Pulsating flow and convective heat transfer in a cavity with inlet and outlet sections

This paper deals with the study of 2-D, laminar, pulsating flow inside a heated rectangular cavity with different aspect ratios. The cooling liquid (water with temperature dependent viscosity and thermal conductivity) comes and leaves the cavity via inlet and outlet ports. The flow topology is characterised by the large recirculation regions that exist at inner corners of the cavity. These low velocity regions cause the heat transfer to be small when compared, for instance, to that of a straight channel. We study the effect that a prescribed pulsation at the inlet port has on the cavity heat transfer. This pulsating boundary condition, of the unsteady Poiseuille type, is described by its frequency and the amplitude of the pressure gradient. The time averaged Reynolds number of the flow, based on the hydraulic diameter of the inlet channel, is 100 and we consider that the dimensionless pulsation frequency (Strouhal number) varies in the range from 0.0 to 0.4. We show that the prescribed pulsation enhances heat transfer in the cavity and that the mechanism that causes this enhancement appears to be the periodic change in the recirculation flow pattern generated by the pulsation. Regarding the quantitative extent of heat transfer recovery, we find that appropriate selection of the pulsation parameters allows for the cavity to behave like a straight channel that is the configuration with the highest Nusselt number

Experimental study of heat transfer and pressure drop in micro-channel based heat sinks with tip clearance

This article presents an experimental study on the optimisation of micro-heat sink configurations when both thermal effects and pressure drop are accounted for. The interest of the latter is that the practical engineering viability of some of these systems also depends on the required pumping power. The working fluid was water and, according to typical power dissipation and system size requirements, the considered fluid regime was either laminar or transitional, and not fully developed from the hydrodynamics point of view. Five configurations were considered: a reference geometry (selected for comparison purposes) made up of square section micro-channels, and four alternative configurations that involved the presence of a variable tip clearance in the design. The performance of the different configurations was compared with regard to both cooling efficiency and pressure drop. Finally, we also provide some practical guidelines for the engineering design of these types of systems

Laminar heat transfer enhancement downstream of a backward facing step by using a pulsating flow

This study is motivated by the need to devise means to enhance heat transfer in configurations, like the back step, that appear in certain types of MEMS that involve fluid flow and that are not very efficient from the thermal transfer point of view. In particular, the work described in this paper studies the effect that a prescribed flow pulsation (defined by two control parameters: velocity pulsation frequency and pressure gradient amplitude at the inlet section) has on the heat transfer rate behind a backward facing step in the unsteady laminar 2-D regime. The working fluid that we have considered is water with temperature dependent viscosity and thermal conductivity. We have found that, for inlet pressure gradients that avoid flow reversal at both the upstream and downstream boundary conditions, the timeaveraged Nusselt number behind the step depends on the two above mentioned control parameters and is always larger than in the steady-state case. At Reynolds 100 and pulsating at the resonance frequency, the maximum time-averaged Nusselt number in the horizontal wall region located behind the step whose length is four times the step height is 55% larger than in the steady-case. Away from the resonant pulsation frequency, the time-averaged Nusselt number smoothly decreases and approaches its steady-state value

The energy spectrum of cosmic rays beyond the turn-down around 10^17 eV as measured with the surface detector of the Pierre Auger Observatory

We present a measurement of the cosmic-ray spectrum above 100 PeV using the part of the surface detector of the Pierre Auger Observatory that has a spacing of 750 m. An inflection of the spectrum is observed, confirming the presence of the so-called second-knee feature. The spectrum is then combined with that of the 1500 m array to produce a single measurement of the flux, linking this spectral feature with the three additional breaks at the highest energies. The combined spectrum, with an energy scale set calorimetrically via fluorescence telescopes and using a single detector type, results in the most statistically and systematically precise measurement of spectral breaks yet obtained. These measurements are critical for furthering our understanding of the highest energy cosmic rays

Search for Large-scale Anisotropy in the Arrival Direction of Cosmic Rays with KASCADE-Grande

Contains fulltext : 200756.pdf (publisher's version ) (Open Access

Amebic monocyte locomotion inhibitory factor peptide ameliorates inflammation in CIA mouse model by downregulation of cell adhesion, inflammation/chemotaxis, and matrix metalloproteinases genes

Objective and design: Monocyte locomotion inhibitory factor (MLIF), an amebic peptide with antiinflammatory properties, was evaluated in collagen-induced arthritis (CIA) to test its effects on the onset and acute inflammatory response of arthritis. Material: DBA1/J mice at 8-10 weeks of age were divided into four groups (eight mice per group). Treatment: The adjuvant group received Freund adjuvant, the CIA group was immunized with collagen II, the MLIF/CIA group received collagen II and MLIF, and the MLIF group received MLIF and Freund adjuvant. Methods: All groups were evaluated clinically. Seven weeks after the collagen injection, at the peak of the clinical arthritis score, limb specimens were collected and histological studies and gene expression analysis using microarrays were performed. Results: MLIF administered weekly as a preventive scheme delayed and reduced the severity of acute arthritis. MLIF induced gene changes in functional categories including adhesion molecules, matrix metalloproteinases, and inflammatory cytokines. Conclusions: MLIF could be an interesting new molecule to investigate in the field of rheumatoid arthritis pathogenesis research for its potential to prevent inflammation. Zapotitlán Springer Basel AG 2010