Title of Invention	A DEVICE AND PROCESS FOR MANUFACTURING PRODUCTS OF GALVANNEALED ENHANCED HEAT TRANSFER SURFACE(S) ADAPTABLE TO HEAT EXCHANGER EQUIPMENTS
Abstract	As described in the background of the invention, present invention uses galvannealing approach for manufacturing enhanced heat transfer surface(s), which provides advantage of having an alloy with porous characteristics. The loosely binded metal particles through various processes described (in the background of invention) do not provide this advantage (obtained using galvannealing approach) of controlling the alloy composition with suitable surface roughness characteristics. Additionally, corrosion resistance is provided by zinc, the strength of which can be manipulated through its concentration and the thickness resulting from the steps of galvannealing. Moreover, the surface preparation separately for galvannealing is not really required. The final surface roughness is essentially dependent on the surface to be galvannealed. The strip surface profiles or patterns can however be made before galvannealing for the end objectives of the enhanced heat transfer surface. Such a prior preparation of surface profiles will produce compound enhancements such as porous fins or porous corrugated surfaces. Once galvannealed, the enhanced heat transfer surface can further be processed to arrive at the accurate profiles and patterns of the steel strips. When specific profiles or patterns (rough/enhanced - surface modifications) are made before galvannealing, compound enhancements such as porous fins or porous corrugated surfaces can be produced. HR strips for such types of enhancements can be galvannealed to obtain heat transfer surfaces of both strip or plate and tubular shapes. The tubular surfaces (non-enhanced type, not Zn coated) once formed can also be processed through the galvannealing approach to obtain the porous surfaces. These porous surfaces may have compound enhancement(s) of the type(s) mentioned above and others providing improved heat transfer. Moreover, the HR strips can have undulations (deformations), which themselves can be used as enhancement structures for heat transfer applications and similar to plain/smooth surfaces after galvannealing can be used for enhanced hear transfer applications having rough, porous surfaces of Fe-Zn alloy. As an enhanced heat transfer surface, the product of this invention finds applications for the basic modes of heat transfer viz., conduction, convention and radiation heat transfer and the applications involving a heat transfer mode or combinations of more that one heat transfer modes in single-phase flows and multi-phase including phase-change processes. The plate or strip forms (of any shape, size, thickness and curvature) having deformed or undeformed surfaces and tubular forms (of any size wall thickness and cross-section, including both ends sealed as in heat pipes) of this enhanced heat transfer surface with or without patterns or profiles delivering single or compound enhancements (the product of this invention) can be used (for example as plates, strips, tubes and fins, among others) in various heat exchange equipments that are both compact and non-compact. The increase in effective heat transfer coefficient, essentially delivers higher performance and compact design.

Title of Invention

A DEVICE AND PROCESS FOR MANUFACTURING PRODUCTS OF GALVANNEALED ENHANCED HEAT TRANSFER SURFACE(S) ADAPTABLE TO HEAT EXCHANGER EQUIPMENTS

Abstract

As described in the background of the invention, present invention uses galvannealing approach for manufacturing enhanced heat transfer surface(s), which provides advantage of having an alloy with porous characteristics. The loosely binded metal particles through various processes described (in the background of invention) do not provide this advantage (obtained using galvannealing approach) of controlling the alloy composition with suitable surface roughness characteristics. Additionally, corrosion resistance is provided by zinc, the strength of which can be manipulated through its concentration and the thickness resulting from the steps of galvannealing. Moreover, the surface preparation separately for galvannealing is not really required. The final surface roughness is essentially dependent on the surface to be galvannealed. The strip surface profiles or patterns can however be made before galvannealing for the end objectives of the enhanced heat transfer surface. Such a prior preparation of surface profiles will produce compound enhancements such as porous fins or porous corrugated surfaces. Once galvannealed, the enhanced heat transfer surface can further be processed to arrive at the accurate profiles and patterns of the steel strips. When specific profiles or patterns (rough/enhanced - surface modifications) are made before galvannealing, compound enhancements such as porous fins or porous corrugated surfaces can be produced. HR strips for such types of enhancements can be galvannealed to obtain heat transfer surfaces of both strip or plate and tubular shapes. The tubular surfaces (non-enhanced type, not Zn coated) once formed can also be processed through the galvannealing approach to obtain the porous surfaces. These porous surfaces may have compound enhancement(s) of the type(s) mentioned above and others providing improved heat transfer. Moreover, the HR strips can have undulations (deformations), which themselves can be used as enhancement structures for heat transfer applications and similar to plain/smooth surfaces after galvannealing can be used for enhanced hear transfer applications having rough, porous surfaces of Fe-Zn alloy. As an enhanced heat transfer surface, the product of this invention finds applications for the basic modes of heat transfer viz., conduction, convention and radiation heat transfer and the applications involving a heat transfer mode or combinations of more that one heat transfer modes in single-phase flows and multi-phase including phase-change processes. The plate or strip forms (of any shape, size, thickness and curvature) having deformed or undeformed surfaces and tubular forms (of any size wall thickness and cross-section, including both ends sealed as in heat pipes) of this enhanced heat transfer surface with or without patterns or profiles delivering single or compound enhancements (the product of this invention) can be used (for example as plates, strips, tubes and fins, among others) in various heat exchange equipments that are both compact and non-compact. The increase in effective heat transfer coefficient, essentially delivers higher performance and compact design.

