冷却システムの用途に適した製品を選択するための最初のステップは、熱負荷、つまりシステムによって生成される熱量を決定することです。 This article explains how to establish heat load for any liquid cooling application. The same process can be adapted for air cooling systems as well.
Rough Estimate for Heat Load
熱負荷を推定する迅速で汚い方法は、プロセスに入るすべての電気エネルギーが熱に変換されると仮定することです。熱力学の第1法則から、システムから出るエネルギーの量は、システムに入るエネルギーの量よりも大きくなることはありません。熱負荷は、電気がシステムに入る唯一のエネルギー形態である場合、消費される電力量に等しいと控えめに見積もることができます。比熱の計算式
To determine heat load more accurately, use the heat transfer equation: Q = m x Cp x ΔT where:- Q = heat load (W [BTU/hr])
- m = mass flow rate (kg/s [lb/hr])
- Cp = specific heat (J/g-K [BTU/lb °F])
- ΔT = change in temperature (°C [°F])
熱負荷を計算するためのテスト・セットアップ
To determine Q using the above heat transfer equation, you will need to obtain the values m and ΔT experimentally. To measure these the temperature differential and mass flow rate values you will need the following equipment: Two (2x) Type "T" Thermocouples - Recommended accuracy: ± 0.2°F A Turbine Flow Meter - Recommended accuracy: ± 1% of Reading The thermocouples and flow meter can be used to measure fluid temperature change and flow rate of the cooling fluid when your system is at peak load operation (see Figure 1). 流体の比熱(一般的に使用される流体の特性は、テクニカルライブラリの熱リファレンスガイドに記載されています)と上記の式を使用して、熱負荷を計算できます。
What Are Thermocouples?
Thermocouples are a sensor built from two dissimilar metals that generate an electrical charge based on the temperature at the joint between those two materials. Thermocouples are a crucial element in thermal testing.
Accurate measurements rely on placing the thermocouple junction as close to the point under test. If a material is in the way, thermal resistance and thickness can also help determine the temperature at a specific point but decrease the overall accuracy of your measurement.
Thermocouples Measurement Accuracy
熱電対と流量計の精度は、精度がわずかに低下すると誤差の割合が大きくなる可能性があるため、特に重要です。 For example: if the temperature rise is 10 °C and the thermocouples are accurate to ± 0.5 °C, the temperature rise measurement could be off by as much as 1 °C, or 10%. This means that the overall heat load calculation cannot be more accurate than that ±10%. If the temperature rise is less than 10 °C, the ± 0.5 °C becomes an even higher error percentage.温度誤差が°Fまたは°Cで与えられる場合、誤差率は、熱電対の精度に2を掛け、次に温度の変化で割り、100を掛けることによって計算できます。Thermocouple Calibration
We recommend calibrating the two thermocouples prior to recording measurements. If this isn't possible, the accuracy of one thermocouple can be compared to the other.これを行うには、熱負荷なしで熱電対に流体の流れを流します。温度が同じ場合は、ピーク動作時の正確な温度上昇を使用できます。 Otherwise, account for the temperature difference of the two thermocouples under no heat load when conducting measurements at peak load operation. For thermocouples measuring different temperatures, subtract the temperature difference with no heat load from the temperature difference with heat load applied. For example: if the two thermocouples read 20.0 and 20.5°C when under no heat load, and 25.0 and 30.5°C with heat load applied, the change in temperature should be calculated to be (30.5 - 25.0) - (20.5 - 20.0), or 5.0°C.How to Measure Liquid Flow Rate Without a Flow Meter
If a flow meter is not available, measure the constant flow rate of the system with a graduated container and a timer. Collect the fluid in the graduated container over a measured period. Divide the amount of fluid by the amount of time that has elapsed.この方法で流量を測定する場合、一定の流量が不可欠です。流体の密度を使用して、体積流量を質量流量に変換する必要があります。
These methods of determining heat load are generic to any liquid cooling application and can be used when sizing a CDU, recirculating chiller, cold plate, or heat exchanger.
Now I Know my Heat Load, What Next?
Once you’ve calculated the heat load of your system, you can start determining the amount of cooling you require. This piece of information combined with the amount of volume allowable for a cooling system will help thermal engineers select or develop a liquid cooling system that will meet your project needs.
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