Search results

This study aims to perform a numerical study of air convection in a rectangular enclosure with two isothermal blocks and oscillating bottom wall temperature under laminar flow conditions. The geometry of the enclosure contains two isothermal blocks placed equidistant along the streamwise direction. The top wall is assumed to be cold (low temperature). The bottom wall temperature is either kept as constant or sinusoidally varied with time. The vertical walls are considered as adiabatic. The flow is diagonally upwards and assisted by the buoyancy force. The inlet is positioned at the bottom of the left wall, and the outlet is placed at the top of the right wall. The parameters considered in this paper are Rayleigh number (104-106), Prantdl number (0.71), amplitude of temperature oscillation (0-0.5) and the period (0.2). The effects of these parameters on heat transfer and fluid flow inside the open cavity are studied. The periodic results of fluid flow are illustrated with streamlines and the heat transfer is represented by isotherms and time-averaged Nusselt number. By virtue of increasing buoyancy, the heat transfer accelerates with an increase in the Rayleigh number. Also, the heat transfer is intensive with an increase in the bottom wall temperature.

The momentum and energy equations are solved simultaneously. The energy equation (3) is initially solved using the alternating direction implicit (ADI) method. The results of the energy equation are updated into the vorticity equation. The unsteady vorticity transport equation is also solved using the ADI method. Dimensionless time step equal to 0.01 is used for high Ra (10⁵ and 10⁶) and 0.001 is used for low Ra (10⁴). Convergence criteria of 10⁻⁵ is used during the vorticity, stream function and temperature calculations, as the sum of error should be very small.

Numerical study of air convection in a rectangular enclosure with two isothermal blocks and oscillating bottom wall temperature is performed under laminar flow condition. The effect of the isothermal blocks on the heat transfer is analyzed for different Rayleigh numbers and the following conclusions are arrived. The hydrodynamic blockage effect is subdued by the isothermal heating of square blocks. Based on the streamline diagrams, it is found that the formation of vortices is greatly influenced by the Rayleigh number when all the walls are exposed to a constant wall temperature. The influence of amplitude on the heat transfer is remarkable on the wall exposed to oscillating temperature and is subtle on the opposite static cold wall. The heat transfer increases with an increase in the Rayleigh number and temperature.

Flow is assumed to be two-dimensional and laminar subject to oscillatory boundary condition. The present investigation aims to study natural convection inside the cavity filled with air whose bottom wall is subject to time-variant temperature. The buoyancy is further intensified through two isothermal square blocks placed equidistant along the streamwise direction at mid-height.

The authors have developed a CFD solver to simulate the situation. Effect of Rayleigh number subject to oscillatory thermal boundary condition is simulated. Streamline contour and isotherm contour are presented. Local and average Nusselt numbers are presented.

The purpose of this paper is to present a method for monitoring transient thermal stresses. This paper also presents the analysis of thermal stresses of boiler pressure element heating during the start-up in real conditions. The inverse methods are used to determine the wall temperature, whereas the commercial software ANSYS is used to determine the thermal stresses in the pressure component.

The method is based on the solution of the inverse heat conduction problem. Thermal stresses are determined indirectly taking into account the measured temperature values at selected points on the outer wall of a pressure component. First, the transient temperature distribution in the entire pressure element is calculated, and then, thermal stresses are determined by the finite element method. Measured pressure changes are used to determine the stresses resultant from the internal pressure.

The obtained stresses and temperature in the thick-walled pipe are illustrated and compared with experimental data. Satisfactory agreement was found between computational and experimental results.

The method can be used in the monitoring of thermal and mechanical stresses during the boiler’s start-up and shut-down. Because the temperature distribution at each time level is determined, it can be applied as a thermal load during the structural analysis.

Natural convection in differentially heated enclosures has been extensively investigated due to its importance in many industrial applications and has been used as a benchmark solution for testing numerical schemes. However, most of the published works considered uniform heating and cooling of the vertical boundaries. This paper aims to examine non-uniform heating and cooling of the mentioned boundaries. The mentioned case is very common in many electronic cooling devices, thermal storage systems, energy managements in buildings, material processing, etc.

Four cases are considered, the left-hand wall’s temperature linearly decreases along the wall, while the right-hand wall’s temperature is kept at a constant, cold temperature. In the second case, the left-hand wall’s temperature linearly increases along the wall, while the right-hand wall’s temperature is kept a constant, cold temperature. The third case, the left-hand wall’s temperature linearly decreases along the wall, while the right-hand wall’s temperature linearly increases along the wall. In the fourth case, the left-hand and the right-hand walls’ temperatures decrease along the wall, symmetry condition. Hence, four scenarios of natural convection in enclosures were covered.

It has been found that the average Nusselt number of the mentioned cases is less than the average Nusselt number of the uniformly heated and cooled enclosure, which reflects the physics of the problem. The work quantifies the deficiency in the rate of the heat transfer. Interestingly one of the mentioned cases showed two counter-rotating horizontal circulations. Such a flow structure can be considered for passively, highly controlled mechanism for species mixing processes application.

