Plate Heat Transfer Research Articles

Heat transfer enhancement of dropwise condensation on a vertical surface with round shaped grooves

In dropwise condensation, the behavior of falling drops strongly affects the heat transfer. It is expected that the heat transfer during dropwise condensation would be enhanced if falling drops more frequently and widely sweep drops in the lower part. In this paper, we investigated heat transfer characteristics of dropwise condensation on the surface with grooves cut in a round shape. The heat transfer plate was made of copper with 30 mm square by 3 mm thick. The round shaped grooves were cut regularly on the surface. The plate was set vertically and the grooves were arranged in two positions, vertical and horizontal. The heat flux, surface temperature and sweeping cycle of falling drops were measured when steam flowed down and condensed on the grooved surface. As the results, it was found that the heat transfer on the vertical grooved surface was enhanced in the range of groove width from 2 to 3 mm. This indicated that the groove width of 2–3 mm was considered to be very effective in making falling drops sweep small droplets on the lower part of grooves.

Using microchannels to cool microprocessors: a transmission-line-matrix study

As microprocessors components density and clock frequency increase, so do heat dissipation. The heat results from Joule effect due to leakage currents in the components area or active region. This region is only few microns thick and can quickly reach destructing temperatures if heat is not quickly removed. On this critical issue depends the system reliability. The active region is separated from the ventilated heat sink by a silicon substrate and a metal integrated heat spreader, both hundreds of microns thick. This interface region is the microprocessor's heat transfer plate where heat exchange is achieved by conduction. Because of the localized heat source, the thermal spreading resistance of the interface region can be high. A novel way of spreading heat in that region is the use of microchannel arrays where an appropriate thermal compound or a phase change liquid can be trapped to increase heat transfer by conduction or to create micro-heat-pipes. Traditional cooling methods, with conventional and well optimised heat sinks, can then be used with less burden.In this paper, the Transmission-Line-Matrix (TLM) technique is used to simulate the effect of microchannels on the temperature distribution in the active region. To minimize the interface heat resistance various microchannel and patterns are examined. In this part of the work, the microchannels are filled with the heat spreader material copper or aluminium. The results show an improved thermal transient behaviour and a reduced active region temperature in steady state.

C125 宇宙太陽光発電システムの実現性に対する搭載機器の排熱処理からの検討

Feasibility of the Space Solar Power System (SSPS) is analyzed for an assumed 10MW model with an idealized generator/transmitter unified modules assembled to make a circular satellite with a diameter of 200m. Even under the operating conditions not advantageous for the heat management and under the use of FC-72 with very low latent heat of vaporization, it is possible to integrate heat transfer area required for keeping the weight fraction of vapor flow at 0.8 and preventing the occurrence of dryout before the radiators. Heat transfer in cold plates and heat transport by two-phase flow loops could be improved much more by using water or other organic fluids with a higher value of latent heat.

Enhancement of steam absorption into a film of LiBr aqueous solution falling over a downward‐facing plate

AbstractAn experimental study was performed on the enhancement of steam absorption into a LiBr aqueous solution. The enhancement method proposed here is to set an absorption heat transfer plate facing downward to generate free convection within a liquid film falling over the plate. The experiment was conducted varying the tilt angle of the heat transfer plate in a range of 40 to 90°. The heat transfer coefficients were compared for both cases of the heat transfer plate facing upward and downward. It was found from the experimental results that the downward‐facing plate has a higher heat transfer coefficient than the upward‐facing plate, which confirmed that free convection and mixing occur in the liquid film and enhance the absorption heat transfer in the case of the downward‐facing plate. The enhancement effect becomes remarkable as the tilt angle approaches horizontal, though the liquid film becomes thick and its thermal resistance increases. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(8): 606–616, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10062

A numerical study of heat transfer of a porous block with the random porosity model in a channel flow

