Neometrix / Thermal Test Equipment / Hot Air Generator / NMX-HAG-66

NMX-HAG-66 · ENGINEERED-TO-ORDER CLASS — SPECIFY · SIZE · TIE · RUN · MAP · PROVE

Hot Air Generator. Never let the heater outrun the air.

Name: Hot Air Generator
Brand: Neometrix
SKU: NMX-HAG-66

A hot air generator is easy to describe: a blower, a heater and a duct. It is harder to make safe, because an electric heater makes heat whatever the air does. Take the air away and the elements go on making heat with nowhere for it to go.

So the generator is built around three things: a flow that is proved before any heat, elements that are watched and limited apart from the stream, and a blower that outlasts the heat.

Discuss a hot air generator Capability note (PDF)

A single electric hot air generator on a plain white studio background: a low welded grey steel skid frame carrying a grey centrifugal blower with a smooth grey electric motor and guarded drive, a long horizontal cylindrical heater vessel wrapped in bright silver insulation cladding with a bolted round flange cover and a round steel terminal box on top, a thick silver insulated outlet duct ending in a bolted flange, and a slim metal-sheathed temperature probe with a thin black lead entering the duct, and no people

Fig · 01 — A hot air generator: a blower on a steel skid feeding an insulated heater vessel, with an insulated outlet duct and a probe in the outlet stream — illustrative render.

The air

proved before heatflow measured and interlocked

The elements

watched and limiteda probe and a separate cut-out

The stream

read at the outletthe control signal is in the air

The stop

heat first, air lastthe blower runs on

Status

engineered to orderno generator claimed

ISO 9001ISO 14001IEC 60519-1 reference standard

Overview

Why the whole job is keeping the heat and the air together.

Because an electric heater makes heat whatever the air does, and only the air carries that heat away.

Fig · 02 — The generator in one picture: the air is made and proved, the heat is allowed only with that air, and the outlet is read in the moving stream.

Never let the heater outrun the air.

What the generator is for

It delivers a stream of clean hot air at a set temperature and a set flow, to heat an article, a duct or a process. It suits a blower-fed unit, a compressed-air heater and a generator with its own test section, and it is built around the flow and the temperature the customer needs.

Why the heat must follow the air

An electric element makes heat at the rate its power sets, and the air carries it off at a rate the flow sets. If the flow falls and the power does not, the heat has nowhere to go, and the elements get hotter than the air by a widening margin. Low airflow is the usual reason an element burns out.

Why the air must be proved

A fan that is running is not a flow that is proved. A blocked inlet, a closed damper or a slipping belt all leave the fan running and the heater starved. The generator measures the flow, with a sensor or a switch across the heater, and gives permission for heat only while the flow is there and above its minimum.

Why the elements are watched twice

The outlet probe tells the controller what the air is doing, and it is the signal the temperature is held on. A probe on an element tells the generator what the metal is doing. A separate high-limit cut-out, usually reset by hand, then guards the elements on its own, so that no fault in the controller can leave them unguarded.

Why the blower outlasts the heat

When the power goes off, the elements and the vessel are still hot. A fan that stops at once leaves that heat to soak into the casing and the duct, so the blower runs on for a set time. The generator sets that time, not the operator.

Why one point is not the generator

At one power, a smaller flow gives a hotter stream and hotter elements, and a larger flow gives the opposite. So the generator is mapped across its whole flow range, not at one point, and the map is part of the record.

The method

Specify, size, tie, run, map, and prove.

Six steps in a fixed order. The two shaded steps are the ones a quick order skips.

FIG · 02HOT AIR GENERATOR · SPECIFY / SIZE / TIE / RUN / MAP / PROVE — NEVER LET THE HEATER OUTRUN THE AIR

The step people underrate is the tie between the heat and the air. A generator whose heat can run without proved air is one lost fan away from a burnt element.

Fig · 03 — Three ways a hot air generator goes wrong: the heat outlasts the air that carries it, less air for the same power is a hotter stream, and the blower stops with the heat — a drawing of the idea, with no values.

