JPH08128978A - Specific heat measuring method and device therefor - Google Patents

Abstract

PURPOSE: To easily measure the specific heat of a sample in a short time by lowering the atmospheric pressure of the sample whose initial weight and initial temperature are preliminarily judged, evaporating the moisture in the sample, measuring the weight change and temperature change at that time, and using a known latent heat of evaporation of water and a specified expression. CONSTITUTION: A sample S whose initial weight W0 and initial temperature T0 are preliminarily measured is placed on the sample placing base 10 of a sealed vessel 1, the vessel 1 is sealed, and a vacuum pump P is started to reduce the atmospheric pressure of the sample S. The moisture in the sample S is evaporated, the weight change ΔW and temperature change ΔT of the sample S at that time are determined by inputting signals from a weight detecting means 3 and a temperature detecting means 4 to a processing device 5, respectively. The specific heat Cm of the sample is calculated from them by use of an expression. The latent heat hm of evaporation of water is known. Thus, the specific heat can be measured in a short time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring specific heat and an apparatus therefor, and particularly important physical properties in cooling, heating and storing foods and in designing such food machinery. The present invention relates to a method and an apparatus for measuring the specific heat of food, which is one of the values.

[0002]

2. Description of the Related Art For example, when operating a food machine for cooling, heating, or storing food, and when designing such a food machine, setting a processing time, a processing temperature, heating or cooling. The specific heat of the food is important for determining the throughput for such purposes. However, for the specific heat of such foods, only the values for a few kinds of foods have been published, and for many of them, the specific heat with high accuracy has not been published. When performing the operation and design of, the rough values were used, such as using estimated values from other known foods. In addition, even for foods of the same type, the values often differ depending on individual properties, and it is necessary to measure each target food.

[0003]

As described above, in designing and operating a food machine, an accurate value for the specific heat of the food is required. Therefore, the problem to be solved by the present invention is to provide a method and an apparatus for measuring the specific heat of a target article in a simple and short time.

[0004]

The present invention has been made in order to solve the above-mentioned problems. First, as the measuring method, the atmospheric pressure of the sample in which the initial weight W ₀ and the initial temperature T ₀ are measured in advance. To evaporate the water in the sample, and the weight change ΔW of the sample and the temperature change ΔT at this time
From the known latent heat of vaporization of water hm corresponding to the initial temperature and temperature change,

It is characterized in that the specific heat C _m of the sample is obtained by the following equation, and the evaporation latent heat hm of the water is corrected by detecting the atmospheric pressure of the sample. Further, as the measuring device, a closed container for containing a sample, a vacuum suction means for depressurizing the inside of the closed container, a weight detection means for detecting the weight of the sample provided in the closed container, and a closed container Temperature detection means for detecting the temperature of the sample, the weight detection means and the temperature detection means are connected to each other, and the inside temperature of the sample is reduced by the initial temperature T _{0 of the} sample and the vacuum suction means. Based on the weight change ΔW of the sample when evaporating the water content and the temperature change ΔT, from the initial temperature T ₀ and the known evaporation latent heat h _m of water corresponding to the temperature change ΔT,
And a processing device for obtaining the specific heat C _m of the sample. Further, the closed container is provided with a pressure detecting means inside the container, and the specific heat C of the sample is calculated by using the evaporation latent heat h _{m of} water corrected based on the signal from the pressure detecting means.
It is characterized by comprising a processing device for obtaining _m . Further, the measuring device is provided with a pressure detecting means inside the container in the closed container, and a processing device for obtaining a specific heat C _m of the sample using the evaporation latent heat h _m corrected based on a signal from the pressure detecting means. It is characterized by

[0005]

According to the method of the present invention, first, the sample (S)
The initial weight W ₀ of the sample (S) and the initial temperature T ₀ are measured, and the temperature change ΔT and the weight change ΔW of the sample (S) when the atmospheric pressure of the sample (S) is gradually decreased are measured. To do. Then, based on the initial weight W ₀ , the initial temperature T ₀ , the temperature change ΔT, and the weight change ΔW, the following equation

