Union of Soviets
Socialist
Republics
State Committee
USSR for Inventions and Discoveries (53) UDC 629. 113. .06.628.83 (088.8) (72) Authors of the invention
V. S. Maisotsenko, A. B. Tsimerman, M. G. and I. N. Pecherskaya
Odessa Civil Engineering Institute (71) Applicant (54) TWO-STAGE EVAPORATORY AIR CONDITIONER
COOLING FOR VEHICLE
The invention relates to the field of transport engineering and can be used for air conditioning in vehicles.
Air conditioners for vehicles are known that contain an air slot evaporator nozzle with air and water channels separated from each other by walls made of microporous plates, while the lower part of the nozzle is immersed in a tray with liquid (1)
The disadvantage of this air conditioner is the low efficiency of air cooling.
The closest technical solution The invention is a two-stage evaporative cooling air conditioner for vehicle, containing a heat exchanger, a tray with liquid in which the nozzle is immersed, a chamber for cooling the liquid entering the heat exchanger with elements for additional cooling of the liquid, and a channel for supplying air to the chamber external environment, made tapering towards the inlet of the chamber (2
In this compressor, elements for additional air cooling are made in the form of nozzles.
However, the cooling efficiency in this compressor is also insufficient, since the limit of air cooling in this case is the wet bulb temperature of the auxiliary air flow in the pan.
10 In addition, the known air conditioner is structurally complex and contains duplicate components (two pumps, two tanks).
The purpose of the invention is to increase the degree of cooling efficiency and compactness of the device.
The goal is achieved by the fact that in the proposed air conditioner the elements for additional cooling are made in the form of a heat exchange partition located vertically and fixed to one of the chamber walls with the formation of a gap between it and the chamber wall opposite it, and
25, on the side of one of the surfaces of the partition, a reservoir is installed with liquid flowing down the said surface of the partition, while the chamber and the tray are made in one piece.
The nozzle is made in the form of a block of capillary-porous material.
In fig. 1 shown circuit diagram air conditioner, Fig. 2 raeree A-A in Fig. 1.
The air conditioner consists of two stages of air cooling: the first stage is cooling the air in heat exchanger 1, the second stage is cooling it in nozzle 2, which is made in the form of a block of capillary-porous material.
A fan 3 is installed in front of the heat exchanger, driven so rotation by an electric motor 4 °. To circulate water in the heat exchanger, a water pump 5 is installed coaxially with the electric motor, supplying water through pipelines 6 and 7 from chamber 8 to reservoir 9 with liquid. Heat exchanger 1 is installed on a tray 10, which is made integral with the chamber
8. A channel is adjacent to the heat exchanger
11 for supplying air from the external environment, while the channel is made planally tapering in the direction towards the inlet 12 of the air cavity
13 chambers 8. Elements for additional air cooling are placed inside the chamber. They are made in the form of a heat exchange partition 14, located vertically and fixed to the wall 15 of the chamber, opposite the wall 16, relative to which the partition is located with a gap. The partition divides the chamber into two communicating cavities 17 and 18.
The chamber is provided with a window 19, in which a drip eliminator 20 is installed, and an opening 21 is made in the pan. When the air conditioner is operating, fan 3 drives the total air flow through heat exchanger 1. In this case, the total air flow L is cooled, and one part of it is the main flow L
Due to the execution of channel 11 tapering towards the inlet hole 12! cavity 13, the flow rate increases, and external air is sucked into the gap formed between the mentioned channel and the inlet hole, thereby increasing the mass of the auxiliary flow. This flow enters the cavity 17. Then this air flow, going around the partition 14, enters the chamber cavity 18, where it moves in the opposite direction to its movement in the cavity 17. In the cavity 17, a film 22 of liquid flows down the partition towards the movement of the air flow - water from the reservoir 9.
