Heat transfer coefficient

A systematic experimental investigation of contact drying operation was carried out in an agitated Charles Thompson filter-dryer. In this study, the effect of process parameters (wall temperature, impeller speed, fill level) on the drying performance in the filter-dryer is quantified as a function of bed temperature and solvent concentration. In addition, the impact of drying conditions on the particle size distribution was also examined. It was found that in the range of parameters investigated, drying rate increased with wall temperature and reduced bed depth. The effect of impeller speed was variable where favorable drying conditions were strongly dependent on the particle properties. Moreover, decrease in the particle size was evident with an increase in impeller speed and decrease in the bed depth due to increased collision frequency and reduction in the fill volume both leading to particle attrition respectively. Besides, the average wall to solid heat transfer coefficient is also estimated for variable operating conditions.

The article discusses experimental measurements of the vertical temperature profile and kiln gas composition in an annular shaft kiln for lime burning. The results obtained confirm that calcination of the limestone in the kiln begins at temperatures between 820°C and 830°C. The average heat transfer coefficient from kiln gases to the stones is determined, as well as the calcination distribution

Effect of Mold Coating Materials and Thickness on Heat Transfer in Permanent Mold Casting of Aluminum Alloys A. HAMASAIID, MS DARGUSCH, CJ DAVIDSON, S. TOVAR, T. LOULOU, F. REZAI¨-ARIA, and G. DOUR ... These coatings maintain mechanical integrity and prevent ...

Power semiconductors can be modeled as a thermal network of resistors and capacitors. The thermal boundary condition of such a model is typically defined as the heat sink surface temperature, which is assumed to be constant. In reality, the heat sink surface temperature underneath the power module is not exactly known. In this paper we show how to set up a thermal model of the heat sink in form of a RC thermal equivalent network that can be directly embedded in any circuit simulator. The proposed thermal heat sink model takes into account convection cooling, thermal hotspots on the heat sink base plate, thermal time constants of the heat sink, and thermal coupling between different power modules mounted onto the heat sink. Experimental results are given and show high accuracy of the heat sink model with temperature errors below 10%.

Background and ObjectiveCryogen sprays are used for cooling human skin during various laser treatments. Since characteristics of such sprays have not been completely understood, the optimal atomizing nozzle design and operating conditions for cooling human skin remain to be determined.Cryogen sprays are used for cooling human skin during various laser treatments. Since characteristics of such sprays have not been completely understood, the optimal atomizing nozzle design and operating conditions for cooling human skin remain to be determined.Materials and MethodsTwo commercial cryogenic spray nozzles are characterized by imaging the sprays and the resulting areas on a substrate, as well as by measurements of the average spray droplet diameters, velocities, temperatures, and heat transfer coefficients at the cryogen-substrate interface; all as a function of distance from the nozzle tip.Two commercial cryogenic spray nozzles are characterized by imaging the sprays and the resulting areas on a substrate, as well as by measurements of the average spray droplet diameters, velocities, temperatures, and heat transfer coefficients at the cryogen-substrate interface; all as a function of distance from the nozzle tip.ResultsSize of spray cones and sprayed areas vary with distance and nozzle. Average droplet diameter and velocity increase with distance in the vicinity of the nozzle, slowly decreasing after a certain maximum is reached. Spray temperature decreases with distance due to the extraction of latent heat of vaporization. At larger distances, temperature increases due to complete evaporation of spray droplets. These three variables combined determine the heat transfer coefficient, which may also initially increase with distance, but eventually decreases as nozzles are moved far from the target.Size of spray cones and sprayed areas vary with distance and nozzle. Average droplet diameter and velocity increase with distance in the vicinity of the nozzle, slowly decreasing after a certain maximum is reached. Spray temperature decreases with distance due to the extraction of latent heat of vaporization. At larger distances, temperature increases due to complete evaporation of spray droplets. These three variables combined determine the heat transfer coefficient, which may also initially increase with distance, but eventually decreases as nozzles are moved far from the target.ConclusionsSprayed areas and heat extraction efficiencies produced by current commercial nozzles may be significantly modified by varying the distance between the nozzle and the sprayed surface. Lasers Surg. Med. 28:113–120, 2001. © 2001 Wiley-Liss, Inc.Sprayed areas and heat extraction efficiencies produced by current commercial nozzles may be significantly modified by varying the distance between the nozzle and the sprayed surface. Lasers Surg. Med. 28:113–120, 2001. © 2001 Wiley-Liss, Inc.

