WO2016174209A1

WO2016174209A1 - Exchanger for a wind tunnel

Info

Publication number: WO2016174209A1
Application number: PCT/EP2016/059622
Authority: WO
Inventors: José María CANCER ABÓITIZ; Isaac PRADA Y NOGUEIRA; Pablo José CANCILLO MARTÍNEZ; Enrique MARTÍN LÓPEZ; Ignacio SERRANO REMÓN
Original assignee: Madrid Fly SL
Current assignee: Madrid Fly SL
Priority date: 2015-04-30
Filing date: 2016-04-29
Publication date: 2016-11-03
Anticipated expiration: 2017-10-30
Also published as: ES2652517B1; ES2652517A2; ES2652517R1

Abstract

The present invention relates to both a system and a method for heat exchange with the airflow inside a wind tunnel. It is necessary to cool the airflow and control the temperature of said airflow inside a wind tunnel, for which purpose an optimally parameterized heat exchanger is used to obtain suitable cooling without an excessive increase in pressure loss. The present invention also relates to a design method for designing said heat exchanger. The present invention also relates to a wind tunnel comprising said system for heat exchange with the airflow circulating inside said wind tunnel.

Description

EXCHANGER FOR A WIND TUNNEL

Object of the Invention

The present invention relates to a system for heat exchange with the airflow inside a wind tunnel, as well as a method for regulating the temperature of the airflow inside a wind tunnel and for designing said exchanger. It is necessary to cool the airflow and control the temperature of the said airflow inside a wind tunnel.

Background of the Invention

Heat exchangers are used in both horizontal and vertical wind tunnels for cooling the airflow, which increases the temperature thereof due to friction between the said airflow and the internal walls of the duct of the wind tunnel.

It is important to keep air temperature and density constant in said wind tunnels, so it is necessary to control the temperature of the airflow. This implies obtaining a uniform temperature profile in the flight or test chamber of the tunnel.

For this purpose, passive air exchange systems expelling hot air from inside the tunnel and replacing it with fresh air, such that heat is dissipated out from inside the tunnel, are known. Said fresh air is introduced by means of a gate system with various designs. This method does not allow thorough control of the temperature of the airflow inside the tunnel.

In addition, heat exchangers inside the duct for cooling the airflow, similar to water radiators used to cool an automobile engine, are known. These devices introduce high pressure losses in the airflow as the heat transfer area increases.

Aerodynamic profiles installed in bends or corners of the wind tunnel, which allow obtaining a better flow profile with the corresponding introduction of certain pressure loss, are also used. For suitable cooling, this system requires including inside said profiles a system designed to act like a heat exchanger . Finally, there are also options for cooling the inside of the wind tunnel by means of spraying water or non-deep geothermal energy, which does not allow for the optimal regulation of the temperature profile of the airflow and cannot be applied in all types of systems, furthermore being able to have unwanted negative effects such as the excessive increase of relative humidity in the air inside the tunnel.

Description of the Invention

The present invention proposes a solution to the preceding problems by means of a heat exchanger according to claim 1, a wind tunnel according to claim 14, a method for regulating the temperature of the airflow inside a wind tunnel according to claim 15 and a design method for designing an exchanger according to claim 16. The dependent claims define preferred embodiments of the invention.

A first inventive aspect provides a heat exchanger for wind tunnels, comprising:

at least a first wall and a second wall, each wall comprising at least a first edge, a second edge, a third edge and a fourth edge,

a total number (N) of tubes (T_ijk) adapted for containing a working fluid, at least a plurality of said tubes (T_ijk) making up at least one series (S_j) , the total number of series (S_j) being n_s,

at least one working fluid inlet manifold connected to a first end of at least one tube (T_ijk) , and

at least one working fluid outlet manifold connected to a second end of at least one tube (T_ijk) ,

wherein the tubes (T_ijk) of each series (S_j) form a plurality (n_Fj) of rows (F_j) and a plurality (n_cjf) of columns (C_j) distributed according to rows (F_j) , and wherein:

the distance (DT_jf) between tubes (T_ijk) of different rows

(F_j) of one and the same series (S_j) ,

the distance (DLl_jfl) between tubes (T_ijk) of the same row (F_j) and of different columns (C_j) of one and the same series (S_j) ,

the distance (DL2_jf) between tubes (T_ijk) of different rows (F_j) and the same column (C_j) , said column (C_j) being the closest to either the third edge or fourth edge with respect to the tube (T_ijk) of the same series (S_j) closest to said third edge or fourth edge,

the distance (DG_j)

o between the closest tubes (T_ijk) of adjacent series (S_j) , or

o between the tube (T_ijk) closest to the first edge or second edge and said first edge or second edge of the heat exchanger,

are parameterized such that:

- distance (DL2jf) > 0, and

distance (DGj ) > distance (DTjf) ,

such that:

the parameterization relative to the rows (F_j) mainly optimizes pressure loss of the heat exchanger, and

- the parameterization relative to the columns (C_j) mainly optimizes the total effective heat transfer area of the heat exchanger .

Throughout this document, it will be understood that the heat exchanger is comprised between at least two walls, between which the total number (N) of tubes (T_ijk) of the heat exchanger are comprised. Said exchanger is partially limited in volume by means of these walls, such that the volume defined by said walls is preferably the volume also defined by the dimensions of the wind tunnel. Airflow thereby completely strikes the total number (N) of tubes (T_ijk) of the heat exchanger.

Advantageously, the section of the wind tunnel is taken up entirely by tubes (T_ijk) of the heat exchanger, such that there is an increased area for heat transfer with the airflow without any obstacles in the path of said airflow except the tubes (T_ijk) themselves. Said tubes (T_ijk) of the heat exchanger contain a working fluid, preferably a coolant, circulating through the tubes (Ti_jk:) r allowing the heat transfer between said tubes (T_ijk) and the airflow outside these tubes (T_ijk) .

In a particular embodiment, the working fluid can be either gaseous or liquid or solid.

In a heat exchanger, said working fluid allows both cooling and heating the airflow, or any other fluid, circulating outside the tubes (T_ijk) of said heat exchanger.

