Showing papers on "Concentric tube heat exchanger published in 1999"

Air-Side Heat Transfer and Friction Correlations for Plain Fin-and-Tube Heat Exchangers With Staggered Tube Arrangements

Abstract: This paper deals with heat exchangers having plain fins on a staggered array of circular tubes. Correlations are developed to predict the air-side heat transfer coefficient and friction factor as a function of the Reynolds number and geometric variables of the heat exchanger such as tube diameter, tube pitch, fin spacing, etc. A multiple regression technique was used to correlate 47 sets of heat exchanger data to develop the heat transfer and friction correlation. The correlations are applicable to heat exchangers having small diameter tubes (or large tube pitch to tube diameter ratio), whose performance previous correlations failed to predict adequately. The heat transfer correlation applicable to three or more row configuration predicts 94% of the data within {+-}20%, and the heat transfer correlation applicable to one- or two-row configuration predicts 94% of the data within {+-}20%. The friction correlation predicts 90% of the data within {+-}20%.

Experimental study on the pressure drop and heat transfer characteristics of tubes with internal wave-like longitudinal fins

Abstract: Experiments were performed to determine the heat transfer and pressure drop characteristics in the entrance and fully developed regions of tubes with internal wave-like longitudinal fins. The test tube has a double-pipe structure, with the inner tube as an insertion. The wave-like fins are in the annulus and span its full width. Experiments were conducted for two cases: one with the inner tube blocked (no air flowing through it) and the other with the inner tube unblocked. The outer tube was electrically heated. Local and average heat transfer coefficients and friction factors were measured. The friction factor and Nusselt number correlations in the fully developed region were obtained in the Reynolds number range of 9×102 to 3.5×103. It has been found that the wave-like fins enhance heat transfer significantly with the blocked case being superior. In addition, the in-tube heat transfer process is characterized by an earlier transition from laminar to turbulent flow and Reynolds number-dependent thermal entrance length.

An Experimental Study on Forced Convection Heat Transfer From Flush-Mounted Discrete Heat Sources

Abstract: Experiments have been performed using water to determine the single-phase forced convection heat transfer from in-line four simulated electronic chips, which are flush-mounted to one wall of a vertical rectangular channel. The effects of the most influential geometric parameters on heat transfer including chip number, and channel height are tested. The channel height is varied over values of 0.5, 0.7, and 1.0 times the heat source length. The heat flux is set at the three values of 5 W/cm2 , 10 W/cm2 , and 20 W/cm2 , and the Reynolds number based on the heat source length ranges from 6 × 102 to 8 × 104 . Transition Reynolds numbers are deduced from the heat transfer data. The experimental results indicate that the heat transfer coefficient is affected strongly by the number of chips and the Reynolds number and weakly by the channel height. Finally, the present results from liquid-cooling are compared with other results from air-cooling, and Prandtl number scaling between air and water is investigated.

Turbulent heat transfer in a horizontal helically coiled tube

Abstract: An experiment has been conducted in detail to study the turbulent heat transfer in horizontal helically coiled tubes over a wide range of experimental parameters. We found that the enhancement of heat transfer in the coils results from the effects of turbulent and secondary flows. With Reynolds number increasing to a high level, the contribution of the secondary flow becomes less to enhance heat transfer, and the average heat transfer coefficient of the coil is closer to that in straight tubes under the same conditions. The local heat transfer coefficients are not evenly distributed along both the tube axis and the periphery on the cross section. The local heat transfer coefficients on the outside are three or four times those on the inside, which is half of the average heat transfer. A correlation is proposed to describe the distribution of the heat transfer coefficients at a cross section. The average cross-section heat transfer coefficients are distributed along the tube axis. The average value at the outlet section should not be taken as the average heat transfer coefficient. © 1999 Scripta Technica, Heat Trans Asian Res, 28(5): 395–403, 1999

Plate tube type heat exchanger having porous fins

Abstract: A plate tube type heat exchanger using porous fins is manufactured of foamed metal. The porous fins used for the plate tube type heat exchanger are formed of a foamed metal such as aluminum or copper having a high thermal conductivity. The plate tube type heat exchanger using such porous fins exhibits an excellent heat transfer capability, compared to a conventional plate tube type heat exchanger using louvered fins, thereby simplifying production steps and realizing an excellent structural rigidity.

