Search results

The presence of air in the water flow over the hydrofoil is investigated. The examined hydrofoil is ClarkY 11.7% with an angle of attack of 8 deg. The flow simulations are performed with the assumption of different models. The Singhal cavitation model and the models which resolve the non-condensable gas including 2phases and 3phases are implemented in the numerical model. The calculations are performed with the uRANS model with assumption of the constant temperature of the mixture. The two-phase flow is simulated with a mixture model. The dynamics and structures of cavities are compared with literature data and experimental results.

The cavitation regime can be observed in some working conditions of turbomachines. The phase transition, which appears on the blades, is the source of high dynamic forces, noise and also can lead to the intensive erosion of the blade surfaces. The need to control this process and to prevent or reduce the undesirable effects can be fulfilled by the application of non-condensable gases to the liquid.

The results show that the Singhal cavitation model predicts the cavity structure and related characteristics differently with 2phases and 3phases models at low cavitation number where the cavitating flow is highly dynamic. On the other hand, the impact of dissolved air on the cloud structure and dynamic characteristic of cavitating flow is gently observable.

The originality of this paper is the evaluation of different numerical cavitation models for the prediction of dynamic characteristics of cavitating flow in the presence of air.

Reinforced lightweight soil (RLS) consisting of dredged soil, cement, air‐foam, and waste fishing net is considered to be an eco‐friendly backfilling material because it provides a means to recycle both dredged soil and waste fishing net. It may be difficult to find an optimum mixing ratio of RLS considering the design criteria and the construction's situation using the limited test results because the unconfined compressive strength is complicatedly influenced by various mixing ratios of admixtures. As a result, in order to expedite the field application of RLS, an appropriate prediction method is needed. The paper aims to address these issues.

In this study, an artificial neural network (ANN) model that was based on experimental test results performed on various mixing ratios, was developed to predict the unconfined compressive strength of RLS.

It was found that the unconfined compressive strength of RLS at a given mixing ratio could be reasonably estimated using the developed neural network model. In addition, sensitivity analysis was also conducted to evaluate the effect of mixing conditions on the compressive strength of RLS.

RLS is considered to be environmentally friendly because it provides a means to recycle both dredged soil and waste fishing net. The contractors could use the proposed ANN model as an alternative method to predict the strength of RLS with a specific mixing ratio.

This paper reveals that the developed ANN model can be served as a simple and reliable predictive tool for the strength of RLS without excessive laboratory tests for various admixture contents. An optimum admixture ratio of composed materials to get a designed strength could be easily found by using the proposed ANN model.

Corrosion of ferrous components or of goods made partly of steel is caused mainly by two factors, namely temperature and humidity content of room air in the storage space. Prevention of corrosion has, therefore, to concentrate on means to keep storage rooms or departments well ventilated and at a definite air temperature. This first part of the article is concerned largely with physics regarding the properties of air. It covers ventilation, the various air‐treatment operations and the question of which systems are best suited to particular circumstances.

Conflicting claims have been made in relation to the effects of polypropylene fibres on the compressive strength of concrete. The purpose of this paper is to examine the effects on compressive strength of various dosages of monofilament polypropylene fibres when used in concrete. Compressive strength is widely used as the key indicator of concrete quality and therefore needs accurate determination. Monofilament fibres and air entrainment provide a similar function in that they provide freeze/thaw protection, they are both compared against a plain concrete sample to determine relative strength and density.

Two different concrete design strengths (medium and high) were examined with varying amounts and types of polypropylene fibre fraction/volume to establish a common link between fibre additions and reduced final compressive strength.

The findings from the test programme showed a linear reduction in strength which was observed as being directly related to fibre inclusion in concrete. Density was also found to be reduced with the addition of fibres in a similar degree to that of air entrainment.

The lower density of concrete with polypropylene fibre additions was not scientifically explained and this aspect currently forms part of a long term freeze/thaw research programme, which will examine pore spacing and void formation compared to plain concrete.