Full Text	FIELD OF THE INVENTION : The present invention relates to a process for the manufacturing of enhanced heat transfer surfaces. More particularly, the present invention relates to a process for manufacturing of enhanced heat transfer surfaces which are galvannealed surfaces and have surface characteristics suitable for applications in the areas of heat exchange equipments having single-phase flow and phase- change processes such as boiling, condensation and evaporation among others. The invention further relates to a device for manufacturing enhanced heat transfer surfaces adaptable to heat exchange equipments. BACKGROUND OF THE INVENTION: A smooth surface has very low values of surface roughness. Such a surface when used for heat transfer applications of both single and multiphase including phase-change (such as boiling, condensation, evaporation) provide heat transfer performance, which is inferior to the rough surfaces. In single-phase flow applications the roughness helps in creating turbulence, whereas in phase- change processes the rough surface primarily provides larger nucleation sites in addition to increase in surface area for heat transfer, which leads to a higher rate of heat transfer. In addition to increased surface area, the porous surface provides interconnecting channels or pathways for the liquid and vapour. At present, the galvannealing surfaces are commonly used for applications in automobile industry (Ref. US# 5,997,664 and USD# 6, 368,728) requiring excellent surface finish and they have very small surface roughness values in the order of 0.5 micro-meter. Finishes that are too rough lead to poor performance after painting on exposed panel applications, whereas excessive smoothness results in poor paint adhesion. The alloy formation may or may not be complete. When there is incomplete alloy formation, smooth zinc films are observed in the surface. So far, for enhanced heat transfer applications, the rough, porous surfaces have been prepared using different approaches other than galvannealing such as binding metal powders (sintered, brazed), flame sprayed metal particles on the surface, electroplating, metal particles gas-blasted and metallic plating of metal particles. (Ref. US# 3,384,154, GB# 1,355,833, US# 4,064,914, US# 3,607,369, GB# 1,371,034 and US# 4,291,758). A porous boiling surface formed of thermally conductive particles integrally and thermally bonded together uses sintering, soldering, brazing or thermally bonding a layer of fine particles to the base heat transfer surface to form interconnected pores and labyrinth spaces. (US# 3384154, GB# 1355833, US# 40649114). The alloy formation however is limited to the region of bonding in these metal particles to the base surface. The overall porous surface structure is therefore highly inhomogenous in its character, where the base of porous surface shows alloy formation and upper surface tends to reflect the original characteristic of the metal powders/particles. A temporary binder such as a plastic material is used (US# 3384154) to establish and maintain uniform coating on the base metal surface. The binder decomposes and vapourizes during the heating and sintering process. The slurry of metal powder and liquid plastic binder material is applied to the base metal by dipping or spraying. The resulting coating is air-dried and solvent is evaporated. The powder metal coating and the substrate are then heated to sinter the metal powder particles together and to the base metal. The coating is however inconvenient and difficult to apply requiring longer drying times and leads to wastage of materials. It also results in non-uniformly thick coating. More uniform coating with lower mass production coating costs is obtained (GB# 1355833) by first coating the metal substance with a liquid binder solution of a low volatile polymer diluted with a high volatility solvent material. Metal powder is uniformally applied to this wet binder layer in such a way that all metal powder is wetted and all the high volatility solvent component is evaporated. The low volatile solvent is evaporated by furnace heating in mildly reduced atmosphere. In the end, the product is heated to cause metal bonding of particles to each other and to the base metal surface. This approach requires less binder than the earlier. A fast and low-bonding temperature characteristic is provided through the application of a loose coating of copper or steel powder matrix, bonding metal alloy consisting of copper and phosphorous or copper and antimony and a liquid binder and heating to braze the bonding metal alloy to the base metal and matrix (US# 4064914). The most important requirement of this process however is that the gas environment during the final heating step must be non-oxidizing. Any presence of oxide coating on the bonding metal alloy requires reducing gas i.e., hydrogen-containing, in order to remove oxide. Additionally, high temperature heating leads to grain size increase thus reducing the strength, the variations however are dependent on the type of bonding i.e. sintering or brazing. Accurate control of physical structure is possible with flame spraying (GB# 1388733). In this approach, particles of metallic primary material are uniformly mixed with particles of a secondary material. This mixture is flame-sprayed on the metal substrate. A molecularly bonded, inhomogeneous layer of the primary material containing regions of secondary material, which is neither alloyed with nor interdiffused with the primary material is formed. Lastly, the secondary material from the regions of pure secondary material is eliminated, which provides a porous continuously bonded primary material layer bonded to the base surface. The accurate control is achieved by controlling the temperature and dimensions of the flame. An alternate approach provides melt-blasting of metal particles to form a porous layer having labyrinth spaces. The particles are heated to a temperature at which the surface begins to melt and then are blasted at high speed to the surface of the base material by gas pressure. This is however not possible with a smooth surface on which the particles cannot be melt-bonded. A rough surface is therefore necessary and an advanced surface preparation by sand-blasting is suggested (US# 4371034). For known enhanced heat transfer applications galvannealed surfaces are produced primarily with zeta and delta phases with complete alloy formation, which provide porous surfaces having pits, cavities. The surface roughness is much higher than that of the galvannealed surfaces for other applications, two examples for which are listed below. 