From Equation 1, the average specific heat C _m of the sample (S) in the case of the temperature change ΔT can be obtained. Here, h _m is the average value of the latent heat of vaporization of water during the temperature change ΔT, and this value is known. Next, according to the device of the present invention, first, the sample
(S) is housed in a closed container, and the weight detection means (3) and
Fit the temperature detection means (4). And weight detection means
(3) The initial weight W ₀ of the sample (S) is measured by the temperature detecting means (4) and the initial temperature T ₀ is measured in advance.
The pressure inside the closed container (1) is gradually reduced by the vacuum suction means (2). Then, the weight change Δ of the sample (S) at this time
The W and the temperature change ΔT are measured by the weight detecting means (3) and the temperature detecting means (4). The above measured values W ₀ , T
_{From 0} , ΔW, and ΔT, the average specific heat C _m of the sample (S) when the temperature change is ΔT can be obtained. Further, the pressure in the closed container (1) (sample (S) is measured by the pressure detection means provided in the closed container (1).
By detecting the atmospheric pressure of
By correcting _m and using this value, a more accurate average specific heat C _m can be obtained.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described in detail below with reference to the drawings. In addition, the examples described below show an example in which a food is an object to be measured, FIG. 1 is a schematic view showing an example of an apparatus for carrying out the specific heat measuring method according to the present invention, and FIG. FIG. 3 is a diagram showing a change in sample temperature with time in the specific heat measuring method according to the invention, and FIG. 3 is a diagram showing a change in sample weight with time in the specific heat measuring method according to the present invention.

According to the present invention, the atmospheric pressure of the sample is lowered to evaporate the water content in the sample, the weight change ΔW of the sample and the temperature change ΔT at this time are measured, and the known change corresponding to the temperature change is performed. since the average value hm evaporation specific heat of water is intended to determine the specific heat C _m of the sample, the specific heat measurement apparatus, the sample sealed container housing the (S) hermetically (1) as shown in FIG. 1, the sealed Vacuum suction means (2) for reducing the pressure in the container (1), weight detection means (3) for detecting the weight of the sample (S) in the closed container (1), and temperature detection means (4) for detecting the temperature And the weight detection means (3) and temperature detection means
A processing device (5) for determining the specific heat C _m of the sample (S) based on the signal from (4).

The closed container (1) is provided with an opening / closing door for loading / unloading a sample and working. The vacuum suction means (2)
Install a vacuum pump in this closed container (1) via a check valve (7).
(P) is connected, and the vacuum pump (P) is a liquid ring type vacuum pump in the illustrated embodiment. In addition, this closed container (1) is for releasing the depressurized state in the closed container (1) after measurement, and the inside of the closed container (1) has an open / close valve.
(8) communicates with the outside air through the filter (9). This on-off valve (8) is, for example, a solenoid valve, and the closed container (1)
Is closed under reduced pressure, that is, during measurement of specific heat. In the illustrated embodiment, the weight detection means (3) is of a form incorporated in a sample table (10) installed on the inner bottom surface of the closed container (1), and uses a strain gauge, a piezoelectric element or the like. It is of a known type. The sample table (10) may be a hanging sample table such as a hanging balance. The temperature detecting means (4) is, in the illustrated embodiment, a sample holder from the upper inside of the closed container (1).
(10) The sample (S) above has a structure in which the measuring end is pierced,
A vertically movable support tube (12) supports a thermocouple (11). The processing device (5) receives the signals from the weight detecting means (3) and the temperature detecting means (4) as described above, and controls the vacuum pump (P) and the opening / closing valve (8). Including, control the whole measuring device. That is, this processing device (5) is configured such that the sample is placed on the sample holder (10) of the closed container (1), the closed container (1) is closed, and then the vacuum pump (P) is operated to close the closed container. (1) The inside pressure is reduced to reduce the atmospheric pressure of the sample (S). At this time, the on-off valve
(8) is switched to the closed state. While lowering the atmospheric pressure, the weight of the sample is measured by the weight detecting means (3) and the temperature detecting means (4), and signals from the weight detecting means (3) and the temperature detecting means (4) are measured. Enter and measure the specific heat. After the measurement is completed, the vacuum pump (P) is stopped, the on-off valve (8) is switched to the circulation state, and the outside air is introduced into the closed container (1) through the filter (9).

