Simulation analysis and calculation method for preheating of lubricating oil of reciprocating piston compressor

Abstract

This invention provides a simulation analysis and calculation method for the preheating of lubricating oil during the start-up of a reciprocating piston compressor. The method includes the heating efficiency of the lubricating oil, the heat dissipation power of components, and the heating power of components. Using CFD software, considering the effects of ambient temperature, thermal radiation, forced air convection, and heat conduction, it simulates the average surface temperature and body temperature of the compressor body, and calculates the total power required for heating the lubricating oil. It can accurately simulate the heating of the compressor body and its heat loss under different ambient temperatures, and accurately calculate the heater power required to heat the lubricating oil to a predetermined temperature within a predetermined time, as well as the impact of different ambient temperatures on the total heater power. This provides a reference for selecting the power of the lubricating oil heater.

Description

Technical Field

[0001] This invention relates to the technical field of compressor lubrication and heating, specifically to a simulation analysis and calculation method for preheating the lubricating oil during startup of a reciprocating piston compressor. Background Technology

[0002] The lubrication system is a crucial component for ensuring the normal operation of a reciprocating piston compressor. It effectively reduces wear on friction pairs, lowers noise, and reduces the operating temperature of the shaft and bearings. Because the viscosity of lubricating oil is greatly affected by temperature, lower winter temperatures result in higher oil viscosity and poor flow, making it difficult for the oil pump to draw oil and for an oil film to form within the bearings. Therefore, before starting the compressor, a heater is needed to heat the lubricating oil in the compressor body (oil tank) to reach the minimum starting temperature requirement, allowing the compressor to start normally.

[0003] During the heating process of lubricating oil, the temperature of the lubricating oil rises. Due to the good thermal conductivity of the materials of the machine body, pipes, and containers, some of the heat from the lubricating oil is transferred to the walls of the machine body, pipes, and containers in contact with it. Therefore, part of the heating power is used for heating the walls of the machine body. When the temperature of the walls of the machine body, pipes, and containers rises above the ambient temperature, the low-temperature air from outside will exchange heat with the outer walls of the machine body, pipes, and containers, resulting in heat loss from the walls. In other words, part of the power of the lubricating oil heater is also used for heat dissipation.

[0004] Therefore, when calculating the power of a lubricating oil heater, the heating of the machine body, pipes, and container, as well as the heat loss of these two parts, must be considered. However, in actual use, some manufacturers select compressor lubricating oil heaters based solely on the required mass of lubricating oil to be heated and the temperature difference, calculating the total heat required, and then calculating the heater power based on the heating time.

[0005] Because the heating and heat dissipation of the machine body, pipes, and container were not taken into account, the heater power was too low, making it difficult to heat the lubricating oil to the required temperature within the specified time. Some manufacturers considered that some heat would be dissipated during the heating process, but due to the complexity of the factors affecting heating and heat dissipation, it was difficult to estimate. They simply added a certain percentage margin to the original power. This estimation is rather crude and cannot be accurately calculated for different ambient temperatures and scenarios. It may be too high when the ambient temperature and wind speed are low; when the ambient temperature is low or the outside wind speed is high, the machine body dissipates heat quickly, and the estimated power is often too low to meet the requirements.

[0006] To calculate the power of the lubricating oil heater as accurately as possible, it is necessary to conduct simulation and analysis of the lubricating oil preheating during the start-up of the reciprocating piston compressor. This involves fully considering the power losses caused by changes in the ambient temperature of the compressor, the heat transfer between the lubricating oil and the compressor body, the heat radiation from the casing, pipes and container walls, and the heat dissipation caused by forced heat convection. The heating and heat dissipation power of the casing walls can be obtained through simulation or on-site testing and monitoring, so that the total power of the lubricating oil heater can be selected reasonably. Summary of the Invention

[0007] The main objective of this invention is to provide a simulation analysis and calculation method for the preheating of lubricating oil during the start-up of a reciprocating piston compressor. Currently, there is a lack of effective and reliable analytical methods for calculating and selecting the power of heaters in compressor lubrication systems. The selected heater power either significantly exceeds the required power, resulting in resource waste, or is too low, failing to meet the heating needs of the lubricating oil. Furthermore, the difficulty in obtaining heating data from the compressor body makes it difficult to calculate heat loss, leading to inaccurate heater power selection.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by this invention is as follows: It includes the heating efficiency of the lubricating oil, the heat dissipation power of the component, and the heating power of the component. Using CFD software, considering the effects of ambient temperature, thermal radiation, forced air convection, and heat conduction, it simulates the average surface temperature and body temperature of the computer casing, and calculates the total power required for heating the lubricating oil accordingly. The steps are as follows:

