Showing papers on "Fin (extended surface) published in 1994"

Application of a Complex Nusselt Number to Heat Transfer During Compression and Expansion

Abstract: Heat transfer during compression and expansion can be out of phase with bulk gas-wall temperature difference. An ordinary convective heat transfer model is incapable of predicting this phenomenon. Expressions for compression/expansion heat transfer developed from simple conduction models use a complex heat transfer coefficient. Thus, heat flux consists of one part proportional to temperature difference plus a second part proportional to rate of change of temperature. Surface-averaged heat flux was calculated from experimental pressure-volume data for piston-cylinder gas springs over a range of speeds, pressures, gases, and geometries. The complex Nusselt number model proved capable of correlating both magnitude and phase of the measured heat transfer as functions of an oscillation Peclet number.

Micro heat exchangers fabricated by diamond machining

Abstract: Machining of thin metal foils with specially contoured diamond cutting tools allows the production of small and very smooth fluid microflow channels for micro heat exchanger applications. Heat exchanger plate wall thickness, as well as fin dimensions, may be carefully controlled and machined to dimensions on the order of tens of micrometers. The plates are stacked and bonded with the vacuum diffusion process to form a cross-flow, plate-type heat exchanger. These fabrication techniques allow the production of small heat exchangers with a very high volumetric heat transfer coefficient and inherent low weight. The design and fabrication process for a copper-based, cross-flow micro heat exchanger has been developed. The micro heat exchanger provided a volumetric heat transfer coefficient of nearly 45 MW/m 3 K under very conservative deisgn and operating conditions. This corresponds to a volumetric capacity nearly 20 times that of more conventional compact heat exchangers. High thermal capacity, coupled with low cost and ease of production, make these devices practical in areas where high thermal flux in a small volume is required. The methods and procedures for this type of micromachining closely parallel those for precision machining.

Enhancement of Heat Transfer by Thermocapillary Convection around Bubbles -a Numerical Study

Abstract: For a gas bubble floating in a liquid-filled rectangular enclosure, the effect of thermocapU-lary convection on fluid flow and heat transfer is studied in a cross section with a two-dimensional model. A transient finite difference scheme is applied for the numerical calculations. For a fluid with Pr = 1.93, the overall heat transfer in the liquid is presented for selected configurations in terms of the dimensionless numbers Nu and Ma. Contrary to the common view that an enclosed gas volume would reduce the heat transfer due to its insulating behavior, the energy transport is rather augmented by the thermocapillary convection acting on the free surface. For higher Marangoni numbers, oscillatory flow behavior occurs.

Pin-fin heat sink

Abstract: A housed integrated circuit unit package is provided with a heat sink for removal and dissipation of heat from electronic circuits housed in packages. The heat sink, mounted on an outer surface of the package, includes a plurality of pins secured at one end with a retainer and flared out at the other end into a starburst or bouquet configuration, the pins being in the form of rods selected from solid cylinders and tubes. The bottom of the retainer-bound end is coated with a securing substance, such as solder or a heat-conducting adhesive, which is planarized to facilitate positioning of the heat sink on the package. The heat sink is secured to the package by means of solder or a heat-conducting adhesive. The heat sink is produced by securing a plurality of elongated rods by retainers placed at intervals corresponding to a height of the heat sink, cutting off said rods adjacent to one side of the retainer, and flaring the rods at the other free end of the cut-off rods into a starburst-like configuration. The retained ends of the rods are dipped into a solder or heat-conducting adhesive and planarized to provide a planar surface for mounting the heat sink on the surface of the package.

Cooling structure for alternator rectifier

Abstract: Briefly, the invention comprises an improved cooling fin arrangement for a triphasic bridge rectifier used in conjunction with a three phase alternator in an automotive vehicle. The heat transfer ability of a metallic air core heat sink and radiator is more than doubled by increasing its thickness (and thus its exposed surface area) and by providing a cutout groove allowing the air to flow in two directions thus reducing the air flow resistance. An improved cover plate cooperates with the newly provided air flow paths and also provides simplified connectors for the electrical elements.

