Method for designing evaporator

Abstract

Provided is a method for designing an evaporator, whereby an index for evaluating performance is provided. This method for designing an evaporator (5) applied to a turbo refrigerator having a refrigeration capacity of 150-1200 USRt, wherein if the number of stages in the vertical direction of heat transfer tubes (17) in each heat transfer tube group (16) is 11-26, the interval between heat transfer tubes (17) belonging to the same stage in each heat transfer tube group (16) is 3.95-9.95 mm, and the interval between heat transfer tube groups (16) is 15.45-54.97 mm, at least one selected from among the dimensions of each heat transfer tube (17), the arrangement of the plurality of heat transfer tubes (17), and the arrangement of the heat transfer tube groups (16) is designed such that an index S falls within a prescribed numeric range, with the index S being calculated on the basis of the dimensions of a pressure vessel (11), the dimensions of each heat transfer tube (17), the arrangement of the plurality of heat transfer tubes (17), the arrangement of the heat transfer tube groups (16), the refrigeration capacity of the turbo refrigerator, and the physical properties of a refrigerant.

Description

Evaporator design method

[0001] The present disclosure relates to a method for designing an evaporator.

[0002] In the evaporator of a turbo chiller, bundling multiple heat transfer tubes into a single heat transfer tube group causes refrigerant gas to stagnate, reducing the heat transfer coefficient outside the tubes. In response to this, for example, Patent Document 1 discloses a configuration in which the heat transfer tubes are divided into multiple heat transfer tube groups and the heat transfer tube groups are spaced apart to improve the escape of refrigerant bubbles and increase the heat transfer coefficient.

[0003] Patent No. 3572234

[0004] Other possible methods for increasing the heat transfer coefficient include reducing the number of heat transfer tube rows or increasing the horizontal spacing between the heat transfer tubes. However, due to the required refrigeration capacity and the size of the evaporator pressure vessel (shell), there are restrictions on the number of heat transfer tube rows and the spacing between the heat transfer tubes (between heat transfer tube groups). Furthermore, even if these restrictions are met, Patent Document 1 does not mention a method for evaluating the performance of the evaporator.

[0005] The present disclosure has been made in view of the above circumstances, and aims to provide a method for designing an evaporator in which an index for evaluating performance is provided.

[0006] In order to solve the above problems, the evaporator design method of the present disclosure employs the following measures.

[0007] A method for designing an evaporator according to one embodiment of the present disclosure is a method for designing an evaporator applied to a turbo chiller with a refrigeration capacity of 150 USRt or more and 1200 USRt or less, the evaporator comprising: a pressure vessel having an axis extending in a first direction along a horizontal direction and into which a refrigerant is guided; and a plurality of heat transfer tubes having axes extending in the first direction and housed inside the pressure vessel, the plurality of heat transfer tubes constituting a plurality of heat transfer tube groups arranged along the horizontal direction at intervals in a second direction perpendicular to the first direction, is set to 11 or more and 26 or less stages, the distance between the heat transfer tubes belonging to the same stage in each heat transfer tube group is set to 3.95 mm or more and 9.95 mm or less, and the distance between the heat transfer tube groups is set to 15.45 mm or more and 54.97 mm or less, at least one of the dimensions of each heat transfer tube, the arrangement of the plurality of heat transfer tubes, and the arrangement of the heat transfer tube group is designed so that an index S calculated based on the dimensions of the pressure vessel, the dimensions of each heat transfer tube, the arrangement of the plurality of heat transfer tubes, the arrangement of the heat transfer tube group, the refrigeration capacity of the turbo chiller, and the physical properties of the refrigerant falls within a predetermined numerical range.

[0008] According to the present disclosure, an index for evaluating the performance of an evaporator can be provided.

[0009] Fig. 3 is an overall view of a turbo chiller including an evaporator according to an embodiment of the present disclosure. Fig. 4 is a side view of an evaporator according to an embodiment of the present disclosure. Fig. 5 is a cross-sectional view taken along line III-III shown in Fig. 2. Fig. 6 is a partially enlarged view of the heat transfer tube group shown in Fig. 3.

[0010] Hereinafter, a method for designing an evaporator according to an embodiment of the present disclosure will be described with reference to the drawings.

[0011] [Overall Configuration of the Centrifugal Chiller] As shown in FIG. 1 , the centrifugal chiller 1 is configured as a unit device including a centrifugal compressor 2 that compresses a refrigerant, a condenser 3 that condenses the refrigerant compressed by the centrifugal compressor 2, an expansion valve 4 that expands the refrigerant condensed by the condenser 3, an evaporator 5 that evaporates the refrigerant expanded by the expansion valve 4, piping connecting the various devices, and other auxiliary equipment.

[0012] The turbo compressor 2 and the upper part of the condenser 3 are connected by a discharge pipe 6. The discharge pipe 6 is a pipe for guiding the refrigerant compressed by the turbo compressor 2 to the condenser 3.

[0013] The bottom of the condenser 3 and the bottom of the evaporator 5 are connected by a refrigerant pipe 7. The refrigerant pipe 7 is a pipe for guiding the refrigerant condensed in the condenser 3 to the evaporator 5.

[0014] The refrigerant pipe 7 is provided with an expansion valve 4. The expansion valve 4 is a device that expands the refrigerant that has been condensed in the condenser 3 and is flowing toward the evaporator 5.

[0015] The upper part of the evaporator 5 and the turbo compressor 2 are connected by a suction pipe 8. The suction pipe 8 is a pipe for guiding the refrigerant evaporated in the evaporator 5 to the turbo compressor 2.

[0016] The turbo compressor 2 is, for example, a centrifugal turbine compressor that is rotationally driven by an electric motor 9. The electric motor 9 is driven by, for example, an inverter unit. The turbo compressor 2 is disposed above the evaporator 5 with its rotation shaft extending substantially horizontally. The turbo compressor 2 compresses gas-phase refrigerant that is supplied from the evaporator 5 via a suction pipe 8.

[0017] The refrigerant used may be, for example, a low-pressure refrigerant used at a maximum pressure of less than 0.2 MPaG. An example of the low-pressure refrigerant is R1233zd(E).

[0018] The condenser 3 is a so-called shell-and-tube heat exchanger. The condenser 3 has a pressure vessel formed in a cylindrical shell shape with high pressure resistance. The vessel is positioned in an orientation in which the central axis extends horizontally.

[0019] The evaporator 5 is a so-called shell-and-tube heat exchanger. The evaporator 5 has a pressure vessel 11 formed in a cylindrical shell shape with high pressure resistance. The pressure vessel 11 is disposed in an orientation in which the central axis extends horizontally (first direction).

[0020] The condenser 3 and the evaporator 5 are arranged substantially parallel to each other so that the central axes of the pressure vessels extend in the same direction. In this case, the condenser 3 may be arranged at a higher position than the evaporator 5.

[0021] Here, the turbo chiller 1 of this embodiment has a refrigeration capacity of 150 USRt or more and 1200 USRt or less (527.4 kW or more and 4219.5 kW or less) (Condition 1).

[0022] [Regarding the Evaporator] As shown in FIGS. 2 and 3 , the evaporator 5 includes a pressure vessel 11 forming an outer shell, and a plurality of heat transfer tube groups 16 housed inside the pressure vessel 11 .

[0023] Each heat transfer tube group 16 has a plurality of heat transfer tubes 17. Each heat transfer tube 17 is arranged with its central axis extending in a substantially horizontal direction. The central axis of each heat transfer tube 17 extends in the same direction as the central axis of the pressure vessel 11 of the evaporator 5. A liquid to be cooled flows through the inside of each heat transfer tube 17. An example of the liquid to be cooled is water.

[0024] 3 and 4, the heat transfer tubes 17 are arranged at predetermined intervals in a direction perpendicular to the central axis (the radial direction of the heat transfer tubes 17; the up-down and left-right directions in FIG. 4). The heat transfer tubes 17 are arranged, for example, in a staggered pattern.

[0025] The number of rows of the heat transfer tubes 17 in the vertical direction in each heat transfer tube group 16 is set to 11 or more and 26 or less (condition 2).

[0026] As shown in FIG. 4 , a set of multiple heat transfer tubes 17 arranged in a row with a gap in the horizontal direction (a horizontal direction perpendicular to the central axis of the heat transfer tubes 17; left-right direction in FIG. 4 ) is considered to be "one row." The multiple heat transfer tubes 17 are arranged, for example, in a staggered pattern. The staggered pattern means that one row, consisting of multiple heat transfer tubes 17 arranged in a row with a gap in the horizontal direction, is stacked in the vertical direction while being horizontally offset from adjacent rows in the vertical direction. Note that the amount of horizontal offset is, for example, half the horizontal distance between the heat transfer tubes 17 in the same row.

[0027] As shown in Fig. 4, the distance between the heat transfer tubes 17 belonging to the same row in each heat transfer tube group 16 is set to 3.95 mm or more and 9.95 mm or less (Condition 3). The distance between the heat transfer tubes 17 does not refer to the center-to-center distance, but refers to the distance between the outer circumferential surface of a first heat transfer tube 17 and the outer circumferential surface of a second heat transfer tube 17 adjacent to the first heat transfer tube 17 in the horizontal direction (the horizontal direction substantially perpendicular to the central axis of the heat transfer tube 17; the left-right direction in Fig. 4). The outer diameter of each heat transfer tube 17 is set to, for example, 19.05 mm.

[0028] Note that the above-mentioned condition 3 does not apply to the spacing between two adjacent heat transfer tubes 17 in the same row but belonging to different heat transfer tube groups 16 .

[0029] As shown in Fig. 3, the plurality of heat transfer tube groups 16 include heat transfer tube group 16A, heat transfer tube group 16B, heat transfer tube group 16C, and heat transfer tube group 16D. Heat transfer tube group 16A, heat transfer tube group 16B, heat transfer tube group 16C, and heat transfer tube group 16D are arranged at predetermined intervals in the horizontal direction (a horizontal direction substantially perpendicular to the central axis of the heat transfer tube 17; a left-right direction in Fig. 3; a second direction). The interval between the heat transfer tube groups 16 is set to be 15.45 mm or more and 54.97 mm or less (Condition 4).

[0030] Here, the gap between the first heat transfer tube group 16 and the second heat transfer tube group 16 adjacent to the first heat transfer tube group 16 is defined as a "hole row." The distance between the heat transfer tube groups 16 corresponds to the width of the hole row. The width of the hole row is larger than the distance between the heat transfer tubes 17 in Condition 3. The hole rows are indicated by cross-hatched areas in FIG. 3. The hole rows are areas extending in the vertical direction.

[0031] The evaporator 5 according to this embodiment is designed so that the following index S falls within a predetermined range while satisfying the conditions 1 to 4 described above. Specifically, at least one of the dimensions of the heat transfer tubes 17, the arrangement of the heat transfer tubes 17 (number of stages and gaps), and the arrangement of the heat transfer tube bank 16 (gas gaps) is designed so that the index S falls within a range of 0.924 to 0.947 while satisfying the conditions 1 to 4. The index S is a formula for calculating the outside-tube heat transfer coefficient of a gas-liquid two-phase flow.

[0032] First, each letter is defined as follows: G: refrigerant mass velocity per stage [kg / m ２ ・s] G １ : refrigerant circulation flow rate per stage [kg s] A: gap area [m ２ ] d: outer diameter of heat transfer tube [m] Re Ｌ : Liquid phase Reynolds number [- (dimensionless)] μ Ｇ : saturated vapor viscosity coefficient [Pa s] μ Ｌ ρ: saturated liquid viscosity coefficient [Pa s] relative to evaporator pressure Ｇ : refrigerant gas density [kg / m ３ ]ρ Ｌ : Refrigerant liquid density [kg / m ３ ] x: Refrigerant quality (quality) [- (dimensionless)] L Ｃ : Total gap width per step [m] L Ｓ W: Length (inner dimension) of the evaporator shell (pressure vessel) [m] Ｓ W: Width (inner dimension) of the evaporator shell (pressure vessel) [m] ｄ : Total width of heat transfer tubes per stage [m]

[0033] The index S is expressed by the formula (1). ...Formula (1)

[0034] Here, Re in formula (1) Ｌ is expressed by equation (2). ...Formula (2)

[0035] Furthermore, F in formula (1) is expressed by formula (3). ...Formula (3)

[0036] Here, 1 / X in equation (3) ｔｔ is expressed by equation (4). ...Formula (4)

[0037] Here, the refrigerant quality x in equations (2) and (4) is the average value of the qualities at the refrigerant inlet and refrigerant outlet of the evaporator 5 calculated from the operating conditions of the turbo chiller 1 (condensing pressure, intermediate pressure, evaporation pressure).

[0038] The mass velocity G in equation (2) is the mass velocity of the refrigerant per stage, and the circulating flow rate G １ is divided by the gap area A.

[0039] Here, the circulating flow rate of the refrigerant G １ is calculated from the physical properties and refrigeration capacity of the refrigerant.

[0040] The gap area A is expressed by equation (5). ...Formula (5)

[0041] Here, L in formula (5) ｃ is expressed by equation (6). ...Formula (6)

[0042] The index S can be calculated using the above formulas. Specifically, the index S can be calculated from the dimensions of the pressure vessel 11 of the evaporator 5, the dimensions of the heat transfer tubes 17, the arrangement of the heat transfer tubes 17, the arrangement of the heat transfer tube bank 16, the refrigeration capacity of the turbo chiller 1, and the refrigerant properties (density and viscosity coefficient).

[0043] [Effects] According to this embodiment, the following effects are achieved.

[0044] An index S for evaluating the performance of the evaporator 5 can be provided.

[0045] Furthermore, by designing at least one of the dimensions of the heat transfer tubes 17, the arrangement of the heat transfer tubes 17 (number of stages and / or gaps), and the arrangement (gap) of the heat transfer tube group 16 so as to satisfy each condition and so that the index S falls within the numerical range of 0.924 or more and 0.947 or less, it is possible to evaluate the performance of the evaporator 5 while improving its performance.

[0046] [Additional Notes] The design method for an evaporator according to an embodiment of the present disclosure described above can be understood, for example, as follows.

[0047] A design method for an evaporator according to a first aspect of the present disclosure is a design method for an evaporator (5) applied to a turbo chiller (1) having a refrigeration capacity of 150 USRt or more and 1200 USRt or less, the evaporator comprising: a pressure vessel (11) having an axis extending in a first direction along a horizontal direction and into which a refrigerant is introduced; and a plurality of heat transfer tubes (17) having axes extending in the first direction and housed inside the pressure vessel, the plurality of heat transfer tubes constituting a plurality of heat transfer tube groups (16) arranged along the horizontal direction and at intervals in a second direction perpendicular to the first direction, and In the case where the number of stages of the heat tubes in the vertical direction is 11 to 26, the distance between the heat transfer tubes belonging to the same stage in each heat transfer tube group is 3.95 mm to 9.95 mm, and the distance between the heat transfer tube groups is 15.45 mm to 54.97 mm, at least one of the dimensions of each heat transfer tube, the arrangement of the plurality of heat transfer tubes, and the arrangement of the heat transfer tube group is designed so that an index S, which is calculated based on the dimensions of the pressure vessel, the dimensions of the plurality of heat transfer tubes, the arrangement of the plurality of heat transfer tubes, the arrangement of the heat transfer tube group, the refrigeration capacity of the turbo chiller, and the physical properties of the refrigerant, falls within a predetermined numerical range.

[0048] According to the method for designing an evaporator of this aspect, at least one of the dimensions of each heat transfer tube, the arrangement of the heat transfer tubes, and the arrangement of the heat transfer tube group is designed so that index S, which is calculated based on the dimensions of the pressure vessel, the dimensions of the plurality of heat transfer tubes, the arrangement of the heat transfer tube group, the refrigeration capacity of the turbo chiller, and the refrigerant properties, falls within a predetermined numerical range, thereby making it possible to provide an index for evaluating the performance of the evaporator.

[0049] In the method for designing an evaporator according to the second aspect of the present disclosure, in the first aspect, the index S is expressed by equation (1). ...Equation (1) where, ...Formula (2) ...Formula (3) ...Equation (4) where Re Ｌis the liquid phase Reynolds number, x is the refrigerant quality in the evaporator, μ Ｇ is the saturated vapor viscosity coefficient [Pa s] relative to the evaporator pressure, and μ Ｌ is the saturated liquid viscosity coefficient [Pa s] relative to the evaporator pressure, and ρ Ｇ is the refrigerant gas density [kg / m ３ ] and ρ Ｌ is the refrigerant liquid density [kg / m ３ ], and the predetermined numerical range of the index S is 0.924 or more and 0.947 or less.

[0050] In the method for designing an evaporator according to a third aspect of the present disclosure, in the second aspect, in the formula (2), G is the mass velocity of the refrigerant per stage [kg / m ２ s], which is the value obtained by dividing the refrigerant circulation flow rate G1 calculated from the physical properties of the refrigerant and the refrigeration capacity by the gap area A, and d is the outer diameter [m] of the heat transfer tube. ...Formula (5) ...Equation (6) and L Ｃ is the total gap width per step [m] L Ｓ is the length [m] of the pressure vessel of the evaporator Ｓ is the width of the pressure vessel of the evaporator "m" W ｄ is the total width of the heat transfer tubes per stage [m].

[0051] REFERENCE SIGNS LIST 1 Centrifugal chiller 2 Centrifugal compressor 3 Condenser 4 Expansion valve 5 Evaporator 6 Discharge pipe 7 Refrigerant pipe 8 Suction pipe 9 Electric motor 11 Pressure vessel 16 (16A, 16B, 16C, 16D) Heat transfer tube group 17 Heat transfer tube

Claims

1. A design method for an evaporator applied to a turbo chiller with a refrigeration capacity of 150 USRt or more and 1200 USRt or less, wherein the evaporator comprises: a pressure vessel having an axis extending in a first direction along the horizontal direction and into which a refrigerant is guided; and a plurality of heat transfer tubes having axes extending in the first direction and housed inside the pressure vessel, wherein the plurality of heat transfer tubes form a plurality of heat transfer tube groups arranged along the horizontal direction and at intervals in a second direction perpendicular to the first direction, wherein the number of rows of the heat transfer tubes in each heat transfer tube group in the vertical direction is 11 to 26, the spacing between the heat transfer tubes belonging to the same row in each heat transfer tube group is 3.95 mm to 9.95 mm, and the spacing between the heat transfer tube groups is 15.45 mm to 54.97 mm, a design method for an evaporator, which designs at least one of the dimensions of each heat transfer tube, the arrangement of the plurality of heat transfer tubes, and the arrangement of the heat transfer tube group so that an index S calculated based on the dimensions of the pressure vessel, the dimensions of each heat transfer tube, the arrangement of the plurality of heat transfer tubes, the arrangement of the heat transfer tube group, the refrigeration capacity of the turbo chiller, and refrigerant properties falls within a predetermined numerical range.

2. The method for designing an evaporator according to claim 1, wherein the index S is expressed by equation (1). ...Equation (1) where, ...Formula (2) ...Formula (3) ...Equation (4) where Re Ｌ is the liquid phase Reynolds number, x is the refrigerant quality in the evaporator, μ Ｇ is the saturated vapor viscosity coefficient [Pa s] relative to the evaporator pressure, and μ Ｌ is the saturated liquid viscosity coefficient [Pa s] relative to the evaporator pressure, and ρ Ｇ is the refrigerant gas density [kg / m ３ ] and ρ Ｌ is the refrigerant liquid density [kg / m ３ ], and the predetermined numerical range of the index S is 0.924 or more and 0.947 or less.

3. In the above formula (2), G is the mass velocity of the refrigerant per stage [kg / m ２ 3. The method for designing an evaporator according to claim 2, wherein d is the outer diameter [m] of the heat transfer tube, and s is a value obtained by dividing the refrigerant circulation flow rate G1 calculated from the physical properties of the refrigerant and the refrigeration capacity of the turbo chiller by the gap area A. ...Formula (5) ...Equation (6) and L Ｃ is the total gap width per step [m] L Ｓ is the length [m] of the pressure vessel of the evaporator Ｓ is the width of the pressure vessel of the evaporator "m" W ｄ is the total width of the heat transfer tubes per stage [m].

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