# What is Thermal resistance: Definition and 21 Discussions

Thermal resistance is a heat property and a measurement of a temperature difference by which an object or material resists a heat flow. Thermal resistance is the reciprocal of thermal conductance.

(Absolute) thermal resistance R in kelvins per watt (K/W) is a property of a particular component. For example, a characteristic of a heat sink.
Specific thermal resistance or thermal resistivity Rλ in kelvin metres per watt (K⋅m/W), is a material constant.
Thermal insulance has the units square metre kelvin per watt (m2⋅K/W) in SI units or square foot degree Fahrenheit hours per British thermal unit (ft2⋅°F⋅h/Btu) in imperial units. It is the thermal resistance of unit area of a material. In terms of insulation, it is measured by the R-value.

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1. ### How can I get steady state of complicated heat transfer problem?

This problem is created by my cousin who is learning about 1-D heat transfer problems. He made this problem and made solve it with fourier's law of heat transfer with calculating thermal resistance by integrating 1/A dx, which presupposes a false assumption; if the distance away from the heat...
2. ### Thermal Resistance of a Hollow Circular Cone

We can write our radius as a function of the height, z, of our cone: $$R(z) = \frac{R_2 - R_1}{h} z + R_1$$ Where h is the height of our cone, ##h = \frac{L}{40}##. Our cross sectional area, $$A = 2 \pi R t$$ can then be written as $$A = 2 \pi t [\frac{R_2 - R_1}{h} z + R_1]$$ This I am all...
3. ### What is the design methodology of a Heatsink for a high-power diode?

In reference of Ned Mohan's book, I have designed a heatsink, firstly natural convection taken into account, but laboratory test results and theoretical calculations are not matching. The test results: For 40 A (means 62 W), 30 Celsius ambient temp, it raised up 51 Celsius. So, Rs-a =...
4. ### Temperature profiles and thermal resistance

I heated two different materials with a laser beam for about 10 seconds and these are the measured temperature profiles: From the various solutions to the general heat conduction equation, temperature rise seems to increase with increasing thermal resistance of the material. The total...
5. ### Negative Heat Sink thermal resistance

I'm currently developing a heat sink for a product that produces up to 150 W max power dissipation. I'm currently getting a negative thermal resistance for the heat sink. I don't think that is possible.. I'm not sure how to move on at this point to properly design a heat sink to meet the heat...
6. ### Thermal Resistance between Chip to Gold Tin Solder

I'm currently doing a heat sink calculation design and having a little confused moment with the area of the chip with a AuSn (Gold Tin Solder) pre-cut that's attached to the bottom of the chip. I've tried looking around online for AuSn's thermal resistance value, but there is none besides a...
7. ### Thermal Resistance to Centerline

Hello, Given an infinitely long cylinder with a specified surface heat flux, the thermal resistance of an annular region is given by, R_th = ln(r_out / r_in) / (2 pi L k). When I'm calculating the thermal resistance to the centerline, r_in = 0. Does that mean there is infinite thermal...
8. ### Thermal resistance without area

I'm (self)studying the physics of heat transfer at the moment. My book gives a relationship between heat transfer rate and thermal resistance as ##\phi=\frac {A \Delta T} {R}##. My book is not in English, so hopefully that is not the cause of this misunderstanding. I double checked that heat...
9. ### Thermal Resistance of Heat Sink

Homework Statement Calculate the thermal resistance of the heat sink required for the regulator of the question above given the information below [from the datasheet] and the data in the table. Max Load Current (Ilm)= 1A Max Ambient Temp (Ta)= 75°C Thermal Resistance Case to Heat (θchs)=...
10. ### Calculating thermal resistance across a metal flange

I've been using the following equation for thermal resistance to make basic calculations for a few different engineering designs: $$R_t = \frac{L}{kA}$$ Where L is the resistance path length, A is the cross-sectional area perpendicular to this path and k is the thermal conductivity of the...
11. ### Calculate thermal resistance of heatsink required

Homework Statement Q4) Calculate the thermal resistance of the heat sink required for the regulator of Q3 above given the information below [from the datasheet] and the data in the table. Q3 FIGURE 2 shows an adjustable voltage regulator using the LT1083*. The LT1083 develops a 1.25V reference...
12. ### Thermal Resistance due to Convection Heat Transfer

Homework Statement 1) A typical wall construction for a single-family residence might consist of 0.375 inches of outer sheathing (insulating board, hardwood siding, etc.), 3.5 inches of mineral fiber insulation and then a 0.375 inches inner surface (gypsum, etc.). Typical thermal...
13. ### LEDs, LED Drivers, Thermal Management

I'm trying to wrap my head around thermal management of LEDs and LED driver circuits. http://blogs.indium.com/blog/amanda-hartnett/controlling-junction-temperature-of-leds-with-thermal-management-materials A concern has been expressed that a lighting supplier needs to demonstrate (not sure...
14. ### What is the significance of thermal resistance in heat transfer?

Hi, I shall be grateful if someone can help with this fundamental understanding, Thermal resistance (in case of conduction mode of heat tarnsfer) can be defined as; Rt = L / kA where k is the thermal conductivity Thus. thermal resistance if inversely proportional to the thermal...
15. ### Understanding Thermal Resistance in Heat Transfer: An Analysis and Explanation

Homework Statement [/B] Explain how the concept of thermal resistance can be used in the analysis of heat transfer problems 2. The attempt at a solution So I'm made a few key points but I am not sure if I have answered the question fully: Thermal resistance is a heat property and a...
16. ### Heat Transfer - Heat Flux (thermal Resistance)

Homework Statement Hi guys, I don't really need help with answering the dollowing question but just have a quick question about it. I solved the first part of the question with an energy balance by letting q_{conduction} = q_{convection} to get the temperature of he outer...
17. ### Convection and Thermal Resistance

I have a question... Suppose you have a thin and long rectangular piece of aluminum. You heat one end (pt A). The thermal resistance (steady state) from one end (pt A) to the other (pt B) would be θ=ΔT/W Where W= Watts of heat energy. ΔT = temperature of ptA - temperature of ptB...
18. ### What factors affect the thermal conductivity of solids?

Hi all Am I correct to say that - in general - the thermal conductivity of metals is higher than that of semiconductors, because metals have more free electrons to help conduct the heat? And is it correct that phonon-contribution to heat conductivy is more or less the same for all solids...
19. ### Thermal Resistance at a single point

Hi All I am having a design problem. I want to melt a fishing line which is in contact at a single point with some material. The problem is that I have a 5 V of supply and Power should be between 1-3W. Some other constraints are that the material to which the fishing line is connected should be...
20. ### Heat Loss Through Wall: Thermal Resistance Calculation

Homework Statement The wall of a house consists of three layers: A wooden outer wall with an R factor of 1.0, a 3 inch layer of fiberglass with an R factor of 11, and a gypsium-board inner wall with an R factor of 0.33. (All R factors are in h*ft^2*F/BTU). When the temperature is 68 degrees...
21. ### Thermal resistance, can i do this?

I have this problem from my book here A house has a wall made of 3 layers: fiberboard, concrete, brick where the fiberboard is on the inside of the house, brick is on the outside and concrete is in between. the fiberboard is 0.02m thick, the concrete is 0.15m thick, the brick is 0.07m thick...