Heat transfer during the boiling of liquids in heat pipe wicks

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National Aeronautics and Space Administration , Washington, DC
Heat -- Transmis
StatementYu. K. Gontarev ... [et al.].
SeriesNASA technical translation -- NASA TT-20108., NASA technical translation -- 20108.
ContributionsGontarev, Yu. K., United States. National Aeronautics and Space Administration.
The Physical Object
FormatMicroform
Pagination1 v.
ID Numbers
Open LibraryOL15288529M

The heat pipe is a well-known cooling module for advanced electronic devices. The heat pipe has many applications, particularly in electronics and related area such as PC, laptop, display, artificial satellite, and telecommunication modules.

The heat pipe utilizes phase change heat transfer inside enveloped structures, where the working fluid evaporates in heated zone, and vapor moves to Cited by: 2. 5 wicks were found to be the most effective for both horizontal and adversely tilted heat pipes.

Overall heat transfer capability in sintered porous media has been shown to be strongly affected by thin film evaporation Further experimental studies of the wick dryout include work by Abhat and Seban28, Wang and Peterson29, among Cited by: This page provides the chapter on boiling heat transfer from the "DOE Fundamentals Handbook: Thermodynamics, Heat Transfer, and Fluid Flow," DOE-HDBK/, U.S.

Department of Energy, June Other related chapters from the "DOE Fundamentals Handbook: Thermodynamics, Heat Transfer, and Fluid Flow" can be seen to the right. Semena et al., “Transition from the evaporation to the boiling regime in low-temperature heat pipes with metal-fiber wicks,” in: Heat and Mass Transfer VI [in Russian], Vol.

4, ITMO Akad. Nauk Belo.

Details Heat transfer during the boiling of liquids in heat pipe wicks PDF

SSR, Minsk (), Part 2, pp. – Google ScholarCited by: 4. In this chapter, two-phase convection processes are examined.

Two-phase processes occur when the fluid is experiencing heat transfer near the vapor dome so that vapor and liquid are simultaneously present.

If the fluid is being transformed from liquid to vapor through heat addition, then the process is referred to as boiling or : Gregory Nellis, Sanford Klein.

This chapter discusses heat transfer during boiling and condensation. Boiling and condensation most often occur together in real processes. The vapor from the boiler is compressed and passed. Here in this section of mechanical books, you will find a collection of free Heat Transfer pdf Books.

Heat and mass transfer, heat exchanger design & methods : Report broken links to Contact us Advances in Heat Transfer Download Computational Fluid Dynamics and Heat Transfer Download Computational methods in fluid and Heat Transfer Download Convection.

“The Relation Between Bubble Diameter and Frequency of Removal From a Sphere During Film Boiling,” J. Heat Transfer, 88, 87–93, CrossRef Google Scholar Enhancement of Heat Transfer in Pool Boiling • Surfaces that provide enhanced heat transfer in nucleate boiling permanently are being manufactured and are available in the market.

• Heat transfer can be enhanced by a factor of up to 10 during nucleate boiling, and the critical heat flux by a factor of 3. Thermoexcel-E. There has been much research on modelling the heat transfer associated with buried pipes with constant wall temperatures [7].

A widely used concept here is the conduction shape factor, S, which for a buried pipe takes the form: S= 2ˇ cosh Y1 a where a is the pipe radius, and Y is the distance of the pipe centre from the ground.

Our problem we are considering is heat-transfer to fluid inside of a heated tube – forced-convection heat transfer plus radial conduction T 1 Laminar flow in pipes: data correlation Geankoplis, 4th ed.

eqnfor liquid metals. air at 1atm in turbulent flow in pipes. In the nucleate boiling dominated regime, heat fluxes of (±) W/cm 2 can be dissipated by wicks with heaters of area 1 cm 2, while heat fluxes up to (±) W/cm 2 can be dissipated by wicks with smaller heaters intended to simulate local hot-spots.

The authors have studied the laws of the heat transfer mechanism in boiling in mesh heat pipe wicks. It is shown that at high heat flux density in the precrisis regime one can stop bubble boiling. The concept of overall coefficient of heat transfer is used in case of heat transfer by (a) conduction (b) convection (c) radiation (d) conduction and convection (e) convection and radiation.

Ans: d. The unit of overall coefficient of heat transfer is (a) kcal/m2 (b) kcal/hr °C (c) kcal/m2 hr °C (4) kacl/m hr °C (e) kcal/m3 hr °C. Submerged pool boiling from porous surfaces has been extensively characterized for a number of surface geometries, working fluids, and flooded porous wick structures often found in heat pipes [15–28].The fundamental mechanism of heat transfer during boiling from a porous surface submerged in a liquid pool differs from that from a wick that is passively fed by capillary action.

At low heat fluxes, vapor is generated at the inner wick surface. As the heat flux increases, the boiling limit is reached when vapor generation in the wick blocks liquid flow in the wick.

The boiling limit is typically 75 W/cm2 for sintered and screen wicks, but can be increased to more than W/cm2 with specially designed wicks. During the past few decades, heat transfer during convective flow boiling inside pipes has been widely studied with the goal of unveiling the physics of the process.