Previous works assumed that the vertical boundary is subjected to a constant temperature or to a sinusoidal varying temperature. The subject of the work is to examine the effect of non-uniformly heating and/or cooling vertical boundaries on the rate of heat transfer and flow structure for natural convection in a square enclosure. The temperature either linearly increases or decreases along the vertical coordinate at the boundary. Four scenarios are explored.

Efforts to contribute to the Sustainable Development Goals are increasingly part of tourism business planning, forming part of their business policies, linking with society and generating a sustainable hotel offer. The great impact it causes and, which in the short term it will achieve, digital tools in hotel activities can be evidenced. It will also help to collect the information that serves for the certifications of hotel companies. In spite of all the efforts, there is still a great knowledge gap that needs to be filled to achieve the expected business results and that it can be evidenced that the hospitality industry is now more than ever focussed on the care of its workers and on contributing to the sustainability of the world.

The purpose of this paper is to first present the key features of the fuzzy logic (FL) approach as a cost-effective technique in simulations of complex systems and then demonstrate the formulation and application of the method.

The FL approach is used as an alternative method of data handling, considering the complexity of analytical and numerical procedures and high costs of empirical experiments. The distance from gas distributor, the temperature and the voidage of the bed, flue gas velocity and the load of the boiler are the input parameters, whereas the overall heat transfer coefficient for the membrane walls constitutes the output. Five overlapping sigmoid and constant linguistic terms are used to describe the input and the output data, respectively. The Takagi–Sugeno inference engine and the weighted average defuzzification methods are applied to determine the fuzzy and crisp output value, respectively.

The performed FL model allows predicting the bed-to-wall heat transfer coefficient in a large-scale 670 t/h circulating fluidized bed (CFB) boiler. The local heat transfer coefficients evaluated using the developed model are in very good agreement with the data obtained in complementary investigations.

The performed model constitutes an easy-to-use and functional tool. The new approach can be helpful for further research on the bed-to-wall heat transfer coefficient in the CFB units.

This chapter examines how structural factors related to gender, managerial level, and economic sector could impact the level of experienced person/role conflict in management based on a representative survey conducted among managers in Norway. Person/role conflict appears relevant for understanding emotions in organizations and is linked with emotional dissonance and emotional labor through theoretical and empirical considerations. Our findings reveal that the effect of gender remains significant when controlled for economic sector and managerial level. This indicates that experienced person/role conflict can be partially caused by perceived incongruity between internalized and gender role-related expectations as well as managerial role-related expectations.

Due to recent Affordable Care Act reforms, prevention of readmissions is a salient issue for hospitals that participate in Medicare, as they are now held accountable for patients who receive post-acute care in facilities over which hospitals have little influence to monitor care. Using resource dependence and transaction cost economics to describe the theoretical advantages of hospital ownership of post-acute care facilities (PACs), we empirically test whether hospitals that own PACs experience reduced readmissions. Our findings indicate partial support for the predicted relationship between PAC ownership and readmission rates. We found that hospital ownership of a skilled-nursing facility (SNF) was related to a lower readmissions rate for some patients, while ownership of other types of PACs did not result in significant findings. Our results offer support for the theoretical advantages of ownership, however, the savings realized by ownership may not merit the ownership investment.

As document supply grows in volume and importance it becomes more necessary to measure its performance. Nearly all measures are relative — over time, across countries, and between systems; they should therefore be consistent and comparable. The main measures are: fill rate (broken down by subject, form and date); speed (broken down into the various processes involved in document supply); user satisfaction (because users' needs may not be articulated); and costs. There may be trade‐offs between different measures (eg speed and costs). Any measurement system must be practical. Most data will be collected by sampling, but well designed automated systems in future should enable better measures to be calculated with less effort.

Hypertension is a key determinant for the development and progression of chronic kidney disease (CKD). The purpose of this study is to assess the rate of uncontrolled blood pressure (BP) and identify its associated factors in patients with predialysis CKD in Bali, Indonesia.

A cross-sectional study was conducted among 165 patients who attended the nephrology clinic in a central public hospital in Bali. Data were obtained by measuring BP at threshold 130/80 mmHg, as well as collected through standardized questionnaires. Univariate analysis was done using Chi-square test, and multivariate analyses were carried out using multiple logistic regression.

A total of 165 patients (111 males and 54 females) with predialysis CKD participated in this study. About 64% of the participants had uncontrolled BP. In multiple logistic regression, all selected variables significantly explained 63.2% of the variance in uncontrolled BP. However, low physical activity (odds ratio [OR] = 24.287, 95% confidence interval [CI]: 3.114–189.445), unhealthy dietary pattern (OR = 10.153, 95% CI: 2.770–37.210), as well as perceived moderate stress (OR = 4.365, 95% CI: 1.024-18.609) and high stress (OR = 10.978, 95% CI: 2.602–46.312) were significantly associated with uncontrolled BP.

The study findings provide evidence for health care providers to improve BP control among patients with predialysis CKD.

Controlling BP among patients with predialysis CKD was poor. Lifestyle modification and stress management are keys to improving BP control.