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Duangthongsuk W.,South East Asia University | Duangthongsuk W.,King Mongkut's University of Technology Thonburi | Wongwises S.,King Mongkut's University of Technology Thonburi | Wongwises S.,Academy of Science
International Journal of Heat and Mass Transfer | Year: 2012

Nanofluids are a suspension of particles with ultrafine size in a conventional base fluid that increases the heat transfer performance of the original base fluid. They show higher thermal performance than base fluids especially in terms of the thermal conductivity and heat transfer coefficient. During the last decade, many studies have been carried out on the heat transfer and flow characteristics of nanofluids, both experimentally and theoretically. The purpose of this article is to propose a dispersion model for predicting the heat transfer coefficient of nanofluids under laminar flow conditions. TiO 2 nanoparticles dispersed in water with various volume fractions and flowing in a horizontal straight tube under constant wall heat flux were used. In addition, the predicted values were compared with the experimental data from He et al. [14]. In the present study, the results show that the proposed model can be used to predict the heat transfer behaviour of nanofluids with reasonable accuracy. Moreover, the results also indicate that the predicted values of the heat transfer coefficient obtained from the present model differ from those obtained by using the Li and Xuan equation by about 3.5% at a particle volume fraction of 2.0%. © 2012 Elsevier Ltd. All rights reserved.


Reidpath D.D.,South East Asia University | Reidpath D.D.,Monash University | Ahmadi K.,Monash University | Ahmadi K.,International Medical University
Emerging Themes in Epidemiology | Year: 2014

Background: Measures of household socio-economic position (SEP) are widely used in health research. There exist a number of approaches to their measurement, with Principal Components Analysis (PCA) applied to a basket of household assets being one of the most common. PCA, however, carries a number of assumptions about the distribution of the data which may be untenable, and alternative, non-parametric, approaches may be preferred. Mokken scale analysis is a non-parametric, item response theory approach to scale development which appears never to have been applied to household asset data. A Mokken scale can be used to rank order items (measures of wealth) as well as households. Using data on household asset ownership from a national sample of 4,154 consenting households in the World Health Survey from Vietnam, 2003, we construct two measures of household SEP. Seventeen items asking about assets, and utility and infrastructure use were used. Mokken Scaling and PCA were applied to the data. A single item measure of total household expenditure is used as a point of contrast. Results: An 11 item scale, out of the 17 items, was identified that conformed to the assumptions of a Mokken Scale. All the items in the scale were identified as strong items (Hi>.5). Two PCA measures of SEP were developed as a point of contrast. One PCA measure was developed using all 17 available asset items, the other used the reduced set of 11 items identified in the Mokken scale analaysis. The Mokken Scale measure of SEP and the 17 item PCA measure had a very high correlation (r =.98), and they both correlated moderately with total household expenditure: r =.59 and r =.57 respectively. In contrast the 11 item PCA measure correlated moderately with the Mokken scale (r =.68), and weakly with the total household expenditure (r =.18). Conclusion: The Mokken scale measure of household SEP performed at least as well as PCA, and outperformed the PCA measure developed with the 11 items used in the Mokken scale. Unlike PCA, Mokken scaling carries no assumptions about the underlying shape of the distribution of the data, and can be used simultaneous to order household SEP and items. The approach, however, has not been tested with data from other countries and remains an interesting, but under researched approach. © 2014 Reidpath and Ahmadi; licensee BioMed Central Ltd.


Duangthongsuk W.,South East Asia University | Duangthongsuk W.,King Mongkut's University of Technology Thonburi | Wongwises S.,King Mongkut's University of Technology Thonburi
Experimental Thermal and Fluid Science | Year: 2010

This article reports a comparison of the differences between using measured and computed thermophysical properties to describe the heat transfer performance of TiO2-water nanofluids. In this study, TiO2 nanoparticles with average diameters of 21 nm and a particle volume fraction of 0.2-1 vol.% are used. The thermal conductivity and viscosity of nanofluids were measured by using transient hot-wire apparatus and a Bohlin rotational rheometer, respectively. The well-known correlations for calculating the thermal conductivity and viscosity of nanofluids were used for describing the Nusselt number of nanofluids and compared with the results from the measured data. The results show that use of the models of thermophysical properties for calculating the Nusselt number of nanofluids gave similar results to use of the measured data. Where there is a lack of measured data on thermophysical properties, the most appropriate models for computing the thermal conductivity and viscosity of the nanofluids are the models of Yu and Choi and Wang et al., respectively. © 2009 Elsevier Inc. All rights reserved.