1. As disclosed in US Patent Number 6982012 for the manufacturing of steel sheet suitable for use in parts such as automotive panels that require a good external appearance, good workability and good shape accuracy i.e. shape retention has surface roughness preferably of at most 1.2 urn and more preferably of at most 1.0 urn. 2. As disclosed in US Patent Number 53245942 for manufacturing of galvannealed steel sheet suitable for use as an anti-corrosive steel sheet for automobiles and which exhibits an excellent press formability has three-dimensional average surface roughness between 0.7 urn and 1.4 urn. One of the approaches to form an alloy surface for steel adaptable for applications other than the areas of heat exchangers, is galvannealing. The steel strip is initially passed through hot-dip galvanizing process. This is typically carried out above the melting temperature of zinc. Galvannealing is carried out by heating the zinc coated strip in a furnace and holding it for some time for the desired composition of Fe-Zn alloy and surface characteristics. According to one approach, the HR strip (plain/smooth or profiled/rough) profiling is carried out using any or the combinations of the processes such as embossing, stamping, pressing and machining among others) which is thereafter cleaned and galvannealed. Cleaning of the strip or plate may take place during cooling in HSM itself. The "Tandem Mill" operation is decided by the profile requirements and the controlled surface roughness (with an workable range of roughness values), which provide enhanced performances in heat transfer applications for example in boiling heat transfer (Thome, 1990). Earlier studies (Ortiz and Rangarajan, 1998; Fossen, et al., 19980 have shown that the galvannealed surface roughness increase with rougher incoming cold rolled strips. Galvannealing process additionally enhances the surface roughness (Bensiger, et al., 1996). As mentioned earlier the porous surface can further be processed for required surfaces before a tubular shape is produced. Usually, the strip is edge slitted and is progressively bent into a tubular form with close control on dimensions. Welding is the carried out and processes of bead trimming and finishing afterwards. However, when porous surfaces are formed with galvannealing, which essentially creates Zn-Fe alloy coating through the process of heat treatment of zinc coated steel, the alloy formation is throughout the porous surface. The porous surface structure is rough and irregular with cavities or pits and having undulating surface. Such products obviously cannot be used for applications in the areas of heat exchangers, which warrant enhanced heat transfer surfaces having at least an alloy with porous characteristics. OBJECTS OF THE INVENTIONS: It is therefore an object of the invention to propose a process for manufacturing products with enhanced heat transfer surfaces which are adaptable in heat transfer applications for example, boiling, condensation and evaporation, among others (heat transfer applications as discussed above). Another object of the invention is to propose a process for manufacturing products with enhanced heat transfer surfaces, which may have different cross- sections with controlled roughness on one or both sides. A further object of the invention is to propose a process for manufacturing products with enhanced heat transfer surfaces, which in the form of galvannealed steel strips or plates can be directly used in heat transfer applications. A still further object of the invention is to propose a device for carrying out the process of the invention. SUMMARY OF THE INVENTION: As described in the background of the invention, present invention uses galvannealing approach for manufacturing enhanced heat transfer surface(s), which provides advantage of having an alloy with porous characteristics. The loosely binded metal particles through various processes described (in the background of invention) do not provide this advantage (obtained using galvannealing approach) of controlling the alloy composition with suitable surface roughness characteristics. Additionally, corrosion resistance is provided by zinc, the strength of which can be manipulated through its concentration and the thickness resulting from the steps of galvannealing. Moreover, the surface preparation separately for galvannealing is not really required. The final surface roughness is essentially dependent on the surface to be galvannealed. The strip surface profiles or patterns can however be made before galvannealing for the end objectives of the enhanced heat transfer surface. Such a prior preparation of surface profiles will produce compound enhancements such as porous fins or porous corrugated surfaces. Once galvannealed, the enhanced heat transfer surface can further be processed to arrive at the accurate profiles and patterns of the steel strips. When specific profiles or patterns (rough/enhanced - surface modifications) are made before galvannealing, compound enhancements such as porous fins or porous corrugated surfaces can be produced. HR strips for such types of enhancements can be galvannealed to obtain heat transfer surfaces of both strip or plate and tubular shapes. The tubular surfaces (non-enhanced type, not Zn coated) once formed can also be processed through the galvannealing approach to obtain the porous surfaces. These porous surfaces may have compound enhancement(s) of the type(s) mentioned above and others providing improved heat transfer. Moreover, the HR strips can have undulations (deformations), which themselves can be used as enhancement structures for heat transfer applications and similar to plain/smooth surfaces after galvannealing can be used for enhanced hear transfer applications having rough, porous surfaces of Fe-Zn alloy. As an enhanced heat transfer surface, the product of this invention finds applications for the basic modes of heat transfer viz., conduction, convention and radiation heat transfer and the applications involving a heat transfer mode or combinations of more that one heat transfer modes in single-phase flows and multi-phase including phase-change processes. The plate or strip forms (of any shape, size, thickness and curvature) having deformed or undeformed surfaces and tubular forms (of any size wall thickness and cross-section, including both ends sealed as in heat pipes) of this enhanced heat transfer surface with or without patterns or profiles delivering single or compound enhancements (the product of this invention) can be used (for example as plates, strips, tubes and fins, among others) in various heat exchange equipments that are both compact and non-compact. The increase in effective heat transfer coefficient, essentially delivers higher performance and compact design. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Fig 1 Shows an exemplary device according to the invention for providing an enhanced heat transfer surface by galvannealing. Fig 2 Is a flow-chart depicting the process steps according to the invention. DETAILED DESCRIPTION OF THE INVENTION As shown in fig 1, a Zinc pot (1)contains molten zinc. A steel strip (2) is caused to pass through the zinc pot (1) and is directed vertically upwardly. Above the zinc pot (1) and on both sides of the steel strip (2) are placed a plurality of air knives (3), which serve to remove the excess molten zinc from the steel strip (2). The steel strip (2) is again made to pass through a galvannealing unit (4), where the steel strip (2) gets heated to a temperature sufficient to enable a zinc and iron alloy to form. The desired phases and the surface characteristic is maintained according to the invention. The major difference with the galvannealing of steel surfaces other than manufacturing heat transfer surfaces lies with the temperature and time. A lower to medium range in temperature (440°C - 575°C) and time 3 s - 25 s) is employed for enhanced heat transfer applications products manufacturing. The galvannealed steel strip is processed further for final finishing. As shown in fig 2, the steel strip (2) is passed through a zinc pot (1). The temperature of the zinc pot (1) is maintained above 420°C. The zinc coated steel strip (2) is taken out of the zinc pot (1). The zinc coated steel strip (2) is arranged to move through the air knives (3), where the strip (2) is wiped out for any additional coating. Galvannealing is then employed in an galvannealing unit (4) for further processing of the zinc coated steel strip (2). The gavannealing is carried out between the temperature range of 420°C to 600°C. The galvannealed steel strip (2) is then further processed for finishing. Surface roughness characterization is carried out for required porous surface for enhanced heat transfer applications. The process time for a maximum thickness of the steel strip including the immersion time is upto two hours. The process is applicable for any metal particle site with any porosity. The surface roughness can be achieved between 100 µm - 200 µm. The alloying metal used is zinc including corrosion resistance element. For the step of galvannealing, the temperature is maintained between 400°C to 575°C with a time between 3 s to 25 s. REFERENCES : Referred Patents 1. Tahara, K., Inagaki, J., Watanabe, T. and Yamashita, M., 1999, "Method for producing steel sheet". US# 5,997,664. 