Throughout this document, it will be understood that a series (S_j) is an assembly of tubes (T_ijk) in turn forming a number of rows (F_j) and columns (C_j) which can be both variable and constant between the different series.

Advantageously, the distribution of the tubes (T_ijk) in rows (F_j) and columns (C_j) in the heat exchanger, following a distribution established by means of parameters DT_jf, DLl_jf , DL2_jf and DG_j, allows thermal power exchange in the heat exchanger with minimal pressure loss.

In a particular embodiment, distances DT_jf and DG_j are considered to be transverse distances, whereas DLl_jfi and DL2_jf are longitudinal distances.

Determining the parameters allows optimal heat transfer in the heat exchanger, given that an excessively low value of parameter DT_jf causes high separation of the airflow striking the tubes (Ti_jk:) , such that a large portion of effective heat transfer area is lost, whereas if the value of said parameter is excessively high, there is a high pressure loss in the heat exchanger .

In addition, determining the parameter DL2_jf allows reducing the separation of the airflow, allowing said airflow to flow between the different rows (F_j) of each series (S_j) .

Additionally, an excessively low value of the parameter DLl_jfi causes a reduction of the heat transfer area of the heat exchanger .

Finally, determining the parameter DG_j allows optimal maintenance of the total number (N) of tubes (T_ijk) of the heat exchanger .

In a particular embodiment, the value of the parameter DG_j between consecutive series (S_j) allows a maintenance operator or unit to access each of the tubes (T_ijk) .

Advantageously, determining each of the different parameters allows improving the features of the heat exchanger. Additionally, the design of these parameters combined in the heat exchanger allows optimal heat exchange with the airflow.

Correct parameterization relative to the rows (F_j) additionally allows optimizing mainly the velocity profile of the airflow at the outlet of the heat exchanger, whereas correct parameterization relative to the columns (C_j) additionally allows optimizing mainly the temperature profile of said airflow, also at the outlet of the heat exchanger.

In a particular embodiment, the heat exchanger comprises at least two tubes (T_ijk) in fluid communication making up at least one coil ( Ri ) .

Coil ( Ri ) is understood as an attachment of tubes (T_ijk) through which the working fluid can circulate continuously.

This allows continuous passage of the working fluid between different tubes (T_ijk) of the heat exchanger, such that connections of the tubes (T_ijk) to both the at least one inlet manifold and to the at least one outlet manifold are reduced.

In a particular embodiment, the heat exchanger comprises a plurality ( ni ) of coils ( Ri ) , wherein:

- each coil ( RJ comprises a plurality (g) of groups (G_j), and

- each group (G_j) comprises a plurality (n_g) of tubes (T_ijk) , wherein each series (S_j) is formed by the same group (G_j) of each coil ( Ri ) , and wherein:

- the number (n_Fj) of rows (F_j) of each series (S_j) is the number of tubes (T_ijk) comprised in each group (G_j), and

- the number (n_cjf) of columns (C_j) of each series (S_j) is the number of coils ( Ri ) .

This distribution of tubes (T_ijk) in the heat exchanger advantageously allows a preferably correlative attachment of tubes (T_ijk) , such that the temperature profile of the working fluid allows homogenous heat transfer with the airflow.

In a particular embodiment, the number (n_g) of tubes (T_ijk) of each group (G_j) is two or three tubes (T_ijk) .

This allows optimal distribution of the total number (N) of tubes (T_ijk) in the heat exchanger, as well as an optimal ratio of the parameters DT_jf, DLl_{j f}i , DL2_jf and DG_j .

In a particular embodiment, at least one tube (T_ijk) does not allow circulation of the working fluid.

In a particular embodiment, at least one coil ( Ri ) does not allow circulation of the working fluid.

This advantageously allows a modular heat exchanger, in which the number of operative coils ( Ri ) or tubes (T_ijk) can be modified during operation of said heat exchanger according to the required specifications.

In a particular embodiment, the total number (N) of tubes (T_ijk) of the heat exchanger satisfies the following expression:

The number of tubes (T_ijk) is thereby obtained according to an expression which depends on the number of rows (F_j), the number of columns (C_j) and the number of series (n_s) of the heat exchanger, taking into account each of the series (S_j), which thereby allows obtaining a heat exchanger with more uniform velocity and temperature profiles at the outlet thereof, with lower pressure loss.

N = g.n n_g

The number of tubes (T_ijk) is thereby obtained according to an expression which depends on both the number of rows (F_j) and the number of columns (C_j) of the heat exchanger, taking into account each of the series (S_j) .

Said number of tubes, arranged according to groups with the same amount of tubes in equal coils, allows obtaining a velocity profile and temperature profile that are more uniform at the outlet of the heat exchanger, with lower pressure losses.

In a particular embodiment, the total number (N) of tubes (T_ijk) of the heat exchanger is obtained from the following expression :

A =∑' ^Nm=l ^rFmⁿAtube m r

A being the total effective heat transfer area of the heat exchanger, F_m being a heat transfer factor which allows taking into account that the airflow of the tunnel does not completely wet the total area of each tube due to the actual separation of said flow, and A_tubem being the total heat transfer area of a tube (T_ijk) .

Advantageously, the total effective heat transfer area of the exchanger according to the number of tubes obtained therefore has a value equal to or greater than the total effective transfer area value required for the design of said heat exchanger.

In a particular embodiment, the heat exchanger comprises a distance DL3_jn, which is the distance from the third edge or fourth edge to the closest tube (T_ijk) of each series (S_j), this distance preferably being the minimum distance established by construction of the heat exchanger.

This minimum distance is established according to manufacturability criteria of the heat exchanger.

Advantageously, introducing the parameter DL3_jn allows a correct manufacturing, transport and/or installation of the heat exchanger, such that the tubes (T_ijk) cannot be damaged during the process and the space available for installing said tubes (T_ijk) in the heat exchanger is maximum.

