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Heat Transfer Enhancement (heat + transfer_enhancement)
Selected AbstractsHeat transfer enhancement of fatty acids when used as PCMs in thermal energy storageINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 2 2008Muhsin Mazman Abstract Phase change materials (PCM) used in latent heat storage systems usually have very low thermal conductivities. This is a major drawback in maintaining the required heat exchange rate between PCM and heat transfer fluid. This paper investigates the enhancement of the heat transfer between PCM and heat transfer fluid, using high thermal conductivity as additives like stainless steel pieces, copper pieces and graphite,PCM composite material. In the experiments, palmitic,lauric acid (80:20) (PL) and stearic,myristic acid (80:20) (SM) were used as PCMs. Test results show that heat transfer enhancement of copper pieces was better at 0.05 Ls,1 flow rate compared to 0.025 Ls,1. Using copper as an additive increased the heat transfer rate 1.7 times for melting and 3.8 times for freezing when flow rate was 0.050 Ls,1. Decreasing the flow rate from 0.050 to 0.025 Ls,1, increased the melting times 1.3 times and freezing times 1.8 times, decreasing heat transfer rates accordingly. The best result of heat transfer enhancement was observed for the PCM,graphite composite. However, changing the flow rate did not affect the heat transfer rate when graphite was used as additive. Copyright © 2007 John Wiley & Sons, Ltd. [source] Experimental study on heat transfer enhancement in the vertical nature convection by using delta-winglet longitudinal vortex generatorsHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 6 2006Taowang Abstract This paper focuses on the study of heat transfer enhancement in natural vertical convection by using delta-winglet longitudinal vortex generators. In the experimental range of Rayleigh numbers, the effect of attack angle, height, and width of the winglet of longitudinal vortex generator (LVG) on heat transfer performance was experimentally investigated. The results showed that there was an optimal attack angle and that the height and width can affect the heat transfer. In terms of array performance, it was shown that initial arrays could enhance the performance of later arrays. Moreover, the effects of LVG and low rectangular fins were compared. The results showed that the effect of LVGs was greater than that of low rectangular fins. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(6): 402,409, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20126 [source] Experimental study on heat transfer enhancement on natural convection in a vertical plate by using longitudinal vortex generators arranged in rowsHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 5 2006JingAn Long Abstract Longitudinal vortices are capable of producing beneficial effects in heat transfer enhancement. Experiments in natural convection heat transfer enhancement were done on a vertical flat heating plate using delta-winglet longitudinal vortex generators (LVGs) arranged in rows. In an experimental range of Rayleigh number, the height and width of the winglet of the longitudinal vortex generator (LVG), the array form of the longitudinal vortex generators on the heat transfer performance were experimentally investigated, and the best height of the winglet of the longitudinal vortex generator was obtained. The results showed the change of the array form of the longitudinal vortex generators could affect the heat transfer effect. Finally by arranging some longitudinal vortex generator arrays with the appropriate interval, the whole heat transfer effect of the interval could reach a prime value. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(5): 351,358, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20119 [source] Experimental study of the flow boiling heat transfer enhancement and pressure drop due to the bubble behavior restricted by a screen sheetHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 4 2003Katsuhiko Kadoguchi Abstract A unique method previously proposed by the authors was applied to the heat transfer augmentation in the flow boiling field. In this method a screen sheet was placed on the horizontal heated surface where bubble nucleation occurred. Generated vapor bubbles were trapped between the screen and the wall, became flat, and moved along the surface. This restricted bubble behavior caused the heat transfer enhancement. Three types of screen sheet were tested in the present experiment and the effect of the screen on the heat transfer and two-phase flow characteristics was investigated. In two of these cases, the screen was displaced upward by the bubble nucleation. Compared with the ordinary flow boiling case, heat transfer was enhanced by a factor of 1.2 to 6 within the present experimental range. Using a simple flow model, it was made clear that the effect of the height of the displaced screen was important in evaluating the increase in pressure drop. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(4): 319,329, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10094 [source] Computation of heat transfer enhancement in a plate-fin heat exchanger with triangular inserts and delta wing vortex generatorINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 9 2010Gulshan Sachdeva Abstract Longitudinal vortices disrupt the growth of the thermal boundary layer, thereby the vortex generators producing the longitudinal vortices are well known for the enhancement of heat transfer in compact heat exchangers. The present investigation determines the heat transfer characteristics with secondary flow analysis in plate fin triangular ducts with delta wing vortex generators. This geometrical configuration is investigated for various angles of attack of the wing i.e. 15°, 20°, 26° and 37° and Reynolds numbers 100 and 200. The constant wall temperature boundary condition is used. The solution of the complete Navier Stokes equation and the energy equation is carried out using the staggered grid arrangement. The performance of the combination of triangular secondary fins and delta wing with stamping on slant surfaces has also been studied. Copyright © 2009 John Wiley & Sons, Ltd. [source] Heat transfer enhancement of fatty acids when used as PCMs in thermal energy storageINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 2 2008Muhsin Mazman Abstract Phase change materials (PCM) used in latent heat storage systems usually have very low thermal conductivities. This is a major drawback in maintaining the required heat exchange rate between PCM and heat transfer fluid. This paper investigates the enhancement of the heat transfer between PCM and heat transfer fluid, using high thermal conductivity as additives like stainless steel pieces, copper pieces and graphite,PCM composite material. In the experiments, palmitic,lauric acid (80:20) (PL) and stearic,myristic acid (80:20) (SM) were used as PCMs. Test results show that heat transfer enhancement of copper pieces was better at 0.05 Ls,1 flow rate compared to 0.025 Ls,1. Using copper as an additive increased the heat transfer rate 1.7 times for melting and 3.8 times for freezing when flow rate was 0.050 Ls,1. Decreasing the flow rate from 0.050 to 0.025 Ls,1, increased the melting times 1.3 times and freezing times 1.8 times, decreasing heat transfer rates accordingly. The best result of heat transfer enhancement was observed for the PCM,graphite composite. However, changing the flow rate did not affect the heat transfer rate when graphite was used as additive. Copyright © 2007 John Wiley & Sons, Ltd. [source] Thermal performance analysis of a tube finned surfaceINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 4 2002Kadir Bilen Abstract The present work submits an experimental work on the heat transfer and friction loss characteristic, employing a tube finned heating surface kept at a constant temperature in a rectangular channel. The tube fins attached on the surface (o.d.=29 mm) were arranged as either in-line or staggered. The parameters for the study were Reynolds number (3700,30 000), depending on hydraulic diameter, the distance between the tube fins in the flow direction (Sy/D=1.72,3.45) and the fin arrangement. The change in the Nusselt number with these parameters was determined. For both tube fin arrangements, it was observed that increasing Reynolds number increased Nusselt number, and maximum heat transfer occurred at Sy/D=2.59. Thermal performances for both arrangements were also determined and compared with respect to heat transfer from the same surface without fins. With staggered array, a heat transfer enhancement up to 25 per cent for Sy/D=3.45 in staggered array was achieved in constant pumping power. Copyright © 2002 John Wiley & Sons, Ltd. [source] CFD Study of Effects of Module Geometry on Forced Convection in a Channel with Non-Conducting Fins and Flow PulsationCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 10 2010B. O. Olayiwola Abstract CFD simulations were carried out to investigate the effects of the module geometry on forced convection in a rectangular channel containing series of regularly spaced non-conducting baffles with flow oscillation. The simulations were performed at constant wall temperature. Steady-flow Reynolds numbers Re in the range of 200 and 600 were studied. The results of the CFD simulations show that, for the effect fin spacing to be significant on heat transfer enhancement in finned system with oscillating flow, the oscillating flow velocity must be higher than the mean flow velocity. Superposition of oscillation yields increasing heat transfer performance with increasing fin height. Fin geometry with pyramidal shape yields highest performance in terms of the heat transfer effectiveness. [source] Enhancement Boiling Heat Transfer Study of a Newly Compact In-line Bundle Evaporator under Reduced Pressure ConditionsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 3 2006Z.-H. Liu Abstract For common flooded-type evaporators, nucleate boiling heat transfer cannot occur on the heated tubes since heat fluxes and wall superheats of heated tubes are generally quite low. However, when the tube spacing is very small, nucleate boiling in restricted spaces can occur easily under low heat flux or low wall superheat conditions. The generation of nucleate boiling can effectively enhance the heat transfer performance of bundle evaporators. This study investigated experimentally the boiling heat transfer enhancement effects of the restricted space in compact in-line tube bundles with smooth tubes under various reduced pressures. The experimental results show that the compact in-line tube bundles have a significantly enhanced heat transfer compared to those of the common tube bundles, and there is an optimum tube spacing that provides the greatest heat transfer enhancement effect. The test pressures have a marked influence on the boiling heat transfer enhancement in the compact bundles. The heat transfer enhancement effect decreases with decreasing test pressure. In addition, the heat transfer enhancement effects of the in-line tube bundles are also compared with those of the staggered bundles. Under reduced pressure, there is no significant difference between the heat transfer enhancement effects for the two types of bundles. [source] | ||||||||||