The UK/IERE Land Rover Owner Daily Digest

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From: CJ BETTON N9203387 <n9203387@hud.ac.uk>
Subject: Missing thermostats.
Date: Mon, 26 Feb 96 09:25:00 gmt

Please all,

No more on thermostats and cooling theory!

I read the list to avoid that sort of thing on my course. Get back to topics 
that distract me from my studying :-)

Cheers,
Chris

------------------------------

From: Mike <MIKE@vrsolns.co.uk>
Date: Mon, 26 Feb 1996 12:29:55 +0000
Subject: Missing Thermostats

Guess what I found some time over the weekend

THEORY TO RELATE RADIATOR TEMPERATURE TO COOLANT FLOW RATE.
(with apologies for the format which is difficult with this medium)

General symbols used:

 a	radiating area associated with the mass m of the coolant below
 A	cross-sectional area of the radiator
 d	density of the coolant
 E	emissivity of the radiator
 F	volume flow rate
 L	length of the radiator
 m	mass of a very small quantity of coolant
 s	specific heat of the coolant
 t	time taken for the coolant to travel to distance x
 T	temperature above ambient at distance x along the radiator
 Tin	coolant temperature above ambient at the inlet to the radiator
 w	energy in excess of ambient of the mass m of coolant
 x	distance along the radiator from the coolant entry point
 Y	width of the radiator

Theory:

energy of coolant	  	           w =  smT

differentiate wrt temp		dw/dT  =  sm	
hence			 dw  =  sm dT

rate of loss of heat		dw/dt  =  - ETa

substituting for dw	                   sm dT/dt  =  -ETa
rearrange for integration	 dT/T  =  -(Ea/sm) dt 

integrate		 	 ln T  =  -(Ea/sm) t + C
or	                    	 T  =  (exp)(-Eat/sm) * (exp)C

when t = 0, T = Tin, hence	 T  =  Tin (exp)(-Eat/sm)		....eq1

The velocity of flow along the radiator is F/A hence the time taken
for the coolant to travel the distance x is given by:

         t  =  xA/F

substitute this into eq1	    T  =  Tin (exp)(-EAax/Fsm)	....eq2

If we consider a strip of the radiator perpendicular to the flow, at
distance x with width dx, its rate of loss of heat is:
                                                                      
                                                              ETY dx

substitute for T from eq2	  =  EY Tin (exp)(-EAax/Fsm) dx

integrate to get the rate                            L
of loss of heat for the full                  (int)  EY Tin (exp)(-EAax/Fsm) dx
radiator		                            0
                                                                      
                                                                    L
  =  EY Tin [-Fsm/EAa (exp)(-EAax/Fsm)]
                                                                    0

       =  (YFsm/Aa) Tin (1 - (exp)(-EAaL/Fsm)) 

In the steady state this equates to the power P, supplied to the
coolant by the engine:

          P =  (YFsm/Aa) Tin (1 - (exp)(-EAaL/Fsm)) 

rearranging      Tin  =  (PAa/YFsm) / (1 - (exp)(-EAaL/Fsm))

lumping constants, J = PAa/Ysm and K = EAaL/sm:

       Tin  =  (J/F) / (1 - (exp)(-K/F))

This is an equation which links the inlet temperature of the coolant
Tin to its flow rate F (all other variables held constant). For
positive values of F its gradient is always negative, i.e. increasing
the flow always results in a decrease of temperature.

Also for small values of F:		 Tin  ~=  J/F
 and for large values of F:		 Tin  ~=  J/K

The shape of the graph of the equation indicates a law of rapidly
diminishing returns at higher flow rates, showing that there is a rate
which is not worth exceeding.

Note that although this assumes an idealised homogeneous radiator, a
real radiator could be put together as an array of small, even
elemental, ideal radiators connected in series and/or parallel each
with different constants. The conclusion for each, and hence for the
whole, would be as above.

That's all folks!!!

Mike
================================
Mike Gavins
VR Solutions Ltd
University Road
Salford
M5 4PP
United Kingdom
  Tel: +44 161 745 7384
  Fax: +44 161 745 8264
Email: m.gavins@vrsolns.co.uk
================================ 

------------------------------

From: JAMES O-SHEA <SAC3JNO@cardiff.ac.uk>
Date: Mon, 26 Feb 1996 15:36:42 GMT
Subject: Re: Cylinder head lifting

The bolts are undone, all pipes, cables have been disconnected, and 
the exhaust manifold is now disconnected from the exhause pipe so how 
the hell do I lift 35kg of head and manifolds off the block and out 
of the engine bay? I'm not built like a concrete out-house so any 
helpful suggestions that don't include hiring and engine hoist would 
be wonderful....but I'll need to hear them before 5:00 p.m. today.

James O'shea
SAC3JNO@Cardiff.ac.uk

------------------------------

Date: Mon, 26 Feb 1996 23:15:02 +0000
From: Ian Robinson <ian@fourx4.demon.co.uk>
Subject: Re: Cylinder head lifting

In message <2A79BED3A71@main2s.cf.ac.uk>, JAMES O-SHEA
<SAC3JNO@cardiff.ac.uk> writes
>The bolts are undone, all pipes, cables have been disconnected, and 
	 [ truncated by lro-digester (was 8 lines)]
>helpful suggestions that don't include hiring and engine hoist would 
>be wonderful....but I'll need to hear them before 5:00 p.m. today.
2.25ltr Series engine, I presume ! It should have lifting rings unless
some lazy amature has not replaced them ! Failing that prize around the
area of the bypass hose; that often siezes on the water pump/head.
Failing that, a stout 2" x 2" up under the manifold on the end of a
floor jack should do the trick. If all else fails, disconect the fuel
pipe (before the pump), disconect the electrics (before the coil) and
razzle her over.

PS stand clear !!!!!
 
Regards, Ian
                Forest Landrovers' 4 x 4 Centre
                Royal Forest of Dean, Glos, UK
                +44 (0)1594 822606/(0)402 000132

------------------------------

Date: Tue, 27 Feb 1996 07:44:14 GMT
From: Gerald Tan <gtan@bbchw.demon.co.uk>
Subject: Fwd: Disco ABS & Comments

Forwarded Message.

:To: Land-Rover-Owner@Land-Rover.Team.Net
:From: Paul Orland <paulor@chs.com>
:Subject: Disco ABS & Comments
:X-edited-by: LRO-Lite

 - Is there any way to temporarily disable ABS? I found it disconcerting to
NOT be able to lock up the wheels on dirt roads or in deep snow. Has anyone
experimented with installing an override switch? The manual describes 3
different fuses for the ABS system! BMW R1100GS motorcycles  (a dual sport)
use a system where if you depress a button when starting the bike, the ABS
remains disabled until next start. ABS light remains lit to remind you of
the override. This would be my ideal modification.

This sounds like a good idea, has anyone on the uk list done this?

Gerald.

------------------------------

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