Asymmetric Temperatures Research Articles

CFD-modeling for more precise operation of the kraft recovery boiler

During kraft recovery boiler operation, situations can be encountered where the furnace temperature is asymmetric when comparing one side of the furnace to the other (i.e., left vs. right). In this paper, computational fluid dynamics (CFD) modeling is applied to study furnace load and liquor spraying as causes for asymmetric furnace temperatures in a 4450 tons dry solids (TDS)/day kraft recovery boiler. The model predictions are compared against validation measurements. Decrease in furnace load is identified as the main cause of the temperature asymmetry. The simulations also suggest that, at decreased load, relatively small differences in the tilts of individual liquor sprays can increase the temperature asymmetry.

Fluorogenic Ribonuclease Protection (FRIP) Analysis of Single Nucleotide Polymorphisms (SNPs) in Japanese Rice (Oryza sativaL.) DNA for Cultivar Discrimination

A rapid and easy method to discriminate plant cultivars is indispensable to confirm food labeling. We established a fluorogenic ribonuclease protection (FRIP) assay to discriminate Japanese rice (Oryza sativa L.) cultivars based on single nucleotide polymorphisms (SNPs). The FRIP assay uses a hybridization technique between fluorescent probes and the target sequence prepared by run-off transcription, but the requirement of two PCR thermocycles is the problem when preparing template DNA for run-off transcription from rice genomic DNA. In this study, we designed new PCR primers with asymmetric melting temperatures. These primers amplified the target SNP marker containing a T7 RNA polymerase promoter sequence upstream of the target sequence in a single PCR. Moreover, 100 cultivars were discriminated with the patterns of 15 SNPs. The assay can be used as a rapid method of analysis to discriminate Japanese rice cultivars.

Experimental study of hydronic panels system and its environment

An experimental analysis of hydronic cooling or heating ceiling panels coupled to the building is present in this investigation as a part of the commissioning study of this system. Two test chambers are adapted in a way to reproduce the interaction of the system to the building (windows, internal thermal loads distribution, building structure and ventilation). A series of experimental tests were performed in which the main objective is to observe the influence of parameters such as the water mass flow rate, supply water temperature, thermal load distribution, window and ventilation system effects on the hydronic ceiling capacity and comfort conditions. Test results show that the influence of asymmetric surfaces temperatures inside the room, especially the window effect is not negligible. Then, it is clear that the cooling hydronic ceiling must be evaluated coupled to the building systems and structure.

Fully Developed Free Convection Heat and Mass Transfer of a Micropolar Fluid Between Porous Vertical Plates

In this article, we consider the problem of fully developed natural convection heat and mass transfer of a micropolar fluid between porous vertical plates with asymmetric wall temperatures and concentrations. The resulting boundary-value problem is solved analytically by the homotopy analysis method (HAM). Profiles for velocity and microrotation are presented for a range of values of the Reynolds number and the micropolar parameter.

Solution of fully developed free convection of a micropolar fluid in a vertical channel by homotopy analysis method

AbstractIn this paper, we reconsider the problem of fully developed natural convection heat and mass transfer of a micropolar fluid in a vertical channel with asymmetric wall temperatures and concentrations. The resulting boundary‐value problem is solved analytically by the homotopy analysis method. The accuracy of the present solution is found to be in excellent agreement with the solutions of Cheng (Int. Commun. Heat Mass Transfer 2006; 33:627–635). Copyright © 2008 John Wiley & Sons, Ltd.

Fully-developed heat transfer in annuli with viscous dissipation

For Newtonian concentric annular flows analytical solutions are obtained under imposed asymmetric constant wall heat fluxes as well as under imposed asymmetric constant wall temperatures, taking into account viscous dissipation and for fluid dynamic and thermally fully-developed conditions. Results for the special case of the heat flux ratio for identical wall temperatures and the critical Brinkman numbers marking changes of sign in wall heat fluxes are also derived. Equations are presented for the Nusselt numbers at the inner and outer walls, bulk temperature and normalised temperature distribution as a function of all relevant non-dimensional numbers. Given the complexity of the derived equations, simpler exact expressions are presented for the Nusselt numbers for ease of use, with their coefficients given in tables as a function of the radius ratio.

