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The prediction of critical velocity at instability threshold for shell and tube heat exchangers is important to avoid failure of tubes as a result of flow-induced vibrations due to water cross flow. The flow-induced vibration in finned tube heat exchangers is affected by various parameters such as fin height, fin pitch, fin material, tube array, pitch ratio, fin type, fluid velocity etc. In this paper, an experimental investigation of fluid elastic instability in shell and tube heat exchangers is carried out by subjecting normal square finned tube arrays of pitch ratio 1.79 to water cross flow.

The five tube arrays, namely plain array, two finned tube arrays with 3 fpi and 9 fpi fin density, and two finned tube arrays with 3 mm and 6 mm fin height are tested in the experimental test setup with water flow loop and vibration measurement system. The research objective is to evaluate the effect of fin density and fin height on the instability threshold. The critical velocity at instability threshold is determined to characterize the fluid elastic instability behavior of different tube arrays. The vortex shedding behavior of the tube arrays is also studied by determining Strouhal number corresponding to the small peaks before fluid elastic instability.

The fluid elastic instability behavior of the tube arrays was found to be the function of fin tube parameters. The experimental results indicate that an increase in fin density and fin height results in delaying the instability threshold for finned tube arrays. It is also observed that critical velocity at instability is increased for finned tube arrays compared to plain tube arrays of the same pitch ratio. The design modifications in the outer box have resulted in further reduction in the natural frequency. This enabled to reach clear instability for all the five-tube arrays.

The research data add the value to the present body of knowledge by knowing the effect of fin height and fin density on the fluid elastic instability threshold of normal square finned tube arrays subjected to water cross flow.

The purpose of this paper is to present investigations on the significant influence of the tube material and fin density on fluid elastic instability and vortex shedding in a parallel triangular finned tube array subjected to water cross flow.

The experiment was conducted on finned tube arrays with a fin height of 6 mm and fin density of 3 fins per inch (fpi) and 9 fpi. A dedicated setup has been developed to examine fluid elastic instability and vortex shedding. Nine parallel triangular tube arrays with a pitch to tube diameter ratio of 1.78 were considered. The plain tube arrays, coarse finned tube arrays and fine finned tube arrays each of steel, copper and aluminium materials were tested. Plain tube arrays were tested to compare the results of the finned tube arrays having an effective tube diameter same as that of the plain tube.

A significant effect of fin density and tube material with a variable mass damping parameter was observed on the instability threshold. In the parallel triangular finned tube array subjected to water cross flow, a delay in the instability threshold was observed with an increase in fin density. For steel and aluminium tube arrays, the natural frequency is 9.77 Hz and 10.38 Hz, which is close to each other, whereas natural frequency of the copper tubes is 7.40 Hz. The Connors’ stability constant K for steel and aluminium tube arrays is 4.78 and 4.87, respectively, whereas it is 5.76 for copper tube arrays, which increases considerably compared to aluminum and steel tube arrays. The existence of vortex shedding is confirmed by comparing experimental results with Owen’s hypothesis and the Strouhal number and Reynolds number relationship.

This paper’s results contribute to understand the effect of tube materials and fin density on fluid elastic instability threshold of finned tube arrays subjected to water cross flow.

The purpose of this paper is to provide a response to a recent government-commissioned review of residential care (Narey, 2016), and the subsequent government response (Department of Education (DfE), 2016), which minimises the correlation between the experience of being looked after and becoming involved in the youth justice system. The Narey review emphasises on the role of early adversity in looked after children’s offending behaviour but minimises the significance of experiences during and after care, and downplays the effect of policies and practices that may exacerbate looked after children’s involvement in the youth justice system.

The paper builds upon a systematic literature review conducted for the Prison Reform Trust (Staines, 2016) to demonstrate the extent of current knowledge about how risk factors, adverse experiences during and after care and the criminalisation of looked after children combine to increase the likelihood of involvement in criminal proceedings. The paper also highlights gaps in the research evidence, particularly in relation to gender and ethnicity.

The findings suggest that the Narey review (2016) and the government response (DfE, 2016), are misguided in their attempts to minimise the role of care in looked after children’s disproportionate representation within the youth justice system. The paper cautions against the over-simplification of a complex relationship and emphasises on the importance of recognising the intersection between different factors.

The paper uses secondary sources to develop an original argument to rebut claims within a recently published review.

Analyses a stage‐by‐stage model to simulate the dynamic response of compression systems operating with axial multistage compressors. The compressor model is coupled with two different downstream volume (plenum) representations: the first is zero‐dimensional and the second is one‐dimensional. Both dynamic models utilize complete stage performance curves (direct unstalled flow, stalled flow and back flow) obtained through experimental investigation, or from theoretical analysis based on turbomachinery geometry and semi‐empirical considerations. Analyses in depth the results of the dynamic simulations, obtained utilizing both methods, compared to the experimental data reported in the literature, and finally compares one to the other through a fast Fourier transformer (FFT) analysis.

Explores development in market segmentation relating to hospitality and tourism research published between 1990 and 1998. The literature is divided into three sections: segmenting a market; market targeting and marketing positioning. Identifies new areas for research, deeper examination of segments, identification of difference between markets, and more segments.

The purpose of this paper is to present the findings on jet array instabilities of molten caprolactam. Initial investigations showed that although a suitable range of parameters was found for stable jetting, there were cases where instabilities occurred due to external sources such as contamination.

