Showing papers on "Micro heat exchanger published in 1989"

Effect of frost growth on the performance of louvered finned tube heat exchangers.

Abstract: An experimental investigation of the effects of frost growth on the performance of heat exchangers with louvered fins has been conducted. Frost accumulation, pressure drop across the heat exchanger and an energy transfer coefficient based on a logarithmic mean enthalpy difference (LMED) were quantified under frosting conditions as functions of the air humidity, air face velocity and fin spacing. Higher air humidity, air face velocities and smaller fin spacing all led to increased frost growth, higher pressure drops and higher energy transfer coefficients. As frost accumulated on the heat exchanger, the overall energy transfer coefficient eventually dropped. These trends are consistent with those reported in the literature.

High-performance single-phase heat exchangers

Abstract: Intended as both instructional text and reference investigating current problems in the design of efficient, single-phase heat exchangers, in hydrodynamics, and in convected heat transfer in flows of both gases and various liquids. Includes analytic and experimental data from laminar, turbulent, and

Effects of tip clearance and fin density on the performance of heat sinks for VLSI packages

Abstract: Motivated by the high heat dissipation requirements of the advanced VLSI packages, experiments were performed with several heat sinks to study their heat transfer characteristics. The thermal resistances and pressure drops of the heat sinks were measured for fin densities of 1.3, 4.6, and 5.6 fins/cm and tip clearances varying from 0 to 2 cm. The mass flow rate varied from 0.01 to 0.1 kg/s. For a fixed mass flow rate and zero tip clearance, the 1.3-fins/cm heat sink dissipated four times more heat than a heat sink without fins, and the 5.6-fins/cm heat sink dissipated seven times more. Accompanying this increased heat transfer, however, is an increase in pressure drop. With an increase in tip clearance, the pressure drop penalty is reduced, but the heat transfer gain is also lower. This information is presented for different fin densities and tip clearances and should be useful to packaging engineers for the optimal design of high-density finned heat sinks. >

Heat exchanger core.

Abstract: Disclosed is a heat exchanger core in which a fluid is caused to flow through a pipe body (11) rectangular in cross section so that the heat exchange is effected between the flowing fluid and a heat medium in contact with the outer walls of the pipe body (11). Within the pipe body (11), a plurality of projections (15A,15B) and/or grooves for flowing the fluid at an inclined angle with respect to the direction of the flow of the fluid (the axis of the heat exchanger core) and the streams flow through the inclined passages, respectively, and then are reversed in direction. Such a flow pattern is repeated so that the efficiency of heat transfer by conduction can be improved without the noticeable increase in pressure loss.

Numerical Prediction of Heat Transfer and Fluid Flow in Rectangular Offset-Fin Arrays

Abstract: A computational study of laminar flow and heat transfer in the channels of a rectangular offset-fin heat exchanger is presented. Computations are carried out for the entrance region and continued till the flow becomes periodically fully developed due to the repetitive nature of the geometry. All the heat transfer surfaces are assumed to be at a uniform temperature. A parametric study is made for various values of the aspect ratio and the fin-length parameter. Results show that developing length is about 5-10 modules. Local results are presented to provide a good physical understanding of the flow and heat transfer phenomena. A comparison of the numerical results with the available experimental data is also presented.

Heat transfer with oscillating pressure and oscillating flow

Abstract: Heat exchangers in Stirling engines and many other reciprocating machines operating under conditions of both oscillating pressure and oscillating flow are discussed. Experiments were done on an apparatus consisting of a piston-cylinder space connected to an annular dead-end heat exchanger space. Instantaneous heat flux and center gas temperature were measured at six locations along the heat exchanger. The results were used to test the model with the complex Nusselt number correlated against oscillating-flow Peclet number. The experimental results showed that the complex Nusselt number was capable of predicting the heat flux, but that there was at least one other important independent variable besides oscillating-flow Peclet number. Dimensional analysis suggested that this was either the ratio of gas thermal properties to those of the wall or a measure of compressibility effects. >