1 · Specify

The flow range, the temperature range and the quality of the air are stated by the customer, and the generator is sized to them.

2 · Size

The power, the elements and the vessel are chosen from the flow range, so that the elements stay within their limit at the smallest flow the generator is allowed to run.

3 · Tie

The heat is tied to the air: heat is allowed only while the flow is proved, an element probe and a separate high limit guard the metal, and the blower runs on.

4 · Run

The generator is brought up air first and heat last, and shut down heat first and air last, the same way every time.

5 · Map

The outlet temperature and its spread across the stream are measured across the whole flow range, and the response to a change is recorded.

6 · Prove

The record is kept, and handed over with the generator.

Work content

What the generator contains, element by element.

Read it as a checklist: a generator missing a row will give heat it cannot hold.

A single withdrawn electric air heater element bundle on a plain white studio background: a thick round grey steel flange plate with a ring of plain bolt holes carrying a parallel bundle of long bright stainless steel finned tubular heating elements bent into hairpins, a plain round grey terminal box with thick black cables on the back of the flange, and a slim metal-sheathed thermocouple strapped to one element with thin black leads, and no people

Fig · 04 — A withdrawn element bundle: finned tubular heating elements on a flange plate, with a thermocouple strapped to one element and thick cables to the terminal box — illustrative render.

Element	What it does	What matters
Blower or air supply	makes the flow	a centrifugal blower on a guarded drive, or a compressed air line with a regulator, a filter and a dryer where the air must be clean
Flow measurement and proof	proves the air	a flow sensor or a pressure switch across the heater, which gives permission for heat only while the flow is above its minimum
Heater vessel and elements	make the heat	finned tubular elements in an insulated vessel, grouped so that the power can be stepped or modulated
Power control	sets the power	thyristor power controllers, switching on and off or in phase angle, matched to the elements
Element probe	watches the metal	a thermocouple on an element, read by the controller and checked against a limit
High-limit cut-out	guards the elements on its own	a separate over-temperature device that drops the power whatever the controller is doing, and is reset by hand
Outlet probe	reads the stream	a probe in the moving air, not on the duct wall, giving the signal that the temperature is held on
Controller	runs the sequence	holds the outlet temperature, lets heat on only with proved air, runs the blower on after the heat is off, and logs everything
Outlet duct and insulation	deliver the air	an insulated duct to the article, so that little heat is lost on the way and the surface is safe to approach
Test section (where fitted)	holds the article	a duct or chamber for the article with probes at its entry and its exit, so that the air is measured where it meets the part
Guarding and safeties	protect the generator and the room	a guard round the turning parts, a pressure relief on a pressurised vessel, and an emergency stop
Procedure	fixes the sequence	specify, size, tie, run, map and prove, the same for every generator
Testing & documentation	prove the generator first	a check of the flow proof, the limits and the probes, a mapped run, and a record the customer can inspect

The element that decides whether the generator is safe is the tie between the heat and the air, because a generator that lets heat run without proved air can burn out an element on a single lost fan and never warn.

Fig · 05 — What the generator watches: the flow at the inlet, the metal of the elements and the air at the outlet, with the blower running on after the heat — a drawing of the idea, not to scale and with no values.

