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Kind of a timely thread as I'm thinking a bit down the line about a microwave boiler.
Has to be the mainstream solution for gas boiler replacement as an easy like-for-like.
but leaving it to spread the heat and thaw the next bit allows that to absorb the waves better.
Well its heat transfer. What you're doing is actually heating up the liquid water on the surface of the ice then that is in turn melting the ice beneath through heat transfer of the hot liquid water to the solid ice. So by leaving it a bit you are preventing superheating the liquid water and allowing the heat to transfer into the ice.
I suspect microwave is far more efficient in heating water. A typical kettle is about 3kw and a typical microwave is around 850w. I would hypothesise that they would heat up the same volume of water in around the same time, so alot more energy wasted in the kettle.
Specific heat ckpacity doesn't really help you here - all that does is tell you how much energy you need to get into the liquid to heat it up, but doesn't tell you anything about the method of getting that energy into the water and how efficient that method is. Microwaves directly impart energy into the water. Kettle heats up elements which in turn uses heat transfer and convection to get the energy into the body of the liquid. That heat also transfers to all the components in the kettle thereby sucking up some of the energy you put in and diverting it from the job of heating up the water and wasting it. Microwaves minimally heat up surrounding environment and components so more energy emitted goes into the water to change its energy state. I would conduct an experiment myself but don't have a kettle (Quooker for the win!).
I’ve found by experience that the best way to thaw frozen food in a microwave is in short bursts
It's not just that - the microwaves only penetrate the first cm or so of food even if it's not frozen. The rest is done by convection just like a normal oven.
I suspect microwave is far more efficient in heating water. A typical kettle is about 3kw and a typical microwave is around 850w. I would hypothesise that they would heat up the same volume of water in around the same time, so alot more energy wasted in the kettle.
No need to hypothesize, it's been done a lot and whilst my report of 98% seems optimistic, every experiment reported that electric jkettles were faster.
but doesn’t tell you anything about the method of getting that energy into the water and how efficient that method is
The point I am making is that because it's a simple resistive load, ALL the energy is lost as heat, and because the element is in the water ALL that heat goes into the water, at least before some of it goes into the surroundings.
The microwave oven itself gets warm, because the process of converting electricity to microwaves isn't 100% efficient of course.
I suspect microwave is far more efficient in heating water. A typical kettle is about 3kw and a typical microwave is around 850w
Resistive electric heaters (the kettle) are 100% efficient at turning electricity into heat. The only losses are any heat that goes somewhere other than the water, so not a lot.
Microwave I don’t know, but I assume 80-90% efficient?
Either way the microwave will be putting nearly 850w into your water, the kettle nearly 3kw into your water. The kettle will win. Neither device will create free energy and neither device will lose much.
For this reason I’m curious about why a microwave domestic hot water boiler is any better than a resistive electric boiler already widely available. Or am I missing something?
From a physics point of view, heat is a thermodynamic concept (the concept of energy moving from one thing to another). This is not exactly in accordance with the everyday language meaning. But as the energy can be transferred via a few mechanisms, I think it is reasonable to say that, whether talking strict physics or more generally, heat can manifest itself in a few different ways.