[0009] S1. Heating calculation of lubricating oil;

[0010] S2, calculation of heat dissipation power of lubricating oil, machine body and pipeline;

[0011] S3. Calculation of heating power for the machine body and piping;

[0012] S4. Analysis and calculation of the total power of the heater under different operating conditions.

[0013] In the preferred embodiment, the heating calculation for the lubricating oil in S1 is as follows:

[0014] Before startup, the mass of lubricating oil contained in the compressor lubrication system is m1. The ambient temperature and the initial temperature of the lubricating oil at the operating site are T0. The heater is required to heat the lubricating oil to a predetermined temperature T1 within time t. The specific heat capacity of the lubricating oil is Cp1. Therefore, the heat required to heat the lubricating oil from the initial temperature T0 to the predetermined temperature T1 is Q1 = m1 * Cp1 * (T1 - T0). Hence, the heating power of the lubricating oil is P1 = Q1 / t.

[0015] In the preferred scheme, the specific steps of S2 are as follows:

[0016] A1. Calculate the heat dissipation power of the lubricating oil to the air;

[0017] A2. Overall heat transfer coefficient of the computer body, simulation analysis of the heat dissipation of the computer body, heat dissipation power of the computer body;

[0018] A3. Calculate the overall heat transfer coefficient of the pipes and containers, and calculate the heat dissipation power of the pipes and containers.

[0019] In the preferred scheme, the heat dissipation power of the lubricating oil to the air in A1 is calculated as follows:

[0020] The volume occupied by the lubricating oil in the machine body is L*W*h, the internal height of the machine body is H0, the compressor body is sealed, so the air inside the machine body can be considered to be stationary. Therefore, there is no convective heat transfer between the lubricating oil and the air above it, only heat conduction. The thermal conductivity of the air is Hfo, P2=Hfo*(H0-h)*(T1-T0)*0.5;

[0021] The thermal conductivity Hfo of still air is very small. Compared with the heat loss due to thermal convection and thermal radiation, the heat loss of lubricating oil through air thermal conduction is negligible.

[0022] In the preferred scheme, the overall heat transfer coefficient of the fuselage in A2 is calculated as follows:

[0023] The fuselage is a cuboid shape with length, width and height of L*W*H. Based on its material, existing literature was consulted to select the thermal radiation heat transfer coefficient HrJ of the outer surface of the fuselage and the forced convection heat transfer coefficient HfJ of the outer surface of the fuselage under different materials, ambient temperatures and wind speeds.

[0024] The total heat transfer coefficient of forced convection and thermal radiation of air on the outer surface of the fuselage is HfJ'=HfJ / L+HrJ;

[0025] The simulation analysis of the chassis heat dissipation is as follows:

[0026] Using CFD software, a simplified model of the fuselage is established, consisting of a rectangular box with length, width, and height L*W*H, thickness dH, and mass m2. The interior of the fuselage is filled with lubricating oil of height h. The overall temperature of the lubricating oil is set to a predetermined temperature T1, and the initial temperature of the fuselage is the same as the ambient temperature, T0. The bottom of the fuselage is set with an adiabatic boundary condition, and the other five outer surfaces are set with a convective heat transfer boundary condition.

[0027] The temperature distribution map of each wall of the fuselage can be obtained by CFD calculation. Then, the weighted average temperature of the five outer surfaces of the fuselage excluding the bottom surface is calculated, that is, the average temperature of the outer surface of the fuselage is Tsv.

[0028] The heat dissipation power of the chassis is calculated as follows:

[0029] The heat dissipation area of ​​the five outer surfaces of the fuselage is Aj = L*W + 2*(L*H + W*H). Since the temperature of the fuselage rises approximately linearly from the initial temperature T0 to the final average surface temperature TsV within time t, the heat dissipation power of the fuselage exterior facing the environment is P3 = HfJ'*Aj*(TsV-T0) / 2.