In a particular embodiment, the parameterized distances

DT_jf, DLl_jfi, DL2_jf, DL3_jn and DG_j of the heat exchanger satisfy the following expressions according to the width (B) and the length (L) of the heat exchanger:

ere o L = max(L_jf) \_{f =i} +∑* _{= 1} DL3_jn , V; = 1, ... , n_s

The maximum value out of the values obtained in each case for the parameter Ljf corresponding to each of the rows (F_j) of one and the same series (S_j), for each of the series (S_j), is taken for sizing the heat exchanger. Said maximum value advantageously allows considering the maximum value of the sum of different values of the parameters DLl_jfl and DL2jf from among those obtained for all the rows (F_j) of one and the same series (S_j), and for each of the series (S_j) .

Advantageously, these ratios allow obtaining a heat exchanger having minimum pressure loss and maximum heat transfer .

In a particular embodiment, at least one of the parameterized distances DT_jf, DLl_jfi, DL2_jf, DL3_jn and DG_j of the heat exchanger maintains a constant value.

This allows an accordingly more uniform distribution of the tubes (T_ijk) in the heat exchanger the more constant the values of the different parameters are.

In a particular embodiment, all the parameterized distances DT_jf are equal, all the parameterized distances DG_j between tubes (Ti_jk:) are equal and the number (n_Fj) of rows (F_j) of each series (S_j) is equal in the heat exchanger, and the following expression is satisfied:

B = (n_s + l)DGj + n_s(n_Fj - l)DT_jf

Advantageously, this allows a more uniform distribution of the tubes (T_ijk) in the heat exchanger and an easier manufacture thereof .

In a particular embodiment, all the parameterized distances DLl_jfi are equal, all the parameterized distances DL3_jn are equal, the number (n_Fj) of rows (F_j) of each series (S_j) is equal and the number (n_cjf) of columns (C_j) of each series (S_j) is equal, and the following expression is satisfied:

L = (n_cjf - l)DLl_jfl + max(DL2_j7)| _=i + 2DL3_jn

Advantageously, this allows a more uniform distribution of the tubes (T_ijk) in the heat exchanger and a simpler and less expensive manufacture thereof.

In a particular embodiment, the heat exchanger comprises two inlet manifolds and two outlet manifolds, wherein each of the coils (Ri) is alternately connected to a different inlet manifold and a different outlet manifold, such that the path of the working fluid has an alternating direction in each coil (Ri) ·

Each adjacent coil (Ri) is thereby alternating as regards the circulation direction of the working fluid.

This advantageously allows a more homogenous distribution of the working flow along the heat exchanger by means of the different coils (Ri) , which allows a more homogenous heat exchange with the airflow, and therefore an also more homogenous temperature profile.

This additionally allows for an increased modularity of the heat exchanger, allowing the closure of certain coils (Ri) by means of any type of closure means to operate with only some coils (Ri) of the heat exchanger, in the event of leaks in any of them, or in the event of heat transfer needs that are less than the maximum heat transfer achievable with the exchanger.

In a particular embodiment, the closure means allow the closure of at least one tube (T_ijk) , allowing the closure of said tube for maintenance work, or in the event of heat transfer needs that are less than the maximum heat transfer achievable with the exchanger.

In a particular embodiment, in the heat exchanger each tube (Ti_jk:) is a circular tube (T_ijk) with the same outer diameter (0) .

The cross section of the tube (T_ijk) is determined by the allowable range of velocities of the working fluid. The determination of the inner diameter of said tube (T_ijk) is therefore also determined by the allowable range of velocities of the working fluid when this tube (T_ijk) is circular. Finally, the outer diameter of said tube (T_ijk) is determined by criteria of maximum pressure that said tube (T_ijk) must withstand or other structural or manufacturability criteria of the heat exchanger.

Advantageously, the heat exchanger is manufactured with commercial elements, preferably circular tubes, which allows reducing the manufacturing cost.

In a particular embodiment, the total effective heat transfer area of the heat exchanger, all the tubes (T_ijk) being circular, is the following:

A = n0FHN

F being an average heat transfer factor for all the tubes (T_ijk) .

In a second inventive aspect, the invention provides a wind tunnel comprising at least one heat exchanger like the one of the first inventive aspect.

This allows the airflow circulating throughout a wind tunnel to maintain a uniform temperature profile without distorting its velocity profile and low pressure losses.

In a third inventive aspect, the invention provides a method for regulating the temperature of the airflow inside a wind tunnel comprising the following steps:

— providing at least one heat exchanger according to the first inventive aspect,

— measuring the temperature of the airflow inside the wind tunnel ,

— regulating the temperature of the airflow by modifying the number of operative tubes (T_ijk) of the heat exchanger by the closure means, the conditions of the working fluid, or the parameterized distances DT_jf, DLl_jfl, DL2_jf and DG_j .

Said modifiable conditions of the working fluid can be the temperature, composition or physical state of said fluid.

Regulation by means of modifying parameterized distances comprises both modifying the distances during the design of the system and physically modifying the arrangement of at least one tube (Ti_jk:) once all the tubes (T_ijk) are installed.

Regulation of the temperature of an airflow in a wind tunnel allows controlling the temperature and density of said airflow, such that both the testing and flight conditions inside the wind tunnel are homogenous and more closely adjusted to the corresponding real situation. In a particular embodiment, the step of regulating the temperature of the airflow is performed by modifying the parameterized distances DT_jf, DLl_{j f}i , DL2_jf, DL3_jn and DG_j .

