Analysis of the heat exchangers

Discussion of the heat exchanger copper-aluminum products commercial air conditioning light.

by Chigo HVAC

1. Types of heat exchangers: The main types of heat exchangers are, among others, the conventional heat exchanger copper-aluminum heat exchanger aluminum-aluminum (aluminum tube) and the heat exchanger of parallel flow ( channel micro step).

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Specifications 1.1 conventional heat exchanger copper-aluminum:
1. φ9.52mm tube diameter, 21.65 mm wide fins;
2. φ7.94mm tube diameter, 19.05 mm wide fins;
3. φ7mm tube diameter, or 13.37mm 19.05 mm wide fins;
4. φ5mm diameter 13.37 mm wide fins.

1.2 The heat exchanger has an aluminum-aluminum aluminum tube φ9.52mm diameter is commonly used on the market of the United States. It presents two major problems in terms of welding and corrosion, and thermal efficiency is only 92% of the offered heat exchanger copper-aluminum.

1.3 The heat exchanger tube parallel process carried out by a flat aluminum tube and aluminum fins. The heat exchange efficiency is determined by the width of the heat exchanger. It provides energy efficiency is to 1.2 1.4 times higher than the heat exchanger copper-aluminum. However, it is not as competitive as the price of copper and a much larger investment is required.

2. Using the heat exchanger in the air conditioning products commercial light:
Use 2.1 heat exchanger copper-aluminum products light commercial air conditioning:

to. The heat exchanger unit air conditioning with a tube diameter 7 and 19.05 wide fins has improved tremendously and has better performance in the heating mode and defrosting. The adoption of this standard will allow large cost savings, the current market standard diameter are 7 mm. As part of Chigo air conditioning solutions also offer this type of product.

b. Distance fin heat exchanger: 1.4 mm for outdoor units and 1.5-1.7 mm for interior units. (The distances of the fins are related to the volume of air).

c. Rows heat exchanger: 2-4 rows for interior units and 1-2 rows for outdoor units.
2.2 The use of the heat exchanger aluminum-aluminum products commercial air conditioning light:

to. the aluminum heat exchanger aluminum in Latin America due to dry weather is preferred. It is commonly used in the roof unit and the outdoor unit to unit.

b. The heat exchanger aluminum-aluminum should not be used in the heat pump or the evaporator because these two parts usually remain long submerged in water, which accelerate corrosion.

Use 2.3 heat exchanger copper-aluminum products φ5mm in commercial air conditioning light:

to. The heat exchanger φ5mm copper-aluminum is used in units with little cooling capacity: it is generally used in indoor units with capacity of less than 18.000 btu and outdoor units with a capacity less than 24.000 btu.

b. The main advantage is the ratio between the low cost of the material and the thermal efficiency of the unit /.

c. It is currently used in the residential air conditioners Chigo, for example, in the wall unit, and is also used in commercial air conditioning unit in the pipeline 1-2 HP.
3. Circuits heat exchangers
The heat exchange design refers to the function between evaporator and condenser.
This defines the high temperature side is the condenser while the low temperature side is the evaporator.

3.1 influence the direction of flow of the circuit in heat exchange. The flow direction includes:

to. The relationship between heat exchangers and the downstream and upstream of the wind field. Usually, the design must be implemented in ascending heat exchanger several rows. Down design should adopt indoor heat pump units, taking into account the water outlet of the evaporator or other possible problems that may occur in the heating mode.

b. The vertical and horizontal position of the inlet and outlet. To make the most of the flotation and gravity, we must use a design of "vertical to the liquid inlet" and "upright to the gas outlet."

3.2 Determine the number of circuits
to. Note the pressure loss, if more circuits in the evaporator and condenser that means there is one more short circuit in the heat exchanger and there is less pressure loss, and improved system capacity. However, this is not entirely accurate for the following two reasons:

(1) When the evaporator and condenser are very large, have more circuits generates a low volume flow and a lower flow velocity in each circuit, which causes the oil to accumulate on the inner surface of the pipe and form a oil film when the system has a very bad oil return. This will decrease the heat exchange efficiency and will impact very negatively on the heating capacity. When the system has insufficient heating capacity, consider reducing the number of circuits.

(2) When more circuits this causes each circuit is irregular, resulting in an incomplete evaporation and other problems. Therefore, the capacity decreases. Usually, the number of circuits has a marked impact on low temperature side and a slight effect on the high temperature side in the cooling mode. A pressure drop of 0.3Kg not affect much in the condensing temperature, as this is the cooling capacity of the system. Usually, in the cooling mode, the number of circuits has more obvious effect on the low temperature side and a less marked in the high temperature side effect, the reason is that a pressure drop 0.3kg has little effect on the condensation temperature, therefore, has little effect on the cooling capacity.

But the increased compressor discharge pressure will cause an increase in energy consumption of the compressor, therefore, to avoid problems caused by power supply, you can try to optimize the number of circuits on the side of the high temperature.

b. For a given system is no precise optimum number of circuits, that number should be determined according to the size of the heat exchanger, the volume of the compressor discharge and the type of refrigerant.

c. The extension of the circuit is also a determining factor for establishing the number of circuits factor. Given the incidence and type of refrigerant pipe diameter, the influence of the dynamic viscosity of the liquid and the diameter of the pipe in the pressure drop is the key factor to establish the extent of the circuit. If we have the following dynamic viscosity liquid: R410A = R22 * 70% R410A extension must be greater than R22.

3.3 design distribution heat exchangers
The design of the distribution of heat exchangers high efficiency is the key issue in the ratio of heat exchange, apart from the considerations in A and B, above, the design must also follow these rules:

to. The layout design should follow the principle of "liquid phase through a single channel, gas phase through various channels", that is, the principle of least input and output evaporator design, which improve the rate mass flow of refrigerant in a dry area. Compared with the method of dividing directly in several flumes, this design of the distribution does not divide any flow channel when the degree of dryness of the refrigerant is low, this will increase the mass flow rate of the coolant, and will increase little pressure drop, therefore, can improve the heat transfer coefficient in boiling flow.

When the dryness is high, a flow channel, or very small flow channels, will cause a very high velocity of the cooling gas and a drop of high pressure, therefore, in these conditions more circuits are needed to decrease effectively the pressure drop.

b. The layout design should avoid the influence of overheating and ensure that the inlet and outlet remain unlocated adjacently on the same side, you must also follow the principle of minimum temperature difference of adjacent pipes (which there is no overheating in adjacent rows).

c. The extent of each distribution circuit must be related to the distribution of the wind field. In a field of uniform wind coextensive circuits it is typically implemented. But in a heterogeneous wind field should reduce the extent of the circuit on the part of high air volume and increase the extent of the circuit in the low volume of the air.

It should reduce the extent of the circuit in the part of high air volume and increase the extent of the circuit in the part of low air volume to ensure uniform heat exchange.

Quoting products and technical services for Latin America

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