[0030] In the preferred scheme, the overall heat transfer coefficient of the pipes and containers in A3 is calculated as follows:

[0031] Based on the materials of the pipes and containers, literature was consulted to select the thermal radiation heat transfer coefficient Hrg of the outer surface of the fuselage and the forced convection heat transfer coefficient Hfg of the outer surface of the fuselage under different materials, ambient temperatures and wind speeds.

[0032] The total heat transfer coefficient of forced convection and thermal radiation of air on the outer surface of pipes and containers is Hfg'=Hfg / L+Hrg;

[0033] The heat dissipation power of pipes and containers is calculated as follows:

[0034] The pipe and container have a diameter Dg and a length Lg. The heat dissipation area of ​​the outer surface Ag = PI * Dg * Lg. The pipe and container have a thin wall thickness and are in complete contact with the lubricating oil. It is assumed that the temperature of the pipe and container is always consistent with the lubricating oil temperature, rising from the initial temperature T0 to the final temperature T1. Therefore, the heat dissipation power of the pipe and container facing the environment is P4 = Hfg' * Ag * (T1 - T0) / 2.

[0035] In the preferred embodiment, the heating power of the S3 body is:

[0036] The temperature distribution of each wall surface of the fuselage is obtained by CFD calculation. Based on this, the average temperature of the fuselage TsT is calculated, that is, the fuselage temperature rises from the initial temperature T0 to TsT. Given that the mass of the fuselage is m2 and the specific heat capacity of the fuselage material is Cp2, the heating heat of the fuselage Q2=m2*Cp2*(TsT-T0), and the heating power of the fuselage P5=Q2 / t;

[0037] The heating power of pipes and containers is calculated as follows:

[0038] The pipes and containers rise from an initial temperature T0 to a final temperature T1. Given that the mass of the pipes and containers is m3 and the specific heat capacity of the materials is Cp3, the heating heat of the pipes and containers is Q3 = m3 * Cp3 * (T1 - T0). Therefore, the heating power of the machine body is P6 = Q3 / t.

[0039] In the preferred scheme, the operating conditions in S4 are divided into two types:

[0040] Operating Condition 1: Compressor hot-running, maintaining the temperature within the start-up temperature range to enable immediate start-up;

[0041] Operating Condition 2: Cold start of the compressor, reaching the start-up conditions within a specified time requirement from different low-temperature environments.

[0042] In the preferred scheme, the total power of the heater in operating condition one is calculated as follows:

[0043] After the lubricating oil heating process is completed, the lubricating oil temperature is T1, the ambient temperature is T0, and the average surface temperature of the machine body is maintained at TsV. At this time, the heat dissipation temperature difference between the machine body and the environment is Tsv-T0, and the heat dissipation temperature difference between the pipes and containers and the environment is T1-T0. If the heat dissipation power is to maintain the lubricating oil temperature at T1, then the power required to maintain the oil temperature is the total heat dissipation power of the machine body, pipes and containers, PA = 2*(P3+P4).

[0044] The total power of the heater in operating condition two is calculated as follows:

[0045] The power P required by the heater to heat the lubricating oil from the ambient temperature T0 to the preset temperature T1 within a predetermined time t is the sum of the above powers, i.e., P1+P2+P3+P4+P5+P6. In industrial applications, a 20% power margin is generally considered, so the final total power of the heater PB = 1.2*(P1+P2+P3+P4+P5+P6).

[0046] In the preferred scheme, CFD software is used to calculate the average surface temperature TsV and the average body temperature TsT of the fuselage under different ambient temperatures T0. These values ​​are then substituted into the power calculation formula to obtain the total heater power P' under different ambient temperatures T0. A curve is plotted with ambient temperature T0 as the abscissa and total heater power P as the ordinate. After data fitting, the fitting relationship between the total heater power and the ambient temperature is P' = f(T0), forming a reference formula for selecting heater power under different ambient temperatures.

[0047] This invention provides a simulation analysis and calculation method for the preheating of lubricating oil during startup of a reciprocating piston compressor, with the following beneficial effects:

[0048] 1. The heating power of the machine body, pipes and containers, as well as the heat dissipation power of the outer surface, are all included in the heating power calculation, which improves the accuracy of heater power calculation.