In a fourth inventive aspect, the invention provides a design method for designing a heat exchanger according to the first inventive aspect for a wind tunnel comprising the following steps:

defining the dimensions of the heat exchanger, said dimensions being width (B) , height (H) and length (L) , - determining the necessary total effective heat transfer area (A) of the heat exchanger as well as the heat transfer factor (F_m) and the total heat transfer area (A_tube _m) , of each tube (T_ijk) ,

determining the total number (N) of tubes (T_ijk) of the heat exchanger by means of the following expression :

_A — yN r Λ

n Διπι=1 ^rmⁿtube m r

determining the total number (n_s) of series (S_j) , the total number (n_Fj) of rows (F_j) of each series (S_j) , and the total number (n_Cjf) of columns (C_j) of each series (S_j) ,

- determining the following parameters :

o the distance (DT_jf) between tubes (T_ijk) of different rows (F_j) of one and the same series (S_j) , o the distance (DLl_jfl) between tubes (T_ijk) of the same row (F_j) and of different columns (C_j) of one and the same series (S_j) ,

o the distance (DL2_jf) between tubes (T_ijk) of different rows (F_j) and the same column (C_j) , said column (C_j) being the closest to either the third edge or fourth edge with respect to the tube (T_ijk) of the same series (S_j) closest to said third edge or fourth edge ,

o the distance (DG_j)

^■ between the closest tubes (T_ijk) of adjacent series (S_j) , or

■ between the tube (T_ijk) closest to the first edge or second edge and said first edge or second edge of the heat exchanger,

o the distance (DL3_jn) from the third edge or fourth edge to the closest tube (T_ijk) of each series (S_j) according to the following expressions:

o Lj_f

^{DL 1}jfi ) + ^{DL 2}jf] . = 1 n_Fj and V; = 1 n_s

o L = max(L_jf) \_f=i +∑*₌₁DL3_jn , V; = \, ... , n_s

The total heat transfer area (A_{tube m}) of a tube (T_ijk) is defined depending on the section of each tube as well as the total number (N) of tubes (T_ijk) .

Additionally, once the step of determining the specified parameters according to the preceding expressions has been performed, the correct determination of the total number (N) of tubes (Ti_jk:) is checked by means of the expression:

> ⁿcjf

Advantageously, determining the parameters DT_jf, DLl_jfi, DL2_jf, DL3_jn, DG_j, n_s, n_Fj and nc_jf allows for the design of a heat exchanger having optimal heat transfer with the airflow inside the wind tunnel and low pressure loss.

In a particular embodiment, the design method further comprises the step of determining the total number (ni) of coils (Ri) , the number (g) of groups (G_j) and the number (n_g) of tubes (Ti_jk:) in each group (G_j), prior to the step of determining the different parameters DT_jf, DLl_jfi, DL2_jf, DL3_jn and DG_j.

This advantageously allows a more uniform distribution of the tubes (T_ijk) in the heat exchanger and a simpler and less expensive manufacture thereof.

All the features and/or steps of methods described in this specification (including the claims, description and drawings) can be combined in any combination, except in combinations of such mutually exclusive features.

Description of the Drawings The foregoing and other features and advantages of the invention will become clearer based on the following detailed description of a preferred embodiment given solely by way of non-limiting illustrative example in reference to the attached drawings .

Figure 1 shows a perspective view of an embodiment of the heat exchanger.

Figure 2A shows a front view of an embodiment of the heat exchanger .

Figure 2B shows a plan view of section A-A of Figure 2A.

Figure 2C shows a detail view of Figure 2B.

Figure 3 shows a front view of an embodiment of the heat exchanger .

Figure 4 shows a diagram of the layout of an embodiment of the heat exchanger inside the wind tunnel.

Figures 5A and 5B show the comparison for the temperature profile contours of the fluid in the tested heat exchangers.

Figures 6A and 6B show the comparison for the velocity profile contours of the fluid in the tested heat exchangers.

Detailed Description of a Preferred Embodiment of the Invention

The following nomenclature will be used in the following detailed description:

- Coil: Ri

- Group: G_j

Series: S_j

Tube: T_ijk

Total number of coils: ni

Total number of groups: g

- Number of tubes per group: n_g

Rows : F_j

Columns: C_j

Total number of rows(F_j) in each series (S_j) : n_Fj

Total number of columns in each series (S_j) distributed according to rows (F_j) : n_cjf Total number of series: n_s

Figure 1 shows a heat exchanger (1) according to a particular embodiment of the invention, envisaged for being installed in a wind tunnel (2) .

Said heat exchanger (1) comprises a first wall (3) as a lower wall and a second wall (4) as an upper wall. The airflow to be cooled coming from the wind tunnel (2) enters the heat exchanger (1) according to the direction depicted in Figure 1, i.e., from the edge (9) of the heat exchanger (1) towards the edge (10) of the heat exchanger (1) .

In this embodiment, the number (ni) of coils (Ri) is 55, each of said coils (Ri) comprising a total (g) of 6 groups (G_j), and each of these groups (G_j) comprising a number (n_g) of 3 tubes (T_ijk) .

Said arrangement of tubes (T_ijk) makes up a total of 6 series (S_j), each of said series (S_j) comprising a total (n_Fj) of 3 rows (F_j), the number of rows (F_j) being the number (n_g) of tubes (Ti_jk:) of each group (G_j), and also comprising a total (n_cjf) of 55 columns (C_j), said number of columns (C_j) being the number (ni) of coils (Ri) .

The total number (N) of tubes (T_ijk) in this particular example is 990 tubes, according to the described arrangement.

The value of the parameters N, n_Fj, n_g, n_cjf, F_j, S_j, G_j, C_j, ni are always integer values.

Said tubes (T_ijk) all have a cylindrical section, with an outer diameter of 28 mm in this particular example.

The heat exchanger (1) also comprises two inlet manifolds (5) and two outlet manifolds (6) which are alternately connected to each of the coils (Ri) . The odd-numbered coils (Ri) are thereby connected to the inlet manifold (5) located on the left side of Figure 1 and to the outlet manifold (6) located on the right side of Figure 1, whereas the even-numbered coils (Ri) are connected to the remaining inlet manifold (5) and outlet manifold ( 6 ) .

The working fluid circulates through the inside of the coils (Ri) and accesses said coil (Ri) through the inlet manifold (5) and exits the coil ( Ri ) through the outlet manifold (6) .

According to said arrangement of connections of the coils ( Ri ) to the inlet manifolds (5) and outlet manifolds (6) an alternating path of the working fluid through the even-numbered and odd-numbered coils ( Ri ) is obtained.

Figure 2A shows a front view of an embodiment of a heat exchanger (1) limited by means of a first wall (3) as a lower wall and a second wall (4) as an upper wall, said walls (3, 4) defining the height (H) of the heat exchanger (1) .

In this particular embodiment, said height (H) has a value of 3 m.

