Study of Multilouvered Heat Exchangers at Low Reynolds numbers

Air Conditioning and Refrigeration Project 13

Large-Eddy Simulations of Flow and Heat Transfer in Complex Three-Dimensional Multilouvered Fins

The paper describes the computational procedure and results from large-eddy simulations in a complex three-dimensional louver geometry. The three-dimensionality in the louver geometry occurs along the height of the fin, where the angled louver transitions to the flat landing and joins with the tube surface. The transition region is characterized by a swept leading edge and decreasing flow area between louvers. Preliminary results show a high energy compact vortex jet forming in this region. The jet forms in the vicinity of the louver junction with the flat landing and is drawn under the louver in the transition region. Its interaction with the surface of the louver produces vorticity of the opposite sign, which aids in augmenting heat transfer on the louver surface. The top surface of the louver in the transition region experiences large velocities in the vicinity of the surface and exhibits higher heat transfer coefficients than the bottom surface.Air Conditioning and Refrigeration Project 9

Erratum: COMPARE CPM-RMI trial: Intramyocardial transplantation of autologous bone marrow-derived CD133+ cells and MNCs during CABG in patients with recent MI: A phase II/III, multicenter, placebo-controlled, randomized, double-blind clinical trial. (Cell Journal (2018) 20:3 (449) DOI: 10.22074/cellj.2018.5197)

This article published in Cell J (Yakhteh), Vol 20, No 2, Jul-Sep 2018, on pages 267-277, four affiliations (1, 4, 5, and 10) were changed based on authors request. © 2018 Royan Institute (ACECR). All rights reserved

COMPARE CPM-RMI Trial: Intramyocardial transplantation of autologous bone marrow-derived CD133+ Cells and MNCs during CABG in patients with recent MI: A Phase II/III, multicenter, placebo-controlled, randomized, double-blind clinical trial

Objective: The regenerative potential of bone marrow-derived mononuclear cells (MNCs) and CD133+ stem cells in the heart varies in terms of their pro-angiogenic effects. This phase II/III, multicenter and double-blind trial is designed to compare the functional effects of intramyocardial autologous transplantation of both cell types and placebo in patients with recent myocardial infarction (RMI) post-coronary artery bypass graft. Materials and Methods: This was a phase II/III, randomized, double-blind, placebo-controlled trial COMPARE CPM-RMI (CD133, Placebo, MNCs - recent myocardial infarction) conducted in accordance with the Declaration of Helsinki that assessed the safety and efficacy of CD133 and MNCs compared to placebo in patients with RMI. We randomly assigned 77 eligible RMI patients selected from 5 hospitals to receive CD133+ cells, MNC, or a placebo. Patients underwent gated single photon emission computed tomography assessments at 6 and 18 months post-intramyocardial transplantation. We tested the normally distributed efficacy outcomes with a mixed analysis of variance model that used the entire data set of baseline and between-group comparisons as well as within subject (time) and group�time interaction terms. Results: There were no related serious adverse events reported. The intramyocardial transplantation of both cell types increased left ventricular ejection fraction by 9 95% confidence intervals (CI): 2.14% to 15.78%, P=0.01 and improved decreased systolic wall thickening by -3.7 (95% CI: -7.07 to -0.42, P=0.03). The CD133 group showed significantly decreased non-viable segments by 75% (P=0.001) compared to the placebo and 60% (P=0.01) compared to the MNC group. We observed this improvement at both the 6- and 18-month time points. Conclusion: Intramyocardial injections of CD133+ cells or MNCs appeared to be safe and efficient with superiority of CD133+ cells for patients with RMI. Although the sample size precluded a definitive statement about clinical outcomes, these results have provided the basis for larger studies to confirm definitive evidence about the efficacy of these cell types (Registration Number: NCT01167751). © 2018 Royan Institute (ACECR). All Rights Reserved