[0049] 2. The influence of ambient temperature on the heat dissipation and heating of the calculated wall was fully considered, and the relationship between the total power P of the heater under different ambient temperatures T0 was fitted, providing a basis for the selection of heater power under different environments.

[0050] 3. This calculation method can provide accurate heater selection calculation formulas for different compressor models under different operating conditions. Attached Figure Description

[0051] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0052] Figure 1 This is a schematic diagram of the oil tank in the fuselage of the present invention;

[0053] Figure 2 This is a temperature curve of the fuselage under different ambient temperatures according to the present invention;

[0054] Figure 3 This is a graph showing the total power curve of the heater under different ambient temperatures according to the present invention; Detailed Implementation

[0055] Example 1

[0056] like Figures 1-3 As shown, the simulation analysis and calculation method for lubricating oil preheating during the start-up of a reciprocating piston compressor includes four parts: analysis and calculation of lubricating oil heating, heat dissipation power, heating power, and total heating power under different ambient temperatures. The specific steps are as follows:

[0057] Calculation of heating power for lubricating oil:

[0058] Before startup, the compressor lubrication system contains a mass of lubricating oil called m1. The ambient temperature at the operating site (i.e., the initial temperature of the lubricating oil) is T0. The heater is required to heat the lubricating oil to a predetermined temperature T1 within time t. The specific heat capacity of the lubricating oil is Cp1. Therefore, the heat required to heat the lubricating oil from the initial temperature T0 to the predetermined temperature T1 is Q1 = m1 * Cp1 * (T1 - T0). Hence, the heating power of the lubricating oil is P1 = Q1 / t.

[0059] Calculation of heat dissipation power for lubricating oil, machine body, and piping:

[0060] The heat dissipation power of the lubricating oil to the air, P2: The volume occupied by the lubricating oil in the machine body is L*W*h, the internal height of the machine body is H0 (the height from the bottom inner wall of the machine body to the top), the compressor body is sealed, so the air inside the machine body can be considered as stationary, then there is no convective heat transfer between the lubricating oil and the air above it, only heat conduction, the thermal conductivity of the air is Hfo, P2=Hfo*(H0-h)*(T1-T0)*0.5.

[0061] The thermal conductivity Hfo of still air is very small. Compared with the heat loss due to thermal convection and thermal radiation, the heat loss of lubricating oil through air thermal conduction is negligible.

[0062] Heat dissipation capacity P3 of the fuselage: Heat dissipation of the fuselage mainly occurs when the fuselage temperature is higher than the ambient temperature. The fuselage interacts with the cool ambient air through thermal radiation, conduction, and convection, primarily through forced convection. Compared to the heat loss from convection and radiation, the heat loss from conduction is negligible. Therefore, only the heat loss due to convection and radiation between the fuselage and the flowing air, caused by wind speed, needs to be calculated.

[0063] The overall heat transfer coefficient of the computer body is HfJ': The body is generally rectangular in shape (length, width and height are L*W*H), and is generally made of gray iron. Based on existing literature, the heat radiation heat transfer coefficient HrJ of the outer surface of the body and the forced convection heat transfer coefficient HfJ of the outer surface of the body are found under different materials, ambient temperatures and wind speeds.

[0064] The total heat transfer coefficient of forced convection and thermal radiation on the outer surface of the fuselage is HfJ'=HfJ / L+HrJ.

[0065] Simulation analysis of chassis heat dissipation: Most compressors have their bottoms in contact with steel structures, concrete, or epoxy resin grout. Therefore, when the temperature of the chassis bottom surface is higher than the temperature of the contact material, the chassis bottom will dissipate heat to the ground through heat conduction. Because the thermal conductivity of the contact material is relatively low, the heat dissipation power of the chassis bottom surface is negligible compared to other external surfaces that experience forced convection with the air. Therefore, only the heat dissipation power of the five external surfaces (front, back, left, right, and top) needs to be considered.

[0066] Using CFD software, a simplified model of the fuselage was created, consisting of a rectangular box with dimensions L*W*H, thickness dH, and mass m². The box contains lubricating oil with a height h. The overall temperature of the lubricating oil was set to a predetermined temperature T1, and the initial temperature of the fuselage was set to T0, the same as the ambient temperature. An adiabatic boundary condition was applied to the bottom of the fuselage, while the other five outer surfaces were subjected to convective heat transfer boundary conditions (heat transfer coefficient HfJ'). CFD calculations yielded the temperature distribution maps for each wall surface of the fuselage. The weighted average temperature of the five outer surfaces (excluding the bottom) was then calculated, resulting in the average temperature of the fuselage's outer surfaces, Tsv.