This paper is of interest to clients, concrete manufacturers, concrete additive manufacturers, designers, surveyors and specifiers who need to know what effect polypropylene fibre additives have upon the final compressive strength.

Suspended timber floors are probably the most common form of construction for ground floors in existing British housing, although they exist in only a small proportion of newly built houses. If moisture builds up in the crawl space beneath the floor, wet or dry rot may begin, leading to structural damage to the floor and foul smells entering the living areas. The crawl space is ventilated by air bricks to prevent this happening, but this is often inadequate, and many houses suffer from damp conditions in the crawl space which are potentially harmful. These can be alleviated by increasing the ventilation, but the increased flow of cool outside air beneath the floor leads to higher heat losses in winter. Examines the relationship between crawl space ventilation rate and relative humidity.

The case describes how Radio Mirchi dealt with competition in the Bangalore FM radio market. Radio Mirchi's market share in Bangalore started declining within a few months of its successful launch, following the entry of new competitors in the market. The case discusses strategies adopted by the company to regain its market share and become the market leader. It describes the initial product offering of the channel, why it felt the need to redesign its product mix, and eventually how the company changed its product offering. The focus of the case is on the dilemma faced by the organization while shifting to a new product and service design in the face of emerging competition. The case highlights the importance of continuously monitoring the market environment and developing a keen understanding of the consumers' behaviour for an organization to gain and sustain its leadership position in the marketplace.

To preserve both cultural collections and historical buildings that house them, a technologically simple yet robust climate control system was installed in the Historic Archive of the Canary Islands. The archive is located in a municipal building, a late nineteenth century massive masonry building in the city of La Laguna, on Tenerife Island, Spain. The system was designed to maintain the RH level necessary for preventing microbial activities on collections in cultural institutions, by operating residential‐type ventilators and a convective heater under a humidistatic control. We have confirmed that the system not only successfully eliminated events of high relative humidity but also stabilized the climate. The annual temperature variation was significantly reduced, although daily variations increased. The room's moisture content was reduced to less than that of the outside, and microbial activities were reduced in the environment. The system was simple to install and inexpensive to operate.

REFRIGERATION in aeroplanes does not, so far, involve the use of any techniques which have not already been established and used in other fields. These techniques must be considerably extended, however, and the features which distinguish this branch of refrigeration from others are that:

THE history of carburettor icing dates back over 20 years. The earliest report which we have is a paper published in 1920 by S. W. Sparrow, then of the National Bureau of Standards, in which he described the phenomenon and pointed out that many unexplained aeroplane crashes almost certainly could be attributed to this cause. He described the icing action as giving the pilot' the impression that: “A demon was operating the throttles.”

This paper aims to clarify the necessity of taking into account the commonly neglected radiation in built environments. Ignoring radiation within acclimatized spaces with moist air, which is a participating medium, can yield inaccurate values of the relevant variables, endangering the Heating, ventilation, and air conditioning design accuracy and leading to energy inefficiencies and discomfort.

The paper uses computational fluid dynamics to predict non-isothermal flows with radiation, for both mixing and displacement ventilation strategies. The tool is applied to a lab-scale model (scale 1:30), and the results are compared with experimental data and predictions without radiation. Furthermore, the radiation influence is also assessed at real-scale level, including a parametric study on the effect of the air relative humidity on radiation.

The paper demonstrates the unequivocal impact of radiation on the flows thermal-kinematics at real-scale: ignoring radiation yields average air temperature differences of 2ºC. This becomes more evident for larger air optical thicknesses (larger relative humidity): changing it from 20 per cent to 50 per cent and 70 per cent yields maximum relative differences of 100 per cent for the velocity components and 0.4ºC for the air temperature. Nevertheless, the results for the lab-scale case are not so conclusive about the effect of moist air radiation on the thermal flow characteristics, but they evidence its impact on the flow kinematics (maximum relative differences of velocity components of 35 per cent).

The paper fulfills an identified need to clarify the relevant effects of air moisture on radiation and on the flow turbulence and thermal-kinematic characteristics for forced convective flows inside built environments.