Heat transfer and flow characteristics of automotive brazed aluminum heat exchangers

Abstract: Extensive experiments on the heat transfer and pressure-drop characteristics of automotive brazed aluminum heat exchangers were carried out. In the present study, 18 samples of louvered-fin heat exchangers with different geometrical parameters, including tube width, louver length, louver pitch, fin height, and fin pitch, were tested in an induced open wind tunnel. Results are presented as plots of friction factor and Colburn j-factor against Reynolds number based on the volumetric hydraulic diameter in the range of 200 to 1,600. The comparisons between the Sahnoun and Webb model and the present test data are reported and good agreement was found. By introducing a finning factor, a simpler correlation of the Colburn j-factor is obtained. The heat transfer data for the Colburn j-factor are correlated within 10%, and those for the friction factor are within 15%.

Natural Convection Heat Transfer from Horizontal Rectangular Fin Arrays

Abstract: In this study, steady state natural convection in rectangular fin arrays on a horizontal base was numerically investigated. To solve the problem, the complete Navier-Stokes equations were transformed to a set of vorticity-vector potential equations. Vorticity transport and energy equations were numerically solved in three dimensions by ADI (Alternating Direction Implicit) method developed by Brain [1]. Vector potential equations were solved by using iterative methods. Steady behavior of the flow and temperature distribution were obtained from transient solution of the governing equations. Effects of geometrical parameters on heat transfer coefficient were investigated and different types of flow occuring in fin arrays were discussed.

Interrupted fin for heat exchanger

Abstract: The present invention involves a flat fin heat exchanger configuration with a plurality of louvers and a rib raised above the plane of the fin connecting adjacent tube collars. The raised rib configuration enhances the heat transfer characteristics of the fin, and allows for the use of thinner materials to lower cost without diminishing performance. The exterior fin surface "scoops" and redirects air flow from the leading edge to the trailing edge of the fin. This "scooping" effect directs the air flow over and in between the interrupted surfaces, thus breaking up air boundary layer around the fin. The louvers of the fin are oriented relative to the air flow in such a manner that each louver in effect creates another leading edge contributing to a higher heat transfer coefficient. Also, the location of the raised rib also enhances the heat transfer between the fin and the circulated air. The fin collars are also surrounded by a raised portion so that one raised rib and its two adjacent raised portions bordering the collar form a "dog bone" type shape. The leading and trailing edges are serrated to improve the structural rigidity and create turbulence in the air flow. Also, the leading and trailing edges are oriented at a slight angle, e.g., 12°, relative to the plane of the fin. The louvers are oriented at a slightly greater angle than the leading and trailing edges, e.g., 20°-35°.

IC package heat sink fin

Abstract: A fin assembly for use as a heat sink and production thereof are disclosed. The fin assembly comprises a plurality of heat dissipating plates formed by means of a multi-wire saw, and the heat dissipating plates each has a thickness t of no more than 1 mm and being spaced apart by a gap g of no more than 1.5 mm the heat dissipating plates or pins having a height h, wherein the ratio h/t is not less than 20 and the ratio h/g is not less than 15 in one embodiment and 19 in another embodiment of the invention.

Thermal design rules for electronic components on conducting boards in passively cooled enclosures