This drawing shows the first coil ( Ri ) of the heat exchanger (1) formed by tubes (T_ijk) attached to one another by means of elbows. Said elbows allow the fluid communication both between tubes (T_ijk) of the same group ( G_j ) and between groups

These elbows are outside the airflow, being located outside the walls (3, 4) of the heat exchanger. This also occurs with the inlet manifolds (5) and outlet manifolds (6) . This allows the airflow to find no obstacles during its passage with the exception of the tubes (T_ijk) , such that pressure loss is minimized.

Figure 2B shows a plan view of section A-A made on the front view of Figure 2A.

Said plan view shows the remaining dimensions of the heat exchanger (1), i.e., its width (B) and length (L) . In this particular embodiment, the width (B) has a value of 6 m and the length (L) has a value of 3.5 m.

Figure 2B also shows the arrangement of the 55 coils ( Ri ) and the 6 series (S_j) they form. The different groups (G_j) making up the series (S_j) are also observed in each of the series (S_j) . As can be seen, a series (S_j) is the cluster of the same group (G_j) of each coil ( RJ . For example, series ( Si ) is the assembly of group ( Gi ) of the 55 coils making up the heat exchanger (1) .

The arrangement of each tube (T_ijk) depending on the row

(F_j) and column (C_j) to which it belongs is also depicted in Figure 2B, where both the arrangement between different series (S_j) and the shifted distribution of rows (F_j) and columns (C_j) according to a parameterization described in detail below are observed .

Figure 2C shows a detail (C) taken from the plan view of the section of Figure 2B.

This particular embodiment shows the different parameters defining the distribution of the tubes (T_ijk) in the heat exchanger .

First, this detail partially shows two series (S_j), series

S₅ and S₆ in this embodiment, and the different groups (G_j) in each of them. Each series (S_j) is formed by 3 rows (F_j) and in them a maximum of 10 columns (C_j) are shown.

The dimensioned parameters in this particular embodiment are DT_jf, DLl_jfi, DL2_jf and DG_j, all of them being constant between different series (S_j), with the exception of the values of DL2_jf in each series (S_j) , which takes a value of zero for the odd- numbered rows (Fi and F₃) of each series and a constant value for the even-numbered rows (F₂) .

First, DT_jf defines the distance existing between two rows

(F_j) of one and the same series (S_j) . In this particular example, said distance has a value of 112 mm, such that it allows a machine or operator access to carry out the maintenance of each of the tubes (T_ijk) of the even-numbered rows (F₂) of each series (S_j) . This distance also allows forming a longitudinal duct, i.e., in the airflow passage direction, for passage of said airflow .

The distance DLl_jfi defines the distance existing between two tubes (Ti_jk:) of one and the same row (F_j), said two tubes (Ti_jk:) of one and the same row (F_j) always being perfectly aligned. The value of the distance DLl_jfi is 59 mm in this particular embodiment.

This distance allows the airflow impacting both tubes (T_ijk) to follow a path suitable for making better use of the heat transfer area of the tube (T_ijk) located behind the previous one.

The distance DL2_jf defines the distance existing between two tubes (T_ijk) of two different rows (F_j) and the same column (C_j) , said column (C_j) being the closest to the third edge (9) with respect to the tube (T_ijk) of the same series (S_j) closest to said third edge (9) . Despite the fact that the columns (C_j) are shifted in Figure 2C, they match up to one another one-by- one. Figure 2B shows the arrangement of a column, i.e., a coil (Ri) . The value of the distance DL2_jf is 0 mm for the odd- numbered rows (Fi and F₃) and 84 mm for the even-numbered rows (F₂) in this particular embodiment.

This distance allows the airflow to strike a larger surface of tubes (Ti_jk:) r reducing separation of the flow, such that heat transfer increases and pressure loss of the exchanger (1) decreases .

The distance DG_j defines the distance which exists between the two closest tubes (T_ijk) of two consecutive series (S_j) . The distance DG_j also defines the distance existing between the tubes (Ti_jk:) of the rows (F_j) located at the ends of the distribution of the total number (N) of tubes (T_ijk) and the edges (7, 8) of the exchanger (1), located on the left and right sides of Figures 2B and 2C. The value of the distance DG_j is 665 mm in this particular embodiment.

This distance allows a machine or operator to access the tubes (T_ijk) and to move freely for the maintenance of each of the tubes (T_ijk) of the odd-numbered rows (F_x and F₃) of each series (S_j) . This distance also allows forming a longitudinal duct, i.e., in the airflow passage direction, for passage of said airflow.

The parameter DL3_jn is also dimensioned in a particular embodiment .

Said distance DL3_jn defines the distance between the edges

(9, 10) of the heat exchanger (1) and the closest tube (T_ijk) in each case.

This distance is taken during parameterization, in a normal manner, as the minimum distance necessary for the correct construction and manufacture of the heat exchanger (1) . In this particular embodiment, DL3_jn takes a value of 115 mm. Figure 3 shows a front view of the particular embodiment of the heat exchanger (1) described in the preceding drawings.

This drawing shows the situation of the upper and lower walls (3, 4) as well as one of the coils ( Ri ) connected to the inlet manifold (5) and to the outlet manifold (6) .

Said drawing also shows the connection between the different tubes (T_ijk) making up the coil, by means of elbows, and the parameterization related with the ducts which allow passage of airflow as well as maintenance of each tube (T_ijk) by both an operator and/or by a machine adapted for this purpose.

Finally, Figure 4 shows a diagram of a wind tunnel (2) through which airflow circulates. A heat exchanger (1) already installed in said wind tunnel (2) is depicted.