2. Tobiyama, Y. and Kato, G, 2002, "Galvannealed steel sheet and manufacturing method', US# 6,368,728. 3. Milton, R.M., 1968, "Heat exchange system". US# 3,384,154. 4. Union Carbide Corporation, 1974, "Method of coating metal substrates". GB# 1,355,833. 5. Grant, A.G, 1977, "Porous metallic layer and formation". US#4,064,914. 6. Batta, L.B., 1971, "Method for forming porous aluminium layer", US#3,607,369. 7. Thome IK., 1973, "Porous surface". GB# 1,388,733. 8. Dahl, M.M. and Erb, L.D., 1976, "Liquid heat exchanger interface and method". US# 3,990,862. 9. Shum, M.S., 1980, "Finned heat transfer tube with porous boiling surface and method for producing same", US# 4,182,412. 10. Shum, M.S., 1980, "Method of producing finned heat transfer tube with porous boiling surface", US# 4,199,414. 11. Yamada, K., Hiroyuki, S., Akira, H. and Kenzo, M., 1983, "Plate type evaporator", US# 4,371,034. 12. Fuji, M., Ogawa, Y. and Morihiro, Y., 1981, "Preparation of boiling heat transfer surface", US# 4,291,758. 13. Wasekar, V.M., 2006, "Manufacturing of galvannealed enhanced heat transfer surface(s)", Provisional Patent Application (Concept patent), MS-word document dated June 03,06 attached with patent #283. Referred Books and Articles 1. Thome, J.R., 1990 Enhanced boiling heat transfer, Hemisphere Publishing Corporation, New York, Figs. 3-11. pg. 37. 2. Ortiz, H. and Rangarajan, V., 1998, "Effects of processing on coating characteristics and performance of galvanneal", 39th MWSP Conf. Proc, ISS, Vol. XXXV, pp. 83-89. 3. Fossen, E.W., Lamb M.G. Makoviczki, T.C., Dalgleish, P.B. and Czerneda, P.P., 1996, "Coating roughness control on automotive coated steel sheet". 37th MWSP Conf. Proc, ISS, Vol. XXXIII, pp. 157- 163. 4. Bensiger, T.R., LaRowe, K.L. and Hreso, D.M., 1996, "Influence of processing parameters on surface characteristics of galvanneal coated sheet", 37th MWSP Conf. Pore, Vol. XXXIII, pp. 139-148. WE CLAIM: 1. A process for manufacturing products with enhanced heat transfer surfaces adaptable to heat exchanger equipments, the process comprising the steps of:  providing a device having means for holding and moving a steel strip,  causing the steel strip to pass through a zinc pot containing molted zinc at a temperature above about 420°C.  withdrawing the steel strip from the zinc pot and causing the zinc coated steel strip to move through a plurality of air knives in which additional coating being wiped-out from the zinc coated steel strip;  allowing the zinc-coated steel strip to pass through a galvannealing unit for further processing of the zinc-coated steel strip, the temperature in the galvannealed unit being maintained between about 440°C to 575°C with a stay-time in the galvannealing unit between about 3 s to 25 s; and  carrying out surface roughness characterization for the desired porous surface. 2. A device for manufacturing products with enhanced heat transfer surfaces adaptable to boiling, condensation and evaporation applications, the device comprising :  a zinc pot (1) capable of containing molten zinc at a desired temperature;  a clamping and moving means encompassing the operational periphery of the device, the clamping means holding a steel strip or any other tubular member of any cross section, and the moving means causing the steel strip (2) to move within the operational periphery of the device;  a plurality of air-knives capable of rotating the steel strip (2).at several rotational speeds,  a galvannealing unit (4) for galvannealing the semi-finished steel strip or the tubular member, and  a roughness characterization means for attaining the desired porous surface of the galvannealed products. 3. A process for manufacturing products with enhanced heat transfer surfaces adaptable to heat exchanger equipments as substantially described and illustrated herein with reference to the accompanying drawings. 4. A device for manufacturing products with enhanced heat transfer surfaces adaptable to boiling, condensation and evaporation applications as substantially described and illustrated herein with reference to the accompanying drawings. As described in the background of the invention, present invention uses galvannealing approach for manufacturing enhanced heat transfer surface(s), which provides advantage of having an alloy with porous characteristics. The loosely binded metal particles through various processes described (in the background of invention) do not provide this advantage (obtained using galvannealing approach) of controlling the alloy composition with suitable surface roughness characteristics. Additionally, corrosion resistance is provided by zinc, the strength of which can be manipulated through its concentration and the thickness resulting from the steps of galvannealing. Moreover, the surface preparation separately for galvannealing is not really required. The final surface roughness is essentially dependent on the surface to be galvannealed. The strip surface profiles or patterns can however be made before galvannealing for the end objectives of the enhanced heat transfer surface. Such a prior preparation of surface profiles will produce compound enhancements such as porous fins or porous corrugated surfaces. Once galvannealed, the enhanced heat transfer surface can further be processed to arrive at the accurate profiles and patterns of the steel strips. When specific profiles or patterns (rough/enhanced - surface modifications) are made before galvannealing, compound enhancements such as porous fins or porous corrugated surfaces can be produced. HR strips for such types of enhancements can be galvannealed to obtain heat transfer surfaces of both strip or plate and tubular shapes. The tubular surfaces (non-enhanced type, not Zn coated) once formed can also be processed through the galvannealing approach to obtain the porous surfaces. These porous surfaces may have compound enhancement(s) of the type(s) mentioned above and others providing improved heat transfer. Moreover, the HR strips can have undulations (deformations), which themselves can be used as enhancement structures for heat transfer applications and similar to plain/smooth surfaces after galvannealing can be used for enhanced hear transfer applications having rough, porous surfaces of Fe-Zn alloy. As an enhanced heat transfer surface, the product of this invention finds applications for the basic modes of heat transfer viz., conduction, convention and radiation heat transfer and the applications involving a heat transfer mode or combinations of more that one heat transfer modes in single-phase flows and multi-phase including phase-change processes. The plate or strip forms (of any shape, size, thickness and curvature) having deformed or undeformed surfaces and tubular forms (of any size wall thickness and cross-section, including both ends sealed as in heat pipes) of this enhanced heat transfer surface with or without patterns or profiles delivering single or compound enhancements (the product of this invention) can be used (for example as plates, strips, tubes and fins, among others) in various heat exchange equipments that are both compact and non-compact. The increase in effective heat transfer coefficient, essentially delivers higher performance and compact design.