Nilpueng K.,South East Asia University | Wongwises S.,King Mongkut's University of Technology Thonburi
Experimental Thermal and Fluid Science | Year: 2010

In the present study, the air-water two-phase flow characteristics including flow pattern and pressure drop inside a plate heat exchanger are experimentally investigated. A plate heat exchanger with single pass under the condition of counter flow is operated for the experiment. Three stainless steel commercial plates with a corrugated sinusoidal shape of unsymmetrical chevron angles of 55° and 10° are utilized for the pressure drop measurement. A transparent plate having the same configuration as the stainless steel plates is cast and used as a cover plate in order to observe the flow pattern inside the plate heat exchanger. The air-water mixture flow which is used as a cold stream is tested in vertical downward and upward flow. The results from the present experiment show that the annular-liquid bridge flow pattern appeared in both upward and downward flows. However, the bubbly flow pattern and the slug flow pattern are only found in upward flow and downward flow, respectively. The variation of the water and air velocity has a significant effect on the two-phase pressure drop. Based on the present data, a two-phase multiplier correlation is proposed for practical application. © 2010 Elsevier Inc.


Ebrahimnia-Bajestan E.,Ferdowsi University of Mashhad | Niazmand H.,Ferdowsi University of Mashhad | Duangthongsuk W.,South East Asia University | Wongwises S.,King Mongkut's University of Technology Thonburi | Wongwises S.,Academy of Science
International Journal of Heat and Mass Transfer | Year: 2011

This article presents a numerical investigation on heat transfer performance and pressure drop of nanofluids flows through a straight circular pipe in a laminar flow regime and constant heat flux boundary condition. Al 2O3, CuO, carbon nanotube (CNT) and titanate nanotube (TNT) nanoparticles dispersed in water and ethylene glycol/water with particle concentrations ranging between 0 and 6 vol.% were used as working fluids for simulating the heat transfer and flow behaviours of nanofluids. The proposed model has been validated with the available experimental data and correlations. The effects of particle concentrations, particle diameter, particles Brownian motions, Reynolds number, type of the nanoparticles and base fluid on the heat transfer coefficient and pressure drop of nanofluids were determined and discussed in details. The results indicated that the particle volume concentration, Brownian motion and aspect ratio of nanoparticles similar to flow Reynolds number increase the heat transfer coefficient, while the nanoparticle diameter has an opposite effect on the heat transfer coefficient. Finally, the present study provides some considerations for the appropriate choice of the nanofluids for practical applications. © 2011 Elsevier Ltd. All rights reserved.


Duangthongsuk W.,South East Asia University | Duangthongsuk W.,King Mongkut's University of Technology Thonburi | Wongwises S.,King Mongkut's University of Technology Thonburi | Wongwises S.,The Academy of Science
Experimental Thermal and Fluid Science | Year: 2013

Heat transfer enhancement and flow behaviors in horizontal circular tubes installed with five rotating turbine-type swirl generators (RTSG) are presented experimentally. This type of RTSG is an innovative design that has not been seen in the previous research. Deionized water is used as a working fluid and flows through the test section under turbulent flow conditions. A smooth, stainless steel tube 9.2 mm in ID, 0.4 mm in thickness, and 2.3 m in length is used as the test section. RTSG made from aluminum, with a twisted angle of 60° and a length of 2 cm, are located at 0.46 m equally distant along the test section. When fluid flows through the RTSG, continuously free rotations are observed, and swirl flow after RTSG is created. A DC power supply is used to supply heat load to the test section. Compared with a common, plain tube (without rotating swirl devices), the experimental results indicate that the local heat transfer coefficient of the tube with RTSG inserts is higher than that of the common, plain tube, and they increase when the working fluid flows through the RTSG. Similarly, the wall temperatures of the tube with RTSG inserts are lower than those of the common tube. However, the pressure drop of the tube fitted with RTSG is significantly greater than that of the common, plain tube. © 2012 Elsevier Inc.