Fully developed natural convection heat and mass transfer in a vertical annular porous medium with asymmetric wall temperatures and concentrations

This work examines the effects of the modified Darcy number, the buoyancy ratio and the inner radius-gap ratio on the fully developed natural convection heat and mass transfer in a vertical annular non-Darcy porous medium with asymmetric wall temperatures and concentrations. The exact solutions for the important characteristics of fluid flow, heat transfer, and mass transfer are derived by using a non-Darcy flow model. The modified Darcy number is related to the flow resistance of the porous matrix. For the free convection heat and mass transfer in an annular duct filled with porous media, increasing the modified Darcy number tends to increase the volume flow rate, total heat rate added to the fluid, and the total species rate added to the fluid. Moreover, an increase in the buoyancy ratio or in the inner radius-gap ratio leads to an increase in the volume flow rate, the total heat rate added to the fluid, and the total species rate added to the fluid.

Fully developed natural convection heat and mass transfer of a micropolar fluid in a vertical channel with asymmetric wall temperatures and concentrations

This work examines the effects of the vortex viscosity parameter and the buoyancy ratio on the fully developed natural convection heat and mass transfer of a micropolar fluid in a vertical channel with asymmetric wall temperatures and concentrations. The closed-form analytic solutions for the important characteristics of fluid flow, heat transfer, and mass transfer are derived. Increasing the vortex viscosity parameter tends to increase the magnitude of microrotation and thus decreases the fluid velocity in the vertical channel. Moreover, the volume flow rate, the total heat rate added to the fluid, and the total species rate added to the fluid for micropolar fluids are lower than those of Newtonian fluids.

Pulsed plasmas as a method to improve uniformity during materials processing

Continuous wave operation of inductively coupled plasma (ICP) reactors as used for materials processing and which have geometrical or flow asymmetries may produce asymmetric species densities, temperatures, and fluxes. Flow asymmetries that produce nonuniformities in plasma conductivity initiate a positive feedback loop. In this feedback loop, asymmetries in conductivity are reinforced by the resulting nonuniform power deposition, which causes electron impact ionization to also be nonuniform. In this article, we discuss results from a computational investigation of long-term transients during pulsed operation of ICPs and their consequences on side-to-side asymmetries in plasma properties. During pulsed operation, diffusion of charged species during the afterglow between pulses smoothens these asymmetries prior to the next power pulse. The power deposition during subsequent pulses is more symmetric and this reduces the positive feedback. The improvement in uniformity afforded by pulsing is determined by the intrapulse plasma dynamics, and so is a function of the pulse repetition frequency, duty cycle, and feedstock gas. Improvements in the azimuthal uniformity of reactant densities were obtained in Ar and Cl2 plasmas in an asymmetrically pumped reactor using pulsed power. As dissociative attachment dominates in the afterglow of Cl2 pulsed plasmas, it provides a more uniform sink for electrons compared to ambipolar diffusion and different systematic behavior is obtained compared to argon.

Thermodynamic analysis of thermomechanical coupling in tangential Couette flow of temperature dependent materials

Thermodynamic analysis of the thermomechanical coupling in a tangential Couette flow is presented for the Nahme number Na range of 0.5< Na <2.5. In the analysis, the temperature and velocity gradients, obtained from the series solutions in the Brinkman number Br , have been used for Newtonian fluids whose viscosity and thermal conductivity are expressed as linear functions of temperature. The entropy generation and the irreversibility distributions due to the thermomechanical coupling are evaluated and displayed graphically across the gap with asymmetric wall temperatures for the Couette flow of ethylene glycol.

Time-modulated convection with zero mean temperature gradient.