In the present invention, the atmospheric pressure of the sample (S) is lowered to evaporate the water content in the sample (S), and the weight change ΔW and the temperature change ΔT of the sample (S) at this time are used to change the sample ( Since the specific heat C _{m of} S) is obtained, the processing device (5) has the following functions. That is, this processing device (5) intermittently or continuously inputs the signals from the weight detecting means (3) and the temperature detecting means (4) at predetermined intervals, and from these signals. sample
Measure the weight change and temperature change of (S). The initial weight W ₀ of the sample (S) at the start of measurement and the initial temperature T ₀ are also measured and recorded. Then, the temperature change Δ
From T, the weight change ΔW, and the known latent heat of vaporization of water h _m corresponding to the initial temperature and the temperature change, the above equation 1, that is,

The specific heat C _m of the sample is obtained by the following equation. This number 1
Is derived from the equation (2) showing the heat balance when the water is evaporated by the weight ΔW from the sample (S) having the weight W.

[Equation 2] Here, the specific heat C _m of the sample is the average specific heat of the sample in the case of temperature change ΔT, and the evaporation latent heat h _{m of the} water is the average value of the evaporation latent heat during the temperature change ΔT. It is listed and highly reliable. In addition, since the temperature and weight can be measured with high accuracy at the current technical level, the specific heat obtained as a result of the above calculation has high accuracy. In addition, the latent heat of vaporization h _{m of the} water is
Since it is a value necessary to calculate the specific heat of the sample (S) in (5), for example, it is stored as data in the processing device (5), and the corresponding value is calculated according to the detected value of the temperature. It is preferably configured so that it is substituted into 1. In addition, in order to simplify the processing and the storage capacity for storing the latent heat of vaporization, the latent heat of vaporization for each predetermined temperature is stored, and the specific heat of the sample is measured every time when the predetermined temperature is reached. Just go.

In the present invention, the sample (S)
In addition to measuring the weight change ΔW and temperature change ΔT of the sample, and detecting the atmospheric pressure of the sample, the latent heat of evaporation of water h
By correcting _m , the accuracy of measuring specific heat is improved. Therefore, in the measuring device, the closed container (1) is provided with a pressure detection means (6) for the pressure inside the vessel, that is, the atmospheric pressure, and a signal from this pressure detection means (6) is applied to the processing device.
It is configured to input in (5).

Further, in the present invention, the specific heat of the sample is measured stepwise at every predetermined temperature as described above.
The specific heat (C _m1 , C _m2 , C _m3 ··) at each stage is
By correcting with the amount of specific heat corresponding to the evaporated water, the specific heat of the sample (S) can be obtained with higher accuracy. That is, in this case, by considering the amount of heat required for the water vaporized at each measurement step to rise to the evaporation temperature, the measured values shown in Table 1 are used to calculate to correct.

[Table 1]

(Equation 3)

Here, an example of measurement using the specific heat measuring device having the above configuration will be described with reference to FIGS. 2 and 3 show cooked rice (weight W ₀ = 1.744).
(kg) as a sample, the horizontal axis shows elapsed time (unit: seconds)
FIG. 2 shows the temperature change, and FIG. 3 shows the weight change. Table 2 shows the measurement results of the average specific heat at this time.

