

Vol. 56, nr 1

7-17

EN

A finite-difference analysis of transient free convection flow of a dissipative fluid past an infinite vertical porous plate is presented here. Velocity, temperature, skin-friction and Nusselt number are shown graphically and the effects of different parameters on the flow field are discussed.

19

Variable viscosity and thermal conductivity effects on heat transfer by natural convection from a cone and a wedge in porous media

Hassanien I. A., Essawy A. H., Moursy N. M.

Archives of Mechanics

|

2003

|

Vol. 55, nr 4

345-356

EN

The problem of steady, laminar heat transfer by natural convection flow over a vertical cone a wedge embedded in a uniform porous medium with variable viscosity and thermal conductivity is investigated. The transformed governing equations are solved numerically by using a finite difference scheme. The obtained results are compared with earlier papers on special cases of the problem and are found to be in excellent agreement. The influence of porous medium inertia effect, viscosity wariation parameter ... and thermal conductivity variation parameter ... on the fluid velocity and temperature is discussed. Including the porous medium inertia effect or viscosity variation parameter in the mathematical model is predicted to reduce the local Nusselt number. Furthermore, the local Nusselt number increases in the presence of thermal conductivity variation parameter.

20

Model matematyczny oraz badania aerodynamiczne i przepływowo-cieplne chłodnicy samochodowej

Taler D.

Archiwum Motoryzacji

|

2001

|

Nr 4

145--162

PL

Przedstawiono analityczny model wymiany ciepła w chłodnicy samochodowej stanowiącej krzyżowo-prądowej lamelowy wymiennik ciepła. Wyprowadzono wzory na rozkład temperatury cieczy wewnątrz rury oraz temperatury powietrza w dwubiegowej chłodnicy o dwóch rzędach rur. Za pomocą wyprowadzonych wzorów można określić strumienie ciepła przekazywane przez poszczególne rzędy rur, a także moc chłodnicy przy zadanych temperaturach wlotowych i strumieniowych masowych czynników. W pracy omówiono wyniki badań aerodynamicznych, hydraulicznych i cieplnych chłodnicy silnika o pojemności skokowej 1580 m[^3]. Na podstawie przeprowadzonych badań wyznaczono wzory na współczynniki charakteryzujące opory przepływu powietrza i płynu chłodzącego oraz wzór na liczbę Nusselta od strony powietrza.

EN

An analytical mathematical model of two-row plate-fin exchangers is presented. The temperature distributions on the fluid and air sides can easily be calculated using the developed model. The comparison of calculated results with experimental data for the automotive radiator shows that the mathematical model is very accurate. The results of the experimental investigation of the plate-fin-and-tube automotive radiator are presented. The tested two-pass radiator consists of two inline rows of tubes with smooth plate fins. The objective was to derive the correlations for the friction factors and the air-side heat transfer coefficient as a function of the Reynolds numbers. The air side heattransfer coefficient was determined from the condition that the calculated and measured coolant outlet temperatures aer equal.