Full Text

FIELD OF THE INVENTION :
The present invention relates to a process for the manufacturing of enhanced
heat transfer surfaces. More particularly, the present invention relates to a
process for manufacturing of enhanced heat transfer surfaces which are
galvannealed surfaces and have surface characteristics suitable for applications
in the areas of heat exchange equipments having single-phase flow and phase-
change processes such as boiling, condensation and evaporation among others.
The invention further relates to a device for manufacturing enhanced heat
transfer surfaces adaptable to heat exchange equipments.
BACKGROUND OF THE INVENTION:
A smooth surface has very low values of surface roughness. Such a surface when
used for heat transfer applications of both single and multiphase including
phase-change (such as boiling, condensation, evaporation) provide heat transfer
performance, which is inferior to the rough surfaces. In single-phase flow
applications the roughness helps in creating turbulence, whereas in phase-
change processes the rough surface primarily provides larger nucleation sites in
addition to increase in surface area for heat transfer, which leads to a higher rate
of heat transfer. In addition to increased surface area, the porous surface
provides interconnecting channels or pathways for the liquid and vapour.
At present, the galvannealing surfaces are commonly used for applications in
automobile industry (Ref. US# 5,997,664 and USD# 6, 368,728) requiring
excellent surface finish and they have very small surface roughness values in the
order of 0.5 micro-meter. Finishes that are too rough lead to poor performance
after painting on exposed panel applications, whereas excessive smoothness
results in poor paint adhesion. The alloy formation may or may not be complete.
When there is incomplete alloy formation, smooth zinc films are observed in the

surface. So far, for enhanced heat transfer applications, the rough, porous
surfaces have been prepared using different approaches other than
galvannealing such as binding metal powders (sintered, brazed), flame sprayed
metal particles on the surface, electroplating, metal particles gas-blasted and
metallic plating of metal particles. (Ref. US# 3,384,154, GB# 1,355,833, US#
4,064,914, US# 3,607,369, GB# 1,371,034 and US# 4,291,758).
A porous boiling surface formed of thermally conductive particles integrally and
thermally bonded together uses sintering, soldering, brazing or thermally
bonding a layer of fine particles to the base heat transfer surface to form
interconnected pores and labyrinth spaces. (US# 3384154, GB# 1355833, US#
40649114). The alloy formation however is limited to the region of bonding in
these metal particles to the base surface. The overall porous surface structure is
therefore highly inhomogenous in its character, where the base of porous
surface shows alloy formation and upper surface tends to reflect the original
characteristic of the metal powders/particles.
A temporary binder such as a plastic material is used (US# 3384154) to establish
and maintain uniform coating on the base metal surface. The binder decomposes
and vapourizes during the heating and sintering process. The slurry of metal
powder and liquid plastic binder material is applied to the base metal by dipping
or spraying. The resulting coating is air-dried and solvent is evaporated. The
powder metal coating and the substrate are then heated to sinter the metal
powder particles together and to the base metal. The coating is however
inconvenient and difficult to apply requiring longer drying times and leads to
wastage of materials. It also results in non-uniformly thick coating. More uniform
coating with lower mass production coating costs is obtained (GB# 1355833) by
first coating the metal substance with a liquid binder solution of a low volatile
polymer diluted with a high volatility solvent material. Metal powder is
uniformally applied to this wet binder layer in such a way that all metal powder is

