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Journal Article

Experimental Study on Air Side Heat Transfer and Fluid Flow Characteristics of Microchannel Heat Exchanger

Microchannel heat exchangers are taken as a great area of research interest for their elevated heat transfer characteristics, higher heating surface area to volume ratio, smaller size, lighter weight, lower fluid inventory and energy efficiency compared to conventional heat exchangers with same heat exchange capacity. Though several investigations have been conducted to find out the air side heat transfer and flow characteristics of common compact cross-flow heat exchangers with various tube and fin geometries, the studies on air side thermal and hydraulic performances of microchannel heat exchangers are rare in open literature. In the present study, the air side heat transfer and fluid flow characteristics of a multiport microchannel heat exchanger in liquid-to-air crossflow orientation were investigated experimentally.
Journal Article

Study of Motor Oil Cooling at Low Reynolds Number in Multi-Port Narrow Channels

Mini and micro-scale channels have drawn researchers' attention in the past three decades. The use of these tiny channels in a heat exchanger is considered as one of the pioneered works on the narrow channels as minichannels provide high heat transfer rates per unit volume. Motor oil, known as engine oil, is one of the vital fluids in automotive applications. Its cooling process is confronted by its thermo-physical properties, especially viscosity, which makes this process difficult. In current investigations, experimental endeavors have been performed using a closed loop thermal wind tunnel to verify the aptness of cooling the motor oil through a cross-flow minichannel heat exchanger. The prototype heat exchanger consists of 3 circuits; each circuit has five slabs which are connected to each other by four serpentines. There are 68 channels of 1 mm circular diameter drilled through each slab. The minichannel heat exchanger comprises of wavy fins arranged parallel to the flow of air.
Technical Paper

Heat and Mass Flow Characterization of Highly Viscous Fluid in Narrow-Channel Heat Exchanger

Channel diameter is one of the most important parameters of a heat exchanger especially for a highly viscous fluid-flow. Narrow channel heat exchangers are believed to have better energy efficiency due to elevated heat transfer characteristics. Heat transfer and Fluid-flow behaviors of Automatic Transmission Fluid (ATF) have been experimentally investigated in a closed loop integrated thermal wind tunnel test facility using wavy finned Minichannel Heat Exchanger (MICHX). The experiment was conducted by varying the ATF Reynolds number from 3 to 30. The flow friction factors in minichannel were evaluated. For a fully developed laminar flow the friction factors were evaluated considering fluid viscosity effects due to temperature variation. The flow correlated with a Poiseuille equation while friction factors were analyzed considering constant property ratio. However, it showed different correlation when considered variable property ratio.
Technical Paper

Experiments of Ethylene Glycol-water Mixture in Multi-port Circular Straight Microchannel Slab

Microchannels (diameter of 1 mm or less) have received significant research attention nowadays due to their high heat transfer and space saving capability compared to the conventional sized tubes for a given heat duty. Use of microchannel core can make an automotive heat exchanger further light-weighted and down-sized while keeping the heat duty similar or even higher as compared to the traditional compact heat exchangers. Automotive engine generally uses heat exchange process in air-glycol crossflow orientation for its cooling system. Research and thermo-hydrodynamic design correlations and sufficient experimental data on single-phase pressure drop and heat transfer using multi-port microchannel slab in air-to-glycol crossflow orientation is rare in the open literature. The availability of a well instrumented dynamic test facility, i.e. both fluids are in motion, for such research is also limited.
Journal Article

An Experimental Characterization of Automatic Transmission Fluid Flowing Through Air Cooled Microchannel Heat Exchanger

Narrow-channel Heat Exchangers have received diversified research and application interests due to the miniaturized geometry, elevated heat transfer characteristics, and better energy efficiency. Automatic Transmission Fluid (ATF) cooling is one of the most important challenges in recent automotive industries due to the quick response to thermo-physical properties with temperature variations. Although a wide range of investigation on characterization of heat transfer and fluid-flow in Minichannel Heat Exchanger (MICHX) for various fluids is available, literatures examining ATF heat transfer and Fluidflow behaviors in the MICHX are scarce. In the current study, attempts have been made to justify the suitability of MICHX application in cooling of ATF. Experimental investigations have been conducted in a well-equipped closed loop integrated thermal wind tunnel test facility using wavy finned-MCHX as a test specimen.
Technical Paper

An Elliptical Tube Array as a Cross Flow Heat Exchanger

Airside heat transfer and fluid flow characteristics of a single array cross flow heat exchanger, made of elliptical tubes, were studied. The heat exchanger, consists of 18 tubes each of 30 cm long with 0.30 minor to major outside axis ratio and equally spaced by 0.61 cm gap, was oriented in a 30 cm by 30 cm test section of a wind tunnel with the major axis parallel to the air flow. Tests were performed with hot water flowing inside the tubes, while cold air flowing across them externally. The mean temperature difference between the approaching air and the surface of the tubes was maintained at roughly 14±2°C. Reynolds number based on the mean free stream air velocity and hydraulic diameter of the elliptical tube was varied from 4500 to 15000, while that based on the mean water velocity inside the tube was altered from 1400 to 7400.
Technical Paper

Transient Response of Minichannel Heat Exchanger Using Al2O3-EG/W Nanofluid

A numerical study is performed to investigate the transient heat transfer and flow characteristics of aluminum oxide (Al2O3) nanoparticles dispersed in 50:50 ethylene glycol/water (EG/W) base fluid in a multipass crossflow minichannel heat exchanger. The time dependent thermal responses of the system in a laminar regime are predicted by solving the conservation equations using the finite volume method and SIMPLE algorithm. The transient regime is caused by a step change of nanofluid mass flow rate at the inlet of the minichannel heat exchanger. This step change can be analogous with a thermostat operation. In this study, three volume fractions up to 3 percent of Al2O3 nanoparticles dispersed to the base fluid EG/W are modeled and analyzed. In the numerical simulation, Al2O3-EG/W nanofluid is considered as a homogenous single-phase fluid. An analysis of the transient response for the variation of nanofluids volume concentrations is conducted.
Technical Paper

Numerical Investigation of Active and Passive Cooling Systems of a Lithium-Ion Battery Module for Electric Vehicles

In this work, a pseudo three-dimensional coupled thermal-electrochemical model is established to estimate the heat generation and temperature profiles of a lithium ion battery as functions of the state of the discharge. Then, this model is used to investigate the effectiveness of active and passive thermal management systems. The active cooling system utilizes cooling plate and water as the working fluid while the passive cooling system incorporates a phase change material (PCM). The thermal effects of coolant flow rate examined using a computational fluid dynamics model. In the passive cooling system, Paraffin wax used as a heat dissipation source to control battery temperature rise. The effect of module size and battery spacing is studied to find the optimal weight of PCM required. The results show that although the active cooling system has the capability to reduce the peak temperatures, it leads to a large temperature difference over the battery module.