It can be seen how, in the operational position, the heat exchanger (1) has fluidic connections between tubes (T_ijk) and the inlet manifolds (5) and outlet manifolds (6) located outside the actual duct of the wind tunnel (2) through which airflow circulates . Tests and simulations

In order to prove the importance of the parameterization of the mentioned variables (DT_jf, DLl_{j f}i , DL2_jf, DL3_jn, DG_j, n_s, n_Fj and n_Cjf) , especially the influence of the parameters DT_jf, DL2_jf, and DG_j in the performance of the heat exchanger, several tests and simulations have been carried out as to compare the performance results of different heat exchangers while varying the values of said parameters . These tests and simulations have been carried out with Computational Fluid Dynamics (CFD) software, and consist of comparing the pressure losses and temperature drops of the studied heat exchangers, in order to establish the behaviour and performance differences of said heat exchangers depending on the values given to the different parameters already mentioned; i.e. parameters DT_jf, DG_j and DL2_jf. Two different heat exchangers with different values of such parameters have been studied. The first heat exchanger (HE1) is the one disclosed in the preferred embodiment already described, with the given parameters values, whereas the second heat exchanger (HE2) corresponds to a known heat exchanger with a classical distribution of tubes, wherein said tubes are arranged as an aligned tube bank, having equal longitudinal and equal transverse distances between tubes. The values of the parameters of both heat exchangers are as follows:

Two different comparisons have been tested, and are shown in Figures 5a, 5b, 6a and 6b. For both cases, the airflow enters the heat exchanger from the top of the figures, and exits said heat exchanger from the bottom of said figures. Figures 5A and 5B show the temperature profile contours of the fluid in the tested heat exchangers. Results of the temperature evolution of the fluid of HE1 can be observed in Figure 5A, wherein there is a wake of cooled fluid on the outlet of the heat exchanger, stronger than the one observed for HE2 in Figure 5B, lowering the average outlet temperature. Consequently, the heat transfer is higher for HE1, which proves that the parameters conditions given in the preferred embodiment improve the performance of the known heat exchanger HE2. Figures 6A and 6B show the velocity profile contours of the fluid in the same tested heat exchangers. Results of the velocity distribution of the fluid of HE1 can be observed in Figure 6A, wherein the wake of the flow for each of the two sets of tubes is slightly wider than the one shown for each of the six sets of tubes of HE2, which can be observed in Figure 6B, suggesting a higher pressure loss for this area in the distribution with two sets of tubes (HE1) . These two sets of tubes can potentially yield higher local pressure losses than the equally spaced tubes in the distribution of HE2. However, due to the parameterization performed in HE1, related to the values of DG, DT and DL2, the local pressure losses in the passages wherein DG is measured will be considerably lower for HE1. Consequently, such a distribution of tubes as the one provided in HE1 can yield higher local pressure losses in the regions affected by the wake of the flow, but a lower overall pressure loss, which proves that the parameters conditions given in this example (i.e. in the present invention) improve the performance of a heat exchanger.

The following table also presents the results obtained from the CFD simulations in the per-unit system:

Heat exchanger Pressure losses [p.u.] Temperature drop [p.u.]

HE1 0, 93 1,09

HE2 1 1

As shown in the table, HE1, i.e. the heat exchanger of the preferred embodiment, has lower pressure losses while improving its temperature drop, thus improving its heat exchanger performance .

Consequently, the parameterization of a heat exchanger according to the first inventive aspect provides a heat exchanger wherein the heat exchange with the fluid is higher, while resulting in lower pressure losses.

Additional remarks

The present invention is also directed to: [1] A heat exchanger (1) for wind tunnels (2), comprising:

at least a first wall (3) and a second wall (4), each wall (3, 4) comprising at least a first edge (7), a second edge (8), a third edge (9) and a fourth edge (10),

a total number (N) of tubes (T_ijk) adapted for containing a working fluid, at least a plurality of said tubes (T_ijk) making up at least one series (S_j), the total number of series (S_j) being (n_s) ,

- at least one working fluid inlet manifold (5) connected to a first end of at least one tube (T_ijk) , and

at least one working fluid outlet manifold (6) connected to a second end of at least one tube (T_ijk) ,

wherein the tubes (T_ijk) of each series (S_j) form a plurality ( n^_j ) of rows (F_j) and a plurality (n_Cjf) of columns (C_j) distributed according to rows (F_j), and wherein:

the distance (DT_jf) between tubes (T_ijk) of different rows (F_j) of one and the same series (S_j),

the distance (DLl_{j f}i ) between tubes (T_ijk) of the same row (F_j) and of different columns (C_j) of one and the same series ( S_j ) ,

the distance (DL2_jf) between tubes (T_ijk) of different rows (F_j) and the same column (C_j), said column (C_j) being the closest to either the third edge (9) or fourth edge (10) with respect to the tube (T_ijk) of the same series (Sj) closest to said third edge (9) or fourth edge (10), the distance (DG_j)

o between the closest tubes (T_ijk) of adjacent series (S_j), or

o between the tube (T_ijk) closest to the first edge or second edge (7, 8) and said first edge or second edge (7, 8) of the heat exchanger (1),

are parameterized such that:

the parameterization relative to the rows (F_j) mainly optimizes pressure loss of the heat exchanger (1), and the parameterization relative to the columns (C_j) mainly optimizes the total effective heat transfer area of the heat exchanger (1) .

[2] The heat exchanger (1) according to [1], wherein at least two tubes (T_ijk) are in fluid communication, making up at least one coil (Ri) .

[3] The heat exchanger (1) according to [2], comprising a plurality (ni) of coils (Ri) , wherein:

- each coil (RJ comprises a plurality (g) of groups (G_j), and

- each group (G_j) comprises a plurality (n_g) of tubes (T_ijk) , wherein each series (S_j) is formed by the same group (G_j) of each coil (Ri) , and wherein:

- the number (n_Fj) of rows (F_j) of each series (S_j) is the number of tubes (T_ijk) comprised in each group (G_j), and the number (n_cjf) of columns (C_j) of each series (S_j) is the number of coils (Ri) .

[4] The heat exchanger (1) according to any of [1-3], wherein the total number (N) of tubes satisfies the expression:

[5] The heat exchanger (1) according to [3], wherein the total number (N) of tubes satisfies the expression:

N = g.n n_g

[6] The heat exchanger (1) according to any of [1-5], wherein the total number (N) of tubes (T_ijk) of the heat exchanger (1) is obtained from the following ratio:

A ∑m=l ^m^tube m r

A being the total effective heat transfer area of the heat exchanger (1), F_m a heat transfer factor and A_tubem the total heat transfer area of a tube (T_ijk) .

