U.S. patent application number 14/872849 was filed with the patent office on 2017-04-06 for heat transfer tubes.
This patent application is currently assigned to Hamilton Sundstrand Corporation. The applicant listed for this patent is Hamilton Sundstrand Corporation. Invention is credited to Robert S. Downing.
Application Number | 20170097180 14/872849 |
Document ID | / |
Family ID | 57136662 |
Filed Date | 2017-04-06 |
United States Patent
Application |
20170097180 |
Kind Code |
A1 |
Downing; Robert S. |
April 6, 2017 |
HEAT TRANSFER TUBES
Abstract
A heat transfer tube includes a tube wall defining a central
axis in a lengthwise direction of the tube. The tube wall includes
a fluid inlet and fluid outlet for directing a coolant into and out
of the tube. A hollow cone is positioned within the tube wall
aligned with the central axis having an interior and exterior. A
plurality of orifices are defined through the core configured to
provide a separation of liquid coolant and vapor within the
tube.
Inventors: |
Downing; Robert S.;
(Rockford, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hamilton Sundstrand Corporation |
Charlotte |
NC |
US |
|
|
Assignee: |
Hamilton Sundstrand
Corporation
Charlotte
NC
|
Family ID: |
57136662 |
Appl. No.: |
14/872849 |
Filed: |
October 1, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F28D 2021/0071 20130101;
F25B 39/00 20130101; F28F 13/06 20130101; F25B 43/00 20130101; F25B
39/02 20130101; F28F 13/12 20130101; F25B 2500/09 20130101; F28F
13/003 20130101 |
International
Class: |
F25B 43/00 20060101
F25B043/00; F28F 13/00 20060101 F28F013/00; F25B 39/00 20060101
F25B039/00 |
Claims
1. A heat transfer tube, comprising: a tube wall defining a central
axis in a lengthwise direction of the tube, the tube wall including
a fluid inlet and fluid outlet for directing a coolant into and out
of the tube; a hollow cone within the tube wall aligned with the
central axis having an interior and exterior; and a plurality of
orifices defined through the cone configured to provide a
separation of liquid coolant within the cone from vapor outside the
cone within the tube wall.
2. The tube of claim 1, wherein the orifices are configured to form
impingement jets of fluid directed from the interior of the cone
towards the tube wall.
3. The tube of claim 2, wherein the orifices are configured to flow
vapor circumferentially and axially between the jets thereby
allowing liquid coolant to impinge on the tube wall.
4. The tube of claim 1, wherein the central cone converges down in
cross-sectional area in a downstream direction from an inlet end of
the cone.
5. The tube of claim 4, wherein the downstream end of the cone is
closed such that all fluid flow from the interior of the cone
passes through the orifices and exits the tube wall from the
outlet.
6. The tube of claim 1, wherein the orifices are dispersed
throughout a length of the central cone.
7. The tube of claim 1, wherein a flow area of liquid coolant
decreases as a flow area of two-phase flow increases thereby making
volumetric flow uniform within the tube wall.
8. The tube of claim 1, wherein an outer wall of the tube is
configured to be in communication with a heat source.
9. A heat exchanger, comprising: a plurality of heat transfer
tubes, each heat transfer tube, comprising: a tube wall defining a
central axis in a lengthwise direction of the tube, the tube wall
including a fluid inlet and fluid outlet for directing a coolant
into and out of the tube; a hollow cone within the tube wall
aligned with the central axis having an interior and exterior; and
a plurality of orifices defined through the core configured to
provide separation of liquid coolant and vapor within the tube.
10. A heat transfer device, comprising: a housing defining a
central axis, the housing including a fluid inlet and fluid outlet
for directing a coolant into and out of the housing; a hollow
insert within the housing aligned with the central axis having an
interior and exterior; and a plurality of orifices defined through
the insert configured to provide a designed distribution of liquid
coolant from the insert to an annular space that provides coolant
for boiling at an outer surface of the insert and carries a vapor
or vapor-liquid mixture axially outside the insert within the
housing.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present disclosure relates to heat exchangers, and more
particularly to heat transfer tubes used with heat exchangers.
[0003] 2. Description of Related Art
[0004] In-tube boiling is used in nearly all two-phase power and
thermal management systems, such as, Rankine power cycles, HVAC
vapor cycles thermal management, two-phase thermal buses and in
many chemical processing applications. Boiling heat transfer is
used to remove heat in cooling applications, for example,
electronics cooling. High heat flux applications like high power
lasers and microwaves rely on thermal management systems that
employ two-phase cooling.