[0067] Computer body heat dissipation power P3: The heat dissipation area of ​​the five outer surfaces of the chassis, front, back, left, right and top, Aj = L*W + 2*(L*H + W*H). Since the temperature of the chassis rises approximately linearly from the initial temperature T0 to the final average surface temperature TsV within time t, the heat dissipation power of the chassis exterior facing the environment, P3 = HfJ'*Aj*(TsV-T0) / 2.

[0068] Heat dissipation power P4 of pipes and containers: When the temperature of pipes and containers is higher than the ambient temperature, they will undergo heat radiation, heat conduction, and heat convection with the cold ambient air through their outer surfaces, with forced convection of air being the primary heat transfer method. Compared to the heat loss due to heat convection and heat radiation, the heat loss due to heat conduction is negligible. Therefore, it is only necessary to calculate the heat loss due to heat convection and heat radiation with the flowing air caused by wind speed.

[0069] The overall heat transfer coefficient of the pipes and containers is calculated as Hfg': The pipes and containers are generally made of stainless steel. Based on existing literature, different materials, ambient temperatures and wind velocities are selected, and the thermal radiation heat transfer coefficient Hrg of the outer surface of the fuselage and the forced convection heat transfer coefficient Hfg of the outer surface of the fuselage are found.

[0070] The total heat transfer coefficient of forced convection and thermal radiation of air on the outer surface of pipes and containers is Hfg'=Hfg / L+Hrg.

[0071] Calculate the heat dissipation power P4 of the pipe and container: pipe and container diameter Dg, length Lg, heat dissipation area of ​​outer surface Ag = PI * Dg * Lg. The pipe and container wall is relatively thin and in complete contact with the lubricating oil. It is assumed that the temperature of the pipe and container is always the same as that of the lubricating oil, rising from the initial temperature T0 to the final temperature T1. Therefore, the heat dissipation power P4 of the outer surface of the pipe and container facing the environment is P4 = Hfg' * Ag * (T1 - T0) / 2.

[0072] Heating power calculation for the machine body and piping:

[0073] Heating power of the fuselage: From the simulation analysis of the fuselage heat dissipation, it can be seen that the temperature distribution of each wall surface of the fuselage is obtained by CFD calculation. Based on this, the average body temperature TsT of the fuselage is calculated, that is, the body temperature rises from the initial temperature T0 to TsT. Given that the mass of the fuselage is m2 and the specific heat capacity of the fuselage material is Cp2, the heating heat of the fuselage is Q2=m2*Cp2*(TsT-T0), so the heating power of the fuselage is P5=Q2 / t.

[0074] Heating power of pipes and containers: The pipes and containers rise from the initial temperature T0 to the final temperature T1. Given that the mass of the pipes and containers is m3 and the specific heat capacity of the materials is Cp3, the heating heat of the pipes and containers is Q3=m3*Cp3*(T1-T0). Therefore, the heating power of the machine body is P6=Q3 / t.

[0075] Calculation of total heater power under different operating conditions:

[0076] Operating Condition 1: Compressor hot-running and cooling, maintaining the temperature within the start-up temperature range to enable start-up at any time;

[0077] After the lubricating oil heating process is completed, the lubricating oil temperature is T1, the ambient temperature is T0, and the average surface temperature of the machine body is maintained at TsV. At this time, the heat dissipation temperature difference between the machine body and the environment is Tsv-T0, and the heat dissipation temperature difference between the pipes and containers and the environment is T1-T0. If the heat dissipation power is to maintain the lubricating oil temperature at T1, then the power required to maintain the oil temperature is the total heat dissipation power of the machine body, pipes and containers, PA = 2*(P3+P4).

[0078] Operating Condition 2: The compressor starts cold, reaching the starting conditions within a specified time requirement from different low-temperature environments;

[0079] The power P required by the heater to heat the lubricating oil from the ambient temperature T0 to the preset temperature T1 within a predetermined time t is the sum of the above powers, i.e., P1+P2+P3+P4+P5+P6. In industrial applications, a 20% power margin is generally considered, so the final total power of the heater PB = 1.2*(P1+P2+P3+P4+P5+P6).

