KR100886379B1 - Method for selecting the optimal number of passes for multipass heat exchangers - Google Patents

Abstract

The present invention provides a method for selecting an optimal number of passes for a multipass heat exchanger that exhibits high performance in designing a multipass heat exchanger by evaluating the thermal and dynamic performance of the multipass heat exchanger according to the inlet diameter and the number of passes. It has its features.

In addition, when the size of the multi-pass heat exchanger and the inlet diameter are fixed, the present invention allows the ratio of the inlet diameter to the header height of each pass to be about 0.5 to easily select the optimal number of passes without further experimentation or analysis. The present invention provides a method for selecting an optimal number of passes for a pass heat exchanger.

In addition, the present invention provides a method for selecting an optimal number of passes for a multi-pass heat exchanger to improve the efficiency of the overall multi-pass heat exchanger to maximize the practical use reliability and satisfaction.

To this end, the present invention is a multi-pass heat exchanger consisting of a plurality of passes and inlet and outlet provided in the center of each header, the selection of the number of passes using the ratio of the inlet diameter to the header height of the heat exchanger However, the ratio of the inlet diameter to the header height of each pass is to select the number of passes in the range of 0.3 ~ 0.7, and if there is a size constraint for the heat exchanger, the selection of the number of passes near 0.5 is performed. .

Multipass, Heat Exchanger, Multi-branch, Header, Height, Diameter, Selected, Thermal Performance, Dynamic Performance

Description

METHOD FOR SELECTION THE OPTIMUM NUMBER OF PASS IN THE MULTI-PASS HEAT EXCHANGER}

1 is a schematic block diagram showing for explaining a multi-pass heat exchanger according to the present invention,

Figure 2 is an exemplary view showing several multipass heat exchangers according to the number of passes implemented by the present invention,

Figure 3 is a graph of the performance change according to the ratio of the header height and the inlet diameter of the path according to the present invention.

<Description of the code | symbol about the principal part of drawing>

10: multipass heat exchanger

11: header of heat exchanger

12: inlet of heat exchanger

13: outlet of the heat exchanger

D: inlet diameter

H: header height

L: heat exchanger overall height

The present invention relates to a method for selecting an optimal number of passes for high performance in the design of a multi-pass heat exchanger,

In more detail, the thermal and dynamic performance of the multipass heat exchanger according to the inlet diameter and the number of passes are evaluated to select the optimal number of passes for the multipass heat exchanger that exhibits high performance in the design of the multipass heat exchanger. It is about.

In general, the heat exchanger used in the refrigeration air conditioner is designed to minimize the space occupied by the heat exchanger while maximizing performance.

As such, the heat exchanger that meets the design goals is a multipass multi-branch heat exchanger, but the thermal performance is greatly reduced due to uneven flow distribution due to complex flow characteristics.

In addition, there is a problem that the dynamic performance is greatly reduced due to the large pressure drop of the inlet and the outlet in the heat exchanger overdesigned to obtain the uniformity of the flow distribution.

Accordingly, in order to improve the thermal and dynamic performance of the heat exchanger, a method of investigating and optimizing heat exchanger design factors (header shape, header and channel area ratio, channel length, inlet / outlet arrangement, etc.) It has been suggested.

In particular, the double-pass heat exchanger of Japanese Patent Laid-Open Publication No. 2002-303498 has been presented, but this describes a method of improving performance by fixing two passes, and changing the number of passes to vary the inlet diameter. How to select the number of passes according to the number of passages, that is, the contents of selecting the number of passes showing the best performance by comparing the thermal performance and the flow performance at the same time in the heat exchanger having various passes according to the inlet diameter It is not.

Therefore, since the efficiency is limited to some extent in improving the thermal performance and the dynamic performance of the conventional heat exchanger, the reliability and satisfaction of practical use to apply the same is minimized.

The present invention has been made to solve the problems of the prior art as described above has the following object.

The present invention provides a method for selecting an optimal number of passes for a multipass heat exchanger that exhibits high performance in designing a multipass heat exchanger by evaluating the thermal and dynamic performance of the multipass heat exchanger according to the inlet diameter and the number of passes. The purpose is.

Another object of the present invention is to make the ratio of the inlet diameter to the header height of each pass close to 0.5 when the size and inlet diameter of the multi-pass heat exchanger are fixed so that the optimal number of passes can be simply selected without further experimentation or analysis. The present invention provides a method for selecting an optimal number of passes for a multipass heat exchanger.

It is another object of the present invention to provide a method for selecting an optimal number of passes for a multi-pass heat exchanger that improves the efficiency of the overall multi-pass heat exchanger and maximizes the reliability and satisfaction of practical use by applying the same.