We study numerically the onset of temporally modulated Rayleigh-Bénard convection with zero mean gradient for cases of antisymmetric and asymmetric boundary temperatures over a continuous range of nondimensional frequencies omega, from omega approximately O(10(-1)) to omega approximately O(10(3)). For omega below 1, the neutral curves for Pr=7 in both cases alternate between synchronous and subharmonic responses, with increasingly shorter intervals as omega becomes small. At large omega, the critical wave number k(c) asymptotes to omega(1/2) and the critical Rayleigh number R(c) asymptotes to omega(3/2), via a subharmonic response in both cases. A comparison with the experimental results of Niemela and Donnelly [Phys. Rev. Lett. 57, 583 (1986)] shows fairly reasonable agreement.

An ergonomics investigation into human thermal comfort using an automobile seat heated with encapsulated carbonized fabric (ECF)

This report presents the results of an ergonomics investigation into human thermal comfort using an automobile seat heated with an encapsulated carbonized fabric (ECF). Subjective and objective thermal comfort data were recorded while participants sat for 90 min in a heated and a non-heated automobile seat in an environmental chamber. Eight male participants each completed eight experimental sessions in a balanced order repeated measures experimental design. The conditions in the chamber were representative of a range of cool vehicle thermal environments (5, 10, 15 and 20°C; in the 20°C trial participants sat beside a 5°C ‘cold wall’). Participants in the heated seat condition used the heating controller with separate temperature control over the back of the seat (squab) and bottom of the seat (cushion) in an effort to maintain their thermal comfort while wearing the provided clothing, which had an estimated insulation value of 0.9 Clo. The trials showed that participants' overall sensations remained higher than ‘slightly cool’ in the heated seat at all temperatures. Participants' overall discomfort remained lower (i.e. more comfortable) than ‘slightly uncomfortable’ at temperatures ranging down to nearly 5°C in the heated seat. Hand and foot comfort, sensation and temperature were similar in both seats. Asymmetric torso and thigh skin temperatures were higher in the heated seat although no significant discomfort was found in the front and back of the torso and thigh in either seat. Participants reported no significant difference in alertness between the control and heated seat.

Mixed convection flow of a Bingham plastic in an eccentric annulus

The modeling of laminar, fully developed mixed convection flow of a Bingham plastic in a vertical eccentric annulus, in which the walls are held at asymmetric constant temperatures is investigated. The momentum, continuity and energy equations are solved numerically using the finite-element method. The results obtained are found to be in good agreement with the analytical solutions found by using a narrow gap approximation; that is, the gap between the walls of the annulus is small compared with the inner radius. It is shown that different flow configurations exist depending on the buoyancy parameter, Grashof/Reynolds, including flow reversal and unsheared plug flow adjacent to the wall. Furthermore, it flow reversal occurs it is shown by the finite-element method that a pair of “true plugs” in which the velocity is independent of both the radial and azimuthal variables can exist at each of the widest and narrowest regions of the annulus.

Fully developed laminar convection in a vertical double-passage channel

The considered channel has asymmetric constant wall temperatures and is divided into two passages by means of a thin plane baffle. Results showed that the presence of the baffle may lead to a higher value of Nu according to the baffle position and the value of Gr Re .

Analytic solutions for the mixed convection flow of non-newtonian fluids in parallel plate ducts

The modelling of laminar, fully-developed, combined convection flows of non- Newtonian fluids in a vertical parallel-plate duct, where the walls are held at asymmetric uniform temperatures is considered. For this fully-developed flow model, the momentum, continuity and energy equations are solved analytically for the Bingham Plastic rheology and for the limiting case of Power Law fluids. It is shown that different flow configurations exist depending on the buoyancy parameter, Grashof/Reynolds, which include flow reversal for both rheologies, and unsheared plug flow adjacent to the cold wall for the Bingham Plastic.