When the air flow and water come into contact, as a result of the evaporation effect, heat from the cavity 17 is transferred through the partition 14 to the water film 22, promoting its additional evaporation. After this, a flow of air with a lower temperature enters the cavity 18. This, in turn, leads to an even greater decrease in the temperature of the partition 14, which causes additional cooling of the air flow in the cavity 17. Consequently, the temperature of the air flow will decrease again after going around the partition and entering the cavity
18. Theoretically, the cooling process will continue until its driving force becomes zero. IN in this case driving force of the evaporative cooling process is the psychometric difference in the temperature of the air flow after it has been rotated relative to the partition and comes into contact with the film of water in cavity 18. Since the air flow is pre-cooled in cavity 17 with a constant moisture content, the psychrometric temperature difference of the air flow in cavity 18 tends to zero when approaching the dew point. Therefore, the limit of water cooling here is the dew point temperature of the outside air. Heat from the water enters the air flow in cavity 18, while the air is heated, humidified and released into the atmosphere through window 19 and drip eliminator 20.
Thus, in chamber 8, a counter-current movement of heat-exchanging media is organized, and the separating heat-exchange partition makes it possible to indirectly pre-cool the air flow supplied for cooling water due to the process of water evaporation. The cooled water flows along the partition to the bottom of the chamber, and since the latter is completed in one whole with the tray, then from there it is pumped into heat exchanger 1, and is also spent on wetting the nozzle due to intracapillary forces.
Thus, the main flow of air.L.„, having been pre-cooled without changes in moisture content in heat exchanger 1, is supplied for further cooling to nozzle 2. Here, due to the heat and mass exchange between the wetted surface of the nozzle and the main air flow, the latter is humidified and cooled without changing its heat content. Next, the main air flow through the opening in the pan
59 yes it cools, at the same time cooling the partition. Entering the cavity
17 of the chamber, the air flow flowing around the partition is also cooled, but there is no change in moisture content. Claim
1. A two-stage evaporative cooling air conditioner for a vehicle, containing a heat exchanger, a sub-tank with liquid in which the nozzle is immersed, a chamber for cooling the liquid entering the heat exchanger with elements for additional cooling of the liquid, and a channel for supplying air from the external environment into the chamber, made tapering in direction to the inlet of the chamber, i.e. in that, in order to increase the degree of cooling efficiency and compactness of the compressor, the elements for additional air cooling are made in the form of a heat exchange partition located vertically and mounted on one of the chamber walls with the formation of a gap between it and the chamber wall opposite it, and on the side of one of the On the surface of the partition, a reservoir is installed with liquid flowing down the said surface of the partition, while the chamber and the tray are made as one whole.
For rooms with large excesses of sensible heat, where maintenance is required high humidity internal air, air conditioning systems using the principle of indirect evaporative cooling are used.
The circuit consists of a main air flow processing system and an evaporative cooling system (Fig. 3.3. Fig. 3.4). To cool water, irrigation chambers of air conditioners or other contact devices, spray pools, cooling towers and others can be used.
Water, cooled by evaporation in the air flow, with a temperature, enters the surface heat exchanger - the air cooler of the air conditioner of the main air flow, where the air changes its state from values to values (t.), the water temperature rises to. The heated water enters the contact apparatus, where it is cooled by evaporation to temperature and the cycle is repeated again. The air passing through the contact apparatus changes its state from parameters to parameters (i.e.). The supply air, assimilating heat and moisture, changes its parameters to the state t., and then to the state.
Fig.3.3. Indirect evaporative cooling circuit
1-heat exchanger-air cooler; 2-contact device
Fig.3.4. indirect evaporative cooling diagram
Line - direct evaporative cooling.
If there is excess heat in the room, then with indirect evaporative cooling consumption supply air will be
with direct evaporative cooling
Since >, then<.
<), что позволяет расширить область возможного использования принципа испарительного охлаждения воздуха.
A comparison of processes shows that with indirect evaporative cooling the SCR productivity is lower than with direct cooling. In addition, with indirect cooling, the moisture content of the supply air is lower (<), что позволяет расширить область возможного использования принципа испарительного охлаждения воздуха.