[0080] The key to heater power calculation lies in calculating the heat dissipation power P3 and heating power P5 of the fuselage. Since the overall heat transfer coefficient HfJ' of heat convection and radiation on the fuselage outer surface does not change significantly over a relatively large temperature range, the key to power calculation lies in the average outer surface temperature TsV and the body average temperature TsT of the fuselage, which are greatly affected by ambient temperature. Using CFD software, the values ​​of the average outer surface temperature TsV and the body average temperature TsT of the fuselage at different ambient temperatures T0 are calculated. These values ​​are then substituted into the power calculation formula to obtain the total heater power P' at different ambient temperatures T0. A curve is plotted with ambient temperature T0 as the abscissa and the total heater power P as the ordinate. After data fitting, the fitting relationship between the total heater power and the ambient temperature is obtained as P' = f(T0), forming a reference formula for heater power selection under different ambient temperatures.

[0081] Example 2

[0082] like Figures 1-3 As shown, further explanation is provided in conjunction with Example 1: Figure 1 A fuselage model with dimensions L*W*H is constructed. A layer of lubricating oil with a thickness of h is placed at the bottom of the fuselage. A heater is used to heat the lubricating oil from ambient temperature T0 to a preset temperature T1 within t hours. The specific parameters of the model are shown in the table below:

[0083]

[0084] According to the heater power calculation and analysis method provided by the present invention, the steps are as follows:

[0085] Calculation of heating power for lubricating oil:

[0086] The heat required to heat the lubricating oil is Q1 = m1 * Cp1 * (T1 - T0) = 9403 KJ.

[0087] The heating power of the lubricating oil is P1 = Q1 / t = 9403 KJ / 4 hours = 0.65 kW.

[0088] Calculation of heat dissipation power for lubricating oil, machine body, and piping:

[0089] The heat dissipation power of lubricating oil to air: P2≈0KW;

[0090] Heat dissipation power of the fuselage: Based on existing literature, HrJ = 0.55 (Btu / h-ft2-F) is selected.

[0091] HfJ = 25(Btu / h-ft2-F);

[0092] The overall heat transfer coefficient of forced convection and thermal radiation on the outer surface of the fuselage is

[0093] HfJ'=HfJ / L+HrJ=22.3(W / m2*K);

[0094] The five outer surface areas of the fuselage

[0095] AJ=2.25*0.626+(0.626*0.756+2.25*0.756)*2m2=5.76m2,

[0096] When the lubricating oil temperature is T1, according to the CFD simulation results, the average temperature of the outer surface of the fuselage is TsV = 14.22℃. Therefore, during the heating process, the heat dissipation power of the five outer surfaces of the fuselage facing the environment is...

[0097] P3=HfJ'*AJ*(TsV-T0) / 2=22.33*5.76*(14.22-3.7) / 2=0.67kW.

[0098] Heat dissipation power of pipes and container body: Based on existing literature, select Hrg = 0.65 (Btu / h-ft2-F) and Hfg = 20 (Btu / h-ft2-F);

[0099] The overall heat transfer coefficient of forced convection and thermal radiation on the outer surface of pipes and containers is:

[0100] Hfg'=Hfg / L+Hrg=19.05(W / m2*K);

[0101] The outer surface area of ​​the pipe and container, Ag = 3.14 * 0.05 * 5 = 0.785 m².

[0102] P4=Hfg'*Ag*(T1-T0) / 2=19.05*0.785*(27-3.7) / 2=0.174kW.

[0103] Heating power calculation for the machine body and piping:

[0104] Heating power of the fuselage: According to the CFD simulation results, the average temperature of the fuselage is TsT = 16.8℃. Therefore, the heating heat of the fuselage is Q3 = m2*Cp2*(TsT-T0) = 23696KJ. Thus, the heating power of the fuselage is P5 = Q3 / t = 23696KJ / 4hour = 1.65kW.

[0105] Heating power of pipes and containers: The pipes and containers rise from an initial temperature T0 to a final temperature T1. Given that the mass of the pipes and containers is m³ and the specific heat capacity of the materials is Cp³, the heating energy of the pipes and containers is Q³ = m³ * Cp³ * (T1 - T0) = 11650 kJ. Therefore, the heating power of the machine body is...