In this paper, heat transfer of a hot plate with a porous block in a channel flow is numerically investigated. A porous block is simulated as a fin type heat sink. The random/artificial porosity models are used to generate the distribution of porosity. In fact, the distribution of porosity in porous medium is irregular, thus the random porosity model is more realistic than the constant or variable porosity model to describe the phenomena happening in porous medium. Therefore, the distribution of porosity of porous block obeys the random porosity model, and the factors of mean porosity and standard deviation are taken into consideration. The variations of the porosity and the velocity in porous block are no longer smooth. For obtaining more heat transfer rate, the artificial porosity model is proposed. The heat transfer rates of the several cases derived by the artificial porosity model are better than those of the random porosity model. The thermal performance of porous block is larger than that of solid block as the mean porosity is larger than 0.5.

Improvement of the Accuracy of Heat Input Estimation Technique based on Inverse Heat Conduction Analysis by the Introduction of Regularization Method

The regularization method, which improves the accuracy and the robustness of inverse heat conduction analysis for the distributions of heat flux and plate face temperature during spot heating, is formulated. Gas temperature right on the plate, TG, and local heat transfer coefficient, α, can be identified from these estimates. A guideline for adjusting the identified TG and α is drawn up. The validity of the proposed method is demonstrated by comparing the estimated and measured plate temperatures during spot and line heating experiments. This result indicates that calculation of the steel plate heat input distribution history can be accomplished for desired plate shape, dimensions, and torch movement history, solely from spot heating experimental results.

An investigation of a block moving back and forth on a heat plate under a slot jet. Part II (the effects of block moving distance and vacant distance)

A continuous investigation of a block moving back and forth on a heat plate under a slot jet was studied numerically. This study investigates the effects of block moving distance and vacant distance between the block and heat plate on the heat transfer of heat plate. This subject belongs to a kind of moving boundary problems, and the modified Arbitrary Lagrangian Eulerian (ALE) method is suitable for solving this subject. The results show that the increment of the heat transfer rate of heat plate is not direct proportion to the block moving distance, and the smaller vacant distance is expected for obtaining the larger heat transfer rate of heat plate.

Plates — the next breakthrough in thermal desalination

In recent years thermal desalination using multiple effect processes, often augmented by thermo-compressors, has become increasingly popular. The basic process has remained unchanged since the late 1800s when scientists such as Rilleaux developed the concepts we use today. At the turn of the century these multiple effect processes almost exclusively used submerged tube designs. Over the years several other equipment configurations have been used with horizontal tube falling film (HTFF) finding new popularity in the last decade. The low pumping power consumption of falling film processes has led to the decline of forced circulation processes, such as MSF, especially in plant sizes less than 10,000 tonnes per day. Plate heat transfer surfaces are the latest development in falling film technology. Various configurations of plates have been tried in the past. Among them have been dimpled plates and corrugated plates. The latest type of plates are Pressed Plate used in a Falling Film (PPFF). This new configuration has several advantages never before available to any thermal desalination process. The use of PPFF leads to higher heat transfer coefficients due to the combination of plate pattern and thickness which is based on 40 years of proprietary manufacturing technology. The PPFF system incorporates a patented distribution system, which provides greater control of fluid distribution and wetting of the surface as well as turbulent boundary layers promoted at low velocities due to the plate pattern. Conversely, all HTFF systems have a vapour space between the distribution system and the top of tubes then successive gaps between each row. The new PPFF system removes these potential sources of scaling due to inadequate wetting found in HTFF. Perhaps the most practical new feature is the flexibility and access to the heat transfer surface. Normal cleaning procedures involve the typical cleaning in place (CIP) circulation of mild acid solution used by most desalination processes. However, the possibility of full access to the heating surfaces in the PPFF means that virtually no irreversible scaling will take place. Even the dreaded calcium sulphate scale, should it arise due to operational errors, can be readily and completely removed. The PPFF configuration can also be configured to allow future addition of the heat transfer surface. This makes it possible to plan for future plant capacity expansion with minimal investment today. While membrane systems may be able to allow for the addition of extra membrane for planned increases in capacity, this has not before been possible with any thermal desalination process, thereby the new PPFF configuration offers a very high design flexibility.

