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  • Open Access

    ARTICLE

    NUMERICAL STUDY OF AIR FORCED CONVECTION IN A CHANNEL PROVIDED WITH INCLINED RIBS

    Oronzio Manca*, Sergio Nardini, Daniele Ricci

    Frontiers in Heat and Mass Transfer, Vol.2, No.1, pp. 1-8, 2011, DOI:10.5098/hmt.v2.1.3007

    Abstract Convective heat transfer may be enhanced passively by adopting rough surfaces. Ribs break the laminar sub-layer and create local turbulence in the channel, reducing thermal resistance and enhancing the heat transfer. However, higher losses are expected. In this paper a numerical investigation is carried out on air forced convection in a rectangular ribbed channel. A three-dimensional model is developed to study the effect of the angle between the fluid flow direction and the ribbed surface, provided with rectangular turbulators, in the turbulent flow. Simulations s that Nusselt numbers as well as the pressure drops increase More >

  • Open Access

    ARTICLE

    A NUMERICAL STUDY OF THE EFFECT OF A BELOW-WINDOW CONVECTIVE HEATER ON THE HEAT TRANSFER RATE FROM A COLD RECESSED WINDOW

    Patrick H. Oosthuizen*

    Frontiers in Heat and Mass Transfer, Vol.2, No.1, pp. 1-8, 2011, DOI:10.5098/hmt.v2.1.3004

    Abstract The convective heat transfer to a window below which is mounted a natural convective heater has been numerically studied. The flow has been assumed to be three-dimensional and steady and to involve regions of laminar and turbulent flow. Fluid properties have been assumed constant except for the density change with temperature which leads to the buoyancy forces. The solution has been obtained using a commercial cfd code. Results have been obtained for a Prandtl number of 0.7. The effects of changes in the flow variables on the window Nusselt number and on the flow and More >

  • Open Access

    ARTICLE

    HEAT TRANSFER IN A MICROTUBE OR MICROCHANNEL WITH PROTRUSIONS

    Muhammad M. Rahman*, Phaninder Injeti

    Frontiers in Heat and Mass Transfer, Vol.2, No.1, pp. 1-9, 2011, DOI:10.5098/hmt.v2.1.3003

    Abstract This paper presents the effects of protrusions on heat transfer in a microtube and in a two-dimensional microchannel of finite wall thickness. The effects of protrusion shape, size, and number were investigated. Calculations were done for incompressible flow of a Newtonian fluid with developing momentum and thermal boundary layers under uniform and discrete heating conditions. It was found that the local Nusselt number near a protrusion changes significantly with the variations of Reynolds number, height, width, and distance between protrusions, and the distribution of discrete heat sources. The results presented in the paper demonstrate that More >

  • Open Access

    ARTICLE

    A CRITICAL REVIEW OF RECENT INVESTIGATIONS ON TWO-PHASE PRESSURE DROP IN FLOW BOILING MICRO-CHANNELS

    Sira Saisorna,b, Somchai Wongwisesb,c,∗

    Frontiers in Heat and Mass Transfer, Vol.3, No.1, pp. 1-7, 2012, DOI:10.5098/hmt.v3.1.3007

    Abstract Two-phase pressure drop during flow boiling has been studied for several decades. Obviously, the publications available on micro-channels are relatively small compared with those for ordinarily sized channels. Although the use of micro-channels yields several advantages, the pressure drop taking p lace in these extremely small channels is higher than that in the ordinarily sized channels because of the increased wall friction. The knowledge of the two-phase pressure drop characteristics in addition to heat transfer phenomena is essential to the design and evaluation of the micro-systems. In this paper, recent research on the flow boiling More >

  • Open Access

    ARTICLE

    A CRITICAL REVIEW OF RECENT INVESTIGATIONS ON FLOW PATTERN AND HEAT TRANSFER DURING FLOW BOILING IN MICRO-CHANNELS

    Sira Saisorna,b, Somchai Wongwisesb,c,*

    Frontiers in Heat and Mass Transfer, Vol.3, No.1, pp. 1-15, 2012, DOI:10.5098/hmt.v3.1.3006

    Abstract A summary of recent research on flow boiling in micro-channels is provided in this article. This review aims to survey and identify new findings arising in this important area, which may contribute to optimum design and process control of high performance miniature devices comprising extremely small channels. Several criteria for defining a micro-channel are presented at first and the recent works on micro-scale flow boiling are subsequently described into two parts including flow visualization and two-phase heat transfer. The results obtained from a number of p revious studies show that the flow behaviours and heat More >