The topic of the paper is the identification of the heat transfer coefficient (HTC) in hot stamping of boron steel sheets under conditions very close to the industrial ones. Two approaches followed by one lab in Germany and one lab in Italy are presented for HTC identification, showing the two experimental apparatuses that were set-up to conduct the tests, the procedures developed and applied to identify the HTC. The obtained results are compared in terms of dependence of HTC from the applied contact pressure, the similarities and the differences of the two approaches are outlined and commented.

Experimental results are reported on simulataneous heat transfer and gas dissolution during the direct-contact condensation of steam on water in the presence of CO2. A column filled with structured packing is used as condenser with the water in counterflow with the steam/CO2 mixture. The region along the column where the bulk of condensation takes place is controllable by suitable choice of the steam/water ratio. Measured local heat-transfer coefficients change by roughly an order of magnitude from the bottom to the top of the column. The extent of CO2 dissolution in the water/condensate under most conditions is unexpectedly high and depends strongly on the exit liquid temperature. A driving force based on the interfacial CO2 concentration, not the overall concentration difference used in conventional absorption operations, is suggested as more appropriate to describe the phenomenon. The data are complemented with preliminary results from a computational model based on the integration along the column of local heat- and mass-transfer rates.

Numerical simulation based on finite numerical methods is used to predict the production process by injection molding of two polymers parts used in low cost domestic refrigerators. The Hele-Shaw fluid mechanics model along with the volume of fluid method are used to calculate velocity and pressure for non- newtonian polymer flows during the injection process using finite elements. The energy equation, with transient, convective, diffusive and viscous dissipation terms, describing the cooling process of the heated polymer while being injected in the cold mold, is solved by the finite difference method. Results for the time evolution of polymer front, pressure and temperature distributions during injection of Polystrol 495F in the mould cavity to produce the freezer door, obtained from two different non-newtonian fluid models, three mold temperatures and two thickness are presented. The effects of the location of the injection point and heat transfer coefficient between polymer flow a...

Boiling heat transfer experiments were performed in a small circular channel (d = 2.46) and a small rectangular channel (dh = 2.40 mm) with Refrigerant 12. The channel sizes are representative of flow passages in compact evaporators. An experimental technique minimized test section end effects which can be appreciable relative to the heat transfer in these small channels. Local heat transfer results were obtained over a range of qualities up to 0.94, a mass flux range of 44–832 kg/m's, and a heat flux range of 3.6–129 kW/m2. Saturation pressure was nearly constant, averaging 0.82 MPa for most of the testing, with some tests performed at a lower pressure of 0.51 MPa. Local heat transfer coefficients were determined experimentally as a function of quality along the length of the test section. Heat transfer rates were compared with results of previous experiments in which Refrigerant 113 in a 2.92-mm diameter small circular tube was used. The effects of channel geometry and fluid properties on heat transfer, as well as insights relative to heat transfer mechanisms in small channels, are presented. Results are presented for both nucleation- (wall superheat above 2.75°C) and convection-dominant boiling heat transfer regimes and compared with large-channel predictions. The heat transfer data for the two fluids were successfully correlated in the nucleation-dominant region.

Experiments were carried out on natural convection heat transfer from square pin fin heat sinks subject to the influence of its geometry and heat flux. A total of 50 fins were bolted into the upper surface of the base plate. The area of the base plate is 250mm by 250mm. The base plate and the fins were made of aluminum .Over the tested range of Rayleigh number, 12.45