Critical Radius Of Insulating Material
Product Code : EL-HTL-11081
Quick answer: The critical radius of insulating material apparatus shows that adding insulation to a small pipe can increase heat loss up to a critical radius, r = k/h. Four heated GI pipes carry plaster of Paris insulation of different thicknesses, each with its own dimmerstat, and temperatures are read on a digital indicator. Lab Exports manufactures it in Delhi for engineering colleges, polytechnics and TVET institutes.
Specifications
| Component | Specification |
|---|---|
| Pipes | 4 nos., GI, with electrical heater inside |
| Insulation | Plaster of Paris, a different thickness on each pipe |
| Heater control | 4 nos. dimmerstats |
| Power measurement | Common voltmeter and ammeter |
| Temperature measurement | Digital temperature indicator |
| Services | 230 V, 5 A AC supply with earthing; floor area 1 x 1 x 1.5 m (H) |
How the critical radius experiment is done
Insulation on a cylinder has two opposing effects. A thicker layer adds conduction resistance, ln(r2/r1) / (2 pi k L), but it also enlarges the outer surface and lowers the convection resistance, 1 / (2 pi r2 L h). The total is smallest, and the heat loss largest, when r2 = k/h, the critical radius. Below it, more insulation increases heat loss; only beyond it does insulation start to save heat.
This matters for thin wires and small pipes, where the bare radius may already be below the critical value, and it is why the insulation on an electrical cable can help cool the conductor. The four pipes with different plaster of Paris thicknesses let students find the effect by experiment.
- Switch on the four heaters and set the input on each with its dimmerstat.
- Wait for steady state on all pipes.
- Record the voltmeter and ammeter readings and the temperatures at the pipe and insulation surfaces.
- Calculate the heat loss per unit temperature difference for each thickness.
- Plot it against outer radius to find the maximum and compare with k/h.
Key features
- Four heated GI pipes side by side for direct comparison
- Plaster of Paris insulation at a different thickness on each pipe
- Separate dimmerstat for every heater
- Common voltmeter and ammeter for the heater input
- Digital temperature indicator for readings across the insulation
Documentation and supply
Installation instructions and a manual are supplied with the apparatus. Most Lab Exports products carry a one-year manufacturer warranty.
Lab Exports manufactures the critical radius apparatus at its works in Laxmi Nagar, Delhi, and supplies it to engineering colleges, polytechnics and TVET institutes in India and 60+ countries, handling the export documents for each shipment. More about the company is on the About Lab Exports page.
Related Heat Transfer Lab products
- Heat Pipe Apparatus (EL-HTL-11080)
- Pin Fin Apparatus (EL-HTL-11082)
- Natural Convection Apparatus (EL-HTL-11083)
- Composite Walls Apparatus (EL-HTL-11078)
- Forced Convection Apparatus (EL-HTL-11084)
- Specific Heat of Air Apparatus (EL-HTL-11085)
The full range is in the Heat Transfer Lab section of the Engineering Lab range.
Frequently asked questions
What is the critical radius of insulation?
It is the outer radius at which heat loss from an insulated cylinder is greatest, equal to the thermal conductivity of the insulation divided by the outside heat transfer coefficient, k/h.
What insulation is used on the pipes?
Plaster of Paris, applied over the four GI pipes at different thicknesses.
What services does the apparatus need?
A 230 V, 5 A AC supply with earthing and a floor area of about 1 x 1 m with 1.5 m height.
What is the price of the critical radius apparatus?
Prices are not published on the website. Add the critical radius apparatus to the Enquiry Cart with the Add To Cart button on this page, or email [email protected] with the house code EL-HTL-11081 and the quantity, to receive a quotation.
Does Lab Exports manufacture the critical radius apparatus?
Yes. Lab Exports manufactures the critical radius apparatus at its works at 11/315, Lalita Park, Laxmi Nagar, Delhi 110092, under house code EL-HTL-11081.
Request a quote
Email [email protected] with the house code EL-HTL-11081 and the quantity, or add the critical radius apparatus to the Enquiry Cart with the Add To Cart button on this page. Tender buyers can also see the Tenders and OEM page.