Single-phase Flow Thermal Performance Characteristics of a Parallel MicroChannel Heat Exchanger

Abstract: The paper outlines the results from a recent study conducted on the single-phase characteristics of a parallel micro-channel heat exchanger. An experimental setup was built to study the characteristics of micro-channel heat exchangers. As a first step, single-phase tests were conducted on a parallel-channel micro-heat-exchanger. The experimental study was conducted for a wide variety of flow parameters. Refrigerant-124 was used as the experimental fluid. The test section was heated by a DC power source. The mass flow rate was varied from 35 ml/min to 300 ml/min. The heat flux varied from 10 W/cm{sup 2} to 100 W/cm{sup 2}. The results showed that the heat transfer coefficient increased by up to 200%. Although the use of micro-channels increases in the surface area significantly, much of the increase in heat-transfer-coefficient may be attributed to the thinning of the boundary layer in the narrow channels, which lowers thermal resistance.

Heat Transfer and Flow Structures Around Circular Cylinders in Cross-Flow

Abstract: An experimental study was carried out to investigate heat transfer and flow characteristics from one tube within a staggered tube bundle and within a row of similar tubes The tube spacing examined St and Sl are 15\times15 and 15\times125 where Sl and St denote the longitudinal and transverse pitches respectively The variation of local Nusselt number was predicted with Reynolds number 48\times 104 The aim of the second part of the investigation was to examined the influence of the blockage of a single tube in a duct and transverse pitch for a single tube row with Reynolds number range of 7960 to 47770 Blockage ratio was varied from 0131 to 0843 Variation of local Nusselt number and local pressure coefficient were shown with different blockages and Reynolds numbers The main results are described below For single tube row experiments, if the blockage ratio is less than 05, the general shape of local Nusselt number distribution around the cylinder varies only slightly with blockage However the local Nusselt number and pressure coefficient distributions are remarkably different for the blockage ratio in the range of 0668-0843 Tube bundle experiments showed that changing longitudinal ratio did not affect the mean Nusselt number

Plate type heat exchanger and method of manufacturing the heat exchanger

Abstract: A plate type heat exchanger, wherein a plurality of plates in which flow paths passing through the plate surfaces are formed are disposed between a pair of end plates, a plurality of flow paths not communicating with each other are provided in the plane of the same or different plates among the plurality of plates, and fluids flowing through the plurality of flow paths are so designed as to flow opposedly to each other, whereby an increased performance and reduced size of the plate type heat exchanger can be provided because a plurality of fluids performs heat exchange in the form of a counter flow having high heat transfer characteristics.

Multi-mode heat transfer using a thermal heat pipe valve

Abstract: An electronic device has a heat pipe containing a heat transfer fluid. The heat pipe has a first section and a second section. Inside the heat pipe is a valve disposed between the first section and second section of the heat pipe. The valve has an actuator that is used to regulate the flow of the heat transfer fluid between the first section and the second section of the heat pipe in response to a changed state detected by a sensor.

Countercurrent Heat Exchangers with Both Fluids Subjected to External Heating

Abstract: A mathematical model was developed to study the performance of a counterflow heat exchanger in which both fluid streams are exposed to external heating. It was found that under the external heat transfer condition, the effectiveness of the heat exchanger was drastically reduced. The hot fluid temperature effectiveness increased as the external thermal conductance ratios, Rh and Rc, decreased. For effective operation and to avoid temperature cross, there exist a maximum possible NTU for a given Rh and Rc.

Second-Law and Experimental Analysis of a Cross-Flow Heat Exchanger

Abstract: This article presents a cross-flow plate-type heat exchanger that has been studied and manufactured in laboratory conditions because of its effective use in waste heat recovery systems. This new heat exchanger was tested with an applicable experimental setup, considering temperatures, velocity of the air, and the pressure losses occurring in the system. These variables were measured and the efficiency of the system was determined. The irreversibility of the heat exchanger was taken into consideration, while the design of the heat exchanger was such that the minimum entropy generation number was analyzed with respect to the second law of thermodynamics in the cross-flow heat exchanger. The minimum entropy generation number depends on the parameters called the optimum flow path length and dimensionless mass velocity. Variations of the entropy generation number with these parameters are analyzed.

The effects of design and operating factors on the frost growth and thermal performance of a flat plate fin-tube heat exchanger under the frosting condition

Abstract: An experimental study of the effects of various factors (fin pitch, fin arrangement, air temperature, air humidity, and air velocity) on the frost growth and thermal performance of a fin-tube heat exchanger has been conducted under the frosting condition. It is found that the thermal performance of a heat exchanger is closely related to the blockage ratio of the air flow passages due to the frost growth. The maximum allowable blockage ratio is used to determine the criteria for the optimal operating conditions of a fin-tube heat exchanger. It is also shown that heat transfer rate of heat exchanger with staggered fin arrangement increases about 17% and the time required for heat transfer rate to reach a maximum value becomes longer, compared with those of an inline fin-tube heat exchanger under the frosting condition. The energy transfer resistance between the air and coolant decreases with the increase of inlet air temperature and velocity and with decreasing inlet air humidity.

