Question 1

What is the saturated steam temperature at 476 kPa(abs)?

Accepted Answer

At 476 kPa absolute (approximately 3.76 bar or 68 psig), the saturation temperature is approximately 150Â°C. This is commonly used in medium-pressure process steam systems, autoclaves, and food processing equipment.

Question 2

What is the latent heat of vaporisation of steam at 100Â°C?

Accepted Answer

At 100Â°C (atmospheric pressure, 101.3 kPa), the latent heat of vaporisation (hfg) is approximately 2256.6 kJ/kg. This is the energy required to convert 1 kg of saturated liquid water to saturated steam â€” or released when steam condenses. At higher pressures, hfg decreases significantly.

Question 3

What is the enthalpy of saturated steam?

Accepted Answer

Enthalpy of saturated vapor (hg) = enthalpy of saturated liquid (hf) + latent heat (hfg). For example, at 150Â°C: hf = 632 kJ/kg, hfg â‰ˆ 2115 kJ/kg, hg â‰ˆ 2747 kJ/kg. For process heating calculations, hg is used to determine the heat content of steam delivered to process equipment.

Question 4

How do I calculate steam consumption for a process?

Accepted Answer

Condensate return steam consumption rate (kg/h) = Heat demand (kW) Ã— 3600 / hfg (kJ/kg). For example, a 500 kW heat exchanger using 150Â°C steam (hfg â‰ˆ 2115 kJ/kg): Steam = 500 Ã— 3600 / 2115 â‰ˆ 851 kg/h.

Question 5

What is superheated steam?

Accepted Answer

Superheated steam is steam heated above its saturation temperature at a given pressure. It contains more energy than saturated steam. Superheated steam is used in turbines and high-temperature process applications. The degree of superheat is the temperature difference above saturation temperature.

Question 6

What is steam quality and why does it matter?

Accepted Answer

Steam quality (dryness fraction x) indicates the fraction of vapor in a wet steam mixture. x = 1 means fully dry saturated steam; x < 1 means wet steam containing liquid droplets. Wet steam causes erosion in turbines and poor heat transfer. Steam traps are used to remove condensate and maintain steam quality in distribution systems.

Question 7

What steam pressures are common in South African industry?

Accepted Answer

Common South African industrial steam pressures: 150 kPa(g) â€” low pressure heating, 350â€“500 kPa(g) â€” medium pressure process steam, 800â€“1000 kPa(g) â€” high pressure process steam, 1.5â€“3 MPa(g) â€” power generation and turbines. Boiler safety regulations are specified under the Pressure Equipment Regulations (PER) of the OHS Act.

Question 8

What is the critical point of water/steam?

Accepted Answer

The critical point of water is at 374.1Â°C and 22.06 MPa. Above this temperature and pressure, water exists as a supercritical fluid â€” there is no distinction between liquid and vapor. Supercritical steam is used in modern power generation for maximum thermal efficiency.

T (Â°C)	P (kPa abs)	hf (kJ/kg)	hfg (kJ/kg)	hg (kJ/kg)	vg (mÂ³/kg)
0	0.6	0.0	2500.9	2500.9	206.3000
20	2.3	83.9	2453.5	2537.4	57.7600
40	7.4	167.5	2406.0	2573.5	19.5200
60	19.9	251.2	2357.6	2608.8	7.6710
80	47.4	334.9	2308.1	2643.0	3.4070
100	101.3	419.1	2256.5	2675.6	1.6730
120	198.5	503.7	2202.6	2706.3	0.8920
140	361.4	589.1	2145.3	2734.4	0.5090
160	618.0	675.5	2084.1	2759.6	0.3070
180	1002.7	763.2	2015.0	2778.2	0.1940
200	1554.0	852.4	1940.1	2792.5	0.1270
220	2319.0	943.7	1857.7	2801.4	0.0862
240	3348.0	1037.6	1765.8	2803.4	0.0597
260	4694.0	1134.4	1662.0	2796.4	0.0421
280	6413.0	1236.1	1542.7	2778.8	0.0302
320	11284.0	1461.5	1238.6	2700.1	0.0152
360	18666.0	1761.7	719.3	2481.0	0.0073

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