8 results on '"Das, S.K."'
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2. A composite heat transfer model for pool boiling on a horizontal tube at moderate pressure
- Author
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Das, S.K., Roetzel, W.
- Subjects
Boiling liquids ,Boundary layers ,Heat conduction ,Heat flux ,Mathematical models ,Pressure effects ,Bubble mechanism ,Moderate pressure ,Pool boiling ,Transient conduction ,Heat transfer ,boiling ,composite ,heat transfer ,mathematical analysis ,model ,pressure ,article ,evaporation ,molecular model ,prediction ,thermal conductivity - Abstract
The present work is aimed at building a comprehensive heat transfer model for pool boiling on horizontal tubes combining sliding bubble mechanism with natural convection, microlayer evaporation and transient conduction during boundary layer reformation, to predict the boiling heat flux for a given wall superheat. The model has been compared to experimental results from literature for R134a and also to independent experiments conducted by the authors for water. Even with a number of simplified assumptions a reasonably good agreement has been observed between model and experiments in the low and medium heat flux region and moderate pressure.
- Published
- 2004
3. Transient response of multipass plate heat exchangers with axial thermal dispersion in fluid
- Author
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Das, S.K. and Murugesan, K.
- Subjects
Mathematical models ,Multipass plate heat exchangers ,Heat exchangers ,Iterative methods ,plate ,Laplace transforms ,Time domain analysis ,Computer simulation ,Plates (structural components) ,transient response ,Transients ,Heat transfer ,Dispersion (waves) ,Axial thermal dispersions ,heat exchanger ,dispersion modeling - Abstract
To predict the transient response of multipass plate heat exchanger, an analysis is presented based on an axial heat dispersion model in the fluid which takes deviation from ideal plug flow into consideration. The method can be utilised to simulate the exit temperatures for both the fluids for any given arbitrary temperature transient at inlets. The methods takes the 'phase-lag' inside the distribution port into consideration and analyse the multipass plate heat exchanger by considering it as an assembly of single pass plate heat exchangers. The solution technique for equal number of passes on both the sides is different from that for unequal number of passes on the two sides. Examples of computation for the response of 1-2 and 2-2 pass configuration have been presented. The 1-2 pass exchanger is solved by analysing successive modules of the heat exchanger. The 2-2 pass heat exchanger is required to be simulated by iterating the responses of two smaller heat exchangers to which it has been divided. The method involves a Laplace transformation with the temporal variable, solution in space domain and numerical inversion of Laplace transform back to the time domain. The results indicate the strong effect of axial dispersion in fluid on the transient response. The effect of number of plates and number of transfer unit has also been studied which brings out a comprehensive picture of responses of a multipass plate heat exchanger in transient regime. (C) 2000 Elsevier Science Ltd. All rights reserved.To predict the transient response of multipass plate heat exchanger, an analysis is presented based on an axial heat dispersion model in the fluid which takes deviation from ideal plug flow into consideration. The method can be utilized to simulate the exit temperatures for both the fluids for any given arbitrary temperature transient at inlets. The methods takes the `phase-lag' inside the distribution port into consideration and analyze the multipass plate heat exchanger by considering it as an assembly of single pass plate heat exchangers. The solution technique for equal number of passes on both the sides is different from that for unequal number of passes on the two sides. Examples of computation for the response of 1-2 and 2-2 pass configuration have been presented. The 1-2 pass exchanger is solved by analyzing successive modules of the heat exchanger. The 2-2 pass heat exchanger is required to be simulated by iterating the responses of two smaller heat exchangers to which it has been divided. The method involves a Laplace transformation with the temporal variable, solution in space domain and numerical inversion of Laplace transform back to the time domain. The results indicate the strong effect of axial dispersion in fluid on the transient response. The effect of number of plates and number of transfer unit has also been studied which brings out a comprehensive picture of responses of a multipass plate heat exchanger in transient regime.
- Published
- 2000
4. Two-dimensional ablation in cylindrical geometry
- Author
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Katte, S.S., Das, S.K., and Venkateshan, S.P.
- Subjects
Inverse problems ,Stefan numbers ,Mathematical models ,Boundary conditions ,Heat flux ,Cylindrical geometry ,Ablation ,Spacecraft ,Computational geometry ,Heat conduction - Abstract
Ablation modeling in cylindrical geometry is a very important problem in the thermal modeling of spacecraft, which has not been dealt with adequately in the literature. In the present work, two-dimensional ablation in cylindrical geometry is considered when the incident heat flux varies axially as well as temporally. A novel idea of using an effective inverse Stefan number, which is analogous to the effective heat of ablation (used in the literature), is proposed to be used as a variable nondimensional latent heat of ablation for ablation modeling, indirectly accounting for various processes involved in ablation. A two-dimensional ablation problem is solved by an alternating direction implicit and adjustable time-step scheme, coupled with boundary immobilization. Quasi-one-dimensional and two-dimensional modeling methods have been compared for two different materials, and the effects of variation of the proposed inverse Stefan number with the incident heat flux and the presence of highly conducting structure bonded to the ablative material have been studied. An optimum modeling method under specific conditions is suggested.
- Published
- 2000
5. Second law analysis of a plate heat exchanger with an axial dispersive wave
- Author
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Das, S.K. and Roetzel, W.
