Calorimeter

Japanese: 熱量計 - ねつりょうけい（英語表記）calorimeter

A device that measures heat quantity, and is used to measure specific heat, latent heat, heat of reaction, etc. It is also called a calorimeter.

Calorimeters are classified into constant pressure calorimeters, in which there are no pressure changes in the measurement system, and constant volume calorimeters, in which the measurement is performed under a constant volume, such as in a sealed container, even if there are pressure changes. Flame calorimeters, which measure the heat of combustion of gases, belong to the former, while bomb calorimeters, which are widely used to measure the heat release of liquid and solid fuels, belong to the latter.

[Yoshio Narusawa]

Classification by measurement principle and its improved types

Calorimeters are broadly divided into three types based on the difference in measurement principle: (1) Those that mix the heat contained in the sample or the heat generated by the reaction of the sample with an object of known heat capacity and measure the temperature rise (metal calorimeter, liquid calorimeter, flame calorimeter, running water calorimeter, bomb calorimeter). (2) Those that absorb the heat of the sample into a two-phase equilibrium system of ice and water with known latent heat, for example, and measure the amount of phase change (ice calorimeter, steam calorimeter). (3) Those that apply a fixed amount of electrical energy to the sample and measure the temperature change (in the case of specific heat) or phase change (in the case of latent heat) of the sample (flow calorimeter).

In the case of (1), the most important thing is to measure the temperature change, so a precision thermometer such as a Beckmann thermometer, a thermocouple, or a resistance thermometer is used. There are various types of electric calorimeters that perform heating and temperature measurement electrically, but the electric calorimeter has the highest accuracy.

In calorimeters, heat leaks out as the temperature of the calorimeter changes, causing errors, so various improvements have been made. These include: (4) Adiabatic shielding around the calorimeter with a metal cylinder or ice bath, adjusting the temperature of the adiabatic shield according to the temperature change of the calorimeter to keep it at the same temperature as the calorimeter, and preventing heat from leaking out of the calorimeter (adiabatic calorimeter); (5) An electrical method that generates heat of equal magnitude and opposite sign to the amount of heat generated by the sample, keeps the calorimeter at a constant temperature, and keeps the surroundings of the calorimeter at a constant temperature to prevent heat from entering or leaving the calorimeter. Recently, this method has been applied to endothermic reaction heat measurements. (6) A method that makes two calorimeters out of the same material, causes a reaction of unknown calorific value in one, and adds electrical energy to the other to keep the two calorimeters at the same temperature, and measures the amount of heat from the amount of electrical energy (twin calorimeter).

Of the above calorimeters, (2) and (5) are collectively referred to as isothermal calorimeters, and all except (6) are called non-isothermal calorimeters.

[Yoshio Narusawa]

Construction of the bomb calorimeter
©Shogakukan ">

Construction of the bomb calorimeter

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

熱量を測定する装置で、比熱、潜熱、反応熱などの測定に用いられる。カロリーメーターともいう。

　測定系に圧力変化のない定圧熱量計と、密閉容器のように圧力変化はあっても一定容積のもとで測定が行われる定容熱量計に分類される。気体の燃焼熱を測定する炎熱量計は前者に属し、液体および固体燃料の発熱量を測定するのに広く用いられるボンブ熱量計は後者に属する。

［成澤芳男］

測定原理による分類とその改良型

熱量計は測定原理の違いにより次の3種に大別される。(1)試料のもつ熱量または試料の反応により発生した熱量を、熱容量既知の物体と混合してその温度上昇を測定するもの（金属熱量計、液体熱量計、炎熱量計、流水熱量計、ボンブ熱量計）。(2)試料の熱量を潜熱既知な、たとえば氷と水の二相平衡系に吸収させ、その相変化した量を測定するもの（氷熱量計、蒸気熱量計）。(3)試料に一定量の電気エネルギーを加え、試料の温度変化（比熱の場合）、相変化量（潜熱の場合）を測定するもの（流動熱量計）。

　(1)のものでは温度変化の測定がもっとも重要で、そのためベックマン温度計、熱電対(つい)または抵抗温度計などの精密温度計が用いられる。加熱と温度測定を電気的に行う各種の電気熱量計が知られているが、電気熱量計が精度はもっとも高い。

　熱量測定においては、熱量計の温度変化に伴って熱量が外部に漏出し、誤差の原因となるので種々の改良が行われている。これには、(4)熱量計の周囲を金属製の円筒または氷槽にて断熱シールドし、熱量計の温度変化に応じ断熱シールドの温度を調節して熱量計と等しい温度に保ち、熱量計から熱が漏出しないようにするもの（断熱熱量計）。(5)電気的な方法で、試料の発生する熱量と大きさが等しく符号反対の熱を発生させ、熱量計を一定温度に保ち、一方、熱量計の周囲も一定温度に保って熱量計からの熱の出入りを防ぐもの。最近は吸熱の反応熱測定にこれを適用しているものが多い。(6)まったく同じ材料で二つの熱量計をつくり、一方で熱量未知の反応をさせ、他方で電気的エネルギーを加えて二つの熱量計をつねに同一温度に保ち、電気的エネルギーの量から熱量を測定するもの（双子型(ふたごがた)熱量計）。

　以上の熱量計のうち、(2)、(5)を等温熱量計と総称し、(6)を除くほかのものを非等温熱量計という。

［成澤芳男］

ボンブ熱量計の構造

出典　小学館　日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について　情報 | 凡例

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