The water source heat pump is a heat pump system that uses water as a heat source and heat sink. It can be divided into two types: groundwater heat source heat pump and surface water heat source heat pump. As far as the current situation is concerned, water source heat pumps have not been widely used as air source heat pumps. There are two reasons for this: on the one hand, the investment in water source heat pump is high, and the access to water source is limited; on the other hand, there is still no reliable design method and calculation model for water source heat pump. The operating characteristics of the water source heat pump must match the air conditioning load characteristics of the building, and there is a problem of load balance.
Based on the analysis and comparison of the existing water source heat pump simulation methods, based on the operating characteristics of several main components of the air conditioning refrigeration system, a set of calculation models for the steady state performance of the water source heat pump is established. The simulation results show that R22 and R22/R142b are in the simulation. The performance of the same heat pump unit under the same working conditions, theoretically and experimentally verified the energy-saving theory of the mixed working fluid, and obtained the possible performance effects of the corresponding working fluid, providing a theoretical basis for further experimental research.
1 Model establishment 1.1 Refrigeration and air conditioning system cycle performance simulation calculation method The actual refrigeration system is a complex dynamic process that combines heat and mass transfer. From the perspective of system performance simulation, several major components of the refrigeration system can be divided into three types of thermal models: the first is the evaporator and the condenser, which belong to the heat exchanger components, in which a certain amount of refrigerant is stored. The accuracy of the simulation results directly affects the calculation results of the system refrigerant storage allocation, but has no direct impact on the system flow. The second category is expansion valves and compressors, which are pressure regulating components in the system that directly determine the system's evaporation and condensing pressures. The accumulator can be classified into the third category. It stores most of the refrigerant in the whole system and has a great influence on the dynamic performance of the whole system. However, it does not require detailed understanding of the heat and mass transfer process, only calculation The overall status of the reservoir and the import and export parameters.
Since evaporators and condensers are very important in refrigeration systems, their research is also very active. Some corresponding mathematical models have been established, which can be divided into four types: black box model, single region model, and two regions. Model and distribution parameter models. The evaporator and condenser of the water source heat pump use circulating water as the carrier. On the basis of the two-region model, the momentum exchange and mass exchange generated by the gas-liquid slip in the two-phase region are considered, and a set of non-causal model is established. . For compressors and accumulators, the complex heat and mass transfer process is generally ignored. It is considered that the refrigerant in the compressor volume is evenly distributed, the refrigerant in the accumulator is in a saturated state, and the entire volume wall is at the same temperature. Lumped Model.
The throttling device has a capillary tube, a thermal expansion valve, etc., and the thermal expansion valve is generally regarded as a throttling device.
1.2 System Introduction The schematic diagram of the water source heat pump system is as follows, the specific parameters are as follows: condenser: casing type heat exchanger (plus insulation layer), copper pipe outer diameter φ0=10 mm, inner diameter φi=8 mm; plastic casing The inner diameter is φ=18 mm; the total length is 10 m. Using a node every 2 cm, a total of 500 nodes are taken along the length of the tube.
Evaporator: A sleeve-type heat exchanger similar to an evaporator with a total length of 8.46 m and a total of 423 nodes along the length of the tube. A thermal expansion valve is employed in which the temperature of the refrigerant in the temperature sensing package corresponds to the response of the evaporator outlet temperature. Compressor: rotary compressor, n = 2 980 r/min, theoretical displacement of the compressor V = 2.16 × 10 -6 m 3 / r. Reservoir: volume is V = 4.75 × 10 -4 m 3 . Four-way reversing valve.
1.3 System Model The goal of the system model is to establish the mathematical model of each component based on the known system structural parameters, the water temperature and flow rate of the heat exchanger inlet and outlet, and finally obtain the steady-state performance of the system.
