{ "node": { "id": "term:heat-transfer-coefficient", "type": "Term", "label": "Heat transfer coefficient", "properties": { "id": "heat-transfer-coefficient", "name": "Heat transfer coefficient", "abbr": "h", "aka": [ "convection coefficient", "film coefficient" ], "section": "topic-thermal", "definition": "The heat carried away per unit area per kelvin of difference between a surface and the fluid passing it. Typical values are 5–25 W/(m²·K) for still air, 25–250 for forced air and hundreds to thousands for pumped liquid, which is why fast-charging packs are liquid-cooled. Thermal models use it as their cooling boundary.", "formula": "Q = h·A·ΔT", "unit": "W/(m²·K)", "related": [ "heat-transfer-modes", "heat-flux", "biot-number", "thermal-model", "cooling-plate", "coolant" ], "example": { "title": "Estimate convective cooling", "text": "For an illustrative h = 20 W/(m²·K), area 0.1 m² and surface-to-fluid temperature difference 10 K, hAΔT gives 20 W of cooling. The coefficient depends on the actual flow and geometry." }, "url": "https://lemonergy.com/learn/glossary/heat-transfer-coefficient/", "mentions": [] } }, "edges": [ { "id": "edge:112", "source": "term:heat-transfer-coefficient", "target": "workflow:charge-thermal", "type": "usedIn", "properties": { "sourceFile": "wiki-blocks.json" } }, { "id": "edge:4596", "source": "term:heat-transfer-coefficient", "target": "topic:topic-thermal", "type": "belongsTo", "properties": { "sourceFile": "terms.json" } }, { "id": "edge:4597", "source": "term:heat-transfer-coefficient", "target": "term:heat-transfer-modes", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:4598", "source": "term:heat-transfer-coefficient", "target": "term:heat-flux", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:4599", "source": "term:heat-transfer-coefficient", "target": "term:biot-number", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:4600", "source": "term:heat-transfer-coefficient", "target": "term:thermal-model", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:4601", "source": "term:heat-transfer-coefficient", "target": "term:cooling-plate", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:4602", "source": "term:heat-transfer-coefficient", "target": "term:coolant", "type": "relatedTo", "properties": { "sourceFile": "terms.json", "meaning": "Related context; not a causal claim" } }, { "id": "edge:4603", "source": "term:heat-transfer-coefficient", "target": "visual:thermal", "type": "illustratedBy", "properties": { "sourceFile": "visual-pages.json" } }, { "id": "edge:4604", "source": "term:heat-transfer-coefficient", "target": "reference:openstax-heat", "type": "cites", "properties": { "sourceFile": "wiki-references.json", "scope": "direct technical reference" } } ], "neighbors": [ { "id": "workflow:charge-thermal", "type": "Workflow", "label": "Inspect pack temperature", "properties": { "id": "charge-thermal", "title": "Inspect pack temperature", "kind": "protocol", "summary": "The separate Charge session can include a lumped thermal node.", "steps": [ "Provide thermal mass and conductance.", "Compare two ambient temperatures." ], "example": "100 kJ/K thermal mass and 100 W/K conductance give a 1000 s no-source temperature-difference time constant.", "observe": "Temperature limits can pause charge; heater and mass are separate.", "limits": "One node does not resolve gradients, coolant geometry or runaway. Studio’s native charger instead uses external temperature.", "url": "https://design.lemonergy.com/", "label": "Open Design → Charge session", "evidence": [ "js/charger.js" ] } }, { "id": "topic:topic-thermal", "type": "Topic", "label": "Thermal management and heat transfer", "properties": { "id": "topic-thermal", "name": "Thermal management and heat transfer", "lede": "How heat is made, moved and removed in cells and packs, and the hardware that keeps a battery at the right temperature.", "context": "Select spatial detail for the question.", "example": "Equal total heat in different layouts can produce different gradients. Average temperature can miss a hot spot.", "lesson_url": "https://lemonergy.com/learn/fundamentals/battery-aging/", "lesson_label": "Open temperature and aging" } }, { "id": "term:heat-transfer-modes", "type": "Term", "label": "Heat transfer modes", "properties": { "id": "heat-transfer-modes", "name": "Heat transfer modes", "aka": [ "conduction", "convection", "thermal radiation" ], "section": "topic-thermal", "definition": "The three ways heat moves: conduction through solids and still fluids, convection carried by a moving fluid, and radiation emitted as infrared by every warm surface. In a pack, conduction takes heat from the cell into the cooling plate and convection carries it away in the coolant; radiation matters mainly at the high temperatures of thermal runaway.", "related": [ "thermal-conductivity", "heat-transfer-coefficient", "thermography", "cooling-plate", "thermal-propagation" ], "url": "https://lemonergy.com/learn/glossary/heat-transfer-modes/", "mentions": [ "thermal-runaway" ] } }, { "id": "term:heat-flux", "type": "Term", "label": "Heat flux", "properties": { "id": "heat-flux", "name": "Heat flux", "abbr": "q″", "section": "topic-thermal", "definition": "The rate of heat flow through a surface per unit area. Dividing a cell’s heat