Time to Heat Oil

By

 

How long does it take to heat up my oilHow long does it take to heat oil? Water typically takes twice as much time to heat up as oil, depending on the oil. We can use the formula below to get a better estimate.

Time in hours = 0.5 X Number of Liters X Temperature rise in °C / by element wattage

Example = 0.5 * 100L * 20°C / 1500 = 0.67 hours or 40 minutes.

These equations assume a well-insulated tank like a water heater. When you are heating oil in a container that is not insulated, like a steel drum, heat losses to the air can be significant. As the temperature rises, heat loss increases, and at some point, heat loss equals heat added, and the temperature stops rising.

 

Deriving the formula:

We start with the formula that calculates the energy needed to raise the temperature of a substance:

Q = cmΔT

Q is the heat required in Joules
c is a constant called the specific heat capacity and is in Joules per gram per °C
m is the mass in grams
ΔT is the temperature rise in °C

.................................................

Next, we use the formula that calculates how much energy an electric heating element adds to our oil:

Q = W * T

Q is the heat in Joules our element puts out
W is the wattage of the element
T is the time the element operates in seconds

.................................................

Since the energy (Q) is the same in both formulas, we can combine the formulas eliminating Q like this:

W * T = cmΔT

Solving for Time (T) gives us:

T = cmΔT / W

............................................

m is for mass. We calculate our mass by multiplying density (ρ) times volume (V)

m = ρV

Substitute ρV for m and our formula becomes:

T = cρVΔT / W

...............................................

To check out our algebra, we verify the units cancel out:

Seconds = (J/gC) * (g/L) * L * C / Watts

Note that the grams, liters, and centigrade all cancel out giving us:

Seconds = Joules/Watts

If we rearrange this to Joules = Watts X Seconds, we have the formula for power, so our algebra checks out.

...............................................

Now we plug in some constants to simplify the equation even further.

c - Various sources place c for vegetable oil between 1.7 and 2.2 Joule/gram°C. Choosing something in the middle, we get 2 Joule/gram°C

ρ - Density also varies with vegetable oil, we will use 0.92g/mL or 920g/L

Plugging what we have so far into our formula for oil we get

T = 2 W s/ gramºC * 920g/L * V * ΔT / W

Substituting into our formula we get:

T = 1840VΔT/W

...........................................

Since T is in seconds, we divide by 3600 to convert to hours

T = 0.511VΔT/W

Rounding we get:

T = 0.5VΔT/W

Where T = time in hours,
V= volume in Liters,
ΔT = temperature rise in °C,
W = the wattage of the element doing the heating.

Note that the formula gives an estimate for time since we used estimated values for both density and specific heat capacity. Your actual time to heat will be a little different and depends on the specific properties of your oil.

Sample Calculations

A 40-gallon Water Heater Appleseed with a 1000 W heating element. The starting temperature of the oil is 20°C (68°F), and we are heating the oil to 50°C (122°F). The typical 40-gallon water heater makes a 25-gallon (95 liters) batch.

T = 0.5 * 95 * 30 / 1000

T =  1.45 hours

Now if we replace the heating element with a 4000W element it becomes:

T = 0.5 * 95 * 30 / 4000

T = 0.356 hours or 21 minutes

Flexible Drum Heaters

Heating times for Flexible Drum HeatersThis chart from Ogden Manufacturing shows how the temperature changes over time for one or more band heaters mounted on an uninsulated steel drum. What it is showing is that as the temperature rises, more heat radiates away from the drum. Eventually, there comes a temperature when the heat radiated away is equal to the heat being put in. When it reaches that point, the temperature goes no higher. Adding additional flexible drum heaters increases the heating power going into the drum and increases both the maximum attainable temperature and how fast the drum heats up.

For a drum filled with water, a 1000W heater can only heat the drum to about 70˚F above the ambient temperature, and it takes 20+ hours to get there.

Of course, this all changes if you insulate the drum so that the heat is not radiated away as quickly.

To compare the difference. In a perfectly insulated world, 1000W would take 2 hours to heat a drum of water from 70F to 120F. With a 1000W band heater on a drum with no insulation, it would take 10 hours and use 5 times as much energy.

Silicon Band heaters with thermostatic controls have a snap-disc built into them that works like a thermostat on a water heater. According to the manufacturer, the snap-disc tends to burn out or catch on fire when covered with insulation. The rest of the drum can be insulated to reduce heat loss via radiation, but the band heater itself must be left exposed.

 

Related Links

Household Energy Use

Chemical Characteristics of Olive Oil

Specific Heat Capacity Table

Liquids and Fluids - Specific Heat Capacities

Wiring the Appleseed Processor

Wiring the Appleseed Biodiesel Processor

Wiring the Applseed is not all that difficult, once you understand the basics. "Wiring the Appleseed" provides the information you make your Appleseed work. If you feel uncomfortable with modifying electrical appliances, get an electrician to help.

Read More...

 

.