[0005] In-tube boiling can have very high heat transfer
coefficients resulting in low wall temperature to fluid saturation
temperature differences. However, in-tube boiling has several
potential limitations. First, at high heat fluxes the voluminous
vapor generated at the heated wall can block the free stream liquid
from rewetting the wall. This well studied phenomenon is called
Critical Heat Flux (CHF), or burnout. Secondly, boiling can be
orientation and gravity sensitive. Beyond shear forces, gravity is
the key force that motivates bubbles to leave the hot boiling
surface. In adverse orientations, buoyancy forces tend to keep the
vapor on the wall and thereby reduce the heat transfer coefficient
and accelerate CHF conditions. For example, in reduced gravity
environments buoyant forces do not exist and boiling heat transfer
is severely limited. Many gravity insensitive geometries, like
swirl flow inserts and curved channels that use centrifugal forces
as a substitute for gravity have been used with limited
success.
[0006] Such conventional methods and systems have generally been
considered satisfactory for their intended purpose. However, there
is still a need in the art for an improved heat transfer tubes. The
present disclosure provides a solution for this need.
SUMMARY OF THE INVENTION
[0007] A heat transfer tube includes a tube wall defining a central
axis in a lengthwise direction of the tube. The tube wall includes
a fluid inlet and fluid outlet for directing a coolant into and out
of the tube. A hollow cone is positioned within the tube wall
aligned with the central axis having an interior and exterior. A
plurality of orifices are defined through the cone configured to
provide a separation of liquid coolant inside the cone from vapor
outside the cone within the tube wall.
[0008] The orifices can be configured to form impingement jets of
liquid directed from the interior of the cone towards the tube
wall. The orifices can further be configured to allow vapor flow
circumferentially and/or axially between the jets thereby allowing
liquid coolant to impinge on the tube wall. The orifices can be
dispersed throughout a length of the central cone.
[0009] The central cone can converge down in cross-sectional area
in a downstream direction from an inlet end of the cone. The
downstream end of the cone can be closed such that all fluid flow
from the interior of the cone passes through the orifices and exits
the tube wall from the outlet of the tube wall. Flow area of liquid
coolant can decrease as a flow r of two-phase flow increases
thereby making volumetric flow uniform within the tube. An outer
surface of the tube is configured to he in thermal communication
with a heat source. A heat exchanger can include a plurality of
heat transfer tubes as described above.
[0010] A heat transfer device including a housing defining a
central axis. The housing includes a fluid inlet and fluid outlet
for directing a coolant into and out of the housing. A hollow
insert within the housing aligned with the central axis having an
interior and exterior. A plurality of orifices defined through the
insert configured to provide a designed distribution of liquid
coolant from the insert to the annular space that provides coolant
for boiling at the outer surface and carries a vapor or
vapor-liquid mixture axially outside the insert within the
housing.
[0011] These and other features of the systems and methods of the
subject disclosure will become more readily apparent to those
skilled in the art from the following detailed description of the
preferred embodiments taken in conjunction with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] So that those skilled in the art to which the subject
disclosure appertains will readily understand how to make and use
the devices and methods of the subject disclosure without undue
experimentation, preferred embodiments thereof will be described in
detail herein below with reference to certain figures, wherein:
[0013] FIG. 1 is a cross-sectional view of a conventional boiling
tube; and
[0014] FIG. 2 is a cross-sectional view of an exemplary embodiment
of a heat transfer tube constructed in accordance with the present
disclosure, showing a hollow cone within the tube wall.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] Reference will now be made to the drawings wherein like
reference numerals identify similar structural features or aspects
of the subject disclosure. For purposes of explanation and
illustration, and not limitation, a partial view of an exemplary
embodiment of a heat transfer tube in accordance with the
disclosure is shown in FIG. 2 and is designated generally by
reference character 100.
[0016] FIG. 1 illustrates a conventional boiling tube 10. In a
horizontal orientation, several flow patterns develop as the
quality (vapor fraction of total flow) increases. At low qualities
bubbly flow dominates, followed by slug and plug (intermittent
liquid and vapor bridges), annular flow and then a mist. These
changes occur in a direction from left to right as oriented in FIG.