Thermodynamic optimisation in cryogenic insulation systems: dependence upon thermophysical conditions of the materials

The thermodynamic optimisation of one-dimensional cryogenic insulation systems where thermal conductivity depends upon temperature and other parameters has been studied. The following main different types have been considered for the general case of one-dimensional heat transfer (plate, hollow cylinder, and hollow sphere) and also for two-dimensional and three-dimensional heat transfer: (a) thermodynamic optimisation with a continuous variation of thermal flux along the insulation; (b) thermodynamic optimisation with a variation of thermal flux by finite steps along the insulation; (c) thermodynamic optimisation in two-layer or multilayer systems.

Natural convection in a vertical rectangular enclosure with localized heating and cooling zones

Experimental and numerical studies of natural convection in a single phase, closed thermosyphon were carried out using a vertical, rectangular enclosure model. Only one vertical plate plays the role of heat transfer surface having 100 mm height and 100 mm width, and others act as the adiabatic wall made of transparent plexi-glass. The heat transfer surface is separated into three horizontal zones with an equal height; top 1/3 and bottom 1/3 of the surface are cooling and heating zones, respectively and intermediate section is an adiabatic zone. Water is used as the working fluid. Variable parameters are distance D between the heat transfer surface and an adiabatic plate opposite to the heat transfer plate, and temperature difference ΔT between heating and cooling zones. By changing both D and ΔT, three regimes of the natural convection flow; quasi-two-dimensional steady, three-dimensional steady and unsteady flows are observed by means of thermo-sensitive liquid crystal powder and numerically simulated very well by solving a set of governing equations.

New developments in solid-state fermentation: II. Rational approaches to the design, operation and scale-up of bioreactors

Over the last decade there has been a significant improvement in understanding how to design, operate and scale-up solid-state fermentation bioreactors. The key to these advances has been the application of mathematical modeling techniques to describe the biological and transport phenomena within the system. This review focuses on the advances in understanding that have come from this modeling work, and the insights it has given us into bioreactor design, operation and scale-up. It also highlights two promising bioreactor designs that have emerged over the last decade or so. For processes in which the substrate bed must remain static throughout the fermentation, the most promising design is the Zymotis design of ORSTOM at Montpellier, France, which involves closely spaced internal heat transfer plates within a packed-bed bioreactor. For those processes in which mixing can be tolerated, the stirred bioreactor developed at INRA, in Dijon, France, has been successfully demonstrated at scales of 1–25 t of substrate. Theoretical work suggests that mathematical models will be useful tools in the scale-up process, however, there are no reports that they have been used in the development of any current large-scale process. Rather, the models have been validated against data obtained from laboratory-scale bioreactors. There is an urgent need to test the accuracy and robustness of the models by applying them within real process development.

Thermal design of an ultraslim notebook computer

We have developed two innovative thermal solutions for ultraslim notebook personal computer (PC) where only natural convection cooling can be used for heat rejection. The first solution is a cooling system for the CPU using the bottom chassis (Mg die-cast) as a heat spreader combining with Al heat transfer plate. The size and geometry were optimized by thermal analysis using finite volume method before making the prototype. As the second solution, a new coating which can reduce the warmth of Mg (magnesium alloy) die-cast enclosure has been developed and has already reached the stage of practical use. This paper describes the outline of these thermal design technologies used for Mitsubishi ultraslim notebook PC "Pedion." As of September 1997 "Pedion" was the world's thinnest at 18 mm thick among A4-size notebook computers for Microsoft(R) Windows(R).