[Table 2] In this measurement example, the temperature change from the start of the measurement is 50 to 60 ° C in 140 seconds, and the weight change is about 100 g in 140 seconds.
Since the amount of change is relatively large, the measurement is easy, and the time required at this time is just over 2 minutes and several minutes. Further, the values of the specific heats in the measurements 1, 2 and 3 shown in Table 2 above are average values when the temperature T of the sample (S) is lowered from 85 ° C to 30 ° C. Therefore, according to the present invention,
It can be seen that the specific heat of the object to be measured can be measured in a short time even with a sample in which the shape, properties and weight are appropriately selected. Moreover, even if the specific heat of the object to be measured has a high temperature dependency, the specific heat can be measured for each appropriate temperature range, so that the specific heat within the desired temperature range can be measured. Here, the measurement target of the specific heat in the present invention is a food (rice in the above example), but the measurement target of the specific heat in the present invention is not limited to such food,
It can be measured if it is hydrous.

As described above, according to the present invention, it is possible to measure the specific heat of an object to be measured in a short time without selecting the shape, property or weight of the sample. Is. Moreover, even if the specific heat of the object to be measured has a high temperature dependency, the specific heat can be measured for each appropriate temperature range, so that the specific heat within the desired temperature range can be measured. Furthermore, by detecting the atmospheric pressure of the sample, the evaporation latent heat h _{m of} water is corrected, and by using this value, the specific heat C _m of the sample can be obtained more accurately.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of an apparatus for carrying out a specific heat measuring method according to the present invention.

FIG. 2 is a diagram showing a change in sample temperature with time in the specific heat measuring method according to the present invention.

FIG. 3 is a diagram showing changes over time in sample weight in the specific heat measuring method according to the present invention.

[Explanation of symbols]

(S) Sample (1) Airtight container (2) Vacuum suction means (3) Weight detection means (4) Temperature detection means (5) Processing device (6) Pressure measurement device W ₀ Initial weight of sample ΔW Weight change of sample T ₀ Initial temperature of sample ΔT Temperature change of sample P Ambient temperature of sample (pressure in closed container) h _m Average value of latent heat of evaporation of water during temperature change ΔT C _m Average specific heat of temperature change ΔT

Claims (4)

[Claims] 1. The atmospheric pressure of the sample (S) whose initial weight W ₀ and initial temperature T ₀ are measured in advance is lowered to evaporate the water in the sample, and the weight change ΔW of the sample (S) at this time, and The temperature change ΔT is measured, and from the initial temperature and the known evaporation latent heat of water h _m corresponding to the temperature change, the following equation A specific heat measuring method, characterized in that the specific heat C _m of the sample (S) is obtained by 2. The specific heat measuring method according to claim 1, wherein the evaporation latent heat hm of the water is corrected by detecting the atmospheric pressure of the sample (S). 3. A closed container (1) for containing a sample (S), a vacuum suction means (2) for depressurizing the inside of the closed container (1), and a closed container (1) provided with the sample (S). The weight detection means (3) for detecting the weight of (S) and the closed container (1)
The temperature detecting means (4) for detecting the temperature of (S), the weight detecting means (3) and the temperature detecting means (4) are connected, and the initial temperature T ₀ of the sample (S) and the vacuum suction means are connected. The initial temperature T ₀ and the temperature change ΔT are calculated based on the weight change ΔW and the temperature change ΔT of the sample (S) when the pressure in the closed container (1) is reduced by (2) to evaporate the water in the sample. from the evaporation latent heat hm known water corresponding to a processing unit for determining the specific heat C _m of the sample (S) by the following equation ## EQU1 ##
(5) A specific heat measuring device comprising: 4. The closed container (1) is provided with a pressure detecting means (6) inside the container, and the evaporation latent heat h _{m of} water corrected on the basis of a signal from the pressure detecting means (6) is used to obtain a sample ( 4. The specific heat measuring device according to claim 3, further comprising a processing device (5) for obtaining a specific heat Cm of S).