  • Open Access

    ARTICLE

    HEAT TRANSFER MEASUREMENTS FOR FLOW OF NANOFLUIDS IN MICROCHANNELS USING TEMPERATURE NANO-SENSORS

    Jiwon Yua , Seok-Won Kanga, Saeil Jeonb, Debjyoti Banerjeea,*

    Frontiers in Heat and Mass Transfer, Vol.3, No.1, pp. 1-9, 2012, DOI:10.5098/hmt.v3.1.3004

    Abstract Experiments were performed to study the forced convective heat transfer of de-ionized water (DI water) and aqueous nanofluids in a microchannel and temperature measurements were obtained using an array of nanosensors (i.e., thin film thermocouples or “TFT”). Heat flux values were calculated from the experimental measurements for temperature recorded by the TFT array. The experiments were performed for the different test fluids where the flow rate, mass concentration (of silica nanoparticles ~10-30 nm diameter) in the colloidal suspension and the wall temperature profile (as well as applied heat flux values) were varied parametrically.
    Anomalous enhancement… More >

  • Open Access

    ARTICLE

    HEAT TRANSFER CHARCACTERISTICS IN A COPPER MICRO-EVAPORATOR AND FLOW PATTERN-BASED PREDICTION METHOD FOR FLOW BOILING IN MICROCHANNELS

    Etienne Costa-Patrya, Jonathan Olivierb, John R. Thomea,∗

    Frontiers in Heat and Mass Transfer, Vol.3, No.1, pp. 1-14, 2012, DOI:10.5098/hmt.v3.1.3002

    Abstract This article presents new experimental results for two-phase flow boiling of R-134a, R-1234ze(E) and R-245fa in a micro-evaporator. The test section was made of copper and composed of 52 microchannels 163μm wide and 1560μm high with the channels separated by 178μm wide fins. The channels were 13.2mm long. There were 35 local heaters and temperature measurements arranged in a 5×7 array as a pseudo-CPU. The total pressure drops of the test section were below 20kPa in all cases. The wall heat transfer coefficients were generally above 10’000W/m2K and a function of the heat flux, vapor quality More >

  • Open Access

    ARTICLE

    THERMO-HYDRAULICS OF TUBE BANKS WITH POROUS INTERCONNECTORS USING WATER AS COOLING FLUID

    P. V. Ramana, Arunn Narasimhan*, Dhiman Chatterjee

    Frontiers in Heat and Mass Transfer, Vol.3, No.2, pp. 1-6, 2012, DOI:10.5098/hmt.v3.2.3007

    Abstract The present experimental study investigates the effect of tube-to-tube porous interconnectors on the pressure drop and heat transfer (Nu) of tube banks. A copper wire mesh porous medium connects successive tubes of the in-line and staggered arrangement of six rows of tubes. The tubes are subjected to constant and uniform heat flux and cooled by forced convection using water as a cooling fluid in the laminar flow range (100 < ReDuct < 625). The inline configuration with the tube-to-tube porous medium inter-connectors provides marginal enhancement of heat transfer and 12% reduction in the pressure drop More >

  • Open Access

    ARTICLE

    NUMERICAL AND EXPERIMENTAL RESEARCH IN HEAT TRANSFER TO SCREW COMPRESSOR ROTORS*

    Nikola Stosic**, Ian K. Smith, Ahmed Kovacevic

    Frontiers in Heat and Mass Transfer, Vol.3, No.2, pp. 1-7, 2012, DOI:10.5098/hmt.v3.2.3003

    Abstract Due to fast rotation of screw compressor rotors, temperature is uniform in the rotor cross section and temperature field is a function of the axial coordinate only. Apart of that the rotors in one cross section the rotors are simultaneously heated by hot gas on one side while cooled at another side by cold gas. As a result of identification of the main modes of heat transfer both in the rotors and between the rotors and their surroundings and the relative significance of each, a novel procedure is suggested to cool the rotors by injection… More >

  • Open Access

    ARTICLE

    HEAT TRANSFER IN METAL FILMS IRRADIATED BY COMBINED NANOSECOND LASER PULSE AND FEMTOSECOND PULSE TRAIN

    Yunpeng Ren, J. K. Chen*, Yuwen Zhang

    Frontiers in Heat and Mass Transfer, Vol.3, No.2, pp. 1-7, 2012, DOI:10.5098/hmt.v3.2.3001

    Abstract Heat transfer in a copper film irradiated by a femtosecond (fs) laser pulse train and by an integrated dual laser beam of a nanosecond pulse with a fspulse train was studied using the semi-classical two-temperature model. The critical point model with three Lorentzian terms was employed to characterize transient optical properties for the laser energy deposition. The effects of pulse number and separation time on the thermal response were investigated. The results showed that with the same total energy in a fs-pulse train, more pulses for shorter separation time, e.g., 1 ps, and fewer pulses More >

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