1.3.1 Heat exchanger model The heat exchanger is the main heat exchange equipment in the refrigeration and air conditioning system. It consists of two main components: the evaporator and the condenser. For water source heat pumps, casing type (small load) heat exchangers and shell-and-tube heat exchangers (large load) are often used. In the experiment, casing type, refrigerant flow path, and heat carrier (cold) agent are selected. The shell-side process, so the dynamic mathematical model of the heat exchanger should include the inside of the tube, the outside of the tube and the metal wall.
The first part is a mathematical model of the refrigerant inside the tube. (4) For a homogeneous fluid, the values ​​in the above formula (1) (4) are 0 or 1, respectively, where R q is the heat exchange amount between the refrigerant and the pipe wall: tp, in tp()R w qαT T =.
(5) The second part is the mathematical model of the pipe wall: it is considered that the temperature inside and outside the pipe is equal, and the heat balance equation of the pipe wall is established by the lumped parameter method. d()()dw R i R waowa TCMATTATT t =α. (6) The third part is a mathematical model of cold (hot) water, which can be assumed as follows: the fluid is an incompressible fluid; the fluid flow is a one-dimensional flow; the viscosity of the fluid is small, and the viscous dissipation term is omitted; Heat conduction along the flow direction, mass equation: d() πd aaoa M d Dωx =.
(8) 1.3.2 Compressor Model The compressor is the core component of the whole system. The volumetric compressor is used in the experiment. Since the refrigerant in the compressor is in a gaseous state, it is treated as follows: simplified to an ideal adiabatic process except 80%.
Compressor displacement: th v R s V mv=λ, (9) where: gas transmission coefficient vλ, including compressor volume factor cλ, pressure coefficient pλ (take 1), preheat coefficient Tλ and leakage coefficient Dλ (According to 0.98), νs is the inlet gas density of the compressor and Vth is the theoretical volumetric gas volume of the compressor.
1.3.3 Thermal expansion valve model The process of refrigerant flow superheat expansion valve can be regarded as an equal process, ignoring the influence of the bulk heat capacity change, then the flow rate through the expansion valve is calculated: st() ()icebem C p Ï, (11) where C is the characteristic coefficient of the expansion valve, Ïi is the expansion valve refrigerant density, pb is the pressure of the temperature sensing package, and p st is the static pressure provided by the expansion valve spring.
1.3.4 Reservoir model The pressure drop of the refrigerant flowing through the accumulator is small. It can be considered that the enthalpy of the inlet vapour is equal to the enthalpy of the outlet vapour. The accumulator is regarded as a whole and the entire wall remains. At the same temperature, the following mathematical model was established using the lumped parameter method. Reservoir mass equation: d ac cemt .
(12) Reservoir energy equation: dd ac ee ac w ac ccmh T mht = +α.
(13) Temperature change of the wall surface of the accumulator: d()dwoaw ac w ac TCMT t = α. (14) 1.3.5 Four-way reversing valve model The four-way reversing valve mainly changes the flow direction of the gas by changing the air flow passage, thereby achieving the purpose of changing the moving direction of the pneumatic actuator. In the four-way valve, the amount of leakage from the high pressure side to the low pressure side can be expressed as: () L ce LC ppm = μ, (15) where CL is the leakage coefficient.
2 Calculation method and result analysis 2.1 Calculation method Steady-state calculation is mainly used to predict the performance of the system when the refrigeration system is running stably under certain working conditions, thus reflecting the compressor, condenser, accumulator, four-way reversing valve, The coupling relationship between the thermal expansion valve and the components of the evaporator. The actual refrigeration system is a closed circulation loop, which characterizes the physical quantity of the working fluid characteristics, which is the output of a certain component of the system and the input quantity of the next component of the system, so that the operating parameters of the system and each component can be conveniently obtained. Coupling relationship. Generally, the upstream boundary point value is used instead of the corresponding parameter value of the internal node, and the forward difference is used for each differential term, and the implicit term is used for the time item.
Calculate the thermal property parameters of pure working fluid R22 and mixed working fluid R22/R142b (according to mass component 46.3:53.7), adopt the improved PT equation, and assume the initial parameters: evaporator outlet superheat is the same as 5 ° C; T c, T The selection principle of e: the pure working fluid takes the condensing pressure and the saturation temperature corresponding to the evaporation pressure, and the mixed working fluid takes the bubble point temperature corresponding to the condensing pressure and the dew point temperature corresponding to the evaporation pressure.
