Calibrated volume displacement apparatus and method for direct measurement of specific heat of a gas

Patent metadata

Field	Value
Publication number	US-10048217-B2
Application number	US-201615067840-A
Country	US
Kind code	B2
Filing date	Mar 11, 2016
Priority date	Mar 11, 2016
Publication date	Aug 14, 2018
Grant date	Aug 14, 2018

Abstract

A method and apparatus for the direct measurement of specific heat at constant pressure (Cp). A control fluid of a known amount is supplied to a near adiabatic test chamber having a volume. A collapsible bladder within the test chamber is inflated with an incompressible fluid, changing the volume of the test chamber. The change in pressure and temperature of the control fluid relative to the change in volume of the test chamber is measured. The steps are repeated with a sample fluid. The isentropic enthalpy and specific heat at constant pressure of the sample fluid is determined.

First claim

The invention claimed is:

1. A method for the direct measurement of specific heat at constant pressure (Cp), comprising:
supplying a control fluid of a known amount to a test chamber having a volume, wherein said test chamber exhibits less than 1% heat loss of the total energy input;
inflating a collapsible bladder with an incompressible fluid to change the volume of said test chamber and measuring a change in pressure and a change in temperature of said control fluid relative to said change in said volume of said test chamber as said collapsible bladder is inflated;
calculating the actual change in enthalpy of said control fluid and calculating a process efficiency parameter;
supplying a sample fluid of a known amount to said test chamber;
inflating said collapsible bladder with said incompressible fluid to change the volume of said test chamber and measuring a change in pressure and a change in temperature of said sample fluid relative to said change in said volume of said test chamber as said collapsible bladder is inflated;
determining a change in isentropic enthalpy of said sample fluid based on 1) said change in pressure of said sample fluid measured relative to said change in volume, 2) said known amount of said sample fluid, and 3) said process efficiency parameter; and
determining the specific heat at constant pressure of said sample fluid based on said change in temperature of said sample fluid measured and said change in isentropic enthalpy of said sample fluid.

2. The method of claim 1 , wherein said change in isentropic enthalpy of said sample fluid, Δh Isentropic , is determined using the following equation:

∫

P
⁡

(
V
)

⁢
dV

m

×

η
Isentropic

=

Δ
⁢

⁢

h
Isentropic

wherein P is pressure, V is volume, m is mass, η Isentropic is the process efficiency parameter.

3. The method of claim 1 , wherein said specific heat at constant pressure of said sample fluid is determined using the following equation:

C
p

=

Δ
⁢

⁢

h
Isentropic

Δ
⁢

⁢
T

wherein Cp is the specific heat at constant pressure of said sample fluid, h isentropic is isentropic enthalpy of said sample fluid, and ΔT is said change in temperature of said sample fluid.

4. The method of claim 1 , wherein said control fluid exhibits an aerodynamic similitude to said sample fluid and has a known change in isentropic enthalpy Δh Isentropic .

5. The method of claim 4 , wherein said aerodynamic similitude is determined by the ratio of the kinematic viscosity of the sample fluid, υ s , to the kinematic viscosity of the control fluid, υ c .

6. The method of claim 5 , wherein the ratio of

υ
s

υ
c

is in the range of 0.5 to 1.5.

7. The method of claim 1 , wherein said actual change in enthalpy of said control fluid is calculating according to the following equation:

Δ
⁢

⁢

h
actual

=

∫

P
⁡

(
V
)

⁢
dV

m

=

C
p

·
Δ

⁢

⁢
T

wherein P is pressure, V is volume, m is mass, C p is specific heat capacity of the control fluid and ΔT is said change in temperature of said control fluid.

8. The method of claim 1 , wherein said process efficiency parameter is calculated according to the following equation:

η
Isentropic

≡

Δ
⁢

⁢

h
Isentropic

Δ
⁢

⁢

h
Actual

wherein η Isentropic is the process efficiency parameter of said control fluid, h Isentropic is the isentropic enthalpy of said control fluid and h Actual is the actual enthalpy of said control fluid.

9. The method of claim 1 , wherein said control fluid is selected from nitrogen and carbon dioxide.

10. The method of claim 1 , wherein said sample fluid is a non-ideal gas mixture.

11. The method of claim 1 , further comprising evacuating said test chamber prior to supplying said sample fluid to said test chamber.

12. The method of claim 1 , further comprising displacing said incompressible fluid from a reservoir into said collapsible bladder with a pump.

13. An apparatus for the direct measurement of specific heat at constant pressure (Cp), comprising:
a test chamber, wherein said test chamber exhibits less than 1% heat loss of the total energy input;
a collapsible bladder positioned within said test chamber;
a reser

Assignees

• Southwest Res Inst

Inventors

• Brun Klaus
• Simons Sarah B
• Bennett Jeffrey A

Classifications

• G01N25/005 Primary

  by investigating specific heat · CPC title