by its cooled area gives the flux the cooling must carry: a 21700 cell shedding 5 W through its roughly 46 cm² side sees about 1 kW/m². Cooling only one face concentrates the flux and steepens the gradient inside.", "formula": "q″ = Q / A", "unit": "W/m²", "related": [ "heat-transfer-coefficient", "thermal-conductivity", "thermal-resistance", "thermal-gradient", "cooling-plate" ], "example": { "title": "Compare equal heat across different areas", "text": "A 10 W heat flow spread uniformly across 0.02 m² has an average flux of 500 W/m². Concentrating the same heat into half the area doubles the average flux." }, "url": "https://lemonergy.com/learn/glossary/heat-flux/", "mentions": [ "cylindrical-cell" ] } }, { "id": "term:biot-number", "type": "Term", "label": "Biot number", "properties": { "id": "biot-number", "name": "Biot number", "abbr": "Bi", "section": "topic-thermal", "definition": "The ratio of the resistance to heat conduction inside a body to the resistance to convection at its surface. Below about 0.1 the body heats almost uniformly and a lumped thermal model is adequate; large, strongly cooled cells with poor through-plane conductivity exceed it and need a model that resolves the internal gradient.", "formula": "Bi = h·L / k", "related": [ "heat-transfer-coefficient", "thermal-conductivity", "thermal-model", "thermal-gradient" ], "example": { "title": "Check a lumped-temperature assumption", "text": "For h = 10 W/(m²·K), characteristic length L = 0.005 m and k = 1 W/(m·K), Bi = 0.05. Small Bi supports a lumped-temperature approximation; the characteristic length must match the geometry." }, "url": "https://lemonergy.com/learn/glossary/biot-number/", "mentions": [ "heat-transfer-modes" ] } }, { "id": "term:thermal-model", "type": "Term", "label": "Thermal model", "properties": { "id": "thermal-model", "name": "Thermal model", "aka": [ "lumped thermal model" ], "section": "topic-thermal", "definition": "A model of cell temperature: at its simplest one thermal mass with heat generation inside and convection outside, at its most detailed a 3D simulation of the pack. Temperature feeds back into every rate, so electrical and thermal models are usually solved together.", "related": [ "heat-generation", "thermal-management", "arrhenius", "newman-model", "thermal-characterisation" ], "url": "https://lemonergy.com/learn/glossary/thermal-model/", "mentions": [ "thermal-mass", "heat-transfer-modes" ] } }, { "id": "term:cooling-plate", "type": "Term", "label": "Cooling plate", "properties": { "id": "cooling-plate", "name": "Cooling plate", "aka": [ "cold plate" ], "section": "topic-thermal", "definition": "A flat aluminium channel assembly under or between the cells through which coolant, usually a water–glycol mix, is pumped. Heat crosses from cell to plate through a thermal interface material; the plate also sets the pack’s temperature uniformity.", "related": [ "thermal-management", "thermal-interface-material", "immersion-cooling" ], "url": "https://lemonergy.com/learn/glossary/cooling-plate/", "mentions": [ "thermal-gradient", "coolant" ] } }, { "id": "term:coolant", "type": "Term", "label": "Coolant", "properties": { "id": "coolant", "name": "Coolant", "aka": [ "water–glycol", "glycol coolant", "ethylene glycol" ], "section": "topic-thermal", "definition": "The liquid pumped through cooling plates and heat exchangers, usually a roughly 50:50 mix of water and ethylene glycol that stays liquid to about −35 °C. It carries heat better than air or dielectric oils, but it conducts electricity, so a leak inside a pack threatens insulation resistance and can short live parts.", "related": [ "cooling-plate", "chiller", "radiator", "heat-exchanger", "immersion-cooling", "insulation-resistance" ], "url": "https://lemonergy.com/learn/glossary/coolant/", "mentions": [] } }, { "id": "visual:thermal", "type": "Visual", "label": "Heat approaches an equilibrium", "properties": { "title": "Heat approaches an equilibrium", "summary": "Thermal resistance sets the steady temperature rise; thermal mass sets the response time.", "readout": "Steady rise: 10 K. Time constant: 8.333 min.", "formula": "ΔT = P R_th [1 − exp(−t / (C_th R_th))]", "note": "C_th = 500 J/K, fixed ambient and heat input, uniform temperature.", "software": { "status": "reference", "label": "Reference concept", "body": "Analysis → Charge session supports optional lumped thermal behavior. This independent explanation uses a 500 J/K thermal mass and constant heat input; it is not an application simulation result.", "href": "https://design.lemonergy.com/" }, "html": "
Temperature above ambient
Temperature above ambientTime (min) versus Temperature rise (K). Lumped response. Interpretation follows the graphs.001515303045456060Time (min)Temperature rise (K)
Lumped response
" } }, { "id": "reference:openstax-heat", "type": "Reference", "label": "University Physics Volume 2, §1.6: Mechanisms of Heat Transfer", "properties": { "title": "University Physics Volume 2, §1.6: Mechanisms of Heat Transfer", "publisher": "OpenStax, Rice University", "url": "https://openstax.org/books/university-physics-volume-2/pages/1-6-mechanisms-of-heat-transfer", "type": "Textbook section", "scope": "Conduction, convection, radiation and thermal resistance.", "accessed": "2026-10-27" } } ] }