Heat transfer coefficient of gas flowing in a circular tube under rarefied condition

Demsis, Anwar; Verma, B. G.; Prabhu, S.V.; Agrawal, Amit

doi:10.1016/j.ijthermalsci.2010.05.018

Cited by 21 publications

(26 citation statements)

References 31 publications

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“…Most of the experimental studies measured the flow rate and pressure variation in the slip regime . However, Demsis et al reported the heat transfer coefficient in the slip regime through experimental investigation. Theoretical models usually employ the velocity slip and temperature jump boundary conditions along with the continuum equations for evaluating the velocity and temperature distribution.…”

Section: Introductionmentioning

confidence: 99%

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Analysis of Gaseous Flow Between Parallel Plates by Second‐ Order Velocity Slip and Temperature Jump Boundary Conditions

Kushwaha

Sahu

2013

Heat Trans. Asian Res.

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In this study the momentum and energy equations are solved to analyze the flow between two parallel plates by employing second-order velocity slip and temperature jump conditions. The flow is considered to be laminar, incompressible, hydrodynamically/thermally fully developed, and steady state. In addition to the isoflux condition, viscous dissipation is included in the analysis. Closed form expressions for the temperature field and Nusselt number are obtained as a function of the Knudsen number and Brinkman number. The Nusselt number obtained by employing the second-order model is found to be lower compared to the continuum value and agrees well with the other theoretical models.

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Section: Introductionmentioning

confidence: 99%

“…Most of the experimental studies measured the flow rate and pressure variation in the slip regime [4][5][6][7]. However, Demsis et al [6] reported the heat transfer coefficient in the slip regime through experimental investigation. Theoretical models usually employ © 2013 Wiley Periodicals, Inc.…”

Section: Introductionmentioning

confidence: 99%

Analysis of Gaseous Flow Between Parallel Plates by Second‐ Order Velocity Slip and Temperature Jump Boundary Conditions

Kushwaha

Sahu

2013

Heat Trans. Asian Res.

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“…Therefore, from Equation , the possibilities of β to be greater than unity are more, which implies that for most of the engineering applications, heat transfer would decrease with increasing rarefaction, and the reduction can become very significant (around 70–80% for β = 10) for very large β values. In fact, very large β values could be one possible explanation for the extremely small Nusselt number values observed in the recent experimental work of Demsis et al compared with the theoretical and numerical results. For β values to become very large for typical engineering applications (with γ ∼ 1.4 and Pr ∼ 0.7), thermal accommodation coefficients ( σ T ) need to be very small, which depends on the gas‐wall surface combinations.…”

Section: Resultsmentioning

confidence: 93%

Slip flow and heat transfer in rectangular and circular microchannels using hybrid FE/FV method

Palle

Aliabadi

2011

Numerical Meth Engineering

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SUMMARYRarefied gas flows typically encountered in MEMS systems are numerically investigated in this study. Fluid flow and heat transfer in rectangular and circular microchannels within the slip flow regime are studied in detail by our recently developed implicit, incompressible, hybrid (finite element/finite volume) flow solver. The hybrid flow solver methodology is based on the pressure correction or projection method, which involves a fractional step approach to obtain an intermediate velocity field by solving the original momentum equations with the matrix-free, implicit, cell-centered finite volume method. The Poisson equation resulting from the fractional step approach is then solved by node based Galerkin finite element method for an auxiliary variable, which is closely related to pressure and is used to update the velocity field and pressure field. The hybrid flow solver has been extended for applications in MEMS by incorporating first order slip flow boundary conditions. Extended inlet boundary conditions are used for rectangular microchannels, whereas classical inlet boundary conditions are used for circular microchannels to emphasize on the entrance region singularity. In this study, rarefaction effects characterized by Knudsen number (Kn) in the range of 0 6 Kn 6 0.1 are numerically investigated for rectangular and circular microchannels with constant wall temperature. Extensive validations of our hybrid code are performed with available analytical solutions and experimental data for fully developed velocity profiles, friction factors, and Nusselt numbers. The influence of rarefaction on rectangular microchannels with aspect ratios between 0 and 1 is thoroughly investigated. Friction coefficients are found to be decreasing with increasing Knudsen number for both rectangular and circular microchannels. The reduction in the friction coefficients is more pronounced for rectangular microchannels with smaller aspect ratios. Effects of rarefaction and gas-wall surface interaction parameter on heat transfer are analyzed for rectangular and circular microchannels. For most engineering applications, heat transfer is decreased with rarefaction. However, for fluids with very large Prandtl numbers, velocity slip dominates the temperature jump resulting in an increase in heat transfer with rarefaction. Depending on the gas-wall surface interaction properties, extreme reductions in the Nusselt number can occur. Present results confirm the existence of a transition point below and above wherein heat transfer enhancement and reduction can occur.