- Subjects
Mathematical models ,Cryogenics ,Heat exchangers ,Heat transfer ,Wave transmission ,Dispersion (waves) ,Peclet number ,Second law analysis - Abstract
A second law analysis is presented for thermally dispersive flow through a plate heat exchanger. It is well known that in plate or plate fin type heat exchangers the backmixing and other deviations from plug flow contribute significantly to the inefficiency of the heat exchanger, which is of importance to heat exchangers working in the cryogenic regime. The conventional axial heat dispersion model which is used so far is found to be better than 'plug flow' model but still unsatisfactory where the timescale related to heat transfer is comparable with the thermal relaxation time for the propagation of dispersion. The present work therefore considers dispersion as a wave phenomenon propagating with a finite velocity. The study discusses the nature of variation of different contributions to total exergy loss in the heat exchanger with respect to dispersion parameters of the Peclet number and propagation velocity of the dispersive wave. The practical example of the single-pass plate heat exchanger demonstrates how a second law optimization can be carried out for heat transfer equipment under such conditions. ? 1998 Elsevier Science Ltd. All rights reserved.
- Published
- 1998
6. A mathematical model to characterise effects of liquid hold-up on bosh silicon transport in the dripping zone of a blast furnace
- Author
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Das, S.K., Kumari, Amrita, Bandopadhay, D., Akbar, S.A., and Mondal, G.K.
- Subjects
- *
BLAST furnaces , *SILICON , *MATHEMATICAL models , *GAS flow , *TEMPERATURE , *CHEMICAL kinetics , *DISTRIBUTION (Probability theory) , *TRANSPORT theory - Abstract
Abstract: A first principle based mathematical model has been developed to characterise the effect of total liquid hold-up on the bosh silicon distribution behaviour in the dripping zone of a blast furnace. Two specific cases of hold-up behaviour have been investigated, namely, hold-up in the absence and in the presence of counter current gas flow conditions. The model exemplifies coupled phenomenon of chemical kinetics, transport processes and liquid hold-up to characterise the silicon behaviour in the dripping zone. The present modelling investigation shows that the bosh silicon level diminishes with the enhanced liquid hold-up in the dripping zone. Further, the influence of counter current gas flow on the hold-up is not significant. However, it has been observed that the liquid phase temperature reduces with increased liquid hold-up in dripping zone under steady state operating conditions. The model predictions of bosh silicon distribution have been validated with the published literatures (bulk values) and found to be in good agreement. [Copyright &y& Elsevier]
- Published
- 2011
- Full Text
- View/download PDF
7. A mathematical model to characterize effect of silica content in the boiler fly ash on erosion behaviour of boiler grade steel
- Author
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Das, S.K., Godiwalla, K.M., Hegde, Shubha S., Mehrotra, S.P., and Dey, P.K.
- Subjects
- *
EROSION , *FLY ash , *WASTE products , *COMBUSTION gases - Abstract
Abstract: Fly ash particles entrained in the flue gas of coal-fired boilers can cause serious erosion on the critical components along the flow path. Such erosion can significantly jeopardise operational life of the boiler. A first principle based theoretical model has been developed embodying the mechanisms of erosion involving cutting wear, plastic deformation wear and effect of temperature on erosion behaviour, to predict erosion rates of pertinent boiler grade steels. Various grades of steels commonly used in the fabrication of boiler components and published data pertaining to boiler fly ash has been used in modelling the phenomena. The model also provides a quantitative predictive framework to study the effect of percentage of silica content in the ash particles on the erosion potential. The erosion sensitivity of particle impact velocity, angle of impingement and variation of surface temperature of the substrate (steel) have also been studied as a function of silica content in the ash. The model has been implemented in a computer code to predict the erosion rates at room and elevated temperature for various grades of steels under different particle impact conditions. The model predictions have been found to be in good agreement with the published data. This investigation illustrated that any minor increase in silica level in the ash can considerably aggravate the erosion rates, signifying the fact that silica content in the ash plays a critical role in characterising erosion potential of fly ash. [Copyright &y& Elsevier]
- Published
- 2008
- Full Text
- View/download PDF
8. Mathematical model for coupled roll and yaw motions of a floating body in regular waves under resonant and non-resonant conditions
- Author
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Das, S.N. and Das, S.K.
- Subjects
- *
RESONANCE , *MATHEMATICAL models , *MATHEMATICAL statistics , *MASS (Serials control system) - Abstract
The prediction of resonance is very important with respect to the vessels stability in the early stages of design. In this paper, an efficient modeling approach is presented to determine coupled roll and yaw motions of a symmetric and slender floating body when the influences of small amplitude regular waves are dominant. The angular motions described in time domain by considering all internal and external forces are transformed into frequency domain to obtain motion characteristics. We adopt a semi-analytical treatment to obtain roll and yaw motions and derive system instability due to roll resonance. To compute hydrodynamic forces, we employ strip theory method where frequency dependent sectional added-mass, damping and restoring coefficients are derived from the Frank’s close-fit curve. Numerical experiments carried out for a vessel of mass 19,190ton under the action of wave of frequencies 0.56 and 0.76rad/s with zero and non-zero initial conditions are reported and the effect of various parameters on system stability is investigated. Model results indicate that damping factor (ς) plays a pivotal role when wave encountering frequency (ω) and undamped natural frequency (β) are nearly equal. The essence of this study lies in the efficient modeling technique to evaluate damping factor and critical encountering frequency regime for a given ship particulars when experimentally derived resonance zone is absent. [Copyright &y& Elsevier]
- Published
- 2005
- Full Text
- View/download PDF
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