An Experimental Study on Unsteady Heat Transfer of Spray-Impinging Plate in a Pressurized Chamber

An experimental investigation on transient heat transfer phenomena of impinging diesel-spray on a flat plate in a pressurized chamber is carried out. A diesel spray is injected from a single-hole nozzle and impinges to a heated flat plate in the chamber. A fast-response thermocouple installed in the top surface of the plate measures the transient variation of surface temperature of the plate under various conditions of the chamber pressures. Utilizing the semi-infinite model, the temporal variation of the heat flux on the plate is determined. Effects of various parameters, such as vertical distances between the nozzle and the plate, radial distances from the injection-axis, and the chamber pressures, on the heat flux characteristics of impinging diesel-spray are studied.

Plate heat exchangers — the new trend in thermal desalination

In recent years thermal desalination using multiple effect processes, often augmented by thermo-compressors, has become increasingly popular. The basic process has remained unchanged since the late 1800s when scientists such as Rilleaux developed the concepts we use today. At the turn of the century these multiple-effect processes almost exclusively used submerged tube designs. Over the years several other equipment configurations have been used with horizontal tube falling film (HTFF) finding new popularity in the last decade. The low pumping power consumption of falling film processes has led to the decline of forced circulation processes, such as MSF, especially in plant sizes less than 10,000 t/d. Plate heat transfer surfaces are the latest development in falling film technology. Various configurations of plates have been tried in the past. Among them have been dimpled plates and corrugated plates. The latest type of plates are pressed plate used in a falling film (PPFF). This new configuration has several advantages never before available to any thermal desalination process. The use of PPFF leads to higher heat transfer coefficients due to the combination of plate pattern and thickness which is based on 40 years of proprietary manufacturing technology. The PPFF system incorporates a patented distribution system, which provides greater control of fluid distribution and wetting of the surface as well as turbulent boundary layers promoted at low velocities due to the plate pattern. Conversely, all HTFF systems have a vapour space between the distribution system and the top row of tubes then successive gaps between each row. The new PPFF system removes these potential sources of scaling due to inadequate wetting found in HTFF. Perhaps the most practical new feature is the flexibility and access to the heat transfer surface. Normal cleaning procedures involve the typical cleaning in place (CIP) circulation of mild acid solution used by most desalination processes. However, the possibility of full access to the heating surfaces in the PPFF means that virtually no irreversible scaling will take place. Even the dreaded calcium sulphate scale, should it arise due to operational errors, can be readily and completely removed. The PPFF configuration can also be configured to allow future addition of the heat transfer surface. This makes it possible to plan for future plant capacity expansion with minimal investment today. While membrane systems may be able to allow for the addition of extra membrane for planned increases in capacity, this has not before been possible with any thermal desalination process, thereby the new PPFF configuration offers a very high design flexibility.

Natural convection heat and mass transfer in partially heated vertical parallel plates

A combined numerical and theoretical investigation of laminar natural convection heat and mass transfer in open vertical parallel plates with unheated entry and unheated exit is presented. Both boundary conditions of uniform wall temperature/uniform wall concentration (UWT/UWC) and uniform heat flux/uniform mass flux (UHF/UMF) are considered. Results of dimensionless induced volume rate Q, average Nusselt number Nu E and Sherwood number Sh E are obtained for air flow under various buoyancy ratio N, Grashof number Gr L, Schmidt number Sc and combinations of unheated entry, heated section and unheated exit length. Theoretical solutions for Q, Nu E and Sh E for both UWT/UWC and UHF/UMF cases are derived under fully developed conditions. The numerical solutions are shown to approach asymptotically the closed form solutions for fully-developed flow. The presence of unheated entry and unheated exit severely affects the heat and mass transfer rates. In addition, the correlation equations of Q, Nu E and Sh E for both boundary conditions are presented.