Flow Efficiency in Multi-Louvered Fins

The paper studies the effect of Reynolds number, fin pitch, louver thickness, and louver angle on flow efficiency in multi-louvered fins. Results show that flow efficiency is strongly dependent on geometrical parameters, especially at low Reynolds numbers. Flow efficiency increases with Reynolds number and louver angle, while decreasing with fin pitch and thickness ratio. A characteristic flow efficiency length scale ratio is identified based on geometrical and first-order hydrodynamic effects, which together with numerical results is used to develop a general correlation for flow efficiency. Comparisons show that the correlation represents more than 95% of numerical predictions within a 10% error band, and 80% of predictions within a 5% error band over a wide range of geometrical and hydrodynamic conditions.Air Conditioning and Refrigeration Project 13

Effect of Fin Pitch on Flow and Heat Transfer in Multilouvered Fins

High resolution time-dependent calculations are performed for developing flow and heat transfer in a multilouvered fin geometry to study the effect of fin pitch. In both cases, transition to unsteadiness occurs in the wake of the exit louver at a Reynolds number of 400. The upstream spatial propagation of instabilities proceeds much faster for the larger fin pitch. It is also found that the nature of instabilities differs between the two fin pitches. For the larger fin pitch, louver wake instabilities play a more dominant role than louver leading edge shear layer instabilities, which dominate the smaller fin pitch. Overall heat transfer increases per fin as the fin pitch increases because of the larger mass flow rate between fins. However, the difference in heat transfer coefficient between the two geometries is small except in the transitional and low Reynolds number range.Air Conditioning and Refrigeration Project 9

Fin-Tube Junction Effects on Flow and Heat Transfer in Flat Tube Corrugated Multilouvered Heat Exchangers

Three-dimensional simulations of four louver-tube junction geometries are performed to investigate the effect on louver and tube friction and heat transfer characteristics. Three Reynolds numbers, 300, 600 and 1100, based on bulk velocity and louver pitch are calculated. Strong three-dimensionality exists in the flow structure in the region where the angled louver transitions to a flat landing adjoining the tube surface, whereas the flow on the angled louver far from the tube surface is essentially two-dimensional. Due to the small spatial extent of the transition region, its overall impact on louver heat transfer is limited, but the strong flow acceleration on the louver top surface augments the heat transfer coefficient on the tube surface by over 50%. In spite of the augmentation, the presence of the tube lowers the overall Nusselt number of the heat exchanger by over 30 %. Comparisons with correlations derived from experiments on full heat exchanger cores show that computational modeling of a small subsystem can be used reliably to extract performance data for the full heat exchanger.Air Conditioning and Refrigeration Project 11

Classification and Effects of Thermal Wakes on Heat Transfer in Multilouvered Fins

The study classifies and isolates the effects of thermal wake interference that occurs in multilouvered fins. Inter-fin interference occurs between adjacent rows of louvers and is dominant at high flow efficiencies when the flow is louver directed. Intra-fin interference occurs on subsequent louvers of the same row or fin and is dominant at low flow efficiencies or when the flow is predominantly duct directed. It is established that thermal wake effects can be expressed quantitatively solely as functions of the flow efficiency and the fin pitch to louver pitch ratio. While the heat capacity of multilouvered fins increases unconditionally when thermal wakes are eliminated, the heat transfer coefficient either increases or decreases depending on the relative location of thermal wakes in the vicinity of louvers. Experimental procedures, which neglect thermal wake effects in determining the heat transfer coefficient, while not introducing large errors at high flow efficiencies, can introduce errors as high as 100 % at low flow efficiencies.Air Conditioning and Refrigeration Project 9

Computational Study of Multi-Louvered Fin Heat Exchangers

Air Conditioning and Refrigeration Project 9

Three-Dimensional Computational Modeling of Augmented Louver Geometries for Air-side Heat Transfer Enhancement

Air Conditioning and Refrigeration Project 11