Hereinafter, the present invention will be described in detail.

In describing the present invention, when it is determined that the detailed description of the related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

In addition, the terms to be described below are terms set in consideration of functions in the present invention, which may vary depending on the intention or custom of the user and the producer, and the definition should be made based on the contents throughout the present specification.

Prior to describing the present invention, numerical analysis is performed by varying the inlet diameter and the number of passes within a geometric limit range. In this case, the JF factor is used to simultaneously compare thermal performance and dynamic performance.

Accordingly, j and f factors of the evaluation index JF factor are defined as follows.

Heat transfer performance and power can be expressed as follows.

Dividing this by the value of the reference model,

If you sum up the two expressions,

The symbols or signs used for the above expressions are represented as follows.

j: j factor

f: f factor

JF: JF factor

h: heat transfer coefficient [W / m ² K]

Pr: Prandtl number

c _p : specipic heat at a constant pressure

ρ: density [kg / m ³ ]

u _in : inlet velocity [m / s]

H _t : flat tube length [m]

△ p: pressure drop [Pa]

D: inlet diameter [m]

Re: Reynolds number

μ: dynamic viscosity [kg / ms]

A: area

ref: reference heat exchanger

The above indicators are very effective for simultaneously evaluating the thermal and dynamic characteristics of the heat exchanger, and use them to evaluate the performance of each heat exchanger.

First, the present invention is a multi-pass heat exchanger composed of inlet and outlet and a plurality of passes provided in the center of each header, in order to evaluate the thermal performance and dynamic performance of the multi-pass heat exchanger to show a high performance in design, The number of passes is selected using the ratio of the inlet diameter to the header height of the heat exchanger, but the ratio of the inlet diameter to the header height of each of the passes is selected from the range of 0.3 to 0.7.

In addition, the ratio of the inlet diameter to the header height of each pass is to select the number of passes close to 0.5 when there is a size constraint for the heat exchanger.

EXAMPLE

With reference to the accompanying drawings, a preferred embodiment for achieving the present invention will be described in detail.

First, the present invention is shown in the accompanying drawings, Figures 1 to 2, Figure 1 is a schematic configuration showing for explaining the multi-pass heat exchanger according to the present invention, Figure 2 is a view of a path implemented by the present invention Exemplary diagrams show several multipass heat exchangers according to number.

That is, the method for selecting the optimal number of passes for the multi-pass heat exchanger of the present invention is to evaluate the thermal performance and the dynamic performance of the multi-pass heat exchanger to show high performance in design.

Accordingly, the multi-pass heat exchanger 10 is provided with an inlet 12 and an outlet 13 in the center of each header 11, it is made of a plurality of passes (pass).

When designing the multi-pass heat exchanger 10 as described above, the number of passes is selected to indicate high performance, which is an inlet 12 with respect to the height H of the header 11 of the multi-pass heat exchanger 10. The ratio (D / H) of the diameter (D) is to be used.

To this end, in order to compare the number of passes of the multi-pass heat exchanger 10 and the performance according to the diameter (D) of the inlet 12, the inlet diameter (D) is a 5mm interval from 20 to 50mm, the geometric limit range The size of the inlet 12 and the outlet 13 were the same.

 Therefore, the number of passes can be selected up to even 2, 4, 6, 8, 12 passes even according to the inlet diameter (D), since the inlet and outlet is attached to the right side due to the installation restrictions, the inlet diameter (D) is 30mm It can be carried out by varying the number of passes in the phosphorus heat exchanger (see Fig. 2 attached).

Inlet diameter (mm) Number of pass (N _p ) D / H Q (W) Δp (Pa) JF   20 2 0.167 104.30 99.04 0.537 4 0.333 111.70 103.51 0.616 6 0.5 117.65 122.23 0.640 8 0.667 121.03 201.64 0.583 12 One 124.86 610.42 0.494  25 2 0.208 103.44 37.00 0.761 4 0.417 111.72 45.65 0.841 6 0.625 117.25 68.84 0.791 8 0.833 120.99 150.02 0.780  30 2 0.25 104.24 18.63 One 4 0.5 111.75 27.09 1.022 6 0.75 117.38 51.18 0.882 8 One 120.80 134.11 0.710  35 2 0.292 104.20 10.61 1.245 4 0.583 111.35 19.33 1.180 6 0.875 116.61 49.92 0.910  40 2 0.333 104.55 6.87 1.517 4 0.667 111.96 15.76 1.322 6 One 116.38 49.89 0.938 45 2 0.375 105.47 5.11 1.749 4 0.75 112.41 14.30 1.356 50 2 0.417 106.45 4.20 1.893 4 0.833 112.37 13.74 1.385

The inlet and the outlet are attached to the center of the header 11 of the first pass and the last pass, and as the number of passes increases, the amount of heat transfer as a net characteristic and the pressure drop as a mesh characteristic increase simultaneously.