Full specification — expand

System	A blower on a guarded drive, or a compressed air line with a regulator, a filter and a dryer; a flow sensor or a pressure switch across the heater that proves the air; an insulated vessel of finned tubular elements grouped so that the power can be stepped or modulated; thyristor power controllers; a thermocouple on an element and a separate high-limit cut-out reset by hand; an outlet probe in the moving air; a controller that holds the outlet temperature, lets heat on only with proved air, runs the blower on after the heat is off and logs everything; an insulated outlet duct and, where fitted, a test section with probes at its entry and exit; guarding and safeties; a written test plan; and testing and documentation before handover
The One Idea	Never let the heater outrun the air.
Why Heat Must Follow The Air	An electric element makes heat at the rate its power sets and the air carries it off at a rate the flow sets, so if the flow falls and the power does not, the elements get hotter than the air by a widening margin, and low airflow is the usual reason an element burns out
Why The Air Must Be Proved	A fan that is running is not a flow that is proved, so the generator measures the flow with a sensor or a switch across the heater and gives permission for heat only while the flow is above its minimum
Why The Elements Are Watched Twice	The outlet probe tells the controller what the air is doing and a probe on an element tells it what the metal is doing, and a separate high-limit cut-out, usually reset by hand, guards the elements even if the controller fails
Why The Blower Outlasts The Heat	The elements and the vessel are still hot when the power goes off, so the blower runs on for a set time to carry the heat out instead of letting it soak into the casing and the duct
Why One Point Is Not The Generator	At one power a smaller flow gives a hotter stream and hotter elements, so the generator is mapped across its whole flow range and the map is part of the record
Standards	IEC 60519-1 is the public reference for the general safety of industrial electroheating installations, including resistance heating, and it leaves out equipment for hazardous areas, which have a series of their own. This page prints none of its limits and no edition year: those come from the standard the customer names and from the installation. Approval of a generator or a test for use rests with the customer and the authority they name; none is claimed here
Configurations	A blower-fed generator, a compressed-air heater and a generator with a test section
Scope Boundary	This page is the hot air generator. It is not a rig that tests valves in hot air (see engine anti-ice and bleed-air valve test rig), not a turbocharger hot gas stand (see turbocharger test rig) and not a thermal shock chamber (see thermal shock test chamber). A fuel-fired heater, a hot air oven and a heat exchanger test bench are different machines again. No certification is claimed here
Status	Neometrix has quoted against successive hot air generator and air heater requirements, and no delivered hot air generator is claimed.

Configurations

One method, three ways to build the generator.

The method, the tie between heat and air, and the map are shared. What changes is where the air comes from and what it is for.

Blower-fed generator

Blower, heater and outlet

Ambient air pushed through the elements by a blower, for large flows at low pressure.

Compressed-air heater

Regulator, heater and outlet

Air from a compressed air line, filtered and dried, heated in a pressure vessel, for clean air at pressure and smaller flows.

Generator with test section

Generator, article and exhaust

A generator with a duct for the article, probes at its entry and its exit and an exhaust, so that the part is heated and measured in one rig.

Fig · 06 — Three ways to build the generator, one method: a blower-fed generator, a compressed-air heater, or a generator with a test section.

And the part that is not equipment at all, yet decides all three: the test plan. It fixes the flow and temperature range, the start and stop order, the limits and the rule for the map, and it is written from the article and the standard, not from the generator.

Where it is used

Wherever a stream of hot air is the test, and the stream has to be trusted.

The common thread is a part that has to be heated in moving air, and an air stream that has to be what was asked for.

Component heating tests

Where a part is brought up to temperature in a stream of hot air and watched while it is there.

Drying and curing

Where a hot air stream dries or cures a part to a set temperature profile.

Thermal conditioning

Where an article is soaked at a set temperature in moving air before another test.

A hot air service for a larger rig

Where another test rig needs a controlled supply of hot air as one of its services.

Watch

See it in motion.

A short walkthrough video of the hot air generator.

FAQ

Common questions.

Longer answers, for readers who want the reasoning.

Q · 01 What does a hot air generator actually do?

It draws in air, from a blower or from a compressed air line, heats it with electric elements to a set temperature, and delivers it through a duct at a set flow. It holds the temperature on a probe in the outlet stream, lets heat on only while the air is proved, and keeps a record. It does not design the test.

Q · 02 Why must the heater never outrun the air?

Because the air is the only thing that carries the heat away. An element makes heat at the rate its power sets. If the flow falls and the power does not, the heat has nowhere to go, the elements get hotter than the air by a growing margin, and an element can burn out. Low airflow is the usual cause. So the generator allows heat only while the flow is proved, and cuts it when the flow falls.

Q · 03 Why prove the flow, rather than check that the blower is running?

Because a blower can run without moving the air that the heater needs. A blocked inlet, a closed damper or a slipping belt all do it. The generator measures the flow itself, with a flow sensor or a switch across the heater, and treats a flow below its minimum as no flow. Heat is then refused, or cut, however well the blower seems to be running.

