Thermofluids Flashcards
(42 cards)
1 Cal in kJ
1 Cal = 4.2kJ
Power Required
Power = AUΔT
Sensible Heat Eq
Q=mC_pΔT
What happens to % of O2, CO2, H20 and N2 when breathing
O2 DECREASE - used to oxidise food to provide energy, used to keep body temp at 37C
CO2 INCREASE - ‘waste’ product of metabolism
H2O INCREASE - evaporation of water from damp lungs to cool unsaturated air
N2 DECREASE - should be same, % will fall slightly due to increased volume of outlet breath (water vapour)
Explain how the kidney functions
Two types of separation:
DIALYSIS - relies upon concentration gradient
- diffusion through a membrane
- 0.5nm molecules or less
ULTRAFILTRATION - relies upon pressure gradient
- larger proteins may not pass but smaller molecules can pass quickly
- forces water, salts and metabolites through selective membrane
- filtrate moves to tubule where dialysis returns some water/salts to achieve correct balance
Why do the kidneys appear inefficient?
- process 1000 times more water than they dispose of
- but uses little energy and runs at low concentration gradient
Why do discontinuities in concentration occur at interfaces?
- convection dominates in free stream
- molecular effects dominate at boundary
- causes discontinuous step change at boundaries
What approximation can simplify dialysis analysis at boundaries?
C_M = ΦC
- ‘removes’ discontinuities
How can you decrease the volume of the dialysis membrane whilst maintaining surface area?
- Folding
- Rolling
- Layering
What are the names of the high and low blood pressure reading and their units?
Systolic - high reading
Diastolic - low reading
mm Hg
Two methods to increase blood flow rate to heart
- Increase pulse
- Increase stroke volume
Reynolds number equation
Re = ρVL / μ
Name the two types of sweat gland
- Eccrine - all over body surface
- Apocrine - concentrated in pubic region and under arms
What are homeotherms and poikilotherms
Homeotherms - regulate their temperature
Poikilotherms - cold blooded animals, operate at environment temp
Define each term in the heat balance eq for animals:
M + R = C + λE + G + S
M - metabolic heat production rate R - radiative heat gain C - convective heat loss λE = λE_s + λE_r - evaporative loss from breathing + sweating G - conduction of heat (small) S - storage of heat (small)
Define each term in metabolic rate eq:
ρ dM/Dt = I - ε(M+M_0)
M - current weight of body fat M_0 - initial weight of body fat ρ - effective energy density of fat ε - energy lost per unit body mass per day I - input energy intake per day
6 methods for controlled drug release
- Oral (pills)
- Injection
- Membrane device - use of membrane to control release (separates rug from body fluid)
- Matrix device - load drug into matrix. Not constant delivery rate but close
- Totally soluble materials
- Shapes which change as material dissolves - reduced mass transfer surface compensated with change in concentration
How does a membrane device work?
- bio-compatible shell holds ingredients
- shell is permeable membrane with defined diffusivity coefficient
- drug release rate determined by shell properties
- saturated solution inside shell containing undissolved particles of drug
- metabolic and other body functions maintain const concentration of drug in body (time independent)
- molar delivery rate, W = const
Explain how dialysis machines work
- counter-current flow of blood and dialysate on either side of a semi-permeable membrane
- counter-current flow provides almost constant driving concentration gradient for length of membrane
- membrane consists of many hollow fibres
Describe the flow circuit of the heart in 8 steps
- Left ventricle (high pressure) pushes blood through aorta and large arteries
- large arteries - smaller arteries - tissue capillaries
- capillaries drain through venules into veins - vena cava - right atrium
- right side pumps blood through pulmonary system
- right atrium - right ventricle - pulmonary arteries - pulmonary capillaries
- pulmonary capillaries close to air in lungs, exchange of gas by diffusion
- blood absorbs 02 and releases CO2
- oxygenated blood (in pulmonary vein) returns to heart via left atrium - left ventricle
What are the 4 sections of the heartbeat cycle
Atrial diastole - atria + ventricles relax + blood under low pressure returns to atria
- oxygenated blood enters left atrium, deoxygenated blood enters right atrium
- biscupid + triscupid valves initially closed
- atria fill, pressure > ventricle and they open
Atrial systole - atria contract, push blood into ventricles
Ventricular systole - ventricles contract and close
Ventricle diastole - ventricles relax, blood flow-back causes semi-lunar valves to close
What are the limitations of the simple weight gain/loss model?
- efficiency of food to energy conversion not constant
- conversion of ‘spare’ energy to bone, muscle and non-fat tissue is different to fat storage, changes ε and ρ values
- rate of weight gain dependent on mechanisms for mass storage
Name the 3 body heat transfer models and their limitations
Effective thermal conductivity - only one temp difference - cannot see local effects - distance from skin to deep body temp is arbitrary but has to be fixed Bioheat equation - need for a perfusion rate - 3 temperatures, need 3 equations - perfusion term is global, other terms are local Thermally significant blood vessels
Speed of a pulse wave eq
c^2 = Eh/2ρa