wetted and all the high volatility solvent component is evaporated. The low
volatile solvent is evaporated by furnace heating in mildly reduced atmosphere.
In the end, the product is heated to cause metal bonding of particles to each
other and to the base metal surface. This approach requires less binder than the
earlier. A fast and low-bonding temperature characteristic is provided through
the application of a loose coating of copper or steel powder matrix, bonding
metal alloy consisting of copper and phosphorous or copper and antimony and a
liquid binder and heating to braze the bonding metal alloy to the base metal and
matrix (US# 4064914). The most important requirement of this process however
is that the gas environment during the final heating step must be non-oxidizing.
Any presence of oxide coating on the bonding metal alloy requires reducing gas
i.e., hydrogen-containing, in order to remove oxide. Additionally, high
temperature heating leads to grain size increase thus reducing the strength, the
variations however are dependent on the type of bonding i.e. sintering or
brazing.
Accurate control of physical structure is possible with flame spraying (GB#
1388733). In this approach, particles of metallic primary material are uniformly
mixed with particles of a secondary material. This mixture is flame-sprayed on
the metal substrate. A molecularly bonded, inhomogeneous layer of the primary
material containing regions of secondary material, which is neither alloyed with
nor interdiffused with the primary material is formed. Lastly, the secondary
material from the regions of pure secondary material is eliminated, which
provides a porous continuously bonded primary material layer bonded to the
base surface. The accurate control is achieved by controlling the temperature
and dimensions of the flame. An alternate approach provides melt-blasting of
metal particles to form a porous layer having labyrinth spaces. The particles are
heated to a temperature at which the surface begins to melt and then are
blasted at high speed to the surface of the base material by gas pressure. This is
however not possible with a smooth surface on which the particles cannot be

melt-bonded. A rough surface is therefore necessary and an advanced surface
preparation by sand-blasting is suggested (US# 4371034).
For known enhanced heat transfer applications galvannealed surfaces are
produced primarily with zeta and delta phases with complete alloy formation,
which provide porous surfaces having pits, cavities. The surface roughness is
much higher than that of the galvannealed surfaces for other applications, two
examples for which are listed below.
1. As disclosed in US Patent Number 6982012 for the manufacturing of
steel sheet suitable for use in parts such as automotive panels that
require a good external appearance, good workability and good shape
accuracy i.e. shape retention has surface roughness preferably of at
most 1.2 urn and more preferably of at most 1.0 urn.
2. As disclosed in US Patent Number 53245942 for manufacturing of
galvannealed steel sheet suitable for use as an anti-corrosive steel
sheet for automobiles and which exhibits an excellent press formability
has three-dimensional average surface roughness between 0.7 urn and
1.4 urn.
One of the approaches to form an alloy surface for steel adaptable for
applications other than the areas of heat exchangers, is galvannealing. The steel
strip is initially passed through hot-dip galvanizing process. This is typically
carried out above the melting temperature of zinc. Galvannealing is carried out
by heating the zinc coated strip in a furnace and holding it for some time for the
desired composition of Fe-Zn alloy and surface characteristics.
According to one approach, the HR strip (plain/smooth or profiled/rough)
profiling is carried out using any or the combinations of the processes such as
embossing, stamping, pressing and machining among others) which is thereafter
cleaned and galvannealed.

Cleaning of the strip or plate may take place during cooling in HSM itself. The
"Tandem Mill" operation is decided by the profile requirements and the controlled
surface roughness (with an workable range of roughness values), which provide
enhanced performances in heat transfer applications for example in boiling heat
transfer (Thome, 1990). Earlier studies (Ortiz and Rangarajan, 1998; Fossen, et
al., 19980 have shown that the galvannealed surface roughness increase with
rougher incoming cold rolled strips. Galvannealing process additionally enhances
the surface roughness (Bensiger, et al., 1996). As mentioned earlier the porous
surface can further be processed for required surfaces before a tubular shape is
produced. Usually, the strip is edge slitted and is progressively bent into a
tubular form with close control on dimensions. Welding is the carried out and
processes of bead trimming and finishing afterwards.
However, when porous surfaces are formed with galvannealing, which essentially
creates Zn-Fe alloy coating through the process of heat treatment of zinc coated
steel, the alloy formation is throughout the porous surface. The porous surface
structure is rough and irregular with cavities or pits and having undulating
surface. Such products obviously cannot be used for applications in the areas of
heat exchangers, which warrant enhanced heat transfer surfaces having at least
an alloy with porous characteristics.
OBJECTS OF THE INVENTIONS:
It is therefore an object of the invention to propose a process for manufacturing
products with enhanced heat transfer surfaces which are adaptable in heat
transfer applications for example, boiling, condensation and evaporation, among
others (heat transfer applications as discussed above).

Another object of the invention is to propose a process for manufacturing
products with enhanced heat transfer surfaces, which may have different cross-
sections with controlled roughness on one or both sides.
A further object of the invention is to propose a process for manufacturing
products with enhanced heat transfer surfaces, which in the form of
galvannealed steel strips or plates can be directly used in heat transfer
applications.
A still further object of the invention is to propose a device for carrying out the
process of the invention.
SUMMARY OF THE INVENTION:
As described in the background of the invention, present invention uses
galvannealing approach for manufacturing enhanced heat transfer surface(s),
which provides advantage of having an alloy with porous characteristics. The
loosely binded metal particles through various processes described (in the
background of invention) do not provide this advantage (obtained using
galvannealing approach) of controlling the alloy composition with suitable surface
roughness characteristics. Additionally, corrosion resistance is provided by zinc,
the strength of which can be manipulated through its concentration and the
thickness resulting from the steps of galvannealing. Moreover, the surface
preparation separately for galvannealing is not really required. The final surface
roughness is essentially dependent on the surface to be galvannealed. The strip
surface profiles or patterns can however be made before galvannealing for the
end objectives of the enhanced heat transfer surface. Such a prior preparation of
surface profiles will produce compound enhancements such as porous fins or
porous corrugated surfaces. Once galvannealed, the enhanced heat transfer