Nilpueng K.,South East Asia University | Wongwises S.,King Mongkut's University of Technology Thonburi
Experimental Thermal and Fluid Science | Year: 2015

Experimental data regarding heat transfer coefficient and pressure drop of water flow inside a plate heat exchanger with a rough surface is investigated and compared with that obtained from a smooth surface. Three commercial stainless steel corrugated plates with symmetrical chevron angle of 25° are used. The water flow inside the plate heat exchanger is arranged for a single pass and counter flow. The test runs are performed at Reynolds numbers ranging between 1300 and 3200 and plate surface roughness ranging between 0.936. μm and 3.312. μm. The experimental results show that increase in surface roughness yields an increase in heat transfer coefficient between 4.46% and 17.95% and an increase in pressure drop between 3.90% and 19.24% with respect to a smooth surface. The correlations for predicting the Nusselt number and friction factor of water flow inside a plate heat exchanger with a rough surface are proposed. © 2015 Elsevier Inc.


Davey T.M.,South East Asia University | Allotey P.,South East Asia University | Reidpath D.D.,South East Asia University
Public Health | Year: 2013

Effective population-level solutions to the obesity pandemic have proved elusive. In low- and middle-income countries the problem may be further challenged by the perceived internal tension between economic development and sustainable solutions which create the optimal conditions for human health and well-being. This paper discusses some of the ecological obstacles to addressing the growing problem of obesity in 'aspiring' economies, using Malaysia as a case study. The authors conclude that current measures to stimulate economic growth in Malaysia may actually be exacerbating the problem of obesity in that country. Public health solutions which address the wider context in which obesity exists are needed to change the course of this burgeoning problem. © 2013 The Royal Society for Public Health.


Le V.T.,South East Asia University
PLoS neglected tropical diseases | Year: 2010

Acute encephalitis is an important and severe disease in children in Vietnam. However, little is known about the etiology while such knowledge is essential for optimal prevention and treatment. To identify viral causes of encephalitis, in 2004 we conducted a one-year descriptive study at Children's Hospital Number One, a referral hospital for children in southern Vietnam including Ho Chi Minh City. Children less than 16 years of age presenting with acute encephalitis of presumed viral etiology were enrolled. Diagnostic efforts included viral culture, serology and real time (RT)-PCRs. A confirmed or probable viral causative agent was established in 41% of 194 enrolled patients. The most commonly diagnosed causative agent was Japanese encephalitis virus (n = 50, 26%), followed by enteroviruses (n = 18, 9.3%), dengue virus (n = 9, 4.6%), herpes simplex virus (n = 1), cytomegalovirus (n = 1) and influenza A virus (n = 1). Fifty-seven (29%) children died acutely. Fatal outcome was independently associated with patient age and Glasgow Coma Scale (GCS) on admission. Acute encephalitis in children in southern Vietnam is associated with high mortality. Although the etiology remains unknown in a majority of the patients, the result from the present study may be useful for future design of treatment and prevention strategies of the disease. The recognition of GCS and age as predictive factors may be helpful for clinicians in managing the patient.


Monpapassorn A.,South East Asia University
International Journal of Electronics | Year: 2013

This article describes the design of a low output impedance dual CCII full-wave rectifier. The proposed dual CCII rectifier yields lower output impedance than the dual CCII full-wave rectifiers proposed previously. The node-Z output of the CCII directly drives the load (R L). The forward resistance and the threshold voltage of diodes are cancelled from the output. Thus the proposed dual CCII rectifier is better for driving loads with lower output impedance and higher output voltage. The proposed rectifier is verified by using the PSPICE program with the CCII in AD844 IC from Analog Devices. The result demonstrates the accurate operation of the proposed rectifier. © 2013 Copyright Taylor and Francis Group, LLC.

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