The inkjet system consisted of a melt supply unit, filtration unit and printhead with pneumatic and thermal control. A start‐up strategy was developed to initiate the jetting trials. A digital microscope camera monitored the printhead nozzle plate to record the jet array stability within the recommended range of parameters from earlier research. The trials with jet instabilities were studied to analyse the instability behaviour.

It was found that instabilities occurred in three forms which were jet trajectory error, single jet failure and jet array failure. Occasionally, the jet with incorrect trajectory remained stable. When a jet failed, bleeding of melt from the nozzle due to the actuations influenced the adjacent jets initiating an array of jets to fail similar to falling dominos.

The research concept is novel and investigating the jet array instability behaviours could give an understanding on jetting reliability issues.

Predicting the critical velocity is crucial at the instability threshold for shell and tube heat exchangers in order to prevent tube failure due to vibrations. In this study, the vibration response of an aluminum tube bundle subjected to water cross flow was analyzed experimentally. Aluminum tubes are preferred over steel tubes because of aluminum tubes' excellent corrosion resistance, ease of manufacture, and high thermal efficiency.

The fluid elastic instability and vortex shedding mechanisms in a finned tube array of aluminum tubes with a base tube diameter of 19.05 mm and pitch of 34 mm were investigated. The current study considers parallel triangular finned tube arrays with fin heights of 3 mm and 6 mm with a uniform fin thickness and fin pitch. The plain tube array was tested to compare the finned tube array results. The tube vibration response was measured using an accelerometer mounted on the middle tube of the third row. In order to define the fluid elastic instability behavior of various tube arrays, the critical velocity at the instability threshold is measured. By finding the Strouhal number at the small peaks before instability, the vortex shedding behavior of the tube arrays is examined.

The results reveal that the critical velocity at instability for coarse finned tube arrays increases as the fin height increases. The effect of the tube material is evaluated by comparing the results with those previously reported for parallel triangular tube arrays made of steel. Finally, the occurrence of vortex shedding in a tube array is confirmed based on the Reynolds number and Strouhal number relationship. The instability constant K for the plain tube array of steel and aluminum material are 4.97 and 4.87, respectively.

This paper provides the research findings on the effect of fin height on coarse density finned tube array. This will add substantial knowledge to the literature in the field of fluid elastic instability and vortex shedding, which is needed for the safe functioning of shell and tube heat exchangers.

The issue of export instability exerts an enduring fascination for economists with an interest in the area of economic development. Over several decades a voluminous literature has emerged embracing debates on the domestic consequences and on the causes of export instability. The purpose here is to examine these debates and an attempt is made to set out different theoretical stances, to classify and examine empirical findings, and to indicate the directions in which the debates have moved. Such a statement of a review article's purpose is, of course, incomplete without more specific delineation of the boundaries within which the general objectives are pursued. Here that delineation has three facets.

This research aims to investigate the influence of political instability, trust and knowledge on the zakat compliance behaviour of Algerian business owners. Based on the lenses of the ethical theory mainly and by reference to Zakat Core Principles (that originally inspired from the Basel Core Principles), the paper aims to provide an understanding of how these factors affect zakat compliance in the Algerian context from an ethical perspective.

A cross-sectional research design was applied. Using self-administered questionnaires, a total of 575 business owners in Algeria participated in this study. The hypothesised model was tested by using the partial least squares structural equation model.

The study results support that the ethical approach can explain zakat compliance among Algerian business owners. Specifically, the results revealed that political instability, zakat knowledge and trust significantly influence zakat compliance.

The results offer meaningful insights for the zakat institutions in Muslim societies to enable them to formulate zakat collection policies, assess the level of societal trust in the zakat authority, evaluate the influence of political instability on Muslim entrepreneurs’ zakat compliance and strengthen the entrepreneurs’ zakat knowledge on the exigency of paying zakat to the authority.

This study breaks new ground by exploring the effects of political instability, zakat knowledge and trust on zakat payers’ compliance ethical decisions in developing countries such as Algeria. More significantly, this research contributes to the existing literature of the ethical theory specifically by investigating the effect of political instability on zakat compliance among Algerian business owners.

The influence of gravity on the Marangoni flow instability in half zone liquid bridges in the case of liquid metals is investigated by direct 3D and time‐dependent simulation of the problem. The computations are carried out for different heating conditions and environments (zero g conditions and on ground liquid zone heated from above or from below). The case of cylindrical shape (simplified model) and of melt/air interface deformed by the effect of gravity (real conditions) are considered. The comparison among these situations gives insight into the separate (gravity) effects of buoyancy forces and of the free surface deviation with respect to straight configuration. Body‐fitted curvilinear co‐ordinates are adopted to handle the non‐cylindrical problem. The liquid bridge exhibits different behaviours according to the allowed bridge shape. If the shape is forced to be cylindrical, the flow field is stabilized in the case of heating from above and destabilized if gravity is reversed. If the deformation is taken into account, gravity always stabilizes the Marangoni flow regardless of its direction (parallel or antiparallel to the axis) and the 3D flow structure is different according to the heating condition (from above or from below). In the latter case, the critical Marangoni number is larger and the critical wave number is smaller, compared with the opposite condition. In addition, for Pr=0.02 (Gallium), a surprising heretofore unseen behaviour arises. No steady bifurcation occurs and the flow becomes unstable directly to oscillatory disturbances. This phenomenon has never been reported before in the case of low Prandtl number liquids.