全部书籍

1 Primary & Middle School Mathematics1–9 年级在线 2 High School Mathematics10–12 年级在线 3 University Mathematics — Year 1本科一年级在线 4 University Mathematics — Year 2本科二年级在线 5 University Mathematics — Year 3本科三年级在线

1 Primary & Middle School Physics1–9 年级在线 2 High School Physics10–12 年级在线 3 University Physics — Year 1本科一年级在线 4 University Physics — Year 2本科二年级在线 5 University Physics — Year 3本科三年级在线

1 School Chemistry — Grades 1 to 121–12 年级在线 2 University Chemistry — Year 1本科一年级在线 3 University Chemistry — Year 2本科二年级在线 4 University Chemistry — Year 3本科三年级在线

1 Primary & Middle School Biology1–9 年级在线 2 High School Biology10–12 年级在线 3 University Biology — Year 1本科一年级在线 4 University Biology — Year 2本科二年级在线 5 University Biology — Year 3本科三年级在线

1 Primary & Middle School Earth and Space Sciences1–9 年级在线 2 High School Earth and Space Sciences10–12 年级在线 3 University Earth and Space Sciences — Year 1本科一年级在线 4 University Earth and Space Sciences — Year 2本科二年级在线 5 University Earth and Space Sciences — Year 3本科三年级在线

1 Markets I: The Ecosystem and Exchange-Traded Markets市场在线 2 Markets II: Rates, FX and Credit市场在线 3 Markets III: Commodities, Energy and Crypto市场在线 4 Quantitative Methods方法在线 5 Derivatives and Volatility衍生品在线 6 Rates, Credit, XVA and Risk利率、信用与风险在线 7 Research Craft: Predictors, Backtests, Measurement, Portfolios研究在线 8 Strategies I: Equities and Futures策略在线 9 Strategies II: Volatility, Relative Value, Macro and the Bank Desks策略在线 10 Microstructure and Execution交易执行在线 11 Market Making and High-Frequency Trading做市在线 12 Machine Learning for Markets机器学习在线 13 Low-Latency Software技术在线 14 Networks, Hardware and Trading Infrastructure技术在线 15 Research, Data and Risk Platforms技术在线 16 The Desk and the Firm公司运营在线 17 The Industry: Firms, Roles and Careers职业发展在线 18 Interviews I: Maths, Probability and Speed职业发展在线 19 Interviews II: Markets, Trading Games and the Final Round职业发展在线 20 Interviews III: Code职业发展在线

全部游戏 Math Fuse Word Reactor Atlas Dash

应用关于

Coach

English Français Español Nederlands Português हिन्दी العربية Bahasa Indonesia 简体中文 বাংলা

登录开始阅读

书籍暂未推出简体中文版——当前显示英文版。

Physics · 术语表

什么是 Heat current density？

又称： thermal flux

Definition 25.1 University Physics — Year 2 · 第 25 章 — Heat Conduction

The heat current density $\vect{j}_Q$ (in $\mathrm{W}/\mathrm{m}^{2}$ ) is the vector such that the energy transferred by conduction through an oriented surface element $\dd\vect S$ during $\dd t$ is $\vect{j}_Q\cdot\dd\vect S\,\dd t$ ; the thermal flux (a power, in watts) through a surface $S$ is $\Phi = \iint_S\vect{j}_Q\cdot\dd\vect S$ .

示例

Example 25.3 (Conductivities)

Metals (electrons carry the heat as well as the current — conductivities track each other): copper $400\,\mathrm{W}/\mathrm{m}/\mathrm{K}$ , aluminium $240\,\mathrm{W}/\mathrm{m}/\mathrm{K}$ , steel $50\,\mathrm{W}/\mathrm{m}/\mathrm{K}$ . Insulating solids: concrete $1.5\,\mathrm{W}/\mathrm{m}/\mathrm{K}$ , glass $1\,\mathrm{W}/\mathrm{m}/\mathrm{K}$ , brick $0.8\,\mathrm{W}/\mathrm{m}/\mathrm{K}$ , wood $0.15\,\mathrm{W}/\mathrm{m}/\mathrm{K}$ . Liquids: water $0.6\,\mathrm{W}/\mathrm{m}/\mathrm{K}$ . Gases: air $0.026\,\mathrm{W}/\mathrm{m}/\mathrm{K}$ — and the best insulators, glass wool or foam at $0.04\,\mathrm{W}/\mathrm{m}/\mathrm{K}$ , are mostly still air, trapped so that it cannot convect. Four orders of magnitude from copper to air.

在原文中阅读 →