On the Reynolds-number independence of mixed convection in a vertical channel subjected to asymmetric wall temperatures with and without flow reversal

The problem of mixed convection in a vertical channel with asymmetric wall temperatures including situations of flow reversal is studied numerically. The SIMPLER algorithm with a staggered grid system is employed to solve the corresponding numerical equations formulated by the finite-volume method. A second-order upwind scheme is used to model the convective term, and a suitable grid distribution is introduced. The ranges of the parameters studied are 0 ⩽ r t ⩽ 1, 1 ⩽ Re ⩽ 1000, and 0 ⩽ Gr/Re ⩽ 500. The numerical results, with the streamwise coordinate scaled by the Reynolds number (Re), show that solutions for the velocity and temperature fields are independent of the Reynolds number when Re ⩾ 50, even in the presence of flow reversal. These solutions, however, are dependent on r t and Gr/Re. Subsequently, correlations are proposed for the bulk temperature distribution and the local Nusselt numbers along the hot wall and the cold wall.

Flows in Vertical Channels With Asymmetric Wall Temperatures and Including Situations Where Reverse Flows Occur

Numerical investigations are conducted into steady laminar combined convection flows in vertical parallel plate ducts with asymmetric constant wall temperature boundary conditions. The streamwise diffusion terms in the governing equations are neglected and the resulting parabolic equations are expressed in an implicit finite difference scheme and solved using a marching technique. In certain situations the combination of the size of the ratio |Gr/Re| and the difference in temperature between the walls of the duct is such that the fully developed flow profile, as the streamwise coordinate tends toward infinity, includes reverse flow in the vicinity of the cold wall. Techniques first used in a previous study are employed in finding a solution through the whole domain of the fluid for those situations involving reverse flow in the fully developed region. Comparisons with existing data near the duct entrance and far along the duct show very good agreement.

Changes in voluntary muscle strength, somatosensory transmission and skin temperature concomitant with pain relief during autotraction in patients with lumbar and sacral root lesions

Earlier clinical observations of rapid changes of certain neurological dysfunctions after autotraction treatment of patients with lumbar and sacral root affections have been evaluated by objective registration methods. Isokinetic recordings of maximal voluntary strength showed that in 6 out of 8 patients, weakness of the foot dorsal flexor muscles could be more or less completely restored after one session of autotraction resulting in pain relief. In a group of patients with clinical signs of impaired sensibility, the low or abolished SEP responses to nerve stimulation on the affected side were restituted in 4 out of 5 cases during autotraction. The asymmetric leg skin temperatures in 10 patients with sciatic pain levelled off in the 6 cases obtaining pain relief by the traction. The results suggest a causal relationship between pain relief and restitution of certain neurological deficits.

Developing Flow and Flow Reversal in a Vertical Channel With Asymmetric Wall Temperatures

Numerical results are presented for the effects of buoyancy on the hydrodynamic and thermal parameters in the laminar, vertically upward flow of a gas in a parallel-plate channel. Solutions of the governing parabolic equations are obtained by the use of an implicit finite difference technique coupled with a marching procedure. It is found that buoyancy dramatically increases the hydrodynamic entry length but diminishes the thermal development distance. At a fixed wall temperature difference ratio, buoyancy enhances the heat transfer on the hot wall but has little impact on the cool wall heat transfer. Flow reversal is observed in some cases. Based on an analytical solution for fully developed flow, criteria for the occurrence of flow reversal are presented. The present numerical solutions yield results that asymptotically approach those from the analytical solution.

Asymmetric self-heating of a circular cylinder

The theoretical problem of determining critical conditions for an asymmetrically self-heating circular cylinder is considered here and some temperature distributions are obtained using the method of conformal mapping. In particular, the family of asymmetric temperatures is determined whose critical Frank-Kamenetskii parameter is δc = 2. It is shown that for a general surface temperature and specified δ the interior solution is unique, but that there exist exceptional cases for which there are just two interior solutions. The problem of determining δc for general surface temperatures is discussed in terms of conformal mapping.