[0106] P6=Q3 / t=11650KJ / 4hour=0.81kW.

[0107] Total power of the heater under different ambient temperatures:

[0108] Operating Condition 1: Compressor hot-running and cooling, maintaining the temperature within the start-up temperature range to enable start-up at any time;

[0109] The power required to maintain the oil temperature is PA = 2*(P3+P4) = 1.688kW;

[0110] Operating Condition 2: The compressor starts cold, reaching the starting conditions within a specified time requirement from different low-temperature environments;

[0111] The heater power is generally considered with a 20% margin, and the final total heater power...

[0112] P=1.2*(P1+P2+P3+P4+P5+P6)=3.954kW.

[0113] Compared to the currently selected heater power of 6.5kW, the total heater power can be reduced by about 39% by using the method of this invention.

[0114] The average surface temperature Ts and the body average temperature Ts1 of the fuselage were simulated at different ambient temperatures T0 (-10℃, -5℃, 0℃, and 3.7℃, respectively). Figure 2 As shown, the total heating power P' of the heater was calculated, and a linear fit was performed to obtain the fitting equation y = -0.119x + 4 for the total heating power (y) of the heater and the ambient temperature (x).

[0115] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A simulation analysis and calculation method for preheating lubricating oil during startup of a reciprocating piston compressor, characterized by: This includes the heating efficiency of the lubricating oil, the heat dissipation power of the components, and the heating power of the components. Using CFD software, considering the effects of ambient temperature, thermal radiation, forced air convection, and heat conduction, the average surface temperature and body temperature of the computer are simulated, and the total power required for heating the lubricating oil is calculated accordingly. The steps are as follows: S1. Heating calculation of lubricating oil; S2, calculation of heat dissipation power of lubricating oil, machine body and pipeline; S3. Calculation of heating power for the machine body and piping; S4. Analysis and calculation of the total power of the heater under different operating conditions; Before startup, the compressor lubrication system contains a mass of lubricating oil called m1. The ambient temperature and the initial temperature of the lubricating oil at the operating site are T0. The heater is required to heat the lubricating oil to a predetermined temperature T1 within time t. The specific heat capacity of the lubricating oil is Cp1. Therefore, the amount of heat required to heat the lubricating oil from its initial temperature T0 to the predetermined temperature T1 is Q1 = m1. Cp1 (T1-T0), therefore the heating power of the lubricating oil is P1=Q1 / t; The specific steps of S2 are as follows: A1. Calculate the heat dissipation power of the lubricating oil to the air; A2. Overall heat transfer coefficient of the computer body, simulation analysis of the heat dissipation of the computer body, heat dissipation power of the computer body; A3. Calculate the overall heat transfer coefficient of the pipes and containers, and calculate the heat dissipation power of the pipes and containers; The volume occupied by the lubricating oil in the machine body is L. W h, the internal height of the compressor body is H0. Since the compressor body is sealed, the air inside can be considered stationary. Therefore, there is no convective heat transfer between the lubricating oil and the air above it, only heat conduction. The thermal conductivity of air is Hfo, and P2 = Hfo. (H0-h) (T1-T0) 0.5; The fuselage is rectangular in shape, with length, width, and height of L. W H, based on its material, consulted existing literature to select the thermal radiation heat transfer coefficient HrJ of the outer surface of the fuselage under different materials, ambient temperatures and wind speeds, and the forced convection heat transfer coefficient HfJ of the outer surface of the fuselage. The total heat transfer coefficient of forced convection and thermal radiation of air on the outer surface of the fuselage is HfJ'=HfJ / L+HrJ; Using CFD software, a simplified model of the fuselage with dimensions L is created. W H is a rectangular box with a thickness of dH and a mass of m2. The box contains lubricating oil with a height of h. The overall temperature of the lubricating oil is set to a predetermined temperature T1. The initial temperature of the machine body is the same as the ambient temperature, T0. The bottom of the machine body is set with an adiabatic boundary condition, and the other five outer surfaces are set with a convective heat transfer boundary condition. The temperature distribution map of each wall of the fuselage can be obtained by CFD calculation. Then, the weighted average temperature of the five outer surfaces of the fuselage excluding the bottom surface is calculated, that is, the average temperature of the outer surface of the fuselage is Tsv. The heat dissipation area Aj=L of