Abstract: A better understanding is needed of the approaches and limitations for rejecting heat dissipated from VLSI components mounted on multi-layer printed circuit boards housed in small enclosures, as for example those encountered in small consumer electronics, and, in notebook, laptop, or hand-held personal computers. This paper derives new first order thermal design formulae for determining the peak temperatures of sources on conducting substrates, and for determining the thermal "zone of influence" or "footprint" associated with a component on a board. A one-dimensional thin board radial fin approach is used with inclusion of a circular source to represent the heat dissipating component. Exact solutions are presented for sources at the center, edge, and corner of a rectangular board. The results are compared with with both 2-d and 3-d calculations for rectangular sources on a board using the finite element method. Excellent agreement is found in predicting the maximum temperature, with maximum differences of order 10%. Simple algebraic design formulae, useful for rapid estimation, are derived from the complete solutions by taking advantage of the asymptotic behavior at small and large values of the board parameter, m. An unambiguous thermal footprint radius is defined in terms of the tangent line at the inflection point of the temperature profile. Parametric studies show that the radius corresponds to the point at which the board temperature drops to roughly 18% of its peak temperature, for all variations of board thickness and conductivity of practical interest. The simple analytical model is used to predict the temperatures on a populated board, using a linear superposition principle, and it is found to be in good agreement with experimental results for boards with multiple heat sources. >

Plate fin heat exchanger built-in type multi-stage thermosiphon

Abstract: The small-sized integrated thermosiphon heat-exchanger apparatus includes a cooling cylinder (1) having a plurality of independent refrigerant tanks (2) formed by partition walls (1c) which are disposed between fluid inlet port (1a) and outlet port (1b) inside the cylinder, and a plate fin type heat exchanger (50) extending inside the cylinder through the partition walls (1c) hermetically sealably.

Some effects of air flow maldistribution on performance of a compact evaporator with R134a

Abstract: An experimental facility has been constructed to enable the effects of air flow non-uniformity on the transfer performance of refrigerant evaporators to be investigated. This is based on an open-circuit wind tunnel, which is equipped with a single component traversing LDA system, capable of determining local mean velocities and turbulence levels. The refrigerant circuit uses R134a and has been designed to allow maximum flexibility in setting test conditions. Preliminary results are presented from tests on a single circuit finned-tube evaporator with 33 tubes, 300 mm long, arranged in an in-line matrix 4 rows deep, with 25 mm spacing. The height of the fin block was 225 mm, the fin spacing and tube external diameter were 4 mm and 9.5 mm respectively. Contrary to expectations, increases in heat transfer duty and overall heat transfer coefficients were recorded as air flow non-uniformities were artificially introduced, whilst a constant mean air velocity was maintained.

Indoor unit for air conditioner

Abstract: PURPOSE:To provide an indoor unit, capable of increasing the degree of freedom of an indoor side heat exchanger while making it hard to drop drain water from the crest line of a fin plate. CONSTITUTION:Fin plates 5, constituting an indoor side heat exchanger 3a provided slantedly so as to cover the upper side of a lateral-flow fan 2, is provided with a slit 10, extended continuously along a direction separating a crest line 5a from a crest line 5b arrayed in up-and-down direction, on the surface thereof. According to this method, drain water A, generated at the upper side of the slit 10 on the fin plate 5, is recovered along an upper side crest line 10a formed by the slit 10 while drain water A, generated at the lower side of the slit 10 of the fin plate 5 is recovered along the lower crest line of the fin plate 5 whereby the load of drain water A with respect to the crest line 5b of the fin plate 5 is reduced and the dropping of drain water A into the lateral-flow fan 2 is prevented even when the inclination of the indoor side heat exchanger 3b is increased.

Fin-tube type heat exchanger

Abstract: A fin-tube type heat exchanger having improved heat transfer rate is disclosed. The heat exchanger effectively restricts forming of separation bubbles on the back surfaces of the tubes fitted to the fin bodies, thus to promote smooth air flow in the heat exchanger and to improve heat transfer rate. The heat exchanger has the vertically placed fin bodies, the tubes horizontally penetrating the fin bodies, a plurality of dimples provided on opposed side surfaces of the fin bodies, and separation bubble controllers for reducing the size of separation bubbles formed about the tubes. The bubble controllers are provided on the opposed side surfaces of the fin bodies about the tubes. In another embodiment, the heat exchanger has no bubble controller but reduces the size of the separation bubbles by controlling configurations and directions of the dimples.