1
[0017] With reference to FIG. 2 a heat transfer tube 100 is shown
in accordance ith the present disclosure. The tube 100 can be part
of a heat exchanger that is in communication with a heat source
120, for example, an electronic heat, a high heat flux load like a
laser, or a hot fluid to he cooled. The tube 100 improves the
boiling process while reducing heat transfer area, system weight,
and increases system capabilities. The tube 100 includes a tube
wall 102 defining a central axis A-A in a lengthwise direction. The
tube wall 102 includes a fluid inlet 104 and fluid outlet 106 for
directing a coolant into and out of the tube 100. A hollow cone 110
is positioned within the tube wall 102 aligned with the central
axis. As shown in FIG. 2, the cone 110 converges down in a
cross-sectional area in a downstream direction from the inlet end
104a of the cone 110 toward outlet 106.
[0018] A plurality of orifices 112 are defined through the cone 110
each extending from an interior 114 of the cone 110 to an exterior
116 of the cone 110. The downstream end 106a of the cone 110 is
closed such that all fluid flow from the interior 114 of cone
passes through the orifices and exits the tube 100 through the
outlet 106. The plurality of orifices 112 are configured to provide
a separation of liquid coolant within the cone 110 from vapor
outside the cone 110 within the tube wall 102. More specifically,
the orifices 112 are configured to form impingement jets of fluid
directed from the interior 114 of the cone 110 towards the tube
wall 102. The impingement of the jets increases the heat transfer
coefficient, compared to conventional systems as shown in FIG. 1,
and more importantly, keep the wall 102 wetted thereby greatly
increasing critical heat flux (CHF). Vapor flows circumferentially
and/or axially between the jets allowing the liquid coolant to
impinge on tube wall 102. Very little distortion of the jets and
degradation of its velocity occurs in areas of high quality
(downstream) and void fraction (volume fraction of vapor). These
"drier" areas are those that benefit most with respect to heat
transfer coefficient and suppressing CHF, when compared to
conventional systems as shown in FIG. 1. In regions where the
two-phase flow is of lower quality (upstream) the jets may have
less of an impact on heat transfer but are not at risk of CHF.
[0019] If the heat flux distribution is not circumferentially or
axially symmetric, two design possibilities can be employed. First,
the orifice distribution can also be made asymmetric so that
orifice pattern produces a mass distribution for a better match the
local heat fluxes. Secondly, the liquid distribution cone can be
situated non-concentrically, with the orifice distribution
providing a greater mass flux in the region that is closest to the
heated outer wall. This embodiment provides better cooling where
locally needed and extra flow space in other arcs to carry the
spent vapor or liquid-vapor mixture.
[0020] The plurality of orifices 112 are disposed throughout the
length of the central cone 110. The flow area of the orifices
determines the jet velocity and pressure required for a given mass
flow on an application by application basis. Fewer or smaller
orifices will have higher velocity jets but a greater pressure
drop. The size, number and distribution of the orifices can be
optimized for any given application.
[0021] The impingement jets also make the heat transfer insensitive
to orientation and gravity level. This feature and makes the device
ideal for applications like micro-gravity. Additionally, due to the
converging cross-sectional area of the cone 110, the flow area of
the liquid coolant is decreasing while two-phase flow area is
increasing. Pressure drops are reduced and the heat transfer is
optimized by making the volumetric flow velocity more uniform in
both regions comparted to conventional systems. Furthermore, the
temperature of the liquid coolant supplied to the tube 100 does not
significantly vary along the tube 100. To have this "fresh" coolant
everywhere is advantageous, especially if the inlet flow is
subcooled (below the saturation temperature). Subcooling increases
the heat transfer coefficient and CHF.
[0022] This concept of impingement boiling may also be extended to
a planar geometry. FIG. 2 can illustrate the planar concept as well
as the cylindrical. For example, if the cross-section represents a
slice in a two dimensional plane, then the heat transfer walls are
flat surfaces rather than a cylindrical wall of a tube. Planar
embodiments are suitable for many two-phase applications in thermal
management, power and process heat transfer. They are also a good
approach for phase management in reduced gravity environments.
[0023] The methods and systems of the present disclosure, as
described above and shown in the drawings, provide for a device for
increasing heat transfer with superior properties including the use
of impingement gets to decrease central heat flux. While the
apparatus and methods of the subject disclosure have been shown and
described with reference to preferred embodiments, those skilled in
the art will readily appreciate that changes and/or modifications
may be made thereto without departing from the scope of the subject
disclosure.
* * * * *