Vahab Hassani

Use of infra-red thermography for automotive climate control analysis

In this paper, several automotive climate control applications for IR thermography are described. Some of these applications can be performed using conventional IR techniques. Others, such as visualizing the air temperature distribution within the cabin, at duct exits, and at heater and evaporator faces, require new experimental methods. In order to capture the temperature distribution within an airstream, a 0.25-mm-thick (0.01 inch) fiberglass screen is used. This screen can be positioned perpendicular or parallel to the flow to obtain three-dimensional spatial measurements. In many cases, the air flow pattern can be inferred from the resulting temperature distribution, allowing improved air distribution designs. In all cases, significant improvement in the speed, ease, and quantity of temperature distribution information can be realized with thermography as compared to conventional thermocouple array techniques. Comparisons are presented between IR thermography images and both thermocouple measurements and computational fluid dynamics (CFD) predictions.

Value analysis of advanced heat rejection systems for geothermal power plants

A computer model is developed to evaluate the performance of the binary geothermal power plants (Organic Rankine Cycles) with various heat rejection systems and their impact on the levelized cost of electricity.

Numerical Simulations of Boiling Jet Impingement Cooling in Power Electronics

Boiling jet impingement cooling is currently being explored to cool power electronics components. In hybrid vehicles, inverters are used for DC-AC conversion. These inverters involve a number of insulated gate bipolar transistors (IGBTs), which are used as on/off switches. The heat dissipated in these transistors can result in heat fluxes of up to 200 W/cm2, which makes the thermal management problem quite important. In this paper, turbulent jet impingement involving nucleate boiling is explored numerically. The framework for these computations is the CFD code FLUENT. For nucleate boiling, the Eulerian multiphase model is used. A mechanistic model of nucleate boiling is implemented in a user-defined function (UDF) in FLUENT. The numerical results for boiling water jets (submerged) are validated against existing experimental data in the literature. Some representative IGBT package simulations that use R134a as the cooling fluid are also presented

The Fin-on-Plate Heat Exchanger: A New Configuration for Air-Cooled Power Plants

Abstract The objective of this work was to study performance of a new design for air-cooled heat rejections units to be used in power plants or process industries. This heat exchanger was specially designed to provide a true counter-current flow path for the vapor (process fluid) and the air. In this new design, offset strip fins were used along the path of the air, thus providing a low pressure drop path for air while periodically breaking the thermal and hydraulic boundary layers at each fin strip. The air-side pressure drop was lower in this configuration compared to the conventional tube-and-fin heat exchangers because the drag force was significantly reduced. Lower pressure drops allowed air at higher velocities to be passed through the fins, hence achieving higher air-side heat-transfer coefficients by as much as 80% for the same pressure drop. In this work, we experimentally investigated the processes of heat and mass transfer in film condensation of steam in forced-flow through the plate side of this new heat exchanger.

Comparison of Different Single-Phase Liquid Jet Impingement Cooling Configurations in the Context of Thermal Management in Power Electronics

Jet impingement has been an attractive cooling option in a number of industries over the past few decades. Over the past fifteen years, jet impingement has been explored as a cooling option in microelectronics. Recently, interest has also been expressed by the automotive industry in exploring jet impingement as an option for cooling power electronics components. The main purpose of this paper is to compare the different single-phase jet impingement configurations, which have been reported in the literature, primarily from a heat transfer viewpoint. The discussion is also from the viewpoint of the cooling of IGBTs (insulated-gate bipolar transistors), which are found in inverters in hybrid automobiles. In the literature, single and multiple submerged as well as free-surface jets have been investigated. A number of correlations for heat transfer from the simulated chip surface have been presented. These correlations, as well as the results from them will be discussed in detail. We will also present results for the average heat transfer coefficient on the chip surface as a function of both coolant mass flow rate as well as velocity. All the results presented are for water jets. A numerical study of some of the single-jet cooling configurations (free-surface as well as submerged) is also performed and the CFD results are compared to the results obtained from the empirical correlations. The pressure drop associated with these jet impingement systems is also examined briefly. From the standpoint of practical implementation, high velocity jets have the potential to erode the material on which they impinge. This paper will briefly discuss erosion rates associated with jets impinging on aluminum and copper.Copyright