surface can further be processed to arrive at the accurate profiles and patterns
of the steel strips.
When specific profiles or patterns (rough/enhanced - surface modifications) are
made before galvannealing, compound enhancements such as porous fins or
porous corrugated surfaces can be produced. HR strips for such types of
enhancements can be galvannealed to obtain heat transfer surfaces of both strip
or plate and tubular shapes. The tubular surfaces (non-enhanced type, not Zn
coated) once formed can also be processed through the galvannealing approach
to obtain the porous surfaces. These porous surfaces may have compound
enhancement(s) of the type(s) mentioned above and others providing improved
heat transfer. Moreover, the HR strips can have undulations (deformations),
which themselves can be used as enhancement structures for heat transfer
applications and similar to plain/smooth surfaces after galvannealing can be used
for enhanced hear transfer applications having rough, porous surfaces of Fe-Zn
alloy.
As an enhanced heat transfer surface, the product of this invention finds
applications for the basic modes of heat transfer viz., conduction, convention and
radiation heat transfer and the applications involving a heat transfer mode or
combinations of more that one heat transfer modes in single-phase flows and
multi-phase including phase-change processes. The plate or strip forms (of any
shape, size, thickness and curvature) having deformed or undeformed surfaces
and tubular forms (of any size wall thickness and cross-section, including both
ends sealed as in heat pipes) of this enhanced heat transfer surface with or
without patterns or profiles delivering single or compound enhancements (the
product of this invention) can be used (for example as plates, strips, tubes and
fins, among others) in various heat exchange equipments that are both compact
and non-compact. The increase in effective heat transfer coefficient, essentially
delivers higher performance and compact design.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig 1 Shows an exemplary device according to the invention for
providing an enhanced heat transfer surface by
galvannealing.
Fig 2 Is a flow-chart depicting the process steps according to the
invention.
DETAILED DESCRIPTION OF THE INVENTION
As shown in fig 1, a Zinc pot (1)contains molten zinc. A steel strip (2) is caused
to pass through the zinc pot (1) and is directed vertically upwardly. Above the
zinc pot (1) and on both sides of the steel strip (2) are placed a plurality of air
knives (3), which serve to remove the excess molten zinc from the steel strip (2).
The steel strip (2) is again made to pass through a galvannealing unit (4), where
the steel strip (2) gets heated to a temperature sufficient to enable a zinc and
iron alloy to form. The desired phases and the surface characteristic is
maintained according to the invention.
The major difference with the galvannealing of steel surfaces other than
manufacturing heat transfer surfaces lies with the temperature and time. A lower
to medium range in temperature (440°C - 575°C) and time 3 s - 25 s) is
employed for enhanced heat transfer applications products manufacturing.

The galvannealed steel strip is processed further for final finishing.
As shown in fig 2, the steel strip (2) is passed through a zinc pot (1).
The temperature of the zinc pot (1) is maintained above 420°C.
The zinc coated steel strip (2) is taken out of the zinc pot (1).
The zinc coated steel strip (2) is arranged to move through the air knives (3),
where the strip (2) is wiped out for any additional coating.
Galvannealing is then employed in an galvannealing unit (4) for further
processing of the zinc coated steel strip (2).
The gavannealing is carried out between the temperature range of 420°C to
600°C. The galvannealed steel strip (2) is then further processed for finishing.
Surface roughness characterization is carried out for required porous surface for
enhanced heat transfer applications.
The process time for a maximum thickness of the steel strip including the
immersion time is upto two hours. The process is applicable for any metal
particle site with any porosity. The surface roughness can be achieved between
100 µm - 200 µm. The alloying metal used is zinc including corrosion resistance

element. For the step of galvannealing, the temperature is maintained between
400°C to 575°C with a time between 3 s to 25 s.

REFERENCES :
Referred Patents
1. Tahara, K., Inagaki, J., Watanabe, T. and Yamashita, M., 1999,
"Method for producing steel sheet". US# 5,997,664.
2. Tobiyama, Y. and Kato, G, 2002, "Galvannealed steel sheet and
manufacturing method', US# 6,368,728.
3. Milton, R.M., 1968, "Heat exchange system". US# 3,384,154.
4. Union Carbide Corporation, 1974, "Method of coating metal
substrates". GB# 1,355,833.
5. Grant, A.G, 1977, "Porous metallic layer and formation".
US#4,064,914.
6. Batta, L.B., 1971, "Method for forming porous aluminium layer",
US#3,607,369.
7. Thome IK., 1973, "Porous surface". GB# 1,388,733.
8. Dahl, M.M. and Erb, L.D., 1976, "Liquid heat exchanger interface and
method". US# 3,990,862.
9. Shum, M.S., 1980, "Finned heat transfer tube with porous boiling
surface and method for producing same", US# 4,182,412.
10. Shum, M.S., 1980, "Method of producing finned heat transfer tube
with porous boiling surface", US# 4,199,414.
11. Yamada, K., Hiroyuki, S., Akira, H. and Kenzo, M., 1983, "Plate type
evaporator", US# 4,371,034.
12. Fuji, M., Ogawa, Y. and Morihiro, Y., 1981, "Preparation of boiling heat
transfer surface", US# 4,291,758.
13. Wasekar, V.M., 2006, "Manufacturing of galvannealed enhanced heat
transfer surface(s)", Provisional Patent Application (Concept patent),
MS-word document dated June 03,06 attached with patent #283.