In contrast to the separate scheme of indirect evaporative cooling, devices of a combined type have been developed (Figure 3.5). The device includes two groups of alternating channels separated by walls. An auxiliary air flow passes through channel group 1. Water supplied through the water distribution device flows along the surface of the channel walls. A certain amount of water is supplied to the water distribution device. When water evaporates, the temperature of the auxiliary air flow decreases (with an increase in its moisture content), and the channel wall also cools.
To increase the cooling depth of the main air flow, multi-stage processing schemes for the main air flow have been developed, using which it is theoretically possible to achieve the dew point temperature (Fig. 3.7).
The installation consists of an air conditioner and a cooling tower. The air conditioner produces indirect and direct isenthalpy cooling of the air in the serviced premises.
The cooling tower provides evaporative cooling of the water that feeds the surface air cooler of the air conditioner.
Rice. 3.5. Diagram of the design of a combined indirect evaporative cooling apparatus: 1,2 - group of channels; 3- water distribution device; 4- pallet
Rice. 3.6. Scheme of SCR two-stage evaporative cooling. 1-surface air cooler; 2-irrigation chamber; 3- cooling tower; 4-pump; 5-bypass with air valve; 6-fan
In order to standardize evaporative cooling equipment, the spray chambers of standard central air conditioners can be used instead of a cooling tower.
Outside air enters the air conditioner and is cooled at the first cooling stage (air cooler) with a constant moisture content. The second stage of cooling is the irrigation chamber, operating in isenthalpy cooling mode. Cooling of the water feeding the surfaces of the water cooler is carried out in a cooling tower. The water in this circuit circulates using a pump. Cooling tower is a device for cooling water with atmospheric air. Cooling occurs due to the evaporation of part of the water flowing down the sprinkler under the influence of gravity (evaporation of 1% of water lowers its temperature by about 6).
Rice. 3.7. diagram with two-stage evaporation mode
cooling
The air conditioner's irrigation chamber is equipped with a bypass channel with an air valve or has an adjustable process, which ensures regulation of the air directed into the room served by the fan.
For servicing individual small rooms or their groups, local air conditioners with two-stage evaporative cooling, based on an indirect evaporative cooling heat exchanger made of aluminum rolling tubes, are convenient (Fig. 139). The air is purified in filter 1 and supplied to fan 2, after the discharge hole of which it is divided into two flows - main 3 and auxiliary 6. The auxiliary air flow passes inside the tubes of the indirect evaporative cooling heat exchanger 14 and provides evaporative cooling of the water flowing down the inner walls of the tubes. The main air flow passes from the fin side of the heat exchanger tubes and transfers heat through their walls to the water, cooled by evaporation. Recirculation of water in the heat exchanger is carried out using pump 4, which takes water from pan 5 and supplies it to irrigation through perforated tubes 15. The indirect evaporative cooling heat exchanger plays the role of the first stage in combined two-stage evaporative cooling air conditioners.
The system under consideration consists of two air conditioners"
the main one, in which air is processed for the serviced premises, and the auxiliary one - the cooling tower. The main purpose of the cooling tower is air-evaporative cooling of water feeding the first stage of the main air conditioner during the warm season (surface heat exchanger PT). The second stage of the main air conditioner - irrigation chamber OK, operating in adiabatic humidification mode, has a bypass channel - bypass B to regulate air humidity in the room.
In addition to air conditioners - cooling towers, industrial cooling towers, fountains, spray pools, etc. can be used to cool water. In areas with a hot and humid climate, in some cases, in addition to indirect evaporative cooling, machine cooling is used.
multistage systems evaporative cooling. The theoretical limit for air cooling using such systems is the dew point temperature.
Air conditioning systems using direct and indirect evaporative cooling have a wider range of applications than systems that use only direct (adiabatic) evaporative cooling.
Two-stage evaporative cooling is known to be most suitable in
areas with dry and hot climates. With two-stage cooling, lower temperatures, fewer air changes and lower relative humidity in rooms can be achieved than with single-stage cooling. This property of two-stage cooling has led to a proposal to switch entirely to indirect cooling and a number of other proposals. However, all other things being equal, the effect of possible evaporative cooling systems directly depends on changes in the state of the outside air. Therefore, such systems do not always ensure the maintenance of the required air parameters in air-conditioned rooms throughout the season or even one day. An idea of the conditions and boundaries of the appropriate use of two-stage evaporative cooling can be obtained by comparing the normalized parameters of indoor air with possible changes in the parameters of outdoor air in areas with a dry and hot climate.
the calculation of such systems should be performed using the J-d diagram in the following sequence.
Points with the calculated parameters of external (H) and internal (B) air are plotted on the J-d diagram. In the example under consideration, according to the design specifications, the following values are accepted: tн = 30 °С; tв = 24 °С; fв = 50%.
For points H and B, we determine the value of the wet thermometer temperature:
tmn = 19.72 °C; tmv = 17.0 °C.
As you can see, the value of tmn is almost 3 °C higher than tmv, therefore, for greater cooling of water and then external supply air, it is advisable to supply air removed by exhaust systems from office premises to the cooling tower.
Note that when calculating a cooling tower, the required air flow may be greater than that removed from the conditioned rooms. In this case, a mixture of external and exhaust air must be supplied to the cooling tower and the wet thermometer temperature of the mixture must be taken as the calculated temperature.
From the calculation computer programs of leading cooling tower manufacturers, we find that the minimum difference between the final water temperature at the outlet of the cooling tower tw1 and the wet thermometer temperature twm of the air supplied to the cooling tower should be taken to be at least 2 °C, that is:
tw2 =tw1 +(2.5...3) °C. (1)
To achieve deeper air cooling in the central air conditioner, the final water temperature at the outlet of the air cooler and at the inlet to the cooling tower tw2 is taken to be no more than 2.5 higher than at the outlet of the cooling tower, that is:
tвк ≥ tw2 +(1...2) °С. (2)
Please note that the final temperature of the cooled air and the surface of the air cooler depend on the temperature tw2, since with a transverse flow of air and water, the final temperature of the cooled air cannot be lower than tw2.
Typically, the final temperature of the cooled air is recommended to be 1–2 °C higher than the final water temperature at the outlet of the air cooler:
tвк ≥ tw2 +(1...2) °С. (3)
Thus, if the requirements (1, 2, 3) are met, it is possible to obtain a relationship connecting the wet thermometer temperature of the air supplied to the cooling tower and the final temperature of the air leaving the cooler:
tвк =tвм +6 °С. (4)
Note that in the example in Fig. 7.14 the values taken are tbm = 19 °C and tw2 – tw1 = 4 °C. But with such initial data, instead of the value tin = 23 °C indicated in the example, it is possible to obtain the final air temperature at the outlet of the air cooler not lower than 26–27 °C, which makes the whole scheme meaningless at tn = 28.5 °C.
Ecology of consumption. The history of the direct evaporative cooling air conditioner. Differences between direct and indirect cooling. Application options for evaporative air conditioners
Air cooling and humidification through evaporative cooling is a completely natural process that uses water as a cooling medium and heat is effectively dissipated into the atmosphere. Simple laws are used - when a liquid evaporates, heat is absorbed or cold is released. Evaporation efficiency increases with increasing air speed, which is ensured by forced circulation of the fan.
The temperature of dry air can be significantly reduced by the phase change of liquid water to vapor, and this process requires significantly less energy than compression cooling. In very dry climates, evaporative cooling also has the advantage of increasing the humidity of the air when conditioning it, making the occupants more comfortable. However, unlike vapor compression cooling, it requires a constant source of water, and constantly consumes it during operation.
