<div dir="ltr"><div dir="ltr"><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><span style="font-family:Arial,Helvetica,sans-serif;line-height:1.5">On Sat, Mar 30, 2019 at 1:05 PM BillK <</span><a href="mailto:pharos@gmail.com" target="_blank" style="font-family:Arial,Helvetica,sans-serif;line-height:1.5">pharos@gmail.com</a><span style="font-family:Arial,Helvetica,sans-serif;line-height:1.5">> wrote:</span><br></div></div><div class="gmail_quote"><div dir="ltr" class="gmail_attr"><br></div> <br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><span class="gmail_default" style="font-family:arial,helvetica,sans-serif">><i> </i></span><i>Heat is incredibly useful, especially in the depths of space.</i></blockquote><div><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><font size="4">The usefulness of heat, that is to say the ability to extract work out of it, depends on how hot it is. The closer that heat comes to the temperature of deep space, 2.7 degrees Kelvin, the less useful it is. The equation for efficiency in extracting work out of heat is 1-Tc/Th when Tc is the temperature of your cold heat sink (which is never less than 2.7 K) and Th is the temperature of your hot heat source. If those 2 temperatures are same then the efficiency is precisely zero. And that means zero work obtained.</font></div><div><span style="line-height:1.5"> </span><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<span class="gmail_default" style="font-family:arial,helvetica,sans-serif">> </span>There could be a whole civilisation living off that 'waste heat'!<br></blockquote><div><br></div><div class="gmail_default"><font size="4"><font face="arial, helvetica, sans-serif">If they're still extracting work out of it then it's not waste heat, but you can be absolutely certain if they are extracting work out of it then they </font><b style="font-family:arial,helvetica,sans-serif">WILL </b><font face="arial, helvetica, sans-serif">produce waste heat. The point is after you've finished using energy it is not destroyed but is converted to a higher entropy form that is much more difficult to obtain work from.</font></font></div><div class="gmail_default"><font size="4"><font face="arial, helvetica, sans-serif"><br></font></font></div><div class="gmail_default"><font size="4"><font face="arial, helvetica, sans-serif"> John K Clark</font></font></div><div><br></div><div><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><br>
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