Referred Books and Articles
1. Thome, J.R., 1990 Enhanced boiling heat transfer, Hemisphere
Publishing Corporation, New York, Figs. 3-11. pg. 37.
2. Ortiz, H. and Rangarajan, V., 1998, "Effects of processing on coating
characteristics and performance of galvanneal", 39th MWSP Conf.
Proc, ISS, Vol. XXXV, pp. 83-89.
3. Fossen, E.W., Lamb M.G. Makoviczki, T.C., Dalgleish, P.B. and
Czerneda, P.P., 1996, "Coating roughness control on automotive
coated steel sheet". 37th MWSP Conf. Proc, ISS, Vol. XXXIII, pp. 157-
163.
4. Bensiger, T.R., LaRowe, K.L. and Hreso, D.M., 1996, "Influence of
processing parameters on surface characteristics of galvanneal coated
sheet", 37th MWSP Conf. Pore, Vol. XXXIII, pp. 139-148.

WE CLAIM:
1. A process for manufacturing products with enhanced heat transfer
surfaces adaptable to heat exchanger equipments, the process comprising
the steps of:
 providing a device having means for holding and moving a steel strip,
 causing the steel strip to pass through a zinc pot containing molted
zinc at a temperature above about 420°C.
 withdrawing the steel strip from the zinc pot and causing the zinc
coated steel strip to move through a plurality of air knives in which
additional coating being wiped-out from the zinc coated steel strip;
 allowing the zinc-coated steel strip to pass through a galvannealing
unit for further processing of the zinc-coated steel strip, the
temperature in the galvannealed unit being maintained between about
440°C to 575°C with a stay-time in the galvannealing unit between
about 3 s to 25 s; and
 carrying out surface roughness characterization for the desired porous
surface.
2. A device for manufacturing products with enhanced heat transfer surfaces
adaptable to boiling, condensation and evaporation applications, the
device comprising :
 a zinc pot (1) capable of containing molten zinc at a desired
temperature;
 a clamping and moving means encompassing the operational periphery
of the device, the clamping means holding a steel strip or any other
tubular member of any cross section, and the moving means causing
the steel strip (2) to move within the operational periphery of the
device;

 a plurality of air-knives capable of rotating the steel strip (2).at several
rotational speeds,
 a galvannealing unit (4) for galvannealing the semi-finished steel strip
or the tubular member, and
 a roughness characterization means for attaining the desired porous
surface of the galvannealed products.
3. A process for manufacturing products with enhanced heat transfer
surfaces adaptable to heat exchanger equipments as substantially
described and illustrated herein with reference to the accompanying
drawings.
4. A device for manufacturing products with enhanced heat transfer surfaces
adaptable to boiling, condensation and evaporation applications as
substantially described and illustrated herein with reference to the
accompanying drawings.

As described in the background of the invention, present invention uses galvannealing approach for manufacturing enhanced heat transfer surface(s), which provides advantage of having an alloy with porous characteristics. The loosely binded metal particles through various processes described (in the background of invention) do not provide this advantage (obtained using
galvannealing approach) of controlling the alloy composition with suitable surface roughness characteristics. Additionally, corrosion resistance is provided by zinc, the strength of which can be manipulated through its concentration and the thickness resulting from the steps of galvannealing. Moreover, the surface
preparation separately for galvannealing is not really required. The final surface roughness is essentially dependent on the surface to be galvannealed. The strip surface profiles or patterns can however be made before galvannealing for the end objectives of the enhanced heat transfer surface. Such a prior preparation of surface profiles will produce compound enhancements such as porous fins or
porous corrugated surfaces. Once galvannealed, the enhanced heat transfer surface can further be processed to arrive at the accurate profiles and patterns of the steel strips.
When specific profiles or patterns (rough/enhanced - surface modifications) are
made before galvannealing, compound enhancements such as porous fins or
porous corrugated surfaces can be produced. HR strips for such types of
enhancements can be galvannealed to obtain heat transfer surfaces of both strip
or plate and tubular shapes. The tubular surfaces (non-enhanced type, not Zn
coated) once formed can also be processed through the galvannealing approach
to obtain the porous surfaces. These porous surfaces may have compound
enhancement(s) of the type(s) mentioned above and others providing improved
heat transfer. Moreover, the HR strips can have undulations (deformations),
which themselves can be used as enhancement structures for heat transfer
applications and similar to plain/smooth surfaces after galvannealing can be used
for enhanced hear transfer applications having rough, porous surfaces of Fe-Zn
alloy. As an enhanced heat transfer surface, the product of this invention finds
applications for the basic modes of heat transfer viz., conduction, convention and
radiation heat transfer and the applications involving a heat transfer mode or
combinations of more that one heat transfer modes in single-phase flows and
multi-phase including phase-change processes. The plate or strip forms (of any
shape, size, thickness and curvature) having deformed or undeformed surfaces
and tubular forms (of any size wall thickness and cross-section, including both
ends sealed as in heat pipes) of this enhanced heat transfer surface with or
without patterns or profiles delivering single or compound enhancements (the
product of this invention) can be used (for example as plates, strips, tubes and
fins, among others) in various heat exchange equipments that are both compact
and non-compact. The increase in effective heat transfer coefficient, essentially
delivers higher performance and compact design.

Documents:

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Patent Number

269835

Indian Patent Application Number

894/KOL/2006

PG Journal Number

46/2015

Publication Date

13-Nov-2015

Grant Date

09-Nov-2015

Date of Filing

05-Sep-2006

Name of Patentee

TATA STEEL LIMITED

Applicant Address

RESEARCH AND DEVELOPMENT DIVISION JAMSHEDPUR-831 001

Inventors:

#	Inventor's Name	Inventor's Address
1	VIVEK M WASEKAR	TATA STEEL LIMITED. RESEARCH AND DEVELOPMENT DIVISION JAMSHEDPUR-831 001

PCT International Classification Number

F04D 31/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA