Dynamic process simulation of air-cooled heat pump water chiller unit

The high and low pressure sections of the system are divided into a refrigerant side wall and three control volumes on the water or air side.

A differential equation of mass and energy balance is established for each control volume.

Since the compressor thermal expansion valve body and the four-way reversing valve have a small thermal inertia, a steady state model is used to describe the expansion process of the compression process and the internal leakage process.

The retardation of the refrigerant temperature in the expansion valve temperature envelope for the evaporator outlet temperature is described by a first order inertia link.

System simulation is achieved by predicting a correction and adaptive step size method.

The simulation results are in good agreement with the test data.

Key words: air-cooled heat pump, hot and cold water unit, dynamic simulation, classification, number one, one, five, one, one, one, one, one, one, one, one

The five dying slaves, the five movements, the dynasty, the dj, the death, the three deaths, the movement, the r, the one, the one, the one, the one, the one, the one, the hurricane, the cold and hot water pump, the hot and cold water unit, which is capable of supplying both cold water and heat. Water air conditioning unit.

Because the unit uses air as a cold source or heat source, it eliminates a complicated cooling water system and boiler heating system, so it is easy to install and use, and has a wide range of applications around the world.

Therefore, the rapid and economic development of high-performance products has important practical significance.

Air-cooled heat pump hot and cold water units usually exhibit dynamic characteristics during operation.

Obtaining the dynamic characteristics of the unit through experimental means is not only long but also costly.

If a dynamic simulation model is established and the model is calibrated with limited experimental data, the model can largely replace the experiment.

Designers can use the calibrated model to arbitrarily modify design parameters and operating conditions, and simulate to select a reasonable design.

At present, some dynamic simulation models have been developed.

They are mainly for small devices, for the purpose of simulation theoretical research, and can only be used independently for refrigeration or heating devices.

Dynamic simulation studies on large-scale units such as hot and cold water units are rarely seen in this context. This paper establishes a simulation model for this unit dynamic process.

The model was verified by experiments.

The model is established to switch the cooling and heating conditions through the four-way reversing valve.

Two dates and one revised date one.

Funded by the National Key Basic Research and Development Planning Project of the Fund Project (Fu Long (a male, Anhui Quanjiao, Ph.D. student, mainly engaged in the research of simulation and optimization of refrigeration and air conditioning units.

The physical processes of the journal Engineering Thermophysics can be represented by graphs.

Among them, in the refrigeration condition, the condenser is an air side heat exchanger, and the evaporator is a water side heat exchanger.

Under heating conditions, the condenser is a water side heat exchanger and the evaporator is an air side heat exchanger.

The dotted line in the figure represents the internal leakage process of the high-pressure side refrigerant to the low pressure side when the refrigerant flows through the four-way switching valve.

In the formula,

For the refrigerant than the internal energy, it is calculated according to the saturation state.

吼, the art is calculated according to the three-zone (gas phase two-phase liquid phase) model.

Cloud only = condenser reservoir compressor Xuanqi liquid separator Bixi stop Chuanchuan leakage diagram Unit diagram High and low pressure section from the compressor outlet to the inlet of the expansion valve is the high pressure section of the system, and the outlet from the expansion valve The inlet to the compressor is a low pressure section.

The dynamic characteristics of the system are mainly reflected in these two thermal processes.

These two thermal links have many features in common.

Therefore, put their models together and describe them.

Here are the following simplifications: (a) ignoring the pressure drop of the refrigerant in the heat exchanger, ignoring the leakage of heat from the water side of the shell-and-tube heat exchanger and the heat exchange between the connecting lines (c) ignoring the connecting line accumulator And the metal heat capacity of the gas-liquid separator.

(l) The energy balance equation of the refrigerant side is one of the two claws and one claw.

In the formula,

And the heat exchange coefficient and the logarithmic mean temperature difference respectively representing the heat exchange coefficients of the respective phase regions.

The first zone of the condenser is the gas phase zone and the first zone of the evaporation zone is the liquid phase zone.

Assuming that the internal refrigerant of the first zone is in a quasi-steady state, its length is easily calculated.

If the evaporator inlet is in two phases, the evaporator liquid phase disappears.

The second zone of the condenser and evaporator is a two phase zone.

We assume that the refrigerant dryness is linearly distributed in the two-phase region. The refrigerant gas in the high-pressure section is concentrated in the gas collecting pipe and the condenser as much as possible, and the liquid-phase refrigerant is considered to be concentrated in the evaporator as much as possible in the low-pressure section.

Based on these two assumptions, the second phase zone length can be determined using the bubble coefficient model.

The remaining portion of the heat exchange tube is the third phase region, which is a liquid phase region for the condenser and a gas phase region for the evaporator.

The simplified calculation of the claws is as follows. When the high-pressure side refrigerant liquid passes through the gas-liquid separator, the degree of subcooling obtained does not exceed the formula, and the angle marks represent the accumulator and the evaporator, respectively. The heat transfer tube wall energy equation, in the formula, the claw, respectively, represents the total internal energy, flow and helium of the refrigerant.

Foot and table imports and exits.

The heat transfer rate of the heat exchange tube to the refrigerant.

It is the heat exchange between the high pressure section (taken the negative sign) and the low pressure section (take the positive sign) in the gas-liquid separator.

In the mass balance equation, è™± is the average temperature of the heat exchange tubes.

The rate of heat transfer to the heat transfer tube wall by the fluid outside the tube (air or water).

The air or water side energy equation is the most in the formula, which means the total mass of the refrigerant.

Phase and liquid phase.

The total volume is an artistic claw and the representative of the gas type, the angular standard indicates the fluid air or water outside the tube.

The air side heat exchanger can be approximated by the heat transfer equation in the form of the refrigerant specific volume, which is approximately calculated according to the saturation state.

The total internal energy of eight pairs of Qiyi Luhu is the dynamic process simulation of the air-cooled heat pump cold and hot water unit of Fulong and other fire-fighting units. The unknown is Mom, Yin.

On the high pressure section) or Yin.

For the high pressure section), a total of two.

The equations are closed.

The equation (integrated by the second-order e-method, and the equation) uses implicit difference.

The compressor ignores the change in heat capacity of the compressor.

For screw compressors, the indicated work and outlet enthalpy are the characteristic constants of the valve, which can be calculated according to the rated operating conditions provided by the valve manufacturer.

For static pressure, it depends on static superheat seven.

The four-way reversing valve refrigerant in the four-way reversing valve, the leakage from the high-pressure side to the low-pressure side is the claw two to one from 9 æ›°æ›°. on. On the 1 win, 20,000 yin Yin Yi Yin dry one from the formula, the foot mark respectively represents the gas-liquid separator and compressor.

And the pressure and specific volume when the internal compression is completed for the compressor, respectively, bow, two, is the variable index of the compression process.

For internal compression volume ratio.

Compressor effective flow rush.

From the knife type, from the theoretical displacement of the compressor.

Is the effective flow coefficient.

Since a portion of the refrigerant liquid is required to cool the compressor interior, a reduction in the effective refrigerant flow rate with refrigeration or heating is caused.

This effect is corrected by the coefficient Cc.

The volumetric efficiency of the compressor is calculated by the following formula.

The power of a Yin compressor is jumped from the squat type to the total efficiency of the compressor.

The response of the temperature of the refrigerant in the temperature-sensing valve of the thermal expansion valve to the temperature of the refrigerant at the outlet of the evaporator is a time constant in the equation 221.

The foot mark represents the temperature sensor package.

Ignoring the influence of the heat capacity change of the expansion valve body, the process of the refrigerant flowing through the expansion valve can be regarded as an equal process, and the flow rate of the valve is calculated by the following formula.

One Yin.

One Yin.

However, the leakage coefficient can be estimated based on the amount of leakage under the design conditions provided by the manufacturer.

The system simulation algorithm calculates the state of the current time system according to the prediction-correction method for a given time step.

The specific steps are the inlet parameters of the high and low pressure sections at the previous moment as the inlet parameters of the high and low pressure sections at the current moment.

For the high and low pressure section, the calculation is based on the calculation of the low pressure section of the high pressure section of the four-way reversing valve of the compressor expansion valve.

The time step is determined by the adaptive algorithm.

The model verification simulates a certain type of air-cooled heat pump water chiller unit.

In addition to the structural parameters, the ambient temperature inlet water temperature and the amount of water measured by the experiment were used as input parameters for the simulation.

In addition, the air volume of the air side heat exchanger is provided by the manufacturer of the fan and serves as an input parameter for the simulation.

The screw compressor used in the unit has 25 four-stage load regulation.

Under the refrigeration and heating conditions, the compressor is loaded and started according to the four-stage load. The interstage delay time 60 shows the simulation and experimental results of the unit from the moment the compressor is started.

The figure shows the evaporation pressure (gauge pressure and condensing pressure gauge pressure as well as the cooling capacity and electric power) under refrigeration conditions.

From. It is the process of starting the compressor step by step.

During this period, the high temperature and high pressure gas entering the condenser from the compressor is too late to be condensed, resulting in a rapid rise in the condensing pressure.

The evaporation pressure drops rapidly and there is a shock.

This oscillation is mainly caused by the oscillation of the expansion valve opening.

In the mean, the simulation results of the unit's electric power can be consistent with the test values ​​in the trend, but there is a significant deviation in accuracy.

The reason is that in the compressor model, the total efficiency of the compressor is the same under four loads.

After the compressor is fully loaded, the unit status changes slowly.

The graphs show the evaporative pressure gauge pressure and condensing pressure (gauge pressure and heat and electric power) under heating conditions.

Within, fluctuations in ambient temperature cause fluctuations in evaporation pressure and unit heat.

Journal of Engineering Thermophysics 卷 飞 飞 飞 召 曰 袱潺 袱潺 袱潺 袱潺 州 州 州 州 州 州 州 州 州 州 州 丫狡 丫狡 丫狡 丫狡 丫狡 丫狡 丫狡 丫狡 丫狡 丫狡 丫狡 丫狡 ( ( ( ( ( ( ( ( ( ( ( ( A pot of books to fight J to protect the claws.

The change of the condensing pressure and the evaporating pressure (gauge pressure) in the time chart of the thousand hours of the figure. The change of the cooling capacity and the electric power. The name of the trousers is captured by the trousers.å°½ å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·ž å·žThe simulation results are in good agreement with the test values, and the simulation model can describe the basic characteristics of the unit operation.

During the above simulation time, the relative error between the simulated value of the cooling capacity and the input electric power and the test value is low. Conclusion and prospect A dynamic simulation model is established for the air-cooled heat pump hot and cold water unit.

The simulation results are in good agreement with the experimental data and can meet the engineering design needs.

Most of the input parameters of the simulation model are well known to the designer. Only the initial distribution of the refrigerant, the time constant of the thermal expansion valve, and the static superheat of the thermal expansion valve are difficult to accurately specify.

However, the research in this paper shows that these three parameters have little influence on the simulation results and the actual performance of the unit, so they can be approximated by constants in the simulation model.

Therefore, the simulation model of this paper can be easily used by ordinary designers.

In the future research, it is necessary to further improve the input electric power calculation of the unit during the compressor loading process.

References Luo.

Intestinal small rise in January, a Ding Guoliang, Fu Long, Su Zujian and so on.

The screw unit dynamically simulates a boot process.

Journal of Engineering Thermophysics, (supplement) Yu Tongfu, Ding Guoliang, Zhang Chunlu and so on.

Dynamic process simulation of air-cooled heat pump water chiller unit.

See the Proceedings of the Chinese Society of Engineering Thermophysics Engineering Thermodynamics and Energy Utilization Conference.

Zhongshan,

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