Electrohydrodynamic enhancement of nucleate boiling heat transfer in heat exchangers

Abstract: The effect of a radial d.c. electric field on nucleate boiling heat transfer was investigated experimentally using a single-tube shell/tube heat exchanger. A dielectric liquid (Freon R. 114) was used in the shell and the tube was heated by circulating water through it. It was found that the application of a sufficiently intense electric field to the boiling heat transfer surface resulted both in the elimination of boiling hysteresis and the enhancement of heat transfer for the range of superheat studied. An application of approximately 20 kV was more than sufficient to eliminate the hysteresis. It was also observed that there appeared to be a transition between two situations. At lower superheat there is an appreciable improvement in the heat transfer coefficient due to both initial (0 to 10 kV) and incremental (10 to 20 kV) voltage increases. At higher superheat, however, the greater improvement (about four times) is obtained with the initial voltage application

Particulate Fouling in Plate Heat Exchangers

Abstract: Particulate fouling in an Alfa-Laval P20 plate heat exchanger was investigated using a suspension of aluminum oxide particles in heptane. Process parameters such as flow velocity, heat flux, and particle concentration were varied over a considerable range. In this paper, the influence of the above parameters on the asymptotic fouling resistance is discussed. Measured values of fouling resistance are compared with results for a double-pipe heat exchanger and with the prediction of a fouling model from the literature.

Performance of a spiral ground heat exchanger for heat pump application

Abstract: A high-efficiency ground heat exchanger has been developed for use with ground-source heat pumps. The exchanger is made of copper tubing, shaped in the form of a spiral, which can be installed in a vertical borehole backfilled with sand. Thermal performance of a full-scale prototype indicated that this heat exchanger can achieve very high heat extraction rates if subfreezing operating temperatures are used. For most soil types cyclic freezing and thawing is not a problem; however, for the sensitive Leda clay in which the prototype tests were conducted, substantial settlement occurred after the first freeze-thaw cycle owing to initial collapse of the soil structure.

Sensible and Latent Heat Transfer in Cross-Counterflow Gas-To-Gas Heat Exchangers

Abstract: Simultaneous heat and mass transfer during condensation in cross-counterflow gas-to-gas heat exchangers has been analyzed. The coupled heat and mass transfer equations are derived for boundary-layer controlled heat and mass transfer and include longitudinal heat conduction in the exchanger wall. A numerical method of the finite-difference type is applied to the steady-state performance. Temperature and absolute humidity distributions are calculated for exchanger parameters that are typical in air conditioning systems. Temperature and humidity efficiencies together with frosting limits are evaluated for different inlet air conditions.

Niobium 1% zirconium/potassium and titanium/potassium life-test heat pipe design and testing

Abstract: Experimental lifetime performance studies currently in progress use Niobium-1% Zirconium (Nb-1Zr) and Titanium (Ti) heat pipes with potassium (K) as the working fluid. A heat pipe life-test matrix has been developed for testing the heat pipes. Because the corrosion rates in alkali metal heat pipes are affected by temperature and working fluid evaporation flux, the variable parameters of the experimental matrix are established as steady operating temperature and input heat flux density. Total impurity inventory is a factor in corrosion rate so impurity levels are being evaluated in the heat pipe materials before and after testing. Eight Nb-1Zr/K heat pipes were designed, fabricated, and tested. Two of the heat pipes have completed testing whereas the other six are currently in test. These are gravity-assist heat pipes operating in a reflux mode. The heat pipes are tested by sets, one set of two and two sets of three heat pipes. Three Ti/K heat pipes are also in life test. These heat pipes are tested as a set in a horizontal position in a capillary pumped annular flow mode. Each of the heat pipes is encapsulated in a quartz vacuum container with a water calorimeter over the vacuum container for power throughputmore » measurements. Thermocouples are attached to the heat pipes for measuring temperature. Heat input to the heat pipes is via an rf coil. The heat pipes are operating at between 800 and 900 K, with heat input fluxes of 13.8 to 30 W/sq cm. Of the Nb-1Zr/K heat pipes, two of the heat pipes have been in operation for 14,000 hours, three over 10,000 hours, and three over 7,000 hours. The Ti/K heat pipes have been in operation for 1,266 hours. 5 refs., 4 figs., 1 tab.« less

