CN102565123A - Method for measuring air ratio and heat capacity ratio by adiabatic compression as well as modifying data - Google Patents

Abstract

The invention discloses adiabatic compression measurement air specific heat capacity ratio and a data correction method, which relate to the field of physical parameter measurement. Due to the time limit of the student experiment to measure multiple data within 3-4 hours, the adiabatic effect of the container containing the air cannot be too good, the adiabatic effect is not good and the pumping speed is too slow, and the adiabatic expansion method is generally used to measure the air specific heat ratio Method to measure, can not use adiabatic compression to measure air specific heat ratio. Due to the influence of non-adiabatic factors, the measured value of the coefficient of air specific heat capacity ratio is too small. The technical solution of the invention is: reducing the volume of the gas container to realize fast inflating, then sampling at a high speed, and then correcting the data. The invention is beneficial for students to understand the method of measuring air specific heat capacity ratio through adiabatic compression, and is conducive to guiding students to understand the influence of heat dissipation on experimental data and its processing method, so that students can better understand air specific heat capacity ratio parameters and initially establish scientific data Approach.

Description

Adiabatic Compression Measuring Air Specific Heat Capacity Ratio and Data Correction Method

technical field

The invention relates to the field of physical parameter measurement, in particular to the measurement of the physical parameter air specific heat ratio.

Background technique

The measurement of the physical parameter air specific heat capacity ratio is a classic experiment in most universities. The time limit of the student experiment is roughly 3-4 hours, and multiple data are measured, so the insulation effect of the container containing the air cannot be too good, otherwise it will take a lot of time. , the container is generally made of glass material. Due to the poor heat insulation effect and the slow pumping speed, the method of adiabatic expansion is generally used to measure the specific heat capacity ratio of air. Air valve to shorten the deflation time. Adiabatic compression cannot be achieved to measure air specific heat ratio.

Due to the influence of non-adiabatic factors, the measured value of the coefficient of air specific heat capacity ratio is too small.

Contents of the invention

To achieve adiabatic compression to measure the specific heat capacity ratio of air, the main problem is to shorten the pumping time, and reducing the volume of the container is one way.

The technical scheme that the present invention adopts to solve its technical problem is: take the 500 milliliter water cup of hard plastic belt lock seal, drill a 4mm hole respectively at the cup cover and the bottom of the cup, one hole is connected to inflate, one hole is connected to the air pressure measuring device, Note that there must be no air leakage in each device.

Experimental data are obtained through experiments, and Table 1 is an example of experimental data.

Reason for data correction: The pressure 10.8hPa measured by the sensor is the pressure difference between the indoor air pressure and the standard air pressure. It takes 0.21 seconds to inflate to the maximum value of 95.3hPa (from 1.67 seconds to 1.88 seconds), and it takes 0.21 seconds to dissipate heat from the maximum value of 95.3hPa (from 1.88 Seconds to 2.09 seconds), the pressure drops by 95.3-89.1=6.2hPa, there is reason to believe that there is also heat dissipation during the 0.21 second pumping time, resulting in the measured maximum value of 95.3hPa being smaller than the actual maximum value.

Data correction method: use the polynomial fitting method to fit the pressure from 95.3hPa to 89.1hPa due to heat dissipation from 1.88 seconds to 2.09 seconds, and obtain a polynomial. Assuming that the air pressure increase in each sampling time interval is the pumping volume of the sampling time, the calculation of the pumping volume uses a polynomial to calculate the pressure value reduced from the sampling time to the maximum pressure of 95.3hPa corresponding to the sampling time of 1.88 seconds, and all the pumping sampling time The reduced pressure values calculated by the polynomial are summed to form the total correction amount.

The calculation result of the experimental data is: the polynomial corresponding to the quadratic fitting is y=84.5 (1-0.5699t+1.195*t*t), where y is the pressure difference relative to the room, and t is the time difference relative to 1.88 seconds Value, 84.5 is the relative indoor pressure difference at 1.88 seconds, the correction formula over time is 1-0.5699t+1.195*t*t; correction value 84.5-80.86=3.64hpa. The calculated value of air specific heat ratio=(95.3-10.8+3.64)/(72.4-10.8)=1.42 is relatively close to the theoretical value of 1.402.

The beneficial effects of the present invention are: it is beneficial for students to understand the method of measuring air specific heat capacity ratio through adiabatic compression, it is beneficial to guide students to understand the influence of heat dissipation on experimental data and its processing method, so that students can better understand the air specific heat capacity ratio parameters, Preliminary establishment of scientific data processing methods, good at finding rules from data.

Table 1 Experimental data

Table 2 Correction for pressure reduction caused by heat dissipation during the pumping process

t_sample(s) P(hPa) t_delta(s) P_delta1(hPa) P_delta2(hPa) 1.67 10.8 0.21 0 0.00 1.68 12 0.2 1.2 1.12 1.69 14.9 0.19 2.9 2.71 1.7 18.6 0.18 3.7 3.46 1.71 22.7 0.17 4.1 3.84 1.72 27.1 0.16 4.4 4.13 1.73 31.9 0.15 4.8 4.52 1.74 36.7 0.14 4.8 4.53 1.75 41.9 0.13 5.2 4.92 1.76 47 0.12 5.1 4.84 1.77 52.2 0.11 5.2 4.95 1.78 57.5 0.1 5.3 5.06 1.79 62.9 0.09 5.4 5.18 1.8 68.1 0.08 5.2 5.00 1.81 73.1 0.07 5 4.83 1.82 77.9 0.06 4.8 4.66 1.83 82.5 0.05 4.6 4.48 1.84 86.5 0.04 4 3.92 1.85 90 0.03 3.5 3.44 1.86 92.8 0.02 2.8 2.77 1.87 94.7 0.01 1.9 1.89 1.88 95.3 0 0.6 0.60 the the the 84.5 80.86

Claims (1)

1. The method of adiabatic compression measurement of air specific heat capacity ratio and data correction of the present invention involves physical parameter measurement, including the design, pumping, measurement and data correction of gas containers. Milliliter water cup, drill a 4mm hole in the lid and the bottom of the cup respectively, one hole is connected to the pump, and the other hole is connected to the air pressure measuring device, pay attention to the air leakage of each device; (2), obtain the pressure change of pumping at high speed and finish pumping (3) Use the pressure change law after pumping to correct the pressure decrease caused by heat dissipation during the pumping interval.