Different heat transfer mechanisms have been suggested based on different assumptions. Malcolm Joyce, in Nuclear Engineering, Departure from nucleate boiling, critical heat flux and boiling crisis. Nucleate boiling results in an increase in heat transfer due to the enhanced mixing caused by the turbulence near to the heated surface due to bubble formation, as described earlier.

However, the pockets of vapour formed (as per stage 4) eventually coalesce to constitute. The heat transfer coefficient increases with the increase of the heat flux. The temperature outside the evaporator is also higher with higher heat flux.

Description Heat transfer during the boiling of liquids in heat pipe wicks PDF

This result should be attributed to more fierce convection or boiling heat transfer caused by higher Δ T. Therefore, the heat transfer mechanism in the RHP was analyzed and is shown in Figure 4. Heat transfer in a laminar pipe flow. The case is a solution of the thermal energy convection-diffusion equation: The left-hand side of the equation represents convective heat transfer, that is heat transfered by the fluid’s motion.

The radial velocity is equal to zero, so the first term of the left-hand side can be neglected. Heat flux in the Benar-Rayleigh problem. Hydrodynamics of free liquid jets and their influence on heat transfer.

Natural convection heat transfer to power law fluids. Natural convection in evaporating droplets. Principles of heat and mass transfer with liquid evaporation. Bubble nucleation, growth, and departure in boiling heat transfer.

Enhanced Heat Transfer in Biporous Wicks in the Thin Liquid Film Evaporation and Boiling Regimes J. Heat Transfer (October,) Numerical Simulation of Evaporating Two-Phase Flow in a High-Aspect-Ratio Microchannel with Bends. MechHEAT TRANSFER HOMEWORK Solutions 4. (Problem in the Book) A vertical plate m high, maintained at a uniform temperature of 54oC, is exposed to saturated steam at atmospheric pressure.

a) Estimate the condensation and heat transfer rates per unit width of the plate. at pool boiling. The experiments [4, 5] were carried out to study heat transfer processes in thin liquid films at low pressure on a capillary-porous surface in operating conditions of flat-plate heat pipe systems.

The experiments showed the difference between heat transfer. •A variety of high-intensity heat transfer processes are involved with combustion and chemical reaction in the gasifier unit itself.

Download Heat transfer during the boiling of liquids in heat pipe wicks FB2

•The gas goes through various cleanup and pipe-delivery processes to get to our heat transfer processes involved in these stages are generally less intense.

A heat pipe is a heat-transfer device that combines the principles of both thermal conductivity and phase transition to effectively transfer heat between two solid interfaces. At the hot interface of a heat pipe, a liquid in contact with a thermally conductive solid surface turns into a vapor by absorbing heat from that surface.

The vapor then travels along the heat pipe to the cold interface. Composite wicks (Table 2), however, can significantly increase the capillary limit of the heat pipe, but have the drawback of high manufacturing costs. When selecting a wick structure for a particular application, one must keep in mind the benefits and drawbacks of each type of wick.

The operating principles of heat pipes (HP) are expounded, along with a discussion of different types of HP, and the underlying theory, design, and fabrication of HP. Working fluids, wick configurations, reservoirs, and pipe materials are dealt with, and cleaning, assembly, evacuation, charging, and closure of HP are covered.

Capillary action, sonic limitation, entrainment limitation, boiling. Q = Rate of Steady State Heat Conductivity (W) S = Conduction Shape Factor (m) which has the dimension of length, and k is the thermal conductivity of the medium between the surfaces. The conduction shape factor depends on the geometry of the system only.

k = Thermal Conductivity (W/m °C) T 1 = Temperature (°C) T 2 = Temperature (°C) D 1. International Heat Pipe Conference inregarding operating conditions, Dr.

Polasek stated that the“For successful operation of an oscillating heat pipe, liquid plugs and vapor bubbles must coexist inside the capillary tube along its length. This can be achieved by vacuuming the tube and then partially filling it with a working fluid.

HEAT TRANSFER IN FREEBOARD REGION. Experimental Studies and Prediction Methods. Recommendations. HEAT TRANSFER BETWEEN GAS AND PARTICLES. GAS-SOLID FLOW IN PIPES. Regimes of Gas-Solid Flow. Experimental Studies of Heat Transfer. Prediction of Heat Transfer. [email protected]{osti_, title = {Physical principles of heat pipes}, author = {Ivanovski, M N and Sorokin, V P and Yagodkin, I V}, abstractNote = {Heat pipes are used whenever high rates of heat transfer or the control or conversion of heat flows are required.

This book covers the physical principles of operation of heat pipes and choice of working fluid related to temperature range.The principal characteristics of the boiling of liquid alkali metals under conditions of free motion are examined with reference to high-temperature heat pipe applications.

Experimental data are presented on the intensity of heat transfer during the evaporation of these metals out of porous wick structures.

Results of studies of the compatibility of structural materials and heat transfer.