Thermal Storage and Heat Transfer in Phase Change Material Outside a Circular Tube with Axial Variation of the Heat Transfer Fluid Temperature

Abstract: A theoretical model is developed to analyze the thermal storage and heat transfer characteristics in a phase change material outside a circular tube with heat transfer fluid inside the tube. A new method, the alternative iteration between temperature and thermal resistance method, is presented to analyze the variation of the phase change radius, the axial temperature variation in the heat transfer fluid and the thermal storage in the circular tube. Dimensionless formulae are developed using theoretical and numerical analysis. The present solutions agree well with those in the literature. The dimensionless correlations are not limited to one condition, so they provide a basis for tube heat transfer design and optimization over a wide range of conditions.

Conjugate natural convection heat transfer in an open-ended vertical concentric annulus

Abstract: This paper is concerned with the steady conjugate heat transfer problem in vertical open-ended concentric annuli under the laminar natural convection flow regime. A finite difference technique has been used to solve the governing equations, with the outer surface of the outer tube wall being isothermally heated while the inner surface of the inner tube is kept adiabatic. Numerical results are presented for a Newtonian fluid of Pr = 0.7 in a fluid annulus of radius ratio 0.5. We present the effect of solid-fluid conductivity ratio on the induced flow behavior and some engineering parameters, such as the heat absorbed and the mixing-cup temperature.

Numerical Investigations on Enhancement of Heat Transfer in a Compact Fin-and-Tube Heat Exchanger Using Delta Winglet Type Vortex Generators

Abstract: Three dimensional flow and heat transfer in a compact fin-tube cross flow heat exchanger have been modeled as the flow in a rectangular channel with built-in cylindrical obstacles. The flow past a tube bank has been simulated by a spacewise periodic fully developed flow in a computational domain consisting of a channel element with one tube. Flow and temperature fields in this element and in another element with two in-line tubes have been computed from the numerical solution of three dimensional Navier-Stokes and energy equations. Comparison of results show that at low Reynolds number (~400) the Nusselt number in the neighborhood of the second tube of a two tube in-line configuration is close to the Nusselt number for spacewise periodic fully developed flow. Computational results also show poor heat transfer in the wake region. In the presence of the winglet type longitudinal vortex generators in the wake behind the cylinder, heat transfer in this region is enhanced significantly. Results show increases in average Nusselt number due to the vortex generators can be between 20 and 50 percent in the Reynolds number range of 400 and 1200. A factor, defined as the ratio of increase in Nusselt number to increase in friction factor, of 0.65 to 0.78 can be obtained, over the range of Reynolds number mentioned above.

Plate heat exchanger assembly with enhanced heat transfer characteristics

Abstract: A plate heat exchanger for accommodating a circulating refrigerant and heat transfer fluid. The plate heat exchanger includes a plurality of heat transfer plates and at least one electrode plate. The plurality of heat transfer plates are mounted in parallel relationship to each other defining alternating flow spaces for a refrigerant and a heat transfer fluid. The electrode plate is located in each refrigerant flow space and is spaced from the adjacent heat transfer plates. The electrode plate includes outer electrode surfaces on each side thereof to produce an electric field. The effect of the electric field is an increase in the heat transfer rate between the refrigerant and heat transfer fluid. The invention also includes a method of exchanging heat between a heat transfer fluid and a refrigerant in a plate heat exchanger.

Heat Transfer Enhancement by Wing-Type Longitudinal Vortex Generators and their Application to Finned Oval Tube Heat Exchanger Elements

Abstract: Wing-type longitudinal vortex generators (LVGs) can be used as fins or fin modifications for heat transfer enhancement in compact heat exchangers. For the last 15 years a group at the Ruhr-University Bochum has studied systematically the characteristics of heat transfer surfaces with vortex generators. Recent results are reported here. Three heat transfer enhancement modes may be induced by LVGs: developing boundary layer, swirl (longitudinal vortices) and flow destabilization. First these enhancement modes were studied numerically and experimentally for a base configuration consisting of a rectangular winglet array in channel flow at a Reynolds number of 175. Then finned oval tube heat exchanger elements with and without punched delta winglets were studied numerically. Winglet number and arrangement on the fin were varied in the Re range from 100 to 500. Flow structure, temperature distribution, local and global heat transfer, and flow loss penalty were presented. Staggered winglet arrangements were superior to in-line arrangements. The fin heat transfer surface may be reduced by more than 50% compared to a plane fin for identical heat duty, pressure loss, mass flow rate and temperature difference of the hot and cold medium. Direction for further research is indicated.

Heat exchanger, more particularly heat exchanger for exhaust gases

Abstract: The flow channels (2) of the heat exchanger are longer than the flow channels (3) and extend through the collection chamber (4) having inlets and outlets (8, 9). In region (l), in which both flow channels run parallel to each other, the heat exchanger does not have a housing. Heat exchanger , especially waste gas heat exchanger, consists of a stack of heat exchange plates forming divided flow channels running parallel to each other, with collection chambers, and inlet and outlet for the waste gas and for liquid coolant. The flow channels (2) of the heat exchanger are longer than the flow channels (3) and extend through the collection chamber (4) having inlets and outlets (8, 9). In region (l), in which both flow channels run parallel to each other, the heat exchanger does not have a housing.

A comparison study on fin surfaces in finned‐tube heat exchangers

Abstract: A three‐dimensional numerical study was conducted to assess the heat transfer performance of extended fins in a two‐row finned tube heat exchanger. Fins under investigation were plane and slit types. A finite volume discretization method and a SIMPLE‐based solution algorithm were, respectively, applied to working differential equations and their discrete counterparts to compute the gas velocities and pressure. The temperatures of solid and gas phases were computed from the same energy equation with different diffusivities and prescribed convective fluxes. The main objective of this study was to compare the transfer capabilities of the two investigated fin shapes. Their capabilities as a whole are presented in terms of the computed Nusselt number and the pressure drop across the flow passage.

Developing mixed convection in an inclined tube with circumferentially nonuniform heating at its outer surface

Abstract: Conjugate heat transfer in an inclined tube combining developing mixed convection of a Boussinesq fluid with nonuniform heating of the outer tube surface has been studied numerically. Viscous dissipation and axial diffusion are neglected. Thus the governing equations are parabolic in the axial direction and elliptic in the other two directions. Although the bottom half of the outer tube surface is assumed adiabatic, circumferential conduction through the wall results in a significantly different heat flux distribution at the solid-fluid interface. Thus, far from the entrance, the fraction of the externally supplied heat reaching the fluid from the bottom half of the interface is 72% for copper, 60% for steel, and 30% for glass tubes. This significant redistribution of the heat flux influences the thermal and hydrodynamic fields and has important effects on the Nusselt number, which cannot be predicted if the thermal boundary condition is applied at the solid-fluid interface.

Vehicle heat exchanger and especially water/air heat exchanger or evaporator

Abstract: The heat exchanger for a vehicle, and especially a water/air heat exchanger or evaporator, has a flat aluminum heat exchanger tube with at least two flows. A water box (6) with a cover (10) and a tube base (8) has a flow connection with the heat exchanger tube at one end. The free ends of the tube are each bonded by solder in slits at the tube base. The water box is divided by at least one wall (30), into an inflow and an outflow side, on the plane of the dividing wall (36) between the two flows in the heat exchanger. The water box dividing wall is gripped in a groove or slit at the tube base, by crossing the free ends (16) of the flat tube. Passages are distributed along the edge (48) of the tube base, to take the tongues (56) at the free edge of the cover in a soldered bond.

Fluid material application system employing tube-in-hose heat exchanger

Abstract: A fluid material application system is provided with an application deck for applying a fluid material that includes printing ink, adhesive or coating, a source of fluid material, a source of heat transfer Iiquid, and a heat exchanger. The heat exchanger includes a tube-in-hose ink heat exchange element having a fluid material carrying seamless tube located within a hose. The hose is adapted to be connected to a heat transfer fluid source so that a heat transfer fluid flows around the fluid material carrying tube to control and maintain the temperature of the fluid material in the tube at a generally constant temperature. The elongated heat exchange element may possess a winding type of configuration (e.g., it may be coiled or helically wound or may be laid out in a serpentine path) to define a winding flow path for the fluid material and the heat transfer fluid, and may be located within an enclosing structure to define an overall compact heat exchanger.

Applicability of Uniform Heat Flux Nusselt Number Correlations to Thermosyphon Heat Exchangers for Solar Water Heaters

Abstract: Nusselt numbers are measured in three counterflow tube-in-shell heat exchangers with flow rates and temperatures representative of thermosyphon operation in solar water heating systems. Mixed convection heat transfer correlations for these tube-in-shell heat exchangers were previously developed in Dahl and Davidson (1998) from data obtained in carefully controlled experiments with uniform heat flux at the tube walls. The data presented in this paper confirm that the uniform heat flux correlations apply under more realistic conditions. Water flows in the shell and 50 percent ethylene glycol circulates in the tubes. Actual Nusselt numbers are within 15 percent of the values predicted for a constant heat flux boundary condition. The data reconfirm the importance of mixed convection in determining heat transfer rates. Under most operating conditions, natural convection heat transfer accounts for more than half of the total heat transfer rate.