History of development
Over the centuries, civilizations have found original methods to combat the heat in their territories. An early form of cooling system, the "windcatcher", was invented many thousands of years ago in Persia (Iran). It was a system of wind shafts on the roof that caught the wind, passed it through the water, and blew cooled air into the interior. It is noteworthy that many of these buildings also had courtyards with large reserves of water, so if there was no wind, then as a result of the natural process of evaporation of water, hot air rising upward evaporated the water in the courtyard, after which the already cooled air passed through the building. Nowadays, Iran has replaced wind catchers with evaporative coolers and uses them widely, and the market, due to the dry climate, reaches a turnover of 150,000 evaporators per year.
In the US, the evaporative cooler was the subject of numerous patents in the twentieth century. Many of whom, since 1906, proposed the use of wood shavings as a gasket that transports large amounts of water in contact with moving air and supports intense evaporation. The standard design, as shown in the 1945 patent, includes a water reservoir (usually equipped with a float valve to adjust the level), a pump to circulate water through the wood chip pads, and a fan to blow air through the pads into the living areas. This design and materials remain a staple of evaporative cooler technology in the southwestern United States. In this region they are additionally used to increase humidity.
Evaporative cooling was common in aircraft engines of the 1930s, such as the engine for the Beardmore Tornado airship. This system was used to reduce or completely eliminate the radiator, which would otherwise create significant aerodynamic drag. In these systems, the water in the engine was kept under pressure using pumps, allowing it to be heated to temperatures in excess of 100°C, since the actual boiling point depends on pressure. Superheated water was sprayed through a nozzle onto an open pipe, where it instantly evaporated, receiving its heat. These tubes could be located under the surface of the aircraft to create zero drag.
External evaporative cooling units were installed on some vehicles to cool the interior. They were often sold as additional accessories. The use of evaporative cooling devices in automobiles continued until vapor compression air conditioning became widespread.
Evaporative cooling is a different principle than vapor compression refrigeration units, although they also require evaporation (evaporation is part of the system). In the vapor compression cycle, after the refrigerant evaporates inside the evaporator coil, the refrigerant gas is compressed and cooled, condensing into a liquid state under pressure. Unlike this cycle, in an evaporative cooler the water evaporates only once. The evaporated water in the cooling device is discharged into a space with cooled air. In a cooling tower, the evaporated water is carried away by the air flow.
Evaporative Cooling Applications
There are direct, oblique, and two-stage evaporative air cooling (direct and indirect). Direct evaporative air cooling is based on the isenthalpic process and is used in air conditioners during the cold season; in warm weather, it is possible only in the absence or insignificant moisture release in the room and the low moisture content of the outside air. Bypassing the irrigation chamber somewhat expands the scope of its application.
Direct evaporative cooling of air is advisable in dry and hot climates in the supply ventilation system.
Indirect evaporative air cooling is carried out in surface air coolers. To cool the water circulating in the surface heat exchanger, an auxiliary contact device (cooling tower) is used. For indirect evaporative cooling of air, you can use devices of a combined type, in which the heat exchanger simultaneously performs both functions - heating and cooling. Such devices are similar to air recuperative heat exchangers.
Cooled air passes through one group of channels, the inner surface of the second group is irrigated with water flowing into the pan and then sprayed again. Upon contact with the exhaust air passing in the second group of channels, evaporative cooling of the water occurs, as a result of which the air in the first group of channels is cooled. Indirect evaporative air cooling makes it possible to reduce the performance of an air conditioning system compared to its performance with direct evaporative air cooling and expands the possibilities of using this principle, because the moisture content of the supply air in the second case is lower.
With two-stage evaporative cooling air conditioners use sequential indirect and direct evaporative cooling of the air in the air conditioner. In this case, the installation for indirect evaporative air cooling is supplemented with an irrigation nozzle chamber operating in direct evaporative cooling mode. Typical spray nozzle chambers are used in evaporative air cooling systems as cooling towers. In addition to single-stage indirect evaporative air cooling, multi-stage air cooling is possible, in which deeper air cooling is carried out - this is the so-called compressor-free air conditioning system.