2.2 Calculation results and analysis In order to test the accuracy of the above model, the experimental data of a small water source heat pump device is compared with the simulation results of the corresponding environmental parameters. The results are shown in Table 1. The comparison data includes the evaporator and the condenser. The outlet water temperature, the cooling capacity of the entire system, the amount of work consumed, and the corresponding coefficient of performance COP. From the comparison between the calculation results in the table and the experimental results, it can be seen that the average error of the outlet water temperature of the evaporator and the condenser is less than 0.62 ° C, and the error of cooling capacity and power consumption is less than 9.95% and 8.7%, indicating the accuracy of the established calculation model. Higher, can better predict the steady state performance of the system.
3 Conclusions The mathematical model of each component of the water source heat pump system is established. According to the change relationship between the parameters of each component in the system, the evaporation temperature T e and the condensation temperature T c are adjusted appropriately. The simulation results are compared with the experimental results. It is shown that the mathematical model established in this paper can be used for computer simulation of steady-state characteristics of multi-parameter air-conditioning system, which provides a more complete dynamic simulation method for optimal design and optimal control of water source heat pump system structure.
Considering the temperature slip phenomenon of non-azeotropic mixed working fluid, the distributed parameter model is adopted in the model of establishing heat exchanger. It can be seen from Table 1 that the calculation accuracy is controlled within 10%, which can be applied to the model of heat pump system. Performance optimization calculations in the design and system.
Mainly used for vibration and leveling of concrete road. Usually be used in bridge and township, frame can be assembled freely, suitable for pavement construction of different width . It is a new equipment for roads, squares and modern factory building. And it is a traditional paver upgrading products.
1.two type:electric/gasoline vibratory truss screed.
2.Vibratory truss screed was used to slurry extracting ,compression, planning of the concrete in the field of bridge ,road,workshop,square and so on.
3. 3~18meter available working length can combine according customer request.
4.single joint ,adopts super strength connection.
5.you can use electric motor or gasoline engine to drive the machine vibration.
6.the electric motor we can supply different voltage and frequency.
Main scope: Concrete Grinding machines, Floor Polishing Machines, Road Line Marking Machines, Truck Cranes, Road Rollers, Excavators, Concrete Leveling Machines, Power Trowels and other Construction machinery .
Jining oking tec co.,ltd, established in 2010, is a professional manufacturer engaged in the research, development, production, sale and service of Concrete Grinding machines, Floor Polishing Machines, Road Line Marking Machines, Truck Cranes, Road Rollers, Excavators, Concrete Leveling Machines, Power Trowels and other Construction machinery .
We are located in Jining city,Shandong province with convenient transportation access. Dedicated to strict quality control and thoughtful customer service, our experienced staff members are always available to discuss your requirements and ensure full customer satisfaction.
In recent years, we have introduced a number of advanced production equipment, and also have an excellent production team and a complete quality assurance system to ensure that each batch of goods is delivered to customers in a timely and high quality.
We also have an excellent management team, experienced technical staffs and professional sales team to solve all problems you encountered before and after sales. In addition, we have obtained I S O 9 0 0 1:2 0 1 5 certificates. Selling well in all cities and provinces around China, our products are also exported to clients in such countries and regions as United States, Europe,Australia, Southeast Asia,Russia,the Middle East,Africa. We also welcome OEM and ODM orders. Whether selecting a current product from our catalog or seeking engineering assistance for your application, you can talk to our customer service center about your sourcing requirements.
Concrete Vibratory Truss Screed
Concrete Vibratory Truss Screed,Concrete Vibrating Screed,Concrete Vibratory Truss Screed Automatic,Road Construction Concrete Vibratory Truss Screed
Jining Oking Tec Co., Ltd. , http://www.okingmachinery.com