Q · 04 Why does the blower keep running after the heat is switched off?

Because the elements and the vessel stay hot after the power is gone. If the blower stops at once, that heat soaks into the casing and the duct, and the elements stay hot for much longer. A run-on lets the stream carry the heat out. The generator sets the run-on time itself, so that it does not depend on the operator remembering.

Q · 05 Is this the same as the valve test rig, the turbocharger test rig or the thermal shock chamber?

No, and the differences are worth stating precisely. The engine anti-ice and bleed-air valve test rig page covers a rig that tests valves in hot air. The turbocharger test rig page covers a hot gas stand for turbochargers. The thermal shock test chamber page covers a chamber that moves a part between hot and cold. This page is the hot air generator, the machine that makes the stream. A fuel-fired heater and a hot air oven are different machines again. It does not replace any of them, and it does not claim what they claim a second time.

Q · 06 Has Neometrix built one of these?

We would rather answer this plainly than let a page imply otherwise. Neometrix has quoted against successive hot air generator and air heater requirements, and no delivered hot air generator is claimed. What stands behind the offer is adjacent: Neometrix engineers a valve test rig that makes its own hot air (see the engine anti-ice and bleed-air valve test rig page), a turbocharger test rig with its own air heater (see the turbocharger test rig page) and a thermal shock chamber (see the thermal shock test chamber page). The blowers, heating elements, power controllers, flow sensors, probes and controller hardware are catalogue items, bought in, not invented. What Neometrix engineers is the generator around them: the vessel and the duct, the tie between heat and air, the start and stop order, the map and the record, the procedure and the test plan. So the honest position is that the generator is engineered to order, the neighbouring disciplines are in the building, and the first generator of this exact kind will be built around the customer's own air, article and range rather than taken off a shelf.

Q · 07 Which standard applies, and what can the generator not do?

IEC 60519-1 is the public reference for the general safety of industrial electroheating installations, including resistance heating. It leaves out equipment for hazardous areas, which have a series of their own. This page prints none of its limits and no edition year: those come from the standard the customer names and from the installation. The generator heats air and keeps a record. It does not certify an installation: this page claims no certification or accreditation. No temperature, flow, power or pressure figure is printed here, and approval for use rests with the customer and the authority they name; none is claimed here.

Q · 08 What do you need from us to quote?

Six things, and most of them describe your article rather than the generator. First, the air: where it comes from, and how clean it must be. Second, the flow: the range, from smallest to largest. Third, the temperature: the range, and how closely it must be held. Fourth, the article: what the air is to heat, and how it is connected. Fifth, the stop rule: what the generator must do on a fault, and how long the blower runs on. Sixth, the record: what you want kept with each run. From that we come back with a generator concept, a written test plan you can check, and a budgetary price.

The neighbouring thermal pages, and how they differ from this one.

Three neighbours: one tests valves in hot air, one tests a turbocharger, one shocks a part between hot and cold.

↗ A valve test rig

Engine Anti-Ice & Bleed-Air Valve Test Rig

A rig that tests valves in hot air - a test of the valve, where this page makes the hot air.

↗ A turbocharger rig

Turbocharger Test Rig

A hot gas stand that maps a turbocharger - a test of the machine, where this page is a source of hot air.

↗ A thermal shock chamber

Thermal Shock Test Chamber

A chamber that moves a part between hot and cold - a test of the part by change of temperature, where this page makes a steady stream of hot air.

Browse all Neometrix product lines.

Get a quotation

Tell us the air, the flow,
and the temperature.

The projects desk replies within two working days with a generator concept, a written test plan you can check, and a budgetary quotation. Write to [email protected] or use the form.

Enquire — hot air generator Capability sheet (PDF) +91 7777 876 876

ISO 9001 / 14001 ENGINEERED-TO-ORDER CLASS — HOT AIR GENERATOR SPECIFY · SIZE · TIE · RUN · MAP · PROVE — NEVER LET THE HEATER OUTRUN THE AIR ENGINEERED IN NOIDA · INDIA