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“…Choi's correlation links the average Nusselt number to the value of Reynolds number and Prandlt number, as usual in the classical Dittus and Boelter [34] correlation validated for conventional flows in turbulent regime; this is only partially in agreement with the expected set of independent parameters which can influence the Nusselt number in laminar regime as evidenced by Eq. (11).…”

Section: Comparisons With Classical Correlationsmentioning

confidence: 99%

“…For instance, the paper of Khan et al [10] on the analysis of convective heat transfer coefficients of laminar liquid flows highlighted a disagreement between the experimental Nusselt numbers and the predictions of the classical correlations without any quantitative explanation about these differences. The paper of Demsis et al [11] about the experimental determination of the convective heat transfer coefficients in minitubes under rarefied conditions reported unusual low values of Nusselt number without any physical explanation. The papers of Park [12] and Mun and Kim [13] proposed new correlations for liquid flows in laminar regime through microchannels avoiding any theoretical justification of the need of these new correlations.…”

Section: Introductionmentioning

confidence: 99%

Guidelines for the Determination of Single-Phase Forced Convection Coefficients in Microchannels

Morini¹,

Yang

2013

Journal of Heat Transfer

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This paper deals with the analysis of the main features of forced microconvection of liquid and gas flows through microchannels. A critical oveiyiew of the main effects that tends to play an important role in the determination of Nusselt number in microchannels is presented. Some experimental data obtained at the Microfluidics Lab of the University of Bologna together with the main results which appeared recently in the open literature both for liquids and gases are used in order to highlight the peculiar characteristics of the convective heat transfer through microchannels and to suggest the guidelines for a physically based interpretation to the experimental results. By means of speciflc examples, it is shown that the thermal behavior at microscale of gas and liquid flows through microchannels in terms of convective heat transfer coefficients can be strongly affected by scaling and micro-effects but also by practical issues linked to the geometry of the test rig, the real thermal boundary conditions, the presence of flttings, position and type of the sensors, and so on. All these aspects have to be taken into account during the data post processing in order to obtain a correct evaluation of the Nusselt numbers. It is also highlighted how it is always useful to couple to the experimental approach a complete computational thermal fluid-dynamics analysis of the whole tested microsystem in order to be able to recognize "a priori" the main effects which can play an important role on the convective heat transfer analysis. It is demonstrated in this paper that this "a priori" analysis is crucial in order to: (i) individuate the main parameters which influence the convective heat transfer coefficients (this is important for the development of new correlations); (ii) compare in a right way the conventional correlations with the experimental results.

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Heat transfer coefficient of gas flowing in a circular tube under rarefied condition

Cited by 21 publications

References 31 publications

Analysis of Gaseous Flow Between Parallel Plates by Second‐ Order Velocity Slip and Temperature Jump Boundary Conditions

Analysis of Gaseous Flow Between Parallel Plates by Second‐ Order Velocity Slip and Temperature Jump Boundary Conditions

Slip flow and heat transfer in rectangular and circular microchannels using hybrid FE/FV method

Guidelines for the Determination of Single-Phase Forced Convection Coefficients in Microchannels

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