the five outer surfaces of the fuselage W+2 (L) H+W H), Since the fuselage temperature rises approximately linearly from the initial temperature T0 to the final average surface temperature TsV within time t, the heat dissipation power of the fuselage exterior facing the environment is P3 = HfJ' Aj (TsV-T0) / 2; Based on the materials of the pipes and containers, literature was consulted to select the thermal radiation heat transfer coefficient Hrg of the outer surface of the fuselage and the forced convection heat transfer coefficient Hfg of the outer surface of the fuselage under different materials, ambient temperatures and wind speeds. The total heat transfer coefficient of forced convection and thermal radiation of air on the outer surface of pipes and containers is Hfg'=Hfg / L+Hrg; Pipe and container diameter Dg, length Lg, and heat dissipation area Ag = PI Dg Lg, the pipe and container walls are relatively thin and in complete contact with the lubricating oil, and it is assumed that their temperature remains consistent with the lubricating oil temperature, rising from the initial temperature T0 to the final temperature T1. Therefore, the heat dissipation power of the pipe and container's outer surface facing the environment is P4 = Hfg' Ag (T1-T0) / 2; The temperature distribution of each wall surface of the fuselage is obtained using CFD calculations. Based on this, the average body temperature TsT of the fuselage is calculated, meaning the fuselage temperature rises from the initial temperature T0 to TsT. Given that the mass of the fuselage is m2 and the specific heat capacity of the fuselage material is Cp2, the amount of heat generated by heating the fuselage is Q2 = m2. Cp2 (TsT-T0), therefore the heating power of the machine body P5=Q2 / t; A pipe and container are heated from an initial temperature T0 to a final temperature T1. Given that the mass of the pipe and container is m³ and the specific heat capacity of the material is Cp³, the amount of heat required to heat the pipe and container is Q³ = m³. Cp3 (T1-T0), therefore the heating power of the machine body is P6=Q3 / t; The operating conditions in S4 are divided into two types: Operating Condition 1: Compressor hot-running, maintaining the temperature within the start-up temperature range to enable immediate start-up; Operating Condition 2: Compressor cold start, reaching the start-up conditions within a specified time requirement from different low-temperature environments; The total power of the heater in operating condition one is calculated as follows: After the lubricating oil heating process is complete, the lubricating oil temperature is T1, the ambient temperature is T0, and the average surface temperature of the machine body is maintained at TsV. At this time, the heat dissipation temperature difference between the machine body and the environment is Tsv-T0, and the heat dissipation temperature difference between the pipes and containers and the environment is T1-T0. If the heat dissipation power is to maintain the lubricating oil temperature at T1, then the power required to maintain the oil temperature is the total heat dissipation power of the machine body, pipes, and containers, PA=2. (P3+P4); The total power of the heater in operating condition two is calculated as follows: The power required for the heater to heat the lubricating oil from ambient temperature T0 to preset temperature T1 within a predetermined time t is PB = P1 + P2 + P3 + P4 + P5 + P6.

2. The simulation analysis and calculation method for preheating of lubricating oil during startup of a reciprocating piston compressor according to claim 1, characterized in that: The thermal conductivity Hfo of still air is very small. Compared with the heat loss due to thermal convection and thermal radiation, the heat loss of lubricating oil through air thermal conduction is negligible.

3. The simulation analysis and calculation method for preheating of lubricating oil during startup of a reciprocating piston compressor according to claim 1, characterized in that: in In industrial applications, a 20% power margin is considered; therefore, the final total power of the heater, PB, is 1.

2. (P1+P2+P3+P4+P5+P6).

4. The simulation analysis and calculation method for preheating of lubricating oil during startup of a reciprocating piston compressor according to claim 1, characterized in that: Using CFD software, the average surface temperature TsV and the average body temperature TsT of the fuselage under different ambient temperatures T0 were calculated. Then, the values ​​were substituted into the power calculation formula to obtain the total heater power P' under different ambient temperatures T0. A curve was plotted with ambient temperature T0 as the abscissa and total heater power P as the ordinate. After data fitting, the fitting relationship between the total heater power and the ambient temperature was P'=f(T0), forming a reference formula for selecting heater power under different ambient temperatures.

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