Showing papers on "Micro heat exchanger published in 2010"

Pool Boiling Heat Transfer and Bubble Dynamics Over Plain and Enhanced Microchannels

Abstract: Pool boiling is of interest in high heat flux applications because of its potential for removing large amount of heat resulting from the latent heat of evaporation and little pressure drop penalty for circulating coolant through the system. However, the heat transfer performance of pool boiling systems is not adequate to match the cooling ability provided by enhanced microchannels operating under single-phase conditions. The objective of this work is to evaluate the pool boiling performance of structured surface features etched on a silicon chip. The performance is normalized with respect to a plain chip. This investigation also focuses on the bubble dynamics on plain and structured microchannel surfaces under various heat fluxes in an effort to understand the underlying heat transfer mechanism. This work is expected to lead to improved enhancement features for extending the pool boiling option to meet the high heat flux removal demands in electronic cooling applications.Copyright © 2010 by ASME

Studies on pumping power in terms of pressure drop and heat transfer characteristics of compact plate-fin heat exchangers—A review

Abstract: Renewable energy sources like solar energy, wind energy, etc. are profusely available without any limitation. Heat exchanger is a device to transfer the energy from one fluid to other fluid for many applications in buildings, industries and automotives. The optimum design of heat exchanger for minimum pumping power (i.e., minimum pressure drop) and efficient heat transfer is a great challenge in terms of energy savings point of view. This review focuses on the research and developments of compact offset and wavy plate-fin heat exchangers. The review is summarized under three major sections. They are offset fin characteristics, wavy fin characteristics and non-uniformity of the inlet fluid flow. The various research aspects relating to internal single phase flow studied in offset and wavy fins by the researchers are compared and summarized. Further, the works done on the non-uniformity of this fluid flow at the inlet of the compact heat exchangers are addressed and the methods available to minimize these effects are compared.

Intensification of heat transfer process: Improvement of shell-and-tube heat exchanger performances by means of ultrasound

Abstract: Heat transfer in the presence of a low-frequency ultrasonic field has been investigated. Experiments were performed using a home-made shell-and-tube heat exchanger. The aim of this study was to investigate the effect of ultrasound on heat exchange performed by this new type of "vibrating" heat exchanger named sonoexchanger. Comparison was then made between overall heat transfer coefficients with and without ultrasound for the same hydrodynamic configurations. It was shown that under ultrasonic conditions, the overall heat transfer coefficient can be increased from 123 to 257%.

Numerical Analysis of Convective Heat Transfer From an Elliptic Pin Fin Heat Sink With and Without Metal Foam Insert

Abstract: A numerical analysis of forced convective heat transfer from an elliptical pin fin heat sink with and without metal foam inserts is conducted using three-dimensional conjugate heat transfer model. The pin fin heat sink model consists of six elliptical pin rows with 3 mm major diameter, 2 mm minor diameter, and 20 mm height. The Darcy‐Brinkman‐ Forchheimer and classical Navier‐Stokes equations, together with corresponding energy equations are used in the numerical analysis of flow field and heat transfer in the heat sink with and without metal foam inserts, respectively. A finite volume code with point implicit Gauss‐Seidel solver in conjunction with algebraic multigrid method is used to solve the governing equations. The code is validated by comparing the numerical results with available experimental results for a pin fin heat sink without porous metal foam insert. Different metallic foams with various porosities and permeabilities are used in the numerical analysis. The effects of air flow Reynolds number and metal foam porosity and permeability on the overall Nusselt number, pressure drop, and the efficiency of heat sink are investigated. The results indicate that structural properties of metal foam insert can significantly influence on both flow and heat transfer in a pin fin heat sink. The Nusselt number is shown to increase more than 400% in some cases with a decrease in porosity and an increase in Reynolds number. However, the pressure drop increases with decreasing permeability and increasing Reynolds number. DOI: 10.1115/1.4000951

Flow boiling heat transfer of ammonia/water mixture in a plate heat exchanger

Abstract: The objective of this work is to contribute to the development of plate heat exchangers as desorbers for ammonia/water absorption refrigeration machines driven by waste heat or solar energy. In this study, saturated flow boiling heat transfer and the associated frictional pressure drop of ammonia/water mixture flowing in a vertical plate heat exchanger is experimentally investigated. Experimental data is presented to show the effects of heat flux between 20 and 50 kW m−2, mass flux between 70 and 140 kg m−2 s−1, mean vapour quality from 0.0 to 0.22 and pressure between 7 and 15 bar, for ammonia concentration between 0.42 and 0.62. The results show that for the selected operating conditions, the boiling heat transfer coefficient is highly dependent on the mass flux, whereas the influence of heat flux and pressure are negligible mainly at higher vapour qualities. The pressure drop increases with increasing mass flux and quality. However, the pressure drop is independent of the imposed heat flux.

Performance enhancement study of mobile air conditioning system using microchannel heat exchangers

Abstract: In the present paper, two retrofitted compact and high efficient microchannel heat exchangers were proposed. The new microchannel heat exchangers have advantages in compactness (17.2% and 15.1% volume reduction for evaporator and condenser, respectively), weight (2.8% and 14.9% lighter for evaporator and condenser, respectively), heat transfer characteristics compared with the currently used heat exchangers in mobile air conditioning (MAC) industry. One enhanced and one baseline R134a MAC systems were established including the new microchannel heat exchangers and the traditional MAC heat exchangers, respectively. The system performances have been experimentally carried out under variable ambient conditions in psychrometric calorimeter test bench. The optimal system refrigerant charge amounts for both systems were tested and the results showed that the enhanced system with more compact heat exchangers could reduce system charge amount and the minimum effective charge amount was less than that of the baseline system. The enhanced system could supply more cooling capacity to car compartment under all test conditions because of higher performance heat exchangers. The coefficient of performance (COP) of the enhanced system was slightly lower than that of the baseline system under idle conditions but higher under all the other test conditions. Cooling capacity and COP of the enhanced system was increased by about 5% and 8% under high vehicle speed condition.

Heat Transfer of Supercritical Carbon Dioxide in Printed Circuit Heat Exchanger Geometries

Abstract: The increasing importance of improving efficiency and reducing capital costs has lead to significant work studying advanced Brayton cycles for high temperature energy conversion. Using compact, highly efficient, diffusion-bonded heat exchangers for the recuperators, has been a noteworthy improvement in the design of advanced carbon dioxide Brayton Cycles. These heat exchangers will operate near the pseudocritical point of carbon dioxide, making use of the drastic variation of the thermo-physical properties. This paper focuses on the experimental measurements of heat transfer under cooling conditions, as well as pressure drop characteristics within a prototypic printed circuit heat exchanger. Studies utilize type-316 stainless steel, nine channel, semi-circular test section, and supercritical carbon dioxide serves as the working fluid throughout all experiments. The test section channels have a hydraulic diameter of 1.16mm and a length of 0.5m. The mini-channels are fabricated using current chemical etching technology, emulating techniques used in current diffusion bonded printed circuit heat exchanger manufacturing. Local heat transfer values were determined using measured wall temperatures and heat fluxes over a large set of experimental parameters that varied system pressure, inlet temperature, and mass flux. Experimentally determined heat transfer coefficients and pressure drop data are compared to correlations and earlier data available in literature. Modeling predictions using the CFD package FLUENT are included to supplement experimental data. All nine channels were modeled using known inlet conditions and measured wall temperatures as boundary conditions. The FLUENT results show excellent agreement in total power removal for the near pseudocritical region, as well as regions where carbon dioxide is a high or low density fluid.Copyright © 2010 by ASME