Direct evaporative cooling (open cycle) is used to reduce the air temperature using the specific heat of evaporation, changing the liquid state of water to a gaseous state. In this process, the energy in the air does not change. Dry, warm air is replaced by cool and humid air. The heat from the outside air is used to evaporate water.
Indirect evaporative cooling (closed loop) is a process similar to direct evaporative cooling, but uses a specific type of heat exchanger. In this case, the moist, cooled air does not come into contact with the conditioned environment.
Two-stage evaporative cooling, or indirect/direct.
Traditional evaporative coolers use only a fraction of the energy required by vapor compression refrigeration units or adsorption air conditioning systems. Unfortunately, they increase air humidity to uncomfortable levels (except in very dry climates). Two-stage evaporative coolers do not increase humidity levels as much as standard single-stage evaporative coolers do.
In the first stage of a two-stage cooler, warm air is cooled indirectly without increasing humidity (by passing through a heat exchanger cooled by external evaporation). In the direct stage, pre-cooled air passes through a water-soaked pad, where it is further cooled and becomes more humid. Because the process includes a first, pre-cooling stage, the direct evaporation stage requires less humidity to achieve the required temperatures. As a result, according to manufacturers, the process cools air with a relative humidity ranging from 50 to 70%, depending on the climate. In comparison, traditional cooling systems increase air humidity to 70 - 80%.
Purpose
When designing a central supply ventilation system, it is possible to equip the air intake with an evaporation section and thus significantly reduce the cost of air cooling during the warm season.
In the cold and transitional periods of the year, when the air is heated by supply heaters of ventilation systems or indoor air by heating systems, the air heats up and its physical ability to assimilate (absorb) increases, and with increasing temperature - moisture. Or, the higher the air temperature, the more moisture it can assimilate. For example, when the outside air is heated by a heater by a ventilation system from a temperature of -22 0 C and a humidity of 86% (outdoor air parameter for HP in Kiev), to +20 0 C - the humidity drops below the boundary limits for biological organisms to an unacceptable 5-8% air humidity. Low air humidity negatively affects the skin and mucous membranes of humans, especially those with asthma or pulmonary diseases. Standardized air humidity for residential and administrative premises: from 30 to 60%.
Evaporative air cooling is accompanied by the release of moisture or an increase in air humidity, up to a high saturation of air humidity of 60-70%.
Advantages
The amount of evaporation - and therefore heat transfer - depends on the outside wet-bulb temperature which, especially in summer, is much lower than the equivalent dry-bulb temperature. For example, on hot summer days when the dry bulb temperature exceeds 40°C, evaporative cooling can cool the water to 25°C or cool the air.
Because evaporation removes much more heat than standard physical heat transfer, heat transfer uses four times less air flow than conventional air cooling methods, saving significant amounts of energy.
Evaporative cooling versus traditional air conditioning methods Unlike other types of air conditioning, evaporative air cooling (bio-cooling) does not use harmful gases (freon and others) as refrigerants, which are harmful to the environment. It also uses less electricity, thereby saving energy, natural resources and up to 80% in operating costs compared to other air conditioning systems.
Flaws
Low performance in humid climates.
An increase in air humidity, which in some cases is undesirable, results in two-stage evaporation, where the air does not contact and is not saturated with moisture.
Operating principle (option 1)
The cooling process is carried out due to the close contact of water and air, and the transfer of heat into the air by evaporation of a small amount of water. The heat is then dissipated through the warm and moisture-saturated air leaving the installation.
Operating principle (option 2) - installation on the air intake
Evaporative cooling units
There are different types of evaporative cooling units, but they all have:
- heat exchange or heat transfer section, constantly wetted with water by irrigation,
- a fan system for forced circulation of outside air through the heat exchange section,
