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Jokar A.,ThermoFluids Technology | Jokar A.,Washington State University
International Journal of Mechanical Engineering Education | Year: 2011

An innovative hands-on approach was taken in teaching thermal/fluid systems design as an upper-level undergraduate course. The objective of using this method was to enhance the students' industrial vision, and to prepare them for mechanical engineering practice before they graduate. For this purpose, the students in this course were divided into three-member groups to design, manufacture, and test specific heat exchangers for given conditions. They were to work within realistic economic, manufacturability, sustainability, ethical, environmental, and safety constraints on their projects. They were then to report the results in a professional fashion, and finally to present their projects in class. The students' communication and interpersonal skills were also examined. The groups came up with different ideas for the design and manufacture of their thermal/fluid systems. Most of the heat exchangers worked the way expected, while some faced problems due to a highpressure drop within the heat exchangers. This approach has had favorable feedback from the students as well as other professionals in the field. The present article reports the details and results of the hands-on class activity. © Manchester University Press.

Hayes N.,Hill Engineering, LLC | Jokar A.,ThermoFluids Technology | Ayub Z.H.,Isotherm Inc.
International Journal of Heat and Mass Transfer | Year: 2012

Condensation pressure drop of carbon dioxide in brazed plate heat exchangers was investigated, and is presented in this paper. Carbon dioxide is known as an environmental friendly refrigerant with an Ozone Depletion Potential (ODP) equal to zero and Global Warming Potential (GWP) equal to unity, and has favorable thermodynamic and transport properties though it requires higher operating pressures (∼15-30 bar). Brazed-type plate heat exchangers that can withstand high pressure are a good choice for such applications. This paper presents the procedure, data collection, and results for three brazed plate heat exchangers with different inner geometries. The test exchangers showed good performance at high system pressures with reasonable pressure drops (less than 8%). The collected experimental data that covered real world operating conditions are valuable for the design of cascade condensers with carbon dioxide as the low-side refrigerant. © 2012 Elsevier Ltd. All rights reserved.

Hayes N.,Hill Engineering, LLC | Jokar A.,ThermoFluids Technology | Ayub Z.H.,Isotherm Inc.
International Journal of Heat and Mass Transfer | Year: 2011

The experimental investigation of carbon dioxide condensation in brazed plate heat exchangers is the main objective of this study. The current level of concern for the environment is at an all time high, therefore, it is important to look into methods and resources that lead to a cleaner and healthier future for the planet. This study details one such effort to reach this goal, focusing on condensation of carbon dioxide as a natural refrigerant in refrigeration systems. Three brazed plate heat exchangers with different geometry, each consisting of three channels, are tested. This paper focuses on the two-phase analysis, where carbon dioxide was the working fluid, flowing through the middle channel, and dynalene brine, the cooling fluid, flowed through the side channels of each geometry. Condensation of carbon dioxide occurred at saturation temperatures ranging from -17.8 °C to -34.4 °C and heat fluxes spanning 2.5-15.7 kW/m2. An in-depth dimensional analysis was completed on the two-phase data yielding heat transfer correlations. Relationships of the two-phase heat transfer characteristics are presented, the data are compared with related studies, and conclusions are made from the two-phase data. © 2010 Elsevier Ltd. All rights reserved.

Jokar A.,ThermoFluids Technology | O'Halloran S.P.,University of Portland
Journal of Thermal Science and Engineering Applications | Year: 2013

The effect of Al2O3 nanofluids in a corrugated plate heat exchanger (PHE) were investigated in this study using computational fluid dynamics (CFD). Nanofluids have received attention recently as potential fluids to increase heat transfer in simple geometries, and work to investigate nanofluids in different systems is ongoing. In this study, a three-channel corrugated PHE with a width of 127 mm, length of 56 mm and channel thickness of 2 mm was investigated. The hot fluid in the system flows through the middle channel while the cold fluid flows through the two side channels. Three chevron angle configurations were considered for the simulation: 60 deg/60 deg, 27 deg/60 deg, and 27 deg/27 deg. Commercially available CFD software (ansys fluent) was used for the simulations. Numerical simulations were conducted for four Al2O3-water nanofluid concentrations: 1%, 2%, 3%, and 4% by volume. In addition, plain water was simulated for comparison. The simulation results show that although the thermal conductivity does increase with increasing nanofluid volume fraction, heat transfer decreases slightly with increasing nanofluid volume fraction. This decrease can be attributed to increased fluid viscosity with increasing volume fraction and the complex flow regimes of nanofluids in the three-dimensional geometries of PHEs. © 2013 American Society of Mechanical Engineers.

O'Halloran S.,University of Portland | Jokar A.,ThermoFluids Technology
ASHRAE Transactions | Year: 2011

Chevron plate type heat exchangers have widely been studied through experimental analysis; however, less computational work has been reported on these types of heat exchangers due to the complexity of their interior configuration with corrugated plates. This study has applied computational thermal and fluid dynamics methods to simulate single-phase flow in three brazed plate corrugated heat exchangers. The heat exchangers have plates with different chevron angles. The three heat exchangers simulated are: 60°/60°, 27°/60°, and 27°/27°. For this purpose, a commercially available CFD software package (Fluent) has been utilized and simulations for different temperature and velocity boundary conditions have been performed. In the numerical simulations, the k-ω SST turbulence model has been used. The resulting outlet temperatures have been found as well as the heat transfer rates between the fluids in the heat exchanger. The heat transfer rates obtained from the simulations are reported and compared for the three different chevron angles. The CFD model established in this study can be used for a variety of design conditions and practical applications, such as investigation of nanofluids in complex geometries. © 2011 ASHRAE.

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