Ronaldo47

McDonalds is usually good for free WiFi!

I found I was getting significant gravity flow in the central heating I installed in my house in the mid-1970's when operating it with the pump turned off. On discussing it with a heating engineer he mentioned that a lot of the older tabulated data I had been using to design my system, would have been based on flow though iron pipes with relatively rough internal walls, and that the smooth bored copper pipes I was using had a lower flow resistance than my tabulated data indicated. My recollection is that, for laminar flow, resistance was inversely proportional to the fourth power of diameter, and that slow bends were highly advisable, as the sharp 90° bends that seem to be the only thing that most stockists have nowadays, do introduce significant resistance. There is a type of system called the one-pipe system, where you only have one pipe which runs around in a loop from boiler flow to boiler return, and to which one pipe the radiators are connected by tees. The radiator closest to the boiler gets the hottest water, while the others get hot water diluted by the cooler water that gets returned to the pipe from the 'return' ports of all the upstream radiators. My school, built in the 1920's, had such a system, where the 'one pipe' was of large diameter (from memory, 4 or 5 inches diameter) and the radiators were connected to that one pipe by 1/2" or 3/4" branches with manual and lockshield valves for balancing. All iron pipes of course.

Theere are fundamental differences between, on the one hand, transformers and rotating electrical machines, and on the other hand, induction hobs and microwave ovens. In simple terms, in the former, steps are taken in their design to minimise the leakage of the magnetic field, because any of the magnetic field created by one primary winding that does not couple with a secondary winding, is lost energy and hence reduced efficiency. So transformers and motors/generators use closed magnetic circuits where the vast majority of their magnetic field is contrained to flow in the iron (or ferrite) of their magnetic circuit to maximise efficiency. Conversely, in an induction hob, you have a primary winding generating an alternating magnetic field above the hotplate surface: an open magnetic circuit. When a suitable metallic pan is placed on the surface, the magnetic field concentrates itself into the metal of the pan, as this offers a lower magnetic resistance than free space (air). However, with an induction hob, the air gap between pan and plate means that the coupling between the part of the magnetic circuit in which the magnetic field is created (plate) , and the part in which energy is extracted from the magnetic field and converted to heat (pan), is not going to be as efficient as the closed magnetic circuits of transformers etc., meaning there will always be some stray magnetic field present during operation. Hence the warnings to pacemaker-wearers.

I think the "switch off mobile phones" notices that you still see in garages, stem from the era when the only mobile phones were those installed in cars, were run from the vehicle's battery, and used relatively high transmit powers. The name of the business "Car Phone Warehouse" seems to have originated in that era, and the name was still used long after they stopped selling car phones. Mobile phones used to need high powers in the pre-cell phone era when masts were spaced widely apart. Modern cell phone systems rely on a dense network of smaller cells where you are normally never far from a mast and so don't need a large range. In fact the frequency bands used in a cellphone network are designed so that adjacent cells use different ranges of frequencies, so a really high powered cell phone would risk interfering with a remote cell that was using the same range of frequencies at the same time. Frequency re-use is the way that the networks cope with the large number of users that we now have.

The London Underground still has two examples of unconnected stations on different lines with identical names: Edgware Road and Shepherd's Bush. At one time, there were two White City stations too.

I recall seeing a video of a fire caused by a pet accidentally turning on a touch screen hotplate burner. The saucepan or frying on it, then ignited.

I understand that official NHS advice is that anyone fitted with a pacemaker should not get closer that about 2 feet from an operating induction hob, because the strong electromagnetic field can damage them.

I used to love Hammond's Chop Sauce, but haven't seen any in our local shops for many years.

The design has changed during the 45 years or so that I have been using them. In the early design, you had to isolate the valve (or drain the system) to fit a new head when the old one failed, usually due to worn teeth on the toothed segmental member driven by the motor pinion. You don't with the later design.

Possibly dropped and fell somewhere unknown or inaccessible? The ones on my valve were brass and hence non-magnetic.

The last time I fitted a replacement head for a Honeywell motorised valve, the screws were an American thread, not a type you could get from an ordinary hardware store.

It's being shown again on BBC1 at 3.45 on Saturday 24th May. "A close shave" is on at 3.00.

My understanding is that the main reason for the progressively reduced use of traditional (eminently hydraulic) limes in favour of Portland, was that most of the quarries they were obtained from, got worked out.