Heat exchanger having a heat exchanger element

Abstract: A heat exchanger comprises a heat exchanger element which has a first channel, through which a first medium flows, and a thermally conductive second channel, through which a second medium flows and which is connected to the first channel. In order to improve the heat exchanger in such a way that there is a heat transfer from the respective medium to the heat exchanger element which is as good and effective as possible, it is proposed that an inside of at least one channel is lined with a thermally conductive foamed article through which the respective medium can flow.

Tube for a shell and tube heat exchanger and process for the manufacture thereof

Abstract: Better mechanical properties are achieved with tubes for shell and tube heat exchangers by providing a coating on the tubes which is formed of fibers and a fluorine-containing polymer covering the fibers. The tubes are formed of fluorine-containing polymers whose use in heat exchangers is normally limited by the comparatively small compressive strength and fatigue resistance of the tubes.

Heat exchanger for condensn. driers - with hollow quadrangular plastic heat exchange plate having partitioning in hollow space

Abstract: Heat exchanger for condnsn. dryers hollow quadrangular plastic heat exchange plate which has partitionings running in the hollow space in the longitudinal direction. The partitionings form flow ducts for guiding a heat transfer medium. The inner and/or outer surfaces of the heat exchange walls of the plate have profilings. ADVANTAGE - Heat exchanger is stable and has a high deg. of efficiency.

Heating apparatus with a heat exchanger

Abstract: The present invention relates in summary to a heating apparatus including a burner and a heat exchanger (1). The burner, which is preferably gas or oil fired, heats a primary fluid, which surrenders its heat in the heat exchanger (1) to a secondary fluid. A pipe (11) formed in a series of loops is arranged to pass into the heat exchanger (1) secondary fluid which has been heated through the combustion gases from the burner.

Consider nonfouling fluidized bed exchangers

Abstract: Applications for fluidized bed heat exchangers in various industries, their operating principles and a detailed analysis of their suitability for replacing double-pipe scraped-surface heat exchangers in lube oil plants are discussed. Development of the fluidized bed heat exchanger started in the early 70s and was totally dedicated to improvement of the multistage flash evaporator for sea water desalination. This resulted in a demonstration plant with a fluidized bed heat exchanger with a total heat transfer surface of over 1,000 m/sup 2/. Over an operating period of more than 15,000 hours untreated sea water was heated to more than 120{sup 0}C without any fouling in the tubes due to scale deposits.

Minimizing the effects of icing in the intakes of aerospace propulsors

Abstract: An air intake suitable for an aerospace propulsor comprises a duct in which are provided two pirmary heat exchangers arranged in parallel relationship and a secondary heat exchanger downstream of the primary heat exchangers. The primary and secondary heat exchangers are arranged to place a cryogenic fluid in heat exchange relationship with the air flow through the duct. Icing of the primary heat exchangers is controlled by interrupting the flow of cryogenic fluid to each of the primary heat exchanger in turn. Thus while one heat exchanger is subject to ice accretion hereon, the temperature of the other increases sufficiently for de-icing thereof to occur.

Method for the manufacture of a comfort heat exchanger

Abstract: A heat exchanger, especially a heat exchanger in the form of a comfort heat exchanger, includes two manifold elements adapted to receive and discharge fluid, and a plurality of tube units transversely located between the manifolds, each tube unit being integrally connected to substantially rigid end elements that fit into the manifolds. The tubes are preferably oriented and expanded to about their original diameter. The heat exchanger is intended to be fabricated from polymer, especially polyamide compositions. The tube units are intended to be manufactured using injection moulding techniques, and then subjected to orientation and expansion steps. Parts fabricated during manufacture of the heat exchangers are also included. The heat exchangers are particularly intended for use as comfort heat exchangers in automobiles.