[7] The heat exchanger (1) according to any of [1-6], wherein the distance (DL3_jn) is the distance from the third edge or fourth edge (9, 10) to the closest tube (T_ijk) of each series (S_j), this distance preferably being the minimum distance established by construction of the heat exchanger (1) .

[8] The heat exchanger (1) according to claim 7, wherein the parameterized distances DT_jf, DLl_{j f}i , DL2_jf, DL3_jn and DG_j of said heat exchanger (1) satisfy the following expressions according to the width (B) and the length (L) of the heat exchanger (1) :

o Ljf = [(∑" f ¹ DLljfi + DL2jf] , V/ = 1, ... , n_Fj and V = 1, ... , n_s , where o L = max(L_jf) \_{f =i} +∑* _{= 1} DL3_jn , V; = \, ... , n_s

[9] The heat exchanger (1) according to [8], wherein at least one of the parameterized distances DT_jf, DLl_jfi, DL2_jf, DL3_jn and DG_j maintains a constant value.

[10] The heat exchanger (1) according to [8] or [9], wherein all the parameterized distances DT_jf are equal, all the parameterized distances DG_j between tubes (T_ijk) are equal and the number (n^_j) of rows (F_j) of each series (S_j) is equal, and the following expression is satisfied:

B = (% + DDGj + n_s(n_Fj - l)DT_jf

[11] The heat exchanger (1) according to any of [8-10], wherein all the parameterized distances DLl_{j f}i are equal, all the parameterized distances DL3_jn are equal, the number (n_Fj) of rows (F_j) of each series (S_j) is equal and the number (n_cjf) of columns (C_j) of each series (S_j) is equal, and where the following expression is satisfied:

L = (n_cjf - l)DLl_jfl + max(DL2_j7)| _=i + 2DL3_jn

[12] The heat exchanger (1) according to any of [2-11], wherein said heat exchanger (1) comprises:

- two inlet manifolds (5), and

- two outlet manifolds (6)

wherein each of the coils ( Ri ) is alternately connected to a different inlet manifold (5) and a different outlet manifold (6), such that the path of the working fluid has an alternating direction in each coil ( Ri ) .

[13] The heat exchanger (1) according to any of [1-12], wherein each tube (T_ijk) is a circular tube with the same outer diameter (Φ) ·

[14] A wind tunnel (2) comprising at least one heat exchanger (1) according to any of [1-13] .

[15] A method for regulating the temperature of airflow inside a wind tunnel (2) comprising the following steps:

- providing at least one heat exchanger (1) according to any of [1-13],

- measuring the temperature of the airflow inside the wind tunnel (2),

regulating the temperature of the airflow by modifying the number of operational tubes (T_ijk) of the heat exchanger (1) by closure means, the conditions of the working fluid, or the parameterized distances DT_jf, DLl_{j f}i , DL2_jf and DG_j .

[16] A design method for designing a heat exchanger (1) for a wind tunnel (2) according to any of [7-13] comprising the following steps:

defining the dimensions of the heat exchanger (1), said dimensions being width (B) , height (H) and length (L) , - determining the total effective heat transfer area ( A) of the heat exchanger (1) necessary as well as the heat transfer factor (F_m) and the total heat transfer area (A _Ube _m) of each tube (T_ijk) ,

determining the total number (N) of tubes (T_ijk) of the heat exchanger (1) by means of the following expression:

A — yN c A

n Διπι=1 ^rmⁿtube m r

determining the total number (n_s) of series (S_j), the total number (n_Fj) of rows (F_j) of each series (S_j), and the total number (n_Cjf) of columns (C_j) of each series (S_j),

- determining the following parameters:

o the distance (DT_jf) between tubes (T_ijk) of different rows (F_j) of one and the same series (S_j), o the distance (DLl_{j f}i ) between tubes (T_ijk) of the same row (F_j) and of different columns (C_j) of one and the same series (S_j), o the distance (DL2_jf) between tubes (T_ijk) of different rows (F_j) and the same column (C_j), said column (C_j) being the closest to either the third edge (9) or fourth edge (10) with respect to the tube (T_ijk) of the same series (S_j) closest to said third edge (9) or fourth edge (10),

o the distance (DG_j),

^■ between the closest tubes (T_ijk) of adjacent series ( S_j ) , or

■ between the tube (T_ijk) closest to the first edge or second edge (7, 8) and said first edge or second edge (7, 8) of the heat exchanger (1), o the distance (DL3_jn) from the third edge or fourth edge (9, 10) to the closest tube (T_ijk) of each series (S_j)

according to the following expression:

o L = max(L_jf) \_f=i +∑*₌₁DL3_jn , V; = 1, ... , n_s

[17] The design method for designing a heat exchanger (1) according to [16], further comprising the step of determining the total number ( ni ) of coils ( Ri ) , the number (g) of groups (G_j) and the number (n_g) of tubes (T_ijk) in each group (G_j), prior to the step of determining the different parameters DT_jf, DLl_{j f}i , DL2_jf, DL3_jn and DG_j.

Claims

1.- A heat exchanger (1) for wind tunnels (2), comprising: at least a first wall (3) and a second wall (4), each wall (3, 4) comprising at least a first edge (7), a second edge

(8), a third edge (9) and a fourth edge (10),

at least one working fluid inlet manifold (5) connected to a first end of at least one tube (T_ijk) , and

wherein the tubes (T_ijk) of each series (S_j) form a plurality (n_Fj) of rows (F_j) and a plurality (n_cjf) of columns (C_j) distributed according to rows (F_j), and wherein:

the distance (DT_jf) between tubes (T_ijk) of different rows

(F_j) of one and the same series (S_j),

- the distance (DLl_{j f}i ) between tubes (T_ijk) of the same row

(F_j) and of different columns (C_j) of one and the same series ( S_j ) ,

o between the closest tubes (T_ijk) of adjacent series (S_j), or

are parameterized such that:

- distance (DL2jf) > 0, and distance (DGj ) > distance (DTjf) ,

such that:

the parameterization relative to the rows (F_j) mainly optimizes pressure loss of the heat exchanger (1), and - the parameterization relative to the columns (C_j) mainly optimizes the total effective heat transfer area of the heat exchanger (1) .

2. - The heat exchanger (1) according to claim 1, wherein at least two tubes (T_ijk) are in fluid communication, making up at least one coil (Ri) .

3. - The heat exchanger (1) according to claim 2, comprising a plurality (ni) of coils (Ri) , wherein:

- each coil (Ri) comprises a plurality (g) of groups (G_j), and

- the number (n_Fj) of rows (F_j) of each series (S_j) is the number of tubes (T_ijk) comprised in each group (G_j), and - the number (n_cjf) of columns (C_j) of each series (S_j) is the number of coils (Ri) .

4. - The heat exchanger (1) according to any of the preceding claims, wherein the total number (N) of tubes satisfies the expression

5.- The heat exchanger (1) according to claim 3, wherein the total number (N) of tubes satisfies the expression:

N = g.n n_g

6.- The heat exchanger (1) according to any of the preceding claims, wherein the total number (N) of tubes (T_ijk) of the heat exchanger (1) is obtained from the following ratio:

A ∑m=l ^m^tube m r

7. - The heat exchanger (1) according to any of the preceding claims, wherein the distance (DL3_jn) is the distance from the third edge or fourth edge (9, 10) to the closest tube (Ti_jk:) of each series (S_j), this distance preferably being the minimum distance established by construction of the heat exchanger (1) .

8. - The heat exchanger (1) according to claim 7, wherein the parameterized distances DT_jf, DLl_jfi, DL2_jf, DL3_jn and DG_j of said heat exchanger (1) satisfy the following expressions according to the width (B) and the length (L) of the heat exchanger (1) :

o L_jf = [(∑" f ¹ DLl + DL2_jf] , V/ = 1, ... , n_Fj and V = 1, ... , n_s , where o L = max(L_jf) , V; = 1, ... , n_s

9. - The heat exchanger (1) according to claim 8, wherein at least one of the parameterized distances DT_jf, DLl_jfi, DL2_jf, DL3_jn and DG_j maintains a constant value.

10. - The heat exchanger (1) according to claims 8 or 9, wherein all the parameterized distances DT_jf are equal, all the parameterized distances DG_j between tubes (T_ijk) are equal and the number (n_Fj) of rows (F_j) of each series (S_j) is equal, and the following expression is satisfied:

B = (% + DDG_j + n_s(n_Fj - l)DT_jf

11. - The heat exchanger (1) according to any of claims 8 to 10, wherein all the parameterized distances DLl_jfi are equal, all the parameterized distances DL3_jn are equal, the number (n_Fj) of rows (F_j) of each series (S_j) is equal and the number (n_cjf) of columns (C_j) of each series (S_j) is equal, and where the following expression is satisfied:

L = (n_cjf - l)DLl_jfl + max(DL2_j7)| _=i + 2DL3_jn 12.- The heat exchanger (1) according to any of claims 2 to

11, wherein said heat exchanger (1) comprises:

- two inlet manifolds (5), and - two outlet manifolds (6)

13. - The heat exchanger (1) according to any of the preceding claims, wherein each tube (T_ijk) is a circular tube with the same outer diameter (Φ) .

14. - A wind tunnel (2) comprising at least one heat exchanger (1) according to any of the preceding claims.

15. - A method for regulating the temperature of airflow inside a wind tunnel (2) comprising the following steps:

- providing at least one heat exchanger (1) according to any of claims 1 to 13,

- measuring the temperature of the airflow inside the wind tunnel (2 ) ,

- regulating the temperature of the airflow by modifying the number of operational tubes (T_ijk) of the heat exchanger (1) by closure means, the conditions of the working fluid, or the parameterized distances DT_jf, DLl_{j f}i , DL2_jf and DG_j .

16. - A design method for designing a heat exchanger (1) for a wind tunnel (2) according to any of claims 7 to 13 comprising the following steps:

defining the dimensions of the heat exchanger (1), said dimensions being width (B) , height (H) and length (L) , determining the total effective heat transfer area ( A) of the heat exchanger (1) necessary as well as the heat transfer factor (F_m) and the total heat transfer area (A _Ube _m) of each tube (T_ijk) ,

- determining the total number (N) of tubes (T_ijk) of the heat exchanger (1) by means of the following expression:

A — yN c A

n Διπι=1 ^rmⁿtube m r

determining the total number (n_s) of series (S_j), the total number (n_Fj) of rows (F_j) of each series (S_j), and the total number (n_Cjf) of columns (C_j) of each series (S_j), determining the following parameters:

o the distance (DT_jf) between tubes (T_ijk) of different rows (F_j) of one and the same series (S_j), o the distance (DLl_{j f}i ) between tubes (T_ijk) of the same row (F_j) and of different columns (C_j) of one and the same series (S_j ) ,

o the distance (DL2_jf) between tubes (T_ijk) of different rows (F_j) and the same column (C_j), said column (C_j) being the closest to either the third edge (9) or fourth edge (10) with respect to the tube (T_ijk) of the same series (S_j) closest to said third edge (9) or fourth edge (10),

o the distance (DG_j),

^■ between the closest tubes (T_ijk) of adjacent series (S_j) , or

^■ between the tube (T_ijk) closest to the first edge or second edge (7, 8) and said first edge or second edge (7, 8) of the heat exchanger (1), o the distance (DL3_jn) from the third edge or fourth edge (9, 10) to the closest tube (T_ijk) of each series

(S_j)

according to the following expression:

o L = max(L_jf) | _=i +∑ ₌₁ DL3_jn , V = 1, ... , n_s

17.- The design method for designing a heat exchanger (1) according to claim 16, further comprising the step of determining the total number ( ni ) of coils ( Ri ) , the number (g) of groups (G_j) and the number (n_g) of tubes (T_ijk) in each group (G_j), prior to the step of determining the different parameters DT_jf, DLl_jf!, DL2_jf, DL3_jn and DG_j.