Accordingly, an example of the analysis is shown in Table 1, and the optimum number of passes according to the inlet diameter is 6 passes at 20 mm, 4 passes at 30 mm, and 2 passes at 50 mm. , Etc., and the optimum number of passes according to the diameter is inconsistently different. Therefore, when designing a heat exchanger, it is difficult to select the optimal number of passes through analysis or experiment.

However, as shown in Figure 3, using the ratio (D / H) of the header height (H) of the path and the inlet diameter (D), it is possible to predict the optimal number of passes according to the inlet diameter (D). For this purpose, the ratio (D / H) of the inlet diameter (D) to the header height (H) of each path is shown. As a result, the ratio (D / H) of the inlet diameter (D) to the header height (H) of each path is shown. ) Within 0.3 to 0.7, it is possible to select the optimal number of passes according to the change in inlet diameter.

In the case of the actual heat exchanger of refrigeration and air conditioning equipment, the diameter of the circulation part is often fixed so that the inlet diameter is fixed as a constraint condition.If the ratio of the inlet diameter to the header height of the path is known, the header height (H) of the path is determined. The number of passes can be easily selected by dividing the header height of the path by the height L of the entire heat exchanger.

In addition, the ratio D / H of the inlet diameter D to the header height H of each pass is preferably selected as the number of passes close to 0.5 when the size of the heat exchanger is limited.

As described above, the range of the ratio of the inlet diameter to the header height is described in relation to the selection of the number of passes, and the description of the JF Factor and the inlet diameter, which are other factors considered in the selection of the number of passes, Implementation is possible.

Based on this, the design factors to be considered as the top priority when designing the multi-pass heat exchanger 10 are the overall size, the inlet diameter and the number of passes, but the size and the inlet diameter of the actual multi-pass heat exchanger are mostly design limitations. Since it is fixed, if the ratio (D / H) of the inlet diameter (D) to the header height (H) of each pass is set to around 0.5, the optimal number of passes can be simply selected without further experimentation or analysis.

Finally, the method for selecting the optimal number of passes for a multipass heat exchanger in accordance with the present invention can be variously modified and can take various forms.

It is to be understood, however, that the present invention is not limited to the specific forms referred to in the above description, but rather includes all modifications, equivalents and substitutions within the spirit and scope of the invention as defined by the appended claims. It should be understood to do.

As described above, the present invention can select the optimal number of passes for the multi-pass heat exchanger by the ratio of the inlet diameter to the header height, the thermal and dynamic performance of the multi-pass heat exchanger according to the inlet diameter and the number of passes It is evaluated that high performance is shown in the design of multipass heat exchanger.

In addition, when the size and inlet diameter of the multi-pass heat exchanger are fixed, the present invention has an effect of simply selecting an optimal number of passes without additional experiments or analysis by setting the ratio of the inlet diameter to the header height of each pass to about 0.5. have.

In addition, the present invention has a number of effects, such as the efficiency of the overall multi-pass heat exchanger is improved due to the effect carried out above to maximize the practical use reliability and satisfaction by applying this.

Claims (3)

In the multi-pass heat exchanger consisting of a plurality of passes and inlet and outlet provided in the center of each header, From the ratio 0.3 to 0.7 of the inlet diameter to the head height of the multipass heat exchanger, the product of the heat exchanger's thermal performance (J factor) and the dynamic performance (F factor) is given by the following formula, Find the head height from the ratio of the head height to the inlet diameter, Dividing the height of the heat exchanger by the head height to determine the number of passes Method for selecting the optimal number of passes for a multipass heat exchanger. [Equation]

In the above formula, h: heat transfer coefficient [W / m ² K] A: area △ p: pressure drop [Pa] ref: reference heat exchanger

(h: heat transfer coefficient [W / m ² K] Pr: Prandtl number ρ: density [kg / m ³ ] c _p : specipic heat at a constant pressure u _in : inlet velocity [m / s])

(△ p: pressure drop [Pa] H _t : flat tube length [m] ρ: density [kg / m ³ ] u _in : inlet velocity [m / s]) The method of claim 1, The ratio of the inlet diameter to the header height of each pass is A method for selecting an optimal number of passes for a multipass heat exchanger that selects a number of passes close to 0.5 when there are size constraints on the heat exchanger. delete

Images