Generation of longitudinal vortices in internal flows with an inclined impinging jet and enhancement of target plate heat transfer

Abstract Flow velocity measurements and heat transfer experiments were carried out for a jet obliquely discharged into a crossflow in a duct. The flow measurements were made with optical fiber laser Doppler velocimetry, and the heat transfer experiments were made by making use of a thermochromic liquid crystal. The obtained velocity data reveal that the inclined jet is effective in generating longitudinal vortices in the crossflow. It is demonstrated that the longitudinal vortices are effective in enhancing target plate jet impingement heat transfer. It is, therefore, promising as a means to effectively cool inner surfaces of high temperature gas turbine vanes. The obtained heat transfer data are discussed in detail in comparison with the measured flow field and turbulence data.

Two-Dimensional Modeling of Heat Transfer Through Sandwich Plates With Inhomogeneous Boundary Conditions on the Faces

This paper presents a thermal model describing heat transfer in multispan sandwich rectangular plates. The model is time-dependent and two-dimensional. Complex thermal phenomena occurring in light cores (honeycomb) and thermal contact resistance are taken into account in the model. Particular attention is paid to the boundary conditions on the faces of the plate: radiative and nonuniform convective exchange are taken into account. The global temperature solution for stationary cases is developed on trigonometric and exponential functions bases. The properties of the Laplace transform are used to solve time-dependent cases. Validation experiments are carried out in a wind tunnel ring for two-span plates submitted to convective exchanges on one face; the same configuration is reproduced for an aluminum sandwich plate in an industrial set-up bench. Experimental results agree well with the numerical simulation.

Enhancement of Steam Absorption into a Film of LiBr Aqueous Solution Falling over a Downward Facing Plate.

An experimental study was performed on the enhancement of steam absorption into a LiBr aqueous solution. The enhancement method proposed here is to set an absorption heat transfer plate facing downward to generate free convection within a liquid film falling over the plate. The experiment was conducted varying the tilt angle of the heat transfer plate in a range of 40 to 90 degrees, and the heat transfer coefficients were compared for both cases of the heat transfer plate facing upward and downward. It was found from the experimental results that the downward facing plate has higher heat transfer coefficient than the upward facing plate, which confirmed that free convection and mixing occur in the liquid film and enhance the absorption heat transfer in case of downward facing plate. The enhancement effect becomes remarkable as the tilt angle approaches horizontal, though the liquid film becomes thick and its thermal resistance increases.

Thermal Design of a Slim Notebook Personal Computer.

This paper describes the outline of thermal design technology used for MITSUBISHI ultra-slim notebook Personal Computer Pedion. As of September 1997, Pedion is the world's thinnest at 18 mm thick among A4-size notebook computers. We have developed innovative thermal solutions for ultra-slim Notebook Pc where only natural convection cooling can be used for heat rejection. The first solution is cooling system for CPU by using the bottom chassis (Mg die-cast) as a heat spreader combining with A1 heat transfer plate. And the size and the thickness of A1 plates were optimized by thermal analysis using Finite Volume Method. As the second solution, a new coating which can reduce touching warmth of Mg die-cast enclosure have developed and already been reached the stage of practical use.

Full Surface Local Heat Transfer Coefficient Measurements in a Model of an Integrally Cast Impingement Cooling Geometry

Cast impingement cooling geometries offer the gas turbine designer higher structural integrity and improved convective cooling when compared to traditional impingement cooling systems, which rely on plate inserts. In this paper, it is shown that the surface that forms the jets contributes significantly to the total cooling. Local heat transfer coefficient distributions have been measured in a model of an engine wall cooling geometry using the transient heat transfer technique. The method employs temperature-sensitive liquid crystals to measure the surface temperature of large-scale perspex models during transient experiments. Full distributions of local Nusselt number on both surfaces of the impingement plate, and on the impingement target plate, are presented at engine representative Reynolds numbers. The relative effects of the impingement plate thermal boundary condition and the coolant supply temperature on the target plate heat transfer have been determined by maintaining an isothermal boundary condition